Nazish Parveen

Simultaneous sulfur doping and exfoliation of graphene from graphite using an electrochemical method for supercapacitor electrode materials

Doping with heteroatoms has become a significant strategy for modifying the electronic properties and enhancing the electrochemical properties of graphene (GN). In this study, an environmental friendly, economical and facile one pot electrochemical method was developed to synthesize sulfur-doped graphene (S-GN). Sodium thiosulphate (Na2S2O3), in addition to acting as a sulfur source, also catalyzed the exfoliation process, resulting in sulfur-doped GN structures. The exfoliation of graphite to GN and sulfur (S) doping occurred simultaneously resulting in well dispersed S-GN frameworks. Transmission electron microscopy and high-resolution transmission electron microscopy revealed the presence of the heteroatom in S-GN, and X-ray photoelectron spectroscopy confirmed the high S content (3.47%), as well as the existence of high-quality sulphureted species (mainly as C–S–C–). The incorporation of S species in GN during the exfoliation process modified the surface chemistry of carbon in the GN. The electrochemical performance of the as-prepared S-GN electrode exhibited a high specific capacitance of 320 F g−1 at a current density of 3 A g−1 and excellent cycling stability up to 1500 cycles as well as high energy density of 160 W h kg−1 at a power density of 5161 W kg−1 in an aqueous electrolyte.

Simple route for gram synthesis of less defective few layered graphene and its electrochemical performance

The mass production of high-quality graphene (GN) sheets is essential for their practical applications on a large scale. This paper reports a simple and less corrosive technique for the electrochemical exfoliation of graphite sheets using an aqueous solution mixture of sodium hydroxide, sodium thiosulfate, and sodium hypochlorite (NaOH + Na2S2O3 + NaClO4) as an electrolyte. The presence of NaClO4 expanded the graphite lattice. NaOH in the electrolyte facilitated the electrochemical reduction of the preformed oxygen functional groups on GN while the sulphate ions of Na2S2O3 accelerated the exfoliation of the graphite sheet. Along a series of chemical reactions, the oxidation process produced O2 and SO2 gases. These gases exerted additional forces on the graphite layers and separated the loosely bonded graphite layers, thereby accelerating the exfoliation process. The methodology produces large quantities of crystalline and high quality GN with few layered structures, and was thus called as few layered graphene (FLGN). The prepared FLGN was characterized using a range of techniques, including Raman spectroscopy and atomic force microscopy, which showed that the as-prepared FLGN has 4–6 layers and a large lateral size, which was also confirmed by other analysis. The electrochemical properties of FLGN were examined by cyclic voltammetry, impedance spectroscopy and charge/discharge studies. The as-prepared FLGN exhibited a high specific capacity and good cyclic stability, which makes this methodology promising for the large scale production of FLGN for practical applications.

Facile strategy for the synthesis of non-covalently bonded and para-toluene sulfonic acid-functionalized fibrous polyaniline@graphene–PVC nanocomposite for the removal of Congo red

This paper reports a simple route for the generation of fibrous polyvinyl chloride (PVC) and graphene (GN) fibers (GN–PVC). The prepared fibrous GN–PVC was functionalized further with para-toluene sulfonic acid (pTSA) and polyaniline (Pani) to obtain pTSA–Pani@GN–PVC fibers with high functionality. The resulting fibers were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, UV-vis diffuse absorbance spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction. The synthesized fibers were used for the adsorption of Congo red (CR) dye from aqueous solutions at different solution pH, initial dye concentrations and temperatures. Langmuir, Freundlich and Temkin isotherm models were applied to determine the interaction between the synthesized fibers and CR. The adsorption efficacy of the pTSA–Pani@GN–PVC composite fiber for the removal of CR was 4.43 and 2.51 times higher than that of the PVC and GN–PVC fibers, respectively. Thermodynamic studies showed that the adsorption of CR onto all the fibers was exothermic in nature and that the spontaneity decreased with increasing solution temperature.

Simple route for the generation of differently functionalized PVC@graphene–polyaniline fiber bundles for the removal of Congo red from wastewater

This paper reports a simple route for the generation of fibrous polyvinyl chloride (PVC) and graphene (GN) fibers (PVC@GN). The prepared fibrous PVC@GN was functionalized further with polyaniline (Pani) via simple in situ oxidative polymerization to prepare PVC@GN-Pani fibers. The resulting PVC@GN-Pani fibers were treated with HCl, NH4OH and cetyltrimethylammonium bromide (CTAB) to impart additional functionality. The fibers were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and ultraviolet-visible diffuse absorbance spectroscopy. The applications of differently doped fibers to the adsorptive removal of Congo red (CR) dye were assessed. The results showed that the surfactant, CTAB, doped, i.e., PVC@GN-Pani-s, has the highest adsorption capacity for CR removal compared to the acid doped, i.e., PVC@GN-Pani-a, and base treated, i.e., PVC@GN-Pani-b fibers. The maximum removal of CR was observed at pH 4.5 suggesting that pH plays an important role in the dye adsorption process. The thermodynamic parameters showed that a low temperature favors the adsorption of CR onto all the fibers studied. The adsorption equilibrium data was fitted to the Langmuir and Freundlich adsorption isotherm models. The best fitted results were obtained using the Langmuir model indicating monolayer adsorption of CR onto the PVC@GN-Pani-b, PVC@GN-Pani-a and PVC@GN-Pani-s surfaces. This study showed that these functionalized PVC@GN-Pani nanofibers can be potential adsorbents for the removal of organic pollutants from aqueous solution.

Facile route to a conducting ternary polyaniline@TiO2/GN nanocomposite for environmentally benign applications: photocatalytic degradation of pollutants and biological activity

A polyaniline@TiO2/graphene (Pani@TiO2/GN) nanocomposite was prepared by the in situ oxidative polymerization of aniline in the presence of TiO2 and GN nanoparticles. The resulting Pani@TiO2/GN nanocomposite was characterized by UV-visible diffuse absorbance/reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), transmission electron microscopy, scanning electron microscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The observance of peaks of Pani, TiO2 and GN in XRD and XPS as well as the observance of TiO2 nanoparticles well distributed inside the network of the Pani and GN nanosheets from morphological characterizations suggests the successful formation of Pani@TiO2/GN nanocomposites. DRS and PL analysis showed that Pani@TiO2/GN had higher visible light absorption and a lower recombination rate than Pani@TiO2. The visible light photocatalytic activity of the Pani@TiO2/GN nanocomposite was tested for methylene blue (MB) degradation. The results revealed high photocatalytic activity, which is partly due to the sensitizing effect of Pani and the low recombination rate due to the GN electron scavenging property. The rate of MB degradation on the Pani@TiO2/GN nanocomposite was strongly dependent on the solution pH, reaction time, catalyst dose, and the initial MB concentration. The high regeneration degradation efficiency of the Pani@TiO2/GN nanocomposite showed high stability and the effectiveness of the synthesized photocatalyst. In a continuation of environmental remediation studies, Pani@TiO2/GN revealed high antibacterial activity towards Escherichia coli and Enterobacter ludwigii, highlighting its potential as a photocatalyst with antibacterial properties for different industrial and medical purposes.

Manganese dioxide nanorods intercalated reduced graphene oxide nanocomposite toward high performance electrochemical supercapacitive electrode materials

The development of manganese dioxide-based nanocomposites as materials for energy storage applications is advantageous because of its polymorphism behavior and structural flexibility. In this study, manganese dioxide (MnO2) nanorod-intercalated reduced graphene oxide (rGO) nanocomposite was obtained through a simple hydrothermal method and their electrochemical supercapacitance was studied in a three electrode half-assembly electrochemical cell. The basic spectroscopic and diffraction data including Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy were employed to characterize the resulting nanocomposite. Cyclic voltammetry and galvanostatic charge-discharge measurements were conducted to evaluate the electrochemical supercapacitance of the rGO-MnO2 nanocomposite electrode. The rGO-MnO2 nanocomposite delivered significantly higher capacitance than the P-MnO2 under similar measurement conditions. This enhanced supercapacitive performance of the rGO-MnO2 nanocomposite was attributed to chemical interactions and the synergistic effect between rGO and MnO2, which was helpful in enhancing the electrical conductivity and providing sufficient space for electrode/electrolyte contact during the electrochemical reaction.

Facile Synthesis of SnS2 Nanostructures with Different Morphologies for High-Performance Supercapacitor Applications

SnS2 is an emerging candidate for an electrode material because of the considerable interlayer spaces in its crystal structures and the large surface area. SnS2 as a photocatalyst and in lithium ion batteries has been reported. On the other hand, there are only a few reports of their supercapacitor applications. In this study, sheetlike SnS2 (SL-SnS2), flowerlike SnS2 (FL-SnS2), and ellipsoid-like SnS2 (EL-SnS2) were fabricated via a facile solvothermal route using different types of solvents. The results suggested that the FL-SnS2 exhibited better capacitive performance than the SL-SnS2 and EL-SnS2, which means that the morphology has a significant effect on the electrochemical reaction. The FL-SnS2 displayed higher supercapacitor performance with a high capacity of approximately ∼431.82 F/g at a current density of 1 A/g. The remarkable electrochemical performance of the FL-SnS2 could be attributed to the large specific surface area and better average pore size. These results suggest that a suitable solvent is appropriate for the large-scale construction of SnS2 with different morphologies and also has huge potential in the practical applications of high-performance supercapacitors.

Electrochemically synthesized sulfur-doped graphene as a superior metal-free cathodic catalyst for oxygen reduction reaction in microbial fuel cells

Platinum nanoparticles (PtNPs) have long been regarded as the benchmark catalyst for the oxygen reduction reaction (ORR) in the cathode of microbial fuel cells (MFCs). On the other hand, the practical applications of these catalysts are limited by the high cost and scarcity of Pt. Therefore, developing an alternative catalyst to PtNPs for efficient ORR activity is essential for meeting the future demands for practical applications in MFCs. In this study, sulfur-doped graphene (S-GN) was synthesized via the environmental friendly, economical and facile one pot electrochemical exfoliation of graphene in a unique combination of electrolytes, which both catalyzed the exfoliation reaction and acted a sulfur source. The initial activity of S-GN as an ORR active catalyst was examined by cyclic voltammetry (CV), which showed that the as-synthesized S-GN exhibited better ORR activity than the plain material. Furthermore, the application of S-GN as a cathode material was also studied in MFCs. The results showed that the MFC equipped with the S-GN cathode produced a maximum power density of 51.22 ± 6.01 mW m−2, which is 1.92 ± 0.34 times higher than that of Pt/C. The excellent performance of S-GN as a cathode catalyst in MFCs could be due to the doping of graphene with heteroatoms, which increased the surface area and improved the conductivity of graphene through a range of interactions. Based on the above MFC performance, the as-synthesized S-GN catalyst could help reduce the cost and scale up the design of MFCs for practical applications in the near future.

Intercalated reduced graphene oxide and its content effect on the supercapacitance performance of the three dimensional flower-like β-Ni(OH)2 architecture

Anchoring of three dimensional (3D) metal oxides with a controlled morphology on a reduced graphene sheet (rGO) is a promising and challenging route towards the development of highly efficient electrode materials for supercapacitor applications. Herein, we have designed an interconnected 3D flower-like β-Ni(OH)2@rGO (3D-FL-NiH@rGO) architecture and studied the effect of rGO on the morphology as well as supercapacitive performance of 3D-FL-NiH in detail. By varying the experimental parameters, the optimized 3D-FL-NiH@rGO composite achieved the highest capacitance of ∼1710 F g−1 at a current load of 2 A g−1 and also exhibited outstanding cycling performance as compared to the bare 3D-FL-NiH. Further investigation revealed that the improved capacitance of 3D-FL-NiH@rGO is due to the unique 3D and flower like architecture of 3D-FL-NiH which provides a high surface area (124.21 m2 g−1) and more optimal mesoporous size (∼8–15 nm) as compared to the corresponding value of 72.9 m2 g−1 and microporous size of the bare 3D-FL-NiH. The presence of rGO and 3D-FL of the β-NiH provided strain relaxation during the charge–discharge procedures, which enhanced the electrical conductivity of the electrode and hence improved the cycling performance of 3D-FL-NiH@rGO.

Lithium ion storage ability, supercapacitor electrode performance, and photocatalytic performance of tungsten disulfide nanosheets

Although tungsten disulfide (WS2), an analogue of graphite, has long been pursued as a promising energy storage material due to its unique layered structure, structural changes, volumetric expansion and poor electronic conductivity have limited its practical use. Here, we report the synthesis of porous WS2 composed of a few layered nanosheets (P-WS2) using a simple and scalable hydrothermal method, as well as its electrochemical properties when used for a lithium storage electrode, a supercapacitor electrode, and a visible light active photocatalytic material. P-WS2 as an anode for lithium-ion batteries showed a high specific capacity of 292 mA h g−1 at a current density of 0.2C with excellent cycling stability over 100 cycles. The half-cell electrochemical assembly test demonstrated that P-WS2 delivered 241.5 F g−1 at a current density of 0.75 A g−1 and showed excellent stability over 2000 consecutive charge–discharge cycles. P-WS2 nanosheets exhibited 10 times higher photocatalytic activity than bulk commercial WS2 (C-WS2) for the degradation of Rhodamine B dye under visible light irradiation. The excellent performance of P-WS2 is due to its sheet-like structure, porous characteristics, and high surface area.