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Home > Synthesis, Characterization and Properties of Transition Metal Oxide and Hydroxide Nanomaterials

Synthesis, Characterization and Properties of Transition Metal Oxide and Hydroxide Nanomaterials

Thesis Info

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Author

Khan, Yaqqob

Program

PhD

Institute

Pakistan Institute of Engineering and Applied Sciences

City

Islamabad

Province

Pakistan

Country

Pakistan

Thesis Completing Year

2012

Thesis Completion Status

Completed

Subject

Applied Sciences

Language

English

Link

http://prr.hec.gov.pk/jspui/handle/123456789/1718

Added

2021-02-17 19:49:13

Modified

2024-03-24 20:25:49

ARI ID

1676727519202

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Material synthesis is a constantly evolving area of research and thus recognizing the limitations of current routes for the synthesis of a range of transition metal oxides is important in devising newer strategies for their growth. Transition metal oxides, as a group of advanced functional materials, exhibit several unique and interesting properties as a result of their small dimensions. Morphology of the products, their surface area, lattice defect structure and nature of the surface directly affect the practical capacity of oxide nanomaterials in different applications. The present work intends to develop common strategies, applicable to the synthesis of more than one binary transition metal oxide or its hydroxide, in solutions using hydrothermal and low temperature aqueous chemical growth routes. This includes surface modification of nanoparticles with a common modifier to tailor the surface properties, achieve control over the phase and morphology of nanostructures by varying a single experimental parameter, or nucleating them on substrates from a common solution under similar conditions. Five different oxide systems that include ZnO, MnO 2 , NiO and Ni(OH) 2 , Fe 2 O 3 , and CuO were at the focus of research. Two novel approaches were used to produce different ZnO nanostructures. First, surface modified, fluorescent ZnO nanoparticles with sizes in the range of 11-15 nm were prepared at 80 o C in 2 hours time. The modified nanoparticles emit strongly in the green region of the spectrum; a property that proved useful in imaging biological tissues. Second, a seedless aqueous chemical growth route was used to grow first, dense single crystalline ZnO nanorod arrays on 3D nickel foam substrates. Growth conditions, both for nanoparticles and nanorod arrays, were optimized by varying the concentration of starting materials, growth time, and synthesis temperature. Next, crystalline α/β-Ni(OH) 2 nanosheets, nanobelts and nanorods were prepared by hydrothermal treatment of amorphous precipitates obtained at different pH values. The morphology and crystal structure of the products was controlled simply by adjusting the pH value at precipitation. Thermal annealing of the hydroxides yielded cubic phase NiO with morphologies similar to their hydroxide precursors. Also, a simple method is presented to grow honeycomb, β-Ni(OH) 2 thick films on 3D nickel foam substrates at 80 o C. The porous honeycomb network with regular pores is built from seamlessly connected nanowalls, xapproximately 10-20 nm thick. Again, air annealing of the as-prepared films resulted in honeycomb NiO films. The procedure used to grow ZnO and Ni(OH) 2 films on the 3D nickel foam substrate was successfully employed to grow thick CuO films. A thick coating of 3-4 μm, consisting of interlaced CuO nanosheets, covered well the entire foam substrate. The sheets were rough at the edges with a mean thickness in the range of 20-30 nm. Due to the faster transformation kinetics of [Cu(OH) 4 ] 2- to CuO in aqueous solutions, all the precursor material tend to nucleate heterogeneously over a short period, extending the growth time had therefore little effect on the thickness of the films formed. For the synthesis of MnO 2 , a simple hydrothermal route was use to grow urchin like γ- MnO 2 nanostructures by a direct reaction between MnSO 4 and KClO 3 under mild conditions. The urchin-like spheres were composed of nanowires with diameters in the range 40-70 nm. The urchins were subsequently transformed to α-MnO 2 nanowires on prolonging the hydrothermal dwell time. A possible rolling-broken-growth mechanism was suggested for the self-assembly of MnO 2 nanowires into urchins and, Ostwald ripening was responsible for their subsequent phase transformation. The urchins when tested by cyclic voltammetry for their charge storage ability exhibit excellent rate capability with a specific capacitance of 225 F g -1 at a scan rate of 5 mVs -1 . Surface modified α-Fe 2 O 3 nanoparticles capped by Tween-80 were prepared by the hydrothermal treatment of Fe(NO 3 ) 2 .9H 2 O at 200 o C. The spherical nanoparticles possessed good crystallinity with an average crystallite size of 21 nm. The presence of Tween-80 on the surface of α-Fe 2 O 3 was confirmed by FTIR and Mossbauer analysis. The surfactant was effective in controlling the particle shape and restricted the particle growth to a narrow range around 40-60 nm as observed by scanning electron microscopy. The α-Fe 2 O 3 nanoparticles obtained without Tween-80 were irregular in shape with a wide size distribution in the range of 150-300 nm.
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جو اُجلا تن نہیں تو کیا ، میں اُجلا من تو رکھتا ہوں

جو اُجلا تن نہیں تو کیا میں اُجلا من تو رکھتا ہوں
میں تشنہ لب ہوں آنکھوں میں مگر ساون تو رکھتا ہوں

اگرچہ تیرگی ہی تیرگی ہے چار سُو میرے
میں ایسی تیرگی میں بھی دلِ روشن تو رکھتا ہوں

مرے دامن میں رنج و غم کی ہے اشکوں کی دولت ہے
مجھے مت جانیے مفلس کہ ایسا دھن تو رکھتا ہوں

میں بستا شہر میںہوں پھر بھی صحرا سے مجھے نسبت
نہیں میں قیس تو کیا ہے میں پاگل پن تو رکھتا ہوں

میں اُن کو دل میں رکھتا ہوں جو تائبؔ دور رہتے ہیں
اگرچہ بے ہنر ہوں پھر بھی اتنا فن تو رکھتا ہوں

عورتوں کے حقوق اسلامی تعلیمات کی روشنی میں

Before the advent of Islam, women were living in worst conditions during the Era of Ignorance. Daughters were buried alive. Women were openly sold in the market. A woman was just a source of enjoyment for males and nothing else. She had no basic rights. Even she had no share in inheritance. In human history, it is Islam that for the first time gave due respect to woman by providing her basic rights and proper status. Islam believes in equality of men and women – ‘Equality’ does not mean ‘to become identical’. Women’s rights in Islam pertain to Spiritual, Economic, Educational and Legal Rights. A woman can adopt any profession, she wants. Thus, she has got full freedom to live a happy and peaceful life. Unfortunately, there are many people who believe that because Islam gives men the right of having authority over their wives, therefore, men are superior to women and that men have priority over women in all matters. The fact is that according to Islamic teachings, men are not superior to women; and so women are not superior to men. There is no gender discrimination in Islam. Allah Almighty states very clearly in the Holy Quran that superior in His eyes are only those who have more taqwa (fear of Almighty Allah).

The Role of the Ribosome Binding Site Sequence and Spacer Length Between Binding Site and Initiation Codon on Cry2 Expression in Bacillus Host

The bacterium Bacillus thuringiensis (Bt) produces Cry toxins that possess toxic properties and can be used as biopesticides. Cry2Aa and Cry2Ac are among unusual subset of crystalline proteins possessing broad insect species specificity by exhibiting high specific activity against larvae from two insect orders, Lepidoptera and Diptera of agricultural and public health significance. The cry2Ac11 gene is located at third position (orf3) in operon comprising of three genes. It needs accessory proteins for crystal formation and high yield. Translation initiation is key rate-limiting step. It is well-known that stable structure at a ribosome binding site (RBS) impedes initiation. Modification in RBS-spacer region tunes translation initiation rates. Genetic manipulation of cry2Ac11 gene without helper protein was carried out in this study by optimizing ribosomal binding site and spacer region (RBS-ATG) in translation initiation region (TIR). The five different types of mutations were introduced in TIR to unveil inhibitory and excitatory effects on translation. These mutants are: 1), operSalI/RBSD and mut/RBSD in which downstream RBS (GGAGG) 6 bp downstream to native RBS was introduced in TIR of cry2Ac11 operon and gene; 2), mut/RBSF in which four nucleotides (ATGGG) were incorporated after RBS-ATG spacer region; 3), mut/RBSSin which overlapping start and two stop codons were introduced after RBS-ATG spacer region; 4), mut/RBSSP in which RBS-ATG spacerregion waslengthened to 23 nucleotides; 5), mut/RBS2 in which consecutive two ATGs were incorporated in TIR. Secondary structures of mutants, estimated by CLC Main Workbench, revealed that mut/RBS2 RNA exhibits most stable structure in RBS-AUG region. RBS Calculator predicts high translation rate in mut/RBSD and mut/RBS2. Mutants were expressed in B. thuringiensis 4Q7 acrystalliferous strain. The transcriptomics-proteomics profiles of all cry2Ac11 constructs provide a unique opportunity to investigate how faithfully the transcriptional profile is manifested at the protein level. Therefore, in this study correlation between mRNA abundance and protein expression profiles in all Cry2Ac11 recombinant strains were also investigated. The highest transcript profile of B. thuringiensis 4Q7-mut/RBS2, (a mutant in which consecutive multiple AUG were introduced), was obtained by Real time PCR. Furthermore, SDS-PAGE profile of total cellular proteins indicated that overexpression of Cry2Ac11 (65kDa) was obtained in 4Q7-mut/RBS2. It was concluded that overexpression of Cry2Ac11 toxin without helper protein in mut/RBS2 mRNA was most likely due to presence of consecutive start codons (AUGs) in TIR. Presence of RBS in the single stranded part of moderately stable hairpin loop (ΔG = 8.7 kcal/mol) in mut/RBS2 facilitates the interaction of RBS to the complementary 16S rRNA sequences of 30S ribosomal subunit. In proposed model, multiple factors are thought to contribute in translation efficiency of mut/RBS2 (cry2Ac11 mutants without helper protein) which includes stabilizer sequence at 5′ and 3′ ends, the availability of the RBS for binding to the anti-SD of 16S rRNA of 30S ribosomal unit and optimal context of RBS-AUG region provided by multiple AUGs in TIR.