Browsing by Author "Llanos, Jaime"

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    Catalytic evaluation of MOF-808 with metallic centers of Zr(IV), Hf(IV) and Ce(IV) in the acetalization of benzaldehyde with methanol
    (Royal Society Chemistry, 2024) Arellano Valderrama, Yazmin Anay; Pazo Carballo, César Alexander; Roa, Vanesa; Hidalgo-Rosa, Yoan; Zarate, Ximena; Llanos, Jaime; Escalona Burgos, Nestor Guillermo; Schott, Eduardo
    In the context of climate change, it is of utmost importance to replace the use of fossil fuels as raw material in areas of industrial interest, for example, in the production of chemical inputs. In this context, a viable option is biomass, since by subjecting it to chemical processes such as pyrolysis, it is possible to obtain platform molecules that are the basis for the generation of value-added chemical products. Acetals are molecules obtained from biomass derIVatIVes, which have various applications in cosmetic chemistry, in the pharmaceutical industry as intermediates or final compounds, food additIVes, among others. Different catalysts have been used in the acetalization reaction, including MOFs, which have the advantage of being porous materials with high surface area values. The large surface area translates into a greater number of catalytically actIVe sites available for the reaction. Among the MOFs that have been used for this purpose is MOF-808, which is characterized by having a lower number of ligands attached to its metal cluster, therefore, it has a greater exposure of the metals that make up its structure. In this context, the work carried out studied the catalytic performance of MOF-808 when its Zr(IV) metal centers are replaced by Hf(IV) and Ce(IV) atoms in the acetalization reaction of benzaldehyde with methanol. The MOFs obtained by solvothermal synthesis were characterized by powder X-ray diffraction, N-2 adsorption and desorption, FT-IR spectroscopy, acid-base potentiometric titration, XPS and thermogravimetric analysis. The results of the catalysis indicate that the MOF with the best performance was MOF-808-Ce, which achieved conversions greater than 80% in a period of ten minutes. MOF-808-Ce exhibits a higher number of defects and therefore a higher availability of catalytic sites for the reaction to occur, which explains the better performance. Finally, the performance of MOF-808 in the acetalization of benzaldehyde with methanol was also supported by density functional theory (DFT) calculations.
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    The development of Au-titania photoanode composites toward semiflexible dye-sensitized solar cells
    (2023) Castillo-Rodriguez, Judith; Ortiz, Pedro D.; Mahmood, Reeda; Gossage, Robert A.; Llanos, Jaime; Espinoza, Dario; Zarate, Ximena; Koivisto, Bryan D.; Schott, Eduardo
    Considering the widespread use of windows in modern urban landscapes, converting these substrates into photovoltaic devices would remarkably impact modern energy generation. A flexible dye-sensitized solar cell (DSSC) architecture is preferred for such applications. A key component of the DSSC is the dye-sensitized photoanode. Herein, we examine different nanoparticle composites within the semiconductor anode formulation and their effect on device performance. Mesoporous titania particles (TiO2) modified with Au-nanoparticles (TiO2@AuNPs) were synthesized using precipitation strategies to assess the solvent effect on the particle size and the efficiency of the devices. The materials were then fully characterized through SEM, XRD, and DRS before and after thermal treatment. A paste prepared from the synthesized semiconductors was applied onto the substrate using the doctor blading technique. The use of high thermal treatment for glass substrates (HTT), low temperature thermal treatment (LTT), and LTT combined with 2 h of UV curing (LTT_UV) was explored. In the case of ITO/PET (flexible substrate) only low temperature thermal treatment were used (LTT and LTT_UV). After characterization (XRD and DRS), the anodes were loaded using a metal-free dye. To complete the comparison, several groups of cells were characterized: considering solvent (EtOH and EtOH:H2O), thermal treatment (HTT, LTT, and LTT_UV), and semiconductor material (TiO2 and TiO2@AuNP). Rigid (glass anode-glass cathode) and semiflexible (flexible anode-glass cathode) DSSCs were obtained with efficiencies from 0.03% to 2.4%, with a substantial performance difference seen using different thermal treatments, and a mild to low effect on semiconductor composition and the used substrate.