Bibliographic Data Elements for Internet Resources using XML: A Proposal

The paper focuses on the possibilities of better organization and retrieval of Internet resources with the advent of eXtensible Markup Language (XML). The paper advocates the need of identifying necessary and sufficient bibliographic data fields for Internet resources, and generating numerical XML elements for the data fields using a standard syntax which brings together existing tag codes. The paper also brings into the issue of standard out put of search results

Tribochemical properties of metastable states of transition metals

Mechanical forces can be used to trigger chemical reactions through activating bonds and to direct the course of such reactions in organic materials, particularly in polymers. In inorganic materials, the small molecules present significant challenges in directing the reaction kinetics. This dissertation studied the dynamics and kinetics of oxidation of transitional metals, particularly on tantalum through mechanical forces. This is a new area of research in surface science. Experimentally using a combined electrochemical and mechanical manipulation technique, we compared the equilibrium and non-equilibrium oxidation processes and states of tantalum. An experimental setup was developed with an electrochemical system attached to a sliding mechanical configuration capable of friction force measurement. The surface chemistry of a sliding surface, i.e., tantalum, was controlled through the electrolyte. The mechanical force was fixed and the dynamics of the surface was monitored in situ through a force sensor. The formation of non-equilibrium tantalum oxides was found in fluid environments of hydrogen peroxide, acetic acid and deionized water. We found that the mechanical energy induced the non-stable state reactions leading to metal-stable oxides. Analytically, we compared the energy dispersion, reaction kinetics, and investigate physical chemical reactions. We proposed a modified Arrhenius equation to predict the effect of mechanical energy on non-spontaneous reaction under nonequilibrium conditions. At the end, we also propose a modified Pourbaix diagram known as the Kar-Liang diagram. The Kar-Liang diagram helps to understand the behavior of tantalum under non-equilibrium conditions. A complete understanding of the tribochemical reaction of tantalum is achieved through this dissertation. The dissertation contains six chapters. After the introduction and approach, oxidation of tantalum is discussed in Chapter IV, kinetics in Chapter V. The nonequilibrium Kar-Liang diagram is discussed in Chapter VI, followed by conclusion. This research has important impacts on the field of surface science in understanding the basics of mechanochemical reactions. The resulting theory is beneficial to understand chemical-mechanical planarization (CMP) and to optimize the current industrial processes in microelectronics in making integrated circuits

Charge transfer between lead halide perovskite nanocrystals and single-walled carbon nanotubes

© 2020 The Royal Society of Chemistry. A charge transfer study between lead halide-based perovskite nanocrystals and single-walled carbon nanotubes (PNC@CNT nanocomposite) was performed. Solution-processed MAPbX3 PNCs displayed very bright luminescence, but it quenched in the presence of CNTs. This was attributed to the electron transfer from PNCs to CNTs. The detailed changes in fluorescence lifetime were investigated through time-correlated single-photon counting (TCSPC), which suggested mixed static and dynamic quenching along with a decrease in the lifetime. Morphological changes were investigated via transmission electron microscopy (TEM) and attributed to the incorporation of PNCs on long CNTs. Also, the PNC@CNT nanocomposite was explored for photoinduced current response, which indicated an ∼3 fold increase in photoconductivity under light illumination (with a 1 mV bias). This electron transfer study between PNCs and CNTs contributes to the exploration of charge dynamics

Facile synthesis of reduced graphene oxide-gold nanohybrid for potential use in industrial waste-water treatment

Here, we report a facile approach, by the photochemical reduction technique, for in situ synthesis of Au-reduced graphene oxide (Au-RGO) nanohybrids, which demonstrate excellent adsorption capacities and recyclability for a broad range of dyes. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) data confirm the successful synthesis of Au-RGO nanohybrids. The effect of several experimental parameters (temperature and pH) variation can effectively control the dye adsorption capability. Furthermore, kinetic adsorption data reveal that the adsorption process follows a pseudo second-order model. The negative value of Gibbs free energy (Delta G(0)) confirms spontaneity while the positive enthalpy (Delta H-0) indicates the endothermic nature of the adsorption process. Picosecond resolved fluorescence technique unravels the excited state dynamical processes of dye molecules adsorbed on the Au-RGO surface. Time resolved fluorescence quenching of Rh123 after adsorption on Au-RGO nanohybrids indicates efficient energy transfer from Rh123 to Au nanoparticles. A prototype device has been fabricated using Au-RGO nanohybrids on a syringe filter (pore size: 0.220 mu m) and the experimental data indicate efficient removal of dyes from waste water with high recyclability. The application of this nanohybrid may lead to the development of an efficient reusable adsorbent in portable water purification. GRAPHICS

Intramolecular charge transfer aromatic amines and their application towards molecular logic gate

The emission response of 1-aminopyrene and 2-aminoanthracene was found to be switched ON or OFF by interrupting the Intramolecular Charge Transfer processes of these integrated systems using two binary ionic inputs like H<SUP>+</SUP> or/and OH<SUP>-</SUP>. These fluorescence responses in the presence of added H<SUP>+</SUP> or/and OH<SUP>-</SUP> could be correlated with Half-subtractor logic operation, revealing the possibility of using simple molecules for demonstrating complex logic operations

Interfacial electron transfer dynamics involving a new bis-thiocyanate ruthenium(II)-polypyridyl complex, coupled strongly to nanocrystalline TiO<SUB>2</SUB>, through a pendant catecholate functionality

Ruthenium(II)-polypyridyl bis-thiocyanate complex (1) with pendant catecholate functionality was synthesized and characterized by various spectroscopic and analytical techniques. Optical absorption studies show that this molecule absorbs in the red region of the solar spectrum. Further, this molecule could couple very strongly with TiO2 nanoparticles through pendant catecholate functionality and sensitize efficiently. Interfacial electron transfer dynamics between 1 and TiO2 nanoparticles was investigated by using femtosecond transient absorption spectroscopy and following kinetics at various wavelengths in the visible and near-infrared region. Electron injection to the conduction band of the nanoparticulate TiO2 was confirmed by direct detection of an electron in the conduction band, the cation radical of the adsorbed dye (1&#183;+), and a bleach of the dye in real time as monitored by transient absorption spectroscopy. A single exponential and pulse width limited (&lt;100 fs) electron injection was observed. Presumably, this originates from the nonthermalized excited states of 1 and tends to suggest that electron injection competes with the thermalization of the photoexcited states due to large coupling elements for the forward ET reaction. Back electron transfer dynamics was determined by monitoring the decay kinetics of 1&#183;+ and the injected electron and also from recovery kinetics of the bleach of the adsorbed dye. Interfacial electron transfer dynamics was also carried out on TiO2 thin film with complex 1 as a sensitizer and compared with that of nanoparticles

Photophyical properties of ligand localized excited state in ruthenium(II) polypyridyl complexes: a combined effect of electron donor-acceptor ligand

We have synthesized ruthenium(II) polypyridyl complexes (1) Ru(II)(bpy)<SUB>2</SUB>(L<SUB>1</SUB>), (2) Ru(II)(bpy)<SUB>2</SUB>(L<SUB>2</SUB>) and (3) Ru(II)(bpy)(L<SUB>1</SUB>)(L<SUB>2</SUB>), where bpy = 2,2'-bipyridyl, L<SUB>1</SUB> = 4-[2-(4'-methyl-2,2'-bipyridinyl-4-yl)vinyl]benzene-1,2-diol) and L<SUB>2</SUB> = 4-(N,N-dimethylamino-phenyl)-(2,2'-bipyridine) and investigated the intra-ligand charge transfer (ILCT) and ligand-ligand charge transfer (LLCT) states by optical absorption and emission studies. Our studies show that the presence of electron donating -NMe<SUB>2</SUB> functionality in L<SUB>2</SUB> and electron withdrawing catechol fragment in L<SUB>1</SUB> ligands of complex 3 introduces low energy LLCT excited states to aboriginal MLCT states. The superimposed LLCT and MLCT state produces redshift and broadening in the optical absorption spectra of complex 3 in comparison to complexes 1 and 2. The emission quantum yield of complex 3 is observed to be extremely low in comparison to that of complex 1 and 2 at room temperature. This is attributed to quenching of the <SUP>3</SUP>MLCT state by the low-emissive <SUP>3</SUP>LLCT state. The emission due to ligand localized CT state (ILCT and LLCT) of complexes 2 and 3 is revealed at 77 K in the form of a new luminescence band which appeared in the 670-760 nm region. The LLCT excited state of complex 3 is populated either via direct photoexcitation in the LLCT absorption band (350-700 nm) or through internal conversion from the photoexcited <SUP>3</SUP>MLCT (400-600 nm) states. The internal conversion rate is determined by quenching of the <SUP>3</SUP>MLCT state in a time resolved emission study. The internal conversion to LLCT and ILCT excited states are observed to be as fast as ~200 ps and ~700 ps for complexes 3 and 2, respectively. The present study illustrates the photophysical property of the ligand localized excited state of newly synthesized heteroleptic ruthenium(II) polypyridyl complexes

Efficient charge separation in TiO<SUB>2</SUB> films sensitized with ruthenium(II)-polypyridyl complexes: hole stabilization by ligand-localized charge-transfer states

We have studied the interfacial electron-transfer dynamics on TiO2 film sensitized with synthesized ruthenium(II)-polypyridyl complexes-[RuII(bpy)2(L1)] (1) and [RuII(bpy)(L1)(L2)] (2), in which bpy=2,2'-bipyridyl, L1=4-[2-(4'-methyl-2,2'-bipyridinyl-4-yl)vinyl]benzene-1,2-diol, and L2=4-(N,N-dimethylaminophenyl)-2,2'-bipyridine-by using femtosecond transient absorption spectroscopy. The presence of electron-donor L2 and electron-acceptor L1 ligands in complex 2 introduces lower energetic ligand-to-ligand charge-transfer (LLCT) excited states in addition to metal-to-ligand (ML) CT manifolds of complex 2. On photoexcitation, a pulse-width-limited (&lt;100 fs) electron injection from populating LLCT and MLCT states are observed on account of strong catecholate binding on the TiO2 surface. The hole is transferred directly or stepwise to the electron-donor ligand (L2) as a consequence of electron injection from LLCT and MLCT states, respectively. This results an increased spatial charge separation between the hole residing at the electron-donor (L2) ligand and the electron injected in TiO2 nanoparticles (NPs). Thus, we observed a significant slow back-electron-transfer (BET) process in the 2/TiO2 system relative to the 1/TiO2 system. Our results suggest that RuII-polypyridyl complexes comprising LLCT states can be a better photosensitizer for improved electron injection yield and slow BET processes in comparison with RuII-polypyridyl complexes comprising MLCT states only

Efficient charge separation in TiO₂ films sensitized with ruthenium(II)–polypyridyl complexes: hole stabilization by ligand-localized charge-transfer states

We have studied the interfacial electron-transfer dynamics on TiO2 film sensitized with synthesized ruthenium(II)–polypyridyl complexes—[RuII(bpy)2(L1)] (1) and [RuII(bpy)(L1)(L2)] (2), in which bpy=2,2′-bipyridyl, L1 = 4-[2-(4′-methyl-2,2′-bipyridinyl-4-yl)vinyl]benzene-1,2-diol, and L2=4-(N,N-dimethylaminophenyl)-2,2′-bipyridine—by using femtosecond transient absorption spectroscopy. The presence of electron-donor L2 and electron-acceptor L1 ligands in complex 2 introduces lower energetic ligand-to-ligand charge-transfer (LLCT) excited states in addition to metal-to-ligand (ML) CT manifolds of complex 2. On photoexcitation, a pulse-width-limited (&#60;100 fs) electron injection from populating LLCT and MLCT states are observed on account of strong catecholate binding on the TiO2 surface. The hole is transferred directly or stepwise to the electron-donor ligand (L2) as a consequence of electron injection from LLCT and MLCT states, respectively. This results an increased spatial charge separation between the hole residing at the electron-donor (L2) ligand and the electron injected in TiO2 nanoparticles (NPs). Thus, we observed a significant slow back-electron-transfer (BET) process in the 2/TiO2 system relative to the 1/TiO2 system. Our results suggest that RuII–polypyridyl complexes comprising LLCT states can be a better photosensitizer for improved electron injection yield and slow BET processes in comparison with RuII–polypyridyl complexes comprising MLCT states only

Sequential energy and electron transfer in polynuclear complex sensitized TiO₂ nanoparticles

Polynuclear–polypyridyl complexes exhibit a directional energy-transfer property that can improve their photosensitization activity. In the present work, the energy-transfer process is explored in a trinuclear Ru2∧Os1 complex using transient absorption spectroscopy. This study reveals an efficient excitation energy transfer from the terminal (RuII complex) to the core (OsII complex) region in the ultrafast time domain (400 fs–40 ps). The excitation energy funnel is useful in improving the functionalized core activity. This is evidenced in an interfacial electron-transfer study of Ru2&#8743;Os1, Ru2&#8743;Ru1, and Os1 complex sensitized TiO2 nanoparticle (TiO2 NP) systems. The intramolecular energy transfer causes sequential excitation of the core part of the Ru2&#8743;Os1 complex, which leads to multiexponential electron injection into TiO2 NP. Besides this, the electronic coupling between the metal ion centers stabilizes the positive charge within the trinuclear complex, which results in a slow charge recombination reaction. This study shows that polynuclear complexes can be very useful for their panchromatic effects, unidirectional energy- and electron-transfer properties