Mohammad Omaish Ansari

Anion selective pTSA doped polyaniline@graphene oxide-multiwalled carbon nanotube composite for Cr(VI) and Congo red adsorption

Multiwalled carbon nanotube (CNT)-graphene oxide (GO) composite was combined with polyaniline (Pani) using an oxidative polymerisation technique. The resulting Pani@GO-CNT was later doped with para toluene sulphonic acid (pTSA) to generate additional functionality. The functional groups exposed on the GO, Pani and pTSA were expected to impart a high degree of functionality to the pTSA-Pani@GO-CNT composite system. The composite was characterised by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The characterisation results revealed the characteristics of Pani, GO, CNT, and pTSA, and suggested the successful formation of the pTSA-Pani@GO-CNT composite system. The composite was utilised successfully for the adsorptive removal of Cr(IV) and Congo red (CR) dye and the adsorption of both pollutants was found to be strongly dependent on the solution pH, adsorbate concentration, contact time, and reaction temperature. The maximum adsorption of Cr(IV) and CR was observed in an acidic medium at 30°C. The kinetics for Cr(IV) and CR adsorption was studied using pseudo-first order, pseudo-second order, and intraparticle diffusion models. The adsorption equilibrium data were also fitted to the Langmuir and Freundlich isotherm models. The thermodynamic results showed that the adsorption process was exothermic in nature. The present study provides a new methodology for the preparation of a highly functionalised Pani-based nanocomposite system and its potential applications to the adsorptive removal of a multicomponent pollutant system from an aqueous solution.

Facile and Scale Up Synthesis of Red Phosphorus-Graphitic Carbon Nitride Heterostructures for Energy and Environment Applications.

The development of heterostructured materials for efficient solar energy conversion and energy storage devices are essential for practical applications. In this study, a simple and relatively inexpensive method was used to improve the visible light-driven photocatalytic activity and electrochemical supercapacitor behavior of the graphitic carbon nitride (g-C3N4) by elemental red phosphorus (RPh). The as-prepared RPh-g-C3N4 was characterized in detail using a range of spectroscopic techniques to understand the structure, morphology, chemical interaction, and chemical state of the materials. The visible light-driven photocatalytic activity and supercapacitive electrode performance were assessed by the photodegradation of model colored, non-colored organic pollutants, and electrochemical half-cell measurements, respectively. The RPh-g-C3N4 heterostructure with 30 weight percent of RPh exhibited remarkably high photocatalytic activity for the degradation of pollutants compared to the bare constituent materials, which was further confirmed by the photoelectrochemical study under similar visible photoirradiation conditions. The RPh-g-C3N4 heterostructure supercapacitor electrode displayed a high capacitance of 465 F/g and excellent cyclic stability with capacitance retention of 90% after 1000 cycles at a current of 10 A/g. The superior performance was attributed mainly to the narrow band gap, high surface area, capacitive nature of RPh, and nitrogen-rich skeleton of g-C3N4.

Earth-abundant stable elemental semiconductor red phosphorus-based hybrids for environmental remediation and energy storage applications

The photocatalytic generation of hydrogen and the photodegradation of organic dyes in wastewater using solar light, preferably visible light, have attracted considerable interest because they are clean, low-cost, and environmentally friendly processes. On the other hand, the major drawbacks with traditional photocatalysts are their limited light absorption ability and wide band gap. Therefore, several studies have focused on elemental semiconductor photocatalysts such as red phosphorus (RP) because of its narrow band gap, high absorption ability for the incident solar spectrum, low cost, earth abundance, and easy accessibility, showing great potential for use in numerous industrial applications. The development of RP and its heterojunctions provides promising candidates for utilizing the largest part of the solar energy spectrum. In addition to the photoinduced properties of RP-based nanocomposites, RP-based nanocomposite materials have recently been considered to be good and advanced anodes for lithium- and sodium-ion batteries because of the high theoretical capacity of RP (2596 mA h g−1). The present review briefly introduces the recent advances in the development of various strategies for constructing efficient RP-based hybrid structures that are responsive to visible light, followed by a description of the utilization of RP and its composites as electrode materials in lithium- and sodium-ion batteries. Finally, a summary and viewpoint are also presented to highlight future work on the development of high-storage RP-based electrodes and visible-light photocatalysts.

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.

Facile spectroscopic approach to obtain the optoelectronic properties of few-layered graphene oxide thin films and their role in photocatalysis

Herein, we report the synthesis of few-layered graphene oxide (GO), reduced graphene oxide (rGO), and rGO/ZnO thin films on a glass substrate by the combination of spin coating, low temperature thermal annealing, and radio frequency (RF) sputtering. A spectroscopic approach was applied for the very first time to calculate the optical and dielectric properties of GO thin films. The GO thin film was characterised for structural, optical, morphological, and surface chemical state composition properties by X-ray diffraction, UV-visible spectroscopy, atomic force microscopy, field emission scanning electron microscopy, and X-ray photoelectron microscopy. The chemical state analysis of O1s and C1s spectra evidently proved the successful reduction of GO at 200–300 °C. The change in grain size, lattice strain, and dislocation density was studied after the reduction of GO to rGO, and the band gap analysis was performed through Tauc plot relation. The optical conductivity of the GO films was estimated by the UV technique. Moreover, the dielectric constant and dielectric loss of GO and rGO thin films were also studied, and the samples annealed at high temperature showed comparatively low loss. Due to the high conductivity and low band gap of few-layered rGO, its composite with RF-sputtered ZnO (rGO/ZnO) was studied for its ability to photocatalytically degrade 2-chlorophenol.

Structural, optical, and photocatalytic investigation of nickel oxide@graphene oxide nanocomposite thin films by RF magnetron sputtering

Despite the recent advancement in graphene oxide (GO) as a host material in energy and environmental sectors, its composite thin films with metal oxides such as nickel oxide (NiO) and its optical, structural, chemical state, and photocatalytic activities have been poorly explored. Herein, we have reported the GO/NiO thin films preparation by a combination of chemical and physical deposition techniques (i.e. spin coating followed by DC/RF sputtering). The as-prepared composites thin films were characterised using Raman spectroscopy, X-ray diffraction/photoelectron spectroscopy scanning electron microscopy, and atomic force microscopy. The surface topography confirmed the uniform deposition of NiO over thin films of GO. The XPS results showed the formation of NiC along with the partial reduction in GO into graphene with their existing four constituents, i.e. NiO, NiC, GO, in the thin film composites. The classical plasmon, Wemple and Didomenico model, was first time applied for GO/NiO to compute energy loss functions, and dispersion energy parameters. The theoretical calculated values for the deposited GO/NiO thin films were found to be in very close agreement to the standard classical plasmon values. The change in spin orbital movement of Ni is considered due to the interaction between its nanoparticles and basal planes of GO. Thin films applied for the photodegradation of recalcitrant organic pollutant 2-chlorophenol (2-CP) revealed the dependence of photocatalytic efficiency on particle size and also on the interaction of GO with NiO rather than the ratio of NiO and GO in the films.