Improving the sustainability of heterogeneous Fenton-based methods for micropollutant abatement by electrochemical coupling.

Advanced oxidation processes such as Fenton reaction-based processes have attracted great interest in recent years as a promising alternative for the removal of persistent pollutants in wastewater. The use of nanocatalysts in advanced oxidation processes overcomes the limitations of homogeneous Fenton processes, where acidic pH values are required, and a large amount of sludge is generated after treatment. Aiming at maximizing the catalytic potential of the process, different configurations include coupling photocatalysis or electrochemistry to Fenton reactions. This manuscript presents a comparative environmental and economic analysis of different heterogeneous Fenton-based process using magnetic nanoparticles: Fenton, photo-Fenton, electro-Fenton and photoelectron-Fenton. These alternatives encompass not only different reaction conditions but also varying degradation kinetics, which control the treatment capability in each specific case. It is not only important to determine the technological feasibility of the proposal based on the removal performance of the target compounds, but also to identify the environmental profile of each configuration. In this regard, the Life Cycle Assessment methodology was applied considering a combination of primary and secondary data from process modeling. Moreover, and aiming towards the future large-scale implementation of the technology, an economic analysis of each configuration was also performed to provide a better understanding about the costs associated to the operation of Fenton-based wastewater treatments.

Exploiting the Potential of Supported Magnetic Nanomaterials as Fenton-Like Catalysts for Environmental Applications.

In recent years, the application of magnetic nanoparticles as alternative catalysts to conventional Fenton processes has been investigated for the removal of emerging pollutants in wastewater. While this type of catalyst reduces the release of iron hydroxides with the treated effluent, it also presents certain disadvantages, such as slower reaction kinetics associated with the availability of iron and mass transfer limitations. To overcome these drawbacks, the functionalization of the nanocatalyst surface through the addition of coatings such as polyacrylic acid (PAA) and their immobilization on a mesoporous silica matrix (SBA15) can be factors that improve the dispersion and stability of the nanoparticles. Under these premises, the performance of the nanoparticle coating and nanoparticle-mesoporous matrix binomials in the degradation of dyes as examples of recalcitrant compounds were evaluated. Based on the outcomes of dye degradation by the different functionalized nanocatalysts and nanocomposites, the nanoparticles embedded in a mesoporous matrix were applied for the removal of estrogens (E1, E2, EE2), accomplishing high removal percentages (above 90%) after the optimization of the operational variables. With the feasibility of their recovery in mind, the nanostructured materials represented a significant advantage as their magnetic character allows their separation for reuse in different successive sequential batch cycles.

Characterizing the CdSe nanodots in the vicinity of the monolayer covering range.

During the past decade, due to their large number of technological applications, a large number of research studies have been devoted to CdSe nanocrystal (NC) systems. Most of the studies of NC grown on substrates present in the literature correspond to a submonolayer coverage. However, interparticle interactions and, consequently, system morphology and its properties can change at higher coverage regime. We combine the X-ray diffraction technique at wide and small angle range with direct space AFM microscopy for the morphological characterization of samples in the monolayer vicinity. We conclude that the CdSe preserves its nanoparticle character and its pyramid shape. This nanoparticle character is also reflected in the CdSe Density Of States (DOS) measured by UPS. We have shown that the particle CdSe atoms are perfectly ordered. They form nanocrystals with a wurtzite structure, grown with an axial and lateral matching with the HOPG substrate lattice in a hexagonal arrangement up to the monolayer coverage, with a strong interaction with the substrate. Above the monolayer coverage this epitaxial match is looser, resulting in a 3D disorder growth.

Degradation Study by Start-Up/Shut-Down Cycling of Superhydrophobic Electrosprayed Catalyst Layers Using a Localized Reference Electrode Technique.

Degradation of a polymer electrolyte membrane fuel cell (PEMFC) with electrosprayed cathode catalyst layers is investigated during cyclic start-up and shut-down events. The study is carried out within a single cell incorporating an array of reference electrodes that enables measurement of cell current as a function of local cathode potential (localized polarization curves). Accelerated degradation of the cell by start-up/shut-down cycling gives rise to inhomogeneous performance loss, which is more severe close to the gas outlet and occurs predominantly during start-up. The degradation consists primarily of loss of cathode catalyst activity and increase in cell internal resistance, which is attributed to carbon corrosion and Pt aggregation in both anode and cathode. Cells with an electrosprayed cathode catalyst layer show lower degradation rates during the first 100 cycles, compared with those of a conventional gas diffusion electrode. This difference in behavior is attributed to the high hydrophobicity of the electrosprayed catalyst layer microstructure, which retards the kinetics of corrosion of the carbon support. In the long term, however, the degradation rate is dominated by the Pt/C ratio in the cathode catalyst layer.

Cl-capped CdSe nanocrystals via in situ generation of chloride anions.

Halide ions cap and stabilize colloidal semiconductor nanocrystal (NC) surfaces allowing for NCs surface interactions that may improve the performance of NC thin film devices such as photo-detectors and/or solar cells. Current ways to introduce halide anions as ligands on surfaces of NCs produced by the hot injection method are based on post-synthetic treatments. In this work we explore the possibility to introduce Cl in the NC ligand shell in situ during the NCs synthesis. With this aim, the effect of 1,2-dichloroethane (DCE) in the synthesis of CdSe rod-like NCs produced under different Cd/Se precursor molar ratios has been studied. We report a double role of DCE depending on the Cd/Se precursor molar ratio (either under excess of cadmium or selenium precursor). According to mass spectrometry (ESI-TOF) and nuclear magnetic resonance ((1)H NMR), under excess of Se precursor (Se dissolved in trioctylphosphine, TOP) conditions at 265 °C ethane-1,2-diylbis(trioctylphosphonium)dichloride is released as a product of the reaction between DCE and TOP. According to XPS studies chlorine gets incorporated into the CdSe ligand shell, promoting re-shaping of rod-like NCs into pyramidal ones. In contrast, under excess Cd precursor (CdO) conditions, DCE reacts with the Cd complex releasing chlorine-containing non-active species which do not trigger NCs re-shaping. The amount of chlorine incorporated into the ligand shell can thus be controlled by properly tuning the Cd/Se precursor molar ratio.