Silicone microreactors for the photocatalytic generation of hydrogen

A silicone microreactor with 500 mu m-width microchannels coated with a Au/TiO2 photocatalyst was manufactured and tested for the photocatalytic generation of hydrogen from gaseous water-ethanol mixtures under dynamic conditions. The manufacture of the microreactor included the fabrication of a polylactic acid (PLA) mold with a 3D printer and casting with polydimethylsiloxane (PDMS) prepolymer. After curing, the silicone microreactor was peeled off and the microchannels were coated with a Au/TiO2 photocatalyst prepared by impregnation of preformed Au nanoparticles over TiO2, and sealed with a thin silicone cover. The microreactor was tested at room temperature and atmospheric pressure under different operational conditions (photon irradiance, residence time, photocatalyst loading, and water ethanol ratio). Hydrogen production rates of 5.4 NmL W-1 h(-1) were measured at a residence time of 0.35 s using a H2O:C2H5OH molar ratio of 9:1, a photocatalyst load of 1.2 mg cm(-2) and a UV irradiance (365 nm) of 1.5 mW cm(-2) achieving an apparent quantum efficiency of 9.2%. The photogeneration of hydrogen with commercial bioethanol was also tested. A long-term photocatalytic test of two days revealed a stable hydrogen photoproduction rate. The use of silicone microreactors represents an attractive and customizable solution for conducting photochemical reactions for producing hydrogen at low cost. (C) 2016 Elsevier B.V. All rights reserved.Postprint (published version

CO oxidation and COPrOx over preformed Au nanoparticles supported over nanoshaped CeO2

Au/CeO2 (0.25% wt. Au) catalysts were prepared by anchoring preformed Au nanoparticles over ceria polycrystals, cubes and rods and tested in the oxidation of CO and COPrOx. The use of preformed Au nanoparticles assured a constant Au particle size (ca. 5 nm by HRTEM) for all samples, which allowed to a precise assessment of the effect of the morphology of nanoshaped ceria on catalytic activity. The catalytic performance of the Au/CeO2-rods was much better than that of the Au/CeO2-polycrystals and Au/CeO2-cubes both in the oxidation of CO and COPrOx reactions. The Au/CeO2-rods exhibited the highest amount of oxidized Au and Ce(III) species by XPS, whereas in the Au/CeO2-cubes gold was totally metallic and the amount of Ce(III) was minimum. An intermediate situation was encountered in the Au/CeO2-polycrystals. Considering the differences in the oxidation states ofAu and Ce and the factthat all samples were prepared with preformed metallic Au nanoparticles of the same size, the results indicate that the intrinsic nature of the different ceria surfaces exerts a prominent role in the gold-ceria interaction and in the electron density transfer from Au to Ce, which in turn has a strong effect on catalytic activity. Gold nanoparticles strongly interact with CeO2-{1 1 0} surfaces with respect to CeO2-{1 1 1} and CeO2-{1 0 0}, even when Au nanoparticles are prepared separately and simply deposited by impregnation.Postprint (author's final draft

Hydrogen photoproduction from ethanol-water mixtures over Au-Cu alloy nanoparticles supported on TiO2

Au/TiO2, Au0.75Cu0.25/TiO2, Au0.5Cu0.5/TiO2 and Au0.25Cu0.75/TiO2 photocatalysts prepared from pre-formed Au and Au-Cu alloy nanoparticles of controlled composition and size were loaded over ceramic honeycombs (2 mg cm(-2)) and tested in an optical fiber photoreactor illuminated with UV LEDs (2.6 mW cm(-2)) to continuously produce hydrogen from water and ethanol mixtures in gas phase at W/F = 4 g min L-1 and 298 K (where W is the weight of the catalyst and F is the flow rate). The photocatalytic honeycombs were characterized by high resolution transmission electron microscopy, high-angle annular dark-field imaging, energy dispersive X-ray, X-ray photoelectron spectroscopy, and UV-Vis spectroscopy. The yield of hydrogen generation was Au0.75Cu0.25/TiO2 > Au0.5Cu0.5/TiO2 similar to Au/TiO2 > Au0.25Cu0.75/TiO2 >> bare TiO2, thus demonstrating that the addition of small quantities of copper to conventional TiO2-supported gold photocatalysts promotes the photocatalyic activity, likely by providing effective charge transfer between Au and Cu in the alloy nanoparticles.Postprint (published version

Estudios hacía la reactividad fotoquímica con el uso de reactivos de organoyodo hipervalente y organo(trifluoro)boratos

Treballs Finals de Grau de Química, Facultat de Química, Universitat de Barcelona, Any: 2019, Tutors: Albert Figuerola Silvestre, Alexandr ShafirControlled photochemical generation of reactive radical species has become a powerful bond-forming tool in organic synthesis. In this project, we have performed initial and preliminary studies towards photochemical radical generation using the C-O bond of hypervalent iodine reagents. We also initiated a project (for the first time in the group) to carry out dual nickel/photoredox coupling of α-substituted C(sp3) trifluoroborates. Studies towards hypervalent iodine compounds have been successfully realized. Focusing on the first goal, the generation and the controlled transfer of ·CF2H and ·CFH2 radicals to C-H positions of activated heterocyclic substrates via homolytic I-O cleavage followed by decarboxylation process has been successfully carried out. Specifically, new hypervalent reagents have been designed and prepared in order to help prevent harmful radical side reactions. In another iodane-based approach, the synthesis of 1,8-diiodonaphthalene by homolytic bond cleavage and later decarboxylation process was assayed. For comparison, the target compound was also obtained by the diazonium salt intermediate. The adaptation of the photochemical (diradical) route to a small-scale photoreactor has proven challenging and will be continued in the group. The last goal which is the synthesis of two different Iridium photocatalyst to be applied in cross-coupling photo-redox reactions has been achieved. The photocatalyst synthesis has been successful realized in all steps, obtaining the desired pure catalysts as a crystalline yellow powder. On the other hand, the cross-coupling photo-redox products have not been obtained due to the air sensitivity of the other photocatalyst used in this process, Ni(COD)2. However, with the use of a more robust Ni complex (e.g. [glyme]NiCl2), we anticipate that this final objective could be successfully achieved in the host research grou

Magnetite-supported palladium single-atoms do not catalyse the hydrogenation of alkenes but small clusters do

The activity of supported noble metal catalysts strongly depends on the particle size. The ultimate small-size limit is the single-atom catalyst (SAC), which maximizes the catalytic efficiency in the majority of the examples. Here, we investigate the catalytic behavior of Pd SACs supported on magnetite nanoparticles and we unambiguously demonstrate that Pd SACs are absolutely inactive in the hydrogenation of various alkene substrates. Instead, Pd clusters of low atomicity exhibit outstanding catalytic performance.Postprint (author's final draft

Operacions bàsiques al laboratori químic en xarxa : una nova eina per a estudiants i professors

Un conjunt de professors de les facultats de Química i Farmàcia de la Universitat de Barcelona hem elaborat un material docent en suport electrònic, d'accés lliure a la xarxa, que descriu el procediment pràctic de diverses operacions bàsiques de treball al laboratori químic. L'objectiu principal és crear un material docent que serveixi de suport a l'aprenentatge dels estudiants i a la tasca docent del professorat involucrat en l'ensenyament del treball pràctic en l'etapa d'inici dels estudis universitaris.A group of lecturers from the Chemistry and Pharmacy faculties at the University of Barcelona has prepared an electronically supported teaching material, of free access on-line, which shows the procedure for several basic chemical laboratory techniques. The main goal of the project was to offer an electronic aid for the student’s learning as well as for the lecturers involved in the teaching process, both at the high school and the graduate levels

Projecte del ramal d'abastament d'aigua a Sant Feliu de Codines - Sant Quirze Safaja

L’objecte del projecte és la definició, descripció i valoració de les obres del Projecte del Ramal d’Abastament d’aigua a Sant Feliu de Codines – Sant Quirze Safaja. Es pretén amb aquesta prolongació de la xarxa d’abastament donar servei a la totalitat de Sant Feliu de Codines, Sant Quirze Safaja, Castellcir i Castellterçol, ja que actualment no estan connectats a la xarxa d’ATLL i s’abasteixen de pous propis i alguns sistemes de camions cisterna

Projecte del ramal d'abastament d'aigua a Sant Feliu de Codines - Sant Quirze Safaja

L’objecte del projecte és la definició, descripció i valoració de les obres del Projecte del Ramal d’Abastament d’aigua a Sant Feliu de Codines – Sant Quirze Safaja. Es pretén amb aquesta prolongació de la xarxa d’abastament donar servei a la totalitat de Sant Feliu de Codines, Sant Quirze Safaja, Castellcir i Castellterçol, ja que actualment no estan connectats a la xarxa d’ATLL i s’abasteixen de pous propis i alguns sistemes de camions cisterna