Atomic force microscopy investigation of the mechanism of calcite microcrystal growth under Kitano conditions

A combined atomic force microscopy (AFM)-inverted optical microscopy technique has been used to image the surface of calcite single microcrystals, with dimensions of 10-20 microm, at high resolution. The microcrystals were grown on a glass substrate using the Kitano method, a process that involves the outgassing of carbon dioxide from a saturated solution of calcium carbonate. The resulting increase in the supersaturation of the solution, with respect to calcium carbonate, induces crystallization. It is demonstrated, for the first time, that calcite microcrystals formed in this way exhibit a single spiral growth hillock on the (104) surface, as evidenced by a spiral step pattern, indicating that growth occurs at steps arising from an individual screw dislocation. The subsequent reactivity of these crystals under Kitano conditions has been followed in situ using AFM imaging.     

Effects of Adsorbed Polyaniline on Redox Processes on As(2)O(3) Surfaces

Polyaniline deposited on As(2)O(3) surface resulted in a new material, which was characterized by infrared spectoscopy, thermogravimetry, differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, and cyclic voltammetry. The mass percentage of polymer deposited on oxide surface is approximately 13%. The scanning electron microscopy images as well as the X-ray diffraction patterns provided conclusive evidence that the oxide surface is coated by the polymer. The cyclic voltammograms of the polyaniline adsorbed on As(2)O(3) surface showed that the adsorbate exerts remarkable effects on redox processes on this oxide. The pure oxide exhibited two oxidation/reduction peaks at 0.25/-0.06 and 0.47/-0.25 V attributed tentatively to the processes As(2)O(3)(s)+6H(+)+6e(-)=2As(s)+3H(2)O and As(s)+3H(+)+3e(-)=AsH(3)(g), respectively. The polyaniline-coated sample exhibited a better-defined voltammogram in which the first oxidation peak of the oxide had its intensity increased about four times. Copyright 2000 Academic Press.     

Formation of polyaniline/Pt nanoparticle composite films and their electrocatalytic properties

Polyaniline (PANI) thin films modified with platinum nanoparticles have been prepared by several methods, characterised and assessed in terms of electrocatalytic properties. These composite materials have been prepared by the in situ reduction of a platinum salt (K₂PtCl₄) by PANI, in a variety of solvents, resulting in the formation of platinum nanoparticles and clusters of different sizes. The further deposition of platinum clusters at spin cast thin films of PANI/Pt composites from a neutral aqueous solution of K₂PtCl₄ has also been demonstrated. Thin-film electrodes prepared from these materials have been investigated for their electrocatalytic activity by studying hydrazine oxidation and dichromate reduction. The properties of the composite materials have been determined using UV–visible spectroscopy, atomic force microscopy and transmission electron microscopy. The nature of the material formed is strongly dependent on the solvent used to dissolve PANI, the method of preparation of the PANI/Pt solution and the composition of the spin cast thin film before subsequent deposition of platinum from the aqueous solution of K₂PtCl₄.Dedicated to Professor Dr. Alan Bond on the occasion of his 60th birthday.     

Effect of composition on the conductivity and morphology of poly(3-hexylthiophene)/gold nanoparticle composite Langmuir-Schaeffer films

Ultrathin Langmuir-Schaeffer (LS) films were fabricated from blends of regioregular poly(3-hexylthiophene) (P3HT) and highly monodispersed dodecanethiolate-capped gold nanoparticles (Au NPs) mixed in varying weight ratios. The morphology of the ultrathin films was investigated by UV-visible absorption spectroscopy, atomic force microscopy (AFM) and field-emission scanning electron microscopy (FE-SEM). The results of the structural investigations were correlated with the lateral conductivity of the films, with P3HT in its unintentionally doped state, probed by scanning electrochemical microscopy (SECM), which proved to be a very sensitive technique. Control over the P3HT/Au NP ratio led to remarkable changes in the morphology and lateral conductivity of the films. Inclusion of Au NPs into P3HT was found to influence the ordering of P3HT, which ultimately determined the macroscopic charge transport characteristics of the films. Composite films with ca. 33% by weight of Au NPs were found to be the most ordered and exhibited the highest conductivity, substantially higher than P3HT alone. To provide insight into the film formation process, LS composite films comprising equal quantities of P3HT and Au NPs (by weight) were transferred at several surface pressures and investigated by SECM, AFM and FE-SEM.     

有关铜锌原电池的问题讨论

针对铜锌原电池中锌电极冒气泡的“异常”现象,通过分析不同类型原电池的工作原理,认为即使使用纯度极高的锌也会产生气泡,并给出其缘由。对在教学中如何处理这一棘手的难题,提出个人见解。同时,建议中学化学教材将“锌片上产生气泡”的现象明确地描述出来。     

Control of electron transfer in supramolecular systems

The fluorescence quantum yield of zinc porphyrin (ZnP) covalently linked to 9,10-bis(phenylethynyl)anthracene (AB) is strongly dependent upon the solvent properties. The bichromophoric system ZnP-AB exhibits 'normal' zinc porphyrin fluorescence in solvents that cannot coordinate to the central zinc atom. In contrast, if a Lewis base, such as pyridine, is added to a sufficiently polar solvent, the fluorescence is significantly quenched. Picosecond transient absorption measurements, in conjunction with fluorescence quenching and cyclic voltammetric measurements, suggest that the quenching mechanism is intramolecular electron transfer from ZnP to AB. The charge separated state. ZnP*+-AB*-, has a lifetime of not more than 220 ps before recombining. If a secondary electron acceptor, iron(III) porphyrin (FeP), is covalently connected to the AB unit, a second electron transfer from AB*- to FeP occurs and the charge separated state, ZnP*+-AB-FeP*-, has a lifetime of at least 5 ns. This demonstrates that electron transfer might be sensitively tuned (switched on) by specific solvent effects.     

Ultrafast transient absorption spectroelectrochemistry: femtosecond to nanosecond excited-state relaxation dynamics of the individual components of an anthraquinone redox couple

Many photoactivated processes involve a change in oxidation state during the reaction pathway and formation of highly reactive photoactivated species. Isolating these reactive species and studying their early-stage femtosecond to nanosecond (fs–ns) photodynamics can be challenging. Here we introduce a combined ultrafast transient absorption-spectroelectrochemistry (TA-SEC) approach using freestanding boron doped diamond (BDD) mesh electrodes, which also extends the time domain of conventional spectrochemical measurements. The BDD electrodes offer a wide solvent window, low background currents, and a tuneable mesh size which minimises light scattering from the electrode itself. Importantly, reactive intermediates are generated electrochemically, via oxidation/reduction of the starting stable species, enabling their dynamic interrogation using ultrafast TA-SEC, through which the early stages of the photoinduced relaxation mechanisms are elucidated. As a model system, we investigate the ultrafast spectroscopy of both anthraquinone-2-sulfonate (AQS) and its less stable counterpart, anthrahydroquinone-2-sulfonate (AH₂QS). This is achieved by generating AH₂QS in situ from AQS via electrochemical means, whilst simultaneously probing the associated early-stage photoinduced dynamical processes. Using this approach we unravel the relaxation mechanisms occurring in the first 2.5 ns, following absorption of ultraviolet radiation; for AQS as an extension to previous studies, and for the first time for AH₂QS. AQS relaxation occurs via formation of triplet states, with some of these states interacting with the buffered solution to form a transient species within approximately 600 ps. In contrast, all AH₂QS undergoes excited-state single proton transfer with the buffered solution, resulting in formation of ground state AHQS⁻ within approximately 150 ps.

A spectroelectrochemical set-up using a boron doped diamond mesh electrode is presented; from ultrafast photodynamics to steady-state, the photochemistry and photophysics of redox active species and their reactive intermediates can be investigated.     

Geometric isomers of chloro(6‐methyl‐1,4,8,11‐tetraazacyclotetradecane‐6‐amine)cobalt(III) tetrachlorozincate(II)

The crystal structures of a pair of cis and trans isomers of the macrocyclic chloro­penta­amine title complex, as their tetra­chloro­zincate(II) salts, [CoCl(C₁₁H₂₇N₅)][ZnCl₄], are re­ported. The two distinct isomeric forms lead to significant variations in the Co—N bond lengths and, furthermore, hydrogen bonding between the complex ions is influenced by the folded (cis) or planar (trans) conformations of the coordinated ligand.     

Structural correlations in heterogeneous electron transfer at monolayer and multilayer graphene electrodes

As a new form of carbon, graphene is attracting intense interest as an electrode material with widespread applications. In the present study, the heterogeneous electron transfer (ET) activity of graphene is investigated using scanning electrochemical cell microscopy (SECCM), which allows electrochemical currents to be mapped at high spatial resolution across a surface for correlation with the corresponding structure and properties of the graphene surface. We establish that the rate of heterogeneous ET at graphene increases systematically with the number of graphene layers, and show that the stacking in multilayers also has a subtle influence on ET kinetics.     

trans‐Cyano(6‐methyl‐1,4,8,11‐tetraazacyclotetradecan‐6‐amine)cobalt(III) bis(perchlorate) hydrate and trans‐hydroxo(6‐methyl‐1,4,8,11‐tetraazacyclotetradecan‐6‐amine)cobalt(III) bis(perchlorate)

The crystal structures of a pair of closely related macrocyclic cyano‐ and hydroxopenta­amine­cobalt(III) complexes, as their perchlorate salts, are reported. Although the two complexes, [Co(CN)(C₁₁H₂₇N₅)](ClO₄)₂·H₂O and [Co(OH)(C₁₁H₂₇N₅)](ClO₄)₂, exhibit similar conformations, significant differences in the Co—N bond lengths arise from the influence of the sixth ligand (cyano as opposed to hydroxo). The ensuing hydrogen‐bonding patterns are also distinctly different. Disorder in the perchlorate anions was clearly resolved and this was rationalized on the basis of distinct hydrogen‐bonding motifs involving the anion O atoms and the N—H and O—H donors.