Hydrothermal synthesis of bare TiO2 nanowires and polystyrene (PS)-TiO2 nanowires used for selective photocatalytic oxidation of 3-pyridinemethanol in water and PS photodegradation in solid state

Abstract

In the present work, nanowire (NW) structured TiO2 nanoparticles were prepared using the hydrothermal method and characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), and BET specific surface area techniques. They were obtained in the anatase phase and presented a high surface area (ca. 300 m2/g). A commercial TiO2 (anatase, Merck) was used for comparison. The TiO2 catalysts were tested for photocatalytic oxidation of 3-pyridinemethanol to 3-pyridinemethanal and vitamin B3 in water under UVA irradiation. The effects of acid treatment and subsequent calcination for TiO2 catalysts after the hydrothermal synthesis were also investigated. The sample, subjected to acid treatment and calcined at 300 °C (NW-HCl-300), showed the highest photocatalytic activity and selectivity towards the products. Consequently, this sample and Merck TiO2 were used to prepare polystyrene (PS)/TiO2 composites using the hydrothermal method. They were characterized by XRD, SEM–EDX, Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), UV–Vis, Gel Permeation Chromatography (GPC), and contact angle measurements and tested for PS (present in the composite) photodegradation. The results indicated that NW-HCl-300 had a high surface area, and was highly hydroxylated, favouring a good distribution of PS in the composite. The composite presented high thermal stability, but under UVA irradiation the polymer underwent solid-state photocatalytic degradation due to the contact with TiO2. The composite photodegradation was investigated using gravimetric, GPC, FT-IR, UV–Vis, and SEM techniques.