Solar Light Assisted nanoZnO Photo Catalytic Mineralization- The Green Technique for the Degradation of Detergents
Wastewater containing detergent from industrial and domestic source creates huge pollution in our cities. To treat this waste containing detergents is quite difficult since detergents are quite rugged and resistant to degrade. I wish to find out a potential Green method to treat this polluted waste.
Nano ZnO assisted photo catalytic degradation using solar light is emerging as new green option for the treatment of contaminated water.
The advantages of my method are summarized as follows: fast reaction, short treatment time, less costs, less exposure for workers, complete reduction pathway to non-toxic end products is possible and less equipment.
Preliminary studies have shown that the proposed method is quite effective in remediating the waste water. After lab synthesis of nanoZnO characterization has been done using various methods such as XRD (X-Ray Diffraction).
I propose to design a batch reaction system demonstrating that the representative detergent Cetyl Pyridinium Chloride can be effectively degraded by using nanoZnO. Mineralization of the detergents would be confirmed using UV spectrum and COD determination.
LINK TO THE GOOGLE DOCS PRESENTATION : https://docs.google.com/presentation/d/1wOm7GzUTjyfPjMsXEah28AsFggO175oXBScLnLLdYA4/pub?start=false&loop=true&delayms=15000
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I went on a school field trip to a Ludhiana which is also known as the industrial town of Punjab. Many industries are established in Ludhiana, especially the woolen industry and the dyeing industry. We visited one of the many textile factories situated in Ludhiana where the owner of the factory explained us how the woolen fibers are dyed. What caught my attention was the huge amount of waste of the factories that was thrown into the nearby drains. I asked the owner that “Was the waste treated before leaving the factory? “And he jokingly said “Do you treat the detergent water that leaves your house after the process of washing clothes?” While everyone was enjoying the trip, the question posed by the owner of the factory kept on troubling me. I thought about the enormous amount of detergent water that leaves our houses and causes huge pollution in our cities. The treatment of this detergent water might be possible in big cities but my country, India, is a land of towns and villages. I finally decided to look for a potential GREEN method for the degradation of detergent water.
I went through the literature for waste remediations and found that advanced oxidation processes are in use to treat potential pollutants. Thus we decided to use nanoZnO for the complete degradation of CPC which was my representative detergent. NanoZno assisted photo catalytic degradation using visible and solar light is emerging as new green option for the treatment of contaminated water. Preliminary studies showed that the proposed method could be quite effective. After lab synthesis of nanoZnO characterization was done using various methods such as XRD.
I proposed to design a batch reaction system demonstrating that the representative detergent Cetyl Pyridinium Chloride can be effectively degraded by using nanoZnO. Mineralization of the detergents was confirmed using UV spectrum and COD determination.
The methods and techniques used in my experiment were X-Ray Diffraction, photo catalytic degradation, UV spectroscopy, COD determination
After carrying out all the Batch Experiments , it was found that CPC is readily and rapidly degraded in aqueous solution by Vis/ZnO NPs in a relatively short time of about 60 min after selection of desired operational parameters (pH=8.0, ZnO NPs=40mg/100ml, [AB]= 9.0 x 10-5, [H2O2]= 8 x 10-5mol dm-3). ZnO NPs with an average diameter of 25-35nm were obtained. The X-ray diffraction and transmission electron microscopy showed a crystalline phase of nanoparticles. With addition of oxidants like H2O2 andK2S2O8 into illuminated ZnO NPs suspension, a synergistic effect was observed leading to an enhancement of the process except of the excessive amount of H2O2 andK2S2O8 which caused a decreased rate of reaction. From the inhibitive effect of NaCl and Na2CO3, it was concluded that OH radicals were the main reactive species. Degradation of AB with Vis/ZnO NPs system followed pseudo-first order reaction kinetics. The reduction in COD of the effluent suggests that the dye molecules were completely mineralized along with color removal. The conclusions of my experiments showed that Vis/Zno NPs system is versatile , environmentally benign , easily adaptable and efficient treatment method for the remediation of detergent contaminated waters and thus , completely supported my hypothesis.
My project will prove to be innovative in the field of chemistry because my method of degradation is a GREEN method , provides a complete reduction pathway to non toxic end products that are carbon dioxide and Water and is cost efficient with minimal equipment and above-ground structures. Also photo catalytic degradation using various other photacatlyst has earlier been used for remediation of dye waters while I have utilized nanoZnO for the treatment of detergent water.
I plan to compare the relative efficiency of this method with the other existing GREEN methods . It will also be my endeavor to make it commercially viable and minimize the costs so that the economically weaker sections of the society are also able to benefit from my efforts.
I live in Chandigarh , India which also known as the City Beautiful because of its greenery and cleanliness. I attend my high school at The Millennium School, Mohali. The reason for my deep interest in Science is that it requires a lot of analysis. From solving a numerical problem of physics to understanding an intricate biology concept , the level of complexity involved ponders me to think until I am able to satisfy myself with a scientific explanation. In my opinion the beauty of science lies in the fact that it never defies logic. I am a critical thinker and all the other aspects of my personality , such as my scientific aptitude, leadership potential have stemmed from the fact that I can reason things logically. Moreover , my critical thinking ability has aided me incredibly in science and I can confidently claim that I have a good understanding of scientific concepts primarily due to the intense thinking process that goes on endlessly in the grey cells of my brain. I can think and look for a solution until I get one. As my source of inspiration , the great scientist , Albert Einstein said , “It is not about being smart , it is about staying with the problems longer.”
Equipped with a sound fundamental knowledge in physics , chemistry , math and biology , I would like to Research Scientist in Chemistry.What inspires me to pursue Chemistry is the vast ocean of knowledge and scope for learning available. Winning the Google Science Fair 2013 means standing out amongst a community of students who are on a similar quest for knowledge. It would boost my confidence and place me on a launch pad from where I can go on to fulfill all my dreams and ambitions.
Detergent water from various industrial and domestic sources causes a huge pollution in our cities. Detergents are amphipathic molecules and they are quite rugged to degrade. I wished to look for a potential GREEN method for the remediation of detergent water
NanoZnO assisted photo catalytic degradation using visible and solar light has emerged as the new green option for the treatment of contaminated water. Preliminary studies have shown that the proposed method could be very effective. I propose to :
- Synthesize and characterize(through XRD) nanoZnO particles
- Design a batch reaction experiment demonstrating that my representative detergent Cetyl Pyridinum Chloride is effectively degrade using nanoZnO
The mineralization of CPC would be confirmed using UV Spectroscopy and COD and CO2 determination.
Earlier the method of photo catalysis has been used for the degradation of other compounds but surfactants have never been used before . I have gone through the various research papers available on the internet and in various libraries to investigate more about the mechanisms and principles involved in photo catalysis. Photo catalysis is a type of an Advanced Oxidation Process and such processes have been in extensive use in waste water treatment Out of the many methods available I decided to go for photo catalytic degradation as it uses visible or solar light rather than the harmful UV radiations used in other advance oxidation processes. In order to adjudge the status of present work I have done a thorough and extensive literature survey. Nanotechnology has been in use for waste water remediation. Thus I went through papers to get the methods of preparation of nanoparticles of a photo catalyst. I wanted to prepare “nano” particles because of their large surface area and cost effectiveness. Since I had decided to go for either visible light or solar light it was prudent to utilize ZnO as a photo catalyst owing to its compatibility with visible or solar light. In the present study the choice of organic pollutants was either carcinogenic textile dyes or other potential pollutant like surfactant in my case. Initial pilot experiments revealed that CPC could be effectively degraded through my method if the reaction conditions were optimized. CPC was chosen as the representative detergent after a thorough literature survey. I found out that upon illumination of nZnO particles with light energy greater than the band gap energy (hυ>Eg =2.63 eV), valance band holes (h+VB) and conduction band electrons (e-CB) are generated. The photo generated holes that are able to migrate to the hydroxylated surface can create the highly reactive hydroxyl radical HO• (standard redox potential 2.8 eV). Valance band holes can also oxidize organic molecule. Conduction band electrons (e-CB) reduce molecular oxygen to generate superoxide radicals. The role of reductive pathways in heterogeneous photo catalysis is very little as compared to oxidation. The formation of relatively harmless end products represents another attractive feature of this process; carbon dioxide, water and mineral acids are the main final products.
ZnO + hvvisible ZnO (h+VB + e-CB ) (1)
ZnO ( h+VB) + H2O ZnO + H+ + HO• (2)
ZnO (h+VB) + OH- ZnO + HO• (3)
ZnO (e-CB) + O2 ZnO + O2.- (4)
O2.-+H+ HO•2 (5)
HO•2 + H+ + ZnO (e--CB) H2O2 + ZnO (6)
H2O2 + ZnO (e-CB) HO• + OH- + ZnO (7)
CPC + HO• Degradation Products (8)
CPC + (h+VB) Oxidation Products (9)
CPC + (e-CB) Reduction Products (10)
The mechanism of semiconductor photo catalysis is of very complex nature. Detergent molecules interact with O2- .OH2, or OH- species to generate intermediates ultimately lead to the formation of degradation products. Hydroxyl radical (OH.) being very strong oxidizing agent (2.8 eV) mineralizes CPC to end product).
Description of Experimental Process:
- In order to initiate the experimental work , I started with the synthesis of nanoZnO particles.
- To prepare ZnO NPs, a 0.45 M aqueous solution of zinc nitrate (Zn (NO3)2.4H2O) and 0.9 M aqueous solution of sodium hydroxide (NaOH) were prepared in distilled water.
- Then, the beaker containing NaOH solution was heated at the temperature of about 55 •C. The Zn (NO3)2 solution was added drop wise to the above heated solution under high speed stirring.
- The beaker was sealed at this condition for 2 h. The precipitated ZnO NPs were cleaned with deionized water and ethanol then dried in air atmosphere at about 60 •C and stored for further use.
- After the synthesis of these particles, I had to get them characterized using XRD. For this, the sample was sent to UGC-DAE Consortium, Devi Ahilya University Campus, Indore (Madhya Pradesh) for characterization.
- With the help of XRD, it was established that the synthesized particles were nano sized.
- The next step was carrying out the photo catalytic batch experiment. The Cetyl Pyridinium Chloride was added to 50 ml of the dye aqueous solution. Suspension was kept in a dark for 15 min to establish adsorption-desorption equilibrium.
- The doubled wall Pyrex vessel was placed on a magnetic stirrer. The suspension containing dye and the photo catalyst was then irradiated under the visible light, and the photo catalytic reaction timing started.
- At specific time intervals, an aliquot (3 ml) of the mixture was withdrawn and centrifuged for 2 minutes at the rate of 3500 rpm to remove the nZnO particles in order to assess the extent of mineralization photo metrically.
(The pH was constantly monitored and not adjusted unless otherwise stated. In all kinetic experiments pseudo-first order kinetics with respect to CPC was monitored at maximum wavelength , using a UV Spectrophotometer)
The chemical oxygen demand test has widely been used as an effective technique to measure the organic strength of wastewater. The test allows the measurement of waste in terms of the total quantity of oxygen required for the oxidation of organic matter to CO2 and water. These tests were carried out using the traditional titremetric methods. The COD of the solution before and after the treatment was estimated. My testing process was fair as the COD determination and UV findings confirmed the removal of the detergent and further , the CO2 determination substantiate the results.
My next target was the optimization of the experiment conditions for which variations in pH and light intensity and photo catalyst loading were carried out. Also I checked the effect of addition of oxidants (Hydrogen Peroxide and Potassium Persulfate) and effect of addition of salts (Sodium Chloride and Sodium Carbonate).
All these experiments were carried out at the Chemistry Laboratory of Madhav Science PG College, (af.Vikram University,) (Madhya Pradesh, India) and the nano particles were sent for characterization to the UGC-DAE Consortium, Devi Ahilya University Campus , Indore (Madhya Pradesh , India).
The various equipment used for carrying out the experiments was as listed below:
- Laboratory Oven
- Mortar and Pestle
- Photo reactor
- Halogen Lamp
- Centrifuge Machine
- Aliquot Vessel
- Systronics UV Visible Spectrophotometer
[Range: 180-900 nm; Method: Interphased with PC]
- pH meter Systronics 160
- Conductivity meter Systronics
The experiments were carried out under the supervision of an experienced Chemistry Professor and were quite safe , therefore , no extra safety measures were required.
LINK TO THE GOOGLE DOCS DOCUMENT: https://docs.google.com/document/d/1Z50nFa7xfhfVWRI7Mn8IG5d87Rt2R_gD515CR3F4TGI/pub
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Photo catalytic processes are considered because of their simplicity, low cost, ease of controlling parameters and their high efficiency in degrading recalcitrant organic and inorganic substances in aqueous systems, and they are being increasingly utilized. It has been found that aniline blue dye is readily and rapidly degraded in aqueous solution by Vis/ZnO NPs in a relatively short time of about 60 min after selection of desired operational parameters (pH=8.0, ZnO NPs=40mg/100ml, [AB]= 9.0 x 10-5, [H2O2]= 8 x 10-5mol dm-3). ZnO NPs with an average diameter of 25-35nm were obtained. The X-ray diffraction and transmission electron microscopy showed a crystalline phase of nanoparticles. With addition of oxidants like H2O2 andK2S2O8 into illuminated ZnO NPs suspension, a synergistic effect was observed leading to an enhancement of the process except of the excessive amount of H2O2 andK2S2O8 which caused a decreased rate of reaction. From the inhibitive effect of NaCl and Na2CO3, it was concluded that OH radicals were the main reactive species. Degradation of AB with Vis/ZnO NPs system followed pseudo-first order reaction kinetics. The reduction in COD of the effluent suggests that the dye molecules were completely mineralized along with color removal. The data presented in the paper clearly indicates that Vis/ZnO NPs, as an advanced oxidation process, is versatile, environmentally benign, easily adaptable and efficient treatment method for the remediation of AB-contaminated waters.
- The advantages of Photo catalytic Degradation can be summarized as follows:
- Fast Reaction
- Complete reduction pathway to non-toxic end products
- Less equipment and above-ground structures required i.e. less cost.
- Less exposure for workers, fauna and flora.
- In situ treatment
The results of my experiment are completely reliable while the efficiency of the photo catalyst could be enhanced either by doping or surface coating.
If my method gets commercialized it would solve a huge environmental problem that the global community is facing today. It will be my endeavor to commercialize this method after comparing it with other GREEN methods and to minimize the costs so that all the sections of the society can benefit from my results. I have also thought of applying this process on removal of other pollutants such as pesticides, insecticides etc as well and efforts are needed to prepare more efficient photo catalyst.
I would like to acknowledge the contribution of Professor Dr. Brijesh Pare, Madhav science PG College, (Af.Vikram University), Ujjain who assisted and guided me all through my research work. He has helped in understanding theory of mechanisms of the various reactions involved, the working of a UV Spectrophotometer and has also assisted me in designing the Photo catalytic Batch Experiment. He permitted me to use the Laboratory and the laboratory equipment present in the Chemistry Laboratory of his department.
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