Biowaste-derived, nanohybrid-reinforced double-function slow-release fertilizer with metal-adsorptive function

• A novel slow-release fertilizer was developed. • The lignin-clay nanohybrid was used to reinforce the function. • The novel fertilizer has nutrition slow release and metal-adsorptive functions. • The coating in the soil can gather micronutrients for the growth of plants. Bio-based slow-release fertilizers (SRFs) have drawn significant attention in resolving food scarcity issues, improving nutrient utilization efficiencies, and preventing environmental pollution. However, current SRFs still need to improve their release profile, reduce the bioresource cost, and resolve multiple environmental issues e.g., different types of soil/water contamination. In this study, we propose an original concept to fabricate double-function and environmentally friendly SRFs with a controllable fertilizer release function and strong adsorption capability of trace metals in soils. The hypothesis is that a hydrophobic nanohybrid synthesized from the low-cost lignin biowaste and clay allows the well-dispersion in the bio-based polyurethane matrix derived from readily available agriculture byproducts. The exfoliation of nanohybrid in the biopolymer membrane not only blocks the path of hydrophobic fertilizer release but also possesses cationic ions absorption function. The results show that the nanohybrid has a strong metal adsorption capability and the synthesized nanohybrid-based controlled-release fertilizers (CRFs) exhibit excellent N release longevity (more than one month). These multiple-function CRFs promote plant growth in trace-metal contaminant soil in a cherry radish matrix study. This work also provides a detailed examination of the synthesis of lignin clay hybrid biocomposite, the encapsulation of fertilizers by the biocomposite membrane, the study of the nutrient release profile, and the metal adsorption mechanism. For the first time, biobased and low-cost CRFs provide multiple functions including controllable fertilizer release, strong metal adsorption capability for soil remediation, or trace metal re-utilization, which is expected to open a new door for large-scale utilization of CRFs in a nutrient contaminant soil environment.