生物质炭/ZnO复合材料的制备及其吸附-光催化性能

以纳米晶纤维素（NCC）为形貌诱导模板，醋酸锌（Zn（CH₃COO）₂·2H₂O）为Zn源，采用原位聚合法制备NCC/ZnO纳米杂化物，再经550℃高温碳化，得到生物质炭/ZnO复合材料。采用TEM、XRD、BET、UV-Vis测试研究生物质炭与ZnO固体质量比（0.03:1、0.17:1、0.67:1）对生物质炭/ZnO复合材料形貌、晶体结构、孔结构及光吸收性能的影响。并进一步以亚甲基蓝（MB）为模型污染物，研究生物质炭/ZnO复合材料的吸附-光催化性能，阐明其吸附-光催化机制。结果表明，经550℃高温碳化后，NCC转化为具有石墨微晶结构的生物质炭，其骨架结构得以保留，纳米ZnO均匀负载在生物质炭表面，形成生物质炭/ZnO复合材料。与纯纳米ZnO相比，生物质炭/ZnO复合材料比表面积显著提高，具备优异的吸附性能，同时，NCC转化得到的生物质炭有效提高了ZnO的光生电子-空穴对的分离率。生物质炭/ZnO复合材料通过吸附-光催化协同效应去除水体中的MB，去除率显著增加。当生物质炭与ZnO的固体质量比为0.17:1时，生物质炭/ZnO复合材料的平均孔径为188.99 nm，比表面积为33.51 m2/g，在室温条件下，避光吸附30 min后，再使用500 W紫外灯照射20 min，即对MB降解率达到99.8%。 

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.