Abstract:

Ni-substituted Zn-Ti layered double hydroxide (NiZnTi-LDH) with different Ni²⁺ substitution ratios were firstly synthesized by using NiCl₂·6H₂O as nickel source via hydrothermal method. The effects of Ni²⁺ 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 Ni²⁺ substitution for Zn²⁺ formed a new intermediate energy level in the band structure of ZnTi-LDH that consequently produced visible light response, meanwhile Ni²⁺ 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 De-NO _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${}_{\mathrm{3}}^{-}$ accounted for 95.6% of total nitrate. Ni²⁺ substitution and the resulting O_V not only promoted the separation of photogenerated carriers, but also facilitated the generation of superoxide radical (·O${}_{\mathrm{2}}^{-}$). As a result, the photo-oxidative activity of NO removal was enhanced and the production of toxic NO₂ was effectively inhibited, consequently achieving deep photo-oxidation of NO to NO${}_{\mathrm{3}}^{-}$.

Key words: ZnTi-LDH, Ni²⁺-substitution, deep photo-oxidation, NO, oxygen vacancy, performance enhancement

摘要：

以NiCl₂·6H₂O为镍源，采用水热法首次合成了不同Ni²⁺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Ni²⁺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：Ni²⁺部分取代Zn²⁺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${}_{\mathrm{3}}^{-}$生成量占总硝酸盐的95.6%。Ni²⁺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${}_{\mathrm{2}}^{-}$)的生成，在增强NO消除性能的同时，抑制有毒NO₂的产生，实现NO至NO${}_{\mathrm{3}}^{-}$的深度光氧化。

关键词: 锌钛LDH, 镍取代, 深度光氧化, 一氧化氮, 氧空位, 性能增强