Hydrogen peroxide is one of the most important chemicals used in pulp bleaching because of environmental restrictions on the use of chlorine-based bleaches. An on-site electrochemical production process of hydrogen peroxide has been developed for an increasing demand in pulp bleaching. The production cost and operation conditions of the electrolyzer were discussed for the commercially competitive on-site production in this study. The operation cost was estimated from the conditions (the current density, the EDTA dosage, and the oxygen supply ratio) of the electrolyzer. At the condition of the higher electricity unit price the electricity cost was the major factor on the total production cost. Then, the cost minimum point is 1500 A·m-2 at the higher electricity unit price. At the condition of cheaper electricity unit price the facility cost is affected by the current density. The higher current density (2500 A·m-2) is desirable to reduce the initial investment. Then, the trickle-bed cathode’s utilization of oxygen was investigated to reduce oxygen supply ratio. The current efficiency is improved at lower oxygen supply ratio by the treatment of fluorocarbon over the carbon fibers (cathode). And thus the current efficiency over 95% is obtained at the oxygen supply ratio of 1.5 times of the stoichiometric requirement at 1500 A·m-2.
We have investigated the light intensity dependent behavior of active oxygen species formed at TO2 film photocatalyst and water interface. Chemiluminescence method was applied to elucidate the behavior of superoxide (O2−), and for the detection of hydrogen peroxide (H2O2), fluorescence probe was used. When TO2 was excited by relatively weak UV light (1 µW cm−2), deactivation process of O2− was almost unchanged even when the solution was stirred. It is likely that O2- is deactivated via electron transfer to the surface trapped hole. On the contrary, under relatively strong UV light illumination (15 mW cm−2), O2− decayed more rapidly when the solution was stirred. This implies that stirring the solution promotes the disproportionation reactions of O2− which results in the formation of H2O2. Consequently, it can be said that strong UV light illumination and stirring the solution induced the desorption of generated O2− from the surface. Amount of H2O2 measured using a fluorescence probe also confirm this photo-induced desorption behavior of O2−.
The electrocatalytic oxidation of NADH at polythionine-modified electrodes was studied by linear potential-sweep voltammetry, rotating disk voltammetry, and ultraviolet spectroscopy. The high overpotential of NADH was decreased by 0.5 V by modifying GC electrode with polythionine. The rate constant for oxidation of NADH decreased with increasing NADH concentration in solution at each pH values, indicating that the electrooxidation of NADH occurs via a intermediate complex [NADH-pTh]. The electrooxidation of NADH at a polythionine-modified electrode was limited by the rate of the conversion of the intermediate complex to NAD+ and pTh. The rate constant for the dissociation of the intermediate complex decreased with decreasing pH value. This decrease may be due to a poor electron-donating property of NADH in an acidic solution or most probably to the great stability of protonated intermediate complex in an acidic solution.
La-Fe complex oxide films were prepared on Si(111), MgO(100) and SiO2 glass substrates by radio frequency magnetron sputtering using a LaFeO3 target. All the films prepared by this method have the La/Fe atomic ratio of about 1.0. The films were amorphous when the substrate temperature was lower than 650°C, while orthorhombic LaFeO3−δ perovskite films were formed at the substrate temperature higher than 700°C in Ar atmosphere. The orthorhombic LaFeO3−δ perovskite films were also obtained on Si(lll), MgO(100) and SiO2 glass substrates by reactive sputtering in O2/Ar = 0.2∼1.0 at the substrate temperature higher than 700°C. However, in the case of MgO(100) substrate, the orthorhombic LaFeO3−δ perovskite film with (101) orientation was formed. The orthorhombic LaFeO3 perovskite films were formed by heat-treatment of the amorphous La-Fe complex oxide and the crystalline LaFeO3−δ perovskite films in air or Ch atmosphere. The electrical conductivities of LaFeO3−δ/MgO(100) and LaFeO3−δ/SiO2 perovskite films were measured in the range from room temperature to 600°C. It was found that both LaFeO3−δ/MgO(100) and LaFeO3−δ/SiO2 perovskite films are n-type semiconductors with hopping conduction in N2, air and O2.
RuO2-mpregnated carbon electrodes for an electrochemical capacitor were prepared by the direct impregnation of RuO2 on carbon with the alkaline neutralization in the RuCl3 aqueous solution, and have a high specific capacitance (180 Fg−1 for 11.0 wt% RuO2/C). RuO2 particles on the carbon are 2 or 3 nm in diameter, and their structure was amorphous even after annealing at 573 K. The specific pseudocapacitances per RuO2 of the 1.45, 5.03 and 11.0 wt% RuO2-impregnated carbon electrodes were 1079, 1055 and 785 Fg−1 RuO2, respectively. They were twice and more as high as calculated value on the basis of a model of hydrogen adsorption on the surface ruthenium and oxygen. This suggests that hydrogen not only adsorbs on the surface but also intercalates into the inner lattice sites of ruthenium and oxygen due to the ultra-fine and amorphous structure of RuO2 particles on the carbon.
A new composite optical waveguide was fabricated using polytungstic acid (PTA). Thin films were prepared by spin coating of aqueous peroxopolytungstic acid (PPTA) solution on potassium ion exchanged glass optical waveguides (OWGs). Polytungstic acid (PTA), which was produced when the films were hardened by drying between 100∼180°C, gave a high refractive index of 1.9∼2.0. A PTA/K+ composite OWG structure (5∼8 mm wide) having tapers at both ends (1∼3 mm in length), was prepared by etching the PTA film in water (pH = 8.0∼8.5). These tapered structures work as optical couplers which efficiently transfer guided light from the potassium ion exchanged layer to the PTA thin film layer. The new PTA/K+ OWGs gave a very high optical sensitivity (e.g., 4.4 × 103 times/cm as compared with the normal incidence of monitoring light) for adsorbed dyes and a low loss value (2.5 dB/cm) at the optimum PTA film thickness of 65-70 nm. Such a PTA/K+ composite optical waveguide (OWG) could be applied to biochemical sensors and to the monitoring of surface chemical reactions with high sensitivity.
The facilitated transfer of chloride/bromide ion encapsulated into macrotricyclic quaternary ammonium ion NtMQA4+ (Nt= –CH2C10H7) through the water (aq)/nitrobenzene (nb) interface was revealed using cyclic voltammetry. The observed anodic-peak current ip,a between 100 and 400 mV vs. Hg/Hg2SO4/SO42- resulted from the transfer of NtMQA4+ as well as Cl- ⊂NtMQA4+ from (aq) to (nb) : the cathodic-peak current ip,a was also observed as a result of their transfer from (nb) to (aq). However, benzyl (=Bn) derivative BnMQA4+ showed no clear anodic peak because of its own less hydrophobicity, compared with NtMQA4+ . The order of I- ≧ Cl- > Br in the magnitude of the observed ip,a resulted from the order, Cl- > Br- > I- , for ip,a controlled by the order, Cl- ~ Br- < I-, for stability constants of the ion-pair of halide ion with NtMQA4+ as well as from the order, Cl- ~ Br- < I-, for ip,a controlled by the inclusion of each halide ion into NtMQA4+ . The plots of ip,a and −ip,a as a function of log [X-] became linear for Cl- and hyperbola for Br between 10-6 M and 10-3 M X-. The chloride-ion transfer across (aq)/(nb) interface may be more selectively facilitated using an advanced NtMQA4+, the electrolytic cell may be developed for its own application to efficient chloride-ion prove.