This study investigates the effect of substituting cobalt with manganese on the magnetic and optical properties of cobalt ferrite inorganic pigments synthesised by solution combustion. X‐ray diffraction analysis confirms the formation of a substitutional solid solution with manganese replacing cobalt, associated with a shift in diffraction peaks to lower angles due to the larger ionic radius of manganese. As the manganese concentration increases ( x = 0 to x = 0.6), lattice parameters and unit cell volumes increase, except at x = 0.5, which could be attributed to changes in cation distribution and lattice micro‐strain. Raman spectroscopy shows shifts in the vibrational modes of metal–oxygen bonds, influenced by differences in atomic masses and bond strength constants between manganese and cobalt. Magnetic measurements indicate a decrease in coercive field, saturation magnetisation and remanence with increasing manganese content, due to weaker super‐exchange interactions. Diffuse reflectance spectroscopy reveals low reflectance in the visible range due to electronic transitions in the metal ions. The substitution of manganese increases the band gap from 2.1 to 2.6 eV between x = 0.0 and x = 0.5, then decreases to 2.4 eV at x = 0.6. Colorimetric analysis shows significant variations in CIELab colorimetric coordinates, with lightness, chroma and hue changing with manganese content. Paints derived from these pigments, applied to cement, plaster and wood substrates, exhibit varied optical properties, demonstrating the influence of manganese on the optical characteristics of the pigments.

Inorganic pigments are widely used in various industries, including ceramics and paints. CoAl2O4 is a highly stable pigment, but its industrial synthesis requires high temperatures, resulting in long synthesis times and high costs. Alternative synthesis routes have been proposed, but they are often expensive and require multiple thermal treatment stages. Solution combustion synthesis shows promise in reducing costs and synthesis time, but optimization is required so that synthesis is achieved in one step. In this work, we studied the problem of synthesizing the inorganic pigment CoAl2O4 using a single-step solution combustion synthesis. Therefore, the aim was to investigate the influence of different fuels: urea and citrulline, and the addition of an extra oxidizing agent, ammonium nitrate (A.N.), on the combustion temperature and the resulting structure, morphology, and colour of the pigment. The addition of A.N. resulted in a significant increase in the combustion temperature and the formation of crystalline CoAl2O4. The color coordinates for the powder following combustion, with the inclusion of 2 g of ammonium nitrate (A.N.) in the fuel mixture at an optimized O/F ratio of 0.5, were determined as follows: L* = 58.23, a* = -8.27, b* = -30.25, C*ab = -31.33, and h*ab = 263 degrees, indicative of a blue hue. These results show that inorganic pigments could be used in ceramic decoration and acrylic paint. These findings are important for the development of new and efficient methods for synthesizing inorganic pigments with desirable properties for various applications.

Single-phase, nanosized La0.7Ca0.3Mn1−xNixO3 (x = 0, 0.02, 0.07, 0.1) manganites were synthesized via the autocombustion route. Information on the local geometric structure and the charge state of the Mn ions in the nanosized samples was gleaned from extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) data analysis, respectively. The experimental absorption spectra were recorded at room temperature at the K-edge of the Mn-ions. Analysis of the normalized XANES spectra showed that the Mn formal valence remained practically unchanged upon Ni2+ doping. Nevertheless, the observed broadening of the ruling absorption edge suggested that the repulsive nearest-neighbor potential, stemming from the shortening of the distances of Mn to the nearest-neighbor oxygen atoms (Mn–O bonds) in the coordination shell, was slightly modified. The values of the Mn–O distances were obtained from the Fourier transformed EXAFS spectra. A slight but sizeable decrease in the value of the Mn–O bond distances was verified, which pointed to a slight variation in the Mn3+/Mn4+ ratio sparked by the Ni2+ doping. Here, a generation of more Mn4+ ions with smaller radius (0.53 Å) was expected. The obtained Mn–O distances were compared with those resulting from the Rietveld refinement of the X-ray powder diffraction data. The variation of the 〈Mn–O–Mn〉 bond angle with Ni2+ doping was also determined from the analysis of the X-ray diffraction patterns, which allowed visualizing the small distortion of the MnO6 octahedra on substitution of Mn with Ni2+.

For the first time, cobalt ferrite spinel (CoFe2O4) was used as a catalyst in the Fenton process for Remazol Red RR dye degradation in water. CoFe2O4 was synthesized via gel combustion using tris(hydroxymethyl)aminomethane as an alternative fuel in one step with a ratio of Ψ = 0.8. Its structural, surface optics, magnetic properties, and the optimal conditions of the Fenton reagents for dye degradation were evaluated. The saturation magnetization and remanence (Ms and Mr, respectively) for the as-prepared powder were 65.7 emu/g and 30.4 emu/g, respectively, and the coercivity (Hc) was 1243 Oe, indicating its ferromagnetic nature and suitability as a magnetic catalyst. Red Remazol RR dye degradation tests were performed using the Fenton process to evaluate the influence of the catalyst dosage and H2O2 concentration. The tests were performed in a batch reactor in the dark with constant agitation for 24 h. The best result was obtained using 1 g/L of catalyst with a dye degradation of 80.6%. The optimal concentration of H2O2 (1.0 M) resulted in 96.5% dye degradation. Nanoparticle recyclability testing indicated that the material could be satisfactorily reused as a catalyst for at least three cycles. The potential use of the CoFe2O4 synthesized in this study as a catalyst for dye degradation by the Fenton process was demonstrated.

The effect of sodium chloride (NaCl) on the magnetism of nanopowders of the spinel ferrite (MgFe2O4) produced using a salt-assisted solution combustion synthesis was investigated. X-ray diffraction (XRD) analysis was conducted to evaluate crystalline structure and phase composition of the synthesized materials. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to evaluate the particle size and morphology. Magnetic behavior was analyzed by measuring and analyzing the respective hysteresis loops using a vibrating sample magnetometer (VSM). The characterization showed that the presence of NaCl affects the phase composition, size, and dispersion of the nanoparticles, as well as their magnetic behavior. The theoretical size of the nanoparticles was calculated using the Scherrer equation, obtaining sizes of about 21.07 nm for the nanoparticles without salt, 5.90 nm for the sample salt content of 1.7 mol and 6.48 nm—for 3.4 mol. The synthesized nanoparticles showed a drastic decrease in coercivity field, remanence, and saturation with increasing salt content. Therefore, the salt content is a crucial parameter in controlling the morphology and magnetic properties of the nanoparticles obtained by the solution combustion route.

In this study, α-Fe 2 O 3 was synthesized by solution combustion method using 6-aminohexanoic acid (AH) as a fuel and with different oxidizer-to-fuel ratios (Φ) of 0.6, 0.8, 1.0, 1.2, and 1.4. The as-prepared powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), and UV–Vis spectroscopy. The results showed that the Φ ratio played a crucial role in determining the crystallinity and purity of the powders of α-Fe 2 O 3 . The α-Fe 2 O 3 powder synthesized at an Φ ratio of 0.6 exhibited phase purity of hematite. This study demonstrates the importance of controlling the Φ ratio in the synthesis of α-Fe 2 O 3 which could be used as an inorganic pigment in paints.

Calcium phosphates are materials of wide interest in the medical and agricultural industries. Advanced in the standardization of protocols to obtain them by combustion in solution in a single step is highly desirable. This is particularly so for the alpha-tricalcium phosphate (α-TCP) phase, widely used in the development of bone cement. In this research, citrulline was used as a fuel for the first time in the one-step synthesis of calcium phosphates, and the effect of adding 0–15 g of ammonium nitrate (AN) as an extra oxidizer agent was studied, allowing the temperature of the reaction to increase from 648 to 950°C. The temperature was measured using low-cost equipment with infrared and type-K thermocouple and contrasted with the estimated theoretical values of adiabatic flame temperature. X-ray diffraction analysis showed the formation of a mixture of α-TCP and hydroxyapatite phases at the lowest combustion temperature, corresponding to 0 g of AN. When the amount of AN was increased, the XRD showed that α-TCP was obtained as a metastable phase, while the amount of hydroxyapatite decreased considerably. At higher combustion temperatures, the crystallite size estimated by Scherrer equation, in turn, increased to a value of 51.61 nm. The SEM images showed the presence of necks between particles in the powders that coincide with the estimation of high reaction temperatures.

Nanocomposites of nickel oxide/yttria-stabilized zirconia (NiO/YSZ) particles were synthesized via solution combustion synthesis using glycine and urea as fuels in one step. The powders were characterized by X-ray diffraction (XRD) analysis, where the synthesis with urea showed the formation of the NiO/YSZ composite, while the presence of Ni with NiO/YSZ were observed when the glycine was used. The morphology of the as-prepared powders and the presence of Ni were corroborated by field emission scanning electron microscopy and energy dispersive X-ray spectroscopy (FE-SEM; EDX). The powders showed catalytic behavior which was evidenced by H2-TPR measurements. These materials could be used for the fabrication of Ni/YSZ anode for fuel cells.

Spinel ferrites are promising candidates for various applications as transformers, transducers, inductors in the electronic field, sensors, biosensors and hyperthermia agents in the biomedical field. Combustion synthesis, as a method for obtaining ferrites, is gaining attention. However, most fuels generate high ignition temperatures, which lead to larger (micrometric) crystallites or even render combustion synthesis unfeasible in a single step. Spinel cobalt ferrite (CoFe2O4) has unique features that facilitate tuning the spinel structure based on modifications in the synthesis parameters. In this study, CoFe2O4 was synthesised via gel combustion using tris (hydroxymethyl)aminomethane (tris) as an alternative fuel. The effect of the oxidizer-to-fuel molar ratio (psi) on their formation and structural, optical, and magnetic properties were evaluated. Gels were prepared from metal nitrates and tris at psi values of 0.6, 0.8, 1.0, 1.2, and 1.4. Thermal analysis of the ignition temperature was found to be dependent on psi. The adiabatic flame temperatures were estimated using thermodynamic calculations, as 2688.36 K when psi = 0.6, and 1017.56 K when psi = 1.4, which indicates that the temperatures would be sufficient to form the phase in one step without additional thermal treatment. X-ray diffraction confirmed the formation of CoFe2O4 as a single-phase for all psi values. Raman and Fourier transform infrared spectroscopy confirmed the formation of CoFe2O4 for all psi values investigated. The low bandgap values (0.92-1.36 eV) suggest several promising applications in photoactivated materials. The magnetic properties of the as-prepared powders measured by a vibrating sample magnetometer revealed saturation magnetisation values, Ms, and coercivity field, Hc, and remanence magnetisation were dependant on psi. These results show that tris can be used as a fuel to synthesise spinel ferrites via one-step gel combustion with excellent properties for several applications.

Calcium phosphates are biomaterials widely used in bone tissue engineering. In recent years, the alternative of obtaining these materials with antimicrobial properties, has been explored due to the multiple advantages that this would imply in the design of devices or implants that prevent the failure of these associated with bacterial colonization. The goal of the present work was obtaining gold nanoparticles supported on biphasic calcium phosphates (BCPs) with high crystallinity by one-step solution combustion technique, and with antimicrobial response, a fact that can significantly reduce the production cost of these materials. X-ray diffractograms (XRD) showed that prepared powders have high crystallinity owing to high temperatures during the combustion reaction, also Rietveld refinement showed that the inclusion of gold nanoparticles (AuNPs) influenced the phases’ ratio obtained. Furthermore, scanning electron microscopy (SEM) showed agglomeration of particles with morphologies with shape tending to be equigranular, while the presence of AuNPs was corroborated by transmission electron microscopy (TEM). All samples that were obtained in a single step, by solution combustion, showed antimicrobial behavior validated through the inhibition halos, whereas particles subjected to thermal treatment lost their antimicrobial response.

In this study, for the first time, caffeine and citrulline were used as fuels for the synthesis of the spinel ferrite CoFe2O4 by gel combustion. The influence of the oxidizer to fuel molar ratio (phi) on the synthesis of cobalt ferrite was studied. X-Ray Diffraction (XRD) showed that the spinel phase was obtained in all the combustions, but the use of caffeine as fuel allowed it to be obtained with high purity, while in the other combustions CoO appeared as a secondary phase due to changes in the reaction. Furthermore, the crystallite size was estimated using the Scherrer equation and considering the plane (311), finding it to be in the range of 32-40 nm, and increasing as the amount of fuel was increased. In addition, the adiabatic flame temperatures were estimated, finding that, in the synthesis with phi = 0.7, the flame temperatures were 1974 K and 1711 K, for the caffeine and citrulline respectively, which could be sufficient to obtain the phase in one stage. The ignition temperatures identified by DSC/TG thermal analysis for caffeine and citrulline samples with 9 = 1.0 were 297 and 191 degrees C, respectively, which are in the range of traditional fuels. The morphology was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which revealed that the particles were agglomerated as a result of high reaction temperatures. The magnetic properties identified by the vibrating sample magnetometer (VSM) for the sample with caffeine and ratio 9 = 0.7 were saturation magnetization Ms = 95.16 emu g-1, coercivity field Hc = 710.76 Oe and remanent magnetization Mr = 44.86 emu g-1. Meanwhile, with citrulline and ratio 9 = 0.7, the properties were saturation magnetization Ms = 59.14 emu g-1, coercivity field Hc 837.15 Oe and remanent magnetization Mr = 32.30 emu g-1. It should be pointed out that the high saturation magnetization values obtained with caffeine fuel exceed those reported with traditional fuels. The obtained results allow us to infer that these fuels could be used as alternatives in synthesizing inorganic oxides by combustion in one step.

Inorganic nanopigments have become a field of interest in color generation research. Consequently, the rise of inkjet printing technology has raised the need to obtain pigments with particle sizes that have nanometric values in order to avoid technical problems such as nozzle clogging during printing. Furthermore, inkjet technology requires that inks must remain stable during storage and temperature changes. Inkjet technology has allowed the proposition of new ways of adding color to products that require high processing temperatures, such as ceramic materials. On the other hand, the use of traditional pigments in the final coloring process of a product can be improved at the nanoscale. Therefore, in this chapter, we will review the nanopigments used in inkjet printing technology and in traditional coloring applications in the textile, paper, plastics and ceramics industries.

J. F. Montoyaa, *, E. A. Chavarriagab, **, S. Villada-Gilc, ***, O. D. Gutierrezd, and O. Restrepoe aGrupo GAMA, Corporación Universitaria Lasallista, Caldas, Colombia bDepartamento de Ciencias Básicas, Universidad Católica Luis Amigó, Medellín, Colombia cFacultad de Ciencias Básicas, Sociales y Humanas, Politécnico Colombiano Jaime Isaza Cadavid, Medellín, Colombia dInstituto Tecnológico Metropolitano, Medellín, Colombia eGrupo del Cemento y Materiales de Construcción. Universidad Nacional de Colombia sede Medellín, Medellín, Colombia *e-mail: jumontoya@lasallistadocentes.edu.co **e-mail: eachavar@unal.edu.co ***e-mail: svillada@elpoli.edu.co Received June 20, 2020; revised August 21, 2020; accepted August 24, 2020

In this work, multiferroic composites were produced from CoFe2O4 and KNbO3 mixtures via control of the heat treatment temperature. For this, CoFe2O4 nanoparticles were produced by sol-gel method, while KNbO3 was synthesized by microwave-assisted hydrothermal synthesis. The powders were homogenized and subjected to heat treatment at 300, 400 and 500 degrees C for 5 h. The structural, electrical and magnetic properties were characterized. The results of X-ray diffraction indicated that there was no formation of secondary phases with heat treatment. Raman vibrational modes confirmed the presence of KNbO3 and CoFe2O4 in the prepared composites. SEM analysis showed that the composite microstructure consists of smaller ferrite particles arranged on the surface of largest cubic KNbO3 particles. The improvement of coercivity (H-C = 382.1Oe) and dielectric constant (epsilon' similar to 7860) was observed for the composite thermally treated at 300 degrees C. The obtained results show the potential application of KN:CFO composites for multifunctional devices.

E. A. Chavarriagaa, *, A. A. Loperab, T. B. Wermuthc, S. Arcarod, C. P. Bergmanne, and J. Alarcónf a Departamento de Ciencias Básicas, Universidad Católica Luis Amigó, Medellín, Colombia b Grupo GICEI, Institución Universitaria Pascual Bravo, Medellín, Colombia c Department of Materials Engineering, School of Engineering, Universidade Federal Do Rio Grande Do Sul, Porto Alegre, Brazil d Graduate Program in Materials Science and Engineering (PPGCEM), Laboratory of Technical Ceramics (CerTec), Universidade Do Extremo Sul Catarinense, Criciuma, 88806-000 Brazil e Deparment of Industrial Engineering, School of Engineering, Universidade Federal Do Rio Grande Do Sul, Porto Alegre, Brazil f University of Valencia, Department of Inorganic Chemistry, Burjasot, Valencia, 46100 Spain *e-mail: edgar.chavarrigami@amigo.edu.co Received January 15, 2021; revised January 26, 2021; accepted January 29, 2021

Manganese ferrite MnFe2O4 was synthesized by gel combustion synthesis using tris(hydroxymethyl)aminomethane (TRIS) as a fuel upon variation of oxidizer-to-fuel ratio Ψ and characterized by XRD, Raman spectra, and vibrating sample magnetometry (VSM). The measured values of saturation magnetization Ms = 27.70 emu g–1 and coercivity Hc = 86.87 Oe are indicative of superparamagnetiс behavior of synthesized materials. Our results also show that TRIS could be readily used as an alternative fuel to synthesize spinel ferrites through a one-step process of solution combustion synthesis.

This research presents the effect on the color of the green ceramic pigment CoCr2O4 when Co2+ was replaced by Mg2+. The objective is to reduce the concentration of cobalt in the pigments, which is considered an expensive and toxic raw material. The pigments were synthesized by solution combustion in one-step. The X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) of the as-prepared powders showed that the spinel structure was obtained during the combustion reaction. The microstructure of the pigments was observed by Scanning Electron Microscopy (SEM) and the powders are porous due to the gases formed during the reaction. Finally, the color change of the powders was evidenced by UV-vis-NIR Diffuse Reflectance Spectroscopy (DRS) and calculation of CIEL*a*b* chromatic coordinates. The largest color change Delta E*(ab) of 9.8 was between CoCr2O4 and MgCr2O4 as a result of the absence of electronic transitions in Mg2+. The results of thermal stability of the green pigments using a commercial frit showed that they could be used in ceramic decoration at 1050 degrees C. (C) 2019 SECV. Published by Elsevier Espana, S.L.U. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

For the first time, 6-aminohexanoic acid is used as an alternative fuel in the synthesis of the spinel ferrites with compositions CoFe2O4, ZnFe2O4 and MgFe2O4 using gel combustion synthesis with different oxidizer-to-fuel (O/F) ratios. The gel precursors were studied by differential thermal analysis and thermogravimetry (DTA/TG), which showed that the ignition temperature depends on the gel precursor, being around 230 degrees C, 130 degrees C and 275 degrees C for CoFe2O4, ZnFe2O4, and MgFe2O4, respectively. These results showed than the 6-aminohexanoic acid has an ignition temperature lower than the urea and the citric acid when were used in the synthesis of the spinel ferrites by gel combustion. Moreover, the adiabatic flame temperature (T-ad) of the reactions of combustion were calculated using thermodynamic analysis, which showed that T-ad increases when the mass of the 6-aminohexanoic acid increases. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques confirmed the formation of the spinel structures for all the O/F ratios, but there is a minor impurity phase for some experiments. The particle morphology was evaluated using scanning electron microscopy (SEM), showing aggregated particles with a sponge-like structure due to the released gases during the combustion. A vibrating sample magnetometer (VSM) was used for measuring the magnetic properties of the as-prepared powders. The values of saturation magnetization, M-s, and coercitivity, H-c, were M-s = 66.9 emu/g and H-c = 1505 Oe for CoFe2O4, M-s = 44.6 emu/g and H-c = 75.2 Oe for ZnFe2O4 and M-s = 28.66 emu/g and H-c = 111.4 Oe for MgFe2O4. The optical band gap for CoFe2O4, ZnFe2O4, and MgFe2O4 were 1.11 eV, 1.37 eV and 1.64 eV, respectively. These results show that 6-aminohexanoic acid can be used as an alternative fuel in the synthesis of spinel ferrites using gel combustion synthesis.

The aim of this work is to find the effect of the cation M (Zn2+, Co2+, Cu2+, and Mg2+) on the optical properties of MFe2(P2O7)(2) synthesized by solution combustion. The crystal structure of the powders was determined by X-ray diffraction (XRD), Infrared spectroscopy (IR), and Raman spectroscopy. The presence of Fe2+ and Fe3+ ions in the pigments was studied using Mossbauer spectroscopy (MS), these spectra showed at 298 K three well-defined Mossbauer doublets belonging to octahedral S1 site and S3 site of Fe3+ and trigonal prismatic S2 site of Fe2+, confirming the formation of ZnFe2(P2O7)(2), CoFe2(P2O7)(2) and MgFe2(P2O7)(2) structures, while in CuFe2(P2O7)(2) there is no presence of trigonal prismatic S2 site of Fe2+ ion. Therefore, the mechanism of color on the ZnFe2(P2O7)(2), CoFe2(P2O7)(2), and MgFe2(P2O7)(2) structures are due to intervalence charge transfer between Fe2+ and Fe3+ ions. In contrast, on the CuFe2(P2O7)(2) structure is due to d-d electronic transitions of the Cu2+ ion, these evidences can also be observed in their UV-Vis diffuse reflectance spectra. Moreover, the inorganic blue pigment MgFe2(P2O7)(2), which is free of cobalt, copper, and zinc could be used as a pigment in applications of low temperatures.