One-way conformation memory polymers for unidirectional removal of dyes and hot wastewater reuse from textile effluents

Abstract

Thermoresponsive polymers that adapt their conformation transition from coil to globule in response to temperature change have aroused great interest in the last two decades. However, thermally induced phase separation behavior often involves dynamically reversible switching between two distinct conformations during multiple heating–cooling cycles, which hinders their potential applications in many directional, nonreturn molecule delivery systems. Here, inspired by a nonreturn valve, a new class of thermo-irreversible starch derivatives (TIRS) is presented. As an unprecedented one-way conformation memory polymer, TIRS exhibits usual lower critical solution temperature type fast responses to temperature stimuli, but this phase transition behavior involves ir-reversible switching upon cooling. The extent of hysteresis (reversible, semi-reversible and ir-reversible) between heating and cooling ramps can be fine-tuned by varying the degree of substitution of starch derivatives. The unique conformation-adaptive feature of TIRS makes it a very interesting candidate for the unidirectional removal of dyes and hot wastewater reuse from textile effluents. TIRS shows a maximum dye uptake capacity of 3984 mg/g and excellent decoloration efficiency of 99.6% at optimized flocculation conditions. After flocculation with dyes, the temporary conformation of flocs can be memorized and self-locked due to the unidirectional solubility switching of TIRS from water-soluble flocculants to water-insoluble adsorbents, which avoids unnecessary desorption and re-solubilization of the flocculant. Clarified hot water can be employed as reuse water in new dyeing operations due to low flocculant residues in reclaimed water. This work offers a new approach to design and fabricate check-valve-like materials for self-adaptive, ir-reversible smart delivery systems.