Electrochemical degradation of 4-chlorophenol in aqueous solution using modified PbO(2) anode

Hydrothermally Synthesized Z-Scheme Nanocomposite of ZIF-9 Modified MXene for Photocatalytic Degradation of 4-Chlorophenol

4-Chlorophenol (4CP) is a well-known environmental contaminant often detected in wastewater, generally arising from industrial processes such as chemical manufacture, pharmaceutical production, and pesticide formulation. 4CP is a matter of great concern since it is persistent and has the potential to have harmful impacts on both aquatic ecosystems and human health, owing to its hazardous and mutagenic properties. Hence, degradation of 4CP is of utmost significance. This research investigates the photocatalytic degradation of 4CP using a novel Z-scheme heterojunction nanocomposite composed of MXene and ZIF-9. The nanocomposite is synthesized through a two-step hydrothermal method and thoroughly characterized by using XRD, SEM, UV-visible spectroscopy, zeta potential, and electrochemical impedance spectroscopy studies, confirming successful fabrication with improved surface properties. The comparative photocatalytic degradation studies between pristine materials and the nanocomposite were performed, and significant enhancement in performance was observed. The effect of pH on the degradation efficiency is also explored and correlated with the surface charge. The Z-scheme photocatalysis mechanism is proposed, which is supported by time-resolved photoluminescence studies and scavenger experiments. The reusability of the nanocomposite is also evaluated. The study contributes to the development of efficient and sustainable photocatalysts for wastewater treatment.

Fabrication of a double-layer membrane cathode based on modified carbon nanotubes for the sequential electro-Fenton oxidation of p-nitrophenol

To improve the electrocatalytic efficiency of the cathode and provide a wider pH range in the electro-Fenton process, N-doped multi-walled carbon nanotubes (NCNTs) and ferrous ion complexed with carboxylated carbon nanotubes (CNT-COOFe²⁺) were used to fabricate the diffusion layer and catalyst layer of a membrane cathode, respectively. The morphology, structure, and composition of CNT-COOFe²⁺ were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The oxygen reduction performance of NCNT was evaluated using cyclic voltammetry (CV) and the rotating disk electrode technique (RDE). In addition, a potential application of the cathode in sequential electro-Fenton degradation of p-nitrophenol (p-NP) was investigated. The results revealed that iron was successfully doped on the carboxylated carbon nanotubes in ionic complexation form and the content of iron atoms in CNT-COOFe²⁺ was 2.65%. Furthermore, the defects on the tube walls provided more reactive sites for the electro-Fenton process. A combination of CV and RDE data indicated that NCNT had better electrocatalytic H₂O₂ generation activity with a more positive onset potential and higher cathodic peak current response than CNT. A p-NP removal rate of 96.04% was achieved within 120 min, and a mineralization efficiency of 80.26% was obtained at 180 min in the sequential electro-Fenton process at a cathodic potential of - 0.7 V vs SCE and neutral pH. The activity of the used cathode was restored simply through electro-reduction at - 1.0 V vs SCE, and a p-NP removal rate of more than 70% was obtained at 60 min after six regeneration cycles.

Electrochemical oxidation treatment of coal tar wastewater with lead dioxide anodes

In this study, coal tar wastewater was treated by electrochemical oxidation technology using lead dioxide anodes. The influence of operating parameters, including applied current density, electrode gap and initial pH value, on the removal ratio of chemical oxygen demand (COD) was investigated. The results demonstrated that the COD removal ratio reached 90.5% after 3.5 h electrolysis with the current density at 3 A dm^-2 and electrode gap at 1.0 cm. Correspondingly, the COD decreased from 5,125 mg L^-1 to 487 mg L^-1, which fitted the wastewater discharge standards of China, and the specific energy consumption (SEC_COD) was 35.3 kWh kg_COD ^-1. Not only was the COD removal ratio only 77.1% after 2 h electrolysis but the BOD₅/COD ratio of the wastewater reached 0.44, which could be biochemically treated, and the SEC_COD decreased by 34.3%. Moreover, the main composition of pristine wastewater before and after 2 h electrolysis was analyzed by GC-MS, and the disappearance of macromolecules (such as ethyl-2-pyrenemethanol) and the production of small molecules (such as propane-1,3-diol) could improve the biodegradability of the wastewater. Therefore, electrochemical oxidation for 2 h is a promising alternative for pretreatment of coal tar wastewater prior to biological treatment.