Effects of the at pi-electrons in fused polycyclic aromatic hydrocarbons on positron annihilation

摘要

The mesoporous phenol-formaldehyde resins (PFR) were synthesized using formaldehyde, phenol, F127 template as raw materials by high temperature hydrothermal method under different temperatures. Nitrogen doped mesoporous PFR were synthesized in the same way with another additional raw material HMTA. Two series of carbon materials PCs and PCNs were obtained after calcinating PFR at 700, 800, 900 degrees C. N-2 adsorption analysis indicates that both the two kind of carbon materials have relatively large specific surface area (325-619 cm(2)/g for PCs and 431-580 cm(2)/g for PCNs). TEM and XRD analyses prove highly ordered mesoporous structure of the samples. Both the elemental analysis and IR results suggest a high carbon content and the abundant fused-ring structure of the test materials. The positron annihilation spectra show that the corresponding intensity I-3 of the longest lifetime component tau(3) is less than 2%, indicating that the pi electrons in the fused rings with low ionization energy are capable of trapping positrons and inhibiting the formation of o-Ps.