Decrease In Gap Energy Research Articles

The interface structural, electronic and optical properties of ZnO nanowires/Graphene nanohybrid (ZnO NWs/G): Experimental and theoretical DFT investigations

In this work, a ZnO nanowires/graphene nanohybrid was synthesized by a three steps approach. Copper substrates were covered with graphene by chemical vapor deposition, further ZnO nanowires were electrochemically deposited on the as grown graphene on copper and finally a transfer process was employed for moving the heterostructure onto a different substrate. A comprehensive structural analysis which included scanning electron microscopy, X-ray diffraction and Raman measurements revealed that the ZnO nanowires crystallize in wurtzite structure perpendicular to graphene, the process leading to the formation of a nanohybrid heterostructure. The band gap energy of the ZnO nanowires deposited on graphene was estimated to be 3.11 eV, as calculated from the reflectance spectrum analysis. The GGA-PBE+U within Grimme (DFT-D) approach was used to provide an accurate description of the interface structure in terms of electronic and optical properties, confirming that the decrease in the band gap energy of ZnO nanowires is caused by the interaction with the graphene surface. The findings of this study could serve as an experimental and theoretical reference for upcoming studies on ZnO NWs/Graphene nanohybrid-based optoelectronic applications.

Synthesis of ZnO co-doped with Er and Co: Effect of the dopants on the structural, optical properties and yellow eosin photocatalytic response

In the present work, the sol-gel method was used to synthesize the Zn1-x-yErxCoyO system with different cations concentrations. The effect of dopant cations on the morphological, structural, and optical properties of particles, as well as their photocatalytic degradation of Yellow Eosin (YE) dye under UV irradiation, was investigated. X-ray diffraction (XRD) indicated excellent crystallinity of Wurtzite-like ZnO structures. Fourier Transform Infrared Spectroscopy showed characteristic absorption bands of ZnO. In addition, the dopant with different ions caused a decrease in the band gap energy compared to pure ZnO (3.16 eV), which is likely due to the defect levels formation. At higher Er3+ concentrations, the materials showed a slight reduction in the band gap (3.10 eV). However, for the samples with the highest Co2+ concentration, a lower band gap (3.0 eV) was observed, indicating that higher Co2+ concentrations favor the ZnO lattice distortion. In photocatalytic tests, the degradation rate of YE (∼48.7 %) was achieved using the ZEC23 sample (2 % of Er3+ and 3 % of Co2+), which is associated with the greater surface area found for this material. In a scavenger study, there was an increase in the rate of dye degradation (66.81 %) using ZEC23 when using an electron (e–) inhibitor reagent. In the presence of MetOH, a degradation rate of 44.0 % was observed, suggesting that the •OH radicals play a key role in the YE degradation.

ZIF-67 hybridization and boron doping to enhance the photo-electrocatalytic properties of g-C3N4

Photo-electrocatalysis is a growing field, and cobalt-based metal-organic frameworks (Co-MOFs) are attracting much interest because of their porous nature, high surface area, and malleable structure. This study investigated the photo-electrocatalytic properties of g-C3N4 and boron-doped-g-C3N4 when hybridized with cobalt-based MOF (ZIF-67). In this work, we describe the preparation of novel g-C3N4/ZIF-67 and B-g-C3N4/ZIF-67 composites by poly-condensation and co-condensation methods, respectively. ZIF-67 hybridization caused a decrease in the band gap energy of g-C3N4 due to changes in the crystalline structure and size. EIS results indicated that only B-g-C3N4/ZIF-67 showed a response to light irradiation. At the same time, both B-g-C3N4/ZIF-67 and g-C3N4/ZIF-67 demonstrated sufficient light response when the potential applied was increased to -1.2 V vs. NHE in LSV analyses. CO2 reduction to ethanol was performed for 3 hours at -1 V vs. NHE under continuous light irradiation and CO2 bubbling for each catalyst. Ethanol production rates were recorded as 10.024, 12.0168, 30.7230, and 32.1096 μmol/cm2.h for g-C3N4, B-g-C3N4, g-C3N4/ZIF-67, and B-g-C3N4/ZIF-67, respectively.

Magnetically separable and reusable Fe3O4/chitosan nanocomposites green synthesized utilizing Moringa oleifera extract for rapid photocatalytic degradation of methylene blue

This study focused on the green synthesis of Fe3O4/Chitosan (Cs) nanocomposites using Moringa oleifera leaf extract, which showed good photocatalytic activity when exposed to ultraviolet (UV) irradiation. X-ray diffraction spectrum of Fe3O4/Cs informs the cubic inverse spinel and has crystallite size in the 10.1 – 11.7 nm range. The crystallite size also increased with the increase of Cs mass. The morphology of Fe3O4 and Fe3O4/Cs was nearly spherical. The transmission electron microscope showed the most uniform size of nanocomposites at around 17.1 nm. The Fourier transform infrared spectrophotometer result identified Fe-O in the 576–583 cm−1 range, indicating that Fe3O4 successfully bonded to Cs. Other functional groups, including O–H, C–H, C–O, C–O–C, and NH2, were also found, indicating that the formation of Cs was effective. The element composition of Fe3O4 is Fe (70.9 %) and O (29.1 %). Meanwhile, Fe3O4/Cs (4:4) is 47.9 %, 36.4 %, 11.3 %, and 4.4 % for Fe, O, C and N, respectively. The hysteresis curve indicated that Fe3O4 and Fe3O4/Cs nanocomposites have soft ferromagnetic properties. Meanwhile, the saturation magnetization of Fe3O4 and Fe3O4/Cs (4:2) nanocomposites are 54.0 and 42.3 emu/g, respectively. Peaks are seen in the UV–visible absorption spectrum of Fe3O4 and Fe3O4/Cs nanocomposites between wavelengths 365–377 nm. The optical band gap energy (Eg) of Fe3O4 and Fe3O4/Cs (4:2) are 3.4 and 3.0 eV, respectively. As the mass of Cs increases, the band gap energy decreases. Under UV light irradiation, 50 mg of Fe3O4 and Fe3O4/Cs were analyzed on 7 ppm of methylene blue, pH = 4. The maximum photocatalytic activity Fe3O4/Cs (4:3), achieved an impressive degradation rate of 94.7 % after 120 min of irradiation. The magnetically separable capability means nanocomposites can be recycled and reused five times with high degradation. Furthermore, Fe3O4/Cs has the potential to be a low-cost and environmentally friendly reusable photocatalyst for rapid wastewater degradation.

Structural, linear and nonlinear optical properties of perovskite BaTiO3 tri-doped Er/Yb/Zn embedded in tellurium-zinc glass

Due to their excellent nonlinear optical characteristics, tellurium-zinc glass and perovskite structures have gained significant attention. In particular, perovskite-type BaTiO3 shows excellent potential for application in photonics devices. This study investigates structural, linear, and nonlinear optical properties of pure tellurium-zinc glass with embedded perovskites. Both glasses were prepared using the conventional melt-quenching method, and their structural modifications were analyzed through Raman spectroscopy. Optical absorption spectra revealed a redshift in the absorption edge, indicating a decrease in the band gap energy by the presence of the perovskite nanoparticles. When adding perovskite nanoparticles, Raman scattering results demonstrated decreased bridging and non-bridging oxygen ratio and structural changes. This suggests that the perovskite nanoparticles alter the local environment by affecting the Te-O- Zn2+ or Te=O bonds, resulting in a variation of the polarizability. Finally, the average nonlinear refractive for the glass containing perovskite nanoparticles is on the order of 0.3 × 10−18 m2 W−1 in the wavelength range of 580–990 nm, which is the same as of the pure glass. Thus, while the NP particles influence the arrangement of structural units and the linear optical response, their impact is not significant in the nonlinear refractive index. The observed modifications in structural and optical properties are relevant for advancing the use of perovskites in photonics.

DFT theoretical and experimental investigations of the effect of Cu doping within SILAR deposited ZnS

In this work, the effect of copper doping within ZnS on glass substrates was studied using integrated theory and experiments. Experimentally the pure ZnS and Cu-doped ZnS, for a variety of Cu concentrations (2 %, 4 %, 6 %), were grown, on a glass substrate, using the SILAR technique with 30 deposition cycles. Theoretically, the full potential linearized enhanced plane wave (FP-LAPW) approach based on density functional theory (DFT), using the TB-mBJ and PBE_GGA approximations, was employed to study the structural, electronic, and optical properties of copper-doped ZnS. The structural, morphological, and optical properties of deposited films were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and ultraviolet–visible-Near Infrared spectroscopy. XRD patterns demonstrate that all films were polycrystalline which corresponds to the hexagonal wurtzite with the (103), (104), and (105) directions as the preferred orientation. The crystalline particle size of the samples decreased, suggesting a change in crystallinity with Cu doping. The surface morphology showed that pure ZnS and Cu-doped ZnS present a rough, granular surface. EDX analysis confirms the expected dopant element presence in ZnS film. UV spectrophotometry experiments reveal that Cu incorporation causes a slight decrease in the optical gap energy from 3.74 to 3.67 eV, which confirms that the Cu atom reduces the band gap of this material.

Theoretical Study of the Photophysical and Photochemical Properties of 1H‐Benzimidazole and 2‐Ethyl‐7‐nitro‐5‐Substituted 1H‐Benzimidazoles

AbstractTheoretical study of the photophysical/photochemical properties of 1H‐benzimidazole and its derivatives was carried out using APFD, B3LYP, CAM‐B3LYP and PBE0 density functionals with 6‐311+G(2d,p) basis set. The effects of ethanol, 1,4‐dioxane, acetonitrile and water was investigated by means of Integral Equation Formalism of the Polarizable Continuum Model (IEPCM) in the framework of Self‐Consistent Reaction Field (SCRF). The results obtained show that S2 state of the 1H‐benzimidazole molecule is more acidic than the S0 state as the N5−H11 bond length increased to ~ 1.01 Å. At B3LYP/6‐311+G(2d,p) level of theory, the excitation energy of 1H‐bensimidazole molecule in ethanol from S0 to the S2 state was calculated to be 273 nm (4.54 eV). The electronic energy for this transition was calculated to be 0.131 a.u. and observed to occur between π→π* orbitals. Calculations with the PBE0, APFD and B3LYP functionals reproduced the experimental dipole moment in 1,4‐dioxane, with values of 4.09, 4.09 and 4.07 Debye respectively. However, the dipole moments of the 2‐ethyl‐7‐nitro‐5‐substituted‐1H‐benzimidazoles were calculated to be higher for electron donating groups (EDGs) than those bearing electron withdrawing groups (EWGs). In addition, the molecular polarizability was observed to increase with decreasing energy gap. Local excitation (LE) and charge‐transfer (CT) were observed to mediate the mechanisms of electronic excitation in 2‐ethyl‐7‐nitro‐5‐substituted‐1H‐benzimidazoles.

In@CdS sensitized TiO2 nano-rod for enhanced photocatalytic and photoelectrochemical performance under visible light

Titanium dioxide (TiO2) nano-rod are synthesized by one step hydrothermal method while cadmium sulphide (CdS) and Indium (In) doped CdS quantum dots (QDs) are sensitized on the surface of TiO2 nano-rod by using successive ionic layer adsorption and reaction (SILAR) approach. Characterization of this material was done using XRD, XPS, FE-SEM, EDX, HR-TEM, Raman, UV-DRS, PL, EPR. XRD pattern attributed that the preferential orientation of TiO2 grains is along the (101) plane perpendicular to the FTO substrate. XRD pattern also reveals the sensitization of CdS QDs in form of hexagonal CdS QDs and doping of In into CdS QDs. FE-SEM analysis suggests that the TiO2 nano-rod are uniform, thick and grown vertically on the FTO plate. Detailed investigations of the ‘In’ sensitization in 2%In-CdS/TiO2 were carried out by HR-TEM studies. UV-DRS analysis shows decrease in the band gap energy as doping of In in CdS/TiO2 nano-rod increases. EPR analysis reveals the presence of oxygen vacancies due to sensitization of ‘In’ on CdS/TiO2 matrix. The photoelectrochemical and photocatalytic performance of In doped CdS QDs embellished on the surface of TiO2 nano-rod photoanode was investigated by varying the concentration of In. The photo electrochemical (PEC) and photocatalytic H2 generation performance under natural sunlight of as prepared photoanode are explored in terms of photocurrent density and amount of H2 generation. 2% In-CdS/TiO2/Pt/FTO nano-rod shows highest 22.12 ml/h/g of hydrogen generation and photocurrent density of 4.78 (mA/cm2).

Optical, magneto-optical properties and fiber-drawing ability of tellurite glasses in the TeO2–ZnO–BaO ternary system

The presented work is focused on the optical and magneto-optical characterization of TeO2-ZnO-BaO (TZB) tellurite glasses. We investigated the refractive index and extinction coefficient dispersion by spectroscopic ellipsometry from ultraviolet, λ ≈ 0.193 μm, up to mid-infrared, λ ≈ 25 μm spectral region. Studied glasses exhibited large values of linear (n632 ≈ 1.91–2.09) and non-linear refractive index (n2 ≈ 1.20–2.67×10−11 esu), Verdet constant (V632 ≈ 22–33 radT−1m−1) and optical band gap energy (Eg ≈ 3.7–4.1 eV). The materials characterization revealed that BaO substitution by ZnO leads (at constant content of TeO2) to an increase in linear and nonlinear refractive index as well as Verdet constant while the optical band gap energy decreases. Fiber drawing ability of TeO2–ZnO–BaO glassy system has been demonstrated on 60TeO2–20ZnO–20BaO glass with presented mid-infrared attenuation coefficient. Specific parameters such as dispersion and single oscillator energy, Abbe number, and first-/third-order optical susceptibility are enclosed together with the values of magneto-optic anomaly derived from the calculation of measured dispersion of the refractive index.

Defect analysis and microstructural characterization of zinc-substituted cadmium oxide nanocrystallites by positron annihilation and supplementary methods

Pure and zinc-doped cadmium oxide nanocrystallites of sizes in the range 25 nm to 16 nm are synthesized by adopting a chemical precipitation method and by varying the doping concentration from 0.0 to 0.25. The decrease in nanocrystallite sizes with increasing substitution is expected from the smaller ionic radii of Zn2+. But more revealing is the interfacial defects formation at higher concentration of doping, which is attributed to the dissimilar crystalline structure of ZnO and CdO. X-ray diffraction patterns show well defined peaks and additional characterisation is done through transmission electron microscopy. The optical band gap measurements indicate the dominance of substitution-induced disorder over the confinement of excitons, leading to a decrease in the band gap energies. The results of positron annihilation studies confirm the cancellation of the existing vacancy type defects in the initial stage, followed by the substitution. Photoluminescence spectra reveal the distinct peaks of optical plasmonic excitations and the defect population in the bandgap and the intensity variations agreed with that of the defect related positron annihilation lifetime intensity. The segregation of ZnO phase leading to the formation of interfacial boundaries is found as a strong deterrent against the success of continued substitution.

Structural, optical, and dielectric characteristics of chitosan/hydroxypropyl cellulose‐modified copper vanadate nanoparticles

AbstractChitosan (Cs) and hydroxypropyl cellulose (HPC) blend films were created and incorporated with copper vanadate nanoparticles. The films were characterized using various techniques, including x‐ray diffraction (XRD), attenuated total reflectance‐Fourier transform infrared (ATR‐FTIR), TEM, SEM, UV/vis spectroscopy, dielectric properties, and AC conductivity. The XRD analysis showed that the prepared films had amorphous characteristics. FT‐IR spectra indicated interactions between the Cs/HPC virgin polymers and copper vanadate nanoparticles. TEM analysis showed that the most prevalent size range of the nanoparticles was 20–60 nm. SEM micrographs revealed surface homogeneity at lower copper vanadate nanoparticle contents but increased inhomogeneity with higher contents. The prepared films showed a decrease in the optical energy gap and an increase in refractive index with increasing copper vanadate nanoparticle content. Copper vanadate nanoparticles enhance AC conductivity in Cs/HPC polymer blend. Dielectric analysis proved the suitability of the films for electroactive polymer applications.Highlights The casting process was used to prepare Cs/HPC—copper vanadate NPs films. XRD shows increased amorphousness post‐addition of copper vanadate NPs. SEM images revealed an increase in inhomogeneity with higher contents of copper vanadate NPs. The optical band gap decreased as the content of copper vanadate NPs increased. Copper vanadate nanoparticles greatly improve electrical conductivity and relaxation time.

Enhancing antimicrobial and photocatalyst properties of Mg-doped ZnO nanotubes via novel laser-assisted chemical bath synthesis

Laser-Assisted Chemical Bath Synthesis (LACBS) was used to fabricate pure and magnesium-doped zinc oxide nanoparticles. Analysis of these nanoparticles' structural, morphological, optical, and antimicrobial characteristics was conducted. This analysis spanned across varying concentrations of magnesium-doped zinc oxide from 1 % to 3 %. XRD confirmed the nanoparticles' crystalline nature, revealing the hexagonal wurtzite phase. SEM analysis showcased their nanometric domain existence and hexagonal crystalline morphology, transforming from nanorods to nanotubes. Optical analysis showed band gap energy decrease from 3.27 to 2.85 eV correlating with the magnesium doping concentration increase. Optical absorption displayed a distinctive redshift for the nanoparticles as magnesium concentration increased from 1 % to 3 %. Photocatalytic assessments highlighted the superior degradation ability of 3 % Mg-doped nanoparticles, showing a 98.04 % degradation rate against methylene orange dye under blue light exposure. Antimicrobial activity tests against various pathogens showed that Mg ions' incorporation significantly enhanced antimicrobial performance, demonstrating the effectiveness of the LACBS method.

Comparative analysis of interaction of ionic liquids with porous and non-porous electrode materials

Fascinating properties of ionic liquids such as their higher ionic conductivity, lower vapor pressure, high thermal and electrochemical stability, make them promising candidates as electrolytes for novel energy storage devices. Interaction of ionic liquids (ILs) as electrolytes with electrode is crucial for optimizing the efficiency of energy storage devices. Herein, we report the interaction mechanism of ionic liquids 1-3 dimethylimidazolium halide (1,3-DMIX) on porous covalent triazine frameworks (CTF-0) and non-porous carbon nitride (C4N) electrode materials. Molecular electrostatic potential (MEP) analysis is performed for the prediction of interacting sites on studied electrolytes and electrode materials. Significant changes in geometric and electronic parameters are observed upon interaction of ionic liquid electrolytes with C4N and CTF-0. The nature of interaction between ionic liquids and electrode surfaces is evaluated through Quantum theory of atoms in molecules (QTAIM) and non-covalent index (NCI) analyses which reveal that there exist only the non-covalent interactions (van der Waals) between them. Frontier molecular orbitals (FMO) analysis shows a significant decrease in energy gap upon interaction of ILs with CTF-0, which results in increase in electrical conductivity. Overall, porous CTF-0 electrode material displays greater interaction with the considered ILs as compared to non-porous C4N electrode material. This study will provide a way for experimentalist to explore ionic liquids and carbon nitride or covalent triazine framework as electrolyte–electrode systems which can be used further in energy storage devices like fuel cells, solar cells, ion batteries, and supercapacitors.

Synthesis and Basic Properties of Y1−xYbxVO4 Obtained by High-Energy Ball Milling and High-Temperature Treatment

The main objective of this work was to experimentally confirm that a continuous, substitutional solid solution of a general formula Y1−xYbxVO4 is formed in the pseudo-binary system YVO4–YbVO4, and to investigate its basic unknown properties as a function of composition for 0.00 < x < 1.00. To date, such a solid solution has been obtained and characterized to a limited extent, but only for a few selected compositions. This solution was obtained by a high temperature and, for the first time, using mechanochemical methods. For the solution obtained by the high-energy ball-milling method, unknown physicochemical properties were established over its entire range of homogeneity. The solution was synthesized from mixtures of yttrium orthovanadate (V) with ytterbium (III) orthovanadate (V) of different compositions and investigated by XRD, IR, SEM, and UV-Vis(DRS) methods. It was found that Y1−xYbxVO4 crystallizes in a tetragonal system. The results confirmed that the solid solution Y1−xYbxVO4 has a structure of YVO4 and YbVO4, and its structure is composed of YbO6 and YO6 octahedrons and VO4 tetrahedrons. Moreover, if the parameter (x) in the solid solution Y1−xYbxVO4 increases, its crystalline lattice contracts and the value of the energy gap decreases. This solid solution is stable in the air atmosphere at least up to ~1500 °C. The estimated band gap for this solid solution indicates that it belongs to the semiconductors.

Atomic scale microparameter analysis of modified natural ester molecules related to impulse discharge characteristics under electric field

Modified natural ester (MNE) has significant potential for application in transformers as an environmentally friendly and renewable energy source. In comparison to natural esters, MNE offers notable advantages in terms of viscosity and power frequency breakdown voltage. However, the lightning impulse breakdown characteristics of MNE and the atomic-scale microscopic mechanisms related to its discharge characteristics remain unclear. Understanding the lightning impulse breakdown characteristics of MNE is crucial for ensuring the safe operation of transformers. In this paper, the density functional theory is used to calculate the change law of the microscopic parameters related to the discharge characteristics of MNE under the electric field under the action of electric field, so as to theoretically evaluate the lightning impulse discharge behavior of MNE. The results reveal that the electronic and geometric structures of MNE molecules are influenced by electric fields, which is the primary factor contributing to the variations in microscopic parameters under different electric field strengths. As the electric field intensity increases, the dipole moment of MNE tends to increase, while the ionization potential and excitation energy of MNE tend to decrease. The decrease of ionization potential, excitation energy and energy gap of MNE molecules is about 6.61%–68.01%, 4.34%–47.66% and 2.01%–69.23%. By comparing the calculated results of mineral oil, natural ester, and MNE microparameters, it can be inferred that the lightning impulse breakdown behavior of MNE is similar to that of natural ester and lightning impulse breakdown voltage of MNE is higher than that of natural ester but still lower than that of mineral oil. The average negative polarity lightning impulse voltages of MNE, natural ester and mineral oil in the 85 mm oil gap are about 245 kV, 199 kV and 304 kV, respectively. The test results confirmed the simulation conclusions. This study provides robust theoretical support for understanding the lightning impulse breakdown characteristics of MNE and ensuring its safe operation in transformers.

Co(II)-TiO2/Ti Thin Film as Antibacterial Photocatalysts Escherichia Coli Under Visible Light Ilumination

A thin layer of TiO2 doped with Cobalt (II) immobilized on the surface of a titanium foil (Co(II)-TiO2/Ti) has been synthesized from a titanium foil (Ti) as a TiO2 precursor as well as a thin layer matrix and CoCl2.6H2O as a source of Co(II) on variations of 0.5%, 1% and 2%. Synthesis was carried out by anodizing method using ethylene glycol electrolyte solution with the addition of NH4F and followed by calcination treatment at 450ºC for 3 hours. The obtained Co(II)-TiO2 /Ti thin films were characterized using Fourier-transform infrared (FT-IR) spectroscopy, Diffuse Reflectance UV-Vis (DRSUV-Vis) and X-ray diffraction (XRD) methods. Doping Co(II) variations of 0.5%, 1.0% dan 2.0% in the TiO2 structure causes a shift in the vibrational absorption peak of Ti-O (460.99 cm-1) towards a smaller wave number of 459.06 cm-1 respectively ; 453.27 cm-1 and 451.34 cm-1. This is supported by the results of the DRUV-Vis analysis using the tauc plot method, which shows a decrease in the band gap energy of TiO2 (3.24 eV) to 2.57 eV, 2.47 eV and 2.28 eV. Based on XRD analysis, it is known that the Co(II)-TiO2/Ti photocatalyst has anatase phase with a crystal size of 15-17 nm. The photocatalytic activity of Co(II)-TiO2/Ti under visible light illumination was evaluated for inhibition of Escherichia coli bacterial growth. Co(II)-TiO2/Ti photocatalyst at 2.0% Co(II) concentration had the best inhibition (43.2%) compared to 0.5% and 1.0% Co(II) concentrations, respectively 18% inhibition and 27%.

A Detailed Comparative Analysis of the Structural Stability and Electron-Phonon Properties of ZrO2: Mechanisms of Water Adsorption on t-ZrO2 (101) and t-YSZ (101) Surfaces.

In this study, we considered the structural stability, electronic properties, and phonon dispersion of the cubic (c-ZrO2), tetragonal (t-ZrO2), and monoclinic (m-ZrO2) phases of ZrO2. We found that the monoclinic phase of zirconium dioxide is the most stable among the three phases in terms of total energy, lowest enthalpy, highest entropy, and other thermodynamic properties. The smallest negative modes were found for m-ZrO2. Our analysis of the electronic properties showed that during the m-t phase transformation of ZrO2, the Fermi level first shifts by 0.125 eV toward higher energies, and then decreases by 0.08 eV in the t-c cross-section. The band gaps for c-ZrO2, t-ZrO2, and m-ZrO2 are 5.140 eV, 5.898 eV, and 5.288 eV, respectively. Calculations based on the analysis of the influence of doping 3.23, 6.67, 10.35, and 16.15 mol. %Y2O3 onto the m-ZrO2 structure showed that the enthalpy of m-YSZ decreases linearly, which accompanies the further stabilization of monoclinic ZrO2 and an increase in its defectiveness. A doping-induced and concentration-dependent phase transition in ZrO2 under the influence of Y2O3 was discovered, due to which the position of the Fermi level changes and the energy gap decreases. It has been established that the main contribution to the formation of the conduction band is made by the p-states of electrons, not only for pure systems, but also those doped with Y2O3. The t-ZrO2 (101) and t-YSZ (101) surface models were selected as optimal surfaces for water adsorption based on a comparison of their surface energies. An analysis of the mechanism of water adsorption on the surface of t-ZrO2 (101) and t-YSZ (101) showed that H2O on unstabilized t-ZrO2 (101) is adsorbed dissociatively with an energy of -1.22 eV, as well as by the method of molecular chemisorption with an energy of -0.69 eV and the formation of a hydrogen bond with a bond length of 1.01 Å. In the case of t-YSZ (101), water is molecularly adsorbed onto the surface with an energy of -1.84 eV. Dissociative adsorption of water occurs at an energy of -1.23 eV, near the yttrium atom. The results show that ab initio approaches are able to describe the mechanism of doping-induced phase transitions in (ZrO2+Y2O3)-like systems, based on which it can be assumed that DFT calculations can also flawlessly evaluate other physical and chemical properties of YSZ, which have not yet been studied quantum chemical research. The obtained results complement the database of research works carried out in the field of the application of biocompatible zirconium dioxide crystals and ceramics in green energy generation, and can be used in designing humidity-to-electricity converters and in creating solid oxide fuel cells based on ZrO2.

Defect-regulated charge carrier dynamics in two-dimensional ZnO/MoS2 heterostructure

Van der Waals ZnO/MoS2 heterostructure has been experimentally demonstrated as one of the potential candidates for photocatalyst, however, the charge carrier dynamics upon photoexcitation still remains unclear. By using nonadiabatic molecular dynamics simulations, we mainly focus on the influences of interfacial point defects on photogenerated charge separation in the ZnO/MoS2. The results reveal that oxygen vacancy in ZnO layer can induce a higher hole transfer efficiency compared to the pristine ZnO/MoS2, which attributes to the enhanced nonadiabatic coupling, originating from an out-of-plane vibration mode of S atoms, a decreased energy gap for intralayer hole transfer and stronger energy state oscillation. Alternatively, S vacancy in MoS2 introducing additional energy states in the band gap of ZnO/MoS2, serves as charge carrier recombination channels, and significantly reduces charge carrier lifetime, while doping O atom in S vacancy can compensate this effect. This study provides helpful guidance to design functional devices for solar energy photovoltaic conversion, based on two-dimensional ZnO/MoS2 heterostructures.

Fine-Tuning of the Electronic and Optical Properties of Dodecabenzocoronene through Boron and Nitrogen Doping: A DFT Insight

Nanographene provides a wide range of possibilities in graphene engineering for future applications due to the higher degrees of configurational freedom with the electronic parameters that may also be continuous or discrete, depending on the intended application. Therefore, the optical and electronic properties of nanographene are of substantial technological interest. Moreover, doping of graphene with heteroatoms (B, P, N, and S, etc.) alters their chemical and electronic characteristics which are suitable for the economical construction of optoelectronic devices. Herein, geometric, electronic, and optical properties of nanographene are evaluated as a function of the nature and position of dopant. Three different nanographene including coronene, hexabenzocoronene (HBC), and dodecabenzocoronene (DBC) are considered for doping (N and B as dopants) in this study with the key focus on DBC-doped systems. For any dopant number, all possible dopant sites are studied except edge position in order to avoid the edge effect. Frontier molecular orbital (FMO) analysis is performed to evaluate the perturbations in electronic characteristics of doped nanographene. A decrease in energy gap is seen for all doped systems. Natural bond orbital (NBO) analysis indicates that doping of boron (B) and nitrogen (N) results in variation in distribution of charges over the nanographene surfaces. The density of states (DOS) analysis reveals that Fermi level ([Formula: see text] is shifted for all B- and N-doped systems. The UV-visible (UV-Vis) absorption spectra are computed to evaluate the changes in the intensity and maximum adsorption wavelength ([Formula: see text] in all doped DBC. Various chemical reactivity descriptors are also evaluated which reveal the degree of stability and chemical reactivity of doped systems. The results indicate that multiple B and N atoms doping offers a new possibility for fine-tuning of electronic and optical properties of nanographene at atomic level, thus providing guidance in development of future advanced optoelectronic devices.

Efficient Photocatalytic Reduction of Hexavalent Chromium by BiVO4-Decorated MXene Photocatalysts and Their Charge Carrier Dynamics.

The synergistically MXene (Ti3C2Tx) co-catalyst-decorated BiVO4-based heterostructured photocatalysts have been synthesized by a hydrothermal approach with varied loading concentrations of MXene (Ti3C2Tx) to drive the hexavalent chromium reduction efficiently. The formation of the heterostructured photocatalyst was confirmed by the appearance of X-ray diffraction (XRD) peaks corresponding to the monoclinic BiVO4 phase and MXene (Ti3C2Tx) and also the antisymmetric (834 cm-1) and symmetric stretching (715 cm-1) of tetrahedral VO4 and D (1330 cm-1) and G (1570 cm-1) bands corresponding to MXene (Ti3C2Tx) in the Raman spectrum. The worm-like structures of BiVO4 nanocrystals grew onto the lamellar sheets of MXene (Ti3C2Tx), as shown by field emission scanning electron microscopy (FESEM), and has an increased surface area of 15.62 m2g-1 in the case of BVO-20-TC. X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of V5+ and Ti3+states, and the uniform distribution of BiVO4 nanocrystals over lamellar sheets of MXene (Ti3C2Tx) is evident from energy-dispersive X-ray (EDX) analysis. The ultraviolet-diffuse reflectance spectroscopy (UV-DRS) spectra suggest a decrease in the band gap energy of BVO-20-TC to 2.335 eV, promoting a higher degree of visible light harvesting. Upon optimization, by varying the pH, the amount of the photocatalyst, and the concentration of Cr(IV), BVO-20-TC exhibits the highest photocatalytic efficiency (96.39%) while using a Cr(VI) concentration of 10 ppm at pH 2 and 15 mg of the photocatalyst, and the photoreduction of Cr(VI) to Cr(III) follows the pseudo-first-order reaction. The decrease in the PL intensity in BVO-20-TC reveals a faster transfer of electrons from MXene (Ti3C2Tx) to BiVO4. Further, the higher degree of band bending at the BiVO4/MXene (Ti3C2Tx) heterojunction, revealed from the Mott-Schottky analysis, facilitates efficient charge transfer and eventually faster and efficient photoreduction of Cr(VI) to Cr(III). The reusability and stability test undertaken for BVO-20-TC reveals that even after five cycles, the Cr (VI) photoreduction efficacy is retained. This work provides insights into photoreduction of Cr (VI) by using such heterostructures.