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Molecular Orbital Anaysis of Water Activation on TiO2(110) Surface

TiO2(110) 표면에 흡착된 물분자의 결합 활성화에 관한 MO 연구

  • Published : 2002.06.20

Abstract

A molecular orbital analysis based on the extended Huckel calculations has been carried out to study the OH bond activation of water on the $TiO_2$(110) surface. $H_2O$ binds with its axis perpendicular to the surfac on top of the five-coordinate $Ti^{4+}$ atom via its $3a_1$ orbital. In this bonding situation, the two-coordinated bridging $O^{2-}$ atom ($O_b$, basic site) on $TiO_2$(110) is too distant from an H atom of water to form hydrogen-bondig interactions with water that facilitate O-H bond cleavage. It has been elucidated that the O-H bond is appreciably weakened when the water molecule is tilted to give a hydrogen bond with the $O_b$ atom. This mechanism includes mutual transfer of electron density from the $3a_1$ orbital of the water molecule to the $Ti^{4+} 3d_{z2}$ orbital and from the $O_b$ P orbitals to the $2b_1$ of the adsorbed water molecule This should result in lengthening of the O-H bond in the surface complex and the subsequent dissociation into the fragments OH and H.

$TiO_2$(110) 표면에서 물의 OH 결합 활성화가 어떤지 전자적 메카니즘에 의해 이루어지는 extended Hiickel 방법을 통해 알아보았다. 물분자는 $3a_1$오비탈의 시그마 상호작용 겨로가로 5배위 $Ti^{4+}$원자바로위에 수직으로 흡착한다. 이 결합구조에서는 물분자의 H원자가 $TiO_2$의 2배위 bridging $O^{2-}(O_b)$원자와 너무 멀리 떨어져 있으므로 OH 결합 해리를 촉진시키는 수소결합 상호 작용을 할 수 없으므로 물분자를 $O_b$ 원자쪽으로 기울여 수소결합이 형성되도록 한다. 이 경우 $O_b$ P 오비탈로부터 흡착 물분자의 LUMO $2b_1$반 결합성 오비탈로 전자밀도의 이동이 일어나고 또 물의 $3a_1$오비탈(약한 결합성)로부터 $Ti^{4+} 3d_{z2}$오비탈로 전자밀도의 이동이 일어남으로써 물의 OH 결합이 상당히 약화됨을 확인할 수 있었고 그 결과 OH와 H로 해리할 것이라는 해석이 가능하다.

Keywords

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