• Volume 42, Issue 5

October 2019

• Structural and magnetic properties of combustion synthesized A₂Ti₂O₇ (A = Gd, Dy and Y) pyrochlore oxides

Nanostructured pyrochlore oxides A2Ti2O7 (A = Gd, Dy and Y) have been synthesized through a single step auto-igniting citrate complex combustion process. The structure and phase formation of the prepared combustion product were characterized by X-ray diffraction (XRD) analysis. From the XRD patterns, the average crystallite size and lattice strain were calculated using the Williamson–Hall method. Pyrochlore oxides A₂Ti₂O₇ (A = Gd, Dy and Y) exhibit a cubic pyrochlore structure with the fd3m space group. The microstructure and average grain size of the samples were examined by scanning electron microscopy. The surface area and pore size of the materials were obtained from Brunauer–Emmett–Teller (BET) analysis. The obtained higher BET surface area of the Gd₂Ti₂O₇ material suggests the possibility of excellent photocatalyst activity. The vibrating sample magnetometer studies show that these materials show paramagnetic behaviour at room temperature. These materials have an entropy change that increases when the temperature decreases. So these materials may be used as active magnetic refrigerants at low-temperature.

• Power-dependent physical properties of GaN thin ﬁlms deposited on sapphire substrates by RF magnetron sputtering

Gallium nitride (GaN) thin ﬁlms were grown on the Al₂O₃ (0001) substrate using radio frequency (RF) magnetron sputtering under various RF powers. Many experimental techniques were used for investigating the effects of RF power on the GaN thin ﬁlm growth and its physical properties. The X-ray diffraction results conﬁrmed that the GaN thin ﬁlm had a polycrystalline structure with planes of (101) and (202). The structural parameters of the thin ﬁlm changed with RF powers. It was also found that the optical band gap energy of GaN thin ﬁlms varied with changing RF power. From the atomic force microscopy images, almost homogeneous, nanostructured and a low-rough surface of the GaN thin ﬁlm can be observed. From scanning electron microscopy analysis, dislocations and agglomerations were observed in some regions of the surface of the GaN thin ﬁlm. $E_{₂}$ (high) optical phonon mode of GaN was observed, proving the hexagonal structure of the thin ﬁlm. The residual stress in the GaN thin ﬁlms was calculated from Raman measurements. Furthermore, an agreement between the experimental measurements was also examined. The morphological, structural and optical properties of the GaN thin ﬁlm could be improved with altering RF power. These ﬁlms could be used in devices such as light emitting diodes, solar cells and diode applications.

• A spring network simulation in three dimensions for designing optimal crack pattern template to fabricate transparent conducting electrodes

Desiccation cracks in colloids are of the order of µm width or less. Therefore, such connected crack networks in a desiccating colloidal ﬁlm can provide a very ﬁne template for the fabrication of transparent conducting surfaces by vapour deposition of a metal onto the crack network (Rao $et al$ 2014 $Adv. Mater. Interfaces$ 1 140009). The colloidal layer is removed leaving a connected metallic network invisible to the eye. So the surface becomes conducting, while retaining its transparency. The challenge lies in maximizing electrical conductivity while retaining the transparency as far as possible. An optimal combination of the system parameters, which affect the morphology of the crack network is necessary to meet this challenge. In this work, we simulate crack pattern in desiccating colloidal ﬁlms in three dimensions using a spring network model. We look for the optimal combination of system parameters, such as ﬁlm thickness, material stiffness and polydispersity, which can produce the best template for producing a conducting network on transparent surfaces.

• Tuning magnetoresistance and electrical resistivity by enhancing localization length in polyaniline and carbon nanotube composites

We report low temperature electrical resistivity and magnetoresistance (MR) measurements of conducting polyaniline (PANI) and multiwalled-carbon nanotube (MWCNT) composites. We have used an in-situ oxidative polymer-ization method to synthesize hydrochloric acid-doped PANI composites with MWCNT weight percentages of 0, 5, 10 and 15. The temperature dependence of resistivity is studied from room temperature to 4.2 K and analysed by a Mott variable range hopping (VRH) model. The resistivity increases from 1.1 × 10⁻³ Ωm at 300 K to 65.75 Ωm at 4.2 K, almost four orders of the magnitude change with temperature for pure PANI. Whereas the PANI composite with 15% MWCNTs shows less variation from 4.6 × 10⁻⁴ to 3.5 × 10⁻² Ωm. The huge change in resistivity is due to the localization of charge carriers in the presence of disorder. At 4.2 K MR shows transition from positive to negative with higher MWCNT loading. Samples with 5 and 10% MWCNTs show positive MR, whereas the 15% MWCNT loaded sample shows negative MR. The positive and negative MR are discussed in terms of the wave function shrinkage effect and quantum interference effect on VRH conduction.

• Structural and optical characterization of Sm-doped ZnO nanoparticles

Micro-structural changes in zinc oxide (ZnO) nanoparticles induced by the substitution of Zn²⁺ in ZnO by a rare earth (RE) metal ion, Sm³⁺, are investigated. Both pristine and Sm-doped ZnO with a nominal doping concentration of 1, 2 and 4% of Sm using a simple wet-chemical synthetic route followed by calcination at a high temperature of $900^{\rm o}$C, are synthesized. Structural investigations are primarily conducted using X-ray powder diffraction (XRPD) and scanning electron microscopy techniques. Evolution of structural parameters (unit cell parameters, average crystallite size, crystallinity percentage, lattice strain, stress, energy density and atomic packing factor) upon Sm doping is investigated together with Rietveld reﬁnement and Le Bail analysis techniques. XRPD data conﬁrmed that the synthesized nanostructures crystallize in a wurtzite hexagonal structure, the dopant Sm is incorporated into the Zn lattice and the annealing treatment plays a crucial role in determining the structural and optical properties of RE-metal-doped nanoparticles. Values of the optical band gap energy estimated from optical absorbance measurements reveal a widening of the band gap.

• Preparation of an aluminium phosphate binder and its inﬂuence on the bonding strength of coating

In this paper, aluminium phosphate binders were synthesized using Al(OH)₃ and H₃PO₄ as the raw materials. These binders, with the curing agent MgO and ﬁller ZrO₂, were used to prepare coatings by brush painting on the carbon ﬁbre-reinforced epoxy resin matrix composites. The inﬂuences of synthesis conditions such as the P/Al ratio, concentration of the reactant and reaction temperature on the viscosity of binders and the bonding strength of corresponding coatings were investigated by using a viscometer and a universal testing machine. The structures and compositions of aluminium phosphate binders were characterized by X-ray diffraction, Fourier transform infrared and Raman spectroscopy. The results show that with a decrease in the ratio of P/Al, the degree of polymerization of the aluminium phosphate binder increases, the viscosity increases, while the bonding strength of the coating decreases. When P/Al = 3:1, the reaction product is Al(H₂PO₄)₃ with the best properties of bonding strength. As the concentration of phosphoric acid solution increases in the range of 60–80%, the viscosity increases on account of larger quantity of viscous molecules in a unit volume and higher extent of polymerization of the phosphorus oxygen tetrahedron. The compositions of aluminium phosphate binders are almost the same when the reaction temperature changes from 120 to $180^{\rm o}$C, so the viscosity of the binder and the bonding strength of the coating do not exhibit obvious changes along with temperature.

• Inclusion of water and KDP as a mechanism for controlling structural and dielectric parameters in PVDF ﬁlms

n this work, the possibility of improving the microstructural and dielectric properties of poly(vinylidene ﬂuoride)(PVDF) by the addition of potassium dihydrogen phosphate (KDP) to the polymer matrix is speculated. Both PVDF and KDP are ferroelectric and piezoelectric materials, so the combination may result in a synergistic interaction. PVDF and KDP were dissolved in water/dimethylformamide at 70#176&;C. The solutions were deposited by casting to obtain ﬁlms. The samples were characterized by energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. XRD tests of the samples showed that hydrated PVDF ﬁlms resume crystallinity up to a maximum content of 3.0% by weight of KDP. FTIR conﬁrmed the possibility of adjusting the intensity of the alpha (α)-and beta (β)-phase peaks in the polymer through water and KDP contents. Finally, the dielectric constant and the dielectric loss factor of the new materials at room temperature were determined.

• Robust optical and electrical properties of TiO₂-sensitized polymeric (PANI–TiO₂) nanocomposites for hybrid solar cell application

A polyaniline (PANI)-based TiO₂-sensitized polymeric active layer was synthesized via an in situ polymerization technique in the presence of ammonium persulphate (APS as the oxidizer) for its use in hybrid solar cell application. TiO₂-sensitized tubular PANI nanocomposites with an average diameter of ∼50 nm proved to be very efﬁcient for optimizing the optical band gap so as to absorb the maximum solar spectrum. The synergistic combination of PANI–TiO₂ (4%) featured the maximum current for varying concentrations of TiO₂ towards current–voltage (I –V ) and cyclic voltammetry measurements. Further, the thermal stability was markedly enhanced by incorporating TiO₂ nanoparticles into the polymer matrix as compared to pure PANI.

• Unprecedented exploration of ionic liquids as additives which astonishes the thermal stability of PVC formulations

he use of ionic liquids as additives and an economic and environmentally benign alternative to conventional inorganic and organic additives in poly(vinyl chloride) (PVC) formulation is investigated by using thermogravimetric anal-ysis. The present study deals with an elegant exploration of the resulting thermal proﬁles to disclose the pattern of thermal degradation for $N$-butylpyridinium hexaﬂuorophosphate and PVC formulation as well. Furthermore, non-isothermal kinetic investigations providing sound information about kinetic parameters, such as activation energy and frequency factor by using the Coats–Redfern equation in the temperature range of 593–663 K for $N$-butylpyridinium hexaﬂuorophosphate and 423–473 K for the resulting PVC formulation were performed.

• Effect of exfoliated few-layered graphene on corrosion and mechanical behaviour of the graphitized Al–SiC surface composite fabricated by FSP

The inﬂuence of friction stir processing parameters and the subsequent evolution of microstructures and cor-rosion behaviour of Al–SiC surface composites fabricated in the presence of graphitic ﬂakes are presented in this paper. The circumferential shear stress exerted by the rotating tool exfoliates the graphite ﬂakes into few-layered graphene during processing. These graphene ﬂakes preferentially occupy both the grain boundaries and the SiC–Al interface during recrys-tallization. The potentiodynamic polarization test, in 3.5 wt% sodium chloride (NaCl) solution, is conducted for samples processed at various tool rotational speeds and it is found that the presence of this thin graphitic layer at these locations reduces the intergranular and interfacial corrosion to a great extent. The tool rotational speed has a signiﬁcant inﬂuence on processing, and samples fabricated at an optimum tool rotational speed of 2200 rpm shows better corrosion resistance and mechanical properties as compared to that at lower and higher speeds. Raman spectroscopic analysis, X-ray diffraction studies and microhardness tests corroborate the experimental results and the proposed mechanisms.

• Synthesis of Li$x$(Ni0.80Co0.15Al0.05)O2 cathodes with deﬁcient and excess lithium using an ultrasonic sound-assisted co-precipitation method for Li-ion batteries

The possible improvements in structural stability and capacity of nickel–cobalt–aluminium cathode mate-rial were investigated by synthesizing this compound with various lithium amounts (Li$x$(Ni0.80Co0.15Al0.05)O2 where $x$ = 0.90, 0.95, 1.00 and 1.05). An ultrasound-assisted co-precipitation method was performed to produce spherical, nanosized powders with a narrow size distribution which satisﬁes a homogeneous and dense ﬁlm during calendaring. Lay-ered Li$x$(Ni0.80Co0.15Al0.05)O2 ($x$ = 0.90, 0.95, 1.00 and 1.05) cathode active materials were successfully synthesized with this method and chemical compositions of the powders synthesized were determined by inductively coupled plasma-mass spectroscopy. Structural characterization was carried out via X-ray diffraction and scanning electron microscopy techniques. The electrochemical properties of the cathode materials were investigated by electrochemical impedance spec-troscopy, galvanostatic charge/discharge and cyclic voltammetry methods. Among the cathode compositions in the currentstudy, Li1.05(Ni0.80Co0.15Al0.05)O2 exhibited the highest capacity, 138 mAh g⁻¹ with 95% capacity retention upon 22 cycles.

• The electronic and optical properties of monovalent atom-doped ZnO monolayers: the density functional theory

The current study deals with the structural, electronic and optical properties of monovalent element-doped ZnO monolayers using density functional theory. Speciﬁcally, we have considered structural and optical properties of monovalent (M = Li, Na and K) atom-doped ZnO monolayers. Among these monovalent elements, the substitution of Li with Zn atom maintains the hexagonal planar geometry of the ZnO monolayer, but Na and K elements protrude out from the plane of the ZnO monolayer. The Li atom binds more strongly with the ZnO sheet compared with Na and K atoms. A Li-doped ZnO monolayer shows metallic behaviour whereas Na- and K-doped ZnO monolayers show half metallic magnetic behaviour. The magnetic moment is of the order of 1μB. The magnetic moment mainly originates from nonbonding O$_{\rm p}$ states. The substitution of an alkali metal element-doped ZnO monolayer leads to a red-shift in optical spectra. The dielectric constant of a monovalent element-doped ZnO sheet increases compared with that of a pristine ZnO sheet. This study provides the basis to develop opto-electronic devices using doped ZnO monolayers.

• Characterization of ultra-ﬁne aluminium particles with potential applications as composite propellants

High performance and reactivity of ultra-ﬁne aluminium is the present new area of interest in aerospace and defence applications. Ultra-ﬁne aluminium is an important ingredient in propellant compositions and formulations, which signiﬁcantly improves the performance parameters of rockets. This paper discusses the characterization of synthesized ultra-ﬁne aluminium, such as active (metallic) aluminium content, bulk density, X-ray diffraction, surface area (Brunauer–Emmett–Teller), scanning electron microscopy, transmission electron microscopy, thermal analysis and X-ray photo-electron spectroscopy. It is observed that the maximum metallic aluminium content of 85.93% was obtained by a gas volumetric method. The synthesized ultra-ﬁne aluminium particles will greatly promote the application of these particles in composite propellants.

• Effect of non-180° polarization invariants on the exchange bias of tetragonal ⟨001⟩ and rhombohedral ⟨111⟩ orientations of bismuth ferrite epitaxial thin ﬁlms

BiFeO₃ (BFO) is the only room temperature multiferroic material that has been extensively studied due to its multifunctional properties. BFO with a canted G-type antiferromagnetic (AFM) ordering exhibits strong exchange bias characteristics with NiFe which offers the potential to design and utilize devices working based on multiferroic features. In the past, it was known that the presence of 180° domain walls of BFO hinders a plausible exchange bias interaction. To understand the role of the strain-induced effects on such 180° domain walls and its effect on the exchange bias, NiFe, a soft ferromagnetic layer, was grown on the epitaxial BFO AFM layers. An approximately 80 nm BFO layer was grown epitaxially in both the tetragonal (001) phase on the LaAlO₃ (001) substrate and the rhombohedral (111) phase on the SrTiO₃ (111) substrate, with a thin (10 nm) layer of Ni₈₀Fe₂₀ on top of it. An exchange bias of 510 Oe was observed in the tetragonal phase of BFO with a $c/a$ ratio of 1.22, which is comparable with the exchange bias shown by the (111) oriented rhombohedral phase (360 Oe). Both the tetragonal (001) and rhombohedral (111) layers possess ferroelectric polarization normal to the sample surface and so the domain walls are mostly 180° oriented which is expected to have a minimum effect on the exchange bias. However, the weak strain-induced structural variants in the (111) oriented rhombohedral BFO and the monoclinic distortion present in the tetragonal BFO introduce non-180° domain walls in the system. These variants arising due to the structural distortion are expected to play a key role in deﬁning the ferroelectric domain wall nature, thereby exhibiting exchange bias characteristics.

• Spectral and optical characterization of the new semi-organic crystal: 4-methylbenzylammonium chloride hemihydrate, to establish protonation and the effect of resultant hydrogen bonding

4-Methylbenzylammonium chloride hemihydrate (4MLBACH) single crystals were obtained by slowly evapo-rating the solvent. The characterization of the title crystal was ﬁrst carried out and reported in this article. The crystal system and space group of the title crystal are identiﬁed as monoclinic and $C$2/$c$, respectively. The lattice parameter values were also calculated. Using Fourier transform infrared spectroscopy the protonation of 4-methylbenzylamine by hydrochloric acid and the formation of the crystal 4MLBACH were conﬁrmed. The transmission window of the grown crystal is between 261 and 1100 nm. The protonation of the amine group is conﬁrmed by nuclear magnetic resonance spectral analysis. Z-Scan analysis was carried out to determine the nonlinear optical parameters. It reveals that the nonlinear susceptibility (χ³) value is greater than some reported crystals. The title crystal exhibits saturable absorption and self-defocussing effects.

• Multifunctional properties of ceria nanocubes synthesized by a hydrothermal method

Nanosized ceria is an extremely versatile and commercially valuable material because of its industrially impor-tant applications. The present work describes the synthesis of ceria nanocubes by a simple hydrothermal method. The size of the synthesized ceria nanocubes are 8–20 nm. The formation of ceria phase has been corroborated by X-ray photoelec-tron spectroscopy and X-ray diffractometry. Selected area electron diffraction patterns obtained for the nanocubes are also precisely indexed to the cubic ceria phase. The synthesized ceria nanocubes exhibit a high surface area of 26 m² g⁻¹ and also high catalytic activity. The work also investigates the inﬂuence of ceria nanocubes on the corrosion resistance of sol–gel hybrid coatings in 3.5% NaCl solution on AA2024 substrates. The corrosion behaviour of the sol–gel coatings revealed that ceria nanocubes reinforce the barrier properties of the sol–gel coatings and confer longer active protection to the metallic substrate.

• Leaching studies on borosilicate glasses for the immobilization of high-level radioactive waste in the pellet form subjected to aggressive test conditions

Pellet leaching and associated thermal and structural changes of sodium borosilicate (NBS) glass, used for the immobilization of high-level radioactive liquid waste, subjected to aggressive test conditions have been compared with international simple glass (ISG) subjected to the same leaching conditions. The crystalline phase getting separated out from NBS glass is found to be different for pellets and powder leaching experiments and this has been explained based on the difference in the extent of leaching occurring with glass samples in the two experiments. Based on Fourier transform infrared studies, it is inferred that, unlike in the ISG sample, Si–O–Si/B structural units become more ordered with the leaching in the case of NBS glass, and this is attributed to the partial network destruction occurring with NBS glass and crystallization of the SiO₂ phase from the glass matrix. Both the NBS glass and ISG sample show L-centre emission and the emission intensity remained unaffected with leaching, conﬁrming that the local environment around non-bridging oxygen atoms in the NBS glass and ISG sample are unaffected and leaching occurs through network dissolution.

• Morphological engineering of SnO₂ and In₂O₃ ﬁlms deposited by spray pyrolysis

This article demonstrates the possibility of controlling the morphology of deposited metal oxide ﬁlms by the preliminary formation of the seed-layers of the appropriate oxide on the substrate surface using a simple and cheap method such as successive ionic layer deposition. The study focuses on SnO₂ and In₂O₃ due to their importance in the ﬁeld of various chemical microsensors.

• A study of the early hydration processes and properties of ﬂy ash-slag binders

The results of a study on the early hydration process of pastes composed of ground granulated blast furnace slag and ﬂy ash from ﬂuidized bed combustion of brown coal are presented here. The results of the tests concerning setting time, hydration processes (spectroscopy, calorimetry and thermogravimetry) and mechanical strength conﬁrm that the hydration process occurs and solid microstructures and hydration products (hydrated calcium silicates and aluminosilicates, sulphoaluminates and calcium hydroxide) are formed. The presence of calcium carbonate was conﬁrmed. Increasing the amount of ﬂy ash in pastes intensiﬁes the process of early hydration, thereby accelerating the initial setting time and increasing the amount of water bound in hydration products. The early compressive strength is also improved. For example, the specimen containing the highest amount of ﬂy ash showed a decrease in the initial setting time by about 20% and an increase in the 2-day compressive strength by 22%, compared to the specimen containing the lowest amount of ﬂy ash.

• Elastic, thermoluminescence and dielectric characterization of lead antimony silicate glass composites doped by small concentrations of Cr₂O₃

A series of glass composites [(Sb₂O₃)0.05(SiO₂)0.65]–[(PbO)(0.3−x):(Cr₂O₃)x ](0 ≤ x ≤ 0.01 mol%) were synthesized. Elastic, thermoluminescence, direct current (dc) conductivity and dielectric characteristics of these glass com-posite materials were studied. The investigations on these glass composites have indicated that the chromium ions exhibit two different oxidation states, such as Cr³⁺ and Cr⁶⁺. The variation in poison ratio (σ ) with micro-hardness (H) plots suggests that the glass composites were prepared with a strongly and covalently connected internal structure. The observed thermoluminescence output increased with an increase in the dose of UV-irradiation. The observed peak positions of these thermoluminescent curves were shifted towards higher temperature regions. The enhanced thermoluminescence output results even recommended that both e− and h+ trap cantres were created at the deeper trap levels and contribute to thermolu-minescence emissions at higher temperatures. The dc conductivity (σ_{dc}) and activation energy evaluations are also observed. Dielectric parameters such as density of energy states $N$($E$_{f} ), temperature region of relaxation and loss tangent (tan δ)were calculated. The linear relationship between variation in alternating current conductivity (σ_{ac}) and activation energy suggests that good amounts of polaron hopping with an increase in Cr₂O₃ concentration in these materials were observed. The grades of loss tangent and the number of energy states near the Fermi level suggest that the materials prepared are highly useful in dielectrics.

• Improvement in electro-optical and dielectric characteristics of ZnO nanoparticles dispersed in a nematic liquid crystal mixture

Reported herein is the effect of dispersion of a ﬁxed amount of 0.5% (wt/wt) ZnO nanoparticles (NPs) in a nematic (E7) liquid crystal (LC) mixture. Dispersion of ZnO NPs results in a signiﬁcant improvement in electro-optical and dielectric parameters of the nematic mixture. Comparative analysis of undoped and NP-dispersed samples shows a reduced threshold voltage with better transmittance without compromising dielectric permittivity characteristics. In addition, an increase in the contrast ratio, birefringence, alternating-current conductivity and band gap was observed after dispersion of ZnO NPs in LCs. A polarized optical microscopic study of the NP-dispersed sample substantiates a slight increase in nematic–isotropic phase transition temperature of LCs.

• Synthesis and application of a polymeric intumescent ﬂame retardant for cotton fabric

A novel polymeric intumescent ﬂame retardant containing phosphorus, nitrogen and sulphur (poly(ditrimethylolphosphono thiourea (PDTPT)) was synthesized, and its chemical structure was characterized by Fourier-transform infrared spectroscopy, ¹Hand ³¹P nuclear magnetic resonance spectroscopy and elemental analysis. The molecular weight and thermal properties of PDTPT were measured by using gel permeation chromatography and thermogravimetric analysis. PDTPT exhibited good thermal stability, char formation and swelling performance. The initial thermal decomposi-tion temperature and quality residual rate at 600°C of PDTPT were 282°C and 48.8%, respectively. When the mass fraction of PDTPT was 25 wt%, the limiting oxygen index-value of the cotton fabric/PDTPT composite was 27, an increase from 18 for the pure cotton fabric. Subsequent thermal analysis and scanning electron microscopy showed that PDTPT addition reduced the initial degradation temperature and the weight loss rate of the cotton fabric by forming a thick and tight carbon layer on its surface.

• Investigation of erosion behaviour of an iron-mud ﬁlled glass-ﬁbre epoxy hybrid composite

Iron-mining and ore processing (mainly laterite) are faced with the major challenge of generated overburden and topsoil aggregates (iron-mud) as a major solid waste. Storage and reclamation are two severe problems with harmful environmental concerns. The present paper investigates the possible uses of iron mine waste for developing a new-class hybrid polymer composite and its tribological characteristics. The polymer composites are fabricated through a hand-layup process by reinforcement of woven glass ﬁbres in an epoxy polymer ﬁlled with different weight proportions of iron-mud. Erosion wear experiments were conducted on the fabricated composites according to a Box–Behnken design approach using an air jet-type erosion tester. The artiﬁcial neural network predicted values which exhibited close relationship with the experimental erosion values. Filler addition resulted in an improvement in the erosion resistance. A meta-heuristic approach like particle swarm optimization reveals the minimum erosion value at an optimal parametric combination. Finally, the morphology of eroded surfaces was critically examined by scanning electron microscopy and possible erosion mechanisms were presented.

• Structural and optical properties of synthesized poly(methyl methacrylate) (PMMA) and lanthanide β-diketonate complexes incorporated electrospun PMMA nanoﬁbres for optical devices

Fabrication of electrospun nanoﬁbres is the glittering area of research because of their ﬂexible characteristics and numerous applications in almost all walks of life and technology. Poly(methyl methacrylate) (PMMA) is one of the signiﬁcant and interested synthetic polymers in the recent research because of their characteristic properties like higher environmental stability, resistance to attack by moulds and enzymes, commercial availability, easiness to handle, etc. In the present study, pristine PMMA nanoﬁbres with diameters of 60–150 nm with 109 nm as the most distributed one are prepared by an electrospinning method using a binary solvent mixture. An enhancement in the intensity of visible photoluminescence emission is observed in PMMA nanoﬁbres embedded with samarium and neodymium β-diketonate complexes. The morphological incorporation of samarium and neodymium β-diketonate complexes in PMMA nanoﬁbres and material composition of the samples are examined by high resolution electron microscopy analyses. The amorphous nature and molecular bonding of pure PMMA nanoﬁbres and incorporated ﬁbre complexes are elucidated through structural and molecular analyses. The supreme optical absorptions and reemissions of samarium and neodymium β-diketonate complexes embedded in the pure PMMA ﬁbre sample in the visible region indicate not only their application in lighting or display devices, but also as active materials in organic light emitting diodes for new era curved/rolled display devices.

• Preparation of polyurethane-acrylate and silica nanoparticle hybrid composites by a free radical network formation method

In this study, hybrid composites of polyurethane-acrylate (PUA) and silica nanoparticle were prepared by a radical method. For this aim, silica nanoparticles were chemically functionalized with 3-methacryloxypropyltrimethoxysilane. Polyurethane was synthesized and then modiﬁed with 2-hydroxyethyl methacrylate to yield PUA. Then, different amounts of modiﬁed-silica were used to prepare PUA composites by the addition of an ethylene glycol dimethacrylate crosslinker. Fourier-transform infrared spectroscopy conﬁrmed the successful functionalization of silica nanoparticles and the prepa-ration of PUA. Structural investigation of the functionalized-nanoparticles and also nanocomposites was carried out using X-ray diffraction and electron microscopy. According to the thermal gravimetric analysis results, char residue of HSiO₂ is 86.6%, which decreases to 81.3% in the case of MSiO₂ as a result of its modiﬁer degradation content of 5.3%. PUAS5 shows main decomposition temperatures of 396.5 and 454.9°C and also char content of 5.7% at 700°C. The high amount of MSiO₂ can also be resulted in higher degree of crosslinking and therefore higher thermal stabilities and char residue.

• AC conductivity and broadband dielectric spectroscopy of a poly(vinyl chloride)/poly(ethyl methacrylate) polymer blend

Alternating-current (ac) conductivity and dielectric relaxation behaviour of a poly(vinyl chloride)/poly(ethyl methacrylate) polymer blend have been investigated intensively in a frequency range from 1 × 10⁻¹ to 2 × 10⁷ Hz through a temperature range from 300 to 393 K. The variation of σac of pure and polyblend samples showed a plateau region at high temperature and low frequency and this plateau region is decreased with decreasing temperature. Values of the exponent $n$ are less than unity indicative of the correlated barrier hopping for conduction. The values of the exponent $n$ are used to calculate the binding energy (Wm) of the charge carriers. The investigation of the frequency dependence of ε' for pure and polyblend samples showed a dielectric dispersion. The high values of dielectric constant at a low frequency and high temperature are attributed to the effects of space charge due to the electrode polarization. The complex electric modulus (M*) of pure and polyblend samples has been investigated. It is found that the real part of the complex electric modulus, M' is increased non-linearly as the frequency increased and reached the steady state at higher frequencies for all samples. On the other hand, the imaginary part of the complex electric modulus, M'' is characterized by a relaxation peak. The different modes of relaxation, such as interfacial polarization and dipolar relaxation, are detected in low and high frequency regions in the variation plot of M'' against frequency. The activation energy values of both interfacial polarization and α-relaxation are calculated.

• Evaluation of anticorrosive behaviour of ZnO nanotetra-pods on a AZ91-grade Mg alloy

Highly cross-linked zinc oxide (ZnO) with the nanorod morphology of tetra-pods was successfully prepared using a microwave irradiation (MWI) technique. In comparison with the available conventional techniques, the MWI tech-nique has the advantage of producing different morphological structures with high purity and in a shorter reaction time. These tetra-pods consist of a ZnO core in the zinc blende from which four ZnO arms emerge in the wurtzite structure. In this investigation, the effects of irradiation times and the growth mechanism of ZnO nanotetra-pods were discussed. The structural, morphological and optical properties of ZnO nanorods were investigated by ﬁeld emission scanning electron microscopy, X-ray diffraction, an ultra violet visible spectrometry and energy-dispersive spectroscopy. The electrochemical corrosion behaviours of an AZ91-grade Mg alloy and a ZnO/PN nanotetra-pod-coated Mg alloy were investigated. The Tafel plot revealed that the corrosion of Mg drastically decreased on coating with a thin layer of ZnO nanotetra-pods and PN (Mg/PN/ZnO) compared to Mg in a KOH electrolyte.

• Investigating silk yield and morphological changes in silk fibres obtained from silkworms fed with Ag and/or TiO$_2$ nanoparticles

Natural polymers like silk can be augmented in vivo with metallic elements to improve their intrinsic properties and stability. This study demonstrates the uptake of Ag and/or TiO$_2$ nanoparticles as diet supplements by silkworms. Nanoparticles dose on morphological changes in silk fibroin fibres and a change in overall silk yield was investigated. Though significant fibre reinforcement with Ag and/or TiO$_2$ was not noticed; an increase of 6% in the silk production was observed when silkworms fed with a particular composition of Ag $+$ TiO$_2$ nanoparticles (0.37 mM each) in their diet. Here, an average diameter of the degummed silk fibre was $\sim$10.91 $\mu$M with a roughness parameter value $R_{\rm q}$ being 134. This valueis comparable to silk fibres obtained from silkworms fed with Ag $+$ TiO$_2$ ($0.22 + 0.53$ mM) nanoparticles and this $R_{\rm q}$ value was also low when compared to the other tested compositions with nanoparticles. Silks from the control samples (devoid of nanoparticles in their feed) had high diameter fibres and are with low $R_{\rm q}$ values and silk yield. However, nanoparticlesupplementation to the silkworm’s diet resulted in low diameter silk fibres with varying roughnessess and with improved silk yield for the tested doses.

• Hydrothermal synthesis of strontium-doped ZnS nanoparticles: structural, electronic and photocatalytic investigations

Strontium-doped ZnS nanoparticles (NPs) (1.5, 5 and 9 wt%) were synthesized through a surfactant free hydrothermal method. The structural characterization by X-ray diffraction confirms the synthesis of ZnS, with its twocrystalline phases (cubic and hexagonal), without apparition of any peaks related to Sr phases. The crystallite size is affected by Sr doping concentration and was estimated in the range of 2.24–2.51 nm. Furthermore, transmission electron microscopy images show that the NPs have great tendency to aggregate into spherical shapes. Spectroscopy analysis revealed vibration modes specific to ZnS materials on the Raman spectra at about 260 and 345 cm$^{−1}$ and on Fourier-transform infrared spectra at 668.9 cm$^{−1}$. Electronic investigation performed by UV–Visible diffuse reflectance spectroscopy showed that thesynthesized ZnS NPs are optically transparent in the visible domain and their band gap energy decreases from 3.42 to 3.38 eV with increasing Sr concentration. Finally, the methyl orange degradation rate increases with Sr concentration, revealing an improvement in the photocatalytic properties of Sr-doped ZnS NPs.

• Hydrothermal synthesis of spindle-like SrMoO$_4$:Ln$^{3+}$ (Ln $=$ Eu and Tb) microarchitectures for selectively detecting Fe$^{3+}$ ions

In this work, spindle-like micrometre SrMoO$_4$:Ln$^{3+}$ (Tb, Eu) phosphors have been synthesized and designed as a fluorescent sensor for Fe$^{3+}$ ions assay. The structural information, morphologies and luminescence properties of the samples were characterized by X-ray diffraction, Fourier-transform infrared, Raman analysis, field-emission scanning electronmicroscopy and photoluminescence patterns. Furthermore, Fe$^{3+}$ ions could be immediately detected using fluorescence quenching methods, and this method shows excellent and satisfying sensitivity. This facile method could be extended to environmental and biological applications.

• Dielectric properties of Ag/Ru$_{0.03}$–PVA/$n$-Si structures

Ag/Ru$_{0.03}$−PVA/$n$-Si structures were successfully prepared and their morphological and electrical properties were investigated. The obtained electrical results suggested that the complex dielectric constant ($\epsilon^* = \epsilon^{\prime} − j\epsilon^{\prime\prime}$), complex electric modulus $M^∗ = M^{\prime} + jM^{\prime\prime}$, loss tangent ($\tan \delta$) and alternating current (ac) electrical conductivity ($\sigma_{\rm ac}$) are all a strong function of the frequency ($f$) and applied voltage. The changes in these parameters are the results of the existence of the surface states ($N_{\rm ss}$) or interface traps ($D_{\rm it} = N_{\rm ss}$), interfacial polymer layer, surface and dipole polarizations and hopping mechanisms. The values of $\epsilon^{\prime}$ and $\epsilon^{\prime\prime}$ show a steep decline with increasing frequency and then reach a constant value at high frequency, whereas the increments of $M^{\prime}$ and $M^{\prime\prime}$ with frequency are exponential. The $\tan \delta$ vs. $\log f$ plot has a strong peak behaviour, especially in the accumulation region. These experimental results suggested that the Ru$_{0.03}$−PVA interfacial layer could be used as a high dielectric material instead of conventional materials.

• Efficiency of sapota leaf extract against aluminium corrosion in a 3 M sodium hydroxide hostile fluid atmosphere: a green and sustainable approach

The present study focussed on the performance of a sapota leaf extract in controlling the aluminium (Al) corrosion in 3 M sodium hydroxide (NaOH) medium thoroughly investigated through gasometric, atomic absorption spectroscopy,electrochemical Tafel diagrams and impedance spectroscopy techniques. The outcome shows that small amounts of the sapota leaf extract are sufficient for the effective mitigation of the Al corrosion process in 3 M NaOH solution. The gasometric data revealed that four different concentrations of the plant extract inhibit the Al corrosion process and the protection efficiency of the inhibitor varies with time of the system.Type of inhibition was studied by an electrochemical potentiodynamic polarizationtechnique. The alternating current impedance spectroscopy results show that the plant extract inhibits the corrosion process by forming a defensive layer on the Al surface through an adsorption process, which confirms the inhibition properties of the plant extract. The presence of electron rich groups in the sapota leaf extract was confirmed by the Fourier transform infrared and energy-dispersive X-ray spectroscopy techniques. The particle size of the sapota leaf extract can be analysed by an X-ray diffraction technique. Further, atomic force microscopy and contact angle results evidence the adsorption of the sapota leaf extract on the Al surface. The morphology of the Al surface in protected and unprotected systems was examined through scanning electron microscopy techniques.

• Preparation of copper–silver alloy with different morphologies by a electrodeposition method in 1-butyl-3-methylimidazolium chloride ionic liquid

Electrodeposition of a copper–silver alloy based on a 1-butyl-3-methylimidazolium chloride (BMIC) ionic liquid was studied. The electrochemical behaviour of copper and silver ions was characterized by cyclic voltammogram.The morphologies and phase compositions of copper–silver alloy coating under different electrodeposition conditions were investigated by scanning electronmicroscopy and X-ray diffraction. The results show that copper–silver alloys with different micro-morphologies can be obtained under different potential conditions in BMIC. Co-deposition of the copper–silver alloy followed a two-step reduction process, the first step is the reduction of the cupric ion to the cuprous ion and the second step is the simultaneous reduction of the cuprous ion and the silver ion to form an alloy. A dendritic alloy can be obtained at $−$0.60 V, a bract alloy can be obtained at $−$0.80 V and a granular alloy can be obtained at $−$1 V. The coating particle size at 60$^{\circ}$C was smaller than the particle size obtained at 40$^{\circ}$C. The Cu–Ag alloy prepared by electrodeposition in ionic liquids consists of single-phase copper and single-phase silver.

• Corrosion behaviour of the Al-2.1–Mg-1.8–Si alloy in chloride solution

The corrosion behaviours of Al–Mg–Si alloys were studied in different Cl$^−$ concentrations by means of scanning electron microscopy, transmission electron microscopy and electrochemical experiments. The results show that the corrosionbehaviours of Al–Mg–Si alloys are closely related to the Cl$^−$ concentration. With an increase in Cl$^−$ concentration, the corrosion rate increases sharply by facilitating the process of chemical and electrochemical reactions. In 2.0 wt.% NaCl solution, slight pitting corrosion occurred around theMgSi phase, but corrosion trenching was not found around the Fe–Mn–Si phase. In 3.5 wt.% NaCl solution, the alloy appeared localized corrosion dominated by intergranular corrosion attack. In 5.0 wt.% NaCl solution, the alloy presented serious overall corrosion, and the passivation platform of the polarization was not obvious. Furthermore, an appropriate corrosion mechanism according to polarization and electrochemical impedance spectroscopy was proposed for the Al–Mg–Si alloy in NaCl solution. In addition, the corrosion rate influenced by differentCl$^−$ concentrations was discussed in detail.

• Experimental and theoretical analyses of transformation temperatures of Cu-based shape memory alloys

Binary-shape memory alloys that are based on copper, mainly copper–aluminium, copper–zinc and copper–tin alloys, either with or without ternary elemental additions, are of special interest to the industry and academia because of their good shape recovery, ease of processing, larger recovery strain and lower cost. However, unlike Ni–Ti shape memory alloys, their uses are moderately limited due to shortcomings, such as stabilization of martensite due to ageing, brittleness and low mechanical strength. Therefore, efforts have been made over the years to overcome these limitations using appropriate ternary and quaternary elemental additions. This work takes into account the data obtained from the experimental work carried out by the authors of this paper as well as the data obtained from the experimental and theoretical works carried out by earlierresearchers in this area that have been published in the literature over the years. It is observed in quaternary shape memory alloys based on copper that with an increase in the atomic radius of the quaternary element, the hysteresis width is found to increase. With the addition of ternary elements to binary Cu-based alloys (Cu–Al and Cu–Zn), and quaternary elements to ternary Cu-based alloys (Cu–Al–Fe, Cu–Al–Ni, Cu–Al–Mn, Cu–Zn–Al, Cu–Zn–Ni and Cu–Zn–Si), the $M_s$ temperature either increases or decreases. This influence is directly correlated with the $e_v/a$ ratio and $c_v$ values. It is also observed that asthe concentration of electrons decreases, the $M_s$ temperature decreases too. In addition, in this paper, we have tried to obtain relationships between the $M_s$ temperature and the mass or atomic% of different elements through multiple regressions to generalize the interpretations.

• Photo-catalytic dye degradation of methyl orange using zirconia–zeolite nanoparticles

In this research, the dye photo-catalytic removal was investigated using zirconia (ZrO$_2$) nanocatalysts, zeolite (Ze), ZrO$_2$–Ze with different percentages and optimized ZrO$_2$–Ze doped via urea, copper oxide and cerium oxide. In order to determine the optimal conditions, the effects of different catalysts and parameters such as dye concentration, UV lamp power, amount of the loaded catalyst and pH were investigated. The response surface methodology was used to obtain optimal experimental conditions. Physical and chemical properties of materials were investigated by X-ray diffraction,Fourier transform infrared, scanning electron microscopy and Brunauer–Emmett–Teller. Completely methyl orange (MO)-dye removal (100%) was achieved at optimal conditions under UV light during 80 min. The optimal operational condition for MO photo-catalytic decomposition using an optimal N-doped 10 wt% ZrO$_2$–zeolite nanocatalyst was obtained at UV lamp power, pH, catalyst loading and dye concentration of 15 W, 3, 0.4 g l$^{−1}$ and 5 mg l$^{−1}$, respectively. Photo-catalytic degradation kinetics of MO described well using pseudo-first order which is in accordance with the Langmuir–Hinshelwoodmodel ($k_{\rm app}$ = 0.031$min$^{−1}$). • Modelling of novel-structured copper barium tin sulphide thin film solar cells In this work, a novel structured Cu$_2$BaSnS$_4$(CBTS)/ZnS/Zn(O, S) photovoltaic device is proposed.Anontoxic, earth-abundant and auspicious quaternary semiconductor compound copper barium tin sulphide (Cu$_2$BaSnS$_4$) is used as an absorber layer.We propose a novel Zn(O, S) buffer layer for a high-power conversion efficiency (PCE) of CBTS-based thinfilm photovoltaic cells. Solar cell capacitance simulator software is used for device modelling and simulations are performed under a 1.5 AM illumination spectrum. The proposed device is investigated by means of numerical modelling and optimized the parameters to maximize its efficiency. Promising optimized functional parameters had been achieved from the proposed structurewith back surface field layer with a PCE of 18.18%, a fill factor of 83.45%, a short-circuit current of 16.13 mA cm$^{−2}$and an open-circuit voltage of 1.3 V. The promising results give an imperative standard for possible manufacturing of highefficiency, eco-friendly inorganic CBTS-based photovoltaic cells. • Synthesis of a high-quality NaP zeolite from epidesmine by a hydrothermal method Epidesmine as a silicon source was used to synthesize NaP zeolite by a hydrothermal method. Parameters such as SiO$_2$/Al$_2$O$_3$and H$_2$O/Na$_2$O molar ratios, reaction temperatures and reaction times were investigated for regulating the purity of the final product. The samples were characterized by X-ray diffraction, infrared spectroscopy and scanning electronmicroscope. The experimental results evidenced that a high-quality NaP zeolite was obtained at SiO$_2$/Al$_2$O$_3$and H$_2$O/Na$_2$O molar ratios of 3.7 and 55, respectively, and at a temperature of 95$^{\circ}$C for 6.5 h of ageing. The BET surface area and total pore volume of the powders were 17.1359 m$^2$g$^{−1}$and 0.006845 cm$^3$g$^{−1}$, and the pore size was$\sim$3.2$\mu$m. • Removal of hexavalent chromium from aqueous solutions using Ni–SiO$_2$nanomaterials This study describes an effective method developed for the removal of hexavalent chromium, Cr(VI), from anaqueous environment. In this study, the Ni–SiO$_2$nanomaterial was synthesized by the sol–gelmethod and then characterizedby field emission scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. The preparednanomaterial was then employed as an adsorbent with significant properties of high surface area and uptake capacity.Adsorption conditions of Cr(VI) onto the Ni–SiO$_2$nanomaterial were optimized by altering different parameters (pH, initial Cr(VI) concentration and different periods of time). An amount of 100.75 mg g$^{−1}$was estimated as the maximum uptakecapacity of the Ni–SiO$_2$nanomaterial at pH 4.0. The experimental data of Cr(VI) adsorption onto the Ni–SiO2 nanomaterialwere fitted well to the Langmuir isotherm and pseudo second-order kinetic models.Moreover, the adsorption of Cr(VI) ontothe Ni–SiO$_2$nanomaterial was not influenced even in the presence of different coexisting ions. Finally, the recommendedmethodology was applied on several environmental water samples. • Evolution of microstructure with increasing carbon content and its effect on mechanical properties of disordered iron–aluminium alloy Correlation of microstructure and mechanical properties of hot-rolled Fe–7 wt.% Al with varying carbon contents has been investigated in detail. The microstructures of the alloys change significantly with an increase in the carboncontent. An alloy with 0.012 wt.% carbon shows a single ferrite phase, whereas with increase in carbon up to 0.65 wt.%, the microstructure evolves into a dual phase consisting of ferrite and$\kappa$-pearlite. At about 1.5 wt.% carbon, the alloy exhibits only$\kappa$-pearlite and with a further increase in carbon to 2.2 wt.%, an additional phase starts precipitating in the form of graphite. The room temperature tensile strength of the alloy increased significantly with an increase in the carbon content, which is in agreement with the microstructure. The yield strength and hardness of the steels with different carbon contents can becorrelated well with the inter-barrier spacing in different steels. • Promotion of bone repair of rabbit tibia defects induced by scaffolds of P(VDF-TrFE)/BaTiO$_3$composites In this work, scaffolds made of a novel experimental 0–3 type composite were implanted onto non-critical defects in rabbit tibiae. This work discusses the bone repair promoted by polyvinylidene fluoride-trifluoroethyleneP(VDF-TrFE)/barium titanate (BaTiO$_3$) composite that scaffolds with 10 vol% BaTiO$_3$. Prior to implant surgery, the P(VDF-TrFE)/BaTiO$_3$scaffolds, moulded into a membrane disk, were subjected to a cytotoxicity test (ASTM F895-84). A standardized transverse osteotomy was made with the following dimensions: 4.5 mm in width by 9 mm in length, at the proximal tibial metaphysis, in adult male rabbits, by using a cylindrical drill, cooled with a physiologic solution. These critical defects were filled with blood clot on the left tibiae (control group), whereas the right tibiae were covered with composite scaffolds, measuring 5 mm in thickness and 10 mm in diameter (experimental group);$n = 12$for each group.After 21 days, the rabbits were sacrificed and the tibiae bone fragments were conducted to demineralization routines, from fixation and stain procedures to histological analysis. The scaffolds promote the growth of the bone, resulting in an increased repair with callus formation around the scaffold and high mitotic activity at newly formed bones. • Surface micro-texturing design for improving tribological behaviour of graphene oxide thin films Effect of micro-scale surface texture with different densities on wear resistance of graphene oxide (GO) films was studied using a revolving ball-on-flat tribometer in humid environments. The micro-scale surface texture was producedby depositing about 363 nm thick GO films onto silicon substrates pre-textured with the patterns of dimples. The goal of the surface patterning was to improve the wear resistance of the GO films so that to extend lubricating life. The experimental results demonstrated excellent ability of the textured films to improve wear resistance of the silicon substrate. Furthermore, the GO films with an appropriate dimple area density (4%) were effective in reducing the friction coefficient (0.024) and exhibiting outstanding wear resistance owing to the entrapment of wear particles in the dimples. Finally, a simple frictionmechanism model was drawn to explain the frictional properties of the different textured area density GO films. • Utility of newly modified chitosan in the removal of heavy metal ions from aqueous medium: ion selectivity, XPS and TGA The purpose of this study is to evaluate the newly prepared modified chitosan, a new environmentally friendly adsorbent, in the field of wastewater treatment. Chitosan (CS) reacted with 3-chloro-2,4-pentanedione to give CS derivatives, CS-CPD. Modified CS with O–O and N–O chelating centres was treated with aqueous solution containing different metal ions to investigate its metal uptake and selectivity. The concentration of metal ions in aqueous solution was measured by inductively coupled plasma-optical emission spectrometry. The structure of the complex was identified by elemental analysis, infrared and solid-nuclear magnetic resonance. In addition, the chelating centres were determined by X-ray photoelectron spectroscopy. The morphology of the modified polymer and its metal complexes was studied to show a dramatic change incases of the CS-CPD–Pb, CS-CPD–Hg, CS-CPD–Cr and CS-CPD–Co complexes. • Villari effect in silicone/FeGa composites This paper presents the results of the Villari effect study in FeGa magnetorheological composites with very low stresses. The composites consist of a silicone matrix and Fe75Ga25 powder of size ranging from 50 to 100$\mu$m. Two types of composites, one is with 45 wt% and the other one with 30 wt% of Fe75Ga25 powder have been manufactured. The Villari effect has been measured in both samples as-manufactured and in those in which a 1 T magnetic field has been applied after curing. The results indicate that the composites with an applied field of 1 T after curing show the greatest Villari signal evenwithout any applied magnetic field. This fact allows a design of a low-cost force sensor and high performance. A simple model, based on the change in the cross-section of the composite, has been developed to explain the results obtained. • Photodegradation of methylene blue over a new down-shifting luminescence catalyst TiO$_2$nanotube arrays prepared by anodization technology are modified with a samarium ion (Sm$^{3+}$) by a hydrothermal method for use in photodegradation of methylene blue (MB). The samarium ion as a down-shifting luminescence material can improve UV radiation harvesting to increase visible light utilization. The efficiency of the photocatalytic activity for the modified-TiO$_2$nanotube arrays in degradation of MB was investigated under UV–Vis light irradiation. The results show that Sm–TiO$_2$nanotubes can increase the photocatalytic efficiency of MB. When TiO$_2$nanotubes are modified by 0.02 M Sm$^{3+}$, MB can be almost completely degraded when compared with bare TiO$_2$nanotubes. This indicates that TiO$_2$nanotubes structure, surface area and good UV radiation harvesting play important roles in the degradation of MB. • A study on zeolite-based adsorbents for CO$_2$capture In this study, zeolite-based sorbents were prepared and examined for CO$_2$adsorption from a simulated flue gas mixture using a fixed-bed flow reactor. Various amines such as monoethanolamine, ethylenediamine, diethylenetriamine and triethylenetetramine (TETA) were impregnated on support materials to prepare the adsorbents. Also, the effects of various parameters on CO$_2$adsorption capacity have been examined in this work. Further, an effort has been made to characterize various physico-chemical properties like surface area, pore volume, chemical composition, etc. of the in-house developedsorbents. Observation showed that the CO$_2$adsorption capacity enhanced with amine loading up to a certain concentration. The maximum carbon capture capacity of the 30-TETA-ZSM-5 sorbent is around 53 g of CO$_2$/kg of adsorbent. The thermochemical stability of the adsorbents has been tested by reusing the same material for multiple adsorption–desorption cycles,and no significant change in CO$_2$adsorption capacities was observed. • Synthesis and mechanism perspectives of a carbon nanotube aerogel via a floating catalyst chemical vapour deposition method An effective and cost-effective approach to synthesize newmaterials can be determined via research on a carbon nanotube (CNT) aerogel. This review paper gives an overview of the current synthetic methodologies and routes to enhanceunderstanding. It also investigates the appropriate issues on the development of CNT-based three-dimensional (3-D) porous materials in an attempt to fill the knowledge gap regarding viability. First, an elaborate description on CNTs is provided, followed by a focus on CNT macrostructure fabrication, showcasing their key features, disadvantages, advantages and other aspects that were considered as related. Then, the methods for synthesis pertaining to the CNT aerogel are discussed with a focus on a floating catalyst chemical vapour deposition method as well as the growth mechanism pertaining to CNTsemploying the method.Key parameters, including catalyst, reaction time, carbon source, carrier gas and reaction temperature, which could cast an impact on the efficiency of the process are discussed subsequently. • Enhanced intercalation of organo-muscovite prepared via hydrothermal reaction at low temperature Muscovite clay is an ideal reinforcing filler due to its high-aspect ratio. However, it does not swell in water, making it hard to be treated and intercalated. In this study, ion exchange treatment is carried out on muscovite clay usingcetyltrimethylammonium bromide (CTAB) cations via two-step intercalation method. The intercalation steps included: inorganic–inorganic ion exchange treatment and inorganic–organic ion exchange treatment under hydrothermal conditions. The intercalation of muscovite particles was examined with various techniques to analyse the physical and chemical changes.Furthermore, the hydrothermal conditions for effective CTA$^+$ion intercalation within muscovite interlayers prepared via the hydrothermal process at low temperature, 180$^{\circ}$C, under different hydrothermal reaction times and CTAB/Li-Mus mass ratio were investigated. Fourier transform infra-red (FTIR) analysis revealed that the CTA$^+$ions are diffused into the interlayers of aluminosilicate and formed a strong electrostatic bond with the clay surface. X-ray powder diffraction analysis showed that the interplanar spacing in the organo-muscovite samples is almost identical as the hydrothermal reaction time is prolonged beyond 12 h. An optimum limit of the CTAB to Li-Mus ratio is observed as the d002 plane spacing is increased with an increase of the mass ratio of CTAB to Li-Mus up to 1.0 C and decreased with a further increase in the mass ratio. In addition, the intercalated CTA$^+$chains are homogenously distributed and formed a paraffin-like arrangement in the muscoviteclay. Besides, the structure of aluminosilicate layers is not affected or damaged after both treatments according to FTIR analysis. • Silica-supported Ni$_x$O$_y$, Zn$_x$O$_y$and Mn$_x$O$_y$nanocomposites: physicochemical characteristics and interactions with water and$n$-decane A series of M$_x$O$_y$/SiO$_2$(where M$=$Ni, Zn and Mn) nanocomposites were synthesized at different M$_x$O$_y$contents (0.2, 1 and 3 mmol per 1 g SiO$_2$) using a deposition method. The samples were characterized using nitrogen adsorption–desorption, X-ray diffraction, Fourier transform infrared spectroscopy, high resolution transmission electronmicroscopy and photon correlation spectroscopy. The heat of immersion in water ($Q_w$) and$n$-decane ($Q_d$) were measured using a microcalorimetry method, and the corresponding values of the hydrophilicity index$K_h = Q_w/Q_d$were analysed.The formation of M$_x$O$_y$on a silica surface leads to diminishing of the$Q_w$and$Q_d$values (calculated per 1 g of nanocomposites) because of the specific surface area reduction. However, the$Q_w$values calculated per 1 m$^2$increase for Zn$_x$O$_y$/SiO$_2$andMn$_x$O$_y$/SiO$_2$in comparison with the unmodified silica, and it remains unchanged for Ni$_x$O$_y$/SiO$_2$. Silica modification with M$_x$O$_y$significantly changes the pH dependence of zeta potential and affects the surface charge density. A shift of the isoelectric point (pH$_{\rm IEP}$) and a character of the zeta potential$\zeta$(pH) curve are affected by the M$_x$O$_y$phase, and pH$_{\rm IEP}$shifts toward higher values as follows Mn < Zn < Ni. • Effect of graphite particle fillers on dielectric and conductivity properties of poly(NIPAM-co-HEMA) Copolymers of 2-hydroxyethyl methacrylate (HEMA) and$N$-isopropylacrylamide (NIPAM) in different ratios were prepared by free radical polymerization using 2,2$^{\prime}$-azobisisobutyronitrile as an initiator at 60$^{\circ}$C. The copolymers were analysed by Fourier transform infrared and proton nuclear magnetic resonance. Thermal behaviours were determined bythermogravimetric analysis and differential scanning calorimetry (DSC). DSC measurements showed that the glass transition temperature ($T_g$) of poly(HEMA) and poly(NIPAM) was 100 and 140$^{\circ}$C, respectively. Electrical properties (dielectric constant, dielectric loss and alternating current conductivity) of polymers and composites prepared with graphite were investigated by using an impedance analyser, in the range of 10–20 kHz. While the dielectric constant values vary from 3.3 to 4.01 for copolymers at 1 kHz, these values are increased about 10 times for composites doped with 10 wt% graphite. Similarly, the dielectric loss and conductivity values were fairly high for composites. The conductivity values of composites doped with 10 wt% graphite showed a significant increase and the insoluble polymer became semiconducting. Itwas observed that the electrical properties of graphite-added composites at different ratios (8, 9 and 10 wt%) increased with the increase in graphite ratio for all polymers. In addition, the direct current conductivity of composites doped with10 wt% graphite was examined according to the temperature and the activation energy ($E_a$) values were calculated. • Thermodynamics of the oxidation of ZrB$_2$–TiB$_2$, ZrB$_2$–SiC and ZrB$_2$–B$_4$C ceramics The thermodynamics of the oxidation of three-high temperature ZrB$_2$-based ceramics (ZrB$_2$–TiB$_2$, ZrB$_2$–SiC and ZrB$_2$–B$_4$C) has been studied in order to find the stability domain of zirconium diboride, in terms of temperature, partial pressure of oxygen and composition, in which it is protected against oxidation. In the case of the ZrB$_2$-TiB$_2$binarysystem, a plot of$\log p$O$_2$vs.$1/T$in the temperature range of 500–2000 K and another plot of$p$O$_2$($\times$10$^{14}$) vs.$x$TiB$_2$for$T = 2000$K are made taking into account the two-extreme possibilities of no solubility and 100% solid solubility between ZrB$_2$and TiB$_2$, respectively. A plot of$\log p$CO vs.$\log p$O$_2$is made for 1773 K for the systems ZrB$_2$–SiC and ZrB$_2$–B$_42$C. It was found that the ZrB$_2$–TiB$_2$ceramics does not have sufficient oxidation resistance in the temperature range of 500–2000 K. ZrB$_2$of ZrB$_2$–SiC ceramics can be protected under 1 atmosphere oxygen or in air if the liquid borosilicate(with the chosen composition, 70% B$_2$O$_3$–30% SiO$_2$), which is an intermediate product, provides a kinetic barrier to the continuation of oxidation by forming an impervious layer on the exposed surfaces. In contrast, the ZrB$_2$–B$_4$C ceramics does not produce the borosilicate upon oxidation. In view of the volatility of pure liquid B$_2$O$_3$, it is recommended that the ZrB$_2$–B$_4$C ceramics can be used at a lower temperature, perhaps below 1373 K, when the vapour pressure of B$_2$O$_3$is significantlysmall. • Thermal, mechanical and electrical properties of lithium phosphate glasses doped with copper oxide Lithium phosphate glasses with the basic composition (P$_2$O$_5$50 and Li$_2$O 50 mol%) series by the addition of copper oxide (0, 10, 15 and 20 g/100 g) were prepared by a melt quenching technique. Fourier-transform infrared (FTIR) absorption spectra and X-ray diffraction (XRD) analysis were used to characterize the glass samples. Thermal expansion and mass density were also measured. The different mechanical properties of the prepared glasses were measured by an ultrasonic non-destructive technique. Additionally, both frequency and temperature dependence of alternating-current conductivity were measured in the frequency range of 40 Hz–1 MHz and the temperature range of 308–488 K. Moreover, direct current conductivity was also measured for the same temperature range. FTIR measurements confirm the appearance ofthe bands of phosphate groups and the assumption of bonds formed between Cu and P. XRD spectra approve the amorphous nature of the studied glasses. Thermal expansion and mass density of the prepared samples show an increase in values by increasing the CuO content. The mechanical properties of the studied glasses (hardness ($H_v$), Young’s modulus ($E$), elastic modulus ($L$), bulk modulus ($K$), shear modulus ($G$) and Poisson’s ratio ($ν$)) were positively affected by the CuO content, reflecting a better packed structure. Furthermore, the electrical conductivity values of the prepared glasses are identified to increase with an increase in both temperature and CuO content. Such trends agree with the data obtained by thermal expansion and FTIR. The progressive addition of CuO is assumed to improve thermal, mechanical and electrical properties of the prepared lithium phosphate glasses. • Use of colorimetric hydrogel as an indicator for food packaging applications A novel hydrogel was synthesized from$N,N$-dimethyl acrylamide (DMAAm), gelatin, citric acid (CA) and Basilicum extract (BE). This study was aimed at creating an advanced food packaging material that allows the detectionof food spoilage, which can be monitored colorimetrically. The poly(gelatin-co-DMAAm)/CA–BE was synthesized in the form of a film on Petri dishes using a redox polymerization technique. Mechanical and water resistance properties of the hydrogel were further improved by the addition of CA and$N,N$-methylene-bis-acrylamide as crosslinkers; BE was added to the reaction mixture and entrapped in the polymer chains with the aim to introduce antimicrobial, antioxidant and anthocyanin properties for the desired utilization. The characterization of the synthesized hydrogel was carried out usinga dynamic and mechanical analyser, thermo gravimetric analyser, Fourier transform infrared spectroscopy and scanning electron microscopy. The antimicrobial activity of the hydrogel was observed as it was tested against Escherichia coli, Bacillus subtilis and Staphylococcus aureus. Furthermore, total antioxidant and anthocyanin activities of the hydrogels were also studied at different pH values to monitor the colour change capabilities. It was concluded that the hydrogel was a strong candidate for use in food packaging. • Photosensitization effect on visible-light-induced photocatalytic performance of TiO$_2$/chlorophyll and flavonoid nanostructures: kinetic and isotherm studies Preparation and performance of natural dye-sensitized photocatalysts of TiO$_2$are described in this study. Such sensitized nanostructures offer visible-light-reactive systems for the photodegradation of organic pollutants. Natural pigments of chlorophyll and flavonoid extracted from parsley leaves and Curcuma longa roots are grated on TiO$_2$nanoparticlesas photosensitizers using an incipient wetness impregnation method. The as-prepared samples are structurally characterized by combined techniques, such as X-ray diffraction, scanning electron microscopy and Fourier transform infrared. The diffuse reflectance UV–Vis spectra are also used to investigate band-gap energies. The resultant band-gap energies confirm the ability of visible light absorption and thereby the ability of more efficient generation of photoexcited charge-carriers. The photocatalytic performance of dye-sensitized nanoparticles is tested in terms of decolourization efficiency of MB dye as a function of involved operating parameters including reaction time, amount of catalyst, initial MB concentration and pH. Both samples show the excellent photocatalytic efficiencies relevant to the red shift generated and high absorption of photons in the visible region. However, the highest efficiency is obtained for TiO$_2$/chlorophyll catalysts (93%) compared to TiO$_2$/flavonoid samples (91%), which is perfectly in agreement with their band-gap energies and visible-light absorption ability. Photodegradation process kinetics is investigated by the Langmuir–Hinshelwood model, while the adsorption equilibrium is described based on Langmuir and Freundlich isotherms. • Investigation of a thermoluminescence response and trapping parameters and theoretical model to explain concentration quenching for Yb³⁺-doped ZrO₂ phosphors under UV exposure In this paper, a thermoluminescence signal centred at 129°C induced by UV radiation of Yb3+-doped ZrO2 is reported. Phosphor was prepared by a solution combustion method and annealed at 600 and 900°C to study the effect of annealing. The prepared phosphor was characterized by X-ray diffraction and scanning electron microscopy methods. Various parameters were optimized. Computerized glow curve deconvolution was employed and kinetic parameters for every deconvoluted peak were calculated. To understand the concentration quenching, a 3T1R (three trap one recombination centre) model has been proposed. • Entropy analysis of Hall current and thermal radiation inﬂuenced by cilia with single- and multi-walled carbon nanotubes Abstract. The present investigation explores the signiﬁcance of creeping viscous nanoﬂuids in an axi-symmetric channel inﬂuenced by metachronal waves containing magnetohydrodynamics and Hall current. Heat transport analysis is also per-formed to derive the impact of thermal radiation on internal heat source phenomena. The use of mathematical formulation resulted in a set of nonlinear coupled partial differential equations. The governed differential system is transformed into an ordinary differential system by considering similar variables. Exact solutions in the closed form have been derived for the temperature, momentum and pressure gradient. Moreover, entropy generation due to heat transfer, thermal radiation and magnetic effects has been measured. The graphical results have been presented to interpret sundry parameters of interest. Streamlines and isotherms are also plotted against the multi-walled carbon nanotube. For the validation of our results, a comparison table is presented. It is also seen that entropy of the system increases and the Bejan number decreases with an increase in the Brinkman number. • Effect of nitrogen ﬂow rate on the mechanical properties of CVD-deposited SiCN thin ﬁlms Silicon carbonitride (SiCN) thin ﬁlms were deposited on p-Si (100) substrates with different N₂ ﬂow rates using SiC and Si₃N₄ powder precursors by chemical vapour deposition. To investigate the structural, vibrational and mechanical properties, the SiCN thin ﬁlms were characterized by atomic force microscopy, Raman spectroscopy, X-ray diffraction (XRD), Fourier transform infrared and nanoindentation techniques. The XRD results reveal nanocrystals embedded with amorphous networks in the SiCN thin ﬁlms. An increase in the$I$_{D}/$I$_{G} ratio with an increase in the N₂ ﬂow rate indicated the increase of sp³ bonds in the SiCN thin ﬁlm. The hardness ($H$), Young’s modulus ($E$), plasticity index ($H/E$) and ($H$³/$E$²) increase with an increase in the N₂ ﬂow rate. • Crystal structure, optical and electrical characteristics of rutile TiO₂ nanocrystallite-based photoanodes doped with GeO₂ The effect of germanium dioxide, GeO₂ doping on dye-sensitized solar cell (DSSC) TiO₂ nanocrystallite photoanodes with composition (TiO₂–(GeO₂)_{$x$} :0 ≤$x$≤ 0.3 wt%) has been studied. The pure sample and GeO₂-doped samples have been synthesized by a conventional solid-state reaction method and analysed by means of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray and ultraviolet–visible spectroscopy techniques. The photovoltaic characteristics of the prepared samples have been studied by employing$J–V$measurements. The pattern of XRD depicted that the dominating phase in the sample with$x$= 0 is a rutile tetragonal phase with the P4₂/$mnm$space group. An increase in GeO₂ concentration leads to an appearance and rise of another hexagonal phase structure of α-GeO₂ with the P3₂21 space group. Data obtained from the UV–visible spectroscopy measurements reﬂect that the optical energy gap ($E$^{optical}) increases with increasing GeO₂ content, while the optical refractive index decreases.$J–V$photovoltaic characteristics conﬁrm that the DSSCs doped with low-concentration doping,$x$= 0.05 and 0.1 of GeO₂ have higher values for conversion efﬁciency (η), ﬁll factor and short circuit current density ($J$_{sc}) compared with samples with high-concentration doping ($x$= 0.2 and 0.3) of GeO₂. The present results showed that TiO₂–(GeO₂)_{$x$} ($x\$ = 0.05 and 0.1 wt%) ﬁlms are potential candidates for optical ﬁlter materials and optoelectrical and photo-conversion energy devices.

• Energy-harvesting enhancement in composites of microwave-exfoliated KNN and multiwall carbon nanotubes

The objective of this research work is to investigate the effect of multiwall carbon nanotube (MWCNT) content (0.3–1.2 wt%) on a potassium sodium niobate (KNN)-based piezoelectric unimorph harvester for enhancing the energy generation capacity. KNN–MWCNT composites were fabricated by using a microwave solid state technique. The energy-harvesting performance of the KNN–MWCNT composite was determined by the base excitation method and sized to resonate between 20 and 100 Hz at 1 MΩ load resistance. The energy performance of the KNN composite at percolation threshold (0.6 wt% MWCNT) showed a maximum power generation of 2.94 μW, the power density of 7.15 μWm⁻₃ and overall efﬁciency of 83.75% at an input acceleration of 0.5 g and a load resistance of 1 MΩ. Improvements observed in the power generation by percolation phenomena and ionic ﬂow over the nanotube surface of KNN composites prove to be a boon for low-power sensing devices.

• A simple solid-state method to synthesize nanosized ferromagnetic α-Fe₂O₃ with enhanced photocatalytic activity in sunlight

α-Fe₂O₃ was synthesized by preparing a mixture of Fe(III) nitrate with urea as a precursor. The yellowish coloured precursor was calcined at 400°C for 2 h, resulting in the formation of bright red coloured hematite. The surface properties and catalytic activity were compared with a reference sample prepared without the use of urea. It was observed that urea-induced synthesis resulted in a sample having nanosize and large lattice strain, accompanied by the development of ferromagnetic behaviour. The catalytic activity was evaluated for the decomposition of H₂O₂ through the photo-Fenton process in sunlight. The urea-synthesized sample showed an usually large photo-Fenton effect and the catalyst could be easily recovered and reused due to its ferromagnetic behaviour.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 6
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019