Solar Light Driven Pure Water Splitting on Quantum Sized BiVO4 without any Cocatalyst

The construction of Z-scheme heterojunction ZnIn2S4@CuO with enhanced charge transfer capability and its mechanism study for the visible light degradation of tetracycline

In this study, copper oxide (CuO) was prepared by the microwave-assisted hydrothermal technique subsequently, CuO was grown in situ onto different rare metal compounds to prepare Z-scheme heterojunctions to improve the degradation efficiency of tetracycline (TC) in water environments. Various characterization proved the successful synthesis of all composite materials, and the formation of tight heterojunction interfaces, among which, the core-shell structure ZnIn2S4@CuO exhibited excellent photocatalytic degradation capability. Research results indicated that the degradation efficiency of ZnIn2S4@CuO for TC (50 mg/L) in the water environment reached 95.8 %, and the degradation rate is 2.41 times and 12.93 times that of CuO and ZnIn2S4 alone, respectively, the reason is because of the introduction of ZnIn2S4, Z-scheme heterojunction structures and internal electric field (IEF) is constructed and formed to extend the visible light response range of photocatalysts to improve electron-hole separation efficiency, and enhance charge transfer. In addition, ZnIn2S4@CuO-2 exhibited good stability and reproducibility, with no significant loss of activity after five cycles. Finally, the precise locations of free radical attack on TC were investigated by the combined use of high-resolution mass spectrometry (HR-MC) and frontier electron densities (FEDs), and a reasonable degradation pathway was provided. The results of this research provide a new and viable approach to overcome the limitations of conventional photocatalytic materials in terms of limited visible light absorption range and fast carrier recombination rates, which offers promising prospects for a wide range of applications in the field of wastewater purification.

Hierarchically, Low Band Gap Nanohybrid InVO4-CdS Heterojunction for Visible Light-Driven Toxic Organic Dye Degradations

The synthesis of InVO4-CdS heterojunction photocatalysts has been achieved by a novel two-step approach, including a microwave-assisted technique, followed by a moderate hydrothermal method, marking the first successful instance of such a synthesis. X-ray diffraction, field-emission scanning electron microscopy, elemental color mapping, high-resolution transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, Raman analysis, photoluminescence, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller were employed to investigate the crystal structures, surface morphologies and particle sizes, chemical compositions, and optical characteristics of the as-synthesized materials. The research results indicated that the heterojunction InVO4-CdS, as synthesized, consisted of InVO4 microrods with an average size of around 15 nm and cadmium sulfide (CdS) microflowers with a diameter of 1.5 μm. Furthermore, all of the heterojunctions had favorable photoabsorption properties throughout the visible-light spectrum. The photocatalytic efficiency of the samples obtained was thoroughly assessed by the degradation of acid violet 7 (AV 7) under visible light irradiation with a wavelength greater than 420 nm. The photocatalytic efficiency for the decomposition of AV 7 was greatly enhanced in the InVO4-CdS (IVCS) heterojunctions when compared to prepared bare InVO4 and CdS. Additionally, it was observed that the composite material consisting of IVCS 3 wt % InVO4 combined with CdS exhibited the most significant enhancement in catalytic effectiveness for the photodegradation of AV 7 dye. Specifically, the catalytic performance of this composite material was found to be around 69.4 and 76.2 times greater than that of pure InVO4 and CdS, respectively. Furthermore, the experimental procedure including active species trapping provided evidence that h+ and •O2- radicals were the primary active species involved in the photocatalytic reaction process. Additionally, a potential explanation for the improved photocatalytic activity of the InVO4-CdS heterojunction was presented, taking into account the determination of band positions.

Photocatalytic chitosan-based bactericidal films incorporated with WO3/AgBr/Ag and activated carbon for ethylene removal and application to banana preservation

Ethylene (C2H4) and pathogenic microorganisms are the two major causes of the deterioration of postharvest fruits and vegetables (F&V). Hence, the development of active packaging with C2H4 scavenging and bactericidal activities is urgently desirable. Herein, a novel photocatalytic active film (CS-PC-AC) is developed for banana preservation by incorporating WO3/AgBr/Ag photocatalyst (PC) and activated carbon (AC) into chitosan (CS). The fabricated PC is a ternary Z-scheme heterojunction and its high photocatalytic activity is achieved by the bridge of Ag between WO3 and AgBr through rapid transfer and separation of photogenerated electrons and holes. AC plays an indispensable role in the photocatalytic reaction through molecule adsorption and transport. PC and AC are hydrogen bonded with chitosan and their incorporation has slight effect on film's thermal stability but decreases the film's mechanical and barrier properties to some extent. CS-PC-AC exhibits strong bactericidal activity (killing ~100 % of Escherichia coli and Staphylococcus aureus within 3 h) and good C2H4 scavenging activity (C2H4 scavenging rate of 49 ± 2 %) under visible light irradiation, which can extend the banana shelf-life by at least 50 % at 25 °C. These results indicate the good perspective of CS-PC-AC in the delay of the deterioration of postharvest F&V.

A Comprehensive Review on the Boosted Effects of Anion Vacancy in the Heterogeneous Photocatalytic Degradation, Part II: Focus on Oxygen Vacancy

Environmental problems, including the increasingly polluted water and the energy crisis, have led to a need to propose novel strategies/methodologies to contribute to sustainable progress and enhance human well-being. For these goals, heterogeneous semiconducting-based photocatalysis is introduced as a green, eco-friendly, cost-effective, and effective strategy. The introduction of anion vacancies in semiconductors has been well-known as an effective strategy for considerably enhancing the photocatalytic activity of such photocatalytic systems, giving them the advantages of promoting light harvesting, facilitating photogenerated electron-hole pair separation, optimizing the electronic structure, and enhancing the yield of reactive radicals. This Review will introduce the effects of anion vacancy-dominated photodegradation systems. Then, their mechanism will illustrate how an anion vacancy changes the photodegradation pathway to enhance the degradation efficiency toward pollutants and the overall photocatalytic performance. Specifically, the vacancy defect types and the methods of tailoring vacancies will be briefly illustrated, and this part of the Review will focus on the oxygen vacancy (OV) and its recent advances. The challenges and development issues for engineered vacancy defects in photocatalysts will also be discussed for practical applications and to provide a promising research direction. Finally, some prospects for this emerging field will be proposed and suggested. All permission numbers for adopted figures from the literature are summarized in a separate file for the Editor.

The visible-light-driven photocatalytic reduction of Cr6+ using BiVO4: assessing the effect of Au deposition and the reaction parameters

In this work, fern-leaf-like BiVO4 was used to photocatalytically reduce Cr6+ in water. Nanosized BiVO4 displayed bandgap energy and specific surface area of 2.49 eV and 5.65 m2 g-1, respectively. Metallic Au nanoparticles were deposited on the BiVO4 to increase the photocatalytic performance. To optimize the reaction conditions, the sacrificial agents methanol, ethanol, formic acid, dimethyl sulfoxide, and KI were tested, while different catalyst dosages and Au loadings were assessed. The best sacrificial agent was formic acid, which was used at an optimal concentration of 0.01 mol L-1. The complete removal of Cr6+ was attained after 90 min of visible light irradiation using a catalyst dosage of 1.5 g L-1. Depositing metallic Au nanoparticles barely improved the photocatalytic performance, thus unmodified BiVO4 was used to remove Cr6+ in tap water. The matrix effect slowed the photocatalytic process, and the complete removal of Cr6+ was achieved in 120 min. Cr3+ and Cr6+ species were precipitated on the catalyst surface at the end of the photocatalytic process; still, BiVO4 displayed high stability after three reaction cycles.

Chemical bonding and facet modulating of p-n heterojunction enable vectorial charge transfer for enhanced photocatalysis

Heterojunctions have been proved to be the promising photocatalysts for hazardous contaminants removal, but the inferior interfacial contact, low carrier mobility and random carrier diffusion seriously hamper the photoactivity improvement of the conventional heterojunctions. Herein, SO chemically bonded p-n oriented heterostructure is fabricated via selectively anchoring of p-type Ag2S nanoparticles on the lateral facet of n-type Bi4TaO8Cl nanosheet. Such a p-n heterojunction engineering on specific facet of Bi4TaO8Cl semiconductor derives ingenious double internal electric field (IEF), which not only effectively creates the spatially separated oxidation and reduction sites, but also delivers the powerful driving forces for impactful spatial directed photocarrier transfer along the cascade path. Additionally, our experimental and theoretical analyses jointly signify that the interfacial SO bond could serve as an efficient atomic-level interfacial channel, which is conducive to encouraging the vectorial charge separation and migration kinetic. As a result, the Ag2S/Bi4TaO8Cl oriented heterojunction exhibits significantly enhanced visible light driven photocatalytic redox ability for tetracycline oxidation and hexavalent chromium reduction than those of single component and the traditional random/mixed heterojunctions. This study could provide a deeper insight into the synergistic effects of multi-IEF modulation and interfacial chemical bond bridging on optimizing the photogenerated carrier behaviors.

Reversible Stacking of 2D ZnIn2 S4 Atomic Layers for Enhanced Photocatalytic Hydrogen Evolution

It is technically challenging to reversibly tune the layer number of 2D materials in the solution. Herein, a facile concentration modulation strategy is demonstrated to reversibly tailor the aggregation state of 2D ZnIn2 S4 (ZIS) atomic layers, and they are implemented for effective photocatalytic hydrogen (H2 ) evolution. By adjusting the colloidal concentration of ZIS (ZIS-X, X = 0.09, 0.25, or 3.0 mg mL-1 ), ZIS atomic layers exhibit the significant aggregation of (006) facet stacking in the solution, leading to the bandgap shift from 3.21 to 2.66 eV. The colloidal stacked layers are further assembled into hollow microsphere after freeze-drying the solution into solid powders, which can be redispersed into colloidal solution with reversibility. The photocatalytic hydrogen evolution of ZIS-X colloids is evaluated, and the slightly aggregated ZIS-0.25 displays the enhanced photocatalytic H2 evolution rates (1.11 µmol m-2 h-1 ). The charge-transfer/recombination dynamics are characterized by time-resolved photoluminescence (TRPL) spectroscopy, and ZIS-0.25 displays the longest lifetime (5.55 µs), consistent with the best photocatalytic performance. This work provides a facile, consecutive, and reversible strategy for regulating the photo-electrochemical properties of 2D ZIS, which is beneficial for efficient solar energy conversion.

Photo-Activated Direct Catalytic Oxidation of Gaseous Benzene with a Cu-Connected Serial Heterojunction Array of Co3 O4 /Cux O/Foam Cu Assembled via Layer upon Layer Oxidation

The foam copper (FCu) has been first used as a promising supporting material to prepare a photo-activated catalyst of Co₃ O₄ /Cu_x O/FCu, in which the fine Co₃ O₄ particles are inlayed on the Cu_x O nanowires to form a Z-type heterojunction array connected by substrate Cu. The prepared samples have been used as a photo-activated catalyst to directly decompose gaseous benzene and the optimized Co₃ O₄ /Cu_x O/FCu demonstrates a 99.5% removal efficiency and 100% mineralizing rate within 15 min in benzene concentration range from 350 to 4000 ppm under simulate solar light irradiation. To track the reactive mechanism, a series of MO_x /Cu_x O/FCu (M = Mn, Fe, Co, Ni, Cu, Zn) is prepared and a novel photo-activated direct catalytic oxidation route is proposed based on the comparative investigation of material properties. Moreover, the approach grew in situ via layer upon layer oxidation on FCu dedicates to the extra lasting reusability and the easy accessibility in the diverse situations. This work provides a novel strategy for the preparation of Cu connected series multidimensional heterojunction array and a promising application for the quick abatement of the high-leveled concentration gaseous benzene and its derivatives from the industrial discharged flow or the accident scene's leakage.

Defect-enriched (H2PO4-, Cr3+)-α-Fe2O3/β-In2S3 composites for visible light degradation of 4-nitrophenol

In this work, the high-activity (H₂PO₄^-, Cr³⁺)-α-Fe₂O₃ (PCF) with abundant oxygen vacancies (OVs) and the high specific area was obtained by co-adding H₂PO₄^- and Cr³⁺. Defect-enriched PCF/β-In₂S₃ composites were prepared by low-temperature hydrothermal processes. The prepared composites exhibited improved photocatalytic degradation of 4-nitrophenol under visible light irradiation.The SO bond between PCF and β-In₂S₃ promoted the formation of tight heterojunction composites and increased the OVs concentration. Under the synergistic effect of photo-Fenton, defects, and heterojunction, the PCF/β-In₂S₃ composites effectively promoted the separation of photogenerated carriers and accelerated the production of active substances (•OH, •O₂^-, ¹O₂, and h⁺), leading to the improvement of photocatalytic-Fenton degradation performance. This work provided a new strategy for the preparation of highly efficient photocatalysts.

Synthesis of Zn3V2O8/rGO Nanocomposite for Photocatalytic Hydrogen Production

In this study, zinc vanadate/reduced graphene oxide (Zn3V2O8/rGO) composite has been synthesized via a simple approach. Advanced characterization techniques (powder X-ray, scanning electron microscopy, energy dispersive X-ray spectroscopy and ultraviolet-visible (UV-vis) spectroscopy) have been used to authenticate the formation of Zn3V2O8/rGO composite. Subsequently, Zn3V2O8/rGO was applied as photo-catalyst for hydrogen generation using photo-catalysis. The Zn3V2O8/rGO photo-catalyst exhibited a good hydrogen generation amount of 104.6 µmolg−1. The Zn3V2O8/rGO composite also demonstrates excellent cyclic stability which indicated better reusability of the photo-catalyst (Zn3V2O8/rGO). This work proposes a new photo-catalyst for H2 production application. We believe that the presence of synergistic interactions was responsible for the improved photo-catalytic properties of Zn3V2O8/rGO composite. The Zn3V2O8/rGO composite is an environmentally friendly and cost-effective photo-catalyst and can be used for photo-catalytic applications.

Increasing electron density by surface plasmon resonance for enhanced photocatalytic CO2 reduction

The photocatalytic CO₂ reduction reaction is a multi-electron process, which is greatly affected by the surface electron density. In this work, we synthesize Ag clusters supported on In₂O₃ plasmonic photocatalysts. The Ag-In₂O₃ compounds show remarkedly enhanced photocatalytic activity for CO₂ conversion to CO compared to pristine In₂O₃. In the absence of any co-catalyst or sacrificial agent, the CO evolution rate of optimal Ag-In₂O₃-10 is 1.56 μmol/g/h, achieving 5.38-folds higher than that of In₂O₃ (0.29 μmol/g/h). Experimental verification and DFT calculation demonstrate that electrons transfer from Ag clusters to In₂O₃ on Ag-In₂O₃ compounds. In Ag-In₂O₃ compounds, Ag clusters serving as electron donators owing to the SPR behaviour are not helpful to decline photo-induced charge recomnation rate, but can provide more electron for photocatalytic reaction. Overall, the Ag clusters promote visible-light absorption and accelerate photocatalytic reaction kinetic for In₂O₃, resulting in the photocatalytic activity enhancement of Ag-In₂O₃ compounds. This work puts insight into the function of plasmonic metal on enhancing photocatalysis performance, and provides a feasible strategy to design and fabricate efficient plasmonic photocatalysts.

Highly efficient removal of organic contaminant with wide concentration range by a novel self-cleaning hydrogel: Mechanism, degradation pathway and DFT calculation

A novel carbon nitride based self-cleaning hydrogel photocatalyst (KI-PCN gel, potassium and iodine co-doped carbon nitride confined in alginate) has been successfully constructed by a facile method. Fabricated photocatalyst showed enhanced synergistic adsorption-photocatalytic degradation property on a high concentration of methylene blue (HMB) because of enhanced carrier separation efficiency and improved light adsorption capacity of KI-PCN. As expected, the KI-PCN gel showed the highest apparent rate constant value ₍K_app =0.0310 min^-1), which was about 38.8 and 5.8 times as that of blank hydrogel (K_app=0.0008 min^-1) and PCN gel (K_app=0.0053 min^-1), respectively. Meanwhile, KI-PCN gel can continuously adsorb low concentration of MB (LMB), and the MB-adsorbed KI-PCN gel can self-clean under light irradiation. The bench-scale experiments simulating real river showed that KI-PCN gel can effectively and continuously remove LMB (0.1-20 ppm), indicating the possibility for the removal of contaminants in natural rivers. Furthermore, the possible degradation pathways were proposed by combining the density functional calculations (DFT) and intermediates identified by liquid chromatography-mass spectrometry (LC-MS). This work proposed a new perspective to acquire a novel self-cleaning and easily recyclable photocatalyst for treatment of wide concentration range organic wastewater as well as remediation of natural waterbody.

Type-II Heterojunction CdIn2S4/BiVO4 Coupling with CQDs to Improve PEC Water Splitting Performance Synergistically

Bismuth vanadate (BiVO₄) has been considered as a promising photoelectrocatalytic (PEC) semiconductor, but suffers from severe hole recombination, attributed to the short hole-diffusion length and the low carrier mobility. Herein, a type-II heterojunction CdIn₂S₄/BiVO₄ is designed to improve the photocurrent density from 1.22 (pristine BiVO₄) to 2.68 mA cm^-2 at 1.23 V vs the reversible hydrogen electrode (RHE), accelerating the bulk separation of photogenerated carriers by the built-in field from the matched energy band. With the introduction of CQDs, CQDs/CdIn₂S₄/BiVO₄ increases the photocurrent density to 4.84 mA cm^-2, enhancing the light absorption and cathodically shifting its onset potential, due to the synergetic effect of the heterojunction and CQDs. Compared with BiVO₄, CQDs/CdIn₂S₄/BiVO₄ promotes the bulk separation efficiency to 94.6% and the surface injection efficiency to 72.2%. Additionally, spin-coating of FeOOH on CQDs/CdIn₂S₄/BiVO₄ could further improve the PEC performance and keep a long stability for water splitting. The density function theory (DFT) calculations illustrated that the type-II heterojunction CdIn₂S₄/BiVO₄ could decrease the oxygen evolution reaction (OER) overpotential and accelerate bulk charge separation for the built-in field of the aligned band structure.

Regulating directional transfer of electrons on polymeric g-C3N5 for highly efficient photocatalytic H2O2 production

Graphite carbon nitride (g-C₃N₅) has been widely used in various photocatalytic reactions due to its higher thermodynamic stability and better electronic properties compared to g-C₃N₄. However, it is still challenging to endow g-C₃N₅ with high performance on photocatalytic hydrogen peroxide (H₂O₂) production. Herein, potassium and iodine are co-doped into g-C₃N₅ (g-C₃N₅-K, I) for photocatalytic production of H₂O₂ with high efficiency. As expected, the photocatalytic H₂O₂ production rate over the g-C₃N₅-K, I (2933.4 μM h^-1) reaches to 84.22 times as that of g-C₃N₅. The excellent photocatalytic H₂O₂ production activity is mainly ascribed to the co-doping of K and I, which significantly improves the capacity of oxygen (O₂) adsorption, selectivity of two-electrons oxygen reduction reaction (2e^- ORR) and separation efficiency of charge carriers. The density functional theory (DFT) calculations reveal that O₂ molecules are more conducive to being adsorbed on g-C₃N₅-K, I. Besides, the result of excited states further indicates that photo-generated electrons can be directionally driven to the adsorbed O₂ molecules, which are effectively activated to form H₂O₂. The findings will contribute to new insights in designing and synthesizing g-C₃N₅ based photocatalysts for the H₂O₂ production.

Coupling band structure and oxidation-reduction potential to expound photodegradation performance difference of biochar-derived dissolved black carbon for organic pollutants under light irradiation

Herein, the photodegradation performances difference of rice straw biochar-derived dissolved black carbon (DBC) for Tetracycline and Methylene Blue under visible light irradiation have been investigated. Tetracycline is easier degraded (degradation rate: 68%), followed by Methylene Blue (degradation rate: 14%). Singlet oxygen (¹O₂), superoxide radicals (O₂^-), holes (h⁺) and triplet DBC (³DBC*) are all make contribution for Tetracycline degradation by DBC, whereas just singlet oxygen (¹O₂), superoxide radicals (O₂^-) and ³DBC* are involved in the MB degradation by DBC. Singlet oxygen (¹O₂) maybe from the fulvic acid-like structure of DBC, while band structure of DBC can explain why superoxide radicals (O₂^-) and holes (h⁺) can be formed, whereas hydroxyl radicals (OH) cannot be formed. The oxidation-reduction potential results of Tetracycline and Methylene Blue suggests that Tetracycline is easier to be oxidized than Methylene Blue as well as Methylene Blue is easier to be reduced than Tetracycline. Furthermore, experimental and theoretical results support that DBC has good interaction with Tetracycline, but the interaction between DBC and Methylene Blue is very weak. This likely explain why holes (h⁺) is not detected for Methylene Blue degradation by DBC since Methylene Blue has not too much chance to meet holes (h⁺). TC photodegradation intermediates are less toxic than Tetracycline based on QSAR method. Two possible photodegradation path of Tetracycline by DBC are proposed according to HPLC-MS results.

The quantum size and spin-orbit coupling effects in BiVO4 with several atomic layers studied by density functional theory

The quantum size and spin-orbit coupling (SOC) effects play an important role in the electronic structure of photocatalytic materials with heavy elements such as Bi, Pb, Ir, Te, Sb, Sn, etc. How these two effects affect the conduction band (CB) or the valence band (VB) edge of a photocatalyst is not well understood. In this work, we investigated the quantum size and SOC effects on the CB and VB edges of BiVO₄ (BVO) with a thickness of several atomic layers. The BVO is a good water oxidation photocatalyst but doesn't have the hydrogen reduction ability. We find that when the thickness of a BVO layer is smaller than 0.64 nm, the CB edge upshifts significantly because of the quantum size effect. But after including the SOC effect, the CB edge remains almost unchanged. The CB edge of BVO upshifts above the equilibrium redox potentials for H₂/H₂O with a thickness of ∼0.64 to 1.28 nm. Within this thickness, only the quantum size effect dominates and the SOC effect is very weak. Both the quantum size and SOC effects are insignificant as the thickness of the BVO layers increases to be larger than 1.28 nm. The results presented here provide an essential step toward the understanding and rational design of photocatalysts from both the quantum size and SOC effects.

Fabrication of CdS/Ti3C2/g-C3N4NS Z-scheme composites with enhanced visible light-driven photocatalytic activity

The Ti₃C₂ and g-C₃N₄NS were obtained first, and the CdS/Ti₃C₂/g-C₃N₄NS Z-scheme composites were prepared via a facile hydrothermal synthesis, and their photocatalytic properties were investigated. The g-C₃N₄NS with a high surface area displayed higher adsorption and degradation capacity. Compared with Ti₃C₂/g-C₃N₄NS and CdS, the visible light photocatalytic activity of CdS/Ti₃C₂/g-C₃N₄NS composites was improved. The as-synthesized CTN-4:1 composite exhibited outstanding photocatalytic performance for degradation of orange II, approximately 3.2 and 10.7 times higher than that of Ti₃C₂/g-C₃N₄NS and CdS, respectively. The fabrication of CdS/Ti₃C₂/g-C₃N₄NS Z-scheme heterostructure using Ti₃C₂ as electron transfer medium improved the separation ability of the photoinduced e^--h⁺ pairs, thereby leading to the improvement of visible light-driven photocatalytic activity. This finding provides new insights into the construction of high efficiency Z-scheme heterostructure photocatalyst.

0D boron carbon nitride quantum dots decorated 2D Bi4O5I2 as 0D/2D efficient visible-light-driven photocatalysts for tetracyclines photodegradation

A series of 0D boron carbon nitride quantum dots (BCNQDs) modified 2D Bi₄O₅I₂ (0D/2D Bi₄O₅I₂/BCNQDs) composites were synthesized and applied to photodegradation of tetracyclines (TCs), including tetracycline (TC) and oxytetracycline (OTC). The Bi₄O₅I₂/BCNQDs (1) (1 mL BCNQDs) composite exhibits the highest photocatalytic performance for TCs degradation. The degradation rate constants of TC and OTC by the optimal sample were 4.95 and 2.17 times that of Bi₄O₅I₂, respectively. This can be attributed to the fact that the narrow bandgap Bi₄O₅I₂ is the electron acceptor, and the oxygen-containing functional group with the negative charge on BCNQDs can promote the formation of photoexcited holes, which makes the effective separation of photoexcited carriers easier. Furthermore, the active substance (h⁺ and ·O₂^-) is the major active substance for TCs photodegradation. On this basis, the possible photocatalytic reaction mechanism of Bi₄O₅I₂/BCNQDs (1) composite is proposed. This study provides a new idea for 0D/2D interface engineering of BCNQDs heterojunction.

Bismuth Redox Catalysis: An Emerging Main-Group Platform for Organic Synthesis

Bismuth has recently been shown to be able to maneuver between different oxidation states, enabling access to unique redox cycles that can be harnessed in the context of organic synthesis. Indeed, various catalytic Bi redox platforms have been discovered and revealed emerging opportunities in the field of main group redox catalysis. The goal of this perspective is to provide an overview of the synthetic methodologies that have been developed to date, which capitalize on the Bi redox cycling. Recent catalytic methods via low-valent Bi(II)/Bi(III), Bi(I)/Bi(III), and high-valent Bi(III)/Bi(V) redox couples are covered as well as their underlying mechanisms and key intermediates. In addition, we illustrate different design strategies stabilizing low-valent and high-valent bismuth species, and highlight the characteristic reactivity of bismuth complexes, compared to the lighter p-block and d-block elements. Although it is not redox catalysis in nature, we also discuss a recent example of non-Lewis acid, redox-neutral Bi(III) catalysis proceeding through catalytic organometallic steps. We close by discussing opportunities and future directions in this emerging field of catalysis. We hope that this Perspective will provide synthetic chemists with guiding principles for the future development of catalytic transformations employing bismuth.

Simple construction of GdBiVO4 assembled on reduced graphene oxide for selective and sensitive electrochemical detection of chloramphenicol in food samples

In the present study, the influence of phase purity and crystallinity on the electrochemical properties of well-designed GdBiVO4@rGO nanocomposite, fabricated by the facile hydrothermal method for the detection of chloramphenicol (CP), is reported.

Facile synthesis of amino-functionalized indium-based metal–organic frameworks and their superior light photocatalytic activity for degradation of tetracycline in water

The synthesized MIL-68(In)-NH2 photocatalyzed the degradation of tetracycline under visible light irradiation.

Understanding the morphology evolution of 1D BiVO4 nanoarrays from nanorods to nanocones with enhanced photocatalytic performance

The controllable synthesis of BiVO4 nanocone and nanorod arrays is reported. The morphology transformation of BiVO4 nanoarrays is accompanied with growth mechanism transformation and the tip structure results in superior photocatalytic performance.

NiO-TiO2 p-n Heterojunction for Solar Hydrogen Generation

Photocatalytic water splitting for hydrogen production has been widely recognized as a promising strategy for relieving the pressure from energy crisis and environmental pollution. However, current efficiency for photocatalytic hydrogen generation has been limited due to a low separation of photogenerated electrons and holes. p-n heterojunction with a built-in electric field emerges as an efficient strategy for photocatalyst design to boost hydrogen evolution activities due to a spontaneous charge separation. In this work, we investigated the effect of different preparation methods on photocatalytic hydrogen production over NiO-TiO2 composites. The results demonstrated that a uniform distribution of NiO on a surface of TiO2 with an intimate interfacial interaction was formed by a sol-gel method, while direct calcination tended to form aggregation of NiO, thus leading to an uneven p-n heterojunction structure within a photocatalyst. NiO-TiO2 composites fabricated by different methods showed enhanced hydrogen production (23.5 ± 1.2, 20.4 ± 1.0 and 8.8 ± 0.7 mmolh−1g−1 for S1-20%, S2-20% and S3-10%, respectively) as compared with pristine TiO2 (6.6 ± 0.7 mmolh−1g−1) and NiO (2.1 ± 0.2 mmolh−1g−1). The current work demonstrates a good example to improve photocatalytic hydrogen production by finely designing p-n heterojunction photocatalysts.

Construction of direct Z-scheme photocatalyst by the interfacial interaction of WO3 and SiC to enhance the redox activity of electrons and holes

The direct Z-scheme heterojunction structure benefits separation and migration of photoinduced carriers while maintaining original redox ability of each component. Nowadays, most Z-scheme structures are fabricated by g-C₃N₄ with other narrow band photocatalysts due to its low conduction band (CB). In this paper, SiC, another kind of photoelectric semiconductor with low CB, was employed to prepare direct Z-scheme photocatalyst with 2D WO₃ by simple water oxidation precipitation method. The component and interface band structure of Z-scheme heterojunction WO₃/SiC (WS) were verified by XPS, KPFM, Mott-Schottky method. The photodegradation efficiency and rate constant values of WS-1 for degrading RhB enhanced 2.5 and 5.3 times respectively compared with pristine WO₃. Radical capture experiments and ESR tests affirmed that WS-1 photocatalyst produced •OH and •O₂^－active species, which further confirmed the photogenerated carriers were transmitted through the Z-scheme mode in principle. Band structure investigation showed that the direct Z-scheme structure assembled by WO₃ with high valence band (VB) and SiC with low CB could maintain the high photocatalytic activity of active species. Therefore, this study offers a feasible method for construction of a novel and efficient direct Z-scheme photocatalyst.

F- regulate the preparation of polyhedral BiVO4 enclosed by High-Index facet and enhance its photocatalytic activity

The selective exposure of high-index facets at the surface of nanocrystals is an important and challenging research topic. Herein, polyhedral bismuth vanadate (BiVO₄) crystals predominantly surrounded by {2 1 3} and {1 2 1} high-index facets were fabricated through the engineering of high-index surfaces by fluorinion (F^-) mediated hydrothermal process. The as-prepared BiVO₄-0.2F (the feeding amount of NaF was 0.2 g) catalyst exhibited high apparent quantum efficiency of 17.7% under 420 nm light irradiation and 9.3 fold enhancement of O₂ evolution relative to its low-index counterparts. Moreover, the growth of high-index facets results in significant enhancement of hydroxyl radical (•OH) production, photocatalytic degradation of Rhodamine B (RhB) and photoelectrochemical (PEC) properties by the BiVO₄ polyhedron, relative to its low-index counterparts. The enhanced photoreactivity is the result of the synergistic effect of F^- on the surface of the BiVO₄ crystals and exposed high-index facets. For one thing, F^- on the surface of the BiVO₄ facilitate the separation and transport of photo-induced charge carriers. For another, the exposed high-index facets on polyhedral BiVO₄ provided much more reactive sites for photocatalytic reactions. Hopefully, this F^- mediated method will be a useful guideline for designing and synthesizing novel high-index faceted micro-/nanostructures for overcoming the practical energy and environment problems.

Fabricating intramolecular donor-acceptor system via covalent bonding of carbazole to carbon nitride for excellent photocatalytic performance towards CO2 conversion

Photocatalytic conversion of CO₂ into hydrocarbon fuels is an ideal technology of mitigating greenhouse effect caused by excessive emission of CO₂. However, the high recombination rate of electron-hole pairs and limited charge carriers transport speed constrained the catalytic performance of many semiconductor catalysts. In this contribution, a series of carbon nitride (g-CN) samples with intramolecular donor-acceptor (D-A) system were successfully prepared by introducing organic donor into their structures. Characterization results confirmed that carbazole was successful connected to the structure of g-CN via chemical bond. The formation of intramolecular D-A system greatly enlarged the light response region of g-CN-xDbc. In addition, a new charge transfer transition mode was formed in g-CN-0.01Dbc due to the incorporation carbazole, which enable it to use light with energy lower than the intrinsic absorption of g-CN. Meanwhile, the D-A structure led to the spatial separation of electrons and holes in g-CN-xDbc and significantly decreased the recombination rate of electron-hole pairs. The g-CN-0.01Dbc presented the best catalytic performance and the CO evolution rate was 9.6 times higher than that of g-CN. Moreover, the reaction was performed in water without any additive, which made it green and sustainable. DFT simulation confirmed the D-A structure and charge carrier migration direction in the prepared samples.

The fabrication of two-dimensional g-C3N4/NaBiO3·2H2O heterojunction for improved photocatalytic CO2 reduction: DFT study and mechanism unveiling

Photocatalytic CO₂ reduction is typically limited by the separation efficiency of photogenerated carriers for a single semiconductor. Thus, fabricating a two-dimensional/two-dimensional (2D/2D) heterojunction photocatalyst with high separation efficiency of photogenerated carriers has become a research priority. Here, a 2D/2D g-C₃N₄/NaBiO₃·2H₂O (CN/NBO) heterojunction photocatalyst was successfully synthesized for CO₂ photoreduction. With the assistance of the nature of CN, the 10CN/NBO composite showed the best performance with the production yield rates of 110.2 and 43.8 µmol g^-1 for CO and CH₄, respectively. Our experiments showed that the introduction of CN in CN/NBO composites, which is under the step-scheme (S-step) transfer direction of photogenerated carriers, could greatly inhibit the recombination of photogenerated e^--h⁺ pairs to prolong the carriers' lifetime, which was further confirmed by analysis of photoluminescence and photochemical characterization. As we expected, the CN/NBO composites show improved photocatalytic CO₂ reduction activity. The in situ infrared spectroscopy was also performed to study the intermediate products of the photocatalytic CO₂ reduction process. This study provides a way to design CN-based heterojunction photocatalysts for CO₂ photoreduction.

UV-light promoted formation of boron nitride-fullerene composite and its photodegradation performance for antibiotics under visible light irradiation

A series of C₆₀/BN composites have been synthesized, which can efficiently photodegrade TC under visible-light irradiation. Compared with C₆₀/BN-D6 and C₆₀/BN-V6 synthesized under dark and visible-light irradiation, C₆₀/BN-U6 synthesized under UV-light irradiation has the largest adsorption and photodegradation performance for TC under visible-light irradiation. FTIR and XPS characterizations suggest that C₆₀/BN composite is most likely the charge transfer composite, in which C₆₀ acts as electron acceptor and BN acts as electron donor. UV-light has the best promotion effect for the formation of C₆₀/BN. The adsorption quantity of TC by C₆₀/BN-U6 is 2.77 times higher than that of BN (131.05 mg g^-1 vs. 47.27 mg g^-1), being due to that C₆₀/BN-U6 has higher surface area than BN (135.7 m² g^-1 vs. 18.8 m² g^-1). The photodegradation of C₆₀/BN-U6 for TC follows Z-scheme heterojunction mechanism, as well as the photo-induced ·O^2- and h⁺ are the dominant photoactive species. Quantitative structure-activity relationship (QSAR) method is applied to evaluate the toxicity of TC and its photodegradation intermediates. The photodegradation rate of C₆₀/BN-U6 for TC is 19.19 times, 10.06 times, 5.83 times, 2.73 times and 1.84 times higher than that of TiO₂ (P25), g-C₃N₄, BNPA, BCNPA, and BN/TiO₂, respectively, implying that C₆₀/BN-U is a good metal-free photocatalyst.

A NIR-Responsive Phytic Acid Nickel Biomimetic Complex Anchored on Carbon Nitride for Highly Efficient Solar Hydrogen Production

A challenge in photocatalysis consists in improving the efficiency by harnessing a large portion of the solar spectrum. We report the design and realization of a robust molecular-semiconductor photocatalytic system (MSPS) consisting of an earth-abundant phytic acid nickel (PA-Ni) biomimetic complex and polymeric carbon nitride (PCN). The MSPS exhibits an outstanding activity at λ=940 nm with high apparent quantum efficiency (AQE) of 2.8 %, particularly λ>900 nm, as it outperforms all reported state-of-the-art near-infrared (NIR) hybrid photocatalysts without adding any noble metals. The optimum hydrogen (H₂ ) production activity was about 52 and 64 times higher with respect to its pristine counterpart under the AM 1.5 G and visible irradiation, respectively, being equivalent to the platinum-assisted PCN. This work sheds light on feasible avenues to prepare highly active, stable, cheap NIR-harvesting photosystems toward sustainable and scalable solar-to-H₂ production.

Green and efficient degradation of cefoperazone sodium by Bi4O5Br2 leading to the production of non-toxic products: Performance and degradation pathway

Photocatalytic process represents a promising approach to overcome the pollution challenge associated with the antibiotics-containing wastewater. This study provides a green, efficient and novel approach to remove cephalosporins, particularly cefoperazone sodium (CFP). Bi₄O₅Br₂ was chosen for the first time to systematically study its degradation for CFP, including the analysis of material structure, degradation performance, the structure and toxicity of the transformation products, etc. The degradation rate results indicated that Bi₄O₅Br₂ had an excellent catalytic activity leading to 78% CFP removal compared with the pure BiOBr (38%) within 120 min of visible light irradiation. In addition, the Bi₄O₅Br₂ presents high stability and good organic carbon removal efficiency. The effects of the solution pH (3.12 - 8.75) on catalytic activity revealed that CFP was mainly photocatalyzed under acidic conditions and hydrolyzed under alkaline conditions. Combined with active species and degradation product identification, the photocatalytic degradation pathways of CFP by Bi₄O₅Br₂ was proposed, including hydrolysis, oxidation, reduction and decarboxylation. Most importantly, the identified products were all hydrolysis rather than oxidation byproducts transformed from the intermediate of β-lactam bond cleavage in CFP molecule, quite different from the mostly previous studies. Furthermore, the final products were demonstrated to be less toxic through the toxicity analysis. Overall, this study illustrates the detailed mechanism of CFP degradation by Bi₄O₅Br₂ and confirms Bi₄O₅Br₂ to be a promising material for the photodegradation of CFP.

Boosting charge carrier separation efficiency by constructing an intramolecular DA system towards efficient photoreduction of CO2

The charge carrier excitation–recombination process between the donor and acceptor, and the photocatalytic reduction of CO₂ to CO over CN based DA composites.

Hydrothermal synthesis of a CoIn2S4/g-C3N4 heterojunctional photocatalyst with enhanced photocatalytic H2 evolution activity under visible light illumination

CoIn₂S₄, a black semiconducting material, possesses an outstanding visible light response and is employed to modify g-C₃N₄. A series of CoIn₂S₄/g-C₃N₄ heterojunctional photocatalysts are synthesized via a hydrothermal method, whereby cubic CoIn₂S₄ nanosheets are in situ immobilized on the surfaces of porous g-C₃N₄ nanosheets. Compared with the pristine g-C₃N₄ and CoIn₂S₄, under visible light (λ > 420 nm) irradiation, the CoIn₂S₄/g-C₃N₄ composite samples show markedly enhanced photocatalytic activity in hydrogen evolution. Among all of the samples, the 30% CoIn₂S₄/g-C₃N₄ sample shows the maximum H₂ evolution rates, 5.2 and 23.9 times higher than those of g-C₃N₄ and CoIn₂S₄, respectively. The efficient photocatalytic activity of CoIn₂S₄/g-C₃N₄ composite photocatalysts is attributed to the formation of an intimate heterostructure, which not only significantly facilitates charge migration, but also enhances visible light absorption. Moreover, a plausible photocatalytic mechanism for the composite photocatalyst has been elucidated. This research provides a novel hint for fabricating visible-light-responsive heterojunction photocatalysts with high performance for energy production.

Inhibition of Sn(ii) oxidation in Z-scheme BiVO4-QD@Sn3O4 for overall water splitting

In this work, it is verified that the preferred oxidation of Sn²⁺ in Sn₃O₄ during photocatalysis is the main cause for inefficient oxygen evolution. This could be inhibited by depositing BiVO₄-QDs attributed to Z-scheme charge transfer. This inhibition, along with promoted charge separation, leads to the achievement of overall water-splitting.