Effect of SiO2/Al2O3 ratio on the electrochemical performance of amorphous zeolite loaded with cobalt oxide grown via steam-assisted crystallization method.

Improving the performance of a supercapacitor is one of the main approaches to solve the energy shortage problem. Electrode material is one of the key components limiting the efficiency of a supercapacitor. Discovering, tuning, and improving electrode materials are very important. This work reports the effect of SiO2/Al2O3 ratio on electrochemical performances of amorphous zeolites ZSM5 (AZ) and H-ZSM5 (H-AZ) loaded with cobalt oxide. Two SiO2/Al2O3 ratios (1 = 6.2 and 2 = 8.3) of AZ1, AZ2 and H-AZ1, H-AZ2 were synthesized by a facile impregnation method. Then, controlled masses of cobalt oxide were introduced to enhance the supercapacitive performances of the amorphous zeolite. Investigation of the SiO2/Al2O3 ratio in the cobalt oxide/zeolite composite (Co/AZ and Co/H-AZ) was carried out to unveil its effect on the electrochemical properties. Worthy of note is the fact that the resulting electrode materials exhibited supercapacitive behavior that is effective over a potential window ranging from 0 to 0.5 V in potassium hydroxide (1 M KOH) aqueous electrolyte. Results from Galvanometry Charging and Discharging (GCD) analyses show that the modified Ni-foam electrodes loaded with Co/H-AZ1 and Co/H-AZ2 are capable of delivering a relatively high specific capacity from 45.97 mA h g-1 to a high value of 72.5 mA h g-1 at 1 A g-1 and Ni-foam electrodes loaded with Co/AZ1 and Co/AZ2 exhibited values from 26 mA h g-1 to 52.83 mA h g-1 respectively. It is clearly shown that, when the mass ratio SiO2/Al2O3 increases, the specific capacity increases as well. It was also noticed that after 2000 cycles, Co/H-AZ1 and Co/AZ1 have a poor coulombic efficiency while Co/H-AZ2 and Co/AZ2 exhibited 98% for coulombic efficiency. Finally, this study shows that to fabricate high performance supercapacitors with amorphous zeolite loaded with cobalt oxide, one should keep the ratio of SiO2/Al2O3 as high as possible during synthesis.

Treatment of Cerebral Ischemia Through NMDA Receptors: Metabotropic Signaling and Future Directions.

Excessive activation of N-methyl-d-aspartic acid (NMDA) receptors after cerebral ischemia is a key cause of ischemic injury. For a long time, it was generally accepted that calcium influx is a necessary condition for ischemic injury mediated by NMDA receptors. However, recent studies have shown that NMDA receptor signaling, independent of ion flow, plays an important role in the regulation of ischemic brain injury. The purpose of this review is to better understand the roles of metabotropic NMDA receptor signaling in cerebral ischemia and to discuss the research and development directions of NMDA receptor antagonists against cerebral ischemia. This mini review provides a discussion on how metabotropic transduction is mediated by the NMDA receptor, related signaling molecules, and roles of metabotropic NMDA receptor signaling in cerebral ischemia. In view of the important roles of metabotropic signaling in cerebral ischemia, NMDA receptor antagonists, such as GluN2B-selective antagonists, which can effectively block both pro-death metabotropic and pro-death ionotropic signaling, may have better application prospects.

Adsorption of cadmium, nickel and lead ions: equilibrium, kinetic and selectivity studies on modified clinoptilolites from the USA and RSA.

The performance of modified clinoptilolites (zeolites) from two different sources (South Africa and the USA) for the adsorption of Ni2+, Cd2+ and Pb2+ from synthetic industrial effluent contaminated with metal concentration levels at 50, 150 and 500 ppm was evaluated. The selectivity of the clinoptilolite for the adsorption of Ni2+, Cd2+ and Pb2+ was investigated with mixed feed solutions containing all three ions in equal concentrations and single-component concentrations containing only one of the ions. The homoionic forms of the clinoptilolite were made of Na+, K+ and Ca2+. Batch experiments were then conducted to measure the uptake of metals by the zeolites. The zeolites were characterised using SEM, XRD and BET. The South African clinoptilolite showed a higher surface area and pore volume (17.52m2/g and 0.047cm3/g respectively) than the USA zeolite (12.26m2/g and 0.028cm3/g respectively) for the Na+ homoionic form. According to the equilibrium studies, the selectivity sequence was found to be Pb2+ > Cd2+ > Ni2+, with good fits being obtained using Langmuir and Freundlich adsorption isotherms for low metal concentrations. Examples of equilibrium adsorption capacities for RSA and USA clinoptilolite modified with Na+ for Pb were 26.94 mg/g and 27.06 mg/g when RSA-Na+ and USA-Na+ were used respectively. The adsorption was found to depend on the homoionic form of the zeolite and to a lesser extent the source of the zeolite. The selectivity of a particular zeolite for a particular heavy metal can be altered by the homoionic form of the zeolite. Overall, the adsorption capacity of the USA clinoptilolite was higher than the adsorption capacity of the SA clinoptilolite, revealing the potential of clinoptilolite in metal-polluted industrial effluent treatment.

Seasonal changes in organotin compounds in water and sediment samples from the semi-closed Port of Gdynia.

The effect of seasonal changes on the distribution of organotin compounds (OTC) in the sediments and seawater from the docks of the Port of Gdynia was investigated. Sediment and seawater samples were collected from four industrial docks in February (winter) and June (summer) in 2009. The samples were analyzed for butyltin, phenyltin, octyltin, and tricyclohexyltin (total of 9 OTC derivatives). The fine fraction (<0.063 mm) accumulated the highest concentration of OTC, although it was not the dominant fraction in the sediment samples from the Port of Gdynia. The average concentration of TBT, DBT and MBT in collected samples were as follows: 4400; 2188; 730 ng cation g⁻¹ d.w. (February) 3638; 1590; 474 ng cation g⁻¹ d.w. (June) in the fine sediment samples, 2805; 1266; 485 ng cation g⁻¹ d.w. (February) in <2.00 mm sediment fractions and 118.6; 39.2; 25.3 ng cation L⁻¹ (February) and 46.5; 12.6; 8.2 ng cation L⁻¹ (June) in the water samples. Higher concentrations of butyltin derivatives (BT) were observed in samples collected in February than in those collected in June. Seasonal changes in BT correlate well with changes in the water pH and concentrations of organic matter and can be attributed to sorption/desorption to sediments, photodegradation and biodegradation. Although the Port of Gdynia does not represent the natural features of a marine environment, seasonal variations recorded in the pH values as well as BT, organic carbon and biogenic element concentrations seem to be influenced by temperature and microbial activity.