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7664058 
Journal Article 
A fluorescence spectroscopic study of phenanthrene sorption on porous silica 
Wang, Z; Friedrich, DM; Beversluis, MR; Hemmer, SL; Joly, AG; Huesemann, MH; Truex, MJ; Riley, RG; Thompson, CJ; Peyton, BM; , 
2001 
1 
Environmental Science & Technology
ISSN: 0013-936X
EISSN: 1520-5851 
AMER CHEMICAL SOC 
WASHINGTON 
35 
13 
2710-2716 
English 
11452596 
WOS:000169600100030 
Fluorescence spectroscopic characteristics of sorbed phenanthrene in porous silica provide information about its chemical state such as monomer vs dimer or higher aggregates, as well as a basis for high sensitivity detection. In this study, the chemical state and distribution of phenanthrene sorbed in two types of porous silica particles, mesoporous silica (365 microns particle diameter, 150 A average pore diameter) and microporous silica (custom synthethized, 1 micron particle diameter, 20 A pore diameter), is determined by fluorescence spectroscopy, fluorescence lifetime measurements, and scanning two-photon excitation fluorescence profiling. From the characteristic fluorescence emission spectra, it is found that at loading levels of < or = 4.7 mg/g (phenanthrene/silica) phenanthrene exists as monomers in both meso- and microporous silica particles for phenanthrene loaded from super critical CO2 (SCF). Two-photon excitation fluorescence intensity distribution profiles indicate that for the mesoporous silica particles phenanthrene is adsorbed throughout the entire silica particle. Introduction of water into phenanthrene-loaded mesoporous silica particles causes instantaneous conversion of phenanthrene from monomer to crystalline form at phenantherene loading levels > or = 4.7 micrograms/g due to hydration of the silica surface. In this process, sorption of water molecules expels phenanthrene from the surface sorption sites and causes localized phenanthrene concentration beyond its solubility limit, resulting in crystallization. In comparison this fast conversion is not observed for phenanthrene-loaded microporous silica particles that show extremely slow conversion even for phenanthrene loading levels as high as 4.7 mg/g. This difference is interpreted as reflecting hindered diffusion of phenanthrene in the nearly monodispersed micropores with pore sizes close to the molecular diameter of phenanthrene.