| The structure-activity relationships between the structure and photocatalytic activity of sulfate-modified titanium-bearing blast furnace slag were studied, and providing a solid theoretical foundation for the development and application of titanium-bearing blast furnace slag. In this paper, the photocatalysis mechanism of Cr6+ single system and Cr6+/organic compound combined pollution system in the presence of titanium-bearing blast furnace slag was first explored, which is profound significance for the real wastewater containing organic species and heavy metals.Firstly, the components and microstructures of TBBFS, SATBBFS and STBBFS photocatalysts were examined by XRF, XRD, SEM, UV-Vis-DRS, TG and FTIR. Then the feasibility of three kinds of photocatalytic materials as photocatalysts is determined. The effects of crystalline phase, surface morphology, powder particle size, calcinations temperature, doped different sulfate and the ratio of sulfate-doped on the photocatalytic activity for Cr6+ by the three kinds of photocatalysts were investigated. By comparing the photocatalytic activities of the 35 kinds of photocatalysts, it can be concluded that the photocatalytic activity of (sulfate-modified titanium-bearing blast furnace slag, STBBFS) photocatalyst is the highest.The effects of the initial concentration, catalyst amount, adsorption temperature and solution pH on the adsorption efficiency for Cr6+ by the STBBFS adsorbents were systematically studied; and the adsorption isotherm model, adsorption kinetics model, thermodynamic parameters and adsorption mechanism were also explored. The results showed that the adsorption data followed the Langmuir model rather than the Freundlich model, and the adsorption equilibrium was described by the Langmuir isotherm model with a maximum adsorption capacity of 8.25 mg/g of Cr6+ ions onto the STBBFS adsorbents at pH= 1.5. A pseudo-second-order kinetic model shows a good fitting to the experimental results at different initial concentrations and adsorption temperatures. The thermodynamic parameters, such as enthalpy change (ΔH°), free energy change (ΔG°) and entropy change (ΔS°) have been analyzed. The thermodynamics of Cr6+ ions onto the STBBFS adsorbents indicates the spontaneous and endothermic nature of the adsorption process. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis show that in the process the reduction of Cr6+ could be followed after the adsorption of Cr6+.The feasibility of photocatalytic reduction of Cr6+ by STBBFS photocatalyst in Cr6+ single system was systematically studied. The UV wavelength and intensity, solution pH, acid medium, the initial concentration, catalyst life and separation efficiency were also studied. The photocatalytic reduction mechanism and L-H kinetic mechanism of Cr6+ in Cr6+ single system were also explored. The results showed that, with the increase of light intensity, the photocatalytic reduction efficiency of Cr6+ increased; the photocatalytic reduction efficiency of Cr6+ reached maximum at pH=1.5; the order of the inhibitory effect of four acidic ions (SO42-, Cl-, NO3-, PO43-) on the photocatalytic reduction efficiency of Cr6+ was PO43->NO3>Cr>SCO42-; the initial concentration had a great influence on the photocatalytic reduction efficiency of Cr6+; in accordance with the results of orthogonal test, influencing ratio of the different factors was:pH> initial concentration> acidic medium> catalyst dosage; the photocatalytic reduction of Cr6+ in Cr6+ single system followed L-H kinetics.The feasibility of photocatalytic reduction of Cr6+ by STBBFS photocatalyst in Cr6+-AA system was systematically studied. The effects of the volume ratio of AA/Cr6+, the initial concentration, solution pH and synergistic effect factor on the photocatalytic reduction efficiency of Cr6+ in Cr6+-AA system were studied; The photocatalytic reduction mechanism and L-H kinetic mechanism of Cr6+ in Cr6+-AA system were also explored. The results showed that, the maximum rate of Cr6+ reduction was obtained for an initial AA/Cr6+ volume ratio, R=0.2%, a further increment in R being disadvantageous; the initial concentration still had a great influence on the photocatalytic reduction efficiency of Cr6+; with the increase of initial solution pH(pH=1.5-3.5), photocatalytic reduction efficiency and adsorption efficiency of Cr6+ decreased significantly; according to the results of orthogonal test, influencing ratio of the different factors was:pH> initial concentration> AA/Cr6+ volume ratio> catalyst dosage; the photocatalytic reduction of Cr6+ in Cr6+-AA system also followed L-H kinetics. The synergistic effect factor is always greater than 0 in the compound system, indicating that a marked synergistic effect between the photocatalytic reduction of Cr6+ and acetic acid.The feasibility of photocatalytic reduction of Cr6+ by STBBFS photocatalyst in Cr6+-CA system was systematically studied. The effects of the molar ratio of CA/Cr6+, the initial concentration, solution pH and synergistic effect factor on the photocatalytic reduction efficiency of Cr6+ in Cr6+-AA system were studied; The photocatalytic reduction mechanism and L-H kinetic mechanism of Cr6+ in Cr6+-CA system were also explored. The results showed that, the maximum rate of Cr6+ reduction was obtained for an initial CA/Cr6+ molar ratio, R=3.75, a further increment in R being disadvantageous; the initial concentration had a little influence on the photocatalytic reduction efficiency of Cr6+; the highest reduction efficiency and adsorption efficiency of Cr6+ were obtained at pH=2.5 and pH=1.5, respectively; with the increase of initial solution pH(pH=1.5-3.5), adsorption efficiency of Cr6+ decreased significantly, and yet photocatalytic reduction efficiency of Cr6+ decreased slightly; the photocatalytic reduction of Cr6+ in Cr6+-CA system also followed L-H kinetics. The synergistic effect factor is always greater than 6 in the compound system, indicating that a marked synergistic effect between the photocatalytic reduction of Cr6+ and citric acid.The feasibility of photocatalytic reduction of Cr6+ by STBBFS photocatalyst in Cr6+-CA-FN system was systematically studied. The effects of the molar ratio of Fe3+-CA/Cr6+, the initial concentration, solution pH and synergistic effect factor on the photocatalytic reduction efficiency of Cr6+ in Cr6+-CA-FN system were studied; The photocatalytic reduction mechanism and L-H kinetic mechanism of Cr6+ in Cr6+-CA-FN system were also explored. The results showed that, the maximum rate of Cr6+ reduction was obtained for an initial Fe3+-CA/Cr6+ molar ratio, R=0.019; the initial concentration had a great influence on the photocatalytic reduction efficiency of Cr6+; the highest reduction efficiency and adsorption efficiency of Cr6+ were obtained at pH=2.5 and pH=1.5, respectively; with the increase of initial solution pH(pH=1.5-3.5), photocatalytic reduction efficiency and adsorption efficiency of Cr6+decreased significantly; the photocatalytic reduction of Cr6+in Cr6+-CA-FN system also followed L-H kinetics. The synergistic effect factor is always greater than 1 in the compound system, indicating that a marked synergistic effect between the photocatalytic reduction of Cr6+, Fe3+ and citric acid.The feasibility of photocatalytic disposal of Cr6+-methyl orange (MO) system by STBBFS photocatalyst was systematically studied. The effects of the initial concentration, solution pH and synergistic effect factor on the photocatalytic disposal of Cr6+-MO system were studied; The mechanism of the photocatalytic disposal of Cr6+-MO system and L-H kinetic were also explored. The results showed that, the synergistic effect factor of MO is always greater than Cr6+ in Cr6+-MO system, indicating that a marked synergistic effect between the photocatalytic reduction of Cr6+ and the photocatalytic oxidation of methyl orange. |
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