Growth characteristics and the mass transfer mechanism of single bubble on a photoelectrode at different electrolyte concentrations.

In the photoelectrochemical water splitting reaction, the bubble attached to the working electrode is an essential factor affecting the reaction resistance, current density and gas-liquid mass transfer. An experimental measurement system based on an electrochemical workstation synchronously coupled with a high-speed microscopic camera was proposed and used to systematically study the growth kinetics and mass transfer mechanism of single oxygen bubbles at different electrolyte concentrations (Na2SO4, 0.1-2.0 M) on the TiO2 photoanode surface. Under constant voltage and constant current control conditions, when the electrolyte concentration increases, the bubble detachment diameter and the bubble detachment frequency gradually decrease. The bubble coverage equation expressed in terms of gas evolution efficiency is proposed and is associated with the photocurrent and bubble radius. The average bubble coverage and average gas evolution efficiency decrease when the electrolyte concentration is increased. According to the Sherwood dimensionless number, various mass transfer coefficients during bubble growth were calculated. The results show that the average total mass transfer coefficient is positively correlated with the change trend of the electrolyte concentration, and the mass transfer coefficient of single-phase natural convection is one order of magnitude larger than the mass transfer coefficient of bubble-induced convection. Finally, a conclusion on the transient mass transfer process in the bubble evolution process was obtained, that is, the mass transfer coefficient of single-phase natural convection and the total mass transfer coefficient remain high during the first growth stage, and gradually decrease during the second growth stage. Therefore, regulating the electrolyte concentration can effectively promote the gas-liquid mass transfer in the photoelectrochemical water splitting reaction.

Establishment and optimization of a wheat germ cell-free protein synthesis system and its application in venom kallikrein.

Wheat germ cell-free protein synthesis systems have the potential to synthesize functional proteins safely and with high accuracy, but the poor energy supply and the instability of mRNA templates reduce the productivity of this system, which restricts its applications. In this report, phosphocreatine and pyruvate were added to the system to supply ATP as a secondary energy source. After comparing the protein yield, we found that phosphocreatine is more suitable for use in the wheat germ cell-free protein synthesis system. To stabilize the mRNA template, the plasmid vector, SP6 RNA polymerase, and Cu(2+) were optimized, and a wheat germ cell-free protein synthesis system with high yield and speed was established. When plasmid vector (30 ng/µl), SP6 RNA polymerase (15 U), phosphocreatine (25 mM), and Cu(2+) (5 mM) were added to the system and incubated at 26°C for 16 h, the yield of venom kallikrein increased from 0.13 to 0.74 mg/ml. The specific activity of the recombinant protein was 1.3 U/mg, which is only slightly lower than the crude venom kallikrein (1.74 U/mg) due to the lack of the sugar chain. In this study, the yield of venom kallikrein was improved by optimizing the system, and a good foundation has been laid for industrial applications and for further studies.