Magnetic minerals from volcanic Ultisols as heterogeneous Fenton catalysts

This study was devoted to the evaluation of the effectiveness of Fenton catalysts, based on magnetically-concentrated portions of iron oxide-rich sand fractions from two magnetic Ultisols, derived from volcanic materials of southern Chile. The samples were labeled according to the municipality where the sample sites are geographically located, namely Metrenco and Collipulli, and were characterized with Mössbauer spectroscopy at 298 K and saturation magnetization (σ) measurements. Mössbauer data revealed a complex magnetic hyperfine structure for these magnetic portions from both soil-sand materials, suggesting relatively complex mineral assemblages. The monitored rate of H₂O₂ decomposition via heterogeneous Fenton reaction revealed that materials from the Collipulli soil are more efficient Fenton catalyst than are those from the Metrenco soil. The reasons for these differences are from now on being explored on basis of a more detailed chemical investigation of these samples.     

One-dimensional iron oxides nanostructures

Iron oxides,including α-Fe2O3,γ-Fe2O3,Fe3O4,etc.are one of the most widely investigated materials for their fundamental properties and potential applications.One-dimensional(1-D) iron oxides nanostructures are the focus of recent research activities because of their wide applications in magnetic refrigeration,information storage,electronics,catalysts,Li-ion battery,pigment,gas sensors,etc.This review covers the recent progress in the synthesis,properties and applications of 1-D iron oxides nanostructures.Th...     

Application of modified nanodiamonds as catalysts of heterogeneous and electrochemical catalyses

The possible use of modified nanodiamond powders in heterogeneous and electrochemical oxidation catalyses is analyzed. It is shown that the efficiency of oxidation catalysis depends on the content of atomic oxygen. The inference is drawn that the electrochemical modification of the surface of nanodiamond powders in a hydrochloric solution and the promotion of the surface with palladium are promising for the preparation of both catalysts of the oxidation of CO to CO₂ and electrodes of low-temperature fuel elements.     

Encapsulation of iron nanoparticles in alginate biopolymer for trichloroethylene remediation

Nanoscale zero-valent iron (NZVI) particles (10–90 nm) were encapsulated in biodegradable calcium-alginate capsules for the first time for application in environmental remediation. Encapsulation is expected to offers distinct advances over entrapment. Trichloroethylene (TCE) degradation was 89–91% in 2 h, and the reaction followed pseudo first order kinetics for encapsulated NZVI systems with an observed reaction rate constant (k _obs) of 1.92–3.23 × 10⁻² min⁻¹ and a surface normalized reaction rate constant (k _sa) of 1.02–1.72 × 10⁻³ L m⁻² min⁻¹. TCE degradation reaction rates for encapsulated and bare NZVI were similar indicating no adverse affects of encapsulation on degradation kinetics. The shelf-life of encapsulated NZVI was found to be four months with little decrease in TCE removal efficiency.     

FePt nanoparticles as heterogeneous Fenton-like catalysts for hydrogen peroxide decomposition and the decolorization of methylene blue

The potential effects of oxidized multi-walled carbon nanotubes (o-MWCNTs) with a length ranging from 50 to 630?nm on the development and physiology of wheat plants were evaluated by examining their effects on seed germination, root elongation, stem length, and vegetative biomass at a concentration ranging from 10 to 160???g/mL in the plant. Results indicated that after 7?days of exposure to the o-MWCNTs medium, faster root growth and higher vegetative biomass were observed, but seed germination and stem length did not show any difference as compared with controls. Moreover, a physiological study was conducted at cellular level using a traditional physiological approach to evidence the possible alterations in morphology, the cell length of root zone, and the dehydrogenase activity of seedlings. Transmission electron microscopy images revealed that o-MWCNTs could penetrate the cell wall and enter the cytoplasm after being taken up by roots. The cell length of root zone for the seedlings germinated and grown in the o-MWCNTs (80???g/mL) medium increased by 1.4-fold and a significant concentration-dependent increase in the dehydrogenase activity for the o-MWCNT-treated wheat seedlings was detected. These findings suggest that o-MWCNTs can significantly promote cell elongation in the root system and increase the dehydrogenase activity, resulting in faster root growth and higher biomass production.     

Thin film photocatalysis for environmental remediation: A status review

This review accounts, various metal oxide and metal sulfide thin films available for photodegradation of several organic compounds. Due to difficulties in recycling and to avoid rigorous recollection of powder catalysts, the thin film catalyst are gaining rapid attention for photocatalytic applications. The semiconducting thin films are growing as promising photocatalyst for water treatment. This review focuses mainly on the photocatalytic activity of metal oxide thin films in terms of its stability, charge transport and absorption properties. Thin film photocatalyst provides the increased efficiency and cost reduction of device. Furthermore, this review summarizes some key factors regarding the enhancement in photocatalytic performance of thin films.     

The surface chemistry of ZnO nanoparticles applied as heterogeneous catalysts in methanol synthesis

Zinc oxide has a variety of applications in catalysis both as support and as active phase for hydrogenation or dehydrogenation reactions. This review provides an overview of the surface chemistry of ZnO nanoparticles concerning the interaction with small molecules such as CO, CO₂, H₂, H₂O, and CH₃OH, which are relevant for the catalytic synthesis of methanol and the water gas shift reaction. These interactions were studied by combining surface-sensitive methods such as infrared spectroscopy, temperature-programmed desorption, and adsorption calorimetry. A thorough understanding of the processes occurring on the different exposed facets of the ZnO particles in an atmosphere of reactive gases was achieved based on the comparison with results obtained in ultra-high vacuum with single-crystalline surfaces, i.e. under well-defined conditions, and by using first-principles calculations.     

Preparation of FeCeOx by ultrasonic impregnation method for heterogeneous Fenton degradation of diclofenac

FeCeO_x has been successfully synthesized by ultrasonic impregnation method and applied in diclofenac removal in heterogeneous Fenton process. The effects of ultrasonic density, impregnation time, mole ratio of Fe and Ce and calcination temperature were investigated. Nitrogen adsorption/desorption, SEM, XRD, HRTEM, Raman and XPS analyses were characterized. Stability and reusability of FeCeO_x were evaluated. The results indicated that 83% degradation efficiency of diclofenac was achieved by FeCeO_x under the optimum preparation conditions. Fe ions were distributed uniformly in crystal structure and the solid solution structure of FeCeO_x with a lattice constriction was formed. Exposed crystalline plane (2 0 0) with a relatively high surface energy may be the main reason to provide high catalytic activity of FeCeO_x. Oxygen vacancies took part in catalytic process and a portion of them were oxidized after reaction. FeCeO_x showed an excellent chemical stability and reusability in heterogeneous Fenton process.     

Study of iron oxide nanoparticles in soil for remediation of arsenic

There is a growing interest in the use of nanoparticles for environmental applications due to their unique physical and chemical properties. One possible application is the removal of contaminants from water. In this study, the use of iron oxide nanoparticles (19.3 nm magnetite and 37.0 nm hematite) were examined to remove arsenate and arsenite through column studies. The columns contained 1.5 or 15 wt% iron oxide nanoparticles and soil. Arsenic experiments were conducted with 1.5 wt% iron oxides at 1.5 and 6 mL/h with initial arsenate and arsenite concentrations of 100 μg/L. Arsenic release occurred after 400 PV, and 100% release was reached. A long-term study was conducted with 15 wt% magnetite nanoparticles in soil at 0.3 mL/h with an initial arsenate concentration of 100 μg/L. A negligible arsenate concentration occurred for 3559.6 pore volumes (PVs) (132.1 d). Eventually, the arsenate concentration reached about 20% after 9884.1 PV (207.9 d). A retardation factor of about 6742 was calculated indicating strong adsorption of arsenic to the magnetite nanoparticles in the column. Also, increased adsorption was observed after flow interruption. Other experiments showed that arsenic and 12 other metals (V, Cr, Co, Mn, Se, Mo, Cd, Pb, Sb, Tl, Th, U) could be simultaneously removed by the iron oxide nanoparticles in soil. Effluent concentrations were less than 10% for six out of the 12 metals. Desorption experiment showed partial irreversible sorption of arsenic to the iron oxide nanoparticle surface. Strong adsorption, large retardation factor, and resistant desorption suggest that magnetite and hematite nanoparticles have the potential to be used to remove arsenic in sandy soil possibly through in situ techniques.     

Cobalt-modified iron oxides with improved aging stability

Surface modification of cobalt-modified iron oxides with silicon- or aluminium-containing inorganic compounds suppresses the coercivity aging that otherwise occurs in these particles. At the same time, the inorganic surface coatings change the adsorption characteristics of the particles, allowing them to be matched with the components of the tape formulation.     

Fast degradation of dyes in water using manganese-oxide-coated diatomite for environmental remediation

By a simple wet-chemical procedure using a permanganate in the acidic medium, diatomite coated with amorphous manganese oxide nanoparticles was synthesized. The structural, microstructural and morphological characterizations of the as-synthesized catalysts confirmed the nanostructure of MnO₂ and its stabilization on the support - diatomite. The highly efficient and rapid degradation of methylene blue and methyl orange over synthesized MnO₂ coated Diatomite has been carried out. The results revealed considerably faster degradation of the dyes against the previously reported data. The proposed mechanism of the dye-degradation is considered to be a combinatorial effect of chemical, physicochemical and physical processes. Therefore, the fabricated catalysts have potential application in waste water treatment, and pollution degradation for environmental remediation.     

Ultra-fast synthesis of carbon dots using the wasted coffee residues for environmental remediation

Currently, the coffee residues are one of waste resources which become a problem because the coffee consumption has increased. This is a worldwide problem due to the increase in disposal costs and environmental problems. Therefore, we use the wasted coffee residue which contains caffeine as starting material of carbon dot for solving disposal costs and environmental problems. The carbon dots were synthesized from coffee residues with different firing times by a facile and fast method. The emission peak of carbon dot is about 445 nm (cyan color) under 360 nm. The transmittance of the prepared carbon dot film reaches 90% which is high transparency. These results represent that carbon dot and carbon dot film can be applied for flexible display and optical application through recycling waste coffee residues.     

Enhanced photocatalytic degradation of Safranin-O by heterogeneous nanoparticles for environmental applications

Nanostructure titanium dioxide (TiO₂) has been synthesized by hydrolysis of titanium tetrachloride in aqueous solution and Ag-TiO₂ nanoparticles were synthesized by photoreduction method. The resulting materials were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier-transform infrared (FT-IR) and UV-vis absorption spectroscopy. The experimental results showed that the sizes of the synthesized TiO₂ and Ag-TiO₂ particles are in the range of 1.9-3.2 nm and 2-10 nm, respectively. Moreover, Ag-TiO₂ nanoparticles exhibit enhanced photocatalytic activity on photodegradation of Safranin-O (SO) dye as compared to pure TiO₂. The positive effect of silver on the photocatalytic activity of TiO₂ may be explained by its ability to trap electrons. This process reduces the recombination of light generated electron-hole pairs at TiO₂ surface and therefore enhances the photocatalytic activity of the synthesized TiO₂ nanoparticles. The effects of initial dye and nanoparticle concentrations on the photocatalytic activity have been studied and the results demonstrate that the dye photodegradation follows pseudo-first-order kinetics. The observed maximum degradation efficiency of SO is about 60% for TiO₂ and 96% for Ag-TiO₂.     

Thermal effects in highly dispersed iron catalysts

The Mössbauer spectra of three Fe/SiO₂ catalysts with 5 wt% iron content show the presence of several Fe species and display different magnetic behaviours when the precursors are subjected to various thermal treatments. Based on the Mössbauer parameters and CO chemisorption measurements, the average crystal sizes of the catalysts are estimated and discussed in connection with the thermal pretreatment severity and magnetic properties of the samples.     

Nanowires of iron oxides embedded in SiO2 templates

To attain the complete filling of the channels of MCM-41 with magnetite and maghemite, we have tried out an alternative method to the incipient wetness impregnation. The mesoporous material was instilled with a Fe-carrying organic salt after subjecting the matrix to a silylation treatment. Thus, a solid of 7.7 wt.% iron-loaded MCM-41 was obtained. Different subsequent thermal treatments were used to produce γ-Fe₂O₃ or Fe₃O₄. The Mössbauer and magnetic results show that after this method, the as-prepared composite displays a size-distribution of magnetic particles. It is mainly made up of fine particles that display a superparamagnetic relaxation at room temperature and get blocked at ≈42 K for the AC susceptibility time-scale measurements both for γ-Fe₂O₃ and Fe₃O₄ particles. For both samples, about 24% of larger iron-containing phases are magnetically blocked at room temperature. For the Fe₃O₄ particles, this fraction undergoes the Verwey transition at about 110 K; in addition, there is a minor Fe (III) fraction that remains paramagnetic down to 4.2 K.     

Magnetism in iron implanted oxides: a status report

Emission Mössbauer spectroscopy on ⁵⁷Fe fed by ⁵⁷Mn ions implanted in the metal oxides ZnO, MgO and Al₂O₃ has been performed. The implanted ions occupy different lattice sites and charge states. A magnetic part of the spectra in each oxide can be assigned to Fe^3?+? ions in a paramagnetic state with unusually long relaxation time observable to temperatures up to several hundreds Kelvin. Earlier expectations that the magnetic spectra could correspond to an ordered magnetic state could not be confirmed. A clear decision for paramagnetism and against an ordered magnetic state was achieved by applying a strong magnetic field of 0.6 Tesla. The relaxation times deduced were compared to spin–lattice relaxation times from electron paramagnetic resonance (EPR).