In-situ constructed 2D/2D ZnIn2S4/Bi4Ti3O12 S-scheme heterojunction for degradation of tetracycline: Performance and mechanism insights

Oxygen Vacancy Engineering of Bi4Ti3O12 Piezocatalyst Driving In Situ H2O2 Evolution for Self-Cycled Fenton-Like Degradation of Pollutants

In this work, we synthesized a Bi4Ti3O12 piezocatalyst with surface oxygen vacancy (BTO-Ov) to facilitate in situ hydrogen peroxide (H2O2) production and to establish a piezocatalytic self-cycled Fenton-like system for degradation of pollutants. Notably, the H2O2 evolution rate from the BTO-Ov catalyst reaches 558.8 μmol g-1 h-1 when utilizing pure water, significantly exceeding the rate obtained from pure BTO (274.6 μmol g-1 h-1). Furthermore, this rate can be enhanced to 1091.6 μmol g-1 h-1 with the addition of ethanol as a sacrificial agent and endows robust stability. In the piezocatalytic self-cycled Fenton-like system (BTO-Ov/Fe0), degradation efficiency of the methyl orange (MO) dye pollutant can achieve 91.9% within 20 min, coupled with a high kinetic coefficient of 0.117 min-1, indicating excellent catalytic activity. Relevant characterization results reveal that the introduction of oxygen vacancy improves piezoelectricity, reduces the band gap of BTO, enhances charge carrier transfer and separation, and facilitates a dual-channel reaction mechanism, thereby achieving superior piezocatalytic performance. This work not only facilitates the in situ synthesis of valuable chemicals but also offers a cost-effective and sustainable approach for wastewater purification.

Efficient Photocatalytic Degradation of Tetracycline Over a Novel Dual Z-Scheme Bi2O3/ZnTiO3-SrTiO3 Composite Photocatalyst

Tetracycline (TC) is a broad-spectrum antibiotic, and its introduction into the environment is known to cause serious water pollution issues and can result in the evolution of drug-resistant genes and superbugs. In this study, a new ZnTiO3-SrTiO3 double perovskite composite photocatalyst, synthesized using a simple molten salt method, was found to exhibit excellent performance in the photocatalytic degradation of TC in an aqueous solution under visible-light photoirradiation at λ = 420 nm. Individually, ZnTiO3 and SrTiO3 were identified as being inactive in the same reaction. However, the addition of Bi2O3 to the ZnTiO3-SrTiO3 composite (Bi2O3/ZnTiO3-SrTiO3) formed a dual-Z-scheme heterojunction, achieving 87.1% photocatalytic degradation rate of TC within 60 min. The obtained reaction rate constant (k = 0.03052 min-1) was 9.5 and 1.62 times higher than those achieved using the individual SrTiO3 (k = 0.00321 min-1) and ZnTiO3-SrTiO3 (k = 0.01882 min-1) species, respectively. Furthermore, a potential degradation pathway and mechanism for TC degradation using the Bi2O3/ZnTiO3-SrTiO3 composite photocatalyst was proposed. Overall, this approach provides a cost-effective and efficient method for preparing dual Z-scheme heterojunction photocatalysts.

Visual Location of Oxygen Vacancies on Bismuth Titanate Nanosheets with Periodic Quantum Well and Promoting H2O2 Photosynthesis

Oxygen vacancy (OV) defect engineering plays a crucial role in enhancing photocatalytic efficiency. However, the direct visual characterization of oxygen vacancies still remains technically limited. Herein, a bismuth titanate (Bi4Ti3O12, BTO-OV) model photocatalyst containing oxygen vacancies is constructed through density functional theory (DFT) calculations to reveal the influence mechanism of distinctive periodic quantum well and oxygen vacancies on the charge transfer behavior in BTO. Notably, the distribution of oxygen vacancies is directly observed using the low-dose integrated differential phase contrast-scanning transmission electron microscopy (iDPC-STEM), providing visual evidence for the location of these oxygen vacancies in BTO-OV. Furthermore, the theoretical calculation results are verified by characterizing the photoelectric properties and conducting performance tests on the hydrogen peroxide (H2O2) photosynthesis. Specifically, the oxygen vacancies and distinctive periodic quantum well in BTO-OV accelerate charge separation, leading to a H2O2 photosynthesis efficiency reaching 5278 µm g-1 h-1, which is 5 times that of the original BTO. This work offers theoretical and experimental references for the visual characterization of oxygen vacancies and the improvement of the charge transfer mechanism.

Construction of a Hierarchical Core-Shell Z-Scheme Two-Dimensioanl/Two-Dimensional ZnIn2S4@TpBpy Heterostructure for Photocatalytic Reduction of U(VI)

The essential nature of the photocatalytic process is charge transfer. To optimize the spatial separation of photogenerated electron-hole (e--h+) pairs for high-performance catalytic efficiency, in this work, we have successfully prepared hierarchical core-shell two-dimensional (2D)/2D ZnIn2S4@TpBpy (ZIS@TpBpy) with well-matched Z-scheme interfacial charge transfer channels for uranium (U(VI)) photoreduction. The Z-scheme electron transfer configuration was confirmed by internal electric field (IEF) formation analysis, XPS characterization, and DMPO spin-trapping EPR spectroscopy. With large specific surface area and abundant active sites, the ZIS@TpBpy composite achieved a U(VI) extraction rate of 94.08%. In addition, the removal rate constant of ZIS@TpBpy (0.0137 min-1) was 2.05 and 4.28 times higher than those of TpBpy (0.0067 min-1) and ZnIn2S4 (0.0032 min-1), respectively. First, the combination of organic and inorganic components expanded the range of visible light absorption and utilization. Afterward, under visible-light irradiation, more photogenerated e--h+ pairs dissociated and migrated to the ZnIn2S4 surface driven by the IEF and Z-scheme heterostructure. Simultaneously, the synergistic effect between the polarization potential generated by the IEF in the ZIS@TpBpy composite and abundant active sites (N and O atoms) in the TpBpy framework further accelerated the depletion and translocation of photogenerated e--h+ pairs, which significantly improved the efficiency of photocatalytic reduction of U(VI).

Enhanced Degradation of Oxytetracycline Antibiotic Under Visible Light over Bi2WO6 Coupled with Carbon Quantum Dots Derived from Waste Biomass

Improving the photogenerated carrier separation efficiency of individual semiconductor materials has always been a key challenge in photocatalysis. In this study, we synthesized a novel photocatalytic material, N-CQDs/UBWO, in situ by combining nitrogen-doped carbon quantum dots (N-CQDs) derived from discarded corn stover with ultrathin Bi2WO6 nanosheets (UBWO). Detailed characterization indicates that the random distribution of N-CQDs on the UBWO surface increases the specific surface area of UBWO, which is beneficial for the adsorption and degradation of oxytetracycline (OTC). More importantly, N-CQDs act as electron acceptors, promoting the effective separation of photogenerated charges, prolonging the lifetime of charge carriers in UBWO, and thereby enhancing the degradation efficiency of OTC. As a result, the optimized 3wt%N-CQDs/UBWO could degrade 85% of OTC within 40 min under visible light, with a removal rate four times that of pure Bi2WO6. The performance of photocatalytic degradation over OTC by 3wt%N-CQDs/UBWO exceeds that of most reported Bi2WO6-based photocatalysts. The EPR analysis confirmed that ∙O2- and ∙OH are the main active species in the photocatalytic degradation of OTC on 3wt%N-CQDs/UBWO. This study provides insight into designing green, low-cost, and efficient photocatalysts using CQDs derived from waste biomass and the degradation of emerging pollutants like antibiotics.

Epitaxial growth of Bi4Ti3O12-BiPO4 Z-scheme heterojunction to promote carrier transfer for photocatalytic oxidation of NO

The lack of compactness in heterojunction interfaces and poor charge separation is a great challenge in developing high-efficiency heterojunction photocatalysts. Herein, a novel Bi4Ti3O12-BiPO4 heterojunction was successfully prepared for the first time by epitaxial growth of BiPO4 on the surface of Bi4Ti3O12 nanosheets. The optimized Bi4Ti3O12-BiPO4-0.5 increased the NO oxidation efficiency to 73.05%, surpassing pure Bi4Ti3O12 (63.45%) and BiPO4 (8.35%). Experiments and theoretical calculations indicated that the closely contacted heterointerface between BTO and BPO promoted the generation of the built-in electric field, which led to the formation of the Z- scheme transfer pathway for the photogenerated carriers. Therefore, the separation of photogenerated carriers was facilitated while retaining high redox potential, generating more ·O2- and ·OH to participate in NO oxidation. Furthermore, the adsorption of NO and O2 was enhanced by introducing BiPO4, further improving the photocatalytic NO oxidation performance. This work emphasizes the critical role of heterointerface in accelerating charge transfer, providing a basis for the design and construction of tightly contacted heterojunction photocatalysts.

Anchoring Perovskite-Like Bi4Ti3O12 and Plasmonic Bi on Defect-Rich Yellow TiO2-x for Enhanced Catalytic Activity toward Degradation of Pollutants upon Visible Light

The efficiency of heterogeneous photocatalytic processes is currently limited due to the fast recombination of photocarriers, poor light absorption, and inefficient surface catalytic characteristics. In this study, defect-rich yellow TiO2-x nanoparticles (abbreviated as D-TiO2) with high surface area and significant absorption in the visible range were integrated with perovskite-like Bi4Ti3O12 to synthesize binary D-TiO2/Bi4Ti3O12 nanocomposites. To overcome the problem of insufficient activity, we integrated the optimized D-TiO2/Bi4Ti3O12 nanocomposite with plasmonic Bi nanoparticles. Significantly, the optimized D-TiO2/Bi4Ti3O12/Bi-2 nanocomposite efficiently removed tetracycline (TC) in 50 min through production of •OH, h+, and •O2- species, whose removal rate promoted 10.6, 3.18, 5.01, and 1.84 compared with the white TiO2 (abbreviated as W-TiO2), D-TiO2, Bi4Ti3O12, and D-TiO2/Bi4Ti3O12 (20%) photocatalysts, respectively. The outstanding performance of the D-TiO2/Bi4Ti3O12/Bi photocatalyst was attributed to its quantum dot size, low resistance for charge migration, increased surface area, oxygen vacancies in D-TiO2, and developed n-n heterojunction among D-TiO2 and Bi4Ti3O12, which accelerated charge transfer and promoted the generation of active species. Furthermore, the stability tests showed that the TC degradation efficiency still reached 96% after four recycles, indicating the remarkable stability of the photocatalyst. Eventually, the biocompatible nature of the treated solution over the optimized photocatalyst was also revealed from an investigation of the growth of lentil seeds.

A self-cleaning photocatalytic membrane loaded with Bi2O2CO3/In(OH)3 S-scheme heterojunction composites for removing tetracycline from aqueous solutions

Bi2O2CO3/In(OH)3 (BON) photocatalysts were synthesized by a one-pot method and loaded onto polyvinylidene fluoride (PVDF) membranes to obtain a Bi2O2CO3/In(OH)3/PVDF (BON-M) catalytic membrane system. The catalytic membranes demonstrated complete degradation of tetracycline within 40 min under visible light. They demonstrated robust photocatalytic activity across a broad pH range (5-11) and in the presence of coexisting ions. The membranes demonstrated excellent self-cleaning performance. Following exposure to light, the irreversible contamination decreased from 27.1% to 4.7% and the membrane's permeability was almost completely restored. Moreover, the charge transfer mechanism at the S-scheme heterojunction interface of BON was demonstrated by Density functional theory and in-situ X-ray Photoelectron Spectroscopy characterisation, and the active sites involved in tetracycline's degradation were identified. Meanwhile, the mechanism of the "anemone effect" of BON-M was demonstrated in conjunction with Electron paramagnetic resonance, and the intrinsic Some factors enhancing the membranes' photocatalytic activity are specified.

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

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

Photocatalytic PAN Nanofibrous Membrane through Anchoring a Nanoflower-Branched CoAl-LDH@PANI Heterojunction for Organic Hazards Degradation and Oil-Containing Emulsified Wastewater Separation

The synergistic treatment of oily wastewater containing organic hazards and emulsified oils remains a big challenge for membrane separation technology. Herein, the photocatalytic membrane, which combined the physical barrier and catalytic oxidation-driven degradation functionality, was fabricated via anchoring a nanoflower-branched CoAl-LDH@PANI Z-scheme heterojunction onto a porous polyacrylonitrile mat and using tannic acid as an adhesive. The assembly of such a Z-scheme heterojunction offered the superior photocatalytic degradation performance of soluble dyes and tetracycline (up to 94.3%) to the membrane with the improved photocatalytic activity of 2.33 times compared with the CoAl-LDH@pPAN membrane. Quenching experiments suggested that the •O2- was the most reactive oxygen species in the catalytic reaction system of the composite membrane. The greatly enhanced photocatalytic activity was attributed to the effective inhibition of photogenerated hole-electron combination using PANI as a carrier, with charge transferring from LDH to PANI. The possible photocatalytic degradation mechanism was proposed based on VB-XPS, electron spin resonance spectroscopy, and DRS technologies, which was confirmed by density functional theory calculation. Meanwhile, benefiting from the superhydrophilic/oleophobic feature and low oil adhesion, the membrane exhibited high permeability for isooctane emulsion (3990.39 L·m-2·h-1), high structure stability, and satisfactory cycling performance. This work provided a strategy to develop superwetting and photocatalytic composite membranes for treating complex multicomponent pollutants in the chemical industry.

Construction of two-dimensional zinc indium sulfide/bismuth titanate nanoplate with S-scheme heterojunction for enhanced photocatalytic hydrogen evolution

Improving the separation efficiency of photogenerated carriers plays an important role in photocatalysis. In this study, two-dimensional (2D)/2D zinc indium sulfide (ZnIn2S4)/bismuth titanate (Bi4Ti3O12) nanoplate heterojunctions were synthesized to alter the Bi4Ti3O12 morphology, modulate the bandgap of Bi4Ti3O12, and enhance the utilization of light. Meanwhile, the construction of the S-scheme heterojunction establishes an internal electric field at the ZnIn2S4/Bi4Ti3O12 heterojunctions interface and achieves the spatial separation of photogenerated charges. The hydrogen production rate of ZnIn2S4/Bi4Ti3O12 nanoplate with the optimal ratio reaches 27.50 mmol h-1 g-1, which is 1.5 times higher than that of ZnIn2S4/Bi4Ti3O12 nanoflower (18.28 mmol h-1 g-1) and 2.4 times higher than that of ZnIn2S4 (11.69 mmol h-1 g-1). The apparent quantum efficiency of ZnIn2S4/Bi4Ti3O12 nanoplate reached 57.9 % under a single wavelength of light at 370 nm. This work provides insights into the study of new materials for photocatalytic hydrogen production.

Carbon quantum dots assisted BiFeO3@BiOBr S-scheme heterojunction enhanced peroxymonosulfate activation for the photocatalytic degradation of imidacloprid under visible light: Performance, mechanism and biotoxicity

A novel S-scheme heterojunction photocatalyst carbon quantum dots (CQDs)/BiFeO3/BiOBr (CBB) was synthesized via a facile hydrothermal method, which was highly effective in activating peroxymonosulfate (PMS) to photodegrade imidacloprid (IMD) (one of the typical neonicotinoid insecticides (NEOs)) under visible light irradiation. Based on the physicochemical and photoelectrochemical analysis, the super photocatalytic performance of the CBB photocatalyst was contributed to the enhanced separation and transfer of photogenerated electrons (e-) and holes (h+), the activation of PMS by reactive species, and the wider light absorption range induced by CQDs. Moreover, the intermediate products and possible photodegradation pathways of IMD were confirmed through high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS) detection and density functional theory (DFT) calculations. Although the photodegradation of IMD in the CBB/PMS/Vis system can be affected by the water quality parameters (i.e., acid group anions, pH, and the presence of humic acid (HA)), the synthesized CBB photocatalyst showed excellent photocatalytic performance in multiple natural water samples. This study provides a new idea to construct an effective and efficient heterojunction photocatalyst, which may have great advantages in photocatalytic degradation of NEOs and possibly other emerging contaminants in the aquatic environment.

Construction of 2D S-Scheme Heterojunction Photocatalyst

Semiconductor photocatalytic technology holds immense promise for converting sustainable solar energy into chemically storable energy, with significant applications in the realms of energy and the environment. However, the inherent issue of rapid recombination of photogenerated electrons and holes hinders the performance of single photocatalysts. To overcome this challenge, the construction of 2D S-scheme heterojunction photocatalysts emerges as an effective strategy. The deliberate design of dimensionality ensures a substantial interfacial area; while, the S-scheme charge transfer mechanism facilitates efficient charge separation and maximizes redox capabilities. This review commences with a fresh perspective on the charge transfer mechanism in S-scheme heterojunctions, followed by a comprehensive exploration of preparation methods and characterization techniques. Subsequently, the recent advancements in 2D S-scheme heterojunction photocatalysts are summarized. Notably, the mechanism behind activity enhancement is elucidated. Finally, the prospects for the development of 2D S-scheme photocatalysts are presented.

Bagasse cellulose-based S-type Bi2O3/Zn3In2S6 photocatalyst for efficient and stable degradation of 2,4-dichlorophenol under visible light

The environmental and human health hazards posed by 2,4-dichlorophenol (2,4-DCP) call for effective degradation technologies. This research investigates the design and application of a Bi2O3/Zn3In2S6 heterojunction photocatalyst, a 'S scheme', which was constructed via a simple hydrothermal method. The photocatalyst was then embedded in a sugarcane bagasse cellulose carrier (SBC/BO/ZIS), demonstrating excellent 2,4-DCP degradation capacity. The results show that S-type Bi2O3/Zn3In2S6 promotes the separation of photogenerated carriers. The SBC/BO/ZIS complex, in comparison with Bi2O3 and Zn3In2S6 alone, amplifies specific surface area (91.7880 m2/g) and broadens the light absorption range (570 nm) of materials, showing robust photocatalytic performance. The degradation rate of 50 mg/L 2,4-DCP reached an impressive 97% within 120 min. The encapsulation of BO/ZIS in SBC not only increases the efficiency of material recovery and recycling but also allows for continuous degradation of 2,4-DCP in cyclic manners, maintaining a degradation rate between 90% and 97%. XRD characterization shows that the physical properties of the material are not affected. The degradation of 2,4-DCP was dominantly controlled by active species (·OH and ·O2-) identified by electron paramagnetic resonance analysis and free radical trapping experiments. This innovative design significantly enhances sunlight utilization and effectively curbs charge carrier recombination, while also promoting material recovery and utilization. These attributes establish a foundation for a cost-effective and efficient means of treating actual wastewater containing 2,4-DCP.

Highly efficient MoS2/MXene aerogel for interfacial solar steam generation and wastewater treatment

Interfacial solar steam generation using aerogels holds great promise for seawater desalination and wastewater treatment. However, to achieve aerogels with both durable, high-efficiency evaporation performance and excellent salt resistance remains challenging. Here, a molybdenum disulphide (MoS2) and MXene composite aerogel with vertical pore channels is reported, which has outstanding advantages in mechanical properties, water transportation, photothermal conversion, and recycling stability. Benefiting from the plasmon resonance effect of MXene and the excellent photothermal conversion performance of MoS2, the aerogel exhibits excellent light absorption (96.58 %). The aerogel is resistant to deformation and able to rebound after water absorption, because of the support of an ordered vertical structure. Moreover, combined with the low water evaporation enthalpy, low thermal conductivity, and super hydrophilicity, the aerogel achieves an efficient and stable evaporation rate of about 2.75 kg m-2h-1 under one sun and exhibits excellent self-cleaning ability. Notably, the evaporator achieves removal rates of 99.9 % for heavy metal ions and 100 % for organic dyes, which has great potential in applications including seawater desalination and wastewater purification.

Contamination distribution and non-biological removal pathways of typical tetracycline antibiotics in the environment: A review

While the occurrence and removal technologies of tetracyclines in the environment have been reported, a comprehensive systematic summary and analysis remain limited, especially for new generations compounds such as doxycycline. In this review, the latest information regarding the distribution of various tetracyclines in different countries over the past seven years (2017-2023) reveals a notable absence of research reports in North America and Oceania. With China as the representative country, the investigation indicates that the maximum concentrations of TCs exceed 5 µg/L. The maximum concentration of tetracyclines in feces (26.22 µg/L) can reach one order of magnitude higher than that in other media. Furthermore, advanced oxidation technologies, such as Fenton processes, electrochemical oxidation, photolysis, ozonation, etc., were also examined, and the median degradation rate achieved 91.9-97.67%. Reactions such as methylation, demethylation, hydroxylation, dehydration, ring cleavage, and oxidation were observed during degradation. The most common intermediate product was identified as m/z = 461 (C22H25N2O9). This review indicates that future efforts should emphasize understanding the occurrence and fate of new-generation tetracyclines in the environment.

Exceptional photo-elimination of antibiotic by a novel Z-scheme heterojunction catalyst composed of nanoscale zero valent iron embedded with carbon quantum dots (CQDs)-black TiO2

Passivation of nanoscale zero valent iron (nZVI, Fe0) impaired its longevity while black TiO2 (b-TiO2) suffered from restricted optical properties. Using a facile approach, a novel Z-scheme heterojunction catalyst (Fe0@CQDs-TiO2(b)) of nZVI decorated with carbon quantum dots (CQDs) implanted into b-TiO2 was designed. Characterization results revealed the optical potential of the passivation coating of nZVI. The incorporation of CQDs stimulated the creation of active •OH during the dark reaction, and led to an accelerated mobility of photo-excited carriers of b-TiO2 and optimized its band gap (narrowing from 2.36 eV to 2.15 eV) during the light reaction. The photo-elimination capacity of metronidazole (MNZ) on Fe0@CQDs-TiO2(b) (99.36%) was 2.64, 8.25 and 1.34 fold beyond that on nZVI, b-TiO2 and Fe0@b-TiO2, respectively. The assembled material offered excellent adaptability to environmental substrates, in addition to being virtually unaffected by tap (95.62%) and river water (92.62%). The mechanism of MNZ degradation was elaborated, and the combination of density functional theory (DFT) calculations and LC-MS discerned 12 intermediates and 3 routes. Toxicity assessment of these products was conducted to ensure no inadvertent negative environmental impacts arose. This work proposed an original direction and mechanism for the application of passivation layers in nZVI-based materials for environmental restoration.

Recent advances of semiconductor photocatalysis for water pollutant treatment: mechanisms, materials and applications

Semiconductor photocatalysis has become an increasing area of interest for use in water treatment methods. This review systematically presents the recent developments of emerging semiconductor photocatalysis system and their application in the removal of water pollutants. A brief overview of the semiconductor photocatalysis mechanism involved with the generation of reactive oxygen species (ROS) is provided first. Then a detailed explanation of the development of TiO2-based, g-C3N4-based, and bismuth-based semiconductor materials and their applications in the degradation of water pollutants are highlighted with recent illustrative examples. Furthermore, the future prospects of semiconductor photocatalysis for water treatment are critically analyzed.

Boosted Photocatalytic Performance for Antibiotics Removal with Ag/PW12/TiO2 Composite: Degradation Pathways and Toxicity Assessment

Photocatalyst is the core of photocatalysis and directly determines photocatalytic performance. However, low quantum efficiency and low utilization of solar energy are important technical problems in the application of photocatalysis. In this work, a series of polyoxometalates (POMs) [H3PW12O40] (PW12)-doped titanium dioxide (TiO2) nanofibers modified with various amount of silver (Ag) nanoparticles (NPs) were prepared by utilizing electrospinning/photoreduction strategy, and were labelled as x wt% Ag/PW12/TiO2 (abbr. x% Ag/PT, x = 5, 10, and 15, respectively). The as-prepared materials were characterized with a series of techniques and exhibited remarkable catalytic activities for visible-light degradation tetracycline (TC), enrofloxacin (ENR), and methyl orange (MO). Particularly, the 10% Ag/PT catalyst with a specific surface area of 155.09 m2/g and an average aperture of 4.61 nm possessed the optimal photodegradation performance, with efficiencies reaching 78.19% for TC, 93.65% for ENR, and 99.29% for MO, which were significantly higher than those of PW12-free Ag/TiO2 and PT nanofibers. Additionally, various parameters (the pH of the solution, catalyst usage, and TC concentration) influencing the degradation process were investigated in detail. The optimal conditions are as follows: catalyst usage: 20 mg; TC: 20 mL of 20 ppm; pH = 7. Furthermore, the photodegradation intermediates and pathways were demonstrated by HPLC-MS measurement. We also investigated the toxicity of products generated during TC removal by employing quantitative structure-activity relationship (QSAR) prediction through a toxicity estimation software tool (T.E.S.T. Version 5.1.2.). The mechanism study showed that the doping of PW12 and the modification of Ag NPs on TiO2 broadened the visible-light absorption, accelerating the effective separation of photogenerated carriers, therefore resulting in an enhanced photocatalytic performance. The research provided some new thoughts for exploiting efficient and durable photocatalysts for environmental remediation.

A review on potential sulfide-based ternary chalcogenides for emerging photo-assisted water purification applications

Sulfide-based ternary chalcogenides have been recognized widely as exceptional photocatalysts, thanks to their narrow band gap enabling them to harvest solar energy to the maximum extent. They provide excellent optical, electrical, and catalytic performance and are of abundant use as a heterogeneous catalyst. Among sulfide-based ternary chalcogenides, compounds exhibiting AB2X4 structure form a new class of materials with excellent stability in photocatalytic performance. In the AB2X4 family of compounds, ZnIn2S4 is one of the top performing photocatalyst for energy and environmental applications. However, to date, only limited information is available on the mechanism behind the photo-induced migration of charge carriers in ternary sulfide chalcogenides. Ternary sulfide chalcogenides with their visible region activity and substantial chemical stability greatly depend on crystal structure, morphology, and optical characteristics for their photocatalytic activity. Hence, in this review, a comprehensive assessment of the reported strategies for enhancement of the photocatalytic efficiency of this compound is presented. In addition, a meticulous investigation of the applicability of ternary sulfide chalcogenide compound ZnIn2S4, in particular, has been delivered. Also, the photocatalytic behavior of other sulfide-based ternary chalcogenides for water remediation applications has also been briefed. Finally, we conclude with an insight into the challenges and future advancements in the exploration of ZnIn2S4-based chalcogenide as a photocatalyst for various photo-responsive applications. It is believed that this review could contribute to a better understanding of ternary chalcogenide semiconductor photocatalysts for solar-driven water treatment applications.

One-step hydrothermal synthesis of rhombohedral ZnIn2S4 with high visible photocatalytic activity for aqueous pollutants removal

The phase composition of photocatalyst has a substantial effect on its photocatalytic activity. In this work, the rhombohedral phase ZnIn₂S₄ was synthesized by a one-step hydrothermal method by using inexpensive Na₂S as a sulfur source with the assistance of NaCl. The Na₂S as the S source can promote the generation of rhombohedral ZnIn₂S₄, and the addition of NaCl enhances the crystallinity of the as-prepared rhombohedral ZnIn₂S₄. The rhombohedral ZnIn₂S₄ nanosheets had a narrower energy gap, more negative conductive band potential, and higher separation efficiency of photogenerated carriers relative to the hexagonal ZnIn₂S₄. The as-synthesized rhombohedral ZnIn₂S₄ exhibited high visible photocatalytic activity with removal efficiencies of 96.7% in 80 min for the methyl orange, 86.3% in 120 min for ciprofloxacin hydrochloride and nearly 100% in 40 min for Cr(VI).

Construction of a dual-signal molecularly imprinted photoelectrochemical sensor based on bias potential control for selective sensing of tetracycline

The two signals validate each other to improve the accuracy and sensitivity of the MIP-PEC sensor.

Self-Doping Based Facet Junctions and Oxygen Vacancies in Ferroelectric Bi3TixNb2-xO9 Nanosheets for Boosting Photocatalytic Degradation and Antibacterial Activity

Constructing facet junction in semiconductor photocatalysts has been demonstrated as an effective method to promote charge-carrier separation and suppress carrier recombination. Herein, we proposed a novel but facile self-doping strategy to regulate the crystal facet exposure ratio in ferroelectric Bi3TixNb2-xO9 single-crystalline nanosheets, thereby optimizing its facet junction effect. Through tuning the atomic ratio of Ti and Nb, the exposure ratio of {001} and {110} crystal planes in Bi3TixNb2-xO9 nanosheets can be delicately modulated, and more {110} facets were exposed with the increase of the Ti/Nb atomic ratio as evidenced by the X-ray diffraction and scanning electron microscopy results. A facet junction between {110} and {001} crystal planes was verified based on the density functional theory calculation and photodeposition experiment results. Photogenerated electrons tend to accumulate in {110}, while holes gathered in {001} crystal planes. Owing to the optimal facet junction effect, the sample of Ti1.05 shows the most efficient charge-carrier separation and transportation compared to Ti0.95 and Ti1.00 as supported by the photoluminescence, surface photovoltage, photoelectrochemistry, and electron paramagnetic resonance (EPR) results. In addition, the oxygen vacancy arising from the inequivalent substitution of Nb5+ by Ti4+ as proved by X-ray photoelectron spectroscopy and EPR results and the enhanced ferroelectricity supported by P-E loops can also assist charge-carrier separation and migration. Benefiting from these properties, Ti1.05 outperformed Ti0.95 and Ti1.00 in the photodegradation of organic dye and antibiotic molecules. Meanwhile, the excellent antibacterial activity of Ti1.05 under visible light was also demonstrated by the Escherichia coli sterilization experiment. This work not only presents a novel pathway to adjust the facet junction but also provides new deep insights into the crystal facet engineering in ferroelectrics as photocatalysts.