Photocatalytic degradation of P-Cresol using TiO₂/ZnO hybrid surface capped with polyaniline

ABSTRACT

This study evaluated the photocatalytic activity of polyaniline (PANI)-capped titanium dioxide and zinc oxide (TiO₂/ZnO) hybrid, for the degradation of P-Cresol. The hybrid was synthesized by precipitating ZnO on the surface of commercial TiO₂. An “in situ” chemical oxidative polymerization method was used to prepare the PANI capped hybrid (TiO₂/ZnO/PANI). The photocatalysts were characterized by powder X-ray diffraction (XRD), a Brunauer Emmett Teller (BET) analyzer, Fourier-transform infrared (FTIR) and photoluminescence spectroscopies, high resolution-transmission electron microscopy (HR-TEM) and thermogravimetric analysis (TGA). During photodegradation under ultraviolet (UV) irradiation, ZnO, TiO₂, TiO₂/ZnO hybrid and TiO₂/ZnO/PANI composite had P-Cresol removal of 43%, 50%, 61% and 99%, respectively. The higher activity of the TiO₂/ZnO hybrid as compared to TiO₂ and ZnO was attributed to a reduced electron–hole pair recombination. The recombination was further significantly reduced upon introduction of PANI; hence, the highest activity observed with TiO₂/ZnO/PANI. The initial reaction rate constant for TiO₂/ZnO/PANI (0.9679 min⁻¹) was more than twice compared to that for TiO₂/ZnO hybrid (0.1259 min⁻¹). A synergistic effect between PANI and TiO₂/ZnO resulted in a highly efficient charge separation caused by the transfer of photogenerated holes from the hybrid to highest occupied molecular orbitals (HOMO) of PANI. The best TiO₂/ZnO/PANI (PANI to TiO₂/ZnO) ratio observed was 0.5:2 for the photodegradation of P-Cresol. Total organic carbon (TOC) analysis indicated a 97.4% mineralization of P-Cresol with PANI/TiO₂/ZnO.

KEYWORDS:

• Annular reactor
• polyaniline
• p-cresol
• titanium dioxide
• UV light
• zinc oxide

Acknowledgments

The authors pay much gratitude to the contribution of Mr. B.M. Xaba for TEM images analysis and their interpretations.

Funding

The authors wish to acknowledge Water Research Commission (WRC, South Africa) for the financial support (Project no. K5/2388).