Thiol-functionalized nano-silica for in-situ remediation of Pb, Cd, Cu contaminated soils and improving soil environment.

Heavy metal contamination has been threatening the health of human beings. To decrease the bio-toxicity of heavy metals, a thiol-functionalized nano-silica (SiO2-SH) was adopted to remediate the soil contaminated by lead (Pb), cadmium (Cd) and copper (Cu). The remediation effect of SiO2-SH on contaminated soils was investigated by the uptake of the heavy metals into lettuce and pakchoi in pot experiment. The bio-toxicity of the SiO2-SH was evaluated, and its immobilization mechanisms were proposed by the fraction distribution of Cd, Pb and Cu. It was found that the SiO2-SH can significantly reduce the uptake of Cd, Pb, Cu into pakchoi by 92.02%, 68.03%, 76.34% and into lettuce by 89.81%, 43.41%, 5.76%, respectively. The chemical species analyses of Cd, Pb, Cu indicate SiO2-SH can transform the heavy metal in acid soluble states into reducible fraction and oxidizable fraction, thereby inhibiting the extraction of heavy metals into soil solution. The concentrations of microbial biomass carbon, organic matter, and cation exchange capacity of the soil increased while the soil bulk density decreased after remediation. Those changes demonstrate that SiO2-SH not only has no bio-toxic impact on the soil environment but also improves the soil environment, which proves the prepared SiO2-SH is environmental-friendly. The SiO2-SH could be a promising amendment for heavy metal contaminated soils.