Engineering pH-responsive multifunctional amphoteric triazine derivative for high-strength and color-enhanced sustainable leather

Amphoteric compounds as metal-free alternatives offer a promising pathway to address the environmental and health challenges associated with chromium salts, as well as the charge mismatch between organic tanned leather and anionic dyes. Herein, we design a multifunctional amphoteric triazine derivative (EDTB) through synergistic modulation of reactivity, molecular size, and surface charge, which features multiple active chlorines, pH-responsive aggregation behavior, and high isoelectric point to achieve efficient tanning and enhanced dyeing performance. EDTB can assemble to form micron-scale aggregates through electrostatic interactions, which enables uniform diffusion and multipoint covalent crosslinking within collagen matrix, while regulates the interfacial electrostatics of fiber to improve the absorption and fixation of dyes. The EDTB-tanned leather exhibits superior hydrothermal stability ( T s ∼82 °C), mechanical strength (tensile strength >24 MPa, tear strength >66 N/mm), and color depth (K/S value of 15.0) compared to leather tanned with commercial tanning agent (i.e., F-90). Moreover, the pickling- and basifying-free EDTB tanning system demonstrates reducing chloride discharge, improving wastewater biodegradability, and lowering the carbon footprint by over 40% relative to chrome tanning. This work establishes a versatile amphoteric triazine-based tanning strategy integrating high tanning efficiency and dyeing assistance, offering a practical and scalable solution for advancing sustainable leather manufacturing.