Qin Shi

The preparation of magnetic biochar usually requires additives and additional synthesis steps, which leads to a significant increase in preparation costs. In this study, self-endowed magnetic biochar derived from iron-rich sludge was prepared via one-step pyrolysis to adsorb carbamazepine in water. The results show that when the initial concentration of carbamazepine is 5 mg L⁻¹ and the dosage of self-endowed magnetic biochar is 0.9 g L⁻¹, the removal efficiency of carbamazepine by self-endowed magnetic biochar can reach 90.1%, and the adsorption performance is excellent in a wide pH range. The adsorption of carbamazepine by self-endowed magnetic biochar can be well fitted by Langmuir an adsorption isotherm and pseudo-second-order adsorption kinetic model, which indicates that the adsorption process is single molecular layer chemisorption. In addition, self-endowed magnetic biochar has good magnetic properties, and can be effectively separated and recovered by an external magnetic field after use, and the adsorption rate of carbamazepine can still reach 81.4% after repeated use for 5 times. The adsorption mechanism of carbamazepine by self-endowed magnetic biochar includes pore filling, complexation, π–π interaction and hydrogen bonding.

Industrial wastewater treatment processes produce a large quantity of iron-rich sludge due to the extensive utilization of iron salt reagent. Reuse of iron-rich sludge is an attractive route for excess sludge disposal and management. In this study, sludge-derived magnetic photocatalyst was prepared using industrial iron-rich sludge as raw materials for the first time. The photocatalytic degradation system constructed by the sludge-derived photocatalysts were evaluated using tetracycline (TC) as the target contaminant, achieving a high degradation rate of 98.3% within 5 h under optimal conditions. Major reactive oxygen species in the photocatalytic systems were investigated using radical quenching experiments and electron paramagnetic resonance spectroscopy. The results suggested that •OH and O₂^•- were activated by photogenerated electrons and holes, respectively. Moreover, bound persistent free radicals induced by quinone-like structure in sludge-derived biochar were the predominant factors affecting radical ¹O₂ formation under the light irradiation. The reactive oxygen species of •OH, O₂^•-, and ¹O₂ played main roles in the degradation of TC. The used magnetic biochar can be effectively separated and recovered in aqueous solutions by the magnetism. This method provides a new cost-effective strategy for antibiotics removal from aqueous solution.

Compared with traditional hydrothermal synthesis, microwave-assisted synthesis has the advantages of being faster and more energy efficient. In this work, the MoS₂/BiVO₄ heterojunction photocatalyst was synthesized by the microwave-assisted hydrothermal method within 30 min. The morphology, structure and chemical composition were characterized by X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and high-resolution transmission electron microscopy (HRTEM). The results of characterizations demonstrated that the synthesized MoS₂/BiVO₄ heterojunction was a spherical structure with dimensions in the nanorange. In addition, the photocatalytic activity of the samples was investigated by degrading tetracycline hydrochloride (TC) under visible light irradiation. Results indicated that the MoS₂/BiVO₄ heterojunction significantly improved the photocatalytic performance compared with BiVO₄ and MoS₂, in which the degradation rate of TC (5 mg L⁻¹) by compound where the mass ratio of MoS₂/BiVO₄ was 5 wt% (MB5) was 93.7% in 90 min, which was 2.36 times of BiVO₄. The active species capture experiments indicated that •OH, •O₂⁻ and h⁺ active species play a major role in the degradation of TC. The degradation mechanism and pathway of the photocatalysts were proposed through the analysis of the band structure and element valence state. Therefore, microwave technology provided a quick and efficient way to prepare MoS₂/BiVO₄ heterojunction photocatalytic efficiently.