Oxygen vacancies, the optical band gap (Eg) and photocatalysis of hydroxyapatite: Comparing modelling with measured data
Oxygen vacancies, the optical band gap (Eg) and photocatalysis of hydroxyapatite: Comparing modelling with measured data
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DOI：
10.1016/j.apcatb.2016.05.014
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发表时间：
2016-11-05
影响因子：
22.1
通讯作者：
Pullar, R. C.
中科院分区：
文献类型：
--
作者：
Bystrov, V. S.;Piccirillo, C.;Pullar, R. C.
羟基磷灰石（Ca-10（PO 4）（6）（OH）（2），HAp）是一种磷酸钙，用于生物医学和环境修复。已知HAp在UV光下也可以是光催化的，可能是由于氧气不足，但机制尚不清楚，并且报道的光学带隙能量变化很大。我们首次提出了可能导致HAp光催化活性的机制和精确的空位种类，并将这些理论数据与我们在海洋来源和商业HAp粉末样品上的测量数据进行了比较。使用密度泛函理论（DFT）（来自第一原理计算和态密度（DOS）建模）来计算由HAp晶格中的各种可能的氧空位产生的光学带隙能量（E-g）：来自PO 4的O、来自OH的O、整个OH基团的损失或来自PO 4和整个OH基团的O的同时损失。模拟值与测量值非常接近，这表明在非光催化HAp中，如果存在任何空位，则它们是来自OH基团的O原子，导致在UVC区域中的带隙类似于5 eV（在地球表面的太阳光中不存在）。然而，在光催化HAp中，在1000 ℃下有机组分燃烧的还原导致磷酸盐基团中的氧缺乏，可能在O 15位置，在UVA区域（存在于阳光中）中给出类似于3.45 eV的E-g。将不含有机组分的HAp加热至1200 ℃也导致整个OH基团和来自PO 4基团的氧的空位，这导致在UVA-UVB区域的边界上的近似于4 eV的中间Eg值。在可见光区也预测了吸收峰与某些类型的空缺。(C)© 2016 Elsevier B. V.版权所有。
Hydroxyapatite (Ca-10(PO4)(6)(OH)(2), HAp) is a calcium phosphate employed both in biomedicine and for environmental remediation. It is known that HAp can also be photocatalytic under UV light, probably due to oxygen deficiencies, but the mechanism is unclear, and reported optical band gap energies vary greatly. For the first time we propose the mechanisms and precise kinds of vacancies which may cause the photocatalytic activity of HAp, and compare these theoretical data with our measured data on both samples of marine origin and commercial HAp powders. Density functional theory (DFT) (from first principles calculations and Density of States (DOS) modelling) was used to calculate the optical band gap energy (E-g) created by various possible oxygen vacancies in the HAp lattice: O from PO4, O from OH, the loss of an entire OH group, or the simultaneous loss of O from PO4 and an entire OH group. The modelled values match the measured values very closely, suggesting that in non-photocatalytic HAp, if any vacancies exist, they are O atoms from the OH group, resulting in a band gap of similar to 5 eV in the UVC region (not present in solar light at the Earth's surface). However, in photocatalytic HAp, reduction from the combustion of an organic component at 1000 degrees C led to oxygen deficiency in the phosphate groups, probably in the O15 position, giving an E-g of similar to 3.45 eV, in the UVA region (present in sunlight). Heating HAp with no organic component to 1200 degrees C also led to vacancies, of both an entire OH group and oxygen from PO4 groups, which led to an intermediate Eg value of similar to 4 eV, on the boundary of the UVA-UVB regions. Absorption peaks were also predicted in the visible-light region with some types of vacancy. (C) 2016 Elsevier B.V. All rights reserved.