Determination of Gold Nanoparticle Sizes

Determination of Gold Nanoparticle Sizes Daron Chua Synopsis In this experiment, the objectives of this experiment was to understand the diverse applications of gold nanoparticles and to synthersize Colloidal gold nanoparticles by liquid chemical method. Z-average of nanoparticles for the reddish solution and the greyish solution was 60.86 and 50.40 respectively. However it was noted that there were impurities in the solution hence affecting the Z-average. As such, the colour of the solution and the Z-average did not tally. It was discovered that by adding salt into the solutions there will be colour change. This is due to NaCl aggregating the nanoparticles together. This causes the nanoparticles to absorb the red light hence reflecting the solution in a more blue colour. Other methods of forming gold nanoparticles and a diverse application for gold nanoparticles were noted. Introduction The objectives of this experiment was to understand the diverse applications of gold nanoparticles. Colloidal gold nanoparticles were synthesized by means of liquid chemical method. Theory Liquid Chemical Method Most of the gold nanoparticles are produced in a liquid (liquid chemical methods) byreduction of hydrogen tetrachloroautate (H[AuCl4]). By dissolving H[AuCl4], the solution is rapidly stirred while a reducing agent is being added. This causes Au3+ ions to be reduced to neutral goldatoms. As more and more of these gold atoms form, the solution becomes supersaturated, and gold gradually starts toprecipitatein the form of sub-nanometer particles. The rest of the gold atoms that form stick to the existing particles, and, if the solution is stirred vigorously enough, the particles will be fairly uniform in size showing the solution as red.To prevent the particles from aggregating, some sort of stabilizing agent that sticks to the nanoparticle surface is usually added. Also, gold colloids can be synthesized without stabilizers bylaser ablationsin liquids. They can be functionalized with various organic ligands to create organic-inorganic hybrids with advanced functionality. Several methods that revolve around this idea are Turkevich method, brust method and perrault method, etc. Gold Nanoparticles Colloidal goldis a suspension particles ofgoldin a fluid, usually water. The liquid is usually either an intense red colour (for particles less than 100nm) or blue/purple (for larger particles). As particle size increases, the wavelength of surface plasmon resonance related absorption shifts to longer, redder wavelengths. Red light is then absorbed, and blue light is reflected, yielding solutions with a pale blue or purple color. A change in temperature will also affect which the gold to be at a different energy band. The diameter of gold nanoparticles determines the Wavelength of light absorbed as shown on the diagram illustrated above. Procedures Stock Solution 0.1g of H[AuCl4] was dissolved in 500ml distilled water to obtain 1.0mM hydrogen tetrachloroautate. 0.5g of Na3C6H5O7.2H2O (trisodium citrate dehydrate) was dissolved in 50ml of distilled water to obtain 1% concentration. 0.5g of NaCl was dissolved in 10ml of distilled water. Experiment 20ml of 1.0mM H[AuCl4] was added to a conical flask. The conical flask was placed in a stirring hot plate and a magnetic stir bar was added. 2 samples were prepared. One was stirred continuously even it was at boiling point. The other sample stopped stirring once it was boiled. 2ml of 1% solution of trisodium citrate dehydrate was then added to the boiling solution. Gold Sol was gradually formed as citrate reduces the gold (III). Presence of a colloidal suspension was observed by the reflection of a laser beam from the particles. The solution of both samples were being transferred to two test tubes. 5 10 drops of 1M NaCl solution was added into one of the test tubes and the color change of the solution was being observed. The two solutions in the test tubes were being filtered with a 0.45 um syringe filter. The solutions were subsequently transferred into a sample holder. The Malvern Zetasizer Nano S Light scattering equipment was used to measure the size of the nanoparticles in the two sample holder. (0.47 refractive index was used.) Results Results as follows : Solution with spin even at boiling point : Colour observed : Reddish Brown Size of Gold nanoparticle : 63.77 with 3 peaks Peak 1 : 41.1, Peak 2 : 433.2, Peak 3 : 3913 Solution without spin at boiling point : Colour observed : Greyish / Bluish / Clear Size of Gold nanoparticle : 53.31 with 3 peaks Peak 1 : 143.9, Peak 2 : 1.651, Peak 3 : 3213 Calculation Standard Calibration 67.54nm 63.63nm = 2.91nm Size of Gold nanoparticle (Reddish/Brown) Z-Average 63.77nm 2.91nm = 60.86 nm Size of Gold nanoparticle (Greyish/Blue) Z-Average 53.31nm 2.91 nm = 50.40 nm Discussion From the results, Z average for the reddish brown solution was calculated at 60.86nm, while the greyish/blue was calculated at 50.40nm. With reference to theory, the results concluded by Z-average is inaccurate. By right, anything at the blue shift is of a larger particle size. By reading off the highest intensity peaks of both graphs of red and blue solutions, size of particles were 41.1nm and 143.9nm respectively. Ideally 1 peak in the chart would be best. Other peaks that affected the Z-average were probably impurities. This error may be due to carelessness of assuming all equipments provided for the experiment were clean. Hence there could be dirt or dust trapped whatsoever. In order to obtain even smaller particle sizes, adding of all solutions should have been done slowly, for example adding trisodium citrate drop by drop, allowing the droplet to fully react with the solution before adding in another. With that, the mixing part is no doubt the most crucial process parameter of the experiment. Other factors that affect particle sizes are mixing time and temperature and concentration. Different temperatures within the reaction will cause heat and mass transfer gradients. A low concentration of solution will yield too low of a result and lastly for our case, mixing time. Insufficient mixing time/stoppage of mixing will disallow the nanoparticles to disperse. Hence having a larger particle size. 1. Explain the functions of trisodium citrate used in this experiment. In this experiment, Trisodium citrate acts as an reducing agent to reduce hydrogen tetrachloroautate in order to produce spheroidal gold paticles. In general, the greater the concentration and power of the reducing agent. The smaller the resultant gold particles in the suspension. 2. Account for the colour change observed in step 4.6 In step 4.6 of the practical booklet, NaCl solution is added into the solution causing a colour change. By adding NaCl into the solution, it causes the gold nanoparticle surface charge to turn neutral, causing the nanoparticle to aggregate. As a result the solution colour changes from red to black blue. As for the greyish bluish solution, it turns to a even clearer solution. A larger particle size will cause absorption of the red light hence reflecting the solution as blue. 3. State two other synthesis methods for gold nanoparticles beside the liquid chemical method. Sonolysis One method for the experimental generation of gold particles is by sonolysis. The process is based on ultrasound. It uses the reaction of an aqueous solution of HAuCl4withglucose. The reducing agentsare hydroxyl radicals and sugar pyrolysis radicals. The morphology obtained is that of nanoribbons with width 30–50nm and length of several micrometers. These ribbons are very flexible and can bend with angles larger than 90Â °. When glucose is being replaced by cyclodetrin (a glucose oligomer), only spherical gold particles are obtained. Block Copolymer-mediated Method Other method for gold nanoparticles is by using a block copolymer.In this synthesis methodology, block copolymer plays the dual role of a reducing agent as well as a stabilizing agent. The formation of gold nanoparticles comprises three main steps: reduction of gold salt ion by block copolymers in the solution and formation of gold clusters, adsorption of block copolymers on gold clusters, and further reduction of gold salt ions on the surfaces of these gold clusters for the growth of gold particles in steps. This method usually has a limited-yield (nanoparticle concentration), which does not increase with the increase in the gold salt concentration. Recently a test has been done that by adding trisodium citrate in 1:1 molar ratio increases the gold formation by many gold. 4. Cite some other application in addition to those mentioned under introduction. Electronics Gold nanoparticles are designed for use as conductors from printable inks to electronic chips. As the world of electronics become smaller, nanoparticles are important components in the chip design. Nanoscale gold nanoparticles are being used to connect resistors, conductors, and other elements of an electronic chip. Probe Gold nanoparticles are relatively dense, making them useful as probes for transmission electron microscopy. Catalyst Gold nanoparticles are used as catalysts in a number of chemical reactions. The surface of a gold nanoparticle can be used for selective oxidation or in certain cases the surface can reduce a reaction (nitrogen oxides). Gold nanoparticles are being developed for fuel cell applications. These technologies would be useful in the automotive and display industry. Conclusion In conclusion, the experiment was not very successful as there were impurities in the solution. Hence the Z average was being affected. However objectives were met as colloidal gold was being synthesized and applications of gold particles were also understood. References http://en.wikipedia.org/wiki/Colloidal_gold http://www.sigmaaldrich.com/materials-science/nanomaterials/gold-nanoparticles.html http://www.webexhibits.org/causesofcolor/9.html http://clustertwo.org/Shaowei Chen lectures/Cluster 2 lecture 2.pdf http://www.ivdtechnology.com/article/manufacturing-high-quality-gold-sol

Molecular Modeling

MOLECULAR MODELING 1. Objectives ? Predictthe shape of identified compounds; ? Construct molecular models of identified compounds; and ? Determine the molecular structure of identified compounds. 2. Theory Building models of molecules are useful for visualizing how atoms are connected in three-dimensional space called molecular geometry, which is best predicted by Valence-Shell Electron-Pair Repulsion (VSPER) theory. The following are the sets of rules summarizing thsi theory: ? Consider molecules and ions where two or more atoms are bonded to a central atom. The electron pairs in the valence shell of the central atom are assumed to position as far apart as possible because electron pair repels one another. The shape of the molecule or ion is a result of the electron-pair repulsion. ? All the valence-shell electron pairs of the central atom are considered both the pairs that form covalent bonds (called bonding pairs) and the pairs that are unshared (called nonbonding pairs or lone pa irs). ? The nonbonding pairs help to determine the position of the atoms in the molecule or ion.Valence –Shell-Electron-Pair Repulsion (VSEPR) theory allows the chemist to predict 3-dimensional shape of molecules from knowledge of their Lewis Dot Structure. In VESPR theory, the position of bound atoms (ligands0 and electron pairs are described relative to a central atom. Once the ligands and lone pair electrons are positioned, the resulting geometrical shape presented by the atoms only (ignoring lone pairs) is used to describe the molecule. Electron Density and Molecular Geometry | d(Be-Cl) = 0,117 nm? = 180  °| | | Linear (B-F) = 0,130 nm ? = 120  ° Triangular Planar d(S-O) = 0,150 nm ? = 109 . 5 ° Tetrahedral | | d(P-Cleq) = 0,202 nmd(P-Clax) = 0,214 nm? (ClPCl) = 90  ° ;  ? (ClPCl) = 120  °| Triangular Biplanar | | d(Xe-F) = 0,190 nm? = 90 °| Octahedral 3. Apparatus and Materials 2- Modeling Clay (diff. colors) 1 – Wire (3mm. diameter, 5ft. long) 1- Pr otractor 4. Procedure 4. 1. Determine the molecular structure of the compounds listed in the table. 4. 2 Fill the table provided for the experiment. 4. 3 Construct the molecular models for each compound. 4. 3. Use color for the central atom diff. from the attached atoms. Use one color for the attached atoms. 4. 3. 2 Make a 2-inch diameter central atom X and ? inch diameter for the attached atoms Y. 4. 3. 3 Cut the wire into 3 inches long. 4. 3. 4 Attach the central atom X to the Y atoms based on the arrangement. 5. MolecularFormula| BondAngles| MolecularStructure| No. ofBond Pairs| No. ofLone Pairs| AngularGeometry| BeCl2| 180 °| | 2| 0| Linear| BF3| 120 °| | 3| 0| TrigonalPlanar| SO4| 109. 5 °| | 4| 0| Tetrahedral| PCl5| 120 °| | 5| 0| TriangularBipyramidal|XeF6| 90 °| | 6| 0| Octahedral| 6. Questions 1. What is valence electron? Give its importance. In chemistry,  valence electrons  are the  electrons  of an  atom  that can participate in the formation of   chemica bonds  with other atoms. Valence electrons are their â€Å"own† electrons, present in the free neutral atom, that combine with valence electrons of other atoms to form chemical bonds. In a single  covalent bond  both atoms contribute one valence electron to form a  shared pair. For  main group elements, only the outermost electrons are valence electrons.In  transition metals, some inner-shell electrons are also valence electrons. Valence electrons can determine the element's chemical properties and if it will bond with others or not. When two atoms approach each other and react with each other, it is their outer shells that come into contact first, and it is therefore the electrons in their outer shells that are normally involved in any chemical reaction. So it is the number of electrons in an atom’s outer shell that determines, to a large extent, how that element will react chemically.

Why People Arent Talking About Essay Writing Samples for 3rd Grade in Georgia Milestones

Why People Aren't Talking About Essay Writing Samples for 3rd Grade in Georgia Milestones It occurred around the start of April in 1988. It is crucial to design the curriculum remembering the developmental characteristics of 8 9 year olds and the milestones that they ought to achieve by the conclusion of the academic calendar year. Then you and your kid can employ your observation skills to try and guess what the picture is. Third grade is the year you would like your student to realize that reading will be a huge portion of their school lives for quite some time. Receive all the books you may get your hands on. Us the folks should step up and make that change which everyone would like to see. And so, I was tasked with helping students develop not just physical abilities but group participation skills also. Have the courage to get and express your specific talents. You will always have your favourite titles, but some years, your classroom library wants a refresh to fulfill everybody's needs. Then children have an opportunity to share'. By the close of the calendar year, your kid will learn how to find meaning in both fiction and non-fiction stories. He or she will learn to use reading as a way to enter other worlds. If You Read Nothing Else Today, Read This Report on Essay Writing Samples for 3rd Grade in Georgia Milestones And if you'd like a person to take part in a specific job or action the most, a variable rewardor reinforcement should become your selection. As the third grader starts to comprehend how to retain knowledge from reading, a variety of doors start to open up. I experimented with a number of unique elements to our day! Do not worry when this is your very first time taking the tests. Your day-to-day schedule may be decided by your administration. There's a period after home', because it's the conclusion of a sentence t hat's a statement. There's a period after tree', because it's the conclusion of a sentence that's a statement. There's a period after them', because it's the conclusion of a sentence that's a statement. Also, individual, silent reading is going to be a normal habit. She may use the collage to fix the issue and explain how she solved it. It's a difficult reality to face. Look at these strategies for organizing interactive notebooks from another wonderful 3rd grade blogger. We've provided below a sample of the very first week from the syllabus together with a list of the books utilised in the syllabus. The very best picture books are so a lot more than they appear. This page can help you create a workable daily schedule that maximizes every moment you've got with your students. Find out more about the topic on the internet or in a book together and then make an informative piece, explaining a topic or the way to do something. A small amount of experimentation with teaching methodology is never a poor thing! A teacher who's going to teach a lesson on the digestive system must first start looking for resources on this subject. I mentioned, You're right, terrific observation. So you ought to have no problem locating a selection of reading material that your third grader will discover interesting and engaging but which you will also find educational. Folks inherently search for patterns to aid with recognizing an object. The truth isn't going to be covered up. The web is a valuable resource for a great many homeschooling parents and teachers who want to draft the 3rd grade curriculum. A student in Florida may learn very different subjects in very different ways a student in California. Students investigate their function for a citizen of Louisiana. Third graders aren't too old for morning meeting. They also begin to study fractions. They love to be read to. Teachers know about test anxiety and attempt to create the exams simple. With the great number of lesson plans readily available online, it's important that teachers choose the most appropriate one for themselves. Students will learn more about the rehearsal process used to ready the ensemble for performance. In third grade, they can write at a more complex level.

Essay on Standardized Testing Is Counterproductive

Excessive testing has been integrated in the public school system to measure student intelligence, observe teacher proficiency, and distribute federal funds since the passage of the No Child Left behind Act (NCLBA) of 2001. The (NCLBA) ‘‘called for 100% of the nation’s public school students to become proficient in mathematics and reading by 2014’’ through the usage of standardized testing (Hanson 3). Since the inception of this policy there have been numerous issues involved in these tests. ‘‘Instead of providing equal access for all children, the frenetic use of mandated testing in schools and in teacher education is having the opposite effect’’ (Richardson 34). Standardized testing is an ineffective and outdated tool that creates a†¦show more content†¦Ã¢â‚¬ËœÃ¢â‚¬Ëœin any large scale testing system, three kinds of errors are possible: errors of test construction (items with more than one correct response), error s of scoring (items marked wrong when they are right), and errors of reporting (reporting that 50 percent of students passed when actually 75 percent did)’’ (Nichols 143). A manmade test is susceptible to typos and other obstructions. Since they are scored by machines, errors and malfunctions can occur. Testing plays an important in student’s academic futures and needs to provide completely accurate information. Proponents in favor of standardized testing believe it is effective. ‘‘There is a fundamental assumption that test taking is a singular experience for students’’ (Ryan 5). Those in favor of it argue standardized testing is equally pushed onto every school in every state. 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