Research

The Department is engaged in four major areas of research. These areas together with their associated investigators are as follows:

A selection of publications from these research areas is listed below.

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2013

Simultaneous functionalization and reduction of graphene oxide with diatom silica

By Enriquez, Erwin P.

Dalagan JQ, Enriquez EP, Li LJ. 2013. Simultaneous functionalization and reduction of graphene oxide with diatom silica. Journal of Materials Science. 48(9):3415-3421.

The simultaneous coupling and reduction of graphene oxide (GO) with diatom silica (Amphora sp., Navicula ramossisira and Skeletonema sp.) were demonstrated in this work. Binding of GO with diatom silica via direct esterification reaction at 100 °C was observed as well as the reduction of GO. The Raman spectra of GO-diatom silica revealed the typical peaks for reduced graphene oxide at 1350 cm−1 (D band) and 1585 cm−1 (G band). Infrared spectroscopy also showed the presence of a unique peak at 1260–1300 cm−1 indicative of Si–O–C=O bond formation. This confirms the successful functionalization of GO with silica. Scanning electron microscopy showed the presence of GO on the diatom. For the pennate diatoms, Amphora sp. and N. ramossisira, their pores were closed demonstrating that GO was able to cover the surface of the diatom via the Si–O–C bond formation. For the centric diatom, Skeletonema sp., GO was found to be on its rib cage-like body structure and on its centric top. Electrochemical measurements by cyclic voltammetry using a redox probe, K3[Fe(CN)6], showed that GO-Amphora and GO-Navicula had more surface negative charge compared with bare GO or bare diatom silica. Furthermore, they demonstrated similar surface charge characteristics as the chemically reduced GO (by hydrazine hydrate). This implies that the composite (reduced GO-diatom) can possibly replace chemically reduced GO (by exposure to hydrazine vapor) and it could probably function as an electrode in sensing cationic biomolecules.

DOI: 10.1007/s10853-012-7128-1

Graphene–anthocyanin mixture as photosensitizer for dye-sensitized solar cell

By Enriquez, Erwin P.

San Esteban ACM, Enriquez EP. 2013. Graphene–anthocyanin mixture as photosensitizer for dye-sensitized solar cell. Solar Energy. 98(C): 392-399.
 
In this study, enhancement in efficiency of anthocyanin-based dye sensitized solar cells (DSSC) through the incorporation of graphene directly into the dye mixture is demonstrated. Graphene was incorporated in the anthocyanin dye mixture and allowed to co-adsorb on the mesoporous titania; this is compared with anthocyanin-only mixture as control, and also compared with DSSC with graphene incorporated directly into the titania. Current–voltage (IV) and electrochemical impedance spectroscopy (EIS) measurements were carried out to characterize the different DSSC cells. Addition of graphene resulted in increased power conversion efficiencies: addition into the TiO2 as a photoanode composite, direct addition to the anthocyanin extracts (anthocyanin:graphene dispersion) during the adsorption step, or a combination of these two. The latter resulted in the highest enhancement in the PCE by as much as 2.4 times. EIS data showed a favorable decrease in charge transfer resistance in the TiO2 layer as graphene is added to the DSSC, with increased magnitude of the short-circuit current (Jsc). This is explained by graphene providing added conducting pathways for the photo-generated electrons; results show that this is also manifested in the co-adsorption of graphene with the anthocyanin dye onto the titania anode.
 

Growth of β-Ga2O3 and GaN nanowires on GaN for photoelectrochemical hydrogen generation

By

Hwang JS, Liu TY, Chattopadhyay S, Hsu GM, Basilio AM, Chen HW, Hsu YK, Tu WH, Lin YG, Chen KH, Li CC, Wang SB, Chen HY, Chen LC. 2013. Growth of β-Ga2O3 and GaN nanowires on GaN for photoelectrochemical hydrogen generation. Nanotechnology. 24(5): 055401.

Enhanced photoelectrochemical (PEC) performances of Ga2O3 and GaN nanowires (NWs) grown in situ from GaN were demonstrated. The PEC conversion efficiencies of Ga2O3 and GaN NWs have been shown to be 0.906% and 1.09% respectively, in contrast to their 0.581% GaN thin film counterpart under similar experimental conditions. A low crystallinity buffer layer between the grown NWs and the substrate was found to be detrimental to the PEC performance, but the layer can be avoided at suitable growth conditions. A band bending at the surface of the GaN NWs generates an electric field that drives the photogenerated electrons and holes away from each other, preventing recombination, and was found to be responsible for the enhanced PEC performance. The enhanced PEC efficiency of the Ga2O3 NWs is aided by the optical absorption through a defect band centered 3.3 eV above the valence band of Ga2O3. These findings are believed to have opened up possibilities for enabling visible absorption, either by tailoring ion doping into wide bandgap Ga2O3 NWs, or by incorporation of indium to form InGaN NWs.

DOI: 10.1088/0957-4484/24/5/055401

Static Conductance of Nitrile-Substituted Oligophenylene and Oligo(phenylene ethynylene) Self-Assembled Monolayers Studied by the Mercury-Drop Method

By

Querebillo CJ, Terfort A, Allara DL, Zharnikov M. 2013. Static Conductance of Nitrile-Substituted Oligophenylene and Oligo(phenylene ethynylene) Self-Assembled Monolayers Studied by the Mercury-Drop Method. The Journal of Physical Chemistry C. 117(48):25556–25561.
 
Static charge transport (CT) properties of nitrile-substituted oligophenylenes and oligo(phenylene ethynylene)s (NC-OPh and NC-OPE, respectively) assembled via the thiolate anchor on gold substrates were measured by the mercury drop junction technique. The derived attenuation factors (β), viz. 0.53 ± 0.1 and 0.30 ± 0.08 Å–1 for the NC-OPh and NC-OPE monolayers, respectively, correlate well with the literature values for the analogous nonsubstituted systems, suggesting that the attachment of the nitrile group to the OPh or OPE backbone does not significantly affect their transport properties. This finding provides a basis for the use of the nitrile moiety as a resonantly addressable group and as specific charge injection site in the measurements of dynamic CT by resonant Auger electron spectroscopy. The comparison between the static and dynamic β values for the NC-OPh monolayers implies that the static value corresponds to nonresonant injection conditions. This suggests, potentially, that the static CT can be performed more efficiently by controlling the specific molecular orbitals into which charge carriers are injected.
 
 

FRET interaction between pyrene-tagged β-hydroxy acid and perylen-3-ylmethylmethacrylate co-N-dodecylmethacrylamide in film and solution

By Guerrero, Raphael A.

Calderon IAC, Lao KS, Chua ET, Romano E, Anore KHS, Cabatuando ACR, Ibabao MJP, Guerrero RA, So RC. 2013. FRET interaction between pyrene-tagged β-hydroxy acid and perylen-3-ylmethylmethacrylate co-N-dodecylmethacrylamide in film and solution. Journal of Applied Polymer Science. 129(5):2865–2872.
 
Synthesis, characterization, and FRET interaction of pyrene-tagged β-hydroxy acid and perylen-3-ylmethylmethacrylate co-N-dodecylmethacrylamide polymer are described. The fluorescent donor, β-hydroxy acid-pyrene boronic ester was synthesized from commercially available alkyl ketene dimer via subsequent hydrolysis, reduction and esterification providing the donor. Conversely, the fluorescent acceptor was synthesized by co-polymerization of N-dodecylmethacryamide and perylen-3-ylmethylmethacrylate, where the latter was prepared from commercially available perylene in three steps. FRET interaction between the donor and acceptor was carried out by titration and monitored using fluorescence spectroscopy. Fluorescence quenching and enhancement in both film and solution formats were observed; furthermore, a more prominent lipophilic-induced interaction was observed in solution. Fluorescence enhancement (at 460 nm) is higher for the acceptor and quenching efficiency (at 420 nm) is higher for donor-acceptor pair, pyrene-tagged β-hydroxy acid and perylen-3-ylmethylmethacrylate co-N-dodecylmethacryl-amide polymer, compared to control, pyrene boronic ester. The quenching is due to dynamic quenching between the donor and acceptor. Furthermore, aggregation was not observed from the pyrene-tagged β-hydroxy acid ester donor as the concentration of the solution is increased up to 3000 ppm.
 

Cholesterol Monohydrate Dissolution in the Presence of Bile Acid Salts

By

Abendan RS, Swift J. 2013. Cholesterol Monohydrate Dissolution in the Presence of Bile Acid Salts. Cryst. Growth Des. 13(8):3596–3602.

The molecular-level dissolution of cholesterol monohydrate single crystal (001) surfaces was systematically investigated in aqueous solutions of chenodeoxycholate (CDC) and ursodeoxycholate (UDC) using in situ atomic force microscopy (AFM). Dissolution via the layer-by-layer step retreat of monolayers was observed in solutions where the bile salt concentration exceeded the critical micelle concentration (cmc). Studies performed in CDC solution revealed markedly lower cmc values than in UDC. An abrupt transition from sporadic to continuous dissolution between 4–7 mM CDC was consistent with a previously proposed 2-step model for micelle formation. In contrast, cholesterol dissolution in UDC was apparent at 14 mM with no abrupt change in dissolution rate with increasing UDC concentration. Comparison with previous dissolution studies performed in aqueous ethanol (Cryst. Growth Des. 2005, 5, 2146–2153) reveal key differences in micelle-mediated versus bulk dissolution mechanisms.

DOI: 10.1021/cg050236k

2012

Colorings of single-wall carbon nanotubes

By Loyola, Mark L., De Las Peñas, Ma. Louise Antonette N.

Loyola ML, De Las Peñas MLAN, Basilio AM. 2012. Colorings of single-wall carbon nanotubes. Zeitschrift für Kristallographie - Crystalline Materials. 227(10): 672-680.

In this work, we describe a process to classify and characterize nanotubes with several types of atoms by constructing colorings associated with single-wall carbon nanotubes. We also illustrate how colored single-wall carbon nanotubes can be used to model rolled-up versions of particular two-dimensional patterns such as carbon-boron nitride ternary graphite-like monolayers.

DOI: 10.1524/zkri.2012.1531

Partial gene sequence and characterization of EDEN-1, a major water-soluble protein from the economically important alga Eucheuma denticulatum

By Rojas, Nina Rosario L.

Suarez-Aspilla PB, Terrado MT, Dancel MCA, Zuccarello GC, Rojas NRL. 2012. Partial gene sequence and characterization of EDEN-1, a major water-soluble protein from the economically important alga Eucheuma denticulatum. Phil. Sci. Lett. 5(1):90-102.