Sonochemical-assisted synthesis of nano-structured lead dioxide

PbO(2) nano-powder was synthesized by the ultrasonic irradiation of an aqueous suspension of dispersed beta-PbO, as precursor, in the presence of ammonium peroxydisulfate as an oxidant. The reaction rate increased with an increase in temperature and ammonium peroxydisulfate concentration. In the presence of ammonium peroxydisulfate, the increased concentration of hydroxyl radical facilitated the oxidation of beta-PbO to PbO(2) under ultrasonic irradiation. The PbO(2) nano-powder was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the applied ultrasonic wave determines the particle size. PbO(2) samples prepared under optimized experimental conditions have lead dioxide particles in the range of 50-100 nm, as shown by SEM. The XRD results reveal that only beta-PbO(2) is formed under optimum conditions. When the reaction mixture was stirred instead of ultrasonically irradiated, only a fraction of the lead oxide was converted to lead dioxide, and lead sulfate was the main reaction product.

A biofuel cell with electrochemically switchable and tunable power output

An electroswitchable and tunable biofuel cell based on the biocatalyzed oxidation of glucose is described. The anode consists of a Cu(2+)-poly(acrylic acid) film on which the redox-relay pyrroloquinoline quinone (PQQ) and the flavin adenine dinucleotide (FAD) cofactor are covalently linked. Apo-glucose oxidase is reconstituted on the FAD sites to yield the glucose oxidase (GOx)-functionalized electrode. The cathode consists of a Cu(2+)-poly(acrylic acid) film that provides the functional interface for the covalent linkage of cytochrome c (Cyt c) that is further linked to cytochrome oxidase (COx). Electrochemical reduction of the Cu(2+)-poly(acrylic acid) films (applied potential -0.5 V vs SCE) associated with the anode and cathode yields the conductive Cu(0)-poly(acrylic acid) matrixes that electrically contact the GOx-electrode and the COx/Cyt c-electrode, respectively. The short-circuit current and open-circuit voltage of the biofuel cell correspond to 105 microA (current density ca. 550 microA cm(-2)) and 120 mV, respectively, and the maximum extracted power from the cell is 4.3 microW at an external loading resistance of 1 kOmega. The electrochemical oxidation of the polymer films associated with the electrodes (applied potential 0.5 V) yields the nonconductive Cu(2+)-poly(acrylic acid) films that completely block the biofuel cell operation. By the cyclic electrochemical reduction and oxidation of the polymer films associated with the anode and cathode between the Cu(0)-poly(acrylic acid) and Cu(2+)-poly(acrylic acid) states, the biofuel cell performance is reversibly switched between "ON" and "OFF" states, respectively. The electrochemical reduction of the Cu(2+)-polymer film to the Cu(0)-polymer film is a slow process (ca. 1000 s) because the formation and aggregation of the Cu(0)-clusters requires the migration of Cu(2+) ions in the polymer film and their reduction at conductive sites. The slow reduction of the Cu(2+)-polymer films allows for the controlling of the content of conductive domains in the films and the tuning of the output power of the biofuel cell. The electron-transfer resistances of the cathodic and anodic processes were characterized by impedance spectroscopy. Also, the overall resistances of the biofuel cell generated by the time-dependent electrochemical reduction process were followed by impedance spectroscopy and correlated with the internal resistances of the cell upon its operation.