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In this study, a simple and low-cost method to synthesize iron(III) oxide nanopowders in large quantity was successfully developed for the photocatalytic degradation of microcystin-LR (MC-LR). Two visible light-active iron(III) oxide samples (MG-9 calcined at 200 °C for 5 h and MG-11 calcined at 180 °C for 16 h) with a particle size of 5-20 nm were prepared via thermal decomposition of ferrous oxalate dihydrate in air without any other modifications such as doping. The synthesized samples were characterized by X-ray powder diffraction, 57 Fe Mössbauer spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller (BET) specific surface area analysis, and UV-visible diffuse reflectance spectroscopy. The samples exhibited similar phase composition (a mixture of α-Fe 2 O 3 and γ-Fe 2 O 3 ), particle size distribution (5-20 nm), particle morphology, and degree of agglomeration, but different specific surface areas (234 m 2  g -1 for MG-9 and 207 m 2  g -1 for MG-11). The results confirmed higher photocatalytic activity of the catalyst with higher specific surface area. The highest photocatalytic activity of the sample to decompose MC-LR was observed at solution pH of 3.0 and catalyst loading of 0.5 g L -1 due to large amount of MC-LR adsorption, but a little iron dissolution of 0.0065 wt% was observed. However, no iron leaching was observed at pH 5.8 even though the overall MC-LR removal was slightly lower than at pH 3.0. Thus, the pH 5.8 could be an appropriate operating condition for the catalyst to avoid problems of iron contamination by the catalyst. Moreover, magnetic behavior of γ-Fe 2 O 3 gives a possibility for an easy separation of the catalyst particles after their use.

Cylindrospermopsin is an important cyanobacterial toxin found in water bodies worldwide. The ever-increasing and global occurrence of massive and prolonged blooms of cylindrospermopsin-producing cyanobacteria poses a potential threat to both human and ecosystem health. Its toxicity is associated with metabolic activation and may involve mechanisms that adversely affect a wide variety of targets in an organism. Cylindrospermopsin has been shown to be cytotoxic, dermatotoxic, genotoxic, hepatotoxic in vivo, developmentally toxic, and may be carcinogenic. Human exposure may occur through drinking water, during recreational activities and by consuming foods in which the toxin may have bioaccumulated. Drinking water shortages of sufficient quality coupled with growing human pressures and climate variability and change necessitate an integrated and sustainable water management program. This review presents an overview of the importance of cylindrospermopsin, its detection, toxicity, worldwide distribution, and lastly, its chemical and biological degradation and removal by natural processes and drinking water treatment processes.

We have demonstrated heterogeneous photocatalytic degradation of microcystin-LR (MC-LR) by visible light activated carbon doped TiO(2) (C-TiO(2)) nanoparticles, synthesized by a modified sol-gel route based on the self-assembly technique exploiting oleic acid as a pore directing agent and carbon source. The C-TiO(2) nanoparticles crystallize in anatase phase despite the low calcination temperature of 350 °C and exhibit a highly porous structure that can be optimized by tuning the concentration of the oleic acid surfactant. The carbon modified nanomaterials exhibited enhanced absorption in the broad visible light region together with an apparent red shift in the optical absorption edge by 0.5 eV (2.69 eV), compared to the 3.18 eV of reference anatase TiO(2). Carbon species were identified by x-ray photoelectron spectroscopy analysis through the formation of both Ti-C and C-O bonds, indicative of substitution of carbon for oxygen atoms and the formation of carbonates, respectively. Electron paramagnetic resonance spectroscopy revealed the formation of two carbon related paramagnetic centers in C-TiO(2), whose intensity was markedly enhanced under visible light illumination, pointing to the formation of localized states within the anatase band gap, following carbon doping. The photocatalytic activity of C-TiO(2) nanomaterials was evaluated for the degradation of MC-LR at pH 3.0 under visible light (λ > 420 nm) irradiation. The doped materials showed a higher MC-LR degradation rate than reference TiO(2), behavior that is attributed to the incorporation of carbon into the titania lattice.

Highlights: [•] Nine products identified during visible light-activated NF-TiO2 photocatalysis. [•] The observed intermediates suggest a significant role of hydroxyl radical. [•] The proposed degradation pathways remove the toxic portion of MC-LR. [Copyright &y& Elsevier]

Abstract: A sol–gel method based on the self-assembly technique with a nonionic surfactant was employed to synthesize visible-light-active Ch name="sbnd" />TiO2 films with rough surface for drinking water treatment. The enhancement of photocatalytic activity of Ch name="sbnd" />TiO2 films on the degradation of microcystin-LR (MC-LR) was subsequently evaluated under visible light irradiation. The films were characterized by XRD, ESEM, AFM, HRTEM, UV–vis diffuse reflectance spectroscopy (DRS), FT-IR, XPS, and porosimetry analysis. The results revealed that the physicochemical properties of the films, such as BET surface area, porosity, crystallite size and pore size distribution, could be controlled by adjusting the calcination temperature. Higher surface area, smaller crystallite size, narrow pore size distribution, and very high surface roughness (360nm) were obtained for C TiO2 films calcined at 400°C. DRS showed that as-prepared Ch name="sbnd" />TiO2 films exhibited higher absorption in the visible light region and a red shift in the band gap transition due to C Ch name="sbnd" />TiO2 films effectively degraded MC-LR under visible light irradiation compared to the reference film. In particular, the film calcined at 400°C showed high mechanical stability during three consecutive cycles for MC-LR degradation. The enhancement on the photocatalytic activity of the Ch name="sbnd" />TiO2 films under visible light irradiation was attributed to the synergistic effects of carbon and nitrogen doping as well as the high surface roughness of the prepared films. [Copyright &y& Elsevier]

Abstract: Visible light-activated sulfur doped TiO2 nanocrystalline films were synthesized by a sol–gel method based on the self-assembly technique with nonionic surfactant to control nanostructure and an inorganic sulfur source (i.e., H2SO4). The films were characterized by UV–vis diffuse reflectance, XRD, TEM, Raman, AFM, ESEM, XPS, FT-IR, EDX, EPR and porosimetry. The results showed that the physicochemical properties of the films, such as BET surface area, porosity, crystallite size and pore size distribution could be controlled by the calcination temperature. The highest surface area, smallest crystallite size and narrow pore size distribution were obtained for sulfur doped TiO2 films calcined at 350°C, which exhibit very smooth surface with minimal roughness (<1nm). The optical absorption edge of sulfur doped TiO2 was red shifted with indirect bandgap energy of 2.94eV. Sulfur species distributed uniformly throughout the films were identified both as S2− ions related to anionic substitutional doping of TiO2 as well as S6+/S4+ cations, attributed mainly to the presence of surface sulfate groups. EPR measurements revealed a sharp signal at g =2.004, whose intensity correlated with the sulfur content and most importantly was markedly enhanced under visible light irradiation, implying the formation of localized energy states in the TiO2 band gap due to anion doping and/or oxygen vacancies. In terms of photocatalytic activity, films calcined at 350°C were the most effective for the degradation of hepatotoxin microcystin-LR (MC-LR) under visible light irradiation, while films calcined at 400°C and 500°C degraded MC-LR to a lower extent, following the evolution of the sulfur content with calcination temperature. The photocatalytic activity of the sulfur doped TiO2 film was stable during three consecutive experiments under visible light irradiation, confirming the mechanical stability and reusability of the doped nanostructured thin film photocatalysts. [Copyright &y& Elsevier]

The photocatalytic degradation of a cyanobacterial toxin, microcystin-LA (MC-LA), was studied in aqueous solutions under both simulated solar light and visible light irradiation. Neat TiO 2 and carbon-based TiO 2 materials, prepared with carbon nanotubes (CNT) or graphene oxide (GO), were compared. The highest photocatalytic activity was obtained with a GO-TiO 2 composite comprising 4 wt.% of carbon content (GO-TiO 2 -4). Complete conversion of MC-LA was achieved under solar light irradiation in 5 min. GO-TiO 2 -4 was also active under visible light illumination, with 88% of MC-LA removal in 2 h. The high photocatalytic activity of GO-TiO 2 -4 was attributed to the optimal assembly and interfacial coupling between the TiO 2 nanoparticles and the GO sheets that can effectively inhibit electron/hole recombination. Reaction intermediates of MC-LA photocatalytic degradation were also identified by LC/Q-TOF and LC/MS/MS, most of them resulting from the attack of hydroxyl radicals to the MC-LA molecule under solar light irradiation. [ABSTRACT FROM AUTHOR]

Highlights: [•] S, N and C co-doped polymorphic TiO2 was synthesized with a modified sol–gel method. [•] The co-doped TiO2 exhibited high surface area and visible light-absorption. [•] CDPM300 showed highest visible light photocatalytic activity for microcystin-LR. [•] Potential environmental application of such visible light-sensitized photocatalysts. [ABSTRACT FROM AUTHOR]

Abstract: Cyanobacteria blooms pose an environmental hazard because of the release of water soluble toxic compounds, called cyanotoxins. Microcystins (MCs), hepatotoxic cyclic peptide toxins, are the most widespread cyanotoxins with microcystin-LR (MC-LR) the most common and toxic variant. Health effects of MCs have resulted in the need of using efficient treatment methods for the removal of this class of toxins in water supplies. While physical treatment methods can remove MCs at full or some extent from contaminated water, their function is primary separation of the whole toxins as intact molecules and further processing is required. On the other hand, chemical oxidation processes are a promising alternative treatment option due to the potential of complete destruction of the MCs, transformation to less toxic by-products, and even complete mineralization. MCs reactivity towards different conventional oxidants is strongly affected by water quality parameters like pH, DOC and oxidant dose. Although there is a general trend for MCs oxidation (ozone>permanganate>chlorine>>>chlorine-based oxidants), the selection of the appropriate oxidant for toxin elimination during water treatment should be assessed for each particular source of water. Although advanced oxidation processes are generally more effective on MCs degradation than conventional oxidation processes, scale-up studies are needed before these methods are considered as economically-feasible and practical sustainable alternatives in water treatment facilities. In this review, recent literature concerning treatment of MCs in water by conventional and advanced oxidation processes are reviewed and discussed in terms of the degree of degradation, reaction kinetics, identity and toxicity of oxidation by-products and possible degradation pathways. [Copyright &y& Elsevier]