Obtenção e caracterização de fotocatalisadores baseados nos óxidos de Ti(IV) e W(VI)

Abstract

In environmental remediation, photocatalysis has great importance due to the possibility of using sunlight as primary energy source. In this work, nanoparticulated metal oxides, specifically TiO2, WO3 and their composites, were synthesized using the sol-gel method aiming at production of high efficient photocatalysts. Moreover Layer-by-Layer (LBL) films of these oxides were produced and evaluated as photocatalytic surfaces. The materials were submitted to structural, optical, morphological and electronic characterization techniques and their properties were correlated to the photocatalytic activity. Hydrolysis of titanium(IV) isopropoxide (TTIP) and tungstic acid followed by hydrothermal treatment and calcination yield anatase/TiO2 and monoclinic/WO3 particles, respectively. When the precursors are hydrolyzed concomitantly to produce TiO2/WO3 composites in different molar ratios (1:1; 4:1, 10:1, 20:1 and 40:1), the formation of monoclinic/WO3 is not observed. For the 1:1 composite, hexagonal WO3 is observed, while for the others composites, only anatase TiO2 diffraction peaks are. Raman and FTIR spectroscopies confirm the presence of W-O vibrations in the composites, probably from amorphous WO3. Shifts in the characteristic Raman peaks of TiO2 indicates a possible W(VI) insertion. In the LBL thin films containing 30 TiO2(ac)/WO3(bas) bilayers, anatase TiO2 with a trace of brookite and orthorhombic WO3 were identified. After characterization, the photocatalytic activities were determined by the degradation of methylene blue (MB) dye or gaseous acetaldehyde (CH3CHO) under UV-A irradiation. The dye removal due dark adsorption, and the photonic efficiency (ξ) of materials were determined. Towards MB degradation, TiO2 showed 30 and 0.06% of adsorption and photonic efficiency, respectively, while WO3 showed 6 and 0.01%. On the other hand TiO2/WO3 composites (1:1, 4:1, 10:1, 20:1 and 40:1) showed discolorations of 78, 91, 65, 37 and 55%, respectively, and photonic efficiencies of 0.11, 0.11, 0.10, 0.13 e 0.16%, respectively. Photocatalytic activities of the thin films against acetaldehyde degradation were analyzed at 1.00 and 5.00 ppm initial concentrations. TiO2(ac)/TiO2(bas) showed 0.8% and 1.7% photonic efficiencies in the presence of 1.00 and 5.00 ppm acetaldehyde, respectively, while the TiO2(ac)/WO3(bas) showed photonic efficiencies of 1.5% and 2.3%.