Lin Chen

Magnetic graphene foam for efficient adsorption of oil and organic solvents

This paper reported the preparation of magnetic graphene foam loaded with magnetite (Fe3O4) nanoparticles and its application for the adsorption of oil and organic solvents. The foam with porous and hierarchical structures was derived from graphene oxide film reduced by gaseous reduction in a hydrothermal system. Drastically different morphologies of Fe3O4 nanoparticles with nanosheet arrays or cubic structures were observed on graphene foam by controlling the reduction degree of graphene oxide under mild conditions. Benefiting from the integration of porous structures and magnetic properties, the graphene foam manifests outstanding oil adsorption capacity, high restoration for absorbates as well as excellent recyclability and stability under cyclic operations. The simple and effective strategy for the preparation of graphene foams developed in this study may offer a new alternative for scale-up production of graphene materials used for the cleanup of oil spills.

Low cost carbon fiber aerogel derived from bamboo for the adsorption of oils and organic solvents with excellent performances

This paper reports the preparation of multi-functional carbon fiber (MCF) aerogel by a simple hydrothermal and carbonization process using disposable bamboo chopsticks. The developed material manifested dramatic multi-functionalities, including excellent flexibility under the mechanical compression, efficient capability to separate oily droplets from water, and high adsorption capacity for a variety of oils and organic solvents by up to 129 times of its own weight. Moreover, the MCF aerogel can be recycled for many times by distillation, combustion or squeezing, making the material satisfy the requirements for oil–water separation in practice. Coupled with economical, environmentally benign manufacturing process, sustainability of precursor and versatility of material, the MCF aerogel developed in this study will be a promising candidate to address the problems arising from the spills of oily compounds.

Graphene foam with hierarchical structures for the removal of organic pollutants from water

Porous materials with hierarchical structures are of increasing importance because of their potential application in separation and electronic technology. Herein, three-dimensional graphene foam (GF) was prepared by using polystyrene particles as a sacrificial template and an autoclaved leavening process, and the GF was further processed by carbon dioxide as an activation agent to produce meso- and nano-pores in the foam. The resulting hierarchical graphene foam (HGF) exhibits high porosity, hydrophobicity and excellent thermal stability. Compared to regular GF, due to the integration of hierarchically porous structures, HGF manifests outstanding performance for oil adsorption when applied to separating oil–water mixtures, through a combination of hydrophobicity and capillary action.

Au–Pt alloy nanoparticles site-selectively deposited on CaIn2S4 nanosteps as efficient photocatalysts for hydrogen production

Au–Pt/CaIn2S4 composites were synthesized for the first time using the photoreduction method by which bimetallic Au–Pt alloy nanoparticles were in situ site-selectively photoreduced on the edges of monoclinic CaIn2S4 nanosteps. The Au–Pt alloy nanoparticles as cocatalysts can spatially separate the oxidation and reduction sites and effectively enhance the photocatalytic hydrogen activity of CaIn2S4 under visible light irradiation. When introducing 0.5 wt% Au–Pt alloy nanoparticles, the rate of hydrogen production could reach 107.6 μmol h−1, which was higher than that of CaIn2S4, Au/CaIn2S4 and Pt/CaIn2S4 by a factor of 18.3, 2.37 and 2.4, respectively. The enhanced photocatalytic activity for hydrogen production could be attributed to the low recombination efficiency of the photogenerated charges and surface-plasmon-resonance-induced effect of Au nanoparticles.

Flame-retardant, electrically conductive and antimicrobial multifunctional coating on cotton fabric via layer-by-layer assembly technique

A multifunctional coating composed of polyhexamethylene guanidine phosphate (PHMGP) and potassium alginate-carbon nanotubes (PA-CNTs) was constructed on cotton fabric via a layer-by-layer assembly technique. The growth of the assembly coating was monitored by Fourier transform infrared spectroscopy and the result shows the assembly coating grows approximately linearly with the increase of bilayer number. The electrical conductivity test shows that the assembly coating endows cotton with electrical conductivity, due to the formation of a CNT network on the cotton fabric. The thermo-stability and flame resistance were evaluated by thermo-gravimetric analysis and a vertical flammability test, and the results indicate that the assembly coating promotes char formation, decreases the burning time and eliminates the afterglow during combustion. The antimicrobial assessment suggests that the assembly coating can effectively inhibit the growth of Escherichia coli, and the inhibiting effect increases with the growth of bilayer number. A multifunctional cotton fabric could be produced by the LBL assembly technique, which enlarges its application area.

Synthesis and Thermal Behavior of Silica‐Graft‐Polypropylene Nanocomposites Studied by Step‐Scan DSC and TGA

Silica graft poly(propylene) (silica‐g‐PP) nanocomposites were successfully prepared by radical grafting copolymerization and ring‐opening reaction. Their thermal properties were studied by step‐scan differential scanning calorimetry (SDSC) and thermogravimetric analysis (TGA). The exothermic peaks in the IsoK baseline (Cp,IsoK, nonreversing signal) of SDSC reveal that PP and silica‐g‐PP nanocomposites undergo melting‐recrystallization‐remelting during heating. The peak temperatures of recrystallization and remelting shift upward with the existence of nanoparticles in the PP matrix. The thermal degradation kinetics of silica‐g‐PP nanocomposites were investigated using nonisothermal TGA and the Flynn‐Wall‐Ozawa method. The results indicate that the thermal stability was significantly improved with increasing silica content, mainly because of the physical‐chemical adsorption of the volatile degradation products on the nanoparticles that delays their volatilization during decomposition, and the covalent interaction between nanoparticles and PP chains, which will also reduce the breakage of PP backbone chains.

Isothermal Crystallization Kinetics and Melting Behavior of Poly(ethylene terephthalate)/Attapulgite Nanocomposites Studied by Step-scan DSC

The crystallization kinetics of poly(ethylene terephthalate)/attapulgite (AT) nanocomposites and their melting behaviors after isothermal crystallization from the melt were investigated by DSC and analyzed using the Avrami method. The isothermal crystallization kinetics showed that the addition of AT increased both the crystallization rate and the isothermal Avrami exponent of PET. Step-scan differential scanning calorimetry was used to study the influence of AT on the crystallization and subsequent melting behavior in conjunction with conventional DSC. The results revealed that PET and PET/AT nanocomposites experience multiple melting and secondary crystallization processes during heating. The melting behaviors of PET and PET/AT nanocomposites varied in accordance with the crystallization temperature and shifted to higher temperature with the increase of AT content and isothermal crystallization temperature. The main effect of AT nanoparticles on the crystallization of PET was to improve the perfection of PET crystals and weaken its recrystallization behavior.

Isothermal crystallization kinetics and mechanical properties of poly(butylene terephthalate)/attapulgite nanocomposites

Poly(butylene terephthalate) (PBT)/attapulgite (AT) nanocomposites were prepared by in situ polymerization. Morphology of the PBT/AT nanocomposites was observed by scanning electron microscope and polarizing optical microscope. Thermogravimetric analyses were used to examine the thermal stability. The melting behaviors, equilibrium melting temperature, isothermal crystallization behavior of pure PBT and PBT/AT nanocomposites were studied by differential scanning calorimetry. The results show that PBT/AT nanocomposites possess higher thermal stability than pure PBT, and AT nanoparticles play a heterogeneous nucleating agent in PBT crystallization that accelerated the crystallization rate. The PBT/AT nanocomposite with higher AT content could retard the transport of polymer chains to the growing crystals compared with that of PBT/AT nanocomposite in lower AT content. According to dynamic mechanical analysis results, the storage modulus of PBT/AT nanocomposites was markedly improved and the addition of AT nanoparticles promotes the crystallization of PBT, which decreases the amorphous area. Meanwhile, the well-dispersed AT nanoparticles also retard the movement of polymer chain segment and increase the proportion of rigid amorphous region.

Three-dimensional titanium dioxide/graphene hybrids with improved performance for photocatalysis and energy storage

A series of three-dimensional (3-D) TiO2/graphene (TiO2/GR) hybrids with different TiO2 weight ratios were prepared using a self-assembly approach followed by the gaseous reduction in a hydrothermal system. The method was based on the electrostatic attraction between the positively charged titanium glycolate precursor and negatively charged graphene oxide in an aqueous medium without any surfactant or template. The structure, morphology, physical and optical properties of the as-synthesized hybrids were characterized, and the results showed that TiO2 spheres were homogeneously confined within the 3-D networks of graphene, and acted as pillars to effectively separate the graphene sheets from each other. By optimizing the ratio of TiO2 in the hybrids, the material was identified as an excellent photocatalyst to remove organic compound in water with high degradation efficiency. Additionally, TiO2/GR hybrids delivered high specific capacity, enhanced rate capability and excellent cyclic stability when used as a freestanding electrode for lithium ion batteries.

Surface roughness induced superhydrophobicity of graphene foam for oil-water separation

Surface free energy and roughness are two predominant factors governing the hydrophilicity/hydrophobicity of materials. This paper reported the surface roughness induced hydrophobicity of graphene foam by incorporating silica nanoparticles onto graphene sheet via a sol-gel method and subsequent modification using silane. Various techniques were employed to characterize the morphology, composition and surface properties of sample. The results showed that the as-prepared graphene foam exhibited a superhydrophobic surface with a high water contact angle of 156°, as well as superoleophilicity with excellent adsorption capacities for a variety of oil compounds. Benefiting from the integration of enhancement on the surface roughness and reduction on the surface free energy of material, the graphene foam developed in this study had the capability to effectively separate oil-water mixture with excellent stability and recyclability.