磁性生物炭及其老化后对Cd^(2+)的吸附性能影响

Effect of magnetic biochar and its aging on the adsorption performance of Cd^(2+)

磁性生物炭(FBC)是一种具有良好吸附性能且可实现磁分离的吸附材料,但制备过程磁性前驱体用量及老化作用是否影响其结构和吸附重金属的能力却鲜有研究。以水稻秸秆和铁盐为原料制备不同铁炭质量比(1∶4、1∶2和1∶1,记作FBC-4、FBC-2、FBC-1)的FBC,比较其表面形态、官能团等理化性质,以及对Cd^(2+)的吸附性能的差异;利用自然老化和高温老化2种物理方法研究老化作用对磁性生物炭理化性质和吸附性能的影响。结果表明:与普通生物炭(BC)相比,FBC具有更大的比表面积和孔容,含氧官能团数量增多,并且出现Fe—O的特征峰,FBC-4、FBC-2、FBC-1的饱和磁化强度随着单位生物炭载铁量增加而增大,分别为0.64、2.21和17.69 A·m^(2)/kg;BC和FBC对Cd^(2+)吸附等温线和动力学曲线均符合Langmuir方程和准二级动力学方程,拟合出的平衡吸附量和理论最大吸附量关系为FBC-1>FBC-4>FBC-2>BC,即磁改性可以提高对Cd^(2+)的平衡吸附量,且FBC-1对Cd^(2+)的吸附能力最强;FBC-1经过2个月的自然老化和高温老化后,比表面积分别下降45.8%和36.4%,平均孔径分别增加72.7%和43.2%,饱和磁化强度分别增加至33.53和26.65 A·m^(2)/kg;老化作用会降低磁性生物炭对Cd^(2+)的吸附能力,其平衡吸附量由老化前的36.97 mg/g减小至30.97 mg/g(自然老化)和28.22 mg/g(高温老化),理论最大吸附量由63.80 mg/g分别下降至46.68和40.29mg/g,相比于自然老化,高温老化作用对磁性生物炭Cd^(2+)的吸附性能的抑制作用更明显。

Magnetic biochar(FBC)is an adsorption material with good adsorption performance and magnetic separation.However,there are few studies on whether the amount of magnetic precursor in the preparation process and the aging effect affect its structure and the ability to adsorb heavy metals.FBC with different iron-carbon ratios(1∶4,1∶2 and 1∶1,denoted as FBC-4,FBC-2 and FBC-1)were prepared from rice straw and iron salts,and their surface morphology,functional groups and other physical and chemical properties,as well as the adsorption properties of Cd^(2+)were compared.Two physical aging methods(spontaneous aging and high temperature aging)were used to study the effect of aging on the physicochemical properties and adsorption properties of magnetic biochar.The results showed that compared with ordinary biochar(BC),FBC had a larger specific surface area and pore volume,the number of oxygen-containing functional groups increased,and the characteristic peaks of Fe—O appeared.The saturation magnetization of FBC-4,FBC-2 and FBC-1 increased with the increase of iron content per unit biochar,which were 0.64,2.21 and 17.69 A·m^(2)/kg,respectively.The adsorption isotherms and kinetic curves of BC and FBC for Cd^(2+)were consistent with the Langmuir equation and the pseudo-second-order kinetic equation.The relationship between the fitted equilibrium adsorption capacity and the theoretical maximum adsorption capacity was FBC-1>FBC-4>FBC-2>BC,that is,magnetic modification could improve the equilibrium adsorption capacity of Cd^(2+),and FBC-1 had a stronger adsorption capacity for Cd^(2+).After two months of spontaneous aging and high temperature aging,the specific surface area of FBC-1 decreased by 45.8%and 36.4%,the average pore size increased by 72.7%and 43.2%,and the saturation magnetization increased to 33.53 and 26.65 A·m^(2)/kg,respectively.Aging could inhibit the adsorption capacity of magnetic biochar for Cd^(2+).The equilibrium adsorption capacity decreased from 36.97 mg/g before aging to 30.97 mg/g(spontaneous aging)and 28.22 mg/g(high temperature aging),and the theoretical maximum adsorption capacity decreased from 63.80 mg/g to 46.68 mg/g and 40.29 mg/g,respectively.Compared with spontaneous aging,high temperature aging had a more obvious inhibitory effect on the adsorption performance of magnetic biochar for Cd^(2+).