Ni^(2+)取代对ZnTi-LDH选择性光氧化去除NO的性能增强

Performance enhancement of selective photo-oxidation for NO removal on ZnTi-LDH by Ni^(2+) substitution

以NiCl_(2)·6H_(2)O为镍源,采用水热法首次合成了不同Ni^(2+)取代量的锌钛层状双金属氢氧化物(NiZnTi-LDH),通过X射线衍射、透射电镜、低温氮吸附、X射线光电子能谱与紫外-可见漫反射等测试研究了Ni^(2+)取代对ZnTi-LDH晶相结构、微观形貌、孔结构、表面氧空位与光吸收性能的影响。以NiZnTi-LDH为催化剂,分别考察了模拟太阳光与可见光照射下的NO光氧化消除性能。结果表明:Ni^(2+)部分取代Zn^(2+)可在ZnTi-LDH的能带结构中形成一新的中间能级,产生可见光响应,同时Ni取代可于ZnTi-LDH表面形成氧空位(O_(V))。可见光照射下,ZnTi-LDH无NO氧化活性,最优催化剂27%NiZnTi-LDH的NO去除率为52.1%,NO_(x)脱除选择性高达97.4%。模拟太阳光照射下,27%NiZnTi-LDH的NO光氧化去除率为64.8%,是ZnTi-LDH的2.76倍,NO_(x)脱除选择性可达96.9%,且NO_(3)^(-)生成量占总硝酸盐的95.6%。Ni^(2+)取代及由此形成的O_(V)不仅促进光生电荷分离,同时利于超氧自由基(·O_(2)^(-))的生成,在增强NO消除性能的同时,抑制有毒NO_(2)的产生,实现NO至NO_(3)^(-)的深度光氧化。

Ni-substituted Zn-Ti layered double hydroxide(NiZnTi-LDH)with different Ni^(2+)substitution ratios were firstly synthesized by using NiCl_(2)·6H_(2)O as nickel source via hydrothermal method.The effects of Ni^(2+)substitution on the crystal phase,morphology,pore structure,surface oxygen vacancy and light absorption properties of ZnTi-LDH were investigated by X-ray diffraction,transmission electron microscopy,low temperature nitrogen adsorption,X-ray photoelectron spectroscopy and UV-visible diffuse reflectance.Using NiZnTi-LDH as catalyst,the photo-oxidation and elimination performance of NO under simulated sunlight and visible light irradiation were investigated respectively.The results showed that partial Ni^(2+)substitution for Zn^(2+)formed a new intermediate energy level in the band structure of ZnTi-LDH that consequently produced visible light response,meanwhile Ni^(2+)substitution generated oxygen vacancies(O_(V))on ZnTi-LDH surface.Under visible light irradiation,ZnTi-LDH had no NO oxidation activity,and the optimal 27%NiZnTi-LDH catalyst showed a NO removal rate of 52.1%with a DeNO_(x) selectivity up to 97.4%.Under simulated solar light irradiation,27%NiZnTi-LDH exhibited a NO photo-oxidation removal rate of 64.8%that was 2.76 times of ZnTi-LDH and De-NO_(x) selectivity was 96.9%,meanwhile the produced NO_(3)^(-) accounted for 95.6%of total nitrate.Ni^(2+)substitution and the resulting O_(V) not only promoted the separation of photogenerated carriers,but also facilitated the generation of superoxide radical(·O_(2)).As a result,the photo-oxidative activity of NO removal was enhanced and the production of toxic NO_(2) was effectively inhibited,consequently achieving deep photo-oxidation of NO to NO_(3)^(-).