生物炭老化后理化性质及微观结构的表征

Characterization of the physical and chemical structures of biochar under simulated aging condition

在长期降水淋洗或温室效应产生酸雨等环境影响下,施入土壤中的生物质炭会随时间的推移而逐渐发生老化作用,而其老化后理化性质及结构等如何改变是广受关注的新问题.本文通过水洗和酸化两种方法对花生壳生物炭进行模拟老化试验,并利用元素分析仪、扫描电镜(SEM)、X射线衍射光谱(XRD)和傅立叶红外光谱分析仪(FTIR)研究生物炭老化前后的理化性质及结构差异.结果表明:(1)生物炭经老化处理后p H值均下降,且酸化生物炭(acidulated biochar,AB)比水洗生物炭(washing biochar,WB)的下降程度大;另外,WB的O/C和(O+N)/C分别下降了8.89%和10.42%,而AB的O/C和(O+N)/C却升高了11.11%和14.58%,表明生物炭老化后其亲水性和极性发生改变;且WB和AB的碱性元素总量分别比原生物炭(primary biochar,PB)下降了26.53%和88.78%,说明生物炭老化后有较多的碱性元素被释放.(2)与原生物炭相比,生物炭水洗老化后表面较平整且微孔结构保持完好,而酸化老化后表面较粗糙、微孔结构严重破坏.(3)生物炭老化后,其表面Al_2SiO_5和SiO_2晶体的含量均明显下降;与PB相比,WB新增加了1166 cm^(-1)和1082 cm^(-1)特征峰2个;而AB新出现了1705 cm^(-1)、1622 cm^(-1)和1546 cm^(-1)特征峰3个,并减少了466 cm^(-1)这个振动峰,且其他特征峰的吸光度较原生物炭整体降低,说明生物炭在老化过程中其含氧官能团增加,而其它官能团数量和其表面的晶体含量都有所减少.因此,生物炭在一定环境作用下,其老化过程中一些元素释放而含量减少,且导致物质结构的破坏.

Biochars added into the soil are agedas time goes on under the influence of the environment such as long-term precipitation leaching or acid rain caused by greenhouse effect. The change of physic-chemical properties and structure are the new problems which have attracted wide attention. The aim of this study was to investigate the aging process of peanut shells biochar by washing and acidification. The physic-chemical properties and structure of biochar and aged biochar were characterized by elemental analysis,scanning electron microscopy（ SEM）,X-ray diffraction spectroscopy（ XRD） and Fourier-transformed infrared spectroscopy（ FTIR）. The results showed that：the p H of biochar declined after the two treatment,and the acidified biochar（ AB） dropped more than washed biochar（ WB）. Moreover,the O/C and（ O ＋ N）/C ratio of WB decreased by 8. 89%and 10.42%,but the ratios of AB increased by 11. 11% and 14. 58%,respectively. These suggest that aging process changed the hydrophilicity and polarity of the biochar. In addition,compared with primary biochar（ PB）,the total content of alkaline elements of WB and AB was reduced by 26.53%and 88. 76% respectively,indicating that more alkaline elements were released after the biochar aging. Compared with PB,the surface of the washed biochar was smoother and the microporous structure remained intactly. However,the surface of biochar was rough and microporous structure was disrupted severely after acidification. The content of the crystal structure of Al2SiO5 and SiO2 was decreased obviously during aging process. Compared with PB,the characteristic peaks at 1166,1082 cm（-1） appeared due to the aging process of the washed biochar,and the characteristic peaks at1705,1622 and 1546 cm（-1） appeared and the characteristic peaks at 466 cm（-1） disappeared due to the aging process of the acidified biochar. Meanwhile the relative absorbance of other peaks was reduced indicating that the amount of oxygen functional groups increased in the process of aging. At the same time,the other functional groups became less and the content of crystal was reduced. Therefore,under a certain environment,during the aging process of biochar,some elements were released and their contents were reduced,which lead to the destruction of the material structure.