Esther Pascual

Bio: Esther Pascual is an academic researcher from University of Barcelona. The author has contributed to research in topics: Thin film & Plasma-enhanced chemical vapor deposition. The author has an hindex of 19, co-authored 55 publications receiving 1931 citations.

Comparison of different advanced oxidation processes for phenol degradation.

Abstract: Advanced Oxidation Processes (O 3 , O 3 /H 2 O 2 , UV, UV/O 3 , UV/H 2 O 2 , O 3 /UV/H 2 O 2 , Fe 2+ /H 2 O 2 and photocatalysis) for degradation of phenol in aqueous solution have been studied in earlier works. In this paper, a comparison of these techniques is undertaken: pH influence, kinetic constants, stoichiometric coefficient and optimum oxidant/pollutant ratio. Of the tested processes, Fenton reagent was found to the fastest one for phenol degradation. However, lower costs were obtained with ozonation. In the ozone combinations, the best results were achieved with single ozonation. As for the UV processes, UV/H 2 O 2 showed the highest degradation rate.

Mueller matrix microscope with a dual continuous rotating compensator setup and digital demodulation

Abstract: In this paper we describe a new Mueller matrix (MM) microscope that generalizes and makes quantitative the polarized light microscopy technique. In this instrument all the elements of the MU are simultaneously determined from the analysis in the frequency domain of the time-dependent intensity of the light beam at every pixel of the camera. The variations in intensity are created by the two compensators continuously rotating at different angular frequencies. A typical measurement is completed in a little over one minute and it can be applied to any visible wavelength. Some examples are presented to demonstrate the capabilities of the instrument.

Boron carbide thin films deposited by tuned-substrate RF magnetron sputtering

Abstract: Boron carbide thin films were deposited in a tuned RF magnetron sputtering system from a target of B4C with Ar as the processing gas. The ion bombardment during film growth was controlled by the substrate-tuning technique, which allows the setting up of a variable DC bias even for insulant materials. The substrate bias was varied from −80 to +15 V. The RF power was fixed at 300 W. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) analyses indicate that the films are stoichiometric B4C and homogeneous. The vibrational properties were studied by Fourier transform infrared spectroscopy (FTIR). The X-ray diffraction results indicated the amorphous or nanocrystalline character of these films. The optical properties were calculated from transmission measurements, and bandgap values from 2.52 to 2.38 eV were obtained. These films present good mechanical properties, such as moderate internal stress (4.5 GPa), high microhardness (19.5–25 GPa) and good adhesion to the substrate.

Structural effects of nanocomposite films of amorphous carbon and metal deposited by pulsed-DC reactive magnetron sputtering

Abstract: The relationship between metal-induced (W, Mo, Nb and Ti) structures and the surface properties of Me–DLC thin films is discussed. Nanocomposite films were deposited on c–Si wafers by pulsed-DC reactive magnetron sputtering controlling the gas ratio CH4/Ar. The sputtering process of metals such as Ti, Nb and Mo (unlike the tungsten) in the presence of methane shows a low reactivity at low methane concentration. The deposition rate and the spatial distribution of sputtered material depend of Z-ratio of each metal. The surface contamination of metal targets by carbon, owing to methane dilution, limits the incorporation of metals into DLC films according to an exponential decay. Results of electron probe microanalysis and X-ray photoelectron spectroscopy indicate a C rich Me/C composition ratio for low relative methane flows. According to the depth profile by secondary ion mass spectrometry, the films are systematically homogeneous in depth, whereas at high carbon contents they exhibit a metal-rich interfacial layer on the substrate. Moreover, high resolution transmission electron microscopy has evidenced important structural modifications with respect to DLC standard films, with marked differences for each Me/C combination, providing nanodendritic, nanocrystallized or multilayered structures. These particular nanostructures favour the stress decrease and induce significant changes in the tribological characteristics of the films. This study shows the possibilities of controlling the amorphous carbon films structure and surface properties by introducing metal in the DLC matrix. © 2007 Elsevier B.V. All rights reserved.

Efficient diffusion barrier layers for the catalytic growth of carbon nanotubes on copper substrates

Abstract: We have investigated the growth of carbon nanotube (CNT) films on copper substrates by the catalytic chemical vapour deposition route. Ferrocene was used as the catalyst precursor and toluene was the carbon feedstock. The copper substrates were coated with nitride and oxide amorphous ceramic barrier coatings in order to prevent diffusion of the iron catalyst during growth. It was found that virtually no CNT grew on pure copper, but long and densely packed mats of CNTs could be grown on TiN-coated copper. Copper substrates coated with SiNx and In2O3:Sn (ITO) also showed better results than pure copper, although the CNT density was much lower than that obtained from TiN/Cu. Auger electron spectroscopy (AES) showed that Fe diffusion occurred into SiNx/Cu and ITO/Cu substrates, which partially inhibited its catalyst activity. In contrast, AES did not detect the presence of diffused Fe into the TiN coating. The estimation of the diffusion coefficient by AES depth profiles for Fe in SiNx, was 3 · 10−3 nm2 s−1. This value establishes an upper limit for Fe diffusion on substrates for proper nanotube nucleation and growth. Secondary ion mass spectrometry provided complementary information on the composition profiles with depth.

Recent Developments in Photocatalytic Water Treatment Technology: A Review

Abstract: In recent years, semiconductor photocatalytic process has shown a great potential as a low-cost, environmental friendly and sustainable treatment technology to align with the “ zero ” waste scheme in the water/wastewater industry. The ability of this advanced oxidation technology has been widely demonstrated to remove persistent organic compounds and microorganisms in water. At present, the main technical barriers that impede its commercialisation remained on the post-recovery of the catalyst particles after water treatment. This paper reviews the recent R&D progresses of engineered-photocatalysts, photoreactor systems, and the process optimizations and modellings of the photooxidation processes for water treatment. A number of potential and commercial photocatalytic reactor configurations are discussed, in particular the photocatalytic membrane reactors. The effects of key photoreactor operation parameters and water quality on the photo-process performances in terms of the mineralization and disinfection are assessed. For the first time, we describe how to utilize a multi-variables optimization approach to determine the optimum operation parameters so as to enhance process performance and photooxidation efficiency. Both photomineralization and photo-disinfection kinetics and their modellings associated with the photocatalytic water treatment process are detailed. A brief discussion on the life cycle assessment for retrofitting the photocatalytic technology as an alternative waste treatment process is presented. This paper will deliver a scientific and technical overview and useful information to scientists and engineers who work in this field.

Electrochromic tungsten oxide films: Review of progress 1993–1998

Abstract: W oxide films are of critical importance for electrochromic device technology, such as for smart windows capable of varying the throughput of visible light and solar energy. This paper reviews the progress that has taken place since 1993 with regard to film deposition, characterization by physical and chemical techniques, optical properties, as well as electrochromic device assembly and performance. The main goal is to provide an easy entrance to the relevant scientific literature.

Utilization of agro-industrial and municipal waste materials as potential adsorbents for water treatment—A review

Abstract: Adsorption process has been proven one of the best water treatment technologies around the world and activated carbon is undoubtedly considered as universal adsorbent for the removal of diverse types of pollutants from water. However, widespread use of commercial activated carbon is sometimes restricted due to its higher costs. Attempts have been made to develop inexpensive adsorbents utilizing numerous agro-industrial and municipal waste materials. Use of waste materials as low-cost adsorbents is attractive due to their contribution in the reduction of costs for waste disposal, therefore contributing to environmental protection. In this review, an extensive list of low-cost adsorbents (prepared by utilizing different types of waste materials) from vast literature has been compiled and their adsorption capacities for various aquatic pollutants as available in the literature are presented. It is evident from the literature survey that various low-cost adsorbents have shown good potential for the removal of various aquatic pollutants. However, there are few issues and drawbacks on the use of low-cost adsorbents in water treatment that have been discussed in this paper. Additionally, more research is needed to find the practical utility of low-cost adsorbents on commercial scale.

Adsorption isotherm, kinetic and mechanism studies of some substituted phenols on activated carbon fibers

Abstract: Activated carbon fibers (ACFs) were used for the adsorption of phenol, 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP), 4-nitrophenol (4-NP) and 2,4-dinitrophenol (DNP) from aqueous solutions, and the adsorption capacities followed the order of TCP > DNP ≈ DCP > 4-NP > 4-CP > 2-CP > phenol. Adsorption isotherms at different temperatures were determined and modeled with Langmuir, Freundlich and Redlich–Peterson equations. Thermodynamic parameters were calculated and correlated with the adsorption behaviors. The effects of solution pH on the adsorption were also studied. The adsorption mechanism was discussed based on the experimental results, and the π–π interactions, solvent effects, hydrophobic interactions and molecular dimensions were considered to be important in the adsorption. Kinetic studies showed rapid adsorption kinetics of the phenols, due to the open pore structure of the ACFs. The kinetics was fitted with the pseudo-first-order, pseudo-second-order and intraparticle diffusion models. Steric effects on adsorption kinetics were observed for TCP, 4-NP and DNP, but serious impact on the ultimate uptake was only found for DNP. The relationship between the steric effects and the molecular dimension was also proposed.

Wastewater treatment by means of advanced oxidation processes at basic pH conditions: a review.

Abstract: Advanced oxidation processes (AOPs) have been used as an alternative and effective option for treatment of industrial wastewater, especially in the case of the non-biodegradable compounds. Despite of several well developed AOPs, the majority of them are effective only at acidic or neutral pH, namely Fenton related processes, making the list of available effective advanced oxidation technologies strongly limited. In many cases, industrial effluents are formed at basic pH conditions. This paper reviews the state of the art of AOPs exclusively at alkaline pH, the type of compounds and effluents effectively degraded, the influence of pH on the efficiency of the processes, economic evaluation and degradation pathways. Spent caustic, polyester and acetate fiber dye effluents, phenol, acidic and sulfur based compounds, specific dyes and drugs were effectively degraded at basic pH. Factors like point of zero charge, pKa of the compounds, amount of radicals produced and activation of the oxidants are crucial factors that affect the treatment efficiency of AOPs at basic pH. H2O2 and O3 were the cheapest processes while peroxone was the most expensive. The treatment costs were in general too expensive and unrealistic using the methodology used in the literature. The alternative methodology proposed in this paper reduced the treatment costs by three orders of magnitude to values more realistic and economical feasible. Literature regarding treatment of real effluents using AOPs at basic pH is scarce and further research is needed to perform complete analysis. It is important to present some alternatives regarding the treatment of alkaline effluents without pH correction using such technologies.