纳米生物炭的制备方法比较及其特性研究

本研究以常见农林废弃物—果木枝条、玉米秸秆和花生秸秆为原料，在350~550℃条件下热解制得五种本体生物炭；采用离心法、球磨法、球磨+离心法3种方法提取纳米生物炭，进而对本体生物炭和纳米生物炭的比表面积、元素含量、矿物组成和表面化学性质等进行比较，以探究物料来源、热解温度和制备方法对纳米生物炭性质及稳定性的影响.与本体生物炭相比，球磨法制得的纳米生物炭比表面积增大1.36~6.94倍，但产物未达到纳米颗粒级别，且在水体中稳定性较弱；球磨+离心法制得的纳米生物炭直径为70.06~103.43nm，在水体中稳定性强；离心法制备的纳米生物炭各项指标均不如其他两种方法.纳米生物炭的产率为2.27%~34.80%，且产率随温度的升高而降低.与本体生物炭相比，纳米生物炭含有更多的羟基等含氧官能团和更少的脂肪碳链.与果木枝条制备的纳米生物炭相比，玉米秸秆和花生秸秆来源的纳米生物炭产率高，但水稳性较差，易发生凝聚.果木枝条来源的纳米生物炭碳酸盐等碱性矿物含量丰富，且由于颗粒表面含氧官能团数量多而zeta电位绝对值高，悬液可以稳定分散.不同方法制备得到的纳米生物炭优缺点各异：球磨法制得的纳米生物炭比表面积更大；球磨+离心法制备的玉米和花生秸秆纳米生物炭的产率更高；低温热解果木炭提取的纳米生物炭水稳性更强.

Preparation methods and properties of nanobiochars

In the present study, three common agricultural wastes, namely corn straw, peanut straw and fruit tree branches were chosen as raw material, and five bulk biochars were produced by pyrolysis at temperature of 350~550℃; Furthermore, the corresponding nanobiochars were extracted by three methods:centrifugation method, ball-milling method and ball milling+ centrifugation method. To investigate the effects of material source, pyrolysis temperature and preparation method on the properties and stability of nanobiochar, the specific surface area, element content, mineral composition and surface chemical properties of bulk biochars and nanobiochars were characterized and compared. The results showed compared with bulk biochars, the specific surface areas of biochars prepared by ball-milling method were increased by 1.36~6.94 times, but their diameters were higher than 100nm, and their suspensions were unstable. The diameters of nanobiochars prepared by ball-milling+centrifugation method were 70.06~103.43nm, which were well dispersed in water. Nanobiochars prepared by centrifugation method did not fall into the regime of nanoscale, and their suspensions were unstable. The yields of nanobiochars prepared by ball-milling+centrifugation method were 2.27%~34.80%, and the yields decreased with the increase of temperature. Compared with bulk biochars, nanobiochars contained more oxygen-containing functional groups such as hydroxyl groups and fewer fatty carbon chains. The nanobiochar yields of corn and peanut straws were higher than that of fruit tree branches, but the nanobiochar suspensions of corn and peanut straws were less stable and prone to coagulation. The nanobiochars derived from fruit trees branches were rich in carbonates and other alkaline minerals; their higher surface oxygen-containing functional groups resulted in larger absolute zeta potentials and more stable suspensions. In conclusion, the specific surface area of nanobiochars prepared by ball-milling method were larger, the yields of corn and peanut straw nanobiochars prepared by ball milling+centrifugation method were higher. The suspensions of nanobiochars extracted from fruit tree branches at low temperature were rather stable.