Investigation of the Kinetics and Reaction Mechanism for Photodegradation Tetracycline Antibiotics over Sulfur-Doped Bi2WO6-x/ZnIn2S4 Direct Z-Scheme Heterojunction

Chemical-Vapor-Deposition-Synthesized Two-Dimensional Non-Stoichiometric Copper Selenide (β-Cu2-xSe) for Ultra-Fast Tetracycline Hydrochloride Degradation under Solar Light

The high concentration of antibiotics in aquatic environments is a serious environmental issue. In response, researchers have explored photocatalytic degradation as a potential solution. Through chemical vapor deposition (CVD), we synthesized copper selenide (β-Cu2-xSe) and found it an effective catalyst for degrading tetracycline hydrochloride (TC-HCl). The catalyst demonstrated an impressive degradation efficiency of approximately 98% and a reaction rate constant of 3.14 × 10-2 min-1. Its layered structure, which exposes reactive sites, contributes to excellent stability, interfacial charge transfer efficiency, and visible light absorption capacity. Our investigations confirmed that the principal active species produced by the catalyst comprises O2- radicals, which we verified through trapping experiments and electron paramagnetic resonance (EPR). We also verified the TC-HCl degradation mechanism using high-performance liquid chromatography-mass spectrometry (LC-MS). Our results provide valuable insights into developing the β-Cu2-xSe catalyst using CVD and its potential applications in environmental remediation.

Modulation of Z-scheme photocatalysts for pharmaceuticals remediation and pathogen inactivation: Design devotion, concept examination, and developments

The recent outbreak of Covid-19 guarantees overconsumption of different drugs as a necessity to reduce the symptoms caused by this pandemic. This triggers the proliferation of pharmaceuticals into drinking water systems. Is there any hope for access to safe drinking water? Photocatalytic degradation using artificial Z-scheme photocatalysts that has been employed for over a decade conveys a prospect for sustainable clean water supply. It is compelling to comprehensively summarise the state-of-the-art effects of Z-scheme photocatalytic systems towards the removal of pharmaceuticals in water. The principle of Z-scheme and the techniques used to validate the Z-scheme interfacial charge transfer are explored in detail. The application of the Z-scheme photocatalysts towards the degradation of antibiotics, NSAIDs, and bacterial/viral inactivation is deliberated. Conclusions and stimulating standpoints on the challenges of this emergent research direction are presented. The insights and up-to-date information will prompt the up-scaling of Z- scheme photocatalytic systems for commercialization.

Enhanced Visible-Light-Responsive Photocatalytic Degradation of Ciprofloxacin by the CuxO/Metal-Organic Framework Hybrid Nanocomposite

Ciprofloxacin (CIP) is a commonly used antibiotic, however, once in the environment, it is highly toxic with a poor biodegradability. Given these attributes, an effective strategy for the removal of CIP is urgently needed for the protection of water resources. Herein, a novel copper metal-organic framework (CuxO/MOF) multifunctional material has been produced, in this work, by the calcination of Cu-MOF urea at 300 °C, in the presence of a 5% H2 atmosphere. The morphological, structural, and thermal properties of the prepared CuxO/MOF were determined through various techniques, and its photocatalytic behavior was investigated for the degradation of CIP under visible-light irradiation. The prepared CuxO/MOF bifunctional material is presented as a graphitic carbon-layered structure with a particle size of 9.2 ± 2.1 nm. The existence of CuO-Cu2O-C, which was found on the CuxO/MOF surface, enhanced the adsorption efficiency and increased the photosensitivity of CuxO/MOF, towards the degradation of CIP in aqueous solutions. The tailored CuxO/MOF, not only shows an excellent CIP degradation efficiency of up to 92% with a constant kinetic rate (kobs) of 0.048 min−1 under visible light, but it can also retain the stable photodegradation efficiency of >85%, for at least six cycles. In addition, CuxO/MOF has an excellent adsorption capacity at pH 6.0 of the maximum Langmuir adsorption capacity of 34.5 mg g−1 for CIP. The results obtained in this study demonstrate that CuxO/MOF is a reliable integrated material and serves as an adsorbent and photocatalyst, which can open a new pathway for the preparation of visible-light-responsive photocatalysts, for the removal of antibiotics and other emerging pollutants.

Recent progress on elemental sulfur based photocatalysts for energy and environmental applications

The growing needs of the rising population and blatant misuse of resources have contributed enormously to environmental problems. Among the various methods, photocatalysis has emerged as one of the effective remediation methods. The continuous search for effective photocatalysts that can be made from abundant, cheap, non-toxic materials is going on. Although sulfur is a known insulator, recent sulfur use as a visible light photocatalyst has ushered a new era in this direction. Sulfur is a non-toxic, cheap, and abundant photocatalyst, exhibiting significant photocatalytic properties. But, hydrophobicity, poor light-harvesting and high recombination rate of charge carriers in elemental sulfur photocatalyst are some of the major drawbacks of the elemental sulfur photocatalyst. The photocatalytic activity of sulfur as a single element was low, but various methods such as nanoscaling, heterojunction formation, doping and surface modifications have been used to enhance it. The review highlights sulfur's crystal structure, electronic and optical properties, and morphological changes, making it an excellent visible light photocatalyst. The article points to the limitations of sulfur as a single photocatalyst and various strategies to improve the shortcomings. More recently, there has been an emphasis on the synthesis of metal-free photocatalysts. This review provides its readers with a comprehensive detail of sulfur being used as a dopant in improving the photocatalytic properties of metal-free photocatalysts and their environmental remediation use. Finally, the conclusion and future perspectives for sulfur-based nanostructures are presented.

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

Semiconductor materials dominated photocatalytic technology is one of the most efficient approaches to degrade organic pollutants. However, the limited light absorption range and rapid recombination of photogenerated carriers greatly restrict the application of photocatalysts. Rational design of photocatalysts to achieve high catalytic activity and stability is of great importance. Herein, ZnIn₂S₄/Bi₄Ti₃O₁₂ S-scheme heterojunction is synthesized by growing the ZnIn₂S₄ nanosheets on the sheet-like Bi₄Ti₃O₁₂ surface via a low-temperature solvothermal method. The TC removal efficiency of optimized heterojunction reaches 82.1% within 60 min under visible light, and the rate constant is nearly 6.8 times than that of pristine ZnIn₂S₄. The favorable photocatalytic performance of heterojunction is attributed to the tight contact interface and efficient separation of photogenerated carriers. Besides, the difference in work function between ZnIn₂S₄ and Bi₄Ti₃O₁₂ leads to band bending and the establishment of built-in electric field on the contact interface of heterojunction, which facilitates the migration and separation of photogenerated carriers. Furthermore, the cycling test demonstrates the attractive stability of heterojunction. The possible TC photodegradation pathways and toxicity assessment of the intermediates are also analyzed. In conclusion, this work provides an effective strategy to prepare S-scheme heterojunction photocatalysts with favorable photocatalytic activity, which can enhance wastewater purification efficiency.

Outlook on bismuth-based photocatalysts for environmental applications: A specific emphasis on Z-scheme mechanisms

Semiconductor photocatalysis is thought to be a viable solution for addressing the growing problem of environmental pollution. Bismuth (Bi) metal oxides can function as a direct plasmonic photocatalyst or cocatalyst to accelerate the photogenerated charge separation and thus improve their photocatalytic activity. Hence, Bi-based photocatalysts have received a lot of attention due to their extensive environmental applications, including pollutant remediation and energy concepts. Massive efforts have been undertaken in the recent decade to find superior Bi-metal oxides (Bi₂XO_6, X = MO, W, or Cr) and to uncover the corresponding photocatalytic reaction mechanism for the degradation of organic contaminants in water. Herein, the unique crystalline and electronic properties and main synthesis methods, as well as the major Bi-Based direct Z-scheme photocatalysts, are timely discussed and summarized in their usage in water treatment. Besides, the impact of Bi₂XO₆ in energy storage devices and solar energy conversion is reviewed as an energy application. Finally, the future development and challenges of Z-scheme-based Bi₂XO₆ photocatalysts are briefly explored, summarized, and forecasted.

The Growth of Extended Melem Units on g-C3N4 by Hydrothermal Treatment and Its Effect on Photocatalytic Activity of g-C3N4 for Photodegradation of Tetracycline Hydrochloride under Visible Light Irradiation

In this work, the growth of extended tri-s-triazine units (melem units) on g-C₃N₄ (CN) by hydrothermal treatment and its effect on the photodegradation efficiency of tetracycline hydrochloride (TC) is investigated. The CN-180-x and CN-200-6 samples were prepared using different hydrolysis times and temperatures, and they were characterized by multiple physicochemical techniques. In addition, their photodegradation performance was evaluated under visible light irradiation. Compared to the CN, CN-180-6 possesses remarkable photocatalytic degradation efficiency at 97.17% towards TC removal in an aqueous solution. The high visible-light-induced photo-reactivity of CN-180-6 directly correlates to charge transfer efficiency, numerous structural defects with a high specific surface area (75.0 m² g^-1), and sufficient O-functional groups over g-C₃N₄. However, hydrothermal treatment at a higher temperature or during a longer time additionally induces the growth of extended melem units on the surface of g-C₃N₄, resulting in the inhibition of the charge transfer. In addition, the superoxide radical is proven to be generated from photoexcited reaction and plays a key role in the TC degradation.

Levofloxacin degradation under visible-LED photo-catalyzing by a novel ternary Fe-ZnO/WO3 nanocomposite

As semiconductor photocatalysts showing their efficient redox ability upon illumination, new development of materials to enhance the pollution degradation is gaining popularity, especially on their oxidation ability. In this study, a highly stable ternary Fe-ZnO/WO₃ nanocomposite photocatalyst has been synthesized in order to improve charge transfer of photocatalytic oxidation under 30W LED light (425-470 nm) to efficiency degrade the Levofloxacin (LVF) in the solution. This catalyst was characterized and analyzed by XRD, FE-SEM, HR-TEM, X-ray XPS, UPS, PL, TRPL, LSV, EIS, and Photocurrent. Various important factors for the photodegradation were investigated, including Fe content, initial LVF concentration, catalyst dosage, and solution pH. The optimal conditions were Fe 1.0 wt%, LVF 10 mg L^-1, Fe-ZnO/WO₃ dosage 0.5 g L^-1, and pH 7 for LVF photodegradation up to 96% with a kinetic rate constant of 0.0342 min^-1 and were stable in photodegradation efficiency (90%) after five test cycles. In the visible LED light, the activation bandgap was estimated to be 2.75 eV with high electron-hole pair separation and charge transfer from Fe-ZnO to WO₃ that could enhance the generation of active species of ^•OH. Moreover, the more effective charge separation of Fe-ZnO/WO₃ were confirmed by lower PL intensity and longer charge carrier lifetime. Fe-ZnO/WO₃ also demonstrated the excellent electrochemical properties with high photocurrent and small resistance. For the LVF degradation, 3 possible pathways were proposed with 12 intermediate products. This study demonstrated that the synthesized Fe-ZnO/WO₃ could serve as a reliable visible-light responsive photocatalysts with the potential for degrading antibiotics in solution.

Rationally Designed Bi2M2O9 (M = Mo/W) Photocatalysts with Significantly Enhanced Photocatalytic Activity

Novel Bi2W2O9 and Bi2Mo2O9 with irregular polyhedron structure were successfully synthesized by a hydrothermal method. Compared to ordinary Bi2WO6 and Bi2MoO6, the modified structure of Bi2W2O9 and Bi2Mo2O9 were observed, which led to an enhancement of photocatalytic performance. To investigate the possible mechanism of enhancing photocatalytic efficiency, the crystal structure, morphology, elemental composition, and optical properties of Bi2WO6, Bi2MO6, Bi2W2O9, and Bi2Mo2O9 were examined. UV-Vis diffuse reflectance spectroscopy revealed the visible-light absorption ability of Bi2WO6, Bi2MO6, Bi2W2O9, and Bi2Mo2O9. Photoluminescence (PL) and photocurrent indicated that Bi2W2O9 and Bi2Mo2O9 pose an enhanced ability of photogenerated electron-hole pairs separation. Radical trapping experiments revealed that photogenerated holes and superoxide radicals were the main active species. It can be conjectured that the promoted photocatalytic performance related to the modified structure, and a possible mechanism was discussed in detail.