The organic matter of lake sediment plays an important role in paleolimnological reconstruction. Here, we report a detailed study of organic matter components (C_org%, N%, δ¹³C, δ¹⁵N) in a dated sediment core of Hulun Lake in northern China. Multiple mixing models based on the stoichiometric ratios and stable isotopic compositions were applied to quantify the contributions of organic matter sources in lake sediment. The results show that the organic matter in the sediments from Hulun Lake mainly comes from terrestrial organic matter: the proportion of terrestrial organic matter is more than 80%. The results of the SIAR mixing model further reveal that the proportions of terrestrial C₃ plants-derived organic matter, soil organic matter, and lake plankton-derived organic matter were 76.0%, 13.9%, and 10.1%, respectively. The organic matter content of lake sediment from terrestrial sources began to increase significantly from 1980 onward, which is consistent with the growth in overgrazing in the Hulun Lake basin. The content of organic matter from endogenous lake-derived sources began to increase significantly after 2000 due to the nutrients gradually becoming concentrated in lake water, indicating that the reduction in rivers’ discharge and the downgrade of the lake water level were the immediate causes of the lake’s environmental deterioration during this period.

With the wide use of polyethylene film, the influence of polyethylene microplastic particles produced by its weathering on the rhizosphere soil microenvironment has attracted more and more attention from scientific research circles. In this study, the effects of low (0.2% w/w), medium (1% w/w), and high (2% w/w) doses of polyethylene particles and the combined reed biomass (2% w/w) on soil environmental factors and bacterial communities and metabolites in the reed rhizosphere were evaluated by a 90-day pot microscopic simulation system. The shape and surface microstructure of polyethylene particles in each treatment group changed obviously. A high (2% w/w) dose of microplastics significantly increased the TKN, TOC, and TP in reed root soil. The addition of the biomass significantly improved the activities of urease and sucrase in the soil. The α diversity of bacteria was not significantly affected by the addition of LDPE microplastics and biomass, but the β diversity of the bacterial community and the relative abundance of the Candidatus_Roku Bacteria, Chloroflexi, Unclassified_Blastocatella_Genus were significantly changed by the addition of middle (1% w/w) and high (2% w/w) doses of microplastics. In addition, the spectrum analysis of the soil metabolites showed that the abundance of soil metabolites was changed in each treatment group, and the differential metabolites were significantly up-regulated or down-regulated. Our findings provide a scientific reference to elucidate the impact of LDPE microplastic particles on the inter-rooted soil microenvironment and improve our understanding of the potential risks of microplastics in soil ecosystems.

We reported the preparation of NGO-Fe₃O₄ by simple hydrothermal-co-precipitation. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). It was demonstrated that norfloxacin (NOR) could be effectively degraded by the UV/NGO-Fe₃O₄/PDS system. The degradation efficiency reached 100% within 13 min (the concentration of NOR and S₂O₈ ^2- were 100 mg·L^-1 and 1 mM, respectively; m(NGO-Fe₃O₄): m(PDS) =4 : 1; pH: 3.0). In addition, NGO-Fe₃O₄ showed stable catalytic activity in recycling. The analysis found that the in-situ generated ·OH was the main active free radicals but SO₄ ^-· also participated in the NOR degradation. Based on the indentified intermediates, the NOR degradation pathways were proposed with UV/NGO-Fe₃O₄/PDS system.

A nitrogen-doped reduced graphene oxide/Fe3O4 composite (NGO-Fe3O4) was prepared through the simplified hydrothermal and deposition-precipitation method and characterized by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The degradation efficiency of oxytetracycline (OTC) by NGO-Fe3O4 activated peroxodisulfate (PDS) under visible light irradiation was studied. The degradation efficiency reached 100% within 32.5 min (the initial OTC concentration 50 mg L−1 and PDS 1 mM; [NGO-Fe3O4]:[ PDS] = 4:1; pH = 3.0). No apparent decrease in degradation efficiency was observed after five cycles. SO4−· and ·OH were the main active oxides for OTC degradation in this system. Moreover, four degradation pathways were proposed, namely hydroxylation, dehydration, decarbonylation and demethylation according to the analysis results of high-performance liquid chromatography mass spectrometry.

This study successfully synthesized a BC/TiO ₂ /g-C ₃ N ₄ composite photocatalyst using the sol–gel method, conducted an in-depth analysis of the influence mechanism of BC on charge transfer performance in heterojunction materials, and revealed its key role in regulating the charge transport process. The introduction of biochar significantly increased the specific surface area of BC/TiO ₂ /g-C ₃ N ₄ compared to the TiO ₂ /g-C ₃ N ₄ catalyst, broadening the visible light absorption range. Under simulated sunlight irradiation with a wavelength greater than 420 nm, the three-component material MBC-500, calcined at 500 °C, exhibits the best catalytic performance, with an adsorption photocatalytic degradation rate of 98.13% for sulfadiazine (SDZ) within 60 min, which is 3.46, 3.40, and 2.36 times that of TiO ₂ , g-C ₃ N ₄ , and TiO ₂ /g-C ₃ N ₄ , respectively. Characterization analysis and density functional theory (DFT) calculations revealed the energy band structure and electron transfer pathways of the composite photocatalyst, indicating the significant role of biochar in electron transfer and storage. Additionally, the calculated adsorption energies demonstrated the good adsorption performance of MBC-500 for O ₂ and sulfadiazine. This composite photocatalyst exhibited good stability and reusability even after five cycles of use. During the degradation process of SDZ, ·O ₂ ⁻ , h ⁺ , ·OH play a major role. Graphical Abstract