Field Emission Scanning Electron Microscopy-energy Dispersive Spectroscopy Research Articles

Molybdenum and Vanadium-Codoped Cobalt Carbonate Nanosheets Deposited on Nickel Foam as a High-Efficient Bifunctional Catalyst for Overall Alkaline Water Splitting.

To address issues of global energy sustainability, it is essential to develop highly efficient bifunctional transition metal-based electrocatalysts to accelerate the kinetics of both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Herein, the heterogeneous molybdenum and vanadium codoped cobalt carbonate nanosheets loaded on nickel foam (VMoCoCOx@NF) are fabricated by facile hydrothermal deposition. Firstly, the mole ratio of V/Mo/Co in the composite is optimized by response surface methodology (RSM). When the optimized composite serves as a bifunctional catalyst, the water-splitting current density achieves 10 mA cm-2 and 100 mA cm-2 at cell voltages of 1.54 V and 1.61 V in a 1.0 M KOH electrolyte with robust stability. Furthermore, characterization is carried out using field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations reveal that the fabricated VMoCoCOx@NF catalyst synergistically decreases the Gibbs free energy of hydrogen and oxygen-containing intermediates, thus accelerating OER/HER catalytic kinetics. Benefiting from the concerted advantages of porous NF substrates and clustered VMoCoCOx nanosheets, the fabricated catalyst exhibits superior electrocatalytic performance. This work presents a novel approach to developing transition metal catalysts for overall water splitting.

Microstructural evolution and mechanical properties of aluminum-graphite composites processed via accumulative roll bonding

In the present work, the aluminum-graphite metal matrix composites were fabricated via accumulative roll bonding (ARB). The graphite powder particles of <50 μm were introduced into aluminum in three different weight percentages. The effect of graphite on the evolution of microstructure, interface formation, and mechanical properties was studied. The microstructural investigation revealed that the amount of graphite played a vital role. A better particle distribution was observed for 1.25 and 1.5 wt%. However, a further increase in the reinforcement to 2.2 wt% shows longer flaky graphite with comparatively sharing a larger interface area with the matrix aluminum. An FE-SEM/EDS (Field Emission-Scanning electron microscopy/Energy dispersive Spectroscopy) line mapping at the aluminum-graphite interface confirmed an intact sound interface with better adherence properties. The ultimate tensile strength of the composites drastically improved with an increasing number of ARB passes. The FE-SEM taken over the fractured surface of the composite revealed that the ARBed Al-1100 and the composites failed in ductile mode. It was observed that the graphite particle was the primary source of nucleation in the composites. The voids have nucleated at the particle-matrix interface, followed by their growth and coalescence.

Characterization of Microplastic Degrading Indigenous Bacteria from Ambon Bay Waters

Microplastic degradation by bacteria can degrade low-density polyethylene (LDPE). This study aimed to analyze the potential of Ambon Bay bacteria for microplastic degradation, the condition of microplastics after degradation, and identification of the potential for microplastic degradation. The results of isolation revealed as many as 20 bacterial isolates, which correlated with physicochemical conditions in the waters of Ambon Bay. Nine of them could degrade microplastics as indicated by the presence of a clear zone, namely KA1, KA2, KA3, KA4, KA5, KA9, KA10, KS6, and KS8. They were checked for biofilm formation, microplastic hydrophobicity, and percentage of microplastic weight reduction. Four isolates with the highest percentage of microplastic weight reduction on day 40 were KA1, KA2, KA3, and KA10 at 36.19%, 10.16%, 28.39%, and 17.07%, respectively. The results of LDPE microplastic degradation showed differences using field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM/EDS), attenuated total reflection-fourier transform infrared (ATR-FTIR), and X-ray diffraction (XRD). The bacterial isolates identified were KA1 (Bacillus cereus), KA2 (Bacillus toyonesis), KA3 (Bacillus paramycoides), and KA10 (Escherichia coli). Indigenous bacteria from the waters of Ambon Bay have the potential to degrade LDPE microplastics, which causes structural changes, decreased crystallinity, weight, and C=C groups in microplastics after degradation, with bacterial isolate KA1 identified as Bacillus cereus showing the best potential with degradation of LDPE microplastics by 36.19%.

Electrochemical treatment of electroplating wastewater using synthesized GO/TiO2 nanotube electrode.

The graphene oxide (GO) deposited TiO2 nanotube (GO/TiO2) electrode on a titania plate was prepared using a simple anodization method. The morphological and structural properties of TiO2 and GO/TiO2 electrodes have been studied using field emission scanning electron microscopy energy dispersive spectroscopy (FESEM-EDS), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), Raman spectroscopy, Fourier transform infrared spectra (FT-IR), and X-ray photoelectron spectroscopy (XPS). FESEM-EDS analysis confirmed that the 13.56% wt of GO nanoparticles was formed over the TiO2 substrate, with the thickness of the wall to be ∼300nm. The crystallite size of GO/TiO2, i.e., 19.53nm, was confirmed by XRD analysis. Analysis of the UV-DRS spectrum showed the bandgap of the synthesized GO/TIO2 nanotube electrode to be 3.052eV. Box-Behnken design (BBD) under response surface methodology (RSM) was used to design the experiments. The effect of operating input parameters like pH, current (i), and degradation time (t) on % COD degradation (X1) and energy consumed (X2) were also examined. At optimum process parameters, the value of X1 and X2 were 57.61% and 15.00 kWh/m3, respectively. Possible intermediates were identified based on the GC-MS data analysis. Scavenger tests showed that •OH radical plays a major role in electroplating effluents degradation. Based on the results, the EO process using GO/TiO2 electrodes could be considered a promising technique for electroplating effluent degradation due to high degradation efficiency.

Anomalous Enrichment of As and Hg in Underground Coal Dust: A Case from Xishan Coalfield, Shanxi Province, North China.

Coal dust is an important source of coal workers' pneumoconiosis, which is harmful to the health of underground workers. The coal dust samples were directly collected using a coal dust sampler from four major production positions in the underground coal mine. The particle size distribution, mineralogy, and occurrence of As and Hg in the coal dust samples were investigated. The results indicated that the contents of As and Hg were depleted or normal in the parent coal samples compared with the average values of C-P coal in North China and Chinese coal, but they were anomalously enriched in coal dusts. The concentrations of As and Hg in the coal dust samples studied are greater than the values of the elements in the parent coal. The As content in the coal dust samples studied is about one to three orders of magnitude above the parent coal value and the Hg content in the studied coal is 1.28 to 20.28 times higher than the parent coal value. The modes of occurrences of As and Hg were studied by sequential chemical extraction in combination with field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS) and high-resolution transmission electron microscopy-EDS (HRTEM-EDS). The occurrence of As is dominated mainly by pyrite and secondarily by carbonate and silicate in the coal dust samples. Pyritic Hg and organic Hg may be the dominant forms in mining face and heading face samples, and carbonate and pyritic Hg are the main forms in rocks roadway and return airway samples. It is considered that the mechanochemical effect resulted in the formation of surface active sites and modification of the morphology. Harmful trace elements, such as As, Cd, Hg, Se, Pb, Co, Sb, and Tl, and minor grains associated with nanominerals that bear much hazardous elements, could easily be originally fractionated or adsorbed by airborne particulates. This research aims to provide a theoretical basis for the prevention of occupational disease and underground environmental evaluation.

Photocatalytic degradation of azo dyes by ultra-small green synthesized silver nanoparticles

BackgroundThe presence of toxic dyes in wastewater is a serious problem for human health. In this work, the degradation of commercial azo dyes sold over-the counter in Mexico was studied, using as a photocatalyst ultra-small silver nanoparticles (AgNPs) green synthesized. MethodsFor the first time, the successful green synthesis of ultra-small AgNPs using, as both reducing-stabilizing agents (RSa), the aqueous extract of Pelargonium hortorum (Phf) flower or Allium fistulosum (Afs) stem, is reported. AgNPs were characterized by ultraviolet-visible (UV–Vis) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopies, field emission scanning electron microscopy-energy dispersive spectroscopy (FE-SEM-EDS), and field emission transmission electron microscopy (FE-TEM). Significant findingsThe morphology of the AgNPs, in both cases, are spherical. AgNPs synthesized with Phf (AgNPs/Phf), which have a mode size of 2 nm (41.9%) and a bandgap of 2.38 eV, resulted in a photocatalytic degradation efficiency of 95%. On the other hand, AgNPs synthesized with Afs (AgNPs/Afs), which have a mode size of 0.6 nm (37.8%) and a bandgap of 2.43 eV, presented a photocatalytic efficiency of 100%. The photocatalytic efficiency and bandgap of the synthesized AgNPs were found to be inversely proportional to the AgNPs size; i.e. the smaller the AgNPs, the higher photocatalytic degradation, and bandgap exhibited.

Enhanced and rapid photocatalytic degradation of toxic dyes by cobalt oxide and modified cobalt oxide under solar light irradiation

A solar light driven photo degradation approach for methylene blue (MB, model molecule of the thiazine dyes class) and malachite green (MG, model molecule of the triphenylmethane category) abatement by Co3O4 and Cr-Co3O4 spinel nanoparticles is reported. The effect of chromium load (5, 10 and 15%) in Co3O4 particles, synthesized by a simple co-precipitation process, was properly studied. The structural and morphological characteristics, chemical composition and optical properties of the materials were investigated by X-ray diffraction (XRD), Transmission Electron Microscopy(TEM), Field Emission Scanning Electron Microscopy – Energy Dispersive Spectroscopy (FE-SEM-EDS), FT-IR spectroscopy, UV–Vis diffuse reflectance spectroscopy (DRS),photoluminescence (PL) and BET surface area analysis. It was observed that properly tuning the initial pH, the initial dye concentration, the agitation time, and the photocatalyst dose, (10)Cr-Co3O4 exhibited an enhanced photocatalytic activity compared to that of pristine Co3O4, demonstrating the positive role of Cr doping In fact, the PL investigation showed that Cr doping in the Co3O4 lattice greatly increase the separation of electron-hole (e−/h+) pairs, whereas the UV DRS spectra and Tauc plot revealed a decrease in the band gap energy for Cr-Co3O4,. The investigations demonstrated that the MB dye degradation increases from 88% to 96% at pH = 11 after doping of Co3Oby 10% of Cr. Similarly, the Cr doping allowed to enhance the MG dye degradation from 85% to 92% at pH = 9. The photo degradation kinetics of both MB and MG dyes by Cr-Co3O4 and Co3O4 NPs were of pseudo-first-order mode. The active species involved in the photocatalytic process were properly identified using various scavengers by trapping holes and radicals. Finally, the photocatalysts showed good stability during recycling maintaining high performances after 5-time usage. .

Solvent-Free Oxidation of Benzyl Alcohol Derivatives by In Situ Generated Redox Couple Pd(0)/PdOx Supported on Ceria Nanorods

Benzyl alcohol (BnOH) oxidation to benzaldehyde (PhCHO) is a pivotal industrial reaction. The aerobic oxidation of BnOH in solvent-free conditions is highly compatible with the necessity of low environmental impact. In this research work, palladium oxide (PdOx) supported on ceria nanorods (CeO2-NR), was synthesized, and utilized for aerobic solvent-free oxidation of BnOH derivatives to the corresponding aldehydes. The catalyst, PdOx/CeO2-NR, was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy/energy-dispersive spectroscopy (FE-SEM/EDS), N2 adsorption-desorption analysis, temperature-programmed reduction with hydrogen (H2-TPR), and X-ray Photoelectron Spectroscopy (XPS), proving that the PdOx (x &gt; 1) particles were highly dispersed on CeO2-NR and have a strong interaction with the support. The PdOx/CeO2-NR catalyst permitted the aerobic oxidation of various benzyl alcohol derivatives with good conversion, and high selectivity towards the corresponding aldehydes. The presence of electron donating groups (EDG) on the benzylic ring enhanced the reactivity as opposed to the electron withdrawing groups (EWG) which were detrimental for the catalytic activity. During the reaction a partial reduction of the metal produced a Pd(0)/PdOx/CeO2-NR redox couple stable in the reaction condition, more reactive and recyclable. Some mechanistic hypotheses are presented.

Characterizing mechanical heterogeneity of coal at nano-to-micro scale using combined nanoindentation and FESEM-EDS

The variations of mechanical properties of coals in nano-to-micro scale play vital roles in defining the coal deformative and failure behaviors with a wide range of engineering applications, including coal stimulation for gas recovery and/or CO2 sequestration in coal seams. Based on the assumption that the heterogeneity in the mechanical properties of coals is combinedly determined by the mineralogical/carbon compositions and microstructures, three coals were experimentally measured through combing nanoindentation test, X-ray diffraction (XRD) analysis and field emission scanning electron microscopy - energy dispersive spectroscopy (FESEM-EDS) imaging. Two sub-bituminous coals from Illinois basin and one bituminous coal from Pittsburgh No.8 seam from Pennsylvania were collected and prepared. The moduli, hardness, and energy dissipations were all analyzed for three coals. The mean Young's moduli and hardness of two sub-bituminous and bituminous coals are ~4.13 GPa, ~4.79 GPa, and ~ 5.56 GPa respectively and the mean hardness of which are ~0.38 GPa, ~0.49 GPa and ~ 0.58 GPa respectively. The results confirmed that the nanoscale mechanical properties are compositional and microstructural dependent. It was also observed that the heterogeneity of sub-bituminous coals is more apparent than the bituminous coal. Also, the bituminous coal is more harder and brittle than sub-bituminous coal, which can better withhold the mechanical response, but the deformations are relatively permanent due to brittle failure. The energy dissipation data showed that the irreversible work decreases with the increase in hardness, which confirmed that the plastic deformation is much more easily to be inducted. The mechanism-based phenomenon pop-in event on the load-displacement curve was also analyzed by linking with the characteristics of the morphology and composition beneath a pointed indenter or cracks formation due to the localized indent.

Dry Reforming of Methane on Ni/Nanorod-CeO2 Catalysts Prepared by One-Pot Hydrothermal Synthesis: The Effect of Ni Content on Structure, Activity, and Stability

The nanorod morphology of the CeO2 support has been recognized as more beneficial than other morphologies for catalytic activity in the dry reforming of methane. Ni/nanorod-CeO2 catalysts with different Ni contents were prepared by one-pot hydrothermal synthesis. Samples were characterized by X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), H2-temperature-programmed desorption (H2-TPD), field emission scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS), Brunauer–Emmet–Teller (BET) and Barrett–Joyner–Halenda (BHJ) analysis. The effect of Ni content on the size and the intrinsic strain of ceria was analyzed by the Size–Strain plot and Williamson–Hall plot of XRD data. The average Ni particle size and Ni dispersion were determined by H2-TPD. XRD and H2-TPR analysis revealed a strong Ni–support interaction that limited nickel sintering. The activity for the dry reforming of methane was tested with the stoichiometric mixture CO2:CH4:N2:He = 20:20:20:140, gas hourly space velocity (GHSV) = 300 L g−1 h−1, and temperatures in the range of 545–800 °C. The turnover frequency (TOF) value increased linearly with the average Ni particle size in the range of 5.5–33 nm, suggesting the structure sensitivity of the reaction. Samples with Ni loading of 4–12 wt.% showed high H2/CO selectivity and stability over time on stream, whereas the sample with a Ni loading of 2 wt.% was less selective and underwent rapid deactivation. Only a small amount of nanotubular carbon was observed by FE-SEM after the time-on-stream experiment. Deactivation of the low-Ni-content sample is ascribed to the easier oxidation of the small Ni particles.

Chalcopyrite UiO-67 metal-organic framework composite for CO2 fixation as cyclic carbonates

The conversion of greenhouse gas carbon dioxide (CO2) into cyclic carbonates which are, used as green solvents and are considered sustainable substitution to toxic chemicals, can be a competent approach to net zero-emission. This work successfully incorporated Chalcopyrite (CuFeS2) in UiO-67 (University of Oslo-67) to form a composite Ch@UiO-67 using a solvothermal method. After characterization by powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), N2 adsorption isotherm, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy- Energy Dispersive Spectroscopy (FESEM-EDS) and Inductively coupled plasma mass spectrometry (ICP-MS), Ch@UiO-67 was tested for CO2 uptake and as a catalyst in the cycloaddition reaction of styrene epoxide (SO) with CO2 to produce cyclic carbonates, in comparison to pristine UiO-67. Ch@UiO-67 was found to be more effective as a catalyst than pristine UiO-67. This catalyst was also successful with different aromatic and aliphatic epoxides for cycloaddition with CO2 and was efficiently recycled for seven consecutive cycles without a noticeable deficit in the catalytic activity.

Separating Silver from Tin Silver Alloy Residue: Effect of Agitation Rate

In this paper, research on the effects of agitation rate for desilvering tin silver alloy residue by using pyrometallurgy was carried out. SnAg alloy residue with 92 wt.% tin and 3.56 wt.% silver was used in this study, and 99.999 wt.% zinc was added as metal solvent. Residues were melted to a temperature of 400 °C for enriching tin silver alloy. The obtained tin silver alloy was melted in a temperature range of 450 °C to 500 °C by adding zinc to evaluate zinc dissolution. The obtained tin silver zinc was agitated at different agitation rates for 20 min at a temperature of 480 °C, then cooled down while stirring to an eutectic point of tin zinc alloy (198.9 °C) to remove silver zinc dross. X-ray Fluorescent-1800 (XRF-1800) and Field Emission Scanning Electron Microscopy Energy Dispersive Spectroscopy (FE-SEM-EDS) analyses were performed in this research. Different factors including holding time, zinc dissolution, agitation time and agitation rate were evaluated. The results revealed that an agitation rate of 600 RPM, 25% Zn and 60 min at a temperature of 198.9 °C were efficient. Zinc silver was removed as dross every 20 min to get 92% silver separation efficiency, and the use of supergravity centrifuge is highly recommended to get best separation efficiency.

Europium doped Ni(BTC) metal-organic framework for detection of heteroaromatic compounds in mixed aqueous media

In this paper, we have prepared europium doped Ni(BTC) (Ni = Nickel, BTC = 1,3,5- benzene tricarboxylic acid) MOF (Metal-Organic Framework), Eu@Ni(BTC). This MOF was characterized by PXRD (powder X-ray diffraction), FT-IR (Fourier-transform infrared spectroscopy), N2 adsorption isotherm, TGA (thermogravimetric analysis), X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy- Energy Dispersive Spectroscopy (FESEM-EDS) and Inductively coupled plasma mass spectrometry (ICP-MS). This MOF was then used as an optical sensor for the detection of heteroaromatic compounds. It was observed that the emission of Eu@Ni(BTC) was selectively and completely quenched by thiophene and partially quenched by pyrrole. The quenching efficiency of this sensor with thiophene and pyrrole was calculated to be 2.7 × 105 and 7.5 × 103, with a detection limit of 0.2 and 8.4 ppm, respectively. This sensor has recyclability up to five cycles and was also applied for the practical detection of thiophene from water.

Effects of grinding media on the flotation performance of cassiterite

Grinding plays an important role in the beneficiation process. Different grinding media can determine the size distribution, shape, and even the surface properties of the produced material. However, comprehensive research related to the effect of grinding media on the flotation performance of cassiterite is lacking. In the current study, the effects on the flotability of the products obtained by grinding with ceramic and stainless steel media were investigated using micro-flotation, laser particle size distribution analysis, inductively coupled plasma optical emission spectroscopy (ICP-OES), chemical element analysis, zeta potential measurements, field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS), and X-ray photoelectron spectroscopy (XPS). The micro-flotation results demonstrate that the flotability of stainless steel ground cassiterite surpasses that of ceramic. The laser particle size distribution test reveals that the two grinding media do not have a strong impact on the particle size distribution. The ICP-OES and chemical element analysis results identify the higher iron content in the samples and pulp of stainless steel ground cassiterite as the principle influencing factor. The zeta potential analysis indicates that the dissolved iron ions absorbed on the cassiterite surface results in a positive shift of the mineral surface potential. This not only reduces electrostatic repulsion but also increases the active sites of salicylhydroxamic acid (SHA) chemisorption. FESEM-EDS results demonstrate the rougher surface and higher iron content of the stainless steel ground cassiterite compared to the ceramic ground cassiterite, thereby increasing the SHA adsorption. The stainless steel grinding cassiterite was observed to alter the chemical environment of Fe species on the cassiterite surface via XPS analysis, with Fe2+ exhibiting a stronger reactivity and stability towards SHA compared to Fe3+. Thus, the stainless steel media ground cassiterite demonstrates an improved flotability performance compared to the ceramic equivalent.

One-step combustion synthesis of C/MgO composite powders with MgO nanofibers

C/MgO composite powders were prepared by combustion synthesis using magnesium oxalate and magnesium powders as raw materials. The phase composition and microstructure of the composite powders were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy/energy dispersive spectroscopy (FESEM/EDS), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The synthetic mechanism was explored through TG-FTIR and combustion front quenching techniques. It was found that the C/MgO composite powders contained a large quantity of MgO nanofibers. When the molar ratio of magnesium oxalate and magnesium was 1:4, the carbon content of the product reached a maximum of 9.45 wt %. In the composite powders, cubic MgO particles were encapsulated by a thin carbon layer, and there was a tiny gap between MgO and the carbon layer; a large number of MgO nanofibers with aspect ratios of 80–100 were found. The cubic MgO particles of the products are the direct decomposition of MgC2O4, and the MgO nanofibers are the reaction product of gaseous Mg and CO2/CO at high temperature. Meanwhile, the carbon deposited on the MgO particles can inhibit the grain growth of MgO particles and result in the refinement of MgO particles. The uniform dispersion of carbon and the weak C/MgO interface combine, making the composite powders a potential additive for low-carbon MgO–C refractories with excellent thermal shock resistance.

Double hydrothermal synthesis of iron oxide/silver oxide nanocomposites with antibacterial activity**

Abstract In this work, iron oxide "gamma phase" (γ-Fe2O3)-silver oxide (Ag2O) nanocomposite is prepared by a double hydrothermal method combined with Punicaceae plant extract as reducing agents. X-ray diffraction (XRD) results confirmed the presence of γ-Fe2O3 and Ag2O and delafossite silver ferrite (AgFeO2) phases. Field Emission Scanning Electron Microscopy-energy dispersive spectroscopy (FESEMEDS) results revealed nanoparticles (NPs) with a shape like a cauliflower plant. Furthermore, the anti-bacterial activity results presented high inhibition rates against Klebsiella pneumoniae, Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Candida albicans. The present study exhibits a new approach to the preparation of metal oxides using a facile and inexpensive method.

Effect of Iron Loading on the Catalytic Activity of Fe/N-Doped Reduced Graphene Oxide Catalysts via Irradiation

The aim of this study is to produce noble-metal-free oxygen reduction reaction (ORR) catalyst via irradiation. Gamma ray irradiation reduction has been utilized to produce N-doped reduced graphene oxide (rGO)-supported iron (Fe)-based catalysts, whose weight percent (wt.%) of Fe loading varies from 10% to 20%. In this study, the physicochemical properties of Fe/N-rGO with various loadings of Fe (10 wt.%, 15 wt.% and 20 wt.%) were explored through X-ray diffraction (XRD), field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). XRD showed that a broad-peak nanocrystallite Fe2O3 phase formed. Raman spectroscopy revealed that Fe insertion increased the disordered GO structure. Fourier transform infrared (FTIR) demonstrated that N was functionalized into rGO. FESEM-EDX presented that Fe nanoparticles existed on the wrinkled rGO surface but their amount was low. Linear sweep voltammetry (LSV) was performed with a rotating disk electrode in 0.1 M KOH at a scanning rate of 20 mVs−1 and revolution rates of 400, 900 and 1600 rpm and the corresponding electron transfer numbers were investigated with a Koutecky–Levich model. This model indicated that the number of electron transfers of 20% Fe/N-rGO was above 2 and its performance toward ORR was higher than those of 10% Fe/N-rGO and 15% Fe/N-rGO.

Preparation, characterization and activity of tea polyphenols-zinc complex

The zinc-complexes of tea polyphenols (TP), including (−)-epigallocatechin gallate (EGCG), were prepared with zinc chloride at pH 6.5 in the absence of oxygen. The complexes were characterized with field emission scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS), ultraviolet–visible (UV–vis), fourier transform infrared (FTIR), 1H nuclear magnetic resonance (1H NMR) spectroscopy and thermogravimetric analysis (TGA), and their antioxidant and antibacterial activities were studied. The results showed that TP/EGCG complexed with zinc ion in the B-ring at 1:1, and the thermal stability of the complexes was better than that of TP/EGCG, and the scavenging activities of 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl and superoxide radicals and the antibacterial activities against Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus) were significantly stronger than those of EGCG/TP. We speculated that the complexation with zinc ion might enhance the thermal stability, the antioxidant activity and the antibacterial activity of TP/EGCG. It can be expected that the zinc-complexes of TP/EGCG will have a bright prospect for their potent biological activity.

Immobilization of heavy metals, selenate, and sulfate from a hazardous industrial side stream by using calcium sulfoaluminate-belite cement

Release of heavy metals from different industries and industrial waste is a major global threat for as well humans as ecosystems. In this study, immobilization of an industrial filter sludge (FS) with an extremely high content of several heavy metals (24.6 wt% Pb, 21.7 wt% Hg, and 9.00 wt% Se) and sulfate via calcium sulfoaluminate-belite (CSAB) cement was tested. The ratios of 25%, 50% and 75% of CSAB addition were tested, and the target was to achieve immobilization of the hazardous components. The leaching of Pb, Hg, SeO4, SO4, Ni, Cd, Cu, and As was monitored, and the structure of the immobilized materials was examined via X-ray powder diffraction (XRD) and field emission scanning electron microscopy-energy dispersive spectroscopy (FESEM-EDS) analysis. It was observed that Hg, Cu, As, Cd, and Ni were immobilized completely and leaching of Pb was reduced by 69% from the theoretical release. On the other hand, the leaching of SeO4 and SO4 experienced major increase when CSAB was added. XRD indicated significant ettringite formation as the amount of added CSAB increased, and the formation of gypsum as the amount was decreased. FESEM-EDS indicated that the immobilization was largely based on encapsulation into the CSAB binder, but chemical immobilization into the ettringite binder was also observed. It was concluded that the increased release of SO4 and SeO4 might have resulted from an excess amount of sulfates (added gypsum) during hydration.

Structure-Sensitivity of CO2 Methanation over Nanostructured Ni Supported on CeO2 Nanorods

Ni-based oxides are widely investigated as catalysts for CO2 methanation due to their high activity, high selectivity and low cost. The catalytic performances of Ni-based catalysts depend on support properties that strongly influence the dispersion of the catalytic active phase and the Ni–support interaction. Although the CO2 methanation is widely studied, the structure sensitivity of methanation on nickel is not completely assessed. Ni/CeO2 nanorods with different nickel/ceria molar ratios (0.05, 0.10, 0.20, 0.30) were prepared by one-pot hydrothermal synthesis. The effect of nickel content and metal particle size on catalytic activity and selectivity for CO2 methanation were studied using CO2:H2 = 1:4 stoichiometric ratio at high space velocity (300 L g−1 h−1). Sample structure and morphology were studied by X-ray diffraction (XRD), Brunauer–Emmet–Teller (BET) analysis, field-emission scanning electron microscopy/energy-dispersive spectroscopy (FE-SEM/EDS), H2-temperature programmed reduction (TPR), H2-temperature-programmed desorption (TPD). Both the CO production and the turnover frequency appear depending on nickel particle size, suggesting a structure sensitivity of the CO2 methanation on nickel supported on ceria.