| Photocatalytic technology, which is capable to convert solar energy to chemical energy and to degrade thoroughly pollutants to such inorganic small molecules as H2O and CO2, is a promising avenue to address environmental pollution and energy shortage and, therefore, has drawn much attention. Photocatalyst is the key of the technology and its responsiveness to wide wavelength light, efficiency and persistence determine whether it can be effectively applied in practice although many semiconductor materials have been demonstrated to have photocatalytic activity. This paper is aimed to investigate preparing photo catalysts through modification and recombination which can effectively degrade organic pollutants under visible light irradiation and then to explore their photocatalytic efficiency and discuss the mechanisms.First, a hierarchical porous TiO2monolith (PTM) with well-defined macroporous and homogeneous mesoporous structure is prepared via a sol-gel phase separation method. P123is used as the mesoporous template and graphene oxide has been applied to increase the activity and integrity of the monolithic TiO2. According to SEM and BJH measurements, PTM is mainly composed of10nm anatase crystallines with3.6nm mesopores and2-8um macropores and its specific surface area is up to163m2/g. The PTM with0.07wt%graphene oxide dosage shows a high efficiency for methyl orange (MO) decolorization under both full spectrum and visible light irradiation (λ>400nm) and is4.1times and2.3times more efficient than without grapheme oxide respectively, and it remains intact after the degradation. The prepared porous TiO2monolith can immobilize nanoparticles and avoid separation process, and is promising to be used in water pollution control.Second, BiVO4treated in HC1aqueous solution can achieve enhanced photo catalytic activity. After being treated in0.1mol/L HC1solution for6hours, the photo catalytic activity of BiVO4for phenol degradation under visible light irradiation is3.5times more efficient. Characterizations have been carried out to analyze the crystal component and surface morphology of the treated sample. Compared to the control samples treated in different acids and chlorides, it indicates that, due to the synergistic effect of H+and Cl-ions in the solution, BiVO4partially dissolved and deposited as BiOCl, and finally a composite formed which contains micron-particle BiVO4with pits over the surface and flake BiOCl with its composition of2.08%. The flat band potential of BiOCl was measured by a slurry method. The results of energy band analysis and photo catalytic activity tests of BiVO4and BiOCl mixed particles suggested that there was no interparticle electron transfer effect between them. Therefore, the enhanced photo catalytic performance of the treated BiVO4can be attributed to the uneven surface which can facilitate the separation of photo generated charges. This kind of surface treating method could be effective to develop photo catalysts with enhanced photo catalytic performance.Third, through blending Au/BiVO4and BiOI in different ratios, a complex was obtained with highly improved photo catalytic activity. In tests on the photo catalytic performance of the complex for phenol degradation under visible light irradiation, the complex showed the highest photocatalytic activity when the ratio of Au/BiVO4to BiOI is5:1. Moreover, the photocatalytic activity of the complex is hardly affected by low pH while, with pH increasing, its performance improves drastically. The cycling runs were carried on to evaluate the photocatalytic stability of the complex and the results showed that the degradation rate of phenol maintained a high level, suggesting that the complex has high photocatalytic stability. The last, the complex mechanism was explored and it is argued that the high photocatalytic performance is likely to be attributed to a Z-scheme. |
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