Sulu çözeltilerden metilen mavisi giderimi için TE/ZNO/C2N3 fotokatalizörünün sentezi, karakterizasyonu ve optimizasyonu
Synthesis, characterization, and optimization of TE/ZNO/c2N3 photocatalyst for methylene blue removal
- Tez No: 965497
- Danışmanlar: DOÇ. DR. FÜSUN BOYSAN, PROF. DR. ABDİL ÖZDEMİR
- Tez Türü: Doktora
- Konular: Çevre Mühendisliği, Environmental Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2025
- Dil: Türkçe
- Üniversite: Sakarya Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Çevre Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 79
Özet
Günümüzde enerji ve çevre sorunları önemli bir tehdit oluşturmaktadır. Özellikle atık su üretimi ve arıtımı, artan nüfus ve sanayileşme nedeniyle çevre sağlığını doğrudan etkilemektedir. Bu durum, insan sağlığı, ekosistem dengesi ve ekonomik sürdürülebilirlik açısından ciddi riskler yaratmaktadır. Aynı zamanda fosil yakıt rezervlerinin azalması ve küresel ısınmanın artması, yenilenebilir enerji kaynaklarının geliştirilmesini zorunlu kılmıştır. Güneş enerjisi; temiz, bol ve sürdürülebilir bir kaynak olarak fotokatalitik uygulamalarda umut vadetmektedir. Güneş ışığı ile çalışan fotokataliz sistemleri, çevre dostu yapıları sayesinde hem enerji hem çevre sorunlarına çözüm sunma potansiyeline sahiptir. Bu çalışmada, tekstil endüstrisinin neden olduğu boyar madde kirliliğinin giderimi için görünür ışık altında etkin bir fotokatalitik sistem geliştirilmesi amaçlanmıştır. Bu kapsamda, C₂N₃ temelli ZnO ve tellür (Te) katkılı heteroyapılar sentezlenerek, metilen mavisi (MM) giderimi üzerindeki performansları incelenmiştir. C₂N₃, yüksek yüzey alanı, uygun bant yapısı ve karbon-nitrür temelli yapısıyla, ZnO gibi geleneksel yarıiletkenlere göre daha etkili ışık absorpsiyonu ve yük taşıyıcı ayrımı sağlayarak fotokatalitik etkinliği artıran bir malzeme olarak öne çıkmaktadır. Kompozitlerin sentezinde, C₂N₃ oranı %2, %4, %6 ve %8 olarak değiştirilmiş ve MM giderim verimi sırasıyla %63,3, %71,27, %97,62 ve %85,5 olarak ölçülmüştür. En yüksek verim, %6 C₂N₃ içeren kompozit ile elde edilmiştir. Ardından Te oranı %2,5, %5, %7,5 ve %10 olacak şekilde artırılmış ve MM giderim verimi sırasıyla %84,4, %97,62, %91,27 ve %82,6 olarak gözlemlenmiştir. Böylece %5 Te içeren kompozit en yüksek fotokatalitik aktiviteyi göstermiştir. Karakterizasyonlar kapsamında; sentezlenen fotokatalizörlerin yüzey morfolojisi FESEM ile, elementel bileşimi EDS ve haritalama ile, kristal fazları XRD ile, yüzey fonksiyonel grupları FT-IR ile ve optik özellikleri DRS analizleriyle değerlendirilmiştir. Elde edilen sonuçlar, ZnO'nun çubuksu yapısının C₂N₃ matrisi içinde homojen dağıldığını ve tellürün başarıyla yapıya entegre olduğunu göstermektedir. DRS analizleri, görünür bölgeye kayma ile birlikte bant aralığında iyileşme olduğunu ortya koymuştur. Sonuç olarak, bu çalışmada geliştirilen Te/ZnO/C₂N₃ kompoziti; güçlü adsorpsiyon kabiliyeti, düşük yük transfer direnci, yüksek taşıyıcı ayrışma etkinliği ve Z yapılı heteroyapı karakteri sayesinde etkili bir fotokatalizör olduğunu göstermiştir. Yenilenebilir enerji kaynaklarından biri olan güneş ışığını kullanarak toksik boyar maddelerin giderimini sağlaması, bu sistemi çevresel sürdürülebilirlik açısından da değerli kılmaktadır. Bu bağlamda, çalışma çevre mühendisliği alanında fotokatalitik arıtım uygulamalarının geliştirilmesine katkı sunmaktadır.
Özet (Çeviri)
Today, energy and environmental issues are major concerns. Problems related to wastewater generation and treatment have become a serious global environmental threat due to the increasing population and urbanization. The negative impacts of wastewater discharges extend to human health, the environment, food quality and safety, as well as socio-economic domains. At the same time, the development of renewable energy sources has become one of the most critical goals of our time in order to combat challenges such as global warming and the depletion of energy resources. Especially, the decline of fossil fuel reserves and the rise in environmental pollution necessitate the development of sustainable and eco-friendly technologies. In a world where nearly 80% of global energy consumption relies on fossil fuels, research on alternative energy solutions that could replace these resources has gained momentum. Renewable energy sources such as solar, hydroelectric, geothermal, biomass, and wind are being proposed and extensively investigated. Among these, solar energy stands out with its abundance, low cost, sustainability, and environmentally friendly nature. The potential for solar energy to replace fossil fuels in the near future is considered to be quite high. Due to its renewable and green nature, sunlight is regarded as one of the most promising energy sources to replace conventional fossil fuels. Solar radiation can be converted into electrical and chemical energy through photon-activated applications. Solar-powered systems are attracting increasing attention today compared to the past, thanks to their ability to operate independently and their lack of harmful emissions or pollutants. Technologies such as photovoltaics, photocatalysis, and photoelectrocatalysis represent various utilization paths of solar energy. Among these, photocatalysis stands out with its efficient, environmentally friendly, and sustainable nature. In recent years, environmental pollution caused by industrial wastewater has emerged as a critical global issue, particularly with the increased discharge of dye-contaminated effluents from textile industries. These pollutants are not only visually displeasing but also toxic, non-biodegradable, and harmful to aquatic ecosystems and human health. In response to these challenges, photocatalytic degradation methods based on semiconductors have gained widespread attention for their potential to effectively remove organic contaminants under light irradiation. This study focuses on the development, characterization, and optimization of novel ternary Te/ZnO/C₂N₃ photocatalysts for the efficient degradation of methylene blue (MB), a model pollutant, in aqueous solutions. The synthesized photocatalysts were prepared via a hydrothermal approach, where tellurium and carbon nitride-based C₂N₃ were incorporated into the ZnO matrix. C₂N₃ was selected due to its nitrogen-rich, conjugated polymer structure, high thermal stability, and visible light absorption capabilities. ZnO, a wide band gap (∼3.37 eV) n-type semiconductor with strong redox potential, was chosen as the base material due to its high photostability and chemical stability. However, due to its limited response to visible light and high electron–hole recombination rate, modifications were made to enhance its photocatalytic performance. Tellurium, a p-type semiconductor, was introduced to facilitate Z-scheme heterojunction formation, aiming to improve charge separation and preserve strong redox potentials. A two-step optimization process was applied for the preparation of the Te/ZnO/C₂N₃ photocatalyst. In the first step, the Te ratio was kept constant while different ratios of C₂N₃ (2%, 4%, 6%, 8%, and 10%) were used along with ZnO. The predetermined amounts of ZnO and C₂N₃ were dispersed in 50 mL of methanol using an ultrasonic bath. Subsequently, 5% Te was added to the mixture, and the suspension was stirred on a magnetic stirrer for 30 minutes to ensure homogeneity. The resulting mixture was then heated until complete evaporation of methanol and subsequently dried. Based on characterization results, the optimum C₂N₃ ratio was determined. In the second step, the identified optimum C₂N₃ content was fixed, and photocatalysts were prepared by varying the Te ratio (2.5%, 5%, 7.5%, and 10%) along with ZnO. Similarly, ZnO and the optimum C₂N₃ amount were dispersed in 50 mL of methanol via ultrasonic treatment, followed by the addition of Te at the specified ratios. After stirring for 30 minutes using a magnetic stirrer, the methanol was evaporated by heating, resulting in the final photocatalyst powders. Photocatalytic experiments were carried out by adding 25 mg of catalyst into 25 mL of methylene blue (MB) solution with a concentration of 10 ppm. The distance between the lamp and the reaction medium was adjusted to 5 cm, and the light intensity was measured as 30,000 lux using a digital luxmeter. The corresponding MB removal efficiencies were found to be 63,3%, 71,27%, 97,62% and 85,5%, respectively. Among these, the composite containing 6% C₂N₃ exhibited the highest photocatalytic degradation performance. Similarly, the Te content was optimized at 2.5%, 5%, 7.5%, and 10%. The removal efficiencies for these compositions were determined as 84,4%, 97.62%, 91,27%, and 82,6%, respectively. The composite with 5% Te showed the highest degradation efficiency, indicating that the photocatalytic performance was highly dependent on the precise ratio of dopants and co-catalysts used in the composite structure. Although tellurium is not a direct photocatalytic phase, it acted as a conductive bridge between ZnO and C₂N₃ and supported charge transfer by maintaining the continuity of the Z-structure. The removal efficiency of 65.20% obtained in the dark showed that the system had strong adsorption capacity. During light exposure, the effective degradation of surface-adsorbed methylene blue revealed that the photocatalytic mechanism was strengthened by surface interactions. To investigate the structural, morphological, optical, and surface chemical properties of the prepared photocatalysts, comprehensive characterization techniques were employed. X-ray diffraction (XRD) was used to confirm the crystalline phases and assess the crystallite size and phase purity. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were applied to examine surface morphology and elemental distribution, while transmission electron microscopy (TEM) provided additional information on the internal structure and nanoscale interactions between the composite components. Fourier transform infrared spectroscopy (FTIR) confirmed the functional groups and bonding interactions in the composite structure. The optical properties and band gap energies were determined using diffuse reflectance UV-Vis spectroscopy (DRS). Electrochemical characterizations were also conducted to gain further insights into charge transfer dynamics. Transient photocurrent response measurements indicated significantly enhanced charge separation efficiency in the optimized composites compared to bare ZnO. Moreover, electrochemical impedance spectroscopy (EIS) results demonstrated reduced charge transfer resistance in the Te/ZnO/C₂N₃ composite, further validating the improved interfacial electron mobility and synergistic charge transport behavior due to the Z-scheme mechanism. The Mott–Schottky plots revealed the n-type and p-type semiconductor behavior of ZnO and Te, respectively, confirming the successful formation of a direct Z-scheme heterojunction with C₂N₃ as a co-catalyst. The enhancement in photocatalytic activity is attributed to the formation of a direct Z-scheme heterojunction between the ZnO and Te components. This structure not only facilitates effective separation of photo-induced electron–hole pairs but also maintains strong oxidative and reductive capabilities by directing electrons from the CB of Te to recombine with holes in the VB of ZnO. As a result, the electrons in the CB of ZnO and holes in the VB of Te retain high redox potentials, which are essential for the degradation of recalcitrant organic pollutants such as methylene blue. The presence of C₂N₃ further promotes visible light absorption and provides active sites for surface reactions, thus contributing synergistically to the degradation process. The experimental findings in this work clearly demonstrate that photocatalytic degradation performance can be effectively enhanced by the rational design and optimization of ternary nanocomposite photocatalysts. The highest MB degradation efficiency (97.7%) was achieved using the composite containing 6% C₂N₃ and 5% Te, under optimal experimental conditions. These results highlight the potential of Te/ZnO/C₂N₃ composites as promising candidates for visible-light-driven photocatalytic water treatment technologies. The facile synthesis, high activity, and good stability of these materials suggest that they could be successfully employed in practical environmental applications targeting the removal of dye pollutants from industrial wastewater. This study not only contributes to the growing field of photocatalysis but also provides an efficient strategy for the design of high-performance, sustainable, and eco-friendly photocatalytic materials.
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