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Solomon, G., Mazzaro, R., You, S., Natile, M. M., Morandi, V., Concina, I. & Vomiero, A. (2019). Ag2S/MoS2 Nanocomposites Anchored on Reduced Graphene Oxide: Fast Interfacial Charge Transfer for Hydrogen Evolution Reaction. ACS Applied Materials and Interfaces, 11(25), 22380-22389
Open this publication in new window or tab >>Ag2S/MoS2 Nanocomposites Anchored on Reduced Graphene Oxide: Fast Interfacial Charge Transfer for Hydrogen Evolution Reaction
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2019 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 11, no 25, p. 22380-22389Article in journal (Refereed) Published
Abstract [en]

Hydrogen evolution reaction through electrolysis holds great potential as a clean, renewable, and sustainable energy source. Platinum-based catalysts are the most efficient to catalyze and convert water into molecular hydrogen; however, their large-scale application is prevented by scarcity and cost of Pt. In this work, we propose a new ternary composite of Ag2S, MoS2, and reduced graphene oxide (RGO) flakes via a one-pot synthesis. The RGO support assists the growth of two-dimensional MoS2 nanosheets partially covered by silver sulfides as revealed by high-resolution transmission electron microscopy. Compared with the bare MoS2 and MoS2/RGO, the Ag2S/MoS2 anchored on the RGO surface (the ternary system Ag2S/MoS2/RGO) demonstrated a high catalytic activity toward hydrogen evolution reaction (HER). Its superior electrochemical activity toward HER is evidenced by the positively shifted (−190 mV vs reversible hydrogen electrode (RHE)) overpotential at a current density of −10 mA/cm2 and a small Tafel slope (56 mV/dec) compared with a bare and binary system. The Ag2S/MoS2/RGO ternary catalyst at an overpotential of −200 mV demonstrated a turnover frequency equal to 0.38 s–1. Electrochemical impedance spectroscopy was applied to understand the charge-transfer resistance; the ternary sample shows a very small charge-transfer resistance (98 Ω) at −155 mV vs RHE. Such a large improvement can be attributed to the synergistic effect resulting from the enhanced active site density of both sulfides and to the improved electrical conductivity at the interfaces between MoS2 and Ag2S. This ternary catalyst opens up further optimization strategies to design a stable and cheap catalyst for hydrogen evolution reaction, which holds great promise for the development of a clean energy landscape.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019
Keywords
electrocatalyst, hydrogen evolution, silver sulfide, molybdenum sulfide, reduced graphene oxide
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-75551 (URN)10.1021/acsami.9b05086 (DOI)000473251100036 ()2-s2.0-85068008830 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-08-16 (johcin)

Available from: 2019-08-16 Created: 2019-08-16 Last updated: 2019-08-16Bibliographically approved
Di Mauro, A., Landström, A., Concina, I., Impellizzeri, G., Privitera, V. & Epifani, M. (2019). Surface Modification by Vanadium Pentoxide Turns Oxide Nanocrystals into Powerful Adsorbents of Methylene Blue. Journal of Colloid and Interface Science, 533, 369-374
Open this publication in new window or tab >>Surface Modification by Vanadium Pentoxide Turns Oxide Nanocrystals into Powerful Adsorbents of Methylene Blue
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2019 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 533, p. 369-374Article in journal (Refereed) Published
Abstract [en]

Hypothesis: If nanocrystals of such semiconductor as SnO2 and TiO2, which are not known as powerful adsorbents, have their surface modified by layer of V2O5, how will the adsorption properties be affected? Answering this question would provide a new set of surface properties to be designed by surface engineering of oxide nanocrystals.

Experiments: SnO2 and TiO2 colloidal nanocrystals were prepared by coupling sol-gel and solvothermal synthesis. By co-processing with V chloroalkoxide and subsequent heat-treatment at 400-500 °C, surface deposition of V2O5 layers was obtained. The methylene blue adsorption onto the prepared materials was tested and compared with the pure oxide supports. Cycling of the materials and analysis of the adsorption process was also investigated.

Findings: The V-modified nanocrystals extracted ∼ 80% methylene blue from 1.5 x 10-5 M aqueous solution after 15 min only, contrarily to pure materials, which took up only 30% of the dye even after 120 min. Comparison with pure commercial V2O5 showed that the peculiar adsorption properties were imparted by the surface deposition of the V2O5-like layers. This report demonstrates that new classes of adsorbing materials can be conceived by suitably coupling different metal oxides.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-70622 (URN)10.1016/j.jcis.2018.08.070 (DOI)000447815200038 ()30172147 (PubMedID)2-s2.0-85052435735 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-09-04 (andbra)

Available from: 2018-08-28 Created: 2018-08-28 Last updated: 2018-11-15Bibliographically approved
Ghamgosar, P., Rigoni, F., You, S., Dobryden, I., Gilzad Kohan, M., Pellegrino, A. L., . . . Vomiero, A. (2018). ZnO-Cu2O core-shell nanowires as stable and fast response photodetectors. Nano Energy, 51, 308-316
Open this publication in new window or tab >>ZnO-Cu2O core-shell nanowires as stable and fast response photodetectors
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2018 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 51, p. 308-316Article in journal (Refereed) Published
Abstract [en]

In this work, we present all-oxide p-n junction core-shell nanowires (NWs) as fast and stable self-powered photodetectors. Hydrothermally grown n-type ZnO NWs were conformal covered by different thicknesses (up to 420 nm) of p-type copper oxide layers through metalorganic chemical vapor deposition (MOCVD). The ZnO NWs exhibit a single crystalline Wurtzite structure, preferentially grown along the [002] direction, and energy gap Eg=3.24 eV. Depending on the deposition temperature, the copper oxide shell exhibits either a crystalline cubic structure of pure Cu2O phase (MOCVD at 250 °C) or a cubic structure of Cu2O with the presence of CuO phase impurities (MOCVD at 300 °C), with energy gap of 2.48 eV. The electrical measurements indicate the formation of a p-n junction after the deposition of the copper oxide layer. The core-shell photodetectors present a photoresponsivity at 0 V bias voltage up to 7.7 µA/W and time response ≤0.09 s, the fastest ever reported for oxide photodetectors in the visible range, and among the fastest including photodetectors with response limited to the UV region. The bare ZnO NWs have slow photoresponsivity, without recovery after the end of photo-stimulation. The fast time response for the core-shell structures is due to the presence of the p-n junctions, which enables fast exciton separation and charge extraction. Additionally, the suitable electronic structure of the ZnO-Cu2O heterojunction enables self-powering of the device at 0 V bias voltage. These results represent a significant advancement in the development of low-cost, high efficiency and self-powered photodetectors, highlighting the need of fine tuning the morphology, composition and electronic properties of p-n junctions to maximize device performances.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-69838 (URN)10.1016/j.nanoen.2018.06.058 (DOI)000440682100034 ()2-s2.0-85049324019 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-08-02 (rokbeg)

Available from: 2018-06-25 Created: 2018-06-25 Last updated: 2019-04-19Bibliographically approved
Memarian, N., Rozati, S. M., Vomiero, A. & Concina, I. (2017). Deposition of nanostructured Cds thin films by thermal evaporation method: Effect of substrate temperature. Materials, 10(7), Article ID 773.
Open this publication in new window or tab >>Deposition of nanostructured Cds thin films by thermal evaporation method: Effect of substrate temperature
2017 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 10, no 7, article id 773Article in journal (Refereed) Published
Abstract [en]

Nanocrystalline CdS thin films were grown on glass substrates by a thermal evaporation method in a vacuum of about 2 × 10-5 Torr at substrate temperatures ranging between 25 °C and 250 °C. The physical properties of the layers were analyzed by transmittance spectra, XRD, SEM, and four-point probe measurements, and exhibited strong dependence on substrate temperature. The XRD patterns of the films indicated the presence of single-phase hexagonal CdS with (002) orientation. The structural parameters of CdS thin films (namely crystallite size, number of grains per unit area, dislocation density and the strain of the deposited films) were also calculated. The resistivity of the as-deposited films were found to vary in the range 3.11-2.2 × 104 Ω·cm, depending on the substrate temperature. The low resistivity with reasonable transmittance suggest that this is a reliable way to fine-tune the functional properties of CdS films according to the specific application.

Place, publisher, year, edition, pages
Basel: MDPI, 2017
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-65048 (URN)10.3390/ma10070773 (DOI)000406683000090 ()28773133 (PubMedID)2-s2.0-85023743510 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-08-14 (andbra)

Available from: 2017-08-14 Created: 2017-08-14 Last updated: 2018-11-26Bibliographically approved
Milan, R., Selopal, G. S., Cavazzini, M., Orlandi, S., Boaretto, R., Caramori, S., . . . Pozzi, G. (2017). Dye-sensitized solar cells based on a push-pull zinc phthalocyanine bearing diphenylamine donor groups: computational predictions face experimental reality. Scientific Reports, 7, Article ID 15675.
Open this publication in new window or tab >>Dye-sensitized solar cells based on a push-pull zinc phthalocyanine bearing diphenylamine donor groups: computational predictions face experimental reality
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2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 15675Article in journal (Refereed) Published
Abstract [en]

Computational studies have suggested that the integration of secondary amine as donor groups in the structure of unsymmetrical zinc phthalocyanine (ZnPc) should have positive effects on photovoltaic performance, once the molecule is integrated as light harvester in dye sensitized solar cells (DSSCs). Aiming at obtaining experimental confirmation, we synthesized a peripherally substituted push-pull ZnPc bearing three electron donating diphenylamine substituents and a carboxylic acid anchoring group and integrated it as sensitizer in TiO2-based DSSCs. Detailed functional characterization of solar energy converting devices resulted in ruling out the original hypothesis. The causes of this discrepancy have been highlighted, leading to a better understanding of the conditions for an effective design of push-pull diarylamino substituted ZnPcs for DSSCs.

Place, publisher, year, edition, pages
Nature Publishing Group, 2017
National Category
Other Physics Topics
Research subject
Experimental physics
Identifiers
urn:nbn:se:ltu:diva-66626 (URN)10.1038/s41598-017-15745-3 (DOI)000415266100024 ()29142212 (PubMedID)2-s2.0-85034445753 (Scopus ID)
Note

Validerad;2017;Nivå 2;2017-11-17 (svasva)

Available from: 2017-11-17 Created: 2017-11-17 Last updated: 2017-12-08Bibliographically approved
Epafini, M., Kaciulis, S., Mezzi, A., Altamura, D., Giannini, C., Díaz, R., . . . Concina, I. (2017). Inorganic Photocatalytic Enhancement: Activated RhB Photodegradation by Surface Modification of SnO2 Nanocrystals with V2O5-like species. Scientific Reports, 7, Article ID 44763.
Open this publication in new window or tab >>Inorganic Photocatalytic Enhancement: Activated RhB Photodegradation by Surface Modification of SnO2 Nanocrystals with V2O5-like species
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2017 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 44763Article in journal (Refereed) Published
Abstract [en]

SnO2 nanocrystals were prepared by precipitation in dodecylamine at 100 °C, then they were reacted with vanadium chloromethoxide in oleic acid at 250 °C. The resulting materials were heat-treated at various temperatures up to 650 °C for thermal stabilization, chemical purification and for studying the overall structural transformations. From the crossed use of various characterization techniques, it emerged that the as-prepared materials were constituted by cassiterite SnO2 nanocrystals with a surface modified by isolated V(IV) oxide species. After heat-treatment at 400 °C, the SnO2 nanocrystals were wrapped by layers composed of vanadium oxide (IV-V mixed oxidation state) and carbon residuals. After heating at 500 °C, only SnO2 cassiterite nanocrystals were obtained, with a mean size of 2.8 nm and wrapped by only V2O5-like species. The samples heat-treated at 500 °C were tested as RhB photodegradation catalysts. At 10-7 M concentration, all RhB was degraded within 1 h of reaction, at a much faster rate than all pure SnO2 materials reported until now.

Place, publisher, year, edition, pages
Nature Publishing Group, 2017
National Category
Other Physics Topics
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-62573 (URN)10.1038/srep44763 (DOI)000396534800001 ()28300185 (PubMedID)2-s2.0-85015710811 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-03-20 (andbra)

Available from: 2017-03-20 Created: 2017-03-20 Last updated: 2018-11-20Bibliographically approved
Epafini, M., Kaciulis, S., Mezzi, A., Altamura, D., Giannini, C., Tang, P., . . . Concina, I. (2017). Solvothermal Synthesis, Gas-Sensing Properties, and Solar Cell-Aided Investigation of TiO2-MoOx Nanocrystals. ChemNanoMat, 3(11), 798-807
Open this publication in new window or tab >>Solvothermal Synthesis, Gas-Sensing Properties, and Solar Cell-Aided Investigation of TiO2-MoOx Nanocrystals
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2017 (English)In: ChemNanoMat, ISSN 2199-692X, Vol. 3, no 11, p. 798-807Article in journal (Refereed) Published
Abstract [en]

Titania anatase nanocrystals were prepared by sol-gel/solvothermal synthesis in oleic acid at 250 °C, and modified by co-reaction with Mo chloroalkoxide, aimed at investigating the effects on gas-sensing properties induced by tailored nanocrystals surface modification with ultra-thin layers of MoOx species. For the lowest Mo concentration, only anatase nanocrystals were obtained, surface modified by a disordered ultra-thin layer of mainly octahedral MoVI oxide species. For larger Mo concentrations, early MoO2 phase segregation occurred. Upon heat treatment up to 500 °C, the sample with the lowest Mo concentration did not feature any Mo oxide phase segregation, and the surface Mo layer was converted to dense octahedral MoVI oxide. At larger Mo concentrations all segregated MoO2 was converted to MoO3. The two different materials typologies, depending on the Mo concentration, were used for processing gas-sensing devices and tested toward acetone and carbon monoxide, which gave a greatly enhanced response, for all Mo concentrations, to acetone (two orders of magnitude) and carbon monoxide with respect to pure TiO2. For the lowest Mo concentration, dye-sensitized solar cells were also prepared to investigate the influence of anatase surface modification on the electrical transport properties, which showed that the charge transport mainly occurred in the ultra-thin MoOx surface layer.

Place, publisher, year, edition, pages
John Wiley & Sons, 2017
National Category
Other Physics Topics
Research subject
Experimental physics
Identifiers
urn:nbn:se:ltu:diva-65740 (URN)10.1002/cnma.201700160 (DOI)000417743700004 ()
Note

Validerad;2017;Nivå 2;2017-11-27 (rokbeg)

Available from: 2017-09-20 Created: 2017-09-20 Last updated: 2017-12-29Bibliographically approved
Jirlèn, J., Concina, I., Lundström, I. & Almqvist, N. (2017). Towards nanolithography with starch and α-amylase: Invited lecture. In: Proceedings and Abstracts Book of European Advanced Materials Congress 2017: . Paper presented at European Advanced Materials Congress (EAMC-17), Stockholm, Sweden, 22-24 August 2017.
Open this publication in new window or tab >>Towards nanolithography with starch and α-amylase: Invited lecture
2017 (English)In: Proceedings and Abstracts Book of European Advanced Materials Congress 2017, 2017Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Nanotechnology using enzyme technology to modify surfaces on the nanometer scale and nanostructuring surfaces is an evolving research field. One of the advantages with enzyme assisted nanolithography is the high substrate specificity. Scanning probe microscopy (SPM) in liquid or ambient conditions is highly suited for such nanolithography: we are in particular using atomic force microscopy (AFM) to develop negative nanolithography based on an enzyme and its substrate. The possibility of high accuracy positioning of the SPM probe tip is combined with the activity of an enzyme. There are very few related such studies by other groups [1-3]. In our approach, the enzyme is α-amylase and the substrate starch, whose hydrolysis into sugars by α-amylase is well studied on the macro-scale. The system α-amylase-starch is exploited as a model to demonstrate the proof of principle that the enzyme can be used with SPM methods to locally degrade starch and ultimately write nanopatterns on starch surfaces. Silicon surfaces are covered with smooth and thin layers of starch, whose roughness, morphology and nanomechanical properties are characterized by AFM methods. In the next step the degradation of these starch layers will be demonstrated with an AFM tip functionalized with amylase molecules, either on the apex of a “sharp” AFM tip (outer radius 5-50 nm) or on a micrometer-sized bead of silicon dioxide glued to an AFM cantilever. The α-amylase molecules may be either spontaneously adsorbed or covalently attached to the tip through established functionalization chemistry. Results will be presented related to the structure and quality of the starch layer and its degradation by amylase in solution as observed by AFM and FTIR-spectroscopy and to the activity of amylase immobilized on (silicon/silicon dioxide) surfaces. Preliminary results will be given on the local degradation of starch caused by AFM tips modified by α-amylase and/or by micro droplets of amylase solution released on the substrate by using the AFM tip in a dip-pen configuration. The ultimate goal is to achieve a situation like that illustrated in the drawing above, where a single (or few) α-amylase molecule(s) is attached on the AFM tip so to maintain its enzymatic activity and can be used to write nanopatterns in a layer of starch.

Keywords
Enzyme; Nanolithography; Starch; Scanning probe microscopy
National Category
Nano Technology
Research subject
Experimental Physics
Identifiers
urn:nbn:se:ltu:diva-65417 (URN)10.5185/eamc.2017 (DOI)978-91-88252-06-7 (ISBN)
Conference
European Advanced Materials Congress (EAMC-17), Stockholm, Sweden, 22-24 August 2017
Available from: 2017-08-30 Created: 2017-08-30 Last updated: 2018-04-26Bibliographically approved
Milan, R., Hassan, M., Selopal, G. ., Borgese, L., Natile, M. M., Depero, L. E., . . . Concina, I. (2016). A Player Often Neglected: Electrochemical Comprehensive Analysis of Counter Electrodes for Quantum Dot Solar Cells (ed.). Paper presented at . ACS Applied Materials and Interfaces, 8(12), 7766-7776
Open this publication in new window or tab >>A Player Often Neglected: Electrochemical Comprehensive Analysis of Counter Electrodes for Quantum Dot Solar Cells
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2016 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 12, p. 7766-7776Article in journal (Refereed) Published
Abstract [en]

The role played by the counter electrode (CE) in quantum dot sensitized solar cells (QDSSCs) is crucial: it is indeed responsible for catalyzing the regeneration of the redox electrolyte after its action to take back the oxidized light harvesters to the ground state, thus keeping the device active and stable. The activity of CE is moreover directly related to the fill factor and short circuit current through the resistance of the interface electrode–electrolyte that affects the series resistance of the cell. Despite that, too few efforts have been devoted to a comprehensive analysis of this important device component. In this work we combine an extensive electrochemical characterization of the most common materials exploited as CEs in QDSSCs (namely, Pt, Au, Cu2S obtained by brass treatment, and Cu2S deposited on conducting glass via spray) with a detailed characterization of their surface composition and morphology, aimed at systematically defining the relationship between their nature and electrocatalytic activity.

National Category
Other Physics Topics
Research subject
Experimental physics
Identifiers
urn:nbn:se:ltu:diva-12118 (URN)10.1021/acsami.5b11508 (DOI)000373519500018 ()26955853 (PubMedID)2-s2.0-84963725490 (Scopus ID)b2fe4c57-1447-44b7-a4ed-6158b1048abd (Local ID)b2fe4c57-1447-44b7-a4ed-6158b1048abd (Archive number)b2fe4c57-1447-44b7-a4ed-6158b1048abd (OAI)
Note
Validerad; 2016; Nivå 2; 20160414 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2018-07-10Bibliographically approved
Milan, R., Cattarin, S., Comisso, N., Baratto, C., Kaunisto, K., Tkachenko, N. & Concina, I. (2016). Compact hematite buffer layer as a promoter of nanorod photoanode performances. Scientific Reports, 6, Article ID 35049.
Open this publication in new window or tab >>Compact hematite buffer layer as a promoter of nanorod photoanode performances
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2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 35049Article in journal (Refereed) Published
Abstract [en]

The effect of a thin α-Fe2O3 compact buffer layer (BL) on the photoelectrochemical performances of a bare α-Fe2O3 nanorods photoanode is investigated. The BL is prepared through a simple spray deposition onto a fluorine-doped tin oxide (FTO) conducting glass substrate before the growth of a α-Fe2O3 nanorods via a hydrothermal process. Insertion of the hematite BL between the FTO and the nanorods markedly enhances the generated photocurrent, by limiting undesired losses of photogenerated charges at the FTO||electrolyte interface. The proposed approach warrants a marked improvement of material performances, with no additional thermal treatment and no use/dispersion of rare or toxic species, in agreement with the principles of green chemistry.

National Category
Other Physics Topics
Research subject
Experimental physics
Identifiers
urn:nbn:se:ltu:diva-59790 (URN)10.1038/srep35049 (DOI)000385536400001 ()27733756 (PubMedID)
Note

Validerad; 2016; Nivå 2; 2016-10-17 (andbra)

Available from: 2016-10-17 Created: 2016-10-17 Last updated: 2018-07-10Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1785-7177

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