Kamali Kannangara

Impact of industrial-age climate change on the relationship between water uptake and tissue nitrogen in eucalypt seedlings

This study explored reductions in tissue nitrogen concentration ([N]) at elevated CO2 concentrations ([CO2]), and changes in plant water and N uptake. Eucalyptus saligna Sm. seedlings were grown under three [CO2] levels (preindustrial (280μLL-1), current (400μLL-1) or projected (640μLL-1)) and two air temperatures (current, (current+4°C)). Gravimetric water use, leaf gas exchange and tissue dry mass and %N were determined. Solid-state 15N-NMR spectroscopy was used for determining the partitioning of N chemical groups in the dry matter fractions. Water use efficiency (WUE) improved with increasing [CO2] at ambient temperature, but strong leaf area and weak reductions in transpiration rates led to greater water use at elevated [CO2]. High temperature increased plant water use, such that WUE was not significantly stimulated by increasing [CO2] at high temperature. Total N uptake increased with increasing [CO2] but not temperature, less than the increase recorded for plant biomass. Tissue [N] decreased with rising [CO2] and at high temperature, but N use efficiency increased with rising [CO2]. Total N uptake was positively correlated with total water use and root biomass under all treatments. Growth [CO2] and temperature did not affect the partitioning of 15N among the N chemical groups. The reductions of tissue [N] with [CO2] and temperature were generic, not specific to particular N compounds. The results suggest that reductions in tissue [N] are caused by changes in root N uptake by mass flow due to altered transpiration rates at elevated [CO2] and temperature.

Influence of bond defects on coiling of graphite

Abstract The effect of annealing at 1400 ˚C in argon on the bond structure of graphite ball milled for 100 h at 400 rpm in polar (water) and in non-polar (n-dodecane) liquids was investigated primarily by near-edge X-ray absorption fine structure spectroscopy (NEXAFS) and transmission electron microscopy (TEM). Carbon K-edge NEXAFS allows the distortion of bonds in the hexagonal lattice to be investigated. It is shown that in-plane sp2 bonds are strained and distorted after ball milling because sp3 bonds are introduced. Not surprisingly, annealing of the milled product restores sp2 bonds but at the same time, coiling and formation of tube-like structures takes place. It is well established that graphite is not formed on annealing, and hence the results shown here demonstrate that the loss of sp3 carbons on annealing must proceed via a different mechanism by which they are formed by milling.

Mechanism of exfoliation of clays

The exfoliated structures of lamellar clays offer potentials as precursor for formation of nano‐structured materials. We explored the Synchrotron Radiation soft X‐ray techniques and nuclear magnetic resonance to study the exfoliation of phyllosilicate clays by polymers. Experiments were carried out in dispersions containing approximately 1% weight phyllosilicate in 5% aqueous solution of poly(acrylic acid) at different temperatures. The clays were exfoliated as the reaction was performed at 85°C. X‐ray photoemission spectroscopy indicated that the exfoliated structures were consisted of virtually pure silica nano‐plates. 29Si nuclear magnetic resonance and oxygen K‐edge near edge X‐ray absorption fine structure indicated that the surface of the plates was terminated by high concentrations of the silanol groups, which created structural branches. The formation of the branches created a steric effect that inhibited the stacking of the plates, which eventually resulted in the exfoliation.

Silica plates as precursor for nano-structured materials

Phyllosilicate clays are assemblies of nano-plates of silicate with the dimension of height to length being 1 : 100 nm or more. The preferential face-to-face stacking of these silicate plates via van der Waals forces leads to formation of lamellar, layered structures. The exfoliated (delaminated) structures of these lamellar clays offer advantages as precursor for formation of nano-structured materials. Various chemical treatments of the clays have resulted in the formation of delaminated, nano-plates of silicate (Si-O-M) or silica (Si-O-Si), which were incorporated in a polymer or dispersed in a liquid phase (Lin, et al., 2005). We present the results for formation of the delaminated, nano-plates of silica using an alternative, one-step treatment of these clays by an aqueous solution of acidic polymers. Experiments were carried out for the mixtures containing approximately 1% weight phyllosilicate in 5% aqueous solution of poly(acrylic acid) at different temperatures. X-ray diffraction and photoemission spectroscopy measurements for the solid products recovered after stirring the mixtures at 20 C showed that the fully extended chains of poly(acrylic acid) were intercalated within the interlayer spaces between the silicate plates of the clays. At 85 C, however, the clays were exfoliated. Photoemission spectroscopy and Fourier transform infrared spectroscopy indicated that the exfoliated structures were primarily consisted of silica nano-plates. These results further indicated that the silica plates are virtually free from impurities including polymeric residues.

The importance of carbonisation atmosphere on char properties derived from poly(divinylbenzene)

Production of activated carbons are a growing industry, and understanding to the processes involved in their synthesis is key to developing a better product. Generally the first step in the synthesis of activated carbon is the carbonisation of a material. During carbonisation the material undergoes aromatisation, and heteroatoms are removed, resulting in a highly aromatic carbon material. The physical and chemical properties are dependent on the degree of carbonisation and elemental makeup, which may be determined by the carbonisation conditions. In this study, properties of carbon chars derived from poly(divinylbenzene) are examined. Carbonisation conditions including, temperature, hold time, and atmosphere are studied to determine how these influence the thermal stability, elemental composition, and surface area and pore volumes of the final material. Surface areas were dependent on reactor gas, for nitrogen the surface area decreased from 665 m2/g to <1 m2/g as did pore volumes from 0.553 cm3/g to <0.01 cm3/g at 500°C; however, when the char was produced under an argon atmosphere, surface area and pore volume increased to 119 m2/g and 0.179 cm3/g. It was hypothesised that the difference between chars were due to a reaction of the char with nitrogen, which hindered the development of pores. Nitrogen reaction products were detected via elemental analysis and gas chromatography-mass spectrometry. This study shows the importance of the atmosphere and other parameters on the chars derived from poly(divinylbenzene).

Carbon nanotube formation from milled iron-phthalocyanine

Organometallics supply carbon and metal catalyst needed for carbon nanotube synthesis. It is shown that experiments involving prior milling of iron-phthalocyanine (FePc, FeC32H16N8) before pyrolysis at 800 °C in argon produces carbon nanotubes with diameters ranging from 5 to 15 nm. Under the same conditions, the diameters of nanotubes produced from non-milled FePc range from 20 to more than 50 nm. Milling decreases the onset of sublimation of FePc from about 450 to 200 °C and also reduces the activation energy barrier of sublimation at 360 °C from 287 to 193 kJ/mol. This appears to be due to changes in molecular packing of the phthalocyanine precursor. It is suggested that the decrease in nanotube diameter is due to greater homogeneity in the gas phase on pyrolysis after milling, which leads to more systematic capture of carbon species during the catalytic growth of the carbon nanotubes.

Micro-structural Evolution in Processed Graphite

The microstructure evolution of graphite milled in n-dodecane and annealed at 1400 C in argon was investigated by Raman spectroscopy, near edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray diffraction line broadening analysis (XRD). During milling, the n-dodecane molecular intercalation resulted in the increase in the interlayer spacing (d002). The intercalation facilitated graphite cleavage reducing the average crystallite thickness (Lc ) from 175 nm to 6 nm. The results of carbon X-edge NEXAFS spectroscopy indicated that the pi-electron system of graphite was disturbed during milling. Annealing increased the crystallite thickness to 10 nm, restored the pi-electron system of graphite but produced a number of coiled sheets These results provided strong evidence that the increased energy potential due to presence of local structure defects and modification of graphite pi-electron system provide the driving force for rolling up of thin graphite particles during annealing