Synthesis, Characterization of SiO₂/TiO₂ and SiO₂/Al₂O₃ Nano-Composites for the Photo-Degradation of Acid Brown- 43 dye with Irradiation of Solar Light  

Introduction

Now a days, photocatalysis of semiconductors havingconcerned a countless deals of investigationowing to its possible application to solve environmental difficulties. Subsequently a photocatalytic practice is based on the generation of electron/hole pairs by means of band-gap radiation; the coupling of dissimilar semiconductor metal-oxides seems beneficial to attain a additional efficient electron-hole pair separation under irradiation and a higher photocatalytic activity.¹ Nanoparticles of Metal-Oxide attract countlessconsideration in current years an account of their superior electronic and chemical properties. TiO₂ is largely used as photocatalyst due to its high photocatalytic efficiency, physical and chemical stability, low cost and toxicity. In recent yearssome research papers concerning the enhancing of TiO₂ photocatalytic activity have been described.^2-4 So manyconcerns modifying the photocatalyst by coupling TiO₂ to other metal-oxides. ZnO could be used as a photocatalyst and has drawn enhancingconsiderationdue to its photocatalytic efficiency is comparable to that of TiO₂.⁵

Last few decades numerous research effects in the field of photocatalysis by semiconducting materials through particular system have been studied. Textile dye produces huge amount of polluted effluents that are usually discharged on the fresh water bodies and ground water aquifers.⁶ This effluent water causes damages to the ecological system of the receiving surface water capacity and certain a lot of disturbance to the surface and ground water resources. Maximum of the dyes used in the cloth industries are constant to light and biodegradable. In order to decrease the danger of environmental contamination from such as effluent water, it is needed it purify them earlier discharging it into the surroundings.^7-9

Though the aqueous phase photochemical degradation of Acid Brown-43 has been investigated under the condition of semi-conducting oxides like ZnO/TiO₂,there are numerous techniques of nano particles creation such as organometallic, sol-gel, microwave methods and hydrothermal techniques.¹⁰ In the current research, ZnO/TiO₂ nano composites were synthesized with help of microwave radiation. Since the intense friction and the collision of molecules produced by microwave treatment, microwave radiation not only offers the energy for reheating but also speed up the nucleation. With microwave radiation on the reactant solution, concentration gradients and temperature could be controlled leading to even nucleation.¹¹ Microwave-based production technique is one of the simplest, energy-saving, green and rapid techniques for huge scale creation of nano materials. Microwave production is the innovative method of synthesis of nano metal oxide semiconductor which is sanitary, eco-friendly, commercial, energy-efficient, quick and suitable technique of heating and outcomes in high quantity in shorter reaction periods.¹²

In this work, the materials which were utilized for the creation of metal oxide nanoparticles TiO₂SiO₂ and Al₂O₃ and the methods of preparation of SiO₂/TiO₂ and SiO₂/Al₂O₃ nano-composites.   The instrumental practices used to the characterization of these Nano-materials and the procedure agreed to study the elimination of colour dyes by photo-degradation under various conditions such as different time interval irradiation and difference concentration of nano composite dosage are described in detail. It has been found that the synthesized SiO₂/TiO₂ and SiO₂/Al₂O₃ Nano-composite of photo-catalyst sample showed tremendous photocatalytic activity for the degradation of Acid Brown – 43 under straight exposure to solar irradiation with respect to exposed time and dose of nanocomposites.

Materials and Methods

Preparation of SiO₂/TiO₂ and SiO₂/Al₂O₃ Nanocomposites

SiO₂/TiO₂ and SiO₂/Al₂O₃ nanocomposites were synthesized using the following procedure. Sol-gel technique was successfully adopted for synthesis of TiO₂ nanoparticles. TTIP (Titanium tetra isopropoxide) was used as precursor; HCl was mixed with ethanol and was stirred for ten minutes. To this mixture TTIP was added in the ratio of 1:4:2 and the stirring were continued for 1 h at room temperature. Then 50 ml of deionized water was added, the temperature was raised to50°C and stirred for 3 hrs until the solution changed into colorless TiO₂ gel.

SiO₂ sol was prepared by mixing 6 gm of silicic acid with 40ml of THF in the ratio of 1:2 and this SiO₂ sol was added drop-wise to the TiO₂ gel, which resulted in yellowish brown solution. This mixture was stirred for 3 h at room temperature, then it was raised to 80°C and the stirring was continued for an hour. Finally, yellowish brown color changed to yellow and the product was dried in microwave oven at about 100°C for one hour. Finally, the composite was calcined at 400°C.¹³

SiO₂ sol was mixed drop-wise to aluminium chloride with HCl and deionized water was added and the procedure was repeated as above.

Preparation of the dye solution

The dyes used for the present study were AB-43. All the dyes used were of analytical grade and purchased. The stock solutions were prepared by dissolving 1000 mg of dye in 1litre of deionized water. Other concentrations (10, 20, 30 and 40 ppm) were prepared from stock solutions by appropriate dilution with double distilled water. The pH of the solution was adjusted to desired values by adding 0.1 M HCl or 0.1 M NaOH. Fresh dilutions were used for each experiment.

Chemical structure of AB-43

Scheme 1 Click here to View scheme

 

Instruments and Chemicals Used for Analysis

Sample colour was analyzed by Spectrophotometer (Genesys10uv, Thermo Electron Corporation). The synthesized nano-composites were scanned by the SEM (JOEL, JSM-3690LV). Additionally the qualitative elemental analysis i.e. Energy Dispersive Analysis of X-Ray (EDAX) was also done by JOEL, JED-2300 analyzer, which would provide the distribution of elemental composition on the surface. The synthesized nano-composites were viewed at high magnification using TEM, JEOL-TEM2100.All the chemicals used were of analytical grade and used as purchased. Titanium tetra isopropoxide, silicic acid, THF, ethanol, isopropyl alcohol, hydrochloric acid and Aluminium chloride were purchased from Merck and Acid Brown-43 dye was purchased from a local firm. Double distilled water was used throughout the studies for the preparation of aqueous solution.

Photocatalytic Activity Evaluation of SiO₂/TiO₂ and SiO_2/Al₂O₃

Photocatalytic activity of the synthesized nano-composites was evaluated by the degradation of aqueous solution of AB-43. All of the experiments were conducted in an opened Pyrex vessel of 250 ml and in identical conditions. The various concentrations of photocatalyst were placed in a different vessel. Prior to irradiation the suspension was manually stirred in the sunlight for 30 – 240 minutes time variations. During irradiation agitation was maintained to keep the suspension homogeneous. The suspension was sampled at regular intervals and immediately centrifuged to remove catalyst particles.  The concentration of the AB-43 dye before and after reaction were measured by means of a UV-Visible spectrophotometer at wavelength 445nm.The Photocatalytic degradation efficiency of the dye solution was calculated using the following equation. The efficiency of the catalyst was calculated using the following equation.

R (%) = (A₀ – (A/A₀)) × 100

Where A₀ is the absorbance of dye solution before the illumination, A is the absorbance of dye solution after degradation.¹⁴

Morphological Studies

Scanning Electron Microscope and EDAX

Scanning electron microscopy is a technique for great resolution surface imaging. The SEM uses an electron beam for surface imaging. The advantages of SEM over light microscopy are greater magnification and much larger depth of field. Different elements and surface topographies emit different quantity of electrons, due to which the contrast in SEM micrograph is representative of the surface topography (Fig 1 & 2). The EDAX analysis of the sample was shown in the Figs 5 & 6. The SEM image of SiO₂/TiO₂ nano-composite SiO₂ with thickly covered on TiO₂. The SiO₂/TiO₂ nano-composite had spherical shapes and some of the TiO₂ nanoparticles agglomerated were also seen in SEM image. EDAX analysis confirmed the presence of metal oxide bonds in the nanoparticles presence of Si, Ti and O in the nano composite. The SEM image of SiO₂/Al₂O₃ nano-composite showed SiO₂ with thickly covered on Al₂O₃. The elements present in EDAX microanalysis spectrum confirmed the presence of Si, Al and O in the nano-composite.

Figure 1: SEM  of  SiO2/TiO2 Nano-composite. Click here to View figure

 

Figure 2: SEM of  SiO2/Al2O3 Nano-composite. Click here to View figure

 

Figure 3: TEM of SiO2/TiO2 Nano-composite. Click here to View figure

 

Figure 4: TEM of  SiO2/Al2O3 Nano-composite. Click here to View figure

 

Figure 5: EDAX of  SiO2/TiO2 Nano-composite. Click here to View figure

 

Figure 6: EDAX of  SiO2/Al2O3 Nano-composite. Click here to View figure

 

Transmission Electron microscope

Transmission electron microscopy (TEM) is an imaging technique whereby a beam of electrons is focused onto a specimen causing an enlarged version to appear on a fluorescent screen or layer of photographic film, or to be detected by a CCD camera. The microstructure, e.g. the grain size, SAED (Selected Area Electron Diffraction) patterns and lattice defects were studied by use of the image mode, while the crystalline structure was studied by the diffraction mode. A small amount of powder samples were re-dispersed in ethanol, solicited, deposited on a copper grid, air dried and used for TEM analysis (Fig 3 & 4). TEM strongly supported the nano phase formation of SiO₂/TiO₂ and SiO₂/Al₂O₃ nano-composites.

Result and Discussion

Table 1: Degradation of AB-43 dye color by nano-composite of SiO₂/TiO₂   and SiO₂/Al₂O₃ with respect to time and concentration of nano-composite.

Nano composite	Agitation time (min) / Dose (mg/l)	10 (mg/l)	20 (mg/l)	30 (mg/l)	40 (mg/l)
		% of degradation	% of degradation	% of degradation	% of degradation
SiO2/TiO2	30	70.8	65.9	59.2	45.3
	60	88.6	78.4	75.6	59.6
	90	97.2	88.6	85.4	75.1
	120	99.8	93.4	91.1	89.4
	150	99.8	99.2	97.5	92.7
	180	99.8	99.2	98	94.2
	210	99.8	99.2	98	94.2
	240	99.8	99.2	98	94.2
SiO2/Al2O3	30	72.2	67.3	64.2	59.8
	60	80.9	78.6	72.8	65.1
	90	95.6	86.9	84.7	72.9
	120	99.8	96.2	93.8	85.6
	150	99.8	99.7	96.4	95.8
	180	99.8	99.7	98.2	96.5
	210	99.8	99.7	98.2	96.5
	240	99.8	99.7	98.2	96.5

 

Consequence of Contact Time on Decolorization

The effect of contact time on the removal of AB-43 was evaluated for various concentrations of nano composite (10 to 40 mg/L), at different time interval 30 to 240 minutes depicts an increase in dye removal with increase in time and concentration of the catalyst. The increase in catalyst amount increased the number of active sites on the photocatalyst surface causing increase in the number of •OH radicals which take part in actual decolorization of dye solution. It is clear that the percentage of degradation colour progressively increased 30 to 90 mg/L, thereafter there is no degradation of colour will occur on AB-43 (Fig 7 & 8).

Consequence of Catalyst Dosage on Decolorization

The effect of concentration was analyzed to optimize the amount of nano composite SiO₂/TiO₂and SiO₂/Al₂O₃ photocatalyst decolorization of AB-43. The experiments were set up with varying the dose from 10 to 40 mg/L for AB-43.  The solutions were kept under sunlight illumination for a period of 30 to 240 minutes. The solutions were then centrifuged at 12,000 rpm for 10min and the supernatant was used for water quality analysis by spectrometrically using UV-Visible spectrometer. It can be deduced from the results obtained that the photocatalytic efficiency of SiO₂/TiO₂ and SiO₂/Al₂O₃ nano-composites.  It could be deduced from the results obtained that photocatalytic efficiency of SiO₂/TiO₂ and SiO₂/Al₂O₃nano composites were shown to be remarkably greater in decolorization of AB-43 dye from 40 mg/L dosage.  It is clear that the photocatalytic activity increase with the increase in the dosage of SiO₂/TiO₂ and SiO₂/Al₂O₃nano composites (Fig 9 & 10).

Decolorization efficiency (%) was calculated by the following formula and all experiments were done in triplicate.

% decolorisation = ((Absorbance at initial –Absorbance at final)/Absorbance at initial) X 100

Figure 7: Effect of contact time on photodegradation of AB-43 dye using SiO2/ TiO2 nano composite. Click here to View figure

 

Figure 8: Effect of contact time on photodegradation of AB-43 dye using SiO2/ Al2O3nano composite. Click here to View figure

 

Figure 9: Effect of catalyst dosage on photo-degradation of AB-43 dye using SiO2/ TiO2nano composite. Click here to View figure

 

Figure 10: Effect of catalyst dosage on photo-degradation of AB-43 dye using SiO2/ Al2O3nano composite. Click here to View figure

 

Conclusion

SiO₂/TiO₂ and SiO₂/Al₂O₃ nano-composites were successfully synthesized by sol-gel technique and it was characterized by SEM, TEM and EDAX. The synthesized nano-composites were used for the photodegradation of AB-43 dye. The mixed metal-oxide nano-composites possess greater photodegradation effect of AB-43 under natural sun light. It is clear that the percentage of degradation of colour progressively increased from 30 to 90 percent. The percentage degradation of colour progressively increased with contact time up to 240 minutes. This environmental friendly composite material was used for the degradation of AB-43 dye with irradiation solar light. It can be concluded that nano-composites of SiO2/TiO₂ and SiO₂/Al₂O₃ is more efficient photocatalyst on AB-43 dye.

Acknowledgement

This research work a was guided and supported by Dr. Venckatesh Rajendran and Dr. Rajeshwari Sivaraj, Department of Chemistry, Government Arts College, Udumalpet – 642 126.

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