The effect of the metal and selenium precursors on the properties of NbSe2 and Nb2Se9 nanostructures and their application in dye-sensitized solar cells

Herein, we report on the effect of the precursors on the structural, morphological, and optical properties of niobium selenide using the heat-up colloidal method. The metal precursor was varied from the conventional NbCl₅ to NbF₅ whilst Se, SeO₂, and selenourea were used as the selenium precursors. The NbCl₅ and NbF₅ resulted in the formation of NbSe₂ and Nb₂Se₉ respectively. While maintaining the two different metal precursors and varying the selenium precursor from Se, SeO₂ to selenourea, the properties of NbSe₂ and Nb₂Se₉ changed slightly, however the effect of changing the selenium precursor was less pronounced than changing the metal precursors. From the XRD and XPS, the NbSe₂ nanostructures were more susceptible to oxidation than Nb₂Se₉ as Nb₂O₅ was observed in the XRD and the percentage of M–O in the XPS was much higher in NbSe₂. NbSe₂ formed nanoflowers whilst Nb₂Se₉ formed rods with 3.29 eV and 2.43 eV band-gaps, respectively. Also, the band-gaps were red-shifted as the selenium precursors were varied. The NbSe₂ nanoflowers and Nb₂Se₉ nanorods were used as counter electrodes in dye-sensitized solar cells. Two methods were used to fabricate the counter electrodes i.e. spin coating and drop casting. The electrochemical properties of the spin coated counter electrodes were better than the drop casted ones; hence, they were employed in dye-sensitized solar cells. The spin coated NbSe₂ nanoflowers had the highest efficiency of 6.84%, attributed to the nanoflower morphology.

NbSe₂ and Nb₂Se₉ as counter electrodes in dye-sensitized solar cells.     

The Impact of Highly Active Antiretroviral Therapy on Activities of Daily Living in HIV-Infected Adults in South Africa

This study investigated the relationship between highly active antiretroviral therapy (HAART) and instrumental activities of daily living (IADLs) among two clinical cohorts in South Africa. Between 2003 and 2008 structured questionnaires were administered to HIV-positive patients attending outpatient clinics at an urban hospital (Soweto, n = 3,081) and a rural hospital (Acornhoek, n = 1,247). Among those receiving help, an average of 4.8 and 5.1 h of assistance with IADLs daily was reported (rural and urban participants, respectively), with the patient’s mother and children assisting the most. Participants on HAART were 17 and 41% less likely to receive assistance with IADLs in the rural and urban cohorts, respectively, after adjusting for demographic characteristics, healthcare utilization, and CD4 counts. HAART significantly decreased the IADL assistance among patients in South Africa. Alongside clinical benefits, HAART has the potential to reduce the burden of HIV-related care, potentially extending wider social and economic gains to other family members.     

The health implications of wastewater reuse in vegetable irrigation: a case study from Malamulele,South Africa

Malamulele is located in an arid region where small-scale irrigation with wastewater is rife. A study was conducted to investigate the health implications of wastewater reuse in vegetable irrigation. Results showed that there are potential health hazards associated with this practice. The wastewater contained 103 helminth eggs/100 ml and zero helminth eggs for control group; vegetable wash water had 3 helminth eggs/100 ml for the exposed group and zero for control. The wastewater results exceeded the WHO guidelines whereas the vegetable wash water counts were within the guideline. Stool samples of farmers and their children indicated common infections with hookworm and Giardia lamblia. Hookworm infections were high (42%) among exposed group in comparison to the control group (27.5%). The farmers were able derive their livelihood from the sale of vegetables. The findings suggest that the health risks of using wastewater are real but can be managed by using the incomes that the farmers earn.     

Resin-gel incorporation of high concentrations of W6+ and Zn2+ into TiO2-anatase crystal to form quaternary mixed-metal oxides: effect on the a lattice parameter and photodegradation efficiency

The search for a viable photocatalyst for water remediation is ongoing and in recent times the efforts have predominantly focused on improving the limitations of the TiO₂ photocatalyst. This paper reports a dual strategy for improving the photocatalytic properties of TiO₂. The first strategy is to dope up to 30% of W⁶⁺ and Zn²⁺ into the crystal lattice of TiO₂ using the resin gel technique to synthesize quaternary mixed metal oxides (QMMOs). It was demonstrated by laser Raman spectroscopy, PXRD and various other strategies, including dislodging the dopants from the crystal lattice of TiO₂, that these materials were successfully synthesized. More importantly, UV-DRS showed that these materials could absorb visible light. TiO₂ and the QMMOs were also supported on 10% NCNTs synthesized from coal fly ash, by slightly modifying the resin gel technique. It was observed from TEM images that the NCNTs were uniformly coated with TiO₂ and QMMO nanoparticles. These composites were observed to have lower photoluminescence emission spectra when compared to neat TiO₂ and unsupported QMMOs. The two-part strategy employed in this project worked as the QMMOs supported on 10% NCNTs had higher visible light photodegradation efficiencies compared to neat TiO₂ and the unsupported QMMOs.

Incorporating up to 30% of W⁶⁺ and/or Zn²⁺ into TiO₂-anatase influences the lattice structure of TiO₂ thus its photocatalytic efficiency.     

Synthesis and characterization of polyaniline,polypyrrole and zero-valent iron-based materials for the adsorptive and oxidative removal of bisphenol-A from aqueous solution

One pot synthesis of a polypyrrole, polyaniline and Fe⁰ nano-composite (Fe⁰-PPY/PANI) was achieved by polymerizing aniline and pyrrole with FeCl₃ followed by the reduction of Fe³⁺ to Fe⁰ with NaBH₄. PPY/PANI was synthesized the same way as Fe⁰-PPY/PANI, except that all the FeCl₃ was removed by rinsing. The presence of Fe⁰ was demonstrated using several analytical techniques; this was shown in comparison to materials that are without Fe⁰. A series of materials were screened as both adsorbents and catalyst for the activation of H₂O₂ towards bisphenol A (BPA) removal in batch experiments. Polymers performed better than composites containing Fe⁰ at adsorption, whereas Fe⁰ based materials were better catalysts for the activation of H₂O₂. BPA samples were then spiked with other contaminants including sewage water to test the performance of the various adsorbents and Fenton catalysts. PPY/PANI was found to be a better adsorbent than the rest, whereas Fe⁰-PPY/PANI was the best Fenton catalyst. The adsorption kinetics of BPA onto PPY/PANI was studied; it was found that the process was governed by the pseudo-second-order kinetic model. The adsorption isotherms revealed that the amount of BPA taken up by PPY/PANI increased with increasing temperature and was governed by the Langmuir adsorption isotherm. The mechanism in which Fe⁰-PPY/PANI and H₂O₂ degraded BPA was studied, it was found that surface-bound hydroxyl radicals were responsible for the degradation of BPA. It was also shown that the degradation process included the formation of smaller compounds leading to the reduction of the total organic content by 57%.

PPY, PANI and Fe⁰ based composites for the adsorption and oxidative removal of BPA in different water matrices.     

Recovery of waste gold for the synthesis of gold nanoparticles supported on radially aligned nanorutile: the growth of carbon nanomaterials

Precious and expensive metals are lost each year through the discarding of old jewellery pieces and mine tailings. In this work, small amounts of gold were recovered by digestion with aqua regia from waste tailings. The recovered gold in the form of HAuCl₄ was then used to deposit Au⁰ onto radially aligned nanorutile (RANR) to form a supported catalyst material. The support material, RANR, was synthesized using the hydrothermal technique whereas the deposition of gold was achieved using the deposition–precipitation with urea method at various loadings. Electron microscopy was used to show that the structure of the support is a sphere formed by multiple nanorods aligned in a radial structure. The Au nanoparticles were observed at the tips of the nanorods. It was confirmed by XRD that the support was indeed a rutile phase of TiO₂ and that the Au nanoparticles had a face-centred cubic structure. The various catalysts were then used to synthesize carbon nanomaterials (CNMs) using the chemical vapour deposition technique. A parametric study varying the reaction temperature, duration and carbon source gas flow rate was conducted to study the effects these conditions have on the structural properties of the resulting CNMs. Here, it was found that mainly carbon nanofibers were formed and that the different reaction conditions influenced their graphicity, width, structure and thermal properties.

A hydrothermal method was used to prepare rutile TiO₂ dandelions. A deposition–precipitation method using urea (DPU) was used to load Au metal nanoparticles in calculated weight percentages and the Au/RANR catalysts where used to synthesise CNFs in a CVD reaction.