Fabrication of Ag3PO4/polyaniline-activated biochar photocatalyst for efficient triclosan degradation process and toxicity assessment

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.

Biochar-based composites for removing chlorinated organic pollutants: Applications, mechanisms, and perspectives

Chlorinated organic pollutants constitute a significant category of persistent organic pollutants due to their widespread presence in the environment, which is primarily attributed to the expansion of agricultural and industrial activities. These pollutants are characterized by their persistence, potent toxicity, and capability for long-range dispersion, emphasizing the importance of their eradication to mitigate environmental pollution. While conventional methods for removing chlorinated organic pollutants encompass advanced oxidation, catalytic oxidation, and bioremediation, the utilization of biochar has emerged as a prominent green and efficacious method in recent years. Here we review biochar's role in remediating typical chlorinated organics, including polychlorinated biphenyls (PCBs), triclosan (TCS), trichloroethene (TCE), tetrachloroethylene (PCE), organochlorine pesticides (OCPs), and chlorobenzenes (CBs). We focus on the impact of biochar material properties on the adsorption mechanisms of chlorinated organics. This review highlights the use of biochar as a sustainable and eco-friendly method for removing chlorinated organic pollutants, especially when combined with biological or chemical strategies. Biochar facilitates electron transfer efficiency between microorganisms, promoting the growth of dechlorinating bacteria and mitigating the toxicity of chlorinated organics through adsorption. Furthermore, biochar can activate processes such as advanced oxidation or nano zero-valent iron, generating free radicals to decompose chlorinated organic compounds. We observe a broader application of biochar and bioprocesses for treating chlorinated organic pollutants in soil, reducing environmental impacts. Conversely, for water-based pollutants, integrating biochar with chemical methods proved more effective, leading to superior purification results. This review contributes to the theoretical and practical application of biochar for removing environmental chlorinated organic pollutants.

Green in situ synthesis of sandwich-like W-bridged siligraphene (g-SiC@WC@g-SiC) heterostructure from Saccharum Ravennae gum for ultrahigh-rate photodegradation of acetaminophen

Herein, the sandwich-like W-bridged siligraphene (W/g-SiC) as a heterojunction of WC and siligraphene nanosheets have been first accomplished via a simple green synthesis using Saccharum Ravennae gum as a natural Si and W sources and gelatin as a natural C and N sources. In a magnesiothermic process, Si and C atoms bond together and form a graphene-like structure where half of the C atoms are replaced by Si atoms. The presence of W in the natural precursor creates a W-doped siligraphene structure. Tungsten in the form of carbide (WC) creates a heterojunction with g-SiC, which reduces the bandgap. According to the experimental and computational data, the proposed structure of W/g-SiC was predicted by replacing the W atoms with Si atoms and bonding with C atoms in the siligraphene structure. The W-C bond in this structure is elongated and the W atom comes out of the siligraphene sheet and is placed between two siligraphene layers to interact with three carbons from the next layer. Under visible light irradiation, holes are generated on the g-SiC layers and electrons in the WC interlayer, which makes it a highly efficient photocatalyst with ultrafast charge separation and active surface for the removal of Acetaminophen.

Degradation of triclosan by peroxydisulfate/peroxomonosulfate binary oxidants activation under thermal conditions: Efficiency and mechanism

Peroxydisulfate (PDS) and peroxymonosulfate (PMS) could be efficiently activated by heat to generate reactive oxygen species (ROS) for the degradation of organic contaminants. However, defects including the inefficiency treatment and pH dependence of monooxidant process are prominent. In this study, synergy of heat and the PDS-PMS binary oxidant was studied for efficient triclosan (TCS) degradation and apply in rubber wastewater. Under different pH values, the degradation of TCS followed pseudo-first-order kinetics, the reaction rate constant (kobs) value of TCS in heat/PDS/PMS system increased from 1.8 to 4.4 fold and 6.8-49.1 fold when compared to heat/PDS system and heat/PMS system, respectively. Hydroxyl radicals (·OH), sulfate radicals (SO4·-) and singlet oxygen (1O2) were the major ROS for the degradation of TCS in heat/PDS/PMS system. In addition, the steady-state concentrations of ·OH/1O2 and SO4·-/·OH/1O2 increased under acidic conditions and alkaline conditions, respectively. It was concluded that the pH regulated the ROS for degradation of TCS in heat/PDS/PMS system significantly. Based on the analysis of degradation byproducts, it was inferred that the dechlorination, hydroxylation and ether bond breaking reactions occurred during the degradation of TCS. Moreover, the biological toxicity of the ten byproducts was lower than that of TCS was determined. Furthermore, the heat/PDS/PMS system is resistant to the influence of water substrates and can effectively improve the water quality of rubber wastewater. This study provides a novel perspective for efficient degradation of TCS independent of pH in the heat/PDS/PMS system and its application of rubber wastewater.

Recent progress in TiO2-biochar-based photocatalysts for water contaminants treatment: strategies to improve photocatalytic performance

Toxic organic pollutants in wastewater have seriously damaged human health and ecosystems. Photocatalytic degradation is a potential and efficient tactic for wastewater treatment. Among the entire carbon family, biochar has been developed for the adsorption of pollutants due to its large specific surface area, porous skeleton structure, and abundant surface functional groups. Hence, combining adsorption and photocatalytic decomposition, TiO2-biochar photocatalysts have received considerable attention and have been extensively studied. Owing to biochar's adsorption, more active sites and strong interactions between contaminants and photocatalysts can be achieved. The synergistic effect of biochar and TiO2 nanomaterials substantially improves the photocatalytic capacity for pollutant degradation. TiO2-biochar composites have numerous attractive properties and advantages, culminating in infinite applications. This review discusses the characteristics and preparation techniques of biochar, presents in situ and ex situ synthesis approaches of TiO2-biochar nanocomposites, explains the benefits of TiO2-biochar-based compounds for photocatalytic degradation, and emphasizes the strategies for enhancing the photocatalytic efficiency of TiO2-biochar-based photocatalysts. Finally, the main difficulties and future advancements of TiO2-biochar-based photocatalysis are highlighted. The review gives an exhaustive overview of recent progress in TiO2-biochar-based photocatalysts for organic contaminants removal and is expected to encourage the development of robust TiO2-biochar-based photocatalysts for sewage remediation and other environmentally friendly uses.

Synthesis of β-FeOOH/polyaniline heterogeneous catalyst for efficient photo-Fenton degradation of AOII dye

Discharge of the untreated dye-containing wastewaters will induce water source pollution and further harm aquatic organisms. In this study, the akaganéite/polyaniline catalyst (β-FeOOH/PANI, about 1.0 μm) could be successfully composed by polyaniline (PANI, (C₆H₇N)_n, 200-300 nm) and akaganéite (β-FeOOH, FeO(OH)_1-xCl_x, less than 200 nm), according to the identification and characterization results of XRD, Ramon, FTIR, XPS, SEAD, EDS, and FESEM (or HRTEM). Due to PANI providing more photogenerated electrons, the β-FeOOH/PANI composite (compared with β-FeOOH) in photo-Fenton system had the more highly catalytic degradation capacity to Acid Orange II (AOII) under an optimal condition (7.5 mmol/L of H₂O₂ oxidant, 40 mg/L of AOII, 0.2 g/L of catalyst dosage, and pH 4.0). The AOII degradation kinetics could be well fitted by pseudo-first-order model. In photo-Fenton catalytic process of AOII dye, the ∙OH and h⁺ were the main reaction substances. The AOII in solutions could be gradually mineralized into non-toxic inorganic H₂O molecule and CO₂. The β-FeOOH/PANI catalyst also had a good reusable ability of about 91.4% AOII degradation after 4 runs. These results can provide a reference for synthesis of catalyst used in photo-Fenton system and the applications in degradation removal of organic dye from wastewaters.

Molecular Toxicity Mechanism Induced by the Antibacterial Agent Triclosan in Freshwater Euglena gracilis Based on the Transcriptome

Triclosan (TCS), a commonly used antibacterial preservative, has been demonstrated to have high toxicological potential and adversely affects the water bodies. Since algae are one of the most significant primary producers on the planet, understanding the toxicological processes of TCS is critical for determining its risk in aquatic ecosystems and managing the water environment. The physiological and transcriptome changes in Euglena gracilis were studied in this study after 7 days of TCS treatment. A distinct inhibition ratio for the photosynthetic pigment content in E. gracilis was observed from 2.64% to 37.42% at 0.3-1.2 mg/L, with TCS inhibiting photosynthesis and growth of the algae by up to 38.62%. Superoxide dismutase and glutathione reductase significantly changed after exposure to TCS, compared to the control, indicating that the cellular antioxidant defense responses were induced. Based on transcriptomics, the differentially expressed genes were mainly enriched in biological processes involved in metabolism pathways and microbial metabolism in diverse environments. Integrating transcriptomics and biochemical indicators found that changed reactive oxygen species and antioxidant enzyme activities stimulating algal cell damage and the inhibition of metabolic pathways controlled by the down-regulation of differentially expressed genes were the main toxic mechanisms of TCS exposure to E. gracilis. These findings establish the groundwork for future research into the molecular toxicity to microalgae induced by aquatic pollutants, as well as provide fundamental data and recommendations for TCS ecological risk assessment.

Nanomaterials Aspects for Photocatalysis as Potential for the Inactivation of COVID-19 Virus

Coronavirus disease-2019 is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and is the most difficult recent global outbreak. Semiconducting materials can be used as effective photocatalysts in photoactive technology by generating various reactive oxidative species (ROS), including superoxide (•O2−) and hydroxyl (•OH) radicals, either by degradation of proteins, DNA, and RNA or by inhibition of cell development through terminating the cellular membrane. This review emphasizes the capability of photocatalysis as a reliable, economical, and fast-preferred method with high chemical and thermal stability for the deactivation and degradation of SARS-CoV-2. The light-generated holes present in the valence band (VB) have strong oxidizing properties, which result in the oxidation of surface proteins and their inactivation under light illumination. In addition, this review discusses the most recent photocatalytic systems, including metals, metal oxides, carbonaceous nanomaterials, and 2-dimensional advanced structures, for efficient SARS-CoV-2 inactivation using different photocatalytic experimental parameters. Finally, this review article summarizes the limitations of these photocatalytic approaches and provides recommendations for preserving the antiviral properties of photocatalysts, large-scale treatment, green sustainable treatment, and reducing the overall expenditure for applications.

Unraveling the critical role of iron-enriched sludge hydrochar in mediating the Fenton-like oxidation of triclosan

The traditional Fenton system is subject to the low efficiency of the Fe(III)/Fe(II) conversion cycle, with significant attempts made to improve the oxidation efficiency by overcoming this hurdle. In support of this goal, iron-enriched sludge-derived hydrochar was prepared as a high-efficiency catalyst by one-step hydrothermal carbonization and its performance and mechanisms in mediating the oxidation of triclosan were explored in the present study. The hydrochar prepared at 240 °C for 4 h (HC_240-4) had the highest removal of triclosan (97.0%). The removal of triclosan in the HC_240-4/H₂O₂ system was greater than 90% in both acidic and near-neutral environments and remained as high as 83.5% after three cycles, indicating the broad pH applicability and great recycling stability of sludge-derived hydrochar in Fenton-like systems. H₂O₂ was activated by both persistent free radicals (PFRs; 19.7%) and iron (80.3%). The binding of Fe(III) to carboxyl decreased the electron transfer energy from H₂O₂ to Fe(III), making its degradation efficiency 2.6 times greater than that of the conventional Fenton reaction. The study provides a way for iron-enriched sludge utilization and reveals a role for hydrochar in promoting iron cycling and electron transfer in the Fenton reaction.

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.

Highly Enhanced Photocatalytic Performances of Composites Consisting of Silver Phosphate and N-Doped Carbon Nanomesh for Oxytetracycline Degradation

Photocatalytic technology based on silver phosphate (Ag₃PO₄) has excellent potential in removing antibiotic pollutants, but the low separation rate of photogenerated hole-electron pairs restricts the application of the photocatalyst. In this study, it was found that the combination of nitrogen-doped carbon (NDC) with carbon defects and Ag₃PO₄ can significantly enhance the photocatalytic ability of Ag₃PO₄. After it was exposed to visible light for 5 min, the photocatalytic degradation efficiency of oxytetracycline (OTC) by the composite photocatalyst Ag₃PO₄@NDC could reach 100%. In addition, the structure of NDC, Ag₃PO_4, and Ag₃PO₄@NDC was systematically characterized by SEM, TEM, XRD, Raman, and EPR. The XPS results revealed intense interface interaction between Ag₃PO₄ and NDC, and electrons would transfer from Ag₃PO₄ to the NDC surface. A possible mechanism for enhancing the photocatalytic reaction of the Ag₃PO₄@NDC composite catalyst was proposed. This study provides a highly efficient visible light catalytic material, which can be a valuable reference for designing and developing a new highly efficient visible light catalyst.

Novel assembly of BiVO4@N-Biochar nanocomposite for efficient detoxification of triclosan

The wide spread of antibacterial and antifungal agents demands in growing multifunctional materials to completely eliminate these organic contaminants in water. BiVO₄ (Bismuth vanadate) is a superior catalyst under visible light but suffers with high photoelectron-hole pair recombination rate and poor adsorption capacity which limits its efficiency. Addition of N-doped Biochar (N-Biochar) to BiVO₄ with large specific surface area and high conductivity are anticipated to overcome the problem and promote the catalytic performance. Thus, the present study developed a simple hydrothermal method to prepare BiVO₄@N-Biochar catalyst for efficient detoxification of Triclosan (TCS). The morphological analysis results suggested that BiVO₄ particles were evenly distributed on carbon surface amongst the N-Biochar matrix. Within 60 min of visible light irradiation, nearly 94.6% TCS degradation efficiency was attained by BiVO₄@N-Biochar (k = 0.02154 min^-1) while only 56.7% was attained with pure BiVO₄ (k = 0.00637 min^-1). In addition, LC-MS/MS technique was utilized to determine the TCS degradation products generation in the photodegradation process and pathway was proposed. Furthermore, the E. coli (Escherichia coli) colony forming unit assay was used to determine the biotoxicity of the degradation products in which 72.3 ± 2.6% of detoxification efficiency was achieved and suggested a substantial reduction in biotoxicity during the photodegradation.

Influence of nitrate/nitrite on the degradation and transformation of triclosan in the UV based disinfection

This study investigated the influence of nitrate/nitrite on the degradation and transformation pathway of triclosan (TCS) in UV, UV/peracetic acid (PAA) and UV/HClO processes. The results indicated that the function of nitrate/nitrite significantly depended on the UV source and wavelength, especially nitrate. Generally, the presence of nitrate decreased the direct photo-degradation of TCS in the UV based disinfection. In the LED-UV and LED-UV/HClO processes, the presence of nitrate improved the radical oxidation, and transformation pathway of TCS was varied accordingly. However, nitrate more played a role of photo-competitor in the UV/PAA process, and the reactive nitrogen species (RNS) was difficult to participant in the degradation of TCS due to low redox potential. Compared to nitrate, the presence of nitrite decreased the degradation of TCS in three different UV based disinfection processes. Under UV irradiation, nitrite primarily acted as an irradiation competitor and radical scavenger. Thus, the indirect photo-degradation of TCS was reduced. Noticeably, nitrate/nitrite were the improtant precersors of nitrogenous products in the UV base disinfection. Many new nitrogenous products were identified. But RNS preferentially reacted with the intermediates by -NO₂ addition compared to directly reacted with TCS.