Sol-Gel Preparation and Characterization of Anti-Reflective and Self-Cleaning Sio2 - Tio2 Double Layer Films

Sol-gel preparation and characterization of anti-reflective and self-cleaning SiO2 - TiO2 double layer films

Ömer Kesmez1, H. Erdem Çamurlu2, Esin Burunkaya1, Ertuğrul Arpaç1,3

1 Nano-N

2 Mechanical Engineering Department, Akdeniz University, 07058, Antalya, Turkey

3 Department of Chemistry, Akdeniz University, 07058, Antalya, Turkey

Abstract

Glass substrates were first coated with SiO2 and then TiO2 by dipping into sols which were prepared by 2 different methods involving complex formation and hydrolysis, using ethanol (EtOH) or butyl glycol (BG). Concentration of TiO2 in the sols was kept at 0.1 wt% and 0.5 wt%. Prepared coatings were investigated by field emission scanning electron microscope (FESEM), atomic force microscope (AFM), hazemeter, UV-visible spectrophotometer and ellipsometer. Rhodamine B (RhB) photodegradation tests were performed in order to evaluate photocatalytic activity. Application of SiO2 as the bottom layer increased the transmittance by 6% points, thereby compensated for the loss of transmittance caused by the TiO2 top layer. Pencil hardness values of the obtained coatings were in 5B-3H range. TiO2 coatings obtained from sols containing 0.5% TiO2 and BG solvent represented the highest photocatalytic activity, with a rate constant of 0.0457 h-1 and a half period of 15.2 h. Self-cleaning surfaces were obtained while maintaining the anti-reflectance.

Keywords: Photocatalysis, TiO2 coating, SiO2/TiO2 coating, anti-reflectance

1. Introduction

Coatings have been applied on glass in order to obtain various properties, which render the glass more useful, such as anti-reflection, anti-static, defogging, anti-abrasion, self-cleaning, solar control, electrical conductivity, etc. Appropriate compounds are coated as a thin film on glass by a variety of techniques, in order to obtain the particular desired property [1-3]. SiO2 coatings, for example, have attracted attention due to their enhancement of light transmittance of glass as a result of their low refractive index and low surface scattering [4-6]. SiO2 coated anti-reflective (AR) glasses are currently used commercially in TV screens, picture framing, optical lenses and solar panels [7-10]. TiO2 coatings, in addition to their many other uses such as in photovoltaic and electrochromic applications, have been applied for self-cleaning, air purification and photocatalytic sterilization purposes due to their well-known photocatalytic activity [1,2,11]. Photocatalytic effect is basically the decomposition of organic contaminant compounds adsorbed on the surface of TiO2, with the aid of visible (VIS) or ultraviolet (UV) light [1,2,11,12]. The self-cleaning (SC) property