Costing out light source and product collection during evaluation of materials for renewable fuels
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Costing out light source and product collection during evaluation of materials for renewable fuels Karthikayini Palanivelu1, Meenakshi Ramalingam1 and Ramnarayanan Ramanathan1*, 1 Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai, India. *Corresponding author email [email protected] ABSTRACT We examined LEDs as a cheap and test lamp source to simulate monochromatic laser radiation to help us cost out optics while evaluating materials for renewable fuels. The light source spectrum was recorded using a fiber optic spectrophotometer and a calibrated silicon photodiode was used to determine the intensity. Photon flux from the LEDs was recorded using actinometry. We chose CdS and Fe3O4 as photocatalysts. The as-prepared and annealed samples were characterised using X-Ray Diffraction, UV-Visible spectroscopy, UV-Visible Diffuse reflectance spectroscopy, Fourier Transform Infra-red spectroscopy, Attenuated Total Reluctance -FTIR spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). CdS and Fe3O4 were evaluated for hydrogen evolution using DI water, sacrificial agents and an electron donor (methyl viologen) using three light sources (LEDs, sunlight and mercury vapour lamp). Products were collected by an inverted burette (Generation1), balloons with a B-14 adapter (Generation2) and septum cells (Generation3). Developing an analytical technique to quantify products continues to remain a challenge. INTRODUCTION We focused on LEDs as inexpensive light source for photocatalytic water splitting. A major drawback with experiments using sunlight as light source is their unavailability at night and inconsistency of intensity during the day. Our measurements during various seasons and various times of a given day in Chennai (not reported for brevity) support this. Our LED fixture delivered light to the intended location with consistent spectrum as recorded by a fiber optic spectrophotometer, consistent photon flux as measured by actinometry and consistent intensity as measured the calibrated silicon photodiode during the experiments. We believe this helps evaluate catalysts in a more rational manner. CdS [1, 2] was chosen as photocatalyst as it has been extensively studied for hydrogen generation [3] and Fe3O4 [4] was considered based on its band gap [5]. We characterized our catalysts using a variety of techniques (details below) to ascertain synthesis reproducibility. We used GC-MS for quantifying products. We optimized product collection by Teflon sealed septum cells. Analysis in the presence of water vapor and complete characterization of headspace gas and solubility remains a challenge. EXPERIMENT Synthesis of Photocatalysts : CdS and Fe3O4 Cadmium acetate was dissolved in 10 volumes of N, N-dimethylformamide in a round bottom flask. Sulfur powder was added to this solution in stoichiometric amounts. The reaction mixture was stirred at about 120oC for 4 – 5 hours under nitrogen atmosphere to obtain bright yellow suspension of CdS [1]. Filtration followed by
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