田间老化生物质炭结构表征及吸附铵态氮效应

Structural Characterization of Field-aging Biochar and Its Adsorption Effect on Ammonia Nitrogen

为探讨田间自然老化生物质炭对土壤铵态氮持留性能的影响机制,通过田间原位埋置尼龙袋法和室内批量平衡吸附试验,采用场发射扫描电镜、BET比表面、差热与热重等分析技术,研究田间自然老化1年(A1)、2年(A2)和3年(A3)的生物质炭的表面结构特征等理化性质的动态变化及其对铵态氮吸附效应的影响。研究结果表明,田间自然老化3年的生物质炭表面孔隙结构塌陷明显,随着田间老化时间增加,生物质炭的BET比表面积、总孔容、介孔孔容与平均孔径增加,而微孔表面积减少,与新鲜生物质炭(A0)相比,A3处理生物质炭的BET比表面积、总孔容和平均孔径分别增加18.93%、42.31%和20.71%,微孔表面积减少26.17%;碳和氮元素含量分别增加7.92%和95.61%,生物质炭的芳构化程度有所降低,热稳定性下降。随着田间老化时间的增加,生物质炭对铵态氮吸附量明显减少,吸附量大小为A0>A1>A2>A3,但生物质炭依然保持较强烈的吸附性。批量平衡吸附试验表明准二级吸附动力学与Langmuir模型能更好地拟合生物质炭对铵态氮的吸附过程,揭示了生物质炭对铵态氮的吸附机制主要为单分子层化学吸附,其次为物理吸附。综上,生物质炭对碳、氮素的富集效应及对铵态氮的吸附机制研究对于生物质炭在农田土壤生态系统中发挥固碳和氮素增效作用上具有积极意义。

【Objective】Biochar application in soil has a positive effect on reducing nitrogen loss and improving nitrogen utilization efficiency.However,information on the interaction between naturally aged biochar and nutrients in the field is limited.Exploring the influence mechanism of aged biochar on soil nitrogen retention is helpful to further understand the environmental and chemical process of biochar in soil.【Method】The method of in-situ embedding of biochar in nylon bags in the field and batch equilibrium adsorption experiment in the laboratory were carried out.The field experiment included four treatments,namely fresh biochar(A0),aged biochar for one year(A1),two years(A2)and three years(A3).The dynamic changes of surface structure characteristics and physicochemical properties of aged biochar and their effects on 4+NH-N adsorption were investigated using scanning electron microscopy,BET-specific surface,differential thermal and thermogravimetric analysis techniques.【Result】The results showed that the surface pore structure of biochar after naturally aging for three years in the field collapsed.With the increase of field aging time,the BET-specific surface area,total pore volume,mesoporous pore volume and average pore size of biochar increased,while the micropore surface area decreased.Compared with the A0 treatment,the BET-specific surface area,total pore volume and average pore size of biochar in the A3 treatment increased by 18.93%,42.31%and 20.71%,respectively,and the micropore surface area decreased by 26.17%.With respect to the chemical structure of aged biochar,the contents of C and N elements increased by 7.92%and 95.61%,respectively,and the aromatization degree and thermal stability of biochar decreased.With the increase of field aging time,the amount of 4+NH-N adsorbed by biochar decreased in the order A0>A1>A2>A3,although aged biochar maintained a strong adsorption capacity.Also,batch equilibrium adsorption experiments showed that the adsorption rate of biochar to 4+NH-N complied with the pseudo-second-order adsorption kinetics and Langmuir models.【Conclusion】The present study suggests that the adsorption of 4+NH-N to biochar mainly occurred through the single-molecular layer mechanism,followed by physical adsorption.Therefore,studies on the enrichment effect of biochar on carbon and nitrogen and the adsorption mechanism of 4+NH-N are significant in exerting carbon sequestration and improving nitrogen utilization efficiency in the soil ecosystem for biochar.