Synthesis and Characterization of Composite WO3 Fibers/g-C3N4 Photocatalysts for the Removal of the Insecticide Clothianidin in Aquatic Media

Photocatalysis is a prominent alternative wastewater treatment technique that has the potential to completely degrade pesticides as well as other persistent organic pollutants, leading to detoxification of wastewater and thus paving the way for its efficient reuse. In addition to the more conventional photocatalysts (e.g., TiO2, ZnO, etc.) that utilize only UV light for activation, the interest of the scientific community has recently focused on the development and application of visible light-activated photocatalysts like g-C3N4. However, some disadvantages of g-C3N4, such as the high recombination rate of photogenerated charges, limit its utility. In this light, the present study focuses on the synthesis of WO3 fibers/g-C3N4 Z-scheme heterojunctions to improve the efficiency of g-C3N4 towards the photocatalytic removal of the widely used insecticide clothianidin. The effect of two different g-C3N4 precursors (urea and thiourea) and of WO3 fiber content on the properties of the synthesized composite materials was also investigated. All aforementioned materials were characterized by a number of techniques (XRD, SEM-EDS, ATR-FTIR, Raman spectroscopy, DRS, etc.). According to the results, mixing 6.5% W/W WO3 fibers with either urea or thiourea derived g-C3N4 significantly increased the photocatalytic activity of the resulting composites compared to the precursor materials. In order to further elucidate the effect of the most efficient composite photocatalyst in the degradation of clothianidin, the generated transformation products were tentatively identified through UHPLC tandem high-resolution mass spectroscopy. Finally, the detoxification effect of the most efficient process was also assessed by combining the results of an in-vitro methodology and the predictions of two in-silico tools.

Architecture of visible-light induced Z-scheme MoS2/g-C3N4/ZnO ternary photocatalysts for malachite green dye degradation

The synthesis of bilayer heterojunctions has received considerable attention recently. Fabrication of novel bilayer composites is of significant interest to improve their photocatalytic efficiency. In this study, molybdenum disulfide (MoS₂), a layered dichalcogenide material exhibiting unique properties, in combination with graphitic carbon nitride (g-C₃N₄), a carbon-based layered material, was fabricated with small amounts of zinc oxide (ZnO). Three composites, MoS₂/g-C₃N₄, MoS₂/ZnO, and MoS₂/g-C₃N₄/ZnO were prepared via a simple exfoliation method and characterized by various physicochemical methods. The Z-scheme charge transfer mechanism in the prepared ternary composite improves efficiency by inhibiting the recombination rate of electron-hole pairs. It has shown excellent performance in degrading a major water contaminant, malachite green (MG) dye, under visible light irradiation.

Gamma-Rays Induced Synthesis of Ag-Decorated ZnCo2O4–MoS2 Heterostructure as Novel Photocatalyst and Effective Antimicrobial Agent for Wastewater Treatment Application

The development of novel semiconductors-based-photocatalysts is a promising strategy for addressing environmental pollution. In the present study, gamma irradiation was utilized to induce the synthesis of the exceptionally efficient Ag-decorated ZnCo2O4–MoS2 heterostructure. XRD and EDX analyses were verified the successful synthesis of Ag-decorated ZnCo2O4–MoS2 heterostructure. Also, SEM and HR-TEM images were illustrated the heterostructure nature of the synthesized photocatalyst in the nanoscale regime. The obtained optical bandgap values verified that photocatalyst possesses a narrow semiconductor bandgap. Further, the Ag-decorated ZnCo2O4–MoS2 heterostructure exhibited superior photodegradation potential towards MB (95.4% removal of the MB). The antimicrobial potency of the synthesized samples had been investigated through ZOI, MIC, growth curve assay, and the effect of UV illumination. Also, the antibiofilm behaviour has been studied. The antibacterial reaction mechanism had been estimated by membrane leakage assay and SEM imaging. The tested samples displayed a positive potency to a broad spectrum of bacteria like Proteus mirabilis, Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans. In particular, Ag–MoS2–ZnCo2O4 nanocomposite possessed the highest impact, followed by the spinal ZnCo2O4 NPs towards all the tested pathogenic microbes. In this assessment, the Ag-decorated ZnCo2O4–MoS2 heterostructure has been shown to be a promising candidate for wastewater treatment application.

MoS2/N-TiO2/Ti mesh plate for visible-light photocatalytic ozonation of naproxen and industrial wastewater: comparative studies and artificial neural network modeling

This paper presents the results of visible-light assisted photocatalytic ozonation for the degradation of naproxen as a model pharmaceutical pollutant from water using MoS₂/N-TiO₂ immobilized on a titanium mesh plate in addition to treatment of a real industrial wastewater. The batch studies were performed for naproxen degradation by varying the reaction variables such as ozone flow rate, initial pH and pollutant concertation. It was observed that almost 90% degradation was achieved at pH = 4, ozone flow rate = 3 L min^-1 and initial naproxen concentration = 5 mg L^-1. The catalyst exhibited constant activity even after seven successive cycles. Comparative studies among sorption, ozonation, photocatalysis, catalytic ozonation and photocatalytic ozonation revealed that the later process had the highest degradation of pollutant. Moreover, an artificial neural network (ANN) model was developed to simulate the performance of visible-light photocatalytic ozonation in naproxen degradation. The developed ANN model could estimate the visible-light photocatalytic ozonation process under the different experimental conditions. Finally, the applicability of the photocatalytic ozonation was successfully approved for industrial wastewater treatment. The results showed that the COD removal efficiency reached 65% within 150 min. HIGHLIGHTS: • MoS₂/N-TiO₂/Ti was synthesized by the quick electrophoretic deposition method. • The catalyst showed good ability in naproxen degradation via visible-light photocatalytic ozonation. • A three-layer artificial neural network model was developed to predict the naproxen degradation. • Naproxen degradation efficiency through the photocatalytic ozonation was higher than the individual methods. • COD of real wastewater was reduced significantly after the visible-light photocatalytic ozonation process.

Artificial Solar Light-Driven APTES/TiO2 Photocatalysts for Methylene Blue Removal from Water

A visible-light photocatalytic performance of 3-aminopropyltriethoxysilane (APTES)-modified TiO2 nanomaterials obtained by solvothermal modification under elevated pressure, followed by calcination in an argon atmosphere at 800–1000 °C, is presented for the first time. The presence of silicon and carbon in the APTES/TiO2 photocatalysts contributed to the effective delay of the anatase-to-rutile phase transformation and the growth of the crystallites size of both polymorphous forms of TiO2 during heating. Thus, the calcined APTES-modified TiO2 exhibited higher pore volume and specific surface area compared with the reference materials. The change of TiO2 surface charge from positive to negative after the heat treatment increased the adsorption of the methylene blue compound. Consequently, due to the blocking of active sites on the TiO2 surface, the adsorption process negatively affected the photocatalytic properties. All calcined photocatalysts obtained after modification via APTES showed a higher dye decomposition degree than the reference samples. For all 3 modifier concentrations tested, the best photoactivity was noted for nanomaterials calcined at 900 °C due to a higher specific surface area than materials calcined at 1000 °C, and a larger number of active sites available on the TiO2 surface compared with samples annealed at 800 °C. It was found that the optimum concentration for TiO2 modification, at which the highest dye decomposition degree was noted, was 500 mM.

Construction of 2D/2D MoS2/g-C3N4 Heterostructures for Photoreduction of Cr (VI)

2D/2D MoS₂/g-C₃N₄ (MCN) surface heterostructures were created by second thermal polymerization of bulk g-C₃N₄ and the reaction of thiourea and MoO₃ at 670 °C. MoS₂ networks grew vertically along the (002) facet on superior thin g-C₃N₄ nanosheets. The layered heterostructures drastically improved the Cr(VI) removal ability. In the dark case, 27% of Cr(VI) was removed within 45 min. The result indicates that the adsorption of Cr(VI) was a chemical adsorption process involving the sharing and transfer of electrons. The equilibrium data indicate that the adsorbent was covered with a monolayer adsorbate, which conformed to the Langmuir isotherm model (R² = 0.9618). In addition, MCN nanocomposites could convert Cr(VI) into non-toxic Cr(III) by photoreduction under visible light irradiation. With an optimized composition, 100% of Cr(VI) was removed within 30 min, which was ∼10 times quicker compared with Cr(VI) removal under dark conditions. Because g-C₃N₄ nanosheets (sample CN₆₇₀) with higher photocurrent density revealed the lowest photoreduction Cr(VI) ability, adsorption plays an important role in Cr(VI) removal. For MoS₂/g-C₃N₄ nanocomposites used in Cr(VI) removal, adsorption and photoreduction were incorporated together to get excellent performance.

An Overview of the Recent Progress in Polymeric Carbon Nitride Based Photocatalysis

Recently, polymeric carbon nitride (g-C₃ N₄ ) as a proficient photo-catalyst has been effectively employed in photocatalysis for energy conversion, storage, and pollutants degradation due to its low cost, robustness, and environmentally friendly nature. The critical review summarized the recent development, fundamentals, nanostructures design, advantages, and challenges of g-C₃ N₄ (CN), as potential future photoactive material. The review also discusses the latest information on the improvement of CN-based heterojunctions including Type-II, Z-scheme, metal/CN Schottky junctions, noble metal@CN, graphene@CN, carbon nanotubes (CNTs)@CN, metal-organic frameworks (MOFs)/CN, layered double hydroxides (LDH)/CN heterojunctions and CN-based heterostructures for H₂ production from H₂ O, CO₂ conversion and pollutants degradation in detail. The optical absorption, electronic behavior, charge separation and transfer, and bandgap alignment of CN-based heterojunctions are discussed elaborately. The correlations between CN-based heterostructures and photocatalytic activities are described excessively. Besides, the prospects of CN-based heterostructures for energy production, storage, and pollutants degradation are discussed.

Fabrication of ternary composites with polymeric carbon nitride/MoS2/reduced graphene oxide ternary hybrid aerogel as high-performance electrode materials for supercapacitors

Presenting a remarkable ternary hybrid aerogel, as an excellent electrode material with a specific capacitance of 467 Fg−1 and capacitance retention upto 80.4% even after 2000 cycles, demonstrating good stability and improved cyclic performance.

Photocatalytic H2 Evolution, CO2 Reduction, and NOx Oxidation by Highly Exfoliated g-C3N4

g-C3N4, with specific surface area up to 513 m2/g, was prepared via three successive thermal treatments at 550 °C in air with gradual precursor mass decrease. The obtained bulk and exfoliated (1ex, 2ex and 3ex) g-C3N4 were characterized and tested as photocatalysts for H2 production, CO2 reduction and NOx oxidation. The exfoliated samples demonstrated graphene-like morphology with detached (2ex) and sponge-like framework (3ex) of layers. The surface area increased drastically from 20 m2/g (bulk) to 513 m2/g (3ex). The band gap (Eg) increased gradually from 2.70 to 3.04 eV. Superoxide radicals (·O2−) were mainly formed under UV and visible light. In comparison to the bulk, the exfoliated g-C3N4 demonstrated significant increase in H2 evolution (~6 times), CO2 reduction (~3 times) and NOx oxidation (~4 times) under UV light. Despite the Eg widening, the photocatalytic performance of the exfoliated g-C3N4 under visible light was improved too. The results were related to the large surface area and low e−-h+ recombination. The highly exfoliated g-C3N4 demonstrated selectivity towards H2 evolution reactions.

Elucidating the structure of the graphitic carbon nitride nanomaterials via X-ray photoelectron spectroscopy and X-ray powder diffraction techniques

By using the most popular method of thermal condensation of dicyandiamide in a semi-closed system, graphitic carbon nitrides (gCNs) were synthesized at 500, 550, and 600 °C. The resulting materials were comprehensively analyzed via X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD)techniques. We show that the use of routine analytical methods provides an insight into the structure of the carbon nitride materials. The analysis of geometric linear structures and fully condensed structure of polymeric carbon nitrides was performed and the ranges within which the contents of different nitrogen species (pyridine, amine, imine and quaternary nitrogen) can change were determined. This analysis, in combination with quantitative XPS studies, permits to state that the carbon nitride structure prepared by the thermal condensation of dicyandiamide is closer to the structure in which poly(aminoimino)heptazine subunits are linked into chains rather than the structure involving fully-condensed polyheptazine network. The XRD analysis proved that the 3D crystal structure of carbon nitride is described more correctly by the orthorhombic cell and space group P21212 applied to condensed chains of poly(aminoimino)heptazine (melon) and not by the hexagonal cell with the space group P6m2.

Biomass-derived functional porous carbons for adsorption and catalytic degradation of binary micropollutants in water

The biomass, bottlebrush flower, is exploited for the preparation of functionalized porous carbons by one-pot thermal activation using NaHCO₃ and dicyandiamide. An intensified cross-linking effect among the precursors boosts pore (especially mesopore) formation in the pyrolysis process, producing N-doped porous carbons (NPCs) with a large specific surface area (SSA, up to 2025 m²  g^-1). The biomass-derived carbon samples turn out to be highly effective in adsorption, and catalytic activation of peroxymonosulfate for degradation of aqueous phenol and p-hydroxybenzoic acid (HBA) in single and binary systems. The effects of N content, porous structure, and trace Ni species on the adsorptive and catalytic behavior of carbon are investigated. It is found that the porous structure plays a more critical role in adsorption than surface N functionality, while the contributions of various reactive species for phenol and HBA degradation are different.

Complete removal of endocrine disrupting compound and toxic dye by visible light active porous g-C3N4/H-ZSM-5 nanocomposite

Photocatalytic degradation of toxic pollutants is an efficient technique to completely remove the toxic pollutants from water bodies. In the present investigation, photocatalytic degradation of pollutants was studied over porous g-C₃N₄/H-ZSM-5 nanocomposite under visible light irradiation. The composite g-C₃N₄/H-ZSM-5 was synthesized by mixing an aqueous solution of H-ZSM-5 zeolite (increases surface area and provides active sites for degradation) with melamine (precursor of g-C₃N₄) for 10-12 h followed by calcinations at 550 °C. The photocatalyst was characterized by XRD, BET, HRTEM, FESEM, EDS and elemental mapping analysis. These techniques confirmed that, g-C₃N₄/H-ZSM-5 composite have layered and porous structure with uniform distribution of g-C₃N₄ on H-ZSM-5 surface. The BET N₂ adsorption-desorption analysis verified that the catalyst has high surface area (∼175 m²/g) having mesopores and micropores. The prepared catalyst was then used for the photodegradation of a model dye, Methylene Blue (MB) and an endocrine disrupting compound, Fipronil (FIP). Effects of various parameters such as pH, catalyst dose and scavengers were also studied. The % photocatalytic degradation of MB and FIP were around ∼92% and ∼84% with a high rate constants of 0.00997 and 0.00875 min^-1, respectively. From the scavenger study, OH (hydroxyl radical) and radical was found to be the major reactive species for MB and FIP degradation. From these studies it is revealed that, the catalyst is visible active, easy to prepare and an efficient photocatalyst for toxic pollutant degradation.

Degradation of bisphenol a using peroxymonosulfate activated by WO3@MoS2/Ag hollow nanotubes photocatalyst

WO₃@MoS₂/Ag (HW@MA) hollow tubes were successfully engineered to photodegrade bisphenol A (BPA) combined with peroxymonosulfate (PMS) for the first time. XRD, XPS, TEM and SEM were conducted. The HW@MA tubes present excellent photocatalytic performance on the removal of BPA. The intermediate products of BPA were investigated by GC-MS analysis and the degradation pathway was proposed. To explore the transferred mechanism of photoproduced carriers, the electron paramagnetic resonance (EPR) technique was carried out. The results revealed that the superoxide radical (O₂^-), hydroxyl radical (OH), sulfate radical (SO₄^-) were the main active radicals. Moreover, the formed schottky junctions enhanced the separation efficiency of photoinduced electron-hole pairs. Besides, the effect of the photocatalysts' dosage, PMS concentration, pH of the initial solution and co-existing anions on the BPA degradation were investigated.

Template-free synthesis of salmon pink tube-shaped structure carbon nitride with enhanced visible light photocatalytic activity

Designing a highly active and stable photocatalyst to directly solve environmental pollution is desirable for solar energy conversion. Herein, an effective strategy, hydrothermal-calcination, for synthesizing extremely active carbon nitride (salmon pink) from a low-cost precursor melamine, is reported. The salmon pink carbon nitride with tube-shaped structure significantly enhanced response to visible light, improved efficiency of charge separation and remarkably enhanced efficiency of methyl orange (MO) degradation than bulk g-C₃N₄ (light orange). The M-10-200-24-600 composite possessed the most wonderful ability towards MO degradation irradiated by visible light, which could achieve a highest degradation efficiency of 84% within 120 min. Our findings may provide a promising and facile approach to highly efficient photocatalysis for solar-energy conversion.

Designing a highly active and stable photocatalyst to directly solve environmental pollution is desirable for solar energy conversion.

Fabrication of 2D heterojunction photocatalyst Co-g-C3N4/MoS2 with enhanced solar-light-driven photocatalytic activity

Co-Doping and formation of a 2D heterojunction with MoS₂ can significantly boost the photocatalytic activity of g-C₃N₄.

Rationally designed MoS2/protonated g-C3N4 nanosheet composites as photocatalysts with an excellent synergistic effect toward photocatalytic degradation of organic pollutants

The positively charged ultrathin g-C₃N₄ nanosheets are prepared by ultrasonic-assisted exfoliation of the protonated g-C₃N₄. Compared with the protonated g-C₃N₄ and exfoliated g-C₃N₄, the positively charged ultrathin g-C₃N₄ has abundant functional groups as well as desired dispersibility in deionized water, thus it could serve as a basic building block for designing related heterojunction composites. To take a full advantage of these features, the positively charged ultrathin g-C₃N₄/MoS₂ composites are fabricated through a simple electrostatic adsorption and self-assembly process followed by a hydrothermal method. By loading an appropriate amount of MoS₂ on the ultrathin g-C₃N₄ nanosheets, the as-fabricated composites exhibit considerable improvement on the photocatalytic activities toward the degradation of typical organic pollutants (i.e., methyl orange and phenol) under visible light irradiation. The composite containing 2 wt% MoS₂ shows the highest efficiency of about 96.5% for the methyl orange degradation, which is about 3.5 times and 8 times compared to those of the positively charged ultrathin g-C₃N₄ and bulk g-C₃N₄, respectively. The superb photocatalytic performance benefits from the unique advantages, including richly available reaction sites, aligned energy levels between g-C₃N₄ and the MoS₂, and efficient electron transfer. This work opens new possibilities for the rational design and construction of the g-C₃N₄ based composites as highly efficient and stable visible-light driven photocatalysts for the degradation of organic pollutants.

Green synthesis of MoS2 nanoflowers for efficient degradation of methylene blue and crystal violet dyes under natural sun light conditions

Hydrothermally synthesized MoS₂ NFs have been employed as an efficient photocatalyst for the degradation of MB and CV dyes under sunlight.

Fabrication of Z-scheme magnetic MoS2/CoFe2O4 nanocomposites with highly efficient photocatalytic activity

MoS₂ thin nanosheets decorated with CoFe₂O₄ nanoparticles have been successfully synthesized via a simple hydrothermal method. The nanocomposites are characterized by XRD, TEM, HRTEM, BET, XPS, UV-Vis DRS, PL and magnetic property analysis. The Z-scheme mechanism at the interface of MoS₂ and CoFe₂O₄ is formed. When the mass ratio of MoS₂ and CoFe₂O₄ is 1:3, the MoS₂/CoFe₂O₄ nanocomposites present excellent photocatalytic performance. The degradation rate of rhodamine B (RhB) and congo red (CR) is 93.80% and 94.43% in 90 and 50 min, respectively, under visible light irradiation. The highly photocatalytic activity could be mainly ascribed to the formed Z-scheme mechanism which facilitates the separation of photoinduced electron-hole pairs. Besides, the MoS₂ thin nanosheets not only provide the most active sites for photocatalytic reactions, but also act as the backing material for CoFe₂O₄ nanoparticles to effectively disperse and avoid the magnetic aggregation. Moreover, the MoS₂/CoFe₂O₄ nanocomposites present a good recyclability and the degradation rate of RhB and CR is still beyond 82% after seven runs. In addition, the nanocomposites can be easily separated by an external magnet.

Synthesis of 3D porous MoS2/g-C3N4 heterojunction as a high efficiency photocatalyst for boosting H2 evolution activity

A novel strategy was applied for the preparation of MoS₂/graphitic carbon nitride (g-C₃N₄) with porous morphology.

Facile synthesis of g-C3N4 nanosheets loaded with WO3 nanoparticles with enhanced photocatalytic performance under visible light irradiation

Possible synthesis and degradation mechanism for photocatalysts under visible light irradiation.