微纳米含氮秸秆生物炭对Pb^(2+)的吸附特性与机理

Performance and Mechanism of Pb^(2+)Adsorption by Micro-nano-engineered Nitrogenous Biochar

将玉米秸秆生物炭进行改性制备得到微纳米含氮生物炭(NBC),并与目前研究较多的铁改性生物炭(FeBC)和巯基改性生物炭(SBC)进行比较,利用扫描电镜(SEM)、BET比表面积测试法等技术对改性生物炭进行表征,通过批量吸附试验分析NBC对Pb^(2+)的吸附行为,比较吸附前后生物炭表面官能团的变化,并结合连续解吸试验探讨NBC对Pb^(2+)的吸附机制。结果表明,NBC的比表面积和总孔体积分别是未改性生物炭的6.30和2.68倍,且与未改性生物炭相比,NBC芳香性增强、亲水性和极性减弱。3种改性生物炭对Pb^(2+)的吸附能力表现为NBC>FeBC>SBC。NBC对Pb^(2+)的等温吸附过程更符合Langmuir模型,为单分子层吸附,最大吸附量为148.25 mg·g^(-1),分别是FeBC和SBC的1.68和1.93倍。NBC对Pb^(2+)的动力学吸附过程更符合准二级动力学模型(R^(2)=0.9524),表明该过程以化学吸附为主。NBC对Pb^(2+)的吸附机制主要有离子交换、络合、阳离子-π键作用以及沉淀作用等。连续解吸结果表明,NBC对Pb^(2+)的吸附较稳定,各吸附方式的贡献率表现为氢键结合(57.98%)>离子交换(29.98%)>络合(11.95%)>物理吸附(0.10%)。微纳米含氮玉米秸秆生物炭对水体中Pb^(2+)的吸附效果优于铁改性生物炭和巯基改性生物炭。

In this study,corn straw biochar was modified to micro-nano-engineered nitrogenous biochar(NBC),and the comparative analysis of the performance of NBC with iron modified biochar(FeBC)and thiol modified biochar(SBC)on Pb^(2+)adsorption in aqueous solutions was conducted.These modified biochars were characterized by SEM and BET,and the Pb^(2+)adsorption behavior of NBC was analyzed by batch adsorption experiments.To better understand the mechanisms of Pb^(2+)adsorption by NBC,a sequential desorption test was performed and the changes of biochar function groups before and after he adsorption were analyzed.The results show that,after modification,the aromaticity was enhanced and hydrophilicity and polarity were weakened,the specific surface area and total pore volume of NBC was increased by 6.30 and 2.68 times,respectively,as compared with the unmodified biochar.The adsorption capacity of the three modified biochar for Pb^(2+)was in the order of NBC>FeBC>SBC.The isothermal adsorption by NBC was better fitted to the Langmuir model,and its maximum adsorption capacity reached to 148.25 mg·g^(-1),which was 1.68 and 1.93 times higher than that of FeBC and SBC,respectively.The adsorption kinetics of NBC well fits the pseudo-second order model(R^(2)=0.9524).Additionally,there are rod-like deposits in pores after the adsorption of Pb^(2+)by NBC.The sorption of Pb^(2+)by biochars likely occurred through greater cation exchange,precipitation,cation-πinteractions and complexation.The sequential desorption test results indicate that the contribution of NBC to the adsorption modes of Pb^(2+)was ranked hydrogen bonding(57.98%)>cation exchange(29.98%)>complexation(11.95%)>physical adsorption(0.10%).Therefore,the micro-nano-engineered nitrogenous biochar has good adsorption effect on Pb^(2+)in solution,and could be a promising adsorbent for recovering Pb^(2+)from waste water.