Diatom Frustules as Substrates for Photocatalysts

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Nanomaterials are quickly becoming highly useful for many applications. The public is concerned with the long-term effects of nanomaterials in the environment. Composite materials as substrates for nanoparticles can be tailored to maintain functionality as well as immobilize the nanoparticles to reduce health concerns. Our patent pending approach uses immobilized photocatalysts on diatom frustules (shells) for removing environmental contaminates from the air. Diatom frustules have been shown to act as light traps for ultra-violet, blue and red wavelengths of light. Twice the number of incident photons can strike catalysts which are immobilized in the pores of the diatom frustules. This can be a major advantage for photocatalysts using these wavelengths especially in low light environments. Diatom frustules are composed primarily of SiO2 and can cheaply and easily be obtained commercially from multiple sources throughout the world. The size can be tailored, in ranges from 10 µm to 100 µm, removing them from the common size ranges of concern for inhalation. Both amorphous and crystalline diatomaceous earth is available and can vary in color from reddish-orange to white. Coloration is caused by the conversion of sequestered bio-iron in the silica shell to iron oxides. Interestingly the iron is sequestered in both elemental form as well as small agglomerations. Understanding the contaminates and characteristics in diatom frustules is necessary for optimal implementation as substrates for nanoparticle composites. Literature reports can be found which immobilize titanium dioxide on diatomaceous earth for photocatalytic purposes yet literature does not differentiate between the type of diatomaceous earth used as the substrate. With the many variations in size, structure, crystallinity and composition it is important to clearly identify the source and type of diatomaceous earth used in experiments. Here in we report on our findings using both amorphous and crystalline (flux-calcined) Aulacoseira and amorphous Cyclotella as composite substrates for titanium dioxide nanoparticulate photocatalysts. In addition, we studied the effect of depositing the titanium dioxide photocatalysts primarily in the pores of the diatom frustule instead of all over the diatom frustule to elucidate if expensive photocatalysts could be used in lower concentrations but maintain the same effectiveness due to the light trapping effects. Our finding indicate that diatoms frustules coated with titanium dioxide photocatalysts are highly effective composites for photocatalytic purposes. Future research efforts are currently focused on addition of the composite to coatings and immobilization on substrates to provide functional photocatalytic additives for degradation of air contaminates and anti-microbial coatings.

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Journal: TechConnect Briefs
Volume: 2, Materials for Energy, Efficiency and Sustainability: TechConnect Briefs 2018
Published: May 13, 2018
Pages: 263 - 266
Industry sectors: Advanced Materials & Manufacturing | Energy & Sustainability
Topics: Sustainable Materials
ISBN: 978-0-9975117-9-6