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The aim of the present study was to prepare nanocomposites with different CoCr2O4 content (20%, 50%, and 80% CoCr2O4/SiO2 mass%) starting from Co(II) carboxylate and ammonium dichromate using a modified sol–gel method and to evaluate the final product (nature, size and shape) based on the different precursor amount. Thermal analysis was used in order to reveal the formation and decomposition of Co(II) carboxylate to CoO and (NH4)2Cr2O7 to Cr2O3+x, inside the silica gel pores. The oxide mixture interacts at temperatures of ~ 400 °C when Cr2O3+x turn to α-Cr2O3 which leads together with CoO to the formation of CoCr2O4 inside the SiO2 matrix. XRD and FTIR analyses revealed the formation of the single spinel structure in all synthesized samples. The results show that a higher cobalt chromite content inside the silica matrix leads to higher crystallinity. The particle sizes were in nanometer range, and the size variation was small from a sample to another, independent on the concentration (3.9–12.4 nm).

This paper deals with the study of compatibility between antihyperlipidemic agent atorvastatin calcium trihydrate (ATV) and eight pharmaceutical excipients used in the development of solid dosage forms, namely citric acid, anhydrous lactose, magnesium citrate, magnesium carbonate, sodium carboxymethyl cellulose, polyvinylpyrrolidone K30, colloidal silica and sorbitol. As investigational tools, universal attenuated total reflectance Fourier transform infrared spectroscopy and powder X-ray diffractogram patterns were used for binary mixtures of ATV with each excipient at ambient condition and then completed by subjecting the samples to thermal stress using thermal analysis (TG/DTG/HF), in non-isothermal conditions and in oxidative medium. It was shown the binary mixtures do not present interactions between ATV and excipients when stored under ambient conditions for 2 months, while under thermal stress, ATV presents interactions with sorbitol.

CuCr2O4 spinel powders were synthesized starting from different chromium sources, namely (i) chromium oxide (α-Cr2O3) and (ii) ammonium dichromate ((NH4)2Cr2O7). The copper source was a Cu(II) carboxylate-type complex. The Cu(II) carboxylate complex was obtained by the redox reaction between Cu(NO3)2·3H2O and 1,3-propanediol (1,3PG) at 130 °C. In the first case (i), we have started from a mixture of α-Cr2O3, Cu(NO3)2·3H2O and 1,3PG that upon heating formed the copper malonate complex, which decomposed around 220 °C forming an oxide mixture (CuO + α-Cr2O3). In the second case (ii), (NH4)2Cr2O7, Cu(NO3)2·3H2O and 1,3PG were homogenously mixed. Heating this mixture at 130 °C resulted, in situ, in the Cu(II) complex. On controlled temperature increase, the violent decomposition of (NH4)2Cr2O7 took place at 180 °C along with the decomposition of the Cu(II) complex, leading to an amorphous oxide mixture of Cr2O3+x and CuO. By annealing the samples in the temperature range 400–1000 °C, the spinel phase (CuCr2O4) was obtained in both cases: (i) at 800 °C and (ii) at 600 °C as a result of the interactions between the precursors used, when the oxide system was amorphous and highly reactive. The presence of CuCr2O4 was highlighted by XRD and FTIR analyses.

Nanoparticles of cobalt–zinc ferrite Co 1− x Zn x Fe 2 O 4 with x varying from 0 to 1.0 were prepared by a new method, the thermal decomposition of carboxylates of Fe(III), Co(II) and Zn(II). The obtained carboxylate precursor was characterized by thermal analysis and FT-IR spectroscopy. The precursor was annealed at 350, 600 and 1000 °C. It was found that the spinel cobalt–zinc ferrite was formed starting at 350 °C, but in mixture with simple oxides γ-Fe 2 O 3 , Co 3 O 4 and ZnO. At 1000 °C Co 1− x Zn x Fe 2 O 4 was formed quantitatively as a single, well-crystallized phase. The saturation magnetization of the samples annealed at 1000 °C decreased significantly with increasing Zn 2+ content from 83.93 emu/g ( x =0) to 4.92 emu/g ( x =1.0). At 350 and 600 °C the saturation magnetization had the same trend, even if there were contributions of other magnetic phases. Obtaining of spinel ferrite was evidenced by X-ray diffractometry and FT-IR spectrometry. Powder morphology was determined by scanning electron microscopy. Magnetic properties of the synthesized ferrites were investigated employing a conventional induction method.

Nickel oxides nanoparticles were successfully obtained using a new sol–gel method approach which is based on the thermal decomposition of some carboxylate compounds formed within the pores of hybrid tetraethyl orthosilicate–diol gels. The Ni(II) carboxylate compounds were obtained in the redox reaction between diols (1,3-, 1,4-, and 2,3-butane diol, respectively) and NO 3 − anion of Ni(NO3)2·6H2O. The diol is the key component of the system by its simultaneous participation in the redox reaction as well as in the interaction with tetraethyl orthosilicate for the formation of the hybrid gels. There were synthesized gels with the three types of diol for compositions of 30, 50, and 70 % NiO/SiO2 in order to see what kind of crystalline species (Ni, NiO or mixtures) are formed within the silica matrix. The gels were thermally treated at different temperatures leading to single-phase, nanosized NiO/SiO2 crystallites, depending on the carboxylate radical, the morphology of the silica matrix, the sample composition, and the annealing temperatures of 350 and 800 °C. Thermal analysis is an excellent tool for the study of different thermal behavior of Ni(II) carboxylates based on the different diols used as reagents and the sample composition. The shape of the X-ray diffraction patterns evidenced the very fine nature of the samples and the nanometer size (5–25 nm) of the nickel oxide crystallites inside the silica matrix.

This paper presents a facile and rapid synthesis route of metallic Ni and Co nanocrystallites at ~150 °C in the mixture composed of the corresponding metal nitrates and 1,3-propanediol, as reducing agent. The metal oxides NiO, CoO, Co3O4 nanocrystallites were, also, successfully synthesized by thermal decomposition at 300 °C of the hydroxycarboxylate coordination products, obtained in the redox reaction between 1,3-propanediol and Ni(II) and Co(II) nitrates. The formation of the Ni(II) and Co(II) hydroxycarboxylate complexes depends on the diol which generates the carboxylate anion, the transition metal and the process parameters. Ni(II) and Co(II) nanocomposites were also synthesized by thermal decomposition of the complex combinations formed within the pores of the hybrid silica gels. One of the purposes of the present study was to investigate the phase constitution of the composites obtained in similar synthesis conditions, from Ni(II) and Co(II) complex combinations embedded in silica gels. These gels were submitted to various thermal treatments and the changes occurring during these treatments were described by X-ray diffraction. Thermal analysis is an excellent tool for the study of the processes implied in the formation and decomposition of the Co(II) and Ni(II) carboxylate complexes. X-ray diffraction evidenced the nanometer sized metal and/or metal oxide phases.

Nanocomposites of the type 30 % CuFe2O4/70 % SiO2 were synthesized using the modified sol–gel method starting from tetraethylorthosilicate, metal nitrates (Fe(NO3)3·9H2O, Cu(NO3)2·3H2O) and the diol: 1,3-propane diol. The obtained hybrid gel, which contains within the pores, the metal nitrates and diol, was thermally treated at 140 °C, when the redox reaction between metal nitrates and 1,3-propane diol takes place forming Cu(II)–Fe(III) carboxylate compounds of malonate type. The thermal decomposition of the carboxylates within the gels pores, at ~300 °C, leads to simple or mixed metal oxides, uniformly distributed within the amorphous silica matrix. The spinel system CuFe2O4/SiO2 was obtained starting with 700 °C. The evolution of the spinel phase with the annealing temperature was investigated and resulted that at 1,000 °C, the matrix crystallizes into cristobalite and quartz. The formation of bulk CuFe2O4, starting from the same type of Cu(II)–Fe(III) carboxylate compounds was also investigated. A comparison between the thermal evolution of bulk CuFe2O4 and CuFe2O4/SiO2 starting from Cu(II)–Fe(III) carboxylate compounds was made. The magnetic behavior of the ferrite nanocrystallites depending on the annealing temperature was also investigated.

The study reports the preparation of CoFe2O4/SiO2 nanocomposites by a new modified sol–gel method starting from cobalt nitrate, iron nitrate, and diols: 1,2-ethanediol (EG), 1,3-propanediol (1,3PG), and tetraethylorthosilicate (TEOS), for final compositions of 30 %CoFe2O4/70 %SiO2 and 50 %CoFe2O4/50 %SiO2. The method is based on the formation of a Co(II), Fe(III)—carboxylate precursors mixture, during the redox reaction between the NO 3 − ion and the diol (~140 °C) within the silica gels. The thermal decomposition of these complex combinations takes place at ~300 °C leading to the corresponding amorphous metal oxides within the pores of the hybrid gels. Depending on the subsequent thermal treatment, CoFe2O4 can be obtained as single phase or in a mixture with Co2SiO4. The CoFe2O4 crystallites sizes are in the nanometer range (3–10 nm). The obtained nanocomposites have a hard magnet behavior, as a result of the high anisotropy of CoFe2O4 having large hysteresis cycles.

This paper presents a study regarding the formation of hybrid gels starting from tetraethyl orthosilicate (TEOS), polyvinyl alcohol (PVA) and 1,3-propanediol (PD) and their thermal evolution to mesoporous silica matrices. The possibility of obtaining homogenously dispersed cobalt ferrite inside the silica matrix starting from (TEOS–PVA–PD–Metal Nitrates) gels was also studied. The formation of the hybrid gels TEOS/PVA/PD with different compositions was studied by FT-IR spectrometry and thermal analysis, in order to evidence the interaction between the diol with the organic and the inorganic polymers. Both thermal analysis and FT-IR spectrometry have evidenced the formation of physical and chemical interaction between polyols and the siloxane network. Elemental mapping performed by SEM-EDX technique evidenced the formation of homogenous hybrids both in the presence of the absence of 1,3-propanediol. SEM images of the powders obtained by annealing the hybrid xerogels at 600 °C have evidenced the formation of mesoporous silica. By thermal treatment of the (TEOS–PVA–PD–Metal Nitrates) gels, 30%CoFe2O4/70%SiO2 (mass percent) nanocomposites uniformly dispersed in silica matrix with characteristic magnetic properties, have been successfully synthesized.

This paper presents a study regarding the obtaining of NiCr2O4 by two new unconventional synthesis methods: (i) the first method is based on the formation of Cr(III) and Ni(II) carboxylate-type precursors in the redox reaction between the nitrate ion and 1,3-propanediol. The thermal decomposition of these complex combinations, at ~300 °C, leads to an oxide mixture of Cr2O3+x and NiO, with advanced homogeneity, small particles and high reactivity. On heating this mixture at 500 °C, Cr2O3 reacts with NiO to form NiCr2O4, which was evidenced by FT-IR and X-ray diffractometry (XRD) analysis; (ii) the second method starts from a mechanical mixture of (NH4)2Cr2O7 and Ni(NO3)2·6H2O. On heating this mixture, a violent decomposition at 240 °C with formation of an oxides mixture (Cr2O3 + CrO3) and NiO takes place. On thermal treatment up to 500 °C, an intermediary phase NiCrO4 is formed, which by decomposition at ~700 °C leads to NiCr2O4, evidenced by FT-IR and XRD analysis. NiCr2O4 is formed, in both cases, starting with a temperature higher than 400 °C, when the non-stoichiometric chromium oxide (Cr2O3+x ) loses the oxygen excess and turns to stoichiometric chromium oxide (Cr2O3), which further reacts with NiO.

The paper presents experimental studies and structural investigations of two new Fe(III) hydroxycarboxylate coordination compounds. The homopolynuclear complex combinations of Fe(III) glyoxylate and succinate type were obtained in the redox reaction between Fe(NO 3 ) 3 and diols (1,2-ethanediol and 1,4-butanediol). The synthesized coordination compounds and the products formed during their thermal conversion were characterized by thermal analysis (in air and nitrogen), FT-IR and UV–VIS spectrometry, Mossbauer spectrometry, electron microscopy and XRD. By thermal decomposition of the complex combinations, at 300 °C, the well crystallized pure phase γ-Fe 2 O 3 as nanoparticles were formed.

The paper presents a study on the preparation of Co2SiO4/SiO2 nanocomposites by a new modified sol–gel method. We have prepared gels starting from tetraethylorthosilicate (Si(OC2H5)4), cobalt nitrate Co(NO3)2·6H2O and some diols: ethylene glycol (C2H6O2), 1,2propanediol (C3H8O2) and 1,3propanediol (C3H8O2), for a final composition: 30% CoO/70% SiO2. During the heating of the gels at 140 °C, a redox reaction takes place between NO3 − ions and diol with formation of some carboxylate anions. These carboxylate anions react with the Co(II) ions to form coordination compounds embedded in silica matrix, as evidenced by FT-IR spectrometry and thermal analysis. These Co(II) coordinative compounds thermally decompose in the range 250–300 °C to the corresponding oxides: CoO and/or Co3O4 inside the matrices pores. When CoO results, it reacts with SiO2 at low temperature leading to Co2SiO4, which crystallizes at 700 °C. XRD patterns of the samples annealed at temperatures lower than 700 °C were characteristic to amorphous phases. The samples annealed at temperatures ≥700 °C, contain Co2SiO4 (olivine) as unique crystalline phase inside the amorphous silica matrix, according to XRD patterns. As evidenced by TEM images, Co2SiO4 nanoparticles are homogenously dispersed inside the silica matrix.

This article presents a study on obtaining Ni, Zn ferrite starting from Fe(III), Ni (II), Zn (II) nitrates and some polyols: 1,2-propane diol, 1,3-propane diol and glycerol. While heating, a redox reaction takes place between nitrate anion and polyol, with formation of carboxylate type precursors. The obtained precursors have been investigated by thermal analysis, FT-IR spectrometry and atomic absorption spectroscopy. The thermal decomposition of the synthesized precursors up to 350 °C leads to the formation of Ni, Zn ferrite as unique phase, evidenced by XRD. The average diameter of the ferrite crystallites, estimated from XRD data, takes values within the range 20–50 nm, depending on the annealing temperature. Transmission Electron Microscopy has evidenced the obtaining of spherical, agglomerated nanoparticles. The magnetic properties of the synthesized samples, measured in cvasistatic magnetic field (50 Hz) are characteristic for the Ni, Zn ferrite nanoparticles, with narrow hysteresis cycle and values of the saturation magnetization

Hybrid organic–inorganic materials, silica–diol, were synthesized by the sol–gel process from mixtures of tetraethylorthosilicate (TEOS) and diols: ethylene glycol (HO–CH2–CH2–OH) and 1,3 propane diol (HO–CH2–CH2–CH2–OH), in acid catalysis. The gels have been synthesized for a molar ratio H2O:TEOS = 4:1 and different molar ratios diol/TEOS: 0.25; 0.5; 0.75; 1.0; 1.25 and 1.5. The resulting gels were studied by thermal analysis and FT-IR spectroscopy, in order to evidence the interaction of diols with silica matrix. Thermal analysis indicated that the condensation degree increases with the molar ratio diol/TEOS until a certain value. The thermal decomposition of the organic chains bonded within the silica network in the temperature range 250–320 °C, leaded to a silica matrix with modified morphology. The adsorption–desorption isotherms type is different for the samples with and without diol. Thus, the specific surface areas have values 200 m2/g for the samples with diols, depending on the annealing temperature.

In this paper we present a study regarding the obtaining of iron oxides embedded in silica matrix, using a modified sol-gel method. This method consists in the formation, inside the silica matrix, of some Fe(III)-carboxylate compounds, resulted in the redox reaction between Fe(NO3)3 and diol. We have synthesized four gels, starting from tetra-ethyl orthosilicate, Fe(NO3)3·9H2O and different diols: ethylene glycol, 1,2-propanediol, 1,3-propanediol and 1,4-butanediol, for a final composition 50% Fe2O3/50% SiO2. The obtained gels have been thermally treated at 130°C, when the redox reaction Fe(NO3)3-diol took place with formation of the precursors in the xerogels pores. The thermal decomposition of all four precursors took place up to 300°C. The samples obtained by annealing at 300, 500, 700°C of the four xerogels lead to crystalline phases inside the amorphous silica matrix. γ-Fe2O3/SiO2 may be obtained as unique phase depending on the diols nature. The formation of the precursors inside the silica matrix and the evolution of the crystalline phases were analyzed by thermal analysis, FTIR spectrometry and XRD.

The synthesis of (Ni 0.65 Zn 0.35 Fe 2 O 4 )/(100 − x )SiO 2 ( x = 35% Si 65%, mass percent) nanocomposites, by a sol–gel method, starting from tetraethylorthosilicate, metal nitrates and polyols is reported here. The gels obtained were thermally treated at 130 °C, when the redox reaction between metal nitrates and polyol took place in the pores, forming Fe(III), Ni(II), Zn(II), carboxylate compounds, which are precursors of the ferrite. The precursors formation and thermal decomposition inside the silica matrix have been studied by thermal analysis and FT-IR spectrometry. The controlled thermal treatment of the gels, which contained the ferrite precursors, lead to the formation of spherical Ni, Zn ferrite nanoparticles embedded in silica matrix. Thus, XRD spectra and TEM images showed that the ferrite particles diameters were under 30 nm in size. The magnetic behaviour of the ferrite nanoparticles embedded in the silica matrix, measured in quasi-static magnetic field (50 Hz), modified from superparamagnetic to ferrimagnetic, depending on the annealing temperature.

In this paper we present a study on the synthesis of Fe(III) oxide, by thermal decomposition of some complex combinations of Fe(III) with carboxylate type ligands, obtained in the redox reaction between some polyols (ethylene glycol (EG), 1,2-propane diol (1,2PG), 1,3-propane diol (1,3PG) and glycerol (GL)) and NO3– ions (from ferric nitrate). Fe2O3 was obtained by thermal decomposition of the synthesized metal-organic precursors at low temperatures. γ-Fe2O3 was obtained as nanoparticles at 300°C, while at higher temperatures α-Fe2O3 starts to crystallize and becomes single phase at ~500°C.

Hybrid organic-inorganic materials, silica – polyols (ethylene-glycol – EG; 1,2 propane diol – 1,2PG; 1,3 propane diol – 1,3PG and glycerol – GL), were prepared by a sol-gel process starting from tetraethylorthosilicate (TEOS) and polyols, in acid catalysis. The resulting materials were studied by thermal analysis (in air and nitrogen), FTIR and solid state 29Si-NMR spectroscopy. These techniques evidenced the presence of polyols in the silica matrix both hydrogen bounded and chemically bounded in the silica network. The thermal analysis proves to be the most appropriate technique to evidence the organic chains linked in the matrix network and to follow the thermal evolution of the gels to the SiO2 matrix.

Hybrid organic-inorganic materials, silica—ethylene glycol (EG), were prepared by the sol-gel process from mixtures of tetraetoxysilane (TEOS) and EG under acidic catalysis. The resulting hybrid material was studied through thermal analysis and FT-IR spectroscopy. This techniques evidenced the presence of EG in the silica matrix in three forms: free in the hybrid matrix pores, hydrogen bonded with the silanol groups and chemically bonded (through condensation) in the silica network. Through the thermal treatment of the hybrid matrix, we obtained a silica matrix, with specific surface of 360 m2/g.

Nanocomposites of the type (Ni–Zn)Fe 2 O 4 /SiO 2 have been synthesized using a novel chemical route involving the liquid phase. Metallic nitrates (MN)–ethylene glycol (EG)–silica gels were prepared as a result of the polycondensation reaction, using as precursors MN of Fe, Ni, Zn and tetraethylorthosilicate, to which EG was added. After gelling and drying, the sols were first subjected to a thermal treatment at a temperature of ∼140 °C, where heteropolynuclear complex combinations with carboxylic ligands are formed as a result of the redox reaction between EG and the nitrate ions. These have been investigated using Fourier transform infrared spectrometry and thermal analysis. The influence of EG on the gels was also studied. While observing the formation of Ni–Zn ferrite using this method, following the thermal treatment of the gels at higher temperatures (500–1000 °C), nanocomposites were obtained made up of ultrafine Ni 0.65 Zn 0.35 Fe 2 O 4 nanoparticles (4–6 nm) that are perfectly spherical, with an ultranarrow distribution (∼1 nm) of diameters around the mean value and homogeneously dispersed in a solid SiO 2 matrix. The synthesized nanocomposites were characterized by means of X-ray diffraction, high-resolution transmission electron microscopy and magnetic measurements.

Hybrid inorganic-organic materials, silica - diol, were prepared by the sol-gel process from mixtures of tetraethyl orthosilicate (TEOS) and two diols (1,2-propanediol and 1,4-butanediol), using different molar ratios TEOS: diol, in acidic catalysis. The resulted materials were studied by thermal analysis, FT-IR spectroscopy, 29Si-NMR and nitrogen adsorption measurements. The thermal analysis of the gels, in air and nitrogen, has clearly evidenced the chemical bonding of the studied diols with the Si-OH groups resulting from the hydrolysis of TEOS, forming hybrid gels. The mass loss registered on TG in the range 250-300 °C, corresponding to the burning of the organic chains from the hybrid network allowed us to calculate the fraction of the bonded diol. This fraction depends on the initial molar ratio TEOS:diol and on the diol's nature. By annealing the hybrid gels at 600 °C we have obtained silica matrices with different textural parameters.