Microwave Irradiation Research Articles

Disruption of the Conjugated π-Electron System of Graphene Oxides Diminishes Their Microwave Reactivity.

Graphenes and graphene-based adsorbents have the potential to be thermally regenerated by microwave irradiation due to their electronic mobility and propensity to absorb microwaves. This article investigates the effect of oxidation on their ability to heat during microwave irradiation in conjunction with their ability to adsorb a polycyclic aromatic hydrocarbon. For this, a series of graphene oxides (GOs) were synthesized, and their chemical properties and surface structures were analyzed systematically. As the oxidation levels increased, the microwave reactivity of GOs decreased notably. This was attributed to the disruption of the sp2-hybridized basal plane despite the introduction of polar oxygen-containing functional groups. The findings of this work indicated the role of the conjugated π-electron system on microwave reactivity, possibly posing a juxtaposition with the influence of polar C-O bonds on dielectric reactivity. In addition, the adsorption of the model compound decreased by oxidation, confirming the decrease in π-π electron donor-acceptor interactions and the increase in the formation of water clusters around oxygen-containing functional groups. This study provides the first mechanistic insight into the relationship between the conjugated π-electron network of graphenes and their microwave reactivity. It paves the way for utilizing microwave irradiation to regenerate spent graphenic adsorbents for water treatment.

A Resilient and Reusable Ion-Tagged Cu(II) Catalyst for the Microwave-Assisted Synthesis of 2-(N-Arylamino)benzothiazoles

AbstractA simple, quick, and cost-effective protocol is presented herein for the sustainable synthesis of 2-(N-arylamino)benzothiazoles from 2-haloanilines and arylisothiocyanates by using an ionic liquid supported heterogeneous Cu(II) catalyst derived from N-methylimidazole. Compared to the use of homogeneous catalysts and additives, which require long reaction times and high reaction temperatures, this methodology has a broad substrate scope and proceeds in short reaction times to afford compounds in excellent yields under microwave irradiation. In addition, the catalyst can be extracted easily and is recyclable up to five times with no significant loss in catalytic activity.

Effect of microwave irradiation on the breaking and linear cutting of hard rock

Microwave technology, emerging as a novel approach to rock-breaking, holds significant promise in the realm of auxiliary mechanical pick rock breaking. In view of the problems existing in the hard rock breaking such as low efficiency and difficulty in one-time cutting, this study conducted experimental research using a method combining microwave irradiation and linear cutting with conical picks. The comprehensive temperature distribution of the rock is reproduced by 3D technology after microwave irradiation, defined the high-temperature zone and calculated the surface area. Moreover, analyzing the relationship between temperature and cutting force. And the effect of microwave-assisted conical pick rock breaking was quantified in terms of cutting force, rock breaking effect, and energy consumption. The results indicate that microwave irradiation induces heating in hard rock, leading to the formation of fissures and even partial fragmentation of rocks. The thermal damage effect of microwave is determined by the differences in the physical and mechanical properties of different rocks. In the experiment, basalt has the best heating effect and sandstone has the best fracturing effect. Compared to non-microwave, microwave (6 kW,60 s) irradiation reduces the cutting force, improves the effect of rock breaking, and reduces the work done (E) by the cutting force and the mechanical specific energy (MSE). Microwave irradiation-assisted mechanical rock breaking is better for sandstone, moderate for basalt, and inferior for granite in this study.

Exploration of microwave absorptivity and catalysis of CMF@Co-MoS2 for microwave-initiated depolymerization of lignin

Obtaining key platform chemicals from lignin is a sustainable refining concept of the non-petroleum route. Rapid pyrolysis is a potential refining technology, and microwave-assisted catalytic depolymerization with low energy consumption is preferred. Herein, we reported the strategy of microwave-initiated depolymerization using a self-designed dynamic vapor flow reaction system with a facilely prepared CMF@Co-MoS2-0.18 catalyst, achieving efficient conversion of lignin (Dealkalize) to monophenol. Under constant microwave irradiation (2.45 GHz), the CMF@Co-MoS2-0.18 catalyst had excellent dielectric properties (Dielectric loss factor: 0.56) and microwave heating properties (∼140 s rise to ∼ 600℃). Therefore, microwave-initiated depolymerization of lignin showed that the CMF@Co-MoS2-0.18 catalyst can improve the monophenol content (54.72 %) and phenol selectivity (35.84 %) under the synergistic effect of microwave absorptivity and catalysis. The reaction of the lignin model and kinetics analysis show that the CMF@Co-MoS2-0.18 catalyst increases the yield of monophenol by reducing depolymerization activation energy and selectively breaking the β-O-4 bond. The finite element analysis pointed out that under microwave irradiation, CMF@Co-MoS2-0.18 continuously conducted heat to lignin and the lignin vapor would have sufficient energy to collide with the catalyst active site at a high frequency, which led to an increase in the pre-exponential factor and initiated catalytic depolymerization lignin. In summary, we provide a potential pathway for the rapid conversion of lignin into key platform chemicals.

High-pressure CO2 adsorption on MCM-41: Efficiency of microwave-assisted synthesis

The rapid increase in atmospheric CO2 concentrations, driven by human activities, has become a critical factor in global climate change, posing severe risks to sustainable development. Addressing this challenge necessitates substantial CO2 removal, which demands innovative and efficient technologies. Carbon dioxide adsorption on porous materials is a promising strategy to mitigate this issue. This study investigates the synthesis of ordered mesoporous silica MCM-41 by microwave irradiation, a technique that offers significant advantages over conventional hydrothermal methods. By optimizing the synthesis conditions, we produced MCM-41 silica with superior structural properties in just 30 min. Characterization techniques, including X-ray diffraction, FTIR, N2 adsorption/desorption isotherms, and transmission electron microscopy, confirmed the formation of well-defined pores and hexagonal channels. Notably, the synthesized MCM-41 exhibited a high CO2 adsorption capacity of 12.78 mmol g−1 at 25 °C and 50 bar, outperforming silicas produced via conventional methods and comparable to amine-modified silicas. These results highlight the potential of microwave-assisted synthesis to improve CO2 capture efficiency, offering a promising approach for future carbon capture and storage applications.

Modified Microwave-assisted Solid-liquid Halex Reaction using Phosphonium Salt as Efficient and Robust Phase Transfer Catalyst

: A modified solid-liquid halex reaction was developed in the presence of a robust phase transfer catalyst under microwave conditions. A fast, mild, and practical microwave- assisted synthesis of 2,3-difluoro-5-chloropyridine 3 starting from 2,3,5- trichlorpyridine 1 and spray-dried KF in polar aprotic solvent was developed. The addition of Tetrakis (piperidino) phosphonium chloride as phase transfer catalyst A was studied under microwave irritation (450W) and increased the yield and significantly reduced the reaction time in contrast to the conventional heating procedure. The highest reaction rate was observed at 5 wt% phase transfer phosphonium salt catalyst to 2,3,5-trichloropyridine 1.

Ciprofloxacin degradation over Co3O4 catalysts by the microwave-assisted persulfate oxidation: a critical role of coordination composition

The combination of catalysts and microwave (MW) effects presents an emerging approach for persulfate (PS) activation, while the effect of active sites of catalysts on the synergistic reaction remains poorly understood. Here, we regulated the coordination composition of Co3O4 by strategically controlling the oxygen atmosphere during fabrication. We found that Co3+ and Co2+ acted as reactive centers for microwave absorption and catalytic activation of persulfate, respectively. By altering the ratio between Co3+ and Co2+, we explored the Co3O4 (2.23)-550 catalysts with significantly improved synergistic activity for degrading ciprofloxacin (CIP), which was 33.0 and 26.8 times higher than PS- Co3O4 (2.23)-550 (without microwave) and MW- Co3O4 (2.23)-550 (without persulfate), respectively. Meanwhile, Co3O4 (2.23)-550 catalyst (0.5mgL-1) showed the highest degradation rate of CIP 92.6% (0.5mgL-1) within 10min under microwave. According to the radical identification and intermediate analysis, the efficient degradation of CIP was ascribed to both free radical and non-free radical pathways. Thus, this work raises new insights into the structure-activity relationship of catalysts, and provides an efficient way to eliminate antibiotics via synergistic catalysis.

A novel mesoporous Bi2MoO6/g-C3N4 nanocomposite as an effective photocatalyst against toxic organic pollutants

This study used microwave irradiation technique to synthesize a sequence of Bi2MoO6@g-C3N4 nanocomposite as photocatalysts. The two narrow band gap nanomaterials used were g-C3N4 and Bi2MoO6. The nanocomposites were thoroughly characterized by XRD, FESEM, EDS, HRTEM, Raman spectroscopy, UV–visible spectra, PL and XPS. Moreover, using sunlight radiation, two distinct dyes including Malachite Green (MG) and Acid Blue 113 (AB 113) were degraded using as synthesized photocatalyst. The outcomes indicated that the photocatalytic degradation efficiency of Bi2MoO6@ g-C3N4 was higher than that of pure g-C3N4. A 95 % degradation efficiency towards Malachite Green and an 84 % degradation efficiency towards Acid Blue 113 shown the great effectiveness of Bi2MoO6@ g-C3N4. This enhanced efficiency is attributed to the increased visible light absorption, effective charge separation due to the heterojunction interface between Bi2MoO6 and g-C3N4, and the increased surface area facilitating greater active site availability. According to these results, the synthesized Bi2MoO6@ g-C3N4 would be very beneficial for the removal of organic contaminants in a variety of industrial environments.

Microwave assisted treatment of carpentry waste wood flour with natural deep eutectic solvents for nanocellulose production and removal of organic pollutants.

Row carpentry waste wood flour, constituted of poplar (∼60%) and fir (∼30%) biomass, was subjected for the first time to microwave-assisted deep eutectic solvent (DES) treatment, with the purposes of solubilizing lignin and hemicellulose, leaving cellulose as solid residue, thus performing a biorefinery. Several acidic (choline chloride/oxalic acid; choline chloride/citric acid; betaine hydrochloride/oxalic acid) and alkaline (urea/choline chloride; glycerol/K2CO3) DESs were employed under the same reaction conditions. Since the highest extraction yield was obtained by using choline chloride/oxalic acid DES, the use of the latter was investigated by varying some parameters (temperature, manner of microwave irradiation, addition of water) aiming at increasing the solubilization yield, which in fact in some cases reached satisfying values (60%) under mild conditions. The solid residues (SRs) recovered after all treatments with all tested DESs were characterized by Thermogravimetric Analysis (TGA), Attenuated Total Reflectance-Fourier Tranform Infrared Spectroscopy, Solid-State NMR Spectroscopy, and titration of surface acid groups. All SRs were also ultrasonicated to produce cellulose nanoparticles which were in turn characterised by transmission electron microscopy (TEM) and dynamic light scattering (DLS) analyses. In addition, the solid residues recovered from acidic DESs were able to decontaminate water from organic pollutants, such as p-nitrophenol, by an adsorption process. Thus, the proposed DES treatment efficiently converted carpentry waste wood flour into a valuable biomaterial useful for environmental decontamination.

A novel strategy for obtaining essential oil and flavonoids from Thymus vulgaris L. using polyethylene glycol-ultrasonic pretreatment followed by microwave hydrodistillation and extraction

As a medicinal plant with high economic value, the green and efficient separation of the main components (essential oil (EO) and flavonoids) from Thymus vulgaris L. can enhance its application prospects. The present study developed a polyethylene glycol-ultrasonic pretreatment followed by microwave hydrodistillation and extraction (PEG-U-MHDE) technique to distill EO and extract flavonoids simultaneously. The parameters involved in the PEG-ultrasonic pretreatment and microwave irradiation processes were investigated using single factor and BBD experiments, from which 25 % PEG200/400/600 (1:1:1, v/v/v) was found to have the highest extraction ability. Under the optimal conditions, the yield of EO, apigenin, and baicalein was 3.72 ± 0.15 μL/g, 0.76 ± 0.03 mg/g, and 0.96 ± 0.03 mg/g, respectively. The PEG-U-MHDE showed good stability, recovery, and repeatability for apigenin and baicalein. In addition, the separation efficiency of EO, apigenin, and baicalein obtained by PEG-U-MHDE was 0.19 μL/g/min, 37.85 μg/g/min, and 48.03 μg/g/min, respectively, and the EO contained 81.77 % oxygenated compounds, which were higher than other reference methods. The inhibition rate of EO (concentration of 0.5 μL/mL) against the agricultural pathogenic fungus (Fusarium graminearum) was 36.65 ± 1.28 %, which was speculated to be closely related to its main oxygenated compounds (thymol and carvacrol). In general, PEG-U-MHDE has the advantages of short time and high efficiency, and can realize the simultaneous separation of volatile EO and non-volatile components, which provides a theoretical basis for the comprehensive utilization of natural medicinal plants and crops.

Bifurcation and multi-stability analysis of microwave engineering systems: Insights from the Burger–Fisher equation

The present article depicts the research being done on the microwave effect realized by the often-used Burger-Fisher equation. A particular view is on the emergence of multi-stability and the bifurcations associated with microwave engineering systems. A novel rational, trigonometric, and hyperbolic form of the traveling waves is furnished by the resolution of the non-linear issue with the aid of the advanced exp (−Ψ(η))-expansion function parameterization. Firstly, we will solve the exact form of the Burger-Fisher equation, which clarifies the behavior of the equation in different conditions. Subsequently, bifurcation analysis techniques will be employed to study the nuanced relationship between the system parameters and the emergence of multistability phenomena. Through our results, we exposed the complicated essential features of microwave physics and established crucial parameters that determine a system’s behavior. Next, we cover control principle issues and practical applications in microwave engineering problems. This model accommodates the essential features of multi-stable dynamic systems and provides an important framework for creating microwave devices and circuits.The main aim of this research work is to analyze the phenomenon of multi-stability and bifurcation in microwave engineering systems by applying Burger-Fisher equation. The study intends to obtain new solutions to the PDEs through the application of a new method, the exp (−Ψ(η))-expansion function method that uses rational, trigonometric, and hyperbolic traveling wave solutions. Existing research of the Burger-Fisher equation is not explicit and by solving the exact form the research aims at exploring the different conditions under which the equation behaves and studying the delicate interactions between the parameters of the multistable system.

Microwave Irradiation-Assisted Synthesis of Anisotropic Crown Ether-Grafted Bamboo Pulp Aerogel as a Chelating Agent for Selective Adsorption of Heavy Metals (Mn+)

Crown ether is widely used in water purification because of its ring structure and good selective adsorption of specific heavy metals. However, its high cost and difficulty in recycling limit the purification of heavy metals in water. The anisotropic [2,4]-dibenzo-18-crown-6-modified bamboo pulp aerogel (DB18C6/PA) is successfully synthesized by microwave irradiation and directional freezing technology. The physical and chemical properties of DB18C6/PA are analyzed by FTIR, XPS, SEM, TEM, TGA, surface area and porosity analyzers. Single or multivariate systems containing Pb2+, Cu2+ and Cd2+ are used as adsorbents. The effects of the DB18C6 addition amount, pH, initial concentration and adsorption temperature on the adsorption of DB18C6/PA are systematically explored. Pseudo-first-order kinetic models, pseudo-second-order kinetic models and the isothermal adsorption models of Langmuir and Freundlich are used to fit the experimental data. The adsorption selectivity is analyzed from the distribution coefficient and the separation factor, and the adsorption mechanism is discussed. The results show that anisotropic DB18C6/PA has the characteristics of 3D directional channels, high porosity (97.67%), large specific surface area (103.7 m2/g), good thermal stability and regeneration (the number of cycles is greater than 5). The surface has a variety of functional groups, including a hydroxyl group, aldehyde group, ether bond, etc. In the single and multivariate systems of Pb2+, Cu2+ and Cd2+, the adsorption process of DB18C6/PA conforms to the pseudo-second-order kinetic model, and the results conform to the Freundlich adsorption isothermal model (a few of them conformed to the Langmuir adsorption isothermal model), indicating that chemical adsorption and physical adsorption are involved in the adsorption process, and the adsorption process is a spontaneous endothermic process. In the single solution system, the maximum adsorption capacities of Pb2+, Cu2+ and Cd2+ by DB18C6/PA are 129.15, 29.85 and 27.89 mg/g, respectively. The adsorption selectivity of DB18C6/PA on Pb2+, Cu2+ and Cd2+ is in the order of Pb2+ >> Cu2+ > Cd2+.

Kinetic study of microwave heating-assisted chemical looping dry reforming of methane over magnetite

Dry reforming of methane carried out via the chemical looping concept and employing microwave heating is a sustainable syngas (a mixture comprising hydrogen and carbon monoxide) production technology. Understanding the intrinsic reaction kinetics of reduction and oxidation is essential for successful scale-up of this technology. By employing magnetite as a microwave absorber oxygen carrier, we investigated the reaction kinetics at bulk temperatures in the range of 650–800 °C for reduction and 500–650 °C for oxidation. Results indicated both reactions followed a phase-boundary controlled (contracting sphere) reaction mechanism. Upon developing the reaction kinetics based on solid temperature relevant to microwave-heated particles, we estimated the activation energy to be 85 kJ/mol for the reduction reaction and 22 kJ/mol for the oxidation reaction. By developing the reaction kinetic of the reduction under microwave heating and based on bulk temperature, we estimated 68 kJ/mol as the activation energy of the reduction reaction. Comparing these values with the activation energy of magnetite reduction by methane under conventional heating (around 90 kJ/mol) indicated that microwave irradiation apparently decreased the activation energy. Consequently, by developing the reaction kinetics based on an appropriate temperature, i.e., solid temperature, we demonstrated that microwave primarily had a thermal effect in our study, increasing the reaction rate constant, rather than a non-thermal effect, like altering the activation energy.

Microwave Green Synthesis of Alumina Nanoparticles and Evaluation of Their Characterization and Microbial Effect

This research set out to provide a faster, easier, and more efficient process for nanoparticle (NP) synthesis of aluminum oxide NPs preparation by microwave irradiation, using plant extracts separately and in the same way (tea, coffee, rosemary), which is an easy-to-use and inexpensive method. The structural properties were investigated by X-ray diffractometer analysis technique (XRD). The X-ray analysis shows the structure has a polycrystalline nature with a hexagonal phase. The optical properties were studied using ultraviolet visible (UV-Vis) spectrometer, where the energy gap was determined. The surface morphology properties of the prepared aluminum NPs were examined by atomic force microscope (AFM). The Fourier transform infrared (FTIR) spectroscopy verified the presence of Al-O, C–O, and C–H bonds, this study confirms the high reducing and capping capacity of aluminum NPs via biomolecules found in the plant extract. The inhibitory activity of these Al2O3-NPs was observed, along with their potential to enter the bacterial cell wall and hinder its activity.

Evaluation of Physicochemical and Biological Properties of Chitosan Hydrolysate Produced by Microwave-Assisted Cellulase Hydrolysis

AbstractThis work estimated the biochemical nature of the enzymatic chitosan hydrolysate (CH) as oligomeric chitooligosaccharide products resulting from microwave-aided cellulase hydrolysis of chitosan from shrimp and crab as well as their biological effects and potential preservative application. The microwave irradiation was conducted at 125 W for 15 min simultaneously during the cellulase degradation of shrimp and crab chitosan, previously prepared by a 30-min microwave-aided deacetylation (86.7% and 82.7% degree of deacetylation), producing shrimp chitosan hydrolysate (SCH) and crab chitosan hydrolysate (CCH), respectively. The products SCH and CCH were tested for their solubility in distilled water, viscosity, molecular weight (Mw), FTIR, mass spectra, antioxidant, and antibacterial activities. The obtained SCH and CCH were incorporated into two food systems (yogurt and orange juice) at proportions of 0.08–0.12 g/100 mL as potential preservatives. The average Mw of SCH and CCH was 14.79 and 13.18 kDa, respectively, coupled in each case with 1–6° of polymerization (DP), strong antibacterial and antioxidant activities, and the capacity to dissolve in water in all proportions, becoming more soluble as weight decreased. The chemical, microbiological, and sensory changes in orange juice and yogurt were investigated at 0, 15, and 30 days of cold storage after being enriched with these ingredients. Over the 30-day storage period, the orange juice and yogurt showed enhanced physicochemical, microbiological, and sensory characteristics based on the content of chitosan hydrolysate. The study provided potentially a new and safe preservation technology for food systems.

Novel flexible and active expanded-starch films enriched with Agrifood waste via microwave irradiation

Expanded materials possess valuable properties for food packaging, including thermal insulation and lightweight. However, developing sustainable alternatives with the potential to replace lightweight petroleum-based plastics is highly challenging. Starch biopolymer is a promising sustainable candidate due to its compostable character, great foamability and processability. Moreover, its chemical characteristics allow its combination with agrifood wastes to promote the circular economy and provide active properties. Most of the starch foams reported with low density are processed via extrusion and they are notably brittle and rigid, restricting their application. In this work, different expanded starch biocomposites, without or enriched with 40 wt.% orange peel (OP), were fabricated using 30 s of microwave (MW) irradiation, acquiring different properties depending on the main blowing agent used (i.e., water, sodium bicarbonate or expandable microspheres). These samples were fully characterized in terms of morphology, density, expansion degree, water uptake and solubility, mechanical properties, migration and antioxidant properties. Remarkably, the final expanded materials reached a considerably low density of 0.3 g/cm3 and they exhibited exceptional flexibility, overcoming the important drawback of starch foams. Finally, the benefits of adding 40 wt.% of agrifood waste were not only environmental, but OP increased the expansion capacity and gave outstanding antioxidant properties.

Fabrication and Characterizations of Microwave‐Assisted Gelatin Cross‐Linked LBG/Guar Gum–Based Super Porous Hydrogels With Metformin Hydrochloride for Open Incision Wound Healing

ABSTRACTThe goal of this study was to fabricate gelatin cross‐linked Locust bean gum (LBG)/guar gum–based hydrogels with microwave assistance for diabetic wound healing applications and evaluate it for physicochemical properties. In the last few years, microwave irradiation has gained acceptance as a reliable technique for quickening and streamlining chemically modified reactions. In order to achieve this, metformin‐loaded LBG and guar gum–based hydrogel were formulated employing microwave radiation. Moreover, the microwave‐assisted–based metformin hydrogel are microwave‐assisted reaction sudden increase in temperature may led to distortion of molecules, very vigorous and which may be hazardous, but environmental sustainability and friendly chemistry concepts are supported by microwave irradiation. The optimized formulation (F3) showed significantly improved physicochemical properties, with a swelling capacity of 480.4% ± 2.5%. The results indicate an appropriate duration for adequate drugs diffusion and nutrition exchange. Controlled disintegrate and sustained release of embedded drug molecules from F3 may have an impact on antibacterial activity. The study indicated that microwave‐assisted polymer blend hydrogels had adequately improved physical qualities, making them a promising candidate for improving diabetic wound healing and hastening skin tissue regeneration.

Stabilized Ag nanoparticles loaded smart poly(chitosan-N-isopropylacrylamide-methacrylic acid) hybrid microgels for catalytic reduction of nitroarenes

Nitroarenes (NAs) are one of the most toxic pollutants in the water which cannot easily be eliminated. This challenge can be resolved with conversion of NAs into less toxic aryl amines (AAs) rapidly in the presence of a suitable catalyst. Therefore, poly(chitosan-N-isopropylacrylamide-methacrylic acid) P(ChS-NIPAM-MAA) P(ChNM) microgels were synthesized by microwave irradiations which were then fabricated with silver (Ag) nanoparticles (NPs) by in-situ reduction method and characterized with TEM, XRD, DLS, FTIR, and SEM techniques. The Ag-P(ChNM) hybrid microgels showed pH and temperature responsive behavior along with long time stability. The catalytic efficiency of Ag-P(ChNM) was evaluated for the reduction of 4-nitroaniline (4NiA) under different conditions such as concentration of NaBH4, temperature, content of Ag-P(ChNM), and 4NiA concentration. The Ag-P(ChNM) successfully converted different NAs into their corresponding AAs catalytically with high yields. The highest yield was obtained for 4-nitrophenol (4NiP) (99%) and the lowest for 2,4-dinitrophenylhydrazine (2,4DNiPH) (71%). Electron-withdrawing group containing derivatives of NAs rapidly reduced into AAs than electron-donating substituents. They exhibited excellent catalytic efficiency, stability, recyclability, and maintained their catalytic efficiency over multiple cycles.

Ni/PiNe Heterogeneous Catalyst from Biomass Waste: Low-Loading, Ligand-Free Suzuki-Miyaura Cross-Coupling.

An efficient Ni-based heterogeneous catalyst from pine needles urban waste valorization was designed and developed with a resource recycling strategy. The Ni/PiNe catalyst was fully characterized and tested in the Suzuki-Miyaura coupling under microwave irradiation. Although Ni is a promising candidate for replacing Pd-based catalytic systems, it generally requires a high catalyst amount and the exploitation of ligands and additives to enhance the reaction rate. On the contrary, with our new Ni/PiNe, 30 different products were efficiently synthesized with an isolated yield of up to 93%, using a very low catalyst amount and in the absence of ligands. Furthermore, the Ni/PiNe catalyst also showed good durability for consecutive cycles and an impressive TON value (1140). In addition to the catalytic efficiency in short reaction time and to the stability and durability under MW irradiation, the Ni/PiNe allowed for further optimization, achieving a low E-factor value (14.0), thus highlighting the potential in further reducing the waste and costs associated to the process.

Microwave-absorbing property, chemical adsorption, and catalytic activity of monolithic LamMnnOx catalyst in microwave catalytic combustion of toluene

To verify the catalytic activity of LamMnnOx (m,n = 1,2; x = 2.5 ∼ 5.5) catalyst in microwave catalytic combustion of volatile organic compounds (VOCs), monolithic LamMnnOx catalysts were prepared and applied in toluene oxidation in this study. The research demonstrated that the LamMnnOx catalysts had strong microwave-absorbing properties due to first dielectric loss and secondary magnetic loss. The bed temperature rose rapidly due to the formation of hotspots under microwave irradiation. Furthermore, LamMnnOx catalysts chiefly adsorbed toluene by chemical adsorption, and the adsorption capacity of Mn was much stronger than that of La. Based on the activity tests, La1Mn1Ox (x = 2.5 ∼ 3.5) catalyst exhibited the highest catalytic activity among the four catalysts, and toluene was converted and mineralized completely at 259 ℃ and 315 ℃, respectively, under the conditions of an initial toluene concentration of 1000 mg/m3, bed height of 150 mm, and gas velocity of 2.5 L/min. Highly active LaMnO3 perovskite, uniform distribution of active particles, and abundant oxygen vacancies ensured the high activity of the La1Mn1Ox catalyst. Hence, the La1Mn1Ox catalyst was stable after a total of 600 min of activity test. According to electron transfers on the active Mn surface, the adsorption and activation of gaseous oxygen, and the transformation of Oads to Olatt on the oxygen vacancies, toluene oxidation speculates to follow the Langmuir-Hinshelwood and the Mars-van Krevelen mechanisms simultaneously. Therefore, this work provides further technological support for applying LamMnnOx catalysts in microwave catalytic combustion of industrial VOCs waste gas.