Electrochemical degradation of tetracycline hydrochloride in sulfate solutions on boron-doped diamond electrode: The accumulation and transformation of persulfate

Single-Step Upcycling of Sugarcane Bagasse and Iron Scrap into Magnetic Carbon for High-Performance Adsorbents

The sugar industry produces significant quantities of waste biomass, while other industrial sectors generate iron scrap as waste. This study seeks to make use of these waste products using an in situ approach that integrates carbonization, activation, and magnetization to convert sugarcane waste and iron scrap into a magnetic carbon composite adsorbent. The porosity of the activated carbon was enhanced by the activating agent potassium hydroxide (KOH) and further improved by the addition of iron scrap, which also imparted magnetic properties to the composite. The developed porosity of the composite increased the overall adsorption capacity of the adsorbent. The synthesis conditions were varied to examine the effects on the properties of the adsorbent. The amount of KOH used in the synthesis influenced the performance of the material. The best-performing adsorbent demonstrated strong potential in the treatment of wastewater by exhibiting an adsorption capacity of 1736.93 mg/g for the antibiotic tetracycline. The magnetic properties of the composite adsorbent enable simple separation and recovery, making the adsorbent reusable and lowering operating costs. This study provides a clear framework for the synthesis of waste-derived magnetic carbon composite adsorbents that can offer financial and environmental advantages while remaining effective in industrial contexts.

A critical review of persulfate-based electrochemical advanced oxidation processes for the degradation of emerging contaminants: From mechanisms and electrode materials to applications

The persulfate-based electrochemical advanced oxidation processes (PS-EAOPs) exhibit distinctive advantages in the degradation of emerging contaminants (ECs) and have garnered significant attention among researchers, leading to a consistent surge in related research publications over the past decade. Regrettably, there is still a lack of a critical review gaining deep into understanding of ECs degradation by PS-EAOPs. To address the knowledge gaps, in this review, the mechanism of electro-activated PS at the interface of the electrodes (anode, cathode and particle electrodes) is elaborated. The correlation between these electrode materials and the activation mechanism of PS is systematically discussed. The strategies for improving the performance of electrode material that determining the efficiency of PS-EAOPs are also summarized. Then, the applications of PS-EAOPs for the degradation of ECs are described. Finally, the challenges and outlook of PS-EAOPs are discussed. In summary, this review offers valuable guidance for the degradation of ECs by PS-EAOPs.

Single-crystal vs polycrystalline boron-doped diamond anodes: Comparing degradation efficiencies of carbamazepine in electrochemical water treatment

The ongoing challenge of water pollution by contaminants of emerging concern calls for more effective wastewater treatment to prevent harmful side effects to the environment and human health. To this end, this study explored for the first time the implementation of single-crystal boron-doped diamond (BDD) anodes in electrochemical wastewater treatment, which stand out from the conventional polycrystalline BDD morphologies widely reported in the literature. The single-crystal BDD presented a pure diamond (sp3) content, whereas the three other investigated polycrystalline BDD electrodes displayed various properties in terms of boron doping, sp3/sp2 content, microstructure, and roughness. The effects of other process conditions, such as applied current density and anolyte concentration, were simultaneously investigated using carbamazepine (CBZ) as a representative target pollutant. The Taguchi method was applied to elucidate the optimal operating conditions that maximised either (i) the CBZ degradation rate constant (enhanced through hydroxyl radicals (•OH)) or (ii) the proportion of sulfate radicals (SO4•-) with respect to •OH. The results showed that the single-crystal BDD significantly promoted •OH formation but also that the interactions between boron doping, current density and anolyte concentration determined the underlying degradation mechanisms. Therefore, this study demonstrated that characterising the BDD material and understanding its interactions with other process operating conditions prior to degradation experiments is a crucial step to attain the optimisation of any wastewater treatment application.

A combined experimental and computational approach to unravel degradation mechanisms in electrochemical wastewater treatment

Electrochemical wastewater treatment is a promising technique to remove recalcitrant pollutants from wastewater. However, the complexity of elucidating the underlying degradation mechanisms hinders its optimisation not only from a techno-economic perspective, as it is desirable to maximise removal efficiencies at low energy and chemical requirements, but also in environmental terms, as the generation of toxic by-products is an ongoing challenge. In this work, we propose a novel combined experimental and computational approach to (i) estimate the contribution of radical and non-radical mechanisms as well as their synergistic effects during electrochemical oxidation and (ii) identify the optimal conditions that promote specific degradation pathways. As a case study, the distribution of the degradation mechanisms involved in the removal of benzoic acid (BA) via boron-doped diamond (BDD) anodes was elucidated and analysed as a function of several operating parameters, i.e., the initial sulfate and nitrate content of the wastewater and the current applied. Subsequently, a multivariate optimisation study was conducted, where the influence of the electrode nature was investigated for two commercial BDD electrodes and a customised silver-decorated BDD electrode. Optimal conditions were identified for each degradation mechanism as well as for the overall BA degradation rate constant. BDD selection was found to be the most influential factor favouring any mechanism (i.e., 52-85% contribution), given that properties such as its boron doping and the presence of electrodeposited silver could dramatically affect the reactions taking place. In particular, decorating the BDD surface with silver microparticles significantly enhanced BA degradation via sulfate radicals, whereas direct oxidation, reactive oxygen species and radical synergistic effects were promoted when using a commercial BDD material with higher boron content and on a silicon substrate. Consequently, by simplifying the identification and quantification of underlying mechanisms, our approach facilitates the elucidation of the most suitable degradation route for a given electrochemical wastewater treatment together with its optimal operating conditions.

A new strategy for enhanced electrochemically activation of persulfate on B and Co co-modified carbon felt in flow-through system for efficient organic pollutants degradation

Electrochemical activation of persulfate (EA-PS) is gradually attracting attention as an emerging method for wastewater treatment. In this study, a novelty flow-through EA-PS system was first attempted for pollutants degradation using boron and cobalt co-doping carbon felt (B, Co-CF) as the cathode. SEM images, XPS and XRD spectra of B, Co-CF were investigated. The optimal doping ration between B and Co was 1:2. Increasing current density, PS concentration and flow rate, decreasing initial pH accelerated the removal of AO7. The mechanism involved in EA-PS were the comprehensive effect of DET, •OH and SO4•-. B, Co-CF cathode for flow-through system was stable with five cycles efficient AO7 decay performance. EA-PS in flow-through system was an efficient method with low cost and efficient pollutants degradation. This work provides a feasible strategy for synergistically enhancing PS activation and promoting the degradation of organic pollutants.

Contamination distribution and non-biological removal pathways of typical tetracycline antibiotics in the environment: A review

While the occurrence and removal technologies of tetracyclines in the environment have been reported, a comprehensive systematic summary and analysis remain limited, especially for new generations compounds such as doxycycline. In this review, the latest information regarding the distribution of various tetracyclines in different countries over the past seven years (2017-2023) reveals a notable absence of research reports in North America and Oceania. With China as the representative country, the investigation indicates that the maximum concentrations of TCs exceed 5 µg/L. The maximum concentration of tetracyclines in feces (26.22 µg/L) can reach one order of magnitude higher than that in other media. Furthermore, advanced oxidation technologies, such as Fenton processes, electrochemical oxidation, photolysis, ozonation, etc., were also examined, and the median degradation rate achieved 91.9-97.67%. Reactions such as methylation, demethylation, hydroxylation, dehydration, ring cleavage, and oxidation were observed during degradation. The most common intermediate product was identified as m/z = 461 (C22H25N2O9). This review indicates that future efforts should emphasize understanding the occurrence and fate of new-generation tetracyclines in the environment.

Tetracycline degradation mechanism of peroxymonosulfate activated by oxygen-doped carbon nitride

In this study, oxygen-doped carbon nitride (O-C3N4) was prepared by thermal polymerization and was applied to activate peroxymonosulfate (PMS) for tetracycline (TC) degradation. Experiments were performed to comprehensively evaluate the degradation performance and mechanism. The oxygen atom replaced the nitrogen atom of the triazine structure, which improves the specific surface area of the catalyst, enriches the pore structure and achieves higher electron transport capacity. The characterization results showed that 0.4 O-C3N4 had the best physicochemical properties, and the degradation experiments showed that the 0.4 O-C3N4/PMS system had a higher TC removal rate in 120 min (89.94%) than the unmodified graphitic-phase C3N4/PMS system (52.04%). Cycling experiments showed that O-C3N4 has good reusability and structural stability. Free radical quenching experiments showed that the O-C3N4/PMS system had free radical and non-radical pathways for TC degradation and that the main active species was singlet oxygen (1O2). Intermediate product analysis showed that TC was mineralized to H2O and CO2 mainly by the ring opening, deamination, and demethylation reactions. The results of this study show that the 0.4 O-C3N4/PMS system is simple to prepare and is efficient at removing TC from contaminated water.