Imidazolium-based ionic liquid immobilized hydrochar: Surface engineering of distillers dried grains with solubles for enhanced adsorption of Cr(VI) and Tartrazine

The release of toxic heavy metals and synthetic dyes into water bodies poses serious environmental and health concerns, driving the need for efficient and sustainable remediation technologies. In this work, a novel ionic liquid immobilized hydrochar (IL@DDGS-HC) was synthesized from distillers dried grains with solubles (DDGS), an abundant bioethanol industry by-product, for the removal of hexavalent chromium [Cr(VI)] and Tartrazine dye from aqueous solutions. The hydrochar was produced via hydrothermal carbonization and subsequently functionalized through chloroacetylation, imidazole grafting, and quaternization to introduce an imidazolium-based ionic liquid. The material characterization confirmed successful ionic liquid immobilization, enhanced surface functionality, and improved porosity, with the BET surface area increasing from 5.51 to 17.52 m 2 /g. Batch adsorption studies demonstrated superior performance of IL@DDGS-HC compared to raw DDGS and unmodified hydrochar, achieving maximum removal efficiencies of 95% and 93% for Cr(VI) and Tartrazine at pH 3 and pH 7, respectively. Adsorption equilibrium data were best described by the Redlich–Peterson isotherm, indicating predominantly monolayer adsorption, with maximum capacities of 284.4 mg/g for Tartrazine and 63.0 mg/g for Cr(VI), respectively, at 303 K. Kinetic analysis revealed pseudo-first-order behavior for Tartrazine and pseudo-second-order behavior for Cr(VI). Overall, IL@DDGS-HC represents a sustainable and highly effective adsorbent for water purification.