Enhancing oxygen reduction reaction by using metal-free nitrogen-doped carbon black as cathode catalysts in microbial fuel cells treating wastewater.

Microbial fuel cells (MFCs) is promising to combat environmental pollution by converting organic waste to electricity. One critical problem for practical application of MFCs treating wastewater is sluggish oxygen reduction reaction (ORR) on cathode. This study focused on developing novel metal-free cost-effective cathodic catalysts to enhance power generation of MFCs. Specifically, carbon powder (Vulcan XC-72R) was modified with acid treatment and pyrazinamide (as nitrogen precursor), and subsequently pyrolyzed at different temperatures. For CN-X (X = 700-1000 °C) materials, chemical compositions (the doping contents of nitrogen species, oxygen-containing groups, and sulfur-containing groups) were altered with pyrolysis temperature. Linear sweep voltammetry showed that CN-800 exhibited the highest ORR activity, with an onset potential of 0.215 V and a half-wave potential of -0.096 V (vs. Ag/AgCl). Electrochemical measurements clearly presented an enhancement of ORR activity by treating carbon powder with sulfuric acid and nitrogen doping, which was well correlated with voltage output in single chamber MFCs (SCMFCs). On the other hand, for the nitrogen-doped cathode catalysts, the best performance in SCMFCs was directly related with the amount of pyridinic nitrogen species and total nitrogen amount. The MFC operated with CN-800 exhibited a maximum power density of 371 ± 3 mW/m2 with the chemical oxygen demand (COD) removal of 77.2 ± 1.5% and coulombic efficiency (CE) of 8.6 ± 0.3%. Furthermore, the MFC with CN-800 exhibited an excellent stability over longer than 580 h of operation with 1.5% voltage reduction. CN-800 possessed comparable COD removal efficiency to conventional costly Pt/C, and exhibited distinct cost-effectiveness for MFC practical applications in wastewater treatment.

[Change of platelet count and P-selectin in preserved platelet concentrates].

To observe the change of quantity and quality of platelets preserved in a full-sealed bag, and explore the difference of platelets preserved in oscillating and static conditions at (22 +/- 2) degrees C, the platelet concentrates were prepared with a CS-3000-plus blood cell separator, the platelet counts were performed with automatic blood cell analyzer and P-selectin in supernatant of platelet concentrates was detected by ELISA. The results showed that both of platelet count and P-selectin content in the platelet concentrates had no significant difference between oscillating and static preservation condition. With prolongation of preserved time, the platelet count decreased and P-selectin content increased gradually in both preserved conditions. There was no difference in the platelet counts during 0 - 72 hours preservation in both conditions, and significant difference was seen in 96 - 120 hours preservation. It was concluded that the expired date for platelet product preserved in CS-3000-plus blood cell separator full-sealed system should be 3 days. Under the condition of (22 +/- 2) degrees C, the quality of the platelet preserved in oscillating state is not superior to static preservation.