325 research outputs found
Observation of charge transfer cascade in α-Fe2O3/IrO2 photoanodes by in-operando X-rays absorption spectroscopy
No full textIn this work we show the direct observation, by means of spectro-photoelectrochemical experiments, of charge transfer between a semiconductor (-Fe2O3) and a metal oxide overlayer (hydrous IrOx) as a photoanode architecture in photoelectrochemical water splitting.1 The aim is to clarify the ambiguous role of oxygen evolving catalysts used as overlayers on top of photoanodes in photoelectrochemical water splitting cells. Previous literature suggested that the real benefit of covering hematite with overlayers like iridium or cobalt oxides is not due to an increase of reaction kinetics but the decrease of the electron density in the hematite2 or the storage of photogenerates holes.3 These effects are likely more important when hydrous overlayer, that can act as adapting catalysts,4 are considered. All these hypothesis can explain the observed improved hole lifetime and reduce recombination with electrons.
The present experimental approach is similar to the one that allowed our recent disclosure of the oxidation states assumed by hydrous IrOx as catalyst for water oxidation.5 In the present case, FEXRAV6 and XANES have been used to probe changes in the charge state of Ir while the hematite was illuminated with 410nm radiation. Thanks to this in-operando setup, we were able to observe an increase of the density of empty Ir 5d states during hematite illumination and in correspondence of water spitting in the photoelectrochemical cell. The main conclusion is that a charge (hole) transfer between hematite and iridium occurs only when the hematite is illuminated. Hydrous iridium oxide is therefore capable of withdrawing holes from the semiconductor thus increasing the probability of interface reaction rather than charge recombination.
1 Minguzzi A., Lugaresi O., Achilli E., D'Acapito F., Naldoni A., Malara F., Locatelli C., Vertova A., Rondinini S., Ghigna P., In preparation
2 Badia-Bou L., Mas-Marza E., Rodenas P., M. Barea E., Fabregat-Santiago F., Gimenez S., Peris E., Bisquert J., J. Phys. Chem. C, 2013, 117, 3826−3833
3 Lin F., Boettcher S.W. Nature Materials, 2014, 13, 81-86
4 Barroso M., Mesa C.A., Pendlebury S.R. , Cowana A.J., Hisatomi T., Sivula K., Grätzel M., Klug D.R., Durrant J.R. PNAS, 2012, 109, 15640–15645
5 Minguzzi A., Lugaresi O., Achilli E., Locatelli C., Vertova A., Ghigna P., Rondinini S., Chem. Sci., 2014, 5, 3591-3597
6 Minguzzi, A.; Lugaresi, O.; Locatelli, C.; Rondinini S.; d'Acapito, F.; Achilli, E.; Ghigna, P. Anal. Chem. 2013, 85, 7009-7013
Challenges in temperature measurements in gas-phase photothermal catalysis
No full textLuca Mascaretti completed his PhD in 2018 at Politecnico di Milano, Italy. Afterwards, he has worked as a postdoc researcher at the Regional Centre of Advanced Technologies and Materials, Palacky University in Olomouc (Czech Republic). His research activity is related to titanium oxide/nitride-based nanostructured materials for solar energy conversion processes.
Andrea Schirato is currently a physics PhD candidate across Politecnico di Milano and the Italian Institute of Technology (Genoa) under the supervision of Profs. G. Della Valle and R. Proietti Zaccaria. His research activities focus on the theoretical study and numerical modeling of ultrafast nonlinear phenomena driven by hot carriers, including non-equilibrium electronic and phononic energy transfer in nanostructured materials and metasurfaces.
Tiziano Montini is associate professor at the University of Trieste in Italy. He received his PhD in chemistry from the University of Trieste in 2006, followed by a postdoc fellowship. His research activity concerns on nanomaterials as catalysts for renewable energy production and environmental protection. Alessandro Alabastri is currently an assistant professor in the Electrical and Computer Engineering Department at Rice University. He received his PhD in nanosciences in 2014 from the Italian Institute of Technology and the University of Genoa. In 2015, he was visiting researcher in the Molecular Foundry at the Lawrence Berkeley National Laboratory. He worked on several aspects of light-to-heat conversion, photothermal effects in nanostructures, and heat recovery in light-powered thermofluidic devices.
Alberto Naldoni is currently an associate professor at University of Turin, Italy. Since 2017, he is the co-leader of the photoelectrochemistry group at the Regional Centre of Advanced Technologies and Materials, Palacky University Olomouc (Czech Republic). He obtained his PhD in chemical sciences from University of Milan (2010). From 2014 to 2017, he was visiting research faculty at the Birck Nanotechnology Center of Purdue University. His group focuses on nanomaterials for plasmonics, photocatalysis, and photoelectrochemistry.
Paolo Fornasiero is a professor at the University of Trieste in Italy. He received his PhD in chemistry from the University of Trieste in 1997, followed by a postdoc fellowship at Reading University (UK). His group currently focuses on research into nanomaterials for environmental and energy-related applications
SECM for the study and the screening of photoelectrode architectures
No full textPhotoelectrochemical water splitting represents an ideal system for the storage of sunlight energy through the production of H2. While many researchers find and design new promising semiconductors, an important effort is dedicated to the research of materials to be deposited on top of the semiconductors (overlayers) to improve the performance of the resulting photoelectrode architecture. The role of overlayers was initially addressed to their ability of improving interfacial reactions or quenching surface traps[1] . However, further study highlighted their more is likely related to an induced modification of the semiconductor electron density[2] or the ability of storing the photogenerated holes thus decreasing the probability of charge recombination [3,4]. This greatly extends the possible candidates for overlayers and requires new efficient screening methods.
In this communication we will show our most recent outcomes obtained using SECM for studying both semiconductors and overlayers. The main part of the work consists in the study and the screening of overlayers deposited onto hematite (α-Fe2O3) photoanodes [5]. This was mainly done in the substrate generation/tip collection mode on arrays of overlayers deposited onto a common semiconductor layer adopting the method recently proposed for screening electrocatalysts for the oxygen evolution [6] that consists in pulsing the substrate potential to achieve a reduced interference between spots while the tip addresses every spot collecting the generated oxygen.
[1] K. Sivula, F. Le Formal, M. Grätzel, ChemSusChem, 4 (2011) 423-449
[2] M. Barroso, C.A. Mesa, S.R. Pendlebury, A.J. Cowana, T. Hisatomi, K. Sivula, M. Grätzel, D.R. Klug, J.R. Durrant PNAS, 109 (2012) 15640–15645
[3] L. Badia-Bou, E. Mas-Marza, Rodenas P., E. M. Barea, F. Fabregat-Santiago, S. Gimenez, E. Peris, J. Bisquert, J. Phys. Chem. C, 117 (2013) 3826−3833
[4] F. Lin, S.W. Boettcher, Nature Materials, 13 (2014) 81-86
[5] M. Marelli, A. Naldoni, A. Minguzzi, M. Allieta, T. Virgili, G. Scavia, S. Recchia, R. Psaro, V. Dal Santo, ACS Appl. Mater. Interfaces, 6 (2014) 11997-12004.
[6] A. Minguzzi, D. Battistel, J. Rodriguez-Lopez, A. Vertova, S. Rondinini, A.J. Bard, S. Daniele, J. Phys. Chem. C, 119 (2015) 2941–294
'NANOSTRUCTURED TIO2 AS A MULTIFUNCTIONAL MATERIAL: FROM PHOTOCATALYSIS TO BIOMEDICAL APPLICATIONS'
No full textThe results presented in this Ph.D. thesis are focused on the use of nanostructured titanium dioxide for environmental remediation and for biomedical applications.
In the first part, the importance of the choice of a suitable and reliable synthetic route for obtaining nanomaterials with tailored properties for a specific application is highlighted. Several research projects on the design and sol-gel synthesis of TiO2 nanoparticles have been carried out.
The experimental evidences suggest that sol-gel synthesis allow tailoring the morphological and superficial properties of the samples. The latter are strictly correlated to the photocatalytic activity of TiO2 home-made samples for the degradation of pollutants in air (e.g., toluene and nitrogen oxides). Moreover, exploiting the capability of sol-gel synthesis, the light absorption of the photocatalyst is extended from UV to the visible spectrum via a nitrogen doping. The morphology, bulk superficial properties, and photocatalytic activity of TiO2 nanoparticle are also influenced by the direct physical/chemical effects of ultrasounds. Interestingly, using ultrasonic spray pyrolysis (USP), we can exploit indirect effects of ultrasounds to synthesized nanostructured materials. Here, it is presented the design, synthesis, characterization, and application in photocatalysis of porous TiO2 microsphere with tunable physico-chemical properties obtained through USP. The second part of this Ph.D. thesis is focused on the study of the interaction among inorganic surfaces and biomolecules or, in general, biological systems. In a first work, we have synthesized sol-gel TiO2 nanoparticles with different morphology and use them for preliminary study of acetyl salicylic acid delivery. Moreover, the possibility to use TiO2 as a material for scaffold for bone regeneration is reported. This study has led to unravel a new bio-inspired crystallization pathway toward the bioactivity of synthetic bone substitutes. Other examples in the biomedical field are reported in Appendix A
Exploring the New Service Development Process of Digital Services: Insights from Expert Interviews
No full textElectro- and photo-electrochemical water splitting as studied by In-Operando X-Rays Absorption Spectroscopy
No full textIn this work we show our most recent results obtained by in-operando X-Ray absorption spectroscopy on hydrous/amorphous [1] and on crystalline/dry [2] iridium oxide electrodes as electrocatalysts for the oxygen evolution reaction (OER). In all cases, XAS evidenced the role of Ir active sites, and the relevant oxidation states assumed during the catalytic cycle. Moreover, the local structure is not significantly influenced by the applied potential, thus suggesting a negligible reorganization energy of the catalyst.On the bases of these results, we were able to directly observe, by means of spectro-photoelectrochemical experiments, the charge transfer between a semiconductor (α-Fe2O3) and hydrous IrOx, the latter used as overlayer for generating a high performance photoanode architecture in photoelectrochemical water splitting[3]. The aim is to clarify the ambiguous role of oxygen evolving catalysts used as overlayers on top of photoanodes in photoelectrochemical water splitting cells. Previous literature suggested that the real benefit of covering hematite with overlayers like iridium or cobalt oxides is not due to an increase of the reaction rate but to a decrease of the electron density in the hematite[4] or to the storage of photogenerates holes[5]. These effects are likely more important when hydrous overlayer, that can act as adapting catalysts[6], are considered. All these hypotheses can explain the observed improved hole lifetime and reduce recombination with electrons. The experimental approach is similar to the one adopted to study Ir oxide particles electrocatalysts[1,2]. In the present case, FEXRAV [7] and XANES have been used to probe changes in the charge state of Ir while the hematite was illuminated with a 410nm diode. Thanks to this setup, we were able to observe an increase of the density of empty Ir 5d states during hematite illumination and in correspondence of water spitting in the photoelectrochemical cell. The main conclusion is that a charge (hole) transfer between hematite and iridium occurs only when the hematite is illuminated. Hydrous iridium oxide is therefore capable of withdrawing holes from the semiconductor thus increasing the probability of interface reaction rather than charge recombination.
References
[1] A. Minguzzi, O. Lugaresi, E. Achilli, C. Locatelli, A. Vertova, P. Ghigna, Rondinini S., Chem. Sci., 2014, 5, 3591-3597
[2] A. Minguzzi, C. Locatelli, O. Lugaresi, E. Achilli, G. Cappelletti, M. Scavini, M. Coduri, P. Masala, B. Sacchi, A. Vertova, P. Ghigna, S. Rondinini, submitted
[3] A. Minguzzi, O. Lugaresi, E. Achilli, F. D'Acapito, A. Naldoni, F. Malara, C. Locatelli, A. Vertova, S. Rondinini, P. Ghigna, In preparation
[4] M. Barroso, C.A. Mesa, S.R. Pendlebury, A.J. Cowana, T. Hisatomi, K. Sivula, M. Grätzel, D.R. Klug, J.R. Durrant PNAS, 2012, 109, 15640–15645
[5] L. Badia-Bou, E. Mas-Marza, P. Rodenas, E M. Barea., F. Fabregat-Santiago, S. Gimenez, E. Peris, J. Bisquert, J. Phys. Chem. C, 2013, 117, 3826−3833
[6] F. Lin, S.W. Boettcher Nature Materials, 2014, 13, 81-86
[7] A. Minguzzi, O. Lugaresi, C. Locatelli, S. Rondinini, F. d'Acapito, E. Achilli, P. Ghigna, Anal. Chem. 2013, 85, 7009-7013
TiO2 hierarchical hollow microspheres with tunable properties
No full textRecently, hierarchical hollow nanostructures (HHNs) have received a great attention for their unique or enhanced physicochemical properties [1]. Numerous strategies have been developed to synthesized TiO2 hollow nano/micro spheres, although obtaining HHNs with tunable properties remains a great scientific challenge.
Here, we use ultrasonic spray pyrolysis (USP) for the generation of TiO2 hierarchical hollow spheres (HHSs) with tunable proprieties. A suspension containing colloidal silica, H2O and a TiIV complex, was nebulized using a home-made ultrasound generator (1.65 MHz). The resulting mist was carried in a gas stream in a hot furnace (1000 °C). After exiting the hot zone, spherical particles a few hundred nanometers in size (microspheres) were collected in a H2O-filled bubbler [2]. The microspheres were then isolated from this solution by centrifugation and etched with HF 10 wt. % solution for 75 min. The resulting hollow nanostructure was confirmed by TEM analysis. We control the morphology of the microspheres by varying the Ti precursor/SiO2 molar ratio. In addition, by using SiO2 nanoparticles with different sizes (12, 35-50, 70-100 nm), we obtained TiO2 HHSs characterized by meso- or macroporosity. The XRD patterns of TiO2 solid spheres (obtained without tamplate, T_USP) and HHSs showed samples with dramatically different phase compositions. T_USP was composed by 36% in anatase and 64% in rutile; otherwise, by adding increasing amounts of SiO2 to the precursor solution, we obtained samples composed by an increasing content of anatase (up to 100%). We propose that the SiO2 surface play a key role in this template-directed process suggesting a possible nucleation mechanism. The photocatalytic activities of the USP microspheres have been evaluated using the NOx (gas phase) degradation as a probe reaction
Porous TiO2 microspheres with tunable properties for photocatalytic air purification
No full textThe synthesis of highly-crystalline porous TiO2 microspheres is reported using ultrasonic spray pyrolysis (USP) in the presence of colloidal silica as a template. We have exploited the interactions between hot SiO2 template particles surface and TiO2 precursor that occur during reaction inside the droplets, to control the physical and chemical properties of the resulting particles. Varying the SiO2 to titanium precursor molar ratio and the colloidal silica dimension, we obtained porous titania microspheres with tunable morphology, porosity, BET surface area, crystallite size, band-gap, and phase composition. In this regard, we have also observed the preferential formation of anatase vs. rutile with increasing initial surface area of the silica template. The porous TiO2 microspheres were tested in the photocatalytic degradation of nitrogen oxides (NOx) in the gas phase. USP prepared nanostructured titania samples were found to have significantly superior specific activity per surface area compared to a commercial reference sample (P25 by Evonik-Degussa)
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