S-scheme 1 T phase MoSe2/AgBr heterojunction toward antibiotic degradation: Photocatalytic mechanism, degradation pathways, and intermediates toxicity evaluation

Tetracycline degradation by dual-frequency ultrasound combined with peroxymonosulfate

Tetracycline has received a great deal of interest for the harmful effects of substance abuse on ecosystems and humanity. The effects of different processes on the degradation of tetracycline were compared, with dual-frequency ultrasound (DFUS) in combination with peroxymonosulfate (PMS) being the most effective for the tetracycline degradation. Free radical scavenging experiments showed that O2∙-,SO4∙- and •OH were the main reactive radicals in the degradation of tetracycline. According to the major intermediates of tetracycline degradation identified, three possible degradation pathways were proposed, which are of significance for translational studies of tetracycline degradation. Notably, these intermediates were found to be significantly less toxicity. The number of active bubbles in the degradation vessel was calculated using a semi-empirical formula, and a higher value of 1.44 × 108 L-1s-1 of bubbles was obtained when using dual-frequency ultrasound at 20 kHz (210 W/L) and 80 kHz (85.4 W/L). Therefore, compared to 20 kHz, although the yield of strong oxidizing substances from individual active bubbles decreased slightly, a significant increment of the number of active bubbles still resulted in a higher synergistic effect, and the combination of DFUS and PMS should be effective in promoting the generation of reactive free radicals and mass transfer processes within the degradation vessel, which provides a method for efficient removal of tetracycline from wastewater.

Synthesis of Acid Mine Drainage (AMD) Sludge-Derived Al-Fe3O4 as Fenton-like Catalysts for the Efficient Degradation of Tetracycline

In recent years, the development of environmentally friendly solid catalysts derived from sludge for the efficient removal of pollutants from wastewater has triggered widespread attention. Acid mine drainage (AMD) sludge is a waste produced in the process of acid mine wastewater treatment and contains multitudes of valuable metal resources. Hence it provides the original conditions for the synthesis of metal-based Fenton catalysts. In this article, the Fenton-like catalyst Al-Fe3O4 derived from AMD sludge was first synthesized by acid leaching coprecipitation methods, and the relationship among catalyst properties and pH, growth temperature, and growth time during coprecipitation was explored. Transmission electron microscope (TEM)/vibrating sample magnetometer (VSM)/particulate size description analyzer (DLS) results showed that the Al-Fe3O4 catalyst with high purity, large particle size, and strong magnetic properties was obtained under the conditions of pH 10, reaction temperature 60 °C, and growth for 45 min. In addition, the introduction of Al active sites promoted the activation of H2O2 and improved the catalytic activity of Al-Fe3O4, and the degradation efficiency of tetracycline was up to 93.9% within 60 min, which was 1.94 times that of pure Fe3O4. Moreover, Al-Fe3O4 exhibited excellent recyclability after four adsorption-desorption cycles. Hence, this study is expected to promote the resource utilization of industrial sludge and provide a new idea for the rapid removal of TC from aqueous solution.

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.

Fabrication of multiphase MoSe2 modified BiOCl nanosheets for efficient piezo-photoelectric hydrogen evolution and antibiotic degradation

Efficient spatial charge separation plays a crucial role in improving the photocatalytic performance. Therefore, 1T/2H MoSe2/BiOCl (1T/2H MS/BOC) and 2H MoSe2/BiOCl (2H MS/BOC) piezo-photocatalysts are synthesized. By combining piezoelectric catalysis and photocatalysis, a highly active piezo-photocatalytic process is realized. The optimal 1T/2H MS/BOC piezo-photocatalyst displays superior diclofenac (DCF) degradation and hydrogen (H2) evolution activity under the combined action of ultrasound and light. In particular, the DCF degradation kinetic constant (k) of optimal 0.5% 1T/2H MS/BOC under the synergistic effect of ultrasound and light is 0.057 min-1, which is 8.1 and 6.3 times higher than those of BiOCl (0.007 min-1) and 0.5% 2H MS/BOC (0.009 min-1). Moreover, the H2 evolution rate of 0.5% 1T/2H MS/BOC is 122.5 μmol g-1 h-1, which is also higher than those of BiOCl (45.8 μmol g-1 h-1) and 2H MS/BOC (49.5 μmol g-1 h-1). The dramatic improvement in the DCF degradation and H2 evolution piezo-photocatalytic performance of 1T/2H MS/BOC catalysts is ascribed to the built-in polarization electric field and abundance of active sites of 1T/2H MS/BOC as well as the advantageous band structure between BiOCl and 1T/2H MoSe2. Additionally, three probable degradation pathways of DCF were put forward from the results of liquid chromatography-mass spectrometry (LCMS) and density functional theory (DFT) calculations. This study provides the design strategy of high efficiency piezo-photocatalysts in environmental purification and energy-generation fields based on phase and band structure engineering.

Ti3 C2 -modified g-C3 N4 /MoSe2 S-Scheme Heterojunction with Full-Spectrum Response for CO2 Photoreduction to CO and CH4

Energy shortage and global warming caused by the extensive use of fossil fuels are urgent problems to be solved at present. Photoreduction of CO2 is considered to be a feasible solution. The ternary composite catalyst g-C3 N4 /Ti3 C2 /MoSe2 was synthesized by hydrothermal method, and its physical and chemical properties were studied by an array of characterization and tests. In addition, the photocatalytic performance of this series of catalysts under full spectrum irradiation was also tested. It is found that the CTM-5 sample has the best photocatalytic activity, and the yields of CO and CH4 are 29.87 and 17.94 μmol g-1  h-1 , respectively. This can be ascribed to the favorable optical absorption performance of the composite catalyst in the full spectrum and the establishment of S-scheme charge transfer channel. The formation of heterojunctions can effectively promote charge transfer. The addition of Ti3 C2 materials provides plentiful active sites for CO2 reaction, and its superior electrical conductivity is also favorable for the migration of photogenerated electrons.

Dual modification based on electrostatic repulsion of bentonite and SPR effect of Bi facilitate charge transfer of Bi2WO6 for antibiotics degradation

Development of efficient photocatalysts is vital for light-driven removal of refractory antibiotics. Herein, Bi₂WO₆ microspheres were successfully anchored on the surface of bentonite, and metallic Bi was reduced in-situ by a one-step solvothermal method. Notably, the Bi/Bi₂WO₆/BT with a mass ratio of 0.15:1:0.1 exhibited the best photocatalytic activity toward degradation of tetracycline (TC) and ciprofloxacin (CIP) after 120 min of visible light irradiation, and their reaction rate constants were 8.0 and 5.5 folds higher than that of pristine Bi₂WO₆, respectively. The boosted photocatalytic activity over Bi/Bi₂WO₆/BT was ascribed to the establishment of electrostatic repulsion and SPR effect, which synergistically promoted charges transfer, thus achieving more h⁺ and ·O₂^- radical generation. Moreover, possible TC and CIP degradation pathways over Bi/Bi₂WO₆/BT were proposed based on the identified intermediates, and most of the intermediates were less toxic than TC and CIP. The study provides options to develop high-efficiency photocatalytic composites for contaminants elimination using semiconductors and readily available bentonite.

Semiconductor photocatalysts: A critical review highlighting the various strategies to boost the photocatalytic performances for diverse applications

The photocatalytic technology illustrates an eco-friendly and sustainable route to overcome environmental and energy issues. The successful construction of a photocatalyst depends on four key elements: light absorption ability, the density of active sites, redox capacity, and photoinduced electron-hole recombination rate. Sincemost of intrinsic semiconductor photocatalysts cannot meet all these requirements, they are often modified to boost their photocatalytic properties. Many strategies have been adopted to design novel and efficient photocatalysts for diverse applications. Herein, we review the most efficient of these strategies and methods focused on effectively overcoming the efficiency limitations of photocatalysts to promote their large-scale application. Subsequently, a particular aim is put on the most current studies for photocatalytic applications, including CO₂ reduction, N₂ fixation, H₂ evolution, and pollutants degradation. Finally, key challenges and future perspectives in designing and implementing semiconductor photocatalysts for large-scale applications are discussed. Therefore, it is foreseen that this review will work as a guide for future research and provides a variety of strategies to develop novel and high-performance photocatalysts for various applications.

Fabrication of a Heterojunction by Coupling a Metal-Organic Framework and N-Doped Carbon for the Photocatalytic Removal of Antibiotic Drugs with High Efficiency

Norfloxacin (NOR) and tetracycline (TC), two widely used antibiotic drugs released to the aquatic environment, induce harm to ecosystems. In this study, an effective method was developed successfully to remove NOR and TC by photocatalysis with a novel heterojunction NC/NH₂-MIL-53(Fe), which was fabricated by combining a metal-organic framework (MOF) material (NH₂-MIL-53(Fe)) and N-doped carbon (NC) nanoparticles via a facile solvent thermal method. The prepared product exhibits outstanding photocatalytic efficiencies toward degradation of NOR and TC that are 15 and 6 times higher than those of pure NH₂-MIL-53(Fe), respectively. Moreover, it is higher than those of the related materials reported previously. The greatly enhanced photocatalytic performance is assigned to the fabricated heterojunction with well-matched energy band gaps, where the NC acts as an efficient electron transfer/reservoir material to effectively promote the migration and transfer and restrain the recombination of charge carriers. In addition, the formed heterojunction increases specific surface area and light absorbance. The photocatalytic activity enhanced mechanism, degradation products, and pathway were investigated. The present study offers a novel strategy to significantly improve the photocatalytic performances of MOFs for highly efficient photocatalytic removal of antibiotic drugs in wastewater.

Visible light driven antibiotics degradation using S-scheme Bi2WO6/CoIn2S4 heterojunction: Mechanism, degradation pathways and toxicity assessment

S-scheme heterojunction photocatalysts with strong redox ability and excellent photocatalytic activity are highly desired for photocatalytic degradation of pollutants. Herein, S-scheme Bi₂WO₆/CoIn₂S₄ heterojunctions were synthesized using hydrothermal method. The photo-induced carriers transfer mechanism of the S-scheme Bi₂WO₆/CoIn₂S₄ heterojunction was clarified by band structure analysis, ultraviolet photoelectron spectrometer (UPS), electron spin resonance (ESR) and radical trapping experiments. Significant enhance of light absortion, and more efficient carriers separation were observed from the Bi₂WO₆/CoIn₂S₄ with CoIn₂S₄ nanoclusters growing on the surface of petal-like Bi₂WO₆ nanosheets. TC degradation efficiency of 90% was achieved by Bi₂WO₆/CoIn₂S₄ (15:1) within 3 h of irradiation, and ·O₂^-and ·OH radicals were dominated contributors. Possible decomposition pathways of TC were proposed, and ECOSAR analysis showed that most of the intermediates exhibited lower ecotoxicity than TC. This work provides reference on the constructing ternary-metal-sulfides-based S-scheme heterojunctions for improving photocatalytic performance.

Boosting Interfacial Charge Transfer with a Giant Internal Electric Field in a TiO2 Hollow-Sphere-Based S-Scheme Heterojunction for Efficient CO2 Photoreduction

The construction of an S-scheme charge transfer pathway is considered to be a powerful way to inhibit charge recombination and maintain photogenerated carriers with high redox capacity to meet the kinetic requirements of the carbon dioxide (CO₂) photoreduction reaction. For an S-scheme heterojunction, an internal electric field (IEF) is regarded as the main driving force for accelerating the interfacial spatial transfer of photogenerated charges. Herein, we designed a TiO₂ hollow-sphere (TH)-based S-scheme heterojunction for efficient CO₂ photoreduction, in which WO₃ nanoparticles (WP) were applied as an oxidation semiconductor to form an intimate interfacial contact with the TH. The S-scheme charge transfer mode driven by a strong IEF for the TH/WP composite was confirmed by in situ X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. As a result, abundant photogenerated electrons with strong reducing ability would take part in the CO₂ reduction reaction. The combination of surface photovoltage spectra and transient photocurrent experiments disclosed that the IEF intensity and charge separation efficiency of the fabricated TH/WP composite were nearly 16.80- and 1.42-fold higher, respectively, than those of the pure TH. Furthermore, sufficient active sites provided by the hollow-sphere structure also enhanced the kinetics of the catalytic reaction. Consequently, the optimized TH/WP composite showed a peak level of CO production of 14.20 μmol g^-1 in 3 h without the addition of any sacrificial agent. This work provides insights into the kinetic studies of the S-scheme charge transfer pathway for realizing high-performance CO₂ photoreduction.

Synergistic Cr(VI) Reduction and Chloramphenicol Degradation by the Visible-Light-Induced Photocatalysis of CuInS2: Performance and Reaction Mechanism

Despite significant scientific efforts in the field of water treatment, pollution of drinking water by toxic metal ions and synthetic organic compounds is becoming an increasing problem. The photocatalytic capabilities of CuInS₂ nanoparticles were examined in this study for both the degradation of chloramphenicol (CAP) and the reduction of Cr(VI). CuInS₂ nanoparticles were produced using a straightforward solvothermal approach and subsequently characterized by many analysis techniques. Simultaneous photocatalytic Cr(VI) reduction and CAP oxidation by the CuInS₂ nanoparticles under visible-light demonstrated that lower pH and sufficient dissolved oxygen favored both Cr(VI) reduction and CAP oxidation. On the basis of active species quenching experiments, the possible photocatalytic mechanisms for Cr(VI) conversion with synchronous CAP degradation were proposed. Additionally, the CuInS₂ retains a high rate of mixed pollutant removal after five runs. This work shows that organic contaminants and heavy metal ions can be treated concurrently by the visible-light-induced photocatalysis of CuInS₂.