杭锦2#土的光谱特征及非均相Fenton反应机理

杭锦2#土是内蒙古鄂尔多斯杭锦旗地区发现的层状含铁天然矿物，利用Ｘ射线衍射、吡啶吸附红外光谱及Ｘ射线光电子能谱技术对样品的性质进行了表征。X射线光电子能谱表明杭锦2#土骨架结构中Si和Al原子结合能与标准硅氧四面体和铝氧八面体中Si和Al结合能相比明显增加，表面存在Lewis酸位和Brönsted酸位，且杭锦2#土中铁物种以Fe(Ⅲ)和Fe(Ⅱ)形式存在于骨架结构中；非均相Fenton反应中杭锦2#土的Fe(Ⅱ)可与H₂O₂反应生成自由基(·OH)与Fe(Ⅲ)，但反应速率慢且难以循环。酸活化后杭锦2#土中Si和Al的结合能进一步增加，铁物种部分转变为非结构铁并以Fe3+与Fe2+转移到样品表面；X射线光电子能谱、吡啶红外和氨气程序升温表征表明酸活化杭锦2#土表面Lewis酸位和Brönsted酸位增多；非均相Fenton反应中，酸活化杭锦2#土表面Fe3+与Fe2+可与H₂O₂循环反应，不断生成·OH并对甲基橙进行降解，且活化杭锦2#土表面Brönsted酸能够提供质子将H₂O₂包围，抑制其分解生成HO-₂并提供更多的·OH，Lewis酸能增加杭锦2#土表面吸附氧（O_ad）含量，而Fe2+可被O_ad氧化为Fe3+，促进Fe2+/Fe3+之间的循环，同时在氧化过程中电子转移到O_ad形成O·-₂，O·-₂能够与Brönsted酸提供的质子反应形成·OH，·OH与O·-₂均为氧化性自由基，能够提升活化杭锦2#土非均相Fenton反应活性。此外，X射线衍射表明酸活化使杭锦2#土中CO2-₃转化为对Fenton反应负面影响更小的SO2-₄进而提升其非均相Fenton反应活性。

Spectral Characteristics of Hangjin2# Clay and Its Mechanism in Heterogeneous Fenton Reaction

Hangjin2# clay is a layered iron-bearing natural mineral found in Ordos, Inner Mongolia. In succession，X-ray diffraction, pyridine adsorption Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize Hangjin2# clay. X-ray photoelectron spectroscopy results indicated that Fe in Hangjin2# clay skeleton structure mainly exists as Fe(Ⅲ) and Fe(Ⅱ). Moreover, the binding energy of Si and Al in Hangjin2# clay has increased significantly compared with the standard binding energy of Si and Al in silicon-oxygen tetrahedron and octahedron aluminum oxygen, which indicated the presence of Lewis and Brönsted acid sites. In heterogeneous Fenton reaction, structural iron in Hangjin2# clay could react with H₂O₂ to produce?OH to degrade methyl orange, but the rate is slow and difficult to cycle. After acid activation, Si and Al’s increased binding energy in activated Hangjin2# clay has been confirmed, and iron in activated Hangjin2# clay has transformed into non-structural iron which coexists in the form of Fe2+ and Fe3+. Whatsmore, the increase Lewis acid and Brönsted acid sites on activated Hangjin2# clay surface have been confirmed by the characterization of X-ray photoelectron spectroscopy, pyridine infrared, and ammonia temperature-programmed desorption. After activation, Fe3+ and Fe2+ could circularly react with H₂O₂ to continuously generate ·OH to degrade methyl orange. Furthermore, Brönsted acid sites on the activated Hangjin2# clay surface could provide protons to surround H₂O₂, and the formation reaction of HO-₂ will be inhibited. Lewis acid sites on activated Hangjin2# clay surface could increase adsorption oxygen content. Moreover, Fe2+ can be oxidized by adsorption oxygen to form Fe3+, promoting the circulation between Fe2+/Fe3+. Furthermore, in the oxidation process, the electron could transfer to adsorption oxygen to form O·-₂ which can be reacted with protons provided by Brönsted acid sites to form ·OH. These ·OH and O·-₂ are oxidizing radicals, which could improve the reaction activity of Hangjin2# clay in heterogeneous Fenton reactions. In addition, X-ray diffraction analysis indicated that acid activation could convert CO2-₃to SO2-₄, while SO2-₄ has a less negative effect on Fenton reaction compared with CO2-₃.