Suchergebnisse

Three-dimensional (3D) Fe/SiC monoliths with parallel interconnected channels and different cell geometries (square, troncoconical, and triangular) were manufactured by robocasting and used as catalytic reactors in hydroxylation of phenol using hydrogen peroxide to produce dihydroxybenzenes; the reaction was performed at Cphenol,0 = 0.33 M, Cphenol,0:CH2O2,0 = 1:1 M, WR = 3.7 g, T = 80-90 °C, and τ = 0-254 gcat·h·L-1 with water as a solvent. The values of the apparent kinetic rate constants demonstrated the superior performance of the triangular cell monoliths for hydrogen peroxide decomposition, phenol hydroxylation, and dihydroxybenzene production reactions. A computational fluid dynamic model was validated with the experimental results. It demonstrated that the triangular cell monoliths, with a lower channel hydraulic diameter and not-facing interconnections, provided a higher internal macrotortuosity that induced an oscillating flow of the liquid phase inside the channels, leading to an additional transverse flow between adjacent parallel channels. This behavior, not observed in the other two geometries, resulted in a better overall performance ; The authors thank the financial support by the Community of Madrid through the project S2018/EMT-4341 and the Government of Spain through the projects: PGC2018- 095642-B-I00 and RTI2018-095052-B-I00 (MCIU/AEI/ FEDER, UE). Also, G. Vega acknowledges the Universidad Autónoma de Madrid for the predoctoral contract

[EN] Three-dimensional (3D) Fe/SiC monoliths with parallel interconnected channels and different cell geometries (square, troncoconical, and triangular) were manufactured by robocasting and used as catalytic reactors in hydroxylation of phenol using hydrogen peroxide to produce dihydroxybenzenes; the reaction was performed at Cphenol,0 = 0.33 M, Cphenol,0:CH2O2,0 = 1:1 M, WR = 3.7 g, T = 80-90 °C, and τ = 0-254 gcat·h·L-1 with water as a solvent. The values of the apparent kinetic rate constants demonstrated the superior performance of the triangular cell monoliths for hydrogen peroxide decomposition, phenol hydroxylation, and dihydroxybenzene production reactions. A computational fluid dynamic model was validated with the experimental results. It demonstrated that the triangular cell monoliths, with a lower channel hydraulic diameter and not-facing interconnections, provided a higher internal macrotortuosity that induced an oscillating flow of the liquid phase inside the channels, leading to an additional transverse flow between adjacent parallel channels. This behavior, not observed in the other two geometries, resulted in a better overall performance. ; The authors thank the financial support by the Community of Madrid through the project S2018/EMT-4341 and the Government of Spain through the projects: PGC2018-095642-B-I00 and RTI2018-095052-B-I00 (MCIU/AEI/FEDER, UE). Also, G. Vega acknowledges the Universidad Autónoma de Madrid for the predoctoral contract.

The manufacturing of three-dimensional (3D) graphene monoliths with remarkable electrical performance has become a challenging issue because their potential applications in the energy and electronic-based fields. Here we show the development of outstanding electrically conductive graphene patterned cellular structures combining a versatile and easily scalable filament printing method, such as Robocasting, with the use of highly crystalline graphene nanoplatelets (GNPs) as the graphene source. Robust 3D pure graphene-based monoliths have been manufactured by printing pseudoplastic aqueous-based GNPs inks with high graphene contents (36.6 wt %) and further thermal treatment by spark plasma sintering. Specific conductivities up to 385 S·cm have been assessed along the longitudinal direction of the 3D structure, i.e., where the current mainly flowed along the struts, being more conductor than reported 3D synthesized graphene structures and up to 2 orders of magnitude higher than 3D printed graphene monoliths. The present findings could open a straightforward pathway for creating, in a controlled way, a wide range of graphene-based hierarchical structures with an excellent electrical performance and robustness that could be employed for energy storage systems. ; Spanish Government (MAT2012-3294 and MAT2015-67437-R projects) and CSIC (PIE 201360E063 project). D. Pérez-Coll also acknowledges the financial support by FCT-BPD grant (SFRH/BPD/112282/2015). ; Peer Reviewed

In-situ grown graphene/SiC composites developed by spark plasma sintering have emerged as a very interesting family of materials with expected high performance for advanced applications. In this work, the local functional properties of graphene/SiC ceramics are elucidated for distinct α- and β- SiC polytypes combining scanning probe microscopies. We unambiguously identify all composite constituents and demonstrate the formation of a three-dimensional graphene conductive network inside the composite. The investigated composites exhibit grains with different doping level depending on growth rate during sintering so that conduction paths associated to graphene and matrix networks may compete. The relevance of nanoscale characterization on functional graphene/semiconductor materials is proved as it evidences the type of doping and carrier concentration of the semiconductor and the critical role played by the graphene constituent in the formation of ohmic contacts. Both issues of crucial importance for understanding the macroscale behavior of these materials and determine their applications. ; This work has been supported by the Spanish Government under projects MAT2013-47869-C4-1-P, MAT2012-32944 and CSIC (PIE201360E063). C. O acknowledges the Spanish MINECO through the Severo Ochoa Program (SEV-2015-0496) and the Generalitat de Catalunya through 2014 SGR 501. L. LM and B. RM thank the Spanish MINECO for FPI BES-2013-063424 and FPI BES-2010-041382 FPI fellowships. The authors acknowledge L. Garzón for his help with some SFM data. ; Peer reviewed

[EN] The promising applications of metal-organic frameworks (MOF) can be widened if these materials were additive manufactured to develop three-dimensional (3D) MOF architectures. In this work, iron-based MOF/silicon carbide (SiC) composite aqueous inks with a high solids content (64 wt%) are printed into 3D periodic lattices by a direct ink writing technique (Robocasting). MOF appear fully integrated within the cellular architectures, which display total porosities in the range of 74–78% depending on the scaffold design. The 3D MOF-Fe/SiC structures exhibit good mechanical strength (~4.6 MPa) and a semiconductor-like behaviour. The structures show a remarkable response in the hydroxylation of phenol with hydrogen peroxide, demonstrating high selectivity and yield to dihydroxybenzene species. ; This work was supported by the following funding organisms and projects: Spanish Government under the project RTI2018-095052-BI00 (MICINN/AEI/FEDER, UE), Community of Madrid under the project S2018/EMT-4341, CSIC project I-COOPþ 2019 (Ref. COOPB20405), TNM projects 7936.20-P and 9063.20-P, and CONACYT under the project 764635. Authors thank Dr. D. Pérez-Coll for his experimental assistance in the electrical measurements.

[EN] Hexagonal boron nitride (h-BN) has been explored as a catalyst for degrading persistent organic pollutants in wastewater by Catalytic Wet Peroxide Oxidation (CWPO). Herein, the superior activity of the h-BN on the phenol degradation (model pollutant) compared to other metal-free catalysts, such as carbon-based ones, and the lower selectivity to CO encourage the potential application of h-BN catalysts in CWPO processes. Through a combined density functional theory calculations, experimental reactions and catalyst characterization approach, a comprehensive study on the reaction mechanism has been conducted. According to this, only defected B atoms in the h-BN layer, protonated as B-(OH), decompose the hydrogen peroxide into highly reactive hydroxyl radicals. The radical species diffuse towards inner h-BN regions and react with the phenol adsorbed by π-π interaction on the h-BN surface. Oxidation by-products cause carbonaceous deposits and progressive deactivation of the h-BN catalyst that can be directly regenerated by burning off in air. ; The authors thank the financial support by the Community of Madrid and the Government of Spain through the projects: S2018/EMT- 4341 and RTI2018-095052-B-I00 (MCIU/AEI/FEDER, UE), respectively. The work done at the University of Sevilla was funded by Spanish Ministerio de Ciencia e Innovación and EU-FEDER, grant PID2019-106871 GB-I00, and the Junta de Andalucía-FEDER, grant: US-1381410. Also, G. Vega acknowledges the Community of Madrid for the Predoctoral contract PEJD-2018-PRE/AMB-9019, co-financed by the European Social Fund through the Youth Employment Operational Program and the Youth Employment Initiative (YEI) 2018. J. Carbajo thanks the financial support by the Government of Spain for a grant under the Juan de la Cierva_Incorporación programme (IJCI-2017- 32682). The authors would like to thank A. Pérez for performing the BET and TGA measurements.