Research Background

UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMIA PROCESS CHEMISTRY (CHE434)group member : nor syaira binti kamrulzaman(2014211654) nur adilla anis binti mohd nawi(2014204658) nabihah binti azron (2014479476)

Group : eh2201bSEMESTER: 1programme / code : eh220submit to : dr. nurul fadhilah

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2Research Background/10

3Characterization/10

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1.1 AbstractNanomaterial is the solid material that having the critical dimensions which is 1 to 100nm. The nanomaterial exhibits the novel properties related to this scale. The novel optical properties appear in nanoparticle are being exploited for biological, information energy technologies and sensing. Sunscreen is the one application in nanotechnology. Sunscreen consists of titanium dioxide and zinc oxide nanoparticles. Zinc oxide and titanium dioxide have their very own unique chemical and physical properties. These nanoparticles are synthesized by using wet chemical method. Wet chemical method best in controlling the particle size, shape, size distribution and crystalline phase. Titanium dioxide and zinc oxide nanoparticles uses top-down approaches ( milling) and bottom up approaches(controlled precipitation). Characterization of these nanoparticles are transmission electron microscopy and scanning electron microscopy. Transmission electron microscopy works with the same basic principles of the light microscopes. Transmission electron microcopy used electron to replace the light. When using the light microscope, it will cause the limit by the wavelength of the light. So, the transmission electron microscopy used electron as their light source that provide much lower wavelength of light. The lower wavelength causes it to get a resolution a thousand times better compared to the light microscope. By using the transmission electron microscopy, the small details in the cell or different matters down to near atomic levels. It means that transmission electron microscopy is made for looking forward to the high magnifications matters which is really useful in biological medical and materials research.Scanning electron microscopy is one of the type of the electron microscope that create the image of the sample by using scanning method. The sample will be scanned with the focused beams of electrons. The electrons cooperate with atoms in the sample to produce the various signals which can be detected and the consist details about the samples surface topography and composition. Generally, the electron beam will be scanned in a raster scan pattern. The detected signal will be combined with the beams position to create an image. The resolution for the scanning electron microscopy is better than 1 nanometer. The specimens can be observed in high vacuum, in wet conditions, in low vacuum and at a wide range of cryogenic or elevated temperatures.Application of nanoparticles titanium dioxide and zinc oxide are used in these days sunscreens. It is an improvement from the last sunscreens that has been used for decades. Sunscreens that have nanoparticles are better options because it gives out better sun protection which means it can absorb and scatter visible light. Other than that, nanoparticles sunscreens look transparent when applied on the skin and they are also more stable in the sun, means less reapplications. Even though titanium dioxide is not bad at all to be used in sunscreens, companies that manufacture this product preferred using zinc oxide because it can protects the skin better against harmful radiations from the sun. Since nanoparticles are in a very small size, there are concerns regarding the using of sunscreens containing these nanoparticles. Consumers are worried that the nanoparticles may penetrate the skin and enter the bloodstream. For this reason, the board of health and safety along with companies has been pushing an effort to convince the consumers about the safety and benefits of sunscreens containing nanoparticles.

1.2 Research Background1.2.1 Introduction and the synthesis of nanomaterials (TiO2 and ZnO)Titanium Dioxide (TiO2)Titanium dioxide is a non-toxic, wide band gap semiconductor, which is most commonly used as a white pigment in tooth paste, wall paint, white paper, etc. Many unique properties can be determined from this material due to its extraordinary chemical stability. Titanium dioxide (TiO2) nanoparticles were prepared by wet chemical method and characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Raman scattering (RS) and photoluminescence (PL). The best method to control the particle size, shape, size distribution and crystalline phase is by using a method called wet chemical route. The experimental procedure has been stated below.Wet chemical method ( TiO2)The analytical grade titanium tetrachloride (TiCl4) was used. Other chemicals used were analytical grade ammonium hydroxide solution (35%), ethylene glycol, polyethylene glycol and sodium acetate. With vigorous stirring titanium chloride (2 ml) was drop wise mixed in ammonium hydroxide/ethylene glycol and continued stirred for 10 minutes. The reaction was exothermic and carried out in 100 ml beaker. In method-I, this mixed precursor was heated to 333K. White 6 particles were washed several times using warm water to remove chlorine impurities. Particles were dried by applying acetone wash. As-prepared particles showed amorphous phase. In order to convert it into crystalline phase, as-prepared particles were heated to 623 K. In method-II, once transparent solution was obtained sodium acetate (3.6 g) and polyethylene glycol (0.9 ml) were added and vigorously stirred for 30 minutes. This mixture was heated to 423 K in closed system. Once the condensation starts white color precipitate formed, this process was continued for 4 hours. The white colored particles were collected using centrifugation. The particles were washed using warm distilled water followed by acetone wash. The as-prepared particles were annealed at 573 K for 1 hr. The samples obtained using method I and II are designated here as A and B respectively. These samples were characterized using Powder X-ray diffractometer (Bruker) to understand the structural characteristics. To study the effect of particle size on the Raman spectra and Photoluminescence (PL) spectra experiments were performed using U1000 and Spex-14018 Raman spectrometer with a backscattering geometry at room temperature with 532 nm line of DPSS laser and 457.9 nm line of an argon-ion laser respectively.However, we have also recorded the micro Raman spectra of powder samples on Horiba Jobin Yuon T64000 spectrometer, Argon ion laser COHERENT INNOVA 400 operating at 514.5 nm, with the laser power ranging from 10-100 mW. We did not observe any change in the spectra except a slight change in Intensity. Transmission electron microscopy (TEM) was performed by using JEOL JEM 2100 200 kV microscope, having point resolution is 50 X to 1.5 MX[1].

Figure 1.2.1.1 shows Titanium dioxide image in transmission electron microscopy

Zinc oxide ( ZnO)Zinc oxide is one of nanomaterial that has its very own unique physical and chemical properties. For example, zinc oxide have high chemical stability, high electrochemical coupling coefficient, broad range of radiation absorption and high photostability. There are several common methods to produce zinc oxide nanoparticles such as sol-gel, microemulsion, thermal decomposition of organic precursor, spray pyrolysis, electrodeposition, ultrasonic, microwave-assisted techniques, chemical vapor deposition, and hydrothermal and precipitation methods[2]. However, the most suitable method to produce zinc oxide nanoparticles is wet chemical method. This is because the method is quiet simple and low cost. The experimental procedure has been discussed in paragraph below.Wet Chemical Method (ZnO)Zinc oxide nanoparticles were synthesized by wet chemical method using Zinc Chloride and Sodium Hydroxide as precursors. The concentration ratio between the Zinc chloride and sodium hydroxide was determined using the chemical equation formula shown below:ZnCl2 + 2 NaOH Zn(OH)2 + 2 NaCl

Hence, 0.4M aqueous methanol solution of zinc chloride was kept under constant stirring using magnetic stirrer to completely dissolve the zinc chloride and 0.8M aqueous methanol solution of sodium hydroxide was also prepared in the same way and kept under stirring. The speed of stirring the Zinc chloride was increased after its complete dissolution and 0.8M aqueous solution of sodium hydroxide was added for 20mins in drops. The colorless solution obtained after complete addition of addition of NaOH was allowed to be under constant stirring for 2hrs and later sealed and kept overnight. After the whole process Zinc hydroxide with some unknown impurities assumed settled at the bottom and the excess mother liquor obtained on top was removed. The remaining solution was centrifuged for 5mins and the precipitate obtained was washed five times with deionized water and methanol to remove the by products which were bound with the Zinc hydroxide and then dried in air atmosphere at about 400oC. After drying Zn (OH)2 is completely converted to into ZnO explained by the equation below.Zn(OH)2 ZnO + H2OThe prepared ZnO nanoparticles were characterized for their optical and nanostructural properties. X-ray diffraction pattern for the ZnO NPs was recorded using an X-ray diffractometer (PANLYTICAL) using Cu K radiation of wavelength =0.1541nm in the scan range 2=20-90. Morphology of the sample was investigated using scanning electron microscope (SEM with EDXA, Sirion) which also has been used for compositional analysis of the prepared ZnO nanoparticles. The optical transmission/absorption spectra of ZnO dispersed in water were recorded using a UV-VIS spectrophotometer (Hitachi, U-3010). The photoluminescence (PL) spectrum of the ZnO nanoparticles dispersed in water has been measured using a spectrofluorimeter (F-2500 FL Spectrophotometer, Hitachi)[3].

Figure 1.2.1.2 shows synthesis of Zinc Oxide nanoparticles 1.2.2 Fabrication of nanomaterialsTitanium dioxide and zinc oxide nanoparticles uses top-down approaches (milling) and bottom up approaches (precipitation).Mechanochemical process (Top-down)The mechanochemical process is a cheap and simple method of obtaining nanoparticles on a large scale. It involves high-energy dry milling, which initiates a reaction through ballpowder impacts in a ball mill, at low temperature. A thinner is added to the system in the form of a solid (usually NaCl), which acts as a reaction medium and separates the nanoparticles being formed. A fundamental difficulty in this method is the uniform grinding of the powder and reduction of grains to the required size, which decreases with increasing time and energy of milling. Unfortunately, a longer milling timeleads to a greater quantity of impurities. The advantages of this method are the low production costs, small particle sizes and limited tendency for particles to agglomerate, as well as the high homogeneity of the crystalline structure and morphology. Controlled Precipitation (Bottom-up)Controlled precipitation is a widely used method of obtaining zinc oxide, since it makes it possible to obtain a product with repeatable properties. The method involves fast and spontaneous reduction of a solution of zinc salt using a reducing agent, to limit the growth of particles with specified dimensions, followed by precipitation of a precursor of ZnO from the solution. At the next stage this precursor undergoes thermal treatment, followed by milling to remove impurities. It is very difficult to break down the agglomerates that form, so the calcined powders have a high level of agglomeration of particles. The process of precipitation is controlled by parameters such as pH, temperature and time of precipitation. Zinc oxide has also been precipitated from aqueous solutions of zinc chloride and zinc acetate [4]. Controlled parameters in this process included the concentration of the reagents, the rate of addition of substrates, and the reaction temperature. Zinc oxide was produced with a monomodal particle size distribution and high surface area.

Reference[1] Titanium dioxide synthesized using titanium chloride: Size effect study using Raman and Photoluminescence[2] Synthesis, Characterization, and Spectroscopic Properties of ZnO Nanoparticles[3]Synthesis and Characterization of ZnO nanoparticles with zinc chloride as zinc source.[4] Zinc OxideFrom Synthesis to Application: A Review

1.3 Characterizations of Titanium dioxide and Zinc oxide1.3.1 Characterization of titanium dioxidea) Transmission electron microscopyTransmission electron microscopy works with the same basic principles of the light microscopes. Transmission electron microscopy used electron to replace the light. When using the light microscope, it will cause the limit by the wavelength of the light. So, the transmission electron microscopy used electron as their light source that provide much lower wavelength of light. The lower wavelength causes it to get a resolution a thousand times better compared to the light microscope. By using the transmission electron microscopy, the small details in the cell or different matters down to near atomic levels. It means that transmission electron microscopy its made for looking forward to the high magnifications matters which is really useful in biological medical and materials research.[5]Transmission electron microscopy will be function by using a tungsten filament. The tungsten filament will provide an electron beam in a vacuum chamber. Through an electromagnetic field, the emitted electrons are accelerated and also restricted focuses on that beam. Then, the beam will be transferred through the sample material. Sample is a very thin which is less than 100nm slice of the materials. The electrons that had been transferred through the sample will hit the CCD, film, phosphor screen and automatically will produce an image. The more electrons get through as the sample has less density and the image also will become brighter. Meanwhile, the darker image is present in the areas which the sample is more dense and it cause the less electrons pass through it. The transmission electron microscopy can create images with the resolution down to 0.2nm. The size of the most atoms will be bigger than this resolution. Hence, the images can be construct using transmission electron microscopy that present the exactly structure arrangement of atoms in the sample material. Consequently, from the research that had been conducted, the titanium dioxide in sunscreen used the transmission electron microscopy as the characterization methods.[6]

Figure 1.3 Transmission electron microscopy machine

Figure 1.3.1 : Mechanism of the transmission electron microscopy

[5]http://www.nobelprize.org/educational/physics/microscopes/tem/[6]http://www.azonano.com/article.aspx?ArticleID=17231.3.2 Characterization of Zinc oxidea) Scanning electron microscopyScanning electron microscopy is one of the type of the electron microscope that create the image of the sample by using scanning method. The sample will be scanned with the focused beams of electrons. The electrons cooperate with atoms in the sample to produce the various signals which can be detected and the consist details about the samples surface topography and composition. Generally, the electron beam will be scanned in a raster scan pattern. The detected signal will be combined with the beams position to create an image. The resolution for the scanning electron microscopy is better than 1 nanometer. The specimens can be observed in high vacuum, in wet conditions, in low vacuum and at a wide range of cryogenic or elevated temperatures.[7]Scanning electron microscopy will be function starting with the gun provides an electron beam which supplied by the tungsten wire that heated by a current. Then, the beam will will accelerate with the high voltage which is up to 30KV that produced between the anode and the wire. After that, it will focus on the sample three electromagnetic lenses in a sensor that has less than 40 nanometers. At the time that the beam touches the surface of the sample, it will cause the interactions with secondary electrons, back scattered electrons and X-ray energy spectrometer. The right detector will collect these interactions and then converted into an electrical signal. The mechanism of deflection coils enables to guide the beam so that the beam can scan the surface of the sample in a rectangular frame. The video screen can examine the sample synchronically with the electron with the electron beam of the optic column. Signal that had been collected by the detector is used to modulate the brightness of the screen.Later, the quantity of the signal created at the fixed point of the sample will link to the brightness of the corresponding point on the video screen. If the electron beam is in the upper left corner of the area scanned on the sample, the electron beam of the video screen will be located in the upper left corner. When this area produces a lot of secondary electrons, the brightness of the image in the upper left will be high. The enlargement produced is the ratio of the surface of the video picture on the surface scanned on the sample. The scanning electron microscopy simulator will make to realize the effect of some of possible adjustments made to in the order to get a good quality of an image. The interactions of the electrons and materials will make to understand more on how the scanning electron microscopy works. In addition, the scanning electron microscopy bounces the electrons off the surface of the sample to create an image. Meanwhile, the transmission electron microscopy shoots the electrons completely through the sample. So, based on the research, zinc oxide used scanning electron microscopy in sunscreen for the characterization methods.[8]

Figure 1.3.2 :Mechanism of scanning electron microscopy

Figure 1.3.2.1 :Mechanism of the scanning electron microscopy

[7]http://www.nanoscience.com/products/sem/technology-overview/[8]http://materiaux.ecam.fr/savoirplus/mebanglais/principes.html

1.4 Application of nanoparticles in sunscreensIn the last decade, nanoparticles have been used increasingly in sunscreens to protect the skin because they contain ingredients that absorb or scatter ultraviolet (UV) radiation to prevent sunburn. Most sunscreens contain a mixture of active ingredients in order to get that broad-spectrum protection. These active ingredients consist of metal oxides such as zinc oxide and titanium dioxide. [9] Before nanoparticles are used in sunscreens manufacturing, bulkier particles of zinc oxide and titanium dioxide are used to reflect or absorb cancer-causing UV light. However, this early sunscreen is indistinguishable from a white paint because these large particles reflect visible light. Sunscreens with nanoparticles technology are more favourable now because they provide strong sun protection; they can absorb and scatter visible light, retain their highly effective UV light-absorbing capacity, and making them look transparent whilst applying on them on skin. Next, this kind of sunscreens did not break in the sun making them more stable so it requires less reapplication. It also has low irritant and low allergen material.[10] On the other hand, nanoparticles properties may vary staggeringly and it depends on their size, shape, coatings and surface area. To illustrate, smaller nanoparticles gives better SPF protection but bad UVA protection. Consequently, manufacturers need to have a balance in manufacturing their sunscreens product; gives out a better UVA protection with larger particles but provide greater transparency using small particles.[10]In production and manufacturing sunscreens using nanoparticles, zinc oxide is more preferable by sunscreen companies to be incorporated in their products. Compared to titanium dioxide, zinc oxide gives a better protection form UVA, UVB, and UVC rays due to its broad spectrum blocker. Not to mention that it is also quite stable in sunlight. Besides, zinc oxide has been safety tested on being used in other topical drugs such as calamine lotion and diaper cream.Having said that, titanium dioxide is not bad themselves to be used in sunscreen. In order to get a better protection against UVB and some UVC rays, it needs to be used with combination of zinc oxide to obtain that true broad spectrum protection. However, it does not protect the skin against UVA rays as good as zinc oxide.[11]One of the most controversial issues regarding sunscreens using nanoparticles is if they are safe to be used and applied on the skin. Consumers are worried if the nanoparticles would penetrate into their skin and enter the bloodstream. According to Paul Wright, toxicology expert at RMIT University, [12] this is not at all true. Theres only inconsequential penetration by the nanoparticles sunscreen. Simon James, research fellow at the Australian Synchotron stated that our body have immune cells that could collect and break down the zinc oxide particles.[10]

Figure 1.4 shows the Transmission electron microscope image of 25nm TiO2 nanoparticles in a diluted cream[9] http://www.csiro.au/Portals/Publications/Brochures--Fact-Sheets/sunscreens-FAQ/Why-are-nanoparticles-put-in-sunscreens.aspx[10] http://www.theguardian.com/science/small-world/2014/mar/13/nanotechnology-sunscreen-skin-cancer[11] http://www.ewg.org/2014sunscreen/nanoparticles-in-sunscreen/[12] http://www.badgerbalm.com/s-33-zinc-oxide-sunscreen-nanoparticles.aspx1.5 Reference Ayodeji Oladiran, A. and Abdul-Mojeed Olabisi, I. (2013). Synthesis and Characterization of ZnO nanoparticles with zinc chloride as zinc source. Asian Journal of Natural and Applied Sciences, 2(2), pp.41-44.Azonano.com, (2014). Transmission Electron Microscope - A Basic Look How TEMs Work. [online] Available at: http://www.azonano.com/article.aspx?ArticleID=1723 [Accessed 19 Dec. 2014].Badgerbalm.com, (2014). Zinc Oxide Sunscreen & Nanoparticles. [online] Available at: http://www.badgerbalm.com/s-33-zinc-oxide-sunscreen-nanoparticles.aspx [Accessed 19 Dec. 2014].Cave, H. (2014). The nanotechnology in your sunscreen | Holly Cave. [online] the Guardian. Available at: http://www.theguardian.com/science/small-world/2014/mar/13/nanotechnology-sunscreen-skin-cancer [Accessed 19 Dec. 2014].Ewg.org, (2014). Nanomaterials in Sunscreen EWG's 2014 Guide to Sunscreens. [online] Available at: http://www.ewg.org/2014sunscreen/nanoparticles-in-sunscreen/ [Accessed 19 Dec. 2014].Gupta, S., Desai, R., Jha, P., Sahoo, S. and Kirin, D. (2009). Titanium dioxide synthesized using titanium chloride: size effect study using Raman spectroscopy and photoluminescence. Journal of Raman Spectroscopy, p.n/a-n/a.Koodziejczak-Radzimska, A. and Jesionowski, T. (2014). Zinc OxideFrom Synthesis to Application: A Review. Materials, 7(4), pp.2833-2881.Materiaux.ecam.fr, (2014). PRINCIPES DE FONCTIONNEMENT. [online] Available at: http://materiaux.ecam.fr/savoirplus/mebanglais/principes.html [Accessed 19 Dec. 2014].Nanoscience.com, (2014). How does Scanning Electron Microscopy work?. [online] Available at: http://www.nanoscience.com/products/sem/technology-overview/ [Accessed 19 Dec. 2014].Nobelprize.org, (2014). The Transmission Electron Microscope. [online] Available at: http://www.nobelprize.org/educational/physics/microscopes/tem/ [Accessed 19 Dec. 2014].Talam, S., Karumuri, S. and Gunnam, N. (2012). Synthesis, Characterization, and Spectroscopic Properties of ZnO Nanoparticles. ISRN Nanotechnology, 2012, pp.1-6.

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