Noble metal-free doped graphitic carbon nitride (g-C3N4) for efficient photodegradation of antibiotics: progress, limitations, and future directions

Self-Assembly Synthesis of Oxygen and Sulfur Co-Doped Porous Graphitic Carbon Nitride Nanosheets for Boosting CO2 Photoreduction

Graphitic carbon nitride (CN) has garnered considerable attention in the field of visible-light CO2 photoreduction, but its efficiency remains limited by the intrinsic π-conjugated skeleton. Here, O and S were co-doped CN (O, S/CN) by a facile "hydrolysis + calcination" approach to modulate the physicochemical and electronic structure. Distinctive from S doped CN (SCN), O, S/CN owned porous layer structure with several nanosheets and less SO4 2- groups on the surface. The amount of heteroatom-doping was achieved by changing the hydrothermal temperature. The optimum O, S/CN-80 achieved moderate CO production rate of 1.29 μmol g-1 h-1, which was 3.79 times as much as SCN (0.34 μmol g-1 h-1). The O and most S atoms were substitutionally doped and the effect of S doped state on the improved efficiency of CO generation in O, S/CN was also explored based on the theoretical calculations. This work provides an inspiration to develop efficient dual-doped CN photocatalysts for photocatalytic CO2 reduction.

Electron Push-Pull Effect of Benzotrithiophene-Based Covalent Organic Frameworks on the Photocatalytic Degradation of Pharmaceuticals and Personal Care Products

A covalent organic framework (COF) has emerged as a promising photocatalyst for the removal of pharmaceutical and personal care product (PPCP) contaminants; however, high-performance COF photocatalysts are still scarce. In this study, three COF photocatalysts were successfully synthesized by the condensation of benzo[1,2-b:3,4-b':5,6-b'']trithiophene-2,5,8-tricarbaldehyde (BTT) with 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline (TAPT), 1,3,5-Tris(4-aminophenyl)benzene (TAPB), and 4,4',4''-nitrilotris(benzenamine) (TAPA), namely, BTT-TAPA, BTT-TAPB, and BTT-TAPT, respectively. The surface areas of BTT-TAPA, BTT-TAPB, and BTT-TAPT were found to be 800.46, 1203.60, and 1413.58 cm2∙g-1, respectively, providing abundant active sites for photocatalytic reactions. Under visible-light irradiation, BTT-TAPT exhibited the highest removal rate of tetracycline (TC), reaching 82.7% after 240 min. The superior photocatalytic performance of BTT-TAPT was attributed to its large specific surface area and the strong electron-acceptor properties of the triazine group. Electron paramagnetic resonance capture experiments and liquid chromatograph mass spectrometer analysis confirmed that superoxide radicals played a pivotal role in the degradation of TC and ciprofloxacin. Moreover, BTT-TAPT exhibited high stability and reproducibility during the photocatalytic degradation process. This study confirms that BTT-based COFs are a class of promising photocatalysts for the degradation of PPCPs in water, and their performance can be further optimized by tuning the structure and composition of the frameworks.

Oxygen-Doped Porous Ultrathin Graphitic Carbon Nitride Nanosheets for Photocatalytic Hydrogen Evolution and Rhodamine B Degradation

Graphite phase carbon nitride (g-C3N4) is a highly promising metal-free photocatalyst, but its low activity, due to limited quantum efficiency and small specific surface area, restricts its practical application. While exfoliating bulk crystals into porous thin-layer nanosheets and incorporating dopants have been shown to improve photocatalytic efficiency, these methods are typically complex, time-consuming, and costly processes. In this study, we developed a simple approach to synthesize oxygen-doped porous g-C3N4 (OCN) nanosheets. The resulting OCN exhibited significantly enhanced light absorption and visible-light photocatalytic activity compared to bulk g-C3N4 (BCN) and g-C3N4 (CN). The OCN achieved an impressive hydrogen evolution reaction (HER) rate of 8.02 mmol g-1 h-1, eight times greater than BCN, and demonstrated a high Rhodamine B (RhB) degradation rate of 97.3 % owing to the generation of abundant singlet oxygen. These improvements in photocatalytic performance are attributed to the narrow band gap and enhanced electron transfer properties, suggesting a promising route for the efficient design of g-C3N4-based photocatalysts.

A focused review on photocatalytic potential of graphitic carbon nitride (g-C3N4) based metal oxide-nanostructures for effective remediation of most overused antibiotics

Researchers in the field of photocatalysis are interested in finding a solution to the problem of charge transfer and recombination in photodegradation mechanisms. The ideal photoactive catalyst would be inexpensive, environmentally friendly, easily manufactured, and highly efficient. Graphitic carbon nitride (g-C3N4) and metal oxide (MOx) based nanocomposites (g-CN/MOx) are among the photocatalysts that provide the best results in terms of charge transfer capacity, redox capabilities, and charge recombination inhibition. This article provides a comprehensive overview of the latest research on antibiotic removal from wastewater using photocatalysts based on g-C3N4 and metal oxides nanocomposites. Amoxicillin (AMX), Azithromycin (AZM), Cefixime (CFM), Ciprofloxacin (CIP), and Tetracycline (TC) are some of the common antibiotics that are the focus of this review article's examination of the photocatalytic behavior of various g-C3N4/metal oxide-based photocatalysts. A research gap demonstrates that many studies are required to use these nanocomposites for photodegradation of antibiotics. By providing a better grasp of the photocatalysis process, this review encourages scientists and researchers to develop an accurate and appropriate photocatalyst to reduce environmental risks. The main findings of this review article suggest that the cost-effective g-C3N4/MOx-based nanocomposites exhibit excellent photodegradation properties, high charge transfer, broadening light response, and charge separation. They promote enhanced charge transportation, superior electron conductivity, high redox capability, and suppressing charge recombination rate. The photodegradation mechanism involves various reactive oxygen species (ROSs), including superoxide radicals, hydroxyl radicals, and holes which promotes the photocatalysis process. The exact transportation mechanism of electrons and holes is unclear, but a rapid charge-carrier transit can significantly increase and speed up the photooxidation process.

Lattice Defects and Electronic Modulation of Flower-Like Zn3In2S6 Promote Photocatalytic Degradation of Multiple Antibiotics

Photocatalysis is an effective technique to remove antibiotic residues from aquatic environments. Typical metal sulfides like Zn3In2S6 have been applied to a wide range of photocatalytic applications. However, there are currently no readily accessible methods to increase its antibiotic-degrading activity. Here, a facile hydrothermal approach is developed for the preparation of flower-like Zn3In2S6 with tunable sulfur lattice defects. Photogenerated carriers can be separated and transferred more easily when there is an adequate amount of lattice defects. Moreover, lattice defect-induced electronic modulation enhances light utilization and adsorption properties. The modified Zn3In2S6 demonstrates outstanding photocatalytic degradation activity for levofloxacin, ofloxacin, and tetracycline. This work sheds light on exploring metal sulfides with sulfur lattice defects for enhancing photocatalytic activity.

Recent progresses in synthesis and modification of g-C3N4 for improving visible-light-driven photocatalytic degradation of antibiotics

Graphitic carbon nitride (g-C3N4) is a widely studied visible-light-active photocatalyst for low cost, non-toxicity, and facile synthesis. Nonetheless, its photocatalytic efficiency is below par, due to fast recombination of charge carriers, low surface area, and insufficient visible light absorption. Thus, the research on the modification of g-C3N4 targeting at enhanced photocatalytic performance has attracted extensive interest. A considerable amount of review articles have been published on the modification of g-C3N4 for applications. However, limited effort has been specially contributed to providing an overview and comparison on available modification strategies for improved photocatalytic activity of g-C3N4-based catalysts in antibiotics removal. There has been no attempt on the comparison of photocatalytic performances in antibiotics removal between modified g-C3N4 and other known catalysts. To address these, our study reviewed strategies that have been reported to modify g-C3N4, including metal/non-metal doping, defect tuning, structural engineering, heterostructure formation, etc. as well as compared their performances for antibiotics removal. The heterostructure formation was the most widely studied and promising route to modify g-C3N4 with superior activity. As compared to other known photocatalysts, the heterojunction g-C3N4 showed competitive performances in degradation of selected antibiotics. Related mechanisms were discussed, and finally, we revealed current challenges in practical application.

Doping matters in carbon nanomaterial efficiency in environmental remediation

Carbon nanomaterials (CNMs) are rapidly emerging in materials science research due to their widespread environmental applications. They are useful for environmental pollutants' remediation through various methods. Heteroatom doping resulted in reliable approaches to overcome pristine CNMs challenges. The engineering of the dopants is believed to be a promising route to improve the efficiency of CNMs in environmental remediation. The idea of doping has been attractive since it allows the control of electronic properties due to the electron transfer between dopants and the host material and the dopants along with the bonding between analogous atoms and carbon atoms. This mini-review, through computational and experimental studies, puts special emphasis on the role of doping different CNMs as an efficient approach to enhance the environmental remediation.

Preparation of MnO2-Carbon Materials and Their Applications in Photocatalytic Water Treatment

Water pollution is one of the most important problems in the field of environmental protection in the whole world, and organic pollution is a critical one for wastewater pollution problems. How to solve the problem effectively has triggered a common concern in the area of environmental protection nowadays. Around this problem, scientists have carried out a lot of research; due to the advantages of high efficiency, a lack of secondary pollution, and low cost, photocatalytic technology has attracted more and more attention. In the past, MnO₂ was seldom used in the field of water pollution treatment due to its easy agglomeration and low catalytic activity at low temperatures. With the development of carbon materials, it was found that the composite of carbon materials and MnO₂ could overcome the above defects, and the composite had good photocatalytic performance, and the research on the photocatalytic performance of MnO₂-carbon materials has gradually become a research hotspot in recent years. This review covers recent progress on MnO₂-carbon materials for photocatalytic water treatment. We focus on the preparation methods of MnO₂ and different kinds of carbon material composites and the application of composite materials in the removal of phenolic compounds, antibiotics, organic dyes, and heavy metal ions in water. Finally, we present our perspective on the challenges and future research directions of MnO₂-carbon materials in the field of environmental applications.

Photocatalytic Degradation of Some Typical Antibiotics: Recent Advances and Future Outlooks

The existence of antibiotics in the environment can trigger a number of issues by fostering the widespread development of antimicrobial resistance. Currently, the most popular techniques for removing antibiotic pollutants from water include physical adsorption, flocculation, and chemical oxidation, however, these processes usually leave a significant quantity of chemical reagents and polymer electrolytes in the water, which can lead to difficulty post-treating unmanageable deposits. Furthermore, though cost-effectiveness, efficiency, reaction conditions, and nontoxicity during the degradation of antibiotics are hurdles to overcome, a variety of photocatalysts can be used to degrade pollutant residuals, allowing for a number of potential solutions to these issues. Thus, the urgent need for effective and rapid processes for photocatalytic degradation leads to an increased interest in finding more sustainable catalysts for antibiotic degradation. In this review, we provide an overview of the removal of pharmaceutical antibiotics through photocatalysis, and detail recent progress using different nanostructure-based photocatalysts. We also review the possible sources of antibiotic pollutants released through the ecological chain and the consequences and damages caused by antibiotics in wastewater on the environment and human health. The fundamental dynamic processes of nanomaterials and the degradation mechanisms of antibiotics are then discussed, and recent studies regarding different photocatalytic materials for the degradation of some typical and commonly used antibiotics are comprehensively summarized. Finally, major challenges and future opportunities for the photocatalytic degradation of commonly used antibiotics are highlighted.