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.

Global impact of COVID-19 on agriculture: role of sustainable agriculture and digital farming.

The rise and spread of the coronavirus pandemic (COVID-19) has created an imbalance in all sectors worldwide, massively disrupting the global economy. Social distancing, quarantine regulations, and strict travel restrictions have led to a major reduction in the workforce and loss of jobs across all industrial sectors. One of the sectors completely exposed was the agriculture and food sector. The initiation of a nationwide lockdown by the government resulted in the shutdown of industries globally impacting the overall supply chain from farmer to consumer. The need of the hour is to propose effective solutions which can serve the dual purpose of market growth as well as customer satisfaction. This paper reviews the impact of COVID-19 on the agro-food system and its economy stressing critical factors like food production, demand, price hikes, security, and supply chain resilience. To conserve natural resources and meet the sustainable development goals (SDG), importance has been given to adopting sustainable agricultural practices with a prime focus on techniques like urban agriculture, crop rotation, hydroponics, and family farming. Possible advancements like the use of digital tools, mainly artificial intelligence, machine learning, deep learning, and block-chain technology, in the agro-food sector have been discussed as they could be a promising tool to develop a self-reliant society. This work would be a perfect platform to understand the growing impact of the pandemic as well as supporting cost-effective solutions for a green ecosystem.

Metformin as an emerging concern in wastewater: Occurrence, analysis and treatment methods.

Metformin is a wonder drug used as an anti-hypoglycemic medication; it is also used as a cancer suppression medicament. Metformin is a first line of drug choice used by doctors for patients with type 2 diabetes. It is used worldwide where the drug's application varies from an anti-hypoglycemic medication to cancer oppression and as a weight loss treatment drug. Due to its wide range of usage, metformin and its byproducts are found in waste water and receiving aquatic environment. This leads to the accumulation of metformin in living beings and the environment where excess concentration levels can lead to ailments such as lactic acidosis or vitamin B12 deficiency. This drug could become of future water treatment concerns with its tons of production per year and vast usage. As a result of continuous occurrence of metformin has demanded the need of implementing and adopting different strategies to save the aquatic systems and the exposure to metformin. This review discuss the various methods for the elimination of metformin from wastewater. Along with that, the properties, occurrence, and health and environmental impacts of metformin are addressed. The different analytical methods for the detection of metformin are also explained. The main findings are discussed with respect to the management of metformin as an emerging contaminants and the major recommendations are discussed to understand the major research gaps.

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.

Photocatalytic degradation of 2,4-dicholorophenoxyacetic acid by TiO2 modified catalyst: kinetics and operating cost analysis.

Effective pesticide remediation technology demands amendments in the advanced oxidation process for its continuous treatment and catalyst recovery. The evidence of 2,4-dichlorophenoxyacetic acid (2,4-D), an herbicide in water bodies, poses a major environmental threat to both humans and aquatic organisms. In the present study, a recirculation type photocatalytic reactor was developed to treat 2,4-dichlorophenoxyacetic acid using chitosan-TiO2 beads prepared via impregnation method under UV light. At optimized conditions, chitosan-TiO2 beads showed a maximum photocatalytic degradation of 86% than commercial TiO2 (65%) and followed pseudo first-order reaction. The 2,4-D degradation follows pseudo first-order kinetics under UV irradiation with a rate constant of 0.12 h-1, and the intermediates were identified using LCMS analysis. The total operational cost of the chitosan-TiO2 catalyst was found to be profitable (Rs. 1323 for 2 L) than that of TiO2 (Rs. 1679) at optimized conditions. The beads were reusable up to 4 consecutive cycles without loss in efficiency. This study briefs photocatalytic removal of 2,4-dichlorophenoxyacetic acid in a recirculation-type reactor for its reliability, low cost, efficiency, reusability, and commercialization.

Immobilized TiO2/chitosan beads for photocatalytic degradation of 2,4-dichlorophenoxyacetic acid.

Advancement in photocatalysis is focused on large-scale commercialization where the immobilization techniques gain attention with an aim to recover and reuse the catalyst for the redemption of pollutants. TiO2 will act as a potential catalyst and chitosan, a natural biopolymer is used to immobilize TiO2. 2,4-Dicholorophenoxyacetic acid, a common broadleaf pesticide found in surface and groundwater is taken as a model pollutant. Thus, the objective is to study TiO2/chitosan beads for the degradation of 2,4-dicholorophenoxyacetic acid. TiO2/chitosan beads were prepared by the phase inversion method and studied for their morphological and physiological features. The beads were observed to be spherical in shape and X-ray diffraction analysis shows the incorporation of chitosan and TiO2. The photocatalytic degradation of 2,4-dicholorophenoxyacetic acid showed 92 % degradation for TiO2/chitosan beads in UV light. The results were also compared with bare TiO2, and extended to the continuous photocatalytic mode of degradation. The kinetics and stability of the TiO2/chitosan beads were monitored for their feasibility.