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Title:	Nanostruktur Ag-ZnO sebagai fotomangkin cekap dalam degradasi metil jingga
Authors:	Tan Sin Tee (P63012)
Supervisor:	Muhammad Yahaya, Prof. Emeritus. Dato' Dr.
Keywords:	Nanostruktur Ag-ZnO Fotodegradasi Photodegradation
Issue Date:	15-Sep-2014
Description:	Fotodegradasi heterogen terhadap bahan cemar organik merupakan satu cara alternatif bagi mengatasi penghasilan bahan pencemar sekunder. Saiz, bentuk dan sifat kehabluran fotomangkin memainkan peranan yang penting dalam penentuan keaktifannya. Kestabilan sifat optik dan ketersediaan bahan ZnO membolehkan ia digunakan sebagai fotomangkin yang cekap. Tesis ini melaporkan kesan jenis nanobenih dan kepekatan pendopan argentum (Ag) terhadap pertumbuhan nanostruktur ZnO melalui proses hidrolisis mikrogelombang berperantara benih dan aplikasi dalam proses penurunan bahan pencemar metil jingga (MO). Pertama, nanorod ZnO ditumbuhkan di atas permukaan nanobenih ZnO dengan mengubahsuaikan parameter pertumbuhan iaitu kepekatan, kuasa mikrogelombang dan masa tindak balas untuk mendapatkan morfologi yang berbeza. Morfologi seperti bentuk dan saiz nanorod ZnO didapati berubah secara mendadak dengan peningkatan kepekatan larutan penumbuhan. Selain itu, ketumpatan nanorod ZnO juga dibuktikan meningkat dengan peningkatan kuasa mikrogelombang dan masa tindak balas. Kedua, pengubahsuaian morfologi nanorod ZnO dijalankan di atas substrat nanobenih Ag. Kesan kuasa pancaran mikrogelombang tunggal (187 W hingga 1100 W) dan berperingkat (187 W dan 994 W) turut dikaji. Dengan menggunakan pendekatan aruhan mikrogelombang yang berkuasa berperingkat, rantaian nanorod ZnO yang bersatah (101) berjaya ditumbuhkan di atas permukaan nanobenih Ag. Fenomena ini adalah bercanggah dengan nanorod ZnO yang bersatah (002) yang bertumbuh di atas nanobenih ZnO. Kepadanan kekisi antara satah atom ZnO dan Ag mendorong kepada kajian kesan pendopan Ag ke dalam larutan penumbuhan. Nanostruktur Ag-ZnO dengan morfologi yang terkawal (ie: nanorod bercabang, nanobunga, nanotiub dan nanocincin) telah berjaya ditumbuhkan di atas nanobenih Ag dengan perubahan kepekatan AgNO3 daripada 2.5 mM hingga 15.0 mM. Sifat fotomangkin nanostruktur Ag-ZnO dikaji melalui proses penurunan MO. Kecekapan fotomangkin dapat ditentukan melalui perubahan keamatan puncak penyerapan MO pada panjang gelombang 463 nm dalam keadaan pendedahan sinaran UV. Kadar penurunan MO didapati meningkat dengan peningkatan kepekatan AgNO3 dari 2.5 mM kepada 10.0 mM jika dibanding dengan nanorod ZnO tulen tetapi menurun apabila kepekatan AgNO3 meningkat kepada 15.0 mM. Secara keseluruhannya, nanotiub Ag-ZnO menunjukkan kecekapan fotomangkin yang paling tinggi iaitu 72 % dalam masa 60 minit, selaras dengan pemalar kinetik iaitu 0.02029 minit-1. Fenomena ini disebabkan Ag-ZnO nanotiub yang disintesis mempunyai ketumpatan nanozarah Ag yang optimum dan bertindak sebagai tapak perangkap elektron yang mengurangkan penggabungan semula elektron-lohong terfotoaruh. Selain itu, nanotiub turut menunjukkan kecacatan intrinsik dan luas permukaan terdedah yang tinggi lalu meningkatkan penjerapan bahan cemar organik pada permukaan nanostruktur. Kesimpulannya, morfologi nanostruktur ZnO dan keaktifan fotomangkin dapat dikawal dengan memperkenalkan pelopor Ag ke dalam larutan penumbuhan.,Heterogeneous photodegradation of organic pollutant is an effective way to prevent formation of secondary pollutant. Size, shape and crystallinity of photocatalyst play an important role to determine its activity. Photostability and availability of ZnO makes it possible to be used as effective photocatalyst.This thesis reports the study on the effects of nanoseed and the incorporation of silver (Ag) with various concentrations on the growth of ZnO nanostructures using seed-mediated microwave hydrolysis process and their photocatalytic performance towards methyl orange (MO) degradation. Firstly, ZnO nanorods have been grown on the ZnO-seeded substrate with variation of growth parameter such as concentration, microwave power and time reaction for obtaining different morphologies. Morphology likes shape and size of ZnO nanorod changed drastically with the increment of growth solution concentration. The density of ZnO nanorod was proven to increase with the increasing of reaction time and microwave power. Secondly, morphology modification of ZnO nanorod was carried out on Ag-seeded substrate. The effect of single (187 W-1100 W) and two-step (187 W and 994 W) microwave power irradiation was also studied. In-plane linkage ZnO nanorod that dominated with (101) facet have been successfully grown on Ag nanoseeds under two-step microwave power irradiation. This phenomenon is in contradiction with ZnO nanorod grown from ZnO-seeded substrate, which only composed of (002) basal plane. In view of the significant lattice mismatch between the atomic layer of ZnO and Ag, the addition of Ag precursor into the growth solution was investigated. Ag-ZnO nanostructures with controllable morphology (ie: nanobranch, nanoflower, nanotube and nanorings) have been grown on Ag-seeded substrate with various AgNO3 concentrations ranging from 2.5 mM to 15.0 mM. The photocatalytic properties of Ag-ZnO nanostructures were examined in the photodegradation of MO. The photocatalytic respond was studied by observing the changes in MO absorption peak intensity at 463 nm under UV irradiation. The degradation rate of MO was found to increase significantly for the sampels prepared with the addition of 2.5 mM to 10.0 mM AgNO3 as compared to that of pure Nanorod ZnOs but it was found to decrease when AgNO3 content was further increased to 15.0 mM. In overall, it was found that Ag-ZnO quasi-nanotube prepared with 10.0 mM AgNO3 showed the highest photodegradation efficiency of 72 % within 60 minute reaction time from this system, which is 103 order higher than the reported results. This is equivalent to the kinectic constant of 0.02029 minute-1. This phenomenon was due to the synthesized Ag-ZnO nanotubes have been loaded with optimum Ag nanoparticles which act as electron trap sites that reduce recombination of photogenerated electron-hole. In addition, the nanotubes also showed high intrinsic defects and exposed surface area which may increase adsorption of organic molecule on the nanostructures surface. In conclusion, the morphology of the ZnO nanostructures and their photocatalytic activity can be controlled by introducing Ag precursor into growth solution.,PhD
Pages:	152
Call Number:	QD708.2.T344 2014 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Science and Technology / Fakulti Sains dan Teknologi

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