Fabrication of SrTiO3 anchored rGO/g-C3N4 photocatalyst for the removal of mixed dye from wastewater: dual photocatalytic mechanism

A metal-free combination of rGO/g-C3N4-coupled SrTiO3 (SRN) ternary nanocomposite prepared via a wet impregnation method for UV-Vis light photocatalytic applications. Various physicochemical properties of the samples were investigated by several spectroscopic techniques including X-ray diffraction (XRD), FT-IR, Raman, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FE-SEM-EDX), high-resolution transmission electron microscopy (HR-TEM), UV-Vis, photoluminescence (PL), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area analysis. The data suggest agglomerated SRT nanoparticles are dispersed and distributed throughout the surface of the rGO sheets and GCN nanostructures. The photocatalytic performance of the SRN towards combined mixed dye and its degradation activities were evaluated towards the most common industrial effluents, Rhodamine B (RhB) and Methylene blue (MB), under UV-Vis light illumination. The results revealed that the degradation efficiency of the SRN photocatalyst shows excellent performance compared with that of the binary composition and the pure SrTiO3 (SRT) sample. The reaction rate constant for RhB was estimated to be 0.0039 min-1 and for MB to be 0.0316 min-1, which are 3.26 (RhB) and 4.21 (MB) times faster than the pure SRT sample. The enhanced degradation efficiency was attained not only by interfacial formation but also by the speedy transportation of electrons across the heterojunction. After 5 runs of the photocatalytic recylic process, the SRN photocatalyst exhibited ultimate stability without structural changes, and no noticeable degradation was observed. The outcomes of the ternary SRN nanocomposite manifest a dual photocatalytic scheme, the photocatalytic enrichment could be caused by the Z-scheme charge transfer process between GCN, SRT, and rGO nanocomposite, which helps effectual charge separation and keeps a high redox potential. From the results, SRN sample provides insight into the integration of an effective and potential photocatalyst for wastewater treatment toward real-time environmental remediation applications.

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.

Enhanced solar-driven photocatalytic performance of a ternary composite of SnO2 quantum dots//AgVO3 nanoribbons//g-C3N4 nanosheets (0D/1D/2D) structures for hydrogen production and dye degradation

Herein, we report the synthesis of between SnO₂ QDs /AgVO₃ nanoribbons/g-C₃N₄ nanosheets of ternary photocatalytic systems for the production of H₂ through light irradiation. The SnO₂/AgVO₃/g-C₃N₄ photocatalyst was successfully produced by using the hydrothermal process. The structural characterizations of the samples revealed the successful formation of ternary heterostructures where SnO₂, AgVO₃ and g-C₃N₄ (quantum dots/nanoribbons/nanosheets) 0D/1D/2D structures make a good interface with each other. The fabricated heterostructures of AgVO₃/g-C₃N₄ and SnO₂/AgVO₃/g-C₃N₄ photocatalytic structures performed enriched photocatalytic performance for H₂ production over that of the pristine g-C₃N₄, AgVO₃ and SnO₂ photocatalysts. The AgVO₃/g-C₃N₄ and SnO₂ /AgVO₃/g-C₃N₄ of photocatalysts were found to produce H₂ of around 17,000 μmol g^-1 and 77,000 μmol g^-1, respectively, which is much 4.5 times greater than that of AgVO₃/g-C₃N₄ photocatalyst. Moreover, the photodegradation behaviours of prepared catalysts were studied with the dye (rhodamine B, RhB) under light irradiation. The ternary composite SnO₂/AgVO₃/g-C₃N₄ performed photodegradation of RhB in 50 min. The higher photocatalytic activity for the ternary photocatalysts is predominantly due to the effective charge separation at the perfect interface formation amid SnO₂ and AgVO₃/g-C₃N₄.

Recent progress in g-C3N4, TiO2 and ZnO based photocatalysts for dye degradation: Strategies to improve photocatalytic activity

Water contamination by dyes is a matter of concern for human health and the environment. Various methods (membrane separation, coagulation and adsorption) have been explored to remove/degrade dyes. However, now the exploitation of semiconductor assisted materials using renewable solar energy has emerged as a potential candidate to resolve the issue. Although, single component photocatalysts (ZnO, TiO₂, ZrO₂) were experimented, due to their low efficiency and stability due to the high recombination rate electron-hole pair and inefficient visible light absorption, composites of semiconductor materials are being used. Semiconductor heterojunction systems are developed by coupling two or more semiconductor components. The synergistic effect of their properties, such as adsorption and improved charge carrier migration, is observed to increase overall stability. This review covers recent progress in advanced nanocomposite materials based on g-C₃N₄, TiO₂ and ZnO used as photocatalysts with details of enhancing the photocatalytic properties by heterojunctions, crystallinity and doping. The conclusion at the end displays a summary, research gaps and future outlook. A holistic analysis of recent progress to demonstrate the efficient heterojunctions for photodegradation with optimal conditions, this review will be helpful for the development of efficient heterostructured systems for photodegradation. This review covers references from the year 2017-2020.

Fast and efficient degradation of water pollutant dyes and fungicide by novel sulfur-doped graphene oxide-modified Ag3PO4 nanocomposite

The sulfur-doped graphene oxide (sGO)-integrated Ag₃PO₄ composite displayed very high catalytic activity toward prominent water pollutants like textile dyes and fungicide under sunlight. The optimum amount of sGO doping was found as 5% for degradation. The novel composite degraded 99% of methylene blue (MB) in only 5 min of sunlight exposure, which is 16 and 8 times faster than Ag₃PO₄ and 5% GO-Ag₃PO₄. High mineralization was observed for MB with a total organic carbon (TOC) removal of 98% in 30 min. The composite mineralized rhodamine B, methyl orange, and acid red 18 dyes with a TOC removal above 95%. Moreover, a toxic dithiocarbamate fungicide thiram was degraded in 1 h with a TOC removal of 82% leaving less toxic thiourea. The formation of sGO-Ag₃PO₄ n-n heterojunction increases charge transport and photocatalytic activity of the composite to incredible extent along with hollow morphology and in situ formed Ag nanoparticles (AgNPs).

Cobalt molybdate nanorods decorated on boron-doped graphitic carbon nitride sheets for electrochemical sensing of furazolidone

A nanorod-like structured CoMoO₄ embedded on boron doped-graphitic carbon nitride composite (CoMoO₄/BCN) has been developed by a simple sonochemical method for electrochemical detection of furazolidone (FUZ). Interestingly, the impedance of CoMoO₄/BCN fabricated screen-printed carbon electrode (SPCE) possesses a lower resistance charge transfer (R_ct), which favors superior electrochemical detection of FUZ. Such CoMoO₄/BCN/SPCE exhibits an ultralow detection limit of 1.6 nM with a concentration range of 0.04-408.9 μM, and high sensitivity of 11.6 μA μM^-1 cm^-2 by DPV method. In addition, biological and water samples were used for demonstration of practical application of CoMoO₄/BCN/SPCE towards electrochemical detection of FUZ, and the result exhibits a satisfactory recovery.Graphical abstract.

Doping of Graphitic Carbon Nitride with Non-Metal Elements and Its Applications in Photocatalysis

This review outlines the latest research into the design of graphitic carbon nitride (g-C3N4) with non-metal elements. The emphasis is put on modulation of composition and morphology of g-C3N4 doped with oxygen, sulfur, phosphor, nitrogen, carbon as well as nitrogen and carbon vacancies. Typically, the various methods of non-metal elements introducing in g-C3N4 have been explored to simultaneously tune the textural and electronic properties of g-C3N4 for improving its response to the entire visible light range, facilitating a charge separation, and prolonging a charge carrier lifetime. The application fields of such doped graphitic carbon nitride are summarized into three categories: CO2 reduction, H2-evolution, and organic contaminants degradation. This review shows some main directions and affords to design the g-C3N4 doping with non-metal elements for real photocatalytic applications.

Rapid sunlight-driven mineralisation of dyes and fungicide in water by novel sulphur-doped graphene oxide/Ag3VO4 nanocomposite

A semiconductor photocatalyst was prepared in facile, standard conditions by integrating 1% metal-free, sulphur-doped graphene oxide (sGO) as cocatalyst and Ag₃VO₄ as photocatalyst and characterised via spectroscopic, microscopic and voltammetric techniques. The catalytic activity was performed on notable water pollutants like textile dyes and fungicide employing various techniques. Cationic dyes such as methylene blue and rhodamine B were degraded > 99% with above 90% organic carbon content removal indicating total mineralisation while anionic dyes were degraded 75-80% in 1 h. For the first time, a dithiocarbamate fungicide thiram is degraded to give thiourea as a product in 1 h. Photocatalysis follows pseudo-first order kinetics with rate 3.67, 49.50 and 3.19 times higher than Ag₃VO₄, sGO and GO-Ag₃VO₄ respectively with excellent stability and recyclability. One percent sGO aided excellent carrier separation boosted by electrons and surface defects from sGO, morphology and n-n heterojunction formation. The catalyst efficiently removed 82.8% of the total organic carbon content of a real water sample from the textile mill under 2-h sunlight irradiation.

Ultrasonically Induced Sulfur-Doped Carbon Nitride/Cobalt Ferrite Nanocomposite for Efficient Sonocatalytic Removal of Organic Dyes

The sulfur-doped carbon nitride/cobalt ferrite nanocomposite (SCN/CoFe2O4) was prepared via ultrasonication and studied for the sonocatalytic degradation of wastewater organic dye pollutants including methylene blue, rhodamine B, and Congo red. The X-ray photoelectron spectroscopy confirmed the presence and atomic ratios of S, C, N, Co, Fe, and O elements and their corresponding bonds with Co2+ and Fe3+ cations. The nanocomposite was found to have aggregated nanoparticles on a sheet-like structure. The bandgap energy was estimated to be 1.85 eV. For the sonocatalytic degradation of 25-ppm methylene blue at 20 kHz, 1 W and 50% amplitude, the best operating condition was determined to be 1 g/L of catalyst dosage and 4 vol % of hydrogen peroxide loading. Under this condition, the sonocatalytic removal efficiency was the highest at 96% within a reaction period of 20 min. SCN/CoFe2O4 outperformed SCN and CoFe2O4 by 2.2 and 6.8 times, respectively. The SCN/CoFe2O4 nanocomposite was also found to have good reusability with a drop of only 7% after the fifth cycle. However, the degradation efficiencies were low when tested with rhodamine B and Congo red due to difference in dye sizes, structural compositions, and electric charges.

Novel La(OH)3-integrated sGO-Ag3VO4/Ag nanocomposite as a heterogeneous photocatalyst for fast degradation of agricultural and industrial pollutants

The composite described couples the benefits of hydroxyl radical formation from sunlight-inactive La(OH)₃ and strong sunlight absorption by Ag₃VO₄.

Self-constructed side-by-side nanofiber photocatalyst via oppositely charged electrospinning and its photocatalytic degradation of rhodamine B

Fabricating side by side (SBS) nanofibers with two distinct materials using dual spinnerets is challenging because of the formation of bulk heterojunctions, which limits the application of these nanofibers.