Solar energy: Potential and toxicology

Abstract

Global energy demands towards 100 PW necessitated a rethink of approaches to generate the required demand through accelerated use of sustainable resources for both heating and generation of electricity. This is to degrade the global warming potential, lower greenhouses gases, and ultimately ensure against depletion of natural resources which may be required for habituation, agro-use or extraction for construction, catalysis, and fabrication of new materials instead of energy. Of the newer types of sustainable resources, solar energy has drawn considerable interest, due to the ability of the sun (a nuclear fusion reactor) to potentially meet all the demands with regard to heating and electrical generation. Current global production of electricity via solar only top 100 GW (less than 10% of the required load) but show promise. Current solar technologies are dominated by crystal silicon solar cells, although newer approaches using thin-films, CdTe, organic photopolymers, and composite devices have come online to meet the anticipated share for energy and heating, in diverse applications (satellite communication, heating, desalination, pumping of water, and electricity generation). While solar cells directly do not generate carbon dioxide and contribute towards global warming, the manufacturing of these devices does expend considerable energy and generates carbon dioxide, although levelized costs (dollar-per-kilowatt hour) are comparable to a coal-derived generation of energy and the roll-out and market deployment of solar cells is expected to increase. Likewise the environmental and health hazard of disposal of solar components at end-of-life is unknown due to their longevity (25-30 year life cycle), although preliminary studies have shown that semiconductor components such as titania (TiO2) are toxic to human cells, microorganism, and freshwater algae, there is considerable variation in lethality of titania, due to exposure, concertation, and type of titania (anatase or rutile, nano or bulk) and microorganism (Gram-negative or Gram-positive). To address the question of toxicity, we undertook synthesis, characterization, photocatalyticity, and cytotoxicity of Ce-doped TiO2 (CTO-NPs). An environmental-friendly and cost-effective sol-gel approach was used to prepare different formulations of CTO-NPs. The starting materials of Ce(NO3)3 and Ti (OBu)4 were used, and a water-isopropanol mixture was used as a solvent to ensure the solubility of the above starting materials. The fabrication variables of CTO-NPs were optimized according to the photocatalytic reactivity and antibacterial activities. The powders of CTO-NPs were prepared after calculation at 200-400 C with an increment of 50°C for 2 h. These so-prepared CTO-NPs were characterized using X-ray powder diffraction, scanning and transmission electron microscopy, and ultraviolet and Raman spectroscopy, to evaluate their crystalline structure, morphology, and vibrational modes. It was found that the TiO2 tetragonal anatase structure (PDF 01-086-1157, 3.7852 x 9.5139 Å and 90 x 90) was obtained. The cerium cation-substituted the lattice Ti, leading to one phase formation. These CTO-NPs were found to be effective at decomposing methylene blue under visible light. Both Gram-negative (S. marcescens, ATCC 49732) and Gram-positive (M. luteus, ATCC 13880) bacteria were also tested using CTO-NPs as disinfectants. The maximum bactericidal concentrations (MBCs) were found to be 0.6 ppm to inactivate both bacteria within 1 h.