Microwave-assisted Reduction Process Research Articles

Microwave‐induced defective PdFe/C nano‐electrocatalyst for highly efficient alkaline glycerol oxidation reactions

Pd-based mono- and bi-metallic nano-electrocatalysts (Pd/C and PdFe/C) have been synthesized using two different methods for comparison: conventional sodium borohydride (NaBH4) route and microwave-assisted reduction process. The performance of the nano-electrocatalysts is tested for glycerol oxidation reaction (GlyOR) in an alkaline medium. DFT simulation proves that incorporation of Fe to Pd(111) leads to an increased partial density of states (PDOS) compared to Pd alone, confirming the importance for bimetallic nano-electrocatalyst. The adsorption energy of glycerol onto PdFe is slightly weaker (A.E. = -48.89 eV) than the Pd alone (A.E. = -48.60 eV), indicating the ease with which glycerol can be generated at the PdFe surface than at the Pd alone. XRD show that microwave-irradiated samples (Pd(MW) and PdFe(MW)) are more crystalline than the conventional Pd and PdFe. TEM images show that the Pd(MW) and PdFe(MW) have slightly larger particle sizes (5.30 – 7.40 nm) than those from the conventional route (2.48 – 3.02 nm). Nitrogen adsorption-desorption analysis shows that the microwave samples exhibit slightly larger surface area compared to samples from NaBH4 route. Raman and XPS show that Pd(MW) and PdFe(MW) are more prone to defects (i.e., oxygen vacancies) compared to the NaBH4 route. The microwave samples gave the highest electrocatalytic properties toward glycerol than the NaBH4 route (including high electrochemical active surface area, high current density response, high resistance to poisoning due to carbonaceous intermediates arising from the GlyOR, and high conductivity or low interfacial resistance) compared to samples from the conventional NaBH4 method. The findings in this work go a long way to understanding the physico-chemical and electrochemical effects of microwave irradiation on bimetallic electrocatalyst for glycerol oxidation reaction, which open new opportunities for developing high-performance direct alkaline glycerol fuel cells.

Microwave-Assisted Synthesis of Silver Nanoparticles: Effect of Reaction Temperature and Precursor Concentration on Fluorescent Property

The fluorescent silver nanoparticles were synthesized using trisodium citrate as a reducing and stabilizing agent in a microwave-assisted reduction process. The influence of synthesizing parameters such as reaction duration, temperature, and trisodium citrate concentration (100, 200, and 400 ppm) were examined on the characteristics and fluorescent properties of synthesized silver nanoparticles (AgNPs). The formation of AgNPs was studied by UV–Vis absorption spectroscopy, X-ray diffraction, ATR-FTIR spectra, and scanning electron microscopy. The low concentration compared to the high concentration of trisodium citrate resulted in a prolonged reduction process, and also the high concentration resulted in the formation of smaller AgNPs (44 nm). The fluorescence emission spectra of the synthesized colloidal AgNPs demonstrated a quite explicit emission peak centered around 335 nm. However, the higher reaction temperature (above 100 °C) resulted in a sharp and narrow emission peak. The synthesized silver nanoparticles exhibited a suitable fluorescent property, which was reliant on the size of synthesized AgNPs.

Persistent luminescence of inorganic nanophosphors prepared by wet-chemical synthesis

The synthesis of efficient nanosized persistent luminescence materials remains a challenge for the community. Paradoxically, due to the dependence of the point lattice defects and the persistent luminescence efficiency, the control of the defect formation, favorable when the materials are prepared at high temperatures, normally leads to particle growth and sintering. In this work, efficient nanosized rare earth doped disilicates Sr2MgSi2O7:Eu2+,Dy3+ were synthesized via three different wet-chemical methods taking advantages of the microwave-assisted reduction process as a support step to produce high-quality polycrystalline materials. The crystallite size of the sample showed to be smaller when the decomposition temperature of the precursors is higher and close to the phase formation energy. The excitation VUV spectroscopy indicated that despite being nanocrystalline, the materials optical band gap has just a small difference compared one to another. The reduction of Eu3+ to Eu2+ was successfully obtained, since the f-d interconfigurational transitions of Eu2+ 4f65d1→4f7 emission were observed in the blue region of the spectra. The persistent luminescence efficiency measured through its lasting decay time was close to the commercial materials references and with the advantage of having size control during the synthesis method that can lead to the size dependent applications of photonic materials.

Fabrication and Enhanced Photoactivities of Plasmonic Ag/TiO₂ Nano-Flower Films.

Titania nano-flower films were in this study decorated with silver nanoparticles (Ag/TiO₂ NFFs) and fabricated through a facile hydrothermal route, followed by a microwave-assisted reduction process. The investigations indicated that the Ag nanoparticles were deposited evenly on the anatase TiO₂ film, forming a heterogeneous structure. The prepared composites exhibited excellent visible light harvesting ability due to the light-scattering TiO₂ nanostructures and localized surface plasmon resonance (LSPR) of Ag NPs. In addition, a lower recombination probability for the photoexcited charge carriers was observed. These experimental results demonstrated that the Ag/TiO₂ NFFs possessed obviously enhanced photocatalytic activities for methyl orange (MO) degradation in comparison with pure TiO₂ NFFs, and the corresponding degradation rate was 3.5 times as much as that of pure TiO₂ NFFs. This enhancement arose from the positive synergetic effect between the charge separation behavior and LSPR effect from the Ag nanoparticles. The results from the present study demonstrate that the visible light capturing ability for the TiO₂-based semiconductors can be achieved through rational design of their nanostructures or through the LSPR effect originating from the plasmonic nanoparticles. This work also offers a facile approach for developing film photocatalysts with high efficiency.

A facile strategy to fabricate plasmonic Cu modified TiO2 nano-flower films for photocatalytic reduction of CO2 to methanol

Cu nanoparticles (NPs) deposited TiO2 nano-flower films were fabricated using a combination of a hydrothermal method and a microwave-assisted reduction process. The investigations indicated that Cu NPs and TiO2 film both exhibit visible light harvesting properties based on localized surface plasmon resonance (LSPR) of Cu NPs and unique nanostructures of TiO2 film. Fluorescence quenching was observed because the recombination of charge carriers was effectively suppressed by Cu NPs deposition. The experimental results indicate that Cu/TiO2 films exhibit better activity for the photocatalytic reduction of CO2 due to the charge transfer property and LSPR effect of Cu NPs. The CH3OH production rate reached 1.8μmolcm−2h−1 (energy efficiency was 0.8%) over 0.5 Cu/TiO2 film under UV and visible light irradiation, which was 6.0 times higher than that observed over pure TiO2 film. In addition, a tentative photocatalytic mechanism is proposed to understand the experimental results over the Cu modified TiO2 nano-flower films.

Effect of active zinc oxide dispersion on reduced graphite oxide for hydrogen sulfide adsorption at mid-temperature

Composites of Zinc oxide (ZnO) with reduced graphite oxide (rGO) were synthesized and used as adsorbents for hydrogen sulfide (H2S) at 300°C. Various characterization methods (TGA, XRD, FT-IR, TEM and XPS) were performed in order to link their H2S adsorption performance to the properties of the adsorbent's surface. Microwave-assisted reduction process of graphite oxide (GO) provided mild reduction environment, allowing oxygen-containing functional groups to remain on the rGO surface. It was confirmed that for the ZnO/rGO synthesize using the microwave-assisted reduction method, the ZnO particle size and the degree of ZnO dispersion remained stable over time at 300°C, which was not the case for only the ZnO particles themselves. This stable highly dispersed feature allows for sustained high surface area over time. This was confirmed through breakthrough experiments for H2S adsorption where it was found that the ZnO/rGO composite showed almost four times higher ZnO utilization efficiency than ZnO itself. The effect of the H2 and CO2 on H2S adsorption was also investigated. The presence of hydrogen in the H2S stream had a positive effect on the removal of H2S since it allows a reducing environment for ZnO and ZnS bonds, leading to more active sites (Zn2+) to sulfur molecules. On the other hand, the presence of carbon dioxide (CO2) showed the opposite trend, likely due to the oxidation environment and also due to possible competitive adsorption between H2S and CO2.

The improved electrocatalytic activity of palladium/graphene nanosheets towards ethanol oxidation by tin oxide

Tin oxide (SnO 2)/graphene nanosheets (GNS) composite was prepared by a simple chemical-solution method as the catalyst support for direct ethanol fuel cells. Then the SnO 2-GNS composites supporting Pd (Pd/SnO 2-GNS) catalysts were synthesized by a microwave-assisted reduction process. The Pd/SnO 2-GNS catalysts were characterized by using X-ray diffraction, transmission electron microscopy and energy-dispersive spectroscopy techniques. The electrocatalytic performances of Pd/SnO 2-GNS catalysts for ethanol oxidation were studied by cyclic voltammetric and chronoamperometric measurements. It was found that compared with Pd/GNS, the Pd/SnO 2-GNS catalyst showed superior electrocatalytic activity for ethanol oxidation when the mass ratio of SnCl 2·2H 2O precursor salt to graphite oxide was about 1:2.

EPR characterisation of platinum nanoparticle functionalised carbon nanotube hybrid materials

The use of nanostructured carbon materials as electrodes for energy storage and conversion is an expanding area of research in recent years. Herein, platinum nanoparticles have been deposited onto both multi-walled and single-walled carbon nanotubes (CNTs) via a microwave assisted polyol reduction method. This interaction has been probed with electron paramagnetic resonance (EPR) and Raman spectroscopies to elucidate the charge/electron transfer interactions between the Pt nanoparticles and the CNTs. Observed shifts in the g factors of the CNTs are indicative of such an electronic interaction, strongly suggesting the covalent attachment of the nanoparticles to the carboxylic groups on the CNTs, formed during the microwave-assisted reduction process. The Pt decorated CNTs show a dramatic increase in electrochemical behaviour in terms of high reversible capacity and relatively stable cycle performance compared to unmodified CNTs increasing their applicability in energy storage devices. For instance, significant increases in the electrochemical double layer capacitance are observed for the CNT-NP composite electrode.