K. Srinivasu

Photocatalytic splitting of water on s-triazine based graphitic carbon nitride: an ab initio investigation

Density functional theory based investigations have been carried out to understand the reaction mechanism of the overall photocatalytic water splitting reaction on s-triazine based carbon nitride (g-CN) and to calculate the overpotentials for both oxygen and hydrogen evolution reactions. The calculated free energy changes for different possible intermediate reactions show that at the equilibrium potential of 1.23 V (against the NHE), the oxygen evolution reaction is not completely downhill indicating that the photo-generated holes at 1.23 V cannot oxidize water to oxygen. The oxygen evolution reaction on the g-CN surface is however found to be completely downhill at and above the potential of 2.16 V. As the valence band of g-CN is shown to be located at a potential of 2.64 V, the photo-generated holes in the valence band can oxidise water to oxygen without the aid of any co-catalyst. However, the hydrogen evolution reaction is found to have an overpotential of around 1.1 V and the photo-generated electrons in the conduction band of g-CN are placed at around 0.26 V above the hydrogen reduction potential indicating that the hydrogen evolution is possible only in the presence of a co-catalyst.

Ab initio studies on the electronic structure and properties of aluminum hydrides that are analogues of boron hydrides.

Although the boron hydrides are well-known in the literature, the aluminum hydride chemistry is limited to very few systems such as AlH(3), its dimer, and its polymeric form. In view of the recent experimental studies on the possible existence of the aluminum hydrides, herein, we have undertaken a systematic study on the electronic structure and properties of these aluminum hydrides. Under this, we have studied different classes of hydrides, viz., closo (Al(n)H(n+2)), nido (Al(n)H(n+4)), and arachno (Al(n)H(n+6)), similar to the boranes. All the aluminum hydrides are found to have exceptionally large highest-occupied molecular orbital-lowest-unoccupied molecular orbital gaps, low electron affinities, large ionization potentials and also large enthalpy and free energy of atomization. In addition, most of the structures are also found to have high symmetries. These exceptional properties can be indicative of the pronounced stability, and hence, it is expected that other aluminum hydride complexes can indeed be observed experimentally.

Hydrogen Trapping Ability of the Pyridine–Lithium+ (1:1) Complex

Theoretical studies have been carried out at different levels of theory to verify the hydrogen adsorption characteristics of pyridine-lithium ion (1:1) complexes. The nature of interactions associated with the bonding between pyridine and lithium as well as that between lithium and adsorbed molecular hydrogen is studied through the calculation of electron density and electron-density-based reactivity descriptors. The pyridine-lithium ion complex has been hydrogenated systematically around the lithium site, and each lithium site is found to adsorb a maximum of four hydrogen molecules with an interaction energy of ∼-4.0 kcal/mol per molecule of H2. The fate of the hydrogen adsorbed in a pyridine-lithium ion complex (corresponding to the maximum adsorption) is studied in the course of a 2 ps time evolution through ab initio molecular dynamics simulation at different temperatures. The results reveal that the complex can hold a maximum of four hydrogen molecules at a temperature of 77 K, whereas it can hold only two molecules of hydrogen at 298 K.

Electronic structure, stability and non-linear optical properties of aza-fullerenes C60-2nN2n(n=1–12)

Through ab initio based density functional theory calculations, we have investigated the electronic structure, stability and non-linear optical properties of a series of nitrogen substituted fullerenes (azafullerenes) with the general formula C60-2nN2n (n=1–12). For each system, we have considered different possible isomers and the minimum energy isomer is subjected to further detailed investigations. We have calculated different properties such as HOMO-LUMO gaps, vertical ionization potentials, vertical electron affinities, etc. to verify the stability of the considered fullerenes. From the Hessian calculations, it is observed that all the fullerenes are not only associated with real vibrational frequencies, but the minimum frequencies are also found to be considerably large which further confirms the stability of the considered fullerenes. We find that the presence of unperturbed C6 rings enhances the stability of the fullerene whereas, the -N-C-N- fragments are found to destabilize the structure. At lo...

Can uranyl complexes encapsulate to carbon nanotubes? A periodic DFT study

Periodic density functional theory (DFT)-based calculations were carried out on a series of uranyl complexes encapsulated within single walled (SW)-CNT to understand their encapsulation affinities. We find that uranyl-aqua complex

Porous Graphitic Carbon Nitride: A Possible Metal-free Photocatalyst for Water Splitting

([\hbox {UO}_{2}(\hbox {H}_{2}\hbox {O})_{5}]^{2+}

Quantum chemical studies on hydrogen adsorption in carbon-based model systems: role of charged surface and the electronic induction effect

([UO2(H2O)5]2+) binds stronger as compared to uranyl-hydroxo-complex