Non-conventional Microwave Research Articles

Mirroring Physical Reality: Nonconventional Microwave Filter Synthesis

Mirroring Physical Reality: Nonconventional Microwave Filter Synthesis

Photocatalytic degradation and kinetic investigations of ZnO-SnO2 heterostructures for treatment of methyl violet using non-conventional approach

Humans and wildlife alike are threatened by the ever-increasing levels of organic pollutants exist in the world's water bodies. Nanomaterials based on metal oxides have been considered strong alternatives for the elimination of organic pollutants. In the present study, ZnO-SnO2 nanocomposites were synthesized via non-conventional microwave and ultrasonic method using fruit extract of Carissa edulis as capping agent. The synthesized nanocomposites were studied using X-ray diffraction (XRD), Diffuse reflectance spectroscopy (UV–Vis-DRS), X-ray photoelectron spectroscopy (XPS), Fourier Infrared spectroscopy (FT-IR), Photoluminescence spectroscopy (PL), and Field emission scanning electron microscope (FE-SEM). Under UV light irradiation, photo-catalytic degradation of methyl violet (MV) was investigated by examining the influence of photocatalyst dosage, initial pollutant concentration, and pH of the reaction medium. The ideal conditions for MV degradation were at initial MV concentration of 10 mg/L, a 20 mg catalyst dose, and a pH of 7. The MV degradation of the synthesised ZnO-SnO2 nanocomposite was 91 % after 120 min. Scavenging experiments demonstrated that hydroxyl radicals (.OH) acts as a key role in the photo-degradation of MV. The reusability studies demonstrate that the synthesised ZnO-SnO2 has good stability for four cycles.

Design and development of Carissa edulis fruit extract mediated bimetallic CuO-NiO-HNT composites for photocatalytic removal of food dye and antibiotic drug

The current study demonstrates the synthesis of one dimensional halloysite nanotube (HNT) based CuO-NiO (CN) photocatalyst using green approach via non-conventional microwave and ultrasonication method. Structural, optical, electrochemical, morphological, stability, and surface area characteristics of the synthesised composite were investigated. From the optical studies, the composite exhibited the absorption band edge above 420 nm in the visible region. Electrochemical studies confirmed that 20CN-HNT composited had good charge carrier separation rate compared to CN. Morphological and elemental analysis revealed that the composite was in microsphere structure with even distribution of elements throughout the composite. Congo red (CR- a dye) and tetracycline (TC- a drug) were used to test the composites' photocatalytic efficacy by the irradiation of visible light. Amongst various synthesized composites, 20CN-HNT composite showed good removal efficiency around 82 % and 84 % against CR and TC respectively, in 90 min. The breakdown of CR and TC is caused by the active species •OH and •O2– radicals which was identified using trapping studies. The reusability study demonstrated that the 20CN-HNT photocatalyst retained its high level of stability after being used for five times.

Fast-low temperature microwave sintering of ZrSiO4–ZrO2 composites

Today, many industrial applications require components that work under extreme conditions, especially at very high temperatures (>1200 °C) for a long time. An excellent combination of properties such as low thermal conductivity, low coefficient of thermal expansion and high chemical resistance are required for such applications. Advanced ceramic materials based on zircon-zirconia composites (ZrSiO4–ZrO2) possess these properties, thus making them attractive for, i.e., high-level radioactive waste immobilisation. The main drawback of these materials are the high temperatures and long residence times required to sinter them and obtain high densities, which entails high energy consumption and costs. Therefore, non-conventional microwave sintering is a very powerful and efficient technique capable of reducing sintering temperatures and holding times. The objective of this study is to evaluate the microwave sinterability of zircon-zirconia powders obtained by colloidal methods (80–20 vol% and 20–80 vol% ZrSiO4–ZrO2). A stability study of the phases present was carried out by X-ray diffraction and the mechanical and microstructural properties were evaluated in order to obtain the best materials with outstanding final properties.

A binary oxide-biochar composite for adsorption of arsenic from aqueous solutions: Combined microwave pyrolysis and electrochemical modification

Biochar composites are promising and cost-effective materials that can be applied in wastewater treatment. In the current study, a novel biochar composite impregnated with Zn and Al oxides (AlZnBC) was synthesized utilizing a non-conventional microwave pyrolysis combined with an electrochemical modification. The temperature distribution inside the sample was modeled using COMSOL Multiphysics (USA) to identify the level of temperature non-uniformity, and a pathway was proposed for the deposition of Al(OH)3 on the composite surface. A temperature gradient of 399 to 741 °C from the reactor surface to the center of the sample was found after 9 min of microwave irradiation. Maximum arsenite and arsenate adsorption capacities of 10,728 and 11,786 µg/g were attained by AlZnBC which were markedly higher than Zn oxide impregnated biochar capacities (ZnBC) of 6,030 µg/g and 7,783 µg/g, respectively. Studying the effect of co-existing ions selenite (SeO32−), selenate (SeO42−), phosphate (PO43−), nitrate (NO3−), and chloride (Cl−) on the biochar arsenic adsorption capacities indicated an interfering effect of the SeO32− and PO43− ions with inner-sphere complexation proposed as the main adsorption mechanism. X-ray absorption near edge structure spectroscopy (XANES) demonstrated that about 24% of the added arsenite was oxidized to arsenate, while no reduction was detected in arsenate adsorption experiments. Overall, both the ZnBC and AlZnBC exhibit promising potential for use in treating arsenic contaminated waters.

Tribological and wear behaviour of alumina toughened zirconia nanocomposites obtained by pressureless rapid microwave sintering

Dense alumina toughened zirconia nanocomposites (ATZ, 3Y-TZP with 20 wt% Al2O3) were densified by non-conventional microwave sintering technology at relatively low temperatures (1200 and 1300 °C). The sintering method and its effect on densification, microstructure, mechanical properties and tribological behaviour were investigated. The outcomes demonstrated that the density rose as the sintering temperature was higher, and therefore the mechanical properties were enhanced, reaching a maximum hardness (18.4 ± 0.4 GPa) and fracture toughness (5.7 ± 0.3MPa· m1/2). In addition, the samples were subjected to a tribological test in dry and wet conditions, using artificial saliva. In both cases, the coefficient of friction and wear volume for samples obtained by microwave sintering are lower than conventional samples, with the wear volume being two times higher in dry conditions than in wet conditions.

Microwave-assisted conditions for the green synthesis of thioacetamide. Optimization of reaction parameters using response surface methodology

An optimized method for the synthesis of thioacetamide (TA) in relation to the consumption of materials and energy, which reduces the production of waste and minimizes costs, is hitherto presented. The most important highlight of this work is the use of an inexpensive and readily accessible reactant for the thionation process (i.e. phosphorus pentasulfide, P4S10), combined with both alumina as solid support and a non-conventional microwave (MW) irradiation technique. In addition to this, Response Surface Methodology (RSM) was used to optimize the entire procedure of the synthesis for simultaneous tripled-maximization of Yield (ε), Mass Intensity (MI) and Mass Productivity (MP). Acetamide (AC)/P4S10 molar ratio, time and temperature of reaction were chosen as independent variables; while ε, MI and MP were chosen as responses. The determination of these green metrics parameters allow to evaluate the sustainability of the reaction and compare with other methodologies. A quadratic regression model was derived with satisfactory prediction. Tripled optimization with desirability function predicts a maximum ε of 100%, maximum MI of 29.00 kg/kg and a maximum MP of 3.45% under the following experimental conditions: AC/P4S10 molar ratio of 2.10, time of irradiation of 14 min and a temperature 140 °C.

Synthesis and surface characterization of the La0.7-xPrxCa0.3MnO3 (LPCM) perovskite by a non-conventional microwave irradiation method

A series of La0.7-xPrxCa0.3MnO3 (x = 0.35, 0.52 or 0.63) perovskites were synthesized using microwave method at different reaction times (3, 4 and 5 min) as possible cathode material for solid oxide fuel cell (SOFCs). SOFCs are a forward looking technology for a highly efficient, environmental friendly power generation. Variation of lattice parameters, unit cell volume and final composition with Pr concentration were analyzed by Rietveld refinement and X-ray photo electron spectroscopy (XPS). Thereafter, samples were sintered (at 1000 °C) to evaluate their electrical properties at room temperature. Rietveld refinement showed that all the samples were a single –phase perovskite –type and belongs to orthorhombic Pnma structure. The atomic composition of doped samples is close to theoretical stoichiometric values. XPS analysis revealed significant changes in the La 3d, Ca 2p, Mn 2p and O 1s intensities as a result of the Pr incorporation.

Synergistic blending of high-valued heterocycles inhibits growth of Plasmodium falciparum in culture and P. berghei infection in mouse model

A series of phthalimide analogues, novelized with high-valued bioactive scaffolds was synthesized by means of click-chemistry under non-conventional microwave heating and evaluated as noteworthy growth inhibitors of Plasmodium falciparum (3D7 and W2) in culture. Analogues 6a, 6h and 6 u showed highest activity to inhibit the growth of the parasite with IC50 values in submicromolar range. Structure-activity correlation indicated the necessity of unsubstituted triazoles and leucine linker to obtain maximal growth inhibition of the parasite. Notably, phthalimide 6a and 6u selectively inhibited the ring-stage growth and parasite maturation. On other hand, phthalimide 6h displayed selective schizonticidal activity. Besides, they displayed synergistic interactions with chloroquine and dihydroartemisinin against parasite. Additional in vivo experiments using P. berghei infected mice showed that administration of 6h and 6u alone, as well as in combination with dihydroartemisinin, substantially reduced the parasite load. The high antimalarial activity of 6h and 6u, coupled with low toxicity advocate their potential role as novel antimalarial agents, either as standalone or combination therapies.

Fretting fatigue wear behavior of Y‐TZP dental ceramics processed by non‐conventional microwave sintering

AbstractThe fretting wear behavior of self‐mated Y‐TZP dental materials obtained by nonconventional microwave and conventional sintering has been investigated. Two 3Y‐TZP materials, a widely utilized commercial dental ceramic (LAVA) and a lab‐prepared 3Y‐TZP powder based equivalent have been assessed. Relative density and mechanical properties as well as the grain size variations upon sintering have been evaluated. After exposure to selected gross slip regime fretting wear conditions, the wear tracks have been characterized allowing the measurement of the coefficient of friction, track profiles, and pit features. The results indicate that microwave sintering results in a similar fretting wear behavior as observed for conventional‐sintered 3Y‐TZP, as the measured volumetric wear loss is of a comparable order of magnitude. Regarding the influence of the grain size, the analysis revealed that a large grain size (>300 nm) results in an increased wear volume and that a higher resistance to fretting wear is constrained to a mid‐range particle size (100–250 nm). Since the fracture toughness of all investigated ceramic grades was comparable, the influence of the fracture toughness on fretting could not be assessed. Abrasive grooving, delamination, and microcracking have been identified as major wear mechanisms inside the wear tracks for both conventional‐ and microwave‐sintered 3Y‐TZP. In general, microwave sintering can provide 3Y‐TZP dental materials with a comparable fretting wear resistance as that observed for conventional sintering using lower dwell sintering temperatures and a shorter processing time.

Synthesis and insecticidal activity of acridone derivatives to Aedes aegypti and Culex quinquefasciatus larvae and non-target aquatic species

A serious Mosquito borne yellow fever is one of the grave diseases which affect the major population. Since there is no specific treatment for yellow fever, there is a necessity to develop an effective agent. The series of acridinone analogues 3 to 5 were synthesized with help of non-conventional microwave heating and confirmed by respective spectral characterization. 5c and 3b showed highest activity to kill 90% of larvae against A. aegypti and C. quinquefasciatus, respectively. Also the active products were treated to check the mortality of non-target aquatic species. Through the reports of the larvicidal bioassay, compounds 3b against C. quinquefasciatus whereas 5c against A. aegypti were found to be more active. By keeping this as a platform, further extension of the work can be done to find out a valuable drug for controlling disease vectors.

Hydrothermal Degradation Behavior of Y‐TZP Ceramics Sintered by Nonconventional Microwave Technology

Different factors such as the characteristics of starting powders, their processing, the sintering technique and the final sintering temperature were assessed with the goal to improve the low‐temperature degradation (LTD) resistance of 3Y‐TZP materials without compromising on the mechanical properties. The degradation of hydrothermally treated specimens was studied by AFM, nanoindentation technique, micro‐Raman spectroscopy, and electron microscopy. 3Y‐TZP previously prepared in laboratory by colloidal processing, and sintered by microwave method at low temperature (1200°C) led to excellent mechanical and LTD resistance, as compared to dental restorations based on Y‐TZP commercial material. In the former, the presence of m‐phase was almost nonexistent even after 200 h of exposure to LTD conditions and the initial mechanical properties were maintained, giving 16 and 250 GPa mean values for hardness and Young's modulus, respectively. The influence of the fast‐technology by microwave heating is presented with a nonconventional sintering method to fabricate 3Y‐TZP ceramics for dental application with very high resistance against LTD and optimized mechanical properties.

Clay catalysed rapid valorization of glycerol towards cyclic acetals and ketals

Efficient clay catalyzed protocol for acetalization of glycerol. Utilization of non-conventional microwave and ultra-sonication energy sources. Value addition to the process by synthesizing chemicals of commercial importance.

Magnetic properties of LiZnCu ferrite synthesized by the microwave sintering method

Abstract Lithium ferrites have attracted considerable attention because they have been used as replacements for garnets due to their low cost. A series of polycrystalline ferrite samples were prepared with the composition of Li X Zn (0.6−2 X ) Cu 0.4 Fe 2 O 4 ( X =0.05, 0.1, 0.15, 0.2, 0.25, 0.3) at chemical reaction temperature 150 °C by sintering with microwave assisted combustion method. The characterization shows the formation of single phase cubic structure when carried out by using the X-rays technique and I – R technique. Magnetization parameters such as saturation magnetization, coercivity, magnetic moment were calculated by using the Hysteresis graph. The Curie temperature obtained using the susceptibility data are found to be in the range 350–700 °C. Anhysteric remanent magnetization is used for estimating the grain size and domain structure of the composition. An attempt has been made to synthesis the nano-particles at lower reaction temperature by using non-conventional microwave sintering method. The advantage of this method is its lower sintering temperature and time compared to the conventional ceramic technique and direct formation of nano-ferrites without ball-milling.

Structural Analysis and Normalised Susceptibility Study of Zn Substituted Li-Cu Ferrite

Lithium ferrites have attracted considerable attention because they have been used as replacements for garnets due to their low cost. A series of polycrystalline ferrite samples with the composition of LixZn0.6-2xCu0.4Fe2O4 (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) at different chemical reaction temperature (100℃, 125℃ and 150℃) were prepared using non-conventional microwave sintering method. The characterization was carried out using X-rays technique. The X-ray analysis confirms the formation of single phase cubic structure. The lattice parameter ranges from 8.3690 &Aring to 8.4653 &Aring. The X-ray density shows the variation as a function of temperature of synthesis. The variation of AC susceptibility with temperature shows the existence of single domain structure for x ≥ 0.2 when the chemical reaction carried at 125℃ and 150℃ and exhibits super paramagnetic structure for all the composition prepared at 100℃. The samples x ≤ 0.2 shows multidomain structure for all the samples prepared at 125℃ and 150℃. The Curie temperature obtained using the susceptibility data are found to be in the range 350℃ to 700℃. An attempt has been made to synthesis the nanoparticles at lower reaction temperature by using non-conventional microwave sintering method.

Preparation and magnetic properties of cadmium substituted lithium ferrite using microwave-induced combustion

Cadmium substituted lithium ferrites with general formula Li 0.5− x/2 Cd x Fe 2.5− x/2 O 4 (where x = 0.45, 0.5, 0.55, 0.6, 0.65, 0.7) were prepared using non-conventional microwave sintering method. The characterization carried out using X-rays and I–R technique indicates the formation of single phase cubic structure. Hysteresis parameters recorded at room temperature using the Magneta make hysteresis loop tracer to show the saturation magnetization (Ms) in the range 10.45 to 35.23 emu/g. The hysteresis loss per cycle is found to be in the range 25.51 to 65.15 erg/cc/cycle. The pulse field magnetization method was used to measure the temperature variation of magnetic susceptibility which shows the single domain behavior for all the samples. The Curie temperatures obtained using the susceptibility data were found to be in the range of 210 to 300 °C.