The application of transition metal-modified biochar in sulfate radical based advanced oxidation processes

Nickel adsorbed algae biochar based oxygen reduction reaction catalyst

Lately, the bio electrochemical systems are emerging as an efficient wastewater treatment and energy conversion technology. However, their scaling-up is considerably restrained by slow-rate of cathodic oxygen reduction reaction (ORR) or otherwise by the high cost associated with the available efficient ORR catalysts. In this investigation, a cost-effective and eco-friendly approach for synthesizing Ni based ORR catalyst utilizing biosorption property of microalgae is accomplished. The synthesised Ni adsorbed algal biochar (NAB) served as an efficient cathode catalyst for enhancing ORR in a microbial carbon-capture cell (MCC). On increasing the initial concentration of Ni2+ in the aqueous medium from 100 mgL-1 to 500 mgL-1, the biosorption capacity was found to increase from 3 mgg-1 to 32 mgg-1 of algae cell. The MCC operated with NAB based cathode catalyst loading of 2 mgcm-2 exhibited 3.5 times higher power density (4.69 Wm-3) as compared to the one with commercial activated carbon. A significant organic matter removal (82 %) in the anodic chamber with simultaneous algal biomass productivity in the cathodic chamber was attained by MCC with cathode loaded with 2 mgcm-2 of NAB. Hence, this easily synthesised low-cost catalyst, out of waste stream, proved its ability to improve the performance of MCC.

Peroxysulfur species-mediated enhanced oxidation of micropollutants by ferrate(VI): Peroxymonosulfate versus peroxydisulfate

Many studies have shown that Peroxymonosulfate (PMS) works synergistically with ferrate (Fe(VI)) to remove refractory organic compounds in a few minutes. However, little has been reported on the combined effects of peroxydisulfate (PDS) and Fe(VI). Since PDS is stable and cost effective, it is of practical significance to study the reaction mechanism and conditions of the PDS/Fe(VI) system. The results of the study indicate that the intermediate Fe(II) is formed during the decomposition of Fe(VI), which is then rapidly oxidized. Due to the asymmetry of the PMS molecular structure, PMS can rapidly trap Fe(II) (kPMS/Fe(II)= 3 × 104 M-1∙s-1), whereas PDS cannot (kPDS/Fe(II)= 26 M-1∙s-1). Hydroxylamine hydrochloride (HA) can reduce Fe(VI) and Fe(III) to Fe(II) to excite PDS to produce SO4•-. Acetate helps to detect Fe(II), but does not help PDS to trap Fe(II). Active species such as SO4•-, •OH, 1O2, and Fe(IV), Fe(V) are present in both systems, but in different amounts. In the PMS/Fe(Ⅵ) system, all these active species react with ibuprofen (IBP) and degrade IBP within several minutes. The effects of the initial pH, PMS or Fe(VI) dosage, and different amounts of IBP on the removal rate of IBP were investigated. According to the intermediates detected by the GC-MS, the degradation process of IBP includes hydroxylation, demethylation and single bond breakage. The degradation pathways of IBP were proposed. The degradation of IBP in tap water and Songhua River was also investigated. In actual water treatment, the dosage needs to be increased to achieve the same results. This study provides a basis and theoretical support for the application of PMS/Fe(Ⅵ) and PDS/Fe(VI) system in water treatment.

A novel cobalt-iron bimetallic hydrochar for the degradation of triclosan in the aqueous solution: performance, reusability, and synergistic degradation mechanism

Low activation performance is a critical issue limiting the practical application of low-cost biochar in the advanced oxidation. Given the high potential of transition metals in the persulfate activation process and abundant oxygen-containing groups of hydrochar, hydrochar derived from cobalt (Co)-modified iron (Fe)-enriched sludge was synthesized and its performance and activation mechanism for the degradation of triclosan were investigated. Co modification significantly altered the morphology of hydrochar, and the increased Co-Fe mass ratios transformed hydrochar from granular to rose-shaped lamellar and then to helical sheet structures. Specific surface area, defect degree, and oxygen-containing groups of hydrochar increased with increasing cobalt-iron mass ratios. The highest removal of triclosan was up to 98% in the hydrochar/peroxymonosulfate (PMS) system under a wide range of pHs (3-10) and still remained higher than 90% after four cycles. Both Radical (mainly hydroxyl radical) and nonradical pathways (singlet oxygen and electron transfer) were evidenced to play roles in the triclosan removal. Fe3+ promoted the regeneration of Co2+ and realized the efficient circulation of Co3+/Co2+. A ternary system consisting of electron donor (triclosan)-electron mediator (hydrochar)-electron acceptor (PMS) provided channels for electron transfer. No measurable Co and Fe were released during the reaction, and the toxicity of degradation intermediates was lower than that of triclosan. Beside triclosan, rhodamine B, bisphenol A, sulfamethoxazole, and phenol were also almost degraded completely in this oxidation system. This study provides a promising way for the enhancement of catalytic activity of carbonaceous material.

Recent advances in catalyst design, performance, and challenges of metal-heteroatom-co-doped biochar as peroxymonosulfate activator for environmental remediation

The escalation of global water pollution due to emerging pollutants has gained significant attention. To address this issue, catalytic peroxymonosulfate (PMS) activation technology has emerged as a promising treatment approach for effectively decontaminating a wide range of pollutants. Recently, modified biochar has become an increasingly attractive as PMS activator. Metal-heteroatom-co-doped biochar (MH-BC) has emerged as a promising catalyst that can provide enhanced performance over heteroatom-doped and metal-doped biochar due to the synergism between metal and heteroatom in promoting PMS activation. Therefore, this review aims to discuss the fabrication pathways (i.e., internal vs external doping and pre-vs post-modification) and key parameters (i.e., source of precursors, synthesis methods, and synthesis conditions) affecting the performance of MH-BC as PMS activator. Subsequently, an overview of all the possible PMS activation pathways by MH-BC is provided. Subsequently, Also, the detection, identification, and quantification of several reactive species (such as, •OH, SO4•-, O2•-, 1O2, and high valent oxo species) generated in the catalytic PMS system by MH-BC are also evaluated. Lastly, the underlying challenges associated with poor stability, the lack of understanding regarding the interaction between metal and heteroatom during PMS activation and quantification of radicals in multi-ROS system are also deliberated.

Research Progress on the Degradation of Organic Pollutants in Water by Activated Persulfate Using Biochar-Loaded Nano Zero-Valent Iron

Biochar (BC) is a new type of carbon material with a high specific surface area, porous structure, and good adsorption capacity, which can effectively adsorb and enrich organic pollutants. Meanwhile, nano zero-valent iron (nZVI) has excellent catalytic activity and can rapidly degrade organic pollutants through reduction and oxidation reactions. The combined utilization of BC and nZVI can not only give full play to their advantages in the adsorption and catalytic degradation of organic pollutants, but also help to reduce the agglomeration of nZVI, thus improving its efficiency in water treatment and providing strong technical support for water resources protection and environmental quality improvement. This article provides a detailed introduction to the preparation method and characterization technology, reaction mechanism, influencing factors, and specific applications of BC and nZVI, and elaborates on the research progress of BC-nZVI in activating persulfate (PS) to degrade organic pollutants in water. It has been proven experimentally that BC-nZVI can effectively remove phenols, dyes, pesticides, and other organic pollutants. Meanwhile, in response to the existing problems in current research, this article proposes future research directions and challenges, and summarizes the application prospects and development trends of BC-nZVI in water treatment. In summary, BC-nZVI-activated PS is an efficient technology for degrading organic pollutants in water, providing an effective solution for protecting water resources and improving environmental quality, and has significant application value.

The activation mechanism of peroxymonosulfate and peroxydisulfate by modified hydrochar: Based on the multiple active sites formed by N and Fe

Modified hydrochar (NHC@Fe), with multiple functional groups and transition metal oxide-containing surface, was successfully synthesized by one-step hydrothermal method. The differences in its catalytic activity for peroxymonosulfate (PMS) and peroxydisulfate (PDS) activation were studied in detail. Experimental and DFT studies showed that abundant active sites, namely, transition metals and functional groups on NHC@Fe provided multiple effective pathways for the activation of persulfate (PS). The NHC@Fe/PMS and NHC@Fe/PDS systems could degrade about 80% of tetracycline hydrochloride (TC) in 120 min and were found to be better than those modified by iron or nitrogen alone. This emphasized the advantage of N-Fe co-modification in persulfate activation. Although the Fe2+/Fe3+ cycle accelerated the activation, the activation of PMS mainly relied on Fe3+, whereas that of PDS mainly relied on Fe2+. Moreover, Fe-N, pyrrolic N, pyridine N, C-O, and O-CO groups also played a key role in the activation process, but the dominant action sites were not the same. Multiple free radicals, such as SO4•-, •OH, O2•-, and 1O2 were generated in PMS and PDS activation systems. 1O2 induced non-free radical pathway was mainly involved in the degradation of TC in both activation systems, but the generation pathway of 1O2 was more direct and rapid in the PDS system. This study provides detailed DFT models of the active sites activated by PMS and PDS and discusses the activation pathways of PMS and PDS along with the similarities and differences in ROS reaction mechanisms.

Effect and mechanism of phosphate enhanced sulfite activation with cobalt ion for effective iohexol abatement

Sulfate radical (SO4•-)-based advanced oxidation processes (AOPs) from sulfite activation have recently received attention for abatement of microorganic pollutants in the aquatic environments. Trace-level Co(II) has been demonstrated to be effective for promoting sulfite activation (simplified as the Co(II)/sulfite system) and the corresponding radical formation, yet this process is challenged by the limited valence inter-transformation of Co(II)/Co(III). In order to enhance this valence inter-transformation, a novel Co(II)/HPO42-/sulfite system is developed in this work, because HPO42-, as a typical radical scavenging agent, has the advantage of complexing with Co(II) without quenching effect. In this work, complexation of Co(II) with HPO42- can regulate the electronic structure of Co(II), accelerate electron transfer, and promote valence inter-transformation of Co(II)/Co(III) during the sulfite activation process. The Co(II)/HPO42-/sulfite system exhibits superior iohexol abatement performance under circumneutral conditions. For pH 8.0 and Co(II) dose of 1 μM, the iohexol abatement efficiency is as high as 98%, which is considerably higher than that of the Co(II)/sulfite system (50%). SO4•- is identified as the predominant reactive radical contributing to iohexol abatement. The presence of HPO42- broadens the pH adaptability of the Co(II)/sulfite system for iohexol abatement. In addition, the coexisting Cl- exerts an inhibitory effect on iohexol abatement while the other cations and anions show negligible effect. The Co(II)/HPO42-/sulfite system displays good reusability and adaptability towards various organic pollutants. This study highlights the important role of complexation of Co(II) with HPO42- in sulfite activation and provides a feasible idea for abatement of the microorganic pollutants.

Removal of organic pollutants through hydroxyl radical-based advanced oxidation processes

The use of Advance Oxidation Process (AOPs) has been extensively examined in order to eradicate organic pollutants. This review assesses the efficacy of photolysis, O3 based (O3/UV, O3/H2O2, O3/H2O2/UV, H2O2/UV, Fenton, Fenton-like, hetero-system) and sonochemical and electro-oxidative AOPs in this regard. The main purpose of this review and some suggestions for the advancement of AOPs is to facilitate the elimination of toxic organic pollutants. Initially proposed for the purification of drinking water in 1980, AOPs have since been employed for various wastewater treatments. AOPs technologies are essentially a process intensification through the use of hybrid methods for wastewater treatment, which generate large amounts of hydroxyl (•OH) and sulfate (SO4·-) radicals, the ultimate oxidants for the remediation of organic pollutants. This review covers the use of AOPs and ozone or UV treatment in combination to create a powerful method of wastewater treatment. This novel approach has been demonstrated to be highly effective, with the acceleration of the oxidation process through Fenton reaction and photocatalytic oxidation technologies. It is clear that Advance Oxidation Process are a helpful for the degradation of organic toxic compounds. Additionally, other processes such as •OH and SO4·- radical-based oxidation may also arise during AOPs treatment and contribute to the reduction of target organic pollutants. This review summarizes the current development of AOPs treatment of wastewater organic pollutants.

Insights into Enhanced Peroxydisulfate Activation with B and Fe Co-Doped Biochar from Bark for the Rapid Degradation of Guaiacol

A boron and iron co-doped biochar (B-Fe/biochar) from Masson pine bark was fabricated and used to activate peroxydisulfate (PDS) for the degradation of guaiacol (GL). The roles of the dopants and the contribution of the radical and non-radical oxidations were investigated. The results showed that the doping of boron and iron significantly improved the catalytic activity of the biochar catalyst with a GL removal efficiency of 98.30% within 30 min. The degradation of the GL mainly occurred through the generation of hydroxyl radicals (·OHs) and electron transfer on the biochar surface, and a non-radical degradation pathway dominated by direct electron transfer was proposed. Recycling the B-Fe/biochar showed low metal leaching from the catalyst and satisfactory long-term stability and reusability, providing potential insights into the use of metal and non-metal co-doped biochar catalysts for PDS activation.

Degradation of 2,4-DCP by immobilized laccase on modified biochar carrier

Rape straw was used as the raw material for the biochar in this study, which was then changed using acid, alkali, and magnetic techniques. The laccase was attached using the adsorptions-crosslinking process, and the three modified biochars served as the carriers. The ideal circumstances for laccase immobilization were explored, and both biochar and immobilized laccase's characteristics were examined. The removal of 2,4-dichlorophenol (2,4-DCP) by immobilized laccase from modified biochar and its degradation products were researched. The main conclusions are as follows: the optimal concentration of glutaraldehyde (GLU) was 4%, and the pH was four, and the enzyme dosage was 1.75 mg/mL for the immobilized laccase of acid-modified biochar (SBC@LAC). The optimal concentration of GLU was 5%; the pH was four, and the enzyme dosage was 2 mg/mL for immobilized laccase from alkali-modified biochar (JBC@LAC). The optimal concentration of GLU was 5%; the pH was four, and the enzyme dosage was 1.75 mg/mL for immobilized laccase from magnetically modified biochar (CBC@LAC). SEM images could show the changes in the surface morphology of biochar caused by three modification methods. The BET results demonstrated that acid and magnetic modification increased the specific surface area of biochar, and alkali modification mainly expanded the pore size of biochar. FT-IR and XRD showed that modification and laccase loading had little effect on the structure of biochar. The stability of immobilized laccase was better than that of free laccase in acid-base, heat, and storage. Among the three modified biochar immobilized laccases, JBC@LAC showed the best acid-base stability and thermal stability, and the relative enzyme activity changed the least when pH and temperature conditions changed. The storage stability of SBC@LAC is the best. After 30 days of storage, the relative enzyme activity is still 83%. The removal rates of 2,4-DCP were 57, 99, and 63%, respectively, by SBC@LAC, JBC@LAC, and CBC@LAC. After five reuses, the removal rates of 2,4-DCP by SBC@LAC, JBC@LAC and CBC@LAC were 26, 42, and 27%, respectively. The intermediate products of 2,4-DCP degradation by immobilized laccase were p-phenol, p-benzoquinone and maleic acid.

Efficiency and selectivity of cost-effective Zn-MOF for dye removal, kinetic and thermodynamic approach

Green synthesis of metal-organic frameworks (MOFs) has attracted a lot of attention as a crucial step for practical industrial applications. In this work, green synthesis of zinc(II) metal-organic framework (Zn-MOF) has been carried out at room temperature. The Zn metal (node) was extracted from spent domestic batteries, and the linker was benzene di-carboxylic acid (BDC). The characterization of the as-prepared Zn-MOF was accomplished by PXRD, FT-IR spectroscopy, SEM, TEM, TGA, and nitrogen adsorption at 77 K. All the characterization techniques strongly supported that as-synthesized Zn-MOF using metallic solid waste Zn is similar to that was reported in the literature. The as-prepared Zn-MOF was stable in water for 24 h without any changes in its functional groups and framework. The prepared Zn-MOF was tested for the adsorption of three dyes, two anionic dyes, aniline blue (AB), and orange II (O(II)) as well as methylene blue (MB), an example of cationic dye from aqueous solution. AB has the highest equilibrium adsorbed amount, qe, of value 55.34 mg g-1 at pH = 7 and 25 °C within 40 min. Investigation of the adsorption kinetics indicated that these adsorption processes could be described as a pseudo-second-order kinetic model. Furthermore, the adsorption process of the three dyes was described well by the Freundlich isotherm model. According to the thermodynamic parameters, the adsorption of AB on the prepared Zn-MOF was an endothermic and spontaneous process. In contrast, it was non-spontaneous and exothermic for the uptake of O(II) and MB. This study complements the business case development model of "solid waste to value-added MOFs."

A Perspective on Removal of Cyanotoxins from Water Through Advanced Oxidation Processes

This perspective discusses the challenges associated with the removal of cyanotoxins from raw water sources for drinking water treatment and the emergence of sulfate radical-based advanced oxidation processes (SR-AOPs) as an effective treatment technique. The advantage of SR-AOPs is that they can be activated using a variety of methods, including heat, UV radiation, and transition metal catalysts, allowing for greater flexibility in treatment design and optimization. In addition, the byproducts of SR-AOPs are less harmful than those generated by •OH-AOPs, which reduces the risk of secondary contamination. SR-AOPs generate sulfate radicals (SO4 •-) that are highly selective to certain organic contaminants and have lower reactivity to background water constituents, resulting in higher efficiency and selectivity of the process. The presence of natural organic matter and transition metals in the natural water body increases the degradation efficiency of SR-AOPs for the cyanotoxins. The bromate formation is also suppressed when the water contaminated with cyanotoxins is treated with SR-AOPs.

UV-activated persulfates oxidation of anthraquinone dye: Kinetics and ecotoxicological assessment

Sulfate radical-based advanced oxidation processes (SR-AOPs) are gaining popularity as a feasible alternative for removing recalcitrant pollutants in an aqueous environment. Persulfates, namely peroxydisulfate (PDS) and peroxymonosulfate (PMS) are the most common sulfate radical donors. Persulfates activation by ultraviolet (UV) irradiation is considered feasible due to the high concentration of radicals produced as well as the lack of catalysts leaching. The research focuses on determining the impact of activated PDS and PMS on the degradation of anthraquinone dye, i.e., Acid Blue 129 (AB129). UV-activated PDS and PMS can quickly degrade the AB129 as well as restrict the formation of by-products. This could explain the reduced ecotoxicity levels of the treated water after degradation, using an aquatic plant (Lemna minor) and a crustacean (Daphnia magna). This, on the other hand, can ensure that the sulfate radical-based processes can be an environmentally friendly technology.

Efficient degradation of norfloxacin using a novel biochar-supported CuO/Fe3O4 combined with peroxydisulfate: Insights into enhanced contribution of nonradical pathway

Nonradical persulfate oxidation techniques have evolved as a new contaminated water treatment approach due to its great tolerance to water matrixes. The catalysts of CuO-based composites have received much attention in that aside from SO₄^•-/^•OH radicals, the nonradicals of singlet oxygen (¹O₂) can be also generated during persulfate activation via CuO. However, the issues regarding particles aggregation and metal leaching from the catalysts during the decontamination process remain to be addressed, which could have a remarkable impact on the catalytic degradation of organic pollutants. Accordingly in the present study, a novel biochar-supported bimetallic Fe₃O₄-CuO catalyst (CuFeBC) was facilely developed to activate peroxodisulfate (PDS) for the degradation of norfloxacin (NOR) in aqueous solution. The results showed CuFeBC has a superior stability against metal ions Cu/Fe leaching, and NOR (30 mg L^-1) was degraded at 94.5% within 180 min in the presence of CuFeBC (0.5 g L^-1) and PDS (6 mM) in pH 8.5. The scavenging of reactive oxygen species and electron spin resonance analysis revealed that ¹O₂ dominated the degradation of NOR. Compared with pristine CuO-Fe₃O₄, the interaction between biochar substrate and metal particles could significantly enhance the contribution of the nonradical pathway to NOR degradation from 49.6% to 84.7%. Biochar substrate could efficiently reduce the leaching of metal species from the catalyst, thereby maintaining excellent catalytic activity and lasting reusability of the catalyst. These findings could enlighten new insights into fine-tuning radical/nonradical processes from CuO-based catalysts for the efficient remediation of organic contaminants in polluted water.

Nitrogen doped magnetic porous carbon derived from starch of oatmeal for efficient activation peroxymonosulfate to degradation sulfadiazine

Nitrogen doped magnetic porous carbon catalyst based on starch of oatmeal was obtained by mixing and pyrolysis process, and its catalytic activity of peroxymonosulfate activation for sulfadiazine degradation was evaluated. When ratio of oatmeal/urea/iron was 1: 2: 0.1, CN@Fe-10 had the best catalytic activity to degrade sulfadiazine. Around 97.8 % removal of 20 mg L^-1 sulfadiazine was achieved under incorporating of 0.05 g L^-1 catalyst and 0.20 g L^-1 peroxymonosulfate. Good adaptability, stability and universality of CN@Fe-10 were verified under different conditions. Electron paramagnetic resonance and radical quenching test suggested that surface-bound reactive oxides species and singlet oxygen were the main reactive oxides species in this reaction. Electrochemical analysis indicated that CN@Fe-10 had a good electrical conductivity and electron transferred did occur among CN@Fe-10 surface, peroxymonosulfate and sulfadiazine. X-ray photoelectron spectroscopy suggested that Fe⁰, Fe₃C, pyridine nitrogen and graphite nitrogen were the potential active sites for peroxymonosulfate activation. Therefore, the work provided a practical approach for recycling biomass.

Current approaches, and challenges on identification, remediation and potential risks of emerging plastic contaminants: A review

Plastics are widely employed in modern civilization because of their durability, mold ability, and light weight. In the recent decade, micro/nanoplastics research has steadily increased, highlighting its relevance. However, contaminating micro/nanoplastics in marine environments, terrestrial ecosystems, and biological organisms is considered a severe threat to the environmental system. Geographical distribution, migration patterns, etymologies of formation, and ecological ramifications of absorption are just a few topics covered in the scientific literature on environmental issues. Degradable solutions from material science and chemistry are needed to address the micro/nanoplastics problem, primarily to reduce the production of these pollutants and their potential effects. Removing micro/nanoplastics from their discharge points has been a central and effective way to mitigate the adverse pollution effects. In this review, we begin by discussing the hazardous effect on living beings and the identification-characterization of micro/nanoplastics. Then, we provide a summary of the existing degradation strategies, which include bio-degradation and advanced oxidation processes (AOPs), and a detailed discussion of their degradation mechanisms is also represented. Finally, a persuasive summary of the evaluated work and projections for the future of this topic is provided.

Cobalt-doped molybdenum disulfide for efficient sulfite activation to remove As(III): Preparation, efficacy, and mechanisms

The sulfite(S(IV))-based advanced oxidation process has attracted significant attention in removing As(III) in the water matrix for its low-cost and environmental-friendly. In this study, a cobalt-doped molybdenum disulfide (Co-MoS₂) nanocatalyst was first applied to activate S(IV) for As(III) oxidation. Some parameters including initial pH, S(IV) dosage, catalyst dosage, and dissolved oxygen were investigated. The experiment results show that >Co(II) and >Mo(VI) on the catalyst surface promptly activated S(IV) in the Co-MoS₂/S(IV) system, and the electron transfer between Mo, S, and Co atoms accelerated the activation. SO₄^•- was identified as the main active species for As(III) oxidation. Furthermore, DFT calculations confirmed that Co doping improved the MoS₂ catalytic capacity. This study has proven that the material has broad application prospects through reutilization test and actual water experiments. It also provides a new idea for developing bimetallic catalysts for S(IV) activation.

Carbonized bacterial cellulose/FeMn composite as efficient catalyst toward contaminant degradation: The crucial role of hydrogen reduction

The structure especially the active site manipulation of Fenton-like catalysts was essential for the efficient removal of organic contaminants in the aquatic environment. In this study, the carbonized bacterial cellulose/FeMn oxide composite (CBC@FeMnO_x) were synthetized and modified by hydrogen (H₂) reduction to obtain the carbonized bacterial cellulose/FeMn composite (CBC@FeMn), with emphasis on the processes and mechanisms for atrazine (ATZ) attenuation. The results showed that H₂ reduction did not change the microscopic morphology of the composites but destroy the Fe-O and Mn-O structures. Compared with the CBC@FeMnO_x composite, the H₂ reduction could promote the removal efficiency from 62% to 100% for CBC@FeMn, as well as the enhancement of degradation rate from 0.021 min^-1 to 0.085 min^-1. The quenching experiments and electron paramagnetic resonance (EPR) displayed that the hydroxyl radicals (•OH) was the major contributor for ATZ degradation. The investigation for Fe and Mn species indicated that H₂ reduction could increase the content of Fe(II) and Mn(III) in the catalyst, thus improving the generation of •OH and accelerating the cycle process between Fe(III)/Fe(II). Owing to the excellent reusability and stability, it was indicated that the H₂ reduction can be considered as an efficient way to regulate the chemical valence of the catalyst, thus enhancing the removal efficiency of aquatic contaminants.

Tuning the intrinsic catalytic sites of magnetite to concurrently enhance the reduction of H2O2 and O2: Mechanism analysis and application potential evaluation

Heterogeneous Fenton-like process based on H₂O₂ activation has been widely tested for water purification, but its application still faces some challenges such as the use of high doses of chemicals (including catalysts and H₂O₂). Herein, a facile co-precipitation method was utilized for small-scale production (∼50 g) of oxygen vacancies (OVs)-containing Fe₃O₄ (V_o-Fe₃O₄) for H₂O₂ activation. Experimental and theoretical results collaboratively verified that H₂O₂ adsorbed on the Fe site of Fe₃O₄ tended to lose electrons and generate O₂^•-. While the localized electron from OVs of V_o-Fe₃O₄ could assist in donating electrons to H₂O₂ adsorbed on OVs sites, this allowed more H₂O₂ to be activated to ^•OH, which was 3.5 folds higher than Fe₃O₄/H₂O₂ system. Moreover, the OVs sites promoted dissolved oxygen activation and decreased the quenching of O₂^•- by Fe(III), thus promoting the generation of ¹O₂. Consequently, the fabricated V_o-Fe₃O₄ achieved much higher oxytetracycline (OTC) degradation rate (91.6%) than Fe₃O₄ (35.4%) at a low catalyst (50 mg/L) and H₂O₂ dosage (2 mmol/L). Importantly, further integration of V_o-Fe₃O₄ into fixed-bed Fenton-like reactor could effectively eliminate OTC (>80%) and chemical oxygen demand (COD) (21.3%∼50%) within the running period. This study provides promising strategies for enhancing the H₂O₂ utilization of Fe mineral.

Heterogeneous Fenton water purification catalyzed by iron phosphide (FeP)

Heterogeneous Fenton reaction has a great application potential in water purification, but efficient catalysts are still lacking. Iron phosphide (FeP) has a higher activity than the conventional Fe-based catalysts for Fenton reactions, but its ability as a Fenton catalyst to directly activate H₂O₂ remains unreported. Herein, we demonstrate that the fabricated FeP has a lower electron transfer resistance than the typical conventional Fe-based catalysts, i.e., Fe₂O₃, Fe₃O₄, and FeOOH, and thus could active H₂O₂ to produce hydroxyl radicals more efficiently. In the heterogeneous Fenton reactions for sodium benzoate degradation, the FeP catalyst presents a superior activity with a reaction rate constant more than 20 times those of the other catalysts (i.e., Fe₂O₃, Fe₃O₄, and FeOOH). Moreover, it also exhibits a great catalytic activity in the treatment of real water samples and has a good stability in the cycling tests. Furthermore, the FeP could be loaded onto a centimeter-sized porous carbon support and the prepared macro-sized catalyst exhibits an excellent water treatment performance and can be well recycled. This work reveals a great potential of FeP as a catalyst for heterogeneous Fenton reactions and may inspire further development and practical application of highly efficient catalysts for water purification.

Efficient photo-Fenton reaction for tetracycline and antibiotic resistant bacteria removal using hollow Fe-doped In2O3 nanotubes: From theoretical research to practical application

The low exposure of active sites and the slow electron transfer rate still restrict the wide application of the photo-Fenton system of Fe-based photocatalyst in practical water treatment. Herein, we prepared a hollow Fe-doped In₂O₃ nanotube (h-Fe-In₂O₃) catalyst for activating hydrogen peroxide (H₂O₂) to remove tetracycline (TC) and antibiotic resistant bacteria (ARB). Incorporation of Fe could shorten the band gap and increase the absorption capacity of visible light. Meanwhile, the increase of electron density at the Fermi level promotes the interfacial electron transport. The large specific surface area of the tubular structure exposes more Fe active site and the Fe-O-In site reduces the energy barrier of H₂O₂ activation, resulting in more and faster formation of hydroxyl radicals (•OH). After continuous operation for 600 min, the h-Fe-In₂O₃ reactor still can remove 85% TC and about 3.5 log ARB in secondary effluent, showing good stability and durability for practical wastewater treatment.

Metal-carbon hybrid materials induced persulfate activation: Application, mechanism, and tunable reaction pathways

Proper wastewater treatment has always been the focus of human society, and many researchers have been working to find efficient and stable wastewater treatment technologies. Persulfate-based advanced oxidation processes (PS-AOPs) mainly rely on persulfate activation to form reactive species for pollutants degradation and are considered to be one of the most effective wastewater treatment technologies. Recently, metal-carbon hybrid materials have been diffusely used for PS activation because of their high stability, abundant active sites, and easy applicability. Metal-carbon hybrid materials can successfully overcome the shortcomings of onefold metal catalysts and carbon catalysts by combing the complementary advantages of the two components. This article reviews recent studies about metal-carbon hybrid materials-mediated PS-AOPs for wastewater decontamination. The interactions of metal and carbon materials, as well as the active sites of metal-carbon hybrid materials, are introduced first. Then, the application and mechanism of metal-carbon hybrid materials-mediated PS activation are presented in detail. Lastly, the modulation methods of metal-carbon hybrid materials and their tunable reaction pathways were discussed. The prospect of future development directions and challenges is proposed to facilitate metal-carbon hybrid materials-mediated PS-AOPs to take a step further for practical application.

The Collision between g-C3 N4 and QDs in the Fields of Energy and Environment: Synergistic Effects for Efficient Photocatalysis

Recently, graphitic carbon nitride (g-C₃ N₄ ) has attracted increasing interest due to its visible light absorption, suitable energy band structure, and excellent stability. However, low specific surface area, finite visible light response range (<460 nm), and rapid photogenerated electron-hole (e^- -h⁺ ) pairs recombination of the pristine g-C₃ N₄ limit its practical applications. The small size of quantum dots (QDs) endows the properties of abundant active sites, wide absorption spectrum, and adjustable bandgap, but inevitable aggregation. Studies have confirmed that the integration of g-C₃ N₄ and QDs not only overcomes these limitations of individual component, but also successfully inherits each advantage. Encouraged by these advantages, the synthetic strategies and the fundamental of QDs/g-C₃ N₄ composites are briefly elaborated in this review. Particularly, the synergistic effects of QDs/g-C₃ N₄ composites are analyzed comprehensively, including the enhancement of the photocatalytic performance and the avoidance of aggregation. Then, the photocatalytic applications of QDs/g-C₃ N₄ composites in the fields of environment and energy are described and further combined with DFT calculation to further reveal the reaction mechanisms. Moreover, the stability and reusability of QDs/g-C₃ N₄ composites are analyzed. Finally, the future development of these composites and the solution of existing problems are prospected.

Application of Deep Eutectic Solvents (DES) for the Synthesis of Iron Heterogeneous Catalyst: Application to Sulfamethoxazole Degradation by Advanced Oxidation Processes

The development of novel approaches to the remotion of pharmaceuticals in wastewater is a subject of concern due to their effect on living beings and the environment. Advanced oxidation processes and the use of relevant catalysts are feasible treatment alternatives that require further development. The development of suitable heterogeneous catalysts is a necessity. This work proposes the synthesis of an iron catalyst in a deep eutectic solvent (Fe-DES) composed of choline chloride and citric acid, which was physically and chemically characterized using SEM-EDS and TEM, FTIR, RAMAN, XRD and XPS. The characterisation confirmed the presence of iron in the form of hematite. Fe-DES was shown to be a multipurpose catalyst that can be applied in the removal of sulfamethoxazole as a reagent in the Fenton and electro-Fenton processes and as an activator of peroxymonosulfate (PMS) processes. After testing the catalyst with the aforementioned techniques, the best result was achieved by combining these processes in an electro-PMS, with great efficiency achieved by dual activation of the PMS with the catalyst and electric field, attaining total elimination at natural pH in 90 min. Furthermore, the degradation was confirmed by the detection of short-chain carboxylic acids (oxalic, succinic, and acetic) and reduction in toxicity values. These results confirm the suitability of Fe-DES to degrade high-priority pharmaceutical compounds.

Fe2O3/diatomite materials as efficient photo-Fenton catalysts for ciprofloxacin removal

In this study, we used Fe₂O₃/diatomite material system toward ciprofloxacin (CIP) photo-Fenton removal in water under visible light (vis) excitation. The characterization of Fe₂O₃/diatomite catalysts was determined by X-ray diffraction patterns, Fourier-transform infrared analysis, inductively coupled plasma mass spectrometry, and scanning electron microscopy. The photo-Fenton catalytic activity of the Fe₂O₃/diatomite was appraised by the removal efficiency of the CIP throughout the effect of the H₂O₂ with various parameters such as initial pH, catalyst amount, and H₂O₂ amount. The results indicate that 0.2 gL^-1 Fe₂O₃/diatomite catalysts achieved the highest performance at approximately 90.03% with a 50 μL H₂O₂ concentration. Furthermore, the Fe₂O₃/diatomite catalysts have high stability, with over 80% CIP removed after five cycles. This study is inspired to develop a potential material for photo-Fenton degradation of antibiotics in wastewater.

Carbonyl heterocycle modified mesoporous carbon nitride in photocatalytic peroxydisulfate activation for enhanced ciprofloxacin removal: Performance and mechanism

Polymer carbon nitride is considered to be a promising photocatalyst with broad application prospects in water treatment. However, the defects of pristine polymer carbon nitride (PCN), such as small specific surface area, fast photogenerated electron-hole recombination, and low mass transfer efficiency, limit its photocatalytic activity. In this work, by introducing 2-thiouracil into the precursor, a carbonyl heterocycle-containing mesoporous carbon nitride photocatalyst (TCN) was successfully obtained with significantly enhanced peroxydisulfate (PDS) photocatalytic activity. In this study, the modulation mechanism of carbonyl heterocycle introduction on surface electronic structure and the band structure were fully discussed by means of a combination of experiments and theoretical calculations. The carbonyl and vicinal carbon-modified heterocycles dominated the electrons, while the adjacent heptazine ring dominated the holes. The photogenerated electron-hole pair recombination efficiency and the electron transition energy barrier were greatly reduced. According to the findings of density functional theory (DFT) calculations, the introduction of carbonyl and vicinal C modulated the electronic structure of catalyst, enhanced the adsorption of PDS at the carbonyl ortho N site, which promoted the electronic interaction between TCN and PDS molecules. Experiments showed that the free radical pathway and non-radical pathway coexisted in TCN/PDS/Vis system. The reactive oxygen species were mainly derived from PDS molecules. DFT calculations provided a more comprehensive theoretical basis for the experimental results. This study provided a fresh perspective on the rational design of carbon nitride-based catalysts and the reaction mechanism of persulfate advanced oxidation systems.

In situ preparation of highly graphitized N-doped biochar geopolymer composites for efficient catalytic degradation of tetracycline in water by H2O2

Advanced oxidation processes (AOPs) hold great prospects for the treatment of antibiotic wastewater. N-doped biochar (NB) has received increasing attention as a catalyst for AOPs because of its green nature, abundant biomass resources, and low cost. However, NB catalysts are complicated to prepare and difficult to recover, limiting their practical application. In this study, an N-doped biochar geopolymer composite (NBGC) was synthesized via in situ doping, simultaneous carbonization, and activation (ISCA) of lignin and urea in the porous geopolymer flake, without additional activators. The ISCA process used a low-cost geopolymer flake that not only served as a carrier to immobilize NB and facilitate the recovery, but also applied its inherent strong alkalinity to activate NB. The composite catalyst obtained at 600 °C (NBGC-600) exhibited excellent activity in activating H₂O₂ to degrade tetracycline (∼100%, 50 mg/L). The EPR results indicated that NBGC-600 had a strong ability to activate and decompose H₂O₂ to •OH, which could be attributed to its rich persistent radicals, graphitized N and CO groups, as well as the high degree of graphitization of biochar. The degradation pathway and intermediates of tetracycline in the NBGC-600-H₂O₂ system were also discussed according to the HPLC-MS results. Moreover, NBGC-600 had excellent reusability and showed great potential for continuous treatment of tetracycline in water. This work paves a new way for the synthesis of cost-effective N-doped biochar composite catalysts for AOPs.

New insight into the mechanism of ferric hydroxide-based heterogeneous Fenton-like reaction

The heterogeneous Fenton-like reaction (HeFR) has always been a research focus for environmental applications. However, it has long been difficult to reach a consensus on the reaction mechanism because the process of metal ions dissolution and its role were not well understood. In this paper, we propose the courses of organics-mediated coordination or/and reduction dissolution of ferric hydroxide to initiate the autocatalytic kinetics of phenol degradation and illustrate it through density functional theory (DFT) and experiments. With the increase of hydrogen peroxide concentration, the degradation of phenol changes from autocatalytic kinetics to first-order kinetics. Furthermore, a novel "limit segmentation method" initiated by us indicates that homogeneous reaction plays a decisive role in the phenol degradation process. The dominant roles of the reactive organics in both iron dissolution and the iron cycle and of the homogeneous reaction in the whole degradation process in the ferric hydroxide-based HeFR system are brand-new insights that pave the pathway for future research.

Controllable synthesis of FeMn bimetallic ferrocene-based metal-organic frameworks to boost the catalytic efficiency for removal of organic pollutants

A series of FeMn bimetallic ferrocene-based metal-organic frameworks (FeMn-Fc-MOFs) with various molar ratios of Fe and Mn (1:9, 2:8, 4:6, 6:4) were successfully synthesized using a simple hydrothermal synthesis method and employed as an efficient activator on persulfate (PS) activation for water decontamination. Characterizations demonstrated that Fe and Mn were smoothly introduced into ferrocene-based MOFs and various molar ratios of Fe:Mn had some influence on crystallinity and surface structure of FeMn-Fc-MOFs. Within 120 min, Fe₄Mn₆-Fc-MOFs demonstrated the best catalytic activity among the different molar ratios, and acid orange 7(AO7) degradation rate was up to 92.0%. In addition, electrochemical experiments revealed that Fe₄Mn₆-Fc-MOFs possessed superior electron transfer capability than other FeMn-Fc-MOFs, leading to better catalytic performance. Moreover, quenching tests and electron paramagnetic resonance (EPR) detection indicated that hydroxyl radicals and sulfate radicals were both responsible for AO7 decomposition. Notably, the redox cycle of Fe(II)/Fe(III) and Mn(II)/Mn(IV) was discovered in the Fe₄Mn₆-Fc-MOFs/PS system, which was considered as the limiting process for the cleavage of the O-O bond in PS to generate active radicals. Ultimately, the Fe₄Mn₆-Fc-MOFs exhibits an excellent universality and good cycling stability for 5 continuous runs. This paper broadens the application of ferrocene-based MOFs on heterogeneous PS activation in environmental catalysis.

Stoichiometric excesses of H2O2 as dosimetry strategy: proof of concept for UVC-H2O2, dark-Fenton, and UVC-Fenton

Hydrochlorothiazide (HCT) is a pharmaceutical micropollutant highly toxic to the environment, being absolutely necessary to oxidize it completely to CO₂. Here, the variables stoichiometric H2O2 excess for (a) degradation and (b) mineralization are defined and used as metric to quantify the dosimetry of the H₂O₂. So that, dose of H₂O₂ qualifies being under- and over-dose respectively for values below and above such standards. In this work, these concepts have been elucidated across AOPs regarding the H₂O₂ degradation excess, whereas only UVC-Fenton was used regarding the H₂O₂ mineralization excess. At a H₂O₂ mineralization excess of 0.68 (equivalent to degradation excess of 36.74), oxidation via UVC-H₂O₂ enables absolute (100%) HCT degradation within 60 min; however, the mineralization of HCT demonstrated limited optimization for all AOPs employed in the beaker-like reactor of this work, being the underlying reasons investigated hereby. At best, 26.70% HCT mineralization was observed within 60 min of UVC photo-Fenton using an initial 2.00 H₂O₂ mineralization excess. Such mineralization of 26.7% is unexpectedly low considering that, in addition, the residual H₂O₂ concentration almost fully depletes within 30 min of UVC-Fenton oxidation. Taken all that together, the loss of H₂O₂ due its decomposition induced by the risen temperature from 28 to 70ºC very likely were the underlying reason preventing better mineralization performance. We successfully demonstrated 18% of mean efficiency of radical •OH consumption signals that the overheating is indeed a designer problem with the photo-reactor since a well-refrigerated photo-reactor shows a mean efficiency of 38% for the same H₂O₂ excess.

Antifouling CuO@TiO2 coating on plasma-grafted PAA/PES membrane based on photocatalysis and hydrogen peroxide activation

Because of the small size effect leading to the high bandgap of TiO₂ P25, the photocatalytic membrane using this photocatalyst has low antifouling efficiency. This study prepared CuO@TiO₂ composite photocatalyst with a lower bandgap than TiO₂ P25 and used it as antifouling coatings on the PES membrane with PAA intermediate adhesive layer. PAA was grafted onto the surface of the PES membranes through free radicals generated by the cold plasma treatment of the PES membrane. The composite photocatalysts were characterized by FTIR, SEM-EDS, TEM-EDS, XRD, BET, UV-Vis DRS, XPS, and ESR methods demonstrating high surface area (51.0 m²/g), decreased bandgap, and the formation of active free radicals under UV light irradiation. Under photocatalysis and hydrogen peroxide activation, the degradation of AB260 (acid blue 260) catalyzed by 10%CuO@TiO₂ reached about 92% after 60 min. Besides, the photocatalytic and antifouling activities of CuO@TiO₂/PAA/PES membranes are high and stable over five continuous cycles. The water flux of the modified membrane was not significantly influenced and only decreased about 10% compared to the pristine membrane. In addition, the flux recovery ratios (FRR) of fouled membranes treated by photocatalysis were almost 100%.

A novel, Z-scheme ZnO@AC@FeO photocatalyst, suitable for the intensification of photo-mediated peroxymonosulfate activation: Performance, reactivity and bisphenol A degradation pathways

In this study, the intensification of a UVC-based PMS activation treatment is performed by a novel photocatalyst. Using ZnO nanoparticles coupled with activated carbon (AC), impregnated by ferroferric oxides (FO, magnetite), as an effective Z-scheme photocatalyst (ZACFO), the effective Bisphenol A (BP-A) removal was attained. Several techniques were applied for the characterization of the as-prepared catalyst and proved the successful preparation of ZACFO. The photocatalytic activity of pristine ZnO was significantly improved after its combination with ACFO. It was found that the fabrication of ZACFO heterostructures could inhibit the charge carriers recombination and also accelerate the charge separation of photo-induced e^-/h⁺ pairs. Under this UVC-based photocatalysis-mediated PMS activation system, ZACFO showed an excellent potential as compared to the single constituent catalysts. The complete degradation of 20 mg/L concentration of BP-A was attained in just 20 min with excellent reaction rate constant of 27.3 × 10^-2 min^-1. Besides, over 60% of TOC was eliminated by the integrated ZACFO/PMS/UV system within 60 min of reaction. The minor inhibition by most matrix components, the high recycling capability with minor metals' leaching and the effectiveness in complex matrices, constitute this composite method an efficient and promising process for treating real wastewater samples. Finally, based on the photo-produced reactive intermediates and by-products identified, the Z-scheme photocatalytic mechanism and the plausible pathway of BP-A degradation were proposed comprehensively. The presence and role of radical and non-radical pathways in the decontamination process of BP-A over ZACFO/PMS/UV system was confirmed.