An assessment of the photostability of South African commercial sunscreens.

Master of Science in Chemistry. University of KwaZulu-Natal, Durban 2006.Abstract available in PDF file

Preparation and evaluation of Lignocellulose-Montmorillonite nanocomposites for the adsorption of some heavy metals and organic dyes from aqueous solution

The need to reduce the cost of adsorption technology has led scientists to explore the use of many low cost adsorbents especially those from renewable resources. Lignocellulose and montmorillonite clay have been identified as potentially low cost and efficient adsorbent materials for the removal of toxic heavy metals and organic substances from contaminated water. Montmorillonite clay has good adsorption properties and the potential for ion exchange. Lignocellulose possesses many hydroxyl, carbonyl and phenyl groups and therefore, both montmorillonite and lignocellulose are good candidates for the development of effective and low cost adsorbents in water treatment and purification. The aim of this study was to prepare composite materials based on lignocellulose and montmorillonite clay and subsequently evaluate their efficacy as adsorbents for heavy metal species and organic pollutants in aqueous solution. It was also important to assess the adsorption properties of the modified individual (uncombined) lignocellulose and montmorillonite. Lignocellulose and sodium-exchanged montmorillonite (NaMMT) clay were each separately modified with methyl methacrylate (MMA), methacrylic acid (MAA) and methacryloxypropyl trimethoxysilane (MPS) and used as adsorbents for the removal of heavy metals and dyes from aqueous solution. The lignocellulose and NaMMT were modified with MMA, MAA and MPS through free radical graft polymerisation and/or condensation reactions. NaMMT was also modified through Al-pillaring to give AlpMMT. The materials were characterised by fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and small angle X-ray scattering (SAXS) and characterisation results showed that the modification of the montmorillonite with MAA, MMA and MPS was successful. The modified lignocellulose and montmorillonite materials were evaluated for the adsorption of heavy metal ions (Cd2+ and Pb2+) from aqueous solution by the batch method. The adsorption isotherms and kinetics of both Cd2+ and Pb2+ onto the NaMMT clay, AlpMMT and lignocellulose materials are presented. The Langmuir isotherm was found to be the best fit for the adsorption of both heavy metals onto all the adsorbents. AlpMMT showed very poor uptake for heavy metals (both Cd2+ and Pb2+). PMMAgMMT, PMAAgMMT, PMAAgLig and PMPSgLig showed improved adsorption for both heavy metals. The mechanism of heavy metal adsorption onto the adsorbents was best represented by the pseudo second-order kinetic model. PMPSgLig, NaMMT and AlpMMT showed relatively high adsorption capacities for methyl orange, while the adsorption of neutral red was comparable for almost all the adsorbents. Neither the Langmuir model nor the Freundlich model was found to v adequately describe the adsorption process of dyes onto all the adsorbents. The pseudo second-order model was found to be the best fit to describe the adsorption mechanism of both dyes onto all the adsorbents. The modification of lignocellulose and montmorillonite with suitable organic groups can potentially produce highly effective and efficient adsorbents for the removal of both heavy metals and dyes from contaminated water. Novel adsorbent composite materials based on lignocellulose and montmorillonite clay (NaMMT) were also prepared and evaluated for the removal of pollutants (dyes and heavy metals) from aqueous solution. The lignocellulose-montmorillonite composites were prepared by in situ intercalative polymerisation, using methyl methacrylate, methacrylic acid and methacryloxypropyl trimethoxysilane (MPS) as coupling agents. The composite materials were characterised by FTIR, TGA, TEM and SAXS. SAXS diffractograms showed intercalated nanocomposites of PMMAgLig-NaMMT and PMAAgLig-NaMMT, whereas PMPSgLig-NaMMT showed a phase-separated composite and the same results were confirmed by TEM. The lignocellulose-montmorillonite composites were assessed for their adsorption properties for heavy metal ions (Cd2+ and Pb2+) and dyes (methyl orange and neutral red) from aqueous solution. Among these composite materials, only PMAAgLig-NaMMT showed a marked increase in the uptake of both Cd2+ and Pb2+ relative to lignocellulose and montmorillonite when used independently. The adsorption data were fitted to the Langmuir and Freundlich isotherms, as well as to the pseudo first-order and pseudo second-order kinetic models. The data were best described by the Langmuir isotherm and the pseudo second-order kinetic model. On the adsorption of dyes, only PMPSgLig-NaMMT showed enhanced adsorption of methyl orange (MetO) compared with lignocellulose and montmorillonite separately. The enhanced adsorption was attributed to the synergistic adsorption due to the presence of MPS, lignocellulose and NaMMT. Competitive adsorption studies were carried out from binary mixtures of MetO and Cd2+ or Pb2+ in aqueous solution. The adsorption process of MetO onto the composite material was found to follow the Freundlich adsorption model, while the mechanism of adsorption followed both the pseudo first-order and pseudo second-order models. This particular composite can be used for the simultaneous adsorption of both heavy metals and organic dyes from contaminated water. The adsorption of neutral red to the composite materials was comparable and the pseudo second-order kinetic model best described the adsorption mechanism

Determination of Titanium Dioxide in Commercial Sunscreens by Inductively Coupled Plasma-Optical Emission Spectrometry

ABSTRACT A variety of sunscreen products have been developed to afford the consumer protection against some of the deleterious effects, for example erythema, caused by solar ultraviolet radiation. The requirement that suncare products offer broad-spectrum protection has resulted in the use of inorganic oxides, such as micronized titanium dioxide (TiO 2 ), in their formulation. However, there are now concerns about the photocatalytic effects of the TiO 2 in these products and its potential phototoxicity to the skin through the generation of reactive oxygen species such as hydroxyl and superoxide anion radicals. It is important, therefore, that the amounts of TiO 2 in suncare products be closely monitored and maintained within stipulated ranges. A simple, fast and reliable analytical method for the determination of TiO 2 in commercial sunscreen products by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed and validated. The limits of detection and quantitation were found to be 0.018 and 0.062 µg mL -1 , respectively. The average percentage recovery of TiO 2 was 102.32 ± 2.87 % with a RSD of 2.81 %. The method was applied to determine the concentration of TiO 2 in 22 commercial suncare samples of which 14 contained TiO 2 . The amounts of TiO 2 measured in these sunscreens ranged from 0.05 to 3.21 %. To our knowledge this is the first study that reports the amounts of TiO 2 in sunscreen products available on the South African market. KEYWORDS Titanium dioxide, sunscreens, physical blocker, inductively coupled plasma-optical emission spectrometry

Determination of Titanium Dioxide in Commercial Sunscreens by Inductively Coupled Plasma–Optical Emission Spectrometry

A variety of sunscreen products have been developed to afford the consumer protection against some of the deleterious effects, for example erythema, caused by solar ultraviolet radiation. The requirement that suncare products offer broad-spectrumprotection has resulted in the use of inorganic oxides, such as micronized titanium dioxide (TiO2), in their formulation. However, there are now concerns about the photocatalytic effects of the TiO2 in these products and its potential phototoxicity to the skin through the generation of reactive oxygen species such as hydroxyl and superoxide anion radicals. It is important, therefore, that the amounts of TiO2 in suncare products be closely monitored and maintained within stipulated ranges. A simple, fast and reliable analytical method for the determination of TiO2 in commercial sunscreen products by inductively coupled plasma–optical emission spectrometry (ICP-OES) was developed and validated. The limits of detection and quantitation were found to be 0.018 and 0.062 μg mL–1, respectively. The average percentage recovery of TiO2 was 102.32 ± 2.87 % with a RSD of 2.81 %. The method was applied to determine the concentration of TiO2 in 22 commercial suncare samples of which 14 contained TiO2. The amounts of TiO2 measured in these sunscreens ranged from 0.05 to 3.21 %. To our knowledge this is the first study that reports the amounts of TiO2 in sunscreen products available on the South African market.Keywords: Titanium dioxide, sunscreens, physical blocker, inductively coupled plasma-optical emission spectrometr

Basic Chemistry: PAC 110

Basic Chemistry: PAC 110, degree examination June 2010

Determination of Titanium Dioxide in Commercial Sunscreens by Inductively Coupled Plasma-Optical Emission Spectrometry

ABSTRACT A variety of sunscreen products have been developed to afford the consumer protection against some of the deleterious effects, for example erythema, caused by solar ultraviolet radiation. The requirement that suncare products offer broad-spectrum protection has resulted in the use of inorganic oxides, such as micronized titanium dioxide (TiO 2 ), in their formulation. However, there are now concerns about the photocatalytic effects of the TiO 2 in these products and its potential phototoxicity to the skin through the generation of reactive oxygen species such as hydroxyl and superoxide anion radicals. It is important, therefore, that the amounts of TiO 2 in suncare products be closely monitored and maintained within stipulated ranges. A simple, fast and reliable analytical method for the determination of TiO 2 in commercial sunscreen products by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed and validated. The limits of detection and quantitation were found to be 0.018 and 0.062 µg mL -1 , respectively. The average percentage recovery of TiO 2 was 102.32 ± 2.87 % with a RSD of 2.81 %. The method was applied to determine the concentration of TiO 2 in 22 commercial suncare samples of which 14 contained TiO 2 . The amounts of TiO 2 measured in these sunscreens ranged from 0.05 to 3.21 %. To our knowledge this is the first study that reports the amounts of TiO 2 in sunscreen products available on the South African market. KEYWORDS Titanium dioxide, sunscreens, physical blocker, inductively coupled plasma-optical emission spectrometry

Light filtration technology for sustainable microalgal biomass production

AbstractThe use of native microalgal strains, which are well adapted to local environmental conditions, for sustainable biofuels production has largely been marred by photonics-related challenges. To date, most photobioreactor systems make use of artificial sources of illumination thus increasing the overall costs of biomass production. Solar energy, although sustainable and cost-effective, is difficult to manage and control. It also contains other wavelengths which are detrimental to microalgae. Thus, this study sought to make use of spectral filters for optimal outdoor algaculture. Hence, solar energy was used in wastewater-mediated algaculture of native and imported Chlorella sp. under blue, green, red and yellow coloured spectral filters. The native Chlorella sp. had the highest growth rate of 0.892 d−1 and 0.754 d−1 under green and blue coloured filters, respectively. In comparison, the imported Chlorella strain had a growth rate of 0.379 d−1 and 0.267 d−1 under green and blue filters, respectively. Both strains produced high lipid yields under the blue coloured filter, with the native and imported Chlorella strains managing lipid yields of 41.87% dry cell weight (dcw) and 32.29% dcw, respectively. The native Chlorella strain also significantly lowered (p < 0.05) the levels of total nitrogen and ammonium from wastewater with removal efficiencies of 92.17% and 44.60%, respectively, whereas the imported Chlorella strain managed a removal efficiency of 80.81% total nitrogen and 26.10% ammonium under the blue coloured filter. The results indicate that light filtration technology can be used, sustainably, in the simultaneous algaculture of native strains and remediation of wastewater