Preparation of p-Phenylenediamine Modified Graphene Foam/Polyaniline@Epoxy Composite with Superior Thermal and EMI Shielding Performance

Microwave-assisted ZnO-decorated carbon urchin resembling 'shish-kebab' morphology with self-healing and enhanced electromagnetic shielding properties

Herein, inspired by Acacia auriculiformis fruit, the shish-kebab-like growth of ZnO on carbon urchin (ZnO@CU) was designed using microwave radiation, thus leading to a hierarchal 3D structure that can promote multiple internal reflections through polarization centers. This hierarchal structure was then dispersed in a designer polyetherimide (PEI) matrix containing dynamic covalent bonds that can undergo metathesis, triggered by temperature, to harness self-healing properties in the composite. Such key attributes are required for their potential use in EMI shielding applications where frequent repairs are indispensable. Morphological investigation revealed that the ZnO flower was periodically nucleated like 'shish-kebab' structures on CU surfaces. CU was designed from short carbon fibers using a facile modified method. The EMI shielding performance of the resulting composites was investigated in the X-band, illustrating a shielding effectiveness of -40.6 dB for 2 wt% of ZnO@CU loading, and the composite can be preserved after the self-healing procedure. The ZnO 'kebabs' on 'CU shish' facilitated multiple scattering and numerous polarization centers to improve the EMI shielding performances at extremely low filler contents. In addition, the mechanical and thermal properties of the composite showed improved structural integrity and superior resistance to extreme temperatures, respectively. Overall, the proposed ZnO@CU/PEI composite has great potential to fulfill the increasing demands for lightweight EMI shielding materials in many fields.

Co-containing metal-organic framework for high-performance asymmetric supercapacitors with functionalized reduced graphene oxide

Nowadays, supercapacitors are the most coveted eco-friendly and sustainable next-generation energy storage devices. In this regard, developing supercapacitors with high energy density and power density has always been a challenge for researchers. Herein, we have exploited an electroactive Co-containing metal-organic framework (Co-MOF) using cheap and commercially available starting materials under refluxing conditions and explored its energy storage properties in three- and two-electrode methods. The Co-MOF exhibited a specific capacitance of 425 F g-1 at 2 A g-1, maintaining a capacitance of ∼78% over 2200 successive charge-discharge cycles in a three-electrode system. The two-electrode asymmetric supercapacitor (ASC) using Co-MOF as the working electrode and as-synthesized p-phenylenediamine (PPD)-functionalized reduced graphene oxide (PPD-rGO) as the counter electrode divulged a specific capacitance of 72.5 F g-1 at 2 A g-1 current density with ∼70% capacitive retention after 2200 successive charge-discharge cycles over a broad potential window of 0-1.6 V. Moreover, the ASC demonstrated a maximum power density of 11.9 kW kg-1 at 10 A g-1 and a maximum energy density of 25.8 W h kg-1 at 2 A g-1 current density. Owing to the stable electrochemical redox (Co2+/Co3+)-mediated pseudocapacitive behavior of the Co-MOF and the high surface area and electrical conductivity of in situ generated PPD-intercalated rGO, the fabricated ASC unveiled high-performance supercapacitive behaviors. To investigate the practical applicability of this material, solid-state (ASC) devices were fabricated by employing the Co-MOF as the positive electrode and PPD-rGO as the negative electrode in a KOH-based gel electrolyte, which could power a commercially available light-emitting diode bulb (∼1.8 V) for several seconds. Therefore, the elucidated high electrochemical energy storage performance of the prepared Co-MOF makes it a very promising electrode material for supercapacitors.

pH-Induced Electrostatic Interaction between Polyacrylates and Amino-Functionalized Graphene Oxide on Stability and Coating Performances

Electrostatic interaction between polymers and nanofillers is of great importance for the properties and design of their composites. Polyacrylates with carboxyl, hydroxyl and acylamino groups were synthesized via emulsion polymerization and marked as P(MMA-BA-AA), P(MMA-BA-HEA) and P(MMA-BA-AM), respectively. Amino-functionalized graphene oxide (NGO) was prepared by Hoffman rearrangement using GO as the raw material. The polyacrylate composites were prepared by mixing NGO with each of the three kinds of polyacrylate. Effects of pH and NGO amounts on the properties of polyacrylate composites were studied. It was found that the surface charge of polyacrylate and NGO had the greatest effect on the composite properties. P(MMA-BA-AM)/NGO was not stable at any pH (2-8). With the same NGO amount of 0.1 wt%, the toughening effect of NGO on P(MMA-BA-AA) was larger than that on P(MMA-BA-HEA). The break strength of P(MMA-BA-AA)/NGO and P(MMA-BA-HEA)/NGO increased to 5.22 MPa by 47% and 3.08 MPa by 31%, respectively. NGO could increase the thermal stability of P(MMA-BA-AA) and P(MMA-BA-HEA) to different degrees. The polyacrylate film-forming processes were tested, and it showed that NGO influenced polyacrylate through the whole film-forming process. The results provide potential methods for the design of polymer-based nanocomposites.