Surface Engineering of SRMIST-2 Using Amine-Functionalized Polyhedral Oligomeric Silsesquioxane for Tunable Wettability and Sustainable Oil-water Separation

Abstract

Oil spills and industrial pollutants represent a severe and enduring danger to aquatic ecosystems and global environmental stability. These contaminants not only degrade water quality but also initiate a cascade of environmental issues that can impact global climate patterns. To address this urgent challenge, metal–organic frameworks have emerged as promising materials due to their structural versatility, high surface area and tunable porosity. However, the inherent hydrophilic nature of MOFs limits their direct applicability in oil absorption and selective separation processes. To overcome this limitation, surface engineering of MOFs is a viable strategy to impart hydrophobicity, thereby enhancing wettability, selectivity, and long-term stability. In this study, we report the fabrication of an environmentally friendly, hydrophobic POSS-NH2@SRMIST–2 material via a solvent-assisted surface grafting method. The material combines strontium-based SRMIST–2 and amine-functionalized polyhedral oligomeric silsesquioxane (POSS-NH2). The incorporation of POSS-NH2, a low-surface-energy and environmentally benign modifier, transforms the originally hydrophilic MOF into a hydrophobic material with a WCA of 140±2°. The resulting material demonstrated excellent performance in the selective adsorption of oils and organic solvents from water mixture, exhibiting both high absorption capacity and material stability. When coated onto polydopamine-modified melamine sponges, the POSS-NH2@SRMIST–2@PDA@MS achieved an exceptional absorption capacity of up to 12,515 wt%, with oil/solvent separation efficiencies exceeding 94% and water rejection rates above 95%, sustained over 30 reuse cycles. Furthermore, the POSS-NH2@SRMIST–2@PDA@MS displayed outstanding performance in water-in-oil emulsion separation, achieving a separation efficiency of 99% for oil and a water rejection rate of 99.9%. The material also exhibited remarkable chemical, mechanical, and thermal stability; even after repeated exposure to corrosive media, mechanical abrasion, and thermal treatment, the sponge maintained its hydrophobic character with WCAs ranging from 138±2° to 148±2°. The POSS-NH2@SRMIST–2@PDA@MS represents a sustainable, scalable, and cost-effective solution for oil–water separation. Its fluorine-free composition, high durability, and excellent reusability make it a promising candidate for practical environmental remediation, particularly in the context of green and sustainable separation technologies.