磁性核壳结构Fe_(3)O_(4)@SiO_(2)@TiO_(2)-Au的制备及其光催化还原性能

Fabrication of magnetic Fe_(3)O_(4)@SiO_(2)@TiO_(2)-Au with core-shell structure and its photocatalytic reduction activity

TiO_(2)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。本文采用液相沉积(LPD)法将锐钛矿型TiO_(2)沉积在非晶SiO_(2)包覆的Fe_(3)O_(4)上,制备了核壳结构的Fe_(3)O_(4)@SiO_(2)@TiO_(2)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Fe_(3)O_(4)@SiO_(2)@TiO_(2)-Au纳米复合材料。对这两种TiO_(2)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Fe_(3)O_(4)@SiO_(2)@TiO_(2)-Au表现出比Fe_(3)O_(4)@SiO_(2)@TiO_(2)更优异的光催化活性。这是由于TiO_(2)表面修饰的Au NPs能有效地促进光激发的电子从TiO_(2)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,极大地提高了其光催化还原效率。

TiO_(2)-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 TiO_(2)shell on amorphous SiO_(2)-coated Fe_(3)O_(4)to form core-shell Fe_(3)O_(4)@SiO_(2)@TiO_(2)magnetic photocatalyst.To further promote its photocatalytic activity,uniformly dispersed Au nanoparticles(NPs)were decorated on its surface to obtain Fe_(3)O_(4)@SiO_(2)@TiO_(2)-Au composite.Both the TiO_(2)-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,Fe_(3)O_(4)@SiO_(2)@TiO_(2)-Au exhibits much superior photocatalytic activity to Fe_(3)O_(4)@SiO_(2)@TiO_(2).The is because Au NPs decorated on the TiO_(2)can efficiently facilitate the photoexcited electron-transfer from the conduction band of TiO_(2)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.