二氧化铈-铈掺杂锰氧化物纳米复合物高效紫外-可见-红外光热催化净化乙酸乙酯

乙酸乙酯是一种重要的有机溶剂,广泛应用于涂料、粘合剂和塑料及石化等工业生产,但作为一种主要的挥发性有机污染物(VOCs),其对大气环境造成严重污染.目前工业上主要采用负载型贵金属催化剂催化燃烧的方法进行净化处理,但该方法存在催化剂价格昂贵和能耗高的问题,迫切需要开发活性高、稳定性好、成本低及能耗小的催化新方法和新材料.本文以硝酸铈和高锰酸钾为原料制备了二氧化铈和具有隐钾锰矿结构的铈掺杂纳米复合物(CeO₂-CeOMS-2).该纳米复合物在紫外-可见-红外光照射下对乙酸乙酯具有极高的光热催化活性、很低的乙醛(副产物)选择性以及较好的催化稳定性,在光照下持续反应45 h,乙酸乙酯的转化率仍然稳定在90%左右;而纳米CeO₂,OMS-2以及纳米TiO₂(P25)光热催化活性很低,且乙醛选择性较高.CeO₂-CeOMS-2初始5 min CO₂生成速率高达1102.5μmolg^-1min^-1,分别是纳米CeO₂,OMS-2和P25的137,17和30倍.CeO₂-CeOMS-2在波长大于420和560 nm的可见-红外光照射下也具有良好的光热催化活性,甚至在波长大于830 nm的红外光照射下仍具有较好的光热催化活性.同位素标记、程序升温还原以及拉曼光谱实验结果表明,CeO₂-CeOMS-2的催化活性远高于CeO₂和OMS-2的主要是由于铈掺杂显著提高了OMS-2的晶格氧活性.乙酸乙酯在CeO₂-CeOMS-2催化剂上被18O2氧化的FTIR光谱结果表明,其在CeO₂-CeOMS-2上的催化氧化遵循Mars-van-Krevelen氧化还原机理,CeO₂的光催化与铈掺杂OMS-2的光致热催化之间存在协同作用,显著提高了催化活性.CeO₂-CeOMS-2还存在与常规半导体光催化不同的光活化效应,进一步提高了其催化活性.

Highly efficient UV-visible-infrared photothermocatalytic removal of ethyl acetate over a nanocomposite of CeO2 and Ce-doped manganese oxide

A unique nanocomposite of CeO2 nanoparticles and Ce-doped manganese oxide nanofibers having a crystalline cryptomelane-type octahedral molecular sieve (KMn8O16·nH2O, abbreviated as OMS-2) structure (denoted CeO2-CeOMS-2) was prepared by the reaction of Ce(NO3)3 and KMnO4 at 90 ℃. CeO2-CeOMS-2 shows extremely high photothermocatalytic activity, very low selectivity for acetal-dehyde (an unfavorable byproduct), and excellent durability for ethyl acetate removal under UV-visible-infrared (UV-vis-IR) irradiation. In striking contrast, pure CeO2, pure OMS-2, and TiO2 (P25) showed much lower photothermocatalytic activities and higher selectivities for acetaldehyde. The CO2 production rate within the first five minutes (rCO2) of reaction with CeO2-CeOMS-2 was as high as 1102.5 μmol g-1 min-1, which is 137, 17, and 30-times higher than those of pure CeO2, pure OMS-2, and TiO2 (P25), respectively. CeO2-CeOMS-2 also shows good photothermocatalytic activity under vis-IR (λ> 420 or 560 nm) irradiation. Further, even under vis-IR (λ> 830 nm) irradiation, efficient photothermocatalytic activity was achieved. In addition, the catalytic activity of CeO2-CeOMS-2 is far superior to those of pure CeO2 and OMS-2, which is attributed to the fact that Ce doping significantly improves the lattice oxygen activity of OMS-2. The high photothermocatalyt-ic activity of CeO2-CeOMS-2 arises from the synergy between the photocatalytic effect of the CeO2 nanoparticles and light-driven thermocatalysis of the Ce-doped OMS-2. The novel photoactivation of Ce-doped OMS-2, which is unlike that of conventional photocatalysis on semiconductor photocata-lysts, further promotes the catalytic activity because the surface oxygen activity of Ce-doped OMS-2 is promoted upon UV-vis-IR or vis-IR (λ> 560 nm) irradiation.