Photocatalytic effect of β-cyclodextrin on semiconductors for the removal of Acid Violet dye under UV light irradiation

Abstract

This study describes an experimental method for the evaluation of the photodecoloration efficiency of Acid Violet (AV) dye under UV light irradiation by comparing TiO_2, ZnO, TiO₂/β-cyclodextrin (TiO₂/β-CD), and ZnO/β-CD. The effects of concentration of dye, pH, and dose of the catalyst on photodecoloration efficiency were assessed. The mechanism for photodecoloration of AV dye under UV light irradiation was proposed. From the results, it is established that photodecoloration efficiency was doubled with TiO₂/β-CD and ZnO/β-CD than compared with pure TiO₂ and ZnO. Photocatalytic decoloration efficiency is increased from 80 to 95% with TiO₂/β-CD and ZnO/β-CD. Kinetics results showed that the photocatalytic decoloration of AV dye follows pseudo-first-order kinetics. Photo decoloration efficiency of ZnO/β-CD was higher than TiO₂/β-CD. The catalysts were characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and ultraviolet-diffuse reflectance spectroscopy (UV-DRS) analyses. FE-SEM analysis showed that there is no change in surface morphology in TiO₂/β-CD and ZnO/β-CD systems compared to bare TiO₂ and ZnO systems. XRD analysis shows that the crystalline features does not change by addition of β-CD. UV-DRS analysis showed that band gap energy of ZnO/β-CD system is higher than other catalytic systems. Therefore, ZnO/β-CD adsorbs more light photons than other systems. Optical thickness measurements showed that 2 g/L of catalysts is optimum for the photocatalytic decoloration process. Fourier transform infrared spectroscopy (FT-IR), UV–visible analysis and ¹H NMR analyses confirm the formation of inclusion complex between AV dye and β-CD. The ¹H NMR analysis of β-CD showed that the phenyl ring of AV dye is protruded into β-CD cavity.

Keywords:

• Acid Violet dye
• COD
• Photo decoloration efficiency
• TiO₂/β-CD and ZnO/β-CD

Acknowledgments

The authors thank the Management and the Principal of Ayya Nadar Janaki Ammal College, Sivakasi, India, for providing necessary facilities. Authors also thank the University Grants Commission, New Delhi, for providing financial support through UGC-Major Research Project [UGC – Ref. No. F. No. 38-22/2009 (SR) Dated: 19.12.2009]. Authors also acknowledged Bharadithasan University, Trichy, for recording FE-SEM and ¹H NMR spectra and Department of Earth Science, Pondicherry University, Pondicherry, for recoding XRD spectrum.