Preparation of nanostructured metals on substrates and textile for electrocatalytic and antibacterial applications

PREPARATION OF NANOSTRUCTURED METALS ON SUBSTRATES AND TEXTILE FOR ELECTROCATALYTIC AND ANTIBACTERIAL APPLICATIONS CHO SWEE JEN (B.Eng., Universiti Sains Malaysia, Malaysia) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF MATERIALS SCIENCE AND ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2013 DECLARATION I hereby declare that the thesis is my original work and it has been written by me in its entirety. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has also not been submitted for any degree in any university previously. _______________________ Cho Swee Jen 8rd February 2013 Acknowledgements I would like to express my sincere thanks to all people who helped me, who walked together with me, who make my life interesting and who developed me into a better personality throughout my four years in Singapore. First, greatest thanks to my supervisor; Assistant Professor Ouyang Jianyong for his continuous guidance throughout these four years. I am really appreciated for his valuable advices and guidance. I would like to extend my greatest gratitude to Dr. Karen Siew Ling Chong and Mr. Lee Yeong Yuh for their help in antimicrobial characterization. I am grateful for giving an opportunity to collaborate with them and expose myself to bacteria culture processes. Special thanks to my group members and friends – Dr. Mei Xiaoguang, Neo Chinyong, Sun Kuan, Dr. Zhang Hongmei, Dr. Zhou Dan, Guiyang, Sherlyn Chua Shu Er, Tang Chunhua, Li Kangle, Tan Sheng Ming Joel and others from E3A laboratories. I definitely will not forget the moments we encourage each others, we laugh together and we outing together. Thanks for decorating my life with these fancy moments. Also, thanks to Tan Yun Foong Charina for her contribution in preparing antimicrobial textiles. Thanks to the laboratory staffs in Department of Materials Science and Engineering, particularly, Agnes Lim, Serene Chooi, Chen Qun, Henche Kuan, Liew Yeow Koon, Dr. Zhang Jixuan, Yang Feng Zhen not only for equipment training but also for sample characterizations. My perseverance to stand strong until now is from the continuous support given by my family, especially, my mother and sister – Cho Swee Teng. I am so grateful to i have them in filling up my sorrowfulness with encouragement. I am also deeply indebted to my husband for his unconditional love and persistent support. Last but not least, thanks to National University of Singapore, Ministry of Education, Singapore and Institute of Materials Research and Engineering for their financial support. Cho Swee Jen July 2012, Singapore ii Table of Contents Acknowledgements . i Table of Contents iii Summary vii List of Tables ix List of Figures . xi List of Publications xvii Chapter 1. Introduction 1.1 An overview of nanostructured metals 1.2 Properties of nanostructured metals . 1.2.1 Electronic structure of nanostructured metals . 1.2.2 Optical properties of nanostructured metals 1.3 Preparation of nanostructured metals 1.3.1 Nucleation . 1.3.1.1 Thermodynamic control 10 1.3.1.2 Kinetic control 11 1.3.2 Growth of nanostructured metals . 12 Chapter 2. Attachment of Platinum Nanoparticles to Substrates by Coating and Polyol Reduction of A Platinum Precursor 32 2.1 Introduction 32 2.2 Experimental details 32 2.2.1 Materials . 32 2.2.2 Deposition and characterization of Pt nanoparticles 33 2.2.3 Electrochemical catalysis of Pt nanoparticles . 33 2.2.4 Deposition of Pt nanoparticles . 34 2.2.5 Fabrication and characterization of dye-sensitized solar cells (DSSCs) with Pt nanoparticles as counter electrode . 34 2.3 Results and discussion 36 2.3.1 Characterization of Pt nanoparticles . 36 2.3.2 Pt nanoparticles as electrochemical catalyst in methanol oxidation and DSSCs . 43 2.4 Conclusions . 49 Chapter 3. Direct deposition of gold nanoplates and porous platinum on substrates through solvent-free chemical reduction of metal precursors with ethylene glycol vapor . 51 iii 3.1 Introduction 51 3.2 Experimental details . 52 3.2.1 Materials and chemicals . 52 3.2.2 Deposition of Au nanostructures 52 3.2.3 Deposition of porous Pt 52 3.2.4 Characterization of materials . 53 3.3 Results and discussion 53 3.3.1 Deposition and characterization of Au nanoplates 53 3.3.2 Deposition and characterization of porous Pt . 62 3.3.3 Mechanism for different morphologies of nanostructured Au and Pt . 68 3.4 Conclusions . 70 Chapter 4. Platinum nanoparticles deposited on substrates by solventless chemical reduction of a platinum precursor with polyol vapor and its application as highly effective electrocatalyst in dye-sensitized solar cells . 71 4.1 Introduction 71 4.2 Experimental details . 74 4.2.1 Chemicals and deposition of Pt nanoparticles . 74 4.2.2 Characterization of materials and DSSCs . 74 4.3 Result and discussion 75 4.3.1 Deposition of Pt nanoparticles through solventless chemical reduction . 75 4.3.2 Pt nanoparticles as the counter electrode of DSSCs. . 81 4.4 Conclusions . 90 Chapter 5. Deposition of Nanometer Truncated Tetrahedron Gold on Graphene through Chemical Reduction of A Gold Precursor with Ethylene Glycol Vapor 93 5.1 Introduction 93 5.2 Experimental details . 93 5.2.1 Materials and chemicals . 93 5.2.2 Preparation of rGO films . 93 5.2.3 Deposition of nanostructured Au on rGO films 94 5.2.4 Characterization of materials . 94 5.3 Results and discussion 96 5.3.1 Characterization of GO and rGO films . 96 5.3.2 Characterization of nanostructured Au/rGO composites . 101 5.3.3 Effect of acid on the shape of Au nanostructures 107 5.4 Conclusions . 109 iv Chapter 6. In Situ Deposition of Ag Nanostructures on Cotton Fabric Through The Solid-state Reduction of Ag Precursor and Their Antimicrobial Activity . 110 6.1 Introduction 110 6.2 Experimental details 110 6.2.1 Materials and chemicals . 110 6.2.2 Preparation of Ag nanostructures on cotton fabric 111 6.2.3 Characterization of Ag/cotton . 111 6.2.4 Antimicrobial testing of Ag/cotton 112 6.3 Results and discussion 113 6.3.1 Characterization of Ag/cotton . 113 6.3.2 Effect of experimental conditions on the morphology of Ag nanostructures . 117 6.3.3 Antimicrobial testing 120 6.4 Conclusions . 122 Chapter 7. Conclusions and future perspectives 123 v vi Chapter 7. Conclusions and future perspectives 7.1 Summary In this thesis, nanostructured metals have successfully synthesized by our novel methods. The advantages of these methods include the in-situ formation of metal nanostructures onto the substrates with good adhesion, without the presence of binding agents. Several morphologies of nanostructured metals have been developed by these methods, which are summarized in Table 7.1. The formation of different morphologies of metal nanostructures is related to the surface energy of the metals. These metal nanostructures have applications in the counter electrodes of DSSCs, fuel cells and antimicrobial activity. The important results in this research work are summarized as follows: 1. The first approach is to deposit Pt nanoparticles with good adhesion to FTO substrate. The deposition involves the solution processing and chemical reduction of H2PtCl6 at 160 oC. This method involves the nucleation of metal atoms in solution, since the EG is drop casted onto the substrate. The EG disappears shortly after the formation of Pt nanoparticle causing them to have a high surface energy during the deposition. Consequently, the Pt nanoparticles can have good adhesion to the substrates. The applications of these Pt nanoparticles as electrochemical catalyst were demonstrated in the oxidation of methanol and as the counter electrode of DSSCs. 2. The second approach is to deposit nanostructured metals onto various substrates through the solvent-free chemical reduction of the metal precursors by EG vapor. No surfactant, seed, template or additive is added during the chemical 123 reduction and metal deposition. The chemical reduction takes place at a temperature below 200 oC and can be completed in a couple of minutes. The deposition of Au, Pt, Ag and Pd on conducting substrates was demonstrated. These metal nanostructures have different morphologies. The Au nanostructures have two-dimensional structures with the majority being triangular nanoplates when the Au loading is low. In contrast, the Pt nanostructures have threedimensional porous structure, while Pd shows dendritic structures. The mechanism of formation for different morphologies of these nanostructured metals are related to the surface energies of these metals. 3. This solvent-free chemical reduction of metal precursors by EG vapor method is extended to deposit Pt on FTO glass. This method can significantly lower the Pt loading used in DSSCs counter electrode. The efficiency (6.61%) of DSSCs with Pt of 0.19 µg cm-2 deposited by the EG vapor reduction is even higher than that (6.19%) of DSSCs with Pt of 0.78 µg cm-2 deposited by pyrolysis. The DSSCs also have good stability. 4. Graphene films and decorated graphene films with truncated tetrahedron Au nanostructures have successfully prepared. This approach can avoid the agglomeration of graphene sheets. In addition, well-distributed Au nanostructures on the planar structure of graphene films can be achieved. The size and shape of Au nanostructures can be manipulated by controlling the Au loading and the addition of acid. The Au nanostructures/ graphene composites can be potentially used in biosensor. 5. This method is also used to deposit Ag nanostructures on textiles. Textiles functionalized with Ag nanostructures can impede the growth of bacteria. The 124 Ag nanostructures have demonstrated good adhesion to the textiles and excellent antibacterial activities against Escherichia coli (Gram-negative) Staphylococus epidermidis (Gram-positive) bacteria, and which are found commonly on the human skin after hour of dynamic contact in aqueous media. 7.2 Future perspectives Since the solvent-free chemical reduction of metal precursors by EG vapor method is versatile and scalable, this method can be used in many systems. The following recommendations are proposed for further study: 1. This thesis mainly reports on the application of nanostructured metals in catalysis. The deposition of Au/Ag on substrate has important usage in surface enhanced Raman scattering (SERS). More works can be carried out in future to deposit metal nanostructures on substrates for the application of metal nanostructures in SERS. 2. It has been reported in the literatures that metal nanostructures can enhance the photoluminescence (PL) due to the surface plasmons effect. Therefore, this enhancement in PL can be utilized to enhance the light absorption in either organic photovoltaic or DSSCs. 3. This main emphasis of this thesis is the synthesis of single metal nanostructures. This method can also be applied in synthesizing alloy or bimetallic systems such as Pd-Pt. Currently, the preparation of alloy systems involves the chemical reduction of the Pd precursors to Pd nanoparticles and subsequently attaching the Pt nanoparticles on these Pd nanoparticles. Our novel method could allow the synthesis of alloy systems in single step by the mixing both of the Pd and Pt 125 precursors. 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Tsukada, T. Arai, G. M. Colonna, A. Boschi, G. Freddi, J. Appl. Polymer Sci., 2003, 89, 638. 138 [...]... of nanostructured metals can be classified into surface phenomena (extrinsic contribution) and quantum confinement (intrinsic contribution) 1.2 Properties of nanostructured metals 1.2.1 Electronic structure of nanostructured metals The electronic properties of the nanostructured metals can be deduced in terms of the electronic properties of the bulk materials In contrast to the continuous energy band... electronic structure also depends on the dimensionality where the electronic density of states, g(E) for 3-dimension, 2- 2 Figure 1.2 Profile of the density state g(E) for different dimensionality [4] dimension, 1-dimension and 0-dimension systems are significantly different (Figure 1.2) For 3-D systems, the critical energy, Ej might correspond to an energy threshold for the onset of optical transitions... [11] 1.3 Preparation of nanostructured metals The preparation of nanostructured metals can be generally divided into two stages: (i) nucleation and seeds formation and (ii) growth of seeds into nanocrystals 1.3.1 Nucleation Nucleation is the first stage of the crystallization process where the seeds form stable structures with a well-defined crystallinity After the generation of the zero-valence metal... [6] Cho SJ, Tan CYF, Lee YY, Chong KSL, Ouyang JY In-situ Attachment of Antibacterial Silver Nanoparticles on Textiles through the Chemical Reduction of Solid AgNO3 with Ethylene Glycol Vapor Submitted Invention Disclosure [1] Ouyang JY, Cho SJ, Mei XG New Invention Disclosure; Title: Preparation of Nanostructured and Porous Metals on Substrates through Chemical Reduction of Metal Precursors in Solid... optical property of metals Plasmons are free electrons collectively oscillating around the fixed positive ions in a metal induced by electromagnetic wave [5] For bulk metals, the plasma frequency (ωp) is ࢔ࢋ૛ ࣓࢖ = ඨ ࣕ૙ ࢓ࢋ where n is the density of the conduction electrons, ε0 is the dielectric constant of vacuum, e is the electronic charge and me is the effective mass of an electron For light with a... xv Figure 6.9 Images of E coli bacteria colonies in (a) “inoculums only” and (b) blank cotton after dilution to the factor of 103, while petri dish after loaded with Ag loading of (c) 0.2 mg cm-2 and (d) 0.1 mg cm-2 at dilution factor of 102 121 xvi List of Publications [1] Cho SJ, Ouyang JY Attachment of Platinum Nanoparticles to Substrates by Coating and Polyol Reduction of a Platinum Precursor... vapor reduction of H2PtCl6 (red dash line), two-step EG solution reduction xiii method (blue dot line) and one-step EG reduction method (green dash dot line) on FTO The area of the working electrodes were kept constant at 1 cm2 82 Figure 4.5 CV curves of Pt electrodes prepared by (a) pyrolysis, (b) EG vapor, (c) two-step EG solution reduction method and (d) one-step EG solution reduction method Dotted... solution reduction and (d) one-step EG solution reduction of H2PtCl6 on FTO glass as the counter electrode The Pt loading was constant at 0.39 µg cm-2 for these four methods 85 Table 6.1 Antimicrobial activity of Ag coated cotton against Gram-negative, E coli (ATCC 25922) and Gram-positive, S epidermidis (ATCC 12228) bacteria The viable bacteria were monitored by counting the number of bacteria colon-forming... colon-forming units (CFU), N/No is a survival fraction 122 Table 7.1 Summary of the metal nanostructures morphologies developed by solution and vapor methods on various substrates 126 ix x List of Figures Figure 1.1 Schematic drawing of energy band levels for molecules, nanoparticles and bulk solid 2 Figure 1.2 Profile of the density state g(E) for different dimensionality... pyrolysis of H2PtCl6 , (c) two-step EG solution reduction method, (d) one-step EG solution reduction method and (e) blank FTO The Pt loading is 3.89 µg cm-2 in (a) to (d) 78 Figure 4.3 SEM images of FTO deposited with nanostructured Pt by (a) the EG vapor reduction and (b) pyrolysis of H2PtCl6 on FTO glass at Pt loading of 0.78 µg cm-2 80 Figure 4.4 CVs of I2/I3- on the Pt . PREPARATION OF NANOSTRUCTURED METALS ON SUBSTRATES AND TEXTILE FOR ELECTROCATALYTIC AND ANTIBACTERIAL APPLICATIONS CHO SWEE JEN (B.Eng., Universiti. Preparation of rGO films 93 5.2.3 Deposition of nanostructured Au on rGO films 94 5.2.4 Characterization of materials 94 5.3 Results and discussion 96 5.3.1 Characterization of. List of Publications xvii Chapter 1. Introduction 1 1.1 An overview of nanostructured metals 1 1.2 Properties of nanostructured metals 1 1.2.1 Electronic structure of nanostructured