Chitosan@TiO₂ composites for the adsorption of copper(II) and antibacterial applications

Chitosan (CS) is a biopolymer that is well known for its ubiquity, biodegradability, lack of toxicity, low cost, antibacterial activity, and excellent heavy metal adsorption ability. We synthesized CS and CS@TiO₂ composites (CST) with different concentrations of glutaraldehyde (crosslinking agent) solution by a simple method involving a crosslinking process (using glutaraldehyde as the crosslinking agent), a freeze-drying technique, and exchange with ammonia solution. The interaction mechanisms of the as-synthesized samples were systematically characterized by scanning electron microscopy, electron dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and the Brunauer-Emmett-Teller method. Among the as-synthesized samples, 3%CS-V (CS composites synthesized using 3% glutaraldehyde for crosslinking and exchanged with ammonia solution) at an initial concentration of 300 ppm exhibited a preferable adsorption capacity for copper ions (Cu²⁺), with a maximum adsorption capacity of 31 mg g^{− 1}. Sorption equilibrium isotherms fit the Freundlich model. Compared to CS, 7%CST-V (CST composite synthesized using 7% glutaraldehyde for crosslinking and exchanged with ammonia solution) exhibited higher antibacterial activity against Staphylococcus epidermidis due to a synergistic effect. The antimicrobial efficacy against Escherichia coli was more affected by copper ions than TiO₂ addition and glutaraldehyde concentration, whereas the antimicrobial efficacy against S. epidermidis was more affected by TiO₂ addition and exchange with ammonia solution.