"Using waste straw to prevent pollution": Enabling closed-loop design of chrome-free tanning agent with tanning-masking dual effect.

Abundant waste crop straw produced in China will be disposed, causing severe pollution to environment. Therefore, it is still a challenge for the cleaner treatment technology and high-value utilization. In this study, we extracted the biochemical fulvic acid (BFA) from crop straw, and then synthesized a novel biomass-based tanning agent (BAA) by coordination of BFA with Al. The self-developed BAA represented tanning-masking dual effect, as well as the BAA-tanned leather demonstrated superior thermal stability (shrinkage temperature: 90.2 °C) and mechanical properties (thickening rate: 104.5 %), surpassing conventional aluminum-tanned leather. Importantly, the tanning wastewater containing residual BFA was recycled as liquid fertilizer for irrigation of crops, exhibiting significant enhancement in plant height (23 %), stem width (18 %), and leaf width (15 %). In the meantime, the aluminum content in irrigated crops (<68.7 mg/kg) was less than the threshold value required by national food safety standards. This study provides a novel way for the high-value utilization of waste crop straw as cleaner chrome-free tanning agents, ultimately achieving the holo-ecological recycling. The innovative closed-loop utilization of crop straw both holds significant potential for sustainable development of agriculture and leather industry.