Influence of crystal structure of polymorphic cotton cellulose on the adsorption and photocatalysis properties of biochar-TiO2 composites

Cellulose derived biochar can be used for adsorbent and photocatalyst mainly because of its good compatibility, high hydrophilicity, and the large amount of electron-rich hydroxy groups. Nevertheless, the impact of the crystal structure of cellulose on the absorption and photocatalytic efficiency of biochar-based composites derived from cellulose remains uncertain. Herein, four different types of biochar derived from cotton (cellulose I-beta, II, III, and IV) were individually impregnated with a TiO2 catalyst through hydrothermal and pyrolysis processes, and were analyzed using various characterization methods. Their adsorption behavior and photocatalytic activities were compared using Congo red and methylene blue dye as the model. The analysis and test outcomes suggested that the crystal structure of cotton cellulose impacted the pore structure and TiO2 content of biochar-TiO2 composites to different degrees, resulting in variations in the adsorption and photocatalytic capabilities of biochar-TiO2 composites. In comparison with cellulose II, III and IV, cellulose I derived biochar-TiO2 composite had a large specific surface area, a more stable structure, a high aromatic carbon content, and a high TiO2 loading, resulting in the strong adsorption ability and superior photoactivity to organic dyes. The adsorption and photocatalysis mechanisms were also clarified.