Ag@AgCl nanoparticles grafted on carbon nanofiber: an efficient visible light plasmonic photocatalyst via bandgap reduction.

A novel silver@silver chloride/carbon nanofiber (Ag@AgCl/CNF) hybrid was synthesized by electrospinning, heat treament, and subsequentin situchemical oxidation strategy. The synthesized materials were characterized using x-ray diffraction, Fourier-transform infrared, UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy, and energy dispersive x-ray. The experimental results reveal that the electrospun AgNO3/PAN was carbonized and reduced to Ag/CNF, the Ag/CNF was then partly oxidized to form Ag@AgCl/CNF in which Ag@AgCl nanoparticles (ca. 10-20 nm in diameter) were uniformly bounded to CNFs (ca. 165 nm in diameter). The obtained Ag@AgCl/CNF was employed for Na2S2O8activation under visible light irradiation to treat Rhodamine B (RhB). A remarkable RhB removal of ca. 94.68% was achieved under optimal conditions, and the influence of various parameters on removal efficiency was studied. Quenching experiments revealed that HO•, SO4•-,1O2, and O2•-were major reactive oxygen species, in which O2•-played a pivotal role in RhB degradation. A possible mechanistic route for RhB degradation was proposed.

One-pot synthesis of manganese oxide/graphene composites via a plasma-enhanced electrochemical exfoliation process for supercapacitors.

In this work, a feasible one-pot approach to synthesize manganese oxide/graphene composites, the so-called plasma-enhanced electrochemical exfoliation process (PE3P), has been developed. Herein, a composite of graphene decorated with manganese oxide nanoparticles was prepared via PE3P from a KMnO4 solution and graphite electrode under a voltage of 70 V in an ambient environment. By controlling the initial KMnO4 concentration, we obtained distinct MnO2/graphene samples. The prepared samples were characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and Raman spectroscopy. The electrochemical measurements of the MnO2/graphene composites revealed that the specific capacitance of the samples is approximately 320 F g-1 at a scan rate of 10 mV s-1, which is comparably very high for manganese oxide/carbon-based supercapacitor electrode materials. Considering the simple, low-cost, one-step and environmentally friendly preparation, our approach has the potential to be used for the fabrication of MnO2/graphene composites as the electrode materials of supercapacitors.

Facile synthesis of Mn-doped NiCo2O4 nanoparticles with enhanced electrochemical performance for a battery-type supercapacitor electrode.

We report the synthesis of manganese-doped nickel cobalt oxide (Mn-doped NiCo2O4) nanoparticles (NPs) by an efficient hydrothermal and subsequent calcination route. The material exhibits a homogeneous distribution of the Mn dopant and a battery-type behavior when tested as a supercapacitor electrode material. Mn-doped NiCo2O4 NPs show an excellent specific capacity of 417 C g-1 at a scan rate of 10 mV s-1 and 204.3 C g-1 at a current density of 1 A g-1 in a standard three-electrode configuration, ca. 152-466% higher than that of pristine NiCo2O4 or MnCo2O4. In addition, Mn-doped NiCo2O4 NPs showed an excellent capacitance retention of 99% after 1000 charge-discharge cycles at a current density of 2 A g-1. The symmetric solid-state supercapacitor device assembled using this material delivered an energy density of 0.87 µW h cm-2 at a power density of 25 µW h cm-2 and 0.39 µW h cm-2 at a high power density of 500 µW h cm-2. The cost-effective synthesis and high electrochemical performance suggest that Mn-doped NiCo2O4 is a promising material for supercapacitors.

Catalytic activation of peroxymonosulfate with manganese cobaltite nanoparticles for the degradation of organic dyes.

In this work, we report the facile hydrothermal synthesis of manganese cobaltite nanoparticles (MnCo2O4.5 NPs) which can efficiently activate peroxymonosulfate (PMS) for the generation of sulfate free radicals (SO4˙-) and degradation of organic dyes. The synthesized MnCo2O4.5 NPs have a polyhedral morphology with cubic spinel structure, homogeneously distributed Mn, Co, and O elements, and an average size less than 50 nm. As demonstrated, MnCo2O4.5 NPs showed the highest catalytic activity among all tested catalysts (MnO2, CoO) and outperformed other spinel-based catalysts for Methylene Blue (MB) degradation. The MB degradation efficiency reached 100% after 25 min of reaction under initial conditions of 500 mg L-1 Oxone, 20 mg L-1 MnCo2O4.5, 20 mg L-1 MB, unadjusted pH, and T = 25 °C. MnCo2O4.5 NPs showed a great catalytic activity in a wide pH range (3.5-11), catalyst dose (10-60 mg L-1), Oxone concentration (300-1500 mg L-1), MB concentration (5-40 mg L-1), and temperature (25-55 °C). HCO3 -, CO3 2- and particularly Cl- coexisting anions were found to inhibit the catalytic activity of MnCo2O4.5 NPs. Radical quenching experiments revealed that sulfate radicals are primarily responsible for MB degradation. A reaction sequence for the catalytic activation of PMS was proposed. The as-prepared MnCo2O4.5 NPs could be reused for at least three consecutive cycles with small deterioration in their performance due to low metal leaching. This study suggests a facile route for synthesizing MnCo2O4.5 NPs with high catalytic activity for PMS activation and efficient degradation of organic dyes.

Free-standing polypyrrole/polyaniline composite film fabricated by interfacial polymerization at the vapor/liquid interface for enhanced hexavalent chromium adsorption.

Interfacial polymerization is an innovative technique for the fabrication of polymeric films. However, the majority of studies on interfacial polymerization has focused on liquid/liquid interfaces, and little work has been done on vapor/liquid interfaces. In this paper, we present the fabrication of free-standing polypyrrole/polyaniline (PPy/PANI) composite films by interfacial polymerization at a vapor/liquid interface using FeCl3 as an oxidant. The obtained PPy/PANI composite films were characterized using Fourier transform infrared spectroscopy, X-ray diffractometry, and scanning electron microscopy. It was found that the PPy/PANI composite films consist of PANI particles evenly distributed on porous PPy film. The influence of FeCl3 concentration on the morphology of the resulting composite films was investigated. The PPy/PANI composite films show an excellent Cr(vi) adsorption capacity of 256.41 mg g-1, much higher than that of PPy-based absorbents prepared from chemical and electrochemical polymerization routes. This work thus suggests a new route for the fabrication of PPy/PANI films with highly enhanced Cr(vi) adsorption capacity for practical applications.

Laser Power Dependent Optical Properties of Mono- and Few-Layer MoS2.

We report on the exponential decay of the red-shift of the photoluminescence A-exciton peak in monolayer molybdenum disulfide (MoS2) with the excitation laser power. The linear relationship found for the thermal variation of the same peak suggests that the laser power effect goes beyond the exciton dynamics associated to temperature variations. Laser exitation power effect on the broadening and red-shifting of the A(1g) and E(2g)1 phonon peaks observed by Raman spectroscopy reflect the damping of vibration due local thermal heating induced by the laser. Our results point out the laser excitation power dependence on the photoluminescence properties of monolayer MoS2.