Proton magnetic resonance study of trimethylamine–trimethylborane

Abstract

Broad-line and pulsed proton magnetic resonance spectra of trimethylamine-trimethylborane have been obtained in the temperature range from approximately liquid-nitrogen temperature to 350 K. Motions of and within the molecules are deduced from a comparison of the observed second moments at various temperatures with theoretically estimated second moments. Reorientation of the methyl groups attached to boron, at frequencies sufficient to narrow the n.m.r. line, is observed at the lowest temperature attained, whereas reorientation of the methyl groups attached to nitrogen and reorientation of the whole molecule at n.m.r. line width frequencies occur simultaneously at higher temperatures. Two minima in the curve of spin-lattice relaxation time as a function of frequency can be interpreted in terms of these reorientational motions, and activation energies are calculated for the reorientation processes.

Effects of oxidation time on the structure and properties of polyacrylonitrile‐based activated carbon hollow fiber

“…In the activated carbon, macropores (>50 nm) have small specific surface area and micropores (<2 nm) have large specific surface area. 12 It indicates that choosing proper oxidation time can increase surface area of PAN-ACHF. Figure 4 shows the variation of adsorption ratio with oxidation time.…”

“…The adsorption ratio to VB 12 increases with oxidation time increasing from 1 to 5 h, reaches a maximum (96%), and then decreases. According to their molecule sizes, creatinine < VB 12 , the molecule size of creatinine is less than 2 nm and primarily adsorbed by micropores (<2 nm). However, the molecule size of VB 12 is larger than 2 nm and primarily adsorbed by mesopores (2-50 nm).…”

“…Adsorption study for creatinine and VB 12 was carried out by a static process. The creatinine aqueous solution was prepared by adding 20 mg of creatinine to 1000 mL of distilled water and the VB 12 aqueous solution was prepared by adding 20 mg of VB 12 to 1000 mL of distilled water.…”

“…Then 100 mg of PAN-ACHF was immersed in 20 mL of creatinine aqueous solution and 100 mg of PAN-ACHF was immersed in 20 mL of VB 12 aqueous solution at 378C for 24 h. The amount of creatinine and VB 12 adsorbed was determined by the concentration difference before and after immersion in the solution. The creatinine and VB 12 concentrations of the solution were determined with a UV/vis spectrophotometer (Shanghai Techcomp 7500) at the wavelength of 510 and 361 nm, respectively. Absorbency of creatinine and VB 12 in the aqueous solutions reflects the difference of solution concentration.…”

Effects of activation temperature on the properties and structure of PAN‐based activated carbon hollow fiber

“…This would hinder the diffusion of CO 2 into the amorphous region to react with carbon. 18 After 800°C of activation, pores began to increase on the surface, as show in Figure 8(b). This suggests that the external surface and the thinner region of the skin of the hollow fibers have been activated.…”