Mechanistic insights of PO43- functionalized carbon nitride homojunction hydrogels in photocatalytic-self-Fenton-peroxymonosulfate system for tetracycline degradation.

In this study, metal-free PO43- enriched g-C3N4/g-C3N4 (PGCN) homojunction alginate 3D beads were developed for in-situ H2O2 production under visible light. Later, the photocatalytic-self-Fenton system was integrated with peroxymonosulfate for tetracycline degradation. Initially, the PO43- enriched g-C3N4 (PCN) and a homojunction composed of PCN and g-C3N4 (GCN) were prepared via the wet-impregnation method. Later, PGCN homojunction was formulated into 3D alginate beads through the blend-crosslinking method. The comprehensive characterization of the homojunction beads affirmed the closer contact between the semiconductors, alteration of the bandgap, faster channelization of electron-hole pairs, and improved separation of charge carriers that attributed to higher catalytic efficacy. The PGCN beads exhibited a maximum H2O2 production of 535 ± 12 µM under visible light irradiation for 60 min. The homojunction hydrogels displayed 99 ± 0.25 % tetracycline degradation in 20 min in the photocatalytic-self-Fenton-PMS system. The experimental studies also claimed a maximum chemical oxygen demand removal of 81 ± 3.6 % in 20 min with maximum reusability of beads up to 20 cycles. The Z-scheme electron migration mechanism is proposed based on the results aided by scavenger and electron spin resonance analysis. Overall, the as-synthesized alginate-supported homojunction-based photocatalytic-self-Fenton-peroxymonosulfate system is highly versatile and reusable for energy and environmental remediation.

Phosphorylated g-C3N4/sulfur self-doped g-C3N4 homojunction carboxymethyl cellulose beads: An efficient photocatalyst for H2O2 production.

The development of highly reusable, affordable, and durable photocatalysts for the production of hydrogen peroxide (H2O2) remained a challenge. In this study, a homojunction photocatalyst (SPGCN) is constructed between phosphorylated g-C3N4 (PCN) and sulfur self-doped g-C3N4 (SCN) using a simple wet impregnation method. Later, the obtained SPGCN homojunction is transformed into hydrogel beads using carboxymethyl cellulose via an effective cross-linking strategy (SPGCN/CMC). The photocatalytic beads displayed a phenomenal H2O2 production of 3.5 mM under visible light illumination for 60 min. The SPGCN/CMC hydrogel beads showed a maximum reusability of 10 cycles with a decline of 1.5 mM H2O2 production. The improved photocatalytic efficiency is indicated by strengthened utilization of visible light via tuning of the band gap, suppressed recombination of electron-hole pairs, and higher separation efficiency through the effective construction of Z-scheme between the phosphorylated carbon nitride and the sulfur-self-doped carbon nitride present in the SPGCN/CMC beads. The mechanistic studies affirmed the dominant role of superoxide radicals in H2O2 production. The photocatalytic H2O2 production followed a highly selective two-electron reduction reaction. Overall, this study highlights the efficient engineering of carbon nitride-based materials towards artificial photosynthesis.

Effective sequestration of tetracycline from aqueous streams using metal-free chemically functionalized porous g-C3N4.

The facile preparation of visible-light-driven low-cost photocatalysts with extraordinary catalytic activity is highly beneficial in treating emerging pharmaceutical contaminants. Herein, oxalic acid-induced chemically functionalized graphitic carbon nitride (OCN) was prepared using a one-pot calcination method for the degradation of tetracycline. The estimated structural, morphological, and optical properties proved the formation of highly porous oxalic acid functionalized g-C3N4 (OCN) with enhanced surface area and abundant amino groups. The photocatalytic degradation studies reported a maximum tetracycline removal of 92% within 90 min of visible light illumination and followed pseudo-first-order kinetics (k = 0.03068min-1). The phenomenal photocatalytic efficacy of the functionalized OCN is ascribed to the increased presence of amino groups, strengthening visible light absorption. The enriched surface area also generated many active sites for the reclamation of tetracycline. The radicals trapping studies show that holes and superoxides are mainly responsible for the redemption of tetracycline. The degradation pathways of the tetracycline using OCN were predicted using HRMS. This study provides more insights into the reclamation of tetracycline using a highly efficient metal-free photocatalyst.

Removal of tetracycline from wastewater using g-C3N4 based photocatalysts: A review.

Tetracycline is currently one of the most consumed antibiotics for human therapy, veterinary purpose, and agricultural activities. Tetracycline worldwide consumption is expected to rise by about more than 30% by 2030. The persistence of tetracycline has necessitated implementing and adopting strategies to protect aquatic systems and the environment from noxious pollutants. Here, graphitic carbon nitride-based photocatalytic technology is considered because of higher visible light photocatalytic activity, low cost, and non-toxicity. Thus, this review highlights the recent progress in the photocatalytic degradation of tetracycline using g-C3N4-based photocatalysts. Additionally, properties, worldwide consumption, occurrence, and environmental impacts of tetracycline are comprehensively addressed. Studies proved the occurrence of tetracycline in all water matrices across the world with a maximum concentration of 54 µg/L. Among different g-C3N4-based materials, heterojunctions exhibited the maximum photocatalytic degradation of 100% with the reusability of 5 cycles. The photocatalytic membranes are found to be feasible due to easiness in recovery and better reusability. Limitations of g-C3N4-based wastewater treatment technology and efficient solutions are also emphasized in detail.

Heterojunction photocatalysts for the removal of nitrophenol: A systematic review.

Nitrophenols are the most widely used raw materials in the chemical, pesticide, and pharmaceutical industries. Due to improper waste management and excessive usage, nitrophenol is listed as a priority pollutant and garnered global research attention. This review highlights the recent progress on heterojunction photocatalysts toward eliminating nitrophenols. The detailed mechanisms of the electron-hole pair separation using different heterojunctions such as traditional, p-n, Z-scheme, S-scheme, and Schottky heterojunctions are elaborated. The performance of the photocatalysts is evaluated using quantum efficiency. Among the heterojunctions, Z-scheme exhibited maximum removal efficiency of 100% and found superior over other heterojunctions. Even though heterojunctions exhibit good efficiency, the reusability of the heterojunction photocatalyst is not reported beyond 5 cycles. Further research is indeed to develop a highly reusable photocatalyst for environmental remediation.

Comprehensive review on advanced reusability of g-C3N4 based photocatalysts for the removal of organic pollutants.

Graphitic carbon nitride (g-C3N4) has attained significant research attention in energy and environmental remediation due to its excellent electronic structure, greater physical and chemical properties, and abundance. However, graphitic carbon nitride faces severe problems because of its high recombination rate and higher mass loss of the catalyst during recovery operations. This review emphasizes the methods to overcome the difficulties associated with recovery and reusability of the g-C3N4 based photocatalyst towards the redemption of pollutants present in wastewater. Different strategies like magnetic g-C3N4 based photocatalysts, immobilized photocatalytic systems, and photocatalytic membranes and their usage in photocatalytic applications are well described. Different preparation strategies of the graphic carbon nitride-based composites are elucidated. The key challenges and future perspectives of adopting these methods for photocatalytic applications are also mentioned.