Construction of 3D sheet-packed hierarchical MoS2/BiOBr heterostructures with remarkably enhanced photocatalytic performance for tetracycline and levofloxacin degradation.

In this paper, MoS2 nanosheets were prepared and deposited on BiOBr microflowers through deposition-hydrothermal strategy. MoS2 exhibited a string of nanosheets with wrinkled layer outlook, and MoS2/BiOBr composites displayed a micro-flower morphology with the diameter of 2-3 µm. Visible-light harvesting performance was significantly improved in the region of 400-600 nm for MoS2/BiOBr. The obtained MoS2/BiOBr samples exhibited tremendous enhanced catalytic activity, which could degrade 92.96% of tetracycline and 90.31% of levofloxacin within 70 min. The photo-generated holes and ⋅OH radicals played the dominant roles in the whole photocatalytic decomposition process. Based on the analysis of DRS, BET, PL, and electrochemical results, the remarkably improved photocatalytic performance may be ascribed to the synergistic effect of strong visible-light harvesting ability, enhanced BET surface area, and faster separation or transfer efficiency of photo-generated charges.

Boosting the capacitive property of nickel cobalt aluminum layered double hydroxide in neutral electrolyte.

Layered double hydroxide (LDH) has shown great potential for energy storage due to their high theoretical specific capacitance, relatively low cost and eco-friendliness. LDH, however, always works in alkali aqueous electrolyte for supercapacitors, which brings serious environmental pollution. In this work, a reduced graphite oxide/Fe(CN)63-- nickel cobalt aluminum LDH (RGO/Fe(CN)63--LDH) composite has been prepared via ion-exchange reaction using RGO/LDH as precursor. RGO/Fe(CN)63--LDH electrode provides a specific capacitance of 221 F g-1 in a wide potential window of -1 ~ 0.8 V vs. SCE in Na2SO4 aqueous electrolyte, and which is much higher than that of LDH electrode (3.56 F g-1). Owing to the wide potential window of RGO/Fe(CN)63--LDH electrode, a symmetrical solid supercapacitor device (RGO/Fe(CN)63--LDH//RGO/Fe(CN)63--LDH) with a high voltage of 2.0 V can deliver a high specific energy of 25.2 Wh kg-1 at a specific power of 250 W kg-1, and a capacitance retention of 75% after galvanostatic charging/discharging at 5 A g-1 for 5000 times. This work supplies enlightenment for boosting the capacitive performance of LDHs in neutral electrolyte.

Methylene blue functionalized graphene as binder-free electrode for high-performance solid state supercapacitors.

Electrochemical active small organic molecules are potential electrode materials for supercapacitors due to their sustainable and good redox reversibility. However, the poor electrical conductivity restricts their application in supercapacitors. Herein, a water soluble organic dye of methylene blue (MB) has been supported on graphene (GR) through a facile ultrasonic method to form a methylene blue/graphene (MB/GR) composite. A small amount of MB (13%) in MB/GR composite improves the wettability of GR and supplies pseudocapacitance. The MB/GR composite can be used as a binder-free electrode for supercapacitors, and gives a high specific capacitance of 517 F g-1 at 0.5 A g-1 in 0.5 mol L-1 H2SO4 aqueous electrolyte with a satisfactory capacitive retention of 91% after 2000 consecutive cyclic voltammetry tests at 10 mV s-1. Benefiting from the high specific capacitance of MB/GR composite, the as-assembled symmetrical solid-state supercapacitor (MB/GR//MB/GR) delivers a high energy density of 30.36 Wh kg-1 at 0.7 kW kg-1, and excellent cycle stability (nearly 27% drop after 10,000 consecutive constant current charge-discharge at 5 A g-1). This work offers some enlightenment to design and preparation of high-performance electrode materials for supercapacitors.

An effective strategy for boosting photoinduced charge separation of Ag3PO4 by BiVO4 with enhanced visible light photodegradation efficiency for levofloxacin and methylene blue.

In this paper, a Z-scheme Ag3PO4/BiVO4 photocatalyst was successfully prepared by precipitation-deposition method. The Ag3PO4/BiVO4 composite exhibited enhanced photocatalytic activity and recyclability for levofloxacin and methylene blue degradation under visible light irradiation. In the Ag3PO4/BiVO4-0.4 system, up to 92.44% of the levofloxacin molecules can be decomposed within 180 min and the photocatalytic degradation efficiency can maintain at 92.02% for methylene blue after recycled for 5 times. The enhanced photocatalytic activity of Ag3PO4/BiVO4 heterojunctions could be mainly attributed to the fabrication of hetero-structure between BiVO4 and Ag3PO4. The photogenerated electron-hole pair separation was effectively enhanced based on the photocurrent, electro-chemical impedance spectra and photoluminescence data. Furthermore, the electrons transfer from photoinduced BiVO4 to Ag3PO4 and the visible light harvesting efficiencies were significantly increased due to the BiVO4 hybridization. The ·OH was the main oxidative species in the Ag3PO4/BiVO4 system for the methylene blue decomposition. Finally, a purposed photocatalytic mechanism for methylene blue degradation was discussed in detail on the basis of experimental results.

Hydrothermal synthesis of p-C3N4/f-BiOBr composites with highly efficient degradation of methylene blue and tetracycline.

Construction of heterojunctions with band-suitable different semiconductors has been demonstrated to be an efficient approach to enhance the separation of photoinduced electrons and holes. In this paper, highly efficient heterojuction photocatalysts consisted of porous-C3N4 (p-C3N4) and flowerlike-BiOBr (f-BiOBr) were successfully synthesized via a deposition-hydrothermal method. The SEM and HRTEM images indicated that BiOBr were successfully deposited on the surface of p-C3N4 and the layered p-C3N4/f-BiOBr heterojunctions were formed between p-C3N4 and f-BiOBr. The optimum photocatalytic activity of the p-C3N4/f-BiOBr nanocomposites with weight ratio of 3%p-C3N4 exhibited dramatically improved visible-light photocatalytic activities with 98.42% and 94.25% degradation rates for methylene blue (MB) and tetracycline, respectively. The enhanced activity was mainly attributed to the unique heteojunction architecture, which creates large interfacial surface between the constituent materials for facilitating charge transfer and effectively inhibits the fast recombination of photogenerated electrons and holes. The active species trapping experiment indicated that the O2- was the dominating reactive oxidizing species of p-C3N4/f-BiOBr for MB degradation under visible light irradiation. Moreover, the as-prepared photocatalysts displayed excellent stability in the recycling experiments with no obvious decrease of the degradation efficiencies for MB and tetracycline. Furthermore, the possible photocatalytic degradation mechanism of MB over p-C3N4/f-BiOBr was proposed to better understand the reaction process. The work provides a facile route for rational design of heterojunction photocatalysts with promising prospect for the treatment of antibiotic residues in various wastewaters.

Free-standing graphene/bismuth vanadate monolith composite as a binder-free electrode for symmetrical supercapacitors.

Preparation of new types of electrode material is of great importance to supercapacitors. Herein, a graphene/bismuth vanadate (GR/BiVO4) free-standing monolith composite has been prepared via a hydrothermal process. Flexible GR sheets act as a skeleton in the GR/BiVO4 monolith composites. When used as a binder-free electrode in a three-electrode system, the GR/BiVO4 composite electrode can provide an impressive specific capacitance of 479 F g-1 in a potential window of -1.1 to 0.7 V vs. SCE at a current density of 5 A g-1. A symmetrical supercapacitor cell which can be reversibly charged-discharged at a cell voltage of 1.6 V has been assembled based on this GR/BiVO4 monolith composite. The symmetrical capacitor can deliver an energy density of 45.69 W h kg-1 at a power density of 800 W kg-1. Moreover, it ensures rapid energy delivery of 10.75 W h kg-1 with a power density of 40 kW kg-1.

Facile preparation of partially reduced graphite oxide nanosheets as a binder-free electrode for supercapacitors.

Preparation of graphene (GR) based electrode materials with excellent capacitive properties is of great importance to supercapacitors. Herein, we report a facile approach to prepare partially reduced graphite oxide (PRG) nanosheets by reducing graphite oxide (GO) using commercial Cu2O powder as a reduction agent, moreover, we demonstrate that the PRG nanosheets can act as building blocks for assembling hydrogels (PRGH) and flexible film (PRGF). The obtained PRGH and PRGF can be directly used as binder-free electrodes for supercapacitors and give high specific capacitance (292 and 273 F g-1 at a current density of 0.5 A g-1 in a three-electrode system, respectively) due to the existence of oxygen-containing functional groups in PRG nanosheets. PRG also gives excellent rate ability and cycle stability. This study suggests a facile pathway to produce GR-based materials with excellent capacitive properties and is meaningful for flexible supercapacitors.

Free-standing graphene/vanadium oxide composite as binder-free electrode for asymmetrical supercapacitor.

Preparation of free-standing electrode materials with three-dimensional network architecture has emerged as an effective strategy for acquiring advanced portable and wearable power sources. Herein, graphene/vanadium oxide (GR/V2O5) free-standing monolith composite has been prepared via a simple hydrothermal process. Flexible GR sheets acted as binder to connect the belt-like V2O5 for assembling three-dimensional network architecture. The obtained GR/V2O5 composite can be reshaped into GR/V2O5 flexible film which exhibits more compact structure by ultrasonication and vacuum filtration. A high specific capacitance of 358Fg-1 for GR/V2O5 monolith compared with that of GR/V2O5 flexible film (272Fg-1) has been achieved in 0.5molL-1K2SO4 solution when used as binder free electrodes in three-electrode system. An asymmetrical supercapacitor has been assembled using GR/V2O5 monolith as positive electrode and GR monolith as negative electrode, and it can be reversibly charged-discharged at a cell voltage of 1.7V in 0.5molL-1 K2SO4 electrolyte. The asymmetrical capacitor can deliver an energy density of 26.22Whkg-1 at a power density of 425Wkg-1, much higher than that of the symmetrical supercapacitor based on GR/V2O5 monolith electrode. Moreover, the asymmetrical supercapacitor preserves 90% of its initial capacitance over 1000 cycles at a current density of 5Ag-1.

Carbon nanotubes/holey graphene hybrid film as binder-free electrode for flexible supercapacitors.

The practical application of graphene (GR) has still been hindered because of its unsatisfied physical and chemical properties resulting from the irreversible agglomerates. Preparation of GR-based materials with designed porosities is essential for its practical application. In this work, a facile and scalable method is developed to synthesize carbon nanotubes/holey graphene (CNT/HGR) flexible film using functional CNT and HGR as precursors. Owing to the existence of the small amount CNT, the CNT-5/HGR flexible film with a 3D conductive interpenetrated architecture exhibit significantly improved ion diffusion rate compared to that of the HGR. Moreover, CNT-5/HGR flexible film can be used as binder-free supercapacitor electrodes with ultrahigh specific capacitances of 268Fg-1, excellent rate capabilities, and superior cycling stabilities. CNT-5/HGR flexible film could be used to fabricate high-performance flexible supercapacitors electrodes.