| BiOCl, with an unique layered structure differing from other semiconductors, has exhibited promising application in the photo-catalysis field. It has been reported that BiOCl with different exposed facet shows various photo-catalytic efficiency. In this work, (001) facet BiOCl was papered through a hydro-thermal method. Pt was loaded on the surface of BiOCl with surface decoration by UV light via diping-method and photo-depositon method. The microstructure, optical property and crystal structure of these samples were characterized by the XRD, SEM, HRTEM, UV-vis DRS and EPR measurements. The photo-activity of the as-prepared BiOCl and BiOCl/Pt were then evaluated by photo-oxidation of NO (gas phase reaction) and photo-degradation of methyl orange (MO) and RhB (liquid phase reaction). The conclusions were listed as follow:1. The photoactivity of BiOCl under different light irradiation(1) BiOCl nanoplates exhibited much higher activities in both oxidation of NO and degradation of MO under UV-visible light than that under visible light irradiation, which is consistent with the fact that BiOCl itself with bang gap of 3.37 eV. Surprisingly, the results for the photo-degradation of RhB are totally different:RhB is decomposed much more quickly under visible light than that under UV-visible light. The corresponding rate constant k was calculated to be 0.034, and 0.013 min-1, respectively, even the light intensity of UV-visible light (196 mW/cm2) is stronger than that of visible light (183 mW/cm2).(2) The degradation of RhB over BiOCl under visible light is mainly due to the photosensitization. Nevertheless, under UV-visible light irradiation, the situation becomes more complicated:on the one hand, RhB could still be excited and electrons would be transferred to the CB of BiOCl; on the other hand, BiOCl would also be excited and oxygen vacancies were in situ generated through the absorption of UV light. These oxygen vacancies, as the acceptor level near the CB, could effectively trap photoexcited electrons on the CB of BiOCl originated from RhB. These trapping effects decrease· the reduction ability of these electrons thermodynamically and make the generation of O2-· much harder, blocking the degradation pathway through O2-· radicals. The electrons trapped by the acceptor level recombine with the holes instead of react with O2.This is the reason why the efficiency of RhB degradation under UV-visible light is far less than that under visible light.2. The photodegredating of NO with the surface-decorated BiOCl and BiOCl/Pt composite(1) After illuminated by the UV light in different condition, the white BiOCl turned to grey, yellow and black, respectively, which indicated the different concentration of oxygen vacancy on the surface of samples. The phase structures of samples were not changed through the light irradiation, while the optical property differs from one to another. The grey and yellow powder shows a little enhanced-adsorption in the visible light region and a broad peak at the 400 nm, meanwhile the black one exhibits strong tail visible light adsorption due to the large amount of oxygen vacancy on the surface of BiOCl.(2) The modified BiOCl do not represent better photocatalytic performance of NO than the white one, which is consist with the photo current test. It is attributed to that the existence of oxygen vacancy accelerated the recombination of charge carriers.(3) The BiOCl/Pt composites synthesized via diping method show higher photooxidation efficiency of NO than the BiOCl. The effective separation of holes and electrons induced by the surface Plasmon resonance should be responsible for the enhancement of photoactivity. Comparing the reaction activity of Pt anchored on the surface of black BiOCl through the diping method and photodepositon, it is concluded that the composites prepared by different ways both reduce the photoreaction activity. The reason for the phenomenon is that the large amount of oxygen vacancy induced by the reductive agent and UV light results in the aggeragation of Pt and the recombination of carriers.3. The preliminary photo-thermal catalytic property study on the BiOCl and BiOCl/Pt composite.(1) For the white and black BiOCl, they both exhibit a stable photo-thermo activity, and the highest oxidative efficiency of them occurs at 130℃. But the reaction cannot be initiated by the visible light and the thermo energy of 200℃, which implies that the light can not only decrease the thermo-catalytic temperature but also increase the reaction rate.(2) For the composite, the photo-thermo activity is inhibited by the gathering of Pt along with the rise of temperature. |
