High-performance adsorbents from spent coffee grounds modified with natural deep eutectic solvents

Abstract

A large quantity of agricultural waste, specifically spent coffee grounds (SCG), is generated globally each year. Developing efficient and safe methods for modifying SCG into high-performance adsorbent materials has become a popular research focus. This study, for the first time, proposes a novel chemical modification approach using natural deep eutectic solvents (NaDES) to directly treat SCG, resulting in the preparation of a new adsorbent material (SCG-NaDES) with enhanced adsorption capacity and improved safety for wastewater treatment applications. SCG-NaDES with the highest Pb(II) adsorption capacity (35.95 mg/g) was obtained under the following preparation conditions: a molar ratio of 1:2 for choline chloride and urea, a mass ratio of 1:5 for SCG to NaDES, and thermal treatment at 120 °C for 2 h. This adsorption capacity is 1.67 times higher than that of the original spent coffee grounds. This significant improvement can be attributed to the optimization of the porous structure and the increased number of surface functional groups during the NaDES treatment process, as confirmed by FTIR, ¹H NMR, and Boehm titration analyses. Compared with untreated SCG, SCG-NaDES exhibits superior safety, as it releases minimal pigments and environmentally harmful organic acids upon contact with water. Interestingly, while chemically modifying SCG, the NaDES process also facilitates the extraction of high-value bioactive compounds from SCG, such as caffeine and kahweol acetate. This extraction process could potentially lower the production cost of SCG-NaDES. This study provides a novel approach and technical pathway for the high-value utilization of agricultural biomass waste and the development of environmentally friendly water treatment materials, offering broad application prospects and significant implications for sustainable development.