Yeşil kimya ile sentezlenen seryum oksit nanoparçacıklar ile sulardan boyaların uzaklaştırılması
Removal of dyes from water with cerium oxide nanoparticles synthesized with green chemistry
Yazar: BERSU GEÇİM
Danışman: PROF. DR. FATMA BEDİA BERKER
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Ana Bilim Dalı / Kimya Bilim Dalı
Derece: Yüksek Lisans, 2020
Konu: Kimya = Chemistry

Özet:
Gün geçtikçe endüstrinin ilerlemesi ile birlikte çevresel kirlilik oranı da artmaktadır. Çevre kirliliğinin ekosistemdeki hedef kitlesi başta insanlar olmak üzere tüm canlılardır. Endüstriyel üretim fabrikalarından salınan tüm kirlilikler doğaya nüfuz etmektedir. Suyu, havayı, toprağı ve daha birçok alanı kirletmektedir. Çevre kirliliğinin nedenlerine bakıldığında, hızlı nüfus artışı, bu kalabalık nüfusun yerleşirken gerekli konut alanını sağlamak amacıyla neden olduğu çarpık kentleşme, şehirleşme ihtiyacı, sanayileşme gibi sebepler söylenebilir. Gerek sanayi tarafından, gerekse insan kaynaklı atık malzemelerin fazlalaşması gibi sebepler çevreyi direkt olarak kirletir. Nedeni insanlar olan çevre kirliliğinin sonuçları da yine en çok insanları etkilemektedir. Kirliliğin sonuçlarına bakıldığında ise gelecek nesil için en büyük tehlike küresel ısınmadır. Küresel ısınmaya bağlı olarak, iklimler değişir, buzullaşma veya kuraklaşma gibi doğa üstü sayılabilecek değişiklikler görülebilir, mevsimlerde kaymalar meydana gelebilir. Çevre kirliliğinin başka bir sonucu olarak bu doğa olaylarından kaynaklı olarak da nesli tükenen canlıları söylenebilir. Tarım ilaçlarının bilinçsizce kullanımının doğurduğu bir sonuç olarak da toprak veriminin, tarım veriminin azaldığı, toprak erozyon oranının sıklaştığı bilinmektedir. Bu toprak verimliliği azaldıkça üretilen besinlerde yetersizlik ve tüketilen besinlerde beslenme sorunları ortaya çıkmaktadır. Hava ve su kirliliğinin bir sonucu olarak sağlık sorunları ve salgın, bulaşıcı hastalıkların yaygınlaştığını söylemek de mümkündür. Ayrıca su kirliliği nedeniyle içme suyunun azaldığı da görülmektedir.
Tüm bu kirliliklerin arasında canlılar için en tehlikelisi yaşam kaynağı olan suyun kirlenmesidir. Çünkü çevre kirliliğinin etkili sonuçlarından birisi de suların kirlenmesi sonucu içme suyunun ve temiz su miktarının gün geçtikçe azalmasıdır. Tekstil, kozmetik, boya ve ilaç başta olmak üzere pek çok endüstrinin atık sularından içme sularına karışan kirleticilerin önemli bir bölümü boyalardır. Günümüzde 100.000 çeşidin üzerinde ticari boya üretilmektedir. Bunların toksik etkisinin ötesinde doğal sulara karışan çok az bir miktarı bile güneş ışığını ve fotosentezi engelleyerek suda çözünen oksijen miktarının azalması ile sulardaki yaşamı etkiler. Doğal su kaynaklarından boya kirliliğinin giderilmesi önemli bir çevre problemidir. Boyaların giderilmesi için en etken yol absorpsiyon olmasına rağmen, boyanın absorbandan giderilmesi ikincil bir problemdir. Son zamanlarda boyaların atık sulardan veya kirlenmiş doğal sulardan fotokatalitik degradasyonla giderilmesi gündemdedir. Sağladığı kolaylıklar ve ekonomik olarak uygun olması sebebiyle, atık su temizlenmesinde yönteme olan ilgi gittikçe artmaktadır. Bu tez çalışmasındaki temel hedef yüksek verim elde edebileceğimiz uygun maaliyetli ve çevre dostu bir yöntem geliştirmektir.
Çalışmamızda boyar madde içeren sulu çözeltilerden fotokatalizör tekniği ile boya giderimi amaçlanmıştır. Fotokatalizör olarak metal oksit nanoparçacık tercih edilmiştir. Yüzdece boya giderimi hesaplamak için bir yöntem geliştirilmiş ve koşullar belirlenmiştir. pH, boya konsantrasyonu ve fotokatalizör konsantrasyonunun etkisi araştırılmış ve her bir parametre için uygun değerler belirlenmiştir. Metot optimizasyonu aşamaları ticari seryum oksit nanopartiküller kullanılarak gerçekleştirilmiştir.
Bu tez kapsamında, boyar madde olarak bir tiazin boya grubunun bir üyesi olan metilen mavisi kullanılmıştır. Fotokatalizör olarak kullanılan metal oksit nanoparçacık ise seryum (IV) oksit nanoparçacıklardır. Hazırlanan metilen mavisi içeren sulu çözeltilere fotokatalitik seryum oksit nanopartikül eklenerek deneyler gerçekleştirilmektedir.
Yöntemin temel prensibi, bu sulu çözeltinin içerisindeki boyar maddenin UV ışık kaynağı ve fotokatalizör sayesinde parçalanmasıdır. Fotokatalitik degredasyon ile boyar maddenin yapısındaki kromofor gruplar biyolojik parçalanmaya uğrayacak ve renk değişimi meydana gelecektir. Degredasyon verimi kontrolü ise UV-Vis spektrofotometre  ile metilen mavisinin karakteristik dalga boyunda gerçekleştirilmiştir. Öncelikle deneyi gerçekleştirebilmek amacıyla pH, boyar madde konsantrasyonu ve fotokatalizör konsantrasyonu gibi koşullar ticari seryum oksit nanopartikülleri kullanımı ile belirlenmiştir. Optimize edilen koşullarda %81,6 lık boya giderme etkisi sağlanmıştır. Daha sonra deney kapsamında optimize edilmiş koşullar geliştirilen metot doğrultusunda bu teknik araştırma grubumuz tarafından kestane balından yeşil kimya yöntemiyle sentezlenmiş seryum oksit nanoparçacıklar ile uygulanmıştır. Bu koşullar sonucunda geliştirilen teknik ile %78,9 giderim elde edilmiştir. Elde edilen değer, ticari nanopartiküller ile elde edilen giderim yüzdesine çok yakındır. Yeşil yöntemlerle elde edilen nanopartiküllerin birçok alanda etkin kullanımı için vaad edici bir sonuçtur.

Abstract:
Lives of the people are depend on everything that happens in the environment. They live according to balance of the nature. The general name of the medium in which all living things in the world can live is called the environment or ecosystem. Water, air, and soil are the parts of the environment. When they are polluted by external factors, will make living beings' lives more difficult. Their life qualities will be decreased because of the environmental pollution. Day by day, the rate of environmental pollution increases. The target audience of environmental pollution in the ecosystem is all living things, especially humans. Not only humans, but also animals and plants will be the most affected by this polution, obviously. Pollution is all the ecological damages in the environment that disrupt the natural balance. Environmental pollution is caused by people mostly. People who pollute the environment are still the most affected living creatures by this environmental pollution.
There are many causes of the pollution. With the adverse effects on all the physical elements of the environment, foreign substances that cause the living elements of all living things to be adversely mixed with air, water and soil. The reaons why pollution is getting worse day after day can be arranged as rapid population growth, urbanization and tourism. But the main cause is industrialization. Pollution can be caused by advancing technology and industry. This industrialization and industrial wastes are very dangerous factors for humanity. The inclusion of foreign substances into this ecosystem, which negatively affects the living elements of living things belonging to this environment, is called environmental pollution.
Obviously, there are some results of pollution, too. The consequences of environmental pollution are sometimes very hazardous. Therefore, environmental pollution negatively affects the future. Global warming is the most dangerous problem for the world and that's why climate changes can happen due to pollution. Seasonal transitions can slow down or extend. Today, that result can be seen clearly. Beacuse of global warming, problems like glacier, desertification etc. can occur. As an another result of pollution, the amount of drinkable water resources is decreasing day by day. And health problems, epidemic and infectious diseases can be experienced. Environmental pollution affects animals and plants as well as humans. The living species are being extinct due to environmental pollution. Also, unconscious use of pesticides, causes to soil erosion. The efficiency of soil is going to be decreased, and consequently inadequate production and nutrition problems will arise.
There are many types of environmental pollution; water pollution, air pollution, noise pollution, soil pollution etc. They are named by the name that is the cause of the pollution or by the area in which it occurs. Plants, animals and, the most importantly, humans are affected by these impurities. However, the biggest quilty of this pollution are people living in the same ecosystem. When it comes to human health, the most dangerous pollution is water pollution. Because the most necessary need for people and the new generation that will come after them is water. These pollutants for living creatures, which are the source of life, are mixed with water and nature as a result of industrial production with the developing technology. And this result creates permanent damage for environment. The environmental pollution that occurs can completely change the balance of the ecosystem. Water born diseases like liver-kidney diseases, diarrhea, vomiting, gastro diseases etc. will occur in human body. 
All impurities released from industrial production factories penetrate into the nature. It pollutes water, air, soil and many other areas. However, the most dangerous is the pollution of water, which is the life source of living things. For this reason, treatment of wastewater is a very important issue. That is why, many studies on water treatment have been carried out in recent years. These studies are important studies for keeping nature clean and living creatures healthy. Dyes are released to the environment as a result of production in many different industries, mainly textiles, cosmetics, and pharmaceutical industries. Dyes with over 100,000 different commercial types are the significant part of the pollutants that cause water pollution. In addition, even a small amount of dye mixed into natural water blocks sunlight, influencing photosynthesis and the reduction of water-soluble oxygen, hence damaging the aquatic life. Thereby, removing dyes from wastewater is very important environmental problem. 
There are many methods to remove impurities from water. These methods include filtration, absorption,  precipitation and photodegradation. The most effective and economical technique used in cleaning wastewater is the absorption method. However, removing the absorbed pollutants are a secondary problem. Recently photocatalitic degradation methods are getting popular due to the convenience of this method and its economical advantage. Photocatalytic methods have become a preferred method for removing pollutants in wastewater in recent years. In photocatalytic reactions, using semiconductor metal oxide compounds has been a highly preferred method in recent years. These metal oxides nanoparticles can be used in wastewater to remove organic pollutants.
The main goal in this thesis study is to develop a cost-effective and environmentally friendly photocatalytic method in which we can achieve high efficiency.
In this study, dye removal is aimed with photocatalyst technique from aqueous solutions containing dyestuff. Methylene blue dye was chosen as a model dye. Methylene blue dye is a basic and cationic dye. The chemical formula C6H18ClN3S. It's molar mass is 319,85 g/mol, so, methylene blue dye is a large and polar molecule with high water solubility that can hold on charged negative surfaces.
Cerium oxide nanoparticles were chosen for photocatalyst. A method has been developed and conditions have been determined to calculate the percentage dye removal. Among the semiconductor metal oxides, the reason cerium oxide compound stands out is that its usage area is very wide. These usage areas are; it can be said as a catalyst, as a material with a high refractive index, as an electrolyte material for fuel cells. The most common usege of cerium oxide nanoparticles is as a photocatalyst. If air or oxygen is present in the experimental environment under UV radiation, semiconductor metal oxides are capable of removing organic pollutants. The metal oxide is activated by light (hυ) and forms pairs of electrons with a strong reducing / oxidizing agent.
Photodegredation process is examined in dark medium. Experiments will be done in UV irradiation source. First of all, the UV irradiation device must be defined. It is a closed box with a UV lamp. Inside this box, there are three UV lamps capable of irradiating at different wavelengths. The lamp of the device is closed by burning the lamp that can emit radiation at the desired wavelength. This is how it is possible to have it irradiate for the desired time.
The aim of this work is to develop a brand new technique for photodegradation of methylene blue dye by using cerium oxide nanoparticles. The effect of pH, dye concentration and photocatalyst concentration were investigated and appropriate values ​​were determined for each parameter. Method optimization steps were performed using commercial cerium oxide nanoparticles. 
In this thesis, methylene blue, a member of a thiazine dye group, is used as dyestuff. The metal oxide nanoparticle used as photocatalyst is the cerium (IV) oxide nanoparticle. Photocatalytic cerium oxide nanoparticle is added to the aqueous solutions containing methylene blue. 
The basic principle of the method is that the disintegration of this obtained solution occurs due to the UV light source. With photocatalytic degradation, chromophore groups in the structure of the dye will undergo biological breakdown and color change will occur. Degradation efficiency control was carried out with UV-Vis spectrophotometer at the characteristic wavelength of methylene blue. Then, the photocatalytic degradation yield was calculated and analyzed as a percentage using appropriate formulas.
pH optimization studies were carried out first. pH values ​​were chosed as 2, 4, 6,8,11,12 for this study. Six 10 mL aqueous solutions containing 5 ppm of methylene blue were prepared for each pH value first. The desired pH values ​​were adjusted using sodium hydroxide and hydrochloric acid solutions. The absorbance value of the solution set at the desired pH value is measured at 664 nm using the UV-Vis spectrophotometer and this value is recorded as A0.
15 mg commercial cerium oxide nanoparticle is added. In order to mix well, it is mixed with an magnetic stirrer for one hour and then in an ultrasonic bath for ten minutes. When the mixing process was over, it was exposed to radiation in the UV device for 20, 40, 60, 80, 100, and 120 minutes. The solutions from the device were centrifuged and the absorbance value of the clear part of the decanted was measured. This value is also recorded as At. Among these pH values, the highest yield was determined at pH 12.
The next condition will be determined is the dye concentration. This time, the same study was done for 2,5, 5 and 7,5 ppm solutions with pH of 12 as determined before. Six methylene blue solutions of 10 mL were prepared at the desired concentration and their pH was adjusted to 12. Initial absorbance values, before adding photocatalysts, are noted as A0. 15 mg commercial cerium oxide was added to it and mixing processes were performed in the same way as before. Thoroughly mixed solutions were put into the UV irradiation source for the specified times. After the irradiation process, the solutions pass through the centrifuge and decante stages and the absorbance values are measured and recorded as At. In the appropriate formula, the values are replaced and % degredation values are calculated. The maximum value was found for 5 ppm MM solution; so, the methylene blue concentration has also been optimized.
The other two conditions are determined. pH was found as 12 and dye concentration was found as 5 ppm in the experiments . And the last condition to be determined is the photocatalyst concentration. Six 10 mL aqueous methylene blue solutions of 5 ppm with a pH of 12 were prepared. As in previous experiments, the initial absorbance value was measured and recorded as A0. This time, 10, 15 and 20 mg of different amounts of commercial cerium oxide nanoparticles were added to the prepared solutions and the same mixing processes were applied. The mixed solutions are left in the UV irradiation source for the specified time (20-120 min). The resulting solutions are rotated for 5 minutes at 7000 rpm and removed from the excess nanoparticles by decanting. The absorbance values of the resulting solutions are measured. After making the necessary calculations, all conditions are optimized.
Thus, all parameters were determined for this experiment. pH, dye concentration, and metal oxide nanoparticle concentration are optimized. In accordance with the determined conditions, 81,6% efficiency was provided. A brand new method has been developed for the removal of dyes from water with conditions determined as pH value 12, methylene blue concentration 5 ppm and cerium (IV) oxide concentration 1,5 g/L.
In line with the determined conditions and the new method developed, the same study was applied for cerium oxide nanoparticles synthesized by chestnut honey by our research group. As a result of this study, dye removal was achieved with a yield of 78,9%. The result with cerium oxide nanoparticles obtained from chesnut honey via a green process was found very close to that obtained with commercial nanoparticles. Thus, the result is promising for the usage areas of nanoparticles obtained by green processes.