Preparation and adsorption-photocatalysis properties of biochar/ZnO composites

The nano crystalline cellulose (NCC)/ZnO nano hybrids were prepared with a procedure of in-situ polymerization using NCC as a morphological-inducing template, and Zn acetate (Zn(CH₃COO)₂·2H₂O) as a Zn source, respectively. The NCC/ZnO nano hybrids were then carbonized at 550℃ to obtain biochar/ZnO composites. The morphology, crystal structure, pore texture and light absorption performance of biochar/ZnO composites influenced by a mass ratio of biochar to ZnO (0.03:1, 0.17:1, 0.67:1) were characterized by TEM, XRD, BET and UV-Vis spectroscopy. The adsorption-photocatalysis performance of biochar/ZnO composites was investigated through removing methylene blue (MB) under UV light irradiation, and the mechanism of biochar/ZnO composites was further studied. The results indicate that the NCC transforms to biochar with graphite crystallite and skeleton structure after a carbonization process at 550℃. The nano ZnO particles are uniformly deposited on the surface of biochar, and then the biochar/ZnO composites are obtained. The obtained biochar/ZnO composites exhibit higher surface area and better absorbability compared with the neat nano ZnO. And the biochar improves the separation of photogenerated electrons and holes of ZnO. The biochar/ZnO composites remove MB with a synergistic effect of adsorption and photocatalysis. In particular, the biochar/ZnO composite has an average pore diameter of 188.99 nm, and a specific surface area of 33.51 m²/g respectively at the mass ratio of 0.17:1 (biochar to ZnO). Consequently, the biochar/ZnO composite has an optimum degradation efficiency to MB, corresponding to 99.8% degradation rate of MB after the absorption for 30 min in dark condition and continuous irradiation for 20 min under 500 W UV light at room temperature.