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Ag_2CO_3是一种典型的银基半导体,可在可见光照射下降解各种有机染料,但制备成本高,光腐蚀严重,稳定性差,难以循环利用等,因而限制了它的实际应用.针对这些问题,目前多数的改进措施是构建异质结,有效的分离光生电子与空穴来提高Ag_2CO_3的光催化性能.比如典型的异质结光催化剂有TiO_2/Ag_2CO_3,Ag_2CO_3/Zn O,Ag_2O/Ag_2CO_3和Ag X/Ag_2CO_3等.也有在表面化学沉积,光化学还原Ag等贵金属形成等离子体等方式提高其光催化性能,但是很少通过特殊形貌控制以提高Ag_2CO_3的光催化性能.最近的研究表明,由于多尺度微球结构催化剂具有高效的光捕能力,同时具有比表面积大、易沉降,良好的物质传输能力和表面的渗透性,因而在液相光催化反应中具有明显的优势.因此,我们期望制备出一个多尺度微球结构Ag_2CO_3光催化剂.CaMg(CO_3)_2是一种具有微球结构的半导体,它与Ag_2CO_3有相同的阴离子结构,但是两者在水溶液中的溶解度相差较大,利用这个特性理论上可以将两个不同的半导体结合在一起,得到一种新型的复合微球.本文以CaMg(CO_3)_2微球为硬模板,通过简单的离子交换成功制备了粒径约为10mm的CaMg(CO_3)_2@Ag_2CO_3微球.利用X射线衍射、N_2物理吸附、扫描电镜、傅里叶变换红外光谱和紫外-可见漫反射吸收光谱、光电流等手段对在不同反应时间与温度下制得的CaMg(CO_3)_2与Ag_2CO_3的复合物进行了表征.结果表明,在40°C下Ag~+与Ca~(2+)、Mg~(2+)离子交换4 h后,得到了一种多尺度CaMg(CO_3)_2@Ag_2CO_3复合微球.此时,微球中Ag_2CO_3的含量约为2.56%.结果表明,这种具有多尺度结构的复合微球能够增强可见光的吸收.电化学阻抗测试和光电流测试表明,CaMg(CO_3)_2核的存在可以降低光生载流子的迁移阻力,进而促进光生电子与空穴的分离.在光降解酸性橙II的测试中,核壳结构的CaMg(CO_3)_2@Ag_2CO_3复合微球表现出了更高的催化活性,而且具有更好的循环使用性能.同时,相对于纯Ag_2CO_3光催化剂来说,CaMg(CO_3)_2@Ag_2CO_3复合微球制备的成本大幅度降低.ESR测试证明了?OH为CaMg(CO_3)_2@Ag_2CO_3复合微球光催化过程中的主要活性物质.
Ag_2CO_3 is a typical silver-based semiconductor that can degrade various organic dyes under visible light irradiation, but its preparation cost is high, light corrosion is serious, its stability is poor, it is difficult to recycle, etc. Therefore, Ag_2CO_3 limits its practical application.In view of these problems, At present, most of the improvement measures are to construct heterojunctions and effectively separate photogenerated electrons and holes to improve the photocatalytic activity of Ag 2 CO 3 .For example, typical heterojunction photocatalysts include TiO 2 / Ag 2 CO 3, Ag 2 CO 3 / Zn O, Ag 2 O 2 / Ag 2 CO 3 and Ag X / Ag_2CO_3, etc. There are also surface chemical deposition, photochemical reduction of noble metals such as Ag to form a plasma and other ways to improve its photocatalytic properties, but rarely through the special morphology control to improve the photocatalytic properties of Ag_2CO_3.Recent studies have shown that as more Scales Microsphere Catalysts with high light trapping ability, large specific surface area, easy sedimentation, good material transfer ability and surface permeability have obvious advantages in liquid phase photocatalytic reaction.Therefore, it is desirable to prepare A multi-scale microstructure of Ag_2CO_3 photocatalyst.CaMg (CO_3) _2 is a semiconductor with a microsphere structure, which is the same with Ag_2CO_3 Ion structure, but the solubility of the two in aqueous solution is quite different. By using this property, theoretically, two different semiconductors can be combined together to obtain a new type of composite microspheres.In this paper, CaMg (CO_3) _2 microspheres are Hard template, CaMg (CO_3) _2 @ Ag_2CO_3 microspheres with a diameter of about 10mm were successfully prepared by simple ion exchange method.Using X-ray diffraction, N 2 physical adsorption, scanning electron microscopy, Fourier transform infrared spectroscopy and UV- The complex of CaMg (CO_3) _2 and Ag_2CO_3 prepared at different reaction time and temperature was characterized by means of absorption spectra, photocurrent and so on.The results showed that Ag ~ + and Ca ~ (2+) ) And Mg 2+ ions for 4 h, a multi-scale CaMg (CO 3) 2 @ Ag 2 CO 3 composite microspheres was obtained, in which the content of Ag_2CO_3 in the microspheres was about 2.56% .The results showed that this The composite microspheres with multi-scale structure can enhance the absorption of visible light.Electrochemical impedance spectroscopy and photocurrent tests show that the existence of CaMg (CO 3) 2 nucleus can reduce the migration resistance of photogenerated carriers and promote the separation of photogenerated electrons and holes In the photodegradation of Acid Orange II, the core-shell junction Of CaMg (CO_3) _2 @ Ag_2CO_3 composite microspheres showed higher catalytic activity and better recycling performance.At the same time, compared with pure Ag_2CO_3 photocatalyst, CaMg (CO_3) _2 @ Ag_2CO_3 composite microspheres The cost of preparation is greatly reduced.The ESR test proves that OH is the main active material in the photocatalysis of CaMg (CO_3) _2 @ Ag_2CO_3 composite microspheres.