Study of Hexane Adsorption on Activated Carbons with Differences in Their Surface Chemistry.

Diana Hernández-Monje,Liliana Giraldo,Juan Moreno-Piraján

doi:10.3390/molecules23020476

Diana Hernández-Monje, Liliana Giraldo + Show 1 more

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https://doi.org/10.3390/molecules23020476

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Abstract

The study of aliphatic compounds adsorption on activated carbon can be carried out from the energetic change involved in the interaction; the energy values can be determined from isotherms or by the immersion enthalpy. Vapor phase adsorption isotherms of hexane at 263 K on five activated carbons with different content of oxygenated groups and the immersion enthalpy of the activated carbons in hexane and water were determined in order to characterize the interactions in the solid–liquid system, and for calculating the hydrophobic factor of the activated carbons. The micropore volume and characteristic energy from adsorption isotherms of hexane, the BET (Brunauer–Emmett–Teller) surface area from the adsorption isotherms of N2, and the area accessible to the hexane from the immersion enthalpy were calculated. The activated carbon with the lowest content of oxygenated groups (0.30 µmolg−1) and the highest surface area (996 m2g−1) had the highest hexane adsorption value: 0.27 mmol g−1; the values for Eo were between 5650 and 6920 Jmol−1 and for ΔHim were between −66.1 and −16.4 Jg−1. These determinations allow us to correlate energetic parameters with the surface area and the chemical modifications that were made to the solids, where the surface hydrophobic character of the activated carbon favors the interaction.

Highlights

Activated carbons are adsorbent solids that can develop different degrees of hydrophobicity, according to the oxygenated group content on the surface; this property favors the adsorption of organic compounds of low molecular weight that may be present in the atmosphere increasing its levels of contamination [1]
As porous material, activated carbon has a high surface area and pore volume, which makes it a good adsorbent in both gas and liquid phase processes; another advantage is its versatility in fabrication, i.e., the possibility of modifying its porous structure and surface chemistry based on the requirements established in a specific application [3]
It can be seen that the apparent surface area values increase proportionally with the thermal treatment carried out on the samples; the micropore volume values are quite similar, which may be due to two processes, oxidation and subsequent thermal treatment: The first is the decrease in microporosity due to oxidation and the subsequent increase due to the increase in temperature, generating opposite effects; if this occurs, microporosity values similar to the starting sample will be obtained

Summary

Introduction

Activated carbons are adsorbent solids that can develop different degrees of hydrophobicity, according to the oxygenated group content on the surface; this property favors the adsorption of organic compounds (aliphatic) of low molecular weight that may be present in the atmosphere increasing its levels of contamination [1]. In recent years, such compounds have been called volatile organic compounds (VOCs) and show high vapor pressure at room temperature, which allows them to reach the gas phase, in case of spills or leaks. As porous material, activated carbon has a high surface area and pore volume, which makes it a good adsorbent in both gas and liquid phase processes; another advantage is its versatility in fabrication, i.e., the possibility of modifying its porous structure and surface chemistry based on the requirements established in a specific application [3].

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