Jianliang Xiao

Grafting of copolymers onto graphene by miniemulsion polymerization for conductive polymer composites: improved electrical conductivity and compatibility induced by interfacial distribution of graphene

A facile and general method to covalently functionalize graphene oxide (GO) with copolymers, using poly(styrene-co-methylmethacrylate) (P(St-co-MMA)) as an example, via miniemulsion polymerization is described in this study. After in situ reduction, insulating GO is converted to conductive reduced-graphene oxide (RGO). P(St-co-MMA) grafted RGO as conducting filler was incorporated into immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend to prepare conductive polymer composites (CPCs). The lowest percolation threshold (0.02 vol%) among all the reported values for graphene-filled CPCs was achieved due to the controllable preferential distribution of the modified RGO at the interfacial region between PS and PMMA phases, attributed to P(St-co-MMA) grafted on the surface of RGO behaving as compatibilizers to improve interfacial interactions with both the two phases. Moreover, P(St-co-MMA) grafting modified RGO could obviously enhance the compatibility reflected by a significant reduction of the size of dispersed phase, for an example, by nearly one order of magnitude for PS/PMMA (4/1 in volume) blends.

Environmentally friendly reduced graphene oxide as a broad-spectrum adsorbent for anionic and cationic dyes via π–π interactions

π–π interactions between graphene and organic dyes with a conjugate aromatic structure play a key role in the field of high-efficiency, broad-spectrum adsorbents for the removal of water contaminants. L-Cysteine reduced graphene oxide (RGO-Cys) has a good conjugate structure and dispersity in aqueous solution, endowing it with great adsorption efficiency towards anionic, nonionic and cationic dyes with a conjugate aromatic structure mainly via π–π interactions, as proved by the Raman spectrum and special adsorption experiments. The maximum adsorption capability for anionic indigo carmine (IC) and cationic neutral red (NR) is as high as 1005.7 mg g−1 and 1301.8 mg g−1, respectively, the former being the highest among those reported for adsorbents known to date. The total adsorption amount in mixed dye solutions is even higher (>3500 mg g−1), the highest total capability for simultaneous adsorption of anionic and cationic dyes in their solution mixtures. The π–π stacking adsorption mechanism ensures RGO-Cys to be used as a broad-spectrum adsorbent with high efficiency for many kinds of dye contaminants in water while the remnant carboxyl groups on graphene nanosheets facilitate effective adsorption towards Cu2+ with a capability as high as 139.2 mg g−1, opening up many possibilities for the use of graphene in water cleaning including disinfection, decontamination, and desalination.

l-cysteine-reduced graphene oxide/poly(vinyl alcohol) ultralight aerogel as a broad-spectrum adsorbent for anionic and cationic dyes

Abstract It is a challenge to develop broad-spectrum, high-efficiency, easy-recyclable adsorbents for the removal of water contaminants. Herein, l-cysteine-reduced graphene oxide/poly(vinyl alcohol) (CRG/PVA) ultralight aerogels with good mechanical strength and reusability are prepared via a direct sol–aerogel transition strategy by freeze drying. At optimized composition, the aerogel shows high adsorption efficiency toward both cationic and anionic dyes, overcoming the defect of many traditional adsorbents that usually can only remove one type of organic dyes. The adsorption is proved to involve in π–π interaction between CRG and dyes, endowing the aerogel with universality in adsorbing a wide range of conjugated dyes. Moreover, a remarkable synergetic effect is observed for removal of two oppositely charged dyes from aqueous system, yielding exceptionally high total adsorption capacities surpassing all known adsorbents examined for removing binary dyes. Thus, the CRG/PVA aerogel demonstrates great potential for usage as reusable, high-efficiency, and broad-spectrum adsorbent in water treatment.

A general strategy for the synthesis of layered double hydroxide nanoscrolls on arbitrary substrates: its formation and multifunction

Synthesis of structure-controlled nanocrystals on target substrates presents an enticing prospect for fabricating multifunctional devices. Herein, layered double hydroxides (LDHs) with different morphologies were fabricated via hydrothermal treatment on various substrate surfaces. The morphology of the LDH nanostructures from ultrathin nanosheets, parallel aligned nanoscrolls and vertically aligned nanoscrolls could be finely tuned by adjusting the reaction time, temperature and metal–salt concentration. A speculative model was proposed to illustrate the reaction process where the LDH growth units interacted with the modified surface at first, then gradually formed the nanosheets and finally developed into nanoscrolls upon termination of the reaction. The investigation confirmed that amino groups and a positively charged surface play key roles in the formation of well-defined LDH nanoscrolls. Benefiting from the unique hierarchical structure and high LDH loading, the hybrid nanofiber membranes with vertically aligned LDH nanoscrolls exhibited excellent adsorption capability toward methyl orange and Cu2+ and could effectively separate a surfactant stabilized oil-in-water emulsion solely by gravity, with high flux and oil rejection. Meanwhile, these hybrid membranes have shown great potential as highly efficient catalysts for degradation of organic pollutants, making them versatile and comprehensive materials for water remediation.

Simultaneous regulation of morphology, crystallization, thermal stability and adsorbability of electrospun polyamide 6 nanofibers via graphene oxide and chemically reduced graphene oxide

Modulating the processability, structure and properties simultaneously remains a challenge for the preparation of high-performance electrospun nanofibers. The influence of incorporating graphene oxide (GO) and chemically reduced graphene oxide (RGO) nanosheets on the rheological behaviors of polyamide 6 (PA 6) solutions was systematically investigated. A small amount (0.5 wt%) of GO could dramatically increase the steady viscosity of PA 6 solution at 0.001 s−1 (η0.001) by a factor of four, while the same content of RGO resulted in a threefold decrease. Based on the modulation of viscosity of the PA 6 spinning solutions by GO and RGO nanosheets, GO/PA 6 and RGO/PA 6 nanofibers with various structures and properties were successfully prepared via electrospinning. The addition of 1 wt% GO and RGO nanosheets improved PA 6 fibrous uniformity and fineness, and the spinnable concentration (SC) range of PA 6 was effectively broadened. The difference in interfacial interaction between nanosheets and the PA 6 matrix led to different crystallization behaviors of the electrospun PA 6 nanofibers. The formation of γ-form crystals was promoted by GO but inhibited by RGO, which offers a convenient strategy to modulate the mechanical properties of PA 6 nanofibers. In addition, the thermal stability and adsorption capacity of PA 6 nanofibers was enhanced by adding GO or RGO.

Revealing the three-dimensional filler structure in a rubber matrix based on fluorescein modified layered double hydroxides

To gain insight into nonlinear viscoelastic behavior, e.g. the Payne effect, and in situ visualize the filler structure in a rubber matrix under strain, a methodology was developed to detect and track structural evolution based on fluorescent labeling. As a model system, layered double hydroxides (LDHs) with different lateral sizes (nanosheets and microsheets) were labeled with fluorescein (FLU) and then uniformly introduced into the rubber matrix through solution blending. The strain-induced deformation and destruction of the three-dimensional LDH filler structure were directly observed for the first time through laser scanning confocal microscopy (LSCM). The contributions of the breakdown of the filler network, strain softening of the glassy layer and macromolecular disentanglement to the Payne effect were qualitatively determined and analyzed in detail based on the structural information probed via LSCM together with transmission electron microscopy, rheometry and modulated differential scanning calorimetry. The primary mechanism for the Payne effect in this system was then proposed and the macromolecular disentanglement in the rubber matrix played a key role. Furthermore, the enhanced Payne effect with increasing LDH content was ascribed to the strain amplification effect induced by the filler network for the LDH nanosheet filled system and the chain sliding on orientated LDHs for microsheet filled compounds, respectively.

A flyweight and superelastic graphene aerogel as a high-capacity adsorbent and highly sensitive pressure sensor

The preparation of ultralight, superelastic and multifunctional graphene aerogels still remains a challenge. Herein we develop a silane-crosslinked and modified graphene aerogel (SGA) using a novel and simple method of chemical vapor deposition of methyltriethoxysilane into graphene oxide aerogels. The SGA is mechanically robust and shows fantastic properties satisfying multiple applications. Firstly, the SGA exhibits hitherto the highest compression recoverability (99.5%), as well as a high energy loss coefficient and cycle stability. Secondly, the compressible and ultralight (minimum density of 0.35 mg cm−3) SGA could serve as a fast and recyclable superadsorbent being able to adsorb various organic liquids with ultrahigh capacity (>1000 g g−1), which is almost the highest value among known adsorbents. Moreover, the electrical resistance of SGA is highly sensitive to compressive strain and applied pressure due to the enhanced connection between adjacent graphene sheets, which makes the SGA a great pressure sensor with high sensitivity (−67.1 kPa−1) and a low detection limit (<30 Pa); the SGA demonstrates great potential in real-time monitoring of subtle actions like the beat of water droplets. Therefore, the flyweight and mechanically robust SGA holds fantastic properties and great potential in multiple applications.