From Waste to Resource: Surface-Engineered Spent Coffee Grounds as a Sustainable Adsorbent for Oil-Water Separation

Oil pollution in water is a serious issue worldwide thaturgently requires an efficient and cost-effective method for separatingoil-water mixtures. Selective adsorption using solid adsorbentsis a promising approach. However, conventional oil-cleaning adsorbents,which are typically derived from non-renewable resources, are expensive,environmentally harmful, incapable of separating oil-wateremulsions, or inefficient in recovering the adsorbed oil. Thus, wedeveloped a sustainable method for cleaning oil pollution that addressesenvironmental challenges and utilizes functionalized organic waste.Superhydrophobic SiO2 nanoparticle-fabricated spent coffeegrounds (SSD-SCGs) were developed, which rapidly adsorb various oilsin water, including viscous crude oil, in both ambient and harsh chemicalenvironments, with 98.5-99.7% removal efficiency. Our separationmethod is an energy-efficient, single-unit, flow-through, and gravity-drivensystem. Furthermore, the unique wettability and hierarchical porosityof the SSD-SCGs enable the effective separation of oil-seawateremulsions. The recovery of adsorbed oils and regeneration of the adsorbentwere easily achieved through mechanical compression. After multipleuses, the SSD-SCGs were converted into coffee logs, a fuel sourcewith a high heat value, thereby realizing the goal of converting wasteto energy. A life-cycle assessment revealed that the SSD-SCGs hadgreater positive environmental and economic impacts than conventionalSCGs. This study reveals an avenue for converting agricultural wasteinto advanced functional materials to address multiple challengesrelated to the United Nations Sustainable Development Goals.