pH值对氮掺杂TiO2物化性质和光催化活性的影响

以TiCl4为前驱体,水合肼和氨水的混合溶液为氮源,采用共沉淀法制备了可见光响应型氮掺杂二氧化钛(N-TiO2)光催化剂,重点研究了制备过程中pH值对催化剂的微结构和光催化活性等物化性质的影响.采用XRD、BET、UV-vis和XPS等表征方法对光催化剂性质进行了表征.催化剂主要以锐钛矿相存在,具有介孔结构和较高的比表面积(～90m2/g).随着pH值增大,锐钛矿相(101)面衍射峰逐步增强,晶粒尺寸逐渐增大,比表面积逐渐减小.XPS结果表明催化剂掺杂的氮主要以系列氮氧化物形式存在.氮掺杂小幅降低了禁带宽度,感光范围拓展到可见光区.光催化降解实验表明,pH=3.5时,催化剂的可见光降解效率最高,为39.65%.随着pH值增大,催化剂可见光催化活性逐渐降低;而在紫外光照射下,pH=9.5时,催化活性最低;pH=5.5时,催化活性最高.

Effects of pH Values on the Physicochemical Properties and Photocatalytic Activities of Nitrogen-doped TiO2

Visible-light-driven nitrogen-doped titanium dioxide (N-TiO₂) was synthesized by the method of coprecipitation, in which titanium tetrachloride was used as Ti-precursor and the mixed solution of ammonia and hydrazine hydrate as nitrogen resource. Effects of pH values on the physicochemical properties and the activities of the as-prepared N-TiO₂ catalysts were studied. The obtained photocatalysts are found to be of anatase phase, higher specific area, mesoporous structure and visible response by means of XRD, BET and UV-vis spectra analysis. With increasing pH values, the intensity of anatase (101) peaks enhances, and the crystallite size increases, while the BET specific area decreases. The doped impurities are found to be NO_x species, which are confirmed by XPS. Minor band-gap narrowing and the visible-light response are due to nitrogen doping. The experiments of photodegradation of 4-chlorophenol show that the degradation ratio (39.65%) of the catalyst prepared at pH=3.5 is the highest under visible light irradiation. The photocatalytic activity decreases when pH values increase. Under UV light irradiation, the catalyst prepared at pH=5.5 has the highest photocatalytic activity, while that derived from pH=9.5 has the lowest.