Gregory L. Rorrer

The potential of diatom nanobiotechnology for applications in solar cells, batteries, and electroluminescent devices

The ability to produce low-cost, hierarchically-structured and nanopatterned inorganic materials could potentially revolutionize the way we fabricate photovoltaic, energy storage, and optoelectronic devices. In nature, many organisms carry out the hierarchical assembly of metal oxide materials through cellular and biochemical processes that replicate periodic micro- and nanoscale features by a bottom-up approach at ambient conditions. For example, single-celled algae called diatoms produce a nanostructured amorphous silica skeleton called a frustule. The insertion of other metal oxide materials such as titanium or germanium dioxide into the nanostructure of the diatom frustule could potentially be utilized to fabricate new dye-sensitized solar cells, nanostructured battery electrodes, and electroluminescent display devices. The exploitation of diatom nanobiotechnology for the development of novel device concepts in these areas is overviewed.

Metabolic Insertion of Nanostructured TiO2 into the Patterned Biosilica of the Diatom Pinnularia sp by a Two-Stage Bioreactor Cultivation Process

Diatoms are single-celled algae that make silica shells or frustules with intricate nanoscale features imbedded within periodic two-dimensional pore arrays. A two-stage photobioreactor cultivation process was used to metabolically insert titanium into the patterned biosilica of the diatom Pinnularia sp. In Stage I, diatom cells were grown up on dissolved silicon until silicon starvation was achieved. In Stage II, soluble titanium and silicon were continuously fed to the silicon-starved cell suspension (approximately 4 x 10(5) cells/mL) for 10 h. The feeding rate of titanium (0.85-7.3 micromol Ti L(-1) h(-1)) was designed to circumvent the precipitation of titanate in the liquid medium, and feeding rate of silicon (48 micromol Si L(-1) h(-1)) was designed to sustain one cell division. The addition of titanium to the culture had no detrimental effects on cell growth and preserved the frustule morphology. Cofeeding of Ti and Si was required for complete intracellular uptake of Ti. The maximum bulk composition of titanium in the frustule biosilica was 2.3 g of Ti/100 g of SiO(2). Intact biosilica frustules were isolated by treatment of diatom cells with SDS/EDTA and then analyzed by TEM and STEM-EDS. Titanium was preferentially deposited as a nanophase lining the base of each frustule pore, with estimated local TiO(2) content of nearly 80 wt %. Thermal annealing in air at 720 degrees C converted the biogenic titanate to anatase TiO(2) with an average crystal size of 32 nm. This is the first reported study of using a living organism to controllably fabricate semiconductor TiO(2) nanostructures by a bottom-up self-assembly process.

Effects of Acylation and Crosslinking on the Material Properties and Cadmium Ion Adsorption Capacity of Porous Chitosan Beads

Abstract Chitosan is a novel glucosamine biopolymer derived from the shells of marine organisms. This biopolymer is very attractive for heavy metal ion separations from wastewater because it is selective for toxic transition metal ions over less toxic alkali or alkane earth metal ions. Highly porous, 3-mm chitosan beads were prepared by an aqueous phase-inversion technique for casting gel beads followed by freeze drying. In the attempt to simultaneously improve material properties and adsorption capacity, chitosan was chemically modified by 1) homogeneous acylation of amine groups with nonanoyl chloride before bead casting, and 2) heterogeneous crosslinking of linear chitosan chains with the bifunctional reagent glutaric dialdehyde (GA) after bead casting but before freeze drying. The random addition of C8 hydrocarbon side chains to about 7% of the amine groups on uncrosslinked chitosan beads via N-acylation improved the saturation adsorption capacity from 169 to 216 mg Cd2+/g-bead at saturation (pH 6.5, ...

Dehydration of glucose to organic acids in microporous pillared clay catalysts

Glucose is an abundant and renewable feedstock for chemicals production. The objective of this study was to determine if microporous pillared-clay catalysts could promote the shape-selective, partial dehydration of glucose to organic acids. Iron-, chromium-, and aluminum-pillared montmorillonite catalyst powders were prepared. The iron-pillared montmorillonite had the most open pore structure in the > 10Arange. Pore slit widths of at least 10Aallowed the 8.6Aglucose molecule to diffuse and react directly within the catalyst micro- and meso-pores. Each catalyst powder was reacted with 0.75 M glucose solution (4 g catalyst/150 ml) within a well-mixed Parr autoclave reactor for 0–24 h at temperatures ranging from 130–170°C. All of the catalysts tested promoted four acid-catalyzed reactions: isomerization of glucose to fructose, partial dehydration of glucose to 5-hydroxymethylfurfural (HMF), rehydration and cleavage of HMF to formic acid and 4-oxopentanoic acid, and coke formation. The Fe-pillared montmorillonite provided the highest glucose conversion rate, with 100% glucose conversion attained within 12 h at 150°C. This catalyst also provided the lowest selectivity of the HMF (the reaction intermediate) and the highest selectivity of formic acid (the final product) in the bulk phase at an optimum temperature of 150°C. Apparently, the fraction of pores in the 10–25Arange allowed glucose to diffuse into the microporous matrix, but also trapped the bulky HMF molecule within the micropores, thus directing the reaction scheme to the final organic acid products. However, 4-oxopentanoic acid selectivities were low ( < 20%), and coke formation was as high as 0.4 g coke/g catalyst, implying carbonization of final reaction products.

Reaction Rates for the Partial Dehydration of Glucose to Organic Acids in Solid-Acid, Molecular-Sieving Catalyst Powders

Molecular-sieving catalysts have the potential to promote the production of oxygenated hydrocarbons from glucose. A kinetic model for the partial dehydration of glucose to organic acids by micro- and mesoporous aluminosilicate catalysts was developed. Kinetic parameters were estimated from glucose conversion and product yield versus time data at 150°C for HY-zeolite, aluminum-pillared montmorillonite, MCM-20 and MCM-41 catalyst powders of 0·5 mmol H+ g−1 solid-acid activity. Rate constants for the partial dehydration of glucose to 5-hydroxymethylfurfural (HMF) and the rehydration and cleavage of HMF to formic acid and 4-oxopentanoic acid were maximized at catalyst pore diameters of 10–30 A. The final organic acid product yields were low, less than 60% of theoretical for formic acid and 10% of theoretical for 4-oxopentanoic acid, due to significant coke formation.

Self-Assembly of Nanostructured Diatom Microshells into Patterned Arrays Assisted by Polyelectrolyte Multilayer Deposition and Inkjet Printing

Individual shells of the diatom Coscinodiscus were self-assembled into a rectangular array on a glass surface that possessed a polyelectrolyte multilayer patterned through inkjet printing. This patterned thin film possessed hierarchical order with nanostructure provided by the diatom biosilica. The process used two polyelectrolytes with opposite electric potentials to control the surface charge of the substrate. The fine features of the diatom frustules were perfectly preserved as a result of the mild conditions of the deposition process. This technique has the potential to enable large-scale device applications that harness the unique properties of functionalized diatom biosilica.

Enhancing surface plasmon resonances of metallic nanoparticles by diatom biosilica

Diatoms are single-celled algaes that make photonic-crystal-like silica shells or frustules with hierarchical micro- & nano-scale features consisting of two-dimensional periodic pores. This article reports the use of diatom frustules as an integration platform to enhance localized surface plasmon resonances of self-assembled silver nanoparticles (NPs) on the surface of diatom frustules. Theoretical and experimental results show enhanced localized surface plasmons due to the coupling with the guided-mode resonances of the frustules. We observed 2 × stronger optical extinction and over 4 × higher sensitivity of surface-enhanced Raman scattering of Rhodmine 6G from the NPs-on-diatom than the NPs-on-glass structure.

Ultra-sensitive immunoassay biosensors using hybrid plasmonic-biosilica nanostructured materials

We experimentally demonstrate an ultra-sensitive immunoassay biosensor using diatom biosilica with self-assembled plasmonic nanoparticles. As the nature-created photonic crystal structures, diatoms have been adopted to enhance surface plasmon resonances of metal nanoparticles on the surfaces of diatom frustules and to increase the sensitivity of surface-enhanced Raman scattering (SERS). In this study, a sandwich SERS immunoassay is developed based on the hybrid plasmonic-biosilica nanostructured materials that are functionalized with goat anti-mouse IgG. Our experimental results show that diatom frustules improve the detection limit of mouse IgG to 10 pg/mL, which is ˜100× better than conventional colloidal SERS sensors on flat glass. Ultra-sensitive immunoassay biosensor using diatom biosilica with self-assembled plasmonic nanoparticles.

Peptide-mediated deposition of nanostructured TiO(2) into the periodic structure of diatom biosilica

Diatoms are single-celled algae that make silica shells called frustules that possess periodic structures ordered at the micro- and nanoscale. Nanostructured titanium dioxide (TiO(2)) was deposited onto the frustule biosilica of the diatom Pinnularia sp. Poly-L-lysine (PLL) conformally adsorbed Onto Surface of the frustule biosilica. The condensation of soluble Ti-BALDH to TiO(2) by PLL-adsorbed diatom biosilica deposited 1.32 +/- 0.17 g TiO(2)/g SiO(2) onto the frustule. The periodic pore array of the diatom frustule served as a template for the deposition of the TiO(2) nanoparticles, which completely filled the 200-nm frustule pores and also Coated the frustule Outer Surface. Thermal annealing at 680 degrees C converted the as-deposited TiO(2) to its anatase form with an average nanocrystal size of 19 nm. as verified by x-ray diffraction. electron diffraction, and SEM/TEM. This is the first reported Study of directing the peptide-mediated deposition of TiO(2) into a hierarchical nanostructure using a biologically fabricated template.

COMPARISON OF DEVELOPMENT AND PHOTOSYNTHETIC GROWTH FOR FILAMENT CLUMPS AND REGENERATED MICROPLANTLET CULTURES OF AGARDHIELLA SUBULATA (RHODOPHYTA, GIGARTINALES)

Two axenic, in vitro liquid suspension cultures were established for Agardhiella subulata (C. Agardh) Kraft et Wynne, and their growth characteristics were compared. This study illustrated how reliable routes for the development of suspension cultures of macrophytic red algae of terete thallus morphology can be achieved for biotechnology applications. Undifferentiated filament clumps of 2–8 mm diameter were established by induction of callus‐like tissue from thallus explants, and lightly branched microplantlets of 2–10 mm length were established by regeneration of filament clumps. The filament clumps were susceptible to regeneration. Adventitious shoot formation was reliably induced from 40% to 70% of the filament clumps by gentle mixing at 100 rev min−1 on an orbital shaker. The specific growth rate of the microplantlets was higher than the filament clumps in nonagitated well plate culture (4%–6% per day for microplantlets vs. 2%–3% per day for filament clumps) at 24° C and 8–36 μmol photons·m−2·s−1 irradiance (10:14 h LD cycle) when grown on ASP12 artificial seawater medium at pH 8.6–8.9 with 20%–25% per day medium replacement. Oxygen evolution rate vs. irradiance measurements showed that relative to the filament clumps, microplantlets had a higher maximum specific oxygen evolution rate (Po,max= 0.181 ± 0.035 vs. 0.130 ± 0.023 mmol O2·g−1 dry cell mass·h−1), but comparable respiration rate (Qo= 0.040 ± 0.013 vs. 0.033 ± 0.017 mmol O2·g−1 dry cell mass·h−1), compensation point (Ic= 3.8 ± 2.4 vs. 5.7 ± 1.2 μmol photons·m−2·s−1), and light intensity at 63.2% of saturation (Ik= 17.5 ± 3.9 vs. 14.9 ± 2.6 μmol photons·m−2·s−1). The microplantlet culture was more suitable for suspension culture development than the filament clump culture because it was morphologically stable and exhibited higher growth rates.