Construction of silver iodide/silver/bismuth tantalate Z-scheme photocatalyst for effective visible light degradation of organic pollutants

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.

Recent advances in degradation of organic pollutant in aqueous solutions using bismuth based photocatalysts: A review

Today, a major concern associated with the environment is the water pollution occurred due to the introduction of variety of persistent organic pollutants and residual dyes from different sources (e.g., dye and dye intermediates industries, paper and pulp industries, textile industries, tannery and craft bleaching industries, pharmaceutical industries, etc.) into our natural water resources. Recently, advanced oxidation processes (AOPs) by photocatalyst have garnered great attention as a new frontier promising eco-friendly and sustainable wastewater treatment technology. Utilization of the photocatalytic technology efficiently is significant for cleaner environment. Bismuth based photocatalyst have aroused widespread attention as a visible light responsive photocatalyst for waste water treatment due to their non-toxicity, low cost, modifiable morphology, and outstanding optical and chemical properties. In this review, we have dealt with the research progress on bismuth-based photocatalysts for waste water treatment. However, it seems to give limitation over pristine photocatalysts such as slow migration of charge carriers, charge carrier recombination, low visible light absorption, etc., Various bismuth based photocatalyst and its modifications via doping, heterojunction, Z-scheme etc., are discussed in detail. Further, the strategies adopted to improve the photocatalytic activity of bismuth based photocatalyst to improve the waste water treatment (mostly drugs and dyes) are critically reviewed. Also, we have discussed the bacterial inactivation by bismuth based photocatalyst. Finally, the challenges and future aspects against bismuth based photocatalyst are explored for further research.

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.

Controlled preparation of hollow Zn0.3Cd0.7S nanospheres modified by NiS1.97 nanosheets for superior photocatalytic hydrogen production

Developing durable and efficient photocatalysts for H₂ evolution is highly desirable to expedite current research on solar-chemical energy conversion. In this work, a novel photocatalytic H₂ evolution system based on Zn_0.3Cd_0.7S/NiS_1.97 nanocomposite was rationally designed for the first time. In this advanced composite structure, NiS_1.97 nanosheets as a co-catalyst were intimately coupled to the inner surface of the hollow spherical Zn_0.3Cd_0.7S. The construction of the hollow spherical shell shortened the distance of charge migration to the surface site and increased the multiple absorption of incident light. The introduction of NiS_1.97 nanosheets increased the light absorption capacity of the composite system and also greatly improved the separation and migration behavior of photo-generated carriers due to its narrower band gap and relatively low conduction band position, which had been confirmed by DRS, EIS and PL. As a result, the hollow Zn_0.3Cd_0.7S/NiS_1.97 composite material exhibited excellent photocatalytic activity. At the loading amount of NiS_1.97 up to 15 at.%, the hollow Zn_0.3Cd_0.7S/NiS_1.97 composite exhibited the best photocatalytic activity with a corresponding H₂ production rate of 22.637 mmol g^-1h^-1, which was 1.42 times and 1.85 times that of hollow Zn_0.3Cd_0.7S and solid Zn_0.3Cd_0.7S, respectively. Moreover, this novel catalyst also displayed a long-term stability without apparent debasement in H₂ evolution activity. It is expected that this work could provide new inspiration to the design and development of other highly active photocatalytic systems for water splitting.

Recent advances in photodegradation of antibiotic residues in water

Antibiotics are widely present in the environment due to their extensive and long-term use in modern medicine. The presence and dispersal of these compounds in the environment lead to the dissemination of antibiotic residues, thereby seriously threatening human and ecosystem health. Thus, the effective management of antibiotic residues in water and the practical applications of the management methods are long-term matters of contention among academics. Particularly, photocatalysis has attracted extensive interest as it enables the treatment of antibiotic residues in an eco-friendly manner. Considerable progress has been achieved in the implementation of photocatalytic treatment of antibiotic residues in the past few years. Therefore, this review provides a comprehensive overview of the recent developments on this important topic. This review primarily focuses on the application of photocatalysis as a promising solution for the efficient decomposition of antibiotic residues in water. Particular emphasis was laid on improvement and modification strategies, such as augmented light harvesting, improved charge separation, and strengthened interface interaction, all of which enable the design of powerful photocatalysts to enhance the photocatalytic removal of antibiotics.

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.

Silver-based semiconductor Z-scheme photocatalytic systems for environmental purification

Silver-based semiconductor photocatalysts are promising materials for solving environmental and energy issues due to their strong optical absorption, excellent quantum efficiency and photoelectrochemical properties. However, the uncontrollable photocorrosion and high use cost of single silver-based semiconductor photocatalysts limit its practical application. The construction of Z-scheme photocatalytic systems that mimic natural photosynthesis can not only enhance the photocatalytic activity of silver-based semiconductor photocatalysts, but also improve their stability and reduce the use costs. This critical review concisely highlights the basic principles of Z-scheme photocatalytic systems, and discusses the construction of silver-based semiconductor Z-scheme photocatalytic systems and the roles of metallic Ag in there and summarizes the synthesis methods of silver-based semiconductor Z-scheme photocatalytic systems. Then, a series of the solar-driven applications are elaborated, including organic pollutants degradation, hydrogen production, and carbon dioxide reduction. Meanwhile, the mechanism and difficult level of these photocatalytic reactions are also described. Besides, metal organic frameworks (MOFs) as a novel type of photocatalysts have attracted growing attention. The novel combination of silver-based semiconductors with typical photoactive MOFs is highlighted based on the Z-scheme photocatalytic systems. Eventually, the future challenges and prospects in the development of silver-based semiconductor Z-scheme photocatalytic systems are presented.

All-solid-state Z-scheme WO3 nanorod/ZnIn2S4 composite photocatalysts for the effective degradation of nitenpyram under visible light irradiation

A Z-scheme WO₃/ZnIn₂S₄ photocatalyst was synthesized via a simple solvothermal method. Compared with pure WO₃ and ZnIn₂S₄, photocatalytic experiments showed that these Z-scheme photocatalysts exhibited enhanced activity for the degradation of nitenpyram (NTP). The apparent rate constant (k) of NTP degradation on 50WZ (WO₃/ 50 wt% Znln₂S₄) was 0.042 min^-1 (∼3.8 times higher than WO₃ and ∼2.5 times higher than ZnIn₂S₄). Photoluminescence (PL), photocurrent (PC), and electrochemical impedance spectroscopy (EIS) showed that the separation and transfer efficiency of photogenerated carriers in 50WZ was markedly enhanced, which was favorable for improving its photocatalytic activity. Active species capture experiments and electron spin resonance (ESR) measurements showed that superoxide radicals and holes were the main active species for NTP degradation, and they confirmed the formation of the Z-scheme structure. Furthermore, a possible NTP degradation pathway was deduced based on the results of high-performance liquid chromatography mass spectrometry (HPLC-MS).

A comparative study in single- and binary-contaminant systems: the photodegradation of tetracycline and imidacloprid on flower-shaped Ag/AgBr/BiOBr under visible-light irradiation

A synergistic effect demonstrated in binary-contaminant systems is shown to be caused by the mutually complementary utilization of active species during photodegradation.

Fabrication of metal-free PTET-T-COOH/g-C3N4 heterostructure for enhancing photocatalytic activity

In this research work, we successfully fabricated a range of PTET-T-COOH/g-C₃N₄ heterostructures via a simple method. The as-prepared PTET-T-COOH/g-C₃N₄ heterostructures show enhanced photocatalytic degradation activity as compared to pure g-C₃N₄. For the photocatalytic degradation of RhB, the optimal PTET-T-COOH/g-C₃N₄-1% heterostructure is nearly 3.83 times that of the pure g-C₃N₄. The enhancement of photocatalytic performance is ascribed to three aspects: one is the strong interaction between PTET-T-COOH and g-C₃N₄; the second is the larger surface area of the PTET-T-COOH/g-C₃N₄ heterostructure compared to that of pure g-C₃N₄; the third is the effectively improved transferability of photogenerated carriers. In addition, the whole photocatalytic reaction mechanism over the PTET-T-COOH/g-C₃N₄ heterostructure is provided. This work may offer a hopeful method to synthesize any other heterostructure with high stability and superior photocatalytic activity.

The metal-free PTET-T-COOH/g-C₃N₄ heterostructure exhibits a high degradation rate for RhB under visible light irradiation.

Iodine ion doped bromo bismuth oxide modified bismuth germanate: A direct Z-scheme photocatalyst with enhanced visible-light photocatalytic performance

A series of Z-scheme I-BiOBr/Bi₁₂GeO₂₀ heterostructures were successfully obtained by a simple method. The Z-scheme I-BiOBr/Bi₁₂GeO₂₀ heterostructures show outstanding photocatalytic performance for degrading the various organic pollutants of the waste water. For degradation of Tetracycline (TC), the Z-scheme 30I-BiOBr/Bi₁₂GeO₂₀ heterostructure exhibits the superior rate constant, which is about 7.73 times, 3.52 times and 1.66 times higher than that of the pure Bi₁₂GeO₂₀, BiOBr and I-BiOBr, respectively. Meanwhile, as we expected, the Z-scheme 30I-BiOBr/Bi₁₂GeO₂₀ heterostructure also displays the enhanced photocatalytic perfomance for degradation of Ciprofloxacin (CIP), 2-Mercaptobenzothiazole (MBT) and reduction of aqueous Cr(VI). The enhancement of photocatalytic performance is attributed to the high redox capacity and the strong interfacial interaction between I-BiOBr and Bi₁₂GeO₂₀, which can effectively improve the separation of photo-induced electron-hole pairs. Additionally, the photocatalytic mechanism over the Z-scheme I-BiOBr/Bi₁₂GeO₂₀ heterostructure is provided. The research work may provide a promising approach to fabricate other Z-scheme heterostructures with efficient photocatalytic performance.

Rodlike AgI/Ag2Mo2O7 Heterojunctions with Enhanced Visible-Light-Driven Photocatalytic Activity

Novel AgI/Ag2Mo2O7 heterojunctions were prepared by reacting Ag2Mo2O7 microrods with an aqueous KI solution at room temperature. The composite materials, compared with neat AgI and Ag2Mo2O7, showed much higher activities in the photocatalytic degradation of aqueous rhodamine B, methyl orange, tetracycline hydrochloride, and levofloxacin solutions under visible-light irradiation. The structures, morphologies, and other physicochemical properties of AgI, Ag2Mo2O7, and AgI/Ag2Mo2O7 composites were studied via various characterization techniques. The active species involved in the photocatalytic process were examined via radical-capturing experiments and electron spin resonance. Superoxide anion radicals (•O2 -) and photogenerated holes (h+) were found to be the main active species. Photocatalytic mechanisms were proposed and reasons for the enhanced photocatalytic activity were explained.

In situ S-doped ultrathin gC3N4 nanosheets coupled with mixed-dimensional (3D/1D) nanostructures of silver vanadates for enhanced photocatalytic degradation of organic pollutants

A novel plasmonic Z-scheme sulphur doped gC₃N₄/Ag₃VO₄/β-AgVO₃/Ag (SGA-x) hybrid quaternary photocatalyst was successfully fabricated via the ultrasonic assisted Kirkendall effect and diffusion processes followed by low temperature phase conversion.

Visible-light degradation of sulfonamides by Z-scheme ZnO/g-C3N4 heterojunctions with amorphous Fe2O3 as electron mediator

ZnO grafted amorphous Fe₂O₃ matrix (ZnO/Fe₂O₃) was coupled with g-C₃N₄ to synthesize heterojunction photocatalysts with a loosened multilayered structure. The ZnO/Fe₂O₃/g-C₃N₄ exhibited enhanced photocatalytic performance in the degradation of sulfamethazine under visible-light irradiation (λ > 420 nm), with an optimum photocatalytic degradation rate approximately 3.0, 2.4 times that of pure g-C₃N₄ and binary ZnO/g-C₃N₄. Moreover, the target sulfonamides spiked in actual surface water samples could be efficiently photodegraded by ZnO/Fe₂O₃/g-C₃N₄ after 8 h of irradiation, demonstrating its practical potential. An amorphous Fe₂O₃-mediated Z-scheme mechanism was proposed for the charge transfer at the heterojunction surface, which involved a Fe(III)/Fe(II) oxidation-reduction center that favored the retarded charge recombination and improved photocatalytic activity. Such a mechanism was well supported by the direct detection of surface generated O₂^- and OH reactive species. Finally, detailed transformation pathways were proposed based on the photodegradation products identified by QToF-MS analyses. This work provides an illustrative strategy for developing efficient Z-scheme photocatalysts for water purification, by taking advantage of amorphous Fe-based oxides in the semiconductor lattice matching.

Synthesis of Flower-Like AgI/BiOCOOH p-n Heterojunctions With Enhanced Visible-Light Photocatalytic Performance for the Removal of Toxic Pollutants

In this study, flower-like AgI/BiOCOOH heterojunctions were constructed through a two-step procedure involving the solvothermal synthesis of BiOCOOH microflowers followed by AgI modification using a precipitation method. These novel photocatalysts were systematically examined by XRD, UV–vis DRS, SEM, TEM, EDS, and PL spectroscopy techniques. The AgI/BiOCOOH heterojunction were studied as a decent photocatalyst for the removal of the industrial dye (rhodamine B, and methyl blue) and antibiotic (tetracycline) under visible light. The AgI/BiOCOOH heterojunctions are much more active than bare BiOCOOH, and AgI, which could be ascribed to the improved separation of charge carriers, resulting from the formation of p-n heterojunction between two constituents. The holes (h⁺) and superoxide radical (•O2-) were detected as the main active species responsible for the pollutant degradation. The results showed that a highly efficient visible-light-driven photocatalytic system was developed for the decomposition of toxic pollutants.