Fabrication Of CaSiO₃-stabilized Silver Series-doped TiO₂Composites And Their Photocatalytic Properties

There were two drawbacks for titanium dioxide powders in a practical application.The one obstacle in the application of TiO2powders was that the small photocatalystparticles were inclined to agglomerate and leaded to the photocatalysts running off afterwater treatment when the photocatalyst was used as suspending liquid. The other one wasthe fast recombination rate of the generated charge carriers and the low transfer rate ofelectrons to oxygen decrease the efficiency of TiO2, in addition, the large band is gappedfor TiO2(3.2and3.0eV for anatase and rutile, respectively), which obstructed itsapplications in visible light range. So, the objective of this study was to improve theperformance of TiO2photocatalyst. In this work, calcium metasilicate was prepared via thechemical reaction between calcium nitrate solution and sodium silicate solution which wasextracted from fly ash. In addition, a range of composites, including TiO2/CaSiO3,Ag-TiO2/CaSiO3and Ag-AgX-TiO2/CaSiO3(X=Cl, Br, I) composites were synthesized.The activity of photocatalysts was evaluated through the degradation rate of MethylOrange (MO). The major studies were shown as follows.First, fly ash was used to extract sodium silicate solution and then obtainedmicrocellular structure calcium metasilicate material via chemical reaction. Then, a rangeof calcium metasilicate-silver promoted-anatase (TiO2-CaSiO3) photocatalysts wasobtained physisorption methods. The photocatalytic results showed that the8wt.%TiO2/CaSiO3products have higher activity during the reaction,Ag-TiO2particles were synthesized by in stiu method and then they were supportedon calcium metasilicate material by a physical adsorption process. The UV and visiblelight photocatalytic activity were investigated. The Ag-TiO2/CaSiO3with4%Ag-depositedconcentration shows optimum activity, and the activity decreased with the further increaseof Ag concentration. The products showed excellent reusability after that these wererepeated five times. The sample with4%Ag concentration exhibited highest activity undervisible light irradiation due to the surface plasmon resonance (SPR) effect of Agnanoparticles. However, the visible light photocatalytic activity of Ag-TiO2/CaSiO3wasinsufficient.Four-component calcium metasilicate (CaSiO3)-loaded Ag-AgX/TiO2(X=Cl, Br, I) photocatalysts were fabricated by chemical precipitation, photoreduction and physicaladsorption processes. The surface structure and morphology of as-prepared products wereconducted by Scanning electron microscope (SEM); the valence state of Ag element inAg-AgX-TiO2(X=Cl, Br, I) were confirmed by the analysis of X-ray photoelectronspectroscopy (XPS). The optical properties of Ag-AgX-TiO2/CaSiO3(X=Cl, Br, I) wereinvestigated by UV-vis spectrophotometer. The visible light photocatalytic for degradationof polycyclic aromatic hydrocarbonsmethyl (MO, sodium fluorescein (NaFI) and ethylrhodamine B (ERB)), the experimental results showed that the Ag-AgX-TiO2/CaSiO3(X=Cl, Br, I) possessed high activity for the three organics under visible light irritation (λ>400nm). The possible visible-light photocatalytic degradation mechanism was discussed.The results indicated that CaSiO3were suitable for catalyst support materials and alsoprovided a workable avenue for utilization of fly ash. The novel composite photocatalystshave profound potential applications in dealing with environmental pollutants.