Sasmita Nayak

Characterization and Dispersion of Multiwalled Carbon Nanotubes (MWCNTs) in Aqueous Suspensions: Surface Chemistry Aspects

Dispersability of multiwalled carbon nanotubes (MWCNTs) in aqueous suspensions was investigated with gum arabic GA (anionic) and polydiallyldimethylammonium chloride (PDADMAC) cationic dispersants. The isoelectric point (iep) of MWCNTs was at pH 4.5. The surface charge of MWCNTs changed to highly negative and iep shifted to pH < 1.5 with GA, whereas with PDADMAC highly positive and iep is shifted to pH 10.2. The interaction energy of MWCNTs with GA and PDADMAC was 9.79 and 10.35 RT unit, respectively. The higher interaction energy with PDADMAC shows more favorable interaction with them. Stabilization mechanism with GA is attributed mainly by electrostatic repulsive forces, whereas with PDADMAC, electrostatic and steric effect.

Nanotitania-coated multi-walled carbon nanotube composite by facile colloidal processing route for photocatalytic applications

Multi-walled carbon nanotubes (MWCNTs) and titanium dioxide nanocomposites (MWCNTs/TiO2) were fabricated by a simple novel colloidal processing route and tested as a photocatalyst for degradation of methylene blue under UV irradiation. The novel idea behind this work is to make MWCNTs and TiO2 nanoparticle suspensions separately highly oppositely charged and utilize the electrostatic force of attraction between two entities to deposit nanotitania onto MWCNTs surface. Particle charge detector, scanning electron microscopy, transmission electron microscope, energy dispersive X-rays, X-rays diffraction (XRD), and Raman spectroscopy were used to characterize the composite. XRD and Raman spectroscopic analysis showed the crystalline structure of deposited TiO2 over MWCNTs surface structure as anatase phase. It was found that MWCNTs/TiO2 composite structure have much higher photocatalytic activity compared to TiO2 nanoparticles. The composite material developed may find potential applications in the degradation of organic pollutants in aqueous medium under UV irradiation.

Graphene as transparent and current spreading electrode in silicon solar cell

Fabricated bi-layer graphene (BLG) has been studied as transparent and current spreading electrode (TCSE) for silicon solar cell, using TCAD-Silvaco 2D simulation. We have carried out comparative study using both Ag grids and BLG as current spreading electrode (CSE) and TCSE, respectively. Our study reveals that BLG based solar cell shows better efficiency of 24.85% than Ag-based cell (21.44%), in all of the critical aspects, including generation rate, recombination rate, electric field, potential and quantum efficiency. Further BLG based cell exhibits pronounce rectifying behavior, low saturation current, and good turn-on voltage while studying in dark.

Photovoltaic and impedance spectroscopic characteristics of heterojunction of graphene-PEDOT:PSS composite and n-silicon prepared via solution-based process

Recent investigations involving nanoscale energy conversion using two-dimensional nanomaterials such as graphene and transition metal dichalcogenides (TMDs) hold promise to mitigate future energy challenges. The heterojunction devices designed by interfacing 2D layers with 3D bulk semiconductors (2D/3D heterojunctions) including graphene/silicon and TMDs/silicon are widely explored for the photovoltaic characteristics. Developing a thorough understanding of the interfacial chemistry via impedance spectroscopic analysis will leverage the potential of these 2D/3D junctions for large-scale integrations. Here, the non-vacuum solution-processed reduced graphene oxide (rGO), poly(3,4-ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS) and their composite (PEDOT:PSS(rGO)) were spin coated on the silicon (n-Si) substrates for fabrication of heterojunctions, with the device construct of rGO/n-Si, PEDOT:PSS/n-Si and PEDOT:PSS(rGO)/n-Si having Ohmic metal contacts in both top and bottom. The significant efficiency improvement of three orders for PEDOT:PSS(rGO)/n-Si device over the rGO/n-Si and PEDOT:PSS/n-Si heterojunction devices can be attributed to (i) increased conducting channels in the active region and (ii) reduced series resistance. Further, the impedance spectroscopy is employed to understand the interfacial chemistry of PEDOT:PSS(rGO)/n-Si solid-state junction, which is explained by a parallel resistance–capacitance circuit model.

A systematic study on the effect of acidic, basic and neutral additives on dispersion of multiwalled carbon nanotubes using a dimethylformamide solution

Presence of acidic, basic and neutral additives on dispersion of multiwalled carbon nanotubes (MWCNTs) in dimethylforamide (DMF) solution has been investigated. The surface charge measurement showed that MWCNTs in the presence of acidic additives in DMF exhibit a higher surface charge (?85 C g?1) than that with the basic additives (?22 C g?1). The stability of the MWCNTs dispersion was visually monitored and it was found that in the presence of acidic and no additives it would be stable and dispersed for more than five days, whereas MWCNTs suspension immediately settle down in the presence of basic and neutral additives. The degree of defects on MWCNTs was determined by analysis of detailed Raman spectra of as-received MWNCTs and MWNCTs dispersed in DMF with different additives. By exploring the correlation between the ID/IG (Raman analysis) ratio and the degree of defects, it was found that the carbon?carbon double bond (C=C) of MWCNTs was slightly damaged by adding additives to the solvent.