The growing global demand for sustainable energy and environmental remediation has accelerated interest in efficient, metal-free photocatalysts. Cellulose, known for its abundance, biodegradability, tunable chemistry, high surface area, and mechanical robustness, has emerged as an ideal support material for photocatalytic systems. This review presents a comprehensive evaluation of cellulose-supported photocatalysts, detailing their structural forms, physicochemical properties, preparation strategies, and design principles. The classification of cellulose-based composites and structured architectures into hydrogels, aerogels, membranes, and sponges highlights the versatility of cellulose in enhancing catalyst dispersion, charge separation, visible-light activity, and reusability. Their applications include hydrogen and hydrogen peroxide generation, nitrogen fixation, CO2 reduction and wastewater treatment and disinfection. Strengths, weaknesses, opportunities, and threats (SWOT) analysis provides insights into their strengths, limitations, and research gaps, emphasizing challenges in large-scale fabrication, stability, and commercial viability. Furthermore, this review highlights the significance of environmental and economic analyses to guide their sustainable scale-up and market adoption. Future directions should focus on heterostructure engineering, defect modulation, green synthesis, AI-guided optimization, and integration into real-world systems. By bridging materials science, catalysis, and environmental engineering, cellulose-supported photocatalysts hold significant potential for scalable, eco-friendly, and multifunctional solutions aligned with the fundamentals of circular economy, green chemistry, and the United Nations Sustainable Development Goals.

The convergence of global water pollution and the demand for clean energy has accelerated interest in photocatalytic systems capable of simultaneously generating hydrogen and degrading recalcitrant organic contaminants. Rather than treating wastewater and energy production as independent challenges, dual-functional photocatalysis offers a unified solar-driven strategy in which photogenerated electrons fuel hydrogen evolution. At the same time, holes and reactive oxygen species drive the mineralization of pollutants. This review explores recent advances in integrated photocatalytic platforms that transform wastewater from an environmental liability into a functional resource for sustainable hydrogen generation. Emphasis is placed on mechanistic coupling between redox reactions, highlighting how band alignment, interfacial charge transfer, and heterojunction architecture govern the balance between hydrogen selectivity and oxidative degradation. Key catalyst engineering strategies, including defect modulation, co-catalyst loading, and Z-scheme and S-scheme heterojunctions, are critically examined across systems targeting pharmaceuticals, dyes, and microplastics. Beyond material innovation, the review evaluates the practical implications of using pollutants as sacrificial electron donors, including trade-offs related to mineralization, catalyst stability, and the complexity of real wastewater. By integrating mechanistic insight with application-oriented assessment, this work provides a roadmap for designing robust photocatalytic systems that bridge environmental remediation and clean energy production, advancing circular economy principles and multiple sustainable development goals.

Ammonia is indispensable for food security and clean energy, yet its production via the Haber–Bosch process consumes vast amounts of fossil resources and contributes significantly to CO2 emissions. The photocatalytic nitrogen reduction reaction (NRR) driven by solar energy offers a sustainable alternative under ambient conditions; however, progress is limited by weak N2 adsorption, strong N≡N bond cleavage, competing hydrogen evolution, and low quantum efficiency. Metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) have emerged as transformative photocatalyst platforms, combining high surface area, tunable porosity, πconjugated structures, and biomimetic active sites to enhance light harvesting, charge separation, and nitrogen activation. This review highlights recent advances in pristine MOF and COF frameworks, composites, and framework-derived catalysts, emphasizing strategies such as defect engineering, heteroatom doping, functionalization, and heterojunction construction toward photocatalytic NRR. Mechanistic insights from spectroscopy and density functional theory reveal associative, Mars–van Krevelen, and defect-assisted pathways, offering guidance for rational catalyst design. Beyond materials, techno-economic aspects, including scalability, durability, cost performance balance, and energy payback, are critically assessed relative to the Haber-Bosch process. This review highlights the importance of integrating molecular-level catalyst design with reactor-scale engineering to translate laboratory breakthroughs into scalable solar ammonia production.

The utilization of photocatalytic nitrogen fixation stands out as a potent technology in the development of ammonia using atmospheric nitrogen, a pivotal stride toward fostering a green economy. Recently, bismuth oxyhalides (BiOX) have emerged as promising catalysts for the conversion of nitrogen into ammonia through photocatalysis. The predominant role of BiOX materials is indicated by their distinctive electronic configuration and optical characteristics. This review encapsulates the recent advancements in BiOX-based materials toward photocatalytic nitrogen fixation. This review also delves into several aspects, such as sources and characteristics of nitrogen, photocatalytic nitrogen fixation mechanisms, and strategies for structural optimization of the BiOX to bolster the catalytic performance. The discourse culminates with a forward-looking perspective that underscores both the potential and hurdles associated with BiOX-based photocatalysts toward nitrogen fixations.

This research focuses on the development of a novel, reusable copper ferrite/kaolinite/polypyrrole carbon black (PCB) impregnated carboxymethyl cellulose (CKP) hydrogel. It explores the degradation of tetracycline under LED light using persulfate activation. The CKP hydrogels, prepared via blend crosslinking methods, achieved 98% tetracycline degradation in 15 minutes under LED light irradiation via persulfate activation. The CKP hydrogels remained highly reusable for up to 20 consecutive cycles. The degradation kinetics were successfully modeled using a machine learning algorithm, and pseudo-first-order kinetics is proposed. The enhanced catalytic performance is attributed to the synergistic interaction between copper ferrite, kaolinite, and PCB within the carboxymethyl cellulose framework, which facilitates the effective separation of reactive oxygen species (ROS), such as sulfate (˙SO4−) and hydroxyl (˙OH) radicals. The presence of polypyrrole carbon black (PCB) leads to higher electrical conductivity in CKP hydrogels. It acts as an efficient electron reservoir, facilitating the rapid transfer of electrons to the CKP hydrogels and helping to suppress charge recombination. The presence of kaolinite enhances the performance of CKP hydrogels by contributing to their high adsorption capacity. The 3D porous network of CKP hydrogels provides abundant reactive sites, further supporting rapid mass transfer and sustained efficiency. The key degradation intermediates were identified via high-resolution mass spectrophotometry (HRMS), their toxicity was assessed using ecological structure–activity relationships (ECOSAR), and the overall greenness of the CKP hydrogel system was validated through sustainability metrics analysis.

A highly efficient, defect-rich, and dimensionally engineered carbon nitride homojunction hydrogel (NTCN hydrogel) was developed for the in-situ generation of H2O2 under the illumination of visible light. The photocatalytic-self-Fenton (PSF) system was integrated with peroxymonosulfate (PMS), enhancing the production of reactive oxygen species, which aided the tetracycline degradation to 99.5 % in 8 min. The NTCN hydrogels also displayed a maximal reusability of 20 cycles with a slight decline in the degradation efficiency. The superior catalytic performance is indicated by the establishment of a Z-scheme junction in the NTCN hydrogel, which is attributed to the higher separation efficiency, rapid H2O2 generation, and synergistic interaction between the PMS and PSF in the hybrid oxidation system. The mechanistic pathways revealed the synergistic interaction between the PMS and H2O2 in the PSF-PMS hybrid oxidation system, enhancing the performance of NTCN hydrogels in a wider range of pH. Under basic pH conditions, the PMS and H2O2 are produced on the surface of NTCN hydrogels to mutually generate [rad]OH and 1O2, which led to enhance the lower degradation efficacy in the PSF system. At acidic pH, the O2[rad]− emerges as a predominant Reactive Oxygen Species (ROS), and the synergistic action of H2O2 and PMS completely avoided the dependency on protons by the PSF-PMS system. This study describes a highly efficient and sustainable hybrid multifunctional oxidation system for the purification of tetracycline from synthetic wastewater.

Photocatalytic technology is considered to be one of the most prominent strategies to address energy and environmental problems by utilizing visible light. As a metal-free semiconductor, graphitic carbon nitride (GCN) has attracted global research attention due to its low toxicity, stability, versatile 2D structure, and phenomenal visible light activity. Higher recombination ratio and poor separation efficiency limited the practical applications of GCN. Recently, the concept of g–C3N4–based homojunction became a research interest due to its phenomenal separation efficiency and suppressed recombination of electron-hole pairs. Based on the charge transfer mechanisms, the g–C3N4–based homojunction predominantly followed type-II, Z-scheme and S-scheme mechanisms. This review describes the construction of GCN-based homojunction towards energy and environmental remediation, including organic pollutant degradation, hydrogen production, carbon dioxide reduction, and hydrogen peroxide production. A detailed emphasis is given to the different types of GCN-homojunction and the charge transfer pathways. Finally, the advantages, disadvantages, and future perspectives of GCN-based homojunction photocatalysts are explained.

This study deals with a dual Z-scheme functionalized g-C3N4/CeO2/Bi2S3 (PCB) heterojunction impregnated with sodium alginate hydrogels have been prepared as photocatalysis-self-Fenton system to investigate the degradation of tetracycline without the need for additional H2O2. The morphological, structural, crystal, optical, and chemical compositions affirmed the construction of g-C3N4/CeO2/Bi2S3 (PCB) hydrogels. Photocatalytic investigations revealed that H2O2 production via a two-step dual-electron reduction pathway achieved the maximum H2O2 production of 1.4 mM within 60 min under the visible light irradiation. Tetracycline degradation efficacy increased to 81 % in 60 min via photocatalysis self-Fenton reaction. Moreover, g-C3N4/CeO2/Bi2S3 (PCB) hydrogels demonstrated a notable reusability up to 5 cycles with a decline of only 5 % in degradation efficiency. Furthermore, g-C3N4/CeO2/Bi2S3 (PCB) heterojunction hydrogels exhibited dual Z-scheme with enhanced electron transfer efficiency, reduced recombination rates, and accelerated H2O2 production. This research offers valuable insights into the on-site H2O2 utilization for the remediation of organic pollutants using recyclable biopolymer-based photocatalysts.

The photocatalytic-self-Fenton system (PSF) is a synergistic approach that combines photocatalysis and Fenton technologies and has garnered considerable attention towards the remediation of noxious compounds. The in-situ generation of H2O2 and effective interaction between Fe ions, or in the absence of Fe ions, produces abundant reactive oxygen species in the reclamation of noxious compounds. The PSF system offers advantages such as the absence of external addition of H2O2 and the accelerated cyclic conversion of the Fe2+/Fe3+. Different materials, including g-C3N4, metal sulfides (CdS, In2S3, and FeS2), metal oxides, and resins, exhibit substantial potential for development in this context. This review delves into the detailed exploration of PSFs, thoroughly examining the concrete mechanism encompassing both photocatalysis and Fenton reactions. Subsequently, the focus extends to the properties, modifications, and applications of the promising catalysts. Finally, this review anticipates novel research directions in the realm of PSFs, offering insights to enhance their practical applications in the future. The comprehensive overview opens up new horizons for advancing the efficacy of PSFs in real-world scenarios.

The growing demand for sustainable energy and environmental remediation has intensified the search for efficient, metal-free catalysts. Among these, graphitic carbon nitride (g-C3N5) has garnered significant attention due to its nitrogen-rich structure, extended π-conjugation, and tunable bandgap. Its abundant raw materials, non-toxic nature, and exceptional physicochemical properties make it a promising candidate for energy and environmental applications. This review comprehensively analyzes advancements in g-C3N5-based photocatalysts for energy and environmental applications. The g-C3N5 structures, highlighting their physicochemical characteristics and bandgap variations, and a detailed overview of synthesis methods are presented. Furthermore, we explore advanced engineering strategies such as doping, defect engineering, heterojunction formation, and co-doping to enhance catalytic efficiency. The applications of g-C3N5 in water treatment, H2 production, nitrogen fixation, CO2 reduction, and H2O2 synthesis are examined, addressing key challenges like stability, efficiency, and recyclability. Unlike previous reviews, this study offers a unified and holistic overview encompassing all energy and environmental applications of g-C3N5, while also identifying critical bottlenecks and future research opportunities for practical implementation. The strengths, limitations, and outlook of g-C3N5-based systems are systematically discussed, with emphasis on innovative strategies to overcome current barriers and accelerate real-world deployment.

In this study, In₂S₃/CuSe (ICS) carboxymethyl cellulose (CMC) 3D photocatalytic hydrogels were developed for the efficient degradation of sulfamethoxazole under LED light irradiation through peroxymonosulfate (PMS) activation. The ICS composites were synthesized via a hydrothermal reaction and incorporated into hydrogels using a blend-crosslinking technique with FeCl₃. The structural, morphological, and optical characterizations confirmed strong interfacial contact between the semiconductors, bandgap modulation, accelerated electron-hole pair transfer, and improved charge separation, all of which contributed to enhanced catalytic performance. The ICS carboxymethyl cellulose hydrogels achieved 100 % sulfamethoxazole degradation within 5 min and demonstrated high reusability, maintaining activity for up to 20 cycles. A type-II heterojunction assisted electron migration mechanism, supported by scavenger tests and optical analysis, was proposed. The presence of selenium, copper and iron in the ICS hydrogel also facilitated the cyclic conversion of transition metals which ubiquitously produced ROS species to aid SMX degradation. The integration of CMC as a catalytic support enhanced reusability, and facilitated catalyst recovery. A special emphasis was given to the sustainability metrics analysis of the ICS hydrogels, evaluating their environmental impact and long-term viability. Overall, the ICS heterojunction system exhibits significant potential for environmental remediation, providing enhanced versatility and durability.

Developing efficient integrated advanced oxidation processes (AOPs) is vital for sustainable treatment of antibiotic-contaminated water. In this work, a novel 3D photocatalyst was engineered by embedding a ternary Se/g-C3N4/Bi2WO6(SGB) heterojunction into a carboxymethyl cellulose hydrogel, yielding a stable and reusable SGB hydrogel system. Structural, optical, electrochemical, and photoelectrochemical analyses confirmed a hybrid Type-II/Z-scheme heterojunction, reducing the bandgap to 1.74 eV and enhancing charge separation. The synergistic effects of the ternary interface and hydrogel matrix enabled efficient in situ H2O2generation (716 μM in water; 958 μM with isopropanol), facilitating a self-Fenton-like reaction. Upon coupling with peroxymonosulfate (PMS) activation, the system achieved 93.86% tetracycline degradation within 30 minutes. Radical scavenging and trapping experiments revealed a multi-radical degradation pathway involving ˙OH, SO4˙−, O2˙−, and1O2, with their roles modulated by pH. At higher pH, PMS activation via O2˙−/e−favored SO4˙−and1O2generation, while lower pH conditions promoted H2O2/˙OH production and hole oxidation. LC-MS analysis confirmed the stepwise degradation of tetracycline into low-mass intermediates, supporting the proposed mechanism. Toxicity analysis further demonstrated that the transformation products exhibited reduced ecological risk, confirming the environmental safety of the process. The SGB hydrogels exhibited excellent stability and reusability, retaining 72.14% degradation efficiency after 12 cycles and retaining performance across a broad pH range. This study introduces a novel photocatalytic platform integrating Type-II/Z-scheme charge transfer, photoelectrochemical performance, multiple AOP pathways, and progressive detoxification within a hydrogel matrix for sustainable pharmaceutical pollutant remediation.

Dihydrogen, commonly named 'hydrogen', is a carbon–neutral and renewable fuel meeting environmental regulations in transportation and industrial production. Hydrogen is currently employed in fuel cells, hydrogen vehicles, and as an efficient energy carrier due to its high energy capacity of 121 kJ per g. Here we review hydrogen production by steam reforming of alcohols including methanol, ethanol, propanol, glycerol and butanol, with focus on catalysts, mechanisms, and analytical methods to characterize deposited carbon. In general, Ru- and Rh-based catalysts show efficient performance with almost 100% feedstock conversion and up to 89% of hydrogen yield, while Ni and Co catalysts exhibit lower ethanol conversion in the range of 40–100% depending on operating conditions. Nevertheless, Ni and Co catalysts have been mainly chosen as active metals for alcohols steam reforming due to their lower cost.

Graphitic carbon nitride (GCN) is an efficient visible-light-driven metal-free semiconductor with superior photocatalytic activity. However, the main drawbacks of GCN include lower adsorption capacity, poor reusability and recoverability. To address these drawbacks, kaolinite/g-C3N4-alginate beads were fabricated using a cross-linking method to remove brilliant green dye from wastewater via photocatalysis. The characterization studies proved the alginate's potential capability in altering photocatalyst bandgap (2.78 to 2.55 eV) and minimizing recombination of electron-hole pairs. Kaolinite/g-C3N4-alginate photocatalyst removed 97 % of brilliant green (10 mg/L) in 90 min under visible light irradiation. The superior performance of the kaolinite/g-C3N4-alginate beads was ascribed to its improved adsorption and effective utilization of visible light. The key advantages of kaolinite/g-C3N4-alginate beads were their quick recovery and extended reusability upto ten cycles. The sustainability metrics analysis of kaolinite/g-C3N4-alginate beads confirmed the environmental suitability and practicability in wastewater remediation. This study provides new insights into the low-cost and sustainable preparation of highly reusable g-C3N4-based photocatalysts for environmental remediation.

Plastics have become an integral part of our lives, offering affordability, convenience resilience, and versatility. Yet their widespread use, coupled with their disposability and resistance to degradation, presents a significant challenge to environmental sustainability. The accumulation of disposed plastics poses significant problems for mankind and nature. Thus photocatalytic technology emerged as an affordable, environmentally suitable, and sustainable process for the conversion of plastics at a normal temperature and pressure under the illumination of visible or solar light. The mild reaction conditions of photocatalysis facilitate the precise transformation of plastic waste into fuels or chemicals. Here, we discuss the recent advancements in photocatalytic plastic conversion using different photocatalysts for the production of hydrogen or value-added chemicals. Among all the catalysts, CdS/NiS is prepared via hydrothermal treatment for the solar-light-assisted transformation of plastics to hydrogen. The developed CdS/NiS is capable of generating a maximum hydrogen (62.9 mmol g-1 h-1) production via photocatalytic conversion of polylactic acid. A special emphasis is provided on the photocatalytic plastic conversion mechanism into fuels. Finally, the important challenges and future research perspectives are outlined.

A hybrid Na, B, and O codoped g-C3N4/polypyrrole carbon black (CCNP) hydrogel is prepared via an in situ cross-linking method for percarbonate activation under visible light irradiation. The structural, morphological, and optical characterizations proved the tuned bandgap, enriched utilization of visible light, minimum recombination ratio, and higher separation efficiency. The CCNP hydrogels could easily activate the percarbonate under visible light, leading to abundant production of reactive radicals, which aids in the degradation of tetracycline in wastewater. About 96% of tetracycline was degraded in 15 min at its natural pH. The superoxide, carbonate, and hydroxyl radicals were the important radical species in tetracycline degradation. The CCNP hydrogels also exhibited high photostability and reusability up to six cycles. The tetracycline degradation pathway is given a special focus, and the percarbonate activation mechanism is highlighted. This study provides a new strategy for boosting the performance of g-C3N4-based catalysts for percarbonate activation and wastewater remediation.

Water pollution and the energy demand are calling for sustainable technologies such as photocatalysis, yet actual methods are difficult to upscale due to the poor recovery and reusability of nanocatalysts. This issue could be solved by using photocatalytic sponges, which display high surface area and reusability. Here we review the applications of photocatalytic sponges for wastewater degradation, disinfection, carbon dioxide reduction, and hydrogen production. Photocatalytic sponges are fabricated by templating, dip coating, sol–gel, polymerization, electrospinning, and freeze drying. Remarkable results include the monolithic microreactor with Ag/AgCl coated on a polydopamine-modified melamine sponge, which exhibits a 100% methylene blue degradation in 15 min, with a reusability of five cycles. An hydrogen production rate of 11.33 mmol h−1 g−1 was obtained with the pyridazine-doped graphitic carbon nitride with nitrogen defects and a spongy structure.

The facile development of highly efficient visible light active metal-free homojunction photocatalysts with phenomenal photoelectron migration is emerging as a prominent method for diverse energy and environmental remediation applications. Through an effective cross-linking technique, citric acid-functionalized g-C3N4 homojunction/carboxymethyl cellulose hydrogel beads (ICN/CMC beads) were prepared. The photocatalytic studies of ICN/CMC beads exhibited 87% tetracycline degradation in 40 min under visible light irradiation. The important advantages of ICN/CMC beads are their ease of recovery and reusability of up to 12 cycles. The ICN/CMC beads were capable of producing 2341 μmol of hydrogen peroxide and 501 μmol/h·g of ammonia production in 60 min under visible light irradiation. The predominant catalytic activity is due to the tuned bandgap of the photocatalyst, which facilitated the effective separation of electron-hole pairs and hindered the recombination of charge carriers. Thus, ICN/CMC beads are affordable and sustainable photocatalysts with multimodal applications.

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.

Graphitic carbon nitride (GCN) has gathered phenomenal research interest as a metal-free, safe, and affordable photocatalyst. However, GCN suffers several problems, such as lower utilization of visible light, higher recombination ratio, slower electron immobility, poor reusability, and a tedious recovery process. Herein, a ternary homojunction (OPACN) was effectively constructed between oxidized GCN (OCN), amino-rich GCN (ACN), and phosphorylated GCN (PCN) and then formulated into 3D hydrogels (OPACN) using pectin as the catalyst support via a crosslinking strategy using FeCl3. The photocatalytic studies using OPACN hydrogel reported 88 % degradation of tetracycline in 30 min with a maximum reusability of 15 cycles. The ternary homojunction hydrogel photocatalyst produced 1204 µM of H2O2 and 404 µM of ammonia in 60 min of visible light irradiation. The phenomenal catalytic activity of the OPACN hydrogel is ascribed to the effective construction of homojunction between the OCN, PCN, and ACN, which facilitated the separation efficiency and boosted the visible light utilization. This study affirmed that the utilization of pectin as a catalytic support enhanced the visible light utilization, reusability, stability, and easiness in recoverability. In addition to this, pectin can act as an electron mediator, and the robust interactions between the GCN components via hydrogen bonding can also facilitate H2O2 production and nitrogen fixation. Overall, this study illuminates the usage of pectin as ideal photocatalytic support for environmental applications.

Remediation of persistent organic pollutants such as pesticides and personal care products in water has attained immense research interest due to the commercialization feasibility of Advanced Oxidation Processes. Thus, the present study focuses on the solar-light assisted photocatalytic degradation of commonly used pesticide, i.e., 2,4-dichlorophenoxyacetic acid. The chitosan-modified g-C3N4 beads (CS/g-C3N4) were synthesized using the phase inversion method. Synergistic activity of chitosan with g-C3N4 in the form of recoverable beads with solar light-based photocatalytic activity has been brought as the novelty of this work. The chitosan-modified g-C3N4 beads have been studied for their morphological and structural characterization. The diffuse reflectance spectroscopy shows the variation in the bandgap from 2.79 (g-C3N4) to 2.6 eV (CS/g-C3N4 beads) due to the incorporation of chitosan. The photocatalytic removal of 2,4-D under solar light using CS/g-C3N4 is found to be 83 %. The prepared beads showed no significant loss in catalytic activity even after four cycles. Therefore, CS/g-C3N4 is a low-cost, affordable, and environmentally friendly material for the redemption of pesticides like 2,4-D.

The nano-sized powder photocatalysts are prone to agglomeration and poor reusability, which cause secondary pollution. To avoid the loss of powder photocatalyst, Titanium dioxide/(TiO2)/impregnated Zirconium (Zr)-chitosan beads were prepared using a simple cross-linking reaction for the peroxymonosulfate activation to aid the tetracycline degradation. The beads' structural, morphological and optical properties were studied using different techniques. The prepared catalysts effectively degraded 97% of tetracycline (10 mg/L) in 20 min of visible light illumination. The sulfate radicals, superoxide radicals, holes and singlet oxygen were found to be the predominant reactive groups that boosted the tetracycline degradation. The key intermediates were analyzed, and the degradation pathway of tetracycline was proposed. The reusable microspheres exhibited maximum reusability up to 10 cycles with an 11% loss in degradation efficiency. Overall, the important advantages of photocatalytic 3D beads include higher reusability, minimal catalytic mass loss during recovery process and stronger visible light utilization via band gap alteration, opening a new horizon toward effective wastewater management.

The ease of synthesis of affordable photocatalysts activated by visible light and exhibiting exceptional photocatalytic performance is highly advantageous for addressing energy and environmental problems. Herein, simultaneous oxygen-doped and defect-engineered carbon nitride (ACN) was easily prepared via thermal calcination using ammonium oxalate as the chemical functionalization agent. The photocatalytic experimental studies claimed a maximum tetracycline degradation of 88% in 60 min of visible light irradiation. The ACN displayed 721 μM of H2O2 and 316 μM of ammonia generation in 60 min of visible light illumination. The remarkable efficiency of the ACN photocatalyst is linked to its enhanced visible light utilization, achieved by modifying the bandgap. Also, its increased surface area facilitates better charge carrier separation, while defect formation and concurrent oxygen doping work to suppress charge carrier recombination. Scavenger studies highlighted the critical role of superoxide radicals and electrons in the photocatalysis process. Nitrogen defects and oxygen heteroatoms facilitate effective charge separation by forming electron-hole pairs within the delocalized system under visible light, which promotes interfacial contact and the decomposition of tetracycline. A metal-free, chemically functionalized carbon nitride photocatalyst, enriched with defects and doped with oxygen, was employed as an affordable, efficient, and environmentally friendly material for energy and environmental remediation.

In this study, a reusable double Z-scheme In2S3/Bi2WO6/CdS (ICB) photocatalytic hydrogels were developed for efficient reclamation of sulfamethoxazole (SMX) using peroxymonosulfate (PMS) activation and H2O2 production. The ternary In2S3/Bi2WO6/CdS nanocomposites were prepared using the hydrothermal method and formulated into hydrogels via an immobilization strategy using sodium alginate as base substrate. The morphological, optical, structural, and electrochemical characterization of ICB hydrogels confirmed the formation of a ternary heterojunction. The ICB hydrogels displayed 99% sulfamethoxazole (10 mg/L) degradation (Rate constant = 0.191 min -1) in 20 min of visible light irradiation via peroxymonosulfate (PMS) activation (400 mg/L) with a reusability of 15 cycles. Also, the ICB hydrogels/PMS/Visible system demonstrated higher mineralization efficiency (56%) and ensured practicability by reclaiming the real wastewater. Higher catalytic efficacy is ascribed to the construction of double Z-scheme heterojunctions between In2S3, Bi2WO6, and CdS, which resulted in enhanced separation efficiency and suppressed recombination ratio of charge carriers. The synergistic interaction between the photocatalyst and PMS activation boosted the production of reactive oxygen species like SO4*-, O2*-, OH*-, and electrons. Additionally, photocatalytic studies revealed a maximum H2O2 production of 302 μM in 60 min. The advantages of ternary photocatalytic hydrogels include higher reusability, easiness in catalyst recovery, higher utilization of visible light (1.34 eV), and sustainability. This research provides perspectives on the successful fabrication of a reusable double Z-scheme photocatalyst for peroxymonosulfate activation in the redemption of noxious contaminants.

Plastics have become an integral part of our lives, offering affordability, convenience resilience, and versatility. Yet, their widespread use, coupled with their disposability and resistance to degradation, presents a significant challenge to environmental sustainability. The accumulation of disposed plastics poses significant problems to entire manhood and nature. Thus photocatalytic technology emerged as an affordable, environmentally suitable, and sustainable process for the conversion of plastics at normal temperature and pressure under the illumination of visible or solar light. The mild reaction conditions of photocatalysis facilitate the precise transformation of plastic waste into fuels or chemicals. Here, we discuss the recent advancements in photocatalytic plastic conversion using different photocatalysts for the production of hydrogen or value-added chemicals. Among all the catalysts, CdS/NiS is prepared via hydrothermal treatment for the solar-light-assisted transformation of plastics to hydrogen. The developed CdS/NiS is capable of generating a maximum hydrogen (62.9 mmol g-1 h-1 ) production via photocatalytic conversion of polylactic acid. A special emphasis is provided on the photocatalytic plastic conversion mechanism into fuels. Finally, the important challenges and future research perspectives are outlined.

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.

Water contamination is increasing worldwide, yet actual methods of water and wastewater treatment are limited, in particular by actual fossil-fuel derived nano-adsorbents that are difficult to regenerate. This calls for advanced methods that use sustainable materials such as chitosan. Chitosan is a biopolymer extracted from the outer skeleton of shellfish, including crab, lobster, and shrimp. Chitosan is non-toxic, abundant, and chemical and physical stable. Moreover, chitosan can be shaped into beads, sheets, membranes, and composites. Here, we review chitosan-based beads for wastewater treatment with focus on adsorption mechanisms, removal of pollutants, functionalization, metal organic frameworks, magnetic beads, imprinted and co-polymeric beads, and regeneration. We found that chitosan/Fe-hydroxyapatite beads exhibit an adsorption capacity of 1385 mg/g for the removal of lead. Imprinted magnetic chitosan beads display a reusability of 15 cycles for nickel removal.

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.

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.

4 Nitrophenol (NP) or para nitrophenol (PNP) is one of the emerging pollutants from pesticides industries and it is a major discharge from any phenol consuming industry and also severs as a major discharge from pharmaceutical wastewater. Design and development of photocatalytic treatment of p-nitrophenol particularly to suit recovery and reuse of catalyst will aid in its commercial scale development. P-nitrophenol degradation has been studied in cellulose acetate immobilized TiO2 in a continuous photocatalytic reactor. The prepared catalyst were characterized using SEM, DRS-UV, XRD, FT-IR. The degradation efficiency is studied for varying the pH, catalyst dosage and also the supports. The overall degradation of p-nitrophenol of 89 % was observed for cellulose acetate doped TiO2 (CA/TiO2) than compared to bare TiO2 (74 %). The kinetics was pseudo first order kinetics and mechanism of p-nitrophenol degradation was also discussed.

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.

Green synthesis is a prominent synthesis route to prevent detrimental effects exhibited by the traditional methods for nanoparticle preparation on a small or large scale. Moreover, the green nanomaterials possess controllable properties, such as shape and size ascribed to the electrical, optical, magnetic, and catalytic properties of the metal nanoparticles. These characteristics make nanomaterials (NMs) unique in addressing environmental issues. This review chapter discusses the preparation of different nanoparticles, such as metal or metal oxide-based nanoparticles using the green pathway and their photocatalytic applications in wastewater treatment.

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.

The sustainable visible light active g-C3N4 hydrogel is synthesized and employed for water reclamation and H2O2 production. In this study, citric acid-assisted chemically functionalized black g-C3N4 isotype heterojunction (BCN) hydrogel was prepared using the blend-crosslinking method. The comprehensive characterization of the BCN hydrogels affirmed its tuned optical bandgap with effective visible light utilization, greater separation efficiency, and restricted recombination ratio of electrons and holes. The BCN hydrogels exhibited a phenomenal photocatalytic efficiency towards tetracycline degradation (86% in 40 min) and H2O2 production (987 µmol in 60 min). The superoxide, holes, and singlet oxygen demonstrated a synergistic role in photocatalytic activity through the effective migration of electrons. As an immobilized system, the predominant advantages of BCN hydrogel beads include ease of recovery and remarkable reusability up to 7 cycles. This study provides insights into systematically modifying g-C3N4 toward sustainable energy and environmental applications.

Chitosan/metal-organic frameworks (CS/MOFs) are versatile materials fabricated by conjugating the chitosan (CS) material with metal-organic frameworks (MOFs). The CS/MOFs demonstrated phenomenal features such as higher surface area, porosity, non-toxicity, environmental safety, and ability to form different structures, making them suitable for diverse applications in adsorption, catalysis, membrane separation, supercapacitors, batteries, fuel cells, sensing, food packaging, and biomedical applications, including drug delivery. The different preparation routes for fabricating CS/MOFs are elucidated in detail. The CS/MOFs mostly remove emerging pollutants via adsorption and membrane separation. However, CS/MOFs are less explored in supercapacitors, fuel cells, and food packaging. This review highlights the preparation, characteristics, and applications of CS/MOFs for energy, environmental and bio-medical applications. The advantages, disadvantages, and perspectives are also elaborated. The following review is expected to be a useful guide for scientists working on CS/MOFs.

Management of hospital wastewater is a challenging task, particularly during the situations like coronavirus 2019 (COVID-19) pandemic. The hospital effluent streams are likely to contain many known and unknown contaminants including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) along with a variety of pollutants arising from pharmaceuticals, life-style chemicals, drugs, radioactive species, and human excreta from the patients. The effluents are a mixed bag of contaminants with some of them capable of infecting through contact. Hence, it is essential to identify appropriate treatment strategies for hospital waste streams. In this work, various pollutants emerging in the context of COVID-19 are examined. A methodical review is conducted on the occurrence and disinfection methods of SARS-CoV-2 in wastewater. An emphasis is given to the necessity of addressing the challenges of handling hospital effluents dynamically involved during the pandemic scenario to ensure human and environmental safety. A comparative evaluation of disinfection strategies makes it evident that the non-contact methods like ultraviolet irradiation, hydrogen peroxide vapor, and preventive approaches such as the usage of antimicrobial surface coating offer promise in reducing the chance of disease transmission. These methods are also highly efficient in comparison with other strategies. Chemical disinfection strategies such as chlorination may lead to further disinfection byproducts, complicating the treatment processes. An overall analysis of various disinfection methods is presented here, including developing methods such as membrane technologies, highlighting the merits and demerits of each of these processes. Finally, the wastewater surveillance adopted during the COVID-19 outbreak is discussed.

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.

The rising water pollution by pesticides, pharmaceuticals and dyes is a major health issue calling for advanced remediation methods such as photocatalysis with titanium dioxide (TiO2), yet the use of TiO2 displays issues of aggregation, mass loss, recovery, and reusability. These issues have been recently solved by synthesizing biopolymer-supported photocatalysts using cheap, biodegradable and safe biopolymers such as chitosan, alginate, cellulose, cyclodextrin, guar gum and starch. Here we review biopolymer-supported TiO2 photocatalysts for the removal of organic compounds, with focus on preparation methods, photo and chemical stability, reusability, and adsorptive capacity. We discuss applications of immobilized photocatalysts at the industrial scale.

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.

Remediation of pesticides by advanced oxidation process gains enormous interest due to its feasible applications at the polluted site. The 2,4-dichlorophenoxyacetic acid (2,4-D), a common herbicide in water bodies, poses a major environmental threat to humans and aquatic organisms. However, the advanced oxidation process offers a possible solution for its effective recovery. Optimisation of the critical parameter will support the possible recovery process of the 2,4-dichlo-rophenoxyacetic degradation. In the present study, response surface methodology based analysis of variance optimization was made for a modified TiO2 catalyst in a glass fabricated photo-catalytic reactor for 2,4-dichlorophenoxyacetic acid degradation. The variables investigated were pH (2–10), initial 2,4-D concentration (10–100 mg/L), and catalyst loading (25–150 mg/L). The maximum removal efficiency of 97% has been achieved at the optimized variable of 87.5 mg/L of catalyst dosage at 55 mg/L of 2,4-D concentration at pH 6.

Metal oxide nanoparticles display unique properties such large bandgap, low electric constant, low refractive index, high chemical stability, and vacant oxygen presence. Magnesium oxide (MgO) nanoparticles are of particular interest because they are abundant, nontoxic, cheap, odorless, and stable. Here we review the synthesis and applications of MgO nanoparticles and their composites in various fields. MgO has antibacterial properties for medicine due to the production of superoxide anion O2−. The reactivity and stability of MgO are of interest for medicine, water purification, catalysis, and gas sensors. For membrane applications, new strategies are needed to control the pore diameter of the membranes with MgO as filler. As food packaging materials, there is a need for methods to assess the release of nanoparticles from the packing materials into food. For sensor applications, challenges include sensitivity, reproducibility, surface fouling, and poisoning. For supercapacitors and semiconductors, controlling the pore structure should improve electron transport.

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.

The global usage of pesticides has increased by more than 1.5 times over the last three decades. As a consequence, waters are increasingly contaminated by pesticides and their degradation products. For example, organochlorine pesticides are considered most hazardous due to their long half-lives in the environment, up to 5–15 years, and because they bioaccumulate. This is a major health issue requiring advanced methods for water cleaning such as adsorption with activated carbon, yet actual methods are limited by the cost, poor recyclability and disposal of current adsorbents. Here, we review pesticide adsorbents made of materials. Biochars derived from plant materials show maximal adsorption capacities up to around 900 mg/g due to high carbon content in the range of 38 to 80%. Strategies for field applications and post-treatment of spent adsorbents are discussed.

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.