Implication for adsorption and degradation of dyes by humic acid: Light driven of environmentally persistent free radicals to activate reactive oxygen species

Occurrence of Imipenem in natural water: Effect of dissolved organic matter and metals

The occurrence of trace antibiotic residues in the environment poses a threat by promoting antibiotic resistance and spreading resistant genes. Recent studies show that these residues interact with metals, forming toxic and persistent antibiotic-metal complexes (AMCs). Investigating the photodegradation of these contaminants in environmental waters is essential to understand their fate and ecotoxicological risk assessment in environmental waters. In this sense, the present work delineates the fate of IMP, a carbapenem antibiotic, in the environmental matrix and studies its interactions with humic acid and metals. The study established that the drug was labile and underwent degradation under light and ambient temperatures. Further, analytical studies with dissolved organic matter (DOM), such as humic acids, established an accelerating effect on antibiotic degradation via indirect photochemical pathways. For instance, for a concentration of 100 mg/L IMP mixed with 20 mg/L HA in volumetric ratios of IMP: HA 1:2, 1:1, and 2:1, the final concentrations of IMP after 24 h were 26.11 mg/L (-73.89 %), 34.44 mg/L (-65.56 %), and 44.22 mg/L (55.78 %), respectively. The higher the humic acid, the faster the degradation of IMP, thereby supporting the photochemical generation of reactive oxygen species (OH•) and subsequent oxidative degeneration of the drug. The interactions with metals, specifically copper, accelerated the degradation kinetics of the drug. The promotion effect was owed to the action of the OH• as the oxidizing agent. Based on the degradation products identified by LC-MS/MS, a scheme of the synergistic action of copper-redox coupling and imipenem, resulting in the oxidative degradation of the drug, was proposed. Understanding the photochemical behavior of antibiotics, and their behavior in the presence of DOM and metal is vital for unravelling their fate and complexity in wastewater.

Facile Synthesis of Bamboo Biochar for Efficient Adsorption of Quinolone Antibiotics: Effects and Mechanisms

The harmful effects of quinolone antibiotics on ecology and human health have attracted widespread attention. In this study, bamboo biochar synthesized at different pyrolysis temperatures was used to remove quinolone antibiotics (moxifloxacin (MFX), ciprofloxacin (CIP), and ofloxacin (OFLX) as models). The pyrolysis temperature of 700 °C led to a high pore volume and average pore size of biochar. The biochar produced at 700 °C presented high adsorption properties for MFX, CIP, and OFLX. The maximum adsorption capacities for MFX, CIP, and OFLX were 135.56, 151.31, and 116.40 mg/g, respectively. The adsorption performance could be described by the Langmuir isotherm model and pseudo-second-order kinetic model. Biochar produced from waste bamboo could be applied as low-cost environmental adsorbents for quinolone antibiotics removal.

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.

Coupled effects of Fenton-like systems with different concentrations of H2O2/Biochar on diethyl phthalate removal: Dominant role of environmental persistent free radicals (EPFRs)

To investigate the impact of different H2O2 concentrations on the Fenton-like systems of H2O2/biochar, this study examined the mechanism of the physical structure and environmental persistent free radicals (EPFRs) of biochar during diethyl phthalate (DEP) removal by the Fenton-like system. The peak-splitting method was utilized to differentiate EPFRs types in cotton stalk biochar produced at different temperatures. High-temperature environments promote π-electron delocalization, which facilitates phenyl π free radicals and σ-π oxygen-containing free radicals. By analyzing relationships between the removal rate K1 and removal constant Kobs of DEP with the structural properties of biochar, it was discovered that EPFRs concentrations in biochar had a significant positive correlation with K1 (r = 0.92) and Kobs (r = 0.97). Different H2O2 concentrations added to the biochar removal system resulted in varied DEP removal efficiency. Among them, CS500, CS550, and CS600 exhibited superior DEP removal efficiency when H2O2 concentration was 5 mM.

Role of low-molecular-weight organic compounds on photochemical formation of Mn(III)-ligands in aqueous systems: Implications for BPA removal

Aqueous trivalent manganese [Mn(III)], an important reactive intermediate, is ubiquitous in natural surface water containing humic acid (HA). However, the effect of low-molecular-weight organic acids (LMWOAs) on the formation, stability and reactivity of Mn(III) intermediate is still unknown. In this study, six LMWOAs, including oxalic acid (Oxa), salicylic acid (Sal), catechol (Cat), caffeic acid (Caf), gallic acid (Gal) and ethylene diamine tetraacetic acid (EDTA), were selected to investigate the effects of LMWOAs on the degradation of BPA induced by in situ formed Mn(III)-L in the HA/Mn(II) system under light irradiation. The chromophoric constituents of HA could absorb light radiation and generate superoxide radical to promote the oxidation of Mn(II) to form Mn(III), which was further involved in transformation of BPA. Our results implied that different LMWOAs did significantly impact on Mn(III) production and its degradation of BPA due to their different functional group. EDTA, Oxa and Sal extensively increased the Mn(III) concentration from 50 to 100 μM compared to the system without LMWOAs, following the order of EDTA > Oxa > Sal, and also enhanced the degradation of BPA with the similar patterns. In contrast, Cat, Caf and Gal had an inhibitory effect on the formation of Mn(III), which is likely because they consumed the superoxide radicals generated from irradiated HA, resulting in the inhibition of Mn(II) oxidation and further BPA removal. The product identification and theoretical calculation indicated that a single electron transfer process occurred between Mn(III)-L and BPA, forming BPA radicals and subsequent self-coupling products. Our results demonstrated that the LMWOAs with different structures could alter the cycling process of Mn via complexation and redox reactions, which would provide new implications for the removal of organic pollutants in surface water.

Photochemical demethylation of methylmercury (MeHg) in aquatic systems: A review of MeHg species, mechanisms, and influencing factors

Photodemethylation is the major pathway of methylmercury (MeHg) demethylation in surface water before uptake by the food chain, whose mechanisms and influence factors are still not completely understood. Here, we review the current knowledge on photodemethylation of MeHg and divide MeHg photolysis into three pathways: (1) direct photodemethylation, (2) free radical attack, and (3) intramolecular electron or energy transfer. In aquatic environments, dissolved organic matter is involved into all above pathways, and due to its complex compositions, properties and concentrations, DOM poses multiple functions during the PD of MeHg. DOM-MeHg complex (mainly by sulfur-containing molecules) might weaken the C-Hg bond and enhance PD through both direct and indirect pathways. In special, synergistic effects of both strong binding sites and chromophoric moieties in DOM might lead to intramolecular electron or energy transfer. Moreover, DOM might play a role of radical scavenger; while triplet state DOM, which is generated by chromophoric DOM under light, might become a source of free radicals. Apart from DOMs, transition metals, halides, NO3-, NO2-, and carbonates also act as radical initialaters or scavengers, and significantly pose effects on radical demethylation, which is generally mediated by hydroxyl radicals and singlet oxygen. Environmental factors such as pH, light wavelength, light intensity, dissolved oxygen, salinity, and suspended particles also affect the PD of MeHg. This study assessed previously published works on three major mechanisms, with the goal of providing general estimates for photodemethylation under various environment factors according to know effects, and highlighting the current uncertainties for future research directions.

Insight into n-CaO2/SBC/Fe(II) Fenton-like system for glyphosate degradation: pH change, iron conversion, and mechanism

Glyphosate has significant adverse effects on creature and ecological balance. Therefore, the efficient treatment of glyphosate wastewater is of great significance. In this study, nano calcium peroxide (n-CaO₂) was loaded onto activated sludge biochar (SBC), and then Fe(II) was added to construct a Fenton-like system (n-CaO₂/SBC/Fe(II)). SBC played the role of both a dispersant and catalyst, which greatly improved the removal capability of glyphosate. The removal efficiency of glyphosate in the n-CaO₂/SBC/Fe(II) system was as high as 99.6%. The persistent free radicals (PFRs) on SBC can promote the conversion of Fe(III) to Fe(II) in the reaction system, and Fe(II) can be maintained at about 15 mg L^-1 until the reaction reached equilibrium. Due to the synergistic effect of Fe(II) hydrolysis and SBC catalysis, n-CaO₂/SBC/Fe(II) system can effectively remove glyphosate in a wide initial pH range (4.0-10.0), and the pH of the reaction system can be remained in a suitable environment (4.0-6.0) for Fenton-like reaction. Advanced oxidation and chemical precipitation were the main mechanisms for the removal of glyphosate. Most of glyphosate could be oxidized into H₂PO^-₄ anions by breaking the bonds of C-P and C-N, and the H₂PO^-₄ can be further adsorbed and bounded on the surface of the composites. This system overcomes the shortcomings of pH rising and Fe(III) precipitation in the CaO₂-based oxidation systems, and realizes the efficient and complete degradation for glyphosate.

Effect of aged biochar after microbial fermentation on antibiotics removal: Key roles of microplastics and environmentally persistent free radicals

For the first time, biochar was prepared by changing the polystyrene (PS) content in sludge, and the efficiency of antibiotics removal by biochar was evaluated after fermentation aging. Fermentation aging affects the efficiency of antibiotics removal by reducing the specific surface area and active sites of biochar. The antibiotics removal efficiency of different types of biochar after aging decreased by 5.95%-13.59%. Owing to the biotoxicity of biochar, the relative abundance of most communities decreased during fermentation, whereas Anaerolineae still increased (14.29% to 33.05% or 33.02%). However, controlled experiments confirmed that biochar was much less toxic to Scenedesmus obliquus than to antibiotics, with concentrations of 11.09 × 10⁵ cells/mL and 0.188 × 10⁵ cells/mL, respectively. With the positive effect of environmentally persistent free radicals (EPFRs) considered, increasing the PS content in sludge facilitated the removal of antibiotics by biochar. This study assesses the stability of biochar in removing antibiotics after long-term microbial aging.

Comparison of different S-doped biochar materials to activate peroxymonosulfate for efficient degradation of antibiotics

The goal of this work was to elucidate the ability of biochar materials prepared by different methods to degrade antibiotics by activating peroxymonosulfate (PMS). S atom was doped into biochar using diphenyl disulfide (DD), sodium thiosulfate (ST), and thiourea (TU) as S precursors. The different doped materials were used to activate PMS and tested for the ability to degrade tetracycline hydrochloride, sulfadiazine sodium salt, and levofloxacin hydrochloride. The average degradation efficiencies of DD-doped hydrothermal + pyrocarbon (DD-HPBC), TU-doped hydrothermal + pyrocarbon (TU-HPBC), and ST-doped hydrothermal + pyrocarbon (ST-HPBC) were 83.76%, 86.74%, and 93.60%, respectively, all higher than the degradation efficiency of the undoped material. When sodium thiosulfate-doped pyrocarbon (ST-PBC), hydrochar (ST-HBC), and hydrothermal + pyrocarbon (ST-HPBC) were used to activate PMS, the highest degradation efficiencies were achieved, with average rates of 71.59%, 78.22% and 97.20%, respectively. ST-HPBC exhibited the highest concentration of environmentally persistent free radicals (EPFRs), 9.47 × 10¹⁸ spin/g, among all biochar materials. Given this high concentration of EPFRs, use of ST-HPBC to activate PMS resulted in a very high rate of antibiotic degradation, and the concentration of EPFRs was positively correlated with the degradation efficiency. Increase of specific surface area, the thiophene S (-C-S-C-) ratio, and concentration of EPFRs in S-doped biochars promoted the degradation of antibiotics. For PMS activated by biochar, reactive oxygen species (ROS) degraded antibiotics in the order of sulfate radical (SO₄^•-) > singlet oxygen (¹O₂) > hydroxyl radical (•OH) > superoxide radical (•O₂^-). This work provides new insight into the application of S-doped sludge biochar materials.

Assessing the influence of sewage sludge and derived-biochar in immobilization and transformation of heavy metals in polluted soil: Impact on intracellular free radical formation in maize

As one of the most common ways to get rid of municipal waste, landfill leachate, waste with complicated compositions and high levels of contaminants, has become a significant threat to the world's environment. Here, the impact of sewage sludge (SS) and derived-biochar (SSB) amendments on the immobilization and potential mobility of heavy metals in a contaminated soil-plant system was investigated. The sequential fractionation findings showed that using SS-2%, SSB-2%, and SSBC-1% reduced the potential mobility of heavy metals while increasing the residual fraction in polluted soils. The translocation and bioconcentration factors showed that heavy metals were slightly transferred into shoots from roots and lowered accumulation in roots from contaminated soils. Fourier transform infrared (FTIR) and X-ray photoelectron spectrum (XPS) comprehensive characterization results indicated the significant role of applied amendments for heavy metals transformation from the exchangeable-soluble fractions to the least available form by lowering their mobility to confirm the adsorption-based complexes, which results in the surface adsorption of heavy metals with functional groups. The electron paramagnetic resonance (EPR) results indicated the dominance of reactive oxygen species (ROS) in the intracellular formation of hydroxyl radicals (•OH) in maize plant roots and shoots. ROS (•OH) generation plays a critical influence in the interaction between the physiological processes of plants and heavy metals. Moreover, all the amendments increased maize growth and biomass production. Our study suggests that alone and combined application of SS and SSB have great potential to remediate heavy metals contaminated soil for environmental sustainability.

Adsorption ability evaluation of the poly(methacrylic acid-co-acrylamide)/cloisite 30B nanocomposite hydrogel as a new adsorbent for cationic dye removal

The performance of poly(methacrylic acid-co-acrylamide)/Cloisite 30B nanocomposite (poly(MAA-co-AAm)/Cl30B) hydrogel to adsorb methylene blue (MB) dye from aqueous solutions was investigated and the adsorption efficiency was improved by incorporating Cloisite 30B nanoclays in the adsorbent structure. The hydrogels were analyzed using FTIR, XRD, TGA, and SEM analysis. The effect of adsorbent dose, temperature, initial dye concentration, contact time, and pH on the efficiency of the adsorption process was investigated. Adsorption efficiencies of 98.57 and 97.65% were obtained for poly(MAA-co-AAm)/Cl30B nanocomposite and poly(MAA-co-AAm) hydrogels, respectively. Kinetic study revealed that the adsorption process followed pseudo-first-order kinetic model and α-parameter values of 6.558 and 1.113 mg/g.min were obtained for poly(MAA-co-AAm)/Cl30B nanocomposite and poly(MAA-co-AAm) hydrogels, respectively indicating a higher ability of nanocomposite hydrogel in adsorbing MB-dye. In addition, the results of the intra-particle diffusion model showed that various mechanisms such as intra-particle diffusion and liquid film penetration are important in the adsorption. The Gibbs free energy parameter of adsorption process showed negative values of -256.52 and -84.071 J/mol.K for poly(MAA-co-AAm)/Cl30B nanocomposite and poly(MAA-co-AAm) hydrogels indicating spontaneous nature of the adsorption. The results of enthalpy and entropy showed that the adsorption process was exothermic and random collisions were reduced during the adsorption. The equilibrium data for the adsorption process using poly(MAA-co-AAm)/Cl30B nanocomposite and poly(MAA-co-AAm) hydrogels followed Freundlich and Langmuir isotherm models, respectively. The maximum adsorption capacity values of 32.83 and 21.92 mg/g were obtained for poly(MAA-co-AAm)/Cl30B nanocomposite and poly(MAA-co-AAm) hydrogels, respectively. Higher adsorption capacity of nanocomposite hydrogel was attributed to the presence of Cloisite 30B clay nanoparticles in its structure. In addition, results of R_L, n, and E parameters showed that the adsorption process was performed optimally and physically.

The effect of persistent free radicals in sludge derived biochar on p-chlorophenol removal

Sewage sludge pyrolysis can effectively dispose of sludge and obtain sludge-derived biochar (SDBC) as an adsorbent for pollutant removal. Recently, persistent free radicals (PFRs), which have also been detected in many types of biochar, have attracted considerable attention for organic pollutant degradation. Sludge collected from a sewage treatment plant was pyrolyzed into SDBC, which contained a large amount of PFRs, and the resulting SDBC was then applied for the removal of p-chlorophenol. An SDBC dosage of 5 g L^-1 was applied for treating 5 mg L^-1 of p-chlorophenol; the highest removal efficiency of 90% was achieved at pH 3, and 22% of the initial p-chlorophenol was degraded by the SDBC. Hydroxyl free radicals were observed and contributed to the degradation of p-chlorophenol. The spent SDBC was reused five times after regeneration through the desorption of adsorbed p-chlorophenol. The p-chlorophenol removal efficiency remained constant, but the degradation decreased with increasing reuse cycles, suggesting that the p-chlorophenol degradation efficiency was positively correlated with the intensity of PFRs on SDBC. Further modification of the SDBC sample in HNO₃ or NaOH increased the amount of PFRs, and consequently, the degradation of p-chlorophenol under low oxygen conditions, further confirming the crucial role of PFRs in p-chlorophenol degradation. This study provides insights into the application of SDBC, a promising material, for contaminant abatement.

Effect of pyrolysis temperature on the activated permonosulfate degradation of antibiotics in nitrogen and sulfur-doping biochar: Key role of environmentally persistent free radicals

Because of the increasingly widespread contamination of antibiotics, the preparation of biochar by heteroatom doping to further improve the catalytic degradation efficiency of antibiotics has become a major focus of research. In this study, N-doped (NBC), S-doped (SBC), and NS-doped (NSBC) moso bamboo biochar were obtained at preparation temperatures of 300-700 °C. The concentration of environmentally persistent free radicals (EPFRs) in all biochars peaked when the preparation temperature was 500 °C: 2.45 × 10¹⁹ spins·g^-1 (BC), 9.23 × 10¹⁹ spins·g^-1 (NBC), 6.10 × 10¹⁹ spins·g^-1 (SBC), and 4.36 × 10¹⁹ spins·g^-1 (NSBC). After heteroatom doping, EPFR species were more abundant, and the distribution of three types of EPFRs (oxygen-centered (g > 2.0040), carbon-centered (g < 2.0030), and carbon-centered radicals with oxygen atom free radicals (2.0030 < g < 2.0040) varied with the preparation temperature. In the process of antibiotic degradation, both NBC and SBC increased the degradation rate of antibiotics, whereas NSBC reduced the degradation rate. Compared with the degradation rate of antibiotics of biochar (79.86%), the degradation rate of antibiotics by NBC, SBC, and NSBC via PMS activation was 92.23%, 88.86%, and 70.97% on average in 30 min, respectively. The greatest contributors to the catalytic degradation were SO₄^•-, followed by ¹O₂, •OH, and O₂^•-. EPFRs and ¹O₂ might be the main contributors to the free radical and non-free radical pathways. The enhancement of EPFRs following the N doping or S doping of biochar is the key factor underlying PMS activation. Therefore, changes in the structure of biochar can better activate PMS to produce reactive oxygen species-degrading antibiotics. The mineralization rate of antibiotics by BC, NBC, SBC, and NSBC was 42.12%, 47.06%, 44.99%, and 39.01%, respectively. This means that a small portion of the antibiotics was completely decomposed into CO₂, H₂O, and inorganic substances after degradation. Cyclic experiments showed that heteroatom-doped biochar had higher reusability, and the degradation rate decreased less than 15%.

Visible light promoted the removal of tetrabromobisphenol A from water by humic acid-FeS colloid

Ferrous sulfide (FeS) and humic acid (HA) are typical black substances in black bloom water. Based on the strong reduction ability of FeS and the photosensitivity of HA, the transformation of toxic organic pollutants by the combination of FeS and HA (HA-FeS) is not clear. In order to explore this issue, the stability of HA-FeS was analyzed by measuring the hydrodynamic diameter and zeta potential of HA-FeS, and then the removal mechanism and possible degradation pathway of tetrabromobisphenol A (TBBPA) by HA-FeS under continuous illumination were discussed. The results showed that the hydrodynamic diameter of FeS was reduced and the stability of FeS was improved, and it was easily suspended after FeS combined with the HA in the water. The combination of HA and FeS promoted the removal of TBBPA in water, no matter it was in the presence or absence of light. Besides, compared with the absence of light, the removal efficiency of TBBPA was improved by HA-FeS with continuous light. There were two reasons for the increase in the removal efficiency of TBBPA by HA-FeS. On the one hand, Fe²⁺ and S^2- of HA-FeS had more stable chemical valence and obtained better reducibility under continuous light than that in the dark. On the other hand, light induced the release of active species (O₂^-, ¹O₂, and OH) in the HA-FeS composite colloid and further promoted the degradation of organic pollutants. Therefore, the black substances (FeS) of black blooms may play a beneficial role in the removal of pollutants under sunlight.

Application of dimensional analysis in sorption modeling of the styryl pyridinium cationic dyes on reusable iron based humic acid coated magnetic nanoparticles

Cationic dyes exist in various industrial wastewaters and removal prior to discharge is necessary due to their carcinogenic behavior which poses a serious threat to human health. Iron based humic acid coated magnetic nanoparticles (HA-MNPs) were evaluated for the removal of 2-[4-(dimethylamino) styryl]-1-methylpyridinium iodide (2-ASP) as a model compound for cationic styryl pyridinium dyes from aqueous media. HA-MNPs were prepared by co-precipitation and characterized. The adsorption of 2-ASP, measured by fluorescence, demonstrates HA-MNPs are efficient for the 2-ASP removal with a maximum adsorption capacity of ~8 mg/g. Kinetic behavior and equilibrium studies showed the adsorption process fits with pseudo 2nd order and Langmuir isotherm models. The adsorption is relatively fast with ~70% of the adsorption complete within 30 min. The overall removal increases by increasing solution pH. The observed increase in adsorption can be assigned to an enhanced electrostatic attraction between the positively charged 2-ASP and the increase in the negative charge on the HA-MNPs surface as a function of increasing solution pH. Effective and repetitive regeneration of the HA-MNPs was achieved using NaOH treatment of saturated sorbent. Regeneration of HA-MNPs showed that removal efficiency remains consistently high after five consecutive cycles. Dimensional analysis suggested that initial concentration/sorbent dose ratio should be considered for accurate sorption modeling confirmed by experimental data. Then generalized empirical models for isothermal study and removal efficiency prediction were accurately deduced. This finding will help researchers in sorption studies to design their experiments more efficiently and to develop improved empirical models in removal prediction.

Mechanism of persulfate activation by biochar for the catalytic degradation of antibiotics: Synergistic effects of environmentally persistent free radicals and the defective structure of biochar

The abuse of antibiotics threatens the water environment and human health. Green treatment method is needed to degrade antibiotics such as biochar. Few studies have examined the environmentally persistent free radicals (EPFRs) and defective structure of biochar during the biochar-mediated catalytic degradation of antibiotics. In this study, biochar prepared from poplar and pine sawdust was used to activate peroxymonosulfate (PMS) to generate instant radicals (SO₄^•- and •OH) and degrade tetracycline (TC), chlortetracycline (CTC) and doxycycline (DOX). The preparation temperatures ranged from 300 °C to 900 °C. EPFRs were the main activator of PMS at 300-500 °C, and the defective structure of biochar was the main activator at 800-900 °C. The concentrations of EPFRs ranged from 1.75 × 10¹⁸ spins/g to 6.44 × 10¹⁸ spins/g. According to the electron paramagnetic resonance (EPR) parameter (g-factor), the main types of EPFRs were carbon-centered radicals (g₁ < 2.0030) or carbon-centered radicals with oxygen atoms (2.0030 < g₂ < 2.0040). Optimization of the degradation experiment revealed that the removal rate of antibiotics peaked when the preparation temperature was 500 °C and 900 °C. In the biochar/PMS system, the antibiotics removal rate of 90% was achieved in 40 min with an average apparent rate constant (k_obs) of 0.0588 min^-1. Analysis of the mechanism revealed that the free radical pathway (EPFRs and defective structure) can effectively activate PMS to generate SO₄^•- and •OH. However, control experiments suggested that the non-free radical pathway (singlet oxygen) had little effect on antibiotic degradation. After five cycles, the removal rate of antibiotics by biochar was still greater than 70%, indicating that biochar retains a high degradation ability. These results indicate that optimizing the preparation conditions can effectively expand the application range of the biochar/PMS system and improve the degradation of antibiotic wastewater.

Regulation of biochar mediated catalytic degradation of quinolone antibiotics: Important role of environmentally persistent free radicals

Antibiotic pollution threatens aquatic ecosystems and water supplies, so analysis of ecofriendly remediation approaches like biochars with catalytic degradation abilities is a top priority. In this work, quinolone antibiotics were degraded by activating oxidants to generate transient radicals using the environmentally persistent free radicals (EPFRs) carried by biochar. The physical and chemical characterization confirmed that biochar is suitable for the removal of organic pollutants. By regulating biochar preparation parameters, it was found that EPFR generation peaked at 500 °C. As the temperature increased from 300 °C to 500 °C, the EPFRs changed from oxygen-centered radicals (g > 2.0040) to carbon-centered radicals (g < 2.0030). The catalytic degradation efficiencies of the EPFR activated oxidants from large to small were: peroxydisulfate (PDS), peroxymonosulfate (PMS), H₂O₂ and flowing O₂. The combined actions of SO₄^•- and •OH effectively degraded antibiotics. The results showed that biochar activating persulfate is a promising technique for the degradation of antibiotics.

Chemico-nanotreatment methods for the removal of persistent organic pollutants and xenobiotics in water - A review

While the technologies available today can generate high-quality water from wastewater, the majority of the wastewater treatment plants are not intended to eliminate emerging xenobiotic pollutants, pharmaceutical and personal care items. Most endocrine disrupting compounds (EDCs) and personal care products (PPCPs) are more arctic than most regulated pollutants, and several of them have acid or critical functional groups. Together with the trace occurrence, EDCs and PPCPs create specific challenges for removal and subsequent improvements of wastewater treatment plants. Various technologies have been investigated extensively because they are highly persistent which leads to bioaccumulation. Researchers are increasingly addressing the human health hazards of xenobiotics and their removal. The emphasis of this review was on the promising methods available, especially nanotechnology, for the treatment of xenobiotic compounds that are accidentally released into the setting. In terms of xenobiotic elimination, nanotechnology provides better treatment than chemical treatments and their degradation mechanisms are addressed.

The key role of persistent free radicals on the surface of hydrochar and pyrocarbon in the removal of heavy metal-organic combined pollutants

We show that persistent free radicals (PFRs) on the surface of biochar can produce hydroxyl radicals (•OH) by catalyzing H₂O₂ to facilitate the removal of the combined pollutant BPA-Cr(VI). Microstructure characterization showed that the structures of pyrocarbon and hydrochar were significantly different when prepared at different temperatures. As the preparation temperature and preparation time for biochar increased, the concentration of PFRs first increased and then decreased. When biochar, PFRs, and H₂O₂ were present in the same solution, the single pollutants BPA and Cr(VI) as well as the combined pollutant BPA-Cr(VI) could be removed effectively, with removal rates greater than 90%. However, when PFRs, BPA, H₂O₂, and Cr(VI) were present in the same solution, Cr(VI) competed with H₂O₂ for electrons and promoted the removal of BPA. The results of this study could be applied to sludge recycling and be used to develop approaches to catalytically degrade combined pollutants.

Abiotic reduction of p-chloronitrobenzene by sulfate green rust: influence factors, products and mechanism

The reduction of p-chloronitrobenzene (p-CNB) by sulfate green rust (GR_SO4) was systematically studied. The results revealed that GR_SO4 has a good removal effect on p-CNB. The removal efficiencies of p-CNB by GR_SO4 improved with the increase of the pH value. The removal efficiencies in the presence of ions were better than that of GR_SO4 alone, while natural organic matter (NOM) could adsorb p-CNB, which competed with GR_SO4. The reductions of p-CNB by GR_SO4 under different conditions followed pseudo-first-order reaction kinetics except for the reactions in the presence of NOM. p-CNB was converted into p-chloroaniline (p-CAN), which produced p-nitrosochlorobenzene and p-chlorophenylhydroxylamine as the intermediate products. The results of the X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed GR_SO4 was gradually transformed into goethite. Fe(ii) in the GR_SO4 structure was the main electron donor involved in the reaction.

Sulfate green rust reduces p-chloronitrobenzene through the electron transfer from the structural Fe(ii) and transforms into goethite.