• Volume 40, Issue 1

February 2017,   pages  1-251

• Synthesis and photoluminescence study of narrow-band UVB-emitting LiSr$_4$(BO$_3$)$_3$:Gd$^{3+}$, Pr$^{3+}$ phosphor

A series of Pr$^{3+}$, Gd$^{3+}$ and Pr$^{3+}$–Gd$^{3+}$-doped inorganic borate phosphors LiSr$_4$(BO$_3$)$_3$ were successfully synthesized by a modified solid-state diffusion method. The crystal structures and the phase purities of samples were characterized by powder X-ray diffraction. Surface morphology of the sample was studied by scanning electronic microscopy (SEM). The optimal concentrations of dopant Gd$^{3+}$ ions in compound LiSr$_4$(BO$_3$)$_3$ were determined through the measurements of photoluminescence (PL) spectra of phosphors. Gd$^{3+}$-doped phosphorsLiSr$_4$(BO$_3$)$_3$ show strong band absorption in UV spectral region and narrow-band UVB emission under the excitation of 276 nm was only due to ${}^{6}$P$_J$ $\to$ ${}^{8}$S$_{7/2}$ transition of Gd$^{3+}$ ions. The effect of Pr$^{3+}$ ion on excitation of LiSr$_4$(BO$_3$)$_3$:Gd$^{3+}$ was also studied. The excitation of LiSr$_4$(BO$_3$)$_3$:Gd$^{3+}$, Pr$^{3+}$ gives a broad-band spectra, which show very good overlap with the Hg 253.7 nm line. The photoluminescence spectra of LiSr$_4$(BO$_3$)$_3$ with differentdoping concentrations Pr$^{3+}$ and keeping the concentration of Gd$^{3+}$ constant at 0.03 mol have also been studied. The emission intensity of LiSr$_4$(BO$_3$)$_3$:Pr$^{3+}$–Gd$^{3+}$ phosphors increases with increasing Pr$^{3+}$ doping concentration and reaches a maximum at 0.01 mol. From the photoluminescence study of LiSr$_4$(BO$_3$)$_3$:Gd$^{3+}$, Pr$^{3+}$ we conclude that there was efficient energy transfer from Pr$^{3+}$\to$Gd$^{3+}$ions in LiSr$_{4−x−y}$Pr$_x$Gd$_y$(BO$_3$)$_3$phosphors. • Synthesis, structure and luminescence properties of phosphates A$_{1−3x}$Eu$_x$Zr$_2$(PO$_4$)$_3$(A—alkali metal) The solid solution row A$_{1−3x}Eu$^{3+}_x$Zr$_2$(PO$_4$)$_3$, where $A= Na$, K, Rb, Cs and x ranging from 0 to 0.25 was obtained by methods based on sol–gel processes in the presence of the salting-out agent, C$_2$H$_5$OH. The formation of phases of the structural type NaZr$_2$(PO$_4$)$_3$ (NZP) and their crystallization in the crystal forms belonging to the space group $R\bar{3}c$ ($0 \le x \le 0.1$) and $P\bar{3}c$ ($x = 0.25$) were determined. Morphotropic transition occurred. Trivalent europium was included as a local probe. Its electric and magnetic dipole was used to characterize the substitutionrule and the localization of this cation in the structure, which is in agreement with the structural characterization. It appears that europium is located in the M1 and M2 sites as a function of the Eu$^{3+}$ concentration.

• Room-temperature ferromagnetic and photoluminescence properties of indium–tin-oxide nanoparticles synthesized by solid-state reaction

In the present study, indium–tin-oxide (ITO) nanoparticles were synthesized using solid-state reaction and studied for their structural, vibrational and magnetic properties. The ITO nanoparticles were prepared under reduced pressure, which can increase the oxygen vacancies in the samples. The X-ray diffraction studies confirmed singe-phase cubic bixbyite structure of ITO with average crystallite size of 47 nm. The lattice vibrational studies (FTIRand Raman spectroscopy) at room temperature indicated that Sn ions were occupied in In$_2$O$_3$ lattice and gives corresponding active vibrational modes in the respective spectra. The magnetic studies at room temperature reveal the ferromagnetic nature of ITO and the strength of magnetization is superior to those of In$_2$O$_3$ and SnO$_2$. However, the magnetic studies at 100 K revealed reduced ferromagnetism, which could be attributed to reduced itinerary electrons at low temperature. Blue and blue–green emissions were found from the ITO nanoparticles, which could be due to vacancies or surface defects present in the system.

• Dy$^{3+}$-activated M$_2$SiO$_4$ (M $=$ Ba, Mg, Sr)-type phosphors

The alkaline orthosilicates of M$_2$SiO$_4$ (M $=$ Ba, Mg, Sr) activated with Dy$^{3+}$ and co-doped with Ho$^{3+}$ are prepared through conventional solid-state method, i.e., mixing and grinding of solid form precursors followedby high-temperature heat treatments of several hours in furnaces, generally under open atmosphere and investigated by X-ray diffraction (XRD) to get phase properties and photoluminescence (PL) analysis to get luminescenceproperties. The thermal behaviours of well-mixed samples were determined by differential thermal analysis (DTA)/thermogravimetry (TG). The PL spectra show that the 478 and 572nm maximum emission bands are attributed, respectively, to ${}^{4}$F$_{9/2}$ $\to$ ${}^{6}$H$_{15/2}$ and ${}^{4}$F$_{9/2}$ $\to$ ${}^{6}$H$_{13/2}$ transitions of Dy$^{3+}$ ions.

• Fabrication, characterization and gas sensing properties of gold nanoparticle and calixarene multilayers

Calixarenes are a group of materials that are widely used for gas sensing studies because of their simple synthesis, conformational flexibility, binding group tunability, variability in their cavity sizes and improved selectivity to different gas molecules. In recent years it has been shown that incorporation of gold nanoparticles (AuNPs) into organic layers further enhances their gas sensing performance. The present study reports on the fabrication of thin films of calixarene and AuNPs using Langmuir–Schaefer (LS) methods. The gas sensing properties of the produced films are investigated on exposure to saturated vapours of volatile organic compounds (VOCs) using surface plasmon resonance as an optical detection technique. Multilayers comprising films of AuNPs and calixarene have been investigated to evaluate the effect of AuNPs on the films sensing performances. It has been demonstrated that the hybrid layers exhibited improved sensing performance in terms of the degree of their response.

• Synthesis and optical characterization of copper nanoparticles prepared by laser ablation

The remarkable size-tunable properties of nanoparticles (NPs) make them a hot research topic with applications in a wide range of fields. Hence, copper (Cu) colloidal NPs were prepared using laser ablation (Nd:YAG, 1064 nm, 7 ns, 10 Hz, 6000 pulses) of a coppermetal plate at different laser fluences (LFs) in the range of 1–2.5 J cm$^{−2}$ in ethylene glycol (EG), at room temperature. Analysis of NPs was carried using different independent techniques such as ultraviolet–visible (UV–vis) spectroscopy; transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. TEM analysis showed that the NPs were spherical with a bimodal distribution and an average particle size of 5 and 16nm influence of 1.2 J cm$^{−2}$, and 9 and 22 nm at 2 J cm$^{−2}$. The UV–vis spectra of colloidal NPs revealed the maximum absorbance at around 584 nm, indicating the formation of Cu NPs, which supported using FTIR spectra. Furthermore, the absorption spectra confirmed the metallic nature of Cu NPs. FTIR spectroscopy was utilized to verify information about the NPs surface state and chemical bonds constructed in the atom groups apparent on their surface.

• Synthesis of high-surface-area spinel-type MgAl$_2$O$_4$ nanoparticles by [Al(sal)$_2$(H$_2$O)$_2$]$_2$[Mg(dipic)$_2$] and [Mg(H$_2$O)$_6$][Al(ox)$_2$(H$_2$O)$_2$]$_2$·5H$_2$O: influence of inorganic precursor type

Spinel-type MgAl$_2$O$_4$ nanoparticles with high surface area were synthesized by thermal decomposition of three different ion-pair complexes precursors, including [Mg(H$_2$O)$_6$][Al(dipic)$_2$]$_2$·6H$_2$O, [Al(sal)$_2$(H$_2$O)$_2$]$_2$[Mg(dipic)$_2$] and [Mg(H$_2$O)$_6$][Al(ox)$_2$(H$_2$O)$_2$]$_2$·5H$_2$O. Influence of the inorganic precursor was investigated on synthesis and textural properties of magnesium aluminate nanopowders. The precursors [Mg(H$_2$O)$_6$][Al(dipic)$_2$]$_2$·6H$_2$O and [Al(sal)$_2$(H$_2$O)$_2$]$_2$[Mg(dipic)$_2$] displayed pure spinel-type MgAl$_2$O$_4$, while the sample synthesized by [Mg(H$_2$O)$_6$][Al(ox)$_2$(H$_2$O)$_2$]$_2$·5H$_2$O precursor consisted of MgAl$_2$O$_4$ and MgO. The MgAl$_2$O$_4$ synthesizedvia [Al(sal)$_2$(H$_2$O)$_2$]$_2$[Mg(dipic)$_2$] precursor exhibited higher BET specific surface area (226.7 m$^2$ g$^{−1}$) and smaller particle size than those of the samples obtained from the two other precursors.

• Modelling, structural, thermal, optical and vibrational studies of a new organic–inorganic hybrid material (C$_5$H$_{16}$N$_2$)Cd$_{1.5}$Cl$_5$

Chemical preparation, theoretical calculations, X-ray single-crystal diffraction, thermal analysis, electrochemical measurements, IR, Raman and UV spectroscopic investigations of a novel organic–inorganic hybridmaterial (C$_5$H$_{16}$N$_2$)Cd$_{1.5}$Cl$_5$ are described. The structure provides a new interesting example of infinite inorganic chains of [Cd$_{1.5}$Cl$_5$]$^{2n}_n$− following the a crystallographic direction. The [Cd$_{1.5}$Cl$_5$]$^{2−}$ anions are interconnected by N–H$\cdots$Cl hydrogen bonds. The Hirshfeld surface and associated fingerprint plots of the compound are presented to explore the nature of intermolecular interactions and their relative contributions in building the solid-state architecture. IR and Raman spectra are reported and discussed on the basis of group theoretical analysis and quantum chemical density functional theory (DFT) calculation. The molecular HOMO–LUMO compositions and their respective energy gaps are also drawn to explain the activity of our compound. Thermal analysis reveals the anhydrouscharacter of the compound.

• Electrical characteristics of metal–insulator–semiconductor and metal–insulator–semiconductor–insulator–metal capacitors under different high-$k$ gate dielectrics investigated in the semi-classical and quantum mechanical models

In this paper the electrical characteristics of metal–insulator–semiconductor (MIS) and metal–insulator–semiconductor–insulator–metal (MISIM) capacitors with (100)-oriented p-type silicon as a substrate under different high-$k$ gate dielectrics (SiO$_2$, HfO$_2$, La$_2$O$_3$ and TiO$_2$) are investigated in the semi-classical and quantum mechanical models. We review the quantum correction in the inversion layer charge density for p-doped structures. The purpose of this paper is to point out the differences between the semi-classical and quantum mechanical charge descriptions at the insulator–semiconductor interface and the effect of the type of oxide and their position (gate oxide or buried oxide) in our structures. In particular, capacitance–voltage ($C–V$), relative position of the sub-band energies and their wavefunctions are studied to examine qualitatively and quantitatively the electron states and charging mechanisms in our devices. We find that parameters such as threshold voltage and device trans-conductance are enormously sensitive to the proper treatment of quantization effects.

• Effect of Co substitution on the physicochemical properties of La$_{0.67}$Sr$_{0.22}$Ba$_{0.11}$Mn$_{1−x}$Co$_x$O$_3$ compounds ($0 \le x \le 0.3$)

We have prepared a novel series of La$_{0.67}$Sr$_{0.22}$Ba$_{0.11}$Mn$_{1−x}$Co$_x$O$_3$ ($0 \le x \le 0.3$) perovskites by a sol–gel method. These oxides were characterized by X-ray diffraction (XRD) and neutron powder diffraction (NPD) at room temperature and magnetization measurements vs. temperature and various applied magnetic fields. The use of NPD data allows us to describe very precisely the octahedral tilting in the orthorhombic structure (Pnma) observed for all the compounds ($x = 0$ to 0.3); in all the samples with $x > 0$, Co is distributed at random in theMn positions of the perovskite. Magnetic susceptibility measurements show that whereas the $x = 0$ perovskite is ferromagnetic at relatively high temperatures ($T_C = 360$ K), the introduction of Co induces a magnetic glass state(cluster or spin glass). The magnetic entropy change ($|\Delta S^{\max}|$) takes values 2.46, 2.43, 1.88 and 1.78 J kg$^{−1}$ K$^{−1}$ for $x = 0$, 0.1, 0.2 and 0.3, respectively. The relative cooling power is 169, 241, 207 and 191 J kg$^{−1}$ for $x = 0$, 0.1, 0.2 and 0.3, respectively, at a field change of 5T. This result suggests that subtle Co doping enhances the magnetocaloric effect in this series, the perovskite La$_{0.67}$Sr${_{0.22}$Ba$_{0.11}$Mn$_{0.9}$Co$_{0.1}$O$_3$ being a candidate that can be used in magnetic refrigeration.

• Investigations on structural, optical and magnetic properties of solution-combustion-synthesized nanocrystalline iron molybdate

Iron molybdate $\beta$-Fe$_2$(MoO$_4$)$_3$ nanoparticles were synthesized by exploiting the self-propagating hightemperaturecombustion strategy using hexamine as a fuel. The obtained $\beta$-Fe$_2$(MoO$_4$)$_3$ nanoparticles exhibited the orthorhombic crystalline structure, which is evidenced from the XRD pattern. FT-IR spectrum revealed the existence of stretching and bending vibrations of Mo–O–Mo and O–Mo–O bonding in the nanocrystals. The binding energy peaks in the X-ray photoelectron spectroscopy (XPS) spectrum positioned at 710 and 725, 231 and 235 and 530 eV, respectively, correspond to the Fe(2p), Mo(3d) and O(1s) orbitals. Absorption spectrum of nanoparticles showed adequate absorbance of visible region photons of the nanoparticles and also optical bandgap valueof $\beta$-Fe$_2$(MoO$_4$)$_3$ nanoparticles as 2.26 eV, which is calculated using the Kubelka–Munk function. The existence of Fe$^{3+}$ and Mo$^{6+}$ in $\beta$-Fe$_2$(MoO$_4$)$_3$ is authenticated with the aid of electron paramagnetic resonance spectrum measurements. The obtained nanoparticles have showed methylene blue dye degradation of 98.4% under sunlightirradiation.

• Structural, magnetic and photocatalytic characterization of Bi$_{1−x}$La$_x$FeO$_3$ nanoparticles synthesized by thermal decomposition method

Single-phase La-substituted bismuth ferrite (Bi$_{1−x}$La$_x$FeO$_3$) nanoparticles have been synthesized by thermal decomposition of a glyoxylate precursor. The crystal structure transition of BiFeO3 from the rhombohedral(R3c) to the cubic $Pm\bar{3}m$ structure by La addition was confirmed by X-ray diffraction and infrared spectrometry methods. Furthermore, the Bi$_{1−x}$La$_x$FeO$_3$ nanoparticles showed a weak ferrimagnetism behaviour, while the magnetization increased from 0.18 to 0.48 emu g$^{−1}$ with La substitution. The Bi$_{1−x}$La$_x$FeO$_3$ nanoparticles exhibitedstrong absorption in the visible region with the optical band gap calculated from Tauc’s plot in the range of 2.19–2.15 eV. Furthermore, the effects of La substitution on the photodegradation of the methylene blue (MB) undervisible light were also studied. The photodegradation of MB dye was enhanced from 64 to $\sim$99% with increasing La substitution from $x = 0$ to 0.1 and then decreased to 8% for $x = 0.15$.

• Influence of oxidant and fuel on the powder characteristics of LiNbO$_3$ synthesized by combustion method

Lithium niobate (LiNbO$_3$) is widely recognized as a promising material for replacing lead-based piezoelectric ceramics. Although the LiNbO3 synthesis by combustion method has been investigated with particular attention recently, the influence of oxidants and different fuels’ sources on the synthesized powders has not yet been thoroughly studied. In this work we investigate the influence of urea and maleic hydrazide as fuels and ammonium nitrate as an oxidant on the powder characteristics of LiNbO$_3$ synthesized by combustion method. In addition, powder characteristics and sinterability of powders prepared by combustion method are compared with those of powders prepared by solid-state reaction. The results show that the second phase LiNb$_3$O$_8$ was detected only when an oxidant agent was used in the synthesis process. Among all combustion reactions, the powders prepared with excess of urea presented better final characteristics. As a result, the sintering temperature for LiNbO$_3$ powders prepared by combustion method was appreciably lowered when compared with those prepared by solid-state reaction.

• Tribological and mechanical behaviour of dual-particle (nanoclay and CaSiO$_3$)-reinforced E-glass-reinforced epoxy nanocomposites

An E-glass-reinforced epoxy-based nanocomposite containing organomodified nanoclay (15–20 nm) and calcium silicate particles (75–149 $\mu$m) was developed through mechanical shearing mixing and hand layup techniques. Three weight fractions (2, 3 and 4%) of nanoclay were selected to study the effects of nanoclay on mechanical and wear behaviour of nanocomposites. Tensile and flexural properties of nanocomposites were evaluated and compared. The wear properties were evaluated for three speed (3.14, 4.19 and 5.24 m s$^{−1}$) and load (20, 50, and 80 N) conditions based on a design of experiment (L16 matrix) concept. The wear loss results were statistically analysed to study the significance of load, speed and nanoclay content. The morphologies of wear surface and fracture surface were examined with the aid of a scanning electron microscope (SEM) to identify the wear and fracture mechanisms. It was found that the wear loss increases with increasing nanoclay amount due to the particle agglomeration effects. Statistical analysis determines that the load is the most significant parameter affecting the wear resistance of nanocomposites. The mean and S/N ratio analyses rank the parameters significance in affecting wear resistance as follows: load $>$ nanoclay content $>$ speed. The wear mechanisms of nanocomposites are complex due to the observation of multiple features such as fibre thinning, matrix wear and fibre/matrix debonding as against abrasive wear in the pure epoxy. Tensile and flexural test results show that a good dispersion of nanoclay is achieved with 2 wt% amount in epoxy-based nanocomposites. The mechanical properties degrade above 2 wt% due to the excessive reinforcement,uneven distribution and the particle agglomeration effects. Fractography studies of tension-failed samples show that pure epoxy resin fails by multimode gauge explosive mode, whereas nanocomposites fail mainly by the matrix/fibre interface failure and fibre breakages.

• Investigation on mechanical properties of woven alovera/sisal/kenaf fibres and their hybrid composites

The go-green concept results in multipoint focus towards materials made from nature; easily decomposable and recyclable polymeric materials and their composites along with natural fibres ignited the manufacturing sectors to go for higher altitudes in engineering industries. This is due to the health hazard and environmental problems faced in manufacturing and disposal of synthetic fibres. This study was undertaken to analyse the suitability of new natural fibre as an alternative reinforcement for composite materials. In this paper, tensile, flexural and impact test is made for the woven alovera and kenaf (AK), sisal and kenaf (SK), alovera, sisal and kenaf fibre hybrid epoxy composites (ASK). The composite laminates are made through a hand-layup process. The surface analysis is studied through scanning electron microscopy. From the investigation the SK hybrid composite shows good tensile property, AK hybrid composite shows better flexural property and the best impact strength is observed for ASK hybrid composite. The natural fibres slowly replace the synthetic fibres from its environmental impact, marching towards a revolution in engineering materials.

• Plant-mediated biosynthesis of silver nanoparticles by leaf extracts of Lasienthra africanum and a study of the influence of kinetic parameters

Lasienthra africanum (LA) leaf extract was employed for nano-silver synthesis. The reducing effect of the plant extract was investigated at different times, pH, temperatures and concentrations. The effect of variouskinetic parameters was studied using UV–vis spectroscopy. Blue-shifted surface plasmon bands indicating smaller sized nanoparticles were obtained at neutral pH (6.8–7.0), temperature of 65$^{\circ}$C and concentration ratio of 1:10 (leafextract: AgNO$_3$) with increasing reaction times under the reaction conditions. The kinetics of the reaction followed pseudo-first- and -second-order rate equations, and was thermodynamically favoured at higher time. Sphericallyshaped nanoparticles were obtained at different reaction conditions.

• Natural fabric sandwich laminate composites: development and investigation

In this work, eco-friendly natural fabric sandwich laminate (NFSL) composites are formulated using jute and linen-fabric-reinforced epoxy with different layer ratios (5:0, 4:1, 3:2, 2:3, 1:4 and 0:5) by hand layup system. Different mechanical attributes (tensile, flexural and impact) of the NFSL composites are quantified. Thermal stability and water absorption behaviour of the NFSL composites are also assessed. A scanning electron microscope (SEM) and optical microscope are used for qualitative analysis of NFSL composites’ interfacial properties. Two layers of jute and three layers of linen sandwich laminate have registered peak values in tensile and impact properties. The five layers of linen laminate composite have exhibited high flexural strength, been proven to have good thermal stability and furthermore shown better water absorption behaviour than any other laminate composites.

• Enhanced antibacterial performance of Fe$_3$O$_4$–Ag and MnFe$_2$O$_4$–Ag nanocomposites

In this work, we have described the antibacterial activities of Fe$_3$O$_4$ nanoparticles with different organic parts, including Humic acid (HA), Nicotinic acid (Nico) and Histidine (His), and the antibacterial activity ofMnFe$_2$O$_4$ nanoparticles coated with PANI and SiO$_2$ against different bacteria and some standard antibacterial drugs. The present study revealed that the newly fabricated various Fe$_3$O$_4$ and MnFe$_2$O$_4$ nanocomposites, when combined with some different organic parts, are superior antibacterial agents. Also, the synthesized nanocomposites can be easily separated from aqueous solution by magnetic filtration without any contamination of the medium.

• Synthesis of bio-inspired Ag–Au nanocomposite and its anti-biofilm efficacy

In the present study, bio-inspired Ag–Au nanocomposite was synthesized using banana peel extract (BPE) powder. The Ag–Au nanocomposite was characterized using various techniques such as UV–vis spectrophotometry,transmission electron microscopy (TEM) attached with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Efficiency of AuNPs, AgNPs and Ag–Au nanocomposite was tested for their antibacterial activity against Pseudomonas aeruginosa NCIM 2948. The Ag–Au nanocomposite exhibits enhanced antimicrobial activity over its monometallic counterparts. Anti-biofilm activity of AgNPs, AuNPs and Ag–Au nanocomposite against P. aeruginosa was evaluated on glass surfaces. The Ag–Au nanocomposite exhibited the highest biofilm reduction (70–80%) when compared with individual AgNPs and AuNPs. Effect of AuNPs, AgNPs and Ag–Au nanocomposite on biofilm formation was evaluated in 96 wells microtiter plates. The percentage of biofilm inhibition was sharply increased with increasing concentration of AuNPs, AgNPs and Ag–Au composite. However, Au–Ag nanocomposite showed the highest biofilm inhibition when compared with individual AuNPs and AgNPs. This synergistic anti-biofilm activity of Ag–Au nanocomposite has an importance in the development of novel therapeutics against multidrug-resistant bacterial biofilm.

• Optically understanding the dependence of catalysis kinetics on work function of nanocatalyst

In this work, biogenic ZnO and CuO nanoparticles were fabricated by adopting a complete green aqueous approach utilizing Centella asiatica plant extract. The phytochemicals involved in tailoring the nanoscopic metaloxide particles were characterized vividly. Both of the as-synthesized metal oxide particles are spherical and have a narrow size distribution with an average diameter of about 7 nm as measured via HRTEM. Interestingly, X-raydiffraction (XRD) pattern of ZnO nanoparticles displays the exposure of its (100) hexagonal facet. The ensuing ZnO and CuO nanoscale particles briskly enhanced the reduction of methylene blue, which was otherwise very slow. Thereaction follows first-order kinetics and the rate constants follow the order $k_{uncat} \lt k_{\rm ZnO \ NPs} \lt k_{\rm CuO \ NPs}$. The highercatalytic performance of copper oxide nanoparticles than zinc oxide nanoparticles is succinctly established on the basis of their difference in work function values optically.

• Na-doped LiMnPO$_4$ as an electrode material for enhanced lithium ion batteries

We report the influence of sodium (Na)-incorporated lithium manganese phosphate as an active material on its performance in electrochemical study for energy storage application. Li$_{1−x}$Na$_x$MnPO$_4$ with different mole ratios ($0.00 \le x \le 0.05$) of sodium is synthesized via a simple sol–gel method. The discharge capacity of Li$_{1−x}$Na$_x$MnPO$_4$ varies with respect to mole ratios of sodium incorporated. The maximum discharge capacityof 92.45 mAh g$^{−1}$ is observed in Li$_{0.97}$Na$_{0.03}$MnPO$_4$, which is higher than that of pristine LiMnPO$_4$ and other Na-incorporated LiMnPO$_4$. The maximum cyclic stability is found to be 84.15% up to 60 cycles. These results demonstrate that Li$_{0.97}$Na$_{0.03}$MnPO$_4$ plays a significant role in future energy storage application.

• Sensitive amperometric determination of hydrazine using a carbon paste electrode modified with silver-doped zeolite L nanoparticles

Silver-loaded nanozeolite-L-modified carbon paste electrode (Ag/L–CPE) was used as a novel sensing platform for enhanced electrocatalytic oxidation and determination of hydrazine. Zeolite L nanoparticles were synthesized via hydrothermal approach and then characterized using various techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electronic microscopy (SEM) and Brunauer–Emmett–Teller (BET). Silver-exchanged nanozeolite L (Ag/L) was prepared and mixed with carbon paste to prepare the modified electrode. Cyclic voltammetry studies revealed the high performance of Ag/L–CPE for electrocatalytic oxidation of hydrazine. Two linear ranges were detected in the amperometric detection of hydrazine. The first range was from10 $\mu$M to 0.4 mM with sensitivity of 103.13 $\mu$A mM$^{−1}$ and the second one was from 0.4 to 4mM with sensitivity of 58.131 $\mu$A mM$^{−1}$. The response time and detection limit ($S/N = 3$) of this sensor were determined to be 2 s and 1.5 $\mu$M, respectively. The unique porous structure of nanozeolite L offers a promising catalyst support candidate for efficient electrochemical sensing of hydrazine. The sensor exhibited appreciable repeatability, reproducibility and stability, and was able to detect hydrazine in the presence of even 500-fold excess concentrations of interfering species. Also, the sensor was used to determine hydrazine concentration in water samples with satisfactory results.

• Sensing of polymeric sensor-based rhodamine B derivative for metal cations in complete aqueous solution

The water-soluble polymeric chemosensor poly(AM-GRBD) has been synthesized by precipitation copolymerization with the functional monomer, GRBD, which was made of N$"$-(rhodamine B-yl) diethylenetriamineand glycidyl methacrylate (GMA) and a hydrophilic co-monomer acrylamide (AM). The chemical sensor behaved as a fluorescent and chromogenic sensor towards various heavy metal cations and transition metal cations; particularly,Cr$^{3+}$, Fe$^{3+}$ and Hg$^{2+}$ ions in completely aqueous media. The fluorescence of poly(AM-GRBD) was enhanced by Cr$^{3+}, Fe$^{3+}$and Hg$^{2+}$metal ions. Moreover, during titration of Cr$^{3+}$, Hg$^{2+}$or Fe$^{3+}$to the aqueous solution of poly(AM-GRBD), the visual colour changed from colourless to pink or brown yellow under visible light. • Sub-micron-sized delafossite CuCrO$_2$with different morphologies synthesized by nitrate–citric acid sol–gel route Currently, copper chromium oxide crystallizing in delafossite structure attracts huge research interest due to its versatile applications arising from its layered structure. In this work, delafossite CuCrO$_2$was synthesized by sol–gel method from their respective hydrated nitrate salts with citric acid as a chelating agent. The phase formation temperature was found to be between 750 and 775$^{\circ}$C. At 750$^{\circ}$C, the partial formation of delafossite CuCrO$_2$spheres with particle size in nano-regime was observed in the midst of platelets of spinel CuCr$_2$O$_4$. A green coloured powder with particle size 125–350 nm exhibiting distorted spheres was obtained at 775$^{\circ}$C. The increase in temperature has a profound impact on the particle size, morphology and the optical properties of CuCrO$_2$. The X-ray powder diffraction studies revealed the formation of 3R-CuCrO$_2$phase (rhombohedral, space group R-3m) as amajor product in the temperature range 775–1000$^{\circ}$C. The unit cell parameters were found to be$a = b = 2.9711$\AA and$c = 17.0723$\AA at 1000$^{\circ}$C. Scanning electron micrographs illustrated the different morphologies from spheres to hexagonal form via distorted spheres and cubes. The UV–Vis diffuse reflectance spectra measured for the powders exhibited semiconductor characteristics with an interesting size-related and temperature-dependent bandgap. • Polysulphone composite membranes modified with two types of carbon additives as a potential material for bone tissue regeneration This study presents a detailed evaluation of the impact of carbon fibrous materials on the physicochemical properties of polysulphone (PSU) membranes and their preliminary osteoblast-like cells response in vitro. Multiwalled carbon nanotubes (MWCNTs) and short carbon fibres (SCFs) were incorporated into PSU and membranes were produced by the phase inversion method. Then, the physicochemical properties of the membranes’ surface were investigated. Scanning electron microscopy (SEM) was used to evaluate microstructure and porosity. Surface properties such as roughness, wettability and surface energy were evaluated using atomic force microscopy (AFM), contact profilometry and a goniometer, respectively. The presence of carbon fibrous additives in the PSU matrix improved its hydrophilicity. Porosity and topography of the PSU membranes were also changed upon incorporation of carbon additives. The mechanical properties of the PSU membranes were improved after SCF addition. All physicochemical properties of the obtained composite membranes had significant impact on the osteoblast-like cells response. Preliminary viability tests indicated biocompatibility of all membranes. • Improved covalent functionalization of multi-walled carbon nanotubes using ascorbic acid for poly(amide–imide) composites having dopamine linkages Ascorbic acid has been covalently linked to multi-walled carbon nanotubes (MWCNTs). The structures of the functionalized MWCNTs were characterized with Fourier-transform infrared spectroscopy. Thermogravimetric analysis results also demonstrated the presence of organic portions of the functionalized MWCNTs. Polymer composites based on a nanostructured poly(amide–imide) (PAI) were fabricated by an ex situ technique with 5, 10 and 15% loading by weight. Composite films were made by the solvent casting method. The thermal stabilityof the composites increased with even a small amount of modified MWCNT added. Tensile tests were conducted and depicted an increase in the elastic modulus with increasing MWCNTs content. X-ray diffraction study of thecomposites also indicated that the composites incorporated MWCNTs in the polymer chain. • Rubber composites cured with sulphur and peroxide and incorporated with strontium ferrite In the present work, rubber magnetic composites were prepared by incorporation of strontium ferrite into rubber matrices based on natural rubber (NR) and acrylonitrile–butadiene rubber (NBR). Sulphur, peroxide and mixed sulphur/peroxide curing systems were introduced in cross-linking of rubber matrices. The aim was to investigate the influence of curing system composition on physical–mechanical, thermo-physical and magnetic properties of prepared rubber composites and the curing process. Then, the determination of cross-link density and the structure of cross-links were under consideration. The achieved results showed that all investigated parameters were changed depending on the composition of curing system, but also on the type of rubber matrix. While the tensile strength of composites based on NR increased with increasing amount of sulphur in mixed curing systems, in case of composites based on NBR, the highest value of tensile strength reached the value of the sample cured with equivalent ratio of sulphur and peroxide. On the other hand, thermo-physical and magnetic characteristics were found not to be dependent on the curing system composition. The results revealed that not only the composition of curingsystem, but also the type of rubber matrix plays an important role when preparing the final materials. • Dense-plasma-driven ultrafast formation of FePt organization on silicon substrate This article demonstrates the removal of organic capping and promotion of long-range 2D organization of chemically synthesized FePt nanoparticles dispersed on Si$\langle 100\rangle$substrate by means of pulsed H+ energetic ion irradiation using a dense plasma focus (DPF) device. The irradiation of energetic H$^+$ions on FePt nanoparticles clearly resulted in enhanced structural and magnetic behaviour of the FePt nanoparticles as a function ofplasma focused irradiation shots. Transmission electron microscopy (TEM)/scanning electron microscopy (SEM) images of the FePt nanoparticles clearly show a marked enhancement in average particle size from 2.5 nm for nonirradiated sample to about 28nm for four plasma focus shots irradiation. The gradual removal of organic capping over chemically synthesized FePt nanoparticles with increasing plasma focus shots exposure is confirmed usingRaman spectroscopy. A uniform 2D organization of bimetallic FePt nanoparticles over 1 cm$\times$1 cm silicon substrate is obtained with three plasma focus shots with better magnetic properties as compared with plasma-untreated FePtnanoparticles. • The effects of lithographic residues and humidity on graphene field effect devices Recently, unknown-manner changes in charge neutrality point (CNP) positioning were ascribed to humidity at graphene field effect transistors (GFETs). While the exactmeans of humidity interacting with hydrophobicgraphene remains unknown, this work examines pristine and lithographic-process-applied graphene surfaces with surface enhanced Raman spectra (SERS). SERS analysis shows that the lithographic-process-applied graphenedoes not have the same properties as those of pristine graphene. Furthermore, this study has experimentally investigated the effect of humidity on the transfer characteristics of GFET and proposed a model to explain the formationof asymmetric$I_{\rm DS}–V_{\rm bg}$branches in accordance with the SERS results and humidity responses. • Impact of divalent dopant Ca$^{2+}$on the electrical properties of ZnO by impedance spectroscopy The electrical properties of Zn$_{1−x}$Ca$_x$O ($x = 0, 0.01$, 0.02 and 0.03) nanoceramics synthesized by solidstate reactionmethod were investigated by complex impedance spectroscopy (CIS) from room temperature to 500$^{\circ}$C. Structural analysis of the synthesized material using the X-ray diffraction technique suggests that they exhibit a single phase with hexagonal wurtzite structure. Experimental results indicate that the synthesized material shows temperature-dependent relaxation phenomena. The variation of frequency exponent ($s\$) with temperature shows the presence of thermally activated polarization mechanism in the synthesized sample. Dielectric constant was found to decrease with increase in frequency and temperature for Ca-doped samples. Ca-doped ZnO sample shows dielectric loss at lower temperature than that of pure ZnO.

• # Bulletin of Materials Science

Current Issue
Volume 40 | Issue 3
June 2017