Switchable biomaterials for wastewater treatment: From material innovations to technological advancements

• Existing studies on switchable biomaterials for wastewater treatment are reviewed. • Switchable biomaterials offer sustainable and cost-effective solutions for wastewater treatment. • The stimulus-responsive properties of switchable biomaterials significantly enhance material recyclability. • Switchable cellulose is promising for large-scale practical applications. • Most of the current switchable biomaterials remain challenges in mechanical strength. Switchable biomaterials have emerged as promising solutions for sustainable and cost-effective wastewater treatment, leveraging stimuli-responsive functionalities for efficient pollutant removal and material recyclability. This review explores the applications and challenges of chitosan, polylactic acid (PLA), cellulose, biochar, rubber, resin, and crude fibers, emphasizing their adsorption capacities, stability, and scalability. Switchable cellulose materials, widely used in dye removal and oil–water separation, exhibit adsorption capacities of 10–52 g/g, yet require mechanical reinforcement for harsh wastewater environments. Heteroatom-doped biochar, with high surface areas (>500 m 2 /g) and porosities, achieves heavy metal adsorption efficiencies exceeding 90%, though feedstock variability affects consistency. Functionalized rubber, resin, and fibers demonstrate over 90% oil–water separation efficiency, benefiting from tunable surface properties and self-cleaning abilities. Despite these advantages, challenges remain in enhancing scalability, recyclability, and multi-contaminant adaptability. While mild regeneration methods, such as CO 2 bubbling and pH adjustments, reduce energy demands, synthesis processes still require optimization for industrial viability. Future efforts should focus on hybrid biomaterials, low-energy synthesis techniques, and integration into existing treatment systems to maximize their long-term sustainability and real-world impact.