Jaganathan Senthilnathan

Role of Peroxide Ions in Formation of Graphene Nanosheets by Electrochemical Exfoliation of Graphite

This study demonstrates a facile, mild and environmentally-friendly sustainable (soft processing) approach for the efficient electrochemical exfoliation of graphite using a sodium hydroxide/hydrogen peroxide/water (NaOH/H2O2/H2O) system that can produce high-quality, anodic few-layer graphene nanosheets in 95% yield at ambient reaction conditions. The control experiment conducted using NaOH/H2O revealed the crucial role of H2O2 in the exfoliation of graphite. A possible exfoliation mechanism is proposed. The reaction of H2O2 with hydroxyl ions (HO−) leads to the formation of highly nucleophilic peroxide ions (O22−), which play a crucial role in the exfoliation of graphite via electrochemical-potential-assisted intercalation and strong expansion of graphite sheets.

Submerged Liquid Plasma for the Synchronized Reduction and Functionalization of Graphene Oxide

Formation of reduced and functionalized graphene oxide (r-FGO) at ambient temperature and pressure is demonstrated by generating liquid plasma submerged in acetonitrile and graphene oxide solution. The partial restoration of conjugation (sp2 domain) and insertion of fluorophores such as nitrile and amine in r-FGO displays enhanced fluorescence property. Presence of nitrile and amine in r-FGO are confirmed by X-ray photoelectron spectroscopy and Fourier transforms infrared spectroscopy. Morphology and optical property of r-FGO are studied with transmission electron microscopy, scanning tunneling microscopy and Ultraviolet–visible spectroscopy measurements. The nitrile and amine present in r-FGO undergo a surface-controlled reversible redox reaction and sp2- enriched r-FGO acts as an electrical double layer, providing additional hybrid capacitance or pseudocapacitance. r-FGO shows high cyclic stability with a specific capacitance value of 349 F/g at the scan rate of 10 mV/s. Only marginal reduction of specific capacitance (<10% reduction) is observed at the end of 1000 cycles.

Submerged liquid plasma – low energy synthesis of nitrogen-doped graphene for electrochemical applications

In this study, micro-plasma discharge is produced by applying a high electric potential between graphite and Pt electrodes in acetonitrile solvent. The electrons generated in the micro-plasma discharge collide with acetonitrile and produce ˙H and ˙CH2CN radicals. The radicalized graphene layer exfoliated from the graphite electrode reacts with nascent hydrogen (˙H) and acetonitrile (˙CH2CN) radicals and partially restores its aromaticity and conjugation. Raman spectra of the product confirm the synthesis of nitrogen-functionalized graphene (N-FG), which has a marginal increase in disorderness compared to that of pure graphite and remarkable dispersibility in both hydrophilic and hydrophobic solvents. The excellent fluorescence properties of N-FG confirm the presence of fluorophores such as –NH and –NC– at the radicalized graphene sites, as supported by ultraviolet-visible spectroscopy and X-ray photoelectron spectroscopy studies. The functional groups present in N-FG lead to excellent electrochemical performance, with distinct redox peaks in cyclic voltammetry and a high specific capacitance of 291 F g−1 at a scan rate of 5 mV s−1. N-FG exhibits excellent cycling stability, with a marginal reduction of specific capacitance (<10% reduction) at the end of 1000 cycles.

Submerged Liquid Plasma for the Synthesis of Unconventional Nitrogen Polymers

Glow discharge polymerization is not well understood due to the rapid/complex reaction at the plasma/gas precursor interface. Plasma reaction in a submerged condition allows post-plasma-polymerization, leading to further polymer growth and thus a stable structure. Electron collision with acetonitrile at the interface initiates the formation of radical monomers, which undergoes further rearrangement to form low-molecular (LM) nitrogen polymers (NPs). The radical-rich LM NPs go through further polymerization, forming stable high-molecular (HM) NPs (as determined using liquid chromatography/mass spectrometry). LM NPs absorb light at a wavelength of 270 nm (λ max) whereas HM NPs show absorption at 420 nm (λ max), as determined from ultraviolet-visible absorption spectra. The fluorescence spectra of HM NPs show characteristic emission at 430 nm, which indicates the presence of nitrogen functional groups with external conjugation. The proposed structure of HM NPs is verified with different analytical instruments.

Formation of reusable Au-acetonitrile polymers and N-doped graphene catalyst under UV light via submerged liquid plasma process

In this study, acetonitrile polymers (ANPs) synthesized using a submerged liquid plasma (SLP) process were used for the direct reduction of Au3+ under ultraviolet (UV) light without the need for reducing or templating agents. Nitrogen-functionalized graphene (NFG) and ANPs, both synthesized via the SLP process were used to form a Au–ANPs–NFG nanohybrid. The pyridinic and pyrrolic nitrogen present in the NFG effectively chemisorbs or binds with ANPs through π–π or σ–π interaction. The ANPs provide excellent control over the Au nanoparticle formation size (∼5 nm), as confirmed by high-resolution transmission electron microscopy. High-resolution X-ray photoelectron spectra revealed that the difference in the chemical shift between Au 4f 5/2 and Au 4f 7/2 peaks was 3.7 eV, which confirms that the reduced form of Au0 was present in Au–ANPs–NFG. A UV-visible absorbance spectrum further confirms the reduction of Au3+ to Au0 under 254 nm UV light. The catalytic activity of the as-synthesized Au–ANPs–NFG was used for the selective oxidation of benzyl alcohol to benzaldehyde in both suspended and immobilized forms. The Au–ANPs–NFG immobilized on Pyrex glass resulted in 69% conversion of benzyl alcohol to benzaldehyde. The reuse of immobilized Au–ANPs–NFG led to 69%, 64%, and 61% successive conversions with a reaction time of 330 min.