A modified glycine–nitrate combustion method for one-step synthesis of LaFeO3

Part I: NiMoO4 Nanostructures Synthesized by the Solution Combustion Method: A Parametric Study on the Influence of Synthesis Parameters on the Materials’ Physicochemical, Structural, and Morphological Properties

The impact of process conditions on the synthesis of NiMoO₄ nanostructures using a solution combustion synthesis (SCS) method, in which agar powder and Ni(NO₃)₂ were utilized as fuel and as the oxidant, respectively, was thoroughly studied. The results show that the calcination temperature had a significant implication on the specific surface area, phase composition, particle size, band gap, and crystallite size. The influence of calcination time on the resulting physicochemical/structural/morphological properties of NiMoO₄ nanostructures was found to be a major effect during the first 20 min, beyond which these properties varied to a lesser extent. The increase in the Ni/Mo atomic ratio in the oxide impacted the combustion dynamics of the system, which led to the formation of higher surface area materials, with the prevalence of the β-phase in Ni-rich samples. Likewise, the change in the pH of the precursor solution showed that the combustion reaction is more intense in the high-pH region, entailing major implications on the physicochemical properties and phase composition of the samples. The change in the fuel content showed that the presence of agar is important, as it endows the sample with a fluffy, porous texture and is also vital for the preponderance of the β-phase.

Nickel Manganite-Sodium Alginate Nano-Biocomposite for Temperature Sensing

Nanocrystalline nickel manganite (NiMn2O4) powder with a pure cubic spinel phase structure was synthesized via sol-gel combustion and characterized with XRD, FT-IR, XPS and SEM. The powder was mixed with sodium alginate gel to form a nano-biocomposite gel, dried at room temperature to form a thick film and characterized with FT-IR and SEM. DC resistance and AC impedance of sensor test structures obtained by drop casting the nano-biocomposite gel onto test interdigitated PdAg electrodes on an alumina substrate were measured in the temperature range of 20–50 °C at a constant relative humidity (RH) of 50% and at room temperature (25 °C) in the RH range of 40–90%. The material constant obtained from the measured decrease in resistance with temperature was determined to be 4523 K, while the temperature sensitivity at room temperature (25 °C) was −5.09%/K. Analysis of the complex impedance plots showed a dominant influence of grains. The decrease in complex impedance with increase in temperature confirmed the negative temperature coefficient effect. The grain resistance and grain relaxation frequency were determined using an equivalent circuit. The activation energy for conduction was determined as 0.45 eV from the temperature dependence of the grain resistance according to the small polaron hopping model, while the activation energy for relaxation was 0.43 eV determined from the Arrhenius dependence of the grain relaxation frequency on temperature.

The Formation of Perovskite during the Combustion of an Energy-Rich Glycine-Nitrate Precursor

The effect of different regimes of combustion of glycine–nitrate precursors on the formation of perovskite phases (LaMnO₃ and LaCrO₃) without additional heat treatment was studied. The following three combustion regimes were compared: the traditional solution combustion synthesis (SCS), volume combustion synthesis (VCS) using a powdered precursor, and self-propagating high-temperature synthesis (SHS) using a precursor pellet. The products of combustion were studied using a series of physicochemical methods (attenuated total reflection infrared spectroscopy (ATR FTIR), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and thermal analysis). SHS was found to be the most productive regime for the formation of perovskite because of its ability to develop high temperatures in the reaction zone, which led to a reduced content of the thermally stable lanthanum carbonate impurities and to an increased yield and crystallite size of the perovskite phase. The reasons for the better crystallinity and purity of LaCrO₃ as compared with LaMnO₃ is also discussed, namely the low temperatures of the onset of the thermolysis, the fast rate of combustion, and the favorable thermodynamics for the achievement of high temperatures in the reaction zone.

Using non-combustion explosion in H2O/DMF to synthesize 3D Structure of ultrathin Bi nanofilm with high catalytic activity for p-nitrophenol reduction

The synthesis of inorganic micro-/nano-materials by dry combustion is somewhat dangerous since it is performed under high temperature. The ultrathin Bi nanofilms with 3D structures were synthesized using a safe approach of non-combustion explosion in H₂O/DMF solution at room temperature and atmospheric pressure. The violent reaction between H₂O₂ and NH₃ · H₂O resulted in a non-combustion explosion due to the fast evolution of gases. Then under high temperature and high pressure during solvothermal process, the further slight explosion occurred where the oxygen-containing molecules of H₂O₂ and NO₃ ^- acted as oxidants, while the hydrogen-containing molecules of NaBH₄, NH₃ · H₂O and DMF acted as reductants. The release of gases was accompanied with Bi^III reduction by NaBH₄. The 3D structure of ultrathin Bi nanofilms with many void spaces formed due to the explosive force and foams from the sharp liberation of gases. Such ultrathin Bi nanofilms with 3D structure exhibited outstanding catalytic activity for p-nitrophenol hydrogenation which is important to treat the environmental pollution from p-nitrophenol discharge. Within only several seconds p-nitrophenol hydrogenation was completed without delay. The non-combustion explosion exhibits potential applications for the synthesis of 3D ultrathin film materials as high efficient catalysts.

Synthesis of fibrous LaFeO3 perovskite oxide for adsorption of Rhodamine B

The LaFeO₃ perovskite oxide decorated active carbon fibers (LFO-ACFs) based on cotton fabric waste were successfully synthesized through sol-gel loading and thermal treatment. LaFeO₃ perovskite and cotton fabric waste were combined to an eco-friendly and cheap adsorbent, which could reuse the leftover materials of textile industry and realize their functional modification. The structural, morphology/microstructure and functional groups were investigated through X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Fourier Transform Infrared spectroscopy (FTIR), respectively. The XRD pattern suggested the cotton fabric matrix didn't influence the structure of LaFeO₃ perovskite oxide. In SEM studies, LFO-ACFs still maintained fibrous shape of the raw cotton fibers, and the EDX analysis showed that the main elements of the prepared LFO-ACFs were La, Fe, O and C. The synthesized LFO-ACF was employed for adsorption of cational dye of Rhodamine B (RhB), and the effects of adsorption parameters, i.e. pH, contact time, solution temperature and initial concentration of dye, on adsorption behavior were investigated. Results suggested the adsorption performance of LFO-ACF for RhB was nearly not affected by solution pH and its maximum adsorption capacity fitted by the Langmuir isothermal model could attain 182.6 mg/g at 293 K. The adsorption kinetics followed the pseudo-second-order equation and the regeneration of LFO-ACF could be well realized through an easy pyrolysis method.