Modified silica gels as recyclable adsorbents of aqueous polycyclic aromatic hydrocarbons

Abstract

Polycyclic aromatic hydrocarbons (PAHs), a class of toxic organic molecules containing multiple fused aromatic rings, are found in air, soil and water as a by-product from the incomplete combustion of organic matter. We report on the modification of silica gel using lipophilic molecules containing carboxylic acids, for anchoring to the surface via hydrogen bonds. The lipophilic component captures aqueous PAH, specifically phenanthrene, through the agency of π-π and π-sp 3 interactions. The structure-sorption-relationships suggest optimum phenanthrene adsorption is achieved with unsaturated bonds in linear chains or two phenyl rings. Examples include linoleic acid or 2,3-diphenylpropionic acid with removal values of 281 and 283 ng PAH per gram of silica gel, respectively. Saturation adsorption is achieved within four hours. Proposed modes of binding of the new reverse phase silica gels with phenanthrene are described. Recycling of the silica gel is accomplished by washing with organic solvents to remove PAH. ARTICLE HISTORY

High-Refractive-Index Polysiloxanes Containing Naphthyl and Phenanthrenyl Groups and Their Thermally Cross-Linked Resins

“…It can be concluded that the isomerism has an influence on the aggregation behavior in the case of naphthyl-substituted alkoxysilanes. 9-PhenPhSi­(OMe) 2 shows a similar but less pronounced emission behavior like 2-NaphPhSi­(OMe) 2 with a shift to higher wavelengths typical for the phenanthrene group. , …”

Emission and Collection of Polycyclic Aromatic Hydrocarbons From Raw Asphalt Samples Heated at 130 °C

“…In fact, to increase the adsorption efficiency of Si, its surface is often modified with hydrophobic groups to facilitate the capture of PAHs. 23 Although the use of HDPE resulted in the highest percentage of Phe retention compared to the other adsorbents, its efficiency in retaining the total amount of PAHs was lower, corresponding to only 19.4% of the total PAH emissions from the asphalt sample. For the gas−solid adsorption of the PAHs in the absence of the asphalt matrix (aqueous solution), it was possible to obtain 81.1% PAH retention with HDPE.…”

“…However, as mentioned before, the adsorption efficiency of Si is governed by the OH groups on its surface. , This probably explains the low percentage of adsorbed PAHs observed in this study. In fact, to increase the adsorption efficiency of Si, its surface is often modified with hydrophobic groups to facilitate the capture of PAHs …”

“…19,20 Thus, the choice of adsorbents depends on their collection efficiency, selectivity, adsorbent capacity, chemical stability, ease of recovering the adsorbed vapors, and low blank levels. 17 Several adsorbents have been used to remove PAHs from aqueous matrices and the air, including activated carbon, 19 high-density polyethylene (HDPE), 20 polyurethane foams (PUF), 21 silica gel, 22 modified silica, 23 XAD (−2, −4, and −16) resins, 24 magnetic nanomaterials, 25 molecularly imprinted polymers, 26 and adsorbents of natural origin like sugar cane bagasse, green coconut shells, chitin, and chitosan. 27 However, as described in the literature, XAD-2 resin is the most common adsorbent used to trap the vapor phase in asphalt fume generators.…”

“…Many factors can affect the adsorption phenomena, such as particle size and surface area, surface functional groups, material hydrophobicity, system temperature, carrier gas flow, contact time, and initial PAH concentrations. , Thus, the choice of adsorbents depends on their collection efficiency, selectivity, adsorbent capacity, chemical stability, ease of recovering the adsorbed vapors, and low blank levels . Several adsorbents have been used to remove PAHs from aqueous matrices and the air, including activated carbon, high-density polyethylene (HDPE), polyurethane foams (PUF), silica gel, modified silica, XAD (−2, −4, and −16) resins, magnetic nanomaterials, molecularly imprinted polymers, and adsorbents of natural origin like sugar cane bagasse, green coconut shells, chitin, and chitosan . However, as described in the literature, XAD-2 resin is the most common adsorbent used to trap the vapor phase in asphalt fume generators. ,,, However, there is scarcely any information about other adsorbents that can be used for this purpose and the factors influencing their effectiveness.…”