Jingfang Yu

Electrically Conductive Polypropylene Nanocomposites with Negative Permittivity at Low Carbon Nanotube Loading Levels

Polypropylene (PP)/carbon nanotubes (CNTs) nanocomposites were prepared by coating CNTs on the surface of gelated/swollen soft PP pellets. The electrical conductivity (σ) studies revealed a percolation threshold of only 0.3 wt %, and the electrical conductivity mechanism followed a 3-d variable range hopping (VRH) behavior. At lower processing temperature, the CNTs formed the network structure more easily, resulting in a higher σ. The fraction of γ-phase PP increased with increasing the pressing temperature. The CNTs at lower loading (0.1 wt %) served as nucleating sites and promoted the crystallization of PP. The CNTs favored the disentanglement of polymer chains and thus caused an even lower melt viscosity of nanocomposites than that of pure PP. The calculated optical band gap of CNTs was observed to increase with increasing the processing temperature, i.e., 1.55 eV for nanocomposites prepared at 120 °C and 1.70 eV prepared at 160 and 180 °C. Both the Drude model and interband transition phenomenon have been used for theoretical analysis of the real permittivity of the nanocomposites.

Large-Scale and Controllable Synthesis of Graphene Quantum Dots from Rice Husk Biomass: A Comprehensive Utilization Strategy

In this work, rice husk biomass was utilized as an abundant source to controllably prepare high-quality graphene quantum dots (GQDs) with a yield of ca. 15 wt %. The size, morphology, and structure of the rice-husk-derived GQDs were determined by high-resolution transmission electron microscopy, atomic force microscopy, and Raman spectroscopy. The as-fabricated GQDs can be stably dispersed in water, exhibiting bright and tunable photoluminescence. A cell viability test further confirmed that the GQDs possess excellent biocompatibility, and they can be easily adopted for cell imaging via a facile translocation into the cytoplasm. It is worth noting that mesoporous silica nanoparticles were also synthesized as a byproduct during the fabrication of GQDs. As such, our strategy achieves a comprehensive utilization of rice husks, exhibiting tremendous benefits on both the economy and environment.

Magnetic graphene oxide nanocomposites: nanoparticles growth mechanism and property analysis

The growth mechanism of magnetic nanoparticles (NPs) in the presence of graphite oxide (GO) has been investigated by varying the iron precursor dosage and reaction time (product donated as MP/GO). The synthesized magnetic NPs were anchored on the GO sheets due to the abundant oxygen-containing functionalities on the GO sheets such as carboxyl, hydroxyl and epoxy functional groups. The introduced NPs changed the intrinsic functionalities and lattice structure of the basal GO as indicated by FT-IR, Raman and XRD analysis, and this effect was enhanced by increasing the amount of iron precursor. Uniform distribution of NPs within the basal GO sheets and an increased particle size from 19.5 to 25.4, 31.5 and 85.4 nm were observed using scanning electron microscope (SEM) and transmission electron microscope (TEM) when increasing the weight ratio of GO to iron precursor from 10:1, to 5:1, 1:1 and 1:5, respectively. An aggregation of NPs was observed when increasing the iron precursor dosage or prolonging the reaction time from 1 to 8 h. Most functionalities were removed and the magnetic NPs were partially converted to iron upon thermal treatment under a reducing condition. The GO and MP/GO nanocomposites reacted for one and two hours (denoted as MP/GO1-1 h and MP/GO1-2 h) were converted from insulator to semiconductor after the annealing treatment as annealed GO (A-GO, 8.86 S cm−1), annealed MP/GO1-1 h (A-MP/GO1-1 h, 7.48 × 10−2 S cm−1) and annealed MP/GO1-2 h (A-MP/GO1-2 h, 7.58 × 10−2 S cm−1). The saturation magnetization was also enhanced significantly after the annealing treatment, increased from almost 0 to 26.7 and 83.6 emu g−1 for A-MP/GO1-1 h and A-MP/GO1-2 h, respectively.

In situ synthesis of polyelectrolyte/layered double hydroxide intercalation compounds

Intercalation is usually achieved through the insertion of guest species into a pre-formed layered compound. Herein, we report our exploration of the formation of intercalation compounds through a direct growth method using cationic layered double hydroxide (LDH) and anionic polyelectrolytes. LDH precursors and intercalant molecules were used as the raw materials to directly grow layered intercalation compounds through a hydrothermal method. Three poly(sodium 4-styrene-sulfonate) (PSSNa) with different molecular weights (i.e., 70000, 200000, and 500000) were systematically studied as an intercalant in terms of their effect on the growth of intercalation compounds. The mass ratio of PSSNa and LDH was also varied to study how the formulation ratio of the raw materials influences the growth of the PSSNa/LDH intercalation compounds. These directly synthesized PSSNa/LDH intercalation compounds were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy, based on which their growth mechanism was discussed. This direct growth method offers an alternative for large-scale production of intercalation compounds for potential commercial applications.