Sulfur-zinc modified kaolin/steel slag: A particle electrode that efficiently degrades norfloxacin in a neutral/alkaline environment

An overview of the recent advances and future prospects of three-dimensional particle electrode systems for treating wastewater

Three-dimensional (3D) electrochemical technology is considered a very effective industrial wastewater treatment method for its high treatment efficiency, high current efficiency, low energy consumption, and, especially, ability to completely mineralize nonbiodegradable organic contaminants. Particle electrodes, which are the fundamental components of 3D electrochemical technology, have multiple functions in the electrochemical reaction process. Various types of particle electrodes have been created and applied for wastewater treatment. Herein, we present a thorough analysis of the research and development of particle electrodes used for electrocatalyzing pollutants. Initially, reactor designs, factors affecting the removal efficiency of pollutants and degradation mechanisms are introduced. In particular, a detailed investigation is conducted into the selection of particle electrode materials and the roles they play in the 3D electrochemical treatment of wastewater. Subsequently, the degradation efficiency and energy consumption associated with 3D electrochemical technology for different pollutants are investigated. Finally, the directions and outlook for further studies on particle electrodes are discussed. We believe that this review will offer a useful perspective on the development and application of particle electrodes for wastewater purification.

Nitrogen-doped carbon-coated Cu0 activates molecular oxygen for norfloxacin degradation over a wide pH range

The Fenton-like activated molecular oxygen technology demonstrates significant potential in the treatment of refractory organic pollutants in wastewater, offering promising development prospects. We prepared a N-doped C-coated copper-based catalyst Cu0/NC3-600 through the pyrolysis of Mel-modified Cu-based metal-organic framework (MOF). The results indicate that the degradation of 20 mg/L norfloxacin (NOR) was achieved using 1.0 g/L Cu0/NC3-600 across a wide pH range, with a removal rate exceeding 95 % and total organic carbon (TOC) removals approaching 70 % after 60 min at pH 5-11. The nitrogen doping enhances the electronic structure of the carbon material, facilitating the adsorption of molecular oxygen. Additionally, the formed carbon layer effectively prevent copper leaching,contributing to increased stability to a certain extent. Subsequently, we propose the catalytic reaction mechanism for the Cu0/NC/air system. Under acidic conditions, Cu0/NC3-600 activates molecular oxygen to produce the •O2-, which serves as the primary active species for NOR degradation. While in alkaline conditions, the high-valent copper species Cu3+ is generated in conjunction with •O2-, both working simultaneously for NOR degradation. Furthermore, based on the LC-MS results, we deduced four possible degradation pathways. This work offers a novel perspective on expanding the pH range of copper-based catalysts with excellent ability to activate molecular oxygen for environmental water treatment.

A review of metallurgical slags as catalysts in advanced oxidation processes for removal of refractory organic pollutants in wastewater

With the rapid growth of the metallurgical industry, there is a significant increase in the production of metallurgical slags. The waste slags pose significant challenges for their disposal because of complex compositions, low utilization rates, and environmental toxicity. One promising approach is to utilize metallurgical slags as catalysts for treatment of refractory organic pollutants in wastewater through advanced oxidation processes (AOPs), achieving the objective of "treating waste with waste". This work provides a literature review of the source, production, and chemical composition of metallurgical slags, including steel slag, copper slag, electrolytic manganese residue, and red mud. It emphasizes the modification methods of metallurgical slags as catalysts and the application in AOPs for degradation of refractory organic pollutants. The reaction conditions, catalytic performance, and degradation mechanisms of organic pollutants using metallurgical slags are summarized. Studies have proved the feasibility of using metallurgical slags as catalysts for removing various pollutants by AOPs. The catalytic performance was significantly influenced by slags-derived catalysts, catalyst modification, and process factors. Future research should focus on addressing the safety and stability of catalysts, developing green and efficient modification methods, enhancing degradation efficiency, and implementing large-scale treatment of real wastewater. This work offers insights into the resource utilization of metallurgical slags and pollutant degradation in wastewater.

A review on three-dimensional electrochemical technology for the antibiotic wastewater treatment

The potential genotoxicity and non-biodegradability of antibiotics in the natural water bodies threaten the survival of various living things and cause serious environmental pollution and destruction. Three-dimensional (3D) electrochemical technology is considered a powerful means for antibiotic wastewater treatment as it can degrade non-biodegradable organic substances into non-toxic or harmless substances and even completely mineralize them under the action of electric current. Therefore, antibiotic wastewater treatment using 3D electrochemical technology has now become a hot research topic. Thus, in this review, a detailed and comprehensive investigation was conducted on the antibiotic wastewater treatment using 3D electrochemical technology, including the structure of the reactor, electrode materials, the influence of operating parameters, reaction mechanism, and combination with other technologies. Many studies have shown that the materials of electrode, especially particle electrode, have a great effect on the antibiotic wastewater treatment efficiency. The influence of operating parameters such as cell voltage, solution pH, and electrolyte concentration was very significant. Combination with other technologies such as membrane and biological technologies has effectively increased antibiotic removal and mineralization efficiency. In conclusion, the 3D electrochemical technology is considered as a promising technology for the antibiotic wastewater treatment. Finally, the possible research directions of the 3D electrochemical technology for antibiotic wastewater treatment were proposed.

Distribution modes of residual carbon and ash in coal gasification fine slag and its feasibility analysis as particle electrodes

From the perspective of environmental protection and resource utilization, the feasibility of treating m-cresol wastewater with coal gasification fine slag (GFS) as particle electrodes in an electrocatalytic system was evaluated to achieve the purpose of treating waste with waste. Characterization by scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), Raman, and fourier transform infrared spectroscopy (FTIR) confirmed that the GFS featured a diverse inorganic framework, large specific surface area (as large as above 155 m² g^-1), hierarchical porous structure, and plenty of catalytic sites. The Venn diagram method was used to systematically propose the following distribution modes of residual carbon (RC) and ash in GFS: discrete distribution, embedded distribution, crosslinked distribution, and association and bonding. Only 8 g L^-1 of GFS particle electrodes prevented the formation of a yellow sticky passivation film on the anode. Compared to the two-dimensional electrocatalytic system (47.89%), the wastewater treatment efficiency was increased by 108.81%. Zero-order kinetic results showed that the reaction rate constant was the highest (2.1106 mg L^-1·min^-1) when the secondary flotation RC was adopted as particle electrodes. It was indicated that GFS in discrete mode played either no role or at most a minor role. Last but not least, the synergy of RC and ash was revealed from a molecular perspective. The RC exhibited hierarchical microporous/mesoporous/macroporous structure, which facilitated the entry of H₂O₂ into the catalytic sites of ash. Abundant catalytic sites in ash accelerated adsorption and oxidation processes on RC surfaces.

Electrochemical-assisted ultraviolet light coupled peroxodisulfate system to degrade ciprofloxacin in water: Kinetics, mechanism and pathways

The persulfate advanced oxidation is an emerging and efficient pollutant treatment method, but usually requires the help of other materials or energy to catalyze and produce highly oxidizing active substances. In this paper, electrochemical-assisted ultraviolet light coupled peroxodisulfate system (E-UV-PDS) was used to degrade ciprofloxacin (CIP), and it was determined that electrolysis and ultraviolet photolysis were synergistic by calculation. The effects of initial pH, voltage, peroxodisulfate dosage, CIP concentration and coexisting anions on the degradation process were explored. The quenching experiments showed that ¹O₂, ⋅OH and SO₄^-⋅ were the main active oxygen species. Under the following conditions, ultraviolet light = 6 W, voltage = 4 V, [peroxodisulfate] = 20 mM, [pH]₀ = 7 and [CIP] = 100 mgL^-1, the degradation rate of CIP reached about 100% after 120 min, and the influence of inorganic anions was also discussed. Several intermediate products were identified by LC-MS, and three degradation pathways were speculated for CIP degradation. Finally, economic evaluation of the E-UV-PDS system was made, and it was useful to construct environmentally friendly and low-cost catalytic processes for the efficient degradation of organic pollutants.