16 research outputs found
A Graphene Acid - TiO2 Nanohybrid as Multifunctional Heterogeneous Photocatalyst for the Synthesis of 1,3,4-Oxadiazoles
The immobilization of TiO2 nanoparticles on
graphene acid (GA), a conductive graphene derivative densely
functionalized with COOH groups, is presented. The interaction
between the carboxyl groups of the surface and the titanium
precursor leads to a controlled TiO2 heterogenization on the
nanosheet according to microscopic and spectroscopic characterizations. Electronic communication shared among graphene and
semiconductor nanoparticles shifts the hybrid material optical
features toward less energetic radiation but maintaining the conductivity. Therefore, GA-TiO2 is employed as heterogeneous
photocatalyst for the synthesis of 2,5-disubstituted 1,3,4-oxadiazoles using ketoacids and hydrazides as substrates. The material
presented enhanced photoactivity compared to bare TiO2, being able to yield a large structural variety of oxadiazoles in reaction
times as fast as 1 h with full recyclability and stability. The carbocatalytic character of GA is the responsible for the substrates
condensation and the GA-TiO2 light interaction ability is able to photocatalyze the cyclization to the final 1,3,4-oxadiazoles,
demonstrating the optimal performance of this multifunctional photocatalytic materialFinancial support was provided by the Spanish Government
(RTI2018-095038-B-I00), FotoaArt “Comunidad de Madrid”,
and European Structural Funds (S2018/NMT-4367) proyectos sinérgicos I+D (Y2020/NMT-6469) and Comunidad
Autónoma de Madrid (SI1/PJI/2019-00237). M.B. and M.B.
thank the Spanish MICINN for the Juan de la Cierva
Incorporación contracts (IJC2019-042157-I and IJC2019-
042430-I). We also acknowledge the electron microscopy
analysis from CNME. This work was supported by the national
project NovaCO2 (PID2020-118593RB-C22) funded by
MCIN/AEI/10.13039/50110001103
Towards the improvement of methane production in CO2 photoreduction using Bi2WO6/TiO2 heterostructures
Russelite bismuth tungstate (Bi2WO6) has been widely reported for the photocatalytic degradation and mineralization of a myriad of pollutants as well as organic compounds. These materials present perovskite-like structure with hierarchical morphologies, which confers excellent optoelectronic properties as potentials candidates for photocatalytic solar fuels production. Here, we propose the development of Bi2WO6/TiO2 heterojunctions for CO2 photoreduction, as a promising solution to produce fuels, alleviate global warming and tackle fossil fuel shortage. Our results show an improvement of the photocatalytic activity of the heterojunctions compared to the pristine semiconductors. Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) experiments reveals a preferential CO2 adsorption over TiO2. On the other hand, transient absorption spectroscopy measurements show that the charge transfer pathway in Bi2WO6/TiO2 hybrids leads to longer-lived photogenerated carriers in spatially separated redox active sites, which favor the reduction of CO2 into highly electron demanding fuels and chemicals, such as CH4 and C2H6Financial support has been received from the European Research
Council (ERC), through HYMAP project (grant agreement No. 648319),
under the European Union's Horizon 2020 research and innovation
program, as well as from the Marie Sklodowska-Curie grant agreement
No. 754382. L.C. acknowledges funding from the project ARMONIA
(PID2020–119125RJ-I00) funded by MCIN/AEI/10.13039/
501100011033. Financial support has also been received from AEIMINECO/FEDER (Nympha Project, PID2019–106315RB-I00), "Comunidad de Madrid" regional government, and the European Structural
Funds (FotoArt-CM project, S2018/NMT-4367). Authors also acknowledge financial support from the grant PLEC2021–007906 funded by MCIN/AEI/10.13039/501100011033 and the "European Union
NextGenerationEU/PRTR"
Hydroxamate Titanium−Organic Frameworks and the Effect of Siderophore-Type Linkers over Their Photocatalytic Activity
The chemistry of Metal-Organic Frameworks (MOFs) relies on the controlled linking of organic molecules and inorganic secondary building units to assemble an unlimited number of reticular frameworks. However, the design of porous solids with chemical stability remains still limited to carboxylate or azolate groups. There is a timely opportunity to develop new synthetic platforms that make use of unexplored metal binding groups to produce metal-linker joints with hydrolytical stability. Living organisms use siderophores (iron carriers in greek) to effectively assimilate iron in soluble form. These compounds make use of hard oxodonors as hydroxamate or catecholate groups to coordinate metal Lewis acids like iron, aluminium or titanium to form metal complexes very stable in water. Inspired by the chemistry of these microorganisms, we report the first hydroxamate MOF prepared by direct synthesis. MUV-11 (MUV = Materials of Universidad de Valencia) is a crystalline, porous material (close to 800 m2·g-1) that combines photoactivity with good chemical stability in acid conditions. By using a high-throughput approach, we also demonstrate that this new chemistry is compatible with the formation of single crystalline phases for multiple titanium salts, thus expanding the scope of precursors accessible. Titanium frameworks are regarded as promising materials for photocatalytic applications. Our photoelectrochemical and catalytic tests suggests important differences for MUV-11. Compared to other Ti-MOFs, changes in the photoelectrochemical and photocatalytic activity have been rationalized with computational modelling revealing how the chemistry of siderophores can introduce changes to the electronic structure of the frontier orbitals, relevant to the photocatalytic activity of these solids
Understanding Charge Transfer Mechanism on Effective Truxene-Based Porous Polymers–TiO2 Hybrid Photocatalysts for Hydrogen Evolution
[EN] Truxene-based porous polymers synthesized through the simple “solvent knitting”
strategy from hexamethyl or tribenzyl truxene-based monomers (TxPP1 and TxPP2), and their
corresponding TxPP@TiO2 hybrids are used as photocatalysts for H2 production from water using
methanol as sacrificial agent, under UV-Vis light. These polymers present higher hydrogen
evolution rate (HER) than TiO2, and remarkable thermo- and photo-stabilities. Hybrids TxPP-TiO2
exhibited intensely enhanced photocatalytic activity compared to TiO2 or TxPPs alone. In the
presence of platinum (1%) as cocatalyst, HER from TxPP1@T-10 significantly boosted reaching
values above 21000 μmol.g-1.h-1 which to the best of our knowledge, represents the highest HER
reported for hybrids based on TiO2 and conjugated porous polymers. Interestingly, small structural
differences of the corresponding truxene monomers result in different photocatalytic behavior. We
focused here on gaining insight on the charge transfer mechanism and rationalizing the different
photocatalytic performances in order to establish clear structure-activity relationships. In fact,
photoluminescence and transient absorption spectroscopy demonstrated that the remarkably
enhanced photocatalytic activity of the most active hybrids (TxPP1@TiO2) can be attributed to the
efficiently photogenerated electron-hole separation by a direct Z-scheme mechanism, while lower performance of TxPP2@TiO2, is probably due to a less efficient heterojunction type II charge
transfer mechanism.Authors acknowledge to MINECO/AEI/FEDER, UE of Spain (Projects MAT2017-82288-C2-2-P, CTQ2016-78557-R and ENE2016-79608-C2-1-R) and regional government of “Comunidad de Madrid” and European Structural Funds for their financial support to FotoArt-CM project (S2018/NMT-4367). AVG thanks Ministerio de Educación y Formación Profesional for FPU17/03463, M. L and M. B thank to MINECO and European Social Fund for a Ramón y Cajal grant (RyC-2015-18677) and Juan de la Cierva Formación grant (FJCI-2016-30567) respectively.Peer reviewe