Biotemplated diatom silica-titania materials for air purification

Abstract

We present a novel manufacture route for silica-titania photocatalysts using the diatom microalga Pinnularia sp. Diatoms self-assemble into porous silica cell walls, called frustules, with periodic micro-, meso- and macroscale features. This unique hierarchical porous structure of the diatom frustule is used as a biotemplate to incorporate titania by a sol-gel methodology. Important material characteristics of the modified diatom frustules under study are morphology, crystallinity, surface area, pore size and optical properties. The produced biosilica-titania material is evaluated towards photocatalytic activity for NOx abatement under UV radiation. This research is the first step to obtain sustainable, well-immobilised silica-titania photocatalysts using diatoms.

The fascinating diatom frustule—can it play a role for attenuation of UV radiation?

“…To further increase the refractive index contrast and thereby enhance the interaction effect between light and the frustule, silica can be substituted in the growth medium with high levels of the trace substances Jeffryes et al 2008;Lang et al 2013). Due to the fact that even the trace amount of impurities may influence photonic characteristics of the frustule, cultivation conditions must be controlled to ensure reproducible products for industrial applications, or it can be done by 3D structural preserving chemical substitution after removal of organic material in the cleaning process (Sandhage et al 2002;Bao et al 2009;van Eynde et al 2013). To further quantify and understand the light-frustule interaction, its implication on biological functions of the diatom, and the possible industrial applications, more advanced photonic studies have to be conducted.…”

Diatom frustules as a biomaterial: effects of chemical treatment on organic material removal and mechanical properties in cleaned frustules from two Coscinodiscus species

“…It has been shown that Thalassiosira pseudonana frustules contained hydrocarbons, protein and lipids after a H2O2 treatment [35] . Furthermore, H2O2 treatment removed more elements from the frustules than SDS/EDTA [34] , and facilitated the access to N embedded in the biosilica [33] . These observations may influence the choice of cleaning methods for frustules that are subjected to elemental analyses.…”

“…acids, bleaching, oxidising or denaturation functions from different chemicals, and thermal treatment. There are few systematic studies with comparisons of different cleaning methods [30] , [31] , [32] , [33] , [34] . Here, a comparative study of two frustule cleaning methods is presented, using carefully described cleaning protocols based on established cleaning principles [35] .…”

“…The three-dimensional nanoporous structure of diatom frustules consists mainly of silica nanoparticles, and the architecturewith layers and different sized pores -gives rise to several interesting material applications, e.g. nano-to micrometer scaled sieves [5] or drug carriers [6] , [7] as well as vectors for drug delivery [8] , protein adsorbents [9] and as photocatalysts [10] . Diatom frustules also show particular optical properties [11] , [12] , [13] , [14] , [15] , [16] , [17] making them interesting for several optical applications [18] .…”

Biogenic nanomaterials from photosynthetic microorganisms

“…Another study combined biogenic silica structures with the sol-gel hydrolysis of titanium (IV) isopropoxide to immobilize titania NP into the frustule pores of Pinnularia sp. for the photocatalytic degradationof NO x [36]. The composite material was calcinated and determined to be a good catalyst support because of both the high surface area and available surface hydroxyl groups, which facilitates the formation of hydroxyl radicals and increases photocatalytic performance.…”