Photocatalytic degradation of aqueous formic acid over the silica composite films based on lacunary Keggin-type polyoxometalates

• Published in: Applied catalysis. A, General Vol. 235; no. 1; pp. 11 - 20
• Main Authors: Li, Danfeng, Guo, Yihang, Hu, Changwen, Mao, Li, Wang, Enbo
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 30.08.2002; Elsevier
• Subjects: Chemistry; Composition film; Exact sciences and technology; Formic acid; General and physical chemistry; Photocatalysis; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Polyoxometalates; Sol–gel; Spin-coating; Polyoxometalates; Spin-coating; Sol–gel; Photocatalysis; Formic acid; Composition film; Water; Heteropolysalt; Carbon dioxide; Transition metal Complexes; Experimental study; Supported catalyst; Heterogeneous catalysis; Tungsten complex; Carboxylic acid; Sol gel process; Silicon Oxides; Aqueous solution; Photochemical degradation
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/S0926-860X(02)00238-7

The composite films [X n+ W 11O 39] (12− n)− /SiO 2 (X=Si, Ge, P) (abbreviated XW 11/SiO 2) were prepared by tetraethoxysilane (TEOS) hydrolysis sol–gel method via a spin-coating technique. Mono-vacant Keggin-type polyoxometalates (POMs) [X n+ W 11O 39] (12− n)− were the inorganic precursors used in this method. Formation of the composite films is due to chemical grafting of organic silanol groups to the surface oxygen atoms at the vacant sites of [X n+ W 11O 39] (12− n)− , resulting in the saturation of the surface of the lacunary POM. Therefore, a coordination structural model of the films was proposed. As for the films, retention of the primary Keggin structure was confirmed by UV–VIS, FT-IR, and MAS NMR spectra. The surface morphology of the films was characterized by scanning electron microscopy (SEM): the film surface is highly uniform, and the layer thickness is in the range of 250–350 nm. Aqueous formic acid (FA) (0–20 mmol/l) was degraded and mineralized into CO 2 and H 2O by irradiating the films in the near-UV area. The disappearance of FA follows Langmuir–Hinshelwood first-order kinetics.