Publications by authors named "V I Parvulescu"

72 Publications

Co-Fe Nanoparticles Wrapped on N-Doped Graphitic Carbons as Highly Selective CO Methanation Catalysts.

ACS Appl Mater Interfaces 2021 Jul 30. Epub 2021 Jul 30.

Instituto Universitario de Tecnología Química, Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas, Avenida de los Naranjos s/n, 46022 Valencia, Spain.

Pyrolysis of chitosan containing various loadings of Co and Fe renders Co-Fe alloy nanoparticles supported on N-doped graphitic carbon. Transmission electron microscopy (TEM) images show that the surface of Co-Fe NPs is partially covered by three or four graphene layers. These [email protected](N)C samples catalyze the Sabatier CO hydrogenation, increasing the activity and CH selectivity with the reaction temperature in the range of 300-500 °C. Under optimal conditions, a CH selectivity of 91% at an 87% CO conversion was reached at 500 °C and a space velocity of 75 h under 10 bar. The Co-Fe alloy nanoparticles supported on N-doped graphitic carbon are remarkably stable and behave differently as an analogous Co-Fe catalyst supported on TiO.
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http://dx.doi.org/10.1021/acsami.1c05542DOI Listing
July 2021

Nanofiltration Composite Membranes Based on KIT-6 and Functionalized KIT-6 Nanoparticles in a Polymeric Matrix with Enhanced Performances.

Membranes (Basel) 2021 Apr 21;11(5). Epub 2021 Apr 21.

National Institute for Research-Development of Biological Sciences, 060031 Bucharest, Romania.

The nanofiltration composite membranes were obtained by incorporation of KIT-6 ordered mesoporous silica, before and after its functionalization with amine groups, into polyphenylene-ether-ether-sulfone (PPEES) matrix. The incorporation of silica nanoparticles into PPEES polymer matrix was evidenced by FTIR and UV-VIS spectroscopy. SEM images of the membranes cross-section and their surface topology, evidenced by AFM, showed a low effect of KIT-6 silica nanoparticles loading and functionalization. The performances of the obtained membranes were appraised in permeation of fruit extracts and the selective separation of phenolic acids and flavonoids. The obtained results proved that the PPEES with functionalized KIT-6 nanofiltration membrane, we have prepared, is suitable for the polyphenolic compound's concentration from the natural extracts.
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http://dx.doi.org/10.3390/membranes11050300DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8143004PMC
April 2021

Biocatalytic Strategy for Grafting Natural Lignin with Aniline.

Molecules 2020 Oct 24;25(21). Epub 2020 Oct 24.

Department of Organic Chemistry, Biochemistry and Catalysis, University of Bucharest, Soseaua Panduri 90, sector 5, 050663 Bucharest, Romania.

This paper presents an enzyme biocatalytic method for grafting lignin (grafting bioprocess) with aniline, leading to an amino-derivatized polymeric product with modified properties (e.g., conductivity, acidity/basicity, thermostability and amino-functionalization). Peroxidase enzyme was used as a biocatalyst and HO was used as an oxidation reagent, while the oxidative insertion of aniline into the lignin structure followed a radical mechanism specific for the peroxidase enzyme. The grafting bioprocess was tested in different configurations by varying the source of peroxidase, enzyme concentration and type of lignin. Its performance was evaluated in terms of aniline conversion calculated based on UV-vis analysis. The insertion of amine groups was checked by H-NMR technique, where NH protons were detected in the range of 5.01-4.99 ppm. The FTIR spectra, collected before and after the grafting bioprocess, gave evidence for the lignin modification. Finally, the abundance of grafted amine groups was correlated with the decrease of the free -OH groups (from 0.030 to 0.009 -OH groups/L for initial and grafted lignin, respectively). Additionally, the grafted lignin was characterized using conductivity measurements, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), temperature-programmed desorption (TPD-NH/CO) and scanning electron microscopy (SEM) analyses. The investigated properties of the developed lignopolymer demonstrated its disposability for specific industrial applications of derivatized lignin.
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http://dx.doi.org/10.3390/molecules25214921DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7662662PMC
October 2020

Optimized Nb-Based Zeolites as Catalysts for the Synthesis of Succinic Acid and FDCA.

Molecules 2020 Oct 22;25(21). Epub 2020 Oct 22.

Department of Organic Chemistry, Biochemistry and Catalysis, Faculty of Chemistry, University of Bucharest, Bdul Regina Elisabeta 4-12, 030016 Bucharest, Romania.

Nb(0.05 moles%)-zeolites prepared via a post synthesis methodology (BEA, Y, ZSM-5), or a direct sol-gel method (Silicalite-1) were investigated in the hydroxymethylfurfural (HMF) oxidation by both molecular oxygen, in aqueous phase, and organic peroxides, in acetonitrile. The catalysts prepared through the post synthesis methodology (i.e., Nb-Y5, Nb-ZSM25, Nb-Y30, Nb-BEA12, and Nb-BEA18) displayed a mono-modal mesoporosity and contain residual framework Al-acid sites, extra framework isolated Nb(V)O-H and NbO pore-encapsulated clusters, while Nb-Sil-1, prepared through a direct synthesis procedure, displayed a bimodal micro-mesoporosity and contains only -Nb=O species. These modified zeolites behave as efficient catalysts in both HMF/glucose wet oxidation to succinic acid (SA) and HMF oxidation with organic peroxides to the 2,5-furandicarboxylic acid (FDCA). The catalytic behavior of these catalysts, in terms of conversion and especially the selectivity, mainly depended on the base/acid sites ratio. Thus, the HMF/glucose wet oxidation occurred with a total conversion and a selectivity to SA of 37.7% (from HMF) or 69.1% (from glucose) on the Nb-Y5 catalyst, i.e., the one with the lowest base/acid sites ratio. On the contrary, the catalysts with the highest base/acid sites ratio, i.e., Nb-ZSM25 and Nb-Sil-1, afforded a high catalytic efficiency in HMF oxidation with organic peroxides, in which FDCA was produced with selectivities of 61.3-63.8% for an HMF conversion of 96.7-99.0%.
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http://dx.doi.org/10.3390/molecules25214885DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7660086PMC
October 2020

Phase Control in Hafnia: New Synthesis Approach and Convergence of Average and Local Structure Properties.

ACS Omega 2019 May 22;4(5):8881-8891. Epub 2019 May 22.

National Institute for Laser, Plasma and Radiation Physics, RO 76900 Bucharest-Magurele, Romania.

Technologically relevant tetragonal/cubic phases of HfO can be stabilized at room temperature by doping with trivalent rare earths using various approaches denoted generically as bulk coprecipitation. Using in situ/ex situ X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy, and in situ/ex situ site-selective, time-gated luminescence spectroscopy, we show that wet impregnation of hafnia nanoparticles with 10% Eu oxide followed by mild calcination in air at 500 °C produces an efficient stabilization of the cubic phase, comparable to that obtained by bulk precipitation. The physical reasons behind the apparently conflictual data concerning the actual crystallographic phase and the local symmetry around the Eu stabilizer and how these can be mediated by luminescence analysis are also discussed. Apparently, the cubic crystal structure symmetry determined by XRD results in a pseudocubic/tetragonal local structure around Eu determined by luminescence. Considering the recent findings on wet impregnated CeO and ZrO, it is concluded that CeO, ZrO, and HfO represent a unique case of a family of oxides that is extremely tolerant to heavy doping by wet impregnation. In this way, the same batch of preformed nanoparticles can be doped with different lanthanide concentrations or with various lanthanides at a fixed concentration, allowing a systematic and reliable investigation of the effect of doping, lanthanide type, and lanthanide concentration on the various functionalities of these technologically relevant oxides.
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http://dx.doi.org/10.1021/acsomega.9b00580DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6648616PMC
May 2019
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