Diptiman Dinda

Highly Selective Detection of Trinitrophenol by Luminescent Functionalized Reduced Graphene Oxide through FRET Mechanism

Among different nitro compounds, trinitrophenol (TNP) is the most common constituent to prepare powerful explosives all over the world. A few works on the detection of nitro explosives have already been reported in the past few years; however, selectivity is still in its infant stage. As all the nitroexplosives are highly electron deficient in nature, it is very difficult to separate one from a mixture of different nitro compounds by the usual photoinduced electron transfer (PET) mechanism. In the present work, we have used a bright luminescent, 2,6-diamino pyridine functionalized graphene oxide (DAP-RGO) for selective detection of TNP in the presence of other nitro compounds. The major advantage of using this material over other reported materials is not only to achieve very high fluorescence quenching of ∼96% but also superior selectivity >80% in the detection of TNP in aqueous medium via both fluorescence resonance energy transfer and PET mechanisms. Density functional theory calculations also suggest the occurrence of an effective proton transfer mechanism from TNP to DAP-RGO, resulting in this tremendous fluorescence quenching compared to other nitro compounds. We believe this graphene based composite will emerge a new class of materials that could be potentially useful for selective detection, even for trace amounts of nitro explosives in water.

Removal of toxic Cr(VI) by UV-active functionalized graphene oxide for water purification

Extraction of hazardous heavy metals like As, Hg, Cd, Cr(VI), etc. for water purification is a great challenge. Exploiting the large surface area of graphene, in the present work, we have synthesized a UV-active 2,6-diamino pyridine–reduced graphene oxide (DAP–RGO) composite to remove Cr(VI) from acidic water solution. Here, the presence of an extra pyridinic-nitrogen lone pair facilitates the removal efficiency of excess Cr(VI) [500 mg L−1 in 3 h only] over reported results so far. In addition to that, the unique advantage of this UV-active material is the enhancement of removal efficiency by 18% at a higher pH value. We believe that this study will bring forth a new class of UV-active graphene based adsorbents with remarkably high removal efficiency for toxic heavy metals from waste-water in future.

Thymine Functionalized Graphene Oxide for Fluorescence “Turn-off-on” Sensing of Hg2+ and I– in Aqueous Medium

Selective detection of either mercury (Hg2+) or iodide (I-) ion using fluorescence turn-on or turn-off processes is an important area of research. In spite of intensive research, simultaneous detection of both mercury and iodide using fluorescence turn-off-on processes, high sensitivity and theoretical support concerning the mechanisms are still lacking. In the present work, graphene oxide is functionalized by thymine to realize simultaneous detection of both Hg2+ and I- selectively using fluorescence turn-off-on mechanism. Ultra high sensitivity to the extent of ppb level exploiting large surface area of graphene is achieved. DFT calculations also assist to realize the detailed mechanisms involving this PL quenching and also its regain during sensing of these ions in aqueous solution.

Sulfuric acid doped poly diaminopyridine/graphene composite to remove high concentration of toxic Cr(VI)

Sulfuric acid doped diaminopyridine polymers are synthesized in situ on graphene oxide surface via mutual oxidation-reduction technique. Exploiting large and highly porous surface, we have used this polymer composite as an adsorbent to remove high concentration of toxic Cr(VI) from water. It shows very high adsorption capacity (609.76 mg g(-1)) during removal process. The composite takes only 100 min to remove high concentration of 500 mg L(-1) Cr(VI) from water. Interesting features for this material is the enhancement of removal efficiency at lower acidic condition due to the formation of acid doped emeraldine salt during polymerization. XPS and AAS measurements reveal that our prepared material mainly follows reduction mechanism at higher acidic condition while anions exchange mechanism at lower acidic condition during the removal experiments. Good recycling ability with ∼ 92% removal efficiency after fifth cycle is also noticed for this material. Easy preparation, superior stability in acidic condition, remarkable removal efficiency and excellent recycling ability make this polymer composite an efficient material for modern filtration units in waste water purification.

High selectivity in water soluble MoS2 quantum dots for sensing nitro explosives

Rapid and selective detection of nitro explosives is one of the most promising issues concerning global security. Intensive research has already been carried out, however, the selectivity is still lacking. In the present work, water soluble MoS2 quantum dots (QDs) are synthesized through a bottom-up approach using (NH4)6Mo7O24·4H2O and Na2S as molybdenum and sulfur sources, respectively, and 1,4-diaminobutane as the capping agent. The as-synthesized QDs detect 2,4,6-trinitrophenol (TNP) selectively up to 2.04 ppm and the selectivity reaches >90% which is remarkably higher than the earlier results. In addition to predominant electron transfer (ET) that occurs mostly in fluorescence quenching processes, Forster resonance energy transfer (FRET) also occurs here. As a result of the occurrence of both these ET and FRET processes, high selectivity is achieved for the present samples. The unique advantage of using QDs is the tuning of photoluminescence as a function of dot size to become comparable with the absorption spectra of the TNP to perform the FRET mechanism.

Role of trap states on storage capacity in a graphene/MoO3 2D electrode material

The trap state in graphene has been recently reported, however its role on charge transport and charge storage capacity in a graphene based electrode material has not yet been explored. In semiconducting devices trap states have a negative role in charge transport and current–voltage characteristics. Therefore, exploiting the huge trap states in chemically synthesized graphene to improve the desired material property is a unique idea. In the present work, trap states have been analyzed in detail using capacitance–voltage and current–voltage characteristics in chemically synthesized graphene/MoO3 composites. The effect of trap states on charge transport and on enhancing the dielectric properties are also demonstrated. Finally, we have shown that storage capacitance of the graphene/MoO3 electrode material increases remarkably to about 160% due to the increase in trap states in the material. We believe that this study will reveal a new way of exploiting trap states to improve the material’s characteristics, such as storage capacity etc.

Amorphous molybdenum sulfide quantum dots: an efficient hydrogen evolution electrocatalyst in neutral medium

To overcome the limitations of active edges, electrical conductivity and the surface area of MoS2 nanosheets, in the present work, we have successfully synthesized amorphous MoSx quantum dots with a larger number of edge atoms using a simple chemical reaction via a bottom-up approach. Structural and chemical characterizations are carried out by TEM, XRD, Raman and XPS measurements. XPS and EDX analyses indicate a larger number of unsaturated ‘S’ atoms in these ultrafine amorphous quantum dots. We have used this material as an efficient electrocatalyst for the hydrogen evolution reaction (HER) in neutral medium. The material shows a remarkably low overpotential (65 mV) towards HER compared to that of other crystalline MoS2 quantum dots or nanomaterials. The origin of such a low onset potential is the presence of more unsaturated sulfur (S22−) ligands and enhanced active edge sites. It also shows very high catalytic activity as well as good stability after 12 h of hydrogen generation in neutral water medium.