Publication: Synthesis and characterization of magnetic photocatalysts for hydrogen generation
Abstract
ÖZETMANYETİK FOTOKATALİZÖRLERİN HİDROJEN ÜRETİMİ İÇİN SENTEZİVE KARAKTERİZASYONUGünümüzde, enerji ve çevre birbiriyle ilişki olan iki önemli alandır. Sanayi devrimi veenerji kaynaklarının tükenmesiyle birlikte çevre kirliliğinde de büyük bir artışyaşanmaktadır. Çevreye olumlu etkileri olan alternatif enerji kaynaklarının aranmayabaşlanmasıyla, organik kirleticilerin fotokatalitik proses ile bozunması ve yenilenebilirkaynak güneş ışığı kullanılarak fotoelektrokimyasal hidrojen üretim yöntemleri oldukçaönem kazanmaya başlamıştır. Bu çalışmada yarı iletken fotokatalizörin kullanıldığıheterojen fotokataliz reaksiyonlarına dayanmaktadır.Yaptığımız bu çalışmada, reaksiyon ortamından kolayca ayrılabilen, fotokatalitik vefotoelektrokatalitik olarak etkin fotokatalizörler malzemelerinin sentezi geniş bantaralığına sahip ve UV bölgede etkin TiO2 karakterize edilerek gerçekleştirildi.Sentezlenen fotokatalizörler reaksiyon sırasında oluşan elektron-boşluk çiftleriniarttırmak ve bu oluşan elektron-boşluk çiftlerinin yeniden birleşmesini baskılamakamacıyla çekirdek-kabuk yapısı şeklinde tasarlandı.İlk olarak, planlanan fotokatalizörler buhar-termal yöntemi ile sentezlendi. Dizayn edilenmalzemeler XRD, UV-DRS, SEM ve Raman spektroskopi analizleri ile karakterizeedildi. Bir diğer aşamada, manyetik çekirdek kabuk yapısında planlanan aynıfotokatalizörler non-termal yöntemi ile sentezlendi. Non-termal yöntemde buhar-termalyönteminden farklı olarak manyetik çekirdek ve TiO2 yapısı ayrı bir şekilde sentezlendive ultrasonikasyon su banyosu ile birleştirildi. Ayrıca, her iki yöntemde fotokatalizörlerefoto(elektrik)katalitik etkisini arttırmak amacıyla Ni2+ yüklemesi yapıldı.Fe3O4/ NiFe2O4@TiO2 örnekleri her iki yöntemle sentezlenmiş aynı tür katalizörlerinfotokatalitik aktivitesini incelemek amacıyla metilen mavisi bozunması görünür ışıkaltında test edildi. Fotokatalitik aktivitelerin test edilmesinden sonra hidrojen üretimkapasitesinin ölçülmesinde önemli bir belirleyici olan foto-akım ölçümleri yapıldı.Elde edilen sonuçlara göre buhar termal yöntemi ile hazırlanan fotokatalizörlerdenNiFe2O4@TiO2-Ni2+ fotokatalizörü diğer fotokatalizörlerin yanında en fazla fotokatalitikaktivite göstermiş ve metilen mavisi 87,7% oranında bozunmaya uğramıştır. Ayrıca, aynıxiiişekilde NiFe2O4@TiO2-Ni2+ fotoelektrokimyasal ölçümlerde en yüksek foto-akım değeri37A/ cm2. Bununla birlikte, non-termal yöntemi ile hazırlanan fotokatalizörler düşükfotokatalitik aktivite göstermiştir. Bu yöntem ile sentezlenen fotokatalizörlerFe3O4@TiO2-Ni2+ ile en yüksek bozunma oranı 59% elde edilmiştir. Ayrıca, non-termalyöntemde NiFe2O4@TiO2 en yüksek fotoelektrokatalitik aktivite göstermiş ve görünürışık altında en yüksek foto-akım değeri 132 A/ cm2 elde edilmiştir.
xABSTRACTSYNTHESIS AND CHARACTERIZATION OF MAGNETICPHOTOCATALYSTS FOR HYDROGEN GENERATIONIn today’s world, the energy and environment are more related to each other. After theindustrial revolution and the depletion of the energy sources the environment pollutionhas increased rapidly. With the investigation for the new alternative methods which havepositive effect to the environment, the degradation of the organic pollutants withphotocatalytic processes and the photoelectrochemical hydrogen production methodsusing the renewable source solar light have gained significant attention. All of this studydepends on the heterogeneous photocatalysis process which uses the semiconductorphotocatalysts.In this work, the easily separable from the reaction medium and photocatalytic andphotoelectrocatalytic active photocatalyst material synthesis were performed to improvethe efficiency in visible light spectrum using the TiO2 semiconductor which has wideband gap energy (active in UV region). Synthesized photocatalysts were designed as acore shell structure to boost the electron hole charge and suppress the recombinationreaction.Firstly, the planned materials were produced by a vapor thermal technique. The materialswere characterized by XRD, UV-DRS and Raman spectroscopy. In the further step samestructure magnetic core-shell photocatalyst were arranged via non-thermal method.Magnetic core and TiO2 were synthesized separately and had been come together withultrasonication. Moreover, for two synthesis method Ni2+ loading had been conducted toexamine the effect of the photo-(electro)-catalytic activity. Fe3O4/ NiFe2O4@TiO2samples were tested under the synthesis technique with methylene blue degradationanalysis to search how photocatalytically efficient under the visible light. After thecomparison for the photocatalytic activities, the photo-current responses importantdeterminant for the photoelectrochemical hydrogen production capacity was measured.According to the obtained results, vapor thermal method prepared the NiFe2O4@TiO2-Ni2+ had given the optimal photocatalytic activity and 87.7% degradation efficiency wasprovided under the visible light irradiation. Moreover, the maximum photo-currentdensity was obtained for NiFe2O4@TiO2-Ni2+which is 37A/ cm2. However, the nonxithermal method samples showed pure photocatalytic activity and only 59.83%degradation efficiency was obtained for the Fe3O4@TiO2-Ni2+ photocatalyst. Besides, thephoto-current response obtained for NiFe2O4@TiO2 photocatalyst was 132 A/ cm2 undervisible light illumination.
xABSTRACTSYNTHESIS AND CHARACTERIZATION OF MAGNETICPHOTOCATALYSTS FOR HYDROGEN GENERATIONIn today’s world, the energy and environment are more related to each other. After theindustrial revolution and the depletion of the energy sources the environment pollutionhas increased rapidly. With the investigation for the new alternative methods which havepositive effect to the environment, the degradation of the organic pollutants withphotocatalytic processes and the photoelectrochemical hydrogen production methodsusing the renewable source solar light have gained significant attention. All of this studydepends on the heterogeneous photocatalysis process which uses the semiconductorphotocatalysts.In this work, the easily separable from the reaction medium and photocatalytic andphotoelectrocatalytic active photocatalyst material synthesis were performed to improvethe efficiency in visible light spectrum using the TiO2 semiconductor which has wideband gap energy (active in UV region). Synthesized photocatalysts were designed as acore shell structure to boost the electron hole charge and suppress the recombinationreaction.Firstly, the planned materials were produced by a vapor thermal technique. The materialswere characterized by XRD, UV-DRS and Raman spectroscopy. In the further step samestructure magnetic core-shell photocatalyst were arranged via non-thermal method.Magnetic core and TiO2 were synthesized separately and had been come together withultrasonication. Moreover, for two synthesis method Ni2+ loading had been conducted toexamine the effect of the photo-(electro)-catalytic activity. Fe3O4/ NiFe2O4@TiO2samples were tested under the synthesis technique with methylene blue degradationanalysis to search how photocatalytically efficient under the visible light. After thecomparison for the photocatalytic activities, the photo-current responses importantdeterminant for the photoelectrochemical hydrogen production capacity was measured.According to the obtained results, vapor thermal method prepared the NiFe2O4@TiO2-Ni2+ had given the optimal photocatalytic activity and 87.7% degradation efficiency wasprovided under the visible light irradiation. Moreover, the maximum photo-currentdensity was obtained for NiFe2O4@TiO2-Ni2+which is 37A/ cm2. However, the nonxithermal method samples showed pure photocatalytic activity and only 59.83%degradation efficiency was obtained for the Fe3O4@TiO2-Ni2+ photocatalyst. Besides, thephoto-current response obtained for NiFe2O4@TiO2 photocatalyst was 132 A/ cm2 undervisible light illumination.