Holes In Valence Band Research Articles

Enhancing the hole utilization efficiency of Ti–Fe2O3 photoelectrode by decorating CoCu-ZIF for efficient photo-assisted rechargeable zinc air batteries

To enhance the oxygen evolution reaction (OER) performance of the zinc-air battery (ZAB), reduce charging voltage, and improve energy utilization efficiency, a sunlight-assisted strategy has been implemented. The photo-assisted rechargeable ZAB was proposed, featuring Ti–Fe2O3 decorated with Co0·8Cu0.2-ZIF as the air electrode. Upon illumination, valence band holes were generated in Ti–Fe2O3, oxidizing Co2+ in Co0·.8Cu0.2-ZIF to Co3+/Co4+, enhancing OER performance, reducing the charging voltage from 2 V to 1.3 V and effectively narrowing the charging-discharging voltage gap from approximately 1.15 V–0.45 V. The Ti–Fe2O3/Co0·8Cu0.2-ZIF structure maintains a round-trip efficiency of 65.3% after 300 cycles. This result demonstrates the successful integration of photoelectrochemical principles with ZAB technology, showcasing its efficacy in solar energy storage and light energy conversion.

Enhanced Photocatalytic Paracetamol Degradation by NiCu-Modified TiO2 Nanotubes: Mechanistic Insights and Performance Evaluation.

Anodic TiO2 nanotube arrays decorated with Ni, Cu, and NiCu alloy thin films were investigated for the first time for the photocatalytic degradation of paracetamol in water solution under UV irradiation. Metallic co-catalysts were deposited on TiO2 nanotubes using magnetron sputtering. The influence of the metal layer composition and thickness on the photocatalytic activity was systematically studied. Photocatalytic experiments showed that only Cu-rich co-catalysts provide enhanced paracetamol degradation rates, whereas Ni-modified photocatalysts exhibit no improvement compared with unmodified TiO2. The best-performing material was obtained by sputtering a 20 nm thick film of 1:1 atomic ratio NiCu alloy: this material exhibits a reaction rate more than doubled compared with pristine TiO2, enabling the complete degradation of 10 mg L-1 of paracetamol in 8 h. The superior performance of NiCu-modified systems over pure Cu-based ones is ascribed to a Ni and Cu synergistic effect. Kinetic tests using selective holes and radical scavengers unveiled, unlike prior findings in the literature, that paracetamol undergoes direct oxidation at the photocatalyst surface via valence band holes. Finally, Chemical Oxygen Demand (COD) tests and High-Resolution Mass Spectrometry (HR-MS) analysis were conducted to assess the degree of mineralization and identify intermediates. In contrast with the existing literature, we demonstrated that the mechanistic pathway involves direct oxidation by valence band holes.

Hot Electron Cooling in n-Doped Colloidal Nanoplatelets Following Near-Infrared Intersubband Excitation.

Intersubband transition was recently discovered in colloidal nanoplatelets, but the associated intersubband carrier relaxation dynamics remains poorly understood. In particular, it is crucial to selectively excite the intersubband transition and to follow the hot electron dynamics in the absence of valence-band holes. This is achieved herein by exciting the predoped electrons in CdSe/ZnS nanoplatelets using near-infrared femtosecond pulses and monitoring nonequilibrium electron dynamics using broad-band visible pulses. We find that the n = 2 electrons relax to the n = 1 subband and establish a Fermi-Dirac distribution within 200 fs, and finally reach an equilibrium with the lattice within a few ps. The cooling dynamics depend mainly on the excitation fluence but weakly on the doping density and the lattice temperature. These characteristics are well captured by our numerical simulation that explicitly accounts for the state occupation effect and optical phonon scattering.

(Invited) Luminescent InP Quantum Dots: They're Not Just Like CdSe

Time-resolved photoluminescence (PL) and transient absorption (TA) spectroscopy have been used to elucidate the electron and hole dynamics in high quality InP/ZnSe/ZnS quantum dots (QDs) at room temperature. These dynamics depend critically on the overall In:P ratio. Stoichiometric QDs (those having an In:P ratio close to unity), have PL quantum yields of > 90% and exhibit dynamics that are very simple: both electron and hole relaxation to the bandedge is fast compared to the ~ 40 ps time-correlated photon-counting instrument response and the PL follows a single exponential decay having a time constant of about 26 ns. However, QDs having an In:P ratio greater than about 1.1 maintain PL quantum yields > 90%, but show much more complicated PL kinetics. In the non-stoichiometric QDs, a significant fraction of the PL exhibits a slower risetime. The PL rises over a range of timescales varying from close to the instrument response to approximately 2.0 ns. The time constant of the slowest component increases with increasing InP core size and the fraction of the PL that has the slow risetime increases with excess indium in the particle. The slow risetime is absent in the TA results, indicating that the slow dynamics may be assigned to relaxation in the valence band. The risetime increases with the thickness of the ZnSe shell, varying from < 40 ps for the thinnest (1.1 nm) to about 2.0 ns for the thickest (2.7 nm) ZnSe shells. In addition to the slow risetime, the QDs having excess indium show a significant long-lived (>100 ns) decay component. The magnitude and time constant of this slow decay also increases with ZnSe shell thickness.These results suggest that holes are transiently trapped at sites associated with indium dopants in the ZnSe shell. The trapped hole has negligible overlap with the conduction band electron, making this an optically dark state. The holes are in an equilibrium between the shell traps and the valence band, giving rise to the delayed emission. Several possible assignments of the trapping species can be considered, and a substitutional indium adjacent to a zinc vacancy, In3+/VZn 2-, is the most likely. This assignment is consistent with the observation that trapping occurs only when the QD has excess indium and is supported by experiments showing that the addition of zinc oleate or acetate decreases the extent of trapping, presumably by filling some of the vacancy traps. Further experiments show that addition of alkyl carboxylic acids causes increased trapping, presumably by the formation of zinc oleate, thereby creating additional zinc vacancies. Chloride ion is a common impurity in the synthesis of InP/ZnSe/ZnS QDs and the possibility of In3+/Cl- impurities acting as the hole trap can be also considered. However, additional experimental data on InP/ZnSe/ZnS QDs synthesized in the absence of chloride show the same PL risetimes and delayed emission, eliminating this possibility. Density functional theory calculations further corroborate assignment of the trapping species to In3+/VZn 2-. These calculations show that either a single In2+ ion or an In2+-In3+ dimer is much too easily oxidized to form the reversible traps observed experimentally, while In3+ is far too difficult to oxidize. However, a zinc vacancy adjacent to a substitutional indium is calculated to have its highest occupied orbitals about 1 eV above the top of the valence band of bulk ZnSe, in the appropriate energy range to act as reversible traps for quantum confined holes in the InP valence band.

Construction of Ag3PO4/g-C3N4 Z-Scheme Heterojunction Composites with Visible Light Response for Enhanced Photocatalytic Degradation.

Ag3PO4/g-C3N4 photocatalytic composites were synthesized via calcination and hydrothermal synthesis for the degradation of rhodamine B (RhB) in wastewater, and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS). The degradation of RhB by Ag3PO4/g-C3N4 composites was investigated to evaluate their photocatalytic performance and cyclic degradation stability. The experimental results showed that the composites demonstrated notable photocatalytic activity and stability during degradation. Their high degradation efficiency is attributed to the Z-scheme transfer mechanism, in which the electrons in the Ag3PO4 conduction band and the holes in the g-C3N4 valence band are annihilated by heterojunction recombination, which greatly limits the recombination of photogenerated electrons and holes in the catalyst and enhances the activity of the composite photocatalyst. In addition, measurements of photocurrent (PC) and electrochemical impedance spectroscopy (EIS) confirmed that the efficient charge separation of photo-generated charges stemmed from strong interactions at the close contact interface. Finally, the mechanism for catalytic enhancement in the composite photocatalysts was proposed based on hole and radical trapping experiments, electron paramagnetic resonance (EPR) analysis, and work function evaluation.

(Keynote) Light Driven H2 Generation in Pt-Tipped CdS Nanorods: Dependence on the Pt Size and CdS Rod Length

Colloidal quantum confined semiconductor-metal nano-heterostructures are a promising class of photocatalysts for solar energy conversion. In these photocatalysts, the semiconductor domain serves as the light absorber and the metal as the catalyst. Such photocatalysts combine the superior light absorption and charge transport properties of the semiconductor with the superior catalytic activity and selectivity of the metal. Furthermore, both domains can be independently tuned to enhance the photocatalytic performance of the heterostructure. Among various semiconductor/metal heterostructures, metal-tipped colloidal semiconductor nanorods have attracted extensive interest because they have been reported to have high quantum efficiencies of light driven H2 generation and their morphology can be systematically tuned. The overall light driven H2 generation process involves multiple elementary charge separation and recombination steps in the semiconductor and across the semiconductor/metal interface as well as proton-coupled electron transfer reactions at the catalytic center. The change of the semiconductor or metal domains can often have effects on multiple competing processes involved in the overall reaction. As a result of these complexities, the mechanisms for the morphological dependence of the observed H2 generation efficiencies are not fully understood, hindering the rational design of these photocatalysts. In this talk, we use Pt tipped CdS nanorods (CdS-Pt) as a model system to examine the effect of Pt size and CdS rod length on their light driven H2 generation efficiency. We show that increasing the Pt particle size increases the overall H2 generation quantum efficiency through both increasing the rate of electron transfer from the CdS to Pt and enhancing the efficiency of water/proton reduction; H2 generation efficiency increases at longer CdS rod length by suppression of charge recombination across the Pt/CdS interface. Furthermore, because of rapid trapping of valence band holes, multi-exciton states in CdS nanorods can be long lived, enabling efficient multi-electron transfer to the Pt. Our work demonstrates that through systematic in situ study of elementary processes involved in the overall H2 generation, it is possible to rationally design and improve semiconductor-metal hybrid photocatalysts.

Visible light-induced photocatalytic degradation of tetrabromobisphenol A on platinized tungsten oxide

In this study, we investigated the degradation of the flame retardant tetrabromobisphenol A (TBBPA) using platinized tungsten oxide (Pt/WO3), synthesized via a simple photodeposition method, under visible light. The results of degradation experiments show a significant enhancement in TBBPA degradation upon surface platinization of WO3, with the degradation rate increasing by 13.4 times compared to bare WO3. The presence of Pt on the WO3 surface stores conduction band electrons, which facilitates the two-electron reduction of oxygen and enhances the production of valence band holes (hVB+) and hydroxyl radicals (●OH). Both hVB+ and ●OH are significantly involved in the degradation of TBBPA in the visible light-irradiated Pt/WO3 system. This was verified through fluorescence spectroscopy employing coumarin as a chemical probe and oxidizing species-quenching experiments. The analysis of degradation products and their toxicity assessment demonstrate that the toxicity of TBBPA-contaminated water is significantly reduced after Pt/WO3 photocatalysis. The degradation rate of TBBPA increased with increasing Pt/WO3 dosage, reached an optimum at a Pt content of 0.5 wt%, but decreased with increasing TBBPA concentration. The decrease in degradation efficiency of Pt/WO3 was minor, both in the presence of various anions and after repeated use. This study proposes that Pt/WO3 is a viable photocatalyst for the degradation of TBBPA in water under visible light.

Dimensionally Intact Construction of Ultrathin S-Scheme CuFe2O4/ZnIn2S4 Heterojunctional Photocatalysts for CO2 Photoreduction.

The conversion of CO2 into carbon-neutral fuels such as methane (CH4) through selective photoreduction is highly sought after yet remains challenging due to the slow multistep proton-electron transfer processes and the formation of various C1 intermediates. This research highlights the cooperative interaction between Fe3+ and Cu2+ ions transitioning to Fe2+ and Cu+ ions, enhancing the photocatalytic conversion of CO2 to methane. We introduce an S-scheme heterojunction photocatalyst, CuFe2O4/ZnIn2S4, which demonstrates significant efficiency in CO2 methanation under light irradiation. The CuFe2O4/ZnIn2S4 heterojunction forms an internal electric field that aids in the mobility and separation of exciton carriers under a wide solar spectrum for exceptional photocatalytic performance. Remarkably, the optimal CuFe2O4/ZnIn2S4 heterojunction system achieved an approximately 68-time increase in CO2 conversion compared with ZnIn2S4 and CuFe2O4 nanoparticles using only pure water, with nearly complete CO selectivity and yields of CH4 and CO reaching 172.5 and 202.4 μmol g-1 h-1, respectively, via a 2-electron oxygen reduction reaction (ORR) process. The optimally designed CuFe2O4/ZnIn2S4 heterojunctional system achieved approximately 96% conversion of BA and 98.5% selectivity toward benzaldehyde (BAD). Additionally, this photocatalytic system demonstrated excellent cyclic stability and practical applicability. The photogenerated electrons in the CuFe2O4 conduction band enhance the reduction of Fe3+/Cu2+ to Fe2+/Cu+, creating a microenvironment conducive to CO2 reduction to CO and CH4. Simultaneously, the appearance of holes in the ZnIn2S4 valence band facilitates water oxidation to O2. The synergistic function within the CuFe2O4/ZnIn2S4 heterojunction plays a pivotal role in facilitating charge transfer, accelerating water oxidation, and thereby enhancing CO2 reduction kinetics. This study offers valuable insights and a strategic framework for designing efficient S-scheme heterojunctions aimed at achieving carbon neutrality through solar fuel production.

Impact of Photo-remediation on Anthracene PAHs in treated wastewater using ZnO/TiO2/H2O2 Catalysis

The remediation of carcinogenic Polycyclic Aromatic Hydrocarbons )PAHs( such as Anthracene (3 Rings) in different sources of wastewater was examined using a mix of Zink Oxide, Titanium Oxide, and Hydrogen peroxide (ZnO/ TiO2/H2O2). Eleven wastewater sources were collected from different industrial wastewater and treated wastewater (5 Farms, Main treatment plant, Tanning factory treated wastewater, Tanning factory non-treated wastewater, Carton factories, Factories Lake, and Grease refining plants. Anthracene was extracted by QuEChERS methodology and Analyzed by GCMSMS/TQD. Remediation techniques were applied by using different UV wavelengths irradiation on photolysis of PAHs under two wavelengths (254 and 306 nm) UV irradiation with ZnO + TiO2+ H2O2catalysts for 10 h. Also, the influence of remediation time and several parameters on Anthracene photolysis have been studied. The results indicate that Tanning factory non-treated wastewater had the highest concentration of Anthracene PAHs. The average recovery of Anthracene ranged from 92-96% and Detection Limit (DL) was 5 µg/l. The results of Anthracene concentration in tested wastewater ranged from 21.09 -223.69 µg/l. Also, the results show the anthracene was not detected after 5, 8, and 10h after the remediation using UV 254nm ZnO + TiO2+ H2O2. On the other side, the Anthracene was not detected after 3, 5, and 8h after the remediation using UV 254nm/ZnO + TiO2+ H2O2. Generally, the results of Photoremediation were effective and sufficient for the Anthracen. The impact of photocatalytic illumination of ZnO + TiO2 + H2O2yields valence band holes and conduction band electrons, which interact with the surface adsorbed molecular oxygen to give superoxide radical anions, and finally, the water produces radicals of HO•. These radicals oxidize the target molecule (Anthracene) to Anthraquinone.

Sweet-spot operation of a germanium hole spin qubit with highly anisotropic noise sensitivity

Spin qubits defined by valence band hole states are attractive for quantum information processing due to their inherent coupling to electric fields, enabling fast and scalable qubit control. Heavy holes in germanium are particularly promising, with recent demonstrations of fast and high-fidelity qubit operations. However, the mechanisms and anisotropies that underlie qubit driving and decoherence remain mostly unclear. Here we report the highly anisotropic heavy-hole g-tensor and its dependence on electric fields, revealing how qubit driving and decoherence originate from electric modulations of the g-tensor. Furthermore, we confirm the predicted Ising-type hyperfine interaction and show that qubit coherence is ultimately limited by 1/f charge noise, where f is the frequency. Finally, operating the qubit at low magnetic field, we measure a dephasing time of T2*\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{2}^{* }$$\\end{document} = 17.6 μs, maintaining single-qubit gate fidelities well above 99% even at elevated temperatures of T > 1 K. This understanding of qubit driving and decoherence mechanisms is key towards realizing scalable and highly coherent hole qubit arrays.

Rational sonochemical engineering of Ag2CrO4/g-C3N4 heterojunction for eradicating RhB dye under full broad spectrum

In this novel research, S-scheme Ag2CrO4/g-C3N4 heterojunctions were generated by sonochemical hybridization of different compositions of Ag2CrO4 nanoparticles [EVB = +2.21 eV] and g-C3N4 sheets [ECB = −1.3 eV] for destructing RhB dye under artificial solar radiation. The as-synthesized nanocomposites were subjected to X-ray diffraction [XRD], diffuse reflectance spectrum [DRS], X-ray photoelectron spectroscopy [XPS], N2-adsorption-desorption isotherm, photoluminescence [PL] and high resolution transmission electron microscope [HRTEM] analysis to explore the interfacial interactions between g-C3N4 sheets and Ag2CrO4 nanoparticles. Spherical Ag2CrO4 nanoparticles deposited homogeneously on the wrinkles points of g-C3N4 sheets at nearly equidistant from each other facilitating the uniform absorption of solar radiations. The absorbability of solar radiations was enhanced by introducing 20 wt % Ag2CrO4 on g-C3N4 sheets. The surface area of g-C3N4 sheets was reduced from 37.5 to 16.4 m2/g and PL signal intensity diminished by 80 % implying the successful interfacial interaction between Ag2CrO4 nanoparticles and g-C3N4 sheets. The photocatalytic performance of heterojunctions containing 20 % Ag2CrO4 and 80 % g-C3N4 destructed 96 % of RhB dye compared with 60 and 33 % removal on the surface of pristine g-C3N4 sheets and Ag2CrO4, respectively. Benzoquinone and ammonium oxalate are strongly scavenged the dye decomposition revealing the strong influence of valence band holes of Ag2CrO4 and superoxide radicals in destructing RhB dye under solar radiations. S-scheme charge transportation mechanism was suggested rather than type II heterojunction on the light of scavenger trapping experiments results and PL spectrum of terephthalic acid. Overall, this research work illustrated the manipulation of novel S-scheme heterojunction with efficient redox power for destructing various organic pollutants persisted in water resources.

Highly intrinsic carrier mobility in tin diselenide crystal accessed with ultrafast terahertz spectroscopy

Tin diselenide (SnSe2), a layered transition metal dichalcogenide (TMDC), stands out among other TMDCs for its extraordinary photoactive ability and low thermal conductivity. Consequently, it has stimulated many influential researches on photodetectors, ultrafast pulse shaping, thermoelectric devices, etc. However, the carrier mobility in SnSe2, as determined experimentally, remains limited to tens of cm2V-1s-1. This limitation poses a challenge for achieving high-performance SnSe2-based devices. Theoretical calculations, on the other hand, predict that the carrier mobility in SnSe2 can reach hundreds of cm2V-1s-1, approximately one order of magnitude higher than experimental value. Interestingly, the carrier mobility could be underestimated significantly in long-range transportation measurements due to the presence of defects and boundary scattering effects. To address this discrepancy, we employ optic pump terahertz probe spectroscopy to access the photoinduced dynamical THz photoconductivity of SnSe2. Our findings reveal that the intrinsic carrier mobility in conventional SnSe2 single crystal is remarkably high, reaching 353.2 ± 37.7 cm2V-1s-1, consistent with the theoretical prediction. Additionally, dynamical THz photoconductivity measurements reveal that the SnSe2 crystal containing rich defects efficiently capture photoinduced conduction-band electrons and valence-band holes with time constants of ∼20 and ∼200 ps, respectively. Meanwhile, we observe an impulsively stimulated Raman scattering at 0.60 THz. Our study not only demonstrates ultrafast THz spectroscopy as a reliable method for determining intrinsic carrier mobility and detection of low frequency coherent Raman mode in materials but also provides valuable reference for the future application of high-performance SnSe2-based devices.

Electrochemical versus Photoelectrochemical Water Oxidation Kinetics on Bismuth Vanadate (Photo)anodes.

This study reports a comparison of the kinetics of electrochemical (EC) versus photoelectrochemical (PEC) water oxidation on bismuth vanadate (BiVO4) photoanodes. Plots of current density versus surface hole density, determined from operando optical absorption analyses under EC and PEC conditions, are found to be indistinguishable. We thus conclude that EC water oxidation is driven by the Zener effect tunneling electrons from the valence to conduction band under strong bias, with the kinetics of both EC and PEC water oxidation being determined by the density of accumulated surface valence band holes. We further demonstrate that our combined optical absorption/current density analyses enable an operando quantification of the BiVO4 photovoltage as a function of light intensity.

Visible-light driven photodegradation of low-density polyethylene (LDPE) using BiOCl–ZrO2 nanocomposite: A sustainable strategy for mitigating plastic pollution

This study aims to reduce plastic pollution by decomposing low-density polyethylene (LDPE) through an environmentally friendly approach using a novel BiOCl–ZrO2 nanocomposite under visible-light irradiation at room temperature. Visible-light irradiation is a form of clean energy, so we explored the feasibility and prospective solution for plastic waste mitigation by utilizing visible-light to attain sustainable development goal 7 (SDG 7). To fabricate photodegradable LDPE, it was blended with BiOCl nanoparticles (NPs) and its nanocomposite (BiOCl–ZrO2) separately via a facile solution casting method. The fabricated samples were assessed for the degradation of LDPE before and after 24 days of visible-light irradiation at room temperature. The prepared nanocomposites were thoroughly characterized by different analytical techniques, including XRD, FT–IR, XPS, FE–SEM, TGA, BET and UV–Vis DRS. The successful photodegradation of low-density polyethylene (LDPE) using a BiOCl–ZrO2 nanocomposite is supported by the presence of a higher carbonyl index, as evidenced by FT–IR analysis. The field-emission scanning electron microscopy (FE–SEM) analysis unveiled numerous perforations and prominent coarse morphological attributes, suggesting significant decomposition and disintegration of the LDPE film across the active surface sites of BiOCl–ZrO2. The weight reduction of LDPE@BiOCl–ZrO2 (600 ˚C) (10 wt%) composite film reached 48.67% under visible-light irradiation for 24 days at room temperature. The degradation rate exhibited significant sensitivity to variations in the concentration of the BiOCl–ZrO2 nanocomposite within the LDPE film. Investigation of the photodegradation mechanism suggested the formation of a type–II heterojunction–based photocatalytic system. The relatively low bandgap energy of ZrO2 (3.1 eV), facilitates the rapid migration of conduction band electrons to the conduction band of BiOCl. This migration process is facilitated by the favourable energy level alignment between the conduction bands of ZrO2 and BiOCl, enabling efficient electron transfer between the two materials. The large band gap of BiOCl (3.56 eV) permits the movement of valence band holes to the ZrO2 valance band. The spontaneous circulation of charge carriers within the heterostructure crystal maintains the charge separation and defers the recombination rate for an extended period. The photodegraded LDPE fragments are biodegradable and help to reduce plastic pollution. The environmental friendliness of the BiOCl–ZrO2 nanocomposite-assisted plastic waste remediation process was investigated using carbon footprint measurement. A tentative estimation suggested that the remediation process of 100 Kg of plastic waste may contribute to around 0.133 tons of carbon footprint.

Gadolinium modified g-C3N4 for S-Scheme heterojunction with monoclinic-WO3: Insights from DFT studies and related charge carrier dynamics

Modifying the surface structures of g-C3N4 through interfacial coupling with other semiconductors has been spotlighted as an efficient approach for improving photocatalytic efficiency. With the surge of S-scheme heterojunctions, the research is intensified towards designing this kind of composite for energy-environmental-related applications. In this context, a new approach involving surface modifications of g-C3N4 through Gd species and integrating with monoclinic-WO3 via a wet chemical approach to form S-scheme heterojunctions is investigated. The characterization results attested that the adopted protocol promotes the better dispersion of Gd species over the g-C3N4 surface and rigidly integrates with WO3. The optical response of the composite spanned a significant portion of the visible region in the solar spectrum. The computational studies and the findings of the Mott-Schottky plot collectively suggested that the position of band edges qualifies for the formation of S-scheme heterojunction. The results derived from photocurrent response measurements and photoluminescence technique attribute to the effective charge carrier separation in the heterostructure. The rate constant of Gd-g-C3N4/WO3 was 1.48 × 10−2 min−1 which was approximately 4.35 and 2.27 times greater than that of WO3 (0.34 × 10−2 min−1) and g-C3N4/WO3 (0.65 × 10−2 min−1) respectively. Furthermore, RhB degradation in the presence of scavengers validated the participation of superoxide and hydroxyl radicals in the degradation mechanisms. This was possible only when the conduction band electrons of WO3 recombined with the valence band holes of Gd-modified g-C3N4. The present work helps to understand the S-scheme heterojunction formation between surface-modified g-C3N4 and metal oxides and retain the involvement of energetic charge carriers in the desired redox reactions.

Sunlight-Driven Nitrate-to-Ammonia Reduction with Water by Iron Oxyhydroxide Photocatalysts.

The photocatalytic reduction of harmful nitrates (NO3-) in strongly acidic wastewater to ammonia (NH3) under sunlight is crucial for the recycling of limited nitrogen resources. This study reports that a naturally occurring Cl--containing iron oxyhydroxide (akaganeite) powder with surface oxygen vacancies (β-FeOOH(Cl)-OVs) facilitates this transformation. Ultraviolet light irradiation of the catalyst suspended in a Cl--containing solution promoted quantitative NO3--to-NH3 reduction with water under ambient conditions. The photogenerated conduction band electrons promoted the reduction of NO3--to-NH3 over the OVs. The valence band holes promoted self-oxidation of Cl- as the direct electron donor and eliminated Cl- was compensated from the solution. Photodecomposition of the generated hypochlorous acid (HClO) produced O2, facilitating catalytic reduction of NO3--to-NH3 with water as the electron donor in the entire system. Simulated sunlight irradiation of the catalyst in a strongly acidic nitric acid (HNO3) solution (pH ∼ 1) containing Cl- stably generated NH3 with a solar-to-chemical conversion efficiency of ∼0.025%. This strategy paves the way for sustainable NH3 production from wastewater.

CdS@CuInS2 nanocomposites for enhanced photocatalytic activity under visible light irradiation

Copper indium sulfide (CuInS2) and CuInS2 modified with different percentages of CdS (10% CdS@CuInS2, 20% CdS@CuInS2, and 30% CdS@CuInS2) were successfully synthesized, as confirmed by structural, optical, and morphological characterization. The photocatalytic performance of the CuInS2 and CdS@CuInS2 composites was evaluated by degrading brilliant green (BG) dye and converting 4-nitrophenol under visible light irradiation. Amongst the synthesized photocatalysts, 30% CdS@CuInS2 exhibited the highest photocatalytic activity, degrading 96.8% of BG within 5 h. The active species involved in the degradation processes were investigated by performing degradation experiments in the presence of suitable trapping agents for superoxide radical ions (O2•−), hydroxyl radicals (•OH), and valence band holes (h+). It was found that O2•− is the main active species in the photocatalytic degradation of BG by CdS@CuInS2. Moreover, the photocatalytic conversion of 4-nitrophenol was also enhanced up to 95.5% under visible light irradiation, and h+ is the main active species involved in the conversion. This work opens new avenues for the development of highly efficient photocatalysts for practical wastewater remediation.

Ultralow charge–discharge voltage gap of 0.05 V in sunlight‐responsive neutral aqueous Zn–air battery

AbstractRechargeable neutral aqueous zinc−air batteries (ZABs) are a promising type of energy storage device with longer operating life and less corrosiveness compared with conventional alkaline ZABs. However, the neutral ZABs normally possess poor oxygen evolution reactions (OERs) and oxygen reduction reactions performance, resulting in a large charge–discharge voltage gap and low round‐trip efficiency. Herein, we demonstrate a sunlight‐assisted strategy for achieving an ultralow voltage gap of 0.05 V in neutral ZABs by using the FeOOH‐decorated BiVO4 (Fe‐BiVO4) as an oxygen catalyst. Under sunlight, the electrons move from the valence band (VB) of Fe‐BiVO4 to the conduction band producing holes in VB to promote the OER process and hence reduce the overpotential. Meanwhile, the photopotential generated by the Fe‐BiVO4 compensates a part of the charging potential of neutral ZABs. Accordingly, the energy loss of the battery could be compensated via solar energy, leading to a record‐low gap of 0.05 V between the charge and discharge voltage with a high round‐trip efficiency of 94%. This work offers a simple but efficient pathway for solar‐energy utilization in storage devices, further guiding the design of high energy efficiency of neutral aqueous ZABs.

Understanding the synergistic interactions between photo-Fenton and photocatalytic reactions in hemin-anchored SnO2

Sensitization of wide-gap metal oxides by the porphyrins has been promising to utilize the major fraction of solar light for photocatalytic reactions. In this context, rutile-SnO2 was anchored with hemin complex and their performance was evaluated for the 4-nitro phenol (4-NP) degradation under UV/visible light. Driven by the significant interactions between -COOH and surface -OH functional groups of hemin and SnO2 respectively, a new linkage O=CO-Sn was formed at the interface, which was vital for charge carrier transfer between them. Both X-ray diffraction studies and scanning electron microscope analysis confirmed that the surface hemin adsorption did not alter the crystal structure and the morphology of pristine SnO2. The light absorption properties revealed a red shift in the optical response of the composite, which facilitated the photocatalytic reactions to operate under visible light. The electrochemical and photoluminescence measurements collectively attested to the enhanced charge carrier separation in the composite compared to pure SnO2. The synergism arising from the photo-Fenton and photocatalytic reactions was derived from the cyclic reactions of Fe(II)/Fe(III) and oxidation of hydroxyl radicals by the valence band holes of SnO2 with H2O2 under UV light. In contrast, the sensitization process resulted in electron transfer from the excited state of hemin to the conduction band (CB) of SnO2 under visible light. Such distinct mechanistic pathways by the metal oxide-porphyrin composite would be promising for wastewater purification under UV–visible light region in near future.

Magic Angles and Fractional Chern Insulators in Twisted Homobilayer Transition Metal Dichalcogenides.

We explain the appearance of magic angles and fractional Chern insulators in twisted K-valley homobilayer transition metal dichalcogenides by mapping their continuum model to a Landau level problem. Our approach relies on an adiabatic approximation for the quantum mechanics of valence band holes in a layer-pseudospin field that is valid for sufficiently small twist angles and on a lowest Landau level approximation that is valid for sufficiently large twist angles. It provides a simple qualitative explanation for the nearly ideal quantum geometry of the lowest moiré miniband at particular twist angles, predicts that topological flat bands occur only when the valley-dependent moiré potential is sufficiently strong compared to the interlayer tunneling amplitude, and provides a convenient starting point for the study of interactions.