Fatigue resistance, re-usable and biodegradable sponge materials from plant protein with rapid water adsorption capacity for microplastics removal

Microplastics in water environment has become a particular concern to global ecosystems and attracted wide attention in recent years. Sponge materials have been developed for efficient removal of various water pollutants including organic dyes. However, such sponge materials for microplastics removal has seldom been explored. Herein, a natural and biodegradable sponge material with high mechanical properties was fabricated from plant protein through chemical crosslinking with a compressive strength of 176 kPa and Young’s modulus of 60.1 kPa. After 100 compression cycles at compressive strain of 70%, the mechanical properties of sponge still remained up to 90%, which shows excellent fatigue-resistance close to commercial polyurethan sponges. The abundant active side chains on amino acid residues have provided the protein sponge good capacity to adsorb microplastics (removal efficiency up to 81.2%) at pH range pH 6–9 with an initial microplastic concentration of 1 mg L−1, which presents the pH and MPs concentration of water systems. The adsorption kinetic study suggested that the hydrophobic interactions and the intra-particle diffusion were driving the adsorption process. The sponge possessed highly interconnected porous structure (83%), thus showed fast adsorption ability to microplastics with 38% adsorbed onto the sponge within 10 s. The entrapped water can be released from the sponge simply by squeezing for cyclic use and the fast adsorption ability was still maintained after 20 cycles. In addition, the sponge demonstrated good be biodegradability, thus avoiding secondary contamination when applied for water treatment. This research has provided new thinking of sponge material fabrication from sustainable plant protein raw materials, and the sponge showed potential to be used as a biodegradable material for microplastic removal.