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With the exceptional advantages of safety, greenness, and low cost, photocatalytic H2O2 generation has kindled a wonderful spark, although being severely hampered by the terrible photoinduced exciton recombination, migration, and surface decomposition. Here, employing reflux method, the Cd–Mo–Se quantum dots of varying molar ratios of Cd and Mo were synthesized using thioglycolic acid as the capping ligand to regulate their growth. This type of metal alloying promotes rapid charge migration, improves light harvesting, and reduces the rate of charge recombination. The improved optoelectronic properties and boosted activity of Cd-rich ternary CMSe-1 QDs led to the observed exceptional photocatalytic H2O2 yield of 1403.5 μmol g−1 h−1 (solar to chemical conversion efficiency, 0.27%) under visible light, outperforming the other ternary and Se-based QD photocatalysts. Additionally, CMSe-1 shows 93.6% (2 h) hazardous Cr(VI) photoreduction. The enhanced catalytic performance of CMSe-1 corresponds to effective charge carrier separation and transfer efficiency, well supported by PL, TRPL, and electrochemical measurements. Photocatalytic H2O2 production was also studied under varying experimental conditions and the scavenger test suggests a superoxide radical intermediate 2-step single electron reduction pathway. The catalyst-assisted Cr(VI) reduction is substantiated by the zero-order kinetics as well as the determination of the pHPZC value. The catalyst can be employed for a maximum of four times while retaining its activity, according to the photostability and reusability test outcomes. This research presents interesting approaches for producing ternary QDs and modified systems for efficient photocatalytic H2O2 production and Cr(VI) reduction. [ABSTRACT FROM AUTHOR]

Designing a heterojunction through oxygen vacancy (OV) has been considered as a well-accepted stratagem for enhanced photo-Fenton activity. Therefore, we have adopted a combination of hydrothermal and calcination methods to fabricate an abundant step-scheme photocatalyst by uniting ZnFe2O4 with an oxygen-defect-oriented WO3 semiconductor and verified their activities towards levofloxacin (LVX) degradation under solar-light illumination. The as-synthesized 15%WO3−X/ZnFe2O4 binary hybrid displayed increased photo-Fenton activity for LVX degradation (kapp value 4–7 times greater than that of pure semiconductors). The increased activity can be attributed to effective charge transmission occurring between the conduction band of defective WO3−X and the valence band of ZnFe2O4 bridged through mediator-free OVs. The existence of OVs was well-supported with the assistance of Raman, XPS, and EPR characterization, whereas the proposed S-scheme charge transfer mechanism was proved by hydroxyl and super-oxide radical generation experiments. Furthermore, the photo-Fenton system constructed by H2O2 and continuous Fe(III)/Fe(II) conversion resulted in high concentration of ˙OH radical that ultimately encouraged faster LVX degradation. Through the identification of reaction intermediates via LC-MS analysis, the LVX degradation pathways were speculated. [ABSTRACT FROM AUTHOR]

Achieving organic transformation reactions using green synthesis methods under mild conditions is always an aspiration of scientists. In the present findings, a Zn–Cr layered double hydroxide (LDH)/graphene oxide (GO) nanocomposite modified with Au–Ag noble metal nanoparticles (NPs) was synthesized via the in situ crystallization of a LDH over a GO surface followed by the simultaneous photo-deposition of a metal alloy and the reduction of GO to reduced graphene oxide (RGO) under UV light irradiation, resulting in AuAg@GO/LDH. All prepared samples were suitably analysed via various sophisticated techniques to explore their structural, morphological, optical and compositional behaviours. The characterization outcomes showed the uniform distribution of AuAg alloyed NPs with a typical diameter of around ∼3 nm on the facade of the GO/LDH nanocomposite. The conversion of GO to RGO is confirmed via Raman analysis. This bimetallic alloy-based nanocomposite provides a novel platform for artificial photocatalysis, and shows excellent catalytic activity for the performed tandem redox reactions. The combined effects of the plasmon active AuAg alloy, the visible photon-responsive ZnCr LDH and the electron trapping and transporting properties of GO illustrate the existence of an intensified green photochemical process, which can be extensively developed to be applied to tandem liquid phase photocatalytic organic reactions. Here the photogenerated electrons and holes can be directly utilized by nitrobenzene (NB) and benzyl alcohol (BA) to produce aniline (AL) and benzaldehyde (BAD) via GO, respectively. This selective photoredox reaction is a synergistic type of process that proceeds via producing and consuming protons. The effective separation of charge carriers is well supported by photoluminescence (PL) studies. Compared to the parent GO/LDH and Au and Ag singly-modified GO/LDH samples, AuAg@GO/LDH revealed proficient photocatalytic potential owing to the existence of combined surface plasmon resonance (SPR) effects, characterised through UV-visible diffuse reflectance spectroscopy (UV-vis DRS), generating hot electrons from both photoexcited Au and Ag atoms under visible light illumination. The AuAg@GO/LDH hybrid photocatalyst showed ∼2.5 times better performance than GO/LDH, without any indication of leached metal or metal alloy over five runs. [ABSTRACT FROM AUTHOR]

In the present study, a series of Ce2Zr2O7@rGO nanocomposites were synthesized using a simple solution combustion method followed by a photoreduction technique. The as-prepared samples were well characterised using various analytical techniques to determine the morphological, optical, structural, electrochemical and compositional properties. The presence of oxygen defects was observed from Raman and photoluminescence spectra. The photoreduction of GO to rGO was determined from Raman and Fourier-transform infrared (FTIR) spectroscopy results. The role of rGO proved to be quite significant for the enhanced photocatalytic activity of the nanocomposites. The synergistic communication between Ce2Zr2O7 and rGO accelerates the photoreduction of 4-nitrophenol along with the degradation of ciprofloxacin under visible light irradiation. Of the rGO nanocomposites, 3 wt% GO loaded Ce2Zr2O7 reduces 99% of 20 ppm of 4-nitrophenol to 4-aminophenol in 120 min and decomposes 10 ppm of ciprofloxacin by up to 89% in 60 min. The significant enhancement in the activity of the Ce2Zr2O7@rGO nanocomposite was ascribed to the effective charge separation of excitons through π-conjugation of graphene at the interface, which is well supported by the impedance, photoluminescence and photocatalytic results. [ABSTRACT FROM AUTHOR]

Prompt recombination of photoproduced charges in bulk and surface of a photocatalyst significantly impedes catalytic efficiency. To address these challenges, FeOOH nanorods (NRs) anchored NaNbO 3 (NNO) piezoelectric microcubes (MCs) have been fabricated for ciprofloxacin (CIP) degradation and oxygen evolution through water splitting by coupling macroscopic spontaneous piezoelectric polarization and a built-in electric field. The local electric field induced by surface oxygen vacancies (Ovs) and orientation of FeOOH NRs over NNO MCs afford the polarization electric field a significant boost, driving the quick separation/migration of charge carriers from bulk to the surface. The polarized NNO/FeOOH composite with ample Ovs demonstrates an outstanding piezophotocatalytic CIP degradation of 93% in 1 h, higher than pristine materials (NNO and FeOOH), and a high O 2 evolution rate of 1155 μmol h -1 . The effect of piezoelectric polarization on the catalytic activity is supplemented by theoretical simulations. This work offers an avenue for selective pollutant remediation and water splitting through the rational design of piezoelectric polarization-mediated heterostructure systems with surface Ovs.

With the exceptional advantages of safety, greenness, and low cost, photocatalytic H 2 O 2 generation has kindled a wonderful spark, although being severely hampered by the terrible photoinduced exciton recombination, migration, and surface decomposition. Here, employing reflux method, the Cd-Mo-Se quantum dots of varying molar ratios of Cd and Mo were synthesized using thioglycolic acid as the capping ligand to regulate their growth. This type of metal alloying promotes rapid charge migration, improves light harvesting, and reduces the rate of charge recombination. The improved optoelectronic properties and boosted activity of Cd-rich ternary CMSe-1 QDs led to the observed exceptional photocatalytic H 2 O 2 yield of 1403.5 μmol g -1 h -1 (solar to chemical conversion efficiency, 0.27%) under visible light, outperforming the other ternary and Se-based QD photocatalysts. Additionally, CMSe-1 shows 93.6% (2 h) hazardous Cr(VI) photoreduction. The enhanced catalytic performance of CMSe-1 corresponds to effective charge carrier separation and transfer efficiency, well supported by PL, TRPL, and electrochemical measurements. Photocatalytic H 2 O 2 production was also studied under varying experimental conditions and the scavenger test suggests a superoxide radical intermediate 2-step single electron reduction pathway. The catalyst-assisted Cr(VI) reduction is substantiated by the zero-order kinetics as well as the determination of the pH PZC value. The catalyst can be employed for a maximum of four times while retaining its activity, according to the photostability and reusability test outcomes. This research presents interesting approaches for producing ternary QDs and modified systems for efficient photocatalytic H 2 O 2 production and Cr(VI) reduction.

Photocatalytic H 2 O 2 production and recalcitrant pollutant degradation are regarded as promising clean technology toward achieving sustainable solar-to-chemical energy conversion. Herein, nonstoichiometric Zn-Cu-In-S (ZCIS) quaternary alloyed quantum dots (QDs) are rationally fabricated via a reflux method toward H 2 O 2 generation and ciprofloxacin degradation under visible light irradiation. The optimum catalyst (ZCIS-2) exhibits a notable H 2 O 2 production of 1685.2 μmole h -1 g -1 (solar-to-chemical conversion efficiency (SCC), 0.19%), which is 5.3 times higher than that of CuInS 2 (CIS), and a ciprofloxacin (CIP) degradation efficiency of 96% in 2 h. The observed improvement in activity corresponds to optimized exciton separation/transfer, broad photon absorption, tunable band alignment, and effective adsorption/activation. In addition, oxygen reduction goes through both direct two-electron single-step reduction and single-electron two-step superoxide radical pathways, whereas CIP degradation proceeds via direct • O 2 - and indirect • OH radical pathways, as confirmed by scavenger experiments. An appropriate amount of defects improves the adsorption/activation of O 2 toward H 2 O 2 and active oxygen species generation that facilitates CIP degradation. The effect of operational parameters, such as pH, surrounding environment, presence of ions, sacrificial agent, etc., on both H 2 O 2 formation and CIP removal is vividly studied. Hence, the current study will provide an in-depth insight into O 2 photoreduction and micropollutant removal, which encourages further advancement of potent alloyed quantum dot-oriented photocatalytic systems.

Designing promising photocatalytic systems with wide photon absorption and better exciton separation ability is a cutting-edge technology for enhanced solar-light-driven hydrogen production. In this context, non-stoichiometric Cu 0.75 In 0.25 S nanocrystals (CIS NCs) coupled with three-dimensional (3D) BiOI micro-flowers (BOI MFs) were synthesized through an ultra-sonication strategy forming a CIS-BOI heterojunction, which was well supported by XRD, photocurrent, XPS and Mott-Schottky analyses. Further, the co-catalyst-free CIS-BOI binary hybrid shows improved hydrogen evolution, i.e. , 588.72 μmol h -1 , which is 3.2 times greater than the pristine CIS NC (183.97 μmol h -1 ). Additionally, the binary composite confers an apparent conversion efficiency (ACE) of 9.44% (8.90 × 10 16 number of H 2 molecule per sec), which is extensively attributed to the robust charge carrier separation and transfer efficiency via the direct Z-scheme mechanism (proved through superoxide and H 2 evolution activity). Moreover, the broad photon absorption range and productive exciton separation over the CIS-BOI composite are substantially justified by UV-Vis DRS, PL, EIS and photocurrent measurements., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

Environmental protection and the necessity of green energy have become fundamental concerns for humankind. However, rapid recombination of photoexcitons in semiconductors often gets in the path of photocatalytic reactions and annoyingly suppresses the photocatalytic activity. In this study, a polypyrrole (PPY)-supported step-scheme (S-scheme) ZnFe 2 O 4 @WO 3- X (PZFW15) ternary composite was fabricated by a multistep process: hydrothermal and calcination processes, followed by polymerization. During the formation of the heterojunction, the oxygen vacancy (OV) on WO 3- X promotes effective separation and increases the redox power of the photogenerated excitons via the built-in internal electric field of S-scheme pathways between ZnF and WO 3- X . The successful construction of the S-scheme heterojunction was substantiated through X-ray photoelectron spectroscopy, experimental calculations, radical trapping experiment, and liquid electron spin resonance (ESR) characterization, whereas the existence of OVs was well confirmed by EPR and Raman analyses. Meanwhile, the PPY served as a supporter, and the polaron and bipolaron species of PPY acted as electron and hole acceptors, respectively, which further enhances the charge-carrier transmission and separation in the ternary PZFW15 photocatalyst. The designed ternary nanohybrid (PZFW15) displays outstanding gemifloxacin detoxification (95%, 60 min) and hydrogen generation (657 μmol h -1 ), i.e., 1.5 and 2.2 times higher than the normal S-scheme ZFW15 heterostructure and pure ZnFe 2 O 4 (ZnF), respectively, with an apparent conversion efficiency of 4.92%. The ESR and trapping experiments indicate that the generated • OH and • O 2 - radicals from the PZFW15 photocatalyst are responsible for gemifloxacin degradation. This unique PPY-supported S-scheme heterojunction is also beneficial for the enhanced electron-transfer rate and provides abundant active sites for photocatalytic reactions., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Lethargic kinetics is the foremost bottleneck of the photocatalytic water oxidation reaction. Hence, in this respect, the CeO 2 coral reef made up of nanosheets is studied focusing on the oxygen vacancy that affects the water oxidation reaction. First, CeO 2 was prepared in an oyster shell/crucible with the presence/absence of urea by a simple calcination technique to tune the oxygen vacancy. More oxygen vacancy was detected in CeO 2 prepared from urea and oyster shell, which is evidenced from Raman and PL analyses. Further, the oyster shell-treated sample was found to be of nanosheet type with numerous pores as observed via TEM analysis. The theoretical approach was adopted to expose the role of oxygen vacancies and the fate of scavenging agents in the water oxidation mechanism. It was observed that an oxygen vacancy plays a vital role in minimizing the activation energy hump and opposes the reverse reaction. The apparent conversion efficiency of 7.1% is calculated for the oxygen evolution reaction. Oxygen vacancy, quantum confinement effect, and charge separation efficiency are mainly responsible for the better photocatalyzed water oxidation reaction and hydroxyl radical production. This investigation will help in providing valuable information toward designing cost-effective oxygen vacancy-oriented nanosheet systems and the importance of vacancy in the water-splitting reaction., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

The present research reports the synthesis of two-dimensional (2D) sheet/flake-like nanostructures of crystalline carbon modified TiO 2 (CT), B-TiO 2 (B-CT), and S-TiO 2 (S-CT) using a facile one-pot synthesis method. The crystallinity and phase purity (anatase) of the prepared nano-photocatalyst were characterised using X-ray diffraction, selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) analysis. Furthermore, the morphological details and elemental content of the sample were studied via scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. Additionally, the optoelectronic features of all of the prepared specimens were measured via UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), impedance and Mott-Schottky studies. After successful characterisation, their photocatalytic performance was tested towards dinitrogen photo-fixation and tetracycline hydrochloride (TCH) degradation under visible light illumination. Moreover, the effective charge separation and greater availability of the active surface area led to the robust photocatalytic activity of the fabricated B-CT compared to the CT and S-CT samples, which correlates well with the PL, impedance and surface area analysis. B-CT displays the highest photocatalytic activity, i.e. 32.38 μmol L -1 (conversion efficiency = 0.076%) of ammonia production, and 95% tetracycline hydrochloride (10 ppm) degradation. Here, we have effectively designed a novel and productive pathway towards the enhancement of the photocatalytic performance of visible photon active TiO 2 -based materials for energy and environmental sustainability., Competing Interests: There is no conflict of interest., (This journal is © The Royal Society of Chemistry.)

For better exciton separation and high catalytic activity, the most trailblazing stratagem is to construct defect engineered low-dimensional p-n heterojunction framed photocatalytic systems. In this context, we have developed a rod-sheet (1D-2D) p-n heterojunction of MCeO 2 -BiFeO 3 by a simple hydrothermal method and scrutinized its photocatalytic performance toward N 2 fixation and phenol/Cr(VI) detoxification. The intimate contact between MCeO 2 and BiFeO 3 in the junction material is well established via X-ray diffraction (XRD), UV-vis diffuse reflectance spectrosopy (DRS), transmission electron microscopy (TEM), and photoelectrochemical studies. Further, scanning electron microscopy (SEM) and TEM pictures clearly support the decoration of MCeO 2 nanorods over BiFeO 3 sheets and also depict the junction boundary. Additionally, photoluminescence (PL), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and Raman measurements give solid evidence toward the presence of an oxygen vacancy. Moreover, the Mott-Schottky result indicates a feasible band edge potential favoring the p-n heterojunction with a built-in electric field between BiFeO 3 and MCeO 2 favoring a double charge dynamic. The MCeO 2 -BFO p-n junction displays a notable catalytic activity, i.e., 98.2% Cr(VI) reduction and 85% phenol photo-oxidation, and produces 117.77 μmol h -1 g -1 of ammonia under light irradiation. Electrochemical analysis suggests a four-electron/five proton-coupled N 2 photoreduction pathway. The designed oxygen vacancy oriented p-n heterojunction suffering double charge migration shows significant catalytic performance due to effective electron-hole separation as justified via PL, electrochemical impedance spectra (EIS), and Bode phase analysis.

To surmount incompatibility provoked efficiency suppression of an anisotype heterojunction and to pursue an improved intrinsic photocatalytic activity by manipulating oriented transfer of photoinduced charge carriers, an In 2 S 3 /BiVO 4 (1:1) n-n isotype heterojunction was fabricated successfully through a simple two-step calcination method, followed by a wet-chemical deposition method. The formation of an n-n isotype heterojunction was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and UV-visible diffuse reflectance spectroscopy. The photocatalytic efficiency of the In 2 S 3 /BiVO 4 catalyst was examined over degradation of oxytetracycline hydrochloride (O-TCH) and oxygen (O 2 ) evolution reaction. Consequently, an n-n In 2 S 3 /BiVO 4 isotype heterojunction exhibits a superior O-TCH degradation efficiency (94.6%, 120 min) and O 2 evolution (695.76 μmol, 120 min) of multiple folds as compared to the pure BiVO 4 and In 2 S 3 solely. This is attributed to the proper band alignment and intimate interfacial interaction promoted charge carrier separation over the n-n isotype heterojunction. The intimate interfacial contact was confirmed by transmission electron microscopy (TEM), high-resolution TEM, and field emission scanning electron microscopy analysis. The proper band alignment was confirmed by Mott-Schottky analysis. The photoelectrochemical linear sweep voltammetric study shows a superior photocurrent density (269 μA/cm 2 ) for In 2 S 3 /BiVO 4 as compared to those for pristine BiVO 4 and In 2 S 3 , which is in good agreement with the photocatalytic results. Furthermore, the superior charge antirecombination efficiency of the n-n isotype heterojunction was established by photoluminescence, electrochemical impedance spectroscopy, Bode analysis, transient photocurrent, and carrier density analysis. The improved photostability of the heterojunction was confirmed by chronoamperometry analysis. An orderly corelationship among physicochemical, electrochemical, and photocatalytic properties was established, and a possible mechanistic pathway was presented to better understand the outcome of the n-n isotype heterojunction. This study presents an effective way to develop new n-n isotype heterojunction-based efficient photocatalysts and could enrich wide applications in other areas., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

The abolition of environmental pollutants and production of hydrogen (H 2 ) from water using a heterogeneous photocatalyst is a demanding science of the current scenario to solve the increasing environmental pollution and worldwide energy catastrophe in modern life. To validate this purpose, the design of low-cost and durable semiconductor-based photocatalysts with great light absorption capacity becomes the most challenging issue for researchers. Regarding this, herein the phosphotungstic acid (HPW)-anchored Zr 6 O 4 (OH) 4 (BDC) 6 (UiO-66) metal-organic framework (MOF), i.e., HPW@UiO-66, has been prepared by a hydrothermal method and is efficient, stable, and capable of harvesting solar energy toward the degradation of tetracycline hydrochloride (TCH) and H 2 production in the presence of a sacrificial donor. The ionic interaction between HPW and UiO-66 plays a key role toward the photostability and charge-transfer mechanism of the composite and is well characterized with X-ray diffraction, UV diffuse-reflectance spectroscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy. A total of 30 wt % HPW@UiO-66 shows a maximum degradation of about 87.24% of a 20 ppm TCH solution in 60 min of solar-light irradiation and about 353.89 μmol/h of H 2 production. The conduction- and valence-band potentials are well characterized with Mott-Schottky measurement and a delay charge recombination process through electrochemical impedance spectroscopy. The proposed mediator-free Z-scheme-oriented electron-hole migration route is well supported by photoluminescence, and the scavenger test well explains the better charge-carrier separation and high catalytic performance of the prepared composite. This research will bestow an advantageous blueprint to fabricate novel and challenging photocatalysts toward the photocatalytic treatment of environmental pollutants and H 2 evolution.

In the present study, a series of Ce2Zr2O7@rGO nanocomposites were synthesized using a simple solution combustion method followed by a photoreduction technique. The as-prepared samples were well characterised using various analytical techniques to determine the morphological, optical, structural, electrochemical and compositional properties. The presence of oxygen defects was observed from Raman and photoluminescence spectra. The photoreduction of GO to rGO was determined from Raman and Fourier-transform infrared (FTIR) spectroscopy results. The role of rGO proved to be quite significant for the enhanced photocatalytic activity of the nanocomposites. The synergistic communication between Ce2Zr2O7 and rGO accelerates the photoreduction of 4-nitrophenol along with the degradation of ciprofloxacin under visible light irradiation. Of the rGO nanocomposites, 3 wt% GO loaded Ce2Zr2O7 reduces 99% of 20 ppm of 4-nitrophenol to 4-aminophenol in 120 min and decomposes 10 ppm of ciprofloxacin by up to 89% in 60 min. The significant enhancement in the activity of the Ce2Zr2O7@rGO nanocomposite was ascribed to the effective charge separation of excitons through π-conjugation of graphene at the interface, which is well supported by the impedance, photoluminescence and photocatalytic results.