The degradation of microcystin-LR using doped visible light absorbing photocatalysts

Innovation, Design and Sustainability Research Institute (IDeaS), The Robert Gordon University, Schoolhill, Aberdeen, UK.
Chemosphere (Impact Factor: 3.34). 02/2010; 78(9):1182-5. DOI: 10.1016/j.chemosphere.2009.12.003
Source: PubMed


Microcystins are one of the primary hepatotoxic cyanotoxins released from cyanobacteria. The presence of these compounds in water has resulted in the death of both humans and domestic and wild animals. Although microcystins are chemically stable titanium dioxide photocatalysis has proven to be an effective process for the removal of these compounds in water. One problem with this process is that it requires UV light and therefore in order to develop effective commercial reactor units that could be powered by solar light it is necessary to utilize a photocatalyst that is active with visible light. In this paper we report on the application of four visible light absorbing photocatalysts for the destruction of microcystin-LR in water. The rhodium doped material proved to be the most effective material followed by a carbon-modified titania. The commercially available materials were both relatively poor photocatalysts under visible radiation while the platinum doped catalyst also displayed a limited activity for toxin destruction.

Download full-text


Available from: Linda A Lawton, Sep 04, 2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this investigation, in order to develop photocatalyst materials with improved photo-efficiency and visible light response compared to the state of the art materials, the role of Evonik Aeroxide® P25-TiO2 (P25) nanoparticles incorporated in a modified sol–gel process to yield composite nitrogen and fluorine doped TiO2-P25 (NF-TiO2-P25) films was investigated. The addition of P25 nanoparticles in the sol leads to higher BET surface area, pore volume, porosity and total TiO2 mass, as well as larger thickness and roughness of the films after heat treatment. Microscopy techniques confirmed partial sintering of NF-TiO2 sol–gel formed and P25 nanoparticles having different average size. The existence of well defined regions of only anatase from NF-TiO2 and anatase–rutile mix from P25 was verified in the micro-Raman spectra. The photocatalytic degradation of four microcystins (microcystin-LR, -RR, -LA and -YR) and cylindrospermopsin was evaluated with NF-TiO2 and NF-TiO2-P25 films under visible and UV–vis light. The general reactivity for the microcystins under acidic conditions (pH 3.0) was: MC-LA > MC-LR ≥ MC-YR > MC-RR where the highest initial degradation rate was achieved with the NF-TiO2-P25 films (5 g L−1 of P25 in sol when irradiated with visible light and 15 g L−1 of P25 in sol when irradiated with UV–vis light). Cylindrospermopsin showed negligible adsorption at pH 3.0 for all films. Nevertheless, significant photocatalytic removal was found under UV–vis light with maximum P25 loaded films indicating that the degradation was mediated by the involvement of photogenerated reactive oxygen species and not by the trapping reaction of the positive hole.
    Applied Catalysis B Environmental 06/2012; s 121–122:30–39. DOI:10.1016/j.apcatb.2012.03.010 · 7.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A study was performed to determine the effect of pH, alkalinity, natural organic matter (NOM) and dissolved oxygen in the performance of nitrogen and fluorine doped TiO(2) (NF-TiO(2)) for the degradation of hepatotoxin microcystin-LR (MC-LR) in synthetic and natural water under visible light irradiation. The initial degradation rate of MC-LR was fastest under acidic conditions (3.50 ± 0.02 × 10(-3) μM min(-1) at pH 3.0) and decreased to 2.29 ± 0.07 × 10(-3) and 0.54 ± 0.02 × 10(-3) μM min(-1) at pH 5.7 and 7.1, respectively. Attractive forces between the opposite charged MC-LR and NF-TiO(2) are likely responsible for the enhancement in the photocatalytic decomposition of MC-LR resulting from increased interfacial adsorption. For carbonate buffered solutions, the photocatalytic activity of NF-TiO(2) was reduced when increasing the carbonate concentration up to 150 mg CaCO(3) L(-1). The scavenging of radical species by the bicarbonate ion at pH 7.1 is discussed. In the presence of NOM, the degradation rates decreased as pH and initial concentration of the NOM increased. The inhibition was higher with fulvic acid than humic acid under alkaline conditions. Oxygenated solution yields higher NF-TiO(2) photocatalytic degradation of MC-LR compared to nitrogen sparged solution at pH 5.7. The involvement of specific reactive oxygen species implicated in the photodegradation is proposed. Finally, no significant degradation is observed with various natural waters spiked with MC-LR under visible light (λ > 420 nm) but high removal was achieved with simulated solar light. This study provides a better understanding of the interactions and photocatalytic processes initiated by NF-TiO(2) under visible and solar light. The results indicate solar photocatalytic oxidation is a promising technology for the treatment of water contaminated with cyanotoxins.
    Water Research 06/2011; 45(12):3787-96. DOI:10.1016/j.watres.2011.04.036 · 5.53 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The whole structure of higher plants is generated dynamically throughout the life cycle by the activity of stem cell niches at the apex of shoot and root. Hormone molecules and many transcription factors cooperate to balance the stem cell maintenance and differentiation. It is becoming increasingly clear that microRNA (miRNA) molecules are also participants in these processes. Here, we highlight the advances that have been made in regarding the roles of miRNAs in plant stem cell control. These advances provide a framework for our understanding of how signals are integrated to specify and position the stem cell niches in plants.
    Biochemical and Biophysical Research Communications 06/2011; 409(3):363-6. DOI:10.1016/j.bbrc.2011.04.123 · 2.30 Impact Factor
Show more