竹炭改性及其对糠醛的吸附性能研究

MODIFIED BAMBOO CHARCOAL AND ITS PERFORMANCE OF ADSORBING FURFURAL

对竹炭采用KMnO_4氧化和高温N_2活化两种方式进行改性,对改性前后的竹炭采用元素分析、N_2等温吸脱附、Boehm滴定、傅里叶红外变换等方法进行物化表征;研究原始及改性后竹炭对糠醛的吸附特性。结果表明:KMnO_4氧化对竹炭表面官能团的种类改变不明显,只在局部引入某些新的官能团,却可减小竹炭的比表面积;高温N_2活化使竹炭结构中有机质大量分解、比表面积明显提高、微孔比例增大。对于表面化学特性,KMnO_4氧化改性可增大竹炭表面酸性含氧官能团的含量,竹炭经高温N_2活化改性后因引入吡喃酮等结构使表面呈碱性。吸附特性表明高温N_2活化处理的竹炭具有极好的吸附特性;进一步的机理分析表明,竹炭的微孔区是糠醛分子的有效吸附区域,较大的比表面积和微孔孔容有利于糠醛的脱除,而竹炭的表面化学特性同样对糠醛的吸附起到重要作用,其中表面酸性含氧官能团的增多不利于糠醛的脱除,而碱性基团因能增强竹炭表面石墨层与糠醛分子间的π-π作用力使吸附作用增强。

Bamboo charcoal was modified by means of chemical treatment with temperature nitrogen flow. Both the fresh bamboo charcoal sample and the KMn04 and thermal treatment under high modified samples were characterized by elemental analysis, nitrogen adsorption-desorption isotherms, Boehm titration and Fourier-transform infrared spectroscopy to get the information of the structure and surface chemical property of the bamboo charcoals. The behaviors of adsorbing furfural were also evaluated. The results show that the treatment with KMn04 has little influence on the changing in types of functional groups on the bamboo charcoals, but causing the reduction of the surface areas. Thermal treatment under nitrogen flow causes the decomposition of the functional group in bamboo charcoal, and the increase of surface area and microporous ratio. The treatment with KMn04 causes the introduction of a significant number of oxygenated acidic surface groups onto the bamboo charcoal surface, while the heat treatment increases the basicity of the bamboo charcoal. The adsorption results show that the thermal treatment sample has the best adsorption capacity. Further mechanism analysis shows that the microporous area of bamboo charcoals is effective area for adsorbing furfural, larger specific surface area and micropore volume benefit desorption of furfural. The surface chemical properties of bamboo charcoals also play an important role in adsorbing furfural. It is observed that the higher the total acidity number of oxygen surface groups is, the lower the desorption capacity of furfural is. The increase of π-πinteraction between graphite layer of bamboo charcoal and furfural molecules led by the basic groups can strengthen the adsorption function.