Sulfuros metálicos para la conversión de energía: Síntesis, caracterización y uso en celdas fotoelectroquímicas para la generación de hidrógeno

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de Materiales. Fecha de lectura: 12-06-201

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

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

Photoinduced Charge Transfer and Trapping on Single Gold Metal Nanoparticles on TiO2

We present a study of the effect of gold nanoparticles (Au NPs) on TiO2 on charge generation and trapping during illumination with photons of energy larger than the substrate band gap. We used a novel characterization technique, photoassisted Kelvin probe force microscopy, to study the process at the single Au NP level. We found that the photoinduced electron transfer from TiO2 to the Au NP increases logarithmically with light intensity due to the combined contribution of electron-hole pair generation in the space charge region in the TiO2-air interface and in the metal-semiconductor junction. Our measurements on single particles provide direct evidence for electron trapping that hinders electron-hole recombination, a key factor in the enhancement of photo(electro)catalytic activity.This work was supported by the Office of Basic Energy Sciences (BES) of the U.S. Department of Energy (DOE) under contract DE-AC02-05CH11231 through the Structure and Dynamics of Materials Interfaces Program (FWP KC31SM) and the Molecular Foundry. M.L. acknowledges funds from Comunidad de Madrid (P2018/EMT-4308), a Fulbright grant PRX16/00564, and the MCIU-AEI-FEDERUE (RTI2018-096937-B-C22 and MAT2014-59772-C2-1-P). J.C. acknowledges financial support from Ministerio de Ciencia e Innovación (MICINN) and the European Union through the project PID2019-104272RB-C52. Also, Y.H. acknowledges financial support from MCIU through MAT2014-59772-C2-2- P and L.M. from EC through ERC-2013-SYG-610256. V.A.P.O. and M.B. acknowledge the financial support from EC through ERC CoG HyMAP 648319, MINECO PID2019- 106315RB-I00 and ENE2017-89170-R, ″Comunidad de Madrid″ and European Structural Funds (FotoArt-CM project S2018/NMT-4367) and Fundación Ramón Areces (Art-Leaf project). M.B. also thanks the Juan de la Cierva Incorporación contract (IJC2019042430-I). X.Z. was supported by the NSF-BSF 359 grant number 1906014. The authors thank Prof. Eran Edri, María Ujué González Sagardoy, and Judit Meseguer- Oliver for fruitful discussions and Asylum customer support for help with modifications of the AFM

Photo-Induced Self-Cleaning and Wettability in TiO2 Nanocolumn Arrays Obtained by Glancing-Angle Deposition with Sputtering

In this work, the preparation of regular nanosized columnar structures of titanium dioxide by means of glancing angle deposition with magnetron sputtering (MS-GLAD) followed by thermal annealing is reported. MS-GLAD gives rise to metallic titanium columnar structures with regular width and length that after thermal treatment are fully oxidized to form TiO2 nanocolumns that maintain the morphological features of the original metallic ones. Further functionalization with gold by means of multiple ion cluster source results in well-dispersed Au nanoparticles across the nanocolumns’ surface with a narrow size distribution centered at ca. 8.5 nm. The obtained nanostructures show photocatalytic self-cleaning activity as shown by the elimination of an organic layer deposited on their surface and the detection of hydroxyl radicals. Photoelectrochemical measurements show a better charge separation at the Au/TiO2 interface. In addition, wettability studies show that the degree of hydrophobicity of the surface is increased by the presence of nanocolumns, both in the dark and under UV illumination. This behavior is not modified by the presence of Au nanoparticles on the surface. The obtained results open up interesting implications in the tunability of the properties of nanostructured thin films for this kind of photo-activated application.Financial support from the Spanish Ministry of Science, Innovation, and Universities (MICINN) through the projects SOLPAC (ENE2017-89170-R, MCIU/AEI/FEDER, EU), MAT2014-59772-C2-1-P, and MAT2014-59772-C2-2-P is gratefully acknowledged. The authors also acknowledge the service from the MiNa Laboratory at IMN funded by Comunidad de Madrid (S2018/NMT-4291 TEC2SPACE), MICINN (CSIC13-4E-1794), and the EU (FEDER, FSE). Also, this work has been funded by the regional government of Madrid and European Structural Funds through their financial support to FotoArt-CM program (S2018/NMT-4367), and from Fundación Ramon Areces though the ArtLeaf project. M.B. thanks MICINN for a Juan de la Cierva Incorporación (IJC2019-042430-I) grant.Peer reviewe

Fundamental Insights into Photoelectrocatalytic Hydrogen Production with a Hole-Transport Bismuth Metal–Organic Framework

[EN] Solar fuels production is a cornerstone in the development of emerging sustainable energy conversion and storage technologies. Light-induced H2 production from water represents one of the most crucial challenges to produce renewable fuel. Metalorganic frameworks (MOFs) are being investigated in this process, due to the ability to assemble new structures with the use of suitable photoactive building blocks. However, the identification of the reaction intermediates remains elusive, having negative impacts in the design of more efficient materials. Here, we report the synthesis and characterization of a new MOF prepared with the use of bismuth and dithieno[3,2-b:2',3'-d]thiophene-2,6-dicarboxylic acid (DTTDC), an electron-rich linker with hole transport ability. By combining theoretical studies and time-resolved spectroscopies, such as core hole clock and laser flash photolysis measurements, we have completed a comprehensive study at different time scales (fs to-ms) to determine the effect of competitive reactions on the overall H2 production. We detect the formation of an intermediate radical anion upon reaction of photogenerated holes withan electron donor, which plays a key role in the photoelectrocatalytic processes. These results shed new light on the use of MOFs for solar fuel production.This work was supported by the EU (ERC CoG HyMAP 648319) and Spanish MCIU, Ra-Phuel (ENE2016-79608-C2-1-R), SOLPAC (ENE2017-89170-R) FOTOFUEL (ENE2016-82025-REDT) and CTQ2017-87262-R (MCIU/AEI/FEDER, UE). We thank "Comunidad de Madrid" and European Structural Funds for their financial support to FotoArt-CM project (S2018/NMT-4367). F.G., M. L and M. B thank to MINECO and European Social Fund for a Ramón y Cajal contract (RyC-2015-18384, RyC-2015-18677) and Juan de la Cierva Formación contract (FJCI-2016-30567), respectively. We thank Diamond Facilities for the access to synchrotron radiation and CESCA for computational resources.Peer reviewe