酸碱改性生物质炭-纳米零价铁增强六价铬去除的机理

通过氢氟酸和氢氧化钠改性水稻秸秆生物质炭(BC)，得到改性材料BC-HF和BC-NaOH，在此基础上负载纳米零价铁(Nanoscale zero-valent iron，nZVI)制得生物质炭负载纳米零价铁(nZVI@BC)、氢氟酸改性生物质炭负载纳米零价铁(nZVI@BC-HF)和氢氧化钠改性生物质炭负载纳米零价铁(nZVI@BC-NaOH)。通过比表面积分析、元素分析、红外光谱分析、X射线衍射分析以及动力学等方法，研究了不同材料对Cr(Ⅵ)的去除性能与机理。结果表明：酸碱改性后的生物质炭比表面积、孔体积显著增加，促进了Cr(Ⅵ)的去除，BC-HF和BC-NaOH对Cr(Ⅵ)的去除量分别为30.87、19.59 mg·g⁻¹，为BC的2.68、1.70倍；负载nZVI后，进一步增强了Cr(Ⅵ)的去除效果，其中，nZVI@BC-HF和nZVI@BC-NaOH对Cr(Ⅵ)的去除效果显著，去除量分别为76.36、65.62 mg·g⁻¹。酸碱改性生物质炭使nZVI得到了有效分散，其表面的Si-O-Si官能团与nZVI耦合成Si-O-Fe键，增强了nZVI对Cr(Ⅵ)的还原；同时，酸碱改性生物质炭负载nZVI促进了铁铬化合物的结晶，有利于反应的持续进行。本研究表明，酸碱改性生物质炭-纳米零价铁复合材料对于地下水中Cr(Ⅵ)的去除具有较大的应用潜力。

Mechanism of enhanced removal of Cr(VI) by acid and alkali modified biochar-nanoscale zero-valent iron

Following rice straw biochar (BC) was modified by hydrofluoric acid and sodium hydroxide to obtain BC-HF and BC-NaOH, respectively. And biochar loaded with nZVI (nZVI@BC), hydrofluoric acid modified biochar loaded with nZVI (nZVI@BC-HF) and sodium hydroxide modified biochar loaded with nZVI (nZVI@BC-NaOH) were prepared. The removal performance and mechanism of Cr(Ⅵ) by different materials were evaluated by the analyses of specific surface areas, elements, infrared spectroscopy, X-ray diffraction and kinetic. The results showed that specific surface area and pore volume of the biochar modified by acid and alkali were significantly increased, which promoted the removal of Cr(Ⅵ). The removal capacities of Cr(Ⅵ) by BC-HF and BC-NaOH were 30.87 and 19.59 mg·g−1, respectively, which were 2.68 and 1.70 times higher than the BC. After nZVI was loaded, the Cr(Ⅵ) removal was further enhanced, in which nZVI@BC-HF and nZVI@BC-NaOH possess significant Cr(Ⅵ) removal capacities of 76.36 and 65.62 mg·g−1, respectively. The acid and alkali modified biochar enables nZVI to be effectively dispersed and the Si-O-Si functional group on its surface with nZVI to form a Si-O-Fe bond, which enhance the Cr(Ⅵ) reduction by nZVI. At the same time, the acid and alkali modified biochar loaded with nZVI promoted the crystallization of iron chromium compounds, sustaining the reaction. The research showed that the acid and alkali modified biochar-nanoscale zero-valent iron composites had a good application potential for the removal of Cr(Ⅵ) in groundwater.