Cross-linked chitosan–carboxymethyl chitosan/nano-TiO₂ composite membrane for efficient microplastic removal from seawater

Microplastic contamination in marine environments has emerged as a critical environmental issue due to its persistence and potential ecological impacts. The development of biodegradable membranes combining filtration and photocatalytic functionalities represents a promising strategy for microplastic remediation. In this study, chitosan–carboxymethyl chitosan (CS–CMC) composite membranes incorporated with nano-TiO 2 were developed for microplastic removal and degradation from seawater. Nano-TiO 2 was synthesized from TiCl 3 via coprecipitation and incorporated into CS–CMC membranes fabricated using the phase inversion method. The resulting materials were characterized through physicochemical, morphological, and thermal analyses, while membrane performance was evaluated in terms of swelling behavior, mechanical properties, permeation flux, rejection efficiency, and photocatalytic activity. The synthesized nano-TiO 2 exhibited anatase crystallinity with an average particle size of 221.96 nm and a polydispersity index of 0.0013. Nano-TiO 2 incorporation influenced the structural and filtration characteristics of the membranes. Among the fabricated membranes, M1 containing 1.3% nano-TiO 2 demonstrated the most balanced performance, achieving the highest rejection coefficient (88.46%), the highest tensile strength, and a permeation flux of 2.23 L m −2 h −1 . Characterization of the optimal membrane confirmed the successful integration of nano-TiO 2 within the CS–CMC matrix, resulting in a porous structure with good thermal stability. Photocatalytic testing reduced the microplastic concentration from 112.5 to 65 particles μL −1 following UV irradiation and was accompanied by observable morphological fragmentation of the microplastic particles. These findings demonstrate the potential of CS–CMC–nano-TiO 2 composite membranes as sustainable materials for integrated microplastic filtration and photocatalytic treatment in seawater purification applications.