Yanhong Tang

Direct Electrodeposition of Graphene Enabling the One‐Step Synthesis of Graphene–Metal Nanocomposite Films

Graphene, a 2D sp 2 -hybridized carbon sheet, has recently attracted great attention due to its unique electrical, optical, and mechanical properties as well as its potential use in various fi elds, such as electronics, supercapacitors, sensors, and composite materials. [ 1 ] Many methods have been proposed for graphene production, among which the chemical reduction of graphene oxide (GO) obtained from ultrasonic exfoliation of oxidized graphite is the most convenient way to yield large quantities of graphene sheets. [ 2 ] However, the practical applications of graphene are challenged by its irreversible agglomeration both in the drying state and in common solvents, which signifi cantly reduces its effectiveness. Introducing metal nanoparticles (NPs) was initially proposed in order to separate graphene sheets. [ 3 ] Nowadays, it is well realized that the dispersion of metal NPs on graphene sheets also potentially provides a new way to develop novel catalytic, magnetic, and optoelectronic materials. [ 4 ] The design and synthesis of graphene–metal nanohybrid assemblies are therefore of great interest for the exploration of their applications. Graphene–metal nanocomposites have typically been prepared by chemical or thermal reduction of mixtures of graphene (or GO) and metallic precursors. [ 3 , 5 ] Obviously, these methods involve highly toxic chemicals, such as hydrazine hydrate, or high temperature and, moreover, multiple steps are required that are time or labor consuming. Recently, electrochemical reduction of GO has been developed. [ 6 ] It is attractive for graphene-fi lm synthesis due to its simple, fast, and green nature. Typically, the electrochemical synthesis of graphene is carried out via two steps, namely, GO being fi rst assembled on the electrodes by dip-coating, drop-casting, or spray-coating methods and then being subjected to electrochemical reduction. Shortly thereafter, an approach, using GO-coated electrodes being immersed in a metallic precursor solution to perform one-step coelectrochemical reduction, was proposed to fabricate graphene– metal nanocomposite fi lms. [ 7 ] However, the above-mentioned

Amino siloxane oligomer-linked graphene oxide as an efficient adsorbent for removal of Pb(II) from wastewater

A high performance sorbent, oligomer-linked graphene oxide (GO) composite, was prepared through simple cross-linking reactions between GO sheets and poly3-aminopropyltriethoxysilane (PAS) oligomers as crosslinking agents. The three-dimensional PAS oligomers prevented GO sheets from aggregation, provided foreign molecules with easier access, and introduced a large amount of amino functional groups. The morphology, structure and property of the PAS-GO composite were determined by scanning electron microscope (SEM), transmission electron microscope (TEM), Fourie transform infrared (FTIR), X-ray diffractometer (XRD), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The adsorption performance of PAS-GO was investigated in removing Pb(II) ions from water. Compared to 3-aminopropyltriethoxysilane functionalized GO (AS-GO) which was prepared by the direct reaction between 3-aminopropyltriethoxysilane and GO, PAS-GO exhibited much higher adsorptivity toward Pb(II) with the maximum adsorption capacity of 312.5mg/g at 303 K and furthermore the maximum adsorption capacity increased with increasing temperature. The adsorption could be conducted in a wide pH range of 4.0-7.0. Importantly, PAS-GO had a priority tendency to adsorb Pb, Cu and Fe from a mixed solution of metal ions, especially from a practical industrial effluent.

Supersensitive Detection of Chlorinated Phenols by Multiple Amplification Electrochemiluminescence Sensing Based on Carbon Quantum Dots/Graphene

A novel electrochemiluminescence (ECL) sensor based on carbon quantum dots (CQDs) immobilized on graphene (GR) has been first developed for the determination of chlorinated phenols (CPs) in water. The detection is based on the ECL signals from the interaction between the analytes and the excited CQDs (C(*+)) using S2O8(2-) as coreactant. GR facilitates both C(•-) and SO4(•-) production, resulting in a high yield of C(*+), and the multistage amplification effect leads to a nearly 48-fold ECL amplification. Pentachlorophenol (PCP) is often monitored as an important indicator for CPs in real environmental samples, but its ultratrace and real-time analysis is an intractable issue in environmental monitoring. The resulting ECL sensor enables the real-time detection of PCP with unprecedented sensitivity reaching 1.0 × 10(-12) M concentration in a wide linear range from 1.0 × 10(-12) to 1.0 × 10(-8) M. The ECL sensor showed high selectivity to CPs, especially to PCP. The practicability of the sensing platform in real water samples showed ideal recovery rates. It is envisaged that the eco-friendly and recyclable sensor could be employed in the identification of key CPs in the environment.

Magnetic TiO2-graphene composite as a high-performance and recyclable platform for efficient photocatalytic removal of herbicides from water

A new photocatalyst, magnetic TiO2-graphene, was designed and facilely produced by combining sol-gel and assembling processes. Taking advantages of graphene and TiO2, the catalyst exhibited strong light absorption in the visible region and high adsorption capacity to organic pollutants, resulting in almost 100% photocatalytic removal efficiency of typical herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) from water under simulated solar light irradiation, far higher than 33% on commercial P25. Toxicity assessment indicates the total decomposition of the original substrate. Furthermore, the catalyst can be rapidly recovered with highly stable photocatalytic performance. After 8 successive cycles, the removal efficiency of 2,4-D maintained 97.7%, and particularly, 99.1% 2,4-D removal efficiency came back at the ninth recycle when the catalyst was re-treated by ultrasonication. Moreover, even after being laid aside for one year the catalyst still kept the 2,4-D removal efficiency as high as 95.6%. For practical application, the photocatalytic also demonstrated high removal efficiencies of herbicide 2,4-D. The photocatalyst is a promising platform for removing herbicide pollutants from water.

Efficient removal of herbicide 2,4-dichlorophenoxyacetic acid from water using Ag/reduced graphene oxide co-decorated TiO2 nanotube arrays.

A new photocatalyst, Ag nanoparticles (NPs) and reduced graphene oxide (RGO) co-decorated TiO(2) nanotube arrays (NTs) (Ag/RGO-TiO(2) NTs), was designed and facilely produced by combining electrodeposition and photoreduction processes. The structures and properties of the photocatalysts were characterized. The ternary catalyst exhibited almost 100% photocatalytic removal efficiency of typical herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) from water under simulated solar light irradiation. The photodegradation rate toward 2,4-D over Ag/RGO-TiO(2) NTs is 11.3 times that over bare TiO(2) NTs. After 10 successive cycles with 1600 min of irradiation, Ag/RGO-TiO(2) NTs maintained as high 2,4-D removal efficiency as 97.3% with excellent stability and easy recovery, which justifies the photocatalytic system a promising application for herbicide removal from water.

A highly efficient polyampholyte hydrogel sorbent based fixed-bed process for heavy metal removal in actual industrial effluent

High sorption capacity, high sorption rate, and fast separation and regeneration for qualified sorbents used in removing heavy metals from wastewater are urgently needed. In this study, a polyampholyte hydrogel was well designed and prepared via a simple radical polymerization procedure. Due to the remarkable mechanical strength, the three-dimensional polyampholyte hydrogel could be fast separated, easily regenerated and highly reused. The sorption capacities were as high as 216.1xa0mg/g for Pb(II) and 153.8xa0mg/g for Cd(II) owing to the existence of the large number of active groups. The adsorption could be conducted in a wide pH range of 3-6 and the equilibrium fast reached in 30xa0min due to its excellent water penetration for highly accessible to metal ions. The fixed-bed column sorption results indicated that the polyampholyte hydrogel was particularly effective in removing Pb(II) and Cd(II) from actual industrial effluent to meet the regulatory requirements. The treatment volumes of actual smelting effluent using one fixed bed column were as high as 684 bed volumes (BV) (7736xa0mL) for Pb(II) and 200 BV (2262xa0mL) for Cd(II). Furthermore, the treatment volumes of actual smelting effluent using tandem three columns reached 924 BV (31,351xa0mL) for Pb(II) and 250 BV (8483xa0mL) for Cd(II), producing only 4 BV (136xa0mL) eluent. Compared with the traditional high density slurry (HDS) process with large amount of sludge, the proposed process would be expected to produce only a small amount of sludge. When the treatment volume was controlled below 209.3 BV (7103xa0mL), all metal ions in the actual industrial effluent could be effectively removed (<0.01xa0mg/L). This wok develops a highly practical process based on polyampholyte hydrogel sorbents for the removal of heavy metal ions from practical wastewater.

A double network gel as low cost and easy recycle adsorbent: Highly efficient removal of Cd(II) and Pb(II) pollutants from wastewater.

A high strength of polyving alcohol/polyacrylic acid double network gel (PVA/PAA gel) adsorbent was successfully prepared by a simple two-step method in this study. The gel adsorbent possessed the advantages of low cost and high adsorptivity for heavy metals in solution. The maximum uptake capacities of PVA/PAA gel were 194.99 mg/g for Pb(II) and 115.88 mg/g for Cd(II) inferred from the Langmuir model at 303 K. At the concentration levels of Pb(II)<150 mg/L and Cd(II)<100mg/L, the Pb(II) and Cd(II) could be completely adsorbed, showing a great potential of removing heavy metals from wastewater. Simultaneously, the PVA/PAA gel adsorbent exhibited an excellent reusability. Even in the fifth cycle, the removal efficiencies of both Pb(II) and Cd(II) remained nearly 100%. Significantly, the gel adsorbent displayed a satisfactory performance of removing heavy metals in actual industrial effluent. The results reveal that the double network gel can be considered as a potential candidate for practical application.

Electrochemical detection of 4-nitrophenol based on a glassy carbon electrode modified with a reduced graphene oxide/Au nanoparticle composite

A new electrochemical sensor for 4-nitrophenol (4-NP) detection based on the reduced graphene oxide (RGO) and Au nanoparticle composite was developed. The RGO film was first electrodeposited onto a glassy carbon electrode (GCE). Then Au nanoparticles (AuNPs) were electrochemically deposited onto the RGO film. The morphology and electrochemical properties of the AuNP/RGO composite were investigated. The synergic effect of AuNPs and RGO nanosheets as co-modifiers greatly facilitates electron-transfer processes between the electrolyte and the GCE, and thus leads to a remarkably improved sensitivity for 4-NP detection. Two detection modes, differential pulse voltammetry (DPV) and square wave voltammetry (SWV), were applied. A wide linear range of values, 0.05–2.0 μM and 4.0–100 μM for DPV and 0.05–2.0 μM for SWV, were obtained. The limit of detection (LOD) of 4-NP was 0.01 μM and 0.02 μM for DPV and SWV, respectively. This sensor was successfully used in the detection of real water samples from Xiangjiang River.

Controllable growth of graphene/Cu composite and its nanoarchitecture-dependent electrocatalytic activity to hydrazine oxidation

Graphene is a promising support for nanosized electrocatalysts, however the conventional stacking arrangement of its graphene sheets substantially decreases the catalytic sites on the catalyst. We report here the fabrication of a graphene/Cu electrocatalyst by the simple cyclic voltammetric electrolysis of graphene oxide (GO) and copper ethylenediamine tetraacetate (Cu–EDTA), and find that the electrochemically reduced GO (RGO) and Cu nanoparticles can be sequentially self-assembled into layer-by-layer, 3D sandwich-type, and homogenous architectures as the concentration ratio of Cu–EDTA/GO increases. The 3D sandwich-type RGO/Cu composite (S-RGO/Cu) shows RGO sheets decorated with Cu nanoparticles which stand nearly perpendicular on the electrode, leading to a significant increase in the electrochemically accessible surface area (0.685 cm2) relative to those of the horizontal layer-by-layer RGO/Cu composite (0.147 cm2) and the homogenous RGO/Cu composite (0.265 cm2). Stemming from its high electrochemical surface area, the S-RGO/Cu composite exhibits a high electrocatalytic activity in hydrazine oxidation in terms of current density and overpotential. Mechanistic analysis of the electrode reactions reveals the reaction pathways of hydrazine on RGO/Cu are closely related to the electrochemical surface area of the RGO/Cu electrocatalyst. The correlation between the architectures and their performances in electrocatalysis presented here can guide the design of novel structures with enhanced properties.

One-step electrodeposition to layer-by-layer graphene-conducting-polymer hybrid films.

One-step fabrication of graphene-polyaniline (graphene-PANI) hybrid film was facilely achieved by cyclic voltammetric electrolysis of a bath containing both graphene oxide (GO) and aniline, where graphene is obtained by electrochemical reduction of GO and PANI is simultaneously obtained by aniline electropolymerization. As there is no strong attraction between aniline and GO under the electrodeposition conditions, the independent depositions of PANI and reduced GO nanosheets at their greatly differed potentials led to alternate layered graphene-PANI films, with the topmost layer being PANI particles or graphene sheets just by changing the initial scan directions. The two kinds of graphene-PANI hybrid films present excellent but different electrical and electrochemical behaviors.