Adsorption and photocatalysed destruction of cationic and anionic dyes on mesoporous titania films: Reactions at the air-solid interface

Cationic dyes, such as methylene blue (MB), Thionine (TH) and Basic Fuschin (BF), but not anionic dyes, such as Acid Orange 7 (AO7), Acid Blue 9 (AB9) and Acid Fuschin (AF), are readily adsorbed onto mesoporous titania films at high pH (pH 11), i.e. well above the pzc of titania (pH 6.5), due to electrostatic forces of attraction and repulsion, respectively. The same anionic dyes, but not the cationic dyes, are readily adsorbed on the same titania films at low pH (pH 3), i.e. well below titania's pzc. MB appears to adsorb on mesoporous titania films at pH 11 as the trimer (lambda(max) = 570 nm) but, upon drying, although the trimer still dominates, there is an absorption peak at 665 nm, especially notable at low [MB], which may be due to the monomer, but more likely MB J-aggregates. In contrast, the absorption spectrum of AO7 adsorbed onto the mesoporous titania film at low pH is very similar to the dye monomer. For both MB and AO7 the kinetics of adsorption are first order and yield high rate constants (3.71 and 1.481 g(-1) min(-1)), indicative of a strong adsorption process. Indeed, both MB and AO7 stained films retained much of their colour when left overnight in dye-free pH 11 and 3 solutions, respectively, indicating the strong nature of the adsorption. The kinetics of the photocatalytic bleaching of the MB-titania films at high pH are complex and not well-described by the Julson-Ollis kinetic model [A.J. Julson, D.F. Ollis, Appl. Catal. B. 65 (2006) 315]. Instead, there appears to be an initial fast but not simple demethylation step, followed by a zero-order bleaching and further demethylation steps. In contrast, the kinetics of photocatalytic bleaching of the AO7-titania film give a good fit to the Julson-Ollis kinetic model, yielding values for the various fitting parameters not too dissimilar to those reported for AO7 adsorbed on P25 titania powder. (C) 2008 Elsevier B.V. All rights reserved.

Voltage-activated currents in cardiac myocytes of the blue mussel, Mytilus edulis

Voltage-sensitive ionic currents were identified and characterised in ventricular myocytes of the bivalve mollusc, Mytilus edulis, using the whole-cell patch-clamp technique. Two outward currents could be distinguished. A potassium A current (I-A) activated at - 30 mV from a holding potential of - 60 mV. This transient current was inactivated by holding the cells at a potential of - 40 mV and was also blocked by applying 4-aminopyridine (3 mM) to the external bath solution. A second current was identified as a delayed rectifier (I-K). This also activated at - 30 mV but exhibited a sustained time course and was still activated at a holding potential of - 40 mV. Both outward currents were reduced in the presence of tetraethylammonium ions (30 mM). A small number of heart cells also showed an inward sodium current (I-Na). This current appeared at potentials more positive than - 50 mV, reached a maximum at - 20 mV, and decreased with further depolarisation. I-Na was inactivated at a holding potential of - 40 mV and was blocked by tetrodotoxin (1 mu M). A second inward current had a sustained time course and was not inactivated by holding the cell at a potential of -40 mV, and was also not abolished by tetrodotoxin. This current peaked at 0 mV, decreasing with further depolarisation. Furthermore, it was enhanced by the addition of barium ions (3 mM) to the bath and was blocked by external cobalt (2 mM) or nifedipine (15 mu M) These findings are consistent with this being an L-type calcium current (I-Ca) The possible physiological roles of these currents in M. edulis heart are discussed. (C) 1999 Elsevier Science Inc. All rights reserved.

Simultaneous, long-term monitoring of valve and cardiac activity in the blue mussel Mytilus edulis exposed to copper

Valve and cardiac activity were simultaneously measured in the blue mussel (Mytilus edulis) in response to 10 d copper exposure. Valve movements, heart rates and heart-rate variability were obtained non-invasively using a Musselmonitor(R) (valve activity) and a modified version of the Computer-Aided Physiological Monitoring system (CAPMON; cardiac activity). After 2 d exposure of mussels (4 individuals per treatment group) to a range of dissolved copper concentrations (0 to 12.5 mu M as CuCl2) median valve positions (% open) and median heart rates (beats per minute) declined as a function of copper concentration. Heart-rate variability (coefficient of variation for interpulse durations) rose in a concentration-dependent manner. The 48 h EC50 values (concentrations of copper causing 50% change) for valve positions, heart rates and heart-rate variability were 2.1, 0.8, and 0.06 mu M, respectively. Valve activity was weakly correlated with both heart rate (r = 0.48 +/- 0.02) and heart-rate variability (r = 0.32 +/- 0.06) for control individuals (0 mu M Cu2+). This resulted from a number of short enclosure events that did not coincide with a change in cardiac activity. Exposure of mussels to increasing copper concentrations (greater than or equal to 0.8 mu M) progressively reduced the correlation between valve activity and heart rates (r = 0 for individuals dosed with greater than or equal to 6.3 mu M Cu2+), while correlations between valve activity and heart-rate variability were unaffected. The poor correlations resulted from periods of valve flapping that were not mimicked by similar fluctuations in heart rate or heart-rate variability. The data suggest that the copper-induced bradycardia observed in mussels is not a consequence of prolonged valve closure.

The initial mode of action of copper on the cardiac physiology of the blue mussel, Mytilus edulis

Previous studies have shown that low levels of copper (down to 0.8 muM) induce bradycardia in the blue mussel (Mytilus edulis) and that this is not caused by prolonged Valve closure. The aim of this study was to determine the precise mechanism responsible. To establish if copper was directly affecting heart cell physiology, recordings of contractions from isolated ventricular strips were made using an isometric force transducer, in response to copper concentrations (as CuCl2) ranging between 1 muM and 1 mM. Inhibition of mechanical activity only occurred at 1 mM copper, suggesting that the copper-induced bradycardia observed in whole animals cannot be attributed to direct cardiotoxicity. Effects of copper on the cardiac nerves were subsequently examined. Following removal of visceral ganglia (from where the cardiac nerves originate), exposure to 12.5 muM copper had no effect on the heart rate of whole animals. The effect of copper on the heart rate of mussels could not be abolished by depletion of the monoamine content of the animal using reserpine. However, pre-treatment of the animals with alpha -bungarotoxin considerably reduced the sensitivity of the heart to copper. These results indicated that the influence of copper on the heart of M. edulis might be mediated by a change in the activity of cholinergic nerves to heart. In the final experiments, mussels were injected with either benzoquinonium or D-tubocurarine, prior to copper exposure, in an attempt to selectively block the inhibitory or excitatory cholinoreceptors of the heart. Only benzoquinonium decreased the susceptibility of the heart to copper, suggesting that copper affects the cardiac activity of blue mussels by stimulating inhibitory cholinergic nerves to the heart. (C) 2001 Elsevier Science B.V. All rights reserved.

A novel reversible relative-humidity indicator ink based on methylene blue and urea

A new relative-humidity sensitive ink based on methylene blue and urea is described which can utilise the deliquescent nature of urea.

Blue bottle light: lecture demonstrations of homogeneous and heterogeneous photo-induced electron transfer reactions

The classic, non-photochemical blue bottle experiment involves the reaction of methylene blue (MB) with deprotonated glucose, to form a bleached form of the dye, leuco-methylene blue (LMB), and subsequent colour recovery by shaking with air. This reaction is a popular demonstrator of key principles in kinetics and reaction mechanisms. Here it is modified so as to highlight features of homogenous and heterogeneous photoinduced electron transfer (PET) (Pure Appl. Chem., 2007, 79, 293-465) reactions, i.e. blue bottle light experiments. The homogeneous blue bottle light experiment uses methylene blue, MB, as the photo-sensitizer and triethanolamine as the sacrificial electron donor. Visible light irradiation of this system leads to its rapid bleaching, followed by the ready restoration of its original colour upon shaking away from the light source. The heterogeneous blue bottle light experiment uses titania as the photo-sensitizer, MB as a redox indicator and glucose as the sacrificial electron donor. UVA light irradiation of this system leads to the rapid bleaching of the MB and the gradual restoration of its original colour with shaking and standing. The latter 'dark' step can be made facile and more demonstrator-friendly by using platinised titania particles. These two photochemical versions of the blue bottle experiment are used to explore the factors which underpin homogeneous and heterogeneous PET reactions and provide useful demonstrations of homogeneous and heterogeneous photochemistry.

Current and possible future methods of assessing the activities of photocatalyst films

The continuing interest in semiconductor photochemistry, SPC, and the emergence of commercial products that utilise films of photocatalyst materials, has created an urgent need to agree a set of methods for assessing photocatalytic activity and international committees are now meeting to address this issue. This article provides a brief overview of two of the most popular current methods employed by researchers for assessing SPC activity. and one which has been published just recently and might gain popularity in the future, given its ease of use. These tests are: the stearic acid (SA) test, the methylene blue (MB) test and the resazurin (Rz) ink test, respectively. The basic photochemical and chemical processes that underpin each of these tests are described, along with typical results for laboratory made sol-gel titania films and a commercial form of self-cleaning glass, Activ (TM). The pros and cons of their future use as possible standard assessment techniques are considered. (C) 2007 Elsevier B.V. All rights reserved.

Platinum Group Metals and Their Oxides in Semiconductor Photosensitisation BASIC PRINCIPLES, METAL PHOTODEPOSITION AND WATER PHOTOSPLITTING REACTIONS

The basic principles of semiconductor photochemistry, particularly using titania as a semiconductor photocatalyst, are discussed. When a platinum group metal or its oxide is deposited onto the surface of a sensitised semiconductor the overall efficiency of the reactions it takes part in are often improved, especially when the deposits are used as hydrogen and oxygen catalysts, respectively. Methods of depositing metal or metal oxide are examined, and a particular focus is given to a photodeposition process that uses a sacrificial electron donor. Platinum group metal and platinum group metal oxide coated semiconductor photocatalysts are prominent in heterogeneous systems that are capable of the photoreduction, oxidation and cleavage of water. There is a recent renaissance in work on water-splitting semiconductor-sensitised photosystems, but there are continued concerns over their irreproducibility, longevity and photosynthetic nature.

Novel photochemistry of leuco-Methylene Blue

leuco-Methylene Blue has a previously unrecognized, very reactive, UV-driven triplet state photochemistry and, in particular, undergoes photo-oxidative quenching with dissolved oxygen.

Kinetics and mechanism of a fast leuco-Methylene Blue oxidation by copper(II)-halide species in acidic aqueous media

The kinetics of a fast leuco-Methylene Blue (LMB) re-oxidation to Methylene Blue (MB) by copper(II)-halide (Cl-, Br-) complexes in acidic aqueous media has been studied spectrophotometrically using a stopped-flow technique. The reaction follows a simple first order rate expression under an excess of the copper(II) species (and H+(aq)), and the pseudo-first order rate constant (k'(obs)) is largely independent of the atmosphere used (air, oxygen, argon). The rate law, at constant Cl- (Br-) anion concentration, is given by the expression: (d[MB+])/dt = ((k(a)K[H+] + k(b))/(1 + K[H+])).[Cu-II][LMB] = k'(obs)[LMB], where K is the protonation constant, and k(a) and k(b) are the pseudo-second order rate constants for protonated and deprotonated forms of LMB, respectively The rate law was determined based on the observed k'(obs) vs. [Cu-II] and [H+] dependences. The rate dramatically increases with [Cl-] over the range: 0.1-1.5 M, reflecting the following reactivity order: Cu2+(aq)