Preparation of Ti-based Yb-doped SnO2–RuO2 electrode and electrochemical oxidation treatment of coking wastewater

Effective degradation of polystyrene microplastics by Ti/La/Co-Sb-SnO2 anodes: Enhanced electrocatalytic stability and electrode lifespan

Microplastics have been identified as an emerging pollutant that poses a risk to the aquatic environment, and it is a challenge to find a suitable removal process. Electrocatalytic oxidation (ECO) technology has shown promising performance in removing various persistent organic pollutants. In this study, we prepared a new anode for removing polystyrene microplastics (PS MPs) by ECO. Ti/La-Sb-SnO2 electrodes doped with the rare earth element La as the active layer were synthesized to enhance the electrocatalytic activity. The lifespan of the electrode was improved by doping Mn, Co, or Ru as an intermediate layer modification between the titanium (Ti) substrate and the La-Sb-SnO2 active layer, respectively. The experimental results indicated that the addition of three types of intermediate layers led to different degrees of decrease in the catalytic activity of the electrode and the degradation performance of PS MPs. The addition of the Co intermediate layer had a negligible effect on the catalytic activity and performance of the Ti/La-Sb-SnO2 anode for PS degradation. In addition, the electrode lifespan with Co intermediate layer was significantly prolonged, which was 4.54, 2.38, and 1.19 times higher than the electrode without intermediate layer and the electrode with Ru and Mn intermediate layer, respectively. Therefore, Co was determined to be the optimal choice as the intermediate layer, and the production technique for the Ti/La/Co-Sb-SnO2 anodes was carefully adjusted. The degradation efficiency of PS MPs was optimized at a heat treatment temperature of 400 °C and a Sn: Co material ratio of 5:1, with a removal rate of 28.0 %. The ECO treatment also resulted in more pronounced changes in the structure and functional groups of the MPs. Various alkyl cleavage and oxidation products were detected after the treatment, suggesting that the oxidant (hydroxyl radicals) strongly interacted with the MPs, leading to their degradation. Overall, this work provided a new insight into removing MPs in water through the use of modified electrodes.

Heterogeneous electro-Fenton treatment of coking wastewater using Fe/AC/Ni cathode: optimization of electrode and reactor organic loading

A self-developed iron-loaded activated carbon-based nickel foam electrode (Fe/AC/Ni cathode) was used to construct electro-Fenton reaction system to treat coking wastewater. To meet the gap between laboratory beaker experiments and field trials for practical applications, we proposed and validated a method for obtaining organic loads, the essential parameters used in the design of electrochemical systems for wastewater treatment. The three influencing factors most relevant to organic loading, the effective surface area of cathode, chemical oxygen demand (COD) concentration of influent, and treatment time, were selected and investigated for their effects on the COD removal rate of coking wastewater by single-factor experiments and further optimized by response surface method. The appropriate electrode area load (La) and reactor volume load (Lv) were calculated by their corresponding intrinsic relationships with the three factors. The optimum application conditions were effective surface area of cathode 28.5 cm2, COD concentration of influent 1.76 kg·m-3, and treatment time 160.43 min. Under these conditions, the maximum COD removal rate was 98.51%. The La and Lv were 8.905 mgCOD·cm-2·h-1 and 0.634 kgCOD·m-3·h-1, respectively. The characterization experiment results showed that the Fe/AC/Ni cathode had a significant effect on the treatment of refractory organic contaminants in coking wastewater.

Advanced treatment of coking wastewater: Recent advances and prospects

Advanced treatment of refractory industrial wastewater is still a challenge. Coking wastewater is one of coal chemical wastewater, which contains various refractory organic pollutants. To meet the more and more rigorous discharge standard and increase the reuse ratio of coking wastewater, advanced treatment process must be set for treating the biologically treated coking wastewater. To date, several advanced oxidation processes (AOPs), including Fenton, ozone, persulfate-based oxidation, and iron-carbon micro-electrolysis, have been applied for the advanced treatment of coking wastewater. However, the performance of different advanced treatment processes changed greatly, depending on the components of coking wastewater and the unique characteristics of advanced treatment processes. In this review article, the state-of-the-art advanced treatment process of coking wastewater was systematically summarized and analyzed. Firstly, the major organic pollutants in the secondary effluents of coking wastewater was briefly introduced, to better understand the characteristics of the biologically treated coking wastewater. Then, the performance of various advanced treatment processes, including physiochemical methods, biological methods, advanced oxidation methods and combined methods were discussed for the advanced treatment of coking wastewater in detail. Finally, the conclusions and remarks were provided. This review will be helpful for the proper selection of advanced treatment processes and promote the development of advanced treatment processes for coking wastewater.

Advancements and sustainable strategies for the treatment and management of wastewaters from metallurgical industries: an overview

Metallurgy is pivotal for societal progress, yet it yields wastewater laden with hazardous compounds. Adhering to stringent environmental mandates, the scientific and industrial sectors are actively researching resilient treatment and disposal solutions for metallurgical effluents. The primary origins of organic pollutants within the metallurgical sector include processes such as coke quenching, steel rolling, solvent extraction, and electroplating. This article provides a detailed analysis of strategies for treating steel industry waste in wastewater treatment. Recent advancements in membrane technologies, adsorption, and various other processes for removing hazardous pollutants from steel industrial wastewater are comprehensively reviewed. The literature review reveals that advanced oxidation processes (AOPs) demonstrate superior effectiveness in eliminating persistent contaminants. However, the major challenges to their industrial-scale implementation are their cost and scalability. Additionally, it was discovered that employing a series of biological reactors instead of single-step biological processes enhances command over microbial communities and operating variables, thus boosting the efficacy of the treatment mechanism (e.g., achieving a chemical oxygen demand (COD) elimination rate of over 90%). This review seeks to conduct an in-depth examination of the current state of treating metallurgical wastewater, with a particular emphasis on strategies for pollutant removal. These pollutants exhibit distinct features influenced by the technologies and workflows unique to their respective processes, including factors such as their composition, physicochemical properties, and concentrations. Therefore, it is of utmost importance for customized treatment and disposal approaches, which are the central focus of this review. In this context, we will explore these methods, highlighting their advantages and characteristics.

Preparation of Yb-Sb co-doped Ti/SnO2 electrode for electrocatalytic degradation of sulfamethoxazole (SMX)

To efficiently break down residual sulfonamide antibiotics in environmental water, Yb-Sb co-doped Ti/SnO2 electrodes were fabricated using a solvothermal method. The effect of different amounts of Yb doping on the properties of the electrodes was studied. When the atom ratio of Sn: Yb is 100 : 7.5 in the preparation, the as-obtained coral-like electrodes (denoted as Yb 7.5%) possessed the smallest diameter of spherical particles on the surfaces, to result in the denser surface, highest electrocatalytic activity and smallest resistance of the electrode. As anode for electrocatalytic degradation of sulfamethoxazole, the Yb 7.5% electrode showed a degradation rate of 92% in 90 min, which was much higher than that of Yb 0% electrode (62.7% degradation rate). The electrocatalytic degradation of sulfamethoxazole was investigated with varying current densities and initial concentrations. Results indicated that the degradation process followed pseudo-first-order kinetics, and the degradation rate constants for Yb 7.5% and Yb 0% electrodes were 0.0278 min-1 and 0.0114 min-1, respectively. Furthermore, the service life of Ti/SnO2 electrodes was significantly improved after Yb doping, as demonstrated by accelerated life testing. Yb 7.5% exhibited a service life that was 2.7 times longer than that of Yb 0%. This work offers a new approach to construct Yb-Sb co-doped Ti/SnO2 electrodes with excellent electrooxidation activity and high stability for the electrochemical oxidation degradation of sulfamethoxazole.

Fabrication of high performance Ti/SnO2-Nb2O5 electrodes for electrochemical textile wastewater treatment

Textile wastewater contains many organic compounds and colors that affect aquatic life and human health when discharged into the environment. High coloration due to excess dyes entering the wastewater causes coloration to the receiving water stream, affects the photosynthesis process of aquatic species, and adversely affects the landscape. SnO₂-based electrodes have been extensively used in electrochemical water treatment, but their low durability decreases the pollutant treatment ability. Therefore, it is necessary to add another stable oxide to improve the performance and stability of SnO₂ electrodes. This study aims to fabricate Ti/SnO₂-Nb₂O₅ electrodes for the textile wastewater treatment using the electrochemical oxidation method. Different molar ratios of SnO₂:Nb₂O₅ coating were prepared using the sol-gel method and then coated on the Ti substrates for calcination in 60 min at 500 °C. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer Emmett Teller (BET), and cyclic voltammetry (CV) were used to determine the surface and electrochemical properties of Ti/SnO₂-Nb₂O₅ electrodes. The SEM images show that SnO₂-Nb₂O₅ electrode surfaces have the appearance of typical cracking structures of mixed metal oxides electrodes. The XRD spectrum show the SnO₂ peaks of facet (110), (101), (200), (301), (321) and Nb₂O₅ peaks of facet (001), (002), (100), (101), (102) on Ti substrates. Furthermore, the specific surface area of the Ti/SnO₂-Nb₂O₅ electrode ranges from 37.354 m²/g (SnO₂:Nb₂O₅ = 9:1) to 71.885 m²/g (SnO₂:Nb₂O₅ = 1:9). The electrochemical properties of SnO₂:Nb₂O₅ electrodes showed high oxygen, chlorine evolution potential and high organic pollutant degradation in textile wastewater with COD removal at 83 %, decolorization at 74 % and the generation of many free radicals such as HO^•, H₂O₂, O₃, Cl₂. The results demonstrate that the Ti/SnO₂-Nb₂O₅ electrode with the mole ratio of 3:7 is the best in textile wastewater treatment with the longest service life (39 h).

Electrochemical Methods for Water Purification, Ion Separations, and Energy Conversion

Agricultural development, extensive industrialization, and rapid growth of the global population have inadvertently been accompanied by environmental pollution. Water pollution is exacerbated by the decreasing ability of traditional treatment methods to comply with tightening environmental standards. This review provides a comprehensive description of the principles and applications of electrochemical methods for water purification, ion separations, and energy conversion. Electrochemical methods have attractive features such as compact size, chemical selectivity, broad applicability, and reduced generation of secondary waste. Perhaps the greatest advantage of electrochemical methods, however, is that they remove contaminants directly from the water, while other technologies extract the water from the contaminants, which enables efficient removal of trace pollutants. The review begins with an overview of conventional electrochemical methods, which drive chemical or physical transformations via Faradaic reactions at electrodes, and proceeds to a detailed examination of the two primary mechanisms by which contaminants are separated in nondestructive electrochemical processes, namely electrokinetics and electrosorption. In these sections, special attention is given to emerging methods, such as shock electrodialysis and Faradaic electrosorption. Given the importance of generating clean, renewable energy, which may sometimes be combined with water purification, the review also discusses inverse methods of electrochemical energy conversion based on reverse electrosorption, electrowetting, and electrokinetic phenomena. The review concludes with a discussion of technology comparisons, remaining challenges, and potential innovations for the field such as process intensification and technoeconomic optimization.

Research trends in the development of anodes for electrochemical oxidation of wastewater

The review focuses on the recent development in anode materials and their synthesis approach, focusing on their compatibility for treating actual industrial wastewater, improving selectivity, electrocatalytic activity, stability at higher concentration, and thereby reducing the mineralization cost for organic pollutant degradation. The advancement in sol–gel technique, including the Pechini method, is discussed in the first section. A separate discussion related to the selection of the electrodeposition method and its deciding parameters is also included. Furthermore, the effect of using advanced heating approaches, including microwave and laser deposition synthesis, is also discussed. Next, a separate discussion is provided on using different types of anode materials and their effect on active •OH radical generation, activity, and electrode stability in direct and indirect oxidation and future aspects. The effect of using different synthesis approaches, additives, and doping is discussed separately for each anode. Graphene, carbon nanotubes (CNTs), and metal doping enhance the number of active sites, electrochemical activity, and mineralization current efficiency (MCE) of the anode. While, microwave or laser heating approaches were proved to be an effective, cheaper, and fast alternative to conventional heating. The electrodeposition and nonaqueous solvent synthesis were convenient and environment-friendly techniques for conductive metallic and polymeric film deposition.