Biomedical Nanotechnology Lecture 3 PDF

BIOMEDICAL NANOTECHNOLOGY LECTURE 3: SYNTHESIS OF NANOMATERIALS BY PHYSICAL AND CHEMICAL METHODS Dr.P.GOPINATH DEPARTMENT OF BIOTECHNOLOGY 1  Contents...

BIOMEDICAL NANOTECHNOLOGY LECTURE 3: SYNTHESIS OF NANOMATERIALS BY PHYSICAL AND CHEMICAL METHODS Dr.P.GOPINATH DEPARTMENT OF BIOTECHNOLOGY 1  Contents Physical methods Chemical methods Nucleation and growth Synthesis of metal nanoparticles & nanorods Silver nanoparticles synthesis (Demonstration) 2  Physical methods Mechanical Milling Laser Ablation 3  Mechanical Milling Nanoparticles from mechanical attrition are produced by a “top-down” process Nanoparticles formed in a mechanical device, generically referred to as a “mill,” in which energy is imparted to a course-grained material to effect a reduction in particle size. Particle size ~ submicron 4  Principles of milling The fundamental principle of size reduction in mechanical attrition devices lies in the energy imparted to the sample during impacts between the milling media. This model represents the moment of collision, during which particles are trapped between two colliding balls within a space occupied by mass of powder particles. Ball mill SEM of Bi4Ti3O12 milled for different times: (a) 3, (b) 9, (c)15, and (d) 20 h. L. B. Kong et al., Mater. Lett. 51, 108 (2001). 6  Laser ablation Light Amplification by Stimulated Emission of Radiation (LASER) Using a laser to vaporize material. 7  Laser Ablation Nanoparticles (NPs) by laser ablation, which involves the generation of NPs by laser ablating a solid target that lies in a gaseous or a liquid environment and collection of the NPs in the form of nanopowder or a colloidal solution. It is an easy, fast and straightforward method for NPs synthesis/generation as compared to other methods. It does not require long reaction times or multi-step chemical synthetic procedures. It does not require the use of toxic/hazardous chemical precursors for nanomaterial synthesis and thus is an environmentally friendly (“green”) and laboratory safe method 8  Laser Ablation In the event that generation occurs in water, the resulting NPs, colloidal solutions are ultrapure, (i.e., they do not contain any counter ions or reaction by- products), and this facilitates the use of the these NPs in biological or biochemical in vivo applications. The produced NPs can easily be functionalized with a ligand of choice, through the subsequent addition of the ligand into the NPs’ colloidal solution after its synthesis or by performing the ablation in a suitable solvent. 9 Synthesis of NPs by laser ablation method To synthesize Ag (Cu) NPs by LA, a high purity silver (copper) slice is placed on the bottom of glass vessel containing 20 mL of distilled water. It is irradiated with focused output of 1064 nm of pulsed Nd:YAG laser (Spectra Physics Inc. USA) operating at fixed energy for 30 minutes. This results a yellow color in Ag (light green in copper) colloidal solution. 10  Experimental configurations and equipment Generation in Liquids Synthesis of NPs by laser ablation in liquids the simplest experimental configuration commonly used by many groups around the world is shown in figure. The target is placed at the bottom of a beaker or a petri dish, which is filled with the liquid and fixed onto an XYZ translational stage. The laser beam irradiates the target vertically. Critical Reviews in Solid State and Materials Sciences, 35:105–124, 2010 11  Synthesis of NPs by laser ablation method 1064nm Mirror Nd : YAG Laser Convex Lens X-Y-Z Aqueous Synthesized Z Stage Media NPs(nm) Target Y 12 Chemical Reduction Method 13 Synthesis of metal nanoparticles 14  Nucleation and growth Nucleation is the phenomenon of initiation of formation of the first nanocrystals in solution. It involves the appearance of very small particles or nuclei of the new phase which are capable of growing. There are two types of nucleation 1)Homogenous-nuclei form simultaneously and uniformly throughout the solution. 2)Heterogenous-nuclei: Nucleated at different time. 15  Nucleation and growth Monodispersed nanoparticles Polydispersed nanoparticles LaMer’s diagram 16  Nucleation The growth of nanocrystals in solution involves two important processes, the nucleation followed by the growth of the nanocrystals (Rao et al., 2007). Nucleation is the creation of nuclei upon which growth can occur. Nucleation plays an important role in controlling the properties of the final product, size distribution and nature of the phase. Nanoparticles need strong nucleation and slow growth. Highly monodisperse nanoparticles are formed if the processes of nucleation and growth can be successfully separated. 17  Nucleation and growth Typical precipitation reaction: Reactant 1 + Reactant 2 T, t Product + By-product Stabilizer Nucleation Agglomeration (critical size) Primary particles Particles Growth Crystallites Clusters 18 Aspects of nanoparticle growth in solution Arrested precipitation Precipitation under starving conditions: a large number of nucleation centers are formed by vigorous mixing of the reactant solutions. If concentration growth is kept small, nuclei growth is stopped due to lack of material. Particles had to be protected from Oswald Ripening by stabilizers Oswald Ripening The growth mechanism where small particles dissolve, and are consumed by larger particles. As a result the average nanoparticle size increases with time and the particle concentration decreases. As particles increase in size, solubility decreases. 19  Tuning of the size of nanoparticles Tuning of the size of nanoparticles can be achieved by control over nucleation and growth rates, as illustrated in Scheme. Fast nucleation provides a high concentration of nuclei, ultimately yielding smaller nanocrystals, whereas slow nucleation provides a low concentration of seeds consuming the same amount of precursors, thus resulting in larger particles. Schematic representation of the synthesis of CoPt3 nanocrystals. Nanoparticles: From Theory to Application. Edited by Gu nter Schmid (2004) 20  Role of stabilizing agent Stabilizing agents/ligands/capping agents/passivating agents prevent uncontrollable growth of particles prevent particle aggregation control growth rate controls particle size Allows particle solubility in various solvents 21 Stabilization of nano clusters against aggregation + --- --+ -- -+- - - -+ 1. Electrostatic stabilization Adsorption of ions to the surface. Creates an - - + electrical double layer which results in a -- + -+- + -- + + +--- - ----- -- --+ Coulombic repulsion force between individual + + + + particles - + - 2. Steric Stabilization Surrounding the metal center by layers of material that are sterically bulky. Examples: polymers, surfactants, etc 22 Parameters affecting particle growth/ shape/ structure Type of capping agent/stabilizers Reducing agent Concentration of the reactants pH value of the solution Duration of heat treatment 23 Metallic nanoparticle synthesis 24  Synthesis of gold colloids Synthesis of a gold colloid in water starting from a solution of hydrogen tetrachloroaurate (HAuCl4) and a solution of trisodium citrate (Na3C6H5O7). Gold colloid with nanoparticles 10-20nm in size. In the reaction, the citrate acts as a weak reducing agent (reducing AuCl4- to Au) and as a stabilizer. A layer of citrate anions adsorbs around each nanoparticle and prevents these from aggregating: the anions electrostatic repulsion keeps the nanoparticle separated. In this state, the colloid appears ruby-red. 25 Synthesis of gold colloids The distinctive colors of colloidal gold and silver are due to a phenomenon known as surface plasmon resonance. Incident light creates oscillations in conduction electrons on the surface of the nanoparticles and electromagnetic radiation is absorbed. 26  Surface plasmon resonance When a nanoparticle is much smaller than the wave length of light, coherent oscillation of the conduction band electrons induced by interaction with an electromagnetic field. This resonance is called Surface Plasmon Resonance (SPR). Figure: Schematic of plasmon oscillation for a sphere, showing the displacement of the conduction electron charge cloud relative to the nuclei. 27 Control Factors 28 Synthesis of Gold nanorods 29 Synthesis of Gold nanorods  Synthesis of gold nanorods Factors related to the growth 1. Seed size 2. Length of “tails” of CTAB (cetyltrimethylammonium bromide ) 31 Growth mechanism of gold nanorods 32 Synthesis of gold nanoparticles of different shapes General idea is the same as the growth of gold nanorods (seed-mediated method) Slightly change the conditions when growing nanorods (concentration of different reactants) Cubes, hexagon, triangle, tetropods, branched T. K. Sau, C. J. Murphy, J. Am. Chem. Soc. 2004, 126, 8648-8649 33 Synthesis of gold nanoparticles of different shapes [AA] increases from A to C and seed concentration increases from C to D. Scale bar = 100 nm 34 Synthesis of gold nanoparticles of different shapes 35 Synthesis and study of silver nanoparticles 36 Synthesis and study of silver nanoparticles 37 Reduction in solution -Seed mediated growth 38  Silver nanoparticles (Ag NPs)-Simple method Synthesis of Ag NPs by NaBH4 reduction method:  Take 1 mL deionized water in a 1.5 mL micro centrifuge tube.  Add 1.67 L of AgNO3 (0.1M) to the above tube.  Immediately add 1.33 L of freshly prepared (2mg/mL) NaBH4 solution to it.  Then add 90 L of SDS solution (0.1 M) to the above solution.  Agitate the micro-centrifuge tube containing all the components vigorously.  Appearance of yellow color is indicative of the formation of silver nanoparticles. 39  Summary Mechanical milling and laser ablation Chemical reduction methods Nucleation and growth Synthesis of metal nanoparticles & nanorods 40