Tetracycline poses a major threat to the aquatic environment and human health, and there is an urgent need for a green, efficient and recyclable technological means to remove its negative effects. To address this need, three Fe₃O₄@SnO₂ modified wheat straw biochar nanocomposites with different Fe/Sn content ratios (Fe/Sn = 0.5, Fe/Sn = 1, and Fe/Sn = 2) were prepared by pyrolysis. The adsorption and degradation properties and related mechanisms of Fe₃O₄@SnO₂ modified wheat straw biochar nanocomposites were investigated by adsorption, degradation and free radical quenching experiments, as well as EPR analysis. The removal of tetracycline by Fe₃O₄@SnO₂ modified wheat straw biochar nanocomposites (Fe/Sn = 0.5) at pH 7.0 within 3 h was up to 91.80%, which is in accordance with the quasi-primary kinetic model. Under the interference of inorganic anions and cations, the removal of tetracycline by the composites was not affected by the coexisting ions except Ca²⁺, Mg²⁺, HCO₃ ⁻ and CO₃ ²⁻. The composites were able to efficiently remove tetracycline from pharmaceutical wastewater with a removal rate of 82.33%. It was found that the composites could be reused at least five times. FTIR, XPS combined with DFT calculations elucidated the mechanism of tetracycline removal by the composites, with •OH and •O₂ ⁻ being the main substances involved in the photodegradation of tetracycline, the incorporation of manganese dioxide quantum dots enhancing the response to visible light, and the incorporation of magnetic nanoparticles resulting in rapid charge transfer and improved spatial separation of photogenerated carriers. The modification measures significantly increased the specific surface area of the biochar and enhanced the adsorption and photocatalytic properties. Based on these studies, the developed nanocomposites provide a new idea for the removal of antibiotics from pharmaceutical wastewater. Graphical Abstract

In this research, a novel metal-organic framework-modified biochar composite (MIL-88b@BC) was created for the first time by modifying rice husk biochar using the excellent adsorption properties of metal-organic framework (MOF), as well as reducing the solubility of MOF using biochar as a substrate, aiming to improve the understanding of the adsorption characteristics of rare-earth metal recycling and to predict its adsorption mechanism. Density functional theory (DFT) computations allowed for rationally constructing the adsorption model. According to DFT calculations, the primary processes involved in the adsorption of La³⁺ were π–π interaction and ligand exchange, wherein the surface hydroxyl group played a crucial role. MIL-88b@BC interacted better with La³⁺ than biochar or MOF did. Accompanying batch tests with the theoretical conjecture's verification demonstrated that the pseudo-second-order model and the Langmuir model, respectively, provided a good fit for the adsorption kinetics and isotherms. The maximum La³⁺ adsorption capacity of MOF@BC (288.89 mg g⁻¹) was achieved at pH 6.0, which was significantly higher than the adsorbents' previously documented adsorption capacities. Confirming the DFT estimations, the adsorption capacity of BC@MIL-88b for La³⁺ was higher than that of MOF and BC. Additionally, MOF@BC can be recycled at least four times. To mitigate the growing scarcity of rare earth elements (REEs) and lessen their negative environmental effects, this work laid the path for effectively treating substantial volumes of wastewater produced while mining REEs. Highlights The novel composite adsorbent was prepared by MOF and biochar in situ growth method. The adsorption mechanism was innovatively investigated based on DFT calculations. Ligand exchange and La–O–Fe formation dominated in lanthanide ion removal. Graphical Abstract

Synergistic dual-defect engineering in Nb-doped SnO ₂ QDs boosts visible-light photocatalysis by creating oxygen vacancies, narrowing bandgaps, and extending carrier lifetimes, enabling efficient degradation of PE microplastics in real-world water.

Tin oxide quantum dots were synthesized in aqueous solution via a simple hydrolysis and oxidation process. The morphology observation showed that the quantum dots had an average grain size of 2.23 nm. The rutile phase SnO₂ was confirmed by the structural and compositional characterization. The fluorescence spectroscopy of quantum dots was used to detect the heavy metal ions of Cd²⁺, Fe³⁺, Ni²⁺ and Pb²⁺, which caused the quenching effect of photoluminescence. The quantum dots showed the response of 2.48 to 100 ppm Ni²⁺. The prepared SnO₂ quantum dots exhibited prospective in the detection of heavy metal ions in contaminated water, including deionized water, deionized water with Fe³⁺, reclaimed water and sea water. The limit of detection was as low as 0.01 ppm for Ni²⁺ detection. The first principle calculation based on the density function theory demonstrated the dependence of fluorescence response on the adsorption energy of heavy metal ions as well as ion radius. The mechanism of fluorescence response was discussed based on the interaction between Sn vacancies and Ni²⁺ ions. A linear correlation of fluorescence emission intensity against Ni²⁺ concentration was obtained in the logarithmic coordinates. The density of active Sn vacancies was the crucial factor that determined fluorescence response of SnO₂ QDs to heavy metal ions.