A review of the microwave-assisted synthesis of carbon nanomaterials, metal oxides/hydroxides and their composites for energy storage applications

Synthesis methods, structure, and recent trends of ZIF-8-based materials in the biomedical field

Zeolitic imidazolate framework-8 (ZIF-8) is a highly porous material with remarkable structural properties and high drug-loading capacity, and hence this material presents as an exceptional candidate for advanced drug delivery systems. Herein, we comprehensively review the recent developments in ZIF-8 synthesis techniques and critically discuss innovative approaches such as the use of green solvents and advanced methods such as microwave- and ultrasound-assisted syntheses. The multifunctional applications of ZIF-8-based biomaterials in biomedical engineering are critically explored with their pivotal roles in antibacterial and anticancer therapies, drug delivery systems, bone tissue engineering, and diagnostic platforms such as biosensing and bioimaging. The present review also clarifies some innovations of ZIF-8-based materials in pH-sensitive and glucose-responsive drug delivery systems and scaffolds for bone regeneration. Despite these promising advancements, we analyze critical concerns, such as the release of Zn(ii) ions, potential cytotoxicity, and biocompatibility challenges, which remain significant hurdles to the broader adoption of ZIF-8. Addressing these outlined challenges may be necessary in realizing the potential of ZIF-8 in biomedical applications.

A Systematic Review of Nanoparticle-Mediated Ferroptosis in Glioma Therapy

Glioma, a highly malignant central nervous system tumor, exhibits aggressive invasiveness, extensive infiltration, and poor prognosis. Conventional treatments such as surgery, radiotherapy, and chemotherapy are hindered by limitations including the inability to overcome the blood-brain barrier (BBB), drug resistance, and high recurrence rates. Ferroptosis induced by nanoparticle-based systems offers an innovative strategy for glioma therapy by efficiently traversing the BBB, precisely delivering ferroptosis inducers, enhancing tumor accumulation, and enabling stimuli-responsive drug release. These features collectively improve the induction efficiency of ferroptosis in glioma cells. Various nanoplatforms, including inorganic nanoparticles, biomimetic carriers, and polymer-based systems, have demonstrated potential in crossing the BBB, inducing ferroptosis, and suppressing glioma progression. These systems enhance reactive oxygen species generation, deplete glutathione, and disrupt tumor microenvironment defense mechanisms, achieving synergistic therapeutic effects. The integration of ferroptosis with nanotechnology is emerging as a promising, non-invasive strategy for the treatment of gliomas, offering substantial therapeutic potential.

Structural control over single-crystalline oxides for heterogeneous catalysis

Oxides are integral to heterogeneous catalysis, serving critical roles such as catalyst supports, active materials and electrodes. A highly ordered subset, single-crystalline oxides, have traditionally been used as model catalyst supports in fundamental surface science studies. However, advancements in bulk synthesis have rendered their general use more feasible for real-world applications. In this review, we explore the efficiency of single-crystalline oxides as active metals and supports across a wide range of heterogeneous processes, often performing exceptionally well. Beginning with synthetic methods, we discuss the advantages of single-crystalline oxides in thermo-, electro- and photocatalysis. Previously held conventions about catalytic activity, deactivation and surface-adsorbate interactions are re-evaluated by understanding how these ordered materials behave during the respective reactions. Last, we assess advances in characterization techniques and their impact on designing the next generation of catalysts based on single-crystalline oxides.

From 0D to 2D: microwave-assisted synthesis of electrically conductive metal-organic frameworks with controlled morphologies

Morphology control of electrically conductive metal-organic frameworks (EC-MOFs) can be a powerful means to tune their surface area and carrier transport pathways, particularly beneficial for energy conversion and storage. However, controlling EC-MOFs' morphology is underexplored due to the uncontrollable crystal nucleation and rapid growth kinetics. This work introduces a microwave-assisted strategy to readily synthesize Cu-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with controlled morphologies. We controlled solvent compositions to facilitate particles' directional growth to 1D and 2D crystals. Meanwhile, we found that ultrasonication can manipulate crystal seeding, yielding 0D spherical Cu-HHTP crystals. Electronic conductivity measurements suggest that the isotropic nature of the 0D crystals allows a conductivity of 7.34 × 10-1 S cm-1, much higher than 1D and 2D counterparts. Additionally, the controlled 0D morphology enhanced the material's capacitance and effective surface area and significantly improved its photocurrent response. These findings underscore the pivotal impact of controlled morphology in optimizing EC-MOFs' physicochemical properties.

Microwave-Assisted Synthesis of Carbon Nanospheres and Their Application as Plugging Agents for Oil-Based Drilling Fluids

Wellbore instability caused by the invasion of drilling fluids into formations remains a significant challenge in the application of oil-based drilling fluids (ODFs). In this study, carbon nanospheres (CNSs) were synthesized using glucose as the carbon source through a microwave-assisted method. The effects of the reaction temperature, carbon source concentration, and reaction time on the particle size of CNSs were systematically investigated. The results revealed that under optimal conditions, CNSs with an average particle size of 670 nm were successfully synthesized, exhibiting high sphericity and excellent dispersibility. CNSs demonstrated stable dispersion in mineral oil when lecithin was used as a dispersant. The plugging performance of CNSs in ODFs was evaluated through low-pressure filtration and high-temperature, high-pressure (HTHP) filtration tests. After aging at 180 °C for 16 h, the addition of 2% CNSs reduced the filtration volume from 10.6 mL to 2.5 mL on standard filter paper (average pore size: 3 μm) and from 8.5 mL to 1.6 mL on microporous membranes (average pore size: 0.5 μm). Additionally, the HTHP filtration volume decreased from 73 mL to 18 mL, and the permeability of the filter cake formed during HTHP filtration was reduced from 26.5 × 10-3 mD to 1.2 × 10-3 mD. Furthermore, CNSs improved the rheological properties and emulsion stability of ODFs. With excellent compatibility and applicability, CNSs offer a promising solution for enhancing the performance of oil-based drilling fluids.

Strategies in photochemical alcohol oxidation on noble-metal free nanomaterials as heterogeneous catalysts

Using light absorbing semiconductors to harvest solar energy has long been considered as a promising approach for driving chemical reactions. Photochemical oxidation of alcohols catalyzed by noble-metal free nanomaterials is particularly attractive due to the bio-derivable nature of the substrate and the wide availability of such catalysts. Here, a number of strategies that could facilitate the progress are discussed, where it is concluded that the photochemical alcohol oxidation process can benefit from both mechanistic optimization of the electron-transfer steps and structural engineering of the light-absorbing nanomaterials.

Carbon carrier-based rapid Joule heating technology: a review on the preparation and applications of functional nanomaterials

Compared to conventional heating techniques, the carbon carrier-based rapid Joule heating (CJH) method is a new class of technologies that offer significantly higher heating rates and ultra-high temperatures. Over the past few decades, CJH technology has spawned several techniques with similar principles for different application scenarios, including ultra-fast high temperature sintering (UHS), carbon thermal shock (CTS), and flash Joule heating (FJH), which have been widely used in material preparation research studies. Functional nanomaterials are a popular direction of research today, mainly including nanometallic materials, nanosilica materials, nanoceramic materials and nanocarbon materials. These materials exhibit unique physical, chemical, and biological properties, including a high specific surface area, strength, thermal stability, and biocompatibility, making them ideal for diverse applications across various fields. The CJH method is a remarkable approach to producing functional nanomaterials that has attracted attention for its significant advantages. This paper aims to delve into the fundamental principles of CJH and elucidate the efficient preparation of functional nanomaterials with superior properties using this technique. The paper is organized into three sections, each dedicated to introducing the process and characteristics of CJH technology for the preparation of three distinct material types: carbon-based nanomaterials, inorganic non-metallic materials, and metallic materials. We discuss the distinctions and merits of the CJH method compared to alternative techniques in the preparation of these materials, along with a thorough examination of their properties. Furthermore, the potential applications of these materials are highlighted. In conclusion, this paper concludes with a discussion on the future research trends and development prospects of CJH technology.

Microwave-assisted synthesis of polyoxometalate-Dy2O3 monolayer nanosheets and nanotubes

Two-dimensional (2D) materials have shown unique chemical and physical properties; however, their synthesis is highly dependent on the layered structure of building blocks. Herein, we developed monolayer Dy2O3-phosphomolybdic acid (PMA) nanosheets and nanotubes based on microwave synthesis. Microwave-assisted synthesis with high-energy input gives a faster and dynamically driven growth of nanomaterials, resulting in high-purity nanostructures with a narrow size distribution. The reaction times of the nanosheets and nanotubes under microwave synthesis are significantly reduced compared with oven-synthesis. Dy2O3-PMA nanosheets and nanotubes exhibit enhanced activity and stability in photoconductance, with higher sensitivities (0.308 μA cm-2 for nanosheets and 0.271 μA cm-2 for nanotubes) compared to the individual PMA (0.12 μA cm-2) and Dy2O3 (0.025 μA cm-2) building blocks. This work demonstrates the promising application potential of microwave-synthesized 2D heterostructures in superconductors and photoelectronic devices.

Micelle-Assisted Confined Coordination Spaces for Benzimidazole: Enhanced Electrochemiluminescence for Nitrite Determination

Selective and sensitive detection of nitrite has important medical and biological implications. In the present work, to obtain an enhanced electrochemiluminescence (ECL) determination of nitrite, a novel nano-ECL emitter CoBIM/cetyltrimethylammonium bromide (CTAB) was prepared via a micelle-assisted, energy-saving, and ecofriendly method based on benzimidazole (BIM) and CTAB. Unlike conventional micelle assistance, the deprotonated BIM (BIM-) preferential placement was in the palisade layer of cationic CTAB-based micelles. Enriching the original CTAB micelle with BIM- disrupted its stability and resulted in the formation of considerably smaller BIM/CTAB-based micelles, providing a confined coordination environment for BIM- and Co2+. As a result, the growth of CoBIM/CTAB was also limited. Owing to the unusual nitration reaction between BIM and nitrite, the prepared CoBIM/CTAB was successfully applied as a novel ECL probe for the detection of nitrite with a wide linear range of 1-1500 μM and a low detection limit of 0.67 μM. This work also provides a promising ECL platform for ultrasensitive monitoring of nitrite and it was applied with sausages and pickled vegetables.

A Review of Transition Metal Boride, Carbide, Pnictide, and Chalcogenide Water Oxidation Electrocatalysts

Transition metal borides, carbides, pnictides, and chalcogenides (X-ides) have emerged as a class of materials for the oxygen evolution reaction (OER). Because of their high earth abundance, electrical conductivity, and OER performance, these electrocatalysts have the potential to enable the practical application of green energy conversion and storage. Under OER potentials, X-ide electrocatalysts demonstrate various degrees of oxidation resistance due to their differences in chemical composition, crystal structure, and morphology. Depending on their resistance to oxidation, these catalysts will fall into one of three post-OER electrocatalyst categories: fully oxidized oxide/(oxy)hydroxide material, partially oxidized core@shell structure, and unoxidized material. In the past ten years (from 2013 to 2022), over 890 peer-reviewed research papers have focused on X-ide OER electrocatalysts. Previous review papers have provided limited conclusions and have omitted the significance of "catalytically active sites/species/phases" in X-ide OER electrocatalysts. In this review, a comprehensive summary of (i) experimental parameters (e.g., substrates, electrocatalyst loading amounts, geometric overpotentials, Tafel slopes, etc.) and (ii) electrochemical stability tests and post-analyses in X-ide OER electrocatalyst publications from 2013 to 2022 is provided. Both mono and polyanion X-ides are discussed and classified with respect to their material transformation during the OER. Special analytical techniques employed to study X-ide reconstruction are also evaluated. Additionally, future challenges and questions yet to be answered are provided in each section. This review aims to provide researchers with a toolkit to approach X-ide OER electrocatalyst research and to showcase necessary avenues for future investigation.

Orange-peel derived carbon-loaded low content ruthenium nanoparticles as ultra-high performance alkaline water HER electrocatalysts

Carbon materials have a very wide range of applications in the field of electrocatalysis, both as catalyst bodies and as excellent supports for catalysts. In this work, we obtained a graphitic-like orange-peel derived carbon (OPC) material through pre-carbonization and KOH activation strategies using discarded orange-peel as a raw material. OPC has good graphitization characteristics and a few-layer structure, making it very suitable as a support for nanoparticle catalysts. In order to compare the performance of OPC, we used commercial graphene as the benchmark, made two carbon materials uniformly loaded with ruthenium nanoparticles under the same conditions, and obtained two HER catalysts (Ru/OPC and Ru/rGO). The results indicate that Ru/OPC has excellent HER catalytic performance under alkaline conditions, not only superior to Ru/rGO, but also surpassing commercial Pt/C. In 1 M KOH; the overpotential of Ru/OPC is only 3 mV at -10 mA cm-2, greatly exceeding those of Ru/rGO (100 mV) and Pt/C (31 mV). Under high current density (j), the performance of Ru/OPC is even better; the overpotential is 79 mV and 136 mV at -100 mA cm-2 and -200 mA cm-2, respectively. More importantly, Ru/OPC also has a very high TOF and long-term stability, with a TOF of up to 10.62 H2 s-1 at an overpotential of 100 mV and almost no attenuation after 72 h of operation at -50 mA cm-2. Ru/OPC also exhibits good catalytic performance under acidic conditions, significantly superior to that of Ru/rGO. For Ru/OPC, the overpotential is 86 mV, 167 mV and 214 mV at -10 mA cm-2, -100 mA cm-2 and -200 mA cm-2, respectively. Under the same conditions, the overpotential of Ru/rGO is 143 mV, 253 mV and 306 mV at -10 mA cm-2, -100 mA cm-2 and -200 mA cm-2, respectively.

Carbon Dots-Types, Obtaining and Application in Biotechnology and Food Technology

Materials with a "nano" structure are increasingly used in medicine and biotechnology as drug delivery systems, bioimaging agents or biosensors in the monitoring of toxic substances, heavy metals and environmental variations. Furthermore, in the food industry, they have found applications as detectors of food adulteration, microbial contamination and even in packaging for monitoring product freshness. Carbon dots (CDs) as materials with broad as well as unprecedented possibilities could revolutionize the economy, if only their synthesis was based on low-cost natural sources. So far, a number of studies point to the positive possibilities of obtaining CDs from natural sources. This review describes the types of carbon dots and the most important methods of obtaining them. It also focuses on presenting the potential application of carbon dots in biotechnology and food technology.

Synthesis and Characterization of ZnO-Nanostructured Particles Produced by Solar Ablation

Nowadays, nanotechnology offers opportunities to create new features and functions of emerging materials. Correlation studies of nanostructured materials' development processes with morphology, structure, and properties represent one of the most important topics today due to potential applications in all fields: chemistry, mechanics, electronics, optics, medicine, food, or defense. Our research was motivated by the fact that in the nanometric domain, the crystalline structure and morphology are determined by the elaboration mechanism. The objective of this paper is to provide an introduction to the fundamentals of nanotechnology and nanopowder production using the sun's energy. Solar energy, as part of renewable energy sources, is one of the sources that remain to be exploited in the future. The basic principle involved in the production of nanopowders consists of the use of a solar energy reactor concentrated on sintered targets made of commercial micropowders. As part of our study, for the first time, we report the solar ablation synthesis and characterization of Ni-doped ZnO performed in the CNRS-PROMES laboratory, UPR 8521, a member of the CNRS (French National Centre for Scientific Research). Also, we study the effect of the elaboration method on structural and morphological characteristics of pure and doped ZnO nanoparticles determined by XRD, SEM, and UV-Vis.

Rapid Microwave-Assisted Synthesis of ZnIn2S4 Nanosheets for Highly Efficient Photocatalytic Hydrogen Production

In this study, a facile and rapid microwave-assisted synthesis method was used to synthesize In₂S₃ nanosheets, ZnS nanosheets, and ZnIn₂S₄ nanosheets with sulfur vacancies. The two-dimensional semiconductor photocatalysts of ZnIn₂S₄ nanosheets were characterized by XRD, FESEM, BET, TEM, XPS, UV-vis diffuse reflectance, and PL spectroscopy. The ZnIn₂S₄ with sulfur vacancies exhibited an evident energy bandgap value of 2.82 eV, as determined by UV-visible diffuse reflectance spectroscopy, and its energy band diagram was obtained through the combination of XPS and energy bandgap values. ZnIn₂S₄ nanosheets exhibited about 33.3 and 16.6 times higher photocatalytic hydrogen production than In₂S₃ nanosheets and ZnS nanosheets, respectively, under visible-light irradiation. Various factors, including materials, sacrificial reagents, and pH values, were used to evaluate the influence of ZnIn₂S₄ nanosheets on photocatalytic hydrogen production. In addition, the ZnIn₂S₄ nanosheets revealed the highest photocatalytic hydrogen production from seawater, which was about 209.4 and 106.7 times higher than that of In₂S₃ nanosheets and ZnS nanosheets, respectively. The presence of sulfur vacancies in ZnIn₂S₄ nanosheets offers promising opportunities for developing highly efficient and stable photocatalysts for photocatalytic hydrogen production from seawater under visible-light irradiation.

Regulating Surface Charge by Embedding Ru Nanoparticles over 2D Hydroxides toward Water Oxidation

Exploring highly active and earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is considered one of the prime prerequisites for generating green hydrogen. Herein, a competent microwave-assisted decoration of Ru nanoparticles (NPs) over the bimetallic layered double hydroxide (LDH) material is proposed. The same has been used as an OER catalyst in a 1 M KOH solution. The catalyst shows an interesting Ru NP loading dependency toward the OER, and a concentration-dependent volcanic relationship between electronic charge and thermoneutral current densities has been observed. This volcanic relation shows that with an optimum concentration of Ru NPs, the catalyst could effectively catalyze the OER by obeying the Sabatier principle of ion adsorption. The optimized Ru@CoFe-LDH(3%) demands an overpotential value of only 249 mV to drive a current density value of 10 mA/cm² with the highest TOF value of 14.4 s^-1 as compared to similar CoFe-LDH-based materials. In situ impedance experiments and DFT studies demonstrated that incorporating the Ru NPs boosts the intrinsic OER activity of the CoFe-LDH on account of sufficient activated redox reactivities for both Co and lattice oxygen of the CoFe-LDH. As a result, compared with the pristine CoFe-LDH, the current density of Ru@CoFe-LDH(3%) at 1.55 V vs RHE normalized by ECSA increased by 86.58%. First-principles DFT analysis shows that the optimized Ru@CoFe-LDH(3%) possesses a lower d-band center that indicates weaker and more optimal binding characteristics for OER intermediates, improving the overall OER performance. Overall, this report displays an excellent correlation between the decorated concentration of NPs over the LDH surface which can tune the OER activity as verified by both experimental and theoretical calculations.

Microwave-Assisted Rapid Substitution of Ti for Zr to Produce Bimetallic (Zr/Ti)UiO-66-NH2 with Congenetic "Shell-Core" Structure for Enhancing Photocatalytic Removal of Nitric Oxide

Efficient nitric oxide (NO) removal without nitrogen dioxide (NO₂ ) emission is desired for the control of air pollution. Herein, a series of (Zr/Ti)UiO-66-NH₂ with congenetic shell-core structure, denoted as Ti-UION, are rapidly synthesized by microwave-assisted post-synthetic modification for NO removal. The optimal Ti-UION (i.e., 2.5Ti-UION) exhibits the highest activity of 80.74% without NO₂ emission with moisture, which is 21.65% greater than that of the UiO-66-NH₂ . The NO removal efficiency of 2.5Ti-UION further increases to 95.92% without photocatalyst deactivation under an anhydrous condition. This is because selectively produced NO₂ in photocatalysis is completely adsorbed into micropores, refreshing active sites for subsequent reaction. In addition, the enhanced photocatalytic activity after Ti substitution is due to the presence of Ti electron acceptor, the potential difference between the shell and core of Ti-UION crystal, and the high conductivity of TiO units. Additionally, the improved adsorption of gas molecules not only favors NO oxidation, but also avoids the emission of NO₂ . This work provides a feasible strategy for rapid metal substitution in metal-organic frameworks and insights into enhanced NO photodegradation.

A Facile Microwave Hydrothermal Synthesis of ZnFe2O4/rGO Nanocomposites for Supercapacitor Electrodes

As a typical binary transition metal oxide, ZnFe₂O₄ has attracted considerable attention for supercapacitor electrodes due to its high theoretical specific capacitance. However, the reported synthesis processes of ZnFe₂O₄ are complicated and ZnFe₂O₄ nanoparticles are easily agglomerated, leading to poor cycle life and unfavorable capacity. Herein, a facile microwave hydrothermal process was used to prepare ZnFe₂O₄/reduced graphene oxide (rGO) nanocomposites in this work. The influence of rGO content on the morphology, structure, and electrochemical performance of ZnFe₂O₄/rGO nanocomposites was systematically investigated. Due to the uniform distribution of ZnFe₂O₄ nanoparticles on the rGO surface and the high specific surface area and rich pore structures, the as-prepared ZnFe₂O₄/rGO electrode with 44.3 wt.% rGO content exhibits a high specific capacitance of 628 F g^-1 and long cycle life of 89% retention over 2500 cycles at 1 A g^-1. This work provides a new process for synthesizing binary transition metal oxide and developing a new strategy for realizing high-performance composites for supercapacitor electrodes.

Tuning oxygen-containing functional groups of graphene for supercapacitors with high stability

To investigate the relationship between the oxygen-containing functional groups of graphene and the stability of supercapacitors, reduced graphene oxide (rGO) containing different oxygenic functional groups was prepared by varying the reduction time of GO using hydrazine as the reducing agent. TEM, XRD, Raman, and XPS characterizations revealed that, as the reduction time increased, the sp² structure in the rGO sheet was restored and the obtained rGO had good crystallinity accompanied by removal of the oxygenic functional groups. The analysis of the content of the different functional groups also suggested that the reduction rate of the oxygenic functional group was C-O > C[double bond, length as m-dash]O > O-C[double bond, length as m-dash]O. The supercapacitive performance of rGO showed that the oxygenic functional groups contributed to some pseudocapacitance and resulted in a larger specific capacitance. At the same time, however, it is also accompanied by poorer rate performance and durability, which will be improved by removing the oxygenic functional groups by extending the reduction time. With an optimized reaction condition of a reduction time of 24 h, the obtained rGO exhibited excellent stability in floating tests at 3.0 V and 45 °C for 60 days. These findings pave the way for the development of high quality graphene materials for cost-effective and practical graphene supercapacitors.

Effect of Surface Treatment on Performance and Internal Stacking Mode of Electrohydrodynamic Printed Graphene and Its Microsupercapacitor

Microelectronic devices are developing rapidly in portability, wearability, and implantability. This puts forward an urgent requirement for the delicate deposition process of materials. Electrohydrodynamic printing has attracted academic and industrial attention in preparing ultrahigh-density microelectronic devices as a new noncontact, direct graphic, and low-loss thin film deposition process. In this work, a printed graphene with narrow line width is realized by combining the electrohydrodynamic printing and surface treatment. The line width of printed graphene on the hydrophobic treatment surface reduced from 80 to 28 μm. The resistivity decreased from 0.949 to 0.263 Ω·mm. Unexpectedly, hydrophobic treatment can effectively induce random stacking of electrohydrodynamic printed graphene, which avoids parallel stacking and agglomeration of graphene sheets. The performance of printed graphene is thus effectively improved. After optimization, a graphene planar supercapacitor with a printed line width of 28 μm is successfully obtained. Its capacitance can reach 5.39 mF/cm² at 50 mV/s, which is twice higher than that of the untreated devices. The device maintains 84.7% capacitance after 5000 cycles. This work provides a reference for preparing microelectronic devices by ultrahigh precision printing and a new direction for optimizing two-dimensional material properties through stacking adjustment.

An optical and electrochemical sensor based on L-arginine functionalized reduced graphene oxide

The electrochemical and photochemical properties of graphene derivatives could be significantly improved by modifications in the chemical structure. Herein, reduced graphene oxide (RGO) was functionalized with L-arginine (L-Arg) by an amidation reaction between the support and amino acid. Deposition of a powerful ligand, L-Arg, on the optically active support generated an effective optical chemosensor for the determination of Cd(II), Co(II), Pb(II), and Cu(II). In addition, L-Arg-RGO was used as an electrode modifier to fabricate L-Arg-RGO modified glassy-carbon electrode (L-Arg-RGO/GCE) to be employed in the selective detection of Pb(II) ions by differential pulse anodic stripping voltammetry (DP-ASV). L-Arg-RGO/GCE afforded better results than the bare GCE, RGO/GCE, and L-Arg functionalized graphene quantum dot modified GCE. The nanostructure of RGO, modification by L-Arg, and homogeneous immobilization of resultant nanoparticles at the electrode surface are the reasons for outstanding results. The proposed electrochemical sensor has a wide linear range with a limit of detection equal to 0.06 nM, leading to the easy detection of Pb(II) in the presence of other cations. This research highlighted that RGO as a promising support of optical, and electrochemical sensors could be used in the selective, and sensitive determination of transition metals depends on the nature of the modifier. Moreover, L-Arg as an abundant amino acid deserves to perch on the support for optical, and electrochemical determination of transition metals.

Secondary-Heteroatom-Doping-Derived Synthesis of N, S Co-Doped Graphene Nanoribbons for Enhanced Oxygen Reduction Activity

The rareness and weak durability of Pt-based electrocatalysts for oxygen reduction reactions (ORRs) have hindered the large-scale application of fuel cells. Here, we developed an efficient metal-free catalyst consisting of N, S co-doped graphene nanoribbons (N, S-GNR-2s) for ORRs. GNRs were firstly synthesized via the chemical unzipping of carbon nanotubes, and then N, S co-doping was conducted using urea as the primary and sulfourea as the secondary heteroatom sources. The successful incorporation of nitrogen and sulfur was confirmed by elemental mapping analysis as well as X-ray photoelectron spectroscopy. Electrochemical testing revealed that N, S-GNR-2s exhibited an E_onset of 0.89 V, E_1/2 of 0.79 V and an average electron transfer number of 3.72, as well as good stability and methanol tolerance. As a result, N, S-GNR-2s displayed better ORR property than either N-GNRs or N, S-GNRs, the control samples prepared with only a primary heteroatom source, strongly clarifying the significance of secondary-heteroatom-doping on enhancing the catalytic activity of carbon-based nanomaterials.

Critical Aspects of Various Techniques for Synthesizing Metal Oxides and Fabricating Their Composite-Based Supercapacitor Electrodes: A Review

Supercapacitors (SCs) have attracted attention as an important energy source for various applications owing to their high power outputs and outstanding energy densities. The electrochemical performance of an SC device is predominantly determined by electrode materials, and thus, the selection and synthesis of the materials are crucial. Metal oxides (MOs) and their composites are the most widely used pseudocapacitive SC electrode materials. The basic requirements for fabricating high-performance SC electrodes include synthesizing and/or chemically modifying unique conducting nanostructures, optimizing a heterostructure morphology, and generating large-surface-area electroactive sites, all of which predominantly rely on various techniques used for synthesizing MO materials and fabricating MO- and MO-composite-based SC electrodes. Therefore, an SC’s background and critical aspects, the challenges associated with the predominant synthesis techniques (including hydrothermal and microwave-assisted syntheses and chemical-bath and atomic-layer depositions), and resulting electrode electrochemical performances should be summarized in a convenient, accessible report to accelerate the development of materials for industrial SC applications. Therefore, we reviewed the most pertinent studies on these synthesis techniques to provide insight into the most recent advances in synthesizing MOs and fabricating their composite-based SC electrodes as well as to propose research directions for developing MO-based electrodes for applications to next-generation SCs.

Microwave as a Tool for Synthesis of Carbon-Based Electrodes for Energy Storage

This Spotlight on Applications highlights the significant impact of microwave-assisted methods for synthesis and modification of carbon materials with enhanced properties for electrodes in energy storage applications (supercapacitors and batteries). For the past few years, microwave irradiation has been increasingly used for the synthesis of carbon materials with different morphologies using various precursors. Microwave processing exhibits numerous advantages, such as short processing times, high yield, expanded reaction conditions, high reproducibility, and high purity of products. On this frontier research area, we have discussed microwave-assisted synthesis, defect creation, simultaneous reduction and exfoliation, and heteroatom doping in carbon materials. By careful manipulation of microwave irradiation parameters, the method becomes a powerful and efficient tool to generate different morphologies in carbon-based materials. Other important outcomes are the flexible control over the degree of reduction and exfoliation of graphene derivatives, the generation of defects in graphene-based materials by metals, the intercalation of metal oxides into graphene derivatives, and heteroatom doping of graphene materials. The Spotlight on Applications aims to provide a condensed overview of the current progress in carbon-based electrodes synthesized by microwave, pointing out outstanding challenges and offering a few suggestions to trigger more research endeavors in this important field.

Investigation of Spatial Orientation and Kinetic Energy of Reactive Site Collision between Benzyl Chloride and Piperidine: Novel Insight into the Microwave Nonthermal Effect

Microwave nonthermal effect in chemical reactions is still an uncertain problem. In this work, we have studied the spatial orientation and kinetic energy of reactive site collision between benzyl chloride and piperidine molecules in substitution reaction under microwave irradiation using the molecular dynamics simulation. Our results showed that microwave polarization can change the spatial orientation of reactive site collision. Collision probability between the Cl atom of the C-Cl group of benzyl chloride and the H atom of the N-H group of piperidine increased by up to 33.5% at an effective spatial solid angle (θ, φ) of (100∼110°, 170∼190°) under microwave irradiation. Also, collision probability between the C atom of the C-Cl group of benzyl chloride and the N atom of the N-H group of piperidine also increased by up to 25.6% at an effective spatial solid angle (θ, φ) of (85∼95°, 170∼190°). Moreover, the kinetic energy of collision under microwave irradiation was also changed, that is, for the collision between the Cl atom of the C-Cl group and the H atom of the N-H group, the fraction of high-energy collision greater than 6.39 × 10^-19 J increased by 45.9 times under microwave irradiation, and for the collision between the C atom of the C-Cl group and the N atom of the N-H group, the fraction of high-energy collision greater than 6.39 × 10^-19 J also increased by 29.2 times. Through simulation, the reaction rate increased by 34.4∼50.3 times under microwave irradiation, which is close to the experimental increase of 46.3 times. In the end, spatial orientation and kinetic energy of molecular collision changed by microwave polarization are summarized as the microwave postpolarization effect. This effect provides a new insight into the physical mechanism of the microwave nonthermal effect.

N-doped graphene encapsulated MoS2nanosphere composite as a high-performance anode for lithium-ion batteries

MoS₂is widely used in lithium-ion batteries (LIBs) due to its high capacity (670 mAh g^-1) and unique two-dimensional structure. However, the further application was limited of MoS₂as anode materials suffer from its volume expansion and low conductivity. In this work, N-doped graphene encapsulated MoS₂nanosphere composite (MoS₂@NG) were prepared and its unique sandwich structure containing abundant mesopores and defects can efficiently enhance reaction kinetics. The MoS₂@NG electrode shows a reversible capacity of 975.9 mAh g^-1at 0.1 A g^-1after 100 cycles, and a reversible capacity of 325.2 mAh g^-1is still maintained after 300 cycles at 5 A g^-1. In addition, the MoS₂@NG electrode exhibites an excellent rate performance benefiting from the electrochemical properties dominated by capacitive behavior. This suggests that MoS₂@NG composite can be used as potential anode materials for LIBs.

Facile and single step produced Ba:Sn-codoped PEDOT:PSS thin film electrode with improved optics and electrochemical properties for transparent and flexible supercapacitor applications

Figure shows preparation and characterization steps of different ratio (0–3 mg ml−1) Ba:Sn-codoped PEDOT:PSS thin films.

Microwave-Enabled Size Control of Iron Oxide Nanoparticles on Reduced Graphene Oxide

Nanoparticle-functionalized 2D material networks are promising for a wide range of applications, but in situ formation of nanoparticles is commonly challenged by rapid growth. Here, we demonstrate controlled synthesis of small and dispersed iron oxide nanoparticles on reduced graphene oxide (rGO) networks through rapid localized heating with microwaves with low-cost iron nitrate as the precursor. The strong coupling of the microwave radiation with the rGO network rapidly heats the network locally to decompose the iron nitrate and generate iron oxide nanoparticles, while cessation of microwaves leads to rapid cooling to minimize crystal growth. Small changes in the microwave reaction time (<1 min) led to very large changes in the iron oxide morphology. The solid-state microwave syntheses produced narrower nanoparticle size distribution than conventional heating. These results illustrate the potential of solid-state microwave syntheses to control the nanoparticle size on 2D materials through rapid localized heating under the microwave process conditions, which should be extendable to a variety of transition metal oxide-rGO systems.