Hongbo Gu

One-Pot Synthesis of Magnetic Graphene Nanocomposites Decorated with Core@Double-shell Nanoparticles for Fast Chromium Removal

A facile thermodecomposition process to synthesize magnetic graphene nanocomposites (MGNCs) is reported. High-resolution transmission electron microscopy and energy filtered elemental mapping revealed a core@double-shell structure of the nanoparticles with crystalline iron as the core, iron oxide as the inner shell and amorphous Si-S-O compound as the outer shell. The MGNCs demonstrate an extremely fast Cr(VI) removal from the wastewater with a high removal efficiency and with an almost complete removal of Cr(VI) within 5 min. The adsorption kinetics follows the pseudo-second-order model and the novel MGNC adsorbent exhibits better Cr(VI) removal efficiency in solutions with low pH. The large saturation magnetization (96.3 emu/g) of the synthesized nanoparticles allows fast separation of the MGNCs from liquid suspension. By using a permanent magnet, the recycling process of both the MGNC adsorbents and the adsorbed Cr(VI) is more energetically and economically sustainable. The significantly reduced treatment time required to remove the Cr(VI) and the applicability in treating the solutions with low pH make MGNCs promising for the efficient removal of heavy metals from the wastewater.

Magnetic polyaniline nanocomposites toward toxic hexavalent chromium removal

The removal of toxic hexavalent chromium (Cr(VI)) from polluted water by magnetic polyaniline (PANI) polymer nanocomposites (PNCs) was investigated. The PNCs were synthesized using a facile surface initiated polymerization (SIP) method and demonstrated unique capability to remove Cr(VI) from polluted solutions with a wide pH range. Complete Cr(VI) removal from a 20.0 mL neutral solution with an initial Cr(VI) concentration of 1.0–3.0 mg L−1 was observed after a 5 min treatment period with a PNC load of 10 mg. The PNC dose of 0.6 g L−1 was found to be sufficient for complete Cr(VI) removal from 20.0 mL of 9.0 mg L−1 Cr(VI) solution. The saturation magnetization was observed to have no obvious decrease after treatment with Cr(VI) solution, and these PNCs could be easily recovered using a permanent magnet and recycled. The Cr(VI) removal kinetics were determined to follow pseudo-first-order behavior with calculated room temperature pseudo-first-order rate constants of 0.185, 0.095 and 0.156 min−1 for the solutions with pH values of 1.0, 7.0 and 11.0, respectively. The Cr(VI) removal mechanism was investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and energy-filter transmission electron microscopy (EFTEM). The results showed that PANI was partially oxidized after treatment with Cr(VI) solution, with Cr(VI) being reduced to Cr(III). The EFTEM observation indicated that the adsorbed Cr(III) had penetrated into the interior of the PNCs instead of simply adsorbing on the PNC surface. This synthesized material was found to be easily regenerated by 1.0 mol L−1p-toluene sulfonic acid (PTSA) or 1.0 mol L−1 hydrochloric acid (HCl) and efficiently reused for further Cr(VI) removal.

Carbon nanostructure-derived polyaniline metacomposites: electrical, dielectric, and giant magnetoresistive properties.

Polyaniline (PANI) nanocomposites incorporating different loadings of graphene and various other carbon nanostructures including carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have been synthesized using a surface-initiated polymerization (SIP) method. Transmission electron microscopy (TEM) results indicate that the graphene has been exfoliated into a few layers (typically one, two, and three layers) during polymerization and has been uniformly dispersed in the PANI matrix. The graphene layer dispersion degree is quantified by a free-path spacing measurement (FPSM) method based on the TEM microstructures. The SIP method also demonstrates its feasibility for coating PANI on one-dimensional (1D) CNFs and CNTs without introducing additional surface functional groups. The effects of graphene size, loading level, and surface functionality on the electrical conductivity and dielectric permittivity of their corresponding nanocomposites have been systematically studied. The temperature-dependent conductivity behavior revealed a quasi-3D variable range hopping (VRH) electron transport mechanism for all the nanocomposites. Giant magnetoresistance (GMR) at room temperature is observed in pure PANI, which can be enhanced by the incorporation of a high loading of graphene (5%) due to the π-π stacking-induced efficient electron transport at the PANI/graphene interface. More interestingly, negative permittivity is found in each composite which can be easily tuned by adjusting the filler loading, morphology, and surface functionality.

Flame-Retardant Electrical Conductive Nanopolymers Based on Bisphenol F Epoxy Resin Reinforced with Nano Polyanilines

Both fibril and spherical polyaniline (PANI) nanostructures have successfully served as nanofillers for obtaining epoxy resin polymer nanocomposites (PNCs). The effects of nanofiller morphology and loading level on the mechanical properties, rheological behaviors, thermal stability, flame retardancy, electrical conductivity, and dielectric properties were systematically studied. The introduction of the PANI nanofillers was found to reduce the heat-release rate and to increase the char residue of epoxy resin. A reduced viscosity was observed in both types of PANI-epoxy resin liquid nanosuspension samples at lower loadings (1.0 wt % for PANI nanospheres; 1.0 and 3.0 wt % for PANI nanofibers), the viscosity was increased with further increases in the PANI loading for both morphologies. The dynamic storage and loss modulii were studied, together with the glass-transition temperature (T(g)) being obtained from the peak of tan δ. The critical PANI nanofiller loading for the modulus and T(g) was different, i.e., 1.0 wt % for the nanofibers and 5.0 wt % for the nanospheres. The percolation thresholds of the PANI nanostructures were identified with the dynamic mechanical property and electrical conductivity, and, because of the higher aspect ratio, nanofibers reached the percolation threshold at a lower loading (3.0 wt %) than the PANI nanospheres (5.0 wt %). The PANI nanofillers could increase the electrical conductivity, and, at the same loading, the epoxy nanocomposites with the PANI nanofibers showed lower volume resistivity than the nanocomposites with the PANI nanospheres, which were discussed with the contact resistance and percolation threshold. The tensile test indicated an improved tensile strength of the epoxy matrix with the introduction of the PANI nanospheres at a lower loading (1.0 wt %). Compared with pure epoxy, the elasticity modulus was increased for all the PNC samples. Moreover, further studies on the fracture surface revealed an enhanced toughness. Finally, the real permittivity was observed to increase with increasing the PANI loading, and the enhanced permittivity was analyzed by the interfacial polarization.

Polyaniline Stabilized Magnetite Nanoparticle Reinforced Epoxy Nanocomposites

Magnetic epoxy polymer nanocomposites (PNCs) reinforced with magnetite (Fe(3)O(4)) nanoparticles (NPs) have been prepared at different particle loading levels. The particle surface functionality tuned by conductive polyaniline (PANI) is achieved via a surface initiated polymerization (SIP) approach. The effects of nanoparticle loading, surface functionality, and temperature on both the viscosity and storage/loss modulus of liquid epoxy resin suspensions and the physicochemical properties of the cured solid PNCs are systematically investigated. The glass transition temperature (T(g)) of the cured epoxy filled with the functionalized NPs has shifted to the higher temperature in the dynamic mechanical analysis (DMA) compared with that of the cured pure epoxy. Enhanced mechanical properties of the cured epoxy PNCs filled with the functionalized NPs are observed in the tensile test compared with that of the cured pure epoxy and cured epoxy PNCs filled with as-received NPs. The uniform NP distribution in the cured epoxy PNCs filled with functionalized NPs is observed by scanning electron microscope (SEM). These magnetic epoxy PNCs show the good magnetic properties and can be attached by a permanent magnet. Enhanced interfacial interaction between NPs and epoxy is revealed in the fracture surface analysis. The PNCs formation mechanism is also interpreted from the comprehensive analysis based on the TGA, DSC, and FTIR in this work.

Epoxy resin nanosuspensions and reinforced nanocomposites from polyaniline stabilized multi-walled carbon nanotubes

The high performance multi-walled carbon nanotubes (MWNTs) reinforced epoxy polymer nanocomposites (PNCs) have been synthesized at different MWNT loading levels. The surface functionalization of MWNTs with conductive PANI was achieved by using a facile surface initiated polymerization method with the aid of the oxidations of CNTs and subsequent anilines by hexavalent chromium (Cr(VI)) oxidant. The effects of MWNT loading, surface functionalization and temperature on the rheological behaviors of liquid epoxy resin nanosuspensions and on the physicochemical properties of cured solid PNCs were systematically investigated. The glass transition temperature (Tg) of the cured epoxy PNCs filled with functionalized MWNTs obtained from the dynamic mechanical analysis (DMA) test was increased about 6–25 °C than that of cured pure epoxy. The PNCs reinforced with functionalized MWNTs demonstrated an enhanced tensile strength than either cured pure epoxy or its PNCs filled with the as-received MWNTs. The electrical conductivity of cured epoxy PNCs with functionalized MWNTs was improved by 5.5 orders of magnitude compared with cured pure epoxy. Thermogravimetric analysis (TGA) revealed an enhanced thermo-stability in the cured epoxy PNCs filled with functionalized MWNTs than that of cured pure epoxy and its PNCs filled with the as-received MWNTs. The observed strong interfacial interaction between MWNTs and the epoxy resin matrix was responsible for the enhanced mechanical tensile strength. The nanocomposite formation mechanism is proposed based on the analysis from Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), Raman and differential scanning calorimetry (DSC) tests.

Mesoporous magnetic carbon nanocomposite fabrics for highly efficient Cr(VI) removal

We have demonstrated that magnetic carbon nanocomposite fabrics prepared by microwave assisted heating are advanced adsorbents in the removal of Cr(VI) with a much higher removal capacity of 3.74 mg g−1 compared to 0.32 mg g−1 for cotton fabrics and 0.46 mg g−1 for carbon fabrics. The enhanced Cr(VI) removal is attributed to the highly porous structure of the nanocomposites. The adsorption kinetics follow the pseudo-second-order model, which reveals a very large adsorption capacity and high adsorption rate. The removal process takes only 10 min, which is much faster than conventional adsorbents such as activated carbon and biomass that often requires hours of operation. The significantly reduced treatment time and the large adsorption capacity make these nanocomposite fabrics promising for the highly efficient removal of heavy metals from polluted water.

An overview of multifunctional epoxy nanocomposites

Epoxy is a crucial engineered thermosetting polymer with wide industrial applications in adhesive, electronics, aerospace and marine systems. In this review, basic knowledge of epoxy resins and the challenge for the preparation of epoxy nanocomposites are summarized. The state-of-art multifunctional epoxy nanocomposites with magnetic, electrically conductive, thermally conductive, and flame retardant properties of the past few years are critically reviewed with detailed examples. The applications of epoxy nanocomposites in aerospace, automotives, anti-corrosive coatings, and high voltage fields are briefly summarized. This knowledge will have great impact on the field and will facilitate researchers in seeking new functions and applications of epoxy resins in the future.

Synergistic interactions between multi-walled carbon nanotubes and toxic hexavalent chromium

In this paper, the synergistic interactions between as-received multi-walled carbon nanotubes (MWNTs) and toxic hexavalent chromium (Cr(VI)) in solutions of different pH were investigated that aimed to functionalize the nanotubes and remove the toxic Cr(VI) by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), Raman spectroscopy and transmission electron microscopy (TEM). The effects of pH value and MWNT concentration (dose) on Cr(VI) removal from polluted water with different initial Cr(VI) concentrations were investigated. Results revealed that MWNTs could be used for complete Cr(VI) removal through the reduction of Cr(VI) to Cr(III) in the polluted water with an initial Cr(VI) concentration ranging from 200 to 1000 μg L−1 during half an hour treatment in a pH = 1.0 solution. The Cr(VI) solutions with different pH values had different effects on MWNTs. For pH = 1.0 Cr(VI) solution with a concentration of 1000 μg L−1, the carboxyl and ether functional groups were found to form on the MWNT surface after 5 to 30 min Cr(VI) treatment and the carboxylate groups were formed as the treatment period increased to 60 min. The kinetics in different pH Cr(VI) solutions were derived. The redox kinetics in the pH = 1.0 solution was described by the pseudo-first-order behavior with respect to Cr(VI) and the typical value of the pseudo-first-order rate constant was calculated to be 0.05786 min−1. In the pH = 7.0 solution, the adsorption kinetics rather than redox reaction dominated the Cr(VI) removal by the calculation and was explained by the pseudo-second-order model with a rate constant of 0.865 g mg−1 min−1.

Cellulose derived magnetic mesoporous carbon nanocomposites with enhanced hexavalent chromium removal

Magnetic carbon–iron nanoadsorbents fabricated by carbonizing cellulose and reducing Fe3O4 nanoparticles or Fe(NO3)3 (the products are denoted as MC–O and MC–N, respectively) have demonstrated great Cr(VI) removal. MC–N with a higher proportion of zero-valence iron (ZVI) and bigger specific surface area exhibited better resistance to oxygen and acid than MC–O due to its smaller pore size. The Cr(VI) removal was highly pH-dependent. For example, 4.0 mg L−1 Cr(VI) neutral solution was completely purified by 2.5 g L−1 MC–O and MC–N within 10 min. 1000 mg L−1 Cr(VI) solution at pH 1.0 was completely removed by both nanoadsorbents in 10 min. The MC–O nanoadsorbents had a higher removal percentage (98.1%) than MC–N (93.5%) at pH 7.0, while MC–N had a removal capacity of 327.5 mg g−1, much higher than 293.8 mg g−1 of MC–O at pH 1.0. A chemical adsorption was revealed from the pseudo-second-order kinetic study. Monolayer adsorption of Cr(VI) was revealed by a better fitting of the Langmuir model isotherm, rather than multilayer adsorption for the Freundlich model. These nanoadsorbents could be easily separated from solution by using a permanent magnet after being treated with Cr(VI). Finally, the Cr(VI) removal mechanisms were proposed considering the Cr(VI) reduction and precipitation of Cr(III).