Flame spray synthesis of catalyst nanoparticles for photocatalytic mineralisation of organics and Fischer-Tropsch synthesis

In this thesis, a range of TiO2-based photocatalysts and cobalt-based Fischer-Tropsch(FT) catalysts were developed and synthesised via the one-step Flame Spray Pyrolysis(FSP). The work starts with the demonstration of bare TiO2 nanoparticles synthesis with controlled characteristics such as specific surface areas, crystallite sizes and anatase content. A comparative study was carried out by benchmarking with commercial Degussa P25 TiO2. The FSP TiO2 was shown to be more efficient in mineralising pollutants requiring direct charge transfer such as the saccharides, while P25 was better formineralising alcoholic and aromatic compounds. Both catalysts were equally as active inmineralising carboxylic acids. Upon identifying the optimal synthesis of bare TiO2, an in situ co-precipitation of highly dispersed Pt on TiO2 was carried out in the flame. Deposition of Pt resulted in enhanced photocatalytic performance as a result of efficient charge trappings. It is highlighted here the inter-relationship between Pt oxidation states and the TiO2photocatalysis of carboxylic acid, alcohol and aromatic compounds. Depending on the mineralisation path adopted by the model organic compounds, they were shown to have direct influence on the Pt oxidation states. These oxidation states in turn affect themineralisation rates of the organic compounds.Substitutional-doping of TiO2 with Fe(III) with tunable bandgap was also possible by FSP synthesis. The high temperature synthesis coupled with rapid quenching resulted in 5 times higher solubility limit (Fe/Ti = 0.05) than that previously reported in the literature. Under visible light irradiation, FSP-made Fe-TiO2 improved the photocatalytic mineralisation of oxalic acid by more than 6 times, with respect to P25 and FSP TiO2. Furthermore, the photocatalyst was reusable over a number of repetitions with minimal leaching or loss in activity. The last part of the work concerns the development of bare and Ru-doped Co-ZrO2 catalysts, where cobalt was finely dispersed within the zirconia matrix. Doping of Ru enhanced significantly the reducibility of cobalt, reducing even the embedded cobalt beneath the zirconia surface. It also increased the extent of CO-chemisorption and as such, enhanced the FT activity. This is the first time, catalysts of such type is synthesised andtested for FT reaction

Floc Strength Characterization Technique. An Insight into Silica Aggregation

This paper tests an approach to the estimation of relative particle bond strength based on the nondimensional floc and aggregation factors. The strength of flocs formed by aggregating nanosized silica particles with the addition of potassium chloride (KCl) or cationic surfactants, alkyltrimethylammonium bromide (mixture of CTAB, DTAB, and MTAB) was analyzed. The bonding force of the flocs formed in surfactant compared to that formed in the KCl system was estimated using the new dimensional analysis approach. This force ratio was then compared to that obtained by atomic force microscopy

Graphene oxide-based electrochemical sensor : a platform for ultrasensitive detection of heavy metal ions

Facile functionalization of graphene oxide sheets on gold surface results in complexation-enhanced electrochemical detection of heavy metal ions, shown here for Pb²⁺, Cu²⁺ and Hg²⁺, with improved detection limits by two orders of magnitude relative to the control electrode.5 page(s

Functionalized-graphene composites : fabrication and applications in sustainable energy and environment

Graphene, including pristine graphene and its analogues of graphene oxide and reduced graphene oxide, is revolutionizing the way we design high performance devices, particularly in the areas of sustainable energy and environmental technologies. From environmental remediation and sensing to energy conversions and storage, there are many successful cases of graphene applications. Instead of being a standalone working material, graphene is almost always coupled with another active material as a composite. With its high surface-to-bulk ratio, efficient heat transfer, and electron conduction, the interfacing with graphene not only helps to overcome such limitations in the bare working material but actually accentuates them. To achieve this, the strategy of surface functionalization of graphene, with either soft matters (e.g., organics, molecular linkers, proteins) or solid inorganic matters (e.g., metal nanoparticles, oxide semiconductors), holds the key to enabling the fabrication of high performance composites. The resultant architectures, in which the graphene is applied to, yield the highest achievable properties and should be unique to the specific applications. This Review provides a bottom-up account encompassing the functionalization of graphene to the design of graphene-based composites and also their selected applications in high performance systems relevant to energy and the environment.37 page(s

Charge transport in dye-sensitized solar cells based on flame-made TiO2 nanoparticles

The fundamental understanding on charge-transport properties of flame-synthesized TiO2 in dye-sensitized solar cells (DSSCs) is established in this work. By employing a one-step flame spray pyrolysis (FSP), predominantly anatase TiO2 nanoparticles with average nanoparticle sizes between 11 and 36 nm were achieved by varying the rate of combustion enthalpy (through varying liquid precursor feed flow rates) and using either an “openflame” or “enclosed-flame” configuration. Electron diffusion coefficient (D), electron lifetime (τ ), open circuit voltage (Voc ), and capacitance (C) measurements carried out on FSP TiO2 -based DSSCs demonstrated that interband charge trap density decreased with increase in particle size. Compared to earlier studies, interband charge trap density could be controlled more independently of particle size. Under one-sun conditions, relatively high Voc was measured with large particle size due to the lowering of interband charge trap density. This was true despite the associated shorter τ . Comparisons with commercial benchmark Nanoxide-T and Degussa P25 TiO2 were also carried out. The results from the current study have significant implications on the design of TiO2 nanoparticles by flame aerosol techniques, for DSSCs as well as other photoelectrochemical applications. Index Terms—Electron diffusion coefficien

The stabilization and bio-functionalization of iron oxide nanoparticles using heterotelechelic polymers

Iron oxide nanoparticles (IONPs) are important tools for nanobiotechnology applications. However, aqueous instability and non-specific biodistribution problems limit the applications of IONPs. Considering this, alpha-phosphonic acid, omega-dithiopyridine functionalized polymers were synthesized via the reversible addition-fragmentation chain transfer (RAFT) polymerization and used for stabilizing and biofunctionalizing IONPs. A new trithiocarbonate RAFT agent bearing dimethyl phosphonate group was utilized in the synthesis of well-defined telechelic polymers of styrene, oligoethylene glycol acrylate (OEG-A) and N-isopropylacrylamide (NIPAAm). IONPs were grafted with alpha-phosphonic acid, omega-dithiopyridine functionalized poly(OEG-A) through the alpha-chain end of the polymer, as evidenced by FTIR-ATR, XPS and zeta potential measurements. Using TGA results, the grafting density of the polymer chains was calculated between 0.12 and 0.23 chains/nm(2) particle depending on the molecular weight of the polymer. DLS measurements indicated that the particles grafted with poly(OEG-A) larger than 10 000 g/mol were stable in water for several days and the mean diameter of the particles was between 40 and 130nm depending on the molecular weight of the polymer. Moreover, particles stabilized with poly(OEG-A) with a M-n = 62 000 g/mol were stable in phosphate buffer (pH 6.5, 0.1 M) containing varying concentrations of BSA. Polymer-stabilized IONPs were successfully functionalized with two different peptides, i. e. reduced glutathione as a model peptide and NGR motif as a tumor-targeting peptide through the omega-dithiopyridine functionality of the polymer, as measured by XPS and zeta potential analysis. Poly(OEG-A)-stabilized IONPs were also found to be resistant to protein adsorption

Efficient Photoelectrochemical Water Splitting over Anodized <i>p</i>‑Type NiO Porous Films

NiO photocathodes were fabricated by alkaline etching-anodizing nickel foil in an organic-based electrolyte. The resulting films have a highly macroporous surface structure due to rapid dissolution of the oxide layer as it is formed during the anodization process. We are able to control the films’ surface structures by varying the anodization duration and voltage. With an onset potential of +0.53 V versus the reversible hydrogen electrode (RHE), the photocurrent efficiency of the NiO electrodes showed dependencies on their surface roughness factor, which determines the extent of semiconductor-electrolyte interface and the associated quality of the NiO surface sites. A maximum incident photon-to-current conversion efficiency (IPCE_max) of 22% was obtained from NiO film with a roughness factor of 8.4. Adding an Al₂O₃ blocking layer minimizes surface charge recombination on the NiO and hence increased the IPCE_max to 28%. The NiO/Al₂O₃ films were extremely stable during photoelectrochemical water splitting tests lasting up to 20 h, continuously producing hydrogen and oxygen in the stoichiometric 2:1 ratio. The NiO/Al₂O₃ and NiO films fabricated using the alkaline anodization process produced 12 and 6 times as much hydrogen, respectively, as those fabricated using commercial NiO nanoparticles

Cascade reaction engineering on zirconia-supported mesoporous MFI zeolites with tunable Lewis-Bronsted acid sites: a case of the one-pot conversion of furfural to gamma-valerolactone

Catalytic cascade reactions are strongly desired as a potential means of combining multistep reactions into a single catalytic reactor. Appropriate catalysts composed of multi-reactive sites to catalyze cascade reactions in a sequential fashion are central to such efforts. Here, we demonstrate a bifunctional zeolite catalyst with close proximity of Bronsted and Lewis acid sites through the synthesis of a mesoporous ZrO2[Al]MFI nanosponge (NS). The unique mesopores of the MFI-NS allow the confinement of zirconium oxide clusters (Lewis acid sites, LA) within the few-unit-cell-thin MFI aluminosilicate zeolite wall (Bronsted acid sites, BA). Such a structure is clearly distinct from the conventional MFI zeolite, where the agglomeration of zirconium oxide clusters onto the external surface area within the crystal bulk is not possible, resulting in segregated BA and LA sites on the internal and external zeolite, respectively. By bringing the BA and LA within ZrO2[Al]MFI-NS 30, we uncovered a more efficient catalytic route for the conversion of furfural (100% within 2 h) to gamma-valerolactone (GVL) (83%). This route is only evident when the long molecular diffusion path, in the most extreme case of physically mixed ZrO2-(LA) and Al-zeolites (BA) (45% of GVL yield), is eliminated. Unlike the bifunctional ZrO2-Al-beta (GVL yield of 75%), where the BA concentration is greatly compromised at the expense of LA formation, we also show that the ZrO2[Al]MFI-NS is able to maintain a high density and good stability of both types of acids11Nsci