Hydrogels exhibit distinctive features. These properties make them suitable for applications across various fields, such as environment, energy, and medicine. In this paper, we conducted a comprehensive search on the CNKI and Web of Science databases spanning from 2000 to 2024. Using tools like CiteSpace and VosViewer, we visualized the evolution, composition, hot spots, and trends in hydrogels in the field of water treatment sustainability. The results show that from 2000 to 2024, there has been a gradual increase in the number of publications in this field. China leads in the total number of publications; although, it ranks fourth in average citation rate. Seven out of the top ten research institutions are based in China. Additionally, three journals, including the International Journal of Biological Macromolecules, Chemical Engineering Journal and Carbohydrate Polymers, stand out, with a relatively high number of publications. The identified research hotspots include a range of preparation methods, including the freezing method and cross-linking method. Additionally, other preparation methods and the examination of water retention rate and adsorption isotherm are part of the research focus. The primary emphasis is on studying the adsorption of heavy metals, microplastics, and organic pollutants in dye wastewater. The main adsorption mechanisms investigated are chelation, electrostatic attraction, and functional group interaction. These findings have potential applications in water purification, seawater desalination, and atmospheric condensation. For the authorized patents in hydrogel-related fields, with the continuous improvement in innovation ability and the continuous enhancement of intellectual property protection awareness, the number of authorized patents continues to rise. China has seven of the top ten institutions in the number of patents granted, and the total number of patents granted in China ranks first in the world. Future work should focus on methods for synthesizing new pollutants and other target pollutants and on improving adsorption efficiency. Additionally, the development of cost-effective hydrogel materials with improved treatment efficacy is essential to advance sustainable practices in water treatment.

The conventional precursor preparation of metal–organic frameworks (MOFs) for nitrogen-doping carbon materials is divided into the preparation of MOFs and the mixing of the nitrogen source, which is a complex and time-consuming step. In this study, Fe-BTC gel/nitrogen source-derived carbon materials were synthesized using one or more of the following raw ingredients: Fe(NO₃)₃·9H₂O, FeCl₃·6H₂O, Fe₂(SO₄)₃, trimesic acid, melamine and dicyandiamide. The influence of different raw ingredients on the preparation and performance of catalysts was investigated. Fe(NO₃₎₃·9H₂O can react with trimesic acid to form a gel with ethanol as solvent, and the gel helped the homogeneous dispersion of the added melamine and did not precipitate. Fe-C-N(M), synthesized from the three materials mentioned, was identified as the optimal catalyst; the removal rate of 5 mg/L sulfadimethoxine (SMZ) reached 100% at 15 min when the Fe-C-N(M) dosage was 50 mg/L, PMS concentration was 0.5 mM, and the pH was 5.78 (initial pH of the solution). The removal of SMZ was not significantly inhibited by the pH (3–9) and 0–10 mM inorganic anions (Cl⁻, NO₃⁻, HCO₃⁻ and H₂PO₄²⁻). Through quenching tests, electron paramagnetic resonance and probe experiments, ¹O₂ and a small amount of free radicals (•OH and SO₄^•−) bound on the catalyst surface are discovered to be the primary active ingredients that activate PMS to degrade SMZ.

Biochar has attracted increasing attention for aquatic pollution control, particularly due to its capacity to accelerate the rate-limiting steps of denitrification in wastewater treatment. While early research primarily focused on the adsorption capacity of biochar, recent studies have increasingly investigated its role as a redox-active mediator that facilitates electron transfer. This review critically synthesizes the multifaceted mechanisms of biochar-enhanced denitrification, establishing a link between synthesis parameters (feedstock, pyrolysis kinetics) and physicochemical functionalities (pore architecture, redox-active functional groups). Specifically, we elucidate how precise regulation of pyrolysis temperature dictates the dominant electron transfer pathway: low-temperature biochar (700 °C) promotes direct interspecies electron transfer (DIET) through graphitic conduction. We systematically decouple biochar-mediated electron transfer into three pathways: functional group-driven shuttling, solid-state conductive matrix transfer via conjugated π-electrons, and material-assisted DIET. Crucially, we emphasize that validating true DIET requires direct biological evidence of electroactive machinery. Furthermore, the review details how biochar modulates the biological microenvironment, upregulating key denitrification genes (narG, nirS/K, nosZ) and enriching functional microbial consortia. By integrating advances in surface modification—such as heteroatom doping and metal loading—we propose strategies to engineer biochar for optimized nitrate-to-nitrogen conversion. Future perspectives underscore the need for balancing electron-donating capacity with structural stability, developing low-energy functionalization techniques, and conducting life-cycle assessments to facilitate the scale-up of sustainable, high-efficiency nitrogen removal systems.

To ensure water source security and sustainability of the national major strategic project “South-to-North Water Diversion”, this study aims to evaluate the spatio-temporal evolution characteristics of the ecosystem service value (ESV) in its water source area from 2002 to 2022. This study reveals its changing trends and main influencing factors, and thereby provides scientific support for the ecological protection and management of the water source area. Quantitative assessment of the ESV of the region was carried out using the Equivalence Factor Method (EFM), aiming to provide scientific support for ecological protection and resource management decision-making. In the past 20 years, the ESV has shown an upward trend year by year, increasing by 96%. The regions with the highest ESV were Garzê Prefecture and Aba Prefecture, which increased by 130.3% and 60.6%, respectively. The ESV of Xinlong county, Danba county, Rangtang county, and Daofu county increased 4.8 times, 1.5 times, 12.5 times, and 8.9 times, respectively. In the last two decades, arable land has decreased by 91%, while the proportions of bare land and water have decreased by 84% and 91%, respectively. Grassland had the largest proportion. Forests and grasslands, vital for climate regulation, water cycle management, and biodiversity conservation, have expanded by 74% and 43%, respectively. It can be seen from Moran’s I index values that the dataset as a whole showed a slight positive spatial autocorrelation, which increased from −0.041396 to 0.046377. This study reveals the changing trends in ESV and the main influencing factors, and thereby provides scientific support for the ecological protection and management of the water source area.

The Western Route of the South-to-North Water Diversion Project is a significant water conservancy project that has undergone years of discussion. This study employed the emergy method to evaluate the ecosystem service value (ESV) of its water source areas from 2002 to 2022, analyzing spatial heterogeneity, and evaluating trade-offs and synergies among ecosystem services. The high-emergy areas for water supply are concentrated in the lower reaches of the basin, Liangshan Prefecture had the highest emergy, increasing from 1.14 × 10²¹ sej to 1.65 × 10²¹ sej over the 20 years. The climate regulation emergy values of Ganzi Prefecture, Aba Prefecture, and Liangshan Prefecture were relatively stable. The biodiversity remained relatively stable with small fluctuations, but exhibited significant spatial heterogeneity. Liangshan Prefecture and Lijiang City had the highest biodiversity emergy values, at 1.21 × 10²¹ sej and 2.05 × 10²¹ sej respectively, corresponding to as many as 7661 and 13,000 species, respectively. Among the service types, provisioning services and supporting services account for a relatively high proportion. The water supply increased by 6.13%, while the biodiversity decreased by 5.42%. The relationship showed particularly intense conflict of −0.965. Analyzing the spatiotemporal evolution of ESV in water source areas is of great significance for rationally guiding the phased and seasonal allocation of water transfer volumes, implementing ecological compensation, and assessing the impacts of water conservancy projects on the ecological environment.