Microwave-assisted Combustion Method Research Articles

Optical, morphological, physical and crystalline properties of type structures CexAl2-xO3 (x = 0; 0.25; 0.50; 0.75 and 1) obtained by microwave assisted combustion

Cerium aluminate is a perovskite type that presents AmBnO3 that has interesting physical, morphological properties and crystalline structures; however it has not been deeply studied when synthesized by microwave-assisted self-combustion specifically. Thus, the objective of this work was to synthesize CeAlO3 by microwave-assisted combustion method in an one-step using only one fuel (urea, 250% excess). Formulations were identified by CexAl2-xO3 (x = 0, 0.25, 0.50, 0.75 and 1; in mol), an α-Al2O3–standard was used how reference. X-ray diffraction (XRD), scanning electron microscopy (SEM-EDS and SEM-FEG), specific gravity, absorption spectroscopy in the ultraviolet and visible region (diffuse reflection), Fourier transform infrared spectroscopy (FTIR) and Raman were the techniques used in the characterizations. The results show that CeAlO3 was formed in the synthesis, as well as CeAl11O18 and CeO2 phase. In the diffuse reflection of light, the beginning of the increase in reflectivity occurs at wavelengths close to 380 nm and band-gap between 3.36 to 3.47 eV; the presence of microstructural and macrostructural defects impacted on the variation of reflectivity in the UV–visible region and on the variation of densities (5.06–5.96 g.cm−³); heterogeneous morphologies expressed by diversified surfaces, particulates tending to equiaxial symmetry and perforation signals, in addition to prismatic crystals growing parallel to the surface. The FTIR confirms the formations of α-Al2O3 and Raman confirms the presence of residual carbon. These results are relevant, since the work produced perovskites with stable structures in a single step, optimizing the manufacturing process of these materials with the elimination of calcination after synthesis.

Application of Cr-doped ZnO for photocatalytic degradation of organic pollutants from aqueous solutions

During the water treatment process, some by-products could be produced by combining the disinfectant with the organic compounds. For example, chlorine can effectively convert humic acid derivatives to trihalomethane. Trihalomethanes are important organohalogen compounds with a hazardous effect on human health. In the present research, Cr-doped ZnO nano-photocatalyst was synthesized using a microwave-assisted solution combustion method, and its ability to degradation of trihalomethane, humic acid and fulvic acid were evaluated by an advanced oxidation process. To investigate the structural morphology and characterization of the synthesized nano-photocatalyst, field emission scanning electron microscopy, X-ray diffraction and diffuse reflectance spectroscopy analysis were used. The influence of various factors such as nano-photocatalyst dosage, pollutant initial concentration, reaction time and pH was evaluated to obtain an optimum condition for degradation. Also, isotherms, kinetic and thermodynamic studies were carried out in the optimum condition. According to the results, the removal process of fulvic acid and humic acid follows the Langmuir and Freundlich isotherm models and second-order kinetic equation. Also, the thermodynamic parameters such as entropy (> 0) and enthalpy (> 0) confirmed a higher degradation efficiency for fulvic acid in comparison with humic acid using the developed method due to less require energy. Isotherms and kinetic studies were carried out in the case of trihalomethane, and the results showed that trihalomethane photodegradation was followed the Langmuir–Hinshelwood isotherm model and more fitted by the first-order kinetic.

Investigation of the usability of zinc ferrite nanoparticles synthesized by microwave assisted combustion method as photocatalyst for removal of organic dyes from wastewaters

In this study, zinc ferrite nanoparticles, which has an important place among the spinel ferrite structured nanomaterials due to its unique properties, were synthesized by microwave-assisted combustion method and later were used as photocatalysts in the removal of dyestuffs by photocatalytic degradation method from wastewaters of textile industry. In the synthesis studies, it was determined that the microwave effect alone was not sufficient to complete the transformation. Heat treatment application is envisaged to solve this problem and in order to determine the optimum heat treatment temperature, the sample produced by microwave effect were subjected to heat treatment at 300℃, 400℃, 500℃, 600℃, 700℃, 800℃ and 900℃, respectively. It has been observed that the heat treatment has a significant effect on the crystal structure of the particles and 700℃ has been determined as the optimum heat treatment temperature. The data obtained showed that, under these conditions, the zinc ferrite nanoparticles were successfully synthesized and the powder produced completely consisted of nano-sized particles. Moreover, results showed that the synhesized zinc ferrite nanoparticles has a saturation magnetization value sufficient to separate them from the aqueous medium. Finally, zinc ferrite nanoparticles produced under optimum conditions were used as photocatalysts in the removal of textile dye known as Procion Yellow HE-3G from wastewater by photocatalytic oxidation. In photocatalysis experiments, it was observed that synthesized zinc ferrite nanoparticles provided very high removal efficiencies as photocatalysts and almost all of the dye content in the solution could be removed.

Removal of organic dye compounds in water and wastewater samples based on covalent organic frameworks -titanium dioxide before analysis by UV-VIS spectroscopy

A simple and rapid microwave-assisted combustion method was developed to synthesize homogenous carbon nanostructures (HCNS). This research presents a new and novel nanocomposite structures for removal of methylene red (2-(4- Dimethylaminophenylazo)benzoic acid), methylene orange (4-[4-(Dimethylamino)phenylazo]benzenesulfonic acid sodium salt) and methylene blue (3,7-bis(Dimethylamino)phenazathionium chloride)with semi degradation-adsorption solid phase extraction (SDA-SPE) procedure before determination by UV-VIS spectroscopy. A covalent organic frameworks (COFs) with high purity were synthesized and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicated that the self-assembled carbon nanostructures (COFs) synthesized with the cost-effective method which was used as a novel adsorbent for adsorption of dyes after semi-degradation of methylene red, orange and blue (1-5 mg L-1) as an organic dye by titanium dioxide (TiO2) nanoparticales in presence of UV radiation. Based on results, the COFs/TiO2 has good agreement with the Langmuir adsorption isotherm model with favorite coefficient of determination (R2= 0.9989). The recovery of dye removal based on semi-degradation/adsorption of COFs/TiO2 and adsorption of COFs were obtained 98.7% and 48.3%, respectively (RSD less than 5%). The method was validated by spiking dye to real samples.

Synthesis of alumina by microwave-assisted combustion method using low fuel content and its use as catalytic support for dry reforming of methane

Alumina powders with high specific surface area (>200 m2g-1) were obtained quickly, easily and using only aluminum nitrate and urea (as fuel) through the microwave-assisted combustion method applying low power (450 W) and low fuel content. The powders obtained were calcined at temperatures of 550, 750 and 950 °C. The X-ray diffraction and Fourrier Transform Infrared (FTIR) results indicate that γ-Al2O3 was formed at temperatures of 550 and 750 °C, while the α and γ phases were identified in calcined alumina at 950 °C. The increase in calcination temperature strongly influenced the specific surface area and the pore size distribution, however no effect on the pore diameter was observed. The Al2O3 powder calcined at 550 °C was evaluated as catalytic support due to its most appropriate textural properties. The catalyst Ni/Al2O3 (Ni-A550) was prepared by wet impregnation method and calcined at 550 °C/3 h. The physical-chemistry properties were evaluated by X-ray diffraction, temperature programmed reduction and scan electron microscopy techniques. The results show that the Ni-A550 have high conversion of CH4 and CO2 and good H2 yield using a gas hourly space velocity (GHSV) of 72 L g−1 h−1. Therefore, the synthesized Al2O3 presents as a potential catalytic support material.

Effect of synthesis method in magnetic properties of Bismuth iron oxide: A prevoskite type multiferroic materials

Multiferroic materials have attracted extensive attention due to their potential applications in multiple state memory elements and other integrated ferroelectric devices. In the present work, we synthesized Bismuth ferrite (BiFeO3-BFO) multiferroic nanoparticles using Sol–gel(SGBFO)and Microwave Assisted Combustion method(MWBFO). We investigated the impact of synthesis routes in the magnetic poperties of BFO. The X-ray diffraction analysis reveals a pure phase Rhombohedral for sol–gel and Hexagonal structurefor microwave assisted combustion methods along with some secondary phases of Bi2Fe4O9. The crystallite size is found to be 32.6 nm and 36.2nm for SGBFO and MWBFO. The FTIR spectrum shows strong absorption around 400–600 cm−1for the materials prepared by both the methods. This reveals the formation of perovskite structure of BFO prepared by both the methods. Non uniform shaped agglomerated nano particles, sheets and rods are seen in Field Emission Scanning Electron Microscopy (FESEM) images. VSM analysis shows synthesis method is a highly effective parameter in determining the properties of nano particles. Weobserved decrease in coercicvity of the BFO synthesized by MWBFO method.

Porous metal-graphene oxide nanocomposite sensors with high ammonia detectability

Nickel oxide-graphene oxide (NiO-GO), zinc oxide-graphene oxide (ZnO-GO) and bismuth oxide-graphene oxide (Bi2O3-GO) metal oxide-graphene oxide nanocomposite (MO-GO NC) sensors, operable at room temperature, were synthesized via a simple and cost-effective microwave-assisted combustion method for chemiresistive gas sensor applications. From the measured structural, morphological, and elemental detection properties, the sensors are found capable of detecting various gases. The Bi2O3-GO NC sensor exhibited excellent response over NiO-GO (~20 at 50 ppm) and ZnO-GO NC (~60 at 50 ppm) sensors for detecting NH3. The response of the Bi2O3-GO NC sensor at 50 ppm NH3 in just 14 s operation duration was ~81.23, which is improved 25-fold and 13-fold compared to pristine GO sensors. Additionally, the as-developed Bi2O3-GO NC sensor demonstrates outstanding repeatability and recovery kinetics, attributed to porosity and the combined effects of MO and GO. The sensing mechanism of the Bi2O3-GO NC gas sensors is proposed herein. The superior sensing performance, including quick response and recovery of the Bi2O3-GO NC sensor is attributed to favorable charge transfer across the Bi2O3 and GO interface. The significance of relative humidity on sensing potential of the Bi2O3-GO NC sensor has also been studied and the sensor is confirmed to be unaffected by relative humidity.

The effects of fuel type onto the structural, morphological, magnetic and photocatalytic properties of nanoparticles in the synthesis of cobalt ferrite nanoparticles with microwave assisted combustion method

In this experimental study, the synthesis of cobalt ferrite nanoparticles, one of the most important types of ferromagnetic spinel ferrite materials was realized by using a method known as microwave assisted combustion method. The effects of the substance used as fuel on the structural, morphological, magnetic and photocatalytic properties of synthesized nanoparticles were investigated. Firstly, samples were prepared using urea, glycine and citric acid as fuel and then the samples were comprehensively characterized by advanced analysis techniques such as XRD, FT-IR, TEM, SEM, VSM, BET. Moreover, the usability of the obtained nanoparticles in photocatalytic degradation process of Procion Yellow H-E3G textile dye as photocatalyst was investigated. The results obtained indicate that the fuel used is highly effective on various properties of the synthesized materials. From the experiments performed to evaluate the photocatalytic performances of the nanoparticles, it was observed that each of the three different fuel matters used for the synthesis of nanoparticles were highly effective on the photocatalytic degradation of the organic pollutant. Furthermore, almost all the dye content in solution was completely removed at the end of the experimental period which lasted for 90 min.

Synthesis of Mn3O4 nanoparticles via microwave combustion route for electrochemical energy storage application

Abstract In the present article, the synthesis of manganese oxide (Mn3O4) nanoparticles (NPs) have been achieved by microwave assisted combustion method, which was further investigated for an electrode material in supercapacitors. The as-synthesized Mn3O4 nanoparticles were characterized by different techniques like powder X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), UV–Visible spectroscopy etc. XRD pattern reveals a crystalline, tetragonal phase of Mn3O4 (hausmannite) nanoparticles with a crystallite size of 28.08 nm. SEM image shows that the Mn3O4 nanoparticles are present as spongy aggregates. From Tauc plot, the band gap of the material was found to be around 1.97 eV, which is suitable for energy storage (supercapacitor) application. Investigation on the electrochemical properties of Mn3O4 nanoparticles were carried out by using Cyclic Voltammetry (CV) and galvanostatic/ potentiostatic charge-discharge studies. The results signify that the obtained Mn3O4 nanoparticles can be used as a potential electrode material for supercapacitor applications.

Investigations on structural, optical, dielectric, electronic polarizability, Z-scan and antibacterial properties of Ni/Zn/Fe2O4 nanoparticles fabricated by microwave-assisted combustion method

In this article, Ni0.5Zn0.5Fe2O4 nanoparticles (NPs) were synthesized by differing concentrations of fuel (lean, stoichiometric, and rich) via microwave-assisted combustion route. The effect of fuel content was used to explore their chemical, electrical, and nonlinear optical properties along with their antibacterial activity of the as-prepared Ni/Zn/ferrite NPs were studied. The XRD assures the cubic crystal structure of prepared NPs with no secondary phase. It is also clear that as lattice parameters increases, the mean crystallite size decreases as a change in fuel ratio. The optical energy bandgap values are estimated as 2.88, 3.28, and 3.0 eV, respectively. From the luminescence spectra, the Ni/Zn ferrite NPs exhibits strong green emission and weak violet emission color. The fuel ratio has a significant influence on the electronic polarizability properties of synthesized NPs. Closed and open aperture Z-scan technique reveals that the Ni/Zn ferrites NPs have self-defocusing nature, and reverse saturable absorption. The calculated values are NLA coefficients (10-5 cmW−1), NLR index (10−9 cm2W−1), and third-order NLO susceptibility χ(3) values of fuel lean (1.408 × 10−5esu), stoichiometric (2.75 × 10−6esu), and rich (2.634 × 10−5esu). Several identified microorganisms such as gram + Ve (S. aureus, B. cereus), and gram -Ve (P. aeruginosa, V. cholerae, and E. coli) have been tested for antibacterial activity against Ni/Zn ferrite nanoparticles. The ZOI values are 27 (lean), 24 (stoichiometric), and 25 mm (rich) which suggest great antibacterial activity against Pseudomonas aeruginosa gram-negative bacterium. However, this study shows excellent feasibility of applying prepared ferrite nanoparticles for optoelectronic devices and pharmaceutical processing applications.

Robust one-step synthesis of bismuth molybdate nanocomposites: A promising negative electrode for high end ultracapacitors

Rare earth metal (La) doped aurivillius structured bismuth molybdate (Bi2MoO6: La) has been prepared by a single pot microwave-assisted combustion method. The characteristics of the bare Bi2MoO6 and Bi2MoO6: La catalysts have been analyzed systematically using different characterization techniques. The crystalline phase purity of the nanostructures has been analyzed by PXRD and Rietveld refinement technique with an average crystallite size approximately 28 nm (Bi2MoO6) and 25 nm (Bi2MoO6: La). The surface morphologies have been nanoplatelets for both samples. The Bi2MoO6: La structure ensures maximum capacitance of 662.8 F g−1 at 5 mVs−1. Also, they performed good cyclic stability of 87.4% over 2000 cycles with a current density of 5 mA cm−2. The prepared active material serves as a novel negative electrode material for supercapacitors.

Rare-earth ions integrated silica nanoparticles derived from rice husk via microwave-assisted combustion method for bioimaging applications

Silica nanoparticles have received great interest in biomedicine due to their high biocompatibility. In this study, we report the preparation of rare-earth ions integrated silica nanoparticles using rice husk biomass through a rapid and simple microwave-assisted combustion technique for making cost-effective bioimaging contrast agents. X-ray diffraction, energy-dispersive X-ray spectroscopy, and transmission electron microscope studies indicated that rare earth (europium/gadolinium) ions were strongly integrated with silica matrix via electrostatic interaction with environmental oxygen atoms. Europium-integrated silica nanoparticles showed a strong red fluorescence imaging capability that was attributed to 5D0→7F1 and 5D0→7F2 transitions of europium ions in the silica host matrix whereas gadolinium-integrated silica nanoparticles showed paramagnetism with T1-weighted magnetic resonance (MR) imaging capability that was ascribed to magnetic moment originated from a spin-orbit coupling of partially filled 4f electrons of gadolinium in the silica host matrix. In vivo toxicity evaluation using zebrafish embryos indicated that the rare-earth ions integrated silica nanoparticles are non-toxic. In view of these results, the prepared rare-earth ions integrated silica nanoparticles may be considered as potential materials in developing new bioimaging contrast agents at low cost.

Rapid Synthesis and Characterization of Pure and Cobalt Doped Zinc Aluminate Nanoparticles via Microwave Assisted Combustion Method.

Zn1-xCoxAl₂O₄ (0 ≤ x ≤ 0.5) nanoparticles were synthesized employing L-alanine as fuel using MACT (microwave assisted combustion technique). The synthesized samples were characterized following methods such as X-ray Diffraction, high resolution scanning electron microscopy, Energydispersive X-ray spectroscopy; UV-visible diffused reflectance spectroscopy, FT-IR and VSM. The XRD confirmed the cubic spinel structure and the average crystallite size observed lying in the range of 12-19 nm deduced using the Debye Scherrer's equation. The morphology of the Zn1-xCoxAl₂O₄ (0 ≤ x ≤ 0.5) nanoparticles is observed using HR-SEM. EDX analysis is opted for the elemental mapping of pure and cobalt doped zinc aluminate nanoparticles. Further band gap value was calculated using Kubelka Munk function, which was seen lying within 3.73 to 5.45 eV. The strong absorption band at 669, 556 and 500 cm-1 was associated with the vibrations of Zn-O, Al-O and Zn-O-Al of zinc aluminate nanoparticles. The hysteresis loops exhibited conversion from diamagnetic into super paramagnetic behaviour with increase in Co doping.

Structural and spectroscopic studies of nanocrystalline Ni1−xMgxFe2O4 ferrites synthesized by a microwave-assisted combustion route

In this work, the synthesis of Ni1−xMgxFe2O4 (0 ≤ x ≤ 1.0) nanoparticles by a facile microwave-assisted combustion method is reported with detailed study of the structural and optical properties. By employing techniques of x-ray diffraction (XRD) with Rietveld refinement, transmission electron microscope (TEM, HRTEM, TEM-EDX), Fourier transform infrared spectroscopy (FTIR) and UV-Visible spectroscopy, the synthesized nanoparticles are characterized and introduced for further study of size-confined properties. Nanocrystals of a pure cubic spinel structured phase with average particle size of 20–40 nm were successfully synthesized in the whole range of x. In consistence with Vegard’s law for a solid solution lattice, the lattice constant increases linearly with the substitution for Ni2+ with the relatively larger Mg2+ cations. The Rietveld analysis of the observed XRD patterns reveals an inversed spinel structure in NiFe2O4 nanoparticles with a decreased inversion factor by Mg-substitution. The results of UV-Visible absorbance indicate a wide energy gap of about 3.6 eV for NiFe2O4 nanoparticles thatmonotonically tuned towards a narrow band gap by Mg-doping.

Investigations on solid-state parameters of third-order nonlinear optical Ni1−xZnxFe2O4 nanoparticles synthesized by microwave-assisted combustion method

In this study, Ni1−xZnxFe2O4 (x = 0, 0.25, and 0.5) nanoparticles were successfully synthesized via microwave-assisted combustion method and characterized by XRD, FTIR, and SEM–EDAX. XRD results enunciate that the nanoparticle crystallizes in cubic spinel structure with an average crystallite size (40.2, 37.2, 35.1 nm), and also, the lattice strain, specific surface area, X-ray density were evaluated. The morphology and chemical compositions of Ni, Zn, Fe, and O elements were confirmed by the SEM–EDAX studies. For all the samples, vibrational stretching modes of Mtetra–O site (597 (S1), 593 (S2), 583 (S3) cm−1) and Moctra–O site (416 (S1), 421 (S2), 422 (S3) cm−1) were related to the distribution of the cation Ni2+/Zn2+ and Fe3+ ions among the octahedral and tetrahedral sites. From the UV–Vis–DRS spectra, the optical energy band gap has been estimated to be 1.75–2.01 eV. The dielectric constant and loss were measured by varying the applied frequency (50 Hz to 200 kHz) at room temperature. The electronic polarizability (α) was calculated using Penn analysis, Clausius–Mossotti equation, and energy band gap value. Third-order nonlinear optical parameters such as the nonlinear absorption coefficients (10−5 cm/W), refractive index (10−9 cm2/W) and the third-order nonlinear susceptibilities (10−6 esu) were determined by Z-scan technique. The antibacterial studies were tested against Bacillus cereus, Staphylococcus aureus, Shigalla flexneri and Klebsiella pneumonia bacterial strains. The existing results point out that the synthesized Ni/Zn/Fe2O4 nanoparticles are possible candidates for photonic devices, optical switches, optical limiting and also for pharmaceutical applications.

Double perovskite (La2-xCa-Bax)NiO4 oxygen carriers for chemical looping reforming applications

Double perovskites La2-xNiO4-δ doped with Ca and Ba were synthesized via microwave-assisted combustion method and studied as an alternative oxygen carrier (OC) for chemical looping reforming processes (CLR). The OCs, La2NiO4, La1.8Ca0.2NiO4, La1.8Ba0.2NiO4 and La1.8Ca0.1Ba0.1NiO4 were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction and oxidation (TPR/TPO) and cyclic thermogravimetric analysis (TGA). Rietveld's refinement, performed after each redox cycle, confirmed that doping allows smaller amounts of nickel to migrate from the perovskite structure. The double perovskites synthesized for the chemical looping reforming process behave as simple nickel oxide and are considered as alternative oxygen carriers to solve the problems of deactivation due to the interaction of NiO with the support. The Ca-doped OC (La1.8Ca0.2NiO4) showed lower NiO concentration outside the structure and smaller crystallite size after the redox cycles, which was associated with a change in the crystal structure, presenting superior performance and stability. The results show that all perovskites have high reactivity in both reduction and oxidation reactions, however the perovskites were not able to uncouple oxygen, which is an unsual behavior for perovskites.

Effect of fuel content on nonlinear optical and antibacterial activities of Zn/Cu/Al2O4 nanoparticles prepared by microwave-assisted combustion method

Nonlinear optical nanoparticles of Zn/Cu/Al2O4 were synthesized by microwave-assisted combustion method with different fuel to oxidizer ratio. And, these nanoparticles were characterized by various analytical techniques to examine their suitability in fascinating applications. XRD results enunciate that the nanoparticle crystallizes in cubic spinel structure. The morphology and quantitative chemical compositions of Zn, Cu, Al and O elements were obtained from SEM with EDAX analysis. The prepared compound was confirmed by FTIR spectrum. The optical energy bandgaps are studied from UV–Vis absorption spectra. The luminescence emission peaks are observed at 371 nm (Violet), 425 nm (violet), 471 nm (blue) and 637 nm (red). In the application point of view from the Z-scan technique, the third order nonlinear optical parameters such as nonlinear refractive index (n2), nonlinear absorption coefficient (β), and third-order nonlinear susceptibility (χ3) of title compound are calculated. For biological application, the antibacterial activities were tested against Bacillus cereus, Staphylococcus aureus, Shigella flexneri, and Vibrio cholera bacterial species by measuring the inhibition zone. Existing results point out that the synthesized Zn/Cu/Al2O4 nanoparticles are possible candidates for photonics devices, optical switches, optical limiting and also for pharmaceutical applications.

Mn/MgAl2O4 oxygen carriers for chemical looping combustion using coal: influence of the thermal treatment on the structure and reactivity

Mn-based solid oxygen carriers supported on MgAl2O4 were prepared by the microwave-assisted combustion method followed by wet impregnation of the active phase. The oxygen carriers were characterized by X-ray diffraction, temperature-programmed reduction and scanning electron microscopy with energy-dispersive spectroscopy of the surface. The study aimed to evaluate the influence of the thermal treatment on the structure and reactivity of the oxygen carriers. Reactivity tests using coal as fuel were carried out in a thermobalance at temperatures of 750–850 °C to evaluate the behavior of the carriers. The results revealed that oxygen carriers, which were subjected to only a heat treatment after the impregnation step (MnC1), showed more reactive surfaces presenting a greater number of non-reactive and irreversible phase and thus displaying lower oxygen transport capacity as well as poorer reactivity. The carriers prepared by heat treating the support after the combustion reaction and again after the impregnation step (MnC2), showed higher oxygen transport capacity and greater reactivity with coal at 850 °C. The better reactivity is associated with the formation of Mg6MnO8 and Mn2O3 phases.

Microwave-assisted combustion design of magnetic Mg–Fe spinel for MgO-based nanocatalyst used in biodiesel production: Influence of heating-approach and fuel ratio

Magnetic MgO/MgFe2O4 nanocatalysts synthesized by microwave-assisted combustion method by using various fuel ratios and employed in the production of biodiesel. To evaluate the influence of microwave heating, its results were compared to those of conventional furnace. MgO was dispersed on all the samples using simple and cost-effective impregnation method. Characterizations of the magnetic spinel nanocatalysts were performed via XRD, FESEM, SPSD, BET-BJH, FTIR, TG and EDX analyses. Accordingly, the sample synthesized by microwave irradiation with a fuel ratio of 1.5 exhibited the largest effective area and pore volume and appropriate pore size for transesterification reaction with coarse molecules.

Influence of Mg doping on ZnO NPs for enhanced adsorption activity of Congo Red dye

A facile microwave-assisted combustion method was adopted to synthesize pure ZnO and Mg-doped ZnO nanoparticles (NPs), and characterization of the NPs and the sorption behavior with Congo Red (CR) Azo dye was extensively investigated. The structure, morphology and chemical assay of the synthesized NPs were studied with respect to the pure and 2% Mg-doped ZnO samples. The X-ray diffraction pattern confirmed the presence of crystalline, cubic phase with fluorite structure of both the NPs. The morphological differences between the pure and Mg-doped ZnO NPs were evaluated by FE-SEM, which revealed that the NPs were in the nanoscale regime with irregular crystalline morphology having a grain size of ~18–45 nm. N2 adsorption/desorption isotherms measured at −196 °C suggested a Type II structure with limited hysteresis loops, likely due to some interparticle porosity. The BET SSA ZnO NPs obtained was found to be 32 m2 g−1, indicating about its potential in sorption processes. Batch adsorption study for the removal of CR carried out showed that, the Mg-doped NPs showed higher loading efficiency (125 mg·g−1) than the ZnO NPs (25 mg·g−1) counterpart. This was corroborated by the isotherm results in which the CR dye sorption followed a Freundlich Isotherm model for both undoped ZnO and Mg-doped ZnO NPs. The sorption of CR dye followed a pseudo-second order kinetics. The negative ΔG° (−31.91 and −109.41 kJ mol−1) showed the feasibility of the adsorption process. The ΔH° was determined as +13.74 kJ mol−1 and 50.7 kJ mol−1 for ZnO NPs and Mg doped-ZnO NPs respectively, confirming the endothermic nature of the adsorption for removing CR dye from the solution.