Functionalized C@TiO2 hollow spherical architecture for multifunctional applications

Abstract

Hierarchical anatase titania (TiO₂) with a hollow spherical architecture decorated with functionalized carbon dots (C^F@THS) was synthesized by a solvothermal decomposition of titanium(IV) isopropoxide (TTIP) in the presence of a solution mixture containing thiourea and citric acid. Interestingly, the concomitant presence of thiourea and citric acid has been found to be essential to obtain such hierarchical hollow architecture because individual constituents produced non-hollow spheres when hydrothermally treated with TTIP. The co-existence of these two constituents also accelerates the growth of hollow spheres. BET surface area study of C^F@THS revealed the existence of a slit like mesoporosity with a surface area value of 81 m² g⁻¹. Time dependent FESEM and TEM studies confirmed the formation of nanoflake like structures in the intermediate stages followed by the growth of a hollow spherical architecture. We proposed that these nanoflakes get accumulated on the bubble surface to form such hollow spherical morphology. The PL spectral study and Raman shift of the as prepared C^F@THS confirmed the presence of functionalized graphitic C dots on the surface. A thorough XPS analysis was conducted to explore the nature and relative atomic concentration of the functional groups (–COOH, –CONH₂, –NH₂). This C^F@THS sample showed very fast and selective dye (methylene blue and methyl violet) adsorption ability (even from a mixture of two different dye solutions) due to these δ-site containing functional groups on the surface. As C^F@THS showed only two times reusability for adsorption, the dye adsorbed C^F@THS was calcined at 450 °C in air to yield organic free anatase TiO₂ hollow spheres (THS) with a retention of the original structure. THS was recycled as an efficient and a reusable photocatalyst (k = 9.36 × 10⁻² min⁻¹) as well as a photoanode in dye sensitized solar cells (DSSCs) having J_sc value of 19.58 mA cm⁻² with overall efficiency of 6.48%.