Cosmas M. Muiva

Extraction of nanocellulose and in-situ casting of ZnO/cellulose nanocomposite with enhanced photocatalytic and antibacterial activity

Polymer hosted metallic nanostructures with diverse applications have become a prominent area of materials science, engineering and technology. In this study nanocellulose (NC) was synthesized from oil palm empty fruit bunches biomass via alkaline treatment and acid hydrolysis and characterized. The obtained NC was used as a host polymer for the synthesis of zinc oxide (ZnO) nanostructures through in-situ solution casting method. Alkaline treatment and acid hydrolysis increased the percentage crystalline index from 35.7% to 43.3% and 53.3% respectively. X-ray diffraction studies pointed to cellulose I, with a monoclinic structure. Zinc oxide/cellulose nanocomposite displayed more photocatalytic activity than pure ZnO nanostructures upon degradation of methylene blue, and also improved antibacterial activity against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli.

Chemical Spray Pyrolysis Path to Synthesis of ZnO Microsausages from Aggregation of Elongated Double Tipped Nanoparticles

The versatile chemical spray pyrolysis was used to prepare elongated double tipped ZnO nanoparticles and microsausages on glass substrates. X-ray diffraction studies revealed several crystallographic plane orientations with the most predominant along the (002) direction. Scanning electron microscope (SEM) observations indicated double tipped nanoparticles with an aspect ratio of 4.5-8.6 which coalesced in regular patterns to form microsized sausages of width ranging up to 1.2 µm. The absorption mechanism was through direct transitions with an absorption edge corresponding to a band gap of 3.18 eV.

Chemical Synthesis and Properties of Novel Nanostructures and Microplatelets

Bi2Se3 nanostructures, microsised fibre bundles, and platelets have been synthesised through a simple chemical spray pyrolysis route on glass substrates. Low substrate temperatures () favoured growth of nanostructures while elevated was accompanied by increased grain growth and formation of microsised platelets. The nanostructures were identified as nanorods, nanofibers, nanotubes, nanoflowers, and nanoneedles of various aspect ratios. There was an observed red shift of the optical band gap () with increased from 2.40 eV at 95°C to 1.25 eV at 360°C. Thermo probe measurements confirmed n-type conductivity with dark resistivities which followed a near exponential decline with elevated . The observed changes in optoelectronic properties existing in the different regimes were explained on the basis of microstructural and textural changes in the pristine clusters.

Effect of Ga Incorporation and Film Thickness on the Optical Properties of as-Deposited Amorphous GaxSel-x Thin Films

Flash evaporated amorphous GaxSe1-x (x = 0, 1, 2, 3, and 4 atomic %) on glass substrates have been investigated within a 500nm-1500nm spectral range. Film thicknesses explored were ; 200±10nm, 265±10nm, 330±10nm, and 400±10nm. The effect of film thickness and gallium content on the as-deposited thin films has been established. As the gallium content increases, both the optical transmittance and band gap energy decrease. Increase in film thickness led to a decrease in optical transmittance and an increase in the band gap energy. The other optical parameters like the absorption coefficient, extinction coefficient, refractive index, real part and imaginary part of dielectric constant increase with increase in gallium content and film thickness.

Optical Properties of Flash Evaporated Amorphous Se 100-X In X Thin Films for CuInSe 2 Solar Cell Applications

Amorphous Se100-XIn X thin films were prepared by flash evaporation of the pre-melt quenched bulk samples. The samples were characterised and the suitability of each composition assessed towards applications as a buffer layers in CuInSe2 photovoltaic cells. XRD studies confirmed that all the samples were amorphous. There was a descending dependence of complex dielectric constant and refractive index on wavelength which levelled in the infra-red (IR) region. A red shift in the optical energy gap Eg opt from 1.76 eV for In = 5 at% to 1.46 eV for In = 20 at% was observed. The Eg opt values were in the range that is compatible with solar energy conversion.