Julia Saloni

Theoretical studies on the bonding and thermodynamic properties of GenSim(m+n=5) clusters: The precursors of germanium/silicon nanomaterials

Theoretical studies on the Ge n Si m clusters have been carried out using advanced ab initio approaches. The lowest energy isomers were determined for the clusters with compositions n+m=2-5. All possible isomers arising due to permutations of Ge and Si atoms were investigated. The L-shaped structure for the trimers, tetragonal with diagonal bond for tetramers, and a trigonal bipyramid for pentamers represent the energy optimized ground state geometries. The bonding analyses revealed that the trimers and tetramers are stabilized through multicenter pi bonding. In pentamers, this stabilizing factor is eliminated due to the further cluster growth. The ionization of clusters does not change their geometrical characteristics. The agreement of the calculated ionization and atomization energies with those obtained from the mass spectrometric studies (through estimated appearance potential) validated the reported structures of the clusters. The bonding properties of these species are discussed using their molecular orbital characteristics and analysis of natural bond orbital population data.

Theoretical Investigation on Monomer and Solvent Selection for Molecular Imprinting of Nitrocompounds

The aim of this work is to serve as a guideline for the initial selection of monomer and solvent for the synthesis of the nitrocompound-based molecularly imprinted polymers, MIPs. Reported data include evaluation of six systems with the ability to form noncovalently bonded monomer-template complexes. These systems are represented by the following aliphatic and aromatic molecules: acrolein, acrylonitrile, 2,6-bisacrylamide, 4-ethylenebenzoic acid, methyl methacrylate, and 2-vinylpyridine. Cave models for selected monomers are also presented and supported by binding energy analysis under various conditions. Solvent effects on monomer-template binding energy have been studied for four solvents: acetone, acetonitrile, chloroform, and methanol. Additionally, systems such as 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), pentachlorophenol (PCP), and 3,6-dichloro-2-methoxybenzoic acid (Dicamba) have been used to study selectivity of acrolein-based MIP toward TNT detection. The density functional theory, DFT, method has been used for all structural, vibrational frequency, and solvent calculations.

Photodegradation of Selected PCBs in the Presence of Nano-TiO2 as Catalyst and H2O2 as an Oxidant

Photodegradation of five strategically selected PCBs was carried out in acetonitrile/water 80:20. Quantum chemical calculations reveal that PCBs without any chlorine on ortho-positions are closer to be planar, while PCBs with at least one chlorine atoms at the ortho-positions causes the two benzene rings to be nearly perpendicular. Light-induced degradation of planar PCBs is much slower than the perpendicular ones. The use of nano-TiO2 speeds up the degradation of the planar PCBs, but slows down the degradation of the non-planar ones. The use of H2O2 speeds up the degradation of planar PCBs greatly (by >20 times), but has little effect on non-planar ones except 2,3,5,6-TCB. The relative photodegradation rate is: 2,2′,4,4′-TCB > 2,3,5,6-TCB > 2,6-DCB ≈ 3,3′,4,4′-TCB > 3,4′,5-TCB. The use of H2O2 in combination with sunlight irradiation could be an efficient and “green” technology for PCB remediation.

The Evolution of Bonding and Thermodynamic Properties of Boron-Doped Small Carbon Clusters: An Ab Initio Study

Theoretical studies on BC(n) (n=1-6) clusters are carried out using density functional theory, Møller-Plesset second-order perturbation theory (MP2), coupled-cluster calculations including up to triple excitations (CCSD(T)), and higher-level approaches. All possible isomers depending on the positions of the boron atom are generated and the lowest-energy isomers are determined for doublet and quartet electronic states. The three potential evolution paths of the clusters are determined as a function of their size. The energetic and electronic consequences for the increased size of structures differ significantly, which leads to representatives of the ground electronic state from different structural groups. The ab initio calculated thermal functions allow enhancements to the available atomization energies and improve the agreement between the calculated and experimental heat content.