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Oxide thermoelectric materials are considered promising for high-temperature thermoelectric applications in terms of low cost, temperature stability, reversible reaction, and so on. Oxide materials have been intensively studied to suppress the defects and electronic charge carriers for many electronic device applications, but the studies with a high concentration of defects are limited. It desires to improve thermoelectric performance by enhancing its charge transport and lowering its lattice thermal conductivity. For this purpose, here, we modified the stoichiometry of cation and anion vacancies in two different systems to regulate the carrier concentration and explored their thermoelectric properties. Both cation and anion vacancies act as a donor of charge carriers and act as phonon scattering centers, decoupling the electrical conductivity and thermal conductivity.

Using first-principles calculations based on density functional theory (DFT) with generalized gradient approximation (GGA), the electronic and thermoelectric properties of KCaF3 are calculated. The electronic structure calculated with GGA shows that KCaF3 is an insulator. The thermoelectric properties of KCaF3 are computed as a function of chemical potential μ and charge carrier concentrations (1018–1022 cm−3). Both hole and electron doping decrease the absolute value of Seebeck coefficient. The calculated power factor shows that p-type KCaF3 has a larger power factor at the optimized charge carriers. The maximum figure of merit (ZT) occurs around 1021 cm−3 hole carrier concentrations and the largest value of ZT ∼0.7 is achieved at 800 K. When KCaF3 is doped with electron, the maximum ZT occurs around 1020 cm−3 and the largest value of ZT at 800 K is about 0.4. Hence, high ZT in KCaF3 is possible at high hole carrier concentrations as compared with electron carrier concentrations. Compared with n-type KCaF3, p-type KCaF3 has good thermoelectric properties, which are attributed to larger effective mass and low thermal conductivity of holes.

Elemental doping is considered to be an effective strategy to improve the photoelectrochemical (PEC) activity of hematite (α-Fe2O3) as a photoanode for water splitting, but the precise function (s) of the dopant remains unclear. In this study, we report on the structural and charge separation properties of titanium-doped hematite (Ti doped Fe2O3) films prepared by a simple electrospray technique for PEC water oxidation. The effect of Ti doping on the structure, morphology, light absorption, and electrical and photoelectrochemical properties was investigated on α-Fe2O3 films. SEM images revealed a reduction in particle sizes for 2% Ti doped α-Fe2O3, while an increase in particle size was observed for higher Ti content. XRD confirmed the presence of α-Fe2O3 without any impurity or other phases. From XPS spectra, the incorporation of Ti was confirmed in the form of Ti4+ as predominant species while no impurities from the substrate were detected. When the Ti doped Fe2O3 (2% Ti) film was used as a photoanode in a PEC cell, it delivered the best performance with a maximum photocurrent density of 1.09 mA cm−2 (at 1.8 V vs. RHE and under standard 1 sun illumination conditions (AM 1.5 G, 100 mW cm−2)), which is 2 times higher than that of the un-doped α-Fe2O3 (0.51 mA cm−2). The photoelectrode also showed a superior incident photon to current efficiency (IPCE) as compared to an un-doped α-Fe2O3. This enhancement in performance was attributed to the better charge separation and transport properties of α-Fe2O3 due to Ti doping, as revealed by an electrochemical impedance spectroscopy (EIS) analysis.

Controlling oxygen vacancy in undoped SrTiO3 was used to realize the phonon-glass electron-crystal (PGEC) concept. The undoped SrTiO3 samples were synthesized through solid-state-reaction method in air and then reduced through annealing under low oxygen partial pressure conditions. We show that decreasing the oxygen partial pressure (Po2) results in increase of the electrical conductivity, and the oxygen vacancies act as phonon scattering centers, which lead to decrease in the lattice thermal conductivity. Both the enhanced electrical conductivity (σ) and reduced thermal conductivity (κ) were achieved simultaneously through oxygen vacancy in undoped SrTiO3. This significantly increases the ratio of σ/κ that results in an enormously enhanced ZT value of about 13 times larger as compared with the samples reduced under relatively high Po2. Density-functional theory calculations also reveal that oxygen vacancies in SrTiO3 reduce the band-gap, and consequently increase the electrical conductivity.

Made available in DSpace on 2021-06-25T11:08:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-02-01 This research study reports the formation of flexible and multifunctional organic-inorganic hybrid membranes (BC-SiO2-TiO2/Ag) based on bacterial cellulose (BC) that contain photoactive (TiO2) and antibacterial (Ag) components, rendering them photocatalytic, self-cleaning and UV-shielding properties (due to TiO2) as well as antibacterial activity. Coating of BC with sol-gel derived silica and titania particles was achieved through hydrolysis-polycondensation of tetraethyl orthosilicate and titanium (IV) isopropoxide, respectively, and a soft hydrothermal treatment (140 °C, 20 h) was used to obtain well-crystalline TiO2. The prepared BC-SiO2-TiO2/Ag photoactive membranes were characterized by an array of analytical techniques including XRD, XRF, SEM-EDS, electronic absorption spectroscopy and vibrational spectroscopy. The morphology of TiO2 coatings changes from a homogenous film-like smooth one to a rougher one consisting of randomly oriented titania particles (170 ± 35 nm) upon increasing the TiO2 loading of the membranes. These prepared photoactive BC-SiO2-TiO2 membranes exhibited excellent TiO2-loading dependent photocatalytic/self-cleaning activity towards crystal violet dye deposited as an over-layer on the surface of the membranes, degrading 97 % of the dye within 50 min of UV illumination. In addition to good photoactivity, the BC-SiO2-TiO2/Ag membranes demonstrated reasonable antibacterial activity against five different bacterial strains under dark conditions. These flexible BC-based hybrid membranes with photocatalytic, self-cleaning, antibacterial properties have the potential to be used in the design of self-cleaning and antibacterial surfaces, filters and facemasks that could be easily disinfected under UV irradiation from a lamp or natural sunlight and safely discarded and even recycled. Institute of Chemical Sciences University of Peshawar Institute of Chemistry São Paulo State University - UNESP, CP 355 Government Girls Degree College Institute of Research and Development Duy Tan University Institute of Physics Federal University of Mato Grosso do Sul Institute of Chemistry São Paulo State University - UNESP, CP 355

Hematite (Fe2O3) is one of the best candidates for photoelectrochemical water splitting due to its abundance and suitable bandgap. However, its efficiency is mostly impeded due to the intrinsically low conductivity and poor light absorption. In this study, we targeted this intrinsic behavior to investigate the thermodynamic stability, photoconductivity and optical properties of rhodium doped hematite using density functional theory. The calculated formation energy of pristine and rhodium doped hematite was − 4.47 eV and − 5.34 eV respectively, suggesting that the doped material is thermodynamically more stable. The DFT results established that the bandgap of doped hematite narrowed down to the lower edge (1.61 eV) in the visible region which enhanced the optical absorption and photoconductivity of the material. Moreover, doped hematite has the ability to absorb a broad spectrum (250–800) nm. The enhanced optical absorption boosted the photocurrent and incident photon to current efficiency. The calculated results also showed that the incorporation of rhodium in hematite induced a redshift in optical properties.

The development of biocompatible, cost effective and more efficient materials to control or inhibit the growth of microorganisms in necessary to fight against resistant microbes. Here, we demonstrate the synthesis of nickel oxide-incorporated polyaniline/polyvinyl alcohol (PANI/PVA/NiOx) composite material by single-step polymerization and its application as antibacterial agent. The composite films were characterized using UV-visible spectroscopy (UV-Vis), Thermogravimetric analysis (TGA), Fourier Transform Infrared spectroscopy (FTIR), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). UV-Vis spectra revealed the enhancement in absorption properties of PANI/PVA/NiOx with optimum 5% incorporation of NiOx. TGA results indicated slightly enhanced thermal stability of the PANI/PVA/NiOx composite film as compared to PANI/PVA. FTIR spectra for composites revealed the existence of NiOx in polymers. However the crystallinity of PANI/PVA was not much affected. The antibacterial activity of the prepared composites was examined against four different gram negative bacteria, Salmonella, Shigella, Pseudomonas and Escherichia coli (E. coli). The composite exhibited excellent antibacterial activity against E. coli, Salmonella and Shigella while pseudomonas showed some resistance. Based on the results, PANI/PVA/ NiOx (5%) composite showed the highest activity against the tested bacterial strains, thus showing its potential to be used as an effective antibacterial agent.

\textit{Ab-initio} calculations based on density functional theory with local spin density approximation are used to study defects-driven magnetism in bulk $\alpha$-Li$ _{3}$N. Our calculations show that bulk Li$ _{3} $N is a non-magnetic semiconductor. Two types of Li vacancies (Li-I and Li-II) are considered, and Li-vacancies (either Li-I or Li-II type) can induce magnetism in Li$ _{3}$N with a total magnetic moment of 1.0 $\mu_{\rm B}$ which arises mainly due to partially occupied N-$p$-orbitals around the Li vacancies. The defect formation energies dictate that Li-II vacancy, which is in the Li$ _{2}$N plane, is thermodynamically more stable as compared with Li-I vacancy. The electronic structures of Li-vacancies show half-metallic behavior. On the other hand N-vacancy does not induce magnetism and has a larger formation energy than Li-vacancies. N vacancy derived bands at the Fermi energy are mainly contributed by the Li atoms. Carbon is also doped at Li-I and Li-II sites, and it is expected that doping C at Li-I site is thermodynamically more stable as compared with Li-II site. Carbon can induce metallicity with zero magnetic moment when doped at Li-I site, whereas magnetism is observed when Li-II site is occupied by the C impurity atom and C-driven magnetism is spread over the N atoms as well. Carbon can also induce half-metallic magnetism when doped at N site in Li$ _{3}$N, and has a smaller defect formation energy as compared with Li-II site doping. The ferromagnetic (FM) and antiferromagnetic (AFM) coupling between the C atoms is also investigated, and we conclude that FM state is more stable than the AFM state., Comment: Accepted; J. Mag. Mag. Mat. (2018)

The production of hydrogen, the future fuel, on stable, efficient, and robust electrocatalysts represents an attractive approach for the conversion and storage of carbon-free energy resources. In this study, earth-abundant nickel sulfide (NiS) electrocatalyst were grown on fluorine-doped tin oxide (FTO) substrate by a simple and cost-effective chemical bath deposition for hydrogen evolution reaction (HER). Energy dispersive X-ray analysis and X-ray photoelectron spectra indicated the presence of highly pure NiS. The HER performance of the catalyst was examined in alkaline solution (1.0 M NaOH; pH = 13.5). Notably, NiS film prepared at 100 °C demonstrated superior HER activity with an overpotential of 290 mV to afford a current density of 10 mA/cm2 and a Tafel slope of 143.4 mV/dec which are among the promising results obtained for sulfide-based HER electrocatalysts. The catalyst exhibited 100% faradaic efficiency and electrochemical stability which indicate its potential as noble-metal-free HER electrocatalyst.

This study reports the one-step in situ synthesis of a hematite–tungsten oxide (α-Fe2O3–WO3) composite on fluorine-doped tin oxide substrate via a simple hydrothermal method. Scanning electron microscopy images indicated that the addition of tungsten (W) precursor into the reaction mixture altered the surface morphology from nanorods to nanospindles. Energy-dispersive x-ray spectroscopy analysis confirmed the presence of W content in the composite. From the ultraviolet–visible spectrum of α-Fe2O3–WO3, it was observed that absorption began at ∼ 600 nm which corresponded to the bandgap energy of ∼ 2.01 eV. The α-Fe2O3–WO3 electrode demonstrated superior performance, with water oxidation photocurrent density of 0.80 mA/cm2 (at 1.6 V vs. reversible hydrogen electrode under standard illumination conditions; AM 1.5G, 100 mW/cm2) which is 2.4 times higher than α-Fe2O3 (0.34 mA/cm2). This enhanced water oxidation performance can be attributed to the better charge separation properties in addition to the large interfacial area of small-sized particles present in the α-Fe2O3–WO3 nanocomposite film.

Polythiophene (PTh) and graphene nanoplatelets (GNPs) nanocomposites with different ratio of GNPs (10–50 wt.%) were prepared by oxidative chemical polymerization technique and applied for the photocatalytic degradation of bromo phenol blue (BPB) and pathogen control. The as-prepared nanomaterials were characterized by scanning electron microscopy (SEM), energy dispersive X-Ray analysis (EDX), UV–Vis spectroscopy, X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The PTh-GNPs(50) achieved the highest photocatalytic degradation efficiency for BPB (94.1%) which was more than three times higher than that of the pristine PTh (31.3%). The enhanced photocatalytic activity of PTh-GNPs was attributed to the improved charge-transport and longer recombination time of e−/h+ pairs from PTh NPs to GNPs. Interestingly, PTh-GNPs(50) proved as a potent inhibitor against E.coli and S.aureus reported 18 mm zone of inhibition as compared to that of the control PTh (showing 9 mm and 5 mm zones of inhibition for the two strains, respectively) at 2000 µg/mL. These results make PTh-GNPs(50) nanocomposites a potential candidate for BPB removal and bacterial growth inhibition.

Thermoelectric properties of cubic (C) and tetragonal (T) BaTiO 3 (BTO) and PbTiO 3 (PTO) are investigated using density functional theory together with semiclassical Boltzmann's transport theory. Both electron and hole doped BTO and PTO are considered in 300–500 K temperature range. We observed that C-BTO has larger power factor( PF ) when doped with holes, whereas n-type carrier concentration in C-PTO has larger PF . Comparing both BTO and PTO, C-PTO has larger figure of merit ZT . Tetragonal distortion reduces the Seebeck coefficient S in n-doped PTO, and the electronic structures revealed that such reduction in S is mainly caused by the increase in the optical band gaps ( Γ − Γ and Γ-X).

Ion diffusion rate and contact surface area of conducting polymers increased by composite formation with nanometric-size materials make them promising materials in the fabrication of energy storage devices. In this work, electronically conducting polyaniline and manganese oxide (PANI/MnO2) nanofibrous composites were electrochemically co-deposited on stainless steel from binder-free electrolyte solution. Structural characterization and morphological characterization of the materials were performed with Fourier-transformed infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). SEM images show fibrous micro/nano-architecture of the composites with cluster networking structure having 200–500 nm length and 100–200 nm diameter. Electrochemical and energy storage properties of the as-synthesized materials were investigated with cyclic voltammetry (CV), galvanostatic charge discharge curves(GCDC), and potentiostatic electrochemical impedance spectroscopy (PEIS) without any binders. Electrochemical measurements as well as galvanostatic charge discharge curves at 1 mA constant current have shown maximum specific capacitance of 149 F/g for the composite prepared with 0.15 M MnSO4 in the co-deposition bath. The composites retain 67% specific capacitance even after 400 cycles, indicating the stability of synthesized composite. PEIS confirms the pseudocapacitive nature of the synthesized composites.

First-principles based on density functional theory is used to study the phase stability, elastic, magnetic, and electronic properties of cubic (c)-Fe$_4$C. Our results show that c-Fe$_{4}$C has a ferromagnetic (FM) ground state structure compared with antiferromagnetic (AFM) and nonmagnetic (NM)states. To study the phase stability of c-Fe$_4$C, BCC Fe$_4$C, FCC Fe$_4$C, and BCC Fe$_{16}$C, where C is considered at tetrahedral and octahedral interstitial sites, are also considered. Although, the formation energy of c-Fe$_4$C is smaller than BCC Fe$_4$C, but the shear moduli of c-Fe$_4$C is negative in the FM and AFM states indicating that c-Fe$_4$C is dynamically not stable in the magnetic (FM/AFM) states. However, NM state has positive shear moduli which illustrates that instability in c-Fe$_4$C is due to magnetism and can lead to soft phonon modes. The calculated formation energy also shows that c-Fe$_4$C has higher formation energy compared with the FCC Fe$_4$C indicating no possibility of c-Fe$_4$C in low carbon steels at low temperature. The magnetic moment of Fe in c-Fe$_4$C is also sensitive to lattice deformation. The electronic structure reveals the itinerant nature of electrons responsible for metallic behavior of c-Fe$_4$C., Comment: Submitted

In the search of high-performance cathodes for next-generation Li-ion batteries (LIBs), iron fluorides are among the most promising materials because of their extremely high theoretical capacity. This study reports on the synthesis, structural and electrochemical characterizations of cobalt doped iron fluoride hydrate as a high-performance cathode material for LIBs. A simple non-aqueous precipitation method is used to synthesize cobalt doped iron fluoride (Fe 0.9 Co 0.1 F 3 ·0.5H 2 O) while its structural and electrochemical properties are also evaluated. The thermogravimetric analysis reveals that the structure of the as-prepared material remains stable up to 243 °C. The structure was then found to collapse beyond this temperature due to the removal of water contents from the crystal structure. The material delivers a high discharge capacity of 227 mAh g −1 at 0.1C in the potential range of 1.8-4.5 V versus Li/Li + . The electrode retains a high reversible capacity of 150 mAh g −1 at a rate of 0.1C after 200 cycles, indicating high reversibility and stability of the material. The electrode also shows a superior rate capability of up to 10C, showing its potential use as a cathode material for LIBs.

The structural, electronic, elastic and optical properties of CsYx I(1 − x)(Y = F, Cl, Br) are investigated using full potential linearized augmented plane wave (FP-LAPW) method within the generalized gradient approximation (GGA). The ground state properties such as lattice constant (ao) and bulk modulus (K) have been calculated. The mechanical properties including Poisson’s ratio (σ), Young’s modulus (E), anisotropy factor (A) and shear modulus (G) were also calculated. The results of these calculations are comparable with the reported experimental and theoretical values. The ductility of CsYx I(1 − x) was analyzed using Pugh’s rule (B/G ratio) and Cauchy’s pressure (C12−C44). Our results revealed that CsF is the most ductile among the CsYxI(1 − x)(Y = F, Cl, Br) compounds. The incremental addition of lighter halogens (Yx) slightly weakens the strength of ionic bond in CsYxI(1 − x). Moreover, the optical transitions were found to be direct for binary and ternary CsYxI(1 − x). We hope that this study will be helpful in designing binary and ternary Cs halides for optoelectronic applications.

Structural and electronic properties of pristine two-dimensional group IV Xenes (X=C, Si, Ge, Sn, Pb) and hydrogenated Xenes are studied, using density functional theory (DFT) calculations with and without spin-orbit coupling (SOC). The pristine hexagonal monolayer Xenes show buckled structure upon relaxation except graphene. The buckling $\delta$ increases linearly from graphene to plumbene. The bond angle $\theta$ between the X atoms is correlated with the degree of hybridization.% $D The band structures without SOC of group-IV Xenes are semi-metallic. However, inclusion of SOC mainly opens the bandgap at the Dirac point. The degree of hybridization and bandgap opening due to SOC are mainly explained in terms of the contribution of $p_{\mathrm{x}}/p_{\mathrm{y}}$ and $p_{z}$ electronic states at Fermi level. Semi hydrogenation (SH) leads to enhanced buckling in all Xenes which indicate a tendency towards more $sp^3$ like structures. The electronic structures of SH Xenes do not show Dirac cones. Incorporating SOC in the non-spin polarized band structure calculations results into splitting of the states. On the other hand, spin polarized band structures show magnetism with magnetic moment of 1.0~$\mu_{\rm{B}}$ and all SH Xenes are magnetic semiconductor except SH plumbene. Full hydrogenation vanishes buckling upon relaxation and the structure becomes planar implying $sp^2$-like hybridization. The band structures for FH Xenes turns out to be semiconducting and the Dirac cones also disappear. The bandgap changes from indirect to direct at FH stanene, while FH plumbene turns out to be semi-metallic. No spin polarized states are observed. The effect of SOC does not instigate any noteworthy changes in the bandgap for FH graphene to FH stanene. On the other hand, the SOC gives rise to bandgap of 0.47 eV in FH plumbene, which is otherwise a semi-metal.

In this work nickel modified polymer composites have been synthesized electrochemically for methanol electrooxidation on platinum and graphite electrodes. Ni (II) ions were incorporated on polyaniline and poly (o-aminophenol)(PANI/POAP) bilayer structure from 0.1 M Nickel sulphate hexahydrate solution at open circuit potential (OCP).TheNi (II) deposited composites were characterized with Fourier Transform Infrared (FTIR) spectroscopy, Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). Cyclic voltammetry characterization exhibits stable redox pair of Ni+3/Ni+2 for both electrodes. Fourier transform infrared spectroscopy was used for functional group analysis. Ni (II) peaks were observed in the region of 400–700 cm−1 along with peaks at 1102 cm−1 and 1400–1600 cm−1 for polyaniline and phenoxazine units. The Ni-polymer composite on platinum and graphite electrode followed different phenomenon for methanol electroxidation in alkaline media. The cyclic voltammetry results showed significantly large methanol oxidation on platinum substrate with charge storage capacity of 196 μ F/cm2 for 1.5 M methanol in alkaline media as compared to 8.306 μF/cm2 of graphite. The diffusion controlled linear response for increase rate of methanol concentration has been obtained for Ni (II)/PANI/POAP-Pt. The electrochemical impedance spectroscopy (EIS)results indicated increase in charge storage capacity from 10−4F/cm2 to 10−3 F/cm2 with increasing potentials at lower frequency region.The phase shift was observed from 60–40 degrees for increased potentials at low frequency range in EIS analysis. The increased conductive behavior from 10−5 to 10−2 s/cm2 has been obtained fornickel modified polymer composite at higher frequency region in EIS analysis.

The electrocatalytic behavior of glassy carbon (GC) electrode modified with ruthenium nanoparticles and ruthenium film was studied for electrochemical reduction of nicotinamide adenine dinucleotide (NAD+). The surface of GC electrode was modified via cathodic deposition of nanosized ruthenium at different potentials. Scanning electron microscopy (SEM) images showed two kinds of surface morphologies based on deposition potential: Ru nanoparticles-decorated GC at −0.3 V and Ru film-coated GC at −0.5 V versus Ag/AgCl. The electrochemical behavior of Ru nanoparticles and Ru film-modified GC electrodes in phosphate buffer solution containing NAD+ was investigated using voltammetric techniques. A prominent cathodic peak was observed on bare GC and Ru nanoparticles-modified GC at −1.2 V versus Ag/AgCl which was related to NAD+ reduction. The electrochemical response of Ru film electrode was reversible, exhibiting a reduction peak at ca. −1.0 V and an oxidation peak at ca. −0.55 V which was attributed mainly to the hydrogen evolution reaction. Electrochemical impedance analysis indicated lower charge transfer resistance of Ru film electrode for hydrogen evolution as compared to GC and Ru nanoparticle electrodes. Ru film-modified electrode was found less reactive than the nanoparticles-modified GC electrode for NAD+ reduction reaction due to hydrogen evolution reaction that proceeds exclusively on Ru film.

In this study, we report on the direct growth of duel-faceted BiVO4 microcrystals on fluorine-doped tin oxide (FTO) coated glass by simple chemical bath deposition as photoanode material for PEC water oxidation. Crystal growth and particle density were affected by bath temperature; films grown in higher bath temperature (95 °C) showed great surface coverage and larger particle sizes, as indicated by scanning electron microscopy (SEM) images. X-ray diffraction (XRD) studies revealed that BiVO4 predominantly occurs in the form of monoclinic scheelite crystal structure in all deposited films. UV–vis spectroscopy and X-ray photoelectron spectroscopy (XPS) investigations confirmed the existence of pure BiVO4. High-temperature treatment of the film was found to improve crystallinity and preferential growth of dual-faceted ((010), (110)) BiVO4 microcrystals. An optimized electrode exhibited excellent PEC water oxidation performance, with 0.78 mA.cm−2 of photocurrent density at 1.23 V versus a reversible hydrogen electrode (RHE) under standard illumination (100 mW.cm−2 and AM 1.5), which was increased up to 1.23 mA.cm−2 before dark current started to flow. The electrode also showed good stability when exposed to longer illumination in a 0.5 M Na2SO4 solution, and n-type character. These findings are thus important for the development of a simple method for synthesis of BiVO4 microcrystals as efficient electrode material for PEC water splitting.

Metal oxide-metal sulfide-based composites of desired properties are of great technological importance because of their applications ranging from photovoltaics to energy storage devices. Herein, we report on the structural and charge storage capabilities of nickel-doped zinc sulfide-decorated zinc oxide (Ni–ZnS/ZnO) composite prepared by wet chemical route. The synthesis of ZnO, Ni–ZnS, and Ni–ZnS/ZnO was performed at 80 °C in a single vessel which was followed by annealing at 300 °C for 1 h. Scanning electron microscopy (SEM) images indicated flower-like morphology of the ZnO decorated with Ni-doped ZnS (Ni–ZnS). The material exhibited characteristic X-ray diffraction (XRD) signals corresponding to ZnO and Ni–ZnS which confirmed the formation of a composite structure. Energy-dispersive X-ray analysis, UV–visible spectroscopy, and Fourier Transform Infrared (FTIR) spectroscopy measurements revealed the successful formation of Ni–ZnS/ZnO composites. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were carried out to examine the energy storage capabilities of the synthesized Ni–ZnS/ZnO composite. The composite electrode demonstrated a specific capacitance of 354 F g−1 in 1 M KOH electrolyte which was higher than that of the Ni–ZnS (154.7 F g−1) and ZnO (132 F g−1). The enhanced capacitive performance of the composite is attributed to the low charge transfer resistance and high electrochemically active specific surface area (27.54 m2 g−1), as revealed by EIS results.

Carbon nanotubes (CNTs) are known as nano-architectured allotropes of carbon, having graphene sheets that are wrapped forming a cylindrical shape. Rolling of graphene sheets in different ways makes CNTs either metals or narrow-band semiconductors. Over the years, researchers have devoted much attention to understanding the intriguing properties CNTs. They exhibit some unusual properties like a high degree of stiffness, a large length-to-diameter ratio, and exceptional resilience, and for this reason, they are used in a variety of applications. These properties can be manipulated by controlling the diameter, chirality, wall nature, and length of CNTs which are in turn, synthesis procedure-dependent. In this review article, various synthesis methods for the production of CNTs are thoroughly elaborated. Several characterization methods are also described in the paper. The applications of CNTs in various technologically important fields are discussed in detail. Finally, future prospects of CNTs are outlined in view of their commercial applications.

Using first-principles calculations based on density-functional theory we systematically investigate the effect of applied strain on the stability and on the electronic and magnetic properties of monolayer phosphorene with single-atom vacancy. We consider two types of single vacancies: the symmetric SV- 55 | 66 , which has a metallic and non-magnetic ground state, and the asymmetric SV- 5 | 9 , which is energetically more favorable and exhibits a semiconducting and magnetic character. Our results show that compressive strain up to 10%, both biaxial and uniaxial along the zigzag direction, reduces the formation energy of both single-atom vacancies with respect to the pristine configuration and can stabilize these defects in phosphorene. We found that the magnetic moment of the SV- 5 | 9 system is robust under uniaxial strain in the range of −10 to +10%, and it is only destroyed under biaxial compressive strain larger than 8%, when the system also suffers a semiconductor-to-metal transition. Additionally, we found that magnetism can be induced in the SV- 55 | 66 system under uniaxial compressive strain larger than 4% along the zigzag direction and under biaxial tensile strain larger than 6%. Our findings of small formation energies and non-zero magnetic moments for both SV- 5 | 9 and SV- 55 | 66 systems under zigzag uniaxial compressive strain larger than 4% strongly suggest that a magnetic configuration in monolayer phosphorene can be easily realized by single-vacancy formation under uniaxial compressive strain.

We report on the passivation of surface defects of ZnO nanorods by surface layer deposition. ZnO nanorods and ZnS-ZnO hybrid nanostructures are grown on FTO coated glass substrate by chemical bath deposition method. XRD spectrum of ZnO nanorods shows the preferential growth along the c-axis. SEM analysis confirms the nearly aligned growth of the ZnO nanorods with a hexagonal shape. XPS measurements were performed to confirm the deposition of the surface layer and surface stoichiometry. Room temperature photoluminescence of ZnO nanorods showed two emission bands, viz. the band edge emission and the blue-green emission, with the latter being associated with the defect states arising from the surface of ZnO nanorods. The band edge emission is significantly increased as compared to blue-green emission after ZnS surface layer deposition on ZnO nanorods. The quenching of blue-green emission is explained in terms of reduced surface defects after ZnS deposition. Density functional theory (DFT) calculations are used to understand the mechanisms of defect passivation in ZnS-ZnO nanostructures and we show that the S atoms prefer the O site as compared with the Zn and interstitial sites, Manuscript has been accepted for publication in Physica E: Low dimensional systems and Nanostructures

The structural, electronic, and magnetic properties of two-dimensional (2D) GaS are investigated using density functional theory (DFT). After confirming that the pristine 2D GaS is a non-magnetic, indirect band gap semiconductor, we consider N and F as substitutional dopants or adsorbed atoms. Except for N substituting for Ga (NGa), all considered cases are found to possess a magnetic moment. Fluorine, both in its atomic and molecular form, undergoes a highly exothermic reaction with GaS. Its site preference (FS or FGa) as substitutional dopant depends on Ga-rich or S-rich conditions. Both for FGa and F adsorption at the Ga site, a strong F-Ga bond is formed, resulting in broken bonds within the GaS monolayer. As a result, FGa induces p-type conductivity in GaS, whereas FS induces a dispersive, partly occupied impurity band about 0.5 e below the conduction band edge of GaS. Substitutional doping with N at both the S and the Ga site is exothermic when using N atoms, whereas only the more favourable site under the prevailing conditions can be accessed by the less reactive N2 molecules. While NGa induces a deep level occupied by one electron at 0.5 eV above the valence band, non-magnetic NS impurities in sufficiently high concentrations modify the band structure such that a direct transition between N-induced states becomes possible. This effect can be exploited to render monolayer GaS a direct-band gap semiconductor for optoelectronic applications. Moreover, functionalization by N or F adsorption on GaS leads to in-gap states with characteristic transition energies that can be used to tune light absorption and emission. These results suggest that GaS is a good candidate for design and construction of 2D optoelectronic and spintronics devices. © 2018 IOP Publishing Ltd.

Using periodic Density Functional Theory (DFT) calculations and DFT-based molecular dynamics simulations, we studied the adhesion mechanism of glycine amino acid and the catechol part of L-dopa on the cristobalite surface. The optimized glycine and catechol molecules are initially placed vertically 3 A above the cristobalite surface with a vacuum thickness of approximately 40 A. The catechol adhesion on the cristobalite surface previously studied showed strong binding energy both in dry and wet adsorption. Glycine is the second most abundant amino acid in the mussel adhesive protein, which would have a significant contribution in mussel adhesion. This study of glycine will further enlighten the understanding of marine mussel adhesion. We believe that all the proteins exist in the Mytilus edulis foot protein (mefp) are contributing in this unique and versatile adhesion of marine mussel. We observed that glycine molecules formed four hydrogen bonds with the surface silanols and acted as donors and acceptors. Four hydrogen bond formation is also observed during catechol adhesion on the cristobalite surface. The average binding energy of both molecules on the cristobalite surface lies in the range of hydrogen binding energy. Surface binding energy values of 20.23 and 14.45 kcal mol−1 were obtained for glycine and catechol adsorption, respectively. Including the dispersion energy term further raised the binding energy to 31.29 kcal mol−1 for glycine and 28.58 kcal mol−1 for catechol. The binding energy values suggest that glycine adsorption on the dry cristobalite surface is much stronger as compared to that of catechol.

Polyaniline/Poly(o-aminophenol) (PANI/POAP) bilayered films were deposited by electro polymerization on platinum (Pt) and graphite (Gra) electrodes for methanol oxidation in direct methanol fuel cells. The chemical composition of bilayered structure was characterized by Fourier transform infrared (FTIR) spectroscopy. Results demonstrated the presence of FTIR peaks associated to PANI and POAP constituents confirming the bonding of PANI and POAP in the bilayered composite structure. The electrochemical properties of PANI/POAP electrodes were examined in pure and sulfuric acid mixed methanol solutions using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). PANI/POAP-Gra electrode showed less reactivity towards methanol oxidation, as well as poor stability upon repeated cycling. On the other hand, PANI/POAP-Pt electrode exhibited superior performance with high methanol oxidation current (Ia), capacitance (C), and specific capacitance (Cs). In addition, PANI-POAP-Pt electrode was found better than PANI-POAP-Gra electrode in terms of operation stability based on continuous cycling in methanol up to 100 cycles. The dielectric properties and AC conductivity (σac) of the PANI/POAP-Pt electrode with respect to the applied potential have been discussed.

Using first-principles calculations, the electronic and magnetic properties of orthorhombic BaFeO (BFO) are investigated with the local spin density approximation (LSDA). The calculations reveal that at the optimized lattice volume, BFO has a lower energy in the ferromagnetic state as compared with the antiferromagnetic state. At the equilibrium volume, BFO shows metallic behavior, however, under a large tensile strain (), BFO shows half-metallic behavior consistent with the integer magnetic moment of fu mainly caused by the and electrons of Fe. Including a Hubbard-like contribution U (LSDA) on Fe d states induced half-metallic behavior without external strain, which indicates that U can be used to tune the electronic structure of BFO. The magnetic moments remained robust against compressive and tensile strain. At large compressive (tensile) strain, the half-metallicity of BFO is mainly destroyed by the Fe-d (O-p) electrons, in agreement with the noninteger value of the magnetic moments of BFO.

In this report we present a systematic structural and magnetic analysis of Co-doped ZnO nanoparticles prepared via a microwave-assisted hydrothermal route. The structural data confirm the incorporation of Co ions into the wurtzite ZnO lattice and a Co concentration mainly near/at the surface of the nanoparticles. This Co spatial distribution is set to passivate the surface of the ZnO nanoparticles, inhibiting the nanoparticle growth and suppressing the observation of a ferromagnetic phase. Based on experimental and theoretical results we propose a kinetic-thermodynamic model for the processes of nucleation and growth of the Co-doped ZnO nanoparticles, and attribute the observed ferromagnetic order to a ferromagnetism associated with specific defects and adsorbed elements at the surface of the nanoparticle. Our findings give valuable contribution to the understanding of both the doping process at the nanoscale and the nature of the magnetic properties of the Co-doped ZnO system.

In this study, a simple and cost-effective chemical bath deposition was employed to deposit nan-sized hematite (α-Fe2O3) directly on fluorine-doped tin oxide (FTO) substrates. The structure, morphology, and optical properties of α-Fe2O3 were manipulated by adjusting the experimental parameters, particularly the deposition temperature and precursor concentration. With increase in Fe precursor concentration from 0.1 M to 0.3 M, the surface morphology was changed from granular-shape condensed particles to vertically aligned rod-like structures. XRD spectra indicated signals from FTO substrate and pure α-Fe2O3 phase which corresponds to the rhombohedral system. The XPS analysis revealed the presence of α-Fe2O3 in the film and no tin (Sn) impurities from the FTO substrate. By changing the deposition temperature from 60 ℃ to 90 ℃, the size of particles increased; whereas, the surface morphology was not altered. The resultant films were examined as photoanode for photoelectrochemical (PEC) water splitting. The optimized electrode exhibited maximum water splitting photocurrent density of 700 μA.cm−2 at 1.6 V versus reversible hydrogen electrode (RHE) under simulated solar illumination (AM 1.5, 100 mW.cm−2) in 1 M NaOH. This could be attributed to the large electrode electrolyte interfacial area and low charge transfer resistance offered by nanorods of α-Fe2O3 of high surface-to-volume ratio.

Half-metallic behavior and ferromagnetism are predicted in strained MoS2 with different light elements adsorbed using density functional theory. We find that strain increases the density of states at the Fermi energy for Y doping (Y = H, Li, and F) at the S sites and strain-driven magnetism develops in agreement with the Stoner mean field model. Strain-driven magnetism requires less strain (∼3%) for H doping as compared with F and Li doping. No saturation of the spin-magnetic moment is observed in Li-doped MoS2 due to less charge transfer from the Mo d electrons and the added atoms do not significantly increase the Spin–orbit coupling. Half-metallic ferromagnetism is predicted in H and F-doped MoS2. Fixed magnetic moments calculations are also performed, and the DFT computed data is fitted with the Landau mean field theory to investigate the emergence of spontaneous magnetism in Y-doped MoS2. We predict spontaneous magnetism in systems with large (small) mag netic moments for H/F (Li) atoms. The large (small) magnetic moments are atttributed to the electronegativity difference between S and Y atoms. These results suggest that H and F adsorbed monolayer MoS2 is a good candidate for spin-based electronic devices., V.M.G.-S. thanks the Spanish Ministerio de Economía, Industria y Competitividad for funding through the project FIS2015-63918-R.

We report the synthesis and thermoelectric properties of a new p-type oxide thermoelectric material (Li1−xNbO2, with x = 0–0.6), in which Li-vacancies play a significant role in the enhancement of the thermoelectric performance. The electrical conductivity drastically increases due to Li-vacancies, resulting in an increase in the hole carrier concentration. A remarkable enhancement in the power factor is observed, which is comparable to well-known oxide thermoelectrics. The carrier concentration was not significantly dependent on the temperature, while the Hall mobility shows negative temperature-dependence. The Seebeck coefficient is linearly proportional to temperature, and the density of the state effective mass Image ID:c7ra10557f-t1.gif was estimated by using the Pisarenko relation. The thermal conductivity was substantially reduced by Li-vacancies and Li-vacancy induced localized double phonon scattering. Density functional theory (DFT) calculations reveal that the enhancement of the thermoelectric properties is mainly due to the increase in the electronic density of states (DOS) at the Fermi energy, which increases with hole concentration. All of the samples after high-temperature measurements are highly stable, which suggests that the well-synthesized nonstoichiometric Li1−xNbO2 could be a new promising candidate material for high temperature thermoelectric applications., This work was partially supported by the Industrial Technology Innovation Program (Industrial Materials Core Technology Development Program) funded by the Ministry of Trade, Industry and Energy, Republic of Korea (10052977). The coauthor, V. M. Garcia-Suarez, thanks the Spanish Ministerio de Economía y Competitividad for funding (FIS2015-63918-R) and Banco Santander for a Mobility Excelence Grant.

The electronic and magnetic structures of cubic BaFeO3 (BFO) in the ferromagnetic (FM) and antiferromagnetic (AFM) states are studied using density functional theory (DFT) with the local spin density approximation (LSDA) and the generalized gradient approximation (GGA), with and without a Coulomb U term. Our LSDA/GGA and LSDA+U/GGA+U results show that cubic BFO has a FM ground state, in agreement with recent experimental studies. Two types of distortions, denoted as D1 and D2, are considered. The source of the distortion in the D1 (D2) case is the displacement of the oxygen (iron) atoms from their equilibrium positions. FM to ferrimagnetic (FIM) and FM to AFM magnetic phase transitions are found in the D1 and D2 distortions, respectively. Larger strains are required for the FM–AFM transition as compared to the FM–FIM. DFT+U calculations also show that the magnetic moments dramatically decrease at large strains due to strong overlapping between the iron and oxygen atoms. The origin of these transitions is discussed in terms of a competition between double exchange and superexchange interactions. From these results it is possible to conclude that oxygen and iron displacements are responsible for the magnetic phase transitions and the reduction of the magnetic moments in BFO., R.F. acknowledges financial support through a Severo-Ochoa grant (Consejería de Educación, Principado de Asturias). V.M.G.S. thanks the Spanish Ministerio de Economía y Competitividad for a Ramón y Cajal fellowship (RYC-2010-06053).

Using density functional theory calculations, the ground state structure of BaFeO$_3$ (BFO) is investigated with local spin density approximation (LSDA). Cubic, tetragonal, orthorhombic, and rhombohedral types BFO are considered to calculate the formation enthalpy. The formation enthalpies reveal that cubic is the most stable structure of BFO. Small energy difference between the cubic and tetragonal suggests a possible tetragonal BFO. Ferromagnetic(FM) and anitiferromagnetic (AFM) coupling between the Fe atoms show that all the striochmetric BFO are FM. The energy difference between FM and AFM shows room temperature ferromagnetism in cubic BFO in agreement with the experimental work. The LSDA calculated electronic structures are metallic in all studied crystallographic phases of BFO. Calculations including the Hubbard potential $U,i.e.$ LSDA+$U$, show that all phases of BFO are half-metallic consistent with the integer magnetic moments. The presence of half-metallicity is discussed in terms of electronic band structures of BFO., Comment: Submitted