Synthesis And Photoctalytic Property Of Titanium Oxide/Tourmaline Sols And Coatings On Porous Ceramics

Photocatalytic technology is an effective way to solve the problem of fossil energy crisis and environmental pollution.Among various photocatalytic materials,titanium dioxide has become an environmentally friendly material in photocatalytically degrading organic pollutants due to the advantages of high photocatalytic activity,low cost and no secondary pollution.Loading titanium dioxide onto ceramic tiles to prepare self-cleaning ceramics is of a broad prospect in the environmental field.The TiO₂ on ceramic surface can purify the air and sterilize though photocatalytic process.However,the shortcomings of TiO₂,such as low photoquantum efficiency and weak response to visible light,limit their practical application of self-cleaning ceramics.Therefore,it is of great theoretical and practical value to modify TiO₂ to develop highly efficient TiO₂ coatings for the application in self-cleaning ceramics.For this purpose,natural tourmaline was used to modify titanium dioxide due to its spontaneous polarization electric field to improve the photocatalytic activity.In this paper,stable single-component TiO₂ sols and two-component tourmaline-TiO₂ sols were prepared by a sol-gel method.Butyl titanate was used as Ti source in a isopropanol and glacial acetic acid solution with a p H=2.The self-cleaning ceramic coatings of nano-TiO₂ and tourmaline-TiO₂ were prepared by spraying the sols on the porous ceramic tiles,followed a calcination at 300～500^oC.The techniques of X-ray diffraction（XRD）,scanning electron microscope（SEM）,infrared spectroscopy（FT-IR）,photoluminescence spectroscopy（PL）and ultraviolet-visible diffuse reflection spectra（UV-Vis）were used to characterize the phase compoations,morphologies and microstructures of the samples.Rhodamine B solution was used as a model pollutant to evaluate the photocatalytic performance of the TiO₂ sols,tourmaline-TiO₂ composites and their coatings on porous ceramics.The effect of heating temperature,time,tourmaline amount and coating amount on the photocatalytic performance were investigated systematically.As the results show,the coating of the single-component TiO₂ sol exhibits a highest photocatalytic activity when the coating amount was 2.5 g m^-2 followed by a heating treatment at 450°C for 2 h.The photocatalytic degradation rate of rhodamine B reaches 80%within 60 minutes in full UV-Vis spectrum.The TiO₂catalyst exhibits an anatase phase.As the heating time increases,the grain size TiO₂ becomes larger and larger,ruducing its specific surface area,leading to the decrease in photocatalytic activity.By coating TiO₂ sol on the ceramic surface,self-cleaning ceramic were obtained.With the increase of the coating amount of TiO₂ sol,the photocatalytic activity of the TiO₂-coated ceramics increases at first and then decreases.In addition,self-cleaning ceramics were used to purify indoor harmful gases,such as formaldehyde and ammonia.After a UV irradiation of 24hours,the removal rate of formaldehyde in a model indoor air reaches 94.4%,and the removal rate of ammonia reaches 90%,indicating that the as-obtained TiO₂-coated ceramics are of good photocatalytic activity in purifing indoor air.The two-component tourmaline-TiO₂ nanocomposite shows an enhanced photocatalytic activity by adding tourmaline.When the adding amount of tourmaline is 20%,the tourmaline-TiO₂catalyst shows the highest photocatalytic acivity,and the degradation rate of rhodamine B reaches 98.7%under the UV-Vis radiation for 60 min.The SEM Characterization shows that the anatase TiO₂nanoparticles are uniformly bounded to the matrix tightly.With the increase in the adding amount of tourmaline,the crystallinity of TiO₂ decreases,and the photocatalytic activity increases at first and then decreases.The addition of a certain amount of tourmaline obviously enhance the photocatalytic activity of TiO₂.The spontaneous polarization electric field of tourmaline can effectively inhibit the recombination of the photogenerated electrons and holes of TiO₂ under UV-Vis radiation.Tourmaline also lead to a red-shift of the UV-Visible diffuse reflection absorption edge of TiO₂.The improvement in recombination of electrons and holes,and the widened absorption light thereby enhance the photocatalytic activity of the Tourmaline/TiO₂ nanocomposites.