Effects of the π-electrons in fused polycyclic aromatic hydrocarbons on positron annihilation. (October 2019)

• Record Type: Journal Article
• Authors: Du, Yijun; Zhao, Junhu; Wang, Chen; Qi, Chenze; Li, Yan; Tao, Hongyu; Zhang, Peng; Cao, Xingzhong; Wang, Baoyi
• Is Part Of: Radiation physics and chemistry. Volume 163(2019:Oct.)
• Page Start: 39
• Page End: 44
• Publication Date: 2019-10
• Subjects: Positron annihilation -- Mesoporous materials -- Polycyclic aromatic hydrocarbons -- Ionization energy; Radiation chemistry -- Periodicals; Radiometry -- Periodicals; Radiation -- Periodicals; Chimie sous rayonnement -- Périodiques; 539.2
• DOI: 10.1016/j.radphyschem.2019.05.015
• Languages: English
• ISSNs: 0969-806X

Abstract

Abstract: 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 °C. N2 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 τ 3 is less than 2%, indicating that the π electrons in the fused rings with low ionization energy are capable of trapping positrons and inhibiting the formation of o -Ps. Highlights: Two kind of PFR-based carbon materials were synthesized under different temperature. N2 adsorption, TEM and XRD data indicate ordered mesoporous structure of the samples. IR and elemental analysis data indicate the fused-ring structure of the materials. The π-electrons in the fused rings with low ionization energy can quench positrons. The formation of free and p -Ps annihilation increases, while that of o -Ps decreases.