HYDROGEN, THE FUTURE ENERGY, PRODUCTION FROM GREEN WASTE BY PHOTOCATALYSIS VIA VISIBLE SOLAR SPECTRUM

Summary

Rapidly increasing population density and developing technology are boosting the energy demand. Considering the limited fossil fuel reserves and environmental hazards such as air pollution, climate changes and global warming, countries inevitably directed their energy policies toward renewable energy sources. High production cost is considered to be a disadvantage; nevertheless, among all known fuels hydrogen has the highest energy content per unit mass. One kg of hydrogen involves the amount of energy equivalent to that of 2.1 kg of natural gas or 2.8 kg of petroleum. Sodium borohydride, produced from boron minerals, is one of the important hydrogen storage agents. 

The aim of our project is to modify TiO2 surface, a photocatalyzer normally in the UV (Ultraviolet) region, by Silver (Ag) nanoparticles in order to achieve photocatalytic effect in the visible (VIS) region of the spectrum and to produce hydrogen gas from grass clippings via photocatalytic method in the visible region.

The surface of the photocatalyst was modified by Ag nanoparticles via reduction method and characterized by XRD, SEM, TEM, UV-VIS spectrophotometer. The enhancement of the photocatalytic effect of the catalyst was proven by methylene blue solution. Hydrogen gas was produced from green waste collected from parks and gardens by photocatalytic method under the sunlight. The quantification and the characterization of the generated gas were carried out by a hydrogen detector and gas chromatography, respectively. The production of hydrogen gas from cellulose via Ag/TiO2 photocatalyst would be a pioneering work in the literature.

Question / Proposal

          Our main purpose in this project is to produce hydrogen with a method that is easier and cheaper than the other methods. After weeks of research we learnt that we can produce hydrogen from cellulose. The reasons we decided to produce hydrogen from celulose were the cheapness and ease of the merhod. In this method, we produce hydrogen from cellulose with the help of some reduction reactions that are getting started by a photocatalyst. So we wanted to find an efficient photocatalyst and synthisize it. We also found that for that kind of reactions on of the best semiconductor(semiconductors generally are used as photocatalyst) to use was TiO2. We also modified the surface of TiO2 with silver nanoparticles to see if we can increase the effinciency of our photocatalyst TiO2. So with the knowledge we got from our teachers our hypothesis is that our recently synthesized photocatalyst will be more and more efficent than the other photocatalysts that were used in that method. So we strongly think that we will se that we produced a highly efficient, recycleable photocatalyst ever used fot that cheap, easy and efficient method, and also with the production of that photocatalyst we hope that we will achieve our main goal which is to make this method even more efficient than before.

 

 

Research

There have been some studies made about the several other potential photocatalyst material that we may have used such as Platinum (Pt), Palladium (Pd), Nickel (Ni), Gold (Au) metals and they have produced considerable amounts of hydrogen gas. Though the use of Pt metal was the most efficient, Ni metal was suggested due to high cost (Caravaca et al., 2016; Zhang et al., 2015). Studies on the photocatalytic activity of TiO2 reported Ag metal to be very efficient following Pt and Pd (Karakaş et al., 2008; Yurdakal et al., 2016). Our project is a distinct project as we aim to obtain hydrogen gas from waste cellulose by using a photocatalyzer that we produced by modifying Ag metal, cheaper than Platinum, to a less costly surface (TiO2 crystalline was not doped) which has nearly generates the same photocatalytic activity. There also have been many studies which were focusing on producing hydrogen gas and they followed methods such as electrolysis, reaction of active metals with water and the reaction of metals with acid, photo-fermentation, dark-fermentation. These methods are commonly used and known today as some of the main hydrogen production methods and we were heavily inspired by these methods as well as one method mentioned by M. Bowker, who suggested that hydrogen production from cellulose was possible with photocatalysis. We were heavily influenced by that bright man and started to do some research and experiments and that is when we chose silver modified TiO2 as our photocatalyst because of what I have mentioned at the start. Our project is also very applicable in the real world since it can reduce the water shortage problem if this method can be extensively used. Also, our project will produce the same amount of energy any non- renewable resource would produce with no harm to the environment. These reactions do not produce any harmful gases and it also helps us make use of the  green wastes produced by cutting the grass or the wastes of farmers which are generally burnt or thrown away at some point. 

Method / Testing and Redesign

      We began our project by synthesizing Ag modified TiO2. We have followed one specific method which we found on an article and we have done these experiments at the university laboratory which many students have legal permission to do such experiments. The basis of the production are redox reactions. After this process, we took the SEM and TEM pictures of the photocatalyst we have produced and we saw that we reached our goal, which was to see if we have successfully modified the Ag nanoparticles to the surface of TiO2 and we could observe that we have successfully produced Ag modified TiO2. Than to measure its photocatalytic properties, we used a solarbox, which produces focused synthetic sunlight, which we originally use in our project. In order to measure this property, we prepared a methylene blue and photocatalyst solution. This solution gets brighter and transparent when there is high photocatalytic activity. As a result, the photocatalytic activity and transparency at the Ag modified TiO2 added solutions were a lot higher than the ones which had TiO2 without any Ag modification. Furthermore, we executed another experiment which we used UV-VIS spectrophotometer which also measured and compared the photocatalytic activity of the Ag modified and non Ag modified TiO2. We got the same results as the solarbox experiment. Then we got to the part where the real hydrogen production happened. We prepared four different erlenmayer flasks and attached balloons to the tip. We observed the inflation at the balloons and tried to get some information about the hydrogen production that we have done. We saw that the erlenmayer flask in which we added grass and Ag modified TiO2 had a much greater gas emission when compared to the ones which we only added Ag modified TiO2 and another erlenmayer flask which we added cellulose and regular TiO2 added solution. We proved that there was some hydrogen gas emission being done during the reactions.

 

   Then we started another but far more complicated experiment which used a three neck flask and prepared the same a solution which contains grass, Ag/TiO2, and water. We tried to get rid of the unnecessary gas molecules by a nitrogen gas baloon and started the experiment. We left the flask under a Xenon lamp since the weather was cloudy at the time however it had approximately the same properties as the sunlight. Afterwards we waited for 24 hours for the reactions to fully occur. The gas emission was measured at Ege University by a gas chromatograph and the results showed that we have produced promising amounts of hydrogen gas. The people who helped us at Ege University told us that the amounts of hydrogen were much more than anticipated and they were pleased with the results.

 

Results

As the result of our XRD measurements we observed that the peaks of our sample are matched with TiO2 anatase phase, TiO2 rutile phase and Ag metal patterns. 

          TEM images of Ag/TiO2. 0.0022 g of powder sample was mixed with 10 mL of ethanol and allowed to disperse homogeneously in an ultrasonic bath for 25 minutes. 10 μL of this mixture was dropped onto the carbon-coated grid and the excess droplet was absorbed with a filter paper. The liquid film formed on the grid was dried in a closed chamber without being exposed to dust. The transmission electron microscopy (TEM) measurements were taken with a Zeiss Leo 906E TEM apparatus. The images were captured at the magnifications of 167,000 and 100,000.

          So with the methylene blue solution test  we heave seen that we achieved to synthesize a visible light activated photocatalyst. We alsaoobserved a numerical finding that we had with our methylene blue test.

          Finally, in our measurement of H2 production experiment by using 0,5 grams of grass clipping and 0,375 grams of Ag/TiO2 catalyst we obtained an average of 16 ppm H2 gas, measured by a PCE hydrogen gas detector, under sunlight (Xe lamp-35W) without any pretreatment. In addition, as measured by GC, 3110 ppm of H2 gas was produced via 5 grams of grass and 3 grams of catalyst. The unit converter  (http://www.lenntech.com/calculators/ppm/converter-parts-per-million.htm) demonstrates that 3110 ppm gas equals to 27 mg/m3 for H2.

 

         

 

 

 

 

 

 

 

 

 

 

Conclusion

* As targeted in the beginning of the project, the surface of TiO2 has been modified with Ag nanoparticles and the synthesis of Ag nanoparticles by XRD was proven.

* The photocatalytic effect of TiO2 in the UV region was shifted to VIS region and enhanced by Ag modification. These phenomena were proved by the effect on methylene blue solution. As shown in Figure 20, the Ag/TiO2 catalyst breaks down the methylene blue before P25 does. There was no change in the control group. No significant difference was observed between 0.07 g of Ag/TiO2 and 0.03 g of Ag/TiO2 containing test tubes.

* The measured spectra of TiO2 and Ag/TiO2 on the UV-VIS spectrophotometer indicate that the absorbance value of Ag/TiO2 noticeably shifted to the visible region. The absorbance value of TiO2 (P25) in the visible region was "0", whereas the absorbance value of Ag/TiO2 nanoparticles increased up to 0.2 Au.

* TEM And SEM images did not allow us to see Ag nanoparticles due to the measurement interval of the device. P25 has an average particle size of 25 nm. A more sensitive measurement is required in order to observe the Ag nanoparticles used in the modification of the surface. However, images were captured to provide information about the particle size.

*** To conclude, by using 0,5 grams of grass clipping and 0,375 grams of Ag/TiO2 catalyst we obtained an average of 16 ppm H2 gas, measured by a PCE hydrogen gas detector, under sunlight (Xe lamp-35W) without any pretreatment. In addition, as measured by GC, 3110 ppm of H2 gas was produced via 5 grams of grass and 3 grams of catalyst. The unit converter  (http://www.lenntech.com/calculators/ppm/converter-parts-per-million.htm) demonstrates that 3110 ppm gas equals to 27 mg/m3 for H2. It is known that the total gas volume is 0,442 L and the annual eggplant and tomato greenhouse wastes in Antalya is 127,351,38 tons. Approximately 1560 tons of hydrogen gas can be produced annually from solely tomato and eggplant wastes in Antalya with the help of solar energy. It is noteworthy to mention that the energy equivalent is 4365 tons of fossil oil.

* Air pollution problem will also be solved when hydrogen is used as a fuel since H2O is alone the the reaction product. Furthermore, the condensation of that water, produced in the system, would also be a partial solution for another environmental problem: the water supply problem. Thus, a big step will be taken FOR A BETTER LIFE.

* In previous studies, TiO2 surface was doped with Ag; however, not used for the production of hydrogen from cellulose. Additionally, TiO2 crystal was doped with Pt, Pd, Ni and Au, and the experiment was carried out at 60 °C to produce hydrogen gas from the cellulose. In our project, on the other hand, experiments were carried out under room conditions; that is, without additional heating. The production of hydrogen gas from cellulose with modified Ag/TiO2 surface would be a pioneering work in the literature.

About me

          We have known each other more than 5 years, that's one the main reasons we consider each other as perfect partners. Me and my partner is not only interested in maths, engineering or technology but also interested in music. My partner Alp is known for his extreme skills of playing clarinet which made him the main clarinet player of school orchestra, and just like him people also call me extremely skillful in playing drums. Furthermore we are also interested in basketball and when we are playing it between our friends we are the ones that everybody wats to play with, so that my  partner was the one who was irreplaceable in the school team before the surgery he got on his shoulder. We both are interested in being engineers and also interested in making something unique to make world a better place and make contribution to unstoppable development of science and technology. My partner has a dream of becoming an electrical engineer in order to study on the effiency of fuel usages, and i want to be an aerospace engineer to study the application of  my own ideas about satellites and jet engines. I want to make an postgraduate study about working mechanics of jet engines in order to be more and more competent about that topic, and Alp wants to be an engineer at a company which works on unique and promising projects about renewable energy usage. Alp is not the only particiant of that project who wants to study on renewable energy. Furthermore, we participated and published our project in the 3rd Hydrogen Technologies Congress which was held in Turkey.

Health & Safety

We conducted our experiments at a local university called Akdeniz University. We were given permission to conduct experiments at Akdeniz Unviersity since there was an agreement made between the education ministry of Turkey and the university and we conducted the experiments with the help of the assistants who worked at the university at the time. They were very careful when it came to the laboratory safety precautions and we were taught what chemicals we should be careful with. We wore lab coats and glasses to protect us from the chemicals we use. The assistants were very helpful and always came to the rescue when necessary. Also, they always taught us about some of the chemical processes that took place in our experiments and they helped a lot when it came to the measurement parts of the project. Our advisor teacher was very helpful and devoted during and after the project. She supported us quite a bit while writing the final paper and we learned a lot about academic writing throughout the project. In conclusion, the experiments were done very carefully and we nearly knew every process and were aware of what kind of mechanisms and reactions took place during the experiments.

Bibliography, references, and acknowledgements

     To begin with, I would like to thank our beloved advisor teacher, Gülay Demirci for never giving up on us and being devoted to the project from the beginning till the end. Also, we would like to thank Akdeniz University for letting us use their experimental tools and also would like to thank the assistants who work at the university for helping us all the time throughout the experiments and being so friendly and helpful.. They were the best. There is another person I would like to thank, who is also the owner of the labs that we have used to conduct the experiments, he works as a material engineering professor at the university. He always shared his knowledge with us and helped us a lot when it came to choosing what material to use and how to use them. We would also like to thank Ege University staff for helping us out at the hydrogen gas measurements and Erzurum Atatürk University for helping us out at the XRD measurements. 

 

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