Photocatalytic Degradation Of microcystin-LR Research Articles

Coating TiO2 with MIL-101(Fe) to decarboxylate D-Glu and D-MeAsp of microcystin-LR from HA-rich water: Diminishing the inhibitory effect of humic acids

Humic acids (HA) released during algal bloom poses a key challenge for efficient photocatalytic degradation of Microcystin-LR (MC-LR) due to their scavenging function on active species. Herein, MIL-101(Fe)/TiO2-P25 (M/P) was constructed to diminish the inhibitory effect of HA on the photocatalytic degradation of MC-LR. Results showed that MC-LR could be efficiently removed assigning to the photogenerated holes (h+) and superoxide radical (O2•−) oxidation under visible light irradiation, where the carboxy groups of D-glutamic acid (Glu) and methyl-D-aspartic acid (MeAsp), and Adda side chain related to MC-LR biotoxicity were selectively destroyed to achieve MC-LR detoxication. More importantly, HA exerted non-inhibitory effect on MC-LR removal by M/P. The counteracting mechanisms were studied. Firstly, the location of TiO2 in the pore structure of MIL-101(Fe) could occupy the adsorption sites of HA, and decrease the HA adsorption on M/P. Furthermore, XPS analyses suggested the coordination of unsaturated Fe metal sites on the surface of M/P hybrids complexed with –OH and –COOH of HA, which could accelerate the electron transfer and reduce hole consumption. Thus, the inhibitory effect of HA was alleviated during photocatalytic MC-LR treatment. This work offers a possible way to remove MC-LR in an abundant HA matrix water system efficiently.

The performance of TiO2 /NaY-zeolite nanocomposite in photocatalytic degradation of Microcystin-LR from aqueous solutions: Optimization by response surface methodology (RSM)

Background: Microcystin (MC) is a hepatotoxic and carcinogenic toxin that is generated by cyanotoxins which can have adverse effects on the human health. Therefore, it is very important to remove it from the environment. This study was performed to investigate the efficiency of titanium dioxide (TiO2)/NaY-zeolite (T/N-Z) nanocomposite for removal of MC-LR under ultraviolet light. Methods: In the present study, T/N-Z nanocomposite was synthesized using the hydrothermal method. Specification of the photocatalysts was determined by the field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR) spectra. The response surface methodology (RSM) was used to survey the effects of operating variables such as pH, contact time, and catalyst dose on the removal of MC-LR. The MC-LR concentration was measured by high-performance liquid chromatography (HPLC). Results: It was revealed that the increase of contact time and catalyst dose had a positive effect on enhancing the removal efficiency of MC-LR, but pH had a negative effect. Finally, the maximum MC-LR removal efficiency was 97.63, which occurred at pH = 5, contact time = 120 min, and catalyst dose = 1.2 g/L. Conclusion: In general, T/N-Z composite in aqueous solutions under the UV light can easily decompose MC-LR and it can also be proposed as an efficient composite for removal of MC-LR from contaminated water.

Photocatalytic degradation of microcystin-LR using BiVO4 photocatalysts under visible light irradiation: modelling by response surface methodology (RSM)

ABSTRACT The microcystin-LR (MC-LR) is a potentially dangerous toxin for animals and human health. So, MC-LR removal from the environment by the use of photocatalysts is recommended. Generally, traditional photocatalysts are dependent on UV light and consume high energy and also produce high heat. So, the use of photocatalysts with low-energy consumption, feasible, and reliable properties that activate in the visible light is very important. The aim of the present study was the removal of microcystin-LR (MC-LR) in visible light by synthesised bismuth vanadate (BiVO4) with the hydrothermal method. The BiVO4 characteristics were determined by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FT-IR) spectra. The Response Surface Methodology (RSM) was used to survey the effects of operating variables such as pH, contact time, and catalyst dose on MC-LR removal. The results showed that the increase of contact time and catalyst dose had a positive effect on enhancing the removal efficiency of MC-LR, but the effect of pH was negative. The maximum removal efficiency of MC-LR at pH = 5, contact time = 180 minutes and catalyst dose = 0.5 g/l was equal to 93.19%. Therefore, BiVO4 as an innovative photocatalyst had a suitable effect on the MC-LR degradation under visible light.

Photocatalytic degradation of microcystin-LR and anatoxin-a with presence of natural organic matter using UV-light emitting diodes/TiO2 process

Cyanotoxins are released into water bodies when cyanobacterial blooms occur. Representative cyanotoxins are microcystin-LR (MC-LR), which is one of the most-frequently detected, and anatoxin-a (ANTX), threatening human health through the liver damage and nervous system, respectively. One of the advanced oxidation processes, UV/TiO2 process is effective for MC-LR degradation; however, applying conventional UV lamps is an ongoing issue owing to disadvantages, such as use of mercury and high energy consumption. To resolve these, this study aims to use light emitting diodes (LEDs), developed by the Lumens Co., combined with commercial TiO2 for the removal of two types of cyanotoxins, MC-LR and ANTX. With 0.05 g L−1 of TiO2, over 99.9 % of the MC-LR was degraded in 15 min. Under acidic conditions, MC-LR and TiO2 were converted into MC-LRH− and TiO2+, then, electrostatic attraction was generated between them. Therefore, the degradation rate constant (k) of MC-LR was higher under acidic conditions than neutral or basic conditions. The natural organic matter (NOM) served as a scavenger of OH, reducing the MC-LR degradation rate under UV-LED/TiO2 process. 35%–53.6% degradation of NOM due to the decrease in humic substances and building blocks, and the increase in low molecular weight neutrals and low molecular weight acids. The degradation efficiency of MC-LR was higher than that of ANTX, and both cyanotoxins were completely degraded within 15 min. The k of MC-LR and ANTX were similar but significantly reduced due to the NOM and alkalinity of the water collected from the Han River.

Photocatalytic degradation of microcystin-LR by modified high-energy {001} titanium dioxide: Kinetics and mechanism study of HF8

Photocatalytic degradation of microcystin-LR by modified high-energy {001} titanium dioxide: Kinetics and mechanism study of HF8

Photocatalytic degradation of microcystin-LR with a nanostructured photocatalyst based on upconversion nanoparticles@TiO2 composite under simulated solar lights

In this work, we prepared advanced upconversion nanoparticle coated with TiO2 photocatalysts (NaYF4:Yb,Tm@TiO2) to utilize not only UV energy but also the large portion of NIR energy in order to improve the utilization efficiency of solar lights. The MC-LR (10 μg/mL) degradation rate can be approached 100% within 30 min at the concentration of NaYF4:Yb,Tm@TiO2 0.4 mg/mL and initial pH value 4, while 61%, using pure TiO2 (P25) under simulated solar lights. The reaction processes were studied and fitted with the pseudo-first-order kinetic model. Highly reactive hydroxyl radicals (•OH) were found to be the major reactive species. Meanwhile, seven degradation intermediates of MC-LR were examined by liquid chromatography/mass spectrometry and the degradation mechanism was analyzed. The main degradation pathways were proposed based on the molecular weight of the intermediates and the reaction mechanism are hydroxylation on the diene bonds and the aromatic ring of Adda. The products were evaluated to be nontoxic based on the construction of the intermediates. This study demonstrated that the NIR energy can be used as the driving source for photocatalysis besides the UV and the NIR-responsed photocatalysis had a high-efficiency and potential for MC-LR degradation.

Removal of Microcystins by Highly Efficient Photo-catalyst Bi2WO6-Activated Carbon Under Simulated Light

The photo-catalytic activities of several Bi2WO6 with various activated carbon (AC) contents were studied for the photo-catalytic degradation of microcystin-LR (MC-LR) and microcystin-RR (MC-RR) under simulated light. Some characterizations of the materials were carried out. Activated carbon increased the reaction rates in the degradation of MC-LR. A significant improvement in the photo-catalytic activity under simulated light was achieved with the 5 wt% activated carbon content when compared with pristine Bi2WO6 or with materials with other content activated carbon additions. Factors besides adsorption capability and surface areas effects may also contribute to the improvement. The kinetics of photo-catalytic degradation of MC-LR and MC-RR by Bi2WO6-activated carbon were explored. The application of the catalyst under sunlight was proven to be better than under simulated light.

Photocatalytic degradation of MC-LR in water by the UV/TiO2/H2O2 process

The ultraviolet (UV)/titanium dioxide (TiO2)/hydrogen peroxide (H2O2) process (UTHP) has been proven to be effective in removing organics because of its high production of free radicals. In this study, UTHP was further investigated for the photocatalytic degradation of microcystin-LR (MC-LR). Results showed that three mechanisms could realize MC-LR photocatalytic degradation using TiO2. H2O2 could effectively inhibit recombination and considerably improve the production of radicals and superoxides. From a correlation of the removal rate with the isomerization and decomposition of MC-LR under UV irradiation it was inferred that isomerization was crucial for MC-LR degradation during photocatalysis given the vulnerability of the exposed conjugated double bonds. The photocatalysis of MC-LR was apparently dependent on pH and MC-LR initial concentration. Under the optimum conditions of pH 3.5, 0.05 g/L TiO2, and 0.05 mmol/L H2O2, 100% MC-LR (308 μg/L) could be removed within 60 min. This process was accompanied by a synergistic effect during the initial 10 min.

Photocatalytic Degradation of Microcystin-LR by Bismuth Tungstate

Photocatalytic Degradation of Microcystin-LR by Bismuth Tungstate

Photocatalytic Degradation of Microcystin-LR and Off-Odor Compounds in Water under UV-A and Solar Light with a Nanostructured Photocatalyst Based on Reduced Graphene Oxide–TiO2 Composite. Identification of Intermediate Products.

Microcystin-LR (MC-LR) is the most common and toxic variant of the group of microcystins (MCs) produced during the formation of harmful cyanobacterial blooms. Geosmin (GSM) and 2-methylisoborneol (MIB) may also be produced during cyanobacterial blooms and can taint water causing undesirable taste and odor. The photocatalytic degradation of MC-LR, GSM, and MIB in water under both UV-A and solar light in the presence of reduced graphene oxide–TiO2 composite (GO–TiO2) was studied. Two commercially available TiO2 materials (Degussa P25 and Kronos) and a reference TiO2 material prepared in the laboratory (ref-TiO2) were used for comparison. Under UV-A irradiation, Degussa P25 was the most efficient photocatalyst for the degradation of all target analytes followed by GO–TiO2, ref-TiO2, and Kronos. Under solar light irradiation GO–TiO2 presented similar photocatalytic activity to Degussa P25, followed by Kronos and ref-TiO2 which were less efficient. Intermediate products formed during the photocatalytic process with GO–TiO2 under solar light were identified and were found to be almost identical to those observed by Degussa P25/UV-A. Assessment of the residual toxicity of MC-LR during the course of treatment with GO–TiO2 showed that toxicity is proportional only to the remaining MC-LR concentration. The photocatalytic performance of GO–TiO2 was also evaluated under solar light illumination in real surface water samples, and GO–TiO2 proved to be effective in the degradation of all target compounds.

Photocatalytic degradation of microcystin-LR using TiO2 nanotubes under irradiation with UV and natural sunlight

In order to investigate the catalytic performance of anodic TiO2 nanotubes and their practical application in the treatment of refractory microcystins (MCs) in natural-water samples, TiO2 nanotubes of diameter of 50–80 nm were fabricated by anodization in C2H2O4·2H2O containing NH4F. Under irradiation with natural sunlight, MC-LR was totally degraded after 1 d using the anodic TiO2 nanotubes. In contrast, the removal efficiency without TiO2 nanotubes was as low as 47.7% within 20 d. In addition, a mixture of anatase and rutile TiO2 gave higher photocatalytic activity than the single phase did. The pH also influenced the adsorption capacity of the TiO2 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.

Photocatalytic degradation of microcystin-LR in aqueous solutions

In this work, the photocatalytic degradation of aqueous microcystin-LR was studied using TiO2 and ZnO as photocatalysts. The process was optimised and characterised at the bench scale (200mL); both semiconductors exhibited a high degradation capacity at reaction times of 1min (degradation greater than 95%). The transient species that were observed indicate that the degradation occurs via the multiple hydroxylation and elimination of the labile peptide residues of the molecule. When photocatalysis was applied in a continuous treatment system (20–50L), the photocatalytic process exhibited a high degradation efficiency, which resulted in residual microcystin-LR concentrations that were less than 1μgL−1 (C0=5μgL−1).

Unique Ability of BiOBr To Decarboxylate d-Glu and d-MeAsp in the Photocatalytic Degradation of Microcystin-LR in Water

Bismuth oxide bromide, BiOBr, was used to catalyze the degradation of microcystin-LR (MC-LR) in water at neutral pH under visible light. During the investigation, twelve intermediates from MC-LR decomposition were identified by LC-MS. In addition to attacking MC-LR at the typically susceptible sites (i.e., the conjugated double bond of the Adda chain and terminal unsaturated bond of the Mdha chain), the BiOBr photocatalyst has the remarkable ability to decarboxylate the free acid groups on d-glutamic acid (Glu) and methyl-d-aspartic acid (MeAsp). This reactivity has not been previously observed with TiO2 photocatalysis or with other MC-LR treatments in which decarboxylation does not occur until the MC-LR ring has been cleaved or mineralized to CO2. Some expected intermediate products were detected with oxygen-18 labeling by using H2(18)O as the solvent to confirm that the decarboxylation process is mediated by BiOBr. Results from characterizing the intermediates as well as oxygen-18 labeling studies indicates that oxidative decarboxylation of MC-LR by BiOBr photocatalysis is not always initiated by hydroxyl radical attack (and/or interaction with a hole followed by hydrolysis) proposed mechanism in TiO2 photocatalysis, whereas likely caused by a direct interaction between photoinduced hole of BiOBr and free carboxyl groups of MC-LR. This unusual decarboxylation behavior seems to be associated with the particular valence band and conduction band state of BiOBr photocatalyst. Also under BiOBr catalysis, a very stable guanidine group of l-arginine (l-Arg) that is nonreactive with TiO2 photocatalysis is converted to an amino group and subsequently oxidized to a nitro group during the decomposition of MC-LR. This reaction sequence is also related to decarboxylation because the guanidine conversion requires a completely or partially decarboxylated precursor. Our results indicate that BiOBr, a photocatalyst that selectively destroys sites crucial to MC-LR toxicity, shows great promise as a means of effectively treating drinking water.

Visible-light-driven photocatalytic degradation of microcystin-LR by Bi-doped TiO2

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 efficient. After irradiation with visible light for 12 h the original MC-LR was removed completely, and 78% of the organic carbon was mineralized into CO2 after irradiation for 20 h. The hydroxyl radical (·OH) is the major active species responsible for the degradation reaction. Identified intermediates primarily originate from attack of ·OH radicals on the double bonds between C4 and C5 (C6 and C7) of Adda and the ethylenic bond of Mdha in MC-LR. Some peptide bonds are also broken with longer irradiation time.

Unveiling New Degradation Intermediates/Pathways from the Photocatalytic Degradation of Microcystin-LR

Mass spectrometry was utilized for structural identification of the intermediates formed during the photocatalytic degradation of the cyanotoxin, microcystin-LR with immobilized TiO2 photocatalysts at neutral pH. Most of the intermediates reported herein have not been found in prior studies. Results indicate that MC-LR degradation is initiated at four sites of the toxin; three on the Adda amino acid (aromatic ring, methoxy group, and conjugated double bonds) and one on the cyclic structure (Mdha amino acid). Several intermediates gave multiple peaks in the TIC (m/z = 1011.5, 1029.5, 1063.5), which were deduced to be geometrical or constitutional isomers. This is the first study that reports the hydroxylation of the aromatic ring and the demethoxylation of MC-LR with TiO2 photocatalysis. The most targeted site was the conjugated diene bonds because of their location in the MC-LR structure. Isomerization at the C4-C5 and C6-C7 of the diene bond of the Adda chain was a direct result of hydroxyl radical addition/substitution. Based on the above, we concluded that oxidation and isomerization of the diene bonds of MC-LR occurred simultaneously. Other steps included hydroxyl substitution, further oxidation, and bond cleavage. As the reaction time progressed, simultaneous oxidation of the Adda chain and the cyclic structure occurred.

Mesoporous Nitrogen-Doped TiO2 for the Photocatalytic Destruction of the Cyanobacterial Toxin Microcystin-LR under Visible Light Irradiation

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 TiO2 (N-TiO2) 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 TiO2 and as a nitrogen dopant for its visible light response. The resulting N-TiO2 exhibited significantly enhanced structural properties including 2-8 nm mesoporous structure (porosity 44%) and high surface area of 150 m2/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 TiO2 lattice. Due to its narrow band gap at 2.65 eV, N-TiO2 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-TiO2 due to electrostatic attraction forces between negatively charged MC-LR and +6.5 mV charged N-TiO2. Even under UV light, MC-LR was decomposed 3-4 times faster using N-TiO2 than control TiO2. The degradation pathways and reaction intermediates of MC-LR were not directly related to the energy source for TiO2 activation (UV and visible) and nature of TiO2 (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.

Solar Pilot-scale Photocatalytic Degradation of Microcystin-LR

AbstractA solar immobilized-catalyst photocatalytic reactor design and TiO

Photocatalytic Degradation of Microcystin-LR: Conceptual Model and Pilot Scale Studies

Photocatalytic Degradation of Microcystin-LR: Conceptual Model and Pilot Scale Studies

Photocatalytic Degradation of Microcystin-LR: Conceptual Model and Pilot Scale Studies

Photocatalytic Degradation of Microcystin-LR: Conceptual Model and Pilot Scale Studies