酸洗处理对生物质炭表面吸附特性及光谱特性的影响

Effect of Acid Elution on the Surface Structure Characteristics and Spectral Characteristics of Biochars

生物质炭表面灰分的存在会严重影响生物质炭的表面结构特性及吸附能力。采用HCl-HF对400和600℃两种温度制备的玉米秸秆生物质炭进行酸洗处理,去除生物质炭表面的灰分。通过对比酸洗前后玉米秸秆生物质炭的元素含量、比表面积、孔径分布、红外光谱分析图和吸附平衡试验结果探究酸洗处理对生物质炭表面吸附特性和光谱特性的影响。结果表明：酸洗处理能有效去除生物质炭表面存在的无机盐、焦油等一系列副产物,显著改变生物质炭的表面结构特性,提高生物质炭的吸附性能。（1）酸洗后生物质炭的碳含量相对增加,疏水性及芳香官能团含量增加,极性降低;（2）酸洗处理显著增加了生物质炭的比表面积,处理后炭比表面积分别增加了3.46倍和6.75倍;酸洗还显著提高了生物质炭的孔容及介孔含量,从而大大增加了生物质炭的吸附能力;（3）两种生物质炭酸洗前后的红外光谱上关键官能团峰强差异显著,尤其在3 398-3 447,2 924-3 056,1 378-1 439cm-1范围内,酸洗后生物质炭的振动峰强度显著减小,表明生物质炭在酸洗后其表面脂肪结构和羟基减少。（4）酸洗前后的吸附试验表明,酸洗处理能够去除炭表面的灰分,增加生物质炭的吸附位点,进而提高其对2,4-D的吸附量。

Biochar often refers to a carbon-rich product obtained by pyrolyzing biomass at relatively low temperatures（700℃）.The increasing interest in the applications of biochar in soil amendment and environmental contaminant reduction has spurred many studies in recent years.Due to the high content of ash in biochar,the adsorption capacity of bichar is limited.The ash of biochar formed during pyrolysis has great influence on the structure characteristics and spectral characteristics of biochar.The ash of biochar is expected to enchance their efficacy and minimize their influence.For this purpose,the corn straw biochar made at two different temperatures（400and 600℃）was used to study the effect on the structure characteristics of biochars under the acid elution.The samples were characterized with element analysis,Brunaner-Emmett-Teller-N2 surface areas,pore size distributions and micro infrared for structure analysis in this study.The result indicate that：the elution solvent could remove the by-products and improve the adsorptive capacity of biochars.（1）After acid elution,the carbon content,hydrophobicity and the aromatic functional group content were increased;the polarity of biochar was decreased.（2）After acid treated,the specific surface area of the biochars was significantly increased,the increment of two biochars was 3.46 times and 6.75times;the pore volume and the mesoporous quantity were also enhanced.（3）After acid elution,the infrared analysis is similar,but the content of key functional groups was different significantly.The result of infrared analysis showed that,several absorbance peaks were decrease at 3 398-3 447,2 924-3 056,1 378-1 439cm-1,and the acid treated can make the content of aliphatic chain char and hydroxyl reduce.（4）Biochar with low polarity and high aromaticity displayed a superior 2,4-dichlorophenoxyacetic acid adsorption capacity.Acid elution made the surface of biochar exposed more organic surface and porosity and it is one of the most important factors for the adsorption of biochar.The date with elemental analyzer,BET,FTIR techniques and batch experiment allowed us to develop a better understanding of evolution of biochar properties during the acid elution and these results have significant implications for using biochar as a soil additive for soil pollution.