Suman Chhetri

Investigation of mechanical and thermal properties of the cetyltrimethylammonium bromide functionalized molybdenum disulfide (MoS2)/epoxy composites

Molybdenum disulfide (MoS2), a 2D layered material has been recognised as a new paradigm in the area of materials science due to its graphene like structure. Herein, we prepared functionalized MoS2 nanosheets through one-pot hydrothermal technique using cationic surfactant, cetyltrimethylammonium bromide (CTAB). The surfactant functionalized MoS2 (CTAB-MoS2) was subsequently dispersed in epoxy matrix at the loading level of 0.1–0.5 wt% to investigate the reinforcing competence of MoS2 on the mechanical and thermal properties of the composites. Fourier transform infrared spectroscopy, X-ray diffraction and field emission scanning electron microscopy (FE-SEM) were used to characterize the microstructure and morphology of the hydrothermally prepared pristine MoS2 and CTAB-MoS2. Dynamic mechanical and tensile properties were studied to comprehend the effect of functionalized MoS2 on the mechanical properties of the composites. At 0.2 wt% loading, the tensile strength and Young’s modulus was improved by ~23 and 26.7%, respectively, while ~83% improvement in storage modulus was recorded. Thermal stability of all the studied specimens were compared by selecting the temperatures at 10 and 50% weight losses which showed small decrease in onset degradation temperature.

Effect of thermally reduced graphene oxide on dynamic mechanical properties of carbon fiber/epoxy composite

The Carbon fiber (CF)/epoxy composites are being used in the automotive and aerospace industries owing to their high specific mechanical strength to weight ratio compared to the other conventional metal and alloys. However, the low interfacial adhesion between fiber and polymer matrix results the inter-laminar fracture of the composites. Effects of different carbonaceous nanomaterials i.e., carbon nanotubes (CNT), graphene nanosheets (GNPs), graphene oxide (GO) etc. on the static mechanical properties of the composites were investigated in detail. Only a few works focused on the improvement of the dynamic mechanical of the CF/epoxy composites. Herein, the effect of thermally reduced grapheme oxide (TRGO) on the dynamic mechanical properties of the CF/epoxy composites was investigated. At first, GO was synthesized using modified Hummers method and then reduced the synthesized GO inside a vacuum oven at 800 °C for 5 min. The prepared TRGO was dispersed in the epoxy resin to modify the epoxy matrix. Then, a number of TRGO/CF/epoxy laminates were manufactured incorporating different wt% of TRGO by vacuum assisted resin transfer molding (VARTM) technique. The developed laminates were cured at room temperature for 24 h and then post cured at 120 °C for 2 h. The dynamic mechanical analyzer (DMA 8000 Perkin Elmer) was used to examine the dynamic mechanical properties of the TRGO/CF/epoxy composites according to ASTM D7028. The dimension of the specimen was 44×10×2.4 mm3 for the DMA test. This test was carried out under flexural loading mode (duel cantilever) at a frequency of 1 Hz and amplitude of 50 μm. The temperature was ramped from 30 to 200 °C with a heating rate of 5 °C min-1. The dynamic mechanical analysis of the 0.2 wt% TRGO incorporated CF/epoxy composites showed ~ 96% enhancement in storage modulus and ~ 12 °C increments in glass transition temperature (Tg) compared to the base CF/epoxy composites. The fiber-matrix interaction was studied by Cole-Cole plot analysis. It proved the homogeneous dispersion of the epoxy resin and TRGO. The homogeneous dispersion of the TRGO in the epoxy matrix increased the overall enhancement of the dynamic mechanical properties of the hybrid composites.

Cobalt sulfide/nickel sulfide heterostructure directly grown on nickel foam: an efficient and durable electrocatalyst for overall water splitting application

Fabrication of high-performance noble-metal-free bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water is a promising strategy toward future carbon-neutral economy. Herein, a one-pot hydrothermal synthesis of cobalt sulfide/nickel sulfide heterostructure supported by nickel foam (CoS x/Ni3S2@NF) was performed. The Ni foam acted as the three-dimensional conducting substrate as well as the source of nickel for Ni3S2. The formation of CoS x/Ni3S2@NF was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The formation of CoS x/Ni3S2@NF facilitated easy charge transport and showed synergistic electrocatalytic effect toward HER, OER, and overall water splitting in alkaline medium. Remarkably, CoS x/Ni3S2@NF showed catalytic activity comparable with that of benchmarking electrocatalysts Pt/C and RuO2. For CoS x/Ni3S2@NF, overpotentials of 204 and 280 mV were required to achieve current densities of 10 and 20 mA cm-2 for HER and OER, respectively, in 1.0 M KOH solution. A two-electrode system was formulated for overall water splitting reaction, which showed current densities of 10 and 50 mA cm-2 at 1.572 and 1.684 V, respectively. The prepared catalyst exhibited excellent durability in HER and OER catalyzing conditions and also in overall water splitting operation. Therefore, CoS x/Ni3S2@NF could be a promising noble-metal-free electrocatalyst for overall water splitting application.