Electricity and clean water -things that we easily have access to are unfortunately luxuries for those in underdeveloped countries.
In fact, not only is there a lack of resources in third-world countries, but also the whole world is facing energy crisis and water pollution. My objective is to find an eco-friendly and economical approach to solve both issues.
My device H2PRO relies on photocatalytic reactions to purify and sterilize wastewater and to generate electricity using hydrogen produced. This sustainable process only requires titania and light. What’s more is that organic pollutant doesn’t only get decomposed but will also enhance the reaction rate.
It is composed of 2 parts –the upper unit for photocatalytic water-purification and hydrogen-generation, which is connected to a fuel cell and the bottom unit for further water filtration.
H2PRO’s feasibility in the removal of organic pollutant was examined to be excellent-almost 90% of organic compound was decomposed after 2hours. However, its performance in electricity generation was quite unstable although theoretically and experimentally the photocatalytic hydrogen yield is proved to be satisfactory and even better in the presence of organic pollutant. I will keep improving this device until stable electricity generation is achieved.
In conclusion, I have successfully introduced a design for a portable electricity-generation and water-purification unit. Generally speaking, H2PRO has demonstrated its potential to feasibly provide clean water and sustainable energy to the needy ones. I will keep "practicalizing" the electricity-generation unit so that people can really benefit from my design one day.
Hello! My name is Cynthia Lam. I go to Balwyn High School in Melbourne, Australia. Besides Science, I love travelling, music and making crafts.
I am always fascinated by the how scientists put imaginations into practice to change the world. Rita Levi-Montalcini's perseverance in science is truly an inspiration to me. Yet, although there was always a spark of passion for science in my heart, I always thought that I was too young for researches and inventions - until last year.
In April 2013, out of curiosity and my love for Chemistry, I started my first research on Titania's Photocatalysis. I investigated the optimum conditions for photocatalytic hydrogen generation and it won the Major Bursary in Victoria's Science Talent Search. It was a very rewarding and exciting experience to complete a research, I was hence motivated to challenge myself and to create a helpful device that puts what I investigated into practice.
I would like to study Medicine or Environmental Science in the future because I want to be able to help those in need. By creating H2PRO, I introduced an eco-friendly alternative for providing people in underdeveloped countries clean water and electricity. There is still a long way to go, but I am glad I took my first step to make a difference. Winning would mean a motivation for me to keep improving my device and to bravely follow my dreams. Hopefully it would also raise the awareness of the importance of clean water and electricity in underdeveloped countries.
Question / Proposal
Is it possible to create a portable device that purifies wastewater while generating electricity sustainably and affordably?
This question is raised not only because of the lack of clean water and electricity in third-world countries, but also because we are all facing energy crisis and water pollution. My objective is to find an eco-friendly and economical approach to solve both issues.
Based on what I developed from investigating photocatalysis, I aim to create a device that can put the mechanisms into practice. In photocatalysis, not only water is purified and sterilized, but hydrogen is also produced through water-splitting, which can be used to generate electricity.
The entire sustainable process only needs titania and light-no additional power source is required. However, hydrogen production is generally low since photoexcited electrons tend to fall back to the hole(i.e.photoinduced electron-hole combination). Fortunately, it can be overcome by adding reductants, while some organic pollutants serve such purpose. Hence, I propose to combine the two mechanisms together to enhance the yield and lower the cost of hydrogen generation, meanwhile efficient water purification can also be achieved.
There are similar designs existing, but they require either an excessively complex use of technology or an external energy source, which means they are not sustainable, affordable and manageable for users in underdeveloped countries. Nonetheless, I hypothesize that photocatalysis can be applied in a manageable scale that allows water purification and electricity production to be economically and sustainably performed in a portable device as well as at a household level.
There is an existing design for mobile hydrogen energy and water supply, although feasible, that design needs an external solar power source to purify water and produce hydrogen through electrolyzer, which makes it costlier and less efficient. This inspires me to create a self-sustainable portable device that can purify wastewater and produce electricity through only photocatalysis (without any additional electricity source).
I. Photocatalytic Redox Reactions
When titania absorbs ultraviolet energy, which is comparable to its band gap, photoexcitation of electron takes place and an electron-hole pair is produced.
Reduced by the excited electron, oxygen forms super oxide anion (•O2－). The hole reacts with water producing hydroxyl radicals (•OH).
The radicals yielded in the process oxidize organic compound, resulting in water purification. Furthermore, organic compounds may also be oxidized by the hole. In either case, the organic compound decomposed to yield harmless CO2 and H2O.
II. Photocatalytic Water Splitting
The effect of water splitting using titania was first discovered by Akira Fujishima. The photoinduced electrons and holes cause redox reactions similarly to electrolysis, causing water molecules to be reduced by the electrons to form hydrogen and oxidized by the holes to form oxygen (most oxygen is consumed in side reactions so hydrogen is the major product).
III. Recombination of the photoinduced electron-hole pairs
Electrons tend to move to lower energies. When this transfer occurs from band to band, it is called recombination.
In this process, an electron (e–), which has been excited from the valence band to the conduction band of titania, falls back into an empty state in the valence band, which is the hole (h+).
This phenomenon hinders photocatalytic redox and water-splitting reactions. Hence, preventing the recombination reaction had long been the centerpiece of the field.
Different attempts to hinder the recombination of electron-hole pairs have been proposed; doping titania with noble metals for example. The addition of a sacrificial agent – a reducing agent or an oxidizing agent – is known as an excellent approach to overcome such limitation. When photocatalysis takes place in an aqueous solution including a reductant, a.k.a. electron donors/ hole scavengers, photoinduced holes irreversibly oxidize the reductant instead of water. Therefore, hydrogen production is enhanced.
Lots of common organic pollutants such as methanol, glycerol and EDTA can act as excellent reductants. As hole scavengers, they minimize the chance of recombination of the photoinduced electron-hole pairs, hence enhancing the rate of hydrogen generation. At the same time, they can be effectively decomposed.
III. Hydrogen Fuel Cell
There are various fuel cells, but generally they work similarly. Hydrogen fuel cell has an anode and a cathode separated by a membrane. Oxygen passes over cathode and hydrogen over anode.
H2 reacts to a catalyst on the anode that converts H2 into electrons and hydrogen ion.
The mobile electrons travel through a wire creating the electric current. The hydrogen ions move through the electrolyte membrane to the cathode where they react with oxygen and electrons to form water.
Method / Testing and Redesign
The entire research consists of two main processes - designing and experimenting.
1. DESIGNING AND CONSTRUCTING THE PROTOTYPE OF THE DEVICE H2PRO
This research aims to create a portable device that purifies wastewater while generating electricity sustainably and affordably. The major intended users are people from third-world countries who lack resources.
Existing designs having similar ideas require either a too complex use of technology (which means not affordable and manageable for underdeveloped places) or an external energy source (which is not self-sufficient).
Therefore, H2PRO is designed to be portable, feasible, self-sustainable and affordable in the process of water purification and electricity generation.
Composed of two parts -
- The upper unit for photocatalytic water-purification and hydrogen generation, connected to a fuel cell
- The bottom unit for further water filtration. (Ideally, the lower unit is unnecessary as decomposition of organic pollutant and water sterilization could effectively perform through photocatalysis. However, household wastewater which has a higher concentration of organic pollutant (e.g.glycerol) may need further filtration. Hence, a self-made filter is used in this prototype for demonstration.)
Acrylic, a highly transparent material, is used to optimize the amount of light available for photocatalysis.
Titania was chosen to be the photocatalyst because of its low price and high stability. Nano-powder cannot be directly applied in this device because it can be easily washed away and constant stirring is required (i.e. additional energy source is needed). Hence, I developed designs to solve this problem -from titania-coated beads to titania-coated membrane, I finally decided to use a hexagonal mesh coated with nano titania to increase the surface area of titania exposed to wastewater and light.
To minimize gas leakage and to allow the upper unit to be easily cleaned at the same time, after several redesigning, this design (click to enlarge) with the use of silicone gas seal and screws was adopted:
H2PRO can also be applied at a household scale. It is proposed that solar panels can also be utilised at the same time to optimize the electrical efficiency.
(Drafts of H2PRO)
Preparation of materials
Construction (2 slides)
2. EXPERIMENTS TESTING
i.the ability of titania photocatalysis to decompose organic pollutants;
ii.the rate of photocatalytic hydrogen generation;
iii.the practicability of H2PRO.
Experimental guidelines were strictly followed-experiments were all safely conducted; all chemicals used did not exceed hazard level of 1.
(Chemicals used and safety precautions taken are listed below)
To test the ability of photocatalysis to decompose organic compounds, titrations were conducted to test the percentage of glycerol in water decomposed in photocatalysis.
*Appropriate rinsing of apparatus was conducted.
To examine the rate of photocatalytic hydrogen generation in different circumstances.
a. To examine the practicability of H2PRO on wastewater purification, back titrations were run to test the percentage of ethanol (representing methanol) decomposed in H2PRO.
b. To examine the practicability of H2PRO on electricity generation, a field test was run on the device and the fuel cell.
Experiment 2.i. -Examination of the ability of photocatalysis to decompose organic compounds
By referring back to the calibration curve, the eventual glycerol concentration in each sample was found and hence the amount of glycerol consumed was calculated.
The results showed that 8.772% glycerol was removed from the 10% standard glycerol solution. The concentration of 20% standard glycerol solution was also reduced to 2.002% while the one of 30% standard solution was reduced to 3.462. Hence, in general, 90% of glycerol in the solution was decomposed after photocatalysis had taken place.
It was shown that glycerol could be efficiently decomposed in photocatalytic redox reactions.
Experiment 2.ii. - The rate of photocatalytic hydrogen generation in different circumstances
(0.5g TiO2, 0.1g FeSO4, Vsolution=20cm3, natural pH)
*Note: The displacement of each droplet in every sample had already been subtracted by the displacement of the droplet in the control, which was 5mm, before being multiplied by the cross-sectional area of the delivery tube.
It was shown that the addition of organic reductants could greatly increase the yield and the rate of hydrogen production, which supported the hypotehsis. As the duration of ultraviolet irradiation increased, the amount of hydrogen gas produced also increased. The rate was highest (15.252mm3/min) in 10% ethanol solution while lowest (9.403mm3/min) in deionised water. The rate in the "simulated" detergent solution, which contains EDTA, glycerol, sodium carbonate and sodium bicarbonate, was the second highest (14.492mm3/min).
Experiment 2.iii.a -Examination of the practicability of H2PRO on wastewater purification
After collecting the data of average titre used to titrate against the eventual amount of I2 in each sample, by referring to the following equations, the eventual ethanol concentration in each flask can be calculated.
The eventual ethanol concentration and the percentage of ethanol decomposed are as follows:
|Original ethanol conc.||Final ethanol conc.||Percentage of ethanol decomposed|
Almost 90% of ethanol in each solution was decomposed. The results indicated that ethanol could be efficiently removed in the device H2PRO.
Experiment 2.iii.b - Examination of the practicability of H2PRO on electricity generation
After the conduction of repetitive experiments, unfortunately there was not an obvious electricity yield observed no matter which solution was used. There was once a slight increase in voltage and current for a short while when the content in the unit was 10% ethanol solution, but I wouldn't say that is enough to draw a valid conclusion. Hence, it was shown that the hydrogen produced in the unit might not be enough to generate a notable amount of electricity through the fuel cell.
As to prove that a significant amount of energy can be generate through hydrogen fuel cell, an electrolyzer was prepared to generate hydrogen. With the hydrogen gas produced in the electrolyzer in 30 minutes, electricity was generate through fuel cell with a voltage of 0.55V and a current of 16mA, which gives a power of 0.0088W in total.
Conclusion / Report
The data collected in Experiment (2.i.) indicated that...
- Decomposition of glycerol could be efficiently performed through photocatalysis;
- Around 90% of the glycerol in each solution was removed after two hours;
- The hypothesis was supported.
The data accuracy could be improved by measuring Chemical/Biochemical Oxygen Demand. However, the data collected could still clearly examine the ability of photocatalysis to remove organic pollutants.
In Experiment (2.ii.), the results showed that
- The addition of organic reductants could greatly enhance the yield of photocatalytic hydrogen generation.
- The reaction rate was the highest in 10% ethanol solution, closely followed by "simulated" detergent solution.
- A possible explanation for the detergent solution, although containing more potential reductants, yielded slightly less hydrogen: its transparency was lower, hence minimizng titania's exposure to light. It might also be because the concentration of titania-photocatalyst had become a limiting-factor.
Approximated Efficiency(in setup)
In terms of H2PRO's practicability, in Experiment (2.iii.a), its feasibility in the removal of organic pollutant was examined to be excellent- 90%of ethanol (as a replacement of methanol) could be decomposed after two hours.
H2PRO's ability to sterilize wastewater could not be examined due to restrictions on bacteria usage. Hence, although it's unideal, pre-existing data was used as requested. An experiment conducted by Y. Kikuchi showed that all 3×104 cells in E.coli suspension on a ultraviolet-irradiated TiO2-coated plate could be killed within 1 hour. In contrast, after 4 hours without TiO2, only 50% of the cells were killed. Hence, titania photocatalyst was shown to be a key to steady performance of water sterilization.
Based on the data collected in the field test, although H2PRO demonstrated high efficiency in water purification, its performance in electricity generation was unsatisfactory. There was once a slight increase in voltage and current for a short while (content: 10%ethanol) but this was not a desirable significant electricity yield. This could be explained by the possibility of flaws in the titania-coated mesh as the coating might haven't been professionally done. Alternatively, it might be because even in the presence of reductants, ordinary titania could not yield enough hydrogen to generate electricity. Adopting TiO2-nanotube array or noble-metal-doped titania could be a solution but it would greatly increase the cost, which would make H2PRO unaffordable for those in need.
Theoretically and experimentally it was indicated that photocatalysis gives a satisfactory hydrogen yield(which is even higher in the presence of organic pollutants), but my aim is to truly create a device that can self-sustainably generate electricity. Thus, in my further research, I would keep searching for economical approach to "practicalize" the electricity-generation unit.
In conclusion, I have successfully introduced a design for a portable electricity generation and water purification unit that only relies on sunlight (photocatalysis) to achieve its goals. There is definitely area for improvement in the electricity generation section, but generally speaking, H2PRO has demonstrated its potential to feasibly provide clean water and sustainable energy to the needy ones. My aim is to keep improving this device until stable electricity generation is achieved.
Bibliography, References and Acknowledgements
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- Y. Kikuchi, K. Sunada, T. Iyoda, K. Hashimoto, A. Fujishima, Photocatalytic bactericidal effect of TiO2 thin films: dynamic view of the active oxygen species responsible for the effect, J. Photochem. Photobiol. A: Chem. 106 (1997) 51–56. (Some experimental data from this paper had been used in Conclusion)
I would like to express my gratitude to the following people:
- My parents for their endearing support. I am so grateful for their assistance provided in the construction of the device as well as the freedom they gave me to develop new ideas and explore the world. I would especially like to thank my father Clive Lam for supervising me while conducting experiments.
- My mentor Matthew Chan for inspiring me to start working on a research and also for the constructive suggestions he gave whenever I encountered a technical problem.
- Natalie Hung for assisting me in video shooting.
- All of my friends for being so encouraging all the time.
I hereby certify that all images and videos were created by myself.