Browsing by Author "Moodley, Vashen."

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Production of nanocellulose composites and catalytic and microbial applications.
(2018) Moodley, Vashen.; Van Zyl, Werner Ewald.
This study describes the preparation, isolation, characterization and application of polysaccharide based nanocrystalline cellulose (NCC) from two source materials (filter paper and bleached pulp). The isolated NCCs were utilized as a composite/support material. Hydroxyapatite (HAp), titanium(IV) oxide (anatase phase, TiO2) and biologically synthesized silver nanoparticles were chosen as the preferred candidates for the incorporation of NCC into their respective matrices, which allowed for the preparation of three new materials. These newly prepared composites were applied in catalytic and anti-microbial studies. NCC formed the basis of this investigation and was prepared via a common acid hydrolysis treatment, using sulfuric acid as the preferred acid hydrolytic medium. The isolated NCCs were obtained in reasonable yields and were characterized using the following techniques: ATR-FTIR, XRD, TEM, HRTEM, FEGSEM equipped with EDX detector, TGA/DTA, NTA (zeta potential) and BET. The rod-shaped particles revealed a high crystallinity, small crystallite sizes and good thermal stabilities. These results led to use the prepared NCC’s as a composite material in the pursuit to prepare a new class of materials with a potential array of applications. The preparation of HAp and subsequently the NCC/HAp (in varied wt%) composite allowed for the use of this newly synthesized material as a versatile catalyst. The catalyst was well characterized and used in the preparation of the two-component one-pot synthesis of triazolidine-3-one derivatives. Preliminary reaction optimization established that the 40 w/w% NCC/HAp composite catalyst returned the best results. The eleven new triazolidine-3-one derivatives (4a - 4k) were synthesized in good yields and maintained good atom economy. The catalyst proved to be an effective tool in this protocol with the supplementary advantage of being recyclable. This approach to organic multicomponent reactions (MCRs) proved to be a cost-effective strategy and allowed for an easy work up with environment-friendly reaction conditions. Compared to non-catalytic protocols this approach required shorter reaction times. With the prospect of employing the optical properties of the prepared NCC, TiO2 was then considered for the use in the second newly prepared composite material as a potential photo-catalyst. The NCC/TiO2 material was synthesized in varying wt% and was characterized via a number of optical, spectroscopic and microscopic techniques to establish if it possessed the potential to be used as a photo-catalyst. Proceeding this evaluation, the NCC/TiO2 material was used in the solar-driven photo-degradation mineralization of o-chloranil (2,3,5,6-tetrachloro-2,5-cyclohexadiene-1,4-dione), a commonly used pesticide. The successful decomposition of o-chloranil led to the identifiable products to 2,3-dichloro-4,5-dioxohex-2-enedoic acid (DCA), 2,3-dioxosuccinic acid (DSA) and oxalic acid (OA). This proved that the 20 w/w% NCC/TiO2 composite could be employed as a successful photo-catalyst, and in particular that NCC could be used as a successful composite material together with TiO2. The rate of degradation was influenced by various parameters such as substrate concentration and photo-catalyst loading. The intermediate product (DCA) formed during the decomposition process was assumed to slow down the progression of the reaction and provided a useful insight into the degradation pathway of the contaminant. The final study demonstrated the synthesis of silver nanoparticles (AgNPs) via a biological (phyto-mediated) route using Lippia javanica plant extract (LPE). The preparation of the colloidal AgNPs involved a variation in the LPE (100 – 400 μL) and AgNO3 (1 – 10 mM) concentration to determine the ideal morphology of AgNPs formed. This biosynthetic approach proved successful in the formation of AgNPs in colloidal form, with superior advantages over the chemical formation. These AgNPs were used in several applications as demonstrated with the inclusion of NCC as a support. Samples were characterized via optical, spectroscopic and microscopic analyses, with the ideal colloidal solution C9 (400 μL LPE, 10 mM AgNO3) established as providing the greatest number of AgNPs with the lowest size. This colloid was chosen for the further incorporation of NCC. NCC (filter paper source) was then incorporated into the quasi-spherical shaped nanoparticle matrix and further characterized, analysed and applied as a catalyst to the synthesis of benzylidene-bis-(4-hydroxycoumarin) derivatives and as a potential bactericidal agent. All colloidal samples were biologically tested against 5 bacterial strains and demonstrated good activity, however, samples with the highest concentration of AgNPs were chosen for further Minimal Bactericidal Concentration (MBC) testing. The results showed that all samples were superior in relation to their anti-biotic counterparts used as standards. Sample C9e (1000 mg NCC, 4 mL of LPE in 10 mL of 10 mM AgNO3 and made up to 50 mL), proved to be an efficient catalyst for a three-component reaction. This led to the catalytic preparation of nine benzylidene-bis-(4-hydroxycoumarin) derivatives (6a – 6i).
Synthesis and characterization of new gold and silver complexes based on P/N and P/S ligands : P/S ligand-stabilized gold nanoparticles.
(2013) Moodley, Vashen.; Van Zyl, Werner Ewald.
This dissertation comprises three distinct studies, two of which concerns molecular inorganic chemistry, and one concerns inorganic materials science. Firstly, the synthesis and characterization of new dithiophosphonate ligands of the type (NH4)[S2P(4-C6H4OMe)(OCH2C6H5)] and (NH4)[S2P(4-C6H4OMe)(OCH2CH2CH2CH3)] followed by their reaction with [AuCl(tht)] (tht = tetrahydrothiophene) and [Ag(NO3)] (molar ratio 1:1). This yielded two new dinuclear gold(I) complexes, [Au{S2P(4-C6H4OMe)(OCH2C6H5})]2, 1 and [Au{S2P(4-C6H4OMe)(OCH2CH2CH2CH3})]2, 2, and one new silver complex [Ag{S2P(4-C6H4OMe)(OCH2CH2CH2CH3})]2, 3. Complex 1 and 2 displayed intramolecular Au···Au interactions of 3.0923(5) and 3.0613(7) Å, respectively, and revealed no intermolecular Au···Au interactions. Complex 1 additionally showed intermolecular hydrogen bonding interactions between the sulfur atom and an aromatic hydrogen atom with a contact distance of ca. 2.895 Å. The reaction of 1 with bis(diphenylphosphino)methane (dppm) (molar ratio 1:1) yielded a metallacyclic mixed-ligand complex tentatively assigned as [Au2(dppm)2{S2P(4-C6H4OMe)(OCH2C6H5)}2] 4, (based on partial X-ray refinement) which is nevertheless a complex type derived from bis-phosphine reactions that has never been observed. Complex 3 followed the same predictable 1H, 13C, 31P and IR patterns as with 1 and 2. Secondly, the synthesis and characterization of a phosphinamide ligand, [(C6H5)2PO(NH-t-C4H9)], 5, has been described. The ligand showed solid state structures with a remarkable number of structural features which include hydrogen bond interactions as well as unique packing properties. Compound 5 contains two molecules in a single asymmetric unit linked via hydrogen bonds with a contact measuring ca. 2.03 Å. The dimeric asymmetric units in turn are held together by a network of weak hydrogen interactions measuring ca. 2.28 Å. The phosphinamide ligand, 5, was further reacted with silver triflate which led to the formation of a novel dinuclear silver(I) complex [Ag(CF3SO3)(OPPh2N(H)CMe3)2}{Ag(OPPh2N(H)CMe3)2}]SO3CF3, 6, that adopts two unique geometries around the silver nuclei, namely a trigonal planar and linear geometry. The two silver atoms show a strong intramolecular argentophillic interaction of 2.8979(3) Å. From the above complexes, 1, 2, 5 and 6 were fully characterized by single crystal X-ray crystallography, 1H, 13C and 31P solution NMR, elemental analysis, and IR. Complex 3 and 4 were characterized using 1H, 13C and 31P solution NMR, elemental analysis, and IR. The final study comprised the synthesis and characterization of gold nanoparticle/silica or AuNP/SiO2-composites. The nanocomposites were prepared by the in-situ thermal reduction of tetrachloroauric acid, H[AuCl4].3H2O. Two variable parameters were considered namely temperature (50 °C, 100 °C, 200 °C and 300 °C) and concentration of the gold acid (0.01 M, 0.5 M and 1.25 M). The gold solution was pipetted onto the silica and allowed to soak for 2 hours and was then reduced in a furnace for one hour. The AuNP/SiO2 composites were characterized by four methods, namely Brunauer Emmet and Teller (BET) surface area analysis, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). SEM revealed the gold particles was deposited on the surface of the silica. TEM results showed the AuNPs were formed with the smallest diameter around 3.6 nm and the largest 54 nm. Not surprisingly, the distribution of AuNPs increased with increase in concentration of gold solution. BET surface area results showed that surface area decreases with increase in concentration of gold solution. In addition to the synthesis of the composites, it was also used in the preparation of self-assembled monolayers (SAMs). SEM results showed post work-up images and analyses of P and S elements derived from a dithiophosphonate-cholesterol compound on the gold surface.