化学老化后稻壳生物炭理化性质的改变及微观结构表征

Characterization of physicochemical properties and microstructure of rice husk-derived biochar after chemical aging

为研究化学老化对生物炭理化性质与微观结构的影响,本研究采用H2O2、HNO3老化不同温度(350℃和550℃)下制备的稻壳生物炭,并利用元素分析、扫描电镜、漫反射红外光谱、X射线光电子能谱等测定比较生物炭老化前后表面理化性质及微观结构的变化.结果表明,经两种氧化剂老化后两种生物炭中O元素含量及O/C原子比均增加.与老化前生物炭相比,老化后两种生物炭中羟基、羧基、酮羰基、脂肪醚、酯基等含氧官能团的含量均发生不同程度的变化.通过漫反射红外与X射线光电子能谱分析相结合,发现两种稻壳生物炭经H2O2、HNO3老化后均生成了羟基、羧基等含氧官能团,从而使得生物炭极性增加.此外,经HNO3老化后稻壳炭表面生成硝基、硝酸盐等含氮基团,N元素含量亦显著增加.但氧化剂对两种温度下制备的生物炭中炭元素含量影响存在差异:经H2O2、HNO3氧化后550℃制备的生物炭(R550)中C元素含量与芳香性降低;而经H2O2氧化后,350℃制备的生物炭(R350)中C元素含量与芳香性均上升.

This study was conducted to investigate the effects of chemical aging on the physicochemical properties and microstructure of biochar.After oxidation by H2O2 and HNO3,rice husk biochars (produced at 350℃ and 550℃ respectively) were characterized by elemental analyzer,scanning electron microscopy,diffuse reflection Fourier-transformed infrared spectroscopy (DRFIRT),and X-ray photoelectron spectroscopy (XPS).The results showed that both the O contents and O/C ratios increased in the two biochars by oxidation with H2O2 and HNO3.After chemical aging,the contents of oxygen-containing functional groups,such as hydroxyl,carboxyl,ketonic carbonyl,aliphatic ether and ester group,changed to different degrees in the two oxidized biochars.After analysis on the results from DRFIRT and XPS results,it was found that the increasing polarity of biochar was resulted from the generation of hydroxyl and carboxyl group after aging by H2O2 and HNO3.In addition,the nitrogen contents were significantly increased after aging,which was attributed to the formation of nitryl,nitrate and other nitrogenous groups on the surface of biochar by oxidation with HNO3.However,the different effects of chemical aging were detected on the carbon contents of these two kinds of biochars.The C contents and aromaticity were increased in the biochar R350 oxidized by H2O2,while the C contents and aromaticity were decreased in the biochar R550 respectively oxidized by H2O2 and HNO3.