Cynthia M. Goh

Photocatalytic H2 production under visible-light irradiation based on covalent attachment of manganese phthalocyanine to graphene

In this paper, a manganese phthalocyanine (MnPc) covalently functionalized graphene nanohybrid (MnPcG) has been successfully synthesized via 1,3-dipolar cycloaddition, and used as a photocatalyst after modifying it with platinum nanoparticles via photodeposition. The nanocomposite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-vis, Fourier transform infrared (FTIR), and Raman spectroscopy. These characterization results confirmed the grafting of MnPc moiety onto the graphene sheets. The intermolecular electron transfer was facilitated and the photoexcited charges recombination was suppressed as confirmed by the fluorescence quenching and enhanced photocurrent density in MnPcG nanohybrid. In comparison to graphene, the MnPcG nanohybrid shows a substantial improvement in the photocatalytic hydrogen evolution. The yields of hydrogen production of MnPcG/Pt reached to 8.59 and 1.45 μmol mg−1 under 10 h of UV-vis and visible light (λ > 400 nm) irradiation, respectively. This work demonstrates that metallophthalocyanines covalently functionalized graphene is a novel photocatalyst for solar energy conversion to produce hydrogen from water.

Raman Spectroscopy of Nanoparticles Using Hollow-Core Photonic Crystal Fibers

Hollow-core photonic crystal fibers (HC-PCF) were employed for enhancing the Raman signal obtained from ZnO nanoparticles (NPs) in solution. By selectively filling the core of HC-PCF, substantial enhancement in the Raman signal was obtained. By employing this technique, four different stages in the synthesis ZnO NPs were studied with record low pump power levels. The concentration of ZnO NPs in the system was <1% by weight of the total mass. Yet, the different synthesis stages could be differentiated and identified through the Raman modes obtained. It was also demonstrated that the concentration of NPs in solution could be obtained with sensitivity in the millimolar range. This could be achieved by examining the amplitude ratios of the relevant Raman modes.

Characterizing the collagen stabilizing effect of crosslinked chitosan nanoparticles against collagenase degradation

UNLABELLED Antibacterial and chelating properties of chitosan has been widely studied for various dental applications. OBJECTIVE To characterize the interaction between chitosan-nanoparticles (CSnp) and collagen, and understand their stabilizing effect against collagenase degradation for dentin matrix stabilization. METHODS Phase-1: a single Type I collagen-fibril model was used to study the interaction with CSnp along with carbodiimides crosslinking treatment. Degradation of the crosslinked fibrils was studied with bacterial collagenase enzyme and monitored using Fourier Transform Infrared (FTIR) spectroscopy, turbidity measurement (400nm), ninhydrin assay and Atomic Force Microscopy (AFM). Interaction of CSnp with collagenase and Type I collagen, were evaluated using SDS-PAGE, and proteolytic cleavage potential of a synthetic peptide. Phase-2: degradation of dentin collagen crosslinked with/without CSnp was evaluated using FTIR, ninhydrin assay and Scanning Electron Microscopy (SEM). Glutaraldehyde crosslinking was used as a positive control. RESULTS Both native collagen-fibrils and dentin collagen after crosslinking showed higher resistance to collagenase degradation, as observed in turbidity measurements and FTIR spectra. AFM images showed the interaction of CSnp with single collagen-fibril and crosslinked collagen resisted collagenase degradation up to 54h. The collagen and collagenase both formed complexes with CSnp resulting in thickening of bands and reduction in collagen degradation. CSnp treated collagenase showed significantly reduced cleavage of the fluorescent peptides. Dentin collagen was coated with CSnp following crosslinking with significant increase in resistance to collagenase degradation. SIGNIFICANCE Crosslinked CSnp on collagen stabilized and enhanced the resistance of dentin matrix against bacterial collagenase degradation due to non-specific interaction with both collagen and collagenase.

Application of raman spectroscopy using hollow core photonic crystal fibers to study aqueous semiconductor colloid nanoparticles

The use of hollow core photonic crystal fibers is demonstrated as an effective analysis technique for studying aqueous colloid nanoparticles with particular emphasis on the semiconductor core crystallinity.

Post-Synthesis Crystallinity Tailoring of Water-Soluble Polymer Encapsulated CdTe Nanoparticles using Rapid Thermal Annealing

The crystallinity of colloidal CdTe nanoparticles has been enhanced post synthesis. This control over the nanoparticles’ properties has been achieved using non-adiabatic thermal processing. The technique preserves the polymer capping and hence introduces no adverse effects on the nanoparticles’ optical properties. The crystallinity is probed primarily through Raman spectroscopy in a hollow core photonic crystal fiber and x-ray diffraction powder studies. INTRODUCTION The process of rapid thermal annealing (RTA) has been applied extensively in semiconductor processing and has been demonstrated to provide numerous benefits in semiconductor systems [1]. RTA has been used to influence the photoluminescence (PL) efficiency, size dispersion and compositional intermixing for epitaxial grown or implanted quantum dots (QDs) [1,2]. However, its influence on the properties of polymer capped nanostructures has not yet been investigated. If characterized, the influence of RTA on colloidal nanostructures can present an attractive processing technique. It can be a particularly enabling processing technology as shown in the case of PEDOT-PSS thin films to influence morphological and microstructural change of this semiconducting polymer while preserving its molecular integrity [3]. NPs of numerous shapes, sizes, and compositions have been reported over the past two decades and continue to exhibit exciting optical and electrical characteristics [4]. In particular, II-VI semiconductor CdTe NPs have been demonstrated suitable for use in applications involving efficient solar cells, ultrafast electron transfer, and negative refractive index materials [5-7]. This study reports on the ability to influence the degree of crystallinity of polymer stabilized CdTe NPs using RTA. Raman spectroscopy, PL, UV-visible absorption, Xray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), have been utilized to analyze the crystalline changes in the polymer capped CdTe NPs. DISCUSSION Dried carboxylate functionalized CdTe NPs obtained from Vive Nano are annealed in inert Argon gas conditions for 30 seconds before a cool off period. The annealing temperature ranges from 200oC to 600oC in 100oC increments with the ramping temperature maintained at a constant 50oC/s gradient in all cases. All annealing is performed in an AnnealSys AS-One rapid thermal annealing system. The sample is then reweighed and dispersed in water to achieve NP concentrations of 2 mg/mL. Mater. Res. Soc. Symp. Proc. Vol. 1207

Raman spectroscopy of nanoparticles in photonic crystal fibers

Photonic crystal fibers were demonstrated as an optimal platform for enhancing the Raman signals to study nanoparticles properties in liquids. Raman was used to analyze stages of low concentrations of ZnO nanoparticles growth in solution.