Semiconductor photocatalysis under natural sunlight is an emergent area in contemporary materials research, which has attracted considerable attention toward the development of catalysts for environmental remediation using solar energy. A series of five-layer Aurivillius-phase perovskites, Bi₅ATi₄FeO₁₈ (A = Ca, Sr, and Pb), are synthesized for the first time. Rietveld refinements of the powder X-ray diffraction data indicated orthorhombic structure for the Aurivillius phases with Fe largely occupying the central octahedral layer, whereas the divalent cations (Ca, Sr, and Pb) are statistically distributed over the cubo-octahedral A-sites of the perovskite. The compounds with visible-light-absorbing ability (E_g ranging from ∼2.0 to 2.2 eV) not only exhibit excellent collective photocatalytic degradation of rhodamine B–methylene blue (MB) and rhodamine B–rhodamine 6G mixture at pH 2 but also show almost 100% photocatalytic selective degradation of MB from the rhodamine B–MB mixture at pH 11 under natural solar irradiation. The selectivity in the alkaline medium is believed to originate from the combined effect of the photocatalytic degradation of MB by the Aurivillius-phase perovskites and the photolysis of MB. Although a substantial decrease in MB adsorption from the mixed dye solution (MB + RhB) together with slower MB photolysis at the neutral pH makes the selective MB degradation sluggish, the compounds showed excellent photocatalytic degradation activity and chemical oxygen demand removal efficacy toward individual RhB (at pH 2) and MB (at pH 11) under sunlight irradiation. The catalysts are exceptionally stable and retain good crystallinity even after five successive cyclic runs without any noticeable loss of activity in both the acidic and alkaline media. The present work provides an important insight into the development of layered perovskite photocatalysts for collective degradation of multiple pollutants and selective removal of one or multiple pollutants from a mixture. The later idea may open up new possibilities for recovery/purification of useful chemical substances from the contaminated medium through selective photocatalysis.

中文翻译：

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pH介导的一系列层状Aurivillius钙钛矿对集体和选择性太阳光的催化作用

在自然光下的半导体光催化是当代材料研究的一个新兴领域，已引起人们对使用太阳能进行环境修复的催化剂的开发的极大关注。首次合成了一系列五层Aurivillius相钙钛矿，Bi ₅ ATi ₄ FeO ₁₈（A = Ca，Sr和Pb）。粉末X射线衍射数据的Rietveld改进表明Aurivillius相的正交结构，其中Fe主要占据了中央八面体层，而二价阳离子（Ca，Sr和Pb）在统计学上分布在C8的立方八面体A-位上钙钛矿。具有可见光吸收能力的化合物（E _g范围从约2.0到2.2 eV）不仅在pH值为2的情况下展现出了若丹明B-亚甲基蓝（MB）和若丹明B-若丹明6G混合物的出色的集体光催化降解性能，而且还显示了若丹明B–在自然太阳辐射下，pH为11的MB混合物。据信在碱性介质中的选择性源自Aurivillius相钙钛矿对MB的光催化降解和MB的光解的综合作用。尽管混合染料溶液（MB + RhB）中的MB吸附量显着下降，而在中性pH下MB的光解速度较慢，使得选择性MB降解缓慢，该化合物在阳光照射下对单个RhB（pH 2）和MB（pH 11）表现出优异的光催化降解活性和化学需氧量去除效果。该催化剂非常稳定，即使在连续五次循环运行后仍保持良好的结晶度，而在酸性和碱性介质中均没有任何明显的活性损失。本工作为层状钙钛矿光催化剂的开发提供了重要的见识，该催化剂可用于多种污染物的集体降解以及从混合物中选择性去除一种或多种污染物。以后的想法可能为通过选择性光催化从受污染的介质中回收/纯化有用的化学物质开辟新的可能性。该催化剂非常稳定，即使在连续五次循环运行后仍保持良好的结晶度，而在酸性和碱性介质中均没有任何明显的活性损失。本工作为层状钙钛矿光催化剂的开发提供了重要的见识，该催化剂可用于多种污染物的集体降解以及从混合物中选择性去除一种或多种污染物。以后的想法可能为通过选择性光催化从受污染的介质中回收/纯化有用的化学物质开辟新的可能性。该催化剂非常稳定，即使在连续五次循环运行后仍保持良好的结晶度，而在酸性和碱性介质中均没有任何明显的活性损失。本工作为层状钙钛矿光催化剂的开发提供了重要的见识，该催化剂可用于多种污染物的集体降解以及从混合物中选择性去除一种或多种污染物。以后的想法可能为通过选择性光催化从受污染的介质中回收/纯化有用的化学物质开辟新的可能性。本工作为层状钙钛矿光催化剂的发展提供了重要见识，该催化剂可用于多种污染物的集体降解以及从混合物中选择性去除一种或多种污染物。以后的想法可能为通过选择性光催化从受污染的介质中回收/纯化有用的化学物质开辟新的可能性。本工作为层状钙钛矿光催化剂的开发提供了重要的见识，该催化剂可用于多种污染物的集体降解以及从混合物中选择性去除一种或多种污染物。以后的想法可能为通过选择性光催化从受污染的介质中回收/纯化有用的化学物质开辟新的可能性。