A ternary photocatalyst of graphitic carbon nitride/cadmium sulfide/titania based on the electrostatic assembly using two-dimensional semiconductor nanosheets

Insights into engineered graphitic carbon nitride quantum dots for hazardous contaminants degradation in wastewater

Increased environmental pollution is a critical issue that must be addressed. Photocatalytic, adsorption, and membrane filtration methods are suitable in environmental governance because of their high selectivity, low cost, environment-friendly nature, and excellent treatment efficiency. Graphitic carbon nitride (g-C₃N₄) quantum dots (QDs) have been considered as photocatalysts, adsorbents, and membrane materials for wastewater treatments, owing to their stability, adsorption capacity, photochemical properties, and low toxicity and cost. This review summarizes g-C₃N₄ QD synthesis techniques, operating parameters affecting the removal performance in the treatment process, modification effects with other semiconductors, and benefits and drawbacks of g-C₃N₄ QD-based materials. Furthermore, this review discusses the practical applications of g-C₃N₄ QDs as adsorbents, photocatalysts, and membrane materials for organic and inorganic contaminant treatments and their value-added product formation potential. Modified g-C₃N₄ QD-based material adsorbents, photocatalysts, and membranes present potentially applicable effects, such as removal of most waterborne contaminants. Excellent results were obtained for the reduction of methyl orange, bisphenol A, tetracycline, ciprofloxacin, phenol, rhodamine B, E. coli, and Hg. Overall, this paper provides comprehensive background on g-C₃N₄ QD-based materials and their diverse applications in wastewater treatment, and it presents a foundation for the enhancement of similar unique materials in the future.

Colloidal properties of the metal-free semiconductor graphitic carbon nitride

The metal-free, polymeric semiconductor graphitic carbon nitride (g-CN) family is an emerging class of materials and has striking advantages compared to other semiconductors, i.e. ease of tunability, low cost and synthesis from abundant precursors in a chemical environment. Efforts have been done to improve the properties of g-CN, such as photocatalytic efficiency, designing novel composites, processability and scalability towards discovering novel applications as a remedy for the problems that we are facing today. Despite the fact that the main efforts to improve g-CN come from a catalysis perspective, many fundamental possibilities arise from the special colloidal properties of carbon nitride particles, from synthesis to applications. This review will display how typical colloid chemistry tools can be employed to make 'better g-CNs' and how up to now overseen properties can be levered by integrating a colloid and interface perspective into materials chemistry. Establishing a knowledge on the origins of colloidal behavior of g-CN will be the core of the review.

Developing the Ternary ZnO Doped MoS2 Nanostructures Grafted on CNT and Reduced Graphene Oxide (RGO) for Photocatalytic Degradation of Aniline

Transition metal sulfide semiconductors have achieved significant attention in the field of photocatalysis and degradation of pollutants. MoS2 with a two dimensional (2D) layered structure, a narrow bandgap and the ability of getting excited while being exposed to visible light, has demonstrated great potential in visible-light-driven photocatalysts. However, it possesses fast-paced recombination of charges. In this study, the coupled MoS2 nanosheets were synthesized with ZnO nanorods to develop the heterojunctions photocatalyst in order to obtain superior photoactivity. The charge transfer in this composite is not adequate to achieve desirable activity. Therefore, heterojunction was modified by reduced graphene oxide (RGO) nanosheets and carbon nanotubes (CNTs) to develop the RGO/ZnO/MoS2 and CNTs/ZnO/MoS2 ternary nanocomposites. The structure, morphology, composition, optical and photocatalytic properties of the as-fabricated samples were characterized through X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray (EDX), elemental mapping, Photoluminescence (PL), Ultraviolet-Visible spectroscopy (UV-VIS), and Brunauer-Emmett-Teller (BET) techniques. The photo-catalytic performance of all samples was evaluated through photodegradation of aniline in aqueous solution. The combination of RGO or CNTs into the ZnO/MoS2 greatly promoted the catalytic activity. However, the resulting RGO/ZnO/MoS2 ternary nanocomposites showed appreciably increased catalytic performance, faster than that of CNTs/ZnO/MoS2. Charge carrier transfer studies, the BET surface area analysis, and the optical studies confirmed this superiority. The role of operational variables namely, solution pH, catalyst dosage amount, and initial concentration of aniline was then investigated for obtaining maximum degradation. Complete degradation was observed, in the case of pH = 4, catalyst dosage of 0.7 g/L and aniline concentration of 80 ppm, and light intensity of 100 W. According to the results of trapping experiments, hydroxyl radical was found to be the main active species in the photocatalytic reaction. Meanwhile, a plausible mechanism was proposed for describing the degradation of aniline upon ternary composite. Moreover, the catalyst showed excellent reusability and stability after five consecutive cycles due to the synergistic effect between its components. Total-Organic-Carbon concentration (TOC) results suggested that complete mineralization of aniline occurred after 210 min of irradiation. Finally, a real petrochemical wastewater sample was evaluated for testing the catalytic ability of the as-fabricated composites in real case studies and it was observed that the process successfully quenched 100% and 93% of Chemical Oxygen Demand (COD) and TOC in the wastewater, respectively.

A mutually isolated nanodiamond/porous carbon nitride nanosheet hybrid with enriched active sites for promoted catalysis in styrene production

A mutually isolated nanodiamond/porous carbon nitride nanosheet hybrid with enriched catalytic sites is fabricated by a facile two-step molten salt-oxidation strategy, generating an excellent catalyst for clean and energy-saving styrene production.

g-C3N4/Uio-66-NH2 nanocomposites with enhanced visible light photocatalytic activity for hydrogen evolution and oxidation of amines to imines

g-C₃N₄/Uio-66-NH₂ (CNUIO) nanocomposites were prepared by growing an NH₂-mediated zirconium-based metal–organic framework (Uio-66-NH₂) in the presence of g-C₃N₄ nanotubes.

Facile surface modification of textiles with photocatalytic carbon nitride nanosheets and the excellent performance for self-cleaning and degradation of gaseous formaldehyde

Great advances in photocatalysis have been made by developing various efficient photocatalysts, but investigation on practical applications of photocatalysis is relatively backward. Herein we report a facile surface modification approach to functionalize textiles with excellent ability for photocatalytic self-cleaning and degradation of indoor volatile organic pollutants. Graphitic carbon nitride nanosheets (CNNS) in colloidal suspension were directly sprayed onto the surface of cellulose fibers in textiles, and the powerful hydrogen bonding action between surface hydroxyl groups of cellulose and plentiful hydroxyl and amino groups of exfoliated CNNS from alkali-treating realizes high stability of CNNS modified textiles. Due to ultrathin 2D thickness and high visible light transparency, the modification of CNNS would not affect the hand feeling of textiles and shield their original colors. The obtained textiles show superior photocatalytic self-cleaning performance to remove stains from various colored pollutants under solar light irradiation, including industrial organic dyes and juices. Meanwhile, gaseous formaldehyde also can be efficiently decomposed using Xe lamp or commercial LED lamp as light sources. This work realizes photocatalytic performance of textiles using a simple spraying method, and it has great potential application in textile self-cleaning, not only for surface stains but also for volatile organic compounds from textile release.

WS2 /Graphitic Carbon Nitride Heterojunction Nanosheets Decorated with CdS Quantum Dots for Photocatalytic Hydrogen Production

Two-dimensional/two-dimensional (2D/2D) stacking heterostructures are highly desirable in fabricating efficient photocatalysts because face-to-face contact can provide a maximized interfacial region between the two semiconductors; this largely facilitates the migration of charge carriers. Herein, a WS₂ /graphitic carbon nitride (CN) 2D/2D nanosheet heterostructure decorated with CdS quantum dots (QDs) has been designed, for the first time. Optimized CdS/WS₂ /CN without another cocatalyst exhibits a significantly enhanced photocatalytic H₂ evolution rate of 1174.5 μmol h^-1  g^-1 under visible-light irradiation (λ>420 nm), which is nearly 67 times higher than that of the pure CN nanosheets. The improved photocatalytic activity can be primarily attributed to the highly efficient charge-transfer pathways built among the three components, which effectively accelerate the separation and transfer of photogenerated electrons and holes, and thus, inhibit their recombination. Moreover, the extended light-absorption range also contributes to excellent photocatalytic efficiency. In addition, the CdS/WS₂ /CN photocatalyst shows excellent stability and reusability without apparent decay in the photocatalytic H₂ evolution within 4 cycles in 20 h. It is believed that this work may shed light on specifically designed 2D/2D nanosheet heterostructures for more efficient visible-light-driven photocatalysts.

Construction of a novel BiSI/MoS2 nanocomposite with enhanced visible-light driven photocatalytic performance

A BiSI/MoS₂ nanocomposite was synthesized for the first time and used as a new efficient and stable visible light driven photocatalyst.

Ferrocene-functionalized graphitic carbon nitride as an enhanced heterogeneous catalyst of Fenton reaction for degradation of Rhodamine B under visible light irradiation

To enhance degradation of Rhodamine B (RhB), a toxic xanthene dye, an iron-doped graphitic carbon nitride (CN) is prepared by establishing a covalent bond (-CN-) bridging ferrocene (Fc) and CN via a Schiff base reaction. The π-conjugation between the aromatic Fc and CN can be much enhanced by the covalent bond, thereby facilitating the bulk-to-surface charge transfer and separation as well as reversible photo-redox reactions during photocatalytic reactions. Thus, the resulting Fc-CN exhibits a much higher catalytic activity than CN to activate hydrogen peroxide (HP) for RhB degradation, because the photocatalytically generated electrons from CN can activate HP and effectively maintain the bivalence state of Fe in Fc, which also induces the activation of HP. The RhB degradation by the Fc-CN activated HP process (Fc-CN-HP) is validated to involve OH^• by examining the effect of radical probe agent as well as electron paramagnetic resonance (EPR) spectroscopic analysis. Fc-CN is also proven to activate HP for RhB degradation over multiple times without loss of catalytic activity. Through determining the degradation intermediates, RhB is indeed fully decomposed by Fc-CN-HP into much lower-molecular-weight organic compounds. These features indicate that Fc-functionalization can be an advantageous technique to enhance the catalytic activity of CN for activating HP. The results obtained in this study are essential to further design and utilize Fc-functionalized CN for Fenton-like reactions. The findings shown here, especially the degradation mechanism and pathway, are also quite important for treating xanthene dyes in wastewater.

A novel supramolecular preorganization route for improving g-C3N4/g-C3N4 metal-free homojunction photocatalysis

Enhancing the novel g-C₃N₄/g-C₃N₄ metal-free homojunction photocatalysis: efficient solar energy harvesting and charge transfer.