Ji Sang Min, Borse Pramod H, Kim Hyun Gyu, Hwang Dong Won, Jang Jum Suk, Bae Sang Won, Lee Jae Sung
Department of Chemical Engineering and School of Environmental Science & Engineering, Pohang University of Science and Technology, San 31, Hyoja-dong, Pohang, 790-784, Republic of Korea.
Phys Chem Chem Phys. 2005 Mar 21;7(6):1315-21. doi: 10.1039/b417052k.
Nitrogen-doped perovskite type materials, Sr2Nb2O7-xNx (0, 1.5 < x < 2.8), have been studied as visible light-active photocatalysts for hydrogen production from methanol-water mixtures. Nitrogen doping in Sr2Nb2O7 red-shifted the light absorption edge into the visible light range and induced visible light photocatalytic activity. There existed an optimum amount of nitrogen doping that showed the maximum rate of hydrogen production. Among the potential variables that might cause this activity variation, the crystal structure appeared to be the most important. Thus, as the extent of N-doping increased, the original orthorhombic structure of the layered perovskite was transformed into an unlayered cubic oxynitride structure. The most active catalytic phase was an intermediate phase still maintaining the original layered perovskite structure, but with a part of its oxygen replaced by nitrogen and oxygen vacancy to adjust the charge difference between oxygen and doped nitrogen. These experimental observations were explained by density functional theory calculations. Thus, in Sr2Nb2O7-xNx, N2p orbital was the main contributor to the top of the valence band, causing band gap narrowing while the bottom of conduction band due to Nb 4d orbital remained almost unchanged.
氮掺杂钙钛矿型材料Sr2Nb2O7 - xNx（0, 1.5 < x < 2.8）已被作为从甲醇 - 水混合物中制氢的可见光活性光催化剂进行研究。在Sr2Nb2O7中进行氮掺杂可使光吸收边红移至可见光范围，并诱导可见光光催化活性。存在一个最佳的氮掺杂量，该掺杂量显示出最大的产氢速率。在可能导致这种活性变化的潜在变量中，晶体结构似乎是最重要的。因此，随着氮掺杂程度的增加，层状钙钛矿的原始正交结构转变为非层状立方氮氧化物结构。最具活性的催化相是一种中间相，它仍保持原始的层状钙钛矿结构，但部分氧被氮取代且存在氧空位，以调节氧与掺杂氮之间的电荷差异。这些实验观察结果通过密度泛函理论计算得到了解释。因此，在Sr2Nb2O7 - xNx中，N2p轨道是价带顶的主要贡献者，导致带隙变窄，而导带底由于Nb 4d轨道几乎保持不变。
