Heptanuclear Cadmium Borovanadate Containing a Sandwich-Type Anionic Partial Structure {B 20 V 12 } as a Heterogeneous Photocatalyst for the Reduction of CO 2 into CH 4 .

The novel heptanuclear cadmium borovanadate [Cd(en) 3 ]{[Cd(H 2 O)(en)] 6 [B 20 V 12 O 60 (OH) 2 ]}·8H 2 O (en = ethylenediamine) has been prepared under hydrothermal condition. It exhibits a 2D layered architecture that is built up from the [Cd(H 2 O)(en)] 2+ coordination cations and new sandwich-type borovanadate anions [B 20 V 12 O 60 (OH) 2 ] 14- constructed by BO 3 , BO 4 , BO 3 (OH), and VO 5 units. It features the first heptanuclear cadmium borovanadate containing the single valence of V 4+ cations and unique B/V ratio (B/V = 20/12). Its thermal, magnetic, XPS, and optical properties have been systematically studied. The E g (2.60 eV), E VB (1.69 eV), and E CB (-0.91 eV) were well determined by the UV-vis diffuse reflectance spectrum, UPS curve, and the formula E CB = E VB - E g , respectively. The photocatalytic experiments revealed that the borovanadate could be selected as an effective and stable heterogeneous catalyst for the reduction of CO 2 to CH 4 by means of visible light (the amount for CH 4 gas could reach 50.57 μmol·g -1 ·h -1 when the reaction time was 3 h). The recycling experiment and photocatalytic mechanism were also well investigated and established in detail.