Fabrication of Magnetic Fe3O4@SiO2@TiO2-Au with Core-shell Structure and Its Photocatalytic Reduction Activity
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摘要: TiO2基的光催化剂已被广泛用于各种有机物污染物的光氧化和水中六价铬Cr(VI)的光还原。然而，对光催化还原硝基芳香化合物为胺基芳香化合物的研究鲜有报道。本研究采用液相沉积(LPD)法将锐钛矿型TiO2沉积在非晶SiO2包覆的Fe3O4上，制备了核壳结构的Fe3O4@SiO2@TiO2磁性光催化剂。为进一步提高其光催化活性，将均匀分散的Au纳米粒子(Au NPs)修饰在其表面，以获得Fe3O4@SiO2@TiO2-Au纳米复合材料。对这两种TiO2基的磁性复合材料进行表征并将其用作光催化剂。在紫外光照射下，用HCOONH4作为空穴捕集剂和H源，以对硝基苯胺(p-NA)光催化还原至对苯二胺(p-PDA)作为模型反应，评价其光催化还原性能。结果表明，虽然两种光催化剂都能将p-NA完全还原成p-PDA，但Fe3O4@SiO2@TiO2-Au表现出比Fe3O4@SiO2@TiO2更优异的光催化活性。这是因为TiO2表面修饰的Au NPs能有效地促进光激发的电子从TiO2的导带转移到Au，最大限度地减少电子和空穴的复合率，延长光电子的寿命。此外，不可或缺的HCOONH4在p-NA的光催化还原中能有效地捕获光生空穴，及大地提高了其光催化还原效率。Abstract: TiO2-based photocatalysts have been widely used for photoxidation of various organic pollutants and photoreduction of Cr(VI) in aqueous solution. However, less attention has been paid to the photocatalyzed reduction of nitro group to amino group of nitroaromatics. In this study, liquid-phase deposition (LPD) technique was adopted to deposit anatase TiO2 shell on amorphous SiO2-coated Fe3O4 to form core-shell Fe3O4@SiO2@TiO2 magnetic photocatalyst. To further promote its photocatalytic activity, uniformly dispersed Au nanoparticles (NPs) were decorated on its surface to obtain Fe3O4@SiO2@TiO2-Au composite. Both the TiO2-based magnetic composites were characterized and used as photocatalysts. To evaluate their photocatalytic performance, the photocatalyzed reduction of p-nitroaniline (p-NA) to p-phenylenediamine (p-PDA) was chosen as a model reaction under UV irradiation using HCOONH4 as a hole scavenger and H source. Although p-NA can be completely reduced to p-PDA by the two photocatalysts, Fe3O4@SiO2@TiO2-Au exhibits much superior photocatalytic activity to Fe3O4@SiO2@TiO2. The is because Au NPs decorated on the TiO2 can efficiently facilitate the photoexcited electron-transfer from the conduction band of TiO2 to Au, which is favorable for minimizing the recombination rate of electrons and holes and prolong the lifetime of the photoelectrons. In addition, HCOONH4 plays an indispensable role in improving the photocatalytic reduction of p-NA via capturing photo-generated holes.
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Key words:
- magnetism /
- TiO2 /
- core-shell structure /
- Fe3O4@SiO2@TiO2-Au /
- photocatalytic reduction /
- p-nitroaniline
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图 1 磁性Fe3O4@SiO2@TiO2-Au核壳结构微球的组装流程图
Figure 1. Schematic diagram for fabricating magnetic Fe3O4@SiO2@TiO2-Au microspheres with core-shell structure
图 2 Fe3O4 (a,b), Fe3O4@SiO2 (c,d), Fe3O4@SiO2@TiO2 (e,f), Au-seed-decorated Fe3O4@SiO2@TiO2 (g) 和 Fe3O4@SiO2@TiO2-Au (h,i)的不同放大倍数的透射电镜照片; the deposited TiO2 and Au NPs on Fe3O4@SiO2 (j)的高分辨透射电镜照片
Figure 2. TEM images with different magnifications: Fe3O4 (a,b), Fe3O4@SiO2 (c,d), Fe3O4@SiO2@TiO2 (e,f), Au-seed-decorated Fe3O4@SiO2@TiO2 (g), Fe3O4@SiO2@TiO2-Au (h,i) and HRTEM of the deposited TiO2 and Au NPs on Fe3O4@SiO2 (j).
图 3 Fe3O4@SiO2@TiO2-Au复合物的扫描透射照片(a)，元素谱分布图(b)-(f)，样品的能量色散谱(g)
Figure 3. (a) STEM of a single sphere Fe3O4@SiO2@TiO2-Au, a series of EDS elemental mapping images (Fe, Si, Ti, O and Au) (b)-(f), its corresponding EDX spectrum (g)
图 4 Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2@TiO2 和 Fe3O4@ SiO2@TiO2-Au的XRD谱图：F, T 和A分别表示Fe3O4, TiO2和Au的特征衍射峰。
Figure 4. XRD patterns of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2 @TiO2 and Fe3O4@SiO2@TiO2-Au. F, T and A represent the diffraction peaks of Fe3O4, TiO2, and Au, respectively
图 5 Fe3O4@SiO2@TiO2-Au的XPS全谱(a)和组成元素的高分辨XPS谱：Fe 2 p (b), Ti 2 p (c)和Au 4 f (d)
Figure 5. XPS survey spectra of composite survey (a) and high-resolution spectra of Fe 2 p (b), Ti 2 p (c) and Au 4 f (d) in the sample
图 6 Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2@TiO2和 Fe3O4@ SiO2@TiO2-Au的室温磁滞洄线
Figure 6. Room-temperature magnetization hysteresis loops of Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2@TiO2 and Fe3O4@SiO2 @TiO2-Au.
图 7 Fe3O4@SiO2@TiO2-Au和Fe3O4@SiO2@TiO2-Au紫外-可见漫反射光谱(a)，能带图(b)
Figure 7. UV-Vis diffuse reflectance spectra of Fe3O4@SiO2@TiO2-Au and Fe3O4@SiO2@TiO2-Au (a), band gap energies of Fe3O4@SiO2@TiO2-Au and Fe3O4@SiO2@TiO2-Au (b)
图 8 Fe3O4@SiO2@TiO2 和 Fe3O4@SiO2@TiO2-Au分别在有HCOONH4 (a,b)和无HCOONH4 (c,d)条件下光催化还原p-NA的UV-Vis谱图(p-NA: 20 mg·L−1，HCOONH4: 800 mg·L−1，催化剂: 50 mg)
Figure 8. UV-vis absorption spectra of the p-NA aqueous solution under UV irradiation catalyzed by Fe3O4@SiO2@TiO2 (a,c) in both the presence and the absence of HCOONH4 and Fe3O4@SiO2@TiO2-Au (b,d) in both the presence and the absence of HCOONH4, respectively.(p-NA: 20 mg·L−1, HCOONH4: 800 mg·L−1,，catalyst: 50 mg)
图 9 金纳米粒子和TiO2之间的电荷转移和紫外光照下Fe3O4@SiO2@TiO2-Au催化还原p-NA的机制示意图
Figure 9. Schematic diagram indicating the charge transfer between Au NPs and TiO2 (EF: Fermi level of Au) and the mechanism for reduction of p-NA over the Fe3O4@SiO2@TiO2-Au photocatalyst under UV light irradiation.
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