Halloysite nanotubes (HNTs) have been pursued as promising carriers for enzyme immobilization, but the lack of functional groups severely limits their applications. Herein, we reported a simple tannic acid (TA)-mediated surface modification strategy for the fabrication of HNT-based efficient enzyme immobilization supports. Particularly, TA was first self-polymerized and deposited onto the surface of HNTs to form a thin active film via a mussel-inspired method, and the model enzyme laccase was directly conjugated via the Michael addition and/or Schiff base condensation between quinone groups on poly(tannic acid) layer surfaces and exposed amine groups on laccase surfaces. Under the optimum conditions, this newly fabricated support retained good enzyme-loading and activity recovery properties with 197.9 mg protein per gram of support and 55.4% of activity recovery being achieved. In addition, this immobilized laccase was less influenced by pH, temperature, and inhibitor changes and exhibited higher storage stability than free laccases as more than 70% of initial activity was retained by the immobilized laccase, while less than 30% was retained for free laccase after one-month storage at 4 °C. Finally, a higher bisphenol-A (BPA) removal efficiency and more reuse cycles were demonstrated for immobilized laccases. As a result, this TA-mediated surface modification is a simple and green method for biological macromolecule immobilization on HNTs in one step.

Waste biomass was used as a carbon precursor to prepare photoluminescent biochar dots for economical and eco-friendly monitoring of Hg ²⁺ and Fe ³⁺ ions.

Peanut yield and quality are often threatened by soil degradation under continuous cropping. Biochar has been known to improve the soil microbial community and plant resistance. However, studies on its functions to reduce soil degradation losses and improve the peanut yield are limited. A field peanut experiment was conducted in an Alfisol soil and biochar was applied at a rate of 20 t ha⁻¹ in 2022. The biochar was prepared from woodchip (WB) and maize straw (MB) feedstocks alone, as well as with co-composted biochar of the same feedstocks with pig manure labeled as WBSC and MBSC amendment, respectively. The conventional organic manure was applied as a control treatment (OM). All plots were base-fertilized with a mineral compound fertilizer of N-P₂O₅-K₂O (16-16-16, %) at 600 kg ha⁻¹. Topsoil (20 cm) and plant samples were collected at the time of peanut harvest. Soil quality, enzyme function, peanut growth traits, microbial abundance, and community composition were analyzed. Compared to OM, peanut yields increased by 22%, 23%, and 18% under WB, WBSC, and MBSC, respectively. The content of oleic acid increased by 4–5%, while the content of linoleic acid decreased by 7–9%, respectively, under biochar–compost treatments. However, biochar amendment alone showed non-significant changes in these fatty acids. The soil extracellular enzyme activity increased by 3.7–5.5% with biochar amendments and 6.4–10.1% with biochar–compost application. The enzyme activity ratio of hydrolase to non-hydrolase, of C cycling to N cycling, and of P cycling increased by 11.4–15.9%, 20.9–33.8%, and 14.7–23.5% under biochar amendments and by 20.5–25.0%, 17.4–39.0%, and 23.5–32.3% under biochar–compost, respectively. Overall, crop residue biochar enhanced peanut yield and quality by improving soil aggregation, enzyme functionality, and fungal community in line with the soil nutrient supply.

Rapid dissolution of conventional fertilizers causes low nutrient-use efficiency and serious leaching losses, contributing to agricultural non-point source pollution. In this study, biomass-based slow-release fertilizer beads were prepared by ionic crosslinking of potato starch (ST), chitosan (CS), and corn-straw biochar (BC), using potassium nitrate (KNO₃) as the model nutrient. The effects of ST/CS ratio and BC incorporation on bead structure, swelling, nutrient loading, release kinetics, and soil-column leaching were systematically investigated. Biochar incorporation formed a more compact and interconnected porous network and reduced the equilibrium swelling ratios of ST90/CS10, ST80/CS20, and ST70/CS30 from 188%, 176%, and 164% to 168%, 136%, and 104%, respectively. Although BC slightly decreased KNO₃ loading capacity, it markedly slowed nutrient release; ST80/CS20/BC20 released 31.09%, 50.09%, and 81.82% of loaded KNO₃ at 24, 72, and 504 h, respectively, which were 28.40%, 25.27%, and 11.30% lower than those of ST80/CS20. Kinetic fitting indicated that BC reduced the apparent release rate and promoted diffusion-controlled release behavior. Soil-column experiments further showed that the beads reduced NO₃⁻-N and K⁺ leaching compared with free KNO₃, with ST80/CS20/BC20 showing the best balance between nutrient loading and release control. These results suggest that starch–chitosan–biochar beads are a promising biodegradable matrix for slow-release fertilizer applications.