Novel catalytic behavior of defective nanozymes with catalase-mimicking characteristics for the degradation of tetracycline.

Although nanozymes have shown significant potential in wastewater treatment, enhancing their degradation performance remains challenging. Herein, a novel catalytic behavior was revealed for defective nanozymes with catalase-mimicking characteristics that efficiently degraded tetracycline (TC) in wastewater. Hydroxyl groups adsorbed on defect sites facilitated the in-situ formation of vacancies during catalysis, thereby replenishing active sites. Additionally, electron transfer considerably enhanced the catalytic reaction. Consequently, numerous reactive oxygen species (ROS) were generated through these processes and subsequent radical reactions. The defective nanozymes, with their unique catalytic behavior, proved effective for the catalytic degradation of TC. Experimental results demonstrate that •OH, •O2-, 1O2 and e- were the primary contributors to the degradation process. In real wastewater samples, the normalized degradation rate constant for defective nanozymes reached 26.0 min-1 g-1 L, exceeding those of other catalysts. This study reveals the new catalytic behavior of defective nanozymes and provides an effective advanced oxidation process for the degradation of organic pollutants.

The profound review of Fenton process: What's the next step?

Fenton and Fenton-like processes, which could produce highly reactive species to degrade organic contaminants, have been widely used in the field of wastewater treatment. Therein, the chemistry of Fenton process including the nature of active oxidants, the complicated reactions involved, and the behind reason for its strongly pH-dependent performance, is the basis for the application of Fenton and Fenton-like processes in wastewater treatment. Nevertheless, the conflicting views still exist about the mechanism of the Fenton process. For instance, reaching a unanimous consensus on the nature of active oxidants (hydroxyl radical or tetravalent iron) in this process remains challenging. This review comprehensively examined the mechanism of the Fenton process including the debate on the nature of active oxidants, reactions involved in the Fenton process, and the behind reason for the pH-dependent degradation of contaminants in the Fenton process. Then, we summarized several strategies that promote the Fe(II)/Fe(III) cycle, reduce the competitive consumption of active oxidants by side reactions, and replace the Fenton reagent, thus improving the performance of the Fenton process. Furthermore, advances for the future were proposed including the demand for the high-accuracy identification of active oxidants and taking advantages of the characteristic of target contaminants during the degradation of contaminants by the Fenton process.

A review on reactive oxygen species-induced mechanism pathways of pharmaceutical waste degradation: Acetaminophen as a drug waste model.

Innately designed to induce physiological changes, pharmaceuticals are foreknowingly hazardous to the ecosystem. Advanced oxidation processes (AOPs) are recognized as a set of contemporary and highly efficient methods being used as a contrivance for the removal of pharmaceutical residues. Since reactive oxygen species (ROS) are formed in these processes to interact and contribute directly toward the oxidation of target contaminant(s), a profound insight regarding the mechanisms of ROS leading to the degradation of pharmaceuticals is fundamentally significant. The conceptualization of some specific reaction mechanisms allows the design of an effective and safe degradation process that can empirically reduce the environmental impact of the micropollutants. This review mainly deliberates the mechanistic reaction pathways for ROS-mediated degradation of pharmaceuticals often leading to complete mineralization, with a focus on acetaminophen as a drug waste model.

Aromatic Structures Govern the Formation of Chlorinated Byproducts in Dichlorine Radical Reactions.

Radical-induced disinfection byproduct (DBP) formation is drawing attention with increasing applications of advanced oxidation processes (AOPs). Cl2•- represents one of the extensively generated radicals in AOPs, whose behavior in DBP formation remains unknown. In this study, we found that aromatic structures serve as the main DBP precursors in Cl2•- reactions by employing diverse groups of model compounds. At a typical Cl2•- exposure of 1.2 × 10-9 M·s, the sum concentrations of 7 regulated aliphatic DBPs (e.g., trichloromethane, chloroacetic acids) are ∼0.10 to 0.48 µM for aromatic precursors and <0.05 µM for aliphatic ones. The DBP formation mechanisms from Cl2•- reactions involved the formation of chlorinated aromatics, radical-induced oxygen incorporation followed by ring cleavage, and the interactions of Cl2•- with ring-cleavage intermediates. In reacting with DOM, Cl2•- reactions produced much fewer aliphatic DBPs (5% of the total organochlorine vs 40% for chlorination) and chloroacetic acids dominated the aliphatic DBPs (usually trihalomethane for chlorination), which can be well interpreted by the precursors and mechanisms proposed. This work comprehensively reveals the precursors, formation patterns, and mechanisms of DBPs during the less-studied Cl2•- reactions, highlighting the importance of eliminating the aromatic structures of DOM before the AOPs.

Exploring non-thermal plasma technology for microalgae removal.

The global population and economic development surge has substantially increased water demand, resulting in heightened sewage and pollutant generation, posing environmental hazards. Addressing this challenge necessitates the implementation of efficient and cost-effective water reclamation methods. Non-thermal plasma technology (NTP) has emerged as a promising solution, garnering attention for its superior efficiency compared to alternatives. While existing studies have predominantly focused on energy efficiency and pollutant removal, limited research has delved into the biological removal aspect, particularly concerning algae. This study utilized a dielectric barrier plasma diffuser to eliminate Spirulina microalgae (Spirulina platensis) from wastewater solutions, demonstrating higher algae removal and superior mass transfer compared to alternative plasma methods. The effect of sample volume, input voltage and power, flow rate, and initial solution concentration on the algae removal was investigated. Investigation of operational parameters revealed the best condition resulting in a 98 % removal rate and 20 g/kWh energy efficiency. The best conditions for the removal of Spirulina microalgae were considered in a sample volume of 50 mL, a voltage of 7.6 kV, a flow rate of 700 mL/min, and an initial solution concentration of 1280 mg/liter. Scanning Electron Microscope (SEM) images illustrated the impact of active species on cell structure, leading to the destruction of spiral form and loss of reproductive ability. The study underscores the potential of NTP for efficient algae removal and identifies key active species involved in the process. The removal of Spirulina microalgae was attributed to a combination of singlet oxygen (1O2), hydroxyl radicals, and ozone.

Treatment of sludge hydrothermal carbonization wastewater by ferrous/sodium percarbonate system: Effect of wastewater composition and role of coagulation and oxidation.

It is crucial to explore the effect of complex wastewater compositions on the ferrous/sodium percarbonate (Fe(Ⅱ)/SPC) system and the role of oxidation-coagulation in designing water treatment processes. This study employed redundancy analysis to investigate the effects of wastewater constituents on oxidation and coagulation. Raman analysis, X-ray Photoelectron Spectroscopy, and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry were used to determine the roles of oxidation and coagulation in the system. The results showed that sulfates and phosphates formed amorphous complexes with iron species via coprecipitation, thereby promoting coagulation to remove organics. Some heavy metals can also be removed by coagulation. The co-activation of SPC by pre-existing transition metals and the added Fe(Ⅱ) facilitated the oxidative removal of organics, while chloride and arsenic were the main inhibitory inorganic substances in the system. Aromatic compounds mainly promoted coagulation, polysaccharides promoted oxidation, humic acid promoted oxidation and coagulation, and C=C/C=O inhibited the Fe(Ⅱ)/SPC system. The oxidation process removed graphitic structures and unsaturated organic matter in the region of (O/C, H/C) = (0.2-0.4, 0.9-2.0) through free radicals and generated amorphous carbon structures and saturated organic matter in the region of (O/C, H/C) = (0.3-0.7, 1.2-1.9). The coagulation process removed aromatic organics with 2-5 rings and unsaturated organics in the region of (O/C, H/C) = (0.2-0.6, 0.7-1.6) with oxygen-containing organics. The combined effects of coagulation and oxidation enhanced the removal efficiency of organic carbon by approximately 40%. This study facilitates the optimization of hydrothermal carbonization wastewater treatment and advanced oxidation processes.

Confronting the Mysteries of Oxidative Reactive Species in Advanced Oxidation Processes: An Elephant in the Room.

Advanced oxidation processes (AOPs) are rapidly evolving but still lack well-established protocols for reliably identifying oxidative reactive species (ORSs). This Perspective presents both the radical and nonradical ORSs that have been identified or proposed, along with the extensive controversies surrounding oxidative mechanisms. Conventional identification tools, such as quenchers, probes, and spin trappers, might be inadequate for the analytical demands of systems in which multiple ORSs coexist, often yielding misleading results. Therefore, the challenges of identifying these complex, short-lived, and transient ORSs must be fully acknowledged. Refining analytical methods for ORSs is necessary, supported by rigorous experiments and innovative paradigms, particularly through kinetic analysis based on in situ spectroscopic techniques and multiple-probe strategies. To demystify these complex ORSs, future efforts should be made to develop advanced tools and strategies to enhance the mechanism understanding. In addition, integrating real-world conditions into experimental designs will establish a reliable framework in fundamental studies, providing more accurate insights and effectively guiding the design of AOPs.

Environmental impact and source-controlled approaches for emerging micropollutants: Current status and future prospects.

Emerging micropollutants, originating from diverse sources, including pharmaceutical, pesticides, and industrial effluents, are a serious environmental concern. Their presence in natural water bodies has negative effects on ecosystems and human health. To address this issue, the importance of a source-controlled approach has grown, highlighting the use of advanced technologies such as oxidation processes, membrane filtration, and adsorption to prevent micropollutants from entering the environment. Therefore, this review provides a comprehensive overview of emerging micropollutants, their analytical detection methods, and their environmental impacts, with a focus on aquatic ecosystems, human health, and terrestrial environments. It also highlights the importance of using a source-controlled approach and provides insights into the benefits and drawbacks of this strategy. The primary micropollutants identified in this review were erythromycin, ibuprofen, and triclocarban, originating from the pharmaceutical industries for their use as antibiotics, analgesic, and antibacterial drugs. The primary analytical methods used for detection involved hybrid techniques that integrate chromatography with spectroscopy. Thus, this review emphasizes the source-controlled approach's benefits and drawbacks, focusing on emerging micropollutants, their detection, and impacts on ecosystems and health.

Online control of UV and UV/H2O2 processes targeted for the removal of contaminants of emerging concern (CEC) by a fluorescence sensor.

This study assessed the online and real-time monitoring of contaminants of emerging concern (CEC) using a microbial/tryptophan-like fluorescence sensor in a quaternary AOP (advanced oxidation process) pilot plant installed downstream of a tertiary municipal wastewater treatment plant (WWTP). Real-time fluorescence measurements were validated with lab-scale tryptophan-like fluorescence. Changes in water quality induced by different UV or UV/H2O2 doses were detected by the fluorescence sensor allowing real-time control of processes. The removal of CEC was discussed considering their photo-susceptibility and reactivity with •OH and then classified into three groups based on their reactivity and removal efficiency (RE). Linear models of CEC removal developed using real-time fluorescence removal as a surrogate parameter resulted very accurate (overall R2≥0.90) for most of CEC. Furthermore, real-time fluorescence data were successfully used to predict i) pseudo-observed first-order degradation rate constants of CEC (R2=0.99), and ii) UV doses during both UV and UV/H2O2 processes (R2>0.90). The findings of this study demonstrated that fluorescence sensors can be employed in operational relevant environment to monitor a broad range of CEC and control UV doses during UV-AOPs. Therefore, the implementation of fluorescence sensors is expected for optimizing costs, energy consumption and efficiency of quaternary wastewater treatments.

Assessing excimer far-UVC (222 nm) irradiation for advanced oxidation processes: Oxidants photochemistry and micropollutants degradation.

The KrCl* excimer lamp (UV222) is a promising alternative of low-pressure mercury lamp (UV254) for UV-based advanced oxidation processes (UV-AOPs), because it is mercury-free and has high photon energy. But there lacks a comprehensive assessment of UV222-AOPs based on different radicals. Herein, the properties (e.g., oxidant decay and innate radical quantum yield), and micropollutant degradation, were comprehensively studied for representative oxidants (i.e., hydrogen peroxide, persulfate (PDS), monochloramine, and free active chlorine (FAC)) under UV222 irradiation. UV222 outperformed UV254 for the activation of oxidants with 2.6-14.4 times fluence-based kinetic constant (kF). The main reason of enhanced activation varied with oxidants: higher UV absorbance for H2O2, higher innate quantum yield for monochloramine and FAC, and both reasons for PDS. Overall, PDS was the optimum oxidant under UV222 for the degradation of 8 representative micropollutants because of effective promotion of radical formation, as confirmed by radical competitive kinetics and modeling simulations. In real water, UV222/PDS still show advantages than UV254/PDS in terms of micropollutant elimination efficacy (3.2-5.3 times) and energy consumption (33.9 %-57.6 % lower) though it was more inhibited by water constituents via competing for UV222 photons. This study fills gaps in photochemistry knowledge and will facilitate engineering practice of UV222-AOPs.

Enhanced mineralization of pharmaceutical residues at circumneutral pH by heterogeneous electro-Fenton-like process with Cu/C catalyst.

Conventional electro-Fenton (EF) process at acidic pH ∼3 is recognized as a highly effective strategy to degrade organic pollutants; however, homogeneous metal catalysts cannot be employed in more alkaline media. To overcome this limitation, pyrolytic derivatives from metal-organic frameworks (MOFs) have emerged as promising heterogeneous catalysts. Cu-based MOFs were prepared using trimesic acid as the organic ligand and different pyrolysis conditions, yielding a set of nano-Cu/C catalysts that were analyzed by conventional methods. Among them, XPS revealed the surface of the Cu/C-A2-Ar/H2 catalyst was slightly oxidized to Cu(I) and, combined with XRD and HRTEM data, it can be concluded that the catalyst presents a core-shell structure where metallic copper is embedded in a carbon layer. The antihistamine diphenhydramine (DPH), spiked into either synthetic Na2SO4 solutions or actual urban wastewater, was treated in an undivided electrolytic cell equipped with a DSA-Cl2 anode and a commercial air-diffusion cathode able to electrogenerate H2O2. Using Cu/C as suspended catalyst, DPH was completely degraded in both media at pH 6-8, outperforming the EF process with Fe2+ catalyst at pH 3 in terms of degradation rate and mineralization degree thanks to the absence of refractory Fe(III)-carboxylate complexes that typically decelerate the TOC abatement. From the by-products detected by GC/MS, a reaction sequence for DPH mineralization is proposed.

Remediation of benzo[α]pyrene contaminated soil using iron naturally bearing in tropical soil: A new frontier in catalyst-free in soil remediation.

Nature iron is considered one of the promising catalysts in advanced oxidation processes (AOPs) that are utilized for soil remediation from polycyclic aromatic hydrocarbons (PAHs). However, the existence of anions, cations, and organic matter in soils considered impurities that restricted the utilization of iron that was harnessed naturally in the soil matrix and reduced the catalytic performance. In this regard, tropical soil naturally containing iron and relatively poor with impurities was artificially contaminated with 100 mg/50 g benzo[α]pyrene (B[α]P) and remediated using a slurry phase reactor supported with persulfate (PS). The results indicated that tropical soil containing iron and relatively poor with impurities capable of activating the oxidants and formation of radicals which successfully degraded B[α]P. The optimum removal result was 86% and obtained under the following conditions airflow = 260 mL/min, temperature 55 °C, pH 7, and [PS]0 = 1.0 g/L, at the same experimental conditions soil organic matter (SOM) mineralization was 48%. After the remediation process, there was a significant reduction in iron and aluminum contents, which considered the drawbacks of this system. Experiments to scavenge reactive species highlighted O2•- and SO4•- as the main radicals that oxidized B[α]P. Additionally, monitoring of by-products post-remediation aimed to assess toxicity and elucidate degradation pathways. Mutagenicity tests yielded positive results for two B[α]P by-products. The toxicity tests considered were the lethal concentration of 50% (LC50 96 h) for fat-head minnows revealed that all B[α]P by-products were less toxic than the parent pollutant itself. This research marks a significant advancement in soil remediation by advancing the use of the AOP method, removing the requirement for additional catalysts in the AOP system for the removal of B[α]P from soil.

Sonocatalytic degradation of tetracycline hydrochloride using SnO2 hollow-nanofiber decorated with UiO-66-NH2.

In this study, a porous hollow nanofiber SnO2 was decorated with UiO-66-NH2 nanoparticles with straightforward solvothermal method and utilized for sonocatalytic degradation of tetracycline (TC) by ultrasonic irradiation (USI). The prepared materials were characterized using different techniques such as SEM, EDS, FTIR, XRD, BET, XPS, UV-DRS, EIS, and zeta potential. SnO2 PHNF/UiO-66-NH2 nanocomposite offered the highest apparent rate constant of 0.0397 min-1 which was 6.3 and 3.1 times higher than those obtained for SnO2 PHNF and UiO-66-NH2, respectively. The integration of nanocomposite components revealed the synergy factor of 1.58, which can be due to the created heterojunctions resulted in efficiently charge carriers separation and retaining high redox ability. The effects of different affecting parameters such as TC initial concentration, pH of the solution, catalyst dosage, trapping agents, and coexisting anions on the catalytic performance were examined. The inhibitory effects of anions were confirmed to be decreased in the sequence of Cl- > NO3- > SO42-, while the sonocatalytic efficiency of the nanocomposite improved considerably in the presence of humic acid and bicarbonate. Also, the excellent performance of the catalyst was preserved during six successive cycles, suggesting the high stability of the prepared catalyst. In addition, based on the scavenger analysis, the created O2·-, OH·, and holes were contributed to the TC degradation. In conclusion, the creation heterojunction is an impressive methodology for improving the sonocatalytic activity of a catalyst, and SnO2 PHNF/UiO-66-NH2 nanocomposite was introduced as a satisfactory catalyst in sonocatalytic degradation of organic contaminants.

Combination of oxidative and reductive effects of phenolic compounds on the degradation of aniline disinfection by-products by free radicals.

In this study, we selected 13 phenolic compounds containing -COOH, -CHO, -OH, and -COCH3 functional groups as model compounds for dissolved organic matter (DOM), and explored the redox reactions during the co-degradation of phenolic compounds with aniline disinfection by-products (DBPs) at the molecular level. When phenolic compounds and aniline DBPs were degraded, phenoxy radicals and aniline radicals were the most important intermediates. Phenoxy radicals can degrade aniline DBPs via hydrogen atom abstraction (HAA) reactions, and the reaction rates were related to the reduction potentials of the compounds. Compounds containing electron-withdrawing groups were more likely to oxidize aniline DBPs. Aniline DBPs were more easily degraded by phenoxy radicals when they contained electron-donating groups, and the increase in the number of chlorine atoms inhibited the reaction rates of aniline DBPs degradation by phenoxy radicals. Although phenolic compounds can reduce aniline DBPs, there was no significant correlation between the reaction rates and the reduction potentials of the compounds. Considering the redox effects of phenolic compounds on aniline DBPs, co-degradation simulations showed that phenolics inhibited the degradation efficiency of aniline DBPs. This work provided new insights into the transformation mechanisms and degradation efficiencies of DOM and aniline DBPs when they were co-degraded.

Advances of carbon-based materials for activating peracetic acid in advanced oxidation processes: A review.

In recent years, the peracetic acid (PAA)-based advanced oxidation process (AOPs) has garnered significant attention in the field of water treatment due to rapid response time and environmentally-friendliness. The activation of PAA systems by diverse carbon-based materials plays a crucial role in addressing emerging environmental contaminants, including various types, structures, and modified forms of carbon materials. However, the structural characteristics and structure-activity relationship of carbon-based materials in the activation of PAA are intricate, while the degradation pathways and dominant active species exhibit diversity. Therefore, it is imperative to elucidate the developmental process of the carbon-based materials/PAA system through resource integration and logical categorization, thereby indicating potential avenues for future research. The present paper comprehensively reviews the structural characteristics and action mechanism of carbon-based materials in PAA system, while also analyzing the development, properties, and activation mechanism of heteroatom-doped carbon-based materials in this system. In conclusion, this study has effectively organized the resources pertaining to prominent research direction of comprehensive remediation of environmental water pollution, thereby elucidating the underlying logic and thought process. Consequently, it establishes robust theoretical foundation for future investigations and applications involving carbon-based materials/PAA system.

Performance evaluation of hybrid electrochemical oxidation and ultraviolet light-based persulfate process for the abatement of sodium dodecyl sulfate from wastewater.

The application of hybrid advanced oxidation processes (AOPs) is an efficacious way to remediate emerging contaminants from wastewater. In the present research work, a hybrid electrochemical oxidation and ultraviolet light-based persulfate activation processes (EO-UV/PS) were used to efficiently degrade sodium dodecyl sulfate (SDS) surfactant from synthetic and municipal wastewater. By operating the EO-UV/PS at optimum operating conditions at pH of 7.0, NaCl of 0.02 M, current density of 6.4 mA/cm2, persulfate dose of 2.5 mM, and operating period of 180 min, about 94.5 ± 2.8% of SDS (20 mg/L) removal was achieved from synthetic wastewater. The abetment of SDS in both EO and UV/PS obeyed pseudo-first-order kinetics with a rate constant of 0.012 and 0.019 min-1, respectively. Moreover, the economic analysis revealed 0.23 $ m-3 order-1 as the operating cost for degrading SDS in EO-UV/PS. The degradation pathway experimentation suggested the generation of lauric acid by-product during SDS abatement. Besides, nearly 89.3 ± 2.9% of SDS and 58.7 ± 2.4% of total organic carbon reduction was also achieved from real municipal wastewater. Phytotoxicity test on Vigna radiata affirms the non-toxic nature of the EO-UV/PS effluent.

A review on hazards and treatment methods of released antibiotics in hospitals wastewater during the COVID-19 pandemic.

Drugs and related goods are widely used in order to promote public health and the quality of life. One of the most serious environmental challenges affecting public health is the ongoing presence of antibiotics in the effluents generated by pharmaceutical industries and hospitals. Antibiotics cannot be entirely removed from wastewater using the traditional wastewater treatment methods. Unmetabolized antibiotics generated by humans can be found in urban and livestock effluent. The antibiotic present in effluent contributes to issues with resistance to antibiotics and the creation of superbugs. Over the recent 2 years, the coronavirus disease 2019 pandemic has substantially boosted hospital waste volume. In this situation, a detailed literature review was conducted to highlight the harmful effects of untreated hospital waste and outline the best approaches to manage it. Approximately 50 to 70% of the emerging contaminants prevalent in the hospital wastewater can be removed using traditional treatment strategies. This paper emphasizes the numerous treatment approaches for effectively eliminating emerging contaminants and antibiotics from hospital wastewater and provides an overview of global hospital wastewater legislation and guidelines on hospital wastewater administration. Around 90% of ECs might be eliminated by biological or physical treatment techniques when used in conjunction with modern oxidation techniques. According to this research, hybrid methods are the best approach for removing antibiotics and ECs from hospital wastewater. The document outlines the many features of effective hospital waste management and might be helpful during and after the coronavirus disease 2019 outbreak, when waste creation on all hospitals throughout the globe has considerably increased.

Activation of Peroxymonosulfate by Co-Ni-Mo Sulfides/CNT for Organic Pollutant Degradation.

To explore advanced oxidation catalysts, peroxymonosulfate (PMS) activation by Co-Ni-Mo/carbon nanotube (CNT) composite catalysts was investigated. A compound of NiCo2S4, MoS2, and CNTs was successfully prepared using a simple one-pot hydrothermal method. The results revealed that the activation of PMS by Co-Ni-Mo/CNT yielded an exceptional Rhodamine B decolorization efficiency of 99% within 20 min for the Rhodamine B solution. The degradation rate of Co-Ni-Mo/CNT was 4.5 times higher than that of Ni-Mo/CNT or Co-Mo/CNT, and 1.9 times as much than that of Co-Ni/CNT. Additionally, radical quenching experiments revealed that the principal active groups were 1O2, surface-bound SO4•-, and •OH radicals. Furthermore, the catalyst exhibited low metal ion leaching and favorable stability. Mechanism studies revealed that Mo4+ on the surface of MoS2 participated in the oxidation of PMS and the transformation of Co3+/Co2+ and Ni3+/Ni2+. The synergism between MoS2 and NiCo2S4 reduces the charge transfer resistance between the catalyst and solution interface, thus accelerating the reaction rate. Interconnected structures composed of metal sulfides and CNTs can also enhance the electron transfer process and afford sufficient active reaction sites. Our work provides a further understanding of the design of multi-metal sulfides for wastewater treatment.

Progress of metal-loaded biochar-activated persulfate for degradation of emerging organic contaminants.

In recent years, studies on the degradation of emerging organic contaminants by sulfate radical (SO4-·) based advanced oxidation processes (SR-AOPs) have triggered increasing attention. Metal-loaded biochar (Me-BC) can effectively prevent the agglomeration and leaching of transition metals, and its good physicochemical properties and abundant active sites induce outstanding in activating persulfate (PS) for pollutant degradation, which is of great significance in the field of advanced oxidation. In this paper, we reviewed the preparation method and stability of Me-BC, the effect of metal loading on the physicochemical properties of biochar, the pathways of pollutant degradation by Me-BC-activated PS (including free radical pathways: SO4-·, hydroxyl radical (·OH), superoxide radicals (O2-·); non-free radical pathways: singlet oxygen (1O2), direct electron transfer), and discussed the activation of different active sites (including metal ions, persistent free radicals, oxygen-containing functional groups, defective structures, etc.) in the SR-AOPs system. Finally, the prospect was presented for the current research progress of Me-BC in SR-AOPs technology.

Electro-photocatalyst effect of N-S-doped carbon dots and covalent organic triazine framework heterostructures for boosting photocatalytic degradation of phenanthrene in water.

In the present study, we introduce a covalent organic triazine framework polymer (COTF-P) using 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) with triazine-based amine. The resulting dark red COTF-P illustrated potential behavior as a photocatalyst under visible light. Due to the inadequate solar energy capture and ultrafast charge recombination of the resulting COTF-P, the prepared COTF-P has been decorated with CQDs (N-CQD and N-S-CQD) to build a Z-scheme CQDs/COTF-P heterojunction photocatalyst and utilizes as photocatalyst for the breakdown of phenanthrene (PHE) exposed to visible light. The prepared COTF-P and CQDs/COTF-P were fully characterized, analyzing the textural (N2 isotherms), structural (XRD and FTIR), chemical (EDX and XPS), morphological (FESEM and TEM), optical (DRS-UV-Vis and photoluminescence), and electrochemical properties (EIS impedance, transient photocurrent, and flat band potential). The prepared N-S-CQD/COTF-P heterojunction displayed optimum activity for the photocatalytic oxidation of PHE from water, owing to an enhanced separation of the photogenerated charges and lower bandgap value, 2.1 vs. 1.9 eV. The N-S-CQD/COTF-P heterojunction showed acceptable stability in terms of activity and structural properties after 5 cycles of reuse. The mechanism of activation highlights the importance played by superoxide radicals and hydroxyl radicals. This project sheds light on the potential use of CQDs for the decoration of polymers, extending the absorbance in the visible region and boosting the migration of charge, which boosts the activity of the resulting material.