Ecofriendly alkali metal cations diffusion improves fabrication of mixed-phase titania polymorphs on fixed substrate by chemical vapor deposition (CVD) for photocatalytic degradation of azo dye

Abstract

Controlling the nanoscale synthesis of semiconductor TiO₂ on a fixed substrate has fascinated the curiosity of academics for decades. Synthesis development is required to give an easy-to-control technique and parameters for TiO₂ manufacture, leading to advancements in prospective applications such as photocatalysts. This study, mixed-phase TiO₂(B)/other titania thin films were synthesized on a fused quartz substrate utilizing a modified Chemical vapor depodition involving alkali-metal ions (Li⁺, Na⁺, and K⁺) solution pre-treatment. It was discovered that different cations promote dramatically varied phases and compositions of thin films. The films had a columnar structure with agglomerated irregular-shaped particles with a mean thickness of 800-2000 nm. Na⁺ ions can promote TiO₂(B) more effectively than K⁺ ions, however Li⁺ ions cannot synthesize TiO₂(B). The amounts of TiO₂(B) in thin films increase with increasing alkali metal (K⁺ and Na⁺) concentration. According to experimental and DFT calculations, the hypothesized TiO₂(B) production mechanism happened via the meta-stable intermediate alkaline titanate transformation caused by alkali-metal ion diffusion. The mixed phase of TiO₂(B) and anatase TiO₂ on the fixed substrate (1 × 1 cm²) obtained from Na⁺ pre-treated procedures showed significant photocatalytic activity for the degradation of methylene blue. K₂Ti₆O₁₂, Li₂TiO₃, Rutile TiO₂, and Brookite TiO₂ phase formations produced by K⁺ and Li ⁺ pretreatment are low activity photocatalysts. Photocatalytic activities were more prevalent in NaOH pre-treated samples (59.1% dye degradation) than in LiOH and KOH pre-treated samples (49.6% and 34.2%, respectively). This revealed that our developed CVD might generate good photocatalytic thin films of mixed-phase TiO₂(B)/anatase TiO₂ on any substrate, accelerating progress in future applications.

Keywords: Alkali metal cation; Chemical vapor deposition; Dye degradation; Phase formation; Photocatalytic TiO(2); Titania/titanate thin films.