Research On The Preparation Of Bismuthoxyhalides And Their Photosensitization Decomposition Of Rhodamine B

Bismuth oxyhalides of Bi OX(X = Cl, Br, I) currently still attracts great attention because of their potential applications in solar light utilization(such as heterogeneous photocatalysis). In the thesis, a new preparation scheme of Bi OX(X=Cl, Br, I) has been obtained through a reduction/oxidation-hydrolysis method, by using Na Bi O3 and hydrogen halide solution as the starting materials. Based on the investigation of microstructure and optical properties of as-prepared samples, the sorption, photosensitized decomposition performance of Rhodamine B(selected as model contaminant) as well as the corresponding mechanisms has been studied. Furthermore, the activity-structure relationship between the photodegradation activity and frontier orbital energy of selected model contaminant has been preliminarily established. The main studies in the thesis are listed as follows,(1) Bi OX(X=Cl, Br, I) semiconductor compounds were prepared through a reduction/oxidation-hydrolysis method, using Na Bi O3 and hydrogen halide solution as the starting materials. It was found that the diameters of as-prepared Bi OCl, Bi OBr and Bi OI nanoplates were measured at around 690 nm,650 nm and 120 nm, respectively. Selected area electron diffraction analysis clearly showed the single crystalline characteristics of as-prepared Bi OX nanoplates which are vertical to the c axis([001] direction). UV-Vis diffuse reflectance indicated that the optical absorption of Bi OX(X=Cl, Br, I) starts from 374 nm, 434 nm and 682 nm, respectively.(2) The sorption kinetics, thermal dynamics and sorption isotherms of Rhodamine B onto Bi OCl and Bi OBr were studied. The sorption kinetics study showed that the pseudo-second-order kinetics model could fit the sorption data better than pseudo-first-order kinetics model. The results from Langmuir fitting suggest that the monolayer saturated sorption capacity of Bi OCl(11.3 μmol g-1) is slightly lower than that of Bi OBr(13.0 μmol g-1). Moreover, the Zeta potential measurement showed that the isoelectrical points of Bi OCl and Bi OBr were 2.2 and 3.4, respectively, indicating the possible electrostatic sorption mechanism of Rh B occurred on negative charged Bi OCl and Bi OBr in Rh B solution(p H value of around 5).(3) It was found that the Rh B molecules could be effectively decomposed in the presence of Bi OX(X=Cl, Br) under visible light exposures from either 532 nm pulse laser or Xenon lamp(λ>400 nm,λ>420 nm,λ=550±15 nm), even if the semiconductors were unexcited. Both UV-Vis absorption measurement and HPLC results demonstrated the de-ethyl process and formation of Rhodamine 100 molecules in the reaction.(4)The ELUMO values of Rhodamine B, Methyl Orange and Methylene blue molecules were calculated, by using density function theory based B3 LYP and MP2 methods in Gaussian 03 program. It was found that higher ELUMO could be benefit for faster photosensitization process, due to the photogenerated electron from model comtaminats could inject into the conduction band of semiconductor much efficiently.