TA–APTES Coating Facilitated Secondary Reactions for Synthesis of Multifunctional Porous Melamine Sponge and Application in Wastewater Treatment

Secondary reactions induced by functional surface coating are of critical significance and have attracted substantial interest, as the surface coating can function as a versatile platform for designing multifunctional coatings by tailoring the surface performance. The surface coating incorporated tannic acid, and 3-aminopropyltriethoxysilane (TA-APTES) contains plentiful nanospheres with secondary reaction sites, which is favorable for surface modification. In this research, a TA-APTES coating with a unique hierarchical structure was grown in situ on the skeleton of a porous melamine sponge under mild conditions. The secondary reactions triggered by the TA-APTES coating were comprehensively employed to construct a multifunctional melamine sponge for various applications. The TA-APTES-coated melamine sponge was first immersed in silver ammonia solutions for the reduction of silver ammonia ions. The decoration of Ag NPs endowed the sponge with catalytic and antibacterial activity, which could be applied for dye reduction and bacterial disinfection in wastewater. The surface energy of the TA-APTES-coated melamine sponge was subsequently decreased by long-chain alkyl molecules. After the condensation polymerization reaction with octadecyltrimethoxysilane, the surface of the melamine sponge coated with TA-APTES was converted into a superhydrophobic state, making it suitable for efficient separation of oil and water mixtures. The prepared superhydrophobic sponge demonstrated remarkable water repellency and strong oil affinity with a water contact angle of 156.5° and oil contact angle of 0°. Significantly, the superhydrophobic sponge retained a relatively stable oil absorption capacity and separation efficiency after multiple recycling utilization. The proposed routine for fabrication and design of TA-APTES coating demonstrates the potential to develop a multifunctional porous melamine sponge in solving water pollution issues.