Visible-light-driven photocatalytic degradation of dye and antibiotics by activated biochar composited with K+ doped g-C3N4: Effects, mechanisms, actual wastewater treatment and disinfection

Highly-efficient photocatalytic removal of methyl orange on CuO hierarchical hollow microspheres modified by ultrathin and porous g-C3N4 nanosheets

Photocatalytic degradation technology is taken as an efficient strategy to alleviate organic dye pollution in wastewater. In order to achieve high catalytic activities, morphology regulation and structure design are crucial for photocatalytic system. In this work, the hierarchical CuO hollow microspheres self-assembled by nanowires (CuO HMS) were successfully synthesized by solvothermal process. Graphitic carbon nitride (g-C3N4) nanosheets (CNN) with ultrathin and porous feature were anchored on the spherical shell of CuO HMS to manufacture the CuO/g-C3N4 p-n heterojunction via one-step calcination. The unique CuO/g-C3N4 composite possesses the nanowire self-assembled hollow hierarchical microstructures, as well as the self-doped CuO by the C and/or N atoms, which conduces to increasing specific surface area, narrowing band gap, improving visible-light-harvesting capacity, promoting the segregation of photo-induced electron-hole pairs, and accelerating carrier movement. Therefore, CuO/g-C3N4 shows outstanding photocatalytic properties of methyl orange (MO) degradation, compared with CuO HMS and CNN. Especially, the CuO/g-C3N4 composite with 10 wt% CuO HMS (CC-3) achieves almost complete decomposition of MO, and its apparent rate constant (kapp) is superior to that of CuO HMS (19.1 times) and CNN (22.5 times). Compared with the similar materials such as CuO/BiVO4, CuO/TiO2 and CuO/ZnO p-n heterojunctions, the resulting CuO/g-C3N4 composite demonstrates the satisfactory photocatalytic performance. The close cooperation of unique hollow hierarchical morphology, C and/or N self-doping, and p-n heterojunction is proposed to account for the extraordinary photocatalytic MO decomposition. This work proposes a feasible and effective paradigm for the construction of CuO/g-C3N4 composite, which demonstrates excellent photocatalytic performance for pollutant removal in wastewater by establishing hollow structure, non-metallic self-doping and p-n junction.

Visible light photocatalytic degradation of pesticides and antibiotics by H3PO4-activated biochar combined with g-C3N4: Effects, mechanism, degradation pathway, and toxicity assessment

In recent decades, aquatic environmental pollution resulting from the extensive use of pesticides and antibiotics in the agriculture and livestock industries has become a major concern. In this study, a H3PO4-activated biochar-g-C3N4 composite photocatalyst (PBC-g-C3N4(0.15)) was synthesized for the degradation of pesticides (imidacloprid (IMI), atrazine (ATR), azoxystrobin (AZO)) and antibiotics (tetracycline (TC), ofloxacin (OFX), sulfadiazine (SDZ)) under visible light. PBC-g-C3N4(0.15) achieved 89.7% degradation efficiency for IMI within 120 min, 1.8 times higher than g-C3N4, mainly due to 4.4 times increase in photocurrent density. Active species identified mainly included 1O2, ·O2-, and ∙OH. Density functional theory and UHPLC-Q Exactive MS analysis suggested three degradation pathways for IMI, with most intermediates predicted to be less toxic than the parent compound. Additionally, PBC-g-C3N4(0.15) was largely unaffected by environmental factors and achieved over 94% degradation efficiencies for AZO, TC, and OFX within 60 min, and over 34% for ATR and SDZ in 120 min. The degradation efficiencies for IMI and TC remained 61.0% and 76.1% after eight cycles, respectively. In natural water, the degradation efficiencies for IMI and TC exceeded 30% and 65%, respectively. This research offers valuable insights into the modification of g-C3N4 and the treatment of pesticides and antibiotics in wastewater.

Photocatalytic degradation of veterinary antibiotics in wastewaters: A review

The extensive use of veterinary antibiotics worldwide has led to their increasing accumulation in aquatic environments, adversely affecting both ecosystems and human health and leading to the emergence of antibiotic-resistant bacteria. Antibiotic residues enter water bodies primarily through wastewater effluent discharge, agricultural runoff, and improper disposal of pharmaceuticals. Several emerging technologies have been developed in response to the challenge of antibiotic contamination in wastewater. Among these, advanced oxidation processes (AOPs), including photocatalysis, have demonstrated significant potential for antibiotic degradation. Photocatalysis relies on the production of powerful oxidants to degrade pollutants under simulated or solar-light irradiation. Apart from the well-known TiO2, various photocatalytic materials have been used with metal oxides on the frontline. In this context, metal doping has been used to reduce the bandgap energy and enhance the absorption of visible light and charge-carrier separation. Doping with non-metals and carbon-based materials is another attractive alternative that promotes better degradation efficiency and suppresses recombination. Moreover, advanced designs, such as heterojunction constructions, have been developed for effective charge separation and wider utilization of the light spectrum. This comprehensive review summarizes recent advances in the design, characterization, efficiency, and mechanisms of various photocatalysts for degrading veterinary antibiotics in wastewater, along with toxicity assessments of the resulting transformation products. By examining these parameters, the current body of knowledge is consolidated, providing valuable insights into wastewater purification processes for effective antibiotic removal. Finally, by emphasizing the critical environmental importance of streamlined photocatalysis and the challenges associated with scaling up the process, this review highlights its feasibility in mitigating veterinary antibiotic pollution, thereby safeguarding aquatic ecosystems and reducing the risks of antibiotic resistance.

Study on stabilization of mercury in wastewater and soil by modified coal-based humic acid residue

Coal-based humic acid residue (HAS), as a waste generated during humic acid production, has been gaining attention in recent years due to its adsorption capacity and containing nutrients. In this study, to improve the adsorption capacity of HAS for and Hg, phosphate-modified materials (N-HAS) were prepared by a hydrothermal method and HAS and N-HAS were characterized by scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), X-ray fluorescence (XRF); batch adsorption experiments investigated the adsorption capacity of N-HAS on Hg2+ under different pH, and isothermal adsorption model and kinetic model fitted the adsorption process to explore the adsorption mechanism; the effects of various amounts of N-HAS on the Hg content in maize and the effective Hg in the soil under Hg-contaminated soil were investigated by field trial. The results showed that the pseudo-second-order kinetic model (R2 = 0.9641) and Langmuir isothermal (R2 = 0.95) adsorption model could better describe the adsorption behavior of N-HAR on Hg2+, the maximum adsorption amount was 124.20 mg/g, and the time to reach adsorption equilibrium was shorter for N-HAS compared to HAS; after 5 times of adsorption-desorption, the removal rate of Hg2+ by N-HAS was still higher than 80%, with stable cyclic adsorption performance; the adsorption mechanism of Hg2+ by N-HAS included physical adsorption, precipitation, and surface complexation, and compared with HAS, the percentage of complexation for Hg2+ adsorption by N-HAS increased by 77.81%, and the percentage of precipitation increased by 7.68%; compared to the control group, it was shown that the addition of N-HAS significantly decreased (p < 0.05) the Hg content of maize kernels by 27.44%-72.09%, increased biomass by 4.34%-11.26%, and decreased the available Hg content in soil by 50.00%-82.80%. In addition, the addition of N-HAS at 0.4 kg/m2 was optimal for the field trial. The study showed that N-HAS not only achieved resource utilization but also demonstrated great potential for treating Hg2+ in water and soil.

Synthesis of magnetic NiFe2O4/g-C3N4 heterojunction photocatalysts for boosting dye degradation performance under visible-light irradiation

Water pollution from dyes in wastewater is a critical global issue, as these stable organic dyes resist biodegradation, posing serious threats to aquatic ecosystems. To address this situation, advanced photocatalysts have been developed. Here, NiFe2O4/g-C3N4 was synthesized for the photocatalytic degradation of Rhodamine B (RhB) dye in the presence of H2O2 and visible light. Physicochemical analysis results showed NiFe2O4 nanoparticles dispersed in the g-C3N4 matrix, with an upward trend in the saturation magnetization of CNFx as NiFe2O4 content rose. The surface area of CNF30 was 62.3 m2 g-1, outperforming both NiFe2O4 (23.2 m2 g-1) and g-C3N4 (48.5 m2 g-1). NiFe2O4/g-C3N4 could be reused up to four cycles, and efficiently catalyzed the degradation of nearly 98% RhB dye, showing a decreased rate of up to 95% COD. Through scavenger studies, the main role of ˙OH was demonstrated. Therefore, highly efficient and recyclable NiFe2O4/g-C3N4 can be a potential photocatalyst for degradation of dyes.

Upcycling Waste Biomass to Biochar: Feedstocks, Catalytic Mechanisms, and Applications in Advanced Oxidation for Wastewater Decontamination

Advanced oxidation technology plays an important role in wastewater treatment due to active substances with high redox potential. Biochar is a versatile and functional biomass material. It can be used for resource management of various waste biomasses. In addition, carbonaceous materials are commonly used to enhance the synergistic mechanisms of advanced oxidation processes, because of their good electrical conductivity and metal-free leaching. Biochar produced from waste biomass through pyrolysis has catalytic potential, is cost-effective, and is environmentally friendly. It is commonly used to activate hydrogen peroxide, persulfate, ozone, photocatalysis, and other systems for degrading organic pollutants in water. This review provides a summary of the feedstocks, pyrolysis conditions, and modification methods used in biochar production. It also described the effects of these factors on the yield, structure, and active sites of the biochar. The review summarized the mechanisms of various catalytic systems and their applications in wastewater decontamination, as well as their potential for practical application. Eventually, the limitations of this current technique and the outlook for future research were noted.

Application of Biochar-Based Materials for Effective Pollutant Removal in Wastewater Treatment

With the growth of the global population and the acceleration of industrialization, the problem of water pollution has become increasingly serious, posing a major threat to the ecosystem and human health. Traditional water treatment technologies make it difficult to cope with complex pollution, so the scientific community is actively exploring new and efficient treatment methods. Biochar (BC), as a low-cost, green carbon-based material, exhibits good adsorption and catalytic properties in water treatment due to its porous structure and abundant active functional groups. However, BC's pure adsorption or catalytic capacity is limited, and researchers have dramatically enhanced its performance through modification means, such as loading metals or heteroatoms. In this paper, we systematically review the recent applications of BC and its modified materials for water treatment in adsorption, Fenton-like, electrocatalytic, photocatalytic, and sonocatalytic systems, and discuss their adsorption/catalytic mechanisms. However, most of the research in this field is at the laboratory simulation stage and still needs much improvement before it can be applied in large-scale wastewater treatment. This review improves the understanding of the pollutant adsorption/catalytic properties and mechanisms of BC-based materials, analyzes the limitations of the current studies, and investigates future directions.

Enhanced removal of tetracycline in light-dark tandem by FeCu-doped carbon composites derived from waste cotton fabrics

It is of great significance to develop an energy-efficient and external oxidant-free strategy for antibiotics removal. In this study, the novel light-dark tandem strategy was established to enhance tetracycline (TC) removal by bifunctional FeCu-doped carbon composites (FeCu@BC) derived from waste cotton fabrics. Interestingly, over 95 % TC was removed by FeCu@BC under light alone and dark alone in 10 min, with the same preferred conditions of pH 7.50 and 0.04 g/L catalyst dosage. Surprisingly, the enhanced mineralization efficiency of TC was achieved by the light-dark tandem without adjusting the parameters as 86.65 %, which was 1.13, 1.46 and 2.12 times higher than those of the dark-light tandem, light alone and dark alone, respectively. The mechanisms were elucidated as that 83.28 % direct degradation and 4.37 % indirect degradation under light while 47.63 % direct degradation and 24.16 % indirect degradation under darkness contributed for TC removal. The synergetic effects of persistent free radicals (PFRs) and FeCu interactions enabled FeCu@BC to work efficiently under both light and darkness, and light enhanced electron transfer between PFRs and FeCu interactions. Furthermore, energetic electrons stored in these active sites under light could be extracted to enhance electron transfer under subsequent darkness and the strongly catalytically active species initiated under light remained in action after cessation of light. Finally, high molecular TC was easily decomposed by energetic photo-catalysis and low molecular intermediates were mineralized under subsequent enhanced dark-catalysis to increase the mineralization efficiency. In general, this study provided an eco-friendly organics removal strategy and mechanisms insights based on the natural day-night cycle.

A new approach for endowing photocatalytic performance to biochar based on peryleneimide: Emphasizing the achievement of highly efficient degradation to RhB

Having unique structural characteristics of biochar contributes great potential in photocatalysis, the preparation process complexity is still a great challenge for biochar-based photocatalysts. Based on this, this study proposes a new, simple, efficient, and flexible approach to preparing biochar-based photocatalysts by perylene diimide (GPC/PDI). The results showed that the hybridization between GPC and PDI was achieved by π-π stacking, which was reduced with increasing pyrolysis temperature, increased first and then decreased with increasing PDI content, and improved with enhanced solvent polarity. When the pyrolysis temperature was 400 °C, the PDI addition was 0.05 mg, and the reaction solvent was water, the degradation of 200 mg/L rhodamine B (RhB) by GPC400/PDI0.5 was 94%, and the reaction rate constant was 10 and 4 times higher than GPC400 and PDI, which were also effective in simulating actual wastewater treatment. This was attributed to the efficient electron-hole separation and migration along the π-π stacking direction due to the hybridization of GPC and PDI, which in turn reacts to produce reactive oxygen species (1O2, •O2-, •OH), facilitating the photocatalytic degradation process.

Adsorptive-Photocatalytic Composites of α-Ferrous Oxalate Supported on Activated Carbon for the Removal of Phenol under Visible Irradiation

Adsorptive-photocatalytic composites based on activated carbon (AC) and α-ferrous oxalate dihydrate (α-FOD) were synthesized by an original two-step method and subsequently used for the removal of phenol from aqueous solutions. To obtain the composites, ferrotitaniferous black mineral sands (0.6FeTiO3·0.4Fe2O3) were first dissolved in an oxalic acid solution at ambient pressure, and further treated under hydrothermal conditions to precipitate α-FOD on the AC surface. The ratio of oxalic acid to the mineral sand precursor was tuned to obtain composites with 8.3 and 42.7 wt.% of α-FOD on the AC surface. These materials were characterized by X-ray powder diffraction, scanning electron microscopy, and the nitrogen adsorption-desorption method. The phenol removal efficiency of the composites was determined during 24 h of adsorption under dark conditions, followed by 24 h of adsorption-photocatalysis under visible light irradiation. AC/α-FOD composites with 8.3 and 42.7 wt.% of α-FOD adsorbed 60% and 51% of phenol in 24 h and reached a 90% and 96% removal efficiency after 12 h of irradiation, respectively. Given its higher photocatalytic response, the 42.7 wt.% α-FOD composite was also tested during successive cycles of adsorption and adsorption-photocatalysis. This composite exhibited a reasonable level of cyclability (~99% removal after four alternated dark/irradiated cycles of 24 h and ~68% removal after three simultaneous adsorption-photocatalysis cycles of 24 h). The promising performance of the as-prepared composites opens several opportunities for their application in the effective removal of organic micropollutants from water.

Ultrasmall copper-metal organic framework (Cu-MOF) quantum dots decorated on waste derived biochar for enhanced removal of emerging contaminants: Synergistic effect and mechanistic insight

This study proposes a novel one-pot hydrothermal impregnation strategy for surface decoration of waste derived pisum sativum biochar with zero‒dimensional Cu‒MOF Quantum dots (PBC‒HK), with an average particle size of 5.67 nm, for synergistic removal of an emerging sulfur containing drug pantoprazole (PTZ) and Basic Blue 26 (VB) dye within 80 min and 50 min of visible-light exposure, respectively. The designed Integrated Photocatalytic Adsorbent (IPA) presented an enhanced PTZ removal efficiency of 95.23% with a catalyst loading of 0.24 g/L and initial PTZ conc. 30 mg/L at pH 7, within 80 min via synergistic adsorption and photodegradation under visible-light exposure. While, on the other hand, 96.31% VB removal efficiency was obtained in 50 min with a catalyst dosage of 0.20 g/L, initial VB conc. 60 mg/L at pH 7 under similar irradiation conditions. An in-depth analysis of the synergistic adsorption and photocatalysis mechanism resulting in the shortened time for the removal of contaminants in the synergistic integrated model has been performed by outlining the various advantageous attributes of this strategy. The first-order degradation rate constant for PTZ was found to be 0.04846 min-1 and 0.04370 min-1 for PTZ and VB, respectively. Adsorption of contaminant molecules on the biochar (PS‒BC) surface can facilitate photodegradation by accelerating the kinetics, and photodegradation promotes regeneration of adsorption sites, contributing to an overall reduction in operation time for removal of contaminants. Besides enhancing the adsorption of targeted pollutants, the carbon matrix of IPAs serves as a surface for adsorption of intermediates of degradation, thereby minimizing the risk of secondary pollution. The photogenerated holes present in the VB is responsible for the generation of •OH radicals. While, the photogenerated electrons present in the CB are captured by Cu2+ of the MOF metal center, reducing it to Cu+, which is subsequently oxidized to produce additional •OH species in the aqueous medium. This process leads to effective charge separation of the photogenerated charge carriers and minimizes the probability of charge recombination as evident from photoluminescence (PL) analysis. Meanwhile, PL studies, EPR and radical trapping experiments indicate the predominant role of •OH radicals in the removal mechanism of PTZ and VB. The investigation of the degradation reaction intermediates was confirmed by HR‒LCMS, on the basis of which the plausible degradation pathway was elucidated in detail. Moreover, effects of pH, inorganic salts, other organic compounds and humic acid concentration have been investigated in detail. The environmental impact of the proposed method was comprehensively evaluated by ICP-OES analysis and TOC and COD removal studies. Furthermore, the economic feasibility and the cost-effectiveness of the catalyst was assessed to address the potential for large scale commercialization. Notably, this research not only demonstrates a rational design strategy for the utilization of solid waste into treasure via the fabrication of IPAs based on MOF Quantum dots (QDs) and waste-derived biochar, but also provides a practical solution for real wastewater treatment systems for broader industrial applications.

Reactive Oxygen Species (ROS)-Mediated Antibacterial Oxidative Therapies: Available Methods to Generate ROS and a Novel Option Proposal

The increasing emergence of multidrug-resistant (MDR) pathogens causes difficult-to-treat infections with long-term hospitalizations and a high incidence of death, thus representing a global public health problem. To manage MDR bacteria bugs, new antimicrobial strategies are necessary, and their introduction in practice is a daily challenge for scientists in the field. An extensively studied approach to treating MDR infections consists of inducing high levels of reactive oxygen species (ROS) by several methods. Although further clinical investigations are mandatory on the possible toxic effects of ROS on mammalian cells, clinical evaluations are extremely promising, and their topical use to treat infected wounds and ulcers, also in presence of biofilm, is already clinically approved. Biochar (BC) is a carbonaceous material obtained by pyrolysis of different vegetable and animal biomass feedstocks at 200-1000 °C in the limited presence of O2. Recently, it has been demonstrated that BC's capability of removing organic and inorganic xenobiotics is mainly due to the presence of persistent free radicals (PFRs), which can activate oxygen, H2O2, or persulfate in the presence or absence of transition metals by electron transfer, thus generating ROS, which in turn degrade pollutants by advanced oxidation processes (AOPs). In this context, the antibacterial effects of BC-containing PFRs have been demonstrated by some authors against Escherichia coli and Staphylococcus aureus, thus giving birth to our idea of the possible use of BC-derived PFRs as a novel method capable of inducing ROS generation for antimicrobial oxidative therapy. Here, the general aspects concerning ROS physiological and pathological production and regulation and the mechanism by which they could exert antimicrobial effects have been reviewed. The methods currently adopted to induce ROS production for antimicrobial oxidative therapy have been discussed. Finally, for the first time, BC-related PFRs have been proposed as a new source of ROS for antimicrobial therapy via AOPs.

Construction of flake ball-shaped Bi2WO6 embedded on phenyl functionalized g-C3N4 nanosheet for efficient degradation insight of colorless pollutants and its biological application

A facile solvent-free solid-state method was adapted to synthesize the spherical-shaped Bi2WO6 engraved on phenyl-doped g-C3N4 nanosheet, i.e., Bi2WO6/Ph-gC3N4 (or BPCN) composites with varying weights of Bi2WO6. Several spectral analyses were used to characterize all the synthesized nanomaterials. The synthesized photocatalyst showed good absorption under visible light as confirmed by UV-visible DRS analysis. Morphological analyses like SEM and TEM determine the successful fabrication of binary heterocomposite. Further, the elements available in the fabricated binary nanocomposite were confirmed by XPS. The photocatalyst was used for the aerobic photocatalytic degradation of a few colorless pollutants like bisphenol A (BPA, 30 mg L-1), a microplastic constituent, and tetracycline (TC, 40 mg L-1), an antibiotic derivative to achieve the impressive results. The less intense PL signal obtained for the 20BPCN heterocomposite reveals the remarkable enhancement in e--h+ pair separation and recombination rate. The quenching study, alkaline terephthalic acid photoluminescence test (TA-PL), and NBT phototransformation study explain the formation of reactive species involved in the decomposition process. An oral cancer cell line (A-254) was tested for the anticancer activity analysis of the 20BPCN photocatalyst. Based on the obtained results, a Z-scheme electron transfer mechanism has been proposed for the photodegradation of model compounds.

Biochar-Derived Persistent Free Radicals: A Plethora of Environmental Applications in a Light and Shadows Scenario

Biochar (BC) is a carbonaceous material obtained by pyrolysis at 200-1000 °C in the limited presence of O2 from different vegetable and animal biomass feedstocks. BC has demonstrated great potential, mainly in environmental applications, due to its high sorption ability and persistent free radicals (PFRs) content. These characteristics enable BC to carry out the direct and PFRs-mediated removal/degradation of environmental organic and inorganic contaminants. The types of PFRs that are possibly present in BC depend mainly on the pyrolysis temperature and the kind of pristine biomass. Since they can also cause ecological and human damage, a systematic evaluation of the environmental behavior, risks, or management techniques of BC-derived PFRs is urgent. PFRs generally consist of a mixture of carbon- and oxygen-centered radicals and of oxygenated carbon-centered radicals, depending on the pyrolytic conditions. Here, to promote the more productive and beneficial use of BC and the related PFRs and to stimulate further studies to make them environmentally safer and less hazardous to humans, we have first reviewed the most common methods used to produce BC, its main environmental applications, and the primary mechanisms by which BC remove xenobiotics, as well as the reported mechanisms for PFR formation in BC. Secondly, we have discussed the environmental migration and transformation of PFRs; we have reported the main PFR-mediated application of BC to degrade inorganic and organic pollutants, the potential correlated environmental risks, and the possible strategies to limit them.

Bamboo-Based Biochar: A Still Too Little-Studied Black Gold and Its Current Applications

Biochar (BC), also referred to as "black gold", is a carbon heterogeneous material rich in aromatic systems and minerals, preparable by the thermal decomposition of vegetable and animal biomasses in controlled conditions and with clean technology. Due to its adsorption ability and presence of persistent free radicals (PFRs), BC has demonstrated, among other uses, great potential in the removal of environmental organic and inorganic xenobiotics. Bamboo is an evergreen perennial flowering plant characterized by a short five-year growth period, fast harvesting, and large production in many tropical and subtropical countries worldwide, thus representing an attractive, low-cost, eco-friendly, and renewable bioresource for producing BC. Due to their large surface area and increased porosity, the pyrolyzed derivatives of bamboo, including bamboo biochar (BBC) or activated BBC (ABBC), are considered great bio-adsorbent materials for removing heavy metals, as well as organic and inorganic contaminants from wastewater and soil, thus improving plant growth and production yield. Nowadays, the increasing technological applications of BBC and ABBC also include their employment as energy sources, to catalyze chemical reactions, to develop thermoelectrical devices, as 3D solar vapor-generation devices for water desalination, and as efficient photothermal-conversion devices. Anyway, although it has great potential as an alternative biomass to wood to produce BC, thus paving the way for new bio- and circular economy solutions, the study of bamboo-derived biomasses is still in its infancy. In this context, the main scope of this review was to support an increasing production of BBC and ABBC and to stimulate further studies about their possible applications, thus enlarging the current knowledge about these materials and allowing their more rational, safer, and optimized application. To this end, after having provided background concerning BC, its production methods, and its main applications, we have reviewed and discussed the main studies on BBC and ABBC and their applications reported in recent years.

Recent advances in visible light-activated photocatalysts for degradation of dyes: A comprehensive review

The rapid development in industrialization and urbanization coupled with an ever-increasing world population has caused a tremendous increase in contamination of water resources globally. Synthetic dyes have emerged as a major contributor to environmental pollution due to their release in large quantities into the environment, especially owing to their high demand in textile, cosmetics, clothing, food, paper, rubber, printing, and plastic industries. Photocatalytic treatment technology has gained immense research attention for dye contaminated wastewater treatment due to its environment-friendliness, ability to completely degrade dye molecules using light irradiation, high efficiency, and no generation of secondary waste. Photocatalytic technology is evolving rapidly, and the foremost goal is to synthesize highly efficient photocatalysts with solar energy harvesting abilities. The current review provides a comprehensive overview of the most recent advances in highly efficient visible light-activated photocatalysts for dye degradation, including methods of synthesis, strategies for improving photocatalytic activity, regeneration and their performance in real industrial effluent. The influence of various operational parameters on photocatalytic activity are critically evaluated in this article. Finally, this review briefly discusses the current challenges and prospects of visible-light driven photocatalysts. This review serves as a convenient and comprehensive resource for comparing and studying the fundamentals and recent advancements in visible light photocatalysts and will facilitate further research in this direction.

Robust PVA/GO@MOF membrane with fast photothermal self-cleaning property for oily wastewater purification

The poor mechanical durability and weak fouling resistance of oil/water separation membranes severely restrict their applications in industry. Herein, a robust PVA/GO@MOF membrane with fast photothermal self-cleaning capability was developed through facile chemical crosslinking and suction-filtration strategies. Attributed to the powerful underwater superoleophobicity, the PVA/GO@MOF membrane exhibited extraordinary anti-oil adhesion even for high-viscosity crude oil and continuous crude oil emulsion purification capability with stable flux (1020 L m-2 h-1 bar-1) and exceptional efficiency (> 99.3%) even after 60 min. Most importantly, in comparison to reported photocatalytic self-cleaning oil/water separation membranes, the PVA/GO@MOF membrane can degrade organic contaminants more rapidly with a higher degradation rate (99.9%) in 50 min due to the superior photothermal conversion capacity. The synergistic photothermal and photocatalytic effects significantly enhanced photodegradation efficiency, which created opportunities for in-depth treatment of complex oily wastewater. Besides, the obtained membrane displayed excellent chemical and mechanical durability with underwater oil contact angle (UWOCA) above 150° even in harsh environments, such as corrosive solutions, UV irradiation, ultrasound treatment, abrasion experiment and bending test. Therefore, the developed PVA/GO@MOF membrane with robust durability and fast photocatalytic self-cleaning property is highly expected to purify oily wastewater and degrade organic pollutants.

Research Progress on Inactivation of Bacteriophages by Visible-Light Photocatalytic Composite Materials: A Mini Review

Infectious diseases caused by waterborne viruses have attracted researchers' great attention. To ensure a safe water environment, it is important to advance water treatment and disinfection technology. Photocatalytic technology offers an efficient and practical approach for achieving this goal. This paper reviews the latest studies on visible-light composite catalysts for bacteriophage inactivation, with a main focus on three distinct categories: modified UV materials, direct visible-light materials and carbon-based materials. This review gives an insight into the progress in photocatalytic material development and offers a promising solution for bacteriophage inactivation.

Adsorption characteristics and mechanism of ammonia nitrogen and phosphate from biogas slurry by Ca2+-modified soybean straw biochar

The utilization of biogas slurry is critical for the sustainable development of animal husbandry. Biomass carbon adsorption is a feasible method for the recycling of nutrients from biogas slurry. However, research on the co-adsorption of ammonia nitrogen and phosphate is scarce. Herein, soybean straw was utilized as the raw material to prepare Ca2+-modified biochar (CaSSB), which was investigated for its ammonia nitrogen and phosphate adsorption mechanisms. Compared with natural biochar (SSB), CaSSB possesses a high H/C ratio, larger surface area, high porosity and various functional groups. Ca2+-modified soybean straw biochar exhibited excellent adsorption performance for NH4+-N (103.18 mg/g) and PO43--P (9.75 mg/g) at pH = 6, using an adsorbent dosage of 2 g/L. The experimental adsorption data of ammonia nitrogen by CaSSB corresponded to pseudo-second-order kinetics and the Langmuir isotherm model, suggesting that the adsorption process was homogeneous and that electrostatic attraction might be the primary adsorption mechanism. Meanwhile, the adsorption of phosphate conformed to pseudo-second-order kinetics and the Langmuir-Freundlich model, whose mechanism might be attributed to ligand exchange and chemical precipitation. These results reveal the potential of CaSSBs as a cost-effective, efficient adsorbent for the recovery of ammonium and phosphate from biogas slurry.

Integrating K and P co-doped g-C3N4 with ZnFe2O4 and graphene oxide for S-scheme-based enhanced absorption coupled photocatalytic real wastewater treatment

Recently, there has been a significant increase in the interest of using photocatalysis for environmental clean-up applications. In this research, potassium, and phosphorus co-doped graphitic carbon nitride (KPCN) photocatalyst modified with graphene oxide (GO) and heterostructured with ZnFe₂O₄ was synthesized via the hydrothermal method (KPCN/GO/ZnFe₂O₄). The photoactivity of KPCN/GO/ZnFe₂O₄ photocatalyst was examined for the photocatalytic degradation of target pollutants such as methylene blue (MB) dye, rhodamine B (RhB) dye, and tetracycline (TC) antibiotic. Furthermore, the chemical oxygen demand (COD) removal efficiency for real wastewater was determined to explore the practical application of KPCN/GO/ZnFe₂O₄ photocatalyst. The degradation efficiencies of bare graphitic carbon nitride, KPCN, KPCN/GO, and KPCN/GO/ZnFe₂O₄ photocatalysts for tetracycline antibiotics were 30%, 42%, 57%, and 87% within 60 min, respectively. Moreover, KPCN/GO/ZnFe₂O₄ photocatalyst showed 71% COD removal efficiency within 240 min. The ^•OH and ^•O₂^- were the major reactive species in the photocatalytic process. Results showed that the degradation efficiencies of graphitic carbon nitride were greatly enhanced upon doping and further improved with the addition of GO and ZnFe₂O₄. Doping improved light harvesting, GO enhanced the adsorption ability and heterojunction with ZnFe₂O₄ enhanced the charge separation as well as the reusability of synthesized KPCN/GO/ZnFe₂O₄ photocatalyst.

Efficient and recyclable Nd3+-doped CoFe2O4 for boosted visible light-driven photocatalytic degradation of Rhodamine B dye

Rare earth metal doping spinel ferrites offer excellent electronic, magnetic, and photocatalytic properties, but they have not been well explored for environmental mitigation. Herein, we report the facile fabrication of novel CoNd _x Fe_2-x O₄ (x = 0-0.05) photocatalysts based on Nd³⁺ incorporated into CoFe₂O₄ for the degradation of Rhodamine B under visible light irradiation. The Nd³⁺ dopant considerably increased the specific surface area (35 m² g^-1) and enhanced the degradation performance (94.7%) of CoNd _x Fe_2-x O₄ catalysts. Nd³⁺-doped CoFe₂O₄ played a role in the formation of radicals, including ˙OH, h⁺, and ˙O₂ ^-. With high recyclability and performance, CoNd_0.05Fe_1.95O₄ nanoparticles can be efficient and reusable photocatalysts for degrading organic dyes, including Rhodamine B from wastewaters.

Construction of activated biochar/Bi2WO6 and /Bi2MoO6 composites to enhance adsorption and photocatalysis performance for efficient application in the removal of pollutants and disinfection

To synergistically enhance the adsorption and photocatalytic performance of Bi2WO6 and Bi2MoO6, using activated biochar (ACB) as substrate, ACB-Bi2WO6 and ACB-Bi2MoO6 composites were facilely prepared by hydrothermal synthesis. Their adsorption-photocatalytic degradation effects on rhodamine B (RhB), tetracycline (TC), and norfloxacin (NOR) were comparatively investigated. Additionally, the effects of environmental factors, wastewater treatment tests, and disinfection were systematically studied, and the enhancement mechanisms and reasons for the degradation differences were highlighted. The results showed that ACB-Bi2WO6 and ACB-Bi2MoO6 were confirmed to form intimately contacted heterojunctions by various advanced characterization techniques. The introduction of ACB narrowed the band-gap energy of Bi2WO6 and Bi2MoO6, and improved the visible light absorption range and specific surface area. The optimal loading ratios of ACB-Bi2WO6 and ACB-Bi2MoO6 were 1:1.06 and 1:0.58, respectively. The removal rate of ACB-Bi2WO6 for high concentrations of RhB (200 mg·L-1), TC and NOR (50 mg·L-1) were 89.15%, 87.27%, and 72.17%, respectively, which were higher than those of ACB-Bi2MoO6 and significantly stronger than those of Bi2WO6 and Bi2MoO6. This was attributed to the more effective inhibition of photogenerated carrier recombination, higher absorbance, and uniform morphology via ACB-Bi2WO6. ·OH and holes were dominant active species in photocatalysis, and the possible photogenerated carrier transfer path is type II heterojunction. Furthermore, ACB-Bi2WO6 possessed good reusability, and the removal of RhB and TC from the actual wastewater exceeded 80.63% and 58.54%, respectively. The sterilization rates of ACB-Bi2WO6 reached 99% and 95% for E. coli and S. aureus within 24 h, respectively. Therefore, ACB-Bi2WO6 was more recommended for environmental applications.

Non-metal activated peroxydisulfate by straw biochar for tetracycline hydrochloride oxidative degradation: catalytic activity and mechanism

In this study, stalk biochar (BC) was prepared by a high-temperature pyrolysis process and used as a non-metallic catalyst to activate peroxydisulfate (PDS) to degrade tetracycline hydrochloride (TCH). Various characterization results showed that BC had a hollow tubular structure, irregular folds, and important active sites such as oxygen-containing functional groups. Under the optimal reaction conditions, the degradation rate of TCH reached 98.1% within 120 min. In addition, the degradation performance was satisfactory and similar under acidic and near neutral pH, and higher temperature promoted the degradation of TCH. The SO₄·^-, ·OH, and ¹O₂ generated by PDS activation were reactive oxygen species (ROS), which degraded TCH through free radical/non-radical synergistic pathways. Quenching experiments proved that the generated SO₄·^- and ·OH might be the dominant reactive oxygen species (ROS) during the oxidative reaction. The research results will provide a theoretical basis for the application of PDS activated by non-metallic catalysts in the remediation of tetracycline antibiotics pollution.

Degradation of organic pollutants from water by biochar-assisted advanced oxidation processes: Mechanisms and applications

Biochar has shown large potential in environmental remediation because of its low cost, large specific surface area, porosity, and high conductivity. Biochar-assisted advanced oxidation processes (BC-AOPs) have recently attracted increasing attention to the remediation of organic pollutants from water. However, the effects of biochar properties on catalytic performance need to be further explored. There are still controversial and knowledge gaps in the reaction mechanisms of BC-AOPs, and regeneration methods of biochar catalysts are lacking. Therefore, it is necessary to systematically review the latest research progress of BC-AOPs in the treatment of organic pollutants in water. In this review, first of all, the effects of biochar properties on catalytic activity are summarized. The biochar properties can be optimized by changing the feedstocks, preparation conditions, and modification methods. Secondly, the catalytic active sites and degradation mechanisms are explored in different BC-AOPs. Different influencing factors on the degradation process are analyzed. Then, the applications of BC-AOPs in environmental remediation and regeneration methods of different biochar catalysts are summarized. Finally, the development prospects and challenges of biochar catalysts in environmental remediation are put forward, and some suggestions for future development are proposed.

Development of Sulfur-Doped Graphitic Carbon Nitride for Hydrogen Evolution under Visible-Light Irradiation

Developing eco-friendly strategies to produce green fuel has attracted continuous and extensive attention. In this study, a novel gas-templating method was developed to prepare 2D porous S-doped g-C₃N₄ photocatalyst through simultaneous pyrolysis of urea (main g-C₃N₄ precursor) and ammonium sulfate (sulfur source and structure promoter). Different content of ammonium sulfate was examined to find the optimal synthesis conditions and to investigate the property-governed activity. The physicochemical properties of the obtained photocatalysts were analyzed by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), scanning transmission electron microscopy (STEM), specific surface area (BET) measurement, ultraviolet-visible light diffuse reflectance spectroscopy (UV/vis DRS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy and reversed double-beam photo-acoustic spectroscopy (RDB-PAS). The as-prepared S-doped g-C₃N₄ photocatalysts were applied for photocatalytic H₂ evolution under vis irradiation. The condition-dependent activity was probed to achieve the best photocatalytic performance. It was demonstrated that ammonium sulfate played a crucial role to achieve concurrently 2D morphology, controlled nanostructure, and S-doping of g-C₃N₄ in a one-pot process. The 2D nanoporous S-doped g-C₃N₄ of crumpled lamellar-like structure with large specific surface area (73.8 m² g^-1) and improved electron-hole separation showed a remarkable H₂ generation rate, which was almost one order in magnitude higher than that of pristine g-C₃N₄. It has been found that though all properties are crucial for the overall photocatalytic performance, efficient doping is probably a key factor for high photocatalytic activity. Moreover, the photocatalysts exhibit significant stability during recycling. Accordingly, a significant potential of S-doped g-C₃N₄ has been revealed for practical use under natural solar radiation.

Direct Z-Scheme Heterojunction α-MnO2/BiOI with Oxygen-Rich Vacancies Enhanced Photoelectrocatalytic Degradation of Organic Pollutants under Visible Light

The degradation efficiency of photoelectrocatalytic (PEC) processes for the removal of organic pollutants is highly dependent on the performance of the photoelectroanode catalyst. The design of PEC systems with a direct Z-scheme charge transfer mechanism and visible light excitation is essential to enhance the degradation efficiency of organic compounds. Here, a α-MnO2/BiOI direct Z-scheme heterojunction photocatalyst was successfully synthesized through a convenient and feasible method. It is remarkable that the photoanode exhibited excellent PEC performance under visible light irradiation; a 95% removal rate of tetracycline (TC) pollutants was achieved within 2 h, and it had excellent stability and reusability, which was expected to degrade antibiotics efficiently and environmentally in harsh environments. The presence of oxygen vacancies (OVs) in the α-MnO2/BiOI heterojunction was confirmed by electron spin resonance technique, and the OVs acted as electron traps that contributed substantially to the separation efficiency of photogenerated carriers. ESR characterization showed that the main reactive radicals during TC degradation were –OH and –O2−. By analyzing the intermediates, the possible degradation pathways of TC were further analyzed and a suitable degradation mechanism was proposed. The toxicity changes in the degradation process were explored by evaluating the toxicity of the intermediates. This study provides a new way to enhance the performance of Bi-based semiconductor photocatalysts for the effective degradation of TC in water.

Recent Advances in Carbon-Based Materials for Adsorptive and Photocatalytic Antibiotic Removal

Antibiotics have been a primary environmental concern due to their widespread dispersion, harmful bioaccumulation, and resistance to mineralization. Unfortunately, typical processes in wastewater treatment plants are insufficient for complete antibiotic removal, and their derivatives in effluent can pose a threat to human health and aquatic communities. Adsorption and photocatalysis are proven to be the most commonly used and promising tertiary treatment methods. Carbon-based materials, especially those based on graphene, carbon nanotube, biochar, and hierarchical porous carbon, have attracted much attention in antibiotic removal as green adsorbents and photocatalysts because of their availability, unique pore structures, and superior physicochemical properties. This review provides an overview of the characteristics of the four most commonly used carbonaceous materials and their applications in antibiotic removal via adsorption and photodegradation, and the preparation of carbonaceous materials and remediation properties regarding target contaminants are clarified. Meanwhile, the fundamental adsorption and photodegradation mechanisms and influencing factors are summarized. Finally, existing problems and future research needs are put forward. This work is expected to inspire subsequent research in carbon-based adsorbent and photocatalyst design, particularly for antibiotics removal.

2D/2D Phosphorus-Doped g-C3N4/Bi2WO6 Direct Z-Scheme Heterojunction Photocatalytic System for Tetracycline Hydrochloride (TC-HCl) Degradation

Bi₂WO₆-based heterojunction photocatalyst for antibiotic degradation has been a research hotspot, but its photocatalytic performance needs to be further improved. Therefore, 2D/2D P-doped g-C₃N₄/Bi₂WO₆ direct Z-scheme heterojunction photocatalysts with different composition ratios were prepared through three strategies of phosphorus (P) element doping, morphology regulation, and heterojunction, and the efficiency of its degradation of tetracycline hydrochloride (TC-HCl) under visible light was studied. Their structural, optical, and electronic properties were evaluated, and their photocatalytic efficiency for TC-HCl degradation was explored with a detailed assessment of the active species, degradation pathways, and effects of humic acid, different anions and cations, and water sources. The 30% P-doped g-C₃N₄/Bi₂WO₆ had the best photocatalytic performance for TC-HCl degradation. Its photocatalytic rate was 4.5-, 2.2-, and 1.9-times greater than that of g-C₃N₄, P-doped g-C₃N₄, and Bi₂WO₆, respectively. The improved photocatalytic efficiency was attributed to the synergistic effect of P doping and 2D/2D direct Z-scheme heterojunction construction. The stability and reusability of the 30% P-doped C₃N₄/Bi₂WO₆ were confirmed by cyclic degradation experiments. Radical scavenging experiments and electron spin resonance spectroscopy showed that the main active species were •O₂^- and h⁺. This work provides a new strategy for the preparation of direct Z-scheme heterojunction catalysts with high catalytic performance.

Facile preparation of visible light-sensitive layered g-C3N4 for photocatalytic removal of organic pollutants

The graphite-phase carbon nitride (g-C₃N₄) photocatalytic materials were prepared by one-step calcination method to degrade methylene blue (MB) and potassium butyl xanthate (PBX) under visible light irradiation. The prepared g-C₃N₄ photocatalytic materials were investigated in detail by various characterizations, and the experiments showed that the graphitic phase carbon nitride photocatalytic materials were successfully prepared by the one-step calcination method. The material possesses excellent optical properties and strong visible light absorption, thus achieving photocatalytic degradation of MB and PBX. The catalyst dosage, pH, the initial concentration of pollutants have important effects on photocatalytic activity of MB and PBX. The photocatalytic degradation efficiency was 98.99% for MB and 96.83% for PBX under the optimal conditions (catalyst dosage, initial pollutant concentration and pH value were 500 mg L^-1, 20 mg L^-1 and 7, respevtively). The photocatalytic mechanisms on MB and PBX were elucidated. ·OH was the key specie for MB, while ·O₂^- was the key specie for PBX. This study advances the development of photocatalytic technology for mineral wastewater.