Juan Manríquez

PhD
Titular Researcher
Centro de Investigación y Desa... · Department of Science

Publications

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    ABSTRACT: a b s t r a c t An air diffusion activated carbon packed electrode was used to promote the in-situ generation of hydro-gen peroxide (H 2 O 2) to support an electro-Fenton based method for the degradation of a typical dye, Methyl Orange (MO) at two different concentrations in an aqueous effluent (250 mg L −1 and 97 mg L −1). Electrochemical experiments were carried out using a one compartment cylindrical cell with granular activated carbon (GAC) configured as an air diffusion cathode. The efficiency of the electrode was explored as a function of H 2 O 2 produced reaching a maximum value of 10 mM. Experimental parameters such as applied current (300, 200, 100 and 50 mA), initial Fe 2+ concentration (0.2, 0.5 and 0.8 mM) and electrode stability (10 cycles) were studied. High Total Organic Carbon (TOC) decay (90%) and color removal (100%) were obtained using this electrode under appropriate operation conditions. Consecutive degradation cycles of electro-Fenton process were performed in the electrochemical cell without great loss of the removal efficiency. Considering that, in the proposed packed electrode, the use of air diffusion GAC as cathode results in efficient degradation and cost reduction for the conventional electro-Fenton process, this electrode approach could constitute an excellent alternative for H 2 O 2 generation when compared to conventional carbon electrodes.
    Electrochimica Acta 09/2014; 140:412-418. · 4.09 Impact Factor
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    ABSTRACT: This research evaluated two electrokinetic remediation systems (EKR) for separating phenanthrene from bentonite and its electrochemical destruction by using a Boron Doped Diamond (BDD) electrode. The effect of the electrochemical potential for the oxidation of phenanthrene in liquid phase with BDD was analyzed by Normal Pulse Voltammetry and Hydroxyl Radical (●OH) analysis using the Spin Trapping Technique. The results showed that 70% of phenanthrene was removed from bentonite through EKR by applying 20 mA for 4 h in alkaline conditions, and that phenanthrene in solution was 100% degraded with BDD by applying 2.3 V vs Hg|Hg2SO4, for 2.5 h. These results demonstrate the potential application of the electrochemical technology in treating soils contaminated with highly toxic compounds, such as Polyaromatic Hydrocarbons (PAHs) and their final destruction using the EKR-BDD process.
    Environmental engineering and management journal 08/2014; · 1.12 Impact Factor
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    ABSTRACT: A review on different arrangements and reactor designs for Advanced Oxidation Processes based on the use of the Fenton reagent is presented. The review focuses on reports that include publications and patents dealing with water contaminated with different recalcitrant pollutants. The work includes a brief introduction that deals with the basics of the Fenton reagent use for the oxidation of pollutants of water effluents, followed by a set of sections in which some of the reports and patents of the different forms in which the Fenton reagent is employed for water treatment processes are presented. In this way, this review includes a section dealing with processes in which the components of the Fenton reagent is administered by means of H 2 O 2 and Fe salts addition, in which it is photo-assisted with UV light and in which it is electro-generated in-situ and photo-assisted taking advantage of the electrochemical reduction of dissolved oxygen on a carbonaceous cathode.
    Evaluation of Electrochemical Reactors as a New Way to Environmental Protection, 1 edited by Juan M Peralta-Hernández, Manuel A Rodrigo-Rodrigo, Carlos A Martínez-Huitle, 07/2014: chapter 6: pages 95-135; Research Signpost., ISBN: 978-81-308-0549-8
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    ABSTRACT: Acrylamide (AA) was electrochemically detected and quantified by means of its voltammetric response on carboxylic modified Single-Walled Carbon Nanotube Screen Printed Electrodes (COOH-SWCNT-SPEs). The electroreduction signal of AA was proportional to AA concentration at low values (below 300 µM) and the observed sensitivity was explained in terms of AA adsorption on the COOH-SWCNT-SPEs that was demonstrated using the electrochemical response of [Fe(CN)6]3− and [Fe(CN)6]4− and Raman spectroscopy experiments. In order to test the suggested analytic approach (LOD of 0.03 µM, LOQ of 0.04 µM), detection and quantification of AA in fried potatoes was carried out using the proposed electrochemical method and HPLC. Both techniques showed similar contents of AA.
    Electroanalysis 04/2014; · 2.82 Impact Factor
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    ABSTRACT: Glassy carbon electrodes (GCE) were sequentially modified by cysteamine-capped gold nanoparticles (AuNp@cysteamine) and PAMAM dendrimers generation 4.5 bearing 128-COOH peripheral groups (GCE/AuNp@cysteamine/PAMAM), in order to explore their capabilities as electrochemical detectors of uric acid (UA) in human serum samples at pH 2. The results showed that concentrations of UA detected by cyclic voltammetry with GCE/AuNp@cysteamine/PAMAM were comparable (deviation <±10%; limits of detection (LOD) and quantification (LOQ) were 1.7×10(-4) and 5.8×10(-4)mgdL(-1), respectively) to those concentrations obtained using the uricase-based enzymatic-colorimetric method. It was also observed that the presence of dendrimers in the GCE/AuNp@cysteamine/PAMAM system minimizes ascorbic acid (AA) interference during UA oxidation, thus improving the electrocatalytic activity of the gold nanoparticles.
    Analytica chimica acta 02/2014; 812:18-25. · 4.31 Impact Factor
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    ABSTRACT: The combined effect of temperature and pretreatment of the substrate on the anaerobic treatment of the organic fraction of slaughterhouse solid waste was studied. The goal of the study was to evaluate the effect of pretreating the waste on the efficiency of anaerobic digestion. The effect was analyzed at two temperature ranges (the psychrophilic and the mesophilic ranges), in order to evaluate the effect of temperature on the performance of the anaerobic digestion process for this residue. The experiments were performed in 6 L batch reactors for 30 days. Two temperature ranges were studied: the psychrophilic range (at room temperature, 18°C average) and the mesophilic range (at 37°C). The waste was pretreated with NaOH before the anaerobic treatment. The result of pretreating with NaOH was a 194% increase in the soluble chemical oxygen demand (COD) with a dose of 0.6 g NaOH per g of volatile suspended solids (VSS). In addition, the soluble chemical oxygen demand/total chemical oxygen demand ratio (sCOD/tCOD) increased from 0.31 to 0.7. For the anaerobic treatment, better results were observed in the mesophilic range, achieving 70.7%, 47% and 47.2% removal efficiencies for tCOD, total solids (TS), and volatile solids (VS), respectively.
    Journal of Bioscience and Bioengineering 01/2014; · 1.74 Impact Factor
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    ABSTRACT: The conductivity mechanism of non-illuminated n-type TiO2 semiconductor films (prepared by electrophoretic deposition) modified with either terpyridine “tpy-Ru(II)” or bipyridine “bpy-Ru(II)” ruthenium complexes, has been investigated using Electrochemical Impedance Spectroscopy (EIS) measurements at different temperatures. While all the films (bare TiO2 and TiO2/Dye) showed that the electronic conductivity in a low temperature window (T < 313.24 K) can be described by a mechanism that follows the Mott equation (3D Variable Range Hopping, 3D-VRH), in a high temperature window (T >313.24 K), the conduction mechanism corresponds to the Nearest Neighbor Hopping (NNH) mechanism. The effect of the complexes is reflected in changes of the energetic parameters caused by the modifications in the distribution of energetic sites induced by the electronic overlapping of the π- molecular orbitals in the bpy or tpy ligands and the TiO2 films.
    Journal of The Electrochemical Society 10/2013; 160(11):H836. · 2.59 Impact Factor
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    ABSTRACT: An electro-Fenton-based method was used to promote the regeneration of granular activated carbon (GAC) previously adsorbed with Toluene. Electrochemical regeneration experiments were carried out using a standard laboratory electrochemical cell with carbon paste electrodes and a batch electrochemical reactor. For each system, a comparison was made using FeSO4 as a precursor salt in solution (homogenous system) and an Fe loaded ion exchange resin (Purolite C-100, heterogeneous system); both in combination with electro-generated H2O2 at the GAC cathode. In the two cases, high regeneration efficiencies were obtained in the presence of Iron using appropriate conditions of applied potential and adsorption-polarization time. Consecutive loading and regeneration cycles of GAC were performed in the reactor without great loss of the adsorption properties, only reducing the regeneration efficiency by 1% per cycle during ten cycles of treatment. Considering that in the proposed resin containing process the use of Fe salts is avoided and that GAC cathodic polarization results in efficient cleaning and regeneration of the adsorbent material, this novel electro-Fenton approach could constitute an excellent alternative for regenerating activated carbon when compared to conventional methods.
    Environmental Science & Technology 06/2013; · 5.48 Impact Factor
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    ABSTRACT: CdS nanoparticles (CdS-nps) were synthesized employing charged and neutral polyamidoamide (PAMAM) dendrimers (generation G3.5, G4.0 and G4.0-OH with 64 –COO−, –NH3+ and –OH peripheral groups, respectively) as templates. The morphological characterization of CdS-nps was carried out using TEM measurements that showed spherical nanoparticles characterized by average diameter values between 3.6 and 4.7 nm. Using UV–vis experiments, CdS-nps formation was evaluated using a diffusion controlled growth model where the S2− diffusion coefficient throughout the external and internal functional groups of dendrimers was found to be an important parameter. In this way, the results indicate that nanoparticle formation is primarily affected by the charged nature of the external functional groups of the dendrimer template.
    Journal of Crystal Growth 12/2012; 361:108–113. · 1.55 Impact Factor
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    ABSTRACT: The kinetics and thermodynamics for the phase transfer of carboxyl-terminated polyamidoamine (PAMAM) dendrimers across the water/dichloroethane interface were analyzed by cyclic voltammetry and electrochemical impedance spectroscopy. A three phase junction was employed by inserting a cylindrical gold electrode through the liquid–liquid interface. The reversible redox species decamethylferrocene (DMFc) was used in the organic phase in order to promote dendrimer transfer. It was found that the electrochemical behaviour of DMFc at the gold/dichloroethane interface depends on the generation and concentration of the dendrimer species in the aqueous phase. In addition, it was observed that the electrochemically driven transfer of these macromolecules corresponds to a quasi-reversible process. The data obtained from thermodynamic studies indicate that dendrimers are transferred between the two phases under study by an entropy controlled process.
    Electrochimica Acta 10/2011; 56(24):8299-8304. · 4.09 Impact Factor
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    ABSTRACT: The radical anions and radical cations of the two tautomers (1e and 1i) of 5,10,15,20-tetraphenyl N-confused free-base porphyrin have been studied using a combination of cyclic voltammetry, steady state absorption spectroscopy, and computational chemistry. N-Confused porphyrins (NCPs), alternatively called 2-aza-21-carba-5,10,15,20-tetraphenylporphyrins or inverted porphyrins, are of great interest for their potential as building blocks in assemblies designed for artificial photosynthesis, and understanding the absorption spectra of the corresponding radical ions is paramount to future studies in multicomponent arrays where electron-transfer reactions are involved. NCP 1e was shown to oxidize at a potential of E(ox) 0.65 V vs Fc(+)|Fc in DMF and reduce at E(red) -1.42 V, while the corresponding values for 1i in toluene were E(ox) 0.60 V and E(red) -1.64 V. The geometries of these radical ions were computed at the B3LYP/6-31+G(d)//B3LYP/6-31G(d) level in the gas phase and in solution using the polarizable continuum model (PCM). From these structures and that of H(2)TPP and its corresponding radical ions, the computed redox potentials for 1e and 1i were calculated using the Born-Haber cycle. While the computed reduction potentials and electron affinities were in excellent agreement with the experimental reduction potentials, the calculated oxidation potentials displayed a somewhat less ideal relationship with experiment. The absorption spectra of the four radical ions were also measured experimentally, with radical cations 1e(•+) and 1i(•+) displaying significant changes in the Soret and Q-band regions as well as new low energy absorption bands in the near-IR region. The changes in the absorption spectra of radical anions 1e(•-) and 1i(•-) were not as dramatic, with the changes occurring only in the Soret and Q-band regions. These results were favorably modeled using time-dependent density functional calculations at the TD-B3LYP/6-31+G(d)//B3LYP/6-31G(d) level. These results were also compared to the existing data of free base tetraphenylporphyrin and free base tetraphenylchlorin.
    The Journal of Physical Chemistry A 06/2011; 115(24):6456-71. · 2.77 Impact Factor
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    ABSTRACT: The successful fabrication of efficient dye-sensitized solar cells containing electrophoretically-deposited mesoporphyrin IX in semiconductor films based on sintered TiO2 nanoparticles is presented in this work. For comparison purposes, photocells utilizing mesoporphyrin IX-sensitized TiO2 electrodes were also constructed following the traditional dip-coating deposition technique. Electrochemical responses obtained from these modified surfaces revealed that the electrophoretic methodology generated perpendicularly-arranged porphyrin layers on the sintered oxide nanoparticles, while the dip-coating deposition technique resulted in parallel layers of porphyrin. It was demonstrated that the photovoltaic performance of cells containing electrophoretically-dyed TiO2 films was three times higher than that of devices having photoelectrodes constructed according to the dip-coating protocol. To better understand this behavior, both types of solar cells were further investigated by means of photoelectrochemical impedance spectroscopy.
    Journal of The Electrochemical Society. 05/2011; 158(6):F100-F105.
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    ABSTRACT: In the present work TiO2 films were formed over Indium Tin Oxide (ITO) employing cathodic electrophoretic deposition (Cathodic-EPD) and Dr. Blade Technique. The films were characterized by electrochemical techniques in order to compare their electronic properties; as well as, their photoelectrochemical behavior. The electrochemical performance showed by the films, allowed to relate the modification occurring during the Cathodic-EPD, with the partial reduction of TiO2 nanoparticles, generating Ti3+ defects. These trapping states are modifying the electronic properties of the film, and diminishing the transport of the photoelectrogenerated electrons toward ITO.
    Química Nova 12/2010; 34(3):390-396. · 0.74 Impact Factor
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    ABSTRACT: This work presents cyclic voltammetry and double potential step chronoamperometry experiments corresponding to the electrochemical reduction of the substituted 1,10-phenanthroline ligands in the coordination compounds [Ru(pdto)(1,10-phenanthroline)]Cl2 (1), [Ru(pdto)(5,6-dimethyl-1,10-phenanthroline)]Cl2 (2), [Ru(pdto)(4,7-diphenyl-1,10-phenanthroline)]Cl2 (3), [Ru(pdto)(4,7-dimethyl-1,10-phenanthroline)]Cl2 (4) and [Ru(pdto)(3,4,7,8-tetramethyl-1,10-phenanthroline)]Cl2 (5). These studies were performed in order to evaluate the stability of the electrogenerated chemical species. An ECi mechanism for all the complexes was proposed and the rate constant value (k1) for the chemical coupled reaction was estimated. The stability is discussed in terms of the rate constant value (k1) and the π*-acceptor properties.
    Polyhedron 01/2010; 29(1):328-332. · 2.05 Impact Factor
  • Electrochemical and Solid State Letters - ELECTROCHEM SOLID STATE LETT. 01/2010; 13(4).
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    ABSTRACT: The transfer of PAMAM dendrimers bearing carboxylic acid peripheral groups between two immiscible liquids was studied by means of the three phase junction system, using a gold wire vertically crossing the interface and decamethyl ferrocene as the redox probe in the organic phase. While the voltammetric behavior indicates kinetic limitations of the overall ion–electron transfer process, thermodynamic data shows that the phase transfer process is entropically controlled. Four dendrimer generations were analyzed and it was found that the kinetics as well as the thermodynamics of the phase transfer reaction are size dependent.
    Electrochemistry Communications 01/2010; 12(1):137-139. · 4.29 Impact Factor
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    ABSTRACT: The present work studies the influence of applied electric field on the cathodic electrophoretic formation of films in an aqueous medium. The growth of the film was followed by measuring current density, deposited mass, and thickness under imposed electric field . In scanning electronic microscopy images of the films formed under different electric fields, three regions can be seen: (i) formation of nuclei that are converted into agglomerates, (ii) uniform and one-sided growth, and (iii) growth by the formation of agglomerates on the surface. The characterization of semiconductor properties showed that increased φ for film growth leads to an increase in the density of donors and to a displacement of the flatband potential toward less negative values. The photoelectrochemical characterization of the oxide films revealed that the photoelectrochemical performance of the films decreases as a function of the electric field used to carry out the electrophoretic deposition (EPD) process. The electrochemical behavior observed for these films seems closely related to the content of doping sites electrogenerated in situ during the EPD, which act as electron traps negatively affecting the electron transport toward the indium tin oxide collector, also making their photoelectrochemical activity inefficient.
    Journal of The Electrochemical Society. 10/2009; 156(11):C377-C386.
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    Polyhedron 04/2009; 28:1186. · 2.05 Impact Factor
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    ABSTRACT: Este artigo descreve a fixação de ferrocenos (Fc) sobre eletrodos policristalinos de ouro, por filmes dendrímeros de poliamidoamina (PAMAM). A superfície eletroativa fornece uma rota viável para investigar quantitativamente a ligação do ferroceno com a ciclodextrina (CD). Em particular, as medidas eletroquímicas, revelam o efeito das interações adsorção-adsorção sobre a constante de associação K, na interface eletrodo-eletrólito, durante a formação do complexo de 1:1 Os resultados obtidos a partir da investigação da isoterma de adsorção de Frumkin indicam que as interações podem ter um forte impacto na afinidade do CD com as superfícies do ferrocenil modificado, estudadas aqui. A técnica apresentada pode ser útil para investigar outras reações de ligação entre hóspede-hospedeiro. This paper describes the tethering of ferrocene (Fc) onto polycrystalline gold electrodes by immobilized polyamidoamine (PAMAM) dendrimers films. The resulting electroactive surface provides a viable route for investigating quantitatively the host-guest binding of ferrocene with cyclodextrin (CD). In particular, electrochemical measurements reveal the effect of adsorbate-adsorbate interactions on the association constant K for the formation of the 1:1 CDFc complex at the electrode-electrolyte interface. The results obtained from fitting the Frumkin isotherm to the adsorption data indicate that adsorbate-adsorbate interactions can have a strong impact on the CD affinity for the ferrocenyl-modified surfaces studied here. The technique presented may be useful for investigating other host-guest binding reactions.
    Journal of the Brazilian Chemical Society 01/2008; 19:1010-1016. · 1.28 Impact Factor
  • Synfacts 01/2008; 2008(1):0033-0033.

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