Solid-state Microwave Irradiation Research Articles

Green carbonaceous material‒fibrous silica-titania composite photocatalysts for enhanced degradation of toxic 2-chlorophenol

In this work, fibrous silica-titania (FST) was successfully prepared by the microemulsion method prior to the addition of three types of carbonaceous materials: graphitic-carbon nitride, g-C3N4 (CN), graphene nanoplatelets (GN), and multi-wall carbon nanotubes, MWCNT (CNT), via a solid-state microwave irradiation technique. The catalysts were characterized using XRD, FESEM, TEM, FTIR, UV-Vis DRS, N2 adsorption-desorption, XPS and ESR, while their photoactivity was examined on the degradation of toxic 2-chlorophenol (2-CP). The result demonstrated that the initial reaction rate was in the following order: CNFST (5.1 × 10–3 mM min-1) > GNFST (2.5 × 10–3 mM min-1) > CNTFST (2.3 × 10–3 mM min-1). The best performance was due to the polymeric structure of g-C3N4 with a good dispersion of C and N on the surface FST. This dispersion contributed towards an appropriate quantity of defect sites, as a consequence of the greater interaction between g-C3N4 and the FST support, that led to narrowed of band gap energy (2.98 eV to 2.10 eV). The effect of scavenger and ESR studies confirmed that the photodegradation over CNFST occurred via a Z-scheme mechanism. It is noteworthy that the addition of green carbonaceous materials on the FST markedly enhanced the photodegradation of toxic 2-CP.

Co-Sn-Cu oxides/graphene nanocomposites as green catalysts for preparing 1,8-dioxo-octahydroxanthenes and apoptosis-inducing agents in MCF-7 human breast cancer cells.

In this work, Co–Sn–Cu oxides/graphene nanocomposite, 30–40 ± 0.5 nm in size, was synthesized by solid‐state microwave irradiation. This method presents several advantages such as operational simplicity, fast, low cost, safe and energy efficient, and suitability for production of high purity of nanoparticles. Other advantages of this method are there is no need for the use of solvent, fuel, and surfactant. Co–Sn–Cu oxides/graphene nanocomposites have been characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometer, energy‐dispersive X–ray spectroscopy, and UV–Vis spectroscopy. The synthesized nanocomposites were used as novel highly efficient catalysts for the synthesis of 1,8‐dioxo‐octahydroxanthenes at room temperature. The catalysts are recoverable and can be reused for six runs without loss of their activity. Also, the obtained nanocomposites exhibited significant anticancer activity against breast cancer cells and they could induce apoptosis in cancer cells.

Solid-state synthesis of few-layer cobalt-doped MoS2 with CoMoS phase on nitrogen-doped graphene driven by microwave irradiation for hydrogen electrocatalysis.

The high catalytic activity of cobalt-doped MoS2 (Co–MoS2) observed in several chemical reactions such as hydrogen evolution and hydrodesulfurization, among others, is mainly attributed to the formation of the CoMoS phase, in which Co occupies the edge-sites of MoS2. Unfortunately, its production represents a challenge due to limited cobalt incorporation and considerable segregation into sulfides and sulfates. We, therefore, developed a fast and efficient solid-state microwave irradiation synthesis process suitable for producing thin Co–MoS2 flakes (∼3–8 layers) attached on nitrogen-doped reduced graphene oxide. The CoMoS phase is predominant in samples with up to 15 at% of cobalt, and only a slight segregation into cobalt sulfides/sulfates is noticed at larger Co content. The Co–MoS2 flakes exhibit a large number of defects resulting in wavy sheets with significant variations in interlayer distance. The catalytic performance was investigated by evaluating the activity towards the hydrogen evolution reaction (HER), and a gradual improvement with increased amount of Co was observed, reaching a maximum at 15 at% with an overpotential of 197 mV at −10 mA cm−2, and a Tafel slope of 61 mV dec−1. The Co doping had little effect on the HER mechanism, but a reduced onset potential and charge transfer resistance contributed to the improved activity. Our results demonstrate the feasibility of using a rapid microwave irradiation process to produce highly doped Co–MoS2 with predominant CoMoS phase, excellent HER activity, and operational stability.

Comparative study of deoxygenation behavior for graphene oxide with different oxidation degree and mildly reduced graphene oxide via solid-state microwave irradiation

The influence of the oxidation degree of graphene oxide (GO) on its deoxygenation efficiency via hybrid microwave heating (HWH) method by using graphite powder as the external susceptor was investigated, and the response behavior was compared with the situation when GO is directly submitted to microwave irradiation. In addition, the deoxygenation behavior of mildly reduced GO (VRGO) that was obtained via chemical reduction by Vitamin C was compared with that of GO during above two microwave heating processes. No response of GO to microwave irradiation when GO samples are exposed directly to microwave, no matter how the oxidation degree is. However, the VRGO sample can be heated when it is solely submitted to microwave irradiation. The partial reduction of GO leads to enhancement of the dielectric parameters, and the residual defects and oxygen-containing functional groups not only can improve the impedance matching characteristics, but also produce defects polarization relaxation and dipole polarization relaxation, which are all beneficial to the microwave penetration and absorption. The deoxygenation efficiency of VRGO is lower in comparison with GO under the HWH condition, which should be attributed to higher amount of epoxides in GO samples that can be easily reduced in a mixed heating mode.

Preparation of sulfur-doped graphite by solid-state microwave method: The effect of reaction conditions on the sulfur-doping process

The high-quality sulfur-doped graphite (SGi) was prepared from concentrated sulfuric acid-graphite intercalation compounds (H2SO4-GICs) by solid-state microwave irradiation, where H2SO4 was the sulfur (S) source and S-doping occurred within a minute. The preparation of H2SO4-GICs was a key step for S-doping and exfoliation process. Notably, it was found that S-doping was influenced by the dosage of H2SO4, where the lower dosage of H2SO4 was beneficial for the S-doping. The exfoliation efficiency was greatly affected by the temperature and dosage of oxidant, where lower temperature and lower dosage of KMnO4 guaranteed efficient exfoliation.

Enhanced deoxygenation efficiency of graphene oxide under solid-state microwave irradiation via chemical pre-reduction

The deoxygenation efficiency of graphene oxide (GO) under solid-state microwave irradiation was improved via chemical pre-reduction using different reductants (Vitamin C, hydrazine hydrate and sodium borohydride). The reduced graphene oxide (RGO) samples obtained by reduction of GO via Vitamin C were denoted as VRGO-x (x = 0.33, 1.5 and 5), where x indicates the mass ratio of VC to GO (RVC/GO). And the products fabricated via reduction of GO by hydrazine hydrate and sodium borohydride are recorded as HRGO and SRGO, respectively. It is found that deoxygenation efficiency of RGO samples at the similar initial oxygen concentrations via further microwave irradiation is different. For instance, the oxygen concentration of VRGO-0.33 and SRGO decreases to 10.75% and 19.19%, and the oxygen concentration of VRGO-5 and HRGO decreases to 10.66% and 13.78%, respectively. The real part of complex permittivity (ε′) of GO increases from 2.25 to 2.4–2.5 and 2.7–2.8 for VRGO-0.33 and SRGO, VRGO-5 and HRGO, demonstrating the absorption ability of VRGO-0.33 and SRGO, VRGO-5 and HRGO is very close, respectively. Compared with SRGO, the deoxygenation efficiency is higher for VRGO-0.33 that with higher content of carbonyls. This can be explained by that the lower energy is required to remove carbonyls relative to that for the other functional groups. Moreover, because HRGO contains high content of stable oxygen functional groups and some amount of nitrogen-containing groups, which are relatively stable at high temperature, especially for pyrrolic N and graphitic N, the reduction efficiency of HRGO is lower than that of VRGO-5.

Effective reduction of graphene oxide via a hybrid microwave heating method by using mildly reduced graphene oxide as a susceptor

Due to the poor microwave absorption ability of graphene oxide (GO), direct reduction of GO by solid-state microwave irradiation is inefficient. In this study, GO was reduced effectively by a hybrid microwave heating (HWH) method by using mildly reduced graphene oxide (MG) membrane as a external susceptor, in which MG was obtained by annealing of GO at 300 °C for 1 h under nitrogen by a conventional heating method. When the mass ratio of MG to GO is 0.045, the C/O atomic ratio of GO increases from 1.8 to 17.84 by microwave irradiation under argon at 2000 W for 30 s. However, when GO was irradiated solely under the same conditions, the ratio of C/O was unchanged (1.88). For comparison, the MG was further irradiated by microwave at 2000 W for 30 s, its C/O ratio is enhanced from 4.17 to 8.46, demonstrating the higher reduction efficiency due to a mixed heating mode in the HWH process. The conventional heating of GO occurs during the initial stage and a two-way heating mode during the later stage, in which MG heats the GO from the surface and the microwave heating from the GO itself. Therefore, more amount of carboxyls and epoxides can be removed in the HWH process to achieve higher C/O ratio compared with that of the product obtained by direct microwave irradiation of MG.

Facile microwave-assisted synthesis of NiO nanoparticles and its effect on soybean (Glycine max).

NiO nanoparticles in high purity, 15 ± 0.5 nm in size, were prepared via solid-state microwave irradiation. The [Ni(NH3)6](NO3)2 complex as a novel source was decomposed in the presence of microwave irradiation for a short time (10 min). The present method is facile, safe, and low-cost. This method exhibits other advantages; there is no need of a solvent, fuel, surfactant, expensive material, or complex instrument. Synthesised NiO nanoparticles were determined by various analyses. Also, for the first time, NiO nanoparticle effects on biochemical factors in soybean were investigated. Seeds of soybean were grown in the Murashige and Skoog agar medium containing different concentrations of NiO nanoparticles (0, 200, and 400 mg/L) for 21 days under growth chamber conditions. Estimates of malondialdehyde, hydrogen peroxide contents, and antioxidant enzymes (catalase and ascorbate peroxidase) under treatment of NiO nanoparticles were assayed. The result showed that by significantly increasing the concentration of NiO nanoparticles, the activity of catalase and ascorbate peroxidase enzymes was enhanced. Malondialdehyde and hydrogen peroxide contents significantly increased in the presence of NiO nanoparticles. In this study, the increasing activity of catalase and ascorbate peroxidase was not enough for radical oxygen species detoxification.

Rapid synthesis of three-dimensional sulfur-doped porous graphene via solid-state microwave irradiation for protein removal in plasma sample pretreatment

In this work, we prepared three-dimensional sulfur-doped porous graphene (3D-SPG) via solid-state microwave method and first introduced it to plasma sample pretreatment as adsorbent for the removal of proteins. The efficient heating effect of solid-state microwave irradiation endowed the as-prepared 3D-SPG with large specific surface area, porous structures and sulfur-doped conjugated π electron surface, thus producing an outstanding adsorbent for proteins adsorption. The adsorption behavior of 3D-SPG towards proteins was explored using bovine serum albumin (BSA) as the model protein and several kinetic models and isotherm models were employed to describe the adsorption process. The results indicated that BSA was adsorbed onto 3D-SPG in a monolayer manner with high adsorption capacity, and chemisorption and intraparticle diffusion was the rate-controlling step in proteins adsorption process. By applying 3D-SPG as adsorbent to remove proteins in real rat plasma, we found that 3D-SPG solid phase extraction (SPE) gained exceedingly high protein removal efficiency compared with other plasma pretreatment methods, suggesting that 3D-SPG SPE could effectively prevent the deterioration of column performance and decrease the interference caused by matrix effect in the follow-up analysis. Furthermore, in comparison with the tandem mass spectra results between 3D-SPG SPE and methanol precipitation, 3D-SPG SPE demonstrated the ability to extract the protein-binding metabolites which usually could not be extracted by methanol precipitation. This ability made 3D-SPG SPE of great value in untargeted metabolomics profiling, because 3D-SPG SPE could be a complementary method to methanol precipitation to improve the coverage of metabolites.

Reduced graphene oxide as a stable and high-capacity cathode material for Na-ion batteries

We report the feasibility of using reduced graphene oxide (RGO) as a cost-effective and high performance cathode material for sodium-ion batteries (SIBs). Graphene oxide is synthesized by a modified Hummers’ method and reduced using a solid-state microwave irradiation method. The RGO electrode delivers an exceptionally stable discharge capacity of 240 mAh g−1 with a stable long cycling up to 1000 cycles. A discharge capacity of 134 mAh g−1 is obtained at a high current density of 600 mA g−1, and the electrode recovers a capacity of 230 mAh g−1 when the current density is reset to 15 mA g−1 after deep cycling, thus demonstrating the excellent stability of the electrode with sodium de/intercalation. The successful use of the RGO electrode demonstrated in this study is expected to facilitate the emergence of low-cost and sustainable carbon-based materials for SIB cathode applications.

Three-Dimensional Expanded Graphene-Metal Oxide Film via Solid-State Microwave Irradiation for Aqueous Asymmetric Supercapacitors.

Carbon-based electrochemical double-layer capacitors and pseudocapacitors, consisting of a symmetric configuration of electrodes, can deliver much higher power densities than batteries, but they suffer from low energy densities. Herein, we report the development of high energy and power density supercapacitors using an asymmetric configuration of Fe2O3 and MnO2 nanoparticles incorporated into 3D macroporous graphene film electrodes that can be operated in a safe and low-cost aqueous electrolyte. The gap in working potential windows of Fe2O3 and MnO2 enables the stable expansion of the cell voltage up to 1.8 V, which is responsible for the high energy density (41.7 Wh kg(-1)). We employ a household microwave oven to simultaneously create conductivity, porosity, and the deposition of metal oxides on graphene films toward 3D hybrid architectures, which lead to a high power density (13.5 kW kg(-1)). Such high energy and power densities are maintained for over 5000 cycles, even during cycling at a high current density of 16.9 A g(-1).

High-Surface-Area Nitrogen-Doped Reduced Graphene Oxide for Electric Double-Layer Capacitors.

A two-step method consisting of solid-state microwave irradiation and heat treatment under NH3 gas was used to prepare nitrogen-doped reduced graphene oxide (N-RGO) with a high specific surface area (1007 m(2) g(-1) ), high electrical conductivity (1532 S m(-1) ), and low oxygen content (1.5 wt %) for electrical double-layer capacitor applications. The specific capacitance of N-RGO was 291 F g(-1) at a current density of 1 A g(-1) , and a capacitance of 261 F g(-1) was retained at 50 A g(-1) , which indicated a very good rate capability. N-RGO also showed excellent cycling stability and preserved 96 % of the initial specific capacitance after 100 000 cycles. Near-edge X-ray absorption fine-structure spectroscopy results provided evidenced for the recovery of π conjugation in the carbon networks with the removal of oxygenated groups and revealed chemical bonding of the nitrogen atoms in N-RGO. The good electrochemical performance of N-RGO is attributed to its high surface area, high electrical conductivity, and low oxygen content.

Solid-state microwave irradiation synthesis of high quality graphenenanosheets under hydrogen containing atmosphere

High quality graphene nanosheets were fabricated within 1 min by solid-state microwave irradiation of a mixture of graphite oxide and graphene nanosheets under a hydrogen atmosphere. The graphene nanosheets in the mixture acted as an effective microwave susceptor under microwave irradiation synthesis, and could provide sufficiently rapid heating for the effective exfoliation of graphite oxide. A hydrogen containing atmosphere played important roles in improving the quality of the graphene nanosheets by increasing the level of reduction and preventing the formation of defects in the graphene nanosheets. The graphene nanosheets thus obtained exhibited a specific surface area of 586 m2 g−1 and an outstanding carbon/oxygen ratio of 18.5.

Understanding solid-state microwave synthesis using the diamond-like semiconductor, AgInSe 2, as a case study

An investigation of the solid-state microwave synthetic method was performed using AgInSe 2 as a model system. Sample volume, irradiation time and grinding time of reactants were investigated in order to determine the effect that these variables have on the phase purity of the reaction product. In addition, the reaction mechanism was probed by carrying out irradiation experiments using the constituent elements and binary mixtures. AgInSe 2 samples synthesized via solid-state microwave irradiation were compared to a sample that was synthesized via high-temperature solid-state synthesis in a furnace. Powder X-ray diffraction, differential thermal analysis and diffuse reflectance spectroscopy in the UV/vis/near IR region were used to characterize all reaction products.