Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr. Ajay K. Ray

2nd Supervisor

Dr. Hassan Gomaa

Joint Supervisor

Abstract

Photocatalysis is a recognized approach where light energy is employed to excite the semiconductor material producing electron/hole pair which eventually involves in the detoxification of pollutants and/or water splitting producing hydrogen. Existing photocatalysts suffer from poor activity or no activity in visible light irradiation which restricts them from solar light utilization. This work is focused on two key applications of photocatalysis (i) sacrificial hydrogen generation, and (ii) phenol degradation in visible and/or solar light. Platinum was loaded on TiO2 photocatalyst by solar photo-deposition method. Eosin Y dye was used as a sensitizer for sensitization of platinum loaded TiO2 photocatalyst. The photocatalyst was irradiated from the top with a solar simulator. The light source was equipped with AM 1.5 G as well as a 420 nm cutoff filter to remove all the UV light. A factorial design at two levels and four factors has been carried out in order to investigate the potential for hydrogen generation using Eosin Y-sensitized TiO2/Pt catalyst under visible solar light in presence of triethanolamine as electron donor. Experimental data were analyzed using both “Pareto analysis” as well as conventional regression analysis techniques. A regression function was proposed that satisfactorily predicts hydrogen generation as a function of various operating parameters. Later, the photocatalytic behavior of the eosin Y–sensitized photocatalyst was studied in solar-UV (300-388 nm), solar-visible (420-650 nm) and full solar spectrum (300-650 nm) to explore the optimum reaction conditions such as (i) light intensity (100 mW cm-2), (ii) solution pH (7.0), (iii) platinum content (wt %) on TiO2 (0.25 %), (iv) mass of eosin Y-TiO2/ Pt (1-1.3 g L-1) , (v) concentration of trietanolamine (0.25 M), and (vi) mass ratio of eosin Y to TiO2/Pt (1:10). The reaction mechanisms were different in solar and visible lights, although in both cases formaldehyde was detected as an intermediate product.

Studies in a pulsating flow reactor showed positive effects of pre-sonication, increased flow rate and bi-directional mixing mode in solar hydrogen generation. A detailed study on the photocatalytic behavior of formaldehyde for sacrificial hydrogen generation was performed for better understanding of the process. Photocatalytic hydrogen generation from formaldehyde was influenced by solution pH, platinum content (wt %) on TiO2, catalyst concentration, light intensity, and initial formaldehyde concentration. A Langmuir-type model was well fitted with the experimental data for photocatalytic hydrogen generation from both triethanolamine and formaldehyde as sacrificial agents. Apparent quantum yield (QY) was much higher for UV light driven hydrogen generation. In solar and visible light the QYs were a function of the light intensity and the wavelength range considered for the calculation. Phenol degradation with eosin Y-sensitized TiO2/Pt photocatalyst under solar-visible light was performed with triethanolamine as electron donor. About 93 % degradation of 40 ppm phenol solution was achieved within 90 minutes using Eosin Y-TiO2/Pt photocatalyst at optimum conditions (pH = 7.0, catalyst loading = 0.8 g L-1, triethnolamine concentration = 0.2 M, 0.5 % Pt loading on TiO2, visible solar light of 100 mW cm-2). Kinetic rate constant and adsorption equilibrium constant were determined and a Langmuir-Hinshelwood type equation was proposed to describe phenol degradation on TiO2 at different visible light intensities. The model equation predicts experimental results quite well.

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