Introduction of porous structure via facile carbon-dot modulation: A feasible and promising approach for improving the photocatalytic capability of sulfur doped g-C3N4

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.

Sulfur-doped graphitic carbon nitride: Tailored nanostructures for photocatalytic, sensing, and energy storage applications

Rapid globalization and industrialization have led to widespread pollution and energy crises, necessitating the development of innovative solutions. Metal-free g-C3N4-based polymeric materials have unique properties but face limitations such as low surface area and inefficient light absorption. Doping, especially sulfur doping, is a prevalent technique to enhance their optical and electronic properties. This comprehensive review focuses on the synthesis techniques employed for sulfur doping of g-C3N4 (S-CN), highlighting the complexities associated with S-doping and the advantages of co-doping. Additionally, the review encompasses the diverse applications of S-CN in catalysis, photocatalysis, sonocatalysis, pollutant remediation, and electrochemical sensing. By incorporating sulfur into the g-C3N4 structure, various desirable properties can be achieved, including improved light absorption efficiency and enhanced charge carrier separation and migration. These advancements have broadened the application potential of S-CN in a range of important fields. S-CN has shown promise as a catalyst, facilitating various chemical reactions, as well as a photocatalyst, harnessing solar energy for environmental remediation and energy conversion processes. Moreover, S-CN exhibits potential in sonocatalysis for ultrasound-mediated reactions, pollutant remediation, and electrochemical sensing applications.

Efficient Combination of G-C3 N4 and CDs for Enhanced Photocatalytic Performance: A Review of Synthesis, Strategies, and Applications

Recently, heterogeneous photocatalysts have achieved much interest on account of their great potential applications in resolving many tough energy and environmental troubles around the world through an ecologically sustainable way. Heterogeneous nanocomposites composed of graphitic carbon nitride (g-C₃ N₄ ) and carbon dots (CDs) possess broad spectrum absorption, appropriate electronic band structures, rapid carrier mobility, abundant reserves, excellent chemical stability, and facile synthesis methods, which make them promising composite photocatalysts for suitable applications such as photocatalytic solar fuels production and contaminant decomposition. With the rapid development in photocatalysis by hybridization of g-C₃ N₄ and CDs, a systematic summary and prospection of performance improvement are urgent and meaningful. This review first focuses on various kinds of effectively synthetic methods of composites. Following, the strategies available for enhanced performance, including morphology optimization, spectral absorption improvement, ternary or quaternary composition hybrid, lateral or vertical heterostructures construction, heteroatom doping, and so forth, are fully discussed. Then, the applications mainly in efficient photocatalytic hydrogen generation, photocatalytic carbon dioxide reduction, and organic pollutants degradation are systematically demonstrated. Finally, the remaining issues and prospect of further development are proposed as some kind of guidance for powerful combination of g-C₃ N₄ and CDs with high efficiency to photocatalysis.

Sulfur-doped graphitic carbon nitride for Tm:YAIO3 laser operation at 2.3 µm

We report on the first, to the best of our knowledge, passive Q-switching operation at 2.3 µm passively based on Tm:YAIO₃ (Tm:YAP) ³H₄→³H₅ transition with sulfur-doped graphitic carbon nitride (g-gC₃N₄) as the saturable absorber. Sulfur-doping engineering in g-C₃N₄ was manifested to enhance its mid-infrared nonlinear saturable absorption characteristics, which was confirmed by the conventional open-aperture Z-scan experiment with the excitation at 2.3 µm. The large effective nonlinear absorption coefficient of S-gC₃N₄ was determined to be -0.68cm/GW, indicating the remarkable MIR optical response. Initiated by S-gC₃N₄, a passively Q-switched laser operating at 2274.6 nm was configured with a-cut 3.0 at.% Tm:YAP as the gain medium. Stable Q-switching pulses were generated with the shortest pulse width of 140 ns, corresponding to the maximum peak power of 21.8 W. The experimental results reveal the effectiveness of sulfur doping to improve the performance of g-C₃N₄ in the MIR pulse generation.

Visible-light-driven photocatalytic degradation of RhB by carbon-quantum-dot-modified g-C3N4 on carbon cloth

Highly efficient semiconductor photocatalysis technology is widely used for water purification.

High crystallinity and conjugation promote the polarization degree in O-doped g-C3N4 for removing organic pollutants

High crystallinity and extended conjugated system improve the polarization of O-doped g-C₃N₄, which efficiently promotes carrier separation.

Effective blockage of chloride ion quenching and chlorinated by-product generation in photocatalytic wastewater treatment

Photocatalytic degradation of pollutants in high salinity wastewater usually shows extremely low activities and produces highly toxic by-products, often related to the presence of excess chloride ion (Cl^-). Herein, we report for the first time that involvement of Cl^- (quenching active species and generating chlorinated by-products) could be effectively blocked during photocatalytic processes. Based on a comprehensive investigation of its mechanism, we found that Cl^- could quench superoxide radicals (O₂^-) through a cyclic indirect quenching model with holes (h⁺) and hydroxyl radicals (OH) quenching as "initiators". Thus, scavenging h⁺ and OH could successfully block the chain reactions between Cl^- and O₂^-, and photocatalytic degradation of methyl orange (a refractory dye, with O₂^- as dominant attacking species) could be enhanced by nearly 50 times, even when Cl^- content was up to 10 wt%. More importantly, both HPLC-MS analyses and DFT calculation validated that, by blocking its quenching effect, Cl^- could be successfully excluded from the pollutant degradation processes, thus preventing the generation of toxic chlorinated by-products. This work provides new insights into control of chlorinated by-products and proposes feasible strategies to extend photocatalytic technology in high salinity wastewater.

One-step preparation of sulfur-doped porous g-C3N4 for enhanced visible light photocatalytic performance

Nonmetal doping is a convenient method to adjust the visible light photocatalytic activity of graphitic carbon nitride (g-C3N4). Herein, highly active sulfur-doped porous g-C3N4 (C3N4-S) was successfully prepared by one-step calcination using thiourea and melamine as the precursors. C3N4-S exhibited excellent photocatalytic performance for the degradation of Rhodamine B (RhB) under visible light irradiation. C3N4-S not only promoted the separation of photogenerated electron-hole pairs, but also enhanced electron transfer, resulting in a great improvement in the photocatalytic efficiency. Based on capture experiments and DMPO spin-trapping ESR spectra, the superoxide radical (˙O2-) was proved to be the predominant active species and the possible photocatalytic mechanism of C3N4-S was proposed. The photocatalytic mechanism of RhB degradation over C3N4-S was further explored using high-resolution mass spectra (HRMS).

Molecularly imprinted carbon nanosheets supported TiO2: Strong selectivity and synergic adsorption-photocatalysis for antibiotics removal

In order to achieve strong specific recognition and remarkable synergy between adsorption and photocatalysis, carbon nanosheets supported TiO₂ (CT) was designed and embellished by molecular imprinting technology with ciprofloxacin (CIP) as template. The molecular imprinted CT (CT-MI) product exhibited remarkable synergy of adsorption-photocatalysis and high selectivity in both aspects, benefitted from specific recognition of imprinted layer, strong carbon adsorption and electroconductivity, and enhanced photocatalysis. Compared to the competitive pollutant, sulfamethoxazole (SMZ) in this study, selectivity coefficient was 7.2 for adsorption and 3.2 for photocatalysis, respectively. This is superior to most of the imprinted photocatalysts reported in the literature. In addition, effect of mass ratio between TiO₂ matrix to imprinted polymers, as well as water quality and composition, to the performance of final product was studied and favorable conditions were proposed. Electron transfer mode, selective recognition mode, and antibiotics degradation mechanism and pathways were also illustrated based on trapping experiments and HPLC-MS technology etc. This study confirmed that alliance between molecular imprinting, carbon nanosheets and well dispersed photocatalyst possessed broad prospect of applications in specific recognition and selective degradation of a highly toxic pollutant in a variety of mixed systems.