Carbon dots sensitized 2D-2D heterojunction of BiVO4/Bi3TaO7 for visible light photocatalytic removal towards the broad-spectrum antibiotics

Simultaneous photocatalytic removal of tetracycline and hexavalent chromium by BiVO4/0.6CdS photocatalyst: Insights into the performance, evaluation, calculation and mechanism

In this study, a novel Z-scheme heterojunction on bismuth vanadium/cadmium sulfide (BiVO4/0.6CdS) was developed and evaluated for simultaneous photocatalytic removal of combined tetracycline (TC) and hexavalent chromium Cr(Ⅵ) pollution under visible light. Based on the analysis of intermediate products and theoretical calculation, the property of the intermediate products of TC degradation and the effect of built-in electric field (IEF) of composite materials on photo-generated carrier separation were illustrated. According to the experiments and evaluation results, the performance of BiVO4/0.6CdS is higher than CdS 2.83 times and 4.82 times under the visible light conditions, with the aspect of simultaneous oxidizing TC and reducing Cr(Ⅵ), respectively. The catalyst has a faster removal rate in the binary composite pollution system than the single one. Therefore, the photocatalytic degradation of TC using BiVO4/0.6CdS can reduce the toxic effect of TC on the environment. The aforementioned evaluation provides a new design strategy for Z-scheme heterojunction to simultaneous photocatalytic degradation of composite organic and inorganic pollutants.

Design and construction of a robust ternary Bi5O7I/Cd0.5Zn0.5S/CuO photocatalytic system for boosted photodegradation of antibiotics via dual-S-scheme mechanisms: Environmental factors and degradation intermediates

The detection of efficacious and environment-friendly nanomaterials with prominent photocatalytic performance is crucial for the detoxification of antibiotics in wastewater. Herein, a dual-S-scheme Bi5O7I/Cd0.5Zn0.5S/CuO semiconductor was designed and fabricated via a simple approach to degrade tetracycline (TC) and other types of antibiotics under LED illumination. However, Cd0.5Zn0.5S and CuO nanoparticles were decorated on the surface of the Bi5O7I microsphere to create a dual-S-scheme system that stimulates visible-light utilization and facilitates the dissolution of excited photo-curriers. Therefore, the Bi5O7I/Cd0.5Zn0.5S/CuO system offers strong redox ability, which reflects reinforced photocatalytic activity and robust stability. The ternary heterojunction discloses enhanced TC detoxification efficiency of 92% in 60 min with TC destruction rate constant of 0.04034 min-1, outperforming pure Bi5O7I, Cd0.5Zn0.5S, and CuO by 4.27, 3.20, and 4.80 folds, respectively. Besides, Bi5O7I/Cd0.5Zn0.5S/CuO manifests outstanding photo-activity against a series of antibiotics like norfloxacin, enrofloxacin, ciprofloxacin, and levofloxacin under the same operational conditions. The active species detection, TC destruction pathways, catalyst stability, and photoreaction mechanisms of Bi5O7I/Cd0.5Zn0.5S/CuO were accurately explained in detail. Summarily, this work introduces a new class of dual-S-scheme system with strengthened catalytic properties to effectively eliminate the antibiotics in wastewater under visible-light illumination.

A Meta-Analysis of Influencing Factors on the Activity of BiVO4-Based Photocatalysts

With the continuous advancement of global industrialization, a large amount of organic and inorganic pollutants have been discharged into the environment, which is essential for human survival. Consequently, the issue of water environment pollution has become increasingly severe. Photocatalytic technology is widely used to degrade water pollutants due to its strong oxidizing performance and non-polluting characteristics, and BiVO4-based photocatalysts are one of the ideal raw materials for photocatalytic reactions. However, a comprehensive global analysis of the factors influencing the photocatalytic performance of BiVO4-based photocatalysts is currently lacking. Here, we performed a meta-analysis to investigate the differences in specific surface area, kinetic constants, and the pollutant degradation performance of BiVO4-based photocatalysts under different preparation and degradation conditions. It was found that under the loading condition, all the performances of the photocatalysts can be attributed to the single BiVO4 photocatalyst. Moreover, loading could lead to an increase in the specific surface area of the material, thereby providing more adsorption sites for photocatalysis and ultimately enhancing the photocatalytic performance. Overall, the construct heterojunction and loaded nanomaterials exhibit a superior performance for BiVO4-based photocatalysts with 136.4% and 90.1% improvement, respectively. Additionally, within a certain range, the photocatalytic performance increases with the reaction time and temperature.

Remediation of environmental toxicants using carbonaceous materials: opportunity and challenges

Adsorption and photocatalytic properties of carbonaceous materials, viz., carbon nanotubes (CNTs), fullerene, graphene, graphene oxide, carbon nanofiber nanospheres, and activated carbon, are the legitimate weapons for the remediation of emerging and persistent inorganic/organic contaminants, heavy metals, and radionucleotides from the environment. High surface area, low or non-toxic nature, ease of synthesis, regeneration, and chemical modification of carbonaceous material make them ideal for the removal of toxicants. The research techniques investigated during the last decade for the elimination of environmental toxicants using carbonaceous materials are reviewed to offer comprehensive insight into the mechanism, efficiency, applications, advantages, and shortcomings. Opportunities and challenges associated with carbon materials have been discussed to suggest future perspectives in the remediation of environmental toxicants.

Construction of an La-BiVO4/O-Doped g-C3N4 Heterojunction Photocatalyst Embedded in Electrospinning Nanofibers

BiVO₄ has been widely used in the field of photocatalysis due to its nontoxic and moderate band gap. However, single BiVO₄ has the disadvantages of a high recombination rate of photogenerated carriers and weak response to visible light, inhibiting its photocatalytic applications. To explore viable solutions, a hybrid material composed of lanthanum-doped bismuth vanadate (La-BiVO₄) and oxygen-doped porous graphite carbon nitride (O-doped g-C₃N₄), i.e., La-BiVO₄/O-doped g-C₃N₄ powder, was prepared by a facile hydrothermal reaction and low-temperature calcination. Then, the powder was loaded on polyacrylonitrile nanofibers (NFs) through the electrospinning fiber technique. Various surface science characterizations, including transmission electron microscopy and nitrogen absorption and desorption analysis, confirmed the successful synthesis of a mesoporous heterojunction material. The La³⁺-doping as well as the porous morphologies and larger specific surface area of the O-doped g-C₃N₄ ultimately improve the photocatalytic abilities via a proposed Z-scheme heterojunction mechanism. The roles of La³⁺-doping and morphology modification in promoting the separation of the photogenerated carriers and broadening the optical absorption range were experimentally discussed. The RhB degradation experiment indicated that the La-BiVO₄/O-doped g-C₃N₄ powder has excellent photocatalytic activity, which is about 2.85 and 2 times higher than that of the pure BiVO₄ and O-doped g-C₃N₄, respectively. Meanwhile, the La-BiVO₄/O-doped g-C₃N₄ NF shows good stability and recoverability after a 10-cycle testing. Such a hybrid photocatalyst with a proposed Z-scheme heterojunction mechanism and good plasticity might pave a feasible way to fabricate a new library of photocatalysts.

CeO2-CDs clusters decorated Co(OH)2 nanosheets for improved photocatalytic ammonia synthesis

The green synthesis process of photocatalytic ammonia production has received more and more attentions. Herein, a Z-scheme heterojunction with all-solid-state structures is constructed, in which carbon dots can act as electron transferring mediators. The photocatalytic measurement shows that the modified photocatalysts exhibit much higher activities, in which the ammonia production rates can reach above 232 µmol·g_cal^-1·h^-1 under the light irradiation. The improved catalytic properties can be credited to the significantly increased number of photoinduced oxygen vacancies, the excellent visible-light adsorption abilities and photogenerated electron-hole separation efficiencies for the carbon dots bridged heterostructures. More hydroxyl and superoxide radicals can be simultaneously produced in the composites. This work provides reasonable guidance for applications in photocatalytic ammonia synthesis and a promising construction strategy of efficient Z-scheme photocatalysts.

Fabrication of Z-scheme Bi7O9I3/g-C3N4 heterojunction modified by carbon quantum dots for synchronous photocatalytic removal of Cr (Ⅵ) and organic pollutants

Chromium(VI) (Cr(VI)), a highly toxic metal ion, generally co-exists with organic pollutants in industrial effluents. The clean and effective technology for water purification is an imperative issue but still a challenging task. A series of Bi₇O₉I₃/g-C₃N₄ (BOI/CN) composites modified by lignin-derived carbon quantum dots (CQDs) were fabricated by hydrothermal method and applied for synchronous photocatalytic removal of Cr (Ⅵ) and levofloxacin (LEV). With the modification of CQDs in BOI/CN heterojunction, the 0.5-CQD/BOI/CN photocatalyst (0.5% content of CQDs) exhibited stronger light-harvesting capacity, more efficient charge separation, and faster electron transfer. Compared to those of BOI (51.2%), CN (36.8%), and BOI/CN (74.4%), the photoreduction efficiency of Cr(VI) reached up to 100% by 0.5-CQD/BOI/CN under 60 min of light irradiation, together with 94.8% degradation efficiency of LEV. The degradation of LEV was dominantly controlled by active species (•OH and •O₂^-) identified by electron paramagnetic resonance analysis and free radical trapping experiments. The intermediates of LEV were determined by LC-MS and the possible degradation pathway was speculated in combination with density functional theory calculation, involving defluorination, decarboxylation, quinolone rings opening, and piperazine moieties oxidation reactions. This work provides an advanced strategy for the fabrication of high-efficiency CQDs-based Z-scheme photocatalysts for environmental remediation.

Facile synthesis CQDs/SnO2-x/BiOI heterojunction photocatalyst to effectively degrade pollutants and antibacterial under LED light

To remove multitudinous pollutants from wastewater, the design of a highly efficient and multifunctional photocatalyst is necessary. A novel CQDs/SnO2-x/BiOI photocatalyst (named CSnBI composite) was prepared by combining carbon quantum dots (CQDs), large specific surface area SnO2-x nanocrystals and BiOI nanocrystals to obtain a compact hybrid structure. TEM and Raman techniques confirmed the structure of CSnBI composite. The photocurrent and EIS showed that the photoexcited electron-hole pairs separation efficiency was improved. As anticipated, novel CSnBI photocatalyst can successfully remove tetracycline, methyl orange, E. coli (Escherichia coli) and S. aureus under a LED light due to the hybridization contaction among CQDs, SnO2-x and BiOI. The mechanism showed that the introduction of CQDs promoted visible light absorption and efficient separation of photogenerated carriers of SnO2-x/BiOI heterojunction. The capture experiment and related measurements showed that h+, •O2- and •OH are active species in the photocatalytic process. This study gave a novel case for facile construction of photocatalysts with tight hybrid structure.

Er3+/Sm3+ co-doped Bi2O2CO3 in photocatalytic water treatment: Immobilization, acute toxicity, sterilization, and catalytic oxidation activity

Defect construction and rare earth doping are the linchpins to completing the target of partial electronic regulation. In Er³⁺/Sm³⁺ co-doping Bi₂O₂CO₃, rare earth doping resulted in the exposure of {001} crystal plane in Bi₂O₂CO₃ and cause surface defects and electron traps, achieving wide light response capability and fast carrier separation. Furthermore, a potential TC degradation route was acknowledged derived from LC-MS. Then, the median lethal concentration LC50 (96 h) is 80 ppm, probing the 2E2SBOC photocatalyst has low toxicity in actual wastewater. Combining with immobilization technology, not only does it have little impact on the organisms in the wastewater, but it is easy to recycle after degradation. In terms of new water disinfection technology, bacterial experiments in natural waters proved that 2E2SBOC has a potential disinfection system, which promotes the exposure of more active sites during degradation. This effective project offers a novel perspective for the development and application of rare-earth-doped photocatalysts.

Insight into the mechanism of deep NO photo-oxidation by bismuth tantalate with oxygen vacancies

Deeply photocatalytic oxidation of nitrogen oxides is still difficult to achieve, mainly limited by few intrinsic active sites and inefficient carrier separation of photocatalysts. Accordingly, we develop a simple room temperature tactic to introduce oxygen vacancies (OVs) into Bi₃TaO₇ (BTO). Based on solid experimental and DFT theoretical supports, we explore the mechanism of NO removal over OVs decorated BTO (OVs-BTO). OVs can not only alter the distribution of local electrons to result in the formation of a fast charge transfer channel between OVs and the adjacent Ta atoms, which improves the transport rate of photogenerated carriers; but also function as active sites to adsorb small molecules (NO, O₂ and H₂O), which being activated and positively drive the NO oxidation reaction. In order to investigate a possible reaction path, a combination of in-situ DRIFTS and simulated Gibbs free energy reveals that the intermediate products of OVs-BTO are helpful to promote the deep oxidation of NO to NO₃^-, while pristine BTO is more likely to produce NO₂ intermediate toxic by-products, which greatly hinders the deep photocatalytic oxidation of NO. This work provides insights into the role of OVs in photocatalysts, and also points out a guideline for the mechanism of semiconductor photocatalysts in eliminating gaseous pollutants.

Carbon quantum dots sensitized 2D/2D carbon nitride nanosheets/bismuth tungstate for visible light photocatalytic degradation norfloxacin

A novel carbon quantum dots (CQDs) sensitized 2D/2D carbon nitride nanosheets and bismuth tungstate composite (CQD-CNs/BWO) was successfully prepared via the facile hydrothermal method and used for the photocatalytic degradation of norfloxacin (NOR). During 120 min irradiation test, CQD-CNs/BWO exhibited 9 and 1.76 times higher photocatalytic activity than CNs and BWO, respectively. CQDs and constructed 2D/2D structure could not only improve the light harvesting but also promote the generation and separation of electron-holes. The existing inorganic ions in solution (e.g. bicarbonate ions, chlorine ions, and sulfate ions) could inhibit NOR degradation. Based on the electron spin resonance and free radicals inhibition tests, the holes and superoxide radicals rather than hydroxyl radicals were the main reactive species. The intermediates and possible pathways were proposed, and the antibacterial activity of the treated solution after the reaction was evaluated via bacteriostatic tests. The prepared composite material with high photocatalytic activity and stability is potentially effective for the degradation of antibiotics in wastewater.

2D/2D Heterojunction systems for the removal of organic pollutants: A review

Photocatalysis is considered to be an effective way to remove organic pollutants, but the key to photocatalysis is finding a high-efficiency and stable photocatalyst. 2D materials-based heterojunction has aroused widespread concerns in photocatalysis because of its merits in more active sites, adjustable band gaps and shorter charge transfer distance. Among various 2D heterojunction systems, 2D/2D heterojunction with a face-to-face contact interface is regarded as a highly promising photocatalyst. Due to the strong coupling interface in 2D/2D heterojunction, the separation and migration of photoexcited electron-hole pairs are facilitated, which enhances the photocatalytic performance. Thus, the design of 2D/2D heterojunction can become a potential model for expanding the application of photocatalysis in the removal of organic pollutants. Herein, in this review, we first summarize the fundamental principles, classification, and strategies for elevating photocatalytic performance. Then, the synthesis and application of the 2D/2D heterojunction system for the removal of organic pollutants are discussed. Finally, the challenges and perspectives in 2D/2D heterojunction photocatalysts and their application for removing organic pollutants are presented.

Construction of Z-scheme Bi3TaO7/Zn0.5Cd0.5S composites with high efficiency for levofloxacin degradation under visible light irradiation

Direct Z-scheme Bi₃TaO₇/Zn_0.5Cd_0.5S composite photocatalysts were successfully prepared via an in situ growth hydrothermal method. The photocatalytic activities of composites were investigated by the degradation of levofloxacin under visible light. All composites exhibited enhanced photocatalytic activities compared with Bi₃TaO₇ and Zn_0.5Cd_0.5S. The structure composition and photoelectric performance of the photocatalysts were investigated by related experiments. The dominant active species (h⁺ and ˙O₂^-) during levofloxacin degradation were identified through capture experiments. Meanwhile, the stability and cyclicity of the optimal photocatalyst (BZCS-2) were studied by cycling experiments. Finally, we proposed a possible direct Z-scheme charge-migration mechanism for levofloxacin degradation. This work would provide a feasible idea and theoretical support for the in-depth research of direct Z-scheme photocatalysts and Zn_xCd_1-xS-based semiconductor materials in the future.

Molecular Self-Assembly of Oxygen Deep-Doped Ultrathin C3N4 with a Built-In Electric Field for Efficient Photocatalytic H2 Evolution

Heteroatom-doped carbon nitride (C₃N₄) with a built-in electric field can reinforce the carrier separation; however, the stability will be greatly reduced due to the loss of surface-doped atoms. Here, molecule self-assembly, as a facile bottom-up approach, is explored for the synthesis and oxygen doping of C₃N₄. The obtained C₃N₄ presents a porous and ultrathin structure and oxygen deep-doping, which generate abundant nitrogen vacancies and a stable built-in electric field. Toward photocatalytic hydrogen evolution, the ultrathin and oxygen deep-doped C₃N₄ exhibits a 3.5-fold higher activity than bulk C₃N₄ under simulated sunlight, and 3.6 times higher stability than the oxygen surface-doped counterpart within five cycles. Femtosecond transient absorption spectroscopy indicates the improved carrier separation, and density functional theory (DFT) calculation reveals the promoted H₂O adsorption and activation under the built-in electric field, which contribute to the excellent photocatalytic performance of oxygen deep-doped ultrathin C₃N₄.

Tetracyclines in the environment: An overview on the occurrence, fate, toxicity, detection, removal methods, and sludge management

Tetracyclines (TCs) are a group of broad-spectrum antibiotics having vast human, veterinary, and aquaculture applications. The continuous release of TCs residues into the environment and the inadequate removal through the conventional treatment systems result in its prevalent occurrence in soil, surface water, groundwater, and even in drinking water. As aqueous TCs contamination is the tip of the iceberg, and TCs possess good sorption capacity towards soil, sediments, sludge, and manure, it is insufficient to rely on the sorptive removal in the conventional water treatment plants. The severity of the TCs contamination is evident from the emergence of TCs resistance in a wide variety of microorganisms. This paper reviews the recent research on the TCs occurrence in the environmental matrices, fate in natural systems, toxic effects, and the removal methods. The high performance liquid chromatography (HPLC) determination of TCs in environmental samples and the associated technology developments are analyzed. The benefits and limitations of biochemical and physicochemical removal processes are also discussed. This work draws attention to the inevitability of proper TC sludge management. This paper also gives insight into the limitations of TCs related research and the future scope of research in environmental contamination by TCs residues.

Novel AgI/BiSbO4 heterojunction for efficient photocatalytic degradation of organic pollutants under visible light: Interfacial electron transfer pathway, DFT calculation and degradation mechanism study

Herein, we constructed a novel AgI/BiSbO₄ heterojunction via a hydrothermal-precipitation method. The heterojunction structure boosts the generation of hydroxyl and superoxide radicals for efficient degradation of organic pollutants. The photocatalytic activities of the optimal sample for ARG and TC degradation are 10 and 1.6 times higher than those of bare AgI, respectively. Characterizations and theoretical calculations together confirm a strong interfacial charge transfer exists between the interlayer in AgI and BiSbO₄ by the formation of Ag‒O bond, making O atoms obtain rich free electrons from Ag atoms of AgI, thus forming an ultrahigh electron transfer tunnel, and ultimately accelerating the separation of photoinduced electrons. More interestingly, low amounts of Ag⁰ NPs formed during the photocatalytic process, enhancing the visible light absorption because of its SPR (surface plasmon resonance) effect and further promoting the separation of photoinduced carriers. Furthermore, photocatalytic degradation pathways were proposed in detail by analyzing intermediates and a reasonable photocatalytic mechanism was unearthed. This work extends the development of AgI-based heterojunction photocatalysts.

BiVO4 prepared by the sol-gel doped on graphite felt cathode for ciprofloxacin degradation and mechanism in solar-photo-electro-Fenton

In this research, bismuth vanadate-doped graphite felt (GF-BiVO₄) was successfully prepared by sol-gel method, in which BiVO₄ owned superior electro-Fenton (EF) and solar-photo-electro-Fenton (SPEF) performance. Combined with the analysis by X-ray diffractometer (XRD), field emission transmission electron microscopy (FE-TEM), nitrogen adsorption-desorption isotherms and cyclic voltammetry (CV), the changes of electrodes were reflected in structure and physicochemical properties. The doping of monoclinic BiVO₄ endued GF with a higher surface area and more electro-active sites and better electrode activity in comparison to Raw-GF. Then, the GFs were used as cathodes to detect •OH concentration with coumarin (COU) as probe molecule and to evaluate photoelectric performance with ciprofloxacin (CIP) in photocatalysis, EF and SPEF processes. The results demonstrated that the concentration of •OH followed an order of SPEF> EF> photocatalysis, which was consistent with the removal rate of CIP (99.8%, 99.4% and 21.2%, respectively) on GF-BiVO₄ at 5 min. Further, five degradation pathways of CIP in SPEF system were proposed including the attack on piperazine ring, oxidation on cyclopropyl group, decarboxylation and hydroxyl radical addition, oxidation on benzene group and defluorination. The study provides insights into the enhancement of EF and SPEF performance and the degradation pathway of CIP in SPEF.

Enhanced visible-light photocatalysis of clofibric acid using graphitic carbon nitride modified by cerium oxide nanoparticles

Recently, the emerging pharmaceutical micropollutants have become an environmental concern. Herein, we report an efficient elimination of clofibric acid (CA) using visible light-driven g-C₃N₄/CeO₂ prepared by hydrothermal method. Among the catalysts with different compound ratios, g-C₃N₄/CeO₂-3 (1.2 g g-C₃N₄ with 3 mmol Ce(NO₃)₃∙6H₂O) exhibited the best photocatalytic performance. The effect of catalyst dosage was investigated and the optimal value was determined as 0.5 g L^-1. The effect of initial pH (pH₀) showed CA elimination decreased with increasing pH₀. The underlying mechanism for CA oxidation was proposed based on synthetical analysis of photoluminescence emission spectra, transient photocurrent responses, electron paramagnetic resonance, chemical quenching experiments and band edge potential of g-C₃N₄ and CeO₂. Photogenerated hole was primarily responsible for CA elimination while singlet oxygen played an auxiliary role. The products of CA oxidation were detected using liquid chromatography mass spectrometry (LC-MS) method and a possible pathway was put forward. Various organics were used as target contaminants to assess photocatalytic performance of g-C₃N₄/CeO₂ heterojunction under acidic and alkaline pH conditions. The analysis of relationship between the oxidation peak potential (E_OP) and the reaction rate constant indicated that photocatalysis using as prepared g-C₃N₄/CeO₂-3 heterojunction is apt to oxidize contaminants with electron withdrawing group under acid condition.

Electrochemically-deposited PANI on iron mesh-based metal-organic framework with enhanced visible-light response towards elimination of thiamphenicol and E. coli

Metal-organic frameworks (MOFs) are emerging class of porous materials that attracted tremendous attention as eco-friendly photocatalysts. However, poor charge separation in most MOFs largely thwarts their photocatalytic performance. In this work, Materials of Institut Lavoisier-100(Fe) (MIL-100 (Fe)) based on iron mesh was successfully fabricated by in situ growth. MIL-100(Fe) doped with polyaniline, namely MIL-100(Fe)/PANI, were then fabricated by galvanostatic deposition followed by annealing. Compared to pure MIL-100(Fe), MIL-100(Fe)/PANI composites exhibited excellent photocatalytic performances towards Thiamphenicol (TAP) degradation and Escherichia coli (E. Coli.) inactivation. The apparent rate constant, k, for TAP elimination of the MIL-100(Fe)/PANI composites with H₂O₂ is approximately 3 times as high as that of pure MIL-100(Fe). The electrochemical studies showed enhanced photocatalytic performances, which can be attributed to the electronic conductivity of PANI polymers. Quenching experiments, fluorescent tests and electron paramagnetic resonance (EPR) all suggested ⋅O₂^-, e^-, ⋅OH and h⁺ as reactive oxidizing species (ROSs) involved in the photocatalytic process, where ⋅OH played the predominant ROSs. The transformation products of TAP were also isolated and characterized by high-resolution mass spectrometry, and transformation pathways of TAP under Vis/MIL-100(Fe)/PANI/H₂O₂ were tentatively clarified based on involved intermediates. Herein, MOFs conjugated conductive polymers nanocomposites look promising as efficient photocatalysts for organic pollutants degradation and bacteria inactivation. This work could offer novel strategies for the development of heterojunction composites with enhanced photocatalytic performances for better environmental remediation.

A novel and high-performance double Z-scheme photocatalyst ZnO-SnO2-Zn2SnO4 for effective removal of the biological toxicity of antibiotics

Visible light-responsive tetradecahedral ZnO-SnO₂-Zn₂SnO₄ photocatalysts possessing double Z-scheme mechanism were prepared via a hydrothermal pathway and subsequent annealing treatment. Due to its enhanced optical absorption ability and effective charge separation, the sample with a Zn/Sn atom ratio of 3:2 (Z32) exhibited superior degradation of the antibiotics ciprofloxacin and sulfamonomethoxine under visible light irradiation and also degraded bisphenol A. Furthermore, five-cycle experiments confirmed that Z32 also exhibited satisfactory photostability. The trapping experiment and electron spin resonance data demonstrated that both OH and O₂^- play important roles in the photocatalytic system, where electron transfer coincides with the double Z-scheme mechanism. Photo-generated electrons in the conduction band (CB) of ZnO can transfer to the valence band (VB) of Zn₂SnO₄, while electrons in the CB of SnO₂ transfer to the VB of ZnO, as a result of the intimate-contact, chemically-bound interface. Therefore, the reduction and oxidation reactions occur at higher reduction and oxidation potentials, producing reactions that can successfully eliminate the biotoxicity of antibiotics to Escherichia coli DH5a after photocatalytic degradation by Z32.

Extensive solar light harvesting by integrating UPCL C-dots with Sn2Ta2O7/SnO2: Highly efficient photocatalytic degradation toward amoxicillin

The carbon dots (C-dots) mediated Sn₂Ta₂O₇/SnO₂ heterostructures with spongy structure were successfully assembled by simple hydrothermal route. The photocatalytic removal efficiency of amoxicillin (AMX, 20 mg L^-1) over C-dots/Sn₂Ta₂O₇/SnO₂ was estimated to reach up 88.3% within 120 min simulated solar light irradiating. Meanwhile, the HPLC-MS/MS analysis and density functional theory (DFT) computation were examined to clarify the photo-degradation pathway of AMX. The mechanism investigation proposed that with the modification of C-dots, the photocatalysts improves the utilization of solar energy by harvesting the long wavelength solar light due to their unique up-converted photoluminescence (UCPL). In addition, the porous spongy structure and plenty of tiny C-dots promote the ability of adsorption by enlarged specific surface area. Furthermore, the C-dots mediated Z-type heterojunction of Sn₂Ta₂O₇/SnO₂ facilitates the efficient separation and transfer of photo-induced carriers. Our work affords a promising approach for the design of the high-efficient photocatalysts to remedy poisonous antibiotics in aqueous environment.

Bi3TaO7/Ti3C2 heterojunctions for enhanced photocatalytic removal of water-borne contaminants

Novel catalysts are of great interest for improved photocatalytic environmental remediation. Using a hydrothermal method, 0D/2D Bi₃TaO₇/Ti₃C₂ heterojunctions were designed rationally and characterized systematically as excellent photocatalysts for photocatalytic degradation. The hybrid catalyst exhibits superior performance in visible-light-driven photocatalytic degradation of methylene blue (about 99% degradation efficiency after 2 h) and excellent stability (up to 10 cycles) under visible light irradiation (300 W Xe lamp; λ > 420 nm; light intensity 150 mW cm^-2). In addition, Bi₃TaO₇/Ti₃C₂ has a larger rate constant (0.032 min^-1) than pristine Bi₃TaO₇ (0.006 min^-1). Quantum yield (2.27 × 10^-5 molecules/photon) and figure of merit (23.3) of the system were obtained, suggesting that our catalyst has potential for application. Both experimental and computational results indicate that synergistic effects between Bi₃TaO₇ and Ti₃C₂ improve photocatalytic performance by enhancing electron-hole pair separation, electronic transmission efficiency, and interfacial charge transfer. These findings contribute to the synthesis of efficient visible-light-driven Bi-based photocatalysts and to the understanding of photocatalytic degradation reactions.

Study of intermediate by-products and mechanism of the photocatalytic degradation of ciprofloxacin in water using graphitized carbon nitride nanosheets

The photocatalytic degradation of the antibiotic ciprofloxacin in water was carried out with nanosheets of graphitic carbon nitride (g-C₃N₄) as catalyst and visible light irradiation using low-power (4 × 10 W) white light LEDs. The aim of this study was to identify the intermediate by-products formed during the degradation and to propose a pathway for CIP degradation. To achieve this goal, photocatalytically degraded CIP solutions were analysed by liquid chromatography coupled to high-resolution mass spectrometry using a QTOF instrument. The accurate mass and the MS/MS data of the detected ions allowed us to determine the elementary composition of eight by-products and to propose the chemical structures for seven of them. Three of these by-products have been reported for the first time and the elementary composition of a fourth one that had been wrongly reported in the literature was accurately established. CIP degradation followed a pseudo-first order kinetics with a pseudo-first order kinetic constant of 0.035 min^-1. In addition, a study of the influence of several scavengers showed that only the presence of triethanolamine dramatically reduced the pseudo-first order kinetic constant (0.00072 min^-1), pointing out that the reactive species were the holes produced in the catalyst. Finally, the main pathway of CIP degradation seems to be the attack to the piperazine group by ·OH radicals, following heterocycle breakup and the subsequent loss of two of its carbon atoms as CO₂ molecules, and then defluorination, oxidation and cleavage of the cycles of this intermediate.

Bi4NbO8Cl {001} nanosheets coupled with g-C3N4 as 2D/2D heterojunction for photocatalytic degradation and CO2 reduction

Photocatalytic activity is largely restricted by insufficient photoabsorption and intense recombination between charge carriers. Here, we first synthesized Bi₄NbO₈Cl nanosheets with {001} exposing facets by a molten-salt growth method, which shows largely promoted photocatalytic performance for the degradation of tetracycline (TC) and bisphenol A (BPA) in comparison with Bi₄NbO₈Cl particles obtained by solid-state reaction. The 2D/2D Bi₄NbO₈Cl/g-C₃N₄ heterojunction photocatalysts were then fabricated via high-energy ball-milling and post-sintering to realize intimate interfacial interaction. The photocatalytic activity of all the Bi₄NbO₈Cl/g-C₃N₄ composites largely enhances compared to Bi₄NbO₈Cl nanosheets and g-C₃N₄, also far exceeding the mechanically-mixed Bi₄NbO₈Cl nanosheets and g-C₃N₄. The impact of different reaction parameters on the photocatalytic degradation activities was investigated, including catalyst concentration, pH value and TC concentration. In addition, Bi₄NbO₈Cl/g-C₃N₄ also presents improved photocatalytic CO₂ reduction activity for CO production. The large enhancement on photocatalytic activity of Bi₄NbO₈Cl/g-C₃N₄ composites is owing to the synergistic effect of favorable 2D/2D structure and construction of type II heterojunction with intimate interfacial interaction, thus boosting the charge separation. The formation of type II heterojunction was evidenced by selective photo-deposition of Pt and MnO_x, which demonstrate that the reductive sites and oxidative sites are on Bi₄NbO₈Cl nanosheets and g-C₃N₄, respectively. This work may provide some insights into fabrication of efficient visible-light driven photocatalysts for environmental and energy applications.

A review on tetracycline removal from aqueous systems by advanced treatment techniques

Tetracycline occurrence and advanced treatment techniques.

Carbon dots-sensitized amorphous MoSx photoanode: Sequential electrodeposition preparation and dual amplified photoelectrochemical aptasensing of adenosine

The design and fabrication of high visible-light activated photoelectrode are essential to precisely detect biomolecule in biological system. Herein, an ultrasensitive photoelectrochemical (PEC) aptasensor for specific recognition of adenosine is established based on carbon dots sensitized-amorphous molybdenum sulfide (a-MoS_x/CDs) photoanode and dual amplification strategy. The heterostructured photoanode achieved by sequential electrodeposition reveals significantly boosted photocurrent with good stability and repeatability under visible light illumination, giving the credit to highly activated visible light absorption, uniform coverage and good electric contact to the underlying substrate, as well as the energy-band alignment between the two components. By stepwisely immobilizing complementary DNA probe (NH₂-DNA) and adenosine aptamer (Apt), followed by methylene blue (MB) binding with the guanine base on Apt, a dual amplified self-powered PEC aptasensor for adenosine detection is constructed. Based on the co-sensitization effect of CDs and MB, ultrasensitive and high-affinitive determination of adenosine is realized over the concentration range of 0.01 nM-1000 nM at 0 V (vs. SCE), with satisfactory stability and reproducibility. The detection limit is as low as 3.3 pM, demonstrating a performance even surpassing most of the sensors reported so far. The prospective application of the co-sensitized a-MoS_x photoanode for ultrasensitive aptasensing is highlighted in this work.