Insights on photochemical activities of organic components and minerals in dissolved state biochar in the degradation of atorvastatin in aqueous solution

Dual role of dissolved black carbon in sensitized ofloxacin photooxidation: Mechanism and influential factors

Dissolved black carbon (DBC) is the more photoactive component of dissolved organic matter (DOM) pool, which plays a dual role in the photoconversion of aquatic contaminants, acting as both a photosensitizer and an inhibitor. However, little is known about the more systematic mechanism by which DBC exhibits a dual effect, which is closely related to the structure composition of DBC. In this study, the differences in characteristics of DBC obtained from 300 °C and 500 °C were compared via UV-vis absorption spectrum, Fluorescence excitation emission matrix spectra (3D-EEM), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS), and evaluated the promoting and inhibiting effects of DBC on ofloxacin (OFL) photodegradation. It was found that higher pyrolysis temperature reduced the UV absorbance, molecular weight, aromaticity, and phenolics of DBC while increasing the content of quinone/aromatic ketone and humic substances. Photochemical data showed that 3DBC*, 1O2 and ·OH were all participated in the DBC-mediated OFL photodegradation. Wherein, DBC300 (DBCT, where T = pyrolysis temperature) had strong light screening and dynamic quenching effect, but the formation ability of 3DBC*, 1O2 and ·OH was poor, which significantly retarded the photodegradation of OFL. While DBC500 exhibited a slight promotion effect due to its higher formation ability of reactive species and weak light screening effect. Moreover, DBC500 had higher steady-state concentration and (kOFL,3DBC⁎) than DBC300, which might be due to the higher contents of quinone/aromatic ketone and the lower contents of phenol in DBC500, thus enhancing the reactivity of 3DBC* and OFL. Our research systematically revealed the trade-off mechanism of DBC on the photodegradation of fluoroquinolones, and provided an important theoretical guidance for the photodegradation of fluoroquinolones under the evolution of DBC composition.

Atorvastatin causes developmental and behavioral toxicity in yellowstripe goby (Mugilogobius chulae) embryos/larvae via disrupting lipid metabolism and autophagy processes

Atorvastatin (ATV) is one of the most commonly prescribed lipid-lowering drugs detected frequently in the environment due to its high use and low degradation rate. However, the toxic effects of residual ATV in the aquatic environment on non-target organisms and its toxic mechanisms are still largely unknown. In the present study, embryos of a native estuarine benthic fish, Mugilogobius chulae, were employed to investigate the developmental and behavioral toxic effects of ATV including environmentally relevant concentrations. The aim of this study was to provide a scientific basis for ecological risk assessment of ATV in the aquatic environment by investigating the changes of biological endpoints at multiple levels in M. chulae embryos/larvae. The results showed that ATV had significantly lethal and teratogenic effects on M. chulae embryos/larvae and caused abnormal changes in developmental parameters including hatch rate, body length, heart rate, and spontaneous movement. ATV exposure caused oxidative stress in M. chulae embryos/larvae subsequently inhibited autophagy and activated apoptosis, leading to abnormal developmental processes and behavioral changes in M. chulae embryos/larvae. The disruptions of lipid metabolism, autophagy, and apoptosis in M. chulae embryos/larvae caused by ATV exposure may pose a potential ecological risk at the population level.

New Insights into Aggregation Behaviors of the UV-Irradiated Dissolved Biochars (DBioCs) in Aqueous Environments: Effects of Water Chemistries and Variation in the Hamaker Constant

The aggregation behavior of ubiquitous dissolved black carbon (DBC) largely affects the fate and transport of its own contaminants and the attached contaminants. However, the photoaging processes and resulting effects on its colloidal stability remain yet unknown. Herein, dissolved biochars (DBioCs) were extracted from common wheat straw biochar as a proxy for an anthropogenic DBC. The influences of UV radiation on their aggregation kinetics were systematically investigated under various water chemistries (pH, electrolytes, and protein). The environmental stability of the DBioCs before and after radiation was further verified in two natural water samples. Hamaker constants of pristine and photoaged DBioCs were derived according to Derjaguin-Landau-Verwey-Overbeek (DLVO) prediction, and its attenuation (3.19 ± 0.15 × 10-21 J to 1.55 ± 0.07 × 10-21 J after 7 days of radiation) was described with decay kinetic models. Pearson correlation analysis revealed that the surface properties and aggregation behaviors of DBioCs were significantly correlated with radiation time (p < 0.05), indicating its profound effects. Based on characterization and experimental results, we proposed a three-stage mechanism (contended by photodecarboxylation, photo-oxidation, and mineral exposure) that DBioCs might experience under UV radiation. These findings would provide an important reference for potential phototransformation processes and relevant behavioral changes that DBC may encounter.

A novel nano-cerium oxide functionalized biochar composite for degradation of organic dye: insight of the photocatalysis mechanism

Recently, visible-light-driven photocatalysis attracts much concerns in the remediation of environmental organic pollutants. In this study, the cerium doped biochar was fabricated through the hydrothermal method, and served as an efficient photocatalyst towards rhodamine B degradation under visible light irradiation. Almost 100% of rhodamine B was removed by 2.0 g·L-1 cerium doped biochar after 60 min of visible light irradiation at pH 3, but only about 25.50% and 29.60% of rhodamine B was removed by cerium dioxide and biochar under identical conditions. The degradation process coincided well with the pseudo-first-order kinetic model, and the photodegradation rate constant of cerium doped biochar was 0.0485·min-1, which was respectively 97 and 44 times that of biochar (0.0005·min-1) and cerium dioxide (0.0011·min-1). According to the trapping experiments and electron spin resonance spectroscopy analysis, h+, O2-∙ and ∙OH all participated in the degradation of rhodamine B in the cerium doped biochar photocatalytic systems, and the function of h+ and ∙OH was dominated. Consequently, the biochar could not only be an excellent carrier for supporting cerium dioxide, but also greatly improved its photocatalytic activity. The band gap of cerium doped biochar was narrower than cerium dioxide, which could improve the separation and migration of photogenerated electron-hole pairs under visible-light excitation, thus ultimately enhanced the degradation of rhodamine B. This work provided a deeper understanding of the preparation of biochar-based photocatalyst and its application in the remediation of environmental organic pollution.

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.

Dissolved black carbon incorporating with ferric minerals promoted photo-Fenton-like degradation of triclosan in acidic conditions

Dissolved black carbon (DBC) has been recognized as an important organic matter that influences the photochemical processes of organic pollutants. The excited triplet state (3DBC*) of DBC usually exhibits activity in neutral and basic aqueous conditions, rather than in acidic conditions. In this study, we found the crop (wheat, rice, maize) straw sourced DBC can substantially enhance the photodegradation of triclosan in relatively acidic conditions, and in the presence of ferric minerals (ferrihydrite and lepidocrocite), when exposed to simulated sunlight irradiation. This should be ascribed to the rapid non-reductive dissolution of ferric minerals by DBC, which leads to the generation of abundant hydrogen peroxides (H2O2) and hydroxyl radicals (•OH) through photo Fenton-like reactions. •OH is the dominant reactive species that leads to triclosan degradation in acidic conditions. Otherwise, triclosan itself is resistant to direct photolysis at pH < 5.0. The triplet state (3DBC*) plays a critical role in accelerating the Fe3+/Fe2+ cycling, which further promotes •OH generation. This study provides a new perspective on the role of DBC in surface water or mineral-water interfaces with acidic conditions and adds a more comprehensive understanding about the environmental implications of the DBC-ferric mineral system in sunlit surface water.

Insight into the effect of pyrolysis temperature on photoreactivity of biochar-derived dissolved organic matter: Impacts of aromaticity and carbonyl groups

Practical application of biochar may result in more biochar-derived dissolved organic matter (denoted as BDOM) inevitably release into surface waters by infiltration and surface runoff. The photochemical reaction of BDOM has gained intense attention, which played a key role in the fate of organic contaminants. However, the relationships between specific characteristics of BDOM and its photoreactivity are still uncertain. In this study, the characteristics of BDOM pyrolyzed from rice husk derived biochar at different temperature (from 400 °C to 700 °C) and their effect on the photodegradation of oxytetracycline (OTC) were carefully investigated. The ¹³C NMR and EEM results indicated the dominated component of BDOM was gradually turned from humic acid like substances with low aromaticity to high aromaticity with abundant oxygen-containing functional groups as pyrolytic temperature increases. Experimental results showed that the apparent rate constants (k_obs) of BDOM700 (4.53 × 10^-2 min^-1) for OTC photodegradation was approximately one order of magnitude higher than BDOM400 (4.52 × 10^-3 min^-1), which was closely correlated with their aromaticity (R² = 0.944). It was found that ³BDOM* rather than ¹O₂ played the major role in BDOM mediated photodegradation of OTC (80.13 % vs 14.34 %), and the carbonyl-containing group was identified as the main ³BDOM* precursor by NaBH₄ reduction experiment. This work highlighted both aromaticity and carbonyl group contents were critical indicators for assessing the potential to generate ³BDOM* and corresponding photoreactivity.

Coupling band structure and oxidation-reduction potential to expound photodegradation performance difference of biochar-derived dissolved black carbon for organic pollutants under light irradiation

Herein, the photodegradation performances difference of rice straw biochar-derived dissolved black carbon (DBC) for Tetracycline and Methylene Blue under visible light irradiation have been investigated. Tetracycline is easier degraded (degradation rate: 68%), followed by Methylene Blue (degradation rate: 14%). Singlet oxygen (¹O₂), superoxide radicals (O₂^-), holes (h⁺) and triplet DBC (³DBC*) are all make contribution for Tetracycline degradation by DBC, whereas just singlet oxygen (¹O₂), superoxide radicals (O₂^-) and ³DBC* are involved in the MB degradation by DBC. Singlet oxygen (¹O₂) maybe from the fulvic acid-like structure of DBC, while band structure of DBC can explain why superoxide radicals (O₂^-) and holes (h⁺) can be formed, whereas hydroxyl radicals (OH) cannot be formed. The oxidation-reduction potential results of Tetracycline and Methylene Blue suggests that Tetracycline is easier to be oxidized than Methylene Blue as well as Methylene Blue is easier to be reduced than Tetracycline. Furthermore, experimental and theoretical results support that DBC has good interaction with Tetracycline, but the interaction between DBC and Methylene Blue is very weak. This likely explain why holes (h⁺) is not detected for Methylene Blue degradation by DBC since Methylene Blue has not too much chance to meet holes (h⁺). TC photodegradation intermediates are less toxic than Tetracycline based on QSAR method. Two possible photodegradation path of Tetracycline by DBC are proposed according to HPLC-MS results.

Enhanced phototransformation of atorvastatin by polystyrene microplastics: Critical role of aging

Reactive oxygen species (ROS) generated from light irradiation of microplastics (MPs) can potentially affect the environmental fate of organic contaminants when they coexist in the same environment. This study investigated the effect of polystyrene (PS) MPs with different aging degrees on the phototransformation of atorvastatin (ATV) under simulated sunlight. Results showed that the presence of PS MPs facilitated the phototransformation of ATV, and the degradation rate was linearly correlated with the aging degree (i.e., carbonyl index) of MPs. The enhanced effects mainly depended on the contents of oxygen-containing functional groups of PS MPs, which increased the absorption of light energy and the generation of ROS (e.g., singlet oxygen (¹O₂) and triplet-excited state PS (³PS*)). Quenching experiments indicated that ¹O₂ generated from photosensitization of PS was the major contributor to the increased phototransformation of ATV. Additionally, the role of ³PS* became more important in the photodegradation mediated by higher degree aged MPs because much more ¹O₂ was generated from the ³PS* . PS MPs also increased the types and yields of degradation products, especially for higher degree aged MPs, despite the low effect on leachate toxicity. The findings provide a novel insight into the critical role of MPs in the fate of organic contaminants in aquatic environments.

Photochemistry of biochar during ageing process: Reactive oxygen species generation and benzoic acid degradation

In this study, the photogeneration of OH and ¹O₂ and the degradation mechanism of organic pollutants in biochar suspension under the simulated solar light irradiations were investigated. Biochar derived from rice husk with 550 °C of charring temperature (R550) was selected to degrade benzoic acid. It was found that 10 g/L of R550 could degrade 78.7% of benzoic acid within 360 min at pH 3, and the degradation efficiency was promoted to 95.2% as ultraviolet (UV) presented. By checking the production of p-hydroxybenzoic acid, UV accelerated the production of OH, which was confirmed by the enhanced degradation efficiency of 59.2% caused by the evaluated OH as UV appeared. The furfuryl alcohol loss in the R550 suspension under light irradiations testified to the production of ¹O₂, which contributed to 9.3% of benzoic acid degradation. Oxidization treatment using gradient concentrations of H₂O₂ was employed to enhance the ageing process of biochar. As the ageing processed, the biochar possessed a declined performance towards OH production from O₂ activation and the radical degradation of organic pollutants. As a contrast, the evaluated content of ¹O₂ and enhanced non-radical degradation of organic pollutants was reached as UV presented. The further study indicated that phenolic hydroxyl groups on biochar facilitated the production of OH via the electron transfer, and quinone like structures (C=O) on biochar boosted the generation of ¹O₂ via the energy transfer. Moreover, upon eliminating the BA degradation, persistent free radicals were formed on biochar, which was enhanced owing to the presence of UV.