Photodegradation of Microcystin-LR Using Visible Light-Activated C/N-co-Modified Mesoporous TiO2 Photocatalyst (original) (raw)
Related papers
Environmental Science & Technology, 2007
The presence of the harmful cyanobacterial toxins in water resources worldwide drives the development of an innovative and practical water treatment technology with great urgency. This study deals with two important aspects: the fabrication of mesoporous nitrogen-doped TiO 2 (N-TiO 2 ) photocatalysts and their environmental application for the destruction of microcystin-LR (MC-LR) under visible light. In a nanotechnological sol-gel synthesis method, a nitrogen-containing surfactant (dodecylammonium chloride) was introduced as a pore templating material for tailor-designing the structural properties of TiO 2 and as a nitrogen dopant for its visible light response. The resulting N-TiO 2 exhibited significantly enhanced structural properties including 2-8 nm mesoporous structure (porosity 44%) and high surface area of 150 m 2 /g. Red shift in light absorbance up to 468 nm, 0.9 eV lower binding energy of electrons in Ti 2p state, and reduced interplanar distance of crystal lattices proved nitrogen doping in the TiO 2 lattice. Due to its narrow band gap at 2.65 eV, N-TiO 2 efficiently degraded MC-LR under visible spectrum above 420 nm. Acidic condition (pH 3.5) was more favorable for the adsorption and photocatalytic degradation of MC-LR on N-TiO 2 due to electrostatic attraction forces between negatively charged MC-LR and +6.5 mV charged N-TiO 2 . Even under UV light, MC-LR was decomposed 3-4 times faster using N-TiO 2 than control TiO 2 . The degradation pathways and reaction intermediates of MC-LR were not directly related to the energy source for TiO 2 activation (UV and visible) and nature of TiO 2 (neat and nitrogen-doped). This study implies a strong possibility for the in situ photocatalytic remediation of contaminated water with cyanobacterial toxins and other toxic compounds using solar light, a sustainable source of energy.
Applied Catalysis B: Environmental, 2009
This study investigated the use of thin transparent TiO 2 photocatalytic films, prepared with novel sol-gel methods containing surfactants as templating materials, for the degradation of the cyanotoxin, microcystin-LR (MC-LR). MC-LR is an emerging contaminant from the Contaminant Candidate Lists (CCLs 1-3) of the USEPA. The effects of UV-A radiation, solution pH, initial toxin concentration, coated surface area of the TiO 2 films and their structural properties (porosity, crystallinity and thickness) on the degradation rate of MC-LR were investigated. Photolysis did not occur with UV-A radiation. Acidic pH was more efficient for the degradation of MC-LR due to toxin interaction with the catalyst surface and increased adsorption into the porous films. The degradation profiles of the toxin at different initial concentrations were fitted with pseudo-first order kinetics. Films prepared with three coatings (0.3 mm thickness) had the best performance at acidic and neutral pH, while the exclusion of surfactant from the preparation method resulted in non-porous films with decreased performance. The parameter that mostly affected the degradation rate was the solution pH. The toxicity of the treated samples, evaluated by an in-house protein phosphatase 1 assay, indicated that treatment with the TiO 2 photocatalytic films indeed resulted in complete removal of MC-LR's toxicity. ß
Journal of Environmental Health Science and Engineering, 2019
Microcystin-Leucine Arginine (MC-LR) is one of the most studied cyanotoxins due to its toxicity and abundant that cause health hazards for humans through of the drinking water. In this study, BiVO 4 /TiO 2 nanocomposite was synthesized by hydrothermal method and employed for the removal of MC-LR. The characteristics of the catalysts were determined by FESEM, XRD and FTIR spectra. Response surface methodology (RSM) was applied to assess the effects of operating variables (pH, contact time, and catalyst dose) on the MC-LR removal. The coefficient of determination (R 2) was calculated 98.7% for the response. The residual concentration of MC-LR was measured by high-performance liquid chromatography (HPLC). The results show that the highest removal efficiency of MC-LR was 98% under the optimum conditions (pH = 5, contact time = 90 min, and catalyst dose = 0.5 g/l). MC-LR decomposition efficiency by BiVO 4 /TiO 2 nanocomposite was enhanced by pH reduction and increasing of contact time and catalyst dose. The prepared BiVO 4 /TiO 2 nanocomposite with technological potential can be used directly in environmental preservation, specifically in the decontamination of MC-LR from aqueous solutions.
Visible-light-driven photocatalytic degradation of microcystin-LR by Bi-doped TiO 2
Research on Chemical Intermediates, 2011
Bi-doped nano-crystalline TiO2 (Bi–TiO2) has been synthesized by sonocrystallization at low temperature. The Bi–TiO2 materials have narrower bandgaps than pristine TiO2, which endow them with significant visible light absorption. Accordingly, these materials had enhanced photocatalytic activity in the degradation of organic dye pollutants and the cyanotoxin microcystin-LR (MC-LR) under visible irradiation. It was found that degradation of MC-LR is rather
Applied Catalysis B: Environmental, 2014
The effect of using only visible light to induce nitrogen-and fluorine-doped titanium dioxide (NF-TiO 2) photocatalysis of degradation products of microcystin-LR (MC-LR), the most common problematic cyanotoxin, was explored by looking at the intermediate degradation products. Although the degradation mechanisms and products of conventional UV-based TiO 2 photocatalysis of MC-LR have been well elucidated, the same is not true for visible light-based TiO 2 photocatalysis. The results of LC/MS 2 (and in one case LC/MS 3) indicated that the intermediates are not drastically altered in comparison to traditional TiO 2 photocatalysis using UV light. The data hint that the degradation is driven by hydroxyl radicals, as is UV-based TiO 2 photocatalysis, although the mechanism for producing hydroxyl radicals is unclear since studies indicate drastically slower kinetics for visible light-based photocatalysis of MC-LR. Notably, the data indicate that visible light-induced NF-TiO 2 photocatalysis degraded the portion of MC-LR that is responsible for biological toxicity. As a result of this, it was concluded that doping TiO 2 with nitrogen and fluorine is an effective method for increasing utilization of visible light while degrading MC-LR in water, although it should still be noted that degradation kinetics are still slower than UV-based TiO 2 photocatalysis.
Applied Catalysis B: Environmental, 2010
This study reports on the synthesis, characterization and environmental application of immobilized nitrogen and fluorine co-doped TiO 2 (NF-TiO 2 ) photocatalyst. A fluorosurfactant-based sol-gel approach was employed to enhance the physicochemical properties and photocatalytic activity of NF-TiO 2 under visible and UV light for the degradation of the hepatotoxin microcystin-LR (MC-LR). The films were characterized by XRD, environmental scanning electron microscope (ESEM), TEM, AFM, EPR, micro-Raman, X-ray photoelectron spectroscope (XPS), UV-vis spectroscopy and porosimeter analysis. The results revealed that by modifying the molar ratio of the fluorosurfactant, we could effectively control the physicochemical properties and obtain films with high BET surface area and porosity, small crystallite size and narrow pore size distribution. UV-vis spectroscopy showed an increase in the absorption capacity of NF-TiO 2 in the visible light range compared to reference films. The existence of interstitial nitrogen and substitutional fluorine in the titanium dioxide (TiO 2 ) lattice was determined by XPS. Comparative EPR measurements between the co-doped and reference samples identified distinct N spin species in NF-TiO 2 , with a high sensitivity to visible light irradiation. The abundance of these paramagnetic centers verifies the formation of localized intra-gap states in TiO 2 and implies synergistic effects between fluorine and nitrogen dopants. Micro-Raman spectroscopy showed the growth of small amounts of brookite concomitantly with the major anatase TiO 2 phase, which could promote the system's photocatalytic activity through the formation of anatase/brookite heterojunctions. Analysis of the lower frequency E g anatase Raman mode indicated the occurrence of size effects reflecting phonon confinement in the anatase nanocrystallites as well as deviations from stoichiometry due to structural defects in the co-doped sample. NF-TiO 2 films effectively degraded MC-LR under visible and UV light compared to reference film. Similar MC-LR degradation rates under visible light after three cycles revealed high mechanical stability and no irreversible changes of the film during photocatalysis. This process has the potential of providing environmentally benign routes for drinking water treatment with solar powered photocatalytic systems.
Photocatalytic Degradation of Microcystins by TiO2 Using UV-LED Controlled Periodic Illumination
Catalysts
Toxic microcystins (MCs) produced by freshwater cyanobacteria such as Microcystis aeruginosa are of concern because of their negative health and economic impacts globally. An advanced oxidation process using UV/TiO2 offers a promising treatment option for hazardous organic pollutants such as microcystins. The following work details the successful degradation of MC-LA, MC-LR, and MC-RR using a porous titanium–titanium dioxide (PTT) membrane under UV-LED light. Microcystin quantitation was achieved by sample concentration and subsequent LC–MS/MS analysis. The PTT membrane offers a treatment option that eliminates the need for the additional filtration or separation steps required for traditional catalysts. Controlled periodic illumination was successfully used to decrease the total light exposure time and improve the photonic efficiency for a more cost-effective treatment system. Individual degradation rates were influenced by electrostatic forces between the catalyst and differently ...
Photocatalytic degradation of microcystin-LR in aqueous solutions
Chemosphere, 2013
In order to investigate the catalytic performance of anodic TiO 2 nanotubes and their practical application in the treatment of refractory microcystins (MCs) in natural-water samples, TiO 2 nanotubes of diameter of 50-80 nm were fabricated by anodization in C 2 H 2 O 4 ·2H 2 O containing NH 4 F. Under irradiation with natural sunlight, MC-LR was totally degraded after 1 d using the anodic TiO 2 nanotubes. In contrast, the removal efficiency without TiO 2 nanotubes was as low as 47.7% within 20 d. In addition, a mixture of anatase and rutile TiO 2 gave higher photocatalytic activity than the single phase did. The pH also influenced the adsorption capacity of the TiO 2 nanotubes. The order of MC-LR degradation efficiencies at different pH values was 3.5 > 8.0 > 10.0. After five repeated experiments on the degradation of MC-LR for 7 h, the degradation efficiency was still stable.
Sift Desk Journals, 2018
Background: Uniquely synthesised titanium dioxide (TiO2) with high-energy {001} exposed facets denoted HF8 was used for the photocatalytic degradation of microcystin-LR (MC-LR) under ultraviolet irradiation at 365 nm. Methods: The influence of various conditions including environmental pH, nutrient anions, TiO2 dose, and MC-LR concentration was studied, and concentration of MC-LR measured using liquid chromatography-tandem mass spectrometry. Results: Within 120 min, 72.6% of an environmentally relevant MC-LR concentration (120 µg/L) was degraded under pH conditions ranging from 3 to 11. Stability tests revealed no loss of TiO2 activity after four applications of the same dose, indicating its stability, reusability, and potential to be re-used for sustainable remediation of MC-LR in eutrophic waters. Mechanism studies suggested that the reaction obeyed the pseudo-first-order equation and that hydroxyl radicals are the major reactive intermediate contributing to the reaction. The structure elucidation of intermediates suggested that hydroxylation and bond cleavage between the Adda chain and Mdha site could be the initiation of reactions in the degradation of MC-LR by HF8 TiO2. Conclusion: The results present a fast, sustainable, and practical method using modified TiO2 to improve MC-LR remediation. Keywords: Degradation, Microcystin-LR, Photocatalysis, Titanium dioxide