Visible Light Response Research Articles

Photocatalytic degradation performance of antibiotics by WO3/α-Fe2O3/zeolite type II heterojunction with core-shell structure.

The accumulation of antibiotics in the environment can be harmful to human health, and research on their disposal technologies is of increasing interest. In this study, WO3/α-Fe2O3/zeolite (WFZ) type II heterojunction composites with core-shell structures were prepared by coupling WO3 semiconductors with visible-light photocatalytic activity with α-Fe2O3 via hydrothermal synthesis using zeolite as a carrier for the adsorption of synergistic photocatalytic degradation of antibiotics in wastewater. X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), specific surface, and porosity measurements were used to characterize the structure of WFZ type II heterojunction. The performance of WFZ heterojunction for the visible photocatalytic degradation of antibiotics (tetracycline hydrochloride (TCH), ciprofloxacin (CIP), and levofloxacin hydrochloride (LVF)) was investigated. Through four photocatalytic cycles, the catalyst exhibited excellent durability and stability. This was attributed to the core-shell structure and type II heterojunction promoting the effective separation of photogenerated carriers and the extended visible light response range, which resulted in the best photocatalytic activity of the catalyst under visible light irradiation. Radical trapping experiments showed that superoxide radicals (•O2-) and hydroxyl radical (•OH) were the main active species that played a major role in the photocatalytic degradation. These findings show that the synthesized WFZ type-II heterojunction can be used as a reliable visible-light-responsive photocatalyst for the treatment of antibiotics in wastewater.

Efficient N-P type charge compensatory synergistic effect for hydrogen production from water splitting: Theoretical design of V/Nb-Re co-doping MoX(X=S or Se)2 photocatalyst

The photocatalytic hydrogen evolution reaction (HER) is a promising method for solving the current environmental and energy crisis. Photocatalysts based on two-dimensional (2D) transition metal dichalcogenides (TMDCs) have received extensive attention in this field, and methods such as doping have been developed to further improve their photocatalytic efficiency. However, the photocatalytic efficiency is limited by the fact that the photogenerated carriers in a single doping system can easily recombine at impurity levels. Designing crystal structures of 2D TMDCs that can efficiently split water for hydrogen evolution is an important problem to solve for photocatalytic efficiency. Herein, we design the crystal structures of MoX(X=S or Se)2 co-doped with V/Nb and Re atoms using the density functional theory (DFT). Through N-P type co-doping, we deduce that this charge compensation effect indeed eliminates the impurity levels introduced by single-atom doping, not only expanding the visible light response range but also matching the thermodynamic conditions of photocatalytic water splitting, exhibiting excellent HER performance. The successful design of a V/Nb-Re co-doped MoX(X=S or Se)2 crystal structure is a key step for the practical application of 2D TMDC-based photocatalysts.

A comprehensive review on tailoring factors of porous bismuth oxyhalide photocatalysts for wastewater treatment application

BackgroundPhotocatalysis is a green, environmentally friendly approach for converting organic contaminants into harmless byproducts. Especially, Bismuth oxyhalides (BiOX, where X = Cl, Br and I) have emerged as promising photocatalysts for wastewater treatment due to their layered-by-layered structure, strong chemical stability and nontoxicity in compare to other metal oxides, which makes the photocatalyst advantageous for photocatalytic application. MethodsThis review provides an overview of recent developments in the synthesis and application of BiOX-based porous photocatalysts for the removal of organic contaminants from wastewater. Firstly, morphology-controlled synthesis of BiOX in degradation of organic contaminants. Then, modulation of electronic structure through doping, facet engineering and surface engineering has been highlighted for better photocatalytic applications. Furthermore, fabrication of diverse heterojunctions and co-catalyst loading upon BiOX are introduced, which can vary photocatalytic activity towards the degradation of organic contaminants. Significant findingsFinally, this review ended on the future trend and prospects of BiOX for the creation of potential high-performance photocatalysts in the near future. The porous structure of BiOX improved photocatalytic activity, pollutant degradation efficiency, visible light response charge carrier separation, and stability. Overall, bismuth oxyhalide photocatalysts have a lot of potential for effective and long-term wastewater treatment, and their development represents an important step towards addressing the global water pollution crisis.

Preparation of g-C3N4/{001}-AR-TiO2 composite photocatalyst and its degradation of tetracycline hydrochloride in sunlight

In this study, a {001}-AR-TiO2 catalyst (001-ART) was prepared by the sol–gel method, where g-C3N4 (CN) was combined with 001-ART to form g-C3N4{001}-AR-TiO2 (CN/001-ART). The crystal shape, morphology, optical properties, photoelectron-hole recombination, and specific surface area of the prepared materials were studied. Tetracycline hydrochloride (TTCH) was used as the target pollutant to investigate the catalytic properties, and the results showed that the specific surface area, visible light response range, band gap, photo-generated carrier separation ability, and average life span of 001-ART after CN composite integration increased. Furthermore, the degradation rate of TTCH within 120 min was 92.48%, and the reaction constant was 0.0215. After 5 repeated use cycles, the degradation rate of TTCH was 85.21%. We also found that OH and O2− were produced in CN/001-ART after exposure to light, and the electrons of 001-ART were excited to the conduction band and combined with the holes in the valence band of CN, thus, forming a Z-type heterostructure. This resulted in the higher activity of CN/001-ART.

Hydrothermal synthesis of Bi2WO6/Bi2O4 heterojunction with WO3 and NaBiO3·2 H2O powders as precursors to improve visible light photocatalytic degradation performance

The limited visible light response range and fast recombination rate of photoinduced carriers restrict the photocatalytic performance of Bi2WO6. Herein, a novel low temperature hydrothermal approach was developed to construct the Bi2WO6/Bi2O4 heterojunction with WO3 and NaBiO3•2 H2O powders as precursors and the latter as the only bismuth source. During the hydrothermal reaction, WO3 first reacts with NaBiO3·2 H2O to generate Bi2WO6 and then the residual NaBiO3·2 H2O converts into Bi2O4, in-situ forming the Bi2WO6/Bi2O4 heterojunction with the co-shared Bi atoms. The content of Bi2WO6 in the heterostructure can be facilely modulated by changing the amount of WO3 added. The construction of Bi2WO6/Bi2O4 heterojunction could not only extend the spectral response range but also improve the separation efficiency of photoinduced charges. Consequently, the photocatalytic degradation performance to tetracycline (phenol) for the optimal Bi2WO6/Bi2O4 heterostructure is 5.19 and 1.77 times (4.75 and 1.66 times) higher than that of single Bi2WO6 and Bi2O4 under visible light, respectively. The capture experiments of active species and electron spin resonance spectra demonstrate that radicals (·O2-) and holes (h+) are the first and second important active species, respectively, during the catalytic degradation. Our work provides a new idea for the fabrication of high-performance Bi2WO6-based junction photocatalysts.

Photo-crosslinked composite hydrogels with silver-deposited polymeric carbon nitride for boosting antibacterial activity

Rational design of antibacterial hydrogels is an important link to promote the multi-scenario application of this promising soft material. Herein, acrylamide and sodium alginate were selected as mixed monomers, silver-deposited polymeric carbon nitride nanosheets were used as a photoinitiator, pre-gelation was achieved under UV irradiation, and then a composite hydrogel was obtained through calcium ion crosslinking. The composite hydrogels exhibit good mechanical stability, structural stability in water and degradability under simulated physiological conditions. The composite hydrogels have the activity of killing Escherichia coli with or without light. The visible light response and surface plasmon resonance effect of the silver-deposited polymeric carbon nitride boosted the photocatalytic antibacterial activity of the composite hydrogels, and the bactericidal rate of the optimal sample reached 95.5% after 120 min of visible light irradiation. This work provides a constructive and green roadmap for the design of composite dual-network photoresponsive antibacterial hydrogels.

A Novel Organic/Inorganic Dual Z-Scheme Photocatalyst with Visible-Light Response for Organic Pollutants Degradation

The design of highly efficient organic/inorganic photocatalysts with visible-light response has attracted great attention for the removal of organic pollutants. In this work, the polyacrylonitrile (PAN) worked as the matrix polymer, while polyaniline (PANI) and Sb2S3–ZnO were used as organic/inorganic photocatalysts. The heterojunction PAN/PANI–Sb2S3–ZnO photocatalyst was prepared using electrospinning and surface ultrasound. PAN/PANI–Sb2S3–ZnO exhibited an excellent visible-light absorption intensity in the wavelength range of 400–700 nm. The maximum removal efficiencies of PAN/PANI–Sb2S3–ZnO for four organic dyes were all greater than 99%. The mechanism study showed that a dual Z-scheme could be constructed ingeniously because of the well-matched bandgaps between organic and inorganic components in the photocatalyst, which achieved efficient separation of photogenerated carriers and reserved photogenerated electrons (e−) and holes (h+) with strong redox ability. The active species •OH and •O2− played an important role in the photocatalytic process. The composite photocatalyst also had excellent stability and reusability. This work suggested a pathway for designing novel organic/inorganic composite photocatalysts with visible-light response.

The significantly boosted photodegradation of tetracycline over a novel hierarchical 0D/3D S-scheme heterojunction ZnSnO3/CdIn2S4

In recent years, constructing S-scheme heterostructure, as a novel and desirable strategy for the improvement of the photocatalytic performance, has attracted extensive interest. Herein, a novel hierarchical 0D/3D S-scheme heterostructure ZnSnO3/CdIn2S4 was constructed. The synthesized ZnSnO3/CdIn2S4 was characterized by various measures. The photodegradation of tetracycline (TC) was conducted under visible light to investigate the photocatalytic activity and stability of ZnSnO3/CdIn2S4. The impacts of pH and typical environmental factors on TC degradation were also explored. The S-scheme electron transfer mode in ZnSnO3/CdIn2S4 heterostructure was proposed based on Fermi level, in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS), and identification of the active species. The ZnSnO3/CdIn2S4 heterojunction exhibits outstanding photocatalytic activity and stability. The degradation efficiency and mineralization rate of TC reach 87% and 33.5%, respectively. After five reuses of ZnSnO3/CdIn2S4, degradation efficiency of TC decreases by only 6.5%. The rate constant (0.0140 min−1) of TC degradation over ZnSnO3/CdIn2S4 is 2.41 and 43.75 times as high as those over CdIn2S4 and ZnSnO3. The dramatically boosted activity of ZnSnO3/CdIn2S4 is owing to the superior visible-light response and the significantly accelerated separation and migration of the photoproduced charge carriers due to the construction of the hierarchical S-scheme heterojunction. Moreover, the photodegradation of TC is enhanced marginally with the rising pH and is slightly inhibited by the typical ions and natural organic matters (NOM). This work brings a new strategy to design highly efficient photocatalysts applied in environmental restoration.

Reasonable decoration of CuO/Cd0.5Zn0.5S nanoparticles onto flower-like Bi5O7I as boosted step-scheme photocatalyst for reinforced photodecomposition of bisphenol A and Cr(VI) reduction in wastewater

Building S-scheme heterostructures is a sophisticated approach to receiving outstanding catalysts for environmental detoxification. Herein, ternary CuO/Cd0.5Zn0.5S/Bi5O7I (CO/CZS/BOI) nanocomposites were constructed by in-situ decorating of CuO and Cd0.5Zn0.5S nanoparticles onto Bi5O7I micro-sphere in a facile route. The optimal CO/CZS/BOI reflected reinforced bisphenol A (BPA) photo-oxidation (95% in 70 min) and Cr(VI) photo-reduction (96.6 in 60 min) under visible light. Besides, CO/CZS/BOI afforded 5.10 (4.44), 4.42 (3.71), and 6.60 (5.27) fold reinforcement in the BPA (Cr(VI)) photo-reaction rate compared to BOI, CZS, and CO, respectively. This behavior was linked to the development of S-scheme mechanisms resulting from the co-effects of BOI, CZS, and CO in retaining the optimum redox capacity, facilitating the dissolution of photo-carriers, increasing reactive sites, and strengthening the visible-light response. The parameters influencing the catalytic reaction of CO/CZS/BOI, such as light intensity, catalyst dosage, and pH, were deeply studied. The quenching tests declared the prominent roles •O2− and •OH in the breaking down of BPA and the participation of electrons and •O2− in the photocatalytic conversion of Cr(VI). The cyclic tests verified the robust photostability of CO/CZS/BOI, which is associated with the reintegration process between the free h+ coming from CZS and the photo-induced e– of CO and BOI in the S-scheme system. In conclusion, the present study provides a profound understanding of the photo-reaction mechanism of CO/CZS/BOI and introduces a novel concept for constructing a superior dual-Scheme system for efficient wastewater detoxification.

Synthesis of PbxCu1−xBi2O4 composites with enhanced visible-light-responsive photocatalytic degradation performance

The unintentional release of highly toxic dyes from various industrial sectors into aquatic environments caused an imminent threat to the aquatic ecosystem and human health. Therefore, it is highly imperative to develop efficient and sustainable treatment technologies. In this work, we have constructed a novel PbxCu1−xBi2O4 nanostructured composite through a facile hydrothermal method. The atomic ratio of Pb to Cu was systematically investigated. The optimized sample of Pb0.10Cu0.90Bi2O4 has a higher visible light responsiveness for the degradation of Congo red (CR) dye than that of CuBi2O4. The results show that CuBi2O4 has the least degradation potential for CR under optimal conditions (catalyst = 0.4 g/L, [CR] = 30 mg/L, pH = 5.0, T = 25 ± 2 °C), and 83.39% degradation was achieved in 80 min under visible light irradiation. Meanwhile, Pb0.10Cu0.90Bi2O4 photocatalyst has shown 99.23% degradation of CR dye. This enhancement in the degradation of CR was considered due to the increase in the surface area of Pb0.10Cu0.90Bi2O4 (67.32 m2/g) and exposed active sites compared with that of pure CuBi2O4 (49.73 m2/g). The insertion of Pb metal ions into basic framework of the CuBi2O4 leads to increase in the specific surface area of the material, resulting in enhanced degradation. Furthermore, the insertion of Pb metal ions also lowered the optical bandgap energy of the catalytic material, which enhanced the degrading potential of Pb0.10Cu0.90Bi2O4. The effect factors were further examined, including catalyst dosage, initial dye concentration, pH, temperature, and agitation rate. In addition, the effect of humic acid and interfering anions on CR degradation was also investigated. The results of these experiments show that these factors also influence the photocatalytic degradation of CR dye. Therefore, appropriate treatment of these factors would increase the wastewater treatment efficiency by the as-prepared Pb0.10Cu0.90Bi2O4 photocatalyst.

Multifunctional continuous solid solution Na0.9Mg0.45Ti3.55O8-Na2Fe2Ti6O16: Preparation, characterization, magnetism, dual absorption, adsorption, and photocatalysis

Multifunctional continuous solid solutions Na0.9Mg0.45Ti3.55O8-Na2Fe2Ti6O16 (NFMTO-x) were synthesized via a one-step hydrothermal method by controlling the ratio of Mg and Fe. The NFMTO-x continuous solid solutions share same monoclinic structure of space group C2/m and same morphology of long hexagonal nanosheets with Na0.9Mg0.45Ti3.55O8 (NMTO) and Na2Fe2Ti6O16 (NFTO). XPS and EDX results reveal five elements Na, Mg, Fe, Ti, and O in the continuous solid solutions to confirm the change in Mg and Fe contents. The NFMTO-x continuous solid solutions enjoy dual absorption, significantly expanding their visible light response in comparison with pure NMTO. The organic pollutant methylene blue (MB) was effectively degraded through the NFMTO-x adsorption and photocatalysis, which exhibits higher performances than the pure NMTO and NFTO. Effective adsorption towards dyes is an important prerequisite to promote photocatalytic effectivity. LC-MS and TOC tests at different times reveal that MB dye was effectively mineralized to some degradation intermediates. NFMTO-x samples also have a certain capacity for CO2 methanation, converting CO2 to CO and CH4. The magnetic properties let us easily collect the powders from water after photodegradation for recycling utilization. The electron spin resonance identified O2− as the important active group in photocatalytic degradation. This research provides a significant multifunctional material used in water purification.

Interfacial Charge Transfer Effects of MoS2/α-Fe2O3 Nano-Heterojunction and Efficient Photocatalytic Hydrogen Evolution under Visible-Light Irradiation.

Researchers have made efforts to develop high-productivity photocatalysts for photocatalytic hydrogen production to reduce the problem of a lack of energy. Bulk semiconductor photocatalysts mainly endure particular limitations, such as low visible light application, a quick recombination rate of electron-hole pairs, and poor photocatalytic efficiency. The major challenge is to improve solar-light-driven heterostructure photocatalysts that are highly active and stable under the photocatalytic system. In this study, the proposed nano-heterojunction exhibits a great capacity for hydrogen production (871.2 μmol g-1 h-1), which is over 8.1-fold and 12.3-fold higher than that of the bare MoS2 and bare α-Fe2O3 samples, respectively. It is demonstrated that the MoS2/α-Fe2O3 heterojunction gives rise to an enhanced visible light response and accelerated photoinduced charge carrier separation. This work provides an improved visible light absorption efficiency and a narrowed energy band gap, and presents a "highway" for electron-hole pairs to promote transfer and inhibit the combination of photoinduced charge carriers for the utilization of nano-heterojunction photocatalysts in the field of hydrogen production.

Efficient degradation of ciprofloxacin by a flower-spherical Bi2MoO6/BiOCl Z-type heterojunction photocatalyst enriched with oxygen vacancies

Ciprofloxacin (CIP) is difficult to degrade naturally, for example by microorganisms, and will persist in water bodies for a long period of time, seriously jeopardizing the ecological environment and human health. Photocatalysis has high practical application value as a green and efficient technology. However, the photogenerated electrons and holes of the photocatalysts are prone to complexation, which limits the degradation efficiency of photocatalysis. Therefore, in this work, spherical Bi2MoO6/BiOCl (OVs-BMO/BOC) Z-type heterojunction photocatalysts enriched with oxygen vacancies (OVs) were successfully synthesized by a hydrothermal-calcination method. A series of characterizations showed that the OVs-BMO/BOC photocatalysts could perform Z-type charge transfer, which increased the visible light response range and improved the separation efficiency of photogenerated electrons and holes, thus improving the degradation efficiency of CIP. Under visible light, the removal efficiency of OVs-BMO/BOC composites for CIP could reach 97.40% at 120 min. It has a quasi-primary rate constant of 0.03008, which is 4.1, 3.48, and 2.19 times higher than that of monomeric BOC, BMO, and BMO/BOC, respectively. Meanwhile, the good stability of OVs-BMO/BOC was verified, and its degradation efficiency could still reach 87.80% after four cycles. Finally, electron spin resonance analysis and trapping experiments were carried out, which demonstrated that a large number of OVs were produced by the BMO/BOC composite photocatalyst generated by calcination, and also identified that the OVs-BMO/BOC produced active substances (•OH, h+, and •O2−), which revealed the mechanism of degradation of CIP by the OVs-BMO/BOC. Our study provides a new way of thinking to achieve efficient elimination of antibiotics from wastewater.

Integrating Bi2MoO6 nanoflakes into TiO2 photoanode for efficient charge separation in photoelectrochemical water splitting

Achieving highly effective water splitting based on conventional TiO2 photoanode is challenging due to its poor visible light response and low electrical conductivity. Herein, a Bi2MoO6/TiO2 heterojunction with a suitable band structure is constructed to broaden light absorption and accelerate oxidation kinetics. In particular, the highest photocurrent density (0.35 mA cm−2 at 1.23 V vs. RHE) of Bi2MoO6/TiO2 is 2.1 times higher than that of pristine TiO2. The integrated Bi2MoO6 nanoflakes enrich more reactive sites and charge transfer tunnels. The surface hole injection efficiency and electron lifetime of Bi2MoO6/TiO2 are 1.4 and 5.5 times larger than those of bare TiO2, respectively. Additionally, the activation energy and charge transfer resistance of Bi2MoO6/TiO2 electrodes are decreased remarkably, dramatically promoting the separation of electron-hole pairs. This work offers a novel strategy for TiO2-based heterojunction with great potential for application in photoelectrochemical water splitting.

Fabricating fragmented intramolecular D-A integrated carbon nitride photocatalyts with elevating activity: Performance and mechanism analysis

Carbon nitride (CN) possesses great potential in photocatalytic solar-energy conversion for environmental pollution removal and hydrogen energy generation. However, pristine CN suffers unsatisfactory photocatalytic activity owing to insufficient visible light response, low activity sites exposure, lazy exciton separation and ready carrier recombination. In this work, fragmented intramolecular D-A integrated CN (FBCN) was contracted via a facile m-aminophenylboronic acid doping followed two-step post-processing. The intramolecular D-A integrated structure can strengthen exciton separation and carrier migration driving forces, while the fragmented nanoflakes structure with rich in-plane edges can shorten the migration distance of charge-to-surface in-plane and vertical direction, as well as expose more marginal active sites. The hydrogen evolution rate of optimized 25-FBCN photocatalyst reaches 2545 μmol h−1 g−1, which is 5.2 times higher than that of pristine CN and 1.3 times over the 25-BCN. The 25-FBCN can degrade 87% sulfamethoxazole, and the kinetic rate constant is 3.9 times higher than that of CN. The radical capture and ESR tests reveal stronger radical signals in 25-FBCN degradation system than that of CN. The MS and online FTIR present photodegradation pathway and intermediate, and in-site record functional groups variation during degradation reaction. The SEM/TEM/AFM/XPS/EPR, N2 adsorption-desorption and water contact analysis confirm the generation of smaller-sized nano fragments with rich in-plane edges. The UV–vis DRS/EIS/PCR/PL/TRPL and band structure verify that more effective charge dissociation/migration behavior of 25-FBCN than pure CN. Finally, DFT theoretical calculations and KPFM test further verify the generation of intramolecular D-A integrated structure and clarify the latent propel mechanism of performances.

Atomically dispersed Au confined by oxygen vacancies in Au-θ-Al2O3/Au/PCN hybrid for boosting photocatalytic CO2 reduction driven by multiple built-in electric fields

A new Au-θ-Al2O3/Au/PCN hybrid is fabricated by the collaborative design strategy of active site and assembled structure, which achieves highly efficient photocatalytic CO2 reduction (CO2R) performance. The energy band structure of PCN is adjusted significantly owing to the strong coupling effect of Au-θ-Al2O3/Au nanosheets intercalated in PCN nanosheets. The result brings about up-shift of CB, VB and Fermi energy level overall and decrease of bandgap, which is in favor of harvesting visible light, exciting VB electrons and increasing reduction ability. In addition, the multiple built-in electric fields are induced by electron diffusion effect between structural units, due to the tight interface contact in the Au-θ-Al2O3/Au/PCN hybrid, which can effectively promote the separation of photoinduced charge carriers. Furthermore, the atomically dispersed Au atoms confined by the oxygen vacancies in Au-θ-Al2O3/Au can provide the plenty of effective active sites for CO2R reaction, and meanwhile, the localized surface plasmon resonance (LSPR) effect induced by Au nanoparticles on Au-θ-Al2O3/Au can improve the visible light response and produce abundant hot electrons to contribute to CO2R reaction. As a consequence, the average CO evolution rate of over the optimizing 10 %-Au-θ-Al2O3/Au/PCN hybrid (7.76 μmol g-1h−1) reaches up to 3.53 times than that of PCN (2.20 μmol g-1h−1) in the CO2R reaction, and maintains basically stable operation within 7 cycles of running, suggesting the superior activity and recyclability.

Boosting photocatalytic H2 evolution on UIO-66-NH2/covalent triazine-based frameworks composites by constructing a covalent heterojunction.

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have been proved as efficient catalysts for photocatalytic hydrogen (H2) evolution, thanks to their tunable functionalities, permanent porosity, excellent visible light response, and physicochemical stability. Herein, a series of photocatalysts (termed NUBC) was fabricated by loading different amounts of Zr-UiO-66-NH2 (NU) onto a benzoic acid-modified covalent triazine-based framework (BC) based on post-synthetic covalent modification. The resulting NUBC catalysts exhibited a type-II Z-scheme heterojunction structure formed via the amide covalent bonds between the amine groups on NU and carboxyl groups on BC. The optimal loading of NU on BC is 30 wt.% (30NUBC) and the corresponding photocatalytic H2 evolution rate was 378 μmol h-1 g-1, almost 445 and 2 times than that of NU and BC, respectively. The synergistic effect between the type-II Z-scheme heterojunctions and amide bonds was conducive to boosting visible light harvesting and facilitating charge transportation and separation. Furthermore, the prepared NUBC catalysts show great reusability and stability. Overall, this work sheds light on the design of novel MOF/COF hybrid materials and provides a systematic exploration of their photocatalytic H2 evolution properties.

Unraveling the synergy of interface engineering α-MnO2/Bi2WO6 heterostructures and defective active sites for superdurable photocatalysis: Mechanistic insights into charge separation/transfer

The construction of visible-light-driven hybrid heterostructure photocatalysts is of great significance for environmental remediation, although the utilization of strong visible-light response photocatalysts with high efficiency and stability remains a major challenge. On the other hand, defect engineering is an excellent way to introduce metal cation vacancies in materials, thereby ensuing in highly enhanced catalytic performance. Inspired by this, we effectively constructed a built-in interface α-MnO2/Bi2WO6 heterostructure with abundant intimate interfaces and defective Mn3+/Mn4+ active sites for photocatalytic tetracycline hydrochloride (TC-HCl), hexavalent chromium Cr6+ reduction, and Escherichia coli (E. coli) inactivation. The experimental results, such as the active species test and X-ray photoelectron spectroscopy, indicated that the defective sites Mn3+/Mn4+, surface oxygen vacancies, and Bi(3+x)+ boosted the visible light absorption, and highly enhanced the photoinduced charge separation/transfer. Furthermore, experimental and DFT calculations reveal the high charge density at the built-in interface heterostructure and the Z-scheme charge transfer mechanism during the photocatalytic process. The results further reveal that O2− and 1O2 are the main reactive active species contributing to the photocatalytic reaction. The exceptional TC-HCl decomposition activity of the α-MnO2/Bi2WO6 heterostructure (97.56%, 2.31, and 2.04 times higher than bulk), enhanced reaction kinetics (Kapp = 0.041 min−1, 6.4, and 5.2 times higher than bulk), removal rate of 80.3%, Cr6+ reduction to Cr3+ (98.56%, Kapp = 0.0599 min−1), and almost 100% bacterial inactivation compared to bulk α-MnO2 (42.22%) and Bi2WO6 (47.76%), were mainly due to the enhanced charge separation/transfer at the built-in interface and high charge density. This study opens new horizons for constructing Z-scheme MnO-based interface heterostructures with abundant defect sites for exceptional photocatalytic applications.

Thermally assisted in situ synthesis of C3N5/TiO2 S-scheme heterojunctions with enhanced visible light response for photocatalytic hydrogen precipitation

Nitrogen-rich C3N5 has emerged as a promising visible light catalyst due to its narrow band gap. Nevertheless, its practical application is hindered by the rapid recombination of photogenerated carriers. To address this limitation and enhance the photocatalytic performance of C3N5-based photocatalysts, one effective measure involves the construction of heterojunctions in conjunction with other semiconductors. In this work, the C3N5/TiO2 S-scheme photocatalysts was constructed by matching C3N5 with a more negative conduction band (CB) and TiO2 with a more positive valence band (VB). Photoelectric tests exhibited that the prepared photocatalysts possessed enhanced visible light photoresponsivity as well as excellent charge separation and transport efficiencies. The characterization results of XPS and EPR confirmed that the existence of internal electric field and the unique S-scheme charge transfer mechanism, which achieves overall spatial separation of effective photogenerated carriers and accelerates the recombination of redundant electrons and holes. The photocatalytic hydrogen production performance of the TCN2 is 6.9 times and 30 times higher than that of C3N5 and TiO2, respectively, which is ascribed to the unique charge transfer mechanism of the S-scheme heterojunction and significantly enhanced photocatalytic activity. The simple construction of S-scheme heterojunctions in this work provides a new strategy for research in other fields.

Efficient hydrogen production over Bi2Te3-modified TiO2 catalysts: A first principles study

First-principles calculations based on the HSE06 exchange-correlation functional were employed to investigate the electronic properties of the TiO2 heterostructure modified with Bi2Te3 co-catalyst. The objective was to gain a deeper understanding of the role of this material in overall photocatalytic hydrogen evolution reaction (HER). We meticulously examined the combined effects of Bi2Te3 and TiO2 on electronic properties, charge transfer and visible light response. Density of states analysis revealed that the Bi2Te3/TiO2 interface structure introduces optimal band offsets, which facilitates the migration of photo-generated electrons in heterostructure, effectively suppressing electron-hole recombination. Furthermore, the Dirac cone characteristics of Bi2Te3 reduced the effective mass of the photo-generated electrons, promoting rapid electron-hole separation and thereby enhancing the utilization efficiency of photo-generated carriers. Additionally, compared to standalone TiO2 films, the Te atoms in Bi2Te3 within the heterostructure introduce extra catalytic active sites, further boosting its photocatalytic HER efficiency. This research not only deepens our understanding of the photocatalytic HER process in the Bi2Te3/TiO2 heterostructure, but also provides a robust theoretical foundation for the design of Bi2Te3-based co-catalysts.