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M.p. Srinivasan - One of the best experts on this subject based on the ideXlab platform.

  • Supercritical fluid immobilization of horseradish peroxidase on high surface area mesoporous activated carbon
    The Journal of Supercritical Fluids, 2016
    Co-Authors: Akshay Jain, Sundaramurthy Jayaraman, Veronica Ong, Rajasekhar Balasubramanian, M.p. Srinivasan
    Abstract:

    Immobilization of enzymes on solid supports is crucial in enzymatic reactions and catalysis as it allows reutilization of soluble enzymes and reduces cost. Covalent immobilization of horseradish peroxidise (HRP) on surface-modified mesoporous activated carbon (SMAC) in combination with Supercritical carbon dioxide (scCO2) has been investigated in this study. The Supercritical Medium achieved higher enzyme loading of 83.5% within 3 h compared to 54% when incubated in aqueous phosphate buffer for 30 h. HRP loading in the scCO2 environment was consistently higher for different HRP: SMAC ratios. The significant increase in the rate and quantity of HRP immobilization is attributed to the favourable transport properties of solutes in scCO2 coupled with greater affinity of HRP for the non-polar Supercritical solvent which enhances the diffusivity of enzymes into the porous matrix. Immobilized HRP retained enzymatic activity after being reutilized 11 times which indicated that immobilization did not detract from HRP's activity. The immobilized HRP was successfully employed in removing phenol from water via polymerization of dissolved phenol in the presence of hydrogen peroxide (H2O2). The study shows the advantage of using a mesoporous substrate as the immobilization platform for enzymes in combination with scCO2 as the transport Medium. It resulted in significant enhancement in the capacity as well as the uptake rate of HRP and resulting in the enhanced phenol removal.

  • Stable Organic Monolayers on Oxide-Free Silicon/Germanium in a Supercritical Medium: A New Route to Molecular Electronics.
    The journal of physical chemistry letters, 2013
    Co-Authors: Sreenivasa Reddy Puniredd, Sundaramurthy Jayaraman, Sai Hooi Yeong, Cedric Troadec, M.p. Srinivasan
    Abstract:

    Oxide-free Si and Ge surfaces have been passivated and modified with organic molecules by forming covalent bonds between the surfaces and reactive end groups of linear alkanes and aromatic species using single-step deposition in Supercritical carbon dioxide (SCCO2). The process is suitable for large-scale manufacturing due to short processing times, simplicity, and high resistance to oxidation. It also allows the formation of monolayers with varying reactive terminal groups, thus enabling formation of nanostructures engineered at the molecular level. Ballistic electron emission microscopy (BEEM) spectra performed on the organic monolayer on oxide-free silicon capped by a thin gold layer reveals for the first time an increase in transmission of the ballistic current through the interface of up to three times compared to a control device, in contrast to similar studies reported in the literature suggestive of oxide-free passivation in SCCO2. The SCCO2 process combined with the preliminary BEEM results opens up new avenues for interface engineering, leading to molecular electronic devices.

  • stable organic monolayers on oxide free silicon germanium in a Supercritical Medium a new route to molecular electronics
    Journal of Physical Chemistry Letters, 2013
    Co-Authors: Sundaramurthy Jayaraman, Sreenivasa Reddy Puniredd, Sai Hooi Yeong, Cedric Troadec, M.p. Srinivasan
    Abstract:

    Oxide-free Si and Ge surfaces have been passivated and modified with organic molecules by forming covalent bonds between the surfaces and reactive end groups of linear alkanes and aromatic species using single-step deposition in Supercritical carbon dioxide (SCCO2). The process is suitable for large-scale manufacturing due to short processing times, simplicity, and high resistance to oxidation. It also allows the formation of monolayers with varying reactive terminal groups, thus enabling formation of nanostructures engineered at the molecular level. Ballistic electron emission microscopy (BEEM) spectra performed on the organic monolayer on oxide-free silicon capped by a thin gold layer reveals for the first time an increase in transmission of the ballistic current through the interface of up to three times compared to a control device, in contrast to similar studies reported in the literature suggestive of oxide-free passivation in SCCO2. The SCCO2 process combined with the preliminary BEEM results opens up new avenues for interface engineering, leading to molecular electronic devices.

  • NANOFABRICATION BY COVALENT MOLECULAR ASSEMBLY: A PATHWAY TO ROBUST STRUCTURES
    COSMOS, 2011
    Co-Authors: S. Punireddy, S. Jayaraman, R. K. Gupta, S. H. Yeong, F. Zhang, Z. Jia, M.p. Srinivasan
    Abstract:

    A wide range of new materials for many applications can be formed by controlling the composition and order of constituents at the molecular level. For systems thus engineered, ensuring chemical, thermal and mechanical robustness is a major challenge. Consequently, polyimides and other imide-containing materials are attractive as matrices for functional materials. We investigate the construction of functional nanostructures in organic/polymeric matrices with clearly demonstrated chemical, thermal and mechanical stability. Surface functionalization, layer-by-layer (LBL) assembly in various media (including Supercritical), incorporation of functional moieties, molecular orientation, and interfacial reactions are areas of interest. We demonstrate the robustness of ultrathin film structures containing polyimides and oligoimides formed by LBL molecular assembly with inter-layer covalent links. Covalent bonding between the layers provides strength, while utilizing a Supercritical Medium for the processing, results in the deployment of a solvent-free environment and avoids problems related to residual solvent, thereby improving film quality when compared to conventional films.

  • Dendrimer-encapsulated Pt nanoparticles in Supercritical Medium: synthesis, characterization, and application to device fabrication.
    Journal of colloid and interface science, 2009
    Co-Authors: Sreenivasa Reddy Puniredd, Chan Mei Yin, Yeong Sai Hooi, Pooi See Lee, M.p. Srinivasan
    Abstract:

    Abstract In this work we describe a general method for formation of Pt nanoparticles within an ultrathin film matrix and its application for non-volatile memory (NVM). Our approach involves the formation of Pt nanoparticles within ultrathin film matrix formed by covalent layer-by-layer (LbL) assembly of pyromellitic dianhydride (PMDA) and second generation of polyamidoamine (PAMAM) dendrimer in Supercritical carbon dioxide (SCCO 2 ). The hyperbranched component in the film structure serves to confine nanoparticle size and improve distribution. The memory effect and retention capability is demonstrated by means of a metal-insulator semiconductor (MIS) device fabricated using the nanoparticle-laden thin film as the insulating layer.

Jesusa Rincón - One of the best experts on this subject based on the ideXlab platform.

  • Enhancing the photocatalytic reduction of CO2 with undoped and Cu-doped TiO2 nanofibers synthesized in Supercritical Medium
    The Journal of Supercritical Fluids, 2019
    Co-Authors: Rafael Camarillo, Daniel Rizaldos, Carlos Jiménez, Fabiola Martínez, Jesusa Rincón
    Abstract:

    Abstract The photocatalytic reduction of CO2 with water vapour using titania nanofibers (TNFs) synthesized in Supercritical Medium has been assessed. TNFs have been produced from titanium isopropoxide (TTIP) precursor at different pressures (200–240 bar) and temperatures (40–80 °C). Synthesized materials were later characterized by scanning and transmission electron microscopy, BET surface area analysis, X-ray diffraction, and UV–vis diffuse reflectance spectroscopy. Better defined morphologies were obtained at the highest pressure and temperatures tested, so the catalyst synthesized at 240 bar and 60 °C was doped with copper (0.4–2 wt. %) in order to study the influence of metal doping on CO2 reduction. All undoped and Cu-doped TNFs have been found to exhibit higher CO2 reduction rates than commercial catalyst (P-25) and other TNF-based catalysts produced with traditional methods, although methane and CO remain the only two reaction products. Moreover, it has been found that copper doping improves CO2 conversion in comparison with the equivalent undoped catalyst.

  • Electrochemical reduction of CO2 using Pb catalysts synthesized in Supercritical Medium
    Journal of Catalysis, 2018
    Co-Authors: Jesús Molero García, Rafael Camarillo, Carlos Jiménez, Fabiola Martínez, Jesusa Rincón
    Abstract:

    Abstract Supercritical fluids have been used to obtain Pb/CNT catalysts consisting of Pb nanoparticles (5–10 nm of predominant size) deposited on CNT. The electrocatalytic activity of Pb/CNT catalysts has been studied by electroreduction of CO2 in gas phase using a PEM type cell in continuous operation mode. The influence of current density (8–24 mA cm−2), temperature (40–80 °C), CO2 flowrate (0.02–0.08 L min−1) and anolyte concentration (0.1–0.5 M KHCO3) have been studied in terms of products formation rate. Formic acid has been the main CO2 reduction product, followed by CO and methane, as well as methanol as minority product. The production of formic acid rises by increasing current density and CO2 flowrate within the experimental ranges studied. High CO formation rates have been observed at 80 °C, but also at low CO2 flowrate (0.02 L min−1) and at high anolyte concentration (0.5 M KHCO3). Formation rate of methane improves with increasing current density in the range studied. Regarding methanol, increasing temperature promotes its production, whereas it diminishes at higher anolyte concentration. A remarkable result that has not been reported yet for Pb electrocatalysts is the change in selectivity observed at 80 °C. At this temperature CO is the main CO2 reduction product (instead of formic acid) and the selectivity to methanol formation increases. In addition, it has been observed that Pb/CNT catalysts yield CO2 conversion rates (normalized by metal surface) 10% higher on average than Pt/CNT catalysts, and that the Pb electrocatalysts lead to larger selectivity to methanol formation. Specifically, using Pb catalysts the selectivity to methanol formation was up to 6.7%, which is almost 4 times higher than the maximum one observed with Pt catalysts.

  • Improving the photo‐reduction of CO2 to fuels with catalysts synthesized under high pressure: Cu/TiO2
    Journal of Chemical Technology & Biotechnology, 2017
    Co-Authors: Rafael Camarillo, Carlos Jiménez, Fabiola Martínez, Susana Tostón, Jesusa Rincón
    Abstract:

    BACKGROUND In previous studies the enhanced activity of TiO2-based catalysts synthesized in Supercritical Medium for photocatalytic reduction of CO2 was proved. RESULTS In this study, Cu/TiO2 photocatalysts were synthesized by hydrothermal methods in Supercritical CO2. Two titanium precursors [titanium tetraisopropoxide and diisopropoxititanium bis(acetylacetonate)], two alcohols (ethanol and isopropyl alcohol), and one metal precursor (Cu (II) acetylacetonate) were used in the synthesis. Catalysts produced showed improved properties in comparison with the commercial reference catalyst (Degussa P-25, Evonik). CONCLUSIONS Specifically, it has been found that Cu/TiO2 catalysts may yield methane production rates 20 times larger than that of commercial TiO2 catalyst without diminishing CO production rate (about 5 times higher than that of commercial catalyst). This result has been mainly imputed to both the formation of oxygen vacancies during the synthesis in Supercritical Medium and the high capacity of copper to adsorb and activate CO2 molecules, while preventing CO molecules from reoxidation, and avoiding the competitive reaction of hydrogen formation. © 2017 Society of Chemical Industry

  • preparation of tio2 based catalysts with Supercritical fluid technology characterization and photocatalytic activity in co2 reduction
    Journal of Chemical Technology & Biotechnology, 2017
    Co-Authors: Rafael Camarillo, Carlos Jiménez, Fabiola Martínez, Susana Tostón, Jesusa Rincón
    Abstract:

    BACKGROUND Titanium dioxide is the photocatalyst par excellence in environmental applications. Nevertheless, over the years various methods aiming to improve its efficiency have been presented. Herein, we report that TiO2 synthesis in Supercritical Medium can result in a significant enhancement in the rate of CO2 photocatalytic conversion. RESULTS Specifically, catalysts obtained from two titanium precursors (titanium tetraisopropoxide and diisopropoxititanium bis(acetylacetonate)) and two alcohols (ethanol and isopropyl alcohol) by hydrothermal synthesis in Supercritical CO2 are shown to exhibit improved properties in comparison with the standard reference catalyst (Degussa P-25, Evonik). CONCLUSION In particular, upgraded characteristics are related to reactants adsorption (higher specific surface areas, presence of surface hydroxyl groups), light absorption and excitation (better absorbance in visible range, lower band gap energy), and charge separation (appropriate morphology and crystallinity). Furthermore, when these catalysts are tested in the photocatalytic reduction of CO2, CO and CH4 production rates 3- and 15.7-fold higher than those corresponding to the commercial catalyst have been found. © 2016 Society of Chemical Industry

  • Electrochemical CO2 Reduction to Fuels Using Pt/CNT Catalysts Synthesized in Supercritical Medium
    Energy & Fuels, 2017
    Co-Authors: Carlos Jiménez, Rafael Camarillo, Fabiola Martínez, Jesús Molero García, Jesusa Rincón
    Abstract:

    The electrochemical reduction of CO2 in the gas phase has been carried out in a solid polymer electrolyte type cell (25 cm2 geometric area) in continuous operation mode using carbon nanotube-supported platinum catalysts (Pt/CNT). The main novelty of this work relies on the use of Supercritical media (Supercritical CO2) for Pt deposition on CNT. Supercritical synthesis has allowed obtaining small Pt nanoparticles divided into two modal distributions (for 3–4 nm and 8–9 nm, respectively) with a high deposition efficiency (about 80%). The main reaction products of the electrocatalytic conversion of CO2 have been formic acid (59–89%), methane (2–33%), CO (3–11%), methanol (0–1.9%), and small amounts of acetone, isopropanol, and methyl acetate. The CO2 conversion rate multiplies almost by four when increasing current density, although selectivity barely changes. Lower temperature promotes further reduction of CO2 to methane (33% of selectivity) to the detriment of formic acid and CO. However, increases of temp...

Sreenivasa Reddy Puniredd - One of the best experts on this subject based on the ideXlab platform.

  • Stable Organic Monolayers on Oxide-Free Silicon/Germanium in a Supercritical Medium: A New Route to Molecular Electronics.
    The journal of physical chemistry letters, 2013
    Co-Authors: Sreenivasa Reddy Puniredd, Sundaramurthy Jayaraman, Sai Hooi Yeong, Cedric Troadec, M.p. Srinivasan
    Abstract:

    Oxide-free Si and Ge surfaces have been passivated and modified with organic molecules by forming covalent bonds between the surfaces and reactive end groups of linear alkanes and aromatic species using single-step deposition in Supercritical carbon dioxide (SCCO2). The process is suitable for large-scale manufacturing due to short processing times, simplicity, and high resistance to oxidation. It also allows the formation of monolayers with varying reactive terminal groups, thus enabling formation of nanostructures engineered at the molecular level. Ballistic electron emission microscopy (BEEM) spectra performed on the organic monolayer on oxide-free silicon capped by a thin gold layer reveals for the first time an increase in transmission of the ballistic current through the interface of up to three times compared to a control device, in contrast to similar studies reported in the literature suggestive of oxide-free passivation in SCCO2. The SCCO2 process combined with the preliminary BEEM results opens up new avenues for interface engineering, leading to molecular electronic devices.

  • stable organic monolayers on oxide free silicon germanium in a Supercritical Medium a new route to molecular electronics
    Journal of Physical Chemistry Letters, 2013
    Co-Authors: Sundaramurthy Jayaraman, Sreenivasa Reddy Puniredd, Sai Hooi Yeong, Cedric Troadec, M.p. Srinivasan
    Abstract:

    Oxide-free Si and Ge surfaces have been passivated and modified with organic molecules by forming covalent bonds between the surfaces and reactive end groups of linear alkanes and aromatic species using single-step deposition in Supercritical carbon dioxide (SCCO2). The process is suitable for large-scale manufacturing due to short processing times, simplicity, and high resistance to oxidation. It also allows the formation of monolayers with varying reactive terminal groups, thus enabling formation of nanostructures engineered at the molecular level. Ballistic electron emission microscopy (BEEM) spectra performed on the organic monolayer on oxide-free silicon capped by a thin gold layer reveals for the first time an increase in transmission of the ballistic current through the interface of up to three times compared to a control device, in contrast to similar studies reported in the literature suggestive of oxide-free passivation in SCCO2. The SCCO2 process combined with the preliminary BEEM results opens up new avenues for interface engineering, leading to molecular electronic devices.

  • Dendrimer-encapsulated Pt nanoparticles in Supercritical Medium: synthesis, characterization, and application to device fabrication.
    Journal of colloid and interface science, 2009
    Co-Authors: Sreenivasa Reddy Puniredd, Chan Mei Yin, Yeong Sai Hooi, Pooi See Lee, M.p. Srinivasan
    Abstract:

    Abstract In this work we describe a general method for formation of Pt nanoparticles within an ultrathin film matrix and its application for non-volatile memory (NVM). Our approach involves the formation of Pt nanoparticles within ultrathin film matrix formed by covalent layer-by-layer (LbL) assembly of pyromellitic dianhydride (PMDA) and second generation of polyamidoamine (PAMAM) dendrimer in Supercritical carbon dioxide (SCCO 2 ). The hyperbranched component in the film structure serves to confine nanoparticle size and improve distribution. The memory effect and retention capability is demonstrated by means of a metal-insulator semiconductor (MIS) device fabricated using the nanoparticle-laden thin film as the insulating layer.

  • Covalent Molecular Assembly in a Supercritical Medium: Formation of Nanoparticles Encapsulated in Immobilized Dendrimers
    Industrial & Engineering Chemistry Research, 2007
    Co-Authors: Sreenivasa Reddy Puniredd, M.p. Srinivasan
    Abstract:

    This work demonstrates the feasibility of forming metallic nanoparticles within the confines of dendrimer-laden ultrathin films that are immobilized on a solid surface. The functional property of the poly amido amine dendrimer (PAMAM) as a sequestering agent for Cu nanoparticles was exploited by the introduction of copper acetylacetonate (Cu(acac)2) as a precursor. The nanoparticle precursors were introduced into the matrix using Supercritical carbon dioxide and liquid tetrahydrofuran (THF) as processing media. The precursors were subsequently reduced to form the nanoparticles. The resulting film assemblies were characterized via X-ray photoelectron and UV−visible absorption spectroscopies, atomic force, scanning electron, transmission electron microscopies, and ellipsometry. Higher yield, a denser distribution of nanoparticles, and greater stability toward polar solvent attack were observed when the structures were assembled in Supercritical CO2 than when THF was employed. TEM images revealed that the em...

  • Covalent molecular assembly of multilayer dendrimer ultrathin films in Supercritical Medium.
    Journal of colloid and interface science, 2006
    Co-Authors: Sreenivasa Reddy Puniredd, M.p. Srinivasan
    Abstract:

    Ultrathin films containing dendrimers are fabricated on amine- and anhydride-derivatized silicon dioxide surface through alternate layer-by-layer (LbL) assembly of pyromellitic dianhydride (PMDA) and poly(amidoamine) (PAMAM) dendrimer in Supercritical carbon dioxide (SCCO2) with interlayer linkage established by covalent bonds. X-ray photoelectron and UV-visible absorption spectroscopies, atomic force microscopy (AFM), and ellipsometry were employed to study the interfacial chemistry, growth, morphology, and thickness of the assembled film. XPS analysis suggests that the PMDA/PAMAM interlayer covalent bond is established to completion, and functional surfaces for immobilization of the next layer are available after deposition of each layer. UV-visible absorption and ellipsometry revealed layer-by-layer growth of the film. The functional property film as a porous matrix was manifested in the reduction of the refractive index upon introduction of the dendrimer.

Rafael Camarillo - One of the best experts on this subject based on the ideXlab platform.

  • Enhancing the photocatalytic reduction of CO2 with undoped and Cu-doped TiO2 nanofibers synthesized in Supercritical Medium
    The Journal of Supercritical Fluids, 2019
    Co-Authors: Rafael Camarillo, Daniel Rizaldos, Carlos Jiménez, Fabiola Martínez, Jesusa Rincón
    Abstract:

    Abstract The photocatalytic reduction of CO2 with water vapour using titania nanofibers (TNFs) synthesized in Supercritical Medium has been assessed. TNFs have been produced from titanium isopropoxide (TTIP) precursor at different pressures (200–240 bar) and temperatures (40–80 °C). Synthesized materials were later characterized by scanning and transmission electron microscopy, BET surface area analysis, X-ray diffraction, and UV–vis diffuse reflectance spectroscopy. Better defined morphologies were obtained at the highest pressure and temperatures tested, so the catalyst synthesized at 240 bar and 60 °C was doped with copper (0.4–2 wt. %) in order to study the influence of metal doping on CO2 reduction. All undoped and Cu-doped TNFs have been found to exhibit higher CO2 reduction rates than commercial catalyst (P-25) and other TNF-based catalysts produced with traditional methods, although methane and CO remain the only two reaction products. Moreover, it has been found that copper doping improves CO2 conversion in comparison with the equivalent undoped catalyst.

  • Electrochemical reduction of CO2 using Pb catalysts synthesized in Supercritical Medium
    Journal of Catalysis, 2018
    Co-Authors: Jesús Molero García, Rafael Camarillo, Carlos Jiménez, Fabiola Martínez, Jesusa Rincón
    Abstract:

    Abstract Supercritical fluids have been used to obtain Pb/CNT catalysts consisting of Pb nanoparticles (5–10 nm of predominant size) deposited on CNT. The electrocatalytic activity of Pb/CNT catalysts has been studied by electroreduction of CO2 in gas phase using a PEM type cell in continuous operation mode. The influence of current density (8–24 mA cm−2), temperature (40–80 °C), CO2 flowrate (0.02–0.08 L min−1) and anolyte concentration (0.1–0.5 M KHCO3) have been studied in terms of products formation rate. Formic acid has been the main CO2 reduction product, followed by CO and methane, as well as methanol as minority product. The production of formic acid rises by increasing current density and CO2 flowrate within the experimental ranges studied. High CO formation rates have been observed at 80 °C, but also at low CO2 flowrate (0.02 L min−1) and at high anolyte concentration (0.5 M KHCO3). Formation rate of methane improves with increasing current density in the range studied. Regarding methanol, increasing temperature promotes its production, whereas it diminishes at higher anolyte concentration. A remarkable result that has not been reported yet for Pb electrocatalysts is the change in selectivity observed at 80 °C. At this temperature CO is the main CO2 reduction product (instead of formic acid) and the selectivity to methanol formation increases. In addition, it has been observed that Pb/CNT catalysts yield CO2 conversion rates (normalized by metal surface) 10% higher on average than Pt/CNT catalysts, and that the Pb electrocatalysts lead to larger selectivity to methanol formation. Specifically, using Pb catalysts the selectivity to methanol formation was up to 6.7%, which is almost 4 times higher than the maximum one observed with Pt catalysts.

  • Improving the photo‐reduction of CO2 to fuels with catalysts synthesized under high pressure: Cu/TiO2
    Journal of Chemical Technology & Biotechnology, 2017
    Co-Authors: Rafael Camarillo, Carlos Jiménez, Fabiola Martínez, Susana Tostón, Jesusa Rincón
    Abstract:

    BACKGROUND In previous studies the enhanced activity of TiO2-based catalysts synthesized in Supercritical Medium for photocatalytic reduction of CO2 was proved. RESULTS In this study, Cu/TiO2 photocatalysts were synthesized by hydrothermal methods in Supercritical CO2. Two titanium precursors [titanium tetraisopropoxide and diisopropoxititanium bis(acetylacetonate)], two alcohols (ethanol and isopropyl alcohol), and one metal precursor (Cu (II) acetylacetonate) were used in the synthesis. Catalysts produced showed improved properties in comparison with the commercial reference catalyst (Degussa P-25, Evonik). CONCLUSIONS Specifically, it has been found that Cu/TiO2 catalysts may yield methane production rates 20 times larger than that of commercial TiO2 catalyst without diminishing CO production rate (about 5 times higher than that of commercial catalyst). This result has been mainly imputed to both the formation of oxygen vacancies during the synthesis in Supercritical Medium and the high capacity of copper to adsorb and activate CO2 molecules, while preventing CO molecules from reoxidation, and avoiding the competitive reaction of hydrogen formation. © 2017 Society of Chemical Industry

  • preparation of tio2 based catalysts with Supercritical fluid technology characterization and photocatalytic activity in co2 reduction
    Journal of Chemical Technology & Biotechnology, 2017
    Co-Authors: Rafael Camarillo, Carlos Jiménez, Fabiola Martínez, Susana Tostón, Jesusa Rincón
    Abstract:

    BACKGROUND Titanium dioxide is the photocatalyst par excellence in environmental applications. Nevertheless, over the years various methods aiming to improve its efficiency have been presented. Herein, we report that TiO2 synthesis in Supercritical Medium can result in a significant enhancement in the rate of CO2 photocatalytic conversion. RESULTS Specifically, catalysts obtained from two titanium precursors (titanium tetraisopropoxide and diisopropoxititanium bis(acetylacetonate)) and two alcohols (ethanol and isopropyl alcohol) by hydrothermal synthesis in Supercritical CO2 are shown to exhibit improved properties in comparison with the standard reference catalyst (Degussa P-25, Evonik). CONCLUSION In particular, upgraded characteristics are related to reactants adsorption (higher specific surface areas, presence of surface hydroxyl groups), light absorption and excitation (better absorbance in visible range, lower band gap energy), and charge separation (appropriate morphology and crystallinity). Furthermore, when these catalysts are tested in the photocatalytic reduction of CO2, CO and CH4 production rates 3- and 15.7-fold higher than those corresponding to the commercial catalyst have been found. © 2016 Society of Chemical Industry

  • Electrochemical CO2 Reduction to Fuels Using Pt/CNT Catalysts Synthesized in Supercritical Medium
    Energy & Fuels, 2017
    Co-Authors: Carlos Jiménez, Rafael Camarillo, Fabiola Martínez, Jesús Molero García, Jesusa Rincón
    Abstract:

    The electrochemical reduction of CO2 in the gas phase has been carried out in a solid polymer electrolyte type cell (25 cm2 geometric area) in continuous operation mode using carbon nanotube-supported platinum catalysts (Pt/CNT). The main novelty of this work relies on the use of Supercritical media (Supercritical CO2) for Pt deposition on CNT. Supercritical synthesis has allowed obtaining small Pt nanoparticles divided into two modal distributions (for 3–4 nm and 8–9 nm, respectively) with a high deposition efficiency (about 80%). The main reaction products of the electrocatalytic conversion of CO2 have been formic acid (59–89%), methane (2–33%), CO (3–11%), methanol (0–1.9%), and small amounts of acetone, isopropanol, and methyl acetate. The CO2 conversion rate multiplies almost by four when increasing current density, although selectivity barely changes. Lower temperature promotes further reduction of CO2 to methane (33% of selectivity) to the detriment of formic acid and CO. However, increases of temp...

Carlos Jiménez - One of the best experts on this subject based on the ideXlab platform.

  • Enhancing the photocatalytic reduction of CO2 with undoped and Cu-doped TiO2 nanofibers synthesized in Supercritical Medium
    The Journal of Supercritical Fluids, 2019
    Co-Authors: Rafael Camarillo, Daniel Rizaldos, Carlos Jiménez, Fabiola Martínez, Jesusa Rincón
    Abstract:

    Abstract The photocatalytic reduction of CO2 with water vapour using titania nanofibers (TNFs) synthesized in Supercritical Medium has been assessed. TNFs have been produced from titanium isopropoxide (TTIP) precursor at different pressures (200–240 bar) and temperatures (40–80 °C). Synthesized materials were later characterized by scanning and transmission electron microscopy, BET surface area analysis, X-ray diffraction, and UV–vis diffuse reflectance spectroscopy. Better defined morphologies were obtained at the highest pressure and temperatures tested, so the catalyst synthesized at 240 bar and 60 °C was doped with copper (0.4–2 wt. %) in order to study the influence of metal doping on CO2 reduction. All undoped and Cu-doped TNFs have been found to exhibit higher CO2 reduction rates than commercial catalyst (P-25) and other TNF-based catalysts produced with traditional methods, although methane and CO remain the only two reaction products. Moreover, it has been found that copper doping improves CO2 conversion in comparison with the equivalent undoped catalyst.

  • Electrochemical reduction of CO2 using Pb catalysts synthesized in Supercritical Medium
    Journal of Catalysis, 2018
    Co-Authors: Jesús Molero García, Rafael Camarillo, Carlos Jiménez, Fabiola Martínez, Jesusa Rincón
    Abstract:

    Abstract Supercritical fluids have been used to obtain Pb/CNT catalysts consisting of Pb nanoparticles (5–10 nm of predominant size) deposited on CNT. The electrocatalytic activity of Pb/CNT catalysts has been studied by electroreduction of CO2 in gas phase using a PEM type cell in continuous operation mode. The influence of current density (8–24 mA cm−2), temperature (40–80 °C), CO2 flowrate (0.02–0.08 L min−1) and anolyte concentration (0.1–0.5 M KHCO3) have been studied in terms of products formation rate. Formic acid has been the main CO2 reduction product, followed by CO and methane, as well as methanol as minority product. The production of formic acid rises by increasing current density and CO2 flowrate within the experimental ranges studied. High CO formation rates have been observed at 80 °C, but also at low CO2 flowrate (0.02 L min−1) and at high anolyte concentration (0.5 M KHCO3). Formation rate of methane improves with increasing current density in the range studied. Regarding methanol, increasing temperature promotes its production, whereas it diminishes at higher anolyte concentration. A remarkable result that has not been reported yet for Pb electrocatalysts is the change in selectivity observed at 80 °C. At this temperature CO is the main CO2 reduction product (instead of formic acid) and the selectivity to methanol formation increases. In addition, it has been observed that Pb/CNT catalysts yield CO2 conversion rates (normalized by metal surface) 10% higher on average than Pt/CNT catalysts, and that the Pb electrocatalysts lead to larger selectivity to methanol formation. Specifically, using Pb catalysts the selectivity to methanol formation was up to 6.7%, which is almost 4 times higher than the maximum one observed with Pt catalysts.

  • Improving the photo‐reduction of CO2 to fuels with catalysts synthesized under high pressure: Cu/TiO2
    Journal of Chemical Technology & Biotechnology, 2017
    Co-Authors: Rafael Camarillo, Carlos Jiménez, Fabiola Martínez, Susana Tostón, Jesusa Rincón
    Abstract:

    BACKGROUND In previous studies the enhanced activity of TiO2-based catalysts synthesized in Supercritical Medium for photocatalytic reduction of CO2 was proved. RESULTS In this study, Cu/TiO2 photocatalysts were synthesized by hydrothermal methods in Supercritical CO2. Two titanium precursors [titanium tetraisopropoxide and diisopropoxititanium bis(acetylacetonate)], two alcohols (ethanol and isopropyl alcohol), and one metal precursor (Cu (II) acetylacetonate) were used in the synthesis. Catalysts produced showed improved properties in comparison with the commercial reference catalyst (Degussa P-25, Evonik). CONCLUSIONS Specifically, it has been found that Cu/TiO2 catalysts may yield methane production rates 20 times larger than that of commercial TiO2 catalyst without diminishing CO production rate (about 5 times higher than that of commercial catalyst). This result has been mainly imputed to both the formation of oxygen vacancies during the synthesis in Supercritical Medium and the high capacity of copper to adsorb and activate CO2 molecules, while preventing CO molecules from reoxidation, and avoiding the competitive reaction of hydrogen formation. © 2017 Society of Chemical Industry

  • preparation of tio2 based catalysts with Supercritical fluid technology characterization and photocatalytic activity in co2 reduction
    Journal of Chemical Technology & Biotechnology, 2017
    Co-Authors: Rafael Camarillo, Carlos Jiménez, Fabiola Martínez, Susana Tostón, Jesusa Rincón
    Abstract:

    BACKGROUND Titanium dioxide is the photocatalyst par excellence in environmental applications. Nevertheless, over the years various methods aiming to improve its efficiency have been presented. Herein, we report that TiO2 synthesis in Supercritical Medium can result in a significant enhancement in the rate of CO2 photocatalytic conversion. RESULTS Specifically, catalysts obtained from two titanium precursors (titanium tetraisopropoxide and diisopropoxititanium bis(acetylacetonate)) and two alcohols (ethanol and isopropyl alcohol) by hydrothermal synthesis in Supercritical CO2 are shown to exhibit improved properties in comparison with the standard reference catalyst (Degussa P-25, Evonik). CONCLUSION In particular, upgraded characteristics are related to reactants adsorption (higher specific surface areas, presence of surface hydroxyl groups), light absorption and excitation (better absorbance in visible range, lower band gap energy), and charge separation (appropriate morphology and crystallinity). Furthermore, when these catalysts are tested in the photocatalytic reduction of CO2, CO and CH4 production rates 3- and 15.7-fold higher than those corresponding to the commercial catalyst have been found. © 2016 Society of Chemical Industry

  • Electrochemical CO2 Reduction to Fuels Using Pt/CNT Catalysts Synthesized in Supercritical Medium
    Energy & Fuels, 2017
    Co-Authors: Carlos Jiménez, Rafael Camarillo, Fabiola Martínez, Jesús Molero García, Jesusa Rincón
    Abstract:

    The electrochemical reduction of CO2 in the gas phase has been carried out in a solid polymer electrolyte type cell (25 cm2 geometric area) in continuous operation mode using carbon nanotube-supported platinum catalysts (Pt/CNT). The main novelty of this work relies on the use of Supercritical media (Supercritical CO2) for Pt deposition on CNT. Supercritical synthesis has allowed obtaining small Pt nanoparticles divided into two modal distributions (for 3–4 nm and 8–9 nm, respectively) with a high deposition efficiency (about 80%). The main reaction products of the electrocatalytic conversion of CO2 have been formic acid (59–89%), methane (2–33%), CO (3–11%), methanol (0–1.9%), and small amounts of acetone, isopropanol, and methyl acetate. The CO2 conversion rate multiplies almost by four when increasing current density, although selectivity barely changes. Lower temperature promotes further reduction of CO2 to methane (33% of selectivity) to the detriment of formic acid and CO. However, increases of temp...