• Volume 42, Issue 2

April 2019

• Thermodynamic analysis of electrodeposition of copper from copper sulphate

The free energy of activation of copper electrodeposition from copper sulphate solution is derived in terms of the dehydration energy of copper sulphate, hydration number of copper sulphate, solvated work function of the host metal and coordination number of the host metal on which the copper deposition is carried out. The free energy of activation for copper electrodeposition on 31 different host metals had been evaluated. The trend in the free energy of activation on different metals is studied and feasible electrodeposition of copper for appropriate applications had been suggested. The methodology is extended to obtain the exchange current densities for copper electrodeposition on different surfaces of Pt in acid medium and compared with the existing literature.

• Synthesis and characterization of Ni–Si$_3$N$_4$ nanocomposite coatings fabricated by pulse electrodeposition

Pure Ni and Ni–silicon nitride (Si$_3$N$_4$) nanocomposite coatings have been successfully fabricated on copper substrates by a pulse electrodeposition method employing the Watts bath. The obtained coatings were characterized withX-ray diffractometry and scanning electron microscopy. Also, surface hardness and the corrosion behaviour of the coatings were analysed by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution. It was found that incorporation of Si$_3$N$_4$ particulates has reduced the crystallite size and also changed the growth orientation of the crystallite from (111) to (220) and (200) crystal planes. The co-deposition of Si$_3$N$_4$ in the Ni matrix led to better properties of these coatings. Accordingly, the hardness value of nanocomposite coatings was about 80–140 Hv higher than that of purenickel due to dispersion-strengthening and matrix grain refining and increased with the enhancement of incorporating Si$_3$N$_4$ particle content. The presence of the Si$_3$N$_4$ particulates slightly decreases the current efficiency. The current efficiency was decreased by increasing current density from 1 to 4 A dm$^{−2}$. Moreover, the corrosion resistance of nanocomposite coatings was significantly higher than the pure Ni deposit. Also, the Ni–Si$_3$N$_4$ coating produced at a density of 4 A dm$^{−2}$ showed thelowest corrosion rate (0.05 mpy).

• Temperature dependence of electrical properties in In/Cu$_2$ZnSnTe$_4$/Si/Ag diodes

Cu$_2$ZnSnTe$_4$ (CZTTe) thin films with In metal contactwere deposited by thermal evaporation on monocrystalline n-type Si wafers with Ag ohmic contact to investigate the device characteristics of an In/CZTTe/Si/Ag diode. The variation in electrical characteristics of the diode was analysed by carrying out current–voltage ($I$ –$V$) measurements in the temperature range of 220–360 K. The forward bias $I$–$V$ behaviour was modelled according to the thermionic emission (TE) theory to obtain main diode parameters. In addition, the experimental data were detailed by taking into account the presence of aninterfacial layer and possible dominant current transport mechanisms were studied under analysis of ideality factor, $n$. Strong effects of temperature were observed on zero-bias barrier height ($\Phi_{\rm B0}$) and n values due to barrier height inhomogeneity at the interface. The anomaly observed in the analysis of TE was modelled by Gaussian distribution (GD) of barrier heightswith 0.844 eV mean barrier height and 0.132 V standard deviation. According to the Tung’s theoretical approach, a linear correlation between $\Phi_{\rm B0}$ and $n$ cannot be satisfied, and thus the modified Richardson plot was used to determine Richardson constant ($A^∗$). As a result, $A^∗$ was calculated approximately as 120.6 A cm$^{−2}$ K$^{−2}$ very close to the theoretical value for n-Si. In addition, the effects of series resistance ($R_s$) by estimating from Cheng’s function and density of surface states ($N_{ss}$) by taking the bias dependence of effective barrier height, were discussed.

• Investigating structural features of Ba and Zr co-substituted strontium bismuth tantalate thin films..

Structural (crystal and microstructure), chemical and electronic states, and ferroelectric and electrical features of Ba and Zr co-substituted strontium bismuth tantalate (SBT) were probed in this study. Distinctly, Ba and Zr were substitutedfor Ta and Sr sites of Sr$_{0.8}$Bi$_{2.2}$Ta$_2$O$_9$ in the form of Sr$_{0.8−x}$Ba$_x$ Bi$_{2.2}$Ta$_{2−y}$Zr$_y$O$_9$. To investigate the impact of the co-substitution on the crystal structure, microstructure, ferroelectric and electrical properties, Sr$_{0.8−x}$Ba$_x$ Bi$_{2.2}$Ta$_{2−y}$Zr$_y$O$_9$ thin films were deposited on Pt/Ti/SiO$_2$/Si(100) wafers by sol–gel spin by coating method. Crystal structure, microstructure, chemical and electronic states, ferroelectric, capacitance and leakage current characteristics of the films were studied to investigate potential for one transistor type ferroelectric random access memories (1T-type FeRAMs). Successful substitutions up to 10 mol% lead to reduction of double remanent polarization ($2P_r$) to 10.26 $\ mu$C cm$^{−2}$, and dielectric constant ($\epsilon_r$) to 135. These values demonstrate that successful co-substitution of limited Ba and Zr in SBT with stable crystal structure has the ability to decrease $P_r$ and $\epsilon_r$ values of the ferroelectric material which can be a candidate gate to be utilized inferroelectric field-effect transistors (FeFETs) for 1T-type FeRAM applications.

• Effects of doping Pr$^{3+}$ and Gd$^{3+}$ into YAG:Ce phosphors on the luminescence properties

A series of (Y$_{0.98−x−y}$Ce$_{0.02}$Pr$_x$Gd$_y$)$_3$Al$_5$O$_{12}$ ($x = 0−0.02$, $y = 0, 0.3$) phosphors were prepared by amodified co-precipitation method. The phases, luminescence properties, effect of calcination temperature on luminescenceproperties and energy transfer (ET) were investigated.The results indicated that the doping of Pr$^{3+} and Gd$^{3+}$in all samples did not produce any new phases but caused a slight lattice expansion. The series of (Y$_{0.98−x}$Ce$_{0.02}$Pr$_x$)$_3$Al$_5$O$_{12}$phosphors emitadditional red light at 612 nm, and when$x = 0.005$, the red/yellow ratio of the emission spectrum is the largest. Compared with the (Y$_{0.975}$Ce$_{0.02}$Pr$_{0.005}$)$_3$Al$_5$O$_{12}$phosphor, continued doping 30 at% Gd$^{3+}$in the (Y$_{0.675}$Ce$_{0.02}$Pr$_{0.005}$Gd$_{0.3}$)$_3$Al$_5$O$_{12}$sample makes the peak wavelength of yellow light emission shift from 533 to 561 nm. Doping Pr$^{3+}$and Gd$^{3+}$results in the decrease of integrated emission intensity, but the emission intensity and the red/yellow ratio can be increased by raising the calcination temperature. In addition, there is only the ET from Ce$^{3+}$to Pr$^{3+}$in the (Y$_{0.675}$Ce$_{0.02}$Pr$_{0.005}$Gd$_{0.3}$)$_3$Al$_5$O$_{12}$sample. • Preparation of Cu nanoparticles by a pulsed wire evaporation process for conductive ink applications In the present study, Cu colloidal nanoparticles and nanopowders were successfully synthesized by a pulsed wire evaporation process. Cu-based nano-inks were prepared by mixing Cu nanoparticles with acrylic resin and solvent.Cu nanoparticles with a particle size of <20 nm were uniformly dispersed in ethylene glycol. The Cu nanopowders were successfully coated with an organic solvent composed of a hydrocarbon compound. This organic coating effectively inhibited the oxidation of Cu nanopowders. In addition, the stability of dispersion of Cu nanoparticles in the inks was improved by a ball-milling process. The electrical conductivity of the prepared Cu nano-inks was 10–28$\mu$S cm$^{−1}$for 20–40 wt% of Cu. • Evaporated porphyrin films as nitrogen dioxide gas sensors In this work, metal-free and copper(II) 5,10,15,20-tetrakis(-4-(methyl 2-phenoxyacetate)) porphyrin films were employed as nitrogen dioxide gas sensors. The films were vacuum evaporated and the sensor response was evaluated as changes in the optical absorption spectra, hydrophobic properties and conductivity at different gas concentrations. The morphology of the films obtained with scanning electron and atomic force microscopy before and after gas exposure indicated different interaction mechanisms. For instance, metal-free film exhibited an absorption phenomenon due to gas diffusion towards the bulk film because of the presence of pores at the film interface, while the copper-porphyrin film showed interfacial film degradation. From UV–vis results, differences in the gas content within the film were detected due to the formation of new peaks around 680 nm in agreement with morphological findings. Contact angle results exhibited less hydrophobic films after gas adsorption as a result of changes in the surface roughness. In addition, the conductivity valueswere not only dependent on the gas concentration but also on the molecular structure. For instance, gas absorption within the metal-free films truncated electron mobility paths decreasing the conductivity response in comparison with the copper system. Finally, the molecular packing arrangement and gas absorption were also investigated by using density functional theory, which provided some insights into the molecular-gas interactions and supported experimental results. • Laccase immobilized onto graphene oxide nanosheets and electrodeposited gold–cetyltrimethylammonium bromide complex to fabricate a novel catechol biosensor In this study, a new biosensor is developed with reliable and easy-to-use biodevice properties for catechol determination in real samples. A method is proposed for the fabrication of biosensors to sense catechol based on theadsorption method of laccase immobilization. Hence, a glassy carbon electrode was modified via graphene oxide nanosheets and then it was modified with a gold–cetyltrimethylammonium bromide nanocomposite to adsorb and immobilize laccase on the electrode surface. The results showed laccase immobilization onto the reformed glassy carbon electrode, and a direct electron transfer reaction between laccase and the electrode. The mechanism of electron transferring was EC$^{\prime}$. Also,$k_s$and$\alpha$were calculated as 0.41 s$^{−1}$and 0.33, respectively. For this biosensor two linear ranges,$0.1 \times 10^{−6}$to$5 \times 10^{−6}$M and$16.7\times 10^{−6}$to$166 \times 10^{−6}$M, and a detection limit of$1.5 \times 10^{−6}$M were obtained. • A facile synthesis of novel$\alpha$-ZnMoO$_4$microspheres as electrode material for supercapacitor applications A mixed metal oxide,$\alpha$-ZnMoO$_4$is prepared in a simple, lucid and facile synthesis route as an active material for supercapacitor applications. The structural and morphological information is provided by X-ray diffraction, Fouriertransform infrared, Raman and scanning electron microscopy data. The as-prepared$\alpha$-ZnMoO$_4$microspheres are subjected to cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy studies to examine its electrochemical behaviour in 2 M KOH aqueous electrolyte. Zinc molybdate microspheres have demonstrated very goodelectrochemical performance with 234.75 F g$^{−1}$at 0.5 Ag−1 with good specific capacitance retention (82%) for sustained1600 charge/discharge cycles. • Study on wear and corrosion properties of functionally graded nickel–cobalt–(Al$_2$O$_3$) coatings produced by pulse electrodeposition Functionally graded nickel–cobalt coatings with/without alumina nanoparticles were pulse electrodeposited on a carbon steel substrate by a continuous decrease in duty cycle from 95 to 10% at different frequencies of 100, 500and 1000 Hz. The effect of pulse parameters on the nanoparticle content, chemical composition, microstructure, corrosion properties and tribological behaviour of coatings was studied. Energy-dispersive X-ray spectroscopy analysis showed that the amount of cobalt is gradually reduced and the content of alumina nanoparticles is increased from the substrate/coating interface to the surface. Based on the electrochemical studies in 3.5 wt% NaCl, the nanocomposite coatings gain the highest corrosion resistance at the lowest frequency. Also, the hardness of coatings gradually increased. Evaluation of the tribological behaviour of coatings by a pin-on-disk wear test showed that the nanoparticles have a positive effect on wear resistance and improve it by increasing frequency. • Preparing photocatalytic paper with improved catalytic activity by in situ loading poly-dopamine on cellulose fibre Photocatalytic paper is a composite photocatalyst generally prepared by loading semiconductors, such as titanium dioxide (TiO$_2$) nanoparticles on paper, and attracts sustaining interests. In this paper, poly-dopamine (PDA) wasloaded on cellulose fibre by in situ oxidative polymerization of dopamine. The PDA-loaded cellulose fibre (PLCF) was used to make TiO$_2$photocatalytic paper together with pristine cellulose fibre (CF) and TiO$_2$nanoparticles to improve the performance of the photocatalytic paper. The loading of PDA on CF and the introduction of TiO$_2$nanoparticles in paper were verified by infrared spectroscopy and X-ray diffraction technique, respectively. As observed by scanning electron microscopy, the introduction of PLCF significantly improved the distribution of TiO$_2$nanoparticles in paper by forming a membranoussubstance. The photocatalytic performance of the as-prepared photocatalytic paper was analysed by decomposing methyl orange under UV light irradiation. It was confirmed that the occurrence of PLCF significantly improved the photocatalytic performance of the photocatalytic paper. The paper with the highest photocatalytic activitywas prepared using a PLCF-to-CF mass ratio of 1:1. The photocatalytic paper with PLCF is stable in the process of repeated application. This work provided a new approach to prepare photocatalytic paper with improved photocatalytic activity. • Controlled release of huperzine-A from biocompatible copolymer microspheres Huperzine-A (Hup-A) is a reversible acetylcholinesterase inhibitor used for patients suffering from Alzheimer’sdisease. Hup-A has to be administered daily because of its short half-life time and narrow therapeutic range, making it lesssuitable for clinical use. In the present study, we studied its controlled drug delivery using biodegradable microspheres toavoid frequent dosing. Hup-A-loaded microspheres were prepared by an emulsion crosslinking method using a mixture ofwater and oil. Calcium chloride was used as a crosslinker. Primarily, we prepared sodium alginate (NaAlg) microspheresand investigated the in vitro release. The in vitro release studies were carried out successively at three different pH (1.2, 6.8 and 7.4) values for 2 h. To increase the durability of the NaAlg microspheres, NaAlg was blended with acrylamide (AAm)-grafted poly(vinyl alcohol) (PVA). It was determined that the presence of the PVA-$g$-AAm increased the physical resistance of the microspheres and also increased the amount of Hup-A loading and release. Additionally, the effect ofthe NaAlg/PVA-$g$-AAm (w/w) blend ratio, drug/polymer (w/w) ratio, crosslinker concentration and crosslinking periodon the release of Hup-A was investigated. The prepared microspheres were characterized using Fourier transform infraredspectroscopy, differential scanning calorimetry and scanning electron microscopy. • Simulation of dielectric and resonance and anti-resonance data using modified Lorentz equation ($T$and$\omega$simultaneously) of relaxor ferroelectric and piezoelectric ceramics Dielectric data of new [Ba(Nd$_x$Ti$1−2xNbx )O$_3$]$_{0.30}$[Na$_{0.5}$Bi$_{0.5}$TiO$_3$]$_{0.70} ($x = 0.075$) relaxor ceramic was modelled using a new modified Lorentz equation ($T$and$\omega$simultaneously) as proposed by us. The activation energy forthermally activated orientation of dipoles and relaxation times were estimated. Dielectric resonance and anti-resonance data as a function of temperature and angular frequency of other piezoelectric compound [Ba(Nd$_{0.1}$Ti$_{0.8}$Nb$_{0.1}$)O$_3$]$_{0.35}$[(Na$_{0.5}$Bi$_{0.5}$)TiO$_{3}$]$_{0.65}$was also modelled using the modified Lorentz equation as proposed by us. It is shown that using thisequation, it is possible to obtain the polarizability, piezoelectric charge constant, piezoelectric voltage constant and activationenergy for resonance and anti-resonance. • Dextran from Leuconostoc mesenteroides-doped ammonium salt-based green polymer electrolyte Biopolymer electrolytes based on dextran from Leuconostoc mesenteroides doped with ammonium nitrate (NH$_4$NO$_3$) are synthesized via a solution cast method. Fourier transform infrared analysis is used to determine the complexation between cation from the salt with functional groups of dextran. The ionic conductivity of undoped dextran film at room temperature is identified as$ (8.24 \pm 0.31) \times 10^{−11}$S cm$^{−1}$. A conductivity of$(3.00 \pm 1.60) \times 10^{−5}$S cm$^{−1}$isachieved with the inclusion of 20 wt% NH$_4$NO$_3$to the pure dextran film. The conductivity at a high temperature of the electrolyte obeys Arrhenius theory. Field emission scanning electron microscopy results show that the highest conducting sample has a porous surface. Results from the dielectric study show a non-Debye characteristic. • Structural, morphological and dielectric traits of Zr$_{1−x}$Ca$_x$TiO$_4$($x = 0$, 0.05, 0.10, 0.15 and 0.2) ceramics The influence of Ca doping on structural, morphological and dielectric characteristics of Zr$_{1−x}$Ca$_x$TiO$_4$($x = 0$, 0.05, 0.10, 0.15 and 0.2) ceramics has been planned in this effort. Un-doped and Ca-doped ZrTiO$_4$(ZT) have been synthesized through a sol–gel auto-combustion approach. The orthorhombic phase of ZT and Ca-doped ZT is confirmed through X-ray diffraction patterns. The variation in structural morphology and particle size due to Ca incorporation in ZT has further been revealed by field emission scanning electron microscopy. The investigation showed that the size of the particlegradually reduced from 0.5 to 0.125$\mu$m with the increase of Ca content. It was confirmed from Fourier transform infrared spectroscopy that organic content was not found in the prepared samples. Dielectric constant, dielectric loss factorand tangent loss reduce with the increase in frequency and increase in Ca content. These dielectric parameters show independency at a higher frequency. The modulus plots confirmed that the capacitive parts were relatively independent of the frequency, whereas ac conductivity exhibited frequency dependent behaviour i.e., an increase with Ca concentrationand with increasing frequency. The impedance plots revealed the resistance dominance due to the grain boundary effect. • Physico-mechanical assessment of plaster of Paris bandage produced from locally sourced materials Despite the abundance of gypsum and other materials needed for the production of plaster of Paris (POP) in the country, Nigeria relies heavily on the importation of orthopaedic POP bandage. Therefore, the present study aimed atproducing POP bandage (LPOP) from locally sourced pure gypsum and cassava starch. Physico-chemical parameters, such as amylose content, amylopectin content, water absorption capacity (WAC), swelling capacity (SC) and browning–charring temperature (BCT) were obtained for the starch binder. A slurry of pure gypsum powder and 2% gelatinized starch binder was impregnated on cotton gauze and cured in an oven at 180$^{\circ}$C for an hour to produce the LPOP. A comparative mechanical test was carried out on the LPOP and a POP bandage (CPOP) acquired from the market using a universal testing machine.The results showed that starch contains 9.06 mg per 100 g amylose and 24.1 mg per 100 g amylopectin which implied that it has a good binding property. The SC, WAC and BCT were evaluated to be 69.79, 81.94 and 190$^{\circ}$C, respectively. The yielding tensile force for LPOP and CPOP are 148 and 460 N, respectively. The horizontal compressive strength of the LPOP and CPOP are 1712 and 1595 N while the vertical compressive strengths are 1070 and 623 N, respectively. These results show that the LPOP produced from locally sourced materials compete favourably in terms of mechanical properties with POP bandage in the market. Thus, based on its strength, it is recommended for orthopaedic casting. • Bentonite polymer composite for water purification A polyethylene glycol (PEG)–bentonite (BT) composite was prepared by direct polymerization of PEG in suspensions of BT. Based on detailed analyses using field-effect scanning electron microscopy, X-ray diffraction, surfacearea measurements and chemical methods, the obtained product was mainly composed of Ca-BT with a specific surface area of 4.13 m$2^$g$^{−1}$. The optimal conditions for adsorption of Pb$^{2+}$and Cd$^{2+}$ions were found to be a PEG content of 0.1% and a contact time of 60 min. The sorption experiments were performed under various operating variables, including polymer concentration, pH and temperature. For both Pb$^{2+}$and Cd$^{2+}$%, the adsorption equilibrium was described by the Freundlichmodel, which confirmed the presence of a heterogeneous system with irregular filling of the active centres. The maximum sorption capacities of BT–PEG for removal of Pb$?^{2+}$and Cd$^{2+}$were found to be 22 and 18 mg g$^{−1}$, respectively. The rate constants calculated for the sorption of Pb$^{2+}$and Cd$^{2+}$were 6.29 and 6.67 g mg$^{−1}$min$^{−1}$, respectively, at 25$^{\circ}$C. This study shows that the obtained sorbents based on BT may be used for treatment of waste water and could help resolve environmentalprotection issues. • Detoxification of dye contaminated water by Mn$^{2+}$-doped ZnS nanostructures Chemical co-precipitation route was successfully employed to synthesize polyethylene glycol-coated pure and doped Zn$_{1−x}$Mn$_x$S (0 ≤ x ≤ 0.1) nanoparticles. The crystallographic and morphological analyses have been done by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The formation of cubic crystal structure and quasi-spherical morphology has been revealed by XRD and TEM, respectively. The optical analyses have been done by UV–Vis absorption spectroscopy and energy resolved photoluminescence spectroscopy. Energy dispersive X-ray spectroscopy study has been carried to analyse the elemental composition. The doping concentration dependent photo-catalytic activity was checked to analyse the photo-catalytic potential of Zn$_{1−x}$Mn$_x$S nanoparticles under UV irradiation. • Prediction of magnetic and magnetocaloric properties in Pr$_{0.8−x}$Bi$_x$Sr$_{0.2}$MnO$_3$($x = 0$, 0.05 and 0.1) manganites In this work, we have investigated the magnetic and magnetocaloric properties of Pr$_{0.8−x}$Bi$_x$Sr$_{0.2}$MnO$_3$($x = 0$, 0.05 and 0.1) polycrystalline manganites prepared by sol–gel route on the basis of a phenomenological model. Temperature dependence of magnetization indicates that all our samples exhibit a second order paramagnetic to ferromagnetic transition with a decrease in temperature. A correlation between experimental results and theoretical analysis based on a phenomenological model is investigated. The magnetic and magnetocaloric measurements are well simulated by this model. Under a magnetic applied field of 5 T, the theoretical absolute values of the maximum of magnetic entropy change$\Delta S_{\rm Max}$are found to be equal to 5.33, 3.33 and 2.97 J kg$^{−1} K$^{−1}$ for $x = 0$, 0.05 and 0.1 respectively. The relative cooling power and the specific heat capacity values are also estimated. The predicted results permit us to conclude that our compounds may be promising candidates for magnetic refrigeration at low temperatures.

• Biosynthesis of cellulose microfibre from peanut shell for the preparation of bio-nanocomposite films for food-packaging application

Synthetic petroleum-based products are normally used for food-packaging application which results in environmental pollution. This creates a need to develop biodegradable polymer and polymer-based films to maintain thestability of packed materials for a defined period of time that will overcome the drawbacks of the synthetic petroleumbased packaging system. The current work is focussed on evaluating the potential of cellulose agar bio-nanocompositefilms in food packaging application. The physical and mechanical properties such as its tensile strength (TS), Young’s modulus (YM) and elongation at break ($E$) were found to be increased on loading with cellulose microfibre (CMF).TS is found to be increased from $38.8\pm 3.2$ to $49.4\pm 4.3$ and there is about 6% increase in the elongation at break. Similarly, CMF films exhibit $54\pm 0.2$% water solubility, 1.304 opacity and $1.71\pm 0.07$ GPa, respectively. Also, the bionanocomposite film showed less swelling property and an increase in soil degradation rate, enabling it to be applied in food packaging.

• Structural and electrical conductivity of CH:MC bio-poly-blend films: optimize the perfect composition of the blend system

In this study, solid polymer blend films based on chitosan (CH) and methylcellulose (MC) were prepared in various compositions by the solution cast technique. The features of structure and complexation of the blend polymer filmswere studied using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The shift of FTIR peaks of the amino groups of CH and the hydroxyl groups of MC reveals the formation of interchain hydrogen-bonding between CH and MC chains in blend films. From the XRD pattern, the semi-crystalline structure of CH was depressed with the addition of MC and shows the CH:MC blend system with ratio 75:25 has the minimum degree of crystallinity. The highest room temperature conductivity was found to be $0.05\times 10^{−6}$ S cm$^{−1}$ for 75CH:25MC blend polymer composition. The dc conductivity exhibits Arrhenius-type behaviour with temperature. The drastic increase in conductivity up to $37.92 \times 10^{−6}$ S cm$^{−1}$ at 373 K, can be explained by free volume model. The highest value of electrical conductivity for all prepared samples was associated with the minimum value of activation energy.

• Graphene quantum dots as a green photosensitizer with carbon-doped ZnO nanorods for quantum-dot-sensitized solar cell applications

Graphene quantum dots (GQDs), N-doped GQDs (NGQDs) and S, N co-doped GQDs (SNGQDs) were synthesized using hydrothermal methods. All GQDs were attached with carbon-doped ZnO nanorods (C-ZnO NRs) grownon fluorine-doped tin oxide (FTO)-coated glass substrates, for the fabrication of metal-free eco-friendly quantum-dotsensitized solar cells (QDSSCs). SNGQD-decorated nanorod-based solar cells demonstrated maximum open circuit voltage($V_{\rm OC}\sim 360$ mV), short circuit current ($J_{\rm SC}\sim 1.84$ mA cm$^{−2}$) and power conversion efficiency ($\eta \sim 0.293$%) comparedto other devices.

• Zeolite X with potassium diformate as a sustained-release antibacterial agent

A reaction of 800 mesh stellerite and a concentration of 15% hydrochloric acid in a solid to liquid ratio of 1:3 was carried out for 2 h at 80$^{\circ}$C. Most of its impurities were removed. It can be used as precursors for the preparationof high quality zeolite. Zeolite X which is octahedral crystal shape as cube, 96% of the degree of crystallinity has been synthesized hydrothermally from $n({\rm SiO}_2/{\rm Al}_2{\rm O}_3) = 3$, $n({\rm Na}_2{\rm O}/{\rm SiO}_2) = 1.14$ and $n({\rm H}_2{\rm O}/{\rm Na}_2{\rm O}) = 37$ by controlling reaction temperature and time. The synthesis included zeolite X as carriers, chitosan as intermediates, a mass ratio of zeolite X:chitosan:potassium diformate $=$ 3:1:2 in weight for 2 h at 40$^{\circ}$C. X-ray photoelectron spectroscopy analysis showed hydrogen bond formation by the chitosan amino hydrogen, potassium diformate oxygen and zeolite X oxygen or hydrogen bond formation by free hydroxyl group of zeolite X and oxygen of chitosan’s C–O, indicating effective grafting. Zeolite Xsustained-release antibacterial agent was prepared with an inhibition rate of 78.16% by the antibacterial.

• Green synthesis, characterization and optical properties of eutectics and 1:1 intermolecular compounds: $N,N$-dimethylaminobenzaldehyde–anthranilic acid and 2-(4-(dimethylamino)benzylideneamino)benzoic acid– $p$-nitroaniline systems

Phase diagrams of $N,N$-dimethylaminobenzaldehyde (DMAB)–anthranilic acid (AA) and 2-(4-(dimethylamino)benzylideneamino)benzoic acid (DMABAB)–$p$-nitroaniline (PNA) systems, determined by the thaw-meltmethod, give two eutectics and a 1:1 intermolecular compound (IMC) in each case. Appropriate amounts (10 g) of each of the eutectics and the IMCs were prepared by a green synthetic method involving a solid state reaction without any solvent. These materials were characterized by X-ray diffraction, thermal and spectral methods and the optical properties of the pure components and the IMCs were studied.While negative values of heat of mixing in the case of a DMAB–AA system suggest clustering of molecules in both eutectic melts, those of positive value in E$_1$ and negative value in E$_2$ of the DMABAB–PNAsystem indicate the formation of a quasi-eutectic structure in E$_1$ melt and clustering of molecules in E$_2$ melt. The IMC of DMAB–AA system shows strong dual emission with two λmax one at 380 nm and the second at 450 nm with a total quantum efficiency of 0.49. The IMC of DMABAB–PNA system also shows a similar observation with two $\lambda_{\rm max}$ one at 390 nm and second at 435 nm with a total quantum efficiency of 0.31.

• Fabrication of Cu$_2$ZnSn(S,Se)$_4$ thin film solar cell devices based on printable nano-ink

Cu$_2$ZnSnS$_4$ (CZTS) as a promising light-absorber material has been extensively applied in photovoltaic solarcells due to its huge absorption coefficient ($\sim$104 cm$^{−1}$) and optimal bandgap ($\sim$1.5 eV). In this study, stable and printable CZTS nano-ink was acquired by dispersing CZTS nanocrystals (NCs) in organic solutions. The kesterite CZTS NCs possess uniform size and good crystallinity. The Raman peak of CZTS is located at 330 cm$^{−1}$, which illustrates that the NCs consist of single-phase CZTS without any impurities. The as-prepared CZTS nano-ink was in turn spin-coated onto the Mo substrate to obtain the desired CZTS thin films under the conditions of anti-vacuum. The compact and dense CZTSSe absorbers were acquired by sulphuring and selenizing the as-prepared thin films. The band gap of the photovoltaic absorber materials is 1.2 eV after incorporating Se into the photovoltaic thin films. Finally, the CZTSSe photovoltaic thin film device, whose power conversion efficiency was $1.40 \pm 0.14$%, was prepared by this easy and green method.

• Role of surface passivation on visible and infrared emission of Ge quantum dots formed by dewetting

The dual action of oxide-related defects in the visible and infrared emission of germanium (Ge) self-assembled quantum dots (QDs) is discussed. TheGe particleswere fabricated by solid-state dewetting on a thin layer of SiO$_2$. Subsequent surface passivation by amorphous silicon was carried out for several samples. All samples were encapsulated by SiO$_2$. Atomic force microscopy analysis indicates a linear relationship between the size of QDs and the initial thickness of the amorphous Ge films. The crystallization of the QDs was evidenced by transmission electron microscopy and Raman spectroscopy. Photoluminescence measurements show that the main visible emission is blue-green centred around 520 nm. The luminescence attributed to the radiative recombination of quantum-confined excitons is only observed when the surfaceis in-situ passivated prior to the deposition of the oxide matrix. The results of this work are helpful for optimizing the performance of the optoelectronic devices based on the infrared emission of Ge nanocrystals.

• Structure and luminescence properties of K$_2$GdF$_5$:Tb$^{3+}$ synthesized by solid-state reaction method

K$_2$GdF$_5$:Tb$^{3+}$ material used in dosimetry field was synthesized by solid-state reaction method. The scanning electron microscopy image showed that the material exhibits porous surface with a very large surface area. The photoluminescence spectrum confirmed energy transfer process from Gd$^{3+}$ ions to Tb$^{3+}$ ions, and the luminescence of this material was entirely due to Tb ions. The high luminescent intensity at 542 nm was perfectly consistent with the sensitive wavelength range of photomultiplier tubes in the thermoluminescence (TL) reader. The TL-glow curve was very simple with the temperatures of the main peak in the range from 200 to 230$^{\circ}$C, and the glow-curve shape was suitable for dosimetry purposes. The TL intensities of K$_2$GdF$_5$:10 mol% Tb$^{3+}$ was higher than that of common CaSO$_4$:Dy$^{3+}$ dosimeters. The estimation on available application of the prepared material in neutron dose measurement was carried out.

• Injectable nanocurcumin-dispersed gelatin–pluronic nanocomposite hydrogel platform for burn wound treatment

To utilize the potent pharmaceutical properties of curcumin (Cur) and gelatin-based materials in tissue regeneration, we fabricated a thermosensitive nanocomposite hydrogel based on pluronic-grafted gelatin (PG) and nanocurcumin (nCur) to enhance burn healing. In this method, the amphiphilic PG played a role as a surfactant to prepare and protect nanosized Cur particles, which could overcome the poor dissolution of the phytochemical. The synthesized PG was identified by ${}^1$H nuclear magnetic resonance. Depending on the amount of Cur, size distribution of the dispersed nCur ranged from $1.5\pm 0.5$to $16\pm 3.2$ nm as observed using transmission electron microscopy and dynamic light scattering. The nCur-dispersed PG solution formed nCur–PG nanocomposite hydrogel on warming up to 35$^{\circ}$C. Release profile indicated sustainable release of Cur from the injectable platform. Fibroblast cells were well proliferated on the nanocomposite hydrogel. The nCur–PGenhanced the healing process of second-degree burn wound. These results showed potential applications of the biomaterial in tissue regeneration.

• Enhancement of ethanol-sensing properties of ZnO nanoplates by UV illumination

ZnO nanoplates with hexagonal wurtzite structure were synthesized by hydrothermal treatment. The averagedimension and average thickness of the plates were $\sim 200 \times 400$ and 40 nm, respectively. ZnO nanoplates were deposited on Pt-interdigitated electrodes for the fabrication of gas-sensing devices. The ethanol-sensing properties of the devices were investigated in the dark vs. ultraviolet (UV) illumination. Under the UV illumination, the optimal operating temperature of the devices can be reduced from 237 to 164$^{\circ}$C and the response of the device was increased from 2.8 to 8.5 towards 1500 ppm ethanol vapour.

• Poly(amido amine) dendrimer and silver nanoparticle–multi-walled carbon nanotubes composite with poly(neutral red)-modified electrode for the determination of ascorbic acid

A new film containing poly(amido amine) dendrimer, silver nanoparticles and multi-walled carbon nanotubes composite with poly(neutral red) was prepared on a paraffin wax impregnated graphite electrode. The PAMAM/AgNPs–MWCNT/PNR film exhibited promising electrocatalytic oxidation of ascorbic acid (AA) in acetate buffer solution of pH 4.0. The PAMAM/AgNPs–MWCNT/PNR film-modified electrode enhanced the sensitivity of detection of AA. The PAMAM/AgNPs–MWCNT/PNR film-modified electrode was characterized by cyclic voltammetry, chronoamperometry, hydrodynamic voltammetry (HDV) and difference pulse voltammetry. These experiments confirmed the electrocatalytic oxidation of AA by PAMAM/AgNPs–MWCNT/PNR film-modified electrode. The PAMAM/AgNPs–WCNT/PNRmodifiedelectrode has been found to possess good electrocatalytic activity towards AA oxidation which has been observed at a lower oxidation potential of around 0.26 V with a higher current response. The electrochemical oxidation of AA by PAMAM/AgNPs–MWCNT/PNR-modified electrode involved a two proton and two electron process. A linear relationshipbetween the catalytic current and AA concentration was obtained in the range from 0.16 to 2500 $\mu$M with a detection limitof 0.053 $\mu$M.

• Colloidally synthesized defect-rich MoSe$_2$ nanosheets for superior catalytic activity

Transition metal dichalcogenide (TMD) nanosheets (NSs) with defect-rich and vertically aligned edges are highly advantageous for various catalytic applications. However, colloidal synthesis of defect-rich NSs with thickness variation has been a challenging task. Here, we report a colloidal synthesis of 2H-MoSe$_2$ NSs having a large number of defects and vertically aligned edges, where the thickness is varied by changing the amount of coordinating solvent. The Se-vacancies in these NSs have introduced defect sites which are corroborated by the presence of additional vibration modes in Raman spectra. These NSs exhibit electrocatalytic hydrogen evolution reaction performances with a low overpotential (210–225 mV) at 10 mA cm$^{−2}$ current density and a small Tafel slope (54–68 mV per decade). Moreover, these MoSe$_2$ NSs are also employed as counter electrodes (CEs) for the fabrication of dye sensitized solar cells via a cost-effective and simplified procedure. The power conversion efficiencies of $7.02\pm 0.18$%, comparable with Pt CE ($7.84\pm 0.10$%) could be routinely achieved. These results demonstrate a novel synthetic strategy to prepare layered TMDs with superior catalytic applications.

• Simulation of graphene–fullerene nanohybrid structure

In the present simulation study, the structure and dynamics of graphene–fullerene nanocomposite has been investigated using all atom molecular dynamics simulation technique. The formation of graphene–fullerene nanocomposite constituting graphene and self-assembly of 12 bucky balls has been demonstrated. The structure, size, interparticle separation, spatial distribution, temperature effect, mobility and conformation of graphene–fullerene nanocomposite, and the influence of single and two layers of graphene on the structure of graphene–fullerene nanocomposite have been determined and discussed in detail. This simulation result may possibly aid the design and development of graphene–fullerene hybrid nanomaterials for future biological and technological applications.

• First principles study of breaking energy and mechanical strength of Kevlar-29

The first principles study is performed for the mechanical strength of Kevlar-29, and is based on density functional theory. The bond strength is investigated relative to the displacement of central nitrogen atom along $X$, $Y$ and $Z$ directions, respectively. The structural property analysis explains the asymmetric nature. A higher bond breaking energy is observed during compression along $Z$ direction and vice versa for elongation. It is an insulator of forbidden energy gap which increases while compression and reduces during elongation. Crystal orbital overlap population reveals the higher strength of anti-bonding orbitals. It is mechanically stronger along the $Z$-axis and weaker along the $Y$-axis.

• Comparative studies on spinal ferrite MFe$_2$O$_4$ (M $=$ Mg/Co) nanoparticles as potential adsorbents for Pb(II) ions

Ferrite nanoparticles (NPs) with composition MFe$_2$O$_4$ (M $=$ Mg/Co) were synthesized by a facile combustion method. NPs were characterized employing various physico-chemical techniques. X-ray diffraction patterns confirmed the phase purity, transmission electron micrographs indicated that NPs are spherical and average diameter of maximum fraction of NPs was in the range of 20–30 nm. Magnetic studies revealed that the saturation magnetization values for MgFe$_2$O$_4$ and CoFe$_2$O$_4$ NPs were 13.17 and 41.12 emu g$^{−1}$, respectively. The Brunauer–Emmett–Teller surface area of CoFe$_2$O$_4$ and MgFe$_2$O$_4$ NPs was 22.98 and 34.39vm$^2$ g$^{−1}$, respectively. Synthesized ferrite NPs and activated charcoal were comparatively analysed as adsorbents for removal of Pb(II) ions. The factors influencing uptake behaviour of Pb(II) ions viz. adsorbent dose,pH, concentration, temperature and contact time were quantified.The adsorption data showed good correlationwith Langmuir and Freundlich models as compared to Dubinin–Radushkevich model. The maximum adsorption capacity displayed a twofold increase for NPs as compared to activated charcoal. The easy magnetic separation of ferrite NPs from the solution and their regeneration with 0.1 N NaOH for reuse without any loss make them potential adsorbents. The trend in ascending order for the elimination of Pb(II) ions from the solution was activated charcoal < CoFe$_2$O$_4$ NPs < MgFe$_2$O$_4$ NPs. The observed differences in the adsorption potential of NPs are explained on the basis of structural and magnetic properties and the surface area of NPs.

• Role of sonication time on thermal behaviour and dynamic mechanical analysis of NiZn ferrite incorporated PLA/LNR nanocomposite

The investigation on thermal properties of polylactic acid/liquid natural rubber (PLA/LNR) blend embedded with nickel zinc (NiZn) ferrite nanoparticles at various loading (1–5 wt%) and treated with different ultrasonication time (1–2 h) is the main core of this study. The novel NiZn nanocomposite based on the matrix of PLA:LNR with a ratio of 90:10 was fabricated via melt blending technique with the aids of ultrasonication. The effects of nanofiller loading and ultrasonic treatment on nanocomposite were examined by scanning electron microscopy, differential scanning calorimetryand dynamic mechanical analyser. The results revealed that the thermal properties of PLA/LNR matrix have improved withincorporation of nanoparticles in which improvement was observed until an optimum level at 4 wt% NiZn ferrite within 1 h of ultrasonic treatment. The optimum ultrasonication for 1 h is believed to be sufficient to promote a good dispersion of NiZn ferrite nanoparticles within the PLA/LNR and in order to enhance the thermal stability, which makes it potentially to be used in electronic applications.

• Effect of off-stoichiometry on properties of tin selenide crystals

The tin selenide crystals with different proportions of Sn and Se were grown by a direct vapour-transport technique. The layer by layer growth of crystals from the vapour phase was promoted by screw dislocation mechanism. The powder X-ray diffraction (XRD) shows good crystallinity of grown compound. The XRD patterns of grown compounds are well-indexed to orthorhombic structure. In the off-stoichiometric compound, evidence of SnSe$_2$ secondary phase is observed due to excess of selenium. The morphological investigations were carried out using a Carl Zeiss optical microscope. The electron diffraction was also recorded from tiny flakes using a transmission electron microscope. The electrical resistivity both parallel and perpendicular to the c-axis was measured in the temperature range of 303–490 K and activation energy was also calculated using Arrhenius relation. The electrical study depicts the extrinsic semiconducting nature of grown compositions.

• Study on electrical conductivity and oxygen migration of the oxide-ion conductors Na$_{0.5}$Bi$_{0.5}$Ti$_{1−x}$Mg$_{x}$O$_{3−x}$

Electrical performance and oxygen relaxation behaviour in Na$_{0.5}$Bi$_{0.5}$Ti$_{1−x}$Mg$_x$O$_{3−x}$ compounds were investigated. The oxide ion conductivity of Na$_{0.5}$Bi$_{0.5}$Ti$_{1−x}$Mg$_x$O$_{3−x}$ compounds increased first and then decreased with increasing Mg-doped content. The highest oxide ion conductivity of $4.7\times 10^{−3}$ S cm$^{−1}$ at 773 K was observed for the Na$_{0.5}$Bi$_{0.5}$Ti$_{0.96}$Mg$_{0.04}$O$_{2.96}$ compound. A typical relaxation peak in the Na$_{0.5}$Bi$_{0.5}$Ti$_{1−x}$Mg$_x$O$_{3−x}$ sampleswas observed. The activation energy and pre-exponential factors were determined as (1.0 eV, $4.7\times 10^{−16}$ s) and($0.94−1.0$ eV, $6.8 \times 10^{−14}$−3.1 \times 10^{−13}$s) from internal friction and dielectric relaxation measurement, respectively. The lower oxide ion conductivity in Na$_{0.5}$Bi$_{0.5}$Ti$_{1−x}$Mg$_x$O$_{3−x}$($x = 0.06$, 0.08, 0.10) compounds may arise from the lower vacancy mobility. Judging from the electrical performance and relaxation parameters, although lower-level Mg doping can improve oxide ionic conductor, oxygen vacancy mobility in Na$_{0.5}$Bi$_{0.5}$Ti$_{1−x}$Mg$_x$O$_{3−x}$compounds cannot be improved with increasing Mg-doping content. These results will be meaningful to ameliorate the electrical properties ofNa$_{0.5}$Bi$_{0.5}$Ti$_{1−x}$Mg$_x$O$_{3−x}$compounds and understand the relationship between the electrical properties and structure. • Glass transition and crystallization kinetics of a new chalcogenide-alkali metal Se$_{80}$Te$_8$(NaCl)$_{12}$alloy A new chalcogenide-alkali metal alloy of Se$_{80}$Te$_8$(NaCl)$_{12}$has been prepared by a melt-quench technique. The crystallized phases due to the thermal annealing are observed by X-ray diffraction of the powdered sample. The glass transition and kinetics of crystallization in the Se$_{80}$Te$_8$(NaCl)$_{12}$alloy are studied using the differential scanning calorimetric technique under non-isothermal conditions. The activation energy of the glass transition is evaluated by Kissinger and Mahadevan methods. The crystallization activation energy ($E_{\rm c}$) is calculated by isoconversion Friedman methods. The decrease of$E_{\rm c}$with increasing crystallization conversion is attributed to the complex mechanism of the crystallization process. Based on the shape of the characteristic kinetic function, the crystallization growth is found to be a three-dimensional growth from the bulk nuclei. The results show that the conditions of the Sestak–Berggren model are satisfied for describing the crystallization process of the studied Se$_{\rm 80}$Te$_8$(NaCl)$_{12}$alloy. The parameters$M$and$N$involved in this model are calculated and related to the crystallization process. • Adsorptive removal of strontium(II) using macroporous poly(AGE-$co$-EGDMA) beads modified with resorcin[4]arene Adsorption behaviour of strontium(II) on macroporous poly(allyl glycidyl methacrylate-$co$-ethylene glycoldimethacrylate) [poly(AGE-$co$-EGDMA)] beads modified with resorcin[4]arene was studied using macroporous crosslinked [poly(AGE-$co$-EGDMA)] beads. The macroporous crosslinked [poly(AGE-$co$-EGDMA)] beads were synthesizedby suspension polymerization techniques, followed by functionalization with amino derivatives of resorcin[4]arene. Thepoly(AGE-$co$-EGDMA) beads were characterized by FTIR,${}^1$H and${}^{13}C-NMR, elemental analysis and particle-size analysis. The surface morphology of beads was studied by scanning electron microscopy. The functionalized poly(AGE-$co$-EGDMA) beads were used as adsorbents for strontium removal. The crucial factors including the effect of pH, time, initial concentration of metal ions and adsorbent dose were investigated to optimize the maximum adsorption efficiency of Sr(II). The equilibrium data of strontium(II) ions adsorbed on functionalized poly(AGE-$co$-EGDMA) beads were analysed by pseudo-first- and pseudo-second-order kinetic models. The pseudo-second-order kinetic model indicated that strontium was adsorbed bychemisorption.

• Unique identification of phonon modes using polarized Raman studies of SnO(001) crystals..

Stannous oxide (SnO), an exclusive p-type oxide semiconductor in the oxide family, is a source of renewed interest because of its ability to be an excellent anode material. So far, there are very few reports on the vibrational propertiesof SnO and controversy remains in the assignment of vibrational modes. Textured single crystals of SnO were synthesized by a one-step solvothermal method. The as-synthesized SnO crystals have a wide (001) plane, as confirmed by high resolution transmission electron microscopy images. Raman spectroscopy is used for the identification of phase as well as crystalline orientation. Moreover, a unique assignment of phonon modes in SnO is also performed using polarized Raman spectroscopic studies for different orientations around c-axis of the crystalwith the incident electric field vector. Thus, a novel methodologyof phonon assignment is adopted with a minimum amount of data collection for a diatomic molecule having a tetragonal symmetry with a number of symmetry elements.

• Dip-coating of 8YSZ nanocrystalline particles on NiO–YSZ substrate

In this study, 8 mol% yttria-stabilized zirconia (8YSZ)-agglomerated particles were dispersed in de-ionized water using different weights of Tiron. The results of viscosity and sedimentation measurements of each suspension were evaluated and the optimum amount of Tiron was selected. The most stable suspension was prepared for dip-coating. The substratewas prepared by mixing NiO and YSZ powders and then pressed and pre-sintered at 1050$^{\circ}$C. The effect of saturated and unsaturated substrates on morphology and thickness of films were investigated. The thickness of YSZ films with different withdrawn speeds and dip-times were calculated. Also, the morphologies of deposited films were characterized by scanning electron microscopy. The above experimental results showed that by adjusting pH about 10, the view point of rheological behaviour, the optimum dispersant was 0.8% and the suspension containing 0.8% Tiron had the lowest viscosity. Finally, the obtained layers from dip-coating method represented that the films deposited on saturated substrate were crack-free andhomogeneous when compared to unsaturated substrates.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 3
June 2019