La掺杂BiOI微球可见光下光催化氧化NO性能研究

La-Doped BiOI Microspheres for Efficient Photocatalytic Oxidation of NO under Visible Light Illumination

光催化氧化技术被广泛认为是一种经济有效的治理低浓度NO的技术。三维BiOI微球是一种典型的可见光光催化剂,其光催化氧化NO的性能常受限于快速的光生载流子复合以及较差的导电性。然而,由于BiOI微球的尺寸较大,其与其它半导体或者助催化剂的复合通常不匹配,缺乏足够的接触界面。本文通过简易的一步水热法,首次采用稀土金属La掺杂策略改性BiOI微球,并系统研究了其可见光光催化氧化NO的性能。实验优化调整了La的前驱体以及掺杂量。研究结果发现,同LaCl3和La(AC)_(3)相比,La(NO3)_(3)的效果最佳。0.3%La/BiOI光催化氧化NO的转化率最优(74%),远高于单纯的BiOI微球(44%),且其在连续5次循环实验中也表现出优异的稳定性。理化性质分析发现,La掺杂可促进BiOI结晶,但对其形貌和结构几乎不产生影响。La^(3+)可能会通过取代Bi^(3+)进入BiOI的晶格中,或形成La_(2)O_(3)纳米簇均匀的分散在BIOI微球的介孔中。机理分析进一步发现,La掺杂不仅减小了BiOI的带隙,促进了对太阳光的吸收,而且可引入更多的氧空位,有利于水分子解离,生成更丰富的·OH。这些因素共同提升了BiOI光催化氧化NO的性能。此外,La/BiOI主要将NO氧化成NO_(2),且形成的NO_(2)倾向于从催化剂表面脱附,这不仅保全了催化剂表面的活性位点,NO光催化氧化反应得以持续进行,而且可避免催化剂频繁洗涤再生,因此La/BiOI具有优异的稳定性,且使用寿命长。此外,生成的NO_(2)可轻易彻底地被尾部碱性液体吸收,有效避免了二次污染。本研究表明掺杂是一种有效改善三维BiOI微球光催化性能的改性方法,期待其可为各种应用于光催化反应的三维半导体材料的改性和合理设计提供新颖的思路。

Photocatalytic oxidation has been widely acknowledged as an economical and effective technology for the treatment of lowconcentration NO.Three-dimensional(3D)BiOI microspheres,which are typical visible-light responsive semiconductor photocatalysts,often suffer from quick recombination of photogenerated carriers and unsatisfactory electrical conductivity when applied in NO photocatalytic oxidation reactions.However,owing to their micro-sized structures,they are usually difficult to couple with other semiconductors and co-catalysts because of their incompact interfaces that provide insufficient contact.In this study,a rare-earth metal(La)doping strategy was first adopted to modify BiOI microspheres via a simple one-step solvothermal method;subsequently,the photocatalytic NO oxidation performance under visible light illumination was systematically investigated.Further,the La precursors and doping contents were optimized.It was found that La(NO_(3))_(2) was the best precursor when compared to LaCl3 and La(AC)_(3).Moreover,0.3%La/BiOI exhibited the best NO photocatalytic conversion efficiency of up to 74%,which was significantly higher than that of the pure BiOI benchmark(44%).It also exhibited excellent stability during the continuous 5-cycle experiments.Analysis of the physicochemical properties revealed that La doping facilitated the crystallization of BiOI without altering its morphology and structure.La^(3+)may enter the BiOI lattice by substituting Bi^(3+)or forming La_(2)O_(3) nanoclusters that homogeneously scatter in the mesopores of BiOI microspheres.The analysis of the underlying mechanism further revealed that La doping not only enhanced the light harvesting properties by decreasing the bandgaps of BiOI and accelerating the charge separation and transfer dynamics,but also introduced more oxygen vacancies and facilitated the formation of more OH radicals by dissociating the water molecules.All these factors co-contributed to the promotion of NO photocatalytic oxidation activities.Furthermore,NO was mainly oxidized to NO_(2) over La/BiOI,and the formed NO_(2) tended to desorb from the catalyst surface,which not only maintained the intactness of active sites and facilitated the sustainable occurrence of NO photocatalytic oxidation reactions,but also prevented the photocatalysts from frequent washing-regeneration;therefore,these factors account for the superior photocatalytic stability of La/BiOI and its long-term operation.The formed NO_(2) could be easily and totally absorbed by the tail alkaline liquid,thereby effectively avoiding secondary pollution.Therefore,this study elucidates that doping is indeed a feasible and effective approach for the modification of 3D BiOI microspheres,while providing inspiration for the rational design and modification of other 3D semiconductor materials for various photocatalytic applications.