Structure, Stability, and Photocatalytic Activity of a Layered Perovskite Niobate after Flux-Mediated Sn(II) Exchange
Structure, Stability, and Photocatalytic Activity of a Layered Perovskite Niobate after Flux-Mediated Sn(II) Exchange
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DOI：
10.1021/acs.inorgchem.1c03846
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发表时间：
2022-03-07
影响因子：
4.6
通讯作者：
Maggard, Paul A.
中科院分区：
文献类型：
--
作者：
O'Donnell, Shaun;Smith, Avery;Maggard, Paul A.
通过利用Ba 5 Nb 4 O 15（111）取向钙钛矿型层内的不对称配位环境，实现了将Sn（II）阳离子及其立体活性孤对引入光催化氧化物结构中的新策略。这种层状钙钛矿代表了为数不多的能够有效分解水的已知光催化剂之一，但由于其大的带隙，其活性仅限于紫外线辐射。通过在低熔点SnCl 2/SnF 2盐中在350 ℃下使该层状铌酸盐反应24小时，已经制备了高纯度的新的（Ba 1-xSnx）Nb 4 O 15（x = 0-0.5; P（3）/bar m1; a = 5.79650（5）埃，c = 11.79288（8）埃; Z = 2），其具有高达50%的Sn（II）阳离子。统计无序的Sn（II）阳离子探测中子衍射Rietveld的改进，发现主要发生在不对称的阳离子网站，Ba 2和Ba 3，为40%的Sn（II）的组合物的x = 0.4。增加的Sn（II）量使带隙（E-g）从x = 0的0%Sn（3.78 eV;紫外，间接）显著红移到x = 0.4的40%Sn（E-g = 2.35 eV;可见，间接），如通过紫外-可见漫反射发现的。密度泛函理论计算表明亚稳性增加，即，热力学不稳定性分解成简单的氧化物SnO，Nb 2 O 5和SnNb 2 O 6。在这些反应条件下，合成限度类似于50%的锡（II）阳离子可以动力学稳定。对于最高的Sn（II）量，观察到从水中产生分子氧的光催化速率高达，类似于77 μ mol O-2 h（-1）g（-1）（可见光照射）和类似于159 μ mol O-2 h（-1）g（-1）（UV-vis照射），表观量子产率分别类似于0.35和0.52%。相比之下，纯Ba_5 Nb_4 O在可见光照射下没有表现出可测量的光催化活性。电子结构计算表明，带隙的减小源于Sn（II）阳离子的引入和由填充的5s（2）价轨道产生的高能价带的形成。因此，可见光带隙激发发生在主要涉及Sn（II）（5s（2））到Nb（V）（4d（0））阳离子的电子跃迁。这项研究表明，新的和强大的实用程序的低温锡（II）交换反应敏化层型氧化物光催化剂的可见光区域的太阳光谱，这是促进利用其不对称的阳离子环境。
A new strategy to incorporate the Sn(II) cation and its stereoactive lone pair into the structure of a photocatalytic oxide has been achieved by leveraging the asymmetric coordination environments within the (111)-oriented perovskite-type layers of Ba5Nb4O15. This layered perovskite represents one of the few known photocatalysts capable of efficiently splitting water, but its activity is restricted to ultraviolet radiation owing to its large band gap. By reacting this layered niobate at 350 degrees C for 24 h within a low-melting SnCl2/SnF2 salt, the new (Ba1-xSnx)Nb4O15 (x = 0-0.5; P (3) over bar m1; a = 5.79650(5) angstrom, c = 11.79288(8) angstrom; Z = 2) has been prepared in high purity with up to similar to 50% Sn(II) cations. Statistical disordering of the Sn(II) cations was probed by neutron diffraction Rietveld refinements and found to occur predominantly over the asymmetric cation sites, Ba2 and Ba3, for the 40% Sn(II) composition of x = 0.4. An increasing Sn(II) amount significantly red-shifts the band gap (E-g) from 0% Sn for x = 0 (3.78 eV; ultraviolet, indirect) to 40% Sn for x = 0.4 (E-g = 2.35 eV; visible, indirect), as found by UV-vis diffuse reflectance. Density functional theory calculations show an increasing metastability, i.e., a thermodynamic instability toward decomposition to the simpler oxides SnO, Nb2O5, and SnNb2O6. A synthetic limit of, similar to 50% Sn(II) cations can be kinetically stabilized under these reaction conditions. For the highest Sn(II) amounts, photocatalytic rates are observed for the production of molecular oxygen from water of up to, similar to 77 mu mol O-2 h(-1) g(-1) (visible irradiation) and, similar to 159 mu mol O-2 h(-1)g(-1) (UV-vis irradiation), with apparent quantum yields of similar to 0.35 and 0.52%, respectively. By comparison, pure Ba5Nb4O is exhibits no measurable photocatalytic activity under visible-light irradiation. Electronic structure calculations show that the decreased band gap stems from the introduction of the Sn(II) cations and the formation of a higher-energy valence band arising from the filled 5s(2) valence orbitals. Thus, visible-light bandgap excitation occurs from electronic transitions predominantly involving the Sn(II) (5s(2)) to Nb(V) (4d(0)) cations. This study demonstrates the new and powerful utility of low-temperature Sn(II)-exchange reactions to sensitize layer-type oxide photocatalysts to the visible region of the solar spectrum, which is facilitated by exploiting their asymmetric cation environments.