Band Gap Reduction Research Articles

Thermoelectric properties of XX- and XY-stacked GeS/GeSe van der Waals heterostructures from DFT and BTP calculations.

This study utilizes density functional theory (DFT) and the Boltzmann transport equation (BTE) to investigate the structural, electronic, and thermoelectric properties of germanium sulfide (GeS) and germanium selenide (GeSe) monolayers, along with their van der Waals (vdW) heterostructures. We analyzed XX-stacked and XY-stacked configurations, where the XX configuration features direct atomic stacking, while the XY configuration exhibits staggered stacking. Our first-principles calculations indicate that the formation of GeS/GeSe heterostructures results in a reduction of bandgaps compared to their bulk and monolayer counterparts, yielding bandgap values of 0.91 eV for the XX configuration and 0.84 eV for the XY configuration. Stability assessments reveal that the XY configuration is more stable, demonstrating a lattice thermal conductivity of 15.21 W/mK compared to 17.95 W/mK for the XX configuration T 300 K. The thermoelectric properties were systematically evaluated across a temperature range of 300-800 K, revealing high Seebeck coefficients of 1.51 mV/K for the XX heterostructure and 1.39 mV/K for the XY heterostructure. reflecting their excellent charge transport capabilities. Notably, the figure of merit (ZT) at 800 K was calculated to be 0.90 for the XX configuration and 1.01 for the XY configuration, underscoring the superior thermoelectric performance of the XY heterostructure. These findings contribute to a comprehensive understanding of 2D GeS/GeSe heterostructures for thermoelectric applications and provide a solid foundation for future research and technological advancements in this domain.

Exploration of bismuth based perovskite materials for organic dyes removal from waste water

The scourge of water pollution due to organic matter is a well-known fact. In order to address this issue, we employed a highly facile method of solid state reaction for the synthesis of bismuth potassium titanate, Bi0.5K0.5TiO3 (BKT) photocatalyst. Furthermore, the bandgap tailoring of the BKT is performed by photo-reduction of Ag onto the BKT, which results in the formation of hetero-structure junctions at the surface of the BKT. The as-prepared BKT and BKT-Ag photocatalysts are systematically characterized by x-ray diffraction, scanning electron microscopy, and high resolution transmission electron spectroscopy. Furthermore, the photocatalyst activity of the BKT and BKT-Ag was analyzed against the target organic pollutants by using UV–Vis spectroscopy. Three organic dyes such as methylene blue, eriochrome Black T, and methylene orange (MO) were used as target organic pollutants. The anchoring of Ag for the formation of hetero-structure junctions at the surface of BKT rendered it to be an ideal photo-catalyst with a bandgap reduction from 3.37 to 2.08 eV. Therefore, lowering the bandgap resulted in enhanced photocatalytic activity of the BKT-Ag. Among the three target dyes, BKT-Ag showed remarkable photo-degradation of MO and Erb T by degrading ≥90% of MO and Erb T in 120 min at neutral pH values. It is believed that BKT based photocatalysts can provide a unique platform for the removal of organic pollutants from wastewater.

Strain induced nitrobenzene sensing performance of MoSi2N4 monolayer: Investigation from density functional theory

The observing of environmental contaminant of Nitrobenzene (NB), from effluent discharges is a critical component of the surveillance to be conducted by public authorities and private sectors. By the way, the present work examines the NB adsorption behaviour of recently synthesized two-dimensional (2D) material MoSi2N4 through density functional theory (DFT). We observed that when increasing the percentage of strain (2, 4, 6 and 10 %) the adsorption energy also increasing reasonably compared to the unstrained case. The bandgap reduction was observed when gas molecule interacts with the strained MoSi2N4 and also the Bader charge calculation claims that the quantity of charge transferred between orbitals of N 2p of MoSi2N4 and the O 2p of NB. 4 % strain shows reasonable binding energy of 1.0201 eV with recovery time of 3.15 min. Moreover, there is strong bonding between N of MoSi2N4 and O of NB as evidenced from wavefunction analysis. 10 % strained system is stable at 600 K, which is examined through ab initio molecular dynamics study. The present theoretical investigation validates the 4 % strained MoSi2N4 can be fabricated as a sensor to detect the NB gas molecule.

Modification of MWCNTs with Bi2WO6 nanoparticles targeting IL-1β and NLRP3 inflammasome via augmented autophagy.

This study reports the facile hydrothermal synthesis of pure Bi2WO6 and Bi2WO6\MWCNTs nanocomposite at specific molar ratio 1:2.5 of Bi2WO6:MWCNTs and elucidates their role in modulating the NLRP3 inflammasome pathway via autophagy induction. Comprehensive characterization techniques, including XRD, Raman, UV.Vis PL,FESEM,EDS and TEM, revealed the successful incorporation of MWCNTs into the Bi2WO6 structures, leading to enhanced crystattlinity, reduced band gap energy (2.4 eV) suppressed charge carrier recombination and mitigated nanoparticles aggregation. Notably, the reduced band gap facikitaed improved visible light harvesting, a crucial attribute for photocatalytic applications. Significantly, the nanocompsoite exhibited a remarkable capacity to augment autophagy in bone marrow-derived macrophages (BMDMs), consequently down-regulating the NLRP3 inflammasom activation and IL-1β secretion upon LPS and ATP stimulation. Immunofluorescence assays unveiled increased co-localization of LC3 and NLRP3, suggestion enhanced targeting of NLRP3 by autophagy. Inhibition of autophagy by 3-MA reversed these effects, confirming the pivotal role of autophagy induction. Furthermore, the nanocomposite attenuated caspase-1 activation and ASC oligomerzation, thereby impeding inflammasome assembly. Collectively, these findings underscore the potential of Bi2WO6\MWCNTs nanocompsite as a multifaceted therapeutic platform, levering its tailored optoelectronic properties and sbility to modulate the NLRP3 infalmmasome via autophagy augmentation. This work covers the way for the development of advanced nanomaterials with tunable functionalities for combating inflammatory disorders and antimicrobial applications.

The Effect of Heat Treatment on the Sol–Gel Preparation of TiO2/ZnO Catalysts and Their Testing in the Photodegradation of Tartrazine

This study aims to synthesize TiO2/ZnO powders and to study the effect of heat treatment on their photocatalytic ability against the Tartrazine anionic dye. The as-obtained powders with the following compositions—90TiO2/10ZnO and 10TiO2/90ZnO (mol%)—were obtained by the sol–gel technique. The prepared gels were annealed at 500 °C and 700 °C and subsequently characterized by XRD, UV–Vis, and SEM methods. The single crystalline phase of TiO2, which has been detected at up to 500 °C is anatase, while for ZnO, it is the hexagonal wurtzite structure. Further increases in the temperature (700 °C) led to the appearance of rutile in the samples. The SEM analysis demonstrated that the binary oxide materials had irregular shaped particles with a tendency to agglomerate. The UV–Vis spectra of the gels exhibited a red shift in the cut-off of the 90TiO2/10ZnO sample compared with pure Ti(IV) butoxide. Photocatalytic tests showed that the investigated samples possessed photocatalytic activity toward Tartrazine. Compared with TiO2, the prepared TiO2/ZnO photocatalysts showed superior properties in the photodegradation of a Tartrazine water solution. The target photocatalysts’ enhanced photocatalytic activities can be explained by their reduced band gap energy, improved surface physicochemical characteristics, separation of photo-induced electron–hole pairs, and lowered recombination rate. Higher photocatalytic activity was observed for powders annealed at 500 °C, with the 10TiO2/90ZnO (mol%) sample exhibiting the highest photocatalytic degradation of the used organic dye.

Fabrication of Reduced Band Gap Copper Oxide Photocatalysts with Enhanced Dye Degradation under Visible Light

Fabrication of Reduced Band Gap Copper Oxide Photocatalysts with Enhanced Dye Degradation under Visible Light

Influence of Subvalent Twin-Rattler for High n-Type Thermoelectric Performance in Bi13S18Br2 Chalcohalide.

Metal chalcohalides, owing to their higher stability over halides and greater tunability of electronic features over chalcogenides, open new avenues for investigating properties of materials. Complex metal chalcohalides can be a good choice for thermoelectric studies for their halide-like low thermal conductivity and chalcogenide-like high electrical conductivity. Here, we have investigated the thermoelectric properties of n-type Bi13S18Br2 and utilized the concept of Fajans' polarization to describe the formation of a dimer and explained how it can help achieve high thermoelectric figure of merit (zT) of ∼1.0 at 748 K. This zT value is so far the highest-reported value for pristine metal chalcohalides. The existence of subunit in Bi13S18Br2 is experimentally verified by synchrotron X-ray pair distribution function (X-PDF) analysis. The complex structure of Bi13S18Br2 having a large unit cell exhibits simultaneous dimer-cation rattler (i.e., "twin-rattler"), which decreases the lattice thermal conductivity drastically. We observed evidence of such low-energy rattling vibrations from DFT-calculated eigen mode visualizations of the phonon dispersion. The subvalent nature of accommodates an extra electron in Bi(6pz) orbital, which helps form a weakly dispersed donor band just below the Fermi energy (EF), leading to a significant reduction in band gap (0.77 eV), which is favorable for high thermoelectric performance. Consequently, we obtained a semiconducting nature of n-type Bi13S18Br2 with moderate electrical conductivity, as well as a high Seebeck coefficient. Our investigation presents the importance of fundamental chemistry in thermoelectrics and demonstrates the influence of subvalent twin-rattler in triggering high thermoelectric performance in metal chalcohalides.

Regulating oxygen vacancies to optimize the electronic structure and catalytic activity of tungsten oxides for hydrogen evolution reaction

The undesirable intrinsic activity of tungsten oxides derived from poor conductivity and adverse hydrogen absorption energy is insufficient for their practical application. Herein, the tungsten oxides with adjustable oxygen vacancies were synthesized by a facile pyrolysis of ammonium paratungstate hydrate in controllable atmospheres. The structural characterizations confirmed that oxygen vacancies and crystalline phases in tungsten oxides depend on the pyrolysis atmosphere. The electrochemical test indicated a strong dependence between catalytic activity and oxygen vacancies in tungsten oxides. Combining experimental results and density functional theory calculations verified that introducing oxygen vacancies into tungsten oxides effectively modulates the surface electronic structure. The enhanced electronic conductivity by reducing band gap accelerates the electron transfer from catalysts into the reactive species. The optimized hydrogen adsorption energy by electron migration from O into W promotes the activation of reactive species at W sites and the desorption from O sites, thereby accelerating the reaction kinetics.

Ultra-broadband emission from Mg7Ga2GeO12:Ni2+,Cr3+ phosphor spanning the NIR I–III regions for spectroscopy applications

Ultra-broadband near-infrared (NIR) lighting sources covering NIR Ⅰ to III regions are pivotal components for NIR spectroscopy devices. However, achieving ultra-broadband and efficient emission covering the entire NIR Ⅰ to III regions remains a significant challenge. To address this, we selected Mg7Ga2GeO12 as host material to realize ultra-broadband NIR emission. Density functional theory calculations on formation energies confirmed the feasibility of doping both Ni2+ and Cr3+ within Mg7Ga2GeO12. Band structure calculations reveal a significantly reduced band gap upon the doping of Ni2+. Following that, we synthesized Mg7Ga2GeO12:Ni2+ through conventional solid-state-reaction method. This phosphor exhibits broadband NIR emission with a full-width-at-half-maximum of 377 nm in the range of NIR II ∼ III (1100–2100 nm). To further enhance the emission efficiency, we co-doped Mg7Ga2GeO12:Ni2+ phosphor with Cr3+. This co-doping strategy not only dramatically enhances the Ni2+ emission intensity, but also extends the lower limit of emission band to 600 nm. However, a spectral gap around 1150 nm remains between Cr3+ and Ni2+ emission centers. To bridge this spectral gap, we employed LiScSiO4:Cr3+ phosphor alongside Mg7Ga2GeO12:Ni2+,Cr3+ phosphor to fabricate a phosphor converted LED (pc-LED) with ultra-broadband NIR emission covering entire NIR Ⅰ to III regions. By utilizing this pc-LED as the lighting source for NIR spectral detection, multiple organic functional group signals can be identified simultaneously in NIR II and III bands from 1000 to 2100 nm. The performance of such an NIR pc-LED not only confirms the application potential of Mg7Ga2GeO12:Ni2+,Cr3+ phosphor in non-destructive spectral analysis but also underscores the feasibility of combining two phosphors to achieve ultra-broadband NIR pc-LEDs, rendering them suitable to be lighting sources for portable spectrometers.

Macroporous material modified efficient silver molybdate composite for effective photocatalytic degradation of dyes

Macroporous banana peel biochar (BBC), silver molybdate (Ag6Mo10O33) and new composite Ag6Mo10O33@BBC were synthesized and characterized. Ag6Mo10O33@BBC was prepared using acid modulator for the first time. The photo degradation efficiency of Ag6Mo10O33@BBC in the degradation of methylene blue (MB) was found to be 95.16 %. The adsorption and degradation properties of the photo catalyst were studied using UV–visible spectroscopic analysis and band gap calculation. The photocatalytic activity favourable properties such as reduced band gap of 2.07 eV and high surface area of 7.28 m2/g of Ag6Mo10O33 was resulted upon compositing it with BBC.

Visible-Light Photodetection by Zero-Dimensional Hybrid Indium-Halide with Minimal Structural Distortion and Reduced Band Gap.

Perovskite-inspired zero-dimensional (0D) hybrid halides exhibit impressive light emission properties; however, their potential in photovoltaics is hindered by the absence of interconnection between the inorganic polyhedra, leading to acute radiative recombination and insufficient charge separation. We demonstrate that incorporating closely-spaced dissimilar polyhedral units with minimal structural distortion leads to a remarkable enhancement in visible-light photodetection capability. We designed 0D C24H72N8In2Br14 (HIB) with a tetragonal crystal system, replacing the Cs+ of Cs2InBr5.H2O (CIB) with 1,6-hexanediammonium (HDA) cation. HIB comprises [InBr6]3- octahedra, and [InBr4]- tetrahedra units spaced 3.9 Å apart by the HDA linker. The [InBr4]- unit is additionally linked to HDA via intercalated bromine through hydrogen and halogen bonding interactions, respectively. This structural arrangement lowers the dielectric confinement, thereby enhancing carrier density and mobility, and increasing the diffusion coefficient compared to CIB. With 3.6 % bromine vacancy within the [InBr4]- block, mid-gap states are created, reducing the direct band gap to 2.19 eV. HIB demonstrates an unprecedently high responsivity of 9975.9±201.6 mA W-1 under 3 V potential bias at 485 nm wavelength, among low-dimensional hybrid halides. In the absence of potential bias, the self-powered photodetection parameters are 81.2±3.0 mA W-1 and (6.98±0.21)×109 Jones.

Visible‐Light Photodetection by Zero‐Dimensional Hybrid Indium‐Halide with Minimal Structural Distortion and Reduced Band Gap

AbstractPerovskite‐inspired zero‐dimensional (0D) hybrid halides exhibit impressive light emission properties; however, their potential in photovoltaics is hindered by the absence of interconnection between the inorganic polyhedra, leading to acute radiative recombination and insufficient charge separation. We demonstrate that incorporating closely‐spaced dissimilar polyhedral units with minimal structural distortion leads to a remarkable enhancement in visible‐light photodetection capability. We designed 0D C24H72N8In2Br14 (HIB) with a tetragonal crystal system, replacing the Cs+ of Cs2InBr5.H2O (CIB) with 1,6‐hexanediammonium (HDA) cation. HIB comprises [InBr6]3− octahedra, and [InBr4]− tetrahedra units spaced 3.9 Å apart by the HDA linker. The [InBr4]− unit is additionally linked to HDA via intercalated bromine through hydrogen and halogen bonding interactions, respectively. This structural arrangement lowers the dielectric confinement, thereby enhancing carrier density and mobility, and increasing the diffusion coefficient compared to CIB. With 3.6 % bromine vacancy within the [InBr4]− block, mid‐gap states are created, reducing the direct band gap to 2.19 eV. HIB demonstrates an unprecedently high responsivity of 9975.9±201.6 mA W−1 under 3 V potential bias at 485 nm wavelength, among low‐dimensional hybrid halides. In the absence of potential bias, the self‐powered photodetection parameters are 81.2±3.0 mA W−1 and (6.98±0.21)×109 Jones.

Visible Light Active 0.95KNbO3‐0.05Ba(Nb1/2Sc1/2)O3 Ferroelectric for Enhanced Photocatalytic Activity

AbstractThis study reports a visible light active Ba/Sc co‐doped potassium niobate (KNbO3) ferroelectric material for enhanced photocatalytic applications. Through 5% Ba and Sc co‐doping in KNbO3 (i.e., 0.95KNbO3‐0.05Ba(Nb1/2Sc1/2)O3), the electronic band gap (Eg) is narrowed down to the visible range of the solar spectrum. The prepared samples are systematically examined by using X‐ray diffraction and Raman spectroscopy, which confirms the successful incorporation of Ba and Sc ions into the KNbO3 lattice. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis reveal particle morphology and chemical homogeneity of prepared samples. The UV–vis spectroscopy and ferroelectric PE‐loop demonstrate enhanced optical absorption compared to host KNbO3 while retaining ferroelectric behavior. The photoelectrochemical (PEC) measurements under visible light irradiation demonstrate a notable enhancement in the photocurrent for 0.95KNbO3‐0.05Ba(Nb1/2Sc1/2)O3 (hereafter denoted by 5KBSNO) compared to undoped KNbO3. Additionally, the 5KBSNO sample displays enhanced RhB dye degradation efficiency, reaching ≈50% compared to parent KNbO3 (≈30%) under light irradiation. First‐principles density functional theory (DFT) calculations are employed to understand the mechanism responsible for the reduced band gap. This study presents a promising material for developing advanced ferroelectric photocatalysts with tailored band structures for efficient solar energy harvesting for energy conversion and contamination remediation applications.

Electronic and photocatalytic properties of Cu4 cluster-modified Ag/g-C3N4 single-atom catalysts: A hybrid DFT study

Increasing the active sites on the catalyst surface has been a key goal to increase the catalyst efficiency. This paper presents an efficient conversion of solar energy into chemical energy, realized by a Cu4 cluster-assisted single-atom catalyst (Ag-doped g-C3N4). The catalyst enhances charge transfer and light absorption, and the unique advantages of this approach in the field of photocatalysis are substantiated by density functional theory. Under the synergistic effect of Cu4 clusters, the electronic state density distribution of the Ag single-atom catalyst substrate is drastically altered, which realizes the increase of substrate active sites and rapid charge separation and transfer. Compared with the pristine substrate g-C3N4, the new electronic state distribution and the generation of impurity energy levels lead to the narrowing of the band gap from 2.77 to 1.83 eV, accelerating the transfer and separation of electrons and holes, and enlarging the visible light absorption range from 410 to 760 nm, thus improving the solar energy utilization. Despite the reduced band gap, the conduction and valance band edges of (Ag, Cu4) codoped g-C3N4 still have sufficient potential to split water. Therefore, to improve the photocatalytic performance under visible light, simultaneous codoping of the Ag single atom and Cu4 cluster on g-C3N4 is an effective strategy. The study provides theoretical support for further optimization of single-atom catalysts.

Enhancing perovskite solar cells performance through tailored design: pyridine-functionalized phenothiazine derivatives with modified end-capped acceptor moieties

Abstract Future energy resources are being developed using clean and renewable energies since these sources offer environmentally friendly and sustainable choices to traditional sources like fossil fuels. Among various renewable energy sources, solar energy is becoming increasingly efficient with advancements in organic photovoltaic systems. Organic semiconductor materials, which require high electron affinity and possess desirable optical and electronic properties, are crucial for these systems. Researchers are constantly trying to increase the role of photovoltaic materials in optoelectronic applications. With current energy demands, there is a shift from traditional solar cells to perovskite photovoltaic materials due to their significant contributions to renewable energy. Therefore, we have designed a new stream of donor- π -acceptor (D- π -A) type pyridine functionalized phenothiazine derivates-based donor materials, resulting in nine fabricated HTMs (PT1-PT9), by substituting the terminals with thiophene and acceptors moieties respectively to enhance the photovoltaic properties of perovskite solar cells (PSCs). All newly proposed materials were computationally examined to estimate their optoelectronics, geometrical, and photovoltaic properties using quantum chemical approach, and then compared to the reference. For organic hole-transporting materials, a heterocyclic phenothiazine core (PTZ) has been proven effective as it has feasible structure modifications, excellent electron-donating properties, and straightforward synthesis. The study of electronic parameters (density of state, frontier molecular orbitals, and electrostatic potential ESP), optical properties (light harvesting efficiency, absorption maxima, dipole moment, and first excitation energies) and charge transfer characteristics (electron–hole overlap, transition density matrix) of designed materials revealed that there is an increase in absorption range under the influence of terminal acceptor groups, with lowering the bandgap values compared to the reference. A density of state (DOS) graph and HOMO–LUMO schema are evidence of the electron-withdrawing effect of acceptor moieties. Transition density matrix (TDM) analysis proves reliable charger transfer in designed molecules. Reorganization energy values for designed molecules are lower than the reference making charge transfer carriers more efficient. Additionally, solvation-free energy values (−17.28 to −33.19 Kcalmol−1) and higher dipole moments suggest better surface-wetting and solubility properties. In general, the fabricated materials have exceptional charge mobilities with higher absorption and reduced band gap values that make them suitable and stable candidates for photovoltaic devices.

Facilitating Charge Transfer via Ti-Knot Pathway in Electrochromic Three-Dimensional Metalated Covalent Organic Frameworks.

Due to the ordered one-dimensional channel as well as accessible redox sites, two-dimensional covalent organic frameworks (2D COFs) have garnered extensive attention in the field of electrochromism. However, organic 2D frameworks impose limitations on charge transfer and the weak interlayer interactions in 2D COFs, adversely affecting the stability during switching processes. Herein, we introduced Ti knots to construct three-dimensional metalated covalent organic frameworks (3D MCOFs), denoted as Ti-DHTA-Py. The Ti knots not only serve as templates for organizing organic units into unique 3D topological structures in a controlled manner but also establish charge transfer pathways conducive to electron delocalization and transmission within the framework. As a result, the 3D Ti-DHTA-Py MCOFs electrode exhibited a reduced band gap and remarkable electrochromic (EC) performances: electrochemical cyclic stability of 93.6% retention after 500 cycles, switching times (2.5 s/0.5 s), and a high coloration efficiency (423 cm2 C-1). This research underscores the potential of 3D MCOFs as promising candidates for advancing EC technologies, surmounting the limitations associated with traditional 2D COFs.

Band Gap Engineering of Spin-Coated <i>α</i>-Fe<sub>2</sub>O<sub>3</sub> for Solar Water Splitting Utilizing a Facile Zinc Doping Route

Iron oxide (hematite, α-Fe2O3) is an earth-abundant material having a favorable band gap for solar energy harvesting by producing Hydrogen (H2) by photoelectrochemical (PEC) water splitting. Although Fe2O3 has a valence band maximum (VBM) more positive than the water oxidation potential in the normalized hydrogen energy scale (NHE), it can not be used as a photocathode because of the more positive conduction band minima (CBM) than the reduction potential of the electrons required for the hydrogen evolution reaction (HER). This paper reports the band gap engineering of Fe2O3 by doping it with Zinc (Zn) through a facile way to modify its CBM and VBM to enable it to work as an ideal and efficient photocatalyst. One-pot synthesis of α-Fe2O3 doped with Zn was achieved by spin-coating a precursor solution prepared with FeCl2 and Zinc acetate (Zn(CH3COO)2.2H2O) on fluorine-doped tin oxide (FTO) or glass substrates. The films were then annealed in air at around 450 °C. The surface morphology and the crystal structure of the Fe2O3 were studied using SEM (Scanning Electron Microscope) and XRD (X-ray diffractometer). The UV-VIS spectrophotometry and spectroelectrochemistry (SEC) determined the band energies of α-Fe2O3 and Zn-doped α-Fe2O3. The band gap and CBM of pristine α-Fe2O3 were found to be -2.09 eV and -5.31 eV vs. EVAC, whereas the band gap and CBM of Zn-doped α-Fe2O3 were -1.96 eV and -4.3 eV vs. EVAC respectively. The outcome of the photoelectrochemical study shows that α-Fe2O3 doped with Zn can have a reduced band gap with more negative CBM than the H+/H2 reduction potential that efficiently ensures both oxygen and hydrogen evolution reaction.

Exposing graphene oxide’s function in enhancing dye sensitized solar cell efficiency

This study aims to explore the potential for increasing the efficiency of the Dye sensitized solar cells through the incorporation of graphene oxide into the titanium dioxide matrix. The presence of defects was observed by Raman spectra. The structural properties and crystallite size of TiO2, GO, and GO/TiO2 composite were investigated using X-ray diffraction analysis, whereas the changes in morphology of graphene oxide and GO/TiO2 were assessed by Field Emission Scanning Electron Microscopy. The presence of functional groups were analyzed by Fourier Transform Infrared Spectroscopy. UV-Visible spectroscopy revealed a reduction in optical bandgap from 3.25 eV for TiO2 to 2.89 eV for GO/TiO2 and optical conductivity were observed increasing from 5.49 × 107 S/cm to 1.19 × 108 S/cm. The efficiency of the fabricated DSSCs was determined through I-V measurement, which showed that the addition of 0.2 wt% of graphene oxide in TiO2 significantly increased the short-circuit current from 0.38 milliampere to 0.75 milliampere, fill factor from 0.71 to 0.82, resulting in a substantial efficiency improvement from 3.99% to 9.11%.

Synthesis and characterization of zinc-doped hematite nanoparticles for photocatalytic applications and their electronic structure studies by density functional theory

Hematite nanoparticles doped with 1, 3 and 5 % Zn (all % are in molar) were prepared using mechanical alloying. Morphological and phase structure studies using scanning electron microscopy and X-ray diffraction showed nanoparticles possessing a semi-spherical shape and particle size of <50 nm crystallized in rhombohedral structure. The lattice parameters of hematite increased upon Zn doping. The energy-dispersive X-ray and Fourier-transform infrared results demonstrated that Zn was successfully incorporated. The optical behavior of nanoparticles was examined by UV–Vis diffuse reflectance spectroscopy and revealed that Zn doping increased the absorption intensity in the visible light region and decreased the band gap from 1.95 (hematite) to 1.83 eV (3 % Zn). Methylene blue dye degradation by the 3 % Zn sample proved doubling of the photocatalytic activity due to electronic structure modification upon Zn doping. First principles studies using density functional theory performed to investigate the effect of Zn on the electronic band structure of hematite showed that Zn doping caused band gap reduction, causing formation of new energy states, mainly above the valence band. Eventually, the enhancement of Urbach energy and reduction of effective mass, respectively accountable for increasing the relaxation time and mobility of charge carriers, were considered the two main mechanisms regarding the increased photocatalytic behavior of hematite by Zn doping.

Structural and optical properties of Ce-stabilized tetragonal phase and intense blue emission of monoclinic phase in ZrO2 nanoparticles

Structural and optical properties of Ce-stabilized tetragonal zirconium dioxide (ZrO2) and intense blue emission of monoclinic ZrO2 are presented in this paper. Nanoparticles of ZrO2 in the stabilized tetragonal and monoclinic phases have been prepared by the solution combustion method. X-ray diffraction studies and Rietveld refinement of the diffraction pattern show the stabilization of ZrO2 in the tetragonal phase (t-ZrO2) with Ce doping. It is the host-dopant ionic size mismatch that leads to lattice distortion and hence the t-ZrO2 stabilized phase. Raman modes confirm the phase transformation from the monoclinic to a tetragonal phase of ZrO2. The presence of oxygen vacancies and surface states in the samples play a role in altering the optical band gap. The dopant Ce-ions create defects/oxygen vacancies, which act as the trapping sites for electrons and holes/the donor and vacancy-related impurity levels. It is transition between these levels or between delocalized conduction bands that lead to band gap reduction. Photoluminescence studies reveal the presence of structural phase transformation dependent emission bands. The monoclinic phase (m-ZrO2) exhibits an intense blue emission originating from the asymmetric and unusual oxygen coordination of Zr in the m-ZrO2. The chromaticity coordinates indicate that the prepared material and adopted strategies are suitable in the field of optoelectronic application.