Lirong Kong

Facile synthesis of nickel–cobalt sulfide/reduced graphene oxide hybrid with enhanced capacitive performance

A uniform hybrid with nickel–cobalt sulfide (NiCo2S4) nanoparticles attached on reduced graphene oxide (RGO) nanosheets is fabricated through a facile one-pot refluxing method. NiCo2S4 nanoparticles with sizes of several nanometers uniformly disperse on the surface of RGO sheets, and the electrochemical properties of the resulting NiCo2S4/RGO hybrids are investigated by using them as electrode materials for a supercapacitor. The NiCo2S4/RGO hybrids deliver a maximum specific capacitance of 1526 F g−1 at the current density of 1.0 A g−1, and a high rate capability, retaining 1109 F g−1 at a high current density of 20 A g−1. Moreover, after 2000 charge–discharge cycles at the current density of 10 A g−1, 83% of the initial capacitance is maintained, indicating a good cycling stability. The enhanced capacitive performance can be attributed to the synergistic effect between NiCo2S4 nanoparticles and RGO, in which RGO can provide conductive channels and serve as an ideal support matrix. The facile synthesis and the remarkable capacitive performance of the NiCo2S4/RGO hybrid make it a promising candidate for electrode materials in electrochemical energy conversion/storage devices.

g-C3N4/AgBr nanocomposite decorated with carbon dots as a highly efficient visible-light-driven photocatalyst

Visible-light-driven photocatalysis as a green technology has attracted intense interest due to its potential applications in environmental remediation. However, the poor visible light utilization and low electron-hole separation efficiency of photocatalysts largely limited their practical application. In this work, a new ternary visible-light driven photocatalyst of g-C3N4/CDs/AgBr has been prepared by the introduction of carbon dots (CDs) onto the surface of g-C3N4, followed by in-situ growth of AgBr nanoparticles on CDs-modified g-C3N4 nanosheets. The g-C3N4/CDs/AgBr nanocomposite exhibits excellent photocatalytic efficiency for organic pollutant degradation, which is about 4.0, 5.3 and 2.3 times higher than that of AgBr, g-C3N4 and g-C3N4/AgBr, respectively. The result indicates the introduction of CDs into g-C3N4/AgBr can largely improve the photocatalytic activity since CDs act as the light absorber and the electron mediator between g-C3N4 and AgBr, which effectively promote the separation of photogenerated charge carriers and the utilization of visible light. Moreover, the photocatalytic activity of g-C3N4/CDs/AgBr has no obvious decrease after four photodegradation cycles, demonstrating a high photocatalytic stability. This study highlights the potential application of highly efficient CDs decorated photocatalysts in waste water purification.

Synthesis of Cu3P nanocubes and their excellent electrocatalytic efficiency for the hydrogen evolution reaction in acidic solution

Cu3P nanocubes are synthesized through a facile two-step strategy, which consists of a simple solution based method followed by a low-temperature phosphidation process. The Cu3P nanocubes have an average size of about 198 nm, and show a three-dimensional (3D) cubic architecture with hollow interiors and thin cubic shells. The material as an electrocatalyst for the hydrogen evolution reaction (HER) is investigated in acidic solution. It is found that the Cu3P nanocubes exhibit a low overpotential (145 mV), a small Tafel slope (70.2 mV per decade), and a large exchange current density (0.016 mA cm−2). Moreover, the Cu3P nanocubes show great electrochemical stability in acidic solution since no obvious decay in current density is observed after 1000 cycles. The excellent electrocatalytic performance can be associated with the electronic structures of Cu and P, as well as the hollow interior structure of Cu3P nanocubes, which supplies more active sites for HER. The approach used here provides an effective route for synthesizing metal phosphides with various microstructures and functions.

Nitrogen-doped carbon dot-modified Ag3PO4/GO photocatalyst with excellent visible-light-driven photocatalytic performance and mechanism insight

In this paper, an all solid Z-scheme Ag3PO4/GO/NCD photocatalyst has been prepared through anchoring nitrogen-doped carbon dots (NCDs) on the Ag3PO4/GO (GO = graphene oxide) composite. The Ag3PO4/GO/NCD photocatalyst exhibits excellent photocatalytic activity for the degradation of organic pollutants, methylene blue (MB), rhodamine B (RhB) and phenol, under visible-light irradiation. The pollutants MB (10 mg L−1), RhB (10 mg L−1) and phenol (50 mg L−1) could be efficiently degraded within 2.5 min, 5 min and 120 min, respectively, which are much better than that over Ag3PO4 and Ag3PO4/GO, indicating that the introduction of NCDs can further improve the photocatalytic activity of Ag3PO4/GO. Moreover, after four photocatalytic cycles, the photocatalytic activity of Ag3PO4/GO/NCDs shows only a slight decrease, demonstrating high photocatalytic stability. It is revealed that GO in the photocatalyst acts as a semiconductor and forms a Z-scheme heterojunction with Ag3PO4, while NCDs improve the oxygen activation, enhance the light harvesting capacity and serve as the reaction sites during the photocatalytic process. This study highlights the potential application of highly efficient NCD-modified photocatalysts in waste water purification.

Reduced graphene oxide uniformly decorated with Co nanoparticles: facile synthesis, magnetic and catalytic properties

Herein, Co nanoparticles with high dispersivity were grown in situ on reduced graphene oxide (RGO) nanosheets by an environmentally friendly and facile one-step strategy. The as-synthesized products were characterized by X-ray powder diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The magnetic and catalytic properties of the RGO/Co nanocomposites were systematically investigated. The results reveal that the RGO/Co nanocomposites have room-temperature ferromagnetic characteristics with Co particle size below single domain size. In addition, these RGO/Co nanocomposites also exhibit excellent catalytic activities toward the reduction of 4-nitrophenol by NaBH4 and enhanced electrocatalytic properties for the oxidation of glucose. It is believed that this eco-friendly and facile route can be extended to synthesize other metal nanostructures on RGO nanosheets with various functions, and provides a new opportunity for the application of graphene/metal nanocomposites.

Metal-organic framework derived Fe/Fe 3 C@N-doped-carbon porous hierarchical polyhedrons as bifunctional electrocatalysts for hydrogen evolution and oxygen-reduction reactions

The development of simple and cost-effective synthesis methods for electrocatalysts of hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is critical to renewable energy technologies. Herein, we report an interesting bifunctional HER and ORR electrocatalyst of Fe/Fe3C@N-doped-carbon porous hierarchical polyhedrons (Fe/Fe3C@N-C) by a simple metal-organic framework precursor route. The Fe/Fe3C@N-C polyhedrons consisting of Fe and Fe3C nanocrystals enveloped by N-doped carbon shells and accompanying with some carbon nanotubes on the surface were prepared by thermal annealing of Zn3[Fe(CN)6]2·xH2O polyhedral particles in nitrogen atmosphere. This material exhibits a large specific surface area of 182.5 m2 g-1 and excellent ferromagnetic property. Electrochemical tests indicate that the Fe/Fe3C@N-C hybrid has apparent HER activity with a relatively low overpotential of 236 mV at the current density of 10 mA cm-2 and a small Tafel slope of 59.6 mV decade-1. Meanwhile, this material exhibits excellent catalytic activity toward ORR with an onset potential (0.936 V vs. RHE) and half-wave potential (0.804 V vs. RHE) in 0.1 M KOH, which is comparable to commercial 20 wt% Pt/C (0.975 V and 0.820 V), and shows even better stability than the Pt/C. This work provides a new insight to developing multi-functional materials for renewable energy application.

Fabrication of N-doped Reduced Graphene Oxide/Ag3PO4 Nanocomposite with Excellent Photocatalytic Activity for the Degradation of Organic Pollutants

An efficient N-doped reduced graphene oxide (N-RGO)/Ag3PO4 nanocomposite with enhanced photocatalytic activity has been prepared through a facile solution-based approach. Since N-RGO could offer more sites for the anchoring of Ag3PO4 nanoparticles, and effectively promote the charge carriers separation and transfer due to its high electrical conductivity, the photocatalytic activity of N-RGO/Ag3PO4 nanocomposite is much higher than bare Ag3PO4 and N-RGO in the degradation of phenol pollutant under simulated solar light irradiation. The mechanism for the photocatalytic process was also investigated. The excellent photocatalytic performance makes the N-RGO/Ag3PO4 nanocomposite a promising photocatalyst for organic pollutant treatment.

Synthesis of GO-AgIO4 nanocomposites with enhanced photocatalytic efficiency in the degradation of organic pollutants

Graphene oxide (GO)–AgIO4 nanocomposites with excellent photocatalytic performance have been prepared through a facile ion-exchange method. The as-prepared samples are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The GO–AgIO4 nanocomposites exhibit an enhanced photocatalytic activity in the degradation of organic pollutants as compared to bare AgIO4. It is revealed that the introduction of GO can relieve the agglomeration of AgIO4 particles, enhance the light absorption of the materials, and promote the separation of photoexcited electron–hole pairs. In addition, the possible transfer and separation behaviors of the charge carriers and the photocatalytic mechanism are discussed in detail. The excellent photocatalytic performance makes the GO–AgIO4 nanocomposites a promising photocatalyst for organic pollutant treatment.

Nitrogen-doped carbon dots modified dibismuth tetraoxide microrods: A direct Z-scheme photocatalyst with excellent visible-light photocatalytic performance

In this work, an all solid direct Z-scheme photocatalyst of monoclinic dibismuth tetraoxide microrods/nitrogen-doped carbon dots (m-Bi2O4/NCDs) has been constructed through a simple one-step hydrothermal method. The m-Bi2O4/NCDs photocatalyst exhibits excellent photocatalytic activity for the degradation of methylene orange (MO) and phenol under visible light irradiation. The pollutants of MO (10 mg L-1) and phenol (45 mg L-1) could be efficiently degraded by m-Bi2O4/NCDs within 30 and 120 min, respectively, which is much better than that of the single m-Bi2O4, indicating that the introduction of NCDs into m-Bi2O4 can effectively improve the photocatalytic activity. Moreover, the m-Bi2O4/NCDs photocatalyst possesses a high photocatalytic stability and durability, and its photocatalytic activity did not show obvious decline after four photodegradation cycles. It is found that both O2- and direct h+ oxidation play important roles in the degradation process, and based on the experimental result a direct Z-scheme photocatalytic mechanism is proposed. This study suggests that the as-prepared m-Bi2O4/NCDs composite is a promising photocatalyst for environmental remediation.

Ionic liquid directed construction of foam-like mesoporous boron-doped graphitic carbon nitride electrode for high-performance supercapacitor

Carbon materials with controllable hierarchically porous structure and high doping level are expect to exhibit superior energy storage performance when used as electrode materials for supercapacitors. Herein, we report the preparation of a novel foam-like boron-doped carbon nitride material with hierarchically porous structure and high doping contents of nitrogen (21.45 ± 0.93 at%) and boron (6.46 ± 0.60 at%). Due to the unique compositional and structural features, this material exhibits high energy storage performance, including a large specific capacitance of ∼ 660.6 F g-1 at 0.1 A g-1 and a high capacitance retention after 10,000 cycles. This study can provide new ideas for the development of carbon based electrode materials with unique hierarchically porous structure and improved doping level.