Microwave Heating Research Articles

Microwave heating intensified in-situ preparation of ZnO-based desulfurization sorbent with multi-stage structure and promoted performance

Fast mass transfer and gas diffusion is crucial to high performance coal gas desulfurization sorbent. In this paper, ZnO/M41-M sorbent is prepared via hydrothermal, in-situ pre-desulfurization and oxidation, combined with microwave treatment for hydrogen sulfide removal. As revealed by the desulfurization test at 500 °C, the highest sulfur capacity of 12.45 g S 100 g-1 sorbent has been achieved upon the ZnO/M41-M sorbent, which can be attributed to the rich pore structures, high activity and well dispersed reaction sites. Methods like N2 adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were applied to characterize the property of sorbents. According to the results, the active components obtained through in-situ method are dispersed uniformly as revealed by the comparison of four preparation methods. Meanwhile, compared to the conventional in-situ heating, microwave radiation reduces the formation of Zn2SiO4 (Zn element: 7.64–7.31 wt.%) with low activity to H2S, maintains better channel structure, and promotes the in-situ oxidation rate (89.56%). After oxidation, the collaboration of S2- preoccupation and microwave effect provides enough space for the replacement of oxygen and sulfur ions. Besides, microwave effect optimizes the reaction activity of ZnO for adsorbing H2S more easily. Overall, effects derived from microwave and in-situ preparation imparted the sorbent with better performance, indicating the potentials in the improvement of sorbents for pollutants removal.

Raman Thermometry for Temperature Assessment of Inorganic Transformations During Microwave Heating

ABSTRACTMicrowave heating is an intriguing method for the synthesis of inorganic solids offering a variety of advantages over conventional furnace heating, such as fast heating and cooling rates as well as volumetric and selective heating of precursors. However, there are many open questions regarding this “black‐box” process, and insights into the effect of microwave radiation on different types of solids are generally missing. In situ Raman spectroscopy is a powerful technique to unravel chemical transformations and identify intermediate species during microwave solid‐state syntheses. A major challenge is the temperature measurement under microwave conditions because (metallic) thermocouples cannot be used and optical pyrometry has significant drawbacks. In contrast, Raman thermometry is a viable method that relies on the temperature‐induced shift of Raman signals. Here, we use this method to estimate the temperature during microwave heating of a model system (titania) that undergoes a phase transition at temperatures >800°C. The estimation is derived from a flexible double exponential calibration function applied to Raman spectroscopic peak shifts in the temperature‐resolved furnace heating data, which was found to describe two titania modes (one anatase and one rutile) extremely well. Based on a detailed error and uncertainty analysis, we suggest options to further optimize Raman thermometry for use in high‐temperature microwave heating conditions.

Rapid Generation of Microplastics and Plastic-Derived Dissolved Organic Matter from Food Packaging Films under Simulated Aging Conditions.

In this study, we show that low-density polyethylene films, a prevalent choice for food packaging in everyday life, generated high numbers of microplastics (MPs) and hundreds to thousands of plastic-derived dissolved organic matter (DOM) substances under simulated food preparation and storage conditions. Specifically, the plastic film generated 66-2034 MPs/cm2 (size range 10-5000 μm) under simulated aging conditions involving microwave irradiation, heating, steaming, UV irradiation, refrigeration, freezing, and freeze-thaw cycling alongside contact with water, which were 15-453 times that of the control (plastic film immersed in water without aging). We also noticed a substantial release of plastic-derived DOM. Using ultrahigh-resolution mass spectrometry, we identified 321-1414 analytes with molecular weights ranging from 200 to 800 Da, representing plastic-derived DOM containing C, H, and O. The DOM substances included both degradation products of polyethylene (including oxidized forms of oligomers) and toxic plastic additives. Interestingly, although no apparent oxidation was observed for the plastic film under aging conditions, plastic-derived DOM was more oxidized (average O/C increased by 27-46%) following aging with a higher state of carbon saturation and higher polarity. These findings highlight the future need to assess risks associated with MP and DOM release from plastic wraps.

A novel route of carburizing through microwave hybrid heating

Abstract Carburizing is a surface treatment process by diffusing carbon into the steel. These days, manufacturing industries demand highly efficient processes that consume low power. Microwave processing is a newly evolving process that consumes low power. This study proposes a novel route for carburizing mild steel (substrate) through experimental and simulation studies using a microwave heating. Charcoal powder was used as a susceptor to convert microwave energy into heat energy and to deposit carbon on the surface of the specimen. The mild steel specimens were exposed to the microwave power input of 900 W and 360 W for exposure time of 1500 s and 1980 s naming it as S2 and S3 respectively. The microstructural analysis of specimens S2 and S3 confirms the formation of pearlite structures at the surface. However, the amount of pearlite structure was significantly higher for the S3. The higher carbon content is confirmed through energy-dispersive x-ray spectroscopy (EDS) analysis of specimen S3. The average hardness of the S3 specimen was determined to be 220.8 HV, which shows an increase of 38.36% compared to the S1 (base metal). x-ray diffraction (XRD) results indicate the additional cementite peaks (Fe3C) and ferrite-confirming phase transformations for carburized samples. The wear analysis of S2 and S3 was conducted through pin-on-disk testing. The peak COF of 0.73 and 0.64 was observed for S2 and S3 respectively. The hard surface of S3 resists the penetration of the counter body to a greater extent due to the fine morphology of pearlite. From the FEM study, the maximum value of 7.96 × 10 3 (V/m) was determined at the center region for the electric field distribution in the microwave cavity, which is the optimum value for efficient heating. The maximum temperature of the mild steel obtained during the carburization process was 900 °C in 1800 s. The microwave carburizing process requires relatively less time than the conventional carburizing process which will save energy consumption.

Hydrothermal pretreatment with microwaves: A new strategy for ensuring the sustainability of biorefineries

Lignocellulosic biomass (LCB) includes agricultural residues, crop wastes, and food wastes that are ubiquitously present and can be used as renewable resources to generate bioenergy or biofuels. Still, direct utilization of LCB to produce biofuel is not an easy task due to the recalcitrance property of LCB. The pretreatment strategy is an important step in a biorefinery to reduce biomass recalcitrance and to use it for bioenergy including value-added product generation. Microwave irradiation is procuring interest regarding LCB and waste material pretreatment over time before moving to biological transformation to biofuels. The coupling of microwave heating with water has made it the most effective treatment for biomass valorization to generate biofuel and other value-added products, turning it into the most cost-effective and eco-friendly approach. Despite its numerous advantages, scaling up microwave pretreatment from laboratory experiments to industrial applications faces several challenges. These limitations become significant hurdles in scaling up. As a result, it is necessary to focus research on cost evaluations and life cycle assessment (LCA) studies for commercialization that will benefit the bioeconomy and the environment. This review discusses microwave-assisted pretreatment significance in valorizing LCB for biofuel generation including the cost evaluation and LCA studies that have the most important role in commercializing the microwave-assisted pretreatment from lab scale to industrial scale.

Anti-icing and de-icing properties of composite superhydrophobic coating with microwave heating performance on asphalt pavement

Severe icing on asphalt pavements significantly impacts traffic safety and efficiency. Superhydrophobic coatings exhibit excellent hydrophobic and anti-icing properties, making them suitable for asphalt pavements. However, the formation of dense and hard ice limits their anti-icing effectiveness in cold regions. Within this paper, we have developed a novel composite superhydrophobic coating (CSC) with microwave heating performance by constructing a hierarchical structure using carbon nanotubes and incorporating micron-sized iron powder as a primary microwave-absorbing material. Scanning electron microscopy, 3D confocal microscopy, and contact angle tests reveal that the optimally mixed CSC possesses a complex micro-nano hierarchical structure, superhydrophobic properties (contact angle of 155.4°), and excellent anti-icing properties. Microwave heating results show that the CSC achieves a maximum heating rate of 1.108 ℃/s and an energy utilization efficiency of 47 %, representing improvements of 118.1 % and 18.3 % compared to uncoated specimens. Durability tests indicate that after wear, the CSC's contact angle decreases by 6.2 %, and the microwave heating rate drops by 13.7 %. Despite these reductions, the coating still maintains high hydrophobicity and microwave heating performance. While the friction coefficient of CSC-coated pavement decreases to μ=0.63, it still meets regulatory requirements. Overall, the application of CSC can effectively increase de-icing efficiency and mitigate the adverse effects of ice and snow on pavements.

In-situ synthesis nano PtRuW/WC HER catalyst for acid hydrogen evolution by microwave method

Abstract One of the primary challenges in electrocatalysis for the hydrogen evolution reaction (HER) lies in the development of highly efficient catalysts suitable in acidic environments. Tungsten carbide-based materials have long been proposed as potential substitutes for Pt due to their “Pt-like” electronic properties in the HER process. However, tungsten carbide still falls short of the performance exhibited by commercial precious-metal catalysts. Herein, PtRuW/WC was prepared by a microwave heating method and acted as a HER electrocatalyst. The microwave method not only enhances the diffraction peaks of the substrate tungsten carbide, but also facilitates the growth of metal ions at specific sites. The PtRuW/WC catalyst demonstrates outstanding performance in acidic HER, characterized by a minimal overpotential of 40.7 mV at 10 mA/cm2 (η10). Furthermore, it exhibits exceptional stability in acidic solutions, showing no substantial degradation during 20 h at 1000 mA/cm2. The catalyst-assembled PEM electrolytic water electrode further proves that PtRuW/WC has excellent electrolytic water performance and makes some efforts for the development of commercial PEM electrolytic water.

Rapid and controllable microwave synthesis of nickel cobalt sulfide electrodes for high-performance asymmetric supercapacitors

The efficient and controllable synthesis method of high-performance energy storage electrode materials is crucial for advancing the development of energy storage technologies. Herein, by leveraging microwave heating technology in the sulfidation of nickel cobalt MOF, we effectively enhanced the efficiency of the synthesis process. Notably, sulfidation time emerged as a pivotal factor in tuning the crystalline phase structure and conductive properties of the material, leading to the successful development of NCS2 electrode material with a unique structure through optimized sulfidation conditions. Electrochemical performance tests of the NCS2 material revealed exceptional results; it exhibited a specific capacity of 1311 Fg[Formula: see text] at a current density of 1 Ag[Formula: see text] and retained 73.4% of its initial capacity when the current density increased to 10 Ag[Formula: see text], demonstrating outstanding rate performance. The composite NCS2//AC supercapacitor exhibits an energy density of 24.2 Whkg[Formula: see text] at power density of 800 Wkg[Formula: see text], even though after 1000 consecutive charge-discharge cycles, the capacity retention rate remained high at 77.1%, validating the exceptional stability and reliability of the NCS2 material during cycling. This work employs microwave sulfidation for the rapid and controlled synthesis of nickel cobalt sulfides, providing a green and efficient synthetic strategy for metal sulfide active materials.

Judicious combinations of gravity, magnetic, electrostatic separators and microwave heat energy on recovery of ilmenite from Humma lean grade beach placer deposit

Microwave heating is an eco-friendly and novel technique for sintering and heating minerals and materials as it has several advantages in terms of phase transformation, energy efficiency, enhancing speed, process simplicity, improved properties. Such heating provides the composite materials to absorb electromagnetic energy volumetrically and transform into heat and produces larger densities as compared to conventional heating. This study focuses on two main objectives: the recovery of ilmenite through a strategic combination of mineral processing equipment, including a spiral concentrator, followed by magnetic and electrostatic separation, and the enhancement of ilmenite concentrate using microwave heat energy on a cleaner magnetic product, followed by electrostatic separation. Continuous magnetic separation results indicate that among the dry high-intensity belt magnetic separator, box mag wet high-intensity magnetic separator and dry rare earth drum magnetic separators, the rare earth magnetic separator yielded the highest quality product. The application of microwave heat energy before the rare earth drum magnetic separator at 1.4 T, followed by high-tension separation, produced the best grade of ilmenite. The magnetic product obtained after microwave treatment contained 98.6% ilmenite, which was further upgraded to a 99.6% ilmenite concentrate through high-tension separation. Therefore, it is recommended that an effective combination of gravity separation, microwave heat energy, rare earth drum dry magnetic separation and high-tension separation be employed to achieve the highest grade of ilmenite concentrate.

Dielectric Heating Protocol of Three Low Moisture Flours as Affected by Moisture, Temperature and Mass at 2.45 and 5.8 GHz

ABSTRACT Present studies investigate the dielectric properties (dielectric constant and dielectric loss factor) of three low moisture flours (barley, chickpea and wheat) in the moisture content range 2%–10% (w. b.) and temperatures 10°C–60°C at 2.45 and 5.8 GHz. Measurements were taken using cavity perturbation method in conjunctions with Vector Network Analyzer. Results show that dielectric constant and loss factor increased with temperature as well as moisture content both at 2.45 and 5.8 GHz but decreased with increase in frequency. Change in mass of all flours during heating does not affect dielectric properties at both frequencies. A second order regression equation is generated to predict dielectric properties at both frequencies for entire temperature and moisture. Penetration depths of all flours decreased with increase in moisture content and temperature at 2.45 and 5.8 GHz. These studies provide valuable insights to heating protocol of flours in view of recent flours-related disease outbreaks.

Molecular Structure and Properties of Resistant Dextrins from Potato Starch Prepared by Microwave Heating.

The dextrinization of potato starch was performed using a sophisticated single-mode microwave reactor with temperature and pressure control using 10 cycles of heating with stirring between cycles. Microwave power from 150 to 250 W, a cycle time from 15 to 25 s, and two types of vessels with different internal diameters (12 and 24 mm) and therefore different thicknesses of the heated starch layer were used in order to estimate the impact of vessel size used for microwave dextrinization. The characteristics of resistant dextrins (RD) including solubility in water, total dietary fiber (TDF) content, color parameters, the share of various glycosidic bonds, and pasting and rheological properties were carried out. The applied conditions allowed us to obtain RDs with water solubility up to 74% at 20 °C, as well as TDF content up to 47%, with a predominance of low-molecular-weight soluble fiber fraction, with increased content of non-starch glycosidic bonds, negligible viscosity, and a slightly beige color. The geometry of the reaction vessel influenced the properties of dextrins obtained under the same heating power, time, and repetition amounts. Among the conditions used, the most favorable conditions were heating 10 times for 20 s at 200 W in a 10 mL vessel and the least favorable were 15 s cycles.

Comparison of Conventional and Microwave Heating

Carnot batteries (or Power-to-Heat-to-Power systems) are capable of increasing the use of electricity from photovoltaic or wind power plants to achieve decarbonisation of the electricity sector. To decouple electricity production from demand, these renewable power plants can be connected to the thermal energy storage system of a concentrated solar thermal power plant via electric heaters. As an alternative to electric heaters, microwaves are studied as a volumetric and selective heating method, avoiding the limitations of the Joule effect conventional heating when having solar salt (non-eutectic mixture of 60 wt % NaNO3 and 40 wt % KNO3), which is a storage medium with low thermal conductivity, working at a temperature very close to its affordable maximum temperature without degradation. In this work, the two heating methods are compared both experimentally and numerically. At experimental level, a microwave oven and a muffle furnace are used to record energy consumption and time for a common objective. Additionally, different crucible materials were used to test their suitability with microwaves. Only quartz glass was validated for microwave heating, while the porcelain and alumina based materials (Corundum and Alsint 99.7) failed while exposed to microwaves. Compared to conventional heating, heating solar salt with microwaves saved fifty minutes of time and ninety percent of consumption. These experiments were validated by numerical simulations, showing a different distribution in each experiment.

The role of the activation heating source on the carbon capture performance of two new adsorbents produced from household-mixed-plastic waste

This study reveals the impact of the activation with microwave and conventional heating sources on textural properties and CO2 uptake of a mixed plastic-based char. Two mixed plastic-based adsorbents, one activated using microwaves and the other using conventional heating, were produced at optimum activation conditions, and subsequently compared. The findings show that both heating sources produced microporous adsorbents, but activation heating sources influenced their physicochemical properties and CO2 uptake. The microwave-produced activated carbon (AC) displayed superior BET surface area, total, micro- and ultra-micropore volumes compared to the conventionally produced AC. The microwave-produced AC possessed CO2 adsorption capacities of 1.66 and 2.37 mmol/g under dynamic and equilibrium conditions, respectively, at 25 °C and 1 bar. These capacities represent an 8 and 30 % higher uptake, respectively, compared to the 1.53 and 1.66 mmol/g displayed by the conventionally prepared AC under the same adsorption conditions. Both samples displayed stable and excellent CO2 recyclability over 10 adsorption-desorption cycles, with desorption efficiencies ranging from 93.46 % to 96.72 % (microwave- and conventionally- produced ACs respectively). The Avrami model most accurately described the experimental CO2 adsorption data under dynamic conditions, while the Sip model gave the best fit for equilibrium conditions. These findings apply to both types of ACs at various temperatures, irrespective of the heating source. Overall microwave heating is more efficient than conventional heating, requiring 300°C lower temperature, 115 minutes shorter time, 0.79 kWh less energy, and less KOH. It improves CO2 uptake and reduces production costs by 80 %, offering a sustainable alternative for CO2 adsorbent production.

Improvement of microwave heating efficiency by parabolic concentrator

The conventional microwave heating reaction cavity has deficiency of low heating efficiency, which will waste energy and even burn the microwave source and equipment. Therefore, to improve the heating efficiency will save energy and protect the microwave device. In this article, without changing the original heating reaction cavity, a parabolic wave concentrator is proposed to improve the heating efficiency of the microwave heating system. The first part of the article introduces the design and principle of the microwave wave concentrator and describes the control equation of microwave heating and the input parameters of the cavity. In the second part, based on the finite element method calculation, four feeding modes (single, dual, side, and inclined feed port) are simulated to verify the heating efficiency improvement after adding the wave concentrator. Finally, a microwave heating reaction cavity with an inclined feed port is built and used to carry out experiments, which validate the simulation results. The simulation and experiment results show that adding the wave concentrator has greatly improved the heating efficiency.

Enhancing photosynthesis of microalgae via photoluminescent g-C3N4 accelerated photoelectrons transfer in photosystem

Using photoluminescent (PL) graphitic carbon nitride (g-C3N4) to convert ultraviolet (UV) light into chloroplast absorbed blue or near infrared (NR) is an attractive methodology to facilitate sunlight energy storage and carbon sequestration by microalgae. However, most researches focus on inhibiting water bloom by g-C3N4, applying PL g-C3N4 to promote growth of microalgae is rarely reported. Accordingly, PL g-C3N4 is synthesized by a microwave heating method and co–cultured with Chlorella vulgaris (C. vulgaris) with concentration of 0, 50, and 250 mg/L, named as C. vulgaris-0, C. vulgaris-50, and C. vulgaris-250, respectively, to study effect of PL g-C3N4 on growth of C. vulgaris. Results indicate that there is no significant effect of microwave synthesized g-C3N4 on morphology of microalgae cells, while cell viability and growth rate of C. vulgaris-50 is obviously enhanced. Further analysis indicates that, on the one hand, PL fluorescence at 615 nm enlarges light absorption of microalgae; on the other hand, photogenerated electrons by g-C3N4 accelerate electron transfer in photosystem, subsequently enhancing formation of NADPH and ATP, which is favorable to growth of microalgae. Metabolism analysis illustrates that glucose, fructose, and galactose, involved in glycolysis and photosynthesis, are all up-regulated in C. vulgaris-50 group. This work reveals low concentration of PL g-C3N4 facilitates protein synthesis and energy metabolism through enhancing light absorption and electron transfers, providing a biochemical strategy to enhance carbon sequestration.

Oxidative Catalytic Depolymerization of Lignin into Value-Added Monophenols by Carbon Nanotube-Supported Cu-Based Catalysts

Lignin valorisation into chemicals and fuels is of great importance in addressing energy challenges and advancing biorefining in a sustainable manner. In this study, on the basis of the high microwave absorption performance of carbon nanotubes (CNTs), a series of copper-oxide-loaded CNT catalysts (CuO/CNT) were developed to facilitate the oxidative depolymerization of lignin under microwave heating. This catalyst can promote the activation of hydrogen peroxide and air, effectively generating a range of reactive oxygen species (ROS). Through the application of electron paramagnetic resonance techniques, these ROS generated under different oxidation conditions were detected to elucidate the oxidation mechanism. The results demonstrate that the •OH and O2•− play a crucial role in the formation of aldehyde and ketone products through the cleavage of lignin Cβ-O and Cα-Cβ bonds. We further evaluated the catalytic performance of the CuO/CNT catalysts with three typical lignin feedstocks to determine their applicability for lignin biorefinery. The bio-enzymatic lignin produced a 13.9% monophenol yield at 200 °C for 20 min under microwave heating, which was higher than the 7% yield via hydrothermal heating conversion. The selectivity of G-/H-/S-type products was slightly affected, while lignin substrate had a noticeable effect on the selective production. Overall, this study explored the structural characteristics of CuO/CNT catalysts and their implications for lignin conversion and offered an efficient oxidation approach that holds promise for sustainable biorefining practices.

Assessment of Zero Waste Approach by Enhancing Chromium-to-Iron Ratio in Chromite Ore Through Magnetizing Roasting: A Novel Comparative Sustainable Study of Conventional and Hybrid Microwave Heating Methods

Assessment of Zero Waste Approach by Enhancing Chromium-to-Iron Ratio in Chromite Ore Through Magnetizing Roasting: A Novel Comparative Sustainable Study of Conventional and Hybrid Microwave Heating Methods

A comparison of the acoustic waves generated in proton and carbon ion therapy

Hadron therapy, which employs particles such as protons and carbon-ions, is a promising method of cancer treatment due to its unique ability to deliver maximum energy at the Bragg peak near the tumor, sparing surrounding healthy tissue. Ionoacoustic waves, generated by thermal expansion from electronic collisions and localized heating, can be detected to optimize dose delivery and verify particle range, thus improving treatment precision. These waves offer a unique opportunity for comparative studies of different particle therapies. In this study, a mathematical model and computational simulations are used to compare the characteristics of ionoacoustic waves generated in tissue by proton and carbon-ion beams. In particular, we assess the impact of the nuclear fragmentation tail on the ionoacoustic signals generated in carbon-ion therapy. Our approach will allow us to make some important observations to study the comparative effects of proton and carbon-ion therapy. The aim of this work is to perform a comprehensive comparative analysis of ionoacoustic waves from proton and carbon-ion treatments, focusing on their potential for in-vivo range verification. This research addresses the current gap in understanding the use of ionoacoustic signals for range verification in ion beam therapy, which is critical given the growing clinical application of carbon ion therapy and its under-explored acoustic properties. This study pioneers the feasibility of using acoustic imaging from carbon-ion beams to detect the Bragg peak position and measure tumor dose in real-time. Carbon-ion dose mapping and relative biological effectiveness (RBE) assessment can be facilitated by real-time signal monitoring. Our study aims to significantly advance the field by addressing the lack of a verification technique for carbon-ion beams, focusing on the considerable impact of the nuclear fragmentation tail on ionoacoustic signal waveforms, which provides crucial insights into the unique energy deposition properties of carbon-ions.

Approach to Validate ISPM-15 Compliance for Commercial Treatment Certification of Dielectric Standard Heating of Bulk Solid Wood Packing Materials using Radio Frequency

Abstract To substantially reduce the risk of alien invasive species moving to new geographic areas, phytosanitary treatment of wood packaging materials (WPM) in compliance with the International Standard of Phytosanitary Measures No. 15 (ISPM-15) is required by trading partners. Approved treatments include conventional heating, methyl bromide and sulfuryl fluoride fumigation, and dielectric heating (DH). The DH standard was officially adopted in 2013 but has not been practiced commercially due primarily to insufficient operational validation at commercial scale. In 2022, we converted our 50-kW radio frequency (RF) unit with a 1,200-board foot capacity from an oscillator electromagnetic field power generator to a solid-state power supply, which allows for selective power input adjustments during treatment; we also switched from a five-plate to a three-plate winged electrode system to improve heating uniformity. Each loading cycle can treat sufficient material to build ∼94 standard Grocery Manufacturers Association pallets. Our research team characterized the dielectric heating pattern and options for monitoring wood temperatures over a wide-ranging test matrix of WPM that varied by wood species, dimension, moisture content, and loading configuration. We found that this upgraded RF system markedly reduced treatment times and improved heating uniformity, allowing us to develop methods that can be used to verify compliance with ISPM-15 for improved technology transfer to industry. We also discuss the operational cost of RF treatment and make general cost comparisons to conventional heat treatment for WPM.

Three-Component Synthesis of 1-Substituted 5-Aminotetrazoles Promoted by Bismuth Nitrate.

A nontoxic bismuth-promoted multicomponent synthesis of 5-aminotetrazoles and bistetrazoles is reported. The reaction of phenyl isothiocyanate, NaN3, and amine (primary aliphatic, aromatic, and aliphatic diamine) promoted by Bi(NO3)3·5H2O under microwave heating affords good yields, short reaction times, simple workup, and purification without column chromatography. A set of diagnostic 1H NMR signals was identified as a guide for quickly elucidating the exclusive (or main) regioisomer formed, with the stronger electron donor group located at heterocyclic nitrogen 1. This regioselectivity is strongly dependent on the electronic density of the amine. It is opposite to that obtained by several thiourea desulfurization methods promoted by thiophilic metals and metal-free protocols.