Microwave Reduction Research Articles

Ultrahigh Pt-mass-activity catalyst for alkaline hydrogen evolution synthesized by microwave method in air

Platinum (Pt) metal is widely acknowledged as a highly efficient electrocatalyst for hydrogen evolution reaction (HER) in acidic electrolyte. However, its performance in alkaline environments is significantly lower owing to the sluggish water dissociation step. Herein, we synthesized an ultrahigh Pt-mass-activity alkaline HER catalyst using microwave reduction method in air. Our catalyst, PtRu@CNT, comprises PtRu alloy nanoparticles uniformly loaded on carbon nanotubes, with Pt and Ru contents of 12.3 wt% and 4.5 wt%, respectively. The PtRu alloy nanoparticles have an average diameter of about 3 nm and a face-centered cubic structure, and the introduction of Ru has led to a modified electronic structure in Pt. As a result, an impressively low HER overpotential of 13 mV was achieved, significantly lower than commercial 20 wt% Pt/C (61 mV). PtRu@CNT exhibited a high turnover frequency based on metal mass of 3.06 s−1 at 100 mV, about 6 times higher than commercial Pt/C (0.46 s−1 at 100 mV), highlighting its excellent intrinsic activity. The HER mechanism of PtRu@CNT is a Volmer-Tafel mechanism, where the rate-limiting step changed to the recombination of hydrogen atoms from initial water dissociation, attributed to the presence of Ru. The alkaline HER activity of PtRu@CNT ranks among the best of currently reported Pt-based catalysts.

Comparative study of the reduction techniques of Graphene Oxide for Zinc Ion hybrid Storage Application

The increasing demand for low cost and high energy storage devices has given rise to the hybrid supercapacitor device. To overcome the safety issues of the Lithium and Sodium-based devices Zinc ion hybrid supercapacitors (ZIHSCs) are a promising alternative. These devices amalgamate the energy density and power density requirements which makes them suitable for varied applications. The device construction comprises of a zinc anode, zinc-based electrolyte and capacitive type cathode material. Carbon based nanomaterials such as reduced graphene oxide (RGO) are predominantly used as potential cathodes. The strategies involved in obtaining RGO changes the structural characteristic of the samples. This study compares three different strategies such as Chemical reduction (c-RGO), Microwave reduction (m-RGO) and Solar reduction (s-RGO). It was observed that the employment of each these techniques render the change in the physical properties of the materials like number of defect, change in the surface are, porosity and in-situed developed functional group, especially oxygen species. These changes were analyzed thoroughly by various techniques like Raman, Fourier, X-ray diffraction and X-Ray photoelectron spectroscopy. The overall study reveals that solar reduction route shows enhanced surface area and porosity and decrease in defect concentration. Further due to this enhanced property in s-RGO the zinc ion storage capacitance of the fabricated ZIHSC was 200 F/g with a high cyclic stability of 5100 cycles at a current density of 10 A/g. The enhanced energy density thus obtained was 111 Wh/kg corresponding to a power density of 10 KW/kg.

Metal-support interface engineering for stable and enhanced hydrogen evolution reaction

Hydrogen has emerged as a green and sustainable pathway towards achieving global decarbonization and net-zero emissions, intensely driving the need for efficient hydrogen production protocols. Electrocatalytic hydrogen evolution reaction (HER) holds great potential as a scalable, eco-friendly and safe avenue for efficient hydrogen production. However, the large-scale implementation of electrocatalytic HER is substantially challenged by the high-cost and unstable materials that are mainly fabricated from noble metals, e.g., Pt and Pd. Given this challenge, we adopted an interface engineering strategy to immobilize nanoscale Pt particles within the framework of nitrogen-doped CNTs, namely Pt@N-CNTs, where electronic metal-support interaction (EMSI) plays an important role in enabling orbital rehybridization and regulating the charge transfer through the metal-support interface, thereby considerably improving the electrocatalytic activity. With limited content of noble metals, our developed Pt@N-CNTs delivered superior HER performance with an ultralow overpotential of 5.8 mV at 10 mA cm−2 and demonstrated a high mass activity of 12.72 A mgPt−1 at an overpotential of 50 mV as well as excellent stability under harsh acidic conditions. At 500 mA cm−2, Pt@N-CNTs surprisingly exhibited an overpotential of 55.2 mV, outperforming that of commercial 20 wt% Pt/C catalysts (131.5 mV). Importantly, we established a straightforward, scalable, and time-saving microwave reduction strategy, alluding to its promising commercial viability. This work therefore sheds light on the development of high-performance electrocatalysts for hydrogen evolution and water electrolysis.

Hydrogen Generation from NaBH4 Methanolysis with Ru/AC Catalyst Synthesized by Microwave Reduction Method

Hydrogen Generation from NaBH4 Methanolysis with Ru/AC Catalyst Synthesized by Microwave Reduction Method

Rapid synthesis of active Pt single atoms and Ru clusters on carbon black via a highly efficient microwave strategy for the hydrogen evolution reaction in acidic and alkaline media

Using a highly efficient microwave reduction strategy, we successfully designed a novel synergistic electrocatalyst, Pt1Rux@C, which was synthesized in an impressively short time of only 50 seconds.

Rapid microwave reduction of electrochemically-derived graphene oxide for high-crystalline graphene membranes

Rapid microwave reduction of electrochemically-derived graphene oxide for high-crystalline graphene membranes

A techno-economic approach for magnetising roasting of iron ore composite pellet using conventional and hybrid microwave furnace

The present study aims to enhance the iron ore fines through reduction roasting using a muffle and hybrid microwave furnace. The Taguchi statistical design was used to optimise the process variables such as temperature, time, and reductant concentration. The reduction roasting was followed by multi-pass low-mid intensity magnetic separation to treat the low-grade iron ore fines (Fe 44.53%, 40.13% silica). The results showed that the conventional reduction roasting at optimum conditions (800 °C, 60 min, 7% coal) produced a concentrate with 52.6% Fe grade and 77.3% recovery. The microwave roasting produced a concentrate with 53.06% Fe grade and 75.7% recovery at 750 °C, 2 min, and 7% coal as the reductant. The effect of both heating methods on compressive strength (CCS) and surface morphology was also studied. The results indicated that microwave heating resulted in a finer and more porous structure that improved the reducibility and ease of grinding. The techno-economic comparison showed that microwave reduction reduced the processing time by 85% and energy consumption by 73%. The study concludes that microwave heating followed by multi-pass magnetic separation can significantly improve the economic viability of exploiting lean iron ore fines.

Three-Dimensional Graphene Aerogel Supported on Efficient Anode Electrocatalyst for Methanol Electrooxidation in Acid Media

This work attempted to improve the catalytic performance of an anodic catalyst for use in direct methanol fuel cells by coating graphene aerogel (GA) with platinum nanoparticles. A hydrothermal, freeze-drying, and microwave reduction method were used to load Pt–Ru bimetallic nanoparticles onto a graphene aerogel. The mesoporous structure of a graphene aerogel is expected to enhance the mass transfer in an electrode. XRD, Raman spectroscopy, SEM, and TEM described the as-synthesized PtRu/GA. Compared to commercial PtRu/C with the same loading (20%), the electrocatalytic performance of PtRu/GA presents superior stability in the methanol oxidation reaction. Furthermore, PtRu/GA offers an electrochemical surface area of 38.49 m2g−1, with a maximal mass activity/specific activity towards methanol oxidation of 219.78 mAmg−1/0.287 mAcm−2, which is higher than that of commercial PtRu/C, 73.11 mAmg−1/0.187 mAcm−2. Thus, the enhanced electrocatalytic performance of PtRu/GA for methanol oxidation proved that GA has excellent potential to improve the performance of Pt catalysts and tolerance towards CO poisoning.

CFD simulation of a shell and multiple tubes condensing heat exchanger in a modified microwave plant applied for reprocessing End of Life Tires (ELTs)

AbstractThe condensation heat exchanger has a critical role in the microwave reduction process to separate and capture valuable by‐products after the microwave reactor. This study aims to perform a computational fluid dynamics (CFD) simulation of a condenser to assess the heat transfer performance of the heat exchanger comprehensively. The type of heat exchanger used for this study is based upon an existing industrial‐scale condenser taken from a conventional thermal pyrolysis end of tires (ELT) reprocessing plant and repurposed for integration into a 1500 kg/h ELT microwave reduction process. The condenser is a shell‐and‐multiple‐tube heat exchanger in which the syngas passes through the tubes while cold water from a cooling tower is placed inside the shell. After the simulation, the effects of inlet temperatures and mass flow rates of the gas and water are investigated. The results show that the heat transfer rate is 58 kW for the inlet air velocity of 0.25 m/s and increases due to the convective heat transfer by 32% and 55% when the air velocity rises to 0.5 and 1 m/s, respectively, for the inlet gas and water temperatures of 80 and 15°C, respectively. Additionally, because the outlet air temperature and the inlet water temperature are strongly correlated with convective heat transfer, the outlet air temperature is equivalent to 17.2, 22.3, and 29.5°C when the inlet water temperature is 15, 20, and 25°C, respectively.

Stable, Cost‐Effective TiN‐Based Plasmonic Nanocomposites with over 99% Solar Steam Generation Efficiency

AbstractPlasmonic nanoparticles (NPs), such as Au, Ag, and Cu, are considered as promising photothermal materials and attract extensive attention for freshwater production by solar steam generation. However, high cost, narrow absorption range and/or poor stability greatly limit their practical applications. Herein, a high‐efficiency solar energy conversion material consisting of low‐cost non‐metal, extremely thermally‐stable plasmonic TiN NPs and hydrophilic semi‐reduced graphene oxide (semi‐rGO), with broadband solar absorption capability, by a fast in situ microwave reduction method is prepared. The 2D semi‐rGO serves as a support for the loading of plasmonic NPs, and meanwhile accelerates the transport and evaporation of water due to its hydrophilicity. Then, decoration of plasmonic TiN NPs further enhances the solar photon absorption and hydrophilicity while suppressing the heat loss, thanks to the layered structure of TiN/semi‐rGO, improving overall solar energy utilization. Owing to the enhanced absorption and unique layered nanostructure with strong interfacial interaction, the optimal sample of TiN/semi‐rGO‐25% absorber achieves a high and stable water evaporation rate of ≈1.76 kg m−2 h−1 with an energy efficiency as high as 99.1% under 1 sun illumination. Furthermore, this plasmonic TiN/semi‐rGO absorber is capable of producing high‐quality freshwater from sustainable seawater desalination and wastewater purification processes.

Ultra-thin freestanding graphene films for efficient thermal insulation and electromagnetic interference shielding.

The preparation of freestanding graphene films by convenient and environmentally friendly preparation methods is still the focus of attention in various industrial fields. Here, we first select electrical conductivity, yield and defectivity as evaluation indicators and systematically explore the factors affecting the preparation of high-performance graphene by electrochemical exfoliation, then further post-process it under volume-limited conditions by microwave reduction. Finally, we obtained a self-supporting graphene film with an irregular interlayer structure but excellent performance. It is found that the electrolyte is ammonium sulfate, the concentration is 0.2 M, the voltage is 8 V, and the pH is 11, which were the optimal conditions for preparing low-oxidation graphene. The square resistance of the EG was 1.6 Ω sq-1, and the yield could be 65%. In addition, electrical conductivity and joule heat were significantly improved after microwave post-processing, especially its electromagnetic shielding performance with a shielding coefficient of 53 dB able to be achieved. At the same time, the thermal conductivity is as low as 0.05 W m-1 K-1. The mechanism for the improvement of electromagnetic shielding performance is that (1) microwave reduction effectively enhances the conductivity of the graphene sheet overlapping network; (2) the gas generated by the instantaneous high temperature causes a large number of void structures between the graphene layers, and the irregular interlayer stacking structure makes the reflective surface more disordered, thereby prolonging the reflection path of electromagnetic waves among layers. In summary, this simple and environmentally friendly preparation strategy has good practical application prospects for graphene film products in flexible wearables, intelligent electronic devices, and electromagnetic wave protection.

Strategically improving electrical conductivity of reduced graphene oxide through a series of reduction processes

Current work aims at producing reduced graphene oxide(rGO) with highest possible conductivity, starting with graphene oxide(GO) produced by electrochemical exfoliation(ECE) of graphite rod salvaged from C-type primary batteries. Six single-step reduction process were used to reduce GO in the first stage. Following that, most effective three reduction methods, namely water-based reduction(W), hydrothermal reduction(H), and microwave reduction(MW), were used in two combinations (W-H-MW and W-MW-H). The conductivity of rGO(W-H-MW) and rGO(W-MW-H) is 43.78Sm−1 and 28.33Sm−1 respectively with rGO(W-H-MW) having highest conductivity of all selected reduction methods. It is also found that sequence of reduction processes has a big impact on the final product's conductivity, ID/IG ratio, and XRD peak intensity. Characterization by XRD, XPS, TEM, FEG-SEM, FTIR, Raman etc. is used to discuss the findings. Chemical structure, morphology and specific surface area of rGO(W-H-MW) are compared to those of GO and their influence on bulk conductivity of rGO’s are discussed.

Confine activation peroxymonosulfate by surface oxygen vacancies of BiO1−xCl to boost its utilization rate

Hinder self-quenching of active species and augment peroxymonosulfate (PMS) utilization rate is a challenging for advanced oxidation processes (AOPs). Therefore, BiO1−xCl with appropriate surface oxygen vacancies (SOVs) was fabricated by microwave reduction method. Experimental results reflect that BOC-2 can remediate 79.4 % doxycycline hydrochloride (50 mg L−1) in 1.75 h under the constantly yield active species population (ASP). Simultaneously, theoretical calculation discerns that reasonable SOVs can increase PMS adsorption energy, change PMS adsorption configuration and peroxy bond length. Thus, photo-induced electrons can fast ferry to the confined PMS via electron shuttles formed by SOVs to activate PMS. Ultimately, ASP self-quenching was halted and PMS utilization rate was ameliorated. Furthermore, the structure–activity relationship between SOVs and PMS utilization rate was established and the environmental toxicity of the intermediates was evaluated. This work offers an ingenious strategy to steer PMS activating behavior and boost its utilization rate by defect engineering.

Electrical, luminescence, and microwave-assisted reduction behaviour of alkali vs. alkaline earth metal ion-modified graphene oxide membranes

Ions are often introduced into graphene oxide (GO) membranes during their preparation and application, which may lead to changes in their properties. In this study, GO membranes regulated by ions were prepared by incorporating alkali and alkaline earth metals. We found that the introduction of different ions led to opposite changes in the electrical properties of the reduced GO (RGO) membranes. The introduction of alkali metal ions improves their conductivity, whereas the introduction of alkaline earth metal ions results in a decrease in their conductivity. Furthermore, we found that the introduction of ions resulted in significantly different changes in the luminescence spectra, which could be used to detect alkali and alkaline earth metal ions. In addition, the introduction of alkali metal and alkaline earth metal ions resulted in significantly different changes in the luminescence spectra and microwave reduction effect of the RGO membranes. The introduction of alkaline earth metal ions was more helpful for the removal of oxygen-containing groups and the restoration of the graphene lattice structure when exposed to microwave irradiation. These results suggest that the properties of GO membranes can be regulated by regulating the introduction of ions, and these findings have potentially important applications in the preparation and application of GO membranes and ion detection.

Carbon quantum dots embedded trimetallic oxide: Characterization and photocatalytic degradation of Ofloxacin

The presence of highly toxic pharmaceutical effluents in the water system has emerged the need for the examination of various methods that could be used for their removal. Considering this, in the present study, we have designed a highly visible- light active trimetallic oxide nanocomposite, CQDs@CoO/La2O3/NiO TONCs using facile microwave reduction technique. Its photocatalytic efficiency was tested for the degradation of highly noxious ofloxacin (OFL) antibiotic from the aqueous solution. Maximum degradation rate of 93.8% was obtained within 75 min with 20 mg of photocatalyst dose and 20 mg/L of initial OFL concentration. The addition of CQDs to the trimetallic oxide nanoparticles helped in enhancing the light- harvesting ability of the composite and shifting it to the visible- region. Major reactive radical species involved in the OFL degradation were found to be •OH and •O2− radicals. In addition, a probable degradation mechanism was also established based the scavenging and band gap studies. The charge transfer study indicated the formation of dual Z- scheme between the 3 constituting units that helped immensely in reducing the charge recombination rate and improving the charge transfer rate.

Design of Au Surface‐doped PtFe Catalyst to Modulate Oxygen Binding Energy for Highly Efficient Oxygen Reduction Reaction

AbstractAs ideal cathode catalysts for proton exchange membrane fuel cells (PEMFCs), the oxygen reduction reaction (ORR) activity and durability of Pt‐based alloys can be improved further. This study presents the catalyst with Au doping on the surface of an ordered PtFe alloy (Au‐PtFe/C) utilizing a synergistic process of microwave reduction and chemical replacement, as well as the reorganization of a Pt‐rich surface using acid etching and high temperature annealing. Physical characterization indicated that the oxygen binding energy on the surface of Au‐PtFe/C was more effective at promoting the ORR reaction than commercial Pt/C, which contributes significantly to its enhanced activity. Further electrochemical tests revealed that the Au‐PtFe/C catalyst exposes abundant active sites for ORR, with mass and specific activity up to 12 and 8 times that of commercial Pt/C, respectively. Additionally, the catalyst demonstrated remarkable durability following 10,000 cycles of accelerated durability tests (ADT) in acidic circumstances. In PEMFC test, the single cell with an Au‐PtFe/C cathode also performed admirably when compared with commercial Pt/C. Owing to its facile synthesis, low cost, and exceptional performance, this bimetal‐doped ordered Pt‐based alloy has the capability to be a promising component in fuel cells commercialization.

Reduction mechanism and optimization of prepare metallic antimony through direct microwave carbothermal reduction of antimony oxide concentrate

In this work, a clean microwave carbothermal reduction of Sb2O3 mineral to prepare metallic antimony ingot is proposed. Response surface methodology was used to optimize condition for microwave carbothermal reduction of Sb2O3. The roasting temperature, roasting duration, carbon powder ratio and NaCl addition ratio was collected to carry out a four-factor and three-level experiment. In the optimized conditions, a >77.0% yield of antimony ingot can be obtained under roasting temperature of 730 °C, roasting time of 60min, carbon powder ratio of 0.3, NaCl addition amount of 4%. More than 99% Sb content of metallic Sb ingot is obtained in the microwave field. The mechanism of microwave carbothermal reduction of Sb2O3 was investigated by XRD, SEM-EDS and Mapping analysis, the results show that the microwave reduction process is divided into three stages based on the melting point of antimony, namely, 25 °C–400 °C, 400 °C–630 °C, and above 630 °C, which differ in terms of phase transformation. In the microwave field, the reduction of Sb2O3 to Sb particles can be completed within 15 min. Microwave metallurgical technology is conducive to the sustainable development of antimony metallurgy, and also provides a clean technology for the metallurgy industry.

Systematic Engineering on Ni-Based Nanocatalysts Effectively Promote Hydrogen Evolution Reaction.

Designing a synthesis of ultra-small Ni-based nanomaterials with high intrinsic activity and stability in alkaline hydrogen evolution reaction (HER) is a major challenge. Herein, a series of noble metal doped ultra-small size (4nm) M-Ni/NiO nanoparticles supported on CNT are rationally designed by a solvent-free microwave reduction method that is fast (60s), simple, includes no surfactants, extensive (>1g), and has high yield (82.7%). The Ir-Ni/NiO@CNT has superior performance with a low overpotential of 24.6mV at 10mAcm-2 . In addition, the turnover frequency (TOF) value up to 2.51s-1 and the exchange current density reaches 4.34mAcm-2 , indicating that the catalyst has better intrinsic catalytic activity. It is further proved by density functional theory (DFT) that the NiO surface is conducive to the adsorption of OH* in the Volmer step while the Ni is inclined to adsorb H*, which synergistically promotes the water-splitting reaction, thereby increasing the catalytic rate of HER. It is believed that this work will provide valuable contributions and inspirations toward the large-scale production of high-performance Ni-based electrocatalysts for HER.

Effective microwave-hydrothermal reduction of graphene oxide for efficient energy storage

Reduced graphene oxide (rGO) is an important member of the family of graphene-based nanomaterials. Conventional strategies for preparing rGO include chemical, thermal, photo, laser, hydrothermal, and microwave reduction. Here we report on a rapid microwave-hydrothermal (MH) method for the effective production of pure rGO (denoted as M-rGO) without using any reducing agents. The MH process was optimized in terms of temperature and duration to tune the structure and composition of the formed M-rGO to attain high specific capacitance for energy storage. The M-rGO possessed a three-dimensional (3D) interconnected porous structure with the C/O ratio of 9:5. The 3D interconnected structure of M-rGO not only increased the active surface area and enhanced the electrical double layer capacitance, but also improved its stability. Retaining the appropriate proportion of active functional groups also made a notable contribution of pseudocapacitance. The synthesized M-rGO exhibited a much higher capacitance of 298 F g−1 (1 A g−1, 0.5 M H2SO4) for a three-electrode system and 263 F g−1 (0.5 A g−1, 20% H2SO4- PVA gel) for a two-electrode system, as well as much better capacitance retention and cyclability, in contrast to conventional chemically reduced graphene oxide (C-rGO) and thermally reduced graphene oxide (T-rGO). Moreover, the energy density of the M-rGO was very high (36.6 Wh kg−1) at a power density of 0.5 kW kg−1. This first-rate energy storage performance of the M-rGO can be attributed to its highly active surface area, appropriate carbon-oxygen ratio, porous structure, and interconnected 3D morphology.

Myrica Rubra-like MnFe2O4 Microsphere: A high efficiency microwave reduction catalyst for Cr(VI) removal from water

Aqueous hexavalent chromium (Cr(VI)) is easy to enter the biological system, causing serious threat to human and aquatic environment health. In this paper, a myrica rubra-like MnFe2O4 catalyst with average diameter of 200–300 nm were prepared by a simple solvothermal method. Benefiting from the knobby surface and the considerable microwave absorption ability, the as-prepared MnFe2O4 microsphere exhibited excellent microwave catalytic reduction ability for Cr(VI) in water, and the catalysts dosage, initial Cr(VI) concentration, solution pH value and temperature showed crucial effect on the catalytic reduction process. When the pH value of the solution was 2, the amount of catalysts was 2 g/L, and the temperature was 100 ℃, the myrica rubra-like MnFe2O4 catalysts could remove as high as 96% of Cr(VI) from a 50 mg/L aqueous solution only after 10 min microwave irradiation, which is much higher than the commercial one. The enhanced catalysis performance could be ascribed to the surface “knob” with a size of ∼ 17 nm, which accelerated the generation of e– under microwave irradiation, finally promoted the catalytic reduction performance. The microwave catalytic reduction strategy is a hopeful alternative for ultrafast reduction of Cr(VI) in sewage with high efficiency.