Lucky Sikhwivhilu

The Effect of Solvents, Acetone, Water, and Ethanol, on the Morphological and Optical Properties of ZnO Nanoparticles Prepared by Microwave

HDA-capped ZnO nanoparticles were prepared by solvothermal method using solvents of different polarities. A number of parameters were kept constant such as temperature, pressure, time, and pH while solvents were varied, that is, water, ethanol, and acetone. The TEM was used for the structural properties and morphologies such as spheres, mixture of rods, and spheres and stars were obtained in ethanol, acetone, and water, respectively, in a given reaction time of 15 minutes. Both ethanol and acetone gave rods with high aspect ratio primarily because of the lengths of the rods. Water and ethanol have the hydroxyl groups which interact with nanoparticles from nucleation, growth, and termination giving rise to nonspherical shapes. The hydroxyl group promotes growth in a nonuniform way resulting in stars and rods. The optical features were typical of ZnO nanoparticles with excitonic peaks in the range 368 to 374 nm from their absorption spectra. The XRD patterns of the particles gave the most stable form of ZnO which is the hexagonal phase, with high degree of crystallinity and with the 101 plane predominant in all solvents.

Fate and behavior of ZnO- and Ag-engineered nanoparticles and a bacterial viability assessment in a simulated wastewater treatment plant.

The fate and behaviour assessment of ZnO- and Ag-engineered nanoparticles (ENPs) and bacterial viability in a simulated wastewater treatment plant (WWTP) fed with municipal wastewater was investigated through determination of ENPs stability at varying pH and continuous exposure of ENPs to wastewater, respectively. The ENPs were introduced to a 3-L bioreactor (simulated WWTP) with a hydraulic residence time (HRT) of 6 h at a dose rate of 0.83 mg/min for 240 h. The stability of the ENPs was found to be dependent on their dissolution and aggregation at different pH, where ZnO ENPs exhibited the highest dissolution at low pH compared to Ag ENPs. The results also showed that both ENPs had high affinity for the sewage sludge as they undergo aggregation under typical wastewater conditions. Results of effluent monitored daily showed mean COD removal efficiencies of 71 ± 7% and 74 ± 8% for ZnO and Ag ENPs in test units, respectively. The treated effluent had low mean concentrations of Zn (1.39 ± 0.54 mg/L) and Ag (0.12 ± 0.06 mg/L); however, elevated mean concentrations of Zn (54 ± 39 mg/g dry sludge) and Ag (57 ± 42 mg/g dry sludge) were found in the sludge – suggesting removal of the ENPs from the wastewater by biosorption and biosolid settling mechanisms. Using X-ray diffraction (XRD) and transmission electron microscopy (TEM), the mineral identities of ZnO and Ag ENPs in the sludge from the test units were found comparable to those of commercial ENPs, but larger due to agglomeration. The bacterial viability assessment after exposure to ENPs using the Live/Dead BacLight kit, although not quantitatively assessed, suggested high resilience of the bacteria useful for biodegradation of organic material in the simulated wastewater treatment system.

Nafion titania nanotubes nanocomposite electrolytes for high-temperature direct methanol fuel cells

Nafion-based nanocomposite membranes containing various amounts of titania nanotubes (TNTs) as an inorganic filler have been prepared using melt-mixing method and have been investigated for proton exchange membrane applications. The onedimensional TNTs have been prepared from potassium hydroxide using hydrothermal route and conventional heating. Nafion R1100 in a protonated form was used, and TNT contents were in a range of 0.5-2.0 wt%. The acid-treated composite membranes, at lowest inorganic additive content, exhibited improved properties in terms of thermal stability and methanol (MeOH) permeability. The best performing nanocomposite was the membrane containing only 0.5 wt% TNTs showing ionic conductivity value of 7.2 × 10-2 S ċ cm-1 at 26°C and 100% of relative humidity.

Novel PVA/MOF Nanofibres: Fabrication, Evaluation and Adsorption of Lead Ions from Aqueous Solution

Plain polyvinyl alcohol (PVA) nanofibres and novel polyvinyl alcohol benzene tetracarboxylate nanofibres incorporated with strontium, lanthanum and antimony ((PVA/Sr-TBC), (PVA/La-TBC) and (PVA/Sb-TBC)), respectively, where TBC is benzene 1,2,4,5-tetracarboxylate adsorbents, were fabricated by electrospinning. The as-prepared electrospun nanofibres were characterized by scanning electron microscope (SEM), Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA). Only plain PVA nanofibres followed the Freundlich isotherm with a correlation coefficient of 0.9814, while novel nanofibres (PVA/Sb-TBC, PVA/Sr-TBC and PVA/La-TBC) followed the Langmuir isotherm with correlation coefficients of 0.9999, 0.9994 and 0.9947, respectively. The sorption process of all nanofibres followed a pseudo second-order kinetic model. Adsorption capacity of novel nanofibres was twofold and more compared to that of plain PVA nanofibres. The thermodynamic studies: apparent enthalpy (ΔH°) and entropy (ΔS°), showed that the adsorption of Pb(II) onto nanofibres was spontaneous and exothermic. The novel nanofibres exhibited higher potential removal of Pb(II) ions than plain PVA nanofibres. Ubiquitous cations adsorption test was also investigated and studied.

Relevance of nanotechnology to Africa: synthesis, applications and safety

In this chapter, two nanotechnology-based applications relevant to Africa in promoting sustainability and achievement of the Millennium development goals (MDGs) are presented. The applications comprise the provision of therapeutic treatment of diseases (HIV/AIDS and malaria) and the treatment of contaminated water through purification, remediation, and disinfection process to promote access to clean water to millions of African inhabitants without clean drinking water. Extensive examination of the available scientific literature suggests that nanotechnology can potentially improve the provision of health and water services in the African continent. While the authors agree these benefits are of great relevance to the continent, the chapter gives insights into the concerns related to the potential risks posed by nanotechnology-based products both to humans and other ecological systems. In addition, the chapter seeks to outline the chemistry underpinning the development of nanotechnology and its relevance in achieving sustainable development within the context of developmental challenges in Africa. Finally, as the future socioeconomic status will be mostly defined by nanotechnology capabilities, Africa should be alert to these changes and take advantage, particularly, at this early development phase of nanotechnology development.

The Effect of Structural Properties of Cu2Se/Polyvinylcarbazole Nanocomposites on the Performance of Hybrid Solar Cells

It has been said that substitution of fullerenes with semiconductor nanocrystals in bulk heterojunction solar cells can potentially increase the power conversion efficiencies PCE of these devices far beyond the 10% mark. However new semiconductor nanocrystals other than the potentially toxic CdSe and PbS are necessary. Herein we report on the synthesis of Cu2Se nanocrystals and their incorporation into polyvinylcarbazole PVK to form polymer nanocomposites for use as active layers in hybrid solar cells. Nearly monodispersed 4 nm Cu2Se nanocrystals were synthesized using the conventional colloidal synthesis. Varying weight % of these nanocrystals was added to PVK to form polymer nanocomposites. The 10% polymer nanocomposite showed retention of the properties of the pure polymer whilst the 50% resulted in a complete breakdown of the polymeric structure as evident from the FTIR, TGA, and SEM. The lack of transport channels in the 50% polymer nanocomposite solar cell resulted in a device with no photoresponse whilst the 10% polymer nanocomposite resulted in a device with an open circuit voltage of 0.50 V, a short circuit current of 7.34 mA/cm2, and a fill factor of 22.28% resulting in a PCE of 1.02%.