• HONEY JOHN

Articles written in Bulletin of Materials Science

• Complex permittivity and conductivity of poly(𝑝-phenylenediazomethine) and its blends at microwave frequencies

Poly(𝑝-phenylenediazomethine) was synthesized by the condensation reaction between glyoxal and 𝑝-phenylene diamine in different solvents like methanol, toluene, 𝑚-cresol and 𝑁,𝑁-dimethylformamide. The dielectric properties and microwave conductivity of the pelletized samples were measured using cavity perturbation technique. The measurements were done at 2.17 GHz at room temperature (25°C). The effect of dopants on the dielectric properties and conductivity was studied using HCl and HClO4. Dielectric properties like dielectric constant, dielectric loss factor and microwave conductivity increased on doping with HCl and HClO4. Conducting polymer composites were prepared by in situ polymerization of glyoxal and 𝑝-phenylenediamine in different solvents containing different amounts of PVC, and silica. The microwave conductivity and complex permittivity of each sample was measured. The effect of dopants like HClO4 and HCl on these dielectric properties was also studied. The d.c. conductivity of the pressed samples measured by the two-probe method was also studied.

• Effect of reaction variables on facet-controlled synthesis of anatase TiO$_2$ photocatalysts

This study reports the effect of various reaction variables of a tailor-made sol–gel synthesis method on the morphology and photocatalytic behaviour of nanostructured anatase TiO$_2$ photocatalysts. Reaction variables like solvent effects, hydrothermal and microwave conditions, type of capping agents and calcination affect the TiO$_2$ crystal growth, and thereby, their optimal conditions are anticipated and discussed in detail. It is proposed that TiO$_2$ exposed with characteristic facets can be prepared by a hydrothermal-modified sol–gel method employing a quaternary solution system at pH 3 along with cetyltrimethylammonium bromide (CTAB) as the capping agent. The optimal hydrothermal temperature affected the restructuring and crystallization of TiO$_2$ by enhancing the phase transformation from amorphous to anatase. TiO$_2$ crystal growth under microwave assistance was faster, which primarily resulted in low-energy facets exposure. The primary determination of photocatalytic efficiency of the samples was obtained from the photodegradation profiles of model dye methylene blue. An interesting find was that TiO$_2$ synthesized under hydrothermal treatment in the presence of CTAB had a morphology determining behaviour at pH 3 favouring the selective stabilization of co-exposing high energy {010}/{100}, {001} and low energy {101} facets in TiO$_2$. The optimum percentage of high- and low-energy facets resulted in superior photocatalytic activity due to the spatial separation of photogenerated charge carriers. Furthermore, the present study has a great perspective on how particularly the reaction variables determine the direction of crystal growth of nano TiO2 and thereby its morphology that directly affect its photocatalytic efficiency.

• A comparative study on the charge storage performance of graphene oxide and reduced graphene oxide in different electrolytes with basic and neutral behaviour

A comparative study on electrochemical supercapacitance performance of graphene oxide (GO) and reduced graphene oxide (rGO) was conducted in neutral and alkaline electrolytes, including Na$_2$S$_2$O$_3$ and KOH. rGO has been prepared through hydrothermal reduction of GO. Before hydrothermal reduction, GO was prepared from bulk graphite via low temperature modified Hummer’s method. The oxygen functional groups were found favourable for base-activated pseudocapacitive reactions that make GO superior to deliver improved supercapacitor performance in KOH electrolytes. On the other hand, a significant increase in effective surface area during hydrothermal reduction make rGO perform better as an electrochemical double-layer capacitor in neutral electrolyte, like sodium thiosulphate. rGO achieved an optimum specific capacitance value of 287 F g$^{–1}$ in Na$_2$S$_2$O$_3$, while GO reported 127 F g$^{–1}$ in 1 M KOH at 1 A g$^{–1}$ current density.

• Bulletin of Materials Science

Volume 46, 2023
All articles
Continuous Article Publishing mode

• Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020