81 5.1 Summary
Chapter one introduces the role of nanotechnology from its evolution to the present day and the multifaceted areas of research that has manifested itself. A brief explanation about the various aspects of research carried out in this thesis was outlined from bio sensors used for colorimetric sensing to semiconductor photocatalysts used for environmental remediation. The second chapter focuses on the synthesis of FeTe NRs prepared from Tellurium nanowires through a galvanic reaction with the cynosure on colorimetric sensing of glucose in blood at high sensitivity (55 nM). The enzyme mimicking FeTe NRs having high catalytic activity for the peroxidase substrate ABTS were synthesized from Te NWs through a galvanic reaction. FeTe NRs were also found to have a higher enzyme activity in comparison to those of HRP and Fe3O4 NPs due to amount of Fe(II) ions on their surfaces, enabling the use of FeTe NRs as enzyme mimics for the detection of various analytes of interest when suitable enzymes are used to generate H2O2. The third chapter carries forward this concept of colorimetric bio-sensing using FeTe NRs through detecting mercury in blood as the FeTe NRs were displaced by Hg2+ ions to form HgTe mainly due to a cation exchange mechanism. The sensing approach was validated by the determination of the concentration of total Hg in a blood sample (SRM 955c). The final chapter focusses on the synthesis of semiconductor photocatalyst (G-ZnO-Au NCs) for the reduction of nitrobenzene to aniline, with conversion efficiency close to 100% within 140 min. This green, efficient and reusable photocatalyst reduced nitrobenzene, without producing any toxic by-products, showing the effectiveness of using this new class of nanocomposite materials capable of utilizing solar energy effectively to reduce nitrobenzene and other potential aromatic compounds used in the industry.
82 5.2 Perspective
Biosensing has taken significant strides over the last few decades due to the advancement in nanomaterials that have been designed and fabricated for specific applications. Iron based nanomaterials such as FeTe NRs provide a cheaper alternative to gold and other similar noble nanomaterials and a useful platform for a wide range of biosensing applications. These newly developed FeTe NRs have shown great advantages over conventional assays, particularly in sensitivity, selectivity, and practicality largely due to its low cost, simplicity, and practicality in addition to robust physical as well as chemical properties of these materials making them promising candidates for colorimetric biosensing.
The next challenge for FeTe NRs would be to develop simple, rapid, and inexpensive detection assays for monitoring of food and water contamination by bacteria and other pathogens, diagnostic applications, and environmental analysis. There is a need to build glucose sensors that utilize “test strips”, particularly so for the developing world, which does not have ready access to laboratory facilities. The fact that FeTe NRs have high thermal stability allows them to be used in geographically hot areas, where biomolecules might undergo thermal denaturation at elevated temperatures (e.g., above 45 °C), leading to loss of sensitivity in traditional bioassays. FeTe NRs can be implemented as dipsticks or in a chromatographic format, the color change observed through the naked eye absolves the need for sophisticated instrumentation.
Another immediate challenge to be met is to functionalize the FeTe NRs with unique optical signatures with different receptors. We foresee that this will enable them to have a unique optical response to biomolecular binding thus allowing detection of various analytes. Finally one can incorporate the FeTe NRs into a nano/micro fluidics channel. The integration of with a lab-on–a-chip bioanalytical devices will enable the
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ultrasensitive detection of a large number of analytes in a single device.
On the other hand, Graphene-based semiconductor photocatalysts have gained traction due their potential in environmental and energy-related applications.
Although considerable progress has been achieved, the studies in this field are at a nascent stage and further developments are required. To begin with, the preparation of graphene is still maturing and there are a variety of issues that requires attention.
There is a need for preparing pure and bulk graphene in cheap and environmentally friendly manner with tunable sizes of layers, compositions and defects. Next, we should be able to tune the performance of graphene-based semiconductor composites by varying the loading of each of the composites. Therefore, there is need for precisely designed composites by achieving uniform morphology to enhance the photocatalytic properties. Finally, an aspect of graphene based semiconductor photocatalysts that has not received great attention is the mechanism and remains to be discussed further. For instance, the exact role of graphene in enhancing the mechanism still remains debatable. Furthermore there is a need to determine the exact mechanistic pathway behind the photocatalytic activity for different semiconductor photocatalysts such as ZnO or TiO2 or noble metal photocatalysts such as gold.
To summarize, we must meet the challenge of fabricating pure carbon and carbon-based composites for the purpose of photocatalytic reduction or oxidation. The perspective is to focus on the principle and the development of photocatalysis in carbon-based nanomaterials synthesis. This needs to be application-driven, but the challenge to further develop the field rests between a simultaneous study of the fundamental processes and a better control of the synthetic routes.
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Publications
(1) Roy, P.; Tsai, T. C.; Liang, C.-T.; Wu, R. J.; Chavalia, M., Application of Impedance Measurement Technology in Distinguishing Different Tea Samples with Ppy/SWCNT Composite Sensing Material. J. Chin. Chem. Soc. 2011, 58, 714-722.
(2) Yang, Z.; Chen, C.-Y.; Roy, P.; Chang, H.-T., Quantum dot-sensitized solar cells incorporating nanomaterials. Chem. Commun. 2011, 47, 9561-9571.
(3) Roy, P.; Lin, Z.-H.; Liang, C.-T.; Chang, H.-T., Synthesis of enzyme mimics of iron telluride nanorods for the detection of glucose. Chem. Commun. 2012, 48, 4079-4081.
(4) Lee, Y.-F.; Deng, T.-W.; Chiu, W.-J.; Wei, T.-Y.; Roy, P.; Huang, C.-C., Visual Detection of Copper (II) Ions in Blood Samples by Controlling the Leaching of Protein-Capped Gold Nanoparticles. Analyst 2012, 137, 1800-1806.
(5) Roy, P.; Lin, Z.-H.; Liang, C.-T.; Chang, H.-T., Iron telluride nanorods-based system for the detection of total mercury in blood. J. Hazard. Mater. 2012, 243, 286-291.
(6) Lin, Z. H.; Shih, Z. Y.; Roy, P.; Chang, H. T., Preparation of Photocatalytic Au–Ag2Te Nanomaterials. Chem,-A Eur. J. 2012, 18, 12330-12336.
(7) Lin, Z. H.; Roy, P.; Shih, Z. Y.; Ou, C. M.; Chang, H. T., Synthesis of Anatase Se/Te‐TiO2 Nanorods with Dominant {100} Facets: Photocatalytic and Antibacterial Activity Induced by Visible Light. ChemPlusChem 2013, 78, 302-309.
(8) Roy, P.; Periasamy, A. P.; Liang, C.-T.; Chang, H.-T., Synthesis of Graphene-ZnO-Au Nanocomposites for Efficient Photocatalytic Reduction of Nitrobenzene. ACS Environ. Sci and Tech. 2013, 47, 6688-6695
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Books
(1) Chen, P.-C.; Roy, P.; Chen, L.-Y.; Chen, Y.-N.; Chang, H.-T., “Gold Nanomaterials Based Absorption and Fluorescence Detection of Mercury, Lead, and Copper”, Interactions of Nanomaterials with Emerging Environmental Contaminants, 2013.
(2) Roy, P.; Periasamy, A. P.; Liang, C.-T.; Chang, H.-T., “Photoluminescent Graphene Quantum Dots: synthetic routes, unique physicochemical properties and bio-application”, Handbook of Graphene Science. Volume 4, Chapter 15, 2013.
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Conferences
(1) 2010 Annual Meeting of the Physical Society of the Republic of China (ROC), February 2010, Tainan, Taiwan. “Preparation of Smart Nanomaterials for Energy Applications”.
(2) 2010 Annual Meeting of Chinese Chemical Society, December 2010, Taipei, Taiwan. “Synthesis of Smart Nanomaterials for Sensing Applications”.
(3) 2011 Annual Meeting of Chinese Chemical Society, December 2011, Hsinchu, Taiwan “Iron Telluride based Nanomaterials for Sensing Glucose and Mercury in Blood”.
(4) National Institute of Material Science Conference, June 2012, Tsukuba, Japan.
“Enzyme Mimicking Iron Telluride based Nanorods for the Detection of Glucose”.
(5) Indo-Taiwan Research Talk on Smart Nanomaterials, August 2012, Kanyakumari, India. “Iron Telluride and Graphene Based Nanomaterials for Sensing and Photocatalytic Applications”.
(6) 2012 Annual Meeting of Chinese Chemical Society, December 2012, Tainan, Taiwan. “Graphene Based Semiconductor Nanocomposites for Photocatalytic Applications”.
(7) Annual NTU Chemistry Graduate Research Sympsoium, December 2012, Taipei, Taiwan. “Iron Telluride and Graphene Based Nanomaterials for Sensing and Photocatalytic Applications”.