Sol-gel Preparation of Hollow Spherical x%B-TiO2 Photocatalyst: The Effect of Boron Content on RBR X-3B Decoloration

Background: The potential of applying TiO2-based materials has been ascertained in both wastewater and polluted air. Boron is proven to be an effective dopant to promote the activity of TiO2 in our previous work. The density of hollow material is little larger than water so that the hollow photocatalyst can suspend in wastewater under stirring or aeration. Methods: The graphical spheres were prepared from glucose using hydrothermal method. The hollow spherical x%B-TiO2 was synthesized through a sol-gel route, using tetrabutyl titanate and tributyl borate in the precursor. The materials were characterized by X-ray diffraction, scanning electron microscope, infrared spectrum, X-ray photoelectron spectroscopy, and N2 adsorption-desorption techniques. Photocatalytic degradation of RBR X-3B dye was studied to show the activity of the x%B-TiO2 materials. Results: Anatase TiO2 phase forms in all the x%B-TiO2 samples despite the difference in boron content. An absolute Ti⁴⁺ oxidation state exists in the x%B-TiO2, which is hardly affected by the doped boron. XPS analysis proves the formation of B-Ti-O structure in anatase TiO2 lattice. BET surface area increases with rising boron doping content in the hollow spherical x%B-TiO2 samples. Photocatalytic activity of TiO2 is enhanced after doping boron. The photocatalytic efficiency on RBR X- 3B degradation reaches the maximum value when n(B)/n(Ti) is 8%. After five photocatalytic cycles, decoloration efficiency on 8%B-TiO2 is as much as 80% of the initial value. Conclusion: A continuous expansion of TiO2 crystal happens with increasing boron content. The Ti4+ oxidation state of titanium in the hollow spherical material is not changed after doping boron. BET surface area of the hollow spherical x%B-TiO2 increases with rising boron doping content. The hollow spherical 8%B-TiO2 has satisfactory performs for recycling and lifetime.