Development of novel nanoengineered materials: chemical synthesis, properties and applications

Abstract

The materials synthesised in this study were designed to have novel morphology coupled with a tightly controlled surface composition that could be varied depending on a application. Preparations with simple single metal oxides (i.e. TiO2, SiO2, Al2O3 and ZrO2) were used as the starting point with the latter stages involving multi-metal oxide coatings and materials. The research was divided into three interconnected areas; i) biotemplating, ii) alternative synthetic morphologies to biotemplating and iii) the synergy between microparticles and insecticides. For the investigation into biotemplating pollen was chosen as the main example due to its ubiquity. Here, good replication of its structure with metal oxides can be achieved by two-dimensional solgel chemistry. Such materials can be further modified to have tunable surface chemistry through dopants and optical properties (i.e. fluorescence) through the use of dyes. Materials were extensively characterised using primarily spectroscopy (UV and IR) and microscopy (i.e. SEM coupled with EDX elemental analysis). These were considered for several applications and examples investigated here included as a taggant technology and photocatalytic removal of methyl orange in an aqueous environment (TiO2-pollen only). For the latter, results have been compared with those of a commercially available alternative (P25) where the preliminary results are very promising. The method of overcoating was also shown to be transferrable to other flora and fauna biotemplates. Synthetic alternatives for the biotemplated pollen were considered in the second investigative area where solution sol-gel processes such as the Stöber method were considered in addition to other suspension based precipitation methods (i.e. refluxes and microemulsions). Processes developed in the biotemplating research were applied here and analysed again using spectroscopy and microscopy as the main techniques. As part of this aspect, a novel fast-drying water-in-oil microemulsion delivery and preparative system was also developed using low boiling point solvents such as isopentane and ethanol and low toxicity sucrose ester surfactants. Hollow oxide shells could be prepared in these using a novel low-temperature route that were comparable in thickness (but significantly smaller in size) to hollow pollen replicas. In this second area attention was shifted to more focus on oxides of Si and Al (as opposed to TiO2 that used extensively in biotemplating) to broaden the scope of the research and investigate other potential applications, such as nanoabrasives (surface roughness and ability to cleave DNA). The third and final area of interest used the materials from the previous two aspects in coatings that were applied to investigating the knockdown (KD) and total mortality (TM) of selected arthropods. Here mosquitoes of the A. Gambiae and S. Aegypti genus were considered with particular focus on synergistic effects with existing commercial insecticides (using mainly CDC bottle tests). Microscopy was used as the primary characterisation technique here to determine particle transfer after each assay. In these tests %TM suggested SiO2 microspheres were particularly effective at in enhancing mortality of the commercial l-cyhalothrin insecticide. Additionally, novel methods of recording mosquito behaviour was investigated through optical and thermographic stills and videos.