TiO₂ nanoparticles versus TiO₂–SiO₂ nanocomposites: A comparative study of photo catalysis on acid red 88

Highlights

• Nano TiO₂ and TiO₂–SiO₂ composites were successfully synthesized by sol–gel method.

• Acid red 88 was degraded by Nano TiO₂ and TiO₂–SiO₂ composites using solar energy.

• TiO₂ nanoparticles and TiO₂–SiO₂ nanocomposites are good photo catalysts.

Abstract

A novel, simple, less time-consuming and cost-effective wet chemical technique was used to synthesis TiO₂ nanoparticles and TiO₂–SiO₂ nanocomposites using Titanium tetra isopropoxide (TTIP) as a precursor relatively at low temperature in acidic pH. Titania sol was prepared by hydrolysis of TTIP and was mixed with silicic acid and tetrahydrofuran mixture. The reaction was carried out under vigorous stirring for 6 h and dried at room temperature. The resulting powders were characterized by UV–Visible spectroscopy, Fourier transform infrared (FT-IR), X-ray diffraction, scanning electron microscope (SEM) and transmission electron microscope (TEM). The grain size of the particles was calculated by X-ray diffraction, surface morphology and chemical composition was determined from scanning electron microscopy–energy dispersive spectroscopy, metal oxide stretching was confirmed from FT-IR spectroscopy, band gap was calculated using UV–Visible spectroscopy. Surface area of the composite as calculated by BET analyzer and it was found to be 65 and 75 m²/g for TiO₂ and TiO₂–SiO₂ respectively. The photocatalytic experiments were performed with aqueous solution of acid red 88 with TiO₂ and TiO₂–SiO₂ batch studies for 4 h irradiation, direct photolysis of TiO₂ and TiO₂–SiO₂ contributed 94.2% and 96.5% decomposition in solar radiation for the optimized concentration of acid red 88.

Introduction

Now-a-days nano crystalline photo catalysts attract the researchers for its environmental applications. Nano crystalline photo catalysts are ultra-small semiconductor particles which are a few nanometers in size. During the past decade, the photochemistry of nano semiconductor particles has been one of the fastest growing research areas in physical chemistry. The interest in these small semiconductor particles originates from their unique photo physical and photocatalytic properties [1].

Titanium dioxide has a special feature that it can use natural UV to appropriate energetic separation between its valence and conduction bands which can be surpassed by the energy content by a solar photon. Therefore, degradation of the organic pollutants present in wastewater using irradiated TiO₂ suspension is the most promising process [2]. Titanium dioxide has strong resistance to chemical and photo corrosion and its safety, low cost and biological harmless issues, limits the choice of convenient alternative [3]. Moreover, TiO₂ is more stable than other photo catalysts in ambient conditions and can be recycled [4]. Among various semiconductor materials tested under similar conditions for the degradation of organic compounds, titanium dioxide (TiO₂) has been demonstrated as the most active photo catalyst [4].

TiO₂ photo catalyst has the advantages of high chemical stability, high photocatalytic activity to oxidize pollutants in air and water, relative low-price and nontoxicity [5]. TiO₂ thin film photo catalysts have been used for environmental applications (air and wastewater treatment and deodorizers), because of its large specific surface area, high photocatalytic activity, strong oxidizing powder, self-cleaning function, bactericidal and detoxification activities [6], [7], [8]. To date, various investigations have been conducted and reported that the mixed oxide (TiO₂/SiO₂) is more effective than that of Titanium dioxide [9]. Moradi et al. [10] investigated that TiO₂/SiO₂/Co nanocomposites with Hydroxyl Propyl Cellulose had the best photo-catalytic activity. The photocatalytic degradation of organic compounds of olive mill wastewater was investigated by using core–shell–shell Fe₃O₄/SiO₂/TiO₂ nanoparticles as catalyst [11]. Balachandran et al. stated that Isolan black dye was decolorized by TiO₂ and SiO₂ doped on TiO₂ [12].

Daneshvar et al. [13] reported that zinc oxide is a suitable alternative to TiO₂ since its photo degradation mechanism have been proven to be similar to that of TiO₂. The textile dyes produce large quantity of highly colored effluents, which are generally toxic and resistant to destruction by biological treatment methods for color removal [13], [14]. Even though many physical and biological methods are available, the direct use of clean and renewable solar light and active photo catalysts for decolourization and degradation of azo dyes have attracted great interest in recent years [15], [16].

Furthermore to improve the efficiency of the catalytic activity more emphasis is placed on mixing TiO₂ with SiO₂ [17]. The addition of SiO₂ helps to create new catalytic active sites due to interaction between TiO₂ and SiO₂ [17], [18], [19], [20]. TiO₂–SiO₂ mixed oxides show higher thermal stability, adsorption capability and good redox properties [21].

In the present work we synthesized TiO₂ nanoparticles and TiO₂–SiO₂ nanocomposites and characterized them by UV spectroscopy, FTIR, XRD, SEM and TEM. The photocatalytic properties of synthesized TiO₂ nanoparticles and TiO₂–SiO₂ nanocomposites were studied using acid red-88 dye under solar radiation.