Hai-Bo Zhao

Excellent Electromagnetic Absorption Capability of Ni/Carbon Based Conductive and Magnetic Foams Synthesized via a Green One Pot Route

Electromagnetic microwave absorption materials have attracted a great deal of attention. Foams for the low density and tunable porosity are considered as ideal microwave absorbents, while with the requirement of improving their inherent electromagnetic properties. In this manuscript, an innovative, easy, and green method was presented to synthesize an electromagnetic functionalized Ni/carbon foam, in which the formation of Ni nanoparticles and carbon occurred simultaneously from an affordable alginate/Ni(2+) foam precursor. The resultant Ni/carbon foam had a low density (0.1 g/cm(-3)) and high Ni nanoparticles loading (42 wt %). These Ni nanoparticles with a diameter of about 50-100 nm were highly crystallized and evenly embedded in porous graphite carbon without aggregation. Also, the resultant foam had a high surface area (451 m(2) g(-1)) and porosity and showed a moderate conductivity (6 S/m) and significant magnetism. Due to these special characteristics, the Ni/carbon foam exhibited greatly enhanced microwave absorption ability. Only with 10 wt % of functional fillers being used in the test template, the Ni/carbon foam based composite could reach an effective absorption bandwidth (below -10 dB) of 4.5 GHz and the minimum reflection value of -45 dB at 13.3 GHz with a thickness of 2 mm, while the traditional carbon foam and nano-Ni powder both showed very weak microwave absorption (the minimum reflection value < -10 dB). This foam was demonstrated to be a lightweight, high performance, and low filler loading microwave absorbing material. Furthermore, the detailed absorption mechanism of the foam was investigated. The result showed that the derived strong dielectric loss, including conductivity loss, interface polarization loss, weak magnetic loss, and naoporosity, contributes a great electromagnetic absorption.

Multi-stimuli sensitive supramolecular hydrogel formed by host–guest interaction between PNIPAM-Azo and cyclodextrin dimers

We reported here a novel three stimuli sensitive hydrogel that was constructed by the formation of host–guest complexes between poly(N-isopropylacrylamide) (PNIPAM) containing azobenzene groups and cyclodextrin dimers connected by disulfide bonds. The obtained hydrogel gives a smart response to the stimuli of temperature, light, and reduction, manifested in the form of a sol–gel phase transition.

A novel flame-retardant-free copolyester: cross-linking towards self extinguishing and non-dripping

In this manuscript, contradiction between the non-flammability and non-dripping of polyesters could be solved by copolymerizing terephthalic acid and ethylene glycol together with a pendent phenylethynyl-based monomer named 4-(phenylethynyl) di(ethylene glycol) phthalate (PEPE), which exhibited a cross-linkable nature at a proper temperature. TG-DSC simultaneous thermal analysis, FTIR, dissolution tests and rheological investigations proved the thermal cross-linking behavior of the copolyester, which was not active at the temperature of polymerization and processing but could cross-link rapidly at higher temperature before burning. LOI tests, cone calorimetry and small-scale flame tests further confirmed the self-extinguishment and inhibition for melt-dripping could be achieved through the cross-linking during burning, despite the absence of any flame-retardant element (say, bromine, chlorine, phosphorus, or nitrogen, etc.). Rheological analyses and the SEM microphotographs of the char showed P(ET-co-P)s exhibited a greater complex viscosity through the cross-linking at high temperature, leading to compact char residue, flame-retardant and anti-dripping effects.

Biomass-Based Mechanically Strong and Electrically Conductive Polymer Aerogels and Their Application for Supercapacitors

A novel biomass-based mechanically strong and electrically conductive polymer aerogel was fabricated from aniline and biodegradable pectin. The strong hydrogen bonding interactions between polyaniline (PANI) and pectin resulted in a defined structure and enhanced properties of the aerogel. All the resultant aerogels exhibited self-surppoted 3D nanoporous network structures with high surface areas (207-331m(2)/g) and hierarchical pores. The results from electrical conductivity measurements and compressive tests revealed that these aerogels also had favorable conductivities (0.002-0.1 S/m) and good compressive modulus (1.2-1.4 MPa). The aerogel further used as electrode for supercapacitors showed enhanced capacitive performance (184 F/g at 0.5 A/g). Over 74% of the initial capacitance was maintained after repeating 1000 cycles of the cylic voltammetry test, while the capacitance retention of PANI was only 57%. The improved electrochemical performance may be attributed to the combinative properties of good electrical conductivity, BET surface areas, and stable nanoporous structure of the aerogel. Thus, this aerogel shows great potential as electrode materials for supercapacitors.

Green Approach to Improving the Strength and Flame Retardancy of Poly(vinyl alcohol)/Clay Aerogels: Incorporating Biobased Gelatin

Biobased gelatins were used to improve the compressive properties and flammability of poly(vinyl alcohol)/montmorillonite (PVA/MMT) aerogels, fabricated using a simple and environmentally friendly freeze-drying method. Because of the excellent compatibility and strong interfacial adhesion between PVA and gelatin, the compressive moduli of aerogels were enhanced dramatically with the incorporation of gelatin. PVA/MMT/porcine-gelatin aerogels exhibit compressive modulus values as much as 12.4 MPa, nearly 300% that of the control PVA/MMT aerogel. The microstructure of the PVA/MMT/gelatin aerogels shows a three-dimensional co-continuous network. Combustion testing demonstrated that with the addition of gelatin, the self-extinguishing time of the aerogel was cut by half and the limiting-oxygen-index values increased to 28.5%. The peak heat-release rate, obtained from cone calorimetry, also decreased with the incorporation of gelatin. Thermogravimetric analysis demonstrated that the gelatins slowed the sharp decomposition of the PVA matrix polymer and increased the thermal stability of the aerogels at the major decomposition stage of the composite aerogels. These results indicate that as a green, biobased material, gelatin could simultaneously improve the mechanical properties and the properties of flame retardancy.

Flame-retardant and smoke-suppressant flexible polyurethane foams based on reactive phosphorus-containing polyol and expandable graphite

In this manuscript, flame-retardant and smoke-suppressant flexible polyurethane foams (FPUFs) were designed and synthesized based on novel liquid phosphorus-containing polyol named as PDEO and expandable graphite (EG). The reactive PDEO can be chemically added into the chain of FPUF, while expandable graphite was blended into the matrix of foam through foaming process. Benefitting from the incorporation of reactive PDEO with a long chain, the resultant FPUF containing EG exhibited considerable mechanical properties. More importantly, the synergistic effect of PDEO and EG can endow FPUF with great flame retardancy, anti-driping performances. Furthermore, the resultant FPUF/EG/PDEO foams exhibit considerable smoke suppression performances. The vertical burning test revealed that the FPUF containing 5 php PDEO and 10 php EG extinguished quickly without dripping and kept the original shape after removing the igniter. The cone calorimeter results demonstrated that the synergistic effect of PDEO and EG can effectively reduce the heat release rate (HRR) and total release rate (THR) of the composite foam. Remarkably, the smoke production release (SPR), total smoke production (TSP), light transmission and specific optical density results indicated significantly smoke-suppressant properties of the composite foam. The mechanism analysis confirmed that the synergistic effect of gas-condensed bi-phase action from PDEO and EG contributed the great flame retardation of the composite foam. This novel FPUF provides a promising strategy for producing the polymer foam with flame retardation, smoke suppression and anti-dripping performances.

Nanoporous Ni with High Surface Area for Potential Hydrogen Storage Application

Nanoporous metals with considerable specific surface areas and hierarchical pore structures exhibit promising applications in the field of hydrogen storage, electrocatalysis, and fuel cells. In this manuscript, a facile method is demonstrated for fabricating nanoporous Ni with a high surface area by using SiO2 aerogel as a template, i.e., electroless plating of Ni into an SiO2 aerogel template followed by removal of the template at moderate conditions. The effects of the prepared conditions, including the electroless plating time, temperature of the structure, and the magnetism of nanoporous Ni are investigated in detail. The resultant optimum nanoporous Ni with a special 3D flower-like structure exhibited a high specific surface area of about 120.5 m2/g. The special nanoporous Ni exhibited a promising prospect in the field of hydrogen storage, with a hydrogen capacity of 0.45 wt % on 4.5 MPa at room temperature.