Citric Acid to Remove Stains | Experiment

Citric Acid to Remove Stains | Experiment BACKGROUND AND PURPOSE: Knowledge about natural bleaches to remove stain may be useful in our daily life. Natural bleaches can be found in various types of fruits juice and many more. This green bleaches are more friendly to environment and cheaper than commercial product. Citric acid is one of bleaching agent that can be found in the citrus fruits such as lemon. This paper will discuss on the process of removing stains by citric acid in different type of fruit juices. The investigation was focused on How does the type of citrus fruits used affect the rate of reaction of stain removable? Since stains have different types, the effectiveness of citric acid on two types of stains (synthetic and vegetable based stain) had been discussed more in this investigation. MATERIALS AND METHODS: The experiment was conducted with different type of fruits; lemon, lime, navel orange and pineapple. The time taken for the different type of stain to be removed by different type of fruits had been recorded and be analyzed to identify the most best used as natural bleaches. RESULTS: Even though the lemon juice is more popularly known as natural bleach but based on the experiment, the best used citrus fruit as bleaching agent is lime and the citric acid is most effective used to remove vegetable based stain. Table of Contents (Jump to) Introduction 1.0: Bleaches 1.1: Chemistry in Bleach 1.2: Mechanism of Bleaching 1.3: Rationale of Study 1.4: Significance of Study 1.5: Limitation of Study 1.6: Research Question Hypothesis Variables 3.0: Apparatus and Materials 4.0 Procedure and Analysis 4.1: Extraction of juices from citrus fruits 4.2: Citric acid determination 4.3: Procedure for stain removable Conclusion Evaluation INTRODUCTION Bleaches Bleaches used worldwide in household to remove or decolorize stains which whiten or lighten the color of clothes. Chemically, bleaches will breaks the stain molecules into smaller molecule that easily be removed. D.Noemia Souza (2008) stated that bleaches are chemical that capable to whitening the fabrics and removing stains by destroying colouring matter. There are two types of reaction that involve in bleaching. Commonly bleaching process involves in oxidation processes such as hydrogen peroxide and some involve the reduction processes such as sodium chlorite. However in bleaching processes, the oxidation and reduction also can occur simultaneously. Bleaching process for stains most effective when both an oxidative and a reductive bleaching steps worked together and this referred as full bleaching (J.M. Cardamone W.N. Marker, 1995) There are various types of bleaches, and each type of bleach is specifically used for certain type of fabrics. The fabrics are very specific and if use d with wrong bleach, the fabric will wear out. Concentration, pH, time and temperature are the various conditions which are affect the action of bleach on fabrics. Chemistry of Bleach Hydrogen peroxide is the most prominent bleach and usually used in commercial bleaches. However, according to D.Noemia Souza (2008), the strongest bleach is sodium hypochlorite while the weakest is sodium chlorate and the hydrogen peroxide is milder. Sodium hypochlorite(Chlorine-containing oxidants) Usually, the sodium hypochlorite will contain 15-18% of chlorine (D.Noemia Souza, 2008). Under certain condition, the solution will decompose into sodium chlorite (eq1) which then reacts with hypochlorite and produce the sodium chlorate (eq2). The sodium hypochlorite will undergoes further reaction to release oxygen (eq3). Thus it is classified as chlorine bleach 2NaOCl NaCl + NaClO2 (1) NaOCl +NaClO2 NaCl+NaClO3. (2) Overall equation: 3 NaOCl 2NaCl+NaClO3 (3) 2NaOCl 2NaCl+O2 (4) Hydrogen peroxide(preoxygen bleach) Hydrogen peroxide bleaching will dissociates into H+ and per hydroxyl ions HOO-(eq1).The per hydroxyl ions is the active bleaching agent. Under alkaline conditions it will release oxygen (eq2).Cotton would damage under this conditions as the bleaching effect is slow and the bleaching rate is fast. The activator and stabilizers are added to control this condition (J.M. Cardamone W.N. Marker, 1995). H2O2 HO2- + H+.. (1) 2H2O2 2H2O +O2 (2) Hydrogen peroxide is a universal bleaching and D.Noemia Souza (2008) said it is the only oxidizing bleach that can be safely used on protein. Mechanism of Bleaching Based on ProcterGamble (2005) the process of bleaching is divided into two, which are; Breaking up the stain The stain consist of molecule chains covering the fabrics The bleach molecule will break the stains into smaller pieces After that process, bleach molecule will disappear The stain is now broken into smaller pieces which can be easily removed by the surfactant Decolorizing the stains The stains color has its origin in the double-bond connections Then, the bleach will break up the bond and convert it into single bond, eliminating its ability to absorb visible light. After that, the bleach molecules will disappear. Once the double-bond connections are broken up, the stains isnt visible anymore. Citric Acid as Natural Bleach Citric acid is weak organic acid and one of the acids found in citrus fruits such as lime and lemon. It popularly used in food industrial as perservative. It also can act as natural bleaching agent and an antioxidant. So it is useful in our daily life to remove stain or dirt from fabric and bleach the spot. Citric acid exist in many type of vegetables and fruits but more concentrated in lime and juice where the dry weight of citric acid in fruit comprimise as much as 8 percent (sciencedaily.com).The concentration of cotric acid in fruits range from 0.005 mol/L for oranges to 0.30 mol/L in lemons and limes (Wiki.Org) Rationale of the Study Nowadays, most of people prefer to use biodegradable product or green product. Especially in current downturn economy, many people change to less expensive products. Using citrus fruits as an alternative ways to remove stain is the good choice. The question that arises here is what the significance of knowing which of the citrus fruits is best used in removing stains? Significance of the Study Sodium hypochlorite (chlorine bleach) and hydrogen peroxide (oxygen bleach) are extremely popular in the market to whiten the fabrics and in stain removable. However, there are some disadvantages using oxygen and chlorine bleaches. Most of them are hazardous if ingested or inhaled and should be used with care. Lindsay Evans (2009) also explained the chlorine can cause negative health effects. Besides, they are costly and give a bad impact to our environment especially rivers and lakes ecosystem. Chlorine that flowing into rivers or lakes will combine with other chemical to form a stable compound where it will remain unchanged in groundwater for many years (Wisconsin, 2010). On the other hand, citric acid best uses as natural bleaches because it does less harm to ecology of rivers and lake. Limitation of the study All of the experiment will conduct in the Mara College Serembans laboratory. Most of the material such as citrus fruits; lemon, lime, navel oranges and pineapple and table salt are obtained from Carrefour Cheras in Cheras, Selangor, Malaysia. So, all of the fruits are not in the same level of freshness due to different condition during storage that may affect the freshness of the fruits. Besides that, the fruits might not come from same tree and this will affect the concentration of acid in the fruits. Research Question The focus of study is to investigate the ability of citrus fruits as natural bleach to remove stain from fabric. The main objective of this study is to identify which of the citrus fruits; lime, lemon, pineapple, and navel oranges is best used as bleaching agent. So the research question of the study is How does the different type of citrus fruit used; lime, lemon, pineapple, and navel oranges affect the rate of reaction of stain removable? The study uses 4 different types of citrus fruits which are lime, lemon, pineapple, and navel oranges that will extract into juice and add with table salt (sodium chloride). Hypothesis The research question of the study is How does the type of citrus fruits used affect the rate of reaction of stain removable? The rate of reaction of stain removable is the highest at the most acidic solution. So the hypothesis is the most acidic fruit in this case is lime or lemon as both contains high concentration of citric acid. Variables Independent Variable There are two independent variables in this experiment as the experiment is divided into several parts. The first independent variable is the different types of citrus fruit juices; lemon, navel orange, lime and pineapple. While the second independent variable is the different type of stains where synthetic stain (syrup) and vegetable stain(tomatoes) are used throughout the experiment. Dependent Variable Rate of reaction to remove the stain from fabric will be the dependent variable. The time taken will be record by stopwatch for the stain to decolorize. Then by using the graph the gradient is determine which represent the rate of reaction. Fixed Variable The fixed variables are type of cloth (cotton), volume of juice (5oml), temperature (100ËÅ ¡c) and volume (100ml) of water bath and quantity of sodium hydroxide (3 teaspoon). All of this material will be use in same quantity throughout of the experiment. Apparatus and Materials Material Quantity Fruit juices (lemon, lime, navel oranges, and pineapples) 50 cm3 100 ËÅ ¡c of water bath 100 cm3 Phenolphthalein Distilled water 40 ml Table salt 1.0M of NaOH solution Dried KHP 3 teaspoon 10 cm3 1.0 g 4.0 Procedure and Analysis Preparation of an approximately 0.1 M Sodium Hydroxide Solution followed by the Standardization of the Sodium Hydroxide Before testing the concentration of citric acid, the standard sodium hydroxide solution needs to be prepared. In order to prepare 0.1 M of NaOH, 9.0 cm3 of 1.0M sodium hydroxide solution was diluted with 100.00cm3 of distilled water. Then the sodium hydroxide solution was standardizing to determine its concentration by titrated it with KHP. This acid base reaction is shown in Equation 1(M.L.Gillette, 1999); KHP(aq) + NaOH (aq) NaKP(aq) + H2O(l)(eq1) Two portion of 0.5g of dried potassium hydrogen phthalate (KHP) was weighed and dissolved with 50ml distilled water in conical flask. The Phenolphthalein solution was added for 2-3 drops into KHP solution to indicate the end point of titration. Phenolphthalein was used because the pH range of product is 8-10 .The sodium hydroxide was titrated with KHP solution until pale pink color was produced. The volume of NaOH solution added was recorded. Data Collection for Standardization of NaOH Number of trials 1sttrial 2ndtrial Initial Burette reading/cm3 ( ±0.05cm3) 0.00 0.00 Final Burette reading/cm3 ( ±0.05cm3) 23.50 25.40 Volume NaOH solution added/cm3 ( ±0.05cm3) 23.50 25.40 Observation After few minutes, the clear solution turned into pale pink before disappeared. After few minutes, the clear solution turned into pale pink before disappeared. Table 4.0 Data Analysis The purpose to standardize sodium hydroxide solution against potassium hydrogen phthalate is to determine the exact value of sodium hydroxide concentration. By titrate the 0.1M of sodium hydroxide solution against KHP solution the results collected are more accurate. The concentration of sodium hydroxide was found to be 0.1002M Calculation for determining the concentration of the sodium hydroxide; KHP (aq) + NaOH (aq) NaKP(aq) + H2O To calculate the number of mole of KHP Number of mole= mass/molar mass = 0.5g KHP/ 204.2 = 2.449ÃÆ'-10-3mol KHP To calculate the number of mole of NaOH required to neutralized KHP solution No. of moles of NaOH = No. of moles of KHP = 2.449ÃÆ'-10-3mol NaOH To calculate molarity of NaOH solution Concentration of NaOH = (number of moles/ volume of NaOH)ÃÆ'-1000 = (2.449ÃÆ'-10-3/ 24.45) ÃÆ'-1000 = 0.1002M Percentage uncertainty of the concentration of the 0.1M of sodium hydroxide % Uncertainty of Concentration of 0.1M NaOH = Volume(H2O) + Volume(NaOH)+ Concentration of NaOH(1.0M) % Uncertainty of VH2o = 0.04/100.00 ÃÆ'- 100 = 0.040% % Uncertainty of VNaOH = 0.05/9 ÃÆ'- 100 = 0.600% % Uncertainty of CNaOH = 0.040+ 0.600 =0.64% Extraction of juices from citrus fruits. The lemon was cut into small pieces and blend with blender. The juice released was putted into the beaker and labeled with A. First step was repeated again until half of the beaker filled. Then, the extracted juice was filtered through muslin cloth. The whole procedure were used again with another type of fruits, lime, navel orange and pineapple and labeled with; Beaker Type of juice A Lemon B Lime C Navel orange D Pineapple Citric Acid Determination The reason of citric acid determination is because to know the exact value of citric acid in juices for data analysis. This process is carried out by adding NaOH into the fruit juices. The approximately 10 mL of lime juice was prepared by using pipette and transferred into a conical flask. Then, the lime juice was diluted with 20ml of distilled water and three drops of phenolphthalein was added into solution. The solution with 0.1M sodium hydroxide (NaOH) was added from burette to the juice sample while swirling the mixture until the reaction mixture turned into faint pink color. The end point was reached when the pink color persists for thirty seconds. The volume of NaOH added was recorded. The processes were repeated again to increase the accuracy. Then, the procedure was repeated with different type of juice; lemon, orange and pineapple. By using the formula, the molarity of citric acid in the fruit juice was calculated. Data Collection for citric acid Determination Type of juice Lemon Number of trials 1sttrial 2ndtrial 3rdtrial Volume of juice pipette/( ±0.5)ml 10 10 10 Final burette 27.6 49.6 76.1 Initial burette 0 27.6 49.6 Volume of NaOH ( ±0.1)mL 27.6 22.0 26.5 Average Volume of NaOH 23.98 Qualitative Data The colour of solution in conical flask change from white colour to faint pink colour. Data Analysis- calculation for determining the citric acid concentration through sodium hydroxide added. The citric fruits consist of citric acid. Citric acid contains carboxyl acid group and reacts with hydroxide ion as indicate in equation 2 (Dr. Ewa Thomas, 2007). The sodium hydroxide will ionize to form sodium ions and hydroxide ions (eq 1). NaOH (s) Na+ (aq) + OH (aq) (eq 1) C3H5O (COOH)3 (aq) + 3 OH- (aq) C3H5O(COO)33- (aq) + 3 H2O (l) (eq 2) The purpose of this experiment is to determine the concentration of citric acid on the citrus fruit by titrating the citrus juice with standard sodium hydroxide solution. The concentration of citric acid can be calculated by measuring the volume of sodium hydroxide used (eq 3). Molarity,M= (eq 3) M1V1 = M2V2 (eq 4) Based on the equation, the molarity of the OH- ions equal with sodium hydroxide as the molecular ratio is 1:1. So, the molarity of hydroxide ions can be known. By using equation 4, the concentration of citric acid can be determined. Calculating the concentration of citric acid By using the data given above, I had calculated the concentration of citric acid in citrus juices. The citric acid C6H8O7 is a triple basic acid that consists of three carboxylic acids and react with one hydroxide ion ,eq 1(Ewa Peter Thomas M Moffet, 2007). In this experiment, I assumed that the citric acid is sole acid found in the citrus fruits. C3H5O(COOH)3 (aq) + 3 OH- (aq) C3H5O(COO)3 (aq) + 3 H2O (l).(eq 1) However, according to experiment conducted by Law.C Solak.E(2009) the citric acid does not always have the 3 carboxylic acid. So, in this experiment I will assume that the citric acids only have 1 carboxylic acids but its less accurate. The following reaction takes place in the titration; C6H8O7 + OH- à ¢Ã¢â‚¬  Ã¢â‚¬â„¢ H2O + C6H7O7- (eq 2) Based on the equation(eq 2), the molarity of the OH- ions equal with C6H8O7 as the molecular ratio is 1:1. By using equation below, the concentration of citric acid can be determined. M1V1 = M2V2 where : m1 = molarity of Sodium hydroxide, NaOH v1 = volume of Sodium hydroxide Solution, NaOH m2 = molarity of dilute citric acids, C6H8O7 v2 = volume of dilute citric acids Solution, C6H8O7 Example of calculation: By Using the volume of NaOH use to titrate lemon juice 0.1M NaOH ÃÆ'- 23.98 ml = M2 ÃÆ'- 10 ml 0f C6H8O7 2.298 mmol OH- = M2 ÃÆ'- 10 ml C6H8O7 M2 = = 0.2398 mole/L C6H8O7 (The calculations showed above are applied to all other experiment, table 5.5) Calculating Uncertainties Percentage uncertainty of Concentration = [(Άn / n) + (ΆVolume / Volume)] x 100% Example; Percentage uncertainty of concentration for Lemon = = 6% Absolute uncertainty of concentration = Percentage uncertainty x Concentration / 100% Example for Lemon = 6% ÃÆ'-0.24/100% = 0.014 moldm-3 0.01 moldm- Data Presentation Type of juice Average NaOH used( ±0.1)mL Concentration of citric acid (mol/L) Lemon 23.98 0.2398 Lime 10.78 0.1078 Navel Oranges 5.35 0.0535 Pineapples 2.95 0.0295 Table 4.6 Procedure for process of stain removable The white cloth cotton was cut into3cmÃÆ'-3cm size for 20 pieces and each pieces of cloth were stained with syrup solution. Then the stained clothes were dried for about 1 hour. 20 cm3 of lime juice was prepared and the initial pH of juice was recorded by using pH meter. For the first trial, a stained cloth was held under the running water and was soaked in the lime solution for more than 30 minutes. After that, the stained cloth was put into100ËÅ ¡c hot water bath and the time taken for the stained decolorize was recorded. However, the stained took longer time to decolorize where the average of time taken cannot be recorded. So I used another method by adding 3 teaspoon of table salt (sodium chloride) into lime juice. The pH value of juice was recorded. The stained cloth was rubbed with salt before soaked into the solution for an hour. Then, the stained cloth was putted into 100 °C hot water bath and the time taken for the stained decolorized was recorded. In order to identi fy the best fruit best use to remove the stain, the whole step was repeated again with another type of fruits; lemon, navel orange, and pineapple. The results from different type of fruits were compared. Besides that, I also used the different type of stain to test which one is more effective been bleached by citric acid. In this experiment I used vegetable based stain which is tomato stain. The first method is used; without adding the table salt (sodium chloride) and the result was recorded and be compared with synthetic stain (syrup). Data Collection for Removable of stain Qualitative data For synthetic stain: The pinks colour of stain turns into colourless. Fabrics become white Fabric cloths smell fruity. The juices become more slippery when added with sodium chloride. For organic stain The red colour of tomatoes decolorize The fabric colour turn into redish The fabric turns white after held under running water. Data Analysis According to the data collected, the different type of fruits and different type of stain will affect the time taken for the stain to decolorize. For the syrup stain, there must be influenced by sodium chloride (cooking salt) as it is hard to remove by citric acid alone. Adding the cooking salt involved the osmosis concept where the solution will become more saturated, the water will moving from the cloth to the salt and taking the stain together (T. Lister J. Renshaw, 2000). When the cooking salt is added into the juice, the pH of juices drop and become more acidic. However, chemically the cooking salt does not affect the acidity of citric acid. The drop in pH value may be due the presence of water in the juices which react with the salt and release the hydrogen ions which might cause this to be happened. The reason putting stained cloth into the hot water is to increase the reaction by increase the movement of particle and reduce the time taken to remove the stain (Kenneth M.S, 194 2). The highest rate of reaction (Table 4.9) calculated is lime juice and the lowest rate of reaction is pineapple juice. The reaction for both juices can be related with its pH and concentration. In term of concentration of citric acid, the higher the concentration of citric acid will increase the acidity of juice and the time taken for stain removable will become faster. However, this might not be true for lemon juices. Even though, it has highest citric acid concentration but the time taken for stain removable is not the fastest. This probably because of error and limitation occurred and will be discussed more in other section. Meanwhile, graph 4.4 shows the rate of reaction of stain removable for both type of stain by using Microsoft Excel. It is show that the rate of reaction for removable stain in tomatoes stain is 0.154, higher than syrup stain. This is might be because the syrup stain is more thick and viscous. While the vegetable based stained (tomatoes) is easier to remove because it is organic in nature and more soluble in lemon juice. 8.0: Conclusion and Evaluation Conclusion The experiments showed that the type of citrus fruits used does affect the average time taken to remove the stain. The hypothesis that rate of reaction would be highest in the most acidic fruit (lime) which consist high concentration of citric acid, is also supported based on the data collected. The pH of lime is 2.2; most acidic among the others citrus fruits. The main objective of this essay is to identify which of the type of citrus fruits; lime, lemon, pineapple, and navel oranges are best used as bleaching agent. As mention above, the type of citrus fruit does affect the rate of reaction to remove the stain. However, it also depends on the type of stain. Test on fabric with synthetic stain without adding sodium chloride (salt) required a long time where the average time taken cannot be collected. Meanwhile, citrus fruits are best used on fabric with vegetable based stain as there in no influence with sodium chloride. It can be said that the sodium chloride act as catalyst and ma king the removable of stain easier. In addition, the time taken to remove the stain for vegetable based stain is fastest compare than synthetic stain. The hot temperature was used in the experiment to speed up the reaction. Thus it can be concluded that, the lime is the best used as bleaching agent but with certain condition; type of stain and temperature. Evaluation Some error and limitation occurring during the experiment which causes the result collected imprecise. The limitation and errors in these experiments can be divided into several parts. For the first part is problem in procedure A. Initially, the sodium hydroxide prepared had been assumed exactly 1.00M. However, to test the accuracy of the concentration, the sodium hydroxide had been standardized using KHP solution. After calculating the concentration of the sodium hydroxide, the concentration of sodium hydroxide is approximately 0.1M with 0.2% of percentage error. There is a limitation occur when calculating the concentration of citric acid by titrate it with sodium hydroxide solution. One problem is the citrus fruits contain several type of acid. So, in the experiment the citric acid had been assumed as sole acid in citrus fruits and be supported by Dr. Ewa Thomas. As a result, the amounts of citric acid concentrations calculated are inaccurate and larger than theoretical value. The citric acid should been standardized to know the exact concentration, where it reduce the uncertainties. Besides that, some common mistake occurred in the experiment such as improper position of burette and parallax error in taking the measurement. To overcome this, there is no other solution except reduce the parallax error by positioning the eyes straight to the scale reading needed and position the apparatus used at the smooth surface. Moreover, it was hard to determine that the colour of the solution turned to faint pink colour because if the titration of NaOH was titrated without care the solution will become too red. So the result of the first faint pink colour come out should be observed and detected properly so it needs a particular partner in doing that job. Based on data collected, there is error between the concentration of citric acid and pH value for lemon juices where supposedly the pH of lemon juice should be most acidic as it has highest citric acid concentration. The problem may arise in determining the citric acid concentration where the value of citric acid calculated in lemon juice was incorrect. Because of the lemon used are in different freshness (as mention earlier in limitation of study), it might affect the result. So, the same lemon must be use throughout the experiment. In the last part (procedure D), one of the error occurs is during taking the average time taken to remove the stain from fabric. When the stained fabric is place into hot water, it is difficult to identify whether the cloth decolorize or not because it is possible for fabric to turn into white without be rub. To improve this, the experiment must be repeated for several times to increase the accuracy. There is also a limitation where the removable of stain cannot be seen clearly when test conducted with coffee at first. So, to overcome this problem, the stain was changed into syrup which the red colour can be seen clearly. However the problem had comes when there is change in pH value of fruit juice after adding with NaCl due to presence f water. This might be because limitation that occurred during extraction of juice. So, it is necessary to ensure all the equipment to rinse and dry first before conducting any experiment. Recommendation for further research More work could be done on the use of sodium chloride (cooking salt) in removing stain; is it effective used and how it will increase the effectiveness of citric acid in removing stain? The other use of citric acid beside remove stain should be investigated as if citric has potential in other cleaning process. Besides that, while the experiment was done by using citrus fruits as natural bleaching agent other natural bleaching agent should be considered. Investigation on the effectiveness of citric acid by comparing it with the commercial bleaches and color safer bleaches has applications in our daily life. CdS Quantum dots: Synthesis and Optical Properties CdS Quantum dots: Synthesis and Optical Properties CdS Quantum dots: Synthesis and Optical Properties Characterization for Solar Cell Raimy Roy Abstract— In this work CdS quantum dots were synthesized using Successive Ionic Layer Adsorption and Reaction (SILAR) method. Then a study of the morphology and optical property were made for the application of solar cell. The structural characterization were made by XRD while the optical characterization where done by UV-vis-NIR spectroscopy techniques. Index Terms—Quantum dots, SILAR I. INTRODUCTION Quantum dot sensitized solar cell is an emerging field of photovoltaic in which the absorbing material is a quantum dot. The advantage of using such solar cell is size tunability and increased surface to volume ratio. In a quantum dot based solar cell the active layer consist of the quantum dot and the scattering layer is formed by the TiO2 layer. The mesoscopic TiO2 when deposited with CdS quantum dot act as an energy harvester and convert the incident photon to electricity. In this work, a model of the photoanode for the solar cell was made with mesoscopic TiO2 layer as scattering layer and quantum dots as absorbing layer. Here instead of ITO a glass slide was used. [1] To synthesize a quantum dot various techniques are used. Among them Successive Ionic Adsorption and Reaction (SILAR) method is a cost effective and is used to prepare quantum dot. In a SILAR method the time of reaction or the number of cycles can be controlled. Depending on which the size of the quantum dot varies. Another advantage of this technique is that it can be prepared at room temperature. Also this method provides a close contact between the quantum dots and the oxide layer, so it is an attractive method for the preparation of electrodes in a solar cell. [1] Cadmium sulfide (CdS) quantum dot is a direct band gap semiconductor. It is a II-VI compound semiconductor that is used for many optoelectronic devices such as solar cell, laser diodes and photoconductors. It is an inorganic semiconductor which has several advantages over conventional dyes. These advantages are band gap tunability, large extinction coefficient (this means that the dark current can be reduced and the overall efficiency can be improved) and multiple electron generation by utilizing hot electrons. [2] II. EXPERIMENTAL SETUP Chemicals Required Titanium dioxide powder (SD Fine-Chem Limited, purity 60%), 2M nitric acid, 0.05M cadmium nitrate, ethanol, 0.05M sodium sulfide hydrate (Sigma Aldrich, assay=60%), methanol. Preparation of TiO2 layer on glass slide A paste of titania (TiO2) was prepared from TiO2 powder and nitric acid. The chemicals were added in 2:1 proportion. A thin layer of titania paste was coated on the glass slide using a technique called doctor blade method [3]. In this method, either a glass rod or a microscope slide is used. We have used a microscope slide of thickness 1.45mm to coat the paste. A glass slide of dimension 2cm X 1cm was cut and cleaned. With the help of an adhesive tape, the glass slide is positioned firmly on the work bench. Another advantage of using such tape is that we could define an area to coat the paste and to deposit the quantum dot. Now place the paste on one side of the glass slide, positioning the microscope slide in 45à ¯Ã¢â‚¬Å¡Ã‚ ° spread the paste across the glass slide. Repeat the operation till a reasonably homogeneous layer is formed. After coating heat the paste to 80à ¯Ã¢â‚¬Å¡Ã‚ °C followed by annealing at 450à ¯Ã¢â‚¬Å¡Ã‚ °C for 30 min. After sintering the paste is white in color . This provides a better surface for adsorption of the CdS quantum dots since sintering makes the mesoporous films to a continuous network. Deposition of CdS Quantum Dots Successive Ionic-Adsorption and Reaction method is commonly used to deposit metal sulphide onto a nanostructured film. CdS quantum dot was deposited onto titania using this method as described in [4]. The first precursor solution used is 0.05M cadmium nitrate (Cd(NO3)2) and the second precursor solution is 0.05M sodium sulphide (Na2S). The bare TiO2 paste is dipped onto the first precursor solution for one minute. The Cd2+ ions have been deposited onto the TiO2 surface. This is then rinsed in an ethanolic solution for one minute and dried under room temperature. It is then dipped in the anionic precursor for one minute and then rinsed in methanolic solution for one minute and allowed to dry at room temperature. This completes one deposition cycle of SILAR. In this work we have performed four deposition cycles of SILAR. III. RESULT AND DISCUSSION The CdS quantum dot was deposited on to the surface of TiO2. An obvious color change was observed during the deposition cycle which is shown in Fig.1. The color change was pale yellow to golden yellow. The characterization was done using XRD and UV-vis spectroscopy techniques. Fig 1: Photograph of glass slides with CdS coating with increasing SILAR cycles XRD Characterization Fig 2. shows the obtained XRD pattern for TiO2 (Fig.2a), TiO2/ CdS (Fig 2b.) . From the peak obtained, we confirm that CdS quantum dot was deposited onto the film. Since the peaks at 44.1à ¯Ã¢â‚¬Å¡Ã‚ °, 51.9à ¯Ã¢â‚¬Å¡Ã‚ °, 64.3à ¯Ã¢â‚¬Å¡Ã‚ °, 70.4à ¯Ã¢â‚¬Å¡Ã‚ ° and 72.9à ¯Ã¢â‚¬Å¡Ã‚ ° coincides with the intensity pattern as defined by the JCPDS 10-0454 for the CdS QD. The corresponding miller indices are (220), (311), (400), (331) and (420). From this we conclude that CdS QD was deposited. It belongs to the cubic crystal system and the mineral name is hawleyite. For TiO2 the XRD pattern exactly matches with JCPDS 21-1272. It belongs to tetragonal crystal system and its mineral name is anatase. Fig.2 : XRD pattern (a) TiO2 (b) TiO2/CdS Size Characterization The size characterization was done by non-contact mode AFM (Atomic Force Microscopy). The size of the CdS quantum dot was found to be 25.83nm. the thickness of the deposited layer was calculated to be 29.65nm. Fig 3. Fig 3 : AFM non-contact mode characterization of CdS quantum dot UV-vis Characterization The optical property was characterized using Jasco Spectrophotometer V670. The absorption spectrum is shown in Fig 4. The absorption spectrum for the TiO2 and CdS/TiO2 is shown in Fig 4a. and TiO2/CdS alone is shown in Fig.4b. The absorption peak for CdS is as reported by Antonio et.al [4]. From the absorption spectrum we could observe a shift in the peak indicating CdS QD is being deposited. The absorption peak was observed in the range of 386nm-484nm. For TiO2 the absorption peak was observed at 341nm. In Fig 4b. the inset is the absorption spectrum that was reported in [5] Fig 4: Absorption spectrum of (a) TiO2 and TiO2/CdS (b) TiO2/CdS Fig 5: UV-Vis absorption spectra showing increase (~49 %) in absorption due to CdS Figure 5. depicts the percentage increase in the absorption peak of CdS with respect to TiO2. It was calculated to be a 49.08% increase in the absorption peak. Determination of Optical Band gap The DRS (Diffuse Reflectance Spectroscopy) characterization was done to obtain the optical band gap. The optical band gap was calculated by plotting the Tauc plot . It is the plot between energy and absorbance. The optical band gap can be determined by Tauc relation Where à ¯Ã‚ Ã‚ ¡ is the absorption coefficient in cm-1, hà ¯Ã‚ Ã‚ ® is the photon energy in eV and A is a constant. The value of n is given as follows n =  ½ for direct allowed transition n = 2 for indirect allowed transition The Tauc plot for TiO2 and TiO2/CdS is shown in Fig 6. TiO2 is an indirect band gap material whereas CdS is a direct band gap semiconductor. The bandgap value of CdS in bulk is given as 2.42eV [5]. From the experiment we calculated the optical band gap to be 2.38eV. Also the absorbance value of the CdS QD is blue shifted. Using the equation The value of the peak was calculated to be 519.16nm which is within the absorption region. Fig 6. Tauc plot of (a) TiO2 (b)TiO2/CdS IV. CONCLUSION In this work CdS quantum dot have been synthesized using SILAR method. Its structural characterization was done that confirmed the deposition of the CdS quantum dot on to TiO2 paste. The optical property was characterized and analysed using UV-vis-NIR spectroscopy. The optical band gap was calculated to be 2.38 eV. The size of the quantum dot deposited was calculated to be in nanometer. REFERENCES [1] Prashant V Kamat , â€Å"Quantum dot Solar cells.The next Big Thing in Photovoltaics† J.Phys.Chem.Lett. 2013, 4, 908-918. [2] Chang Liu,Yitan Li,Lin Wei,Cuncun Wu,Yanxue Chen,Liangmo MeiandJun Jiao, â€Å"CdS quantum dot-sensitized solar cells based on nano-branched TiO2arrays† Nanoscale Research Letters 2014,9. [3] A. Berni, M. Mennig, H. Schmidt, â€Å"Doctor blade method†, Springer. [4] Antonio Braga,SixtoGimenez, Isabella Concina, Alberto Vomiero and Ivan Mora-Ser, â€Å"Panchromatic Sensitized Solar Cells Based on Metal Sulfide Quantum Dots Grown Directly on Nanostructured TiO2 Electrodes†, J. Phys. Chem. Lett. 2011, 2, 454–460. [5] B. T. Huy, Min-Ho Seo, Jae-Min Lim, Dong-Soo Shin and Yong-Ill Lee, â€Å"A Systematic Study on Preparing CdS Quantum Dots† Journal of the Korean Physical Society, Vol. 59, No. 5, November 2011, 3293-3299