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2. Microwave Synthesis of Poly(Acrylic) Acid-Coated Magnetic Nanoparticles as Draw Solutes in Forward OsmosisSabina Vohl, Irena Ban, Mihael Drofenik, Hermina Bukšek, Sašo Gyergyek, Irena Petrinić, Claus Hélix-Nielsen, Janja Stergar, 2023, original scientific article Abstract: Polyacrylic acid (PAA)-coated magnetic nanoparticles (MNP@PAA) were synthesized and evaluated as draw solutes in the forward osmosis (FO) process. MNP@PAA were synthesized by microwave irradiation and chemical co-precipitation from aqueous solutions of Fe2+ and Fe3+ salts. The results showed that the synthesized MNPs have spherical shapes of maghemite Fe2O3 and superparamagnetic properties, which allow draw solution (DS) recovery using an external magnetic field. Synthesized MNP, coated with PAA, yielded an osmotic pressure of ~12.8 bar at a 0.7% concentration, resulting in an initial water flux of 8.1 LMH. The MNP@PAA particles were captured by an external magnetic field, rinsed in ethanol, and re-concentrated as DS in repetitive FO experiments with deionized water as a feed solution (FS). The osmotic pressure of the re-concentrated DS was 4.1 bar at a 0.35% concentration, resulting in an initial water flux of 2.1 LMH. Taken together, the results show the feasibility of using MNP@PAA particles as draw solutes.
Keywords: magnetic nanoparticles, microwave synthesis, polyacrilic acid, osmotic pressure, draw solution, forward osmosis
Published in DKUM: 05.12.2023; Views: 433; Downloads: 20
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3. Synthesis of magnetic nanoparticles with covalently bonded polyacrylic acid for use as forward osmosis draw agentsIrena Ban, Mihael Drofenik, Hermina Bukšek, Irena Petrinić, Claus Hélix-Nielsen, Sabina Vohl, Sašo Gyergyek, Janja Stergar, 2023, original scientific article Abstract: Multicoated magnetite (Fe3O4) magnetic nanoparticles (MNPs) with polyacrylic acid (PAA) as a terminal hydrophilic ligand were synthesized and examined for use as a draw solution (DS) agent in forward osmosis (FO). After coating superparamagnetic iron-oxide MNPs with (3-aminopropyl)triethoxysilane (APTES) the carboxyl groups of PAA were bound to APTES amino groups via the crosslinker 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) forming a peptide bond resulting in stable water-soluble particles (MNP@APTES@PAA) with a concentration-normalised osmotic pressure of 1.56 bar L g−1. The MNP@APTES@PAA solution was evaluated as a DS in two FO filtrations with deionized (DI) water as a feed solution (FS): one using freshly prepared MNP@APTES@PAA and one using magnetically recovered (re-concentrated) MNP@APTES@PAA. The resulting MNP@APTES@PAA nanocomposites exhibit good colloidal stability in aqueous solution with a concentration-normalized osmotic pressure of 1.56 bar L g−1. This is 12-fold higher than that in our previous studies of poly-sodium-acrylate coated MNPs and 3-fold higher than that of citric acid coated MNPs. The water recoveries of the two filtrations were 25.7% and 13.6%, respectively, after 2 h of FO filtration time resulting in a DS osmotic pressure of 2.5 bar with a concentration of 4.3 g L−1 and a DS osmotic pressure of 2.6 with a concentration of 3.7 g L−1 respectively.
Keywords: magnetic nanoparticle, forward osmosis, draw solution, osmose
Published in DKUM: 16.08.2023; Views: 424; Downloads: 14
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4. FORMULATION, PREPARATION AND CHARACTERIZATION OF NANOEMULSIONS FOR PARENTERAL NUTRITION : doctoral disertationDušica Mirković, 2019, doctoral dissertation Abstract: The aim of this doctoral research was to develop and optimize parenteral nanoemulsions as well as the total parenteral nutrition (TPN) admixture containing a nanoemulsion obtained in the course of the optimization process (hereinafter referred to as optimal nanoemulsion), and to examine their physicochemical and biological quality as well. In addition, the quality of the prepared nanoemulsions was compared with the quality of the industrial nanoemulsion (Lipofundin® MCT/LCT 20%), and, in the end, the TPN admixture initially prepared was also compared with the admixture into which the industrial emulsion was incorporated.
Parenteral nanoemulsions that were considered in this dissertation were prepared by the high-pressure homogenization method. This method is the most widely applied method for the production of nanoemulsions due to the shortest length of homogenization time, the best-obtained homogeneity of the product and the smallest droplet diameter.
For the nanoemulsion formulation, preparation and optimization purposes, by using, firstly, the concept of the computer-generated fractional design, and, after that, the full experimental design, the assessment of both direct effects of different formulation and process parameters (the oil phase type, the emulsifier type and concentration, a number of homogenization cycles and the pressure under which homogenization was carried out) as well as the effects of their interactions on the characteristics of prepared nanoemulsions was performed.
Monitoring the nanoemulsion physical and chemical stability parameters was carried out immediately after their preparation, and then after 10, 30 and 60 days. It included the visual inspection, the measurement of the droplet diameter (the mean and volume droplet diameter), the polydispersity index, the ζ-potential, the pH value, the electrical conductivity, and the peroxide number. After the preparation and after 60 days, the biological evaluation (the sterility test and the endotoxic test) of the prepared nanoemulsions was carried out. As far as the characterization of the TPN admixture is concerned, it included practically the same parameters. The dynamics of monitoring the characteristics of the TPN admixture was determined on the basis of practical needs of hospitalized patients (0h, 24h and 72h).
The scope and comprehensiveness of this issue indicated the need to divide the doctoral dissertation into three basic stages. The first stage was preliminary. Using the 24-1 fractional factorial design, nanoemulsions for the parenteral nutrition were prepared. They contained either a combination of soybean and fish oil, or a combination of medium chain triglycerides and fish oil. In addition, the type and the amount of an emulsifier used, a number of high-pressure homogenization cycles, and the homogenization pressure, were also varied. The measurement of the above-mentioned parameters for the industrial nanoemulsion was parallely carried out (Lipofundin® MCT/LCT 20%). The objective of this part of the research was to identify critical numerical factors having the most significant effect on the characteristics that define the prepared parenteral nanoemulsions. Parameters that were singled out as the result of this stage of the research (the emulsifier concentration and a number of homogenization cycles) were used as independent variables in the second stage of the research.
Keywords: nanoemulsions, total parenteral nutrition admixtures, high pressure homogenization, design of experiments, optimization, analysis of variance, artificial neural networks
Published in DKUM: 07.06.2019; Views: 11996; Downloads: 19
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5. The magnetic and colloidal properties of $CoFe_2O_4$ nanoparticles synthesized by co-precipitationSašo Gyergyek, Mihael Drofenik, Darko Makovec, 2014, original scientific article Abstract: Magnetic $CoFe_2O_4$ nanoparticles were synthesized by co-precipitation at 80 °C. This co-precipitation was achieved by the rapid addition of a strong base to an aqueous solution of cations. The investigation of the samples that were quenched at different times after the addition of the base, using transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS) and X-ray powder diffractometry, revealed the formation of a Co-deficient amorphous phase and $Co(OH)_2$, which rapidly reacted to form small $CoFe_2O_4$ nanoparticles. The nanoparticles grew with the time of aging at elevated temperature. The colloidal suspensions of the nanoparticles were prepared in both an aqueous medium and in a non-polar organic medium, with the adsorption of citric acid and ricinoleic acid on the nanoparticles, respectively. The measurements of the room-temperature magnetization revealed the ferrimagnetic state of the $CoFe_2O_4$ nanoparticles, while their suspensions displayed superparamagnetic behaviour.
Keywords: cobalt ferrite, nanoparticles, co-precipitation, colloidal suspensions, magnetic properties
Published in DKUM: 30.08.2017; Views: 2809; Downloads: 108
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6. Synthesis, crystal structure and magnetic properties of a new hydroxylammonium fluoroferrateBrina Dojer, Matjaž Kristl, Zvonko Jagličić, Amalija Golobič, Marta Kasunič, Mihael Drofenik, 2012, original scientific article Abstract: This paper reports on the synthesis of a new hydroxylammonium fluoroferrate, with the formula $(NH_3OH)_3FeF_6$, obtained after dissolving iron powder in hydrofluoric acid and adding solid $NH_3OHF$. This new compound has been characterized by chemical and thermal analysis, single-crystal X-ray diffraction, and magnetic measurements. The title compound crystallizes trigonal, R3c, with cell parameters a = 11.4154(2) Å, c = 11.5720(2) Å, Z = 6. The structure consists of $NH_3OH^+$ cations and isolated $FeF_6^{3–}$ octahedra in which the central ion lies on a threefold axis. The oxygen and nitrogen atoms of the hydroxylammonium cations are donors of hydrogen bonds to fluoride anions, resulting in a network of hydrogen bonds between counterions. The effective magnetic moment $µ_{eff}$ = 5.8 BM was calculated and perfectly matches the expected value of high-spin Fe(III) ions. The thermal decomposition of the compound was studied by TG, DSC, and X-ray powder diffraction.
Keywords: inorganic chemistry, crystallography, coordination compounds, synthesis, crystal structure, characterization of compounds, determination of the structure of compounds, X-ray diffraction, magnetic measurements, thermal analysis, TG, DSC, hydrogen bond, metal complexes, hydroxylammonium fluoromethalatehydroxylammonium, fluoroferrate
Published in DKUM: 25.08.2017; Views: 2076; Downloads: 70
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7. Synthesis and characterisation of hydroxylammonium fluorochromateMatjaž Kristl, Mihael Drofenik, Ljubo Golič, Amalija Golobič, 2003, original scientific article Abstract: Reactions in the system $Cr – NH_3OHF – HF – H_2O$ were investigated. Green crystals of a new compound with the formula $(NH_3OH)_3CrF_6$ have been isolated from the water solution and characterized by chemical analysis. The compound crystallizes as triclinic, P-1, with cell parameters: a = 6.5461(2) Å, b = 6.9347(2) Å, c = 9.4072(3) Å, α = 86.772(1)°, β = 83.804(1)°, γ = 70.283(1)°. The effective magnetic moment, $µ_{eff}$ = 3.82 BM, was calculated from magnetic susceptibility measurements in the temperature range 80-290 K. The thermal decomposition of the compound was studied by TG and DSC analysis. $(NH_3OH)_3CrF_6$ decomposes above 125 °C in three steps and the residue has been identified by X-ray powder diffraction as $α – Cr_2O_3$.
Keywords: inorganic chemistry, structural chemistry, crystalline structure, coordination compounds, synthesis, inorganic reactions, thermal decomposition, characterization of compounds, TG, DSC, X-ray diffraction, chromium complexes, hydroxylammonium fluoro chromates, crystals
Published in DKUM: 25.08.2017; Views: 1893; Downloads: 114
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8. Reactive sintering of $MnZn$ ferritesTomaž Kosmač, Mihael Drofenik, 2001, original scientific article Abstract: Reaction-formed $MnZn$ ferrite was prepared and the decrease in shrinkage after sintering due to the volume expansion accompanying iron oxidation was studied.
Green compacts consisting of the milled raw oxides $Fe_2O_3$, $Mn_3O_4$, $ZnO$ and metallic iron powder were sintered at 1350 °C in air. During the first hold at 800 °C, $Fe$ was oxidized to $\alpha-Fe_2O_3$ and $Zn$ ferrite was formed. Above 1300 °C the reaction bonding was completed and $MnZn$ ferrite, exhibiting a relatively low shrinkage, was formed. The chemical reactions involved during reaction bonding were associated with a volume expansion and porosity formation, compensating for the shrinkage on sintering. Intensive milling decreases the porosity after sintering but induces the oxidation of iron, and partially removes the shrinkage compensation caused by the presence of metallic iron.
Keywords: reaction-forming, $MnZn$ ferrite, inorganic technology, ferrite ceramics, reaction bonded ceramics, sintering, iron oxides, iron
Published in DKUM: 25.08.2017; Views: 1182; Downloads: 112
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9. Ammoniumbis(hydroxylammonium) pentafluoridooxidovanadate(IV) : synthesis and characterisation of a new fluorovanadateBrina Dojer, Matjaž Kristl, Zvonko Jagličić, Mihael Drofenik, Anton Meden, 2008, original scientific article Abstract: Turquoise crystals of a new hydroxylammonium compound with the formula $NH_4(NH_3OH)_2[VOF_5]$ have been synthesized by the reaction of solid $NH_3OHF$ and the aqueous solution of vanadium in HF. The compound crystallizes monoclinic, $P2_1/n$, with cell parameters: a = 10.5658(2) Å, b = 6.6143(1) Å, c = 11.6618(2) Å, β = 96.282(1). Magnetic susceptibility was measured using a SQUID device over a temperature range 2–300 K at magnetic field $10^3 Oe$ giving the result $µ_{eff}$ = 1.65 BM. The thermal decomposition was studied by TG and DSC analysis. $NH_4(NH_3OH)_2[OF_5V]$ decomposes above 354 K in three steps, obtaining $NH_4VOF_3$ after the first step and $V_2O_5$ as the final residue.
Keywords: hydroxylammonium fluorovanadates, x-ray powder diffraction, x-ray structure determination, thermal analysis
Published in DKUM: 17.08.2017; Views: 1850; Downloads: 112
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10. Efekt PTKU v močno donorsko dopirani keramiki ▫$BaTiO_3$▫Nina Ule, Darko Makovec, Mihael Drofenik, 2000, original scientific article Abstract: Navadno izdelujejo upore s pozitivnim temperaturnim koeficientom upornosti (PTK-upore) s sintranjem nizko donorsko dopiranega ▫$BaTiO_3$▫ na zraku. Koncentracija donorja ne sme preseči kritične velikosti (-0,3 mol.% med sintranjem na zraku), ki povzroči zaustavitev pretirane rasti zrn med sintranjem. S sintranjem v redukcijski atmosferi lahko povišamo kritično koncentracijo donorja, in tako dobimo močno donorsko dopiran ▫$BaTiO_3$▫ z grobo zrnato mikrostrukturo. V grobo zrnatem ▫$BaTiO_3$▫ lahko s poznejšo reoksidacijo z žganjem na zraku uravnavamo PTKU-efekt. V tem delu so predstavljeni rezultati raziskave PTKU-efekta v keramikah ▫$BaTiO_3$▫, dopiranih s koncentracijami La od o do 20 ml.%. Vzorci so bili sintrani v redukcijski mešanici ▫$N_2$▫ z 1 % ▫$H_2$▫ in pozneje reoksidirani z žganjem na zraku.
Keywords: polprevodni ▫$BaTiO_3$▫, donorsko dopiranje, električne lastnosti, PTKU-efekt, mikrostruktura
Published in DKUM: 27.07.2017; Views: 1143; Downloads: 105
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