Photophysics and photochemistry of porphyrin core PAMAM dendrimers. Excited states interaction with quinones

Quenching of excited states of the meso-substituted tetraphenyl porphyrins with PAMAM branches, and one with PAMAM generation 1 peripherally-modified with thiazole groups by p-benzoquinones, were studied in DMF solution. Fluorescence lifetime measurements evidence a static component in the quenching process. The dynamic quenching rate constants were close to the diffusional limit except for the case of duroquinone. Apparent association constants of the porphyrin compounds with the quinones were determined by comparison of static and dynamic measurements of fluorescence quenching. The ground state interaction is very weak with the exception of tetrachlorobenzoquinone. The triplet state decay kinetics and the transient absorption spectra in the presence of the quinones were determined by laser flash photolysis. Triplet quenching rate constants were lower than those of singlet quenching. An electron transfer mechanism was proposed to explain the results. The long-time transient absorption spectra were assigned to the radical cation of the dyes. Relative radical yields were determined and a dependence on the side chains and the quencher was observed.Fil: Militello, María Paula. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Arbeloa, Ernesto Maximiliano. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Hernández Ramírez, Raquel E.. Tecnológico de Estudios Superiores de Coacalco; MéxicoFil: Lijanova, Irina Victorovna. Instituto Politécnico Nacional; MéxicoFil: Montejano, Hernan Alfredo. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Previtali, Carlos Mario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentin

Successful application of a commercial cationic surfactant mixture (benzalkonium chloride) as porosity stabilizer in porous carbons fabrication

Porous carbons (BSPCs) were obtained by carbonization of resorcinol-formaldehyde gels in the presence of cationic surfactants mixture (benzalkonium chloride) which act as porosity stabilizer. The application of an inexpensive industrial grade surfactant mixture as porosity stabilizer permits obtaining porous carbons with well-developed micro and mesoporosity at low cost. The stabilizing effect on the sol–gel nanostructure allows maintaining the gels porosity during conventional air drying, simplifying the production of porous carbon by making unnecessary complex drying procedures (e.g. supercritical drying), cumbersome solvent exchanges, and long curing times. The carbonization process of BSPCs studied by TGA shows that the stabilizer and non-carbon elements (hydrogen and oxygen) are only eliminated during pyrolysis at temperature above 600 °C. The BSPCs morphological and textural properties were studied by scanning electron microscopy and nitrogen physisorption isotherms. The BSPCs present large specific surface areas (up to 645 m2/g) containing mesopores and micropores. Furthermore, the pore distribution and morphology depend on the monomer (resorcinol) to stabilizer (benzalkonium chloride) ratio. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to study the electrochemical properties of the carbon materials. The BSPCs exhibit a large specific capacitance (up to 179 F/g at 2.8 mHz in 1 M H2SO4) The results suggest that porosity stabilization of resorcinol/formaldehyde gels could be performed using different cationic surfactants, even commercial mixtures like benzalkonium chloride.D.F. Acevedo and C.A. Barbero, are permanent research fellows of CONICET. L. Tamborini and P. Militello thank CONICET for graduate fellowships. The funding of FONCYT (PICT 2013-2716), CONICET (PIP 2014–2016, No. 11220130100663CO), MinCyT-Cordoba and SECYT-UNRC is gratefully acknowledged. L. Tamborini thanks the program BECAR (MinCTIP-AR) for the financing of a research stay at Alicante University (Spain)

Photosensitizer-dendrimer systems in anticancer treatments: From photophysics to PDT applications

Photodynamic therapy (PDT) is a modern form of treatment of cancers and other diseases. It is based on the use of a photosensitizer (PS), a molecule that after absorbing light generates reactive oxygen species with the potential to cause the destruction of the target tumoral cells. A great deal of research in this area has improved the efficiency of the process and eliminated its side effects by properly combining PS with nanomaterials. In this context, dendrimers are excellent candidates because their highly branched 3D architectures allow them to form a wide variety of supramolecular assemblies with PSs (PS-Ds) either covalently or by complexation, which possess a number of advantages for PDT application. This chapter reviews the recent progress in the development of PS-Ds systems, their photophysical characterization and achievements in PDT technology.Fil: Arbeloa, Ernesto Maximiliano. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Militello, María Paula. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Previtali, Carlos Mario. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentin

The interaction of the excited states of safranine-O with low generation carboxyl terminated PAMAM dendrimers in an aqueous medium

The interaction of the singlet and triplet excited states of the synthetic dye safranine-O with carboxyl-terminated poly(amidoamine) (PAMAM) dendrimers was investigated in a buffer solution at pH 8. Low half-generation PAMAM dendrimers (G -0.5; G +0.5: G 1.5) were employed. The UV-vis absorption spectrum of the dye presents only a very small red shift in the presence of dendrimers. Fluorescence quenching was detected and it was interpreted by a static mechanism in terms of the association of the dye with the dendrimer. Laser flash photolysis experiments were carried out and transient absorption spectra of the triplet and radicals were obtained. The triplet state is quenched by the dendrimers with rate constants well below the diffusional limit. The quenching process was characterized as an electron transfer process and the quantum yield of radicals was estimated. It was found that radicals are formed with a high efficiency in the triplet quenching reaction.Fil: Militello, María Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Altamirano, Marcela Susana. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Bertolotti, Sonia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Previtali, Carlos Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentin

New dendritic porphyrins: Synthesis, spectroscopic and antibacterial evaluation

In this work, a new porphyrin-dendrimer (Pf-PPI) was synthesized, which can form complex Ag + leading to a Pf-PPI-Ag + stable compound. The molecular structure of the dendrimers was characterized by 1 H NMR and 13 C NMR, FT-IR, TGA and UV–vis. The metal complexation capacity of dendritic nanostructures was evaluated using filtration followed by atomic absorption, and the binding sites were elucidated by FT-IR spectrometry and TGA analysis. The results show that the functional groups in dendrimer branches are involved in the retention rate of cations. Transient studies proved good capacity for singlet oxygen generation even in the presence of the cation, showing that both complexing and sensitizing properties are compatible with each other. The antibacterial effect of the compounds on E. coli was also evaluated. Although some dark toxicity was observed, a complete and faster bacterial inactivation was recorded under visible light irradiation, demonstrating high photodynamic efficiency of the tested compounds.Fil: Hernández Ramírez, Raquel Eunice. Tecnológico de Estudios Superiores de Coacalco; MéxicoFil: Militello, María Paula. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Arbeloa, Ernesto Maximiliano. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Lijanova, Irina Victorovna. No especifíca

Fast photodegradation of Orange II azo dye under visible light irradiation using a semiconducting n-p heterojunction of ZnO nanoparticles/polypyrrole as catalyst

Preparation of innovative nano- and microstructured heterojunctions consisting of two semiconductors for highly efficient p–n photocatalysts has been of growing interest due to their advanced applications. n-type ZnO nanoparticles were synthesized by a simple precipitation method from ZnCl2 and NaOH and coated with semiconducting p-type polypyrrole (PPy) nanospheres by chemical oxidation in the presence of sodium dodecyl sulfate (SDS) as surfactant, obtaining a n-p type ZnO/PPy composite. The composite was characterized by scanning electron microscopy (SEM), FTIR and UV/Vis–NIR spectroscopies, and thermogravimetric analysis (TGA). It was observed that composite consisted of ZnO nanoparticles with rice-like morphology of sizes in the range of 180–600 nm long and between 70 and 227 nm wide, which were well dispersed into a matrix made of agglomerated spherical nanoparticles of PPy. The composite was tested as photocatalyst in the degradation of Orange II azo dye using visible light irradiation at different initial dye concentrations, catalyst loading, initial pH, and in the presence of hole and radical scavengers. Photodegradation efficiencies after 30 min of reaction in the range of 90.9–100% and fast photodegradation rates depending on the initial dye concentration and catalyst load were observed. The best photodegradation efficiency was observed at acidic pH, which was ascribed to an improved electrostatic interaction of dissociated dye molecules with the positively charged surface of photocatalyst. It was demonstrated that ·O2- and other ROS are the main reactive species formed via reaction between O2 and photogenerated electrons, following a pseudo-first order of reaction.Fil: Escobar-Villanueva, Alondra G.. Universidad Autonoma de San Luis Potosi; MéxicoFil: Ovando-Medina, Víctor M.. Universidad Autonoma de San Luis Potosi; MéxicoFil: Martínez-Gutiérrez, Hugo. INSTITUTO POLITÉCNICO NACIONAL (IPN);Fil: Militello, María Paula. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentin

The effect of PAMAM dendrimers on the excited states of little-explored xanthene dyes: In search of eco-friendly photoinitiating systems

A complete photophysical and photochemical study on the little explored xanthene dyes 2´,7´-dichlorofluorescein; 4, 5, 6, 7- tetrachlorofluorescein; 4´, 5´-dibromofluorescein and 4´, 5´-diiodofluorescein was carried out in aqueous solution. The effect of three PAMAM dendrimers of low generations (G0, G1 and G3) on their excited states was also evaluated. Absorption and fluorescence measurements showed that although the ground and singlet-excited states of the dyes interact weakly with dendrimers, the binding constants obtained correlated with dendrimer size. The triplet-excited states of the dyes were analyzed by laser flash photolysis even for chlorinated ones; which, to the best of our knowledge, had not been characterized until now. Chlorinated fluoresceins showed triplet quantum yields in the order of 0.10, indicating that the intersystem crossing is not a negligible process. Efficient electron transfer reactions were observed between amino moieties of PAMAM and the triplet states of the dyes. The triplet quenching rate constants also correlated with dendrimer size and the semi-reduced species of the dyes were characterized by their transient spectra. Radical formation efficiencies similar to those obtained with a typical tertiary amine were estimated, so the present results suggest that these dye/dendrimer couples might be promising as photoinitiating systems for polymerizations with low ecological impact.Fil: Militello, María Paula. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Porcal, Gabriela Valeria. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Previtali, Carlos Mario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Arbeloa, Ernesto Maximiliano. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentin

A fast, efficient, inexpensive and green way to outdoor photopolymerization

A series of environmentally friendly photoinitiating systems operating under mild conditions of visible light (Vis-PIs) were tested for vinyl polymerization using sunlight as a free of charge radiation source. These Vis-PIs based on water soluble xanthene dyes showed good performances after deaerating with an inert gas, obtaining colorless polymers with gravimetric yields up to 80–90% after short irradiation times (2–15 min). Aqueous solutions of the materials were highly viscous and viscosimetric measurements yielded molecular weights up to 106. Surprisingly, the evaluated Vis-PIs also worked successfully under ambient air atmosphere, obtaining similar polymer yields in the same irradiation times. Photolysis experiments and transient spectroscopy were used to shed light on the mechanism of the process, allowing both triplets and radicals formation of the dyes to be identified even in the presence of air. The kinetics of photopolymerization was studied following the monomer conversion at several irradiation times by FTIR. The results were interpreted based on kinetic data collected as competitive quenching mechanisms between the co-initiator and oxygen for the excited dyes. The present report represents a breakthrough in the search for fast, efficient and inexpensive Vis-PIs with low ecological impact, which can be very useful in outdoor coating applications among others.Fil: Militello, María Paula. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Porcal, Gabriela Valeria. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Previtali, Carlos Mario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Arbeloa, Ernesto Maximiliano. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentin

The effect of PAMAM dendrimers on the excited states of little-explored xanthene dyes: In search of eco-friendly photoinitiating systems

A complete photophysical and photochemical study on the little explored xanthene dyes 2´,7´-dichlorofluorescein; 4, 5, 6, 7- tetrachlorofluorescein; 4´, 5´-dibromofluorescein and 4´, 5´-diiodofluorescein was carried out in aqueous solution. The effect of three PAMAM dendrimers of low generations (G0, G1 and G3) on their excited states was also evaluated. Absorption and fluorescence measurements showed that although the ground and singlet-excited states of the dyes interact weakly with dendrimers, the binding constants obtained correlated with dendrimer size. The triplet-excited states of the dyes were analyzed by laser flash photolysis even for chlorinated ones; which, to the best of our knowledge, had not been characterized until now. Chlorinated fluoresceins showed triplet quantum yields in the order of 0.10, indicating that the intersystem crossing is not a negligible process. Efficient electron transfer reactions were observed between amino moieties of PAMAM and the triplet states of the dyes. The triplet quenching rate constants also correlated with dendrimer size and the semi-reduced species of the dyes were characterized by their transient spectra. Radical formation efficiencies similar to those obtained with a typical tertiary amine were estimated, so the present results suggest that these dye/dendrimer couples might be promising as photoinitiating systems for polymerizations with low ecological impact.Fil: Militello, María Paula. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Porcal, Gabriela Valeria. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Previtali, Carlos Mario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Arbeloa, Ernesto Maximiliano. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentin

Application of sulfonated nanoporous carbons as acid catalysts for Fischer esterification reactions

Heterogeneous acid catalysts were prepared by sulfonation of nanoporous carbons (NPCs). The NPCs were produced by pyrolysis of resorcinol-formaldehyde nanoporous resins (NPRs). The NPRs were synthesized as wet gels by condensation of resorcinol and formaldehyde in a sol-gel polycondensation using Na2CO3 as catalyst. A cationic polyelectrolyte (poly(diallyl dimethyl ammonium chloride)) was used as pore stabilizer, allowing to dry the gels in air without any special procedures. Five NPRs with different properties were synthesized by varying the monomer to catalyst ratio (Resorcinol/Na2CO3, R/C). The morphological and textural characterizations of the NPCs were performed by scanning electron microscopy and nitrogen adsorption-desorption isotherms. The results indicate that using a molar ratio of R/C=200, a nanoporous carbon NPC with large surface area (695m2/g) is obtained. This NPC was sulfonated by reaction with three different sulfonating agents: (i) concentrated sulfuric acid; (ii) fuming sulfuric acid and (iii) chlorosulfonic acid in order to obtain a novel Fischer esterification catalyst. The amount of acid groups attached to the NPC surface was determined by titration using a modified Boehm method. The catalytic activity, for Fischer esterification reaction of different sulfonated NPCs, was compared with sulfonated NPRs, sulfonated commercial porous carbons and polymeric acid catalyst (cationic ion exchange resins, sulfonated fluoropolymers). The modification of NPCs with concentrated sulfuric acid seems to render the materials with more catalytic activity. The best sulfonated material NPC (PC200-H2SO4) shows a high catalytic activity for the esterification of acetic acid (90.8%) and oleic acid (60.6%) with ethanol. The conversion and conversion rate values are better than commercial acid catalysts. The results suggest that sulfonated NPC catalysts are promising materials for the synthesis of biodiesel and related reactions.Fil: Tamborini, Luciano Henri. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Militello, María Paula. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Balach, Juan Manuel. Leibniz Institute for Solid State and Materials Research; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Moyano, J. M.. Universidad Nacional de Rio Cuarto. Facultad de Ingeniería. Departamento de Tecnología Química; ArgentinaFil: Barbero, César Alfredo. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Acevedo, Diego Fernando. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Universidad Nacional de Rio Cuarto. Facultad de Ingeniería. Departamento de Tecnología Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin