Jiang Gong

Converting real-world mixed waste plastics into porous carbon nanosheets with excellent performance in the adsorption of an organic dye from wastewater

Waste plastic utilization and wastewater treatment are the two most serious challenges on the path to urbanization and industrialization, due to the limited fossil fuel resources, ever-increasing energy demands, and severe environmental pollution. The conversion of waste plastics into high value-added carbon nanomaterials has become a promising way to utilize waste plastics; however, most current studies are limited to single component waste plastic; besides, little attention has been paid to porous carbon nanosheets (PCNSs). Herein, a facile approach was established to prepare PCNSs by the carbonization of real-world mixed waste plastics on organically-modified montmorillonite and subsequent KOH activation. The morphology, microstructure, textural property, phase structure, surface element composition, and thermal stability of the PCNSs were investigated. The PCNSs showed high specific surface area (2315 m2 g−1) and large pore volume (3.319 cm3 g−1) with high purity (>99.6%). More importantly, the PCNSs exhibited fast adsorption (about 95% of methylene blue (MB) was removed during the first 10 min of adsorption), an unprecedented adsorption capacity of 769.2 mg g−1 (higher than most of reported adsorbents), and excellent recyclability (after ten cycles, an adsorption capacity of 692.0 mg g−1 remained and 90 wt% of the PCNS was reclaimed) for MB from wastewater. This was attributed to the high specific surface area and large pore volume of the PCNS, and due to multiple adsorption mechanisms, including pore filling, hydrogen bonding, and π–π and electrostatic interactions between MB and the PCNS. It is believed that this work not only provides a novel potential way to utilize waste plastics, but also presents a facile sustainable approach to synthesize PCNSs, which will be an ideal candidate for various applications.

Catalyzing carbonization of poly(L-lactide) by nanosized carbon black combined with Ni2O3 for improving flame retardancy

Catalyzing the carbonization of a polymer itself to form a protective carbonaceous layer has attracted tremendous interest in the flame retardancy of polymers, but the efficiency of this strategy was largely limited to polymers containing heteroatoms within their backbone. In this study, a novel type of combined catalyst, consisting of nanosized carbon black (CB) and Ni2O3, was found to efficiently catalyze the carbonization of poly(L-lactide) (PLA) for the first time. The combined catalyst was more efficient than CB or Ni2O3 alone to enhance the char yield of PLA and improve its char layer structure, which greatly improved the flame retardancy of PLA. The catalytic pyrolysis for PLA composites and model carbonization experiments for their degradation products were carried out to investigate the carbonization process of PLA during combustion. The results indicated that the carbonization mechanism was attributed to the combined effect of the combined catalysts: CB catalyzed the degradation of PLA to selectively produce more aldehydes and ketones with lower carbon numbers, then these carbonyl compounds were dehydrogenated (and/or dehydrated) and transferred into carbon products catalyzed by the combination of CB and Ni catalysts.

Synthesis and characterization of a novel organophosphorus oligomer and its application in improving flame retardancy of epoxy resin

A novel organophosphorus, poly(4,4-dihydroxy-1-methyl-ethyl diphenol-o-bicyclic pentaerythritol phosphatephosphate) (PCPBO), was synthesized and characterized by FTIR, 1H NMR and 31P NMR. The flame retardancy and thermal stability of epoxy resin with different PCPBO loadings were investigated using the limited oxygen index (LOI), vertical burning test, cone calorimeter test and thermogravimetric analysis. The results showed that the incorporation of PCPBO into epoxy resin (EP) significantly improved its flame retardancy and thermal stability. The reduction of the peak heat release rate, total heat release and the increased char yield at high temperature further confirmed the improvement of the flame retardancy. FT-IR at different temperatures and the scanning electron microscopy of residual char revealed that the addition of PCPBO could induce the formation of an intumescent char layer, which retarded the degradation and combustion process of EP.

Striking influence of Fe2O3 on the “catalytic carbonization” of chlorinated poly(vinyl chloride) into carbon microspheres with high performance in the photo-degradation of Congo red

A one-pot approach was demonstrated to effectively synthesize carbon microspheres through “catalytic carbonization” of commercial chlorinated poly(vinyl chloride) (CPVC) microspheres by Fe2O3 at 700 °C. Without Fe2O3, a “sponge-like” carbon lump was obtained. However, after adding Fe2O3 (even 0.5 g per 100 g CPVC) into CPVC, carbon microspheres with octahedral Fe3O4 microcrystals uniformly embedded on the surface (Fe/CMS) were synthesized. The influence of Fe2O3 on the carbonization of CPVC microspheres was investigated. It was found that Fe2O3 significantly accelerated the dehydrochlorination of CPVC into polyene before the melting of the CPVC microsphere surface. As a result, the microspheres of raw CPVC showed a “shape-duplicate” carbonization behaviour. The resultant Fe/CMS showed high photo-degradation efficiency of Congo red under UV irradiation via a heterogeneous photo-Fenton process with high recyclablity, reusability and long-term stability. This indicated that the resultant Fe/CMS has a potential application in wastewater treatment. Therefore, the initial catalytic substance could be effectively used as a catalyst twice in the carbonization of CPVC microspheres and in the subsequent application of Fe/CMS. More importantly, the strategy of “catalytic carbonization” offers a new potential way to largely convert charring polymers into functional carbon and carbon-based materials with various morphologies.

Flammability properties and electromagnetic interference shielding of PVC/graphene composites containing Fe3O4 nanoparticles

The effects of combined graphene/Fe3O4 nanoparticles on the flame retardancy and smoke suppression of PVC were studied. The dispersion state of graphene in the PVC matrix was improved with the help of Fe3O4 nanoparticles. As a result, the peak values of heat release rate and smoke production rate measured by cone calorimetry were obviously decreased in the PVC/graphene/Fe3O4 composites. According to the results from TGA tests and structural characterization of residual char, the improved flame retardancy was partially attributed to the formation of a network-like structure due to the good dispersion state of graphene in the PVC matrix, and partially to the carbonization of degradation products of PVC catalyzed by Fe3O4 nanoparticles. In addition, ternary PVC composites showed higher mechanical properties than pure PVC. More importantly, the resulting material possessed both electrical and magnetic properties. As a result, the ternary composites showed favorable electromagnetic shielding efficiency in the X-band frequency region (8–12 GHz), due to the formation of conducting interconnected graphene-based networks in the insulating PVC matrix and the magnetic properties.

Nanosized carbon black combined with Ni2O3 as "universal" catalysts for synergistically catalyzing carbonization of polyolefin wastes to synthesize carbon nanotubes and application for supercapacitors.

The catalytic carbonization of polyolefin materials to synthesize carbon nanotubes (CNTs) is a promising strategy for the processing and recycling of plastic wastes, but this approach is generally limited due to the selectivity of catalysts and the difficulties in separating the polyolefin mixture. In this study, the influence of nanosized carbon black (CB) and Ni2O3 as a novel combined catalyst system on catalyzing carbonization of polypropylene (PP), polyethylene (PE), polystyrene (PS) and their blends was investigated. We showed that this combination was efficient to promote the carbonization of these polymers to produce CNTs with high yields and of good quality. Catalytic pyrolysis and model carbonization experiments indicated that the carbonization mechanism was attributed to the synergistic effect of the combined catalysts rendered by CB and Ni2O3: CB catalyzed the degradation of PP, PE, and PS to selectively produce more aromatic compounds, which were subsequently dehydrogenated and reassembled into CNTs via the catalytic action of CB together with Ni particles. Moreover, the performance of the synthesized CNTs as the electrode of supercapacitor was investigated. The supercapacitor displayed a high specific capacitance as compared to supercapacitors using commercial CNTs and CB. This difference was attributed to the relatively larger specific surface areas of our synthetic CNTs and their more oxygen-containing groups.

A facile approach to prepare porous cup-stacked carbon nanotube with high performance in adsorption of methylene blue

Novel porous cup-stacked carbon nanotube (P-CSCNT) with special stacked morphology consisting of many truncated conical graphene layers was synthesized by KOH activating CSCNT from polypropylene. The morphology, microstructure, textural property, phase structure, surface element composition and thermal stability of P-CSCNT were investigated by field-emission scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM, N2 sorption, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and thermal gravimetric analysis. A part of oblique graphitic layers were etched by KOH, and many holes with a diameter of several to a doze of nanometers connecting inner tube with outside were formed, which endowed P-CSCNT with high specific surface area (558.7 m(2)/g), large pore volume (1.993 cm(3)/g) and abundant surface functional groups. Subsequently, P-CSCNT was used for adsorption of methylene blue (MB) from wastewater. Langmuir model closely fitted the adsorption results, and the maximum adsorption capacity of P-CSCNT was as high as 319.1mg/g. This was ascribed to multiple adsorption mechanisms including pore filling, hydrogen bonding, π-π and electrostatic interactions. Pseudo second-order kinetic model was more valid to describe the adsorption behavior. Besides, P-CSCNT showed good recyclablity and reusability. These results demonstrated that P-CSCNT had potential application in wastewater treatment.

One-pot synthesis of core/shell Co@C spheres by catalytic carbonization of mixed plastics and their application in the photo-degradation of Congo red

Much attention has been paid to the synthesis of core/shell metal@carbon composites, but many of the proposed methods are limited by sophisticated procedure and expensive precursors. Herein, a facile one-pot approach is established to prepare magnetic core/shell Co@C spheres through catalytic carbonization of mixed plastics (consisting of polypropylene, polyethylene and polystyrene) by Co3O4 at 700 °C. The yield, composition, morphology, phase structure, textural property, surface element composition, thermal stability and magnetic property of core/shell Co@C spheres are investigated. The core/shell Co@C spheres have a distinct ordered and curved graphitic structure, and their main diameters are in the range of 110–130 nm. Besides, they show a ferromagnetic behavior with high saturation magnetization (85.6–101.6 emu g−1). Furthermore, it was observed that Co3O4 was uniformly distributed in mixed plastics and formed a network structure, which provided a precondition for the carbonization of mixed plastics into core/shell Co@C spheres with uniform sizes. Finally, the core/shell Co@C spheres were found to show high performance in photo-degradation of Congo red (CR) with good recyclablity, reusability and long-term stability. It was demonstrated that the outer carbon shell promoted the degradation of CR and served as a protective layer for cobalt core to improve acid resistance, while the inner cobalt core accelerated the decomposition of H2O2 into radicals, which catalyzed the degradation of CR. More importantly, this simple approach offers a potential way to prepare magnetic core/shell metal@carbon composites from cheap waste plastics.

Striking influence of NiO catalyst diameter on the carbonization of polypropylene into carbon nanomaterials and their high performance in the adsorption of oils

Recently, there has been intense interest in the conversion of plastics into high value-added carbon nanomaterials (CNMs), however, the effect of catalyst diameter on the formation of CNMs is still ambiguous. Herein, uniform NiO catalysts with different diameter (18–227 nm) were firstly prepared by a sol–gel combustion synthesis method and calcination at different temperatures. Subsequently, the combined organically-modified montmorillonite (OMMT)/NiO catalyst was used to catalyze carbonization of polypropylene (PP, selected as an example of plastics) into CNMs at 700 °C. The effect of NiO catalyst diameter on the yield, morphology, microstructure, phase structure, thermal stability and texture properties of CNMs including sponge-like cup-stacked carbon nanotubes (CS-CNTs) and carbon fibers were investigated by scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, X-ray diffraction, Raman spectroscopy, thermal gravimetric analysis and N2 sorption. Besides, the effects of NiO catalyst diameter on the coalescence and reconstruction of NiO particles were explored. It was demonstrated that NiO catalysts with small diameter were more susceptible to coalescence and reconstruction into rhombic shape, which facilitated the growth of long, straight CS-CNTs. Finally, the obtained sponge-like CS-CNTs were found to show high performance in the adsorption of diesel, vegetable oil, kerosene and mineral oil with good recycling performance. It is believed that this work will contribute to the conversion of waste plastics into high value-added CNMs.

Effect of polystyrene long branch chains on melt behavior and foaming performance of poly(vinyl chloride)/graphene nanocomposites

Several poly(vinyl chloride)-g-polystyrene graft copolymers (PVC-g-PS) with well defined molecular structures were synthesized via atom transfer radical polymerization (ATRP) from the structural defects of PVC. The effects of PS branch chains on the shear and extensional rheology as well as foaming properties were investigated. Compared to linear PVC, the introduction of PS branches results in increased complex viscosity, an elevated value of storage modulus at low shear frequencies, more pronounced shear-thinning behavior, more significant upshifted deviation from linear behaviour and a strain hardening phenomenon. Under the same foaming conditions, most of the resulting PVC-g-PS foams exhibit a closed cell structure, increased cell density and uniform cell size distribution while the linear PVC foam has serious cell coalescence. Moreover, graphene nanosheets could be well dispersed in the PVC-g-PS matrix due to the π–π stacking with PS relative to the PVC without PS branch chains. As expected, both the nucleation effect and increased melt viscosity from well-dispersed graphene sheets significantly improve the foaming behavior of PVC-g-PS/graphene nanocomposites, in comparison with the poor foamability of PVC/graphene composites due to the non-uniform dispersion of graphene.