杭锦2^(#)土的光谱特征及非均相Fenton反应机理

Spectral Characteristics of Hangjin 2^(#) Clay and Its Mechanism in Heterogeneous Fenton Reaction

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Bronsted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H_(2)O_(2)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Fe^(3+)与Fe^(2+)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Bronsted酸位增多;非均相Fenton反应中,酸活化杭锦2^(#)土表面Fe^(3+)与Fe^(2+)可与H_(2)O_(2)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Bronsted酸能够提供质子将H_(2)O_(2)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Fe^(2+)可被O_(ad)氧化为Fe^(3+),促进Fe^(2+)/Fe^(3+)之间的循环,同时在氧化过程中电子转移到O_(ad)形成^(·-)_(2), ^(·-)_(2)能够与Br9nsted酸提供的质子反应形成·OH,·OH与^(·-)_(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CO^(2-)_(3)转化为对Fenton反应负面影响更小的SO42-进而提升其非均相Fenton反应活性。

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 Bronsted acid sites. In heterogeneous Fenton reaction, structural iron in Hangjin2^(#) clay could react with H_(2)O_(2) 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 Fe^(2+) and Fe^(3+). Whatsmore, the increase Lewis acid and Bronsted 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, Fe^(3+) and Fe^(2+) could circularly react with H_(2)O_(2) to continuously generate ·OH to degrade methyl orange. Furthermore, Bronsted acid sites on the activated Hangjin2^(#) clay surface could provide protons to surround H_(2)O_(2), and the formation reaction of HO-2 will be inhibited. Lewis acid sites on activated Hangjin2^(#) clay surface could increase adsorption oxygen content. Moreover, Fe^(2+) can be oxidized by adsorption oxygen to form Fe^(3+), promoting the circulation between Fe^(2+)/Fe^(3+). Furthermore, in the oxidation process, the electron could transfer to adsorption oxygen to form ^(·-)_(2) which can be reacted with protons provided by Br9 nsted acid sites to form ·OH. These ·OH and ^(·-)_(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 CO^(2-)_(3)to SO42-, while SO42- has a less negative effect on Fenton reaction compared with CO^(2-)_(3).