Abstract
It has been shown that the VOC adsorption capacity of soil decreases significantly with increasing relative humidity levels in the vapor phase. It might be due to the competition of adsorption sites by water molecules on the soil surfaces. Generally, the surface of nature adsorbents, such as soil and clay mineral, is highly heterogeneous owing to their complex chemical composition and irregularities of physical structure. It is necessary to describe the adsorption phenomena of nature adsorbent microscopically. Based on gas-solid adsorption isotherm, the energy distribution function of sorbing sites on soil surface were constructed. The variation of adsorption energy distribution function reveals that the adsorption energy for water was higher than that for toluene and, therefore, the soil surface would prefer to adsorb water vapor rather than toluene vapor. In addition, the adsorption energy of water vapor shifts towards the lower side at higher relative humidity level. It appears that the water vapor is condensed onto the surface. It is found that the previously adsorbed water molecules modified the soil surface and changed the energy spectrum of the adsorption sites. The shift of the adsorption energy spectrum to lower adsorption energy is the reason of the suppression of the soil uptake of organic vapors by water vapor.
Highlights
Adsorption is one of the most important processes affecting the fate of volatile organic compound (VOC)in the v&dose zone
It has hecn suggested that the surfaces of nature adsorbents, soils and clay minerals, are highly heterogeneous owing to their complex chemical composition and the irregularities of their physical structure’
The objective of this study is to explore the mechanisms of the suppression of uptake of organic vapors by humidity and to establish a model which can explain the change in the adsorption behavior of soil surface before and after the sorption of water vapor
Summary
Adsorption is one of the most important processes affecting the fate of volatile organic compound (VOC)in the v&dose zone. There has been many articles discussing the effects of relative humidity on the adsorption of VOC on soils. The adsorption capacity of VOC of soil was reported to decrease significantly with increasing relative humidity in the vapor phase’.‘. The extent to which the adsorbed water vapor modifies the surfaces of soils is determined by the vapor pressure of water (i.e. relative humidity) and the characteristics of the sorbing site. The adsorption energy can be a measurable property to describe the tendency of association of sorbcnt and sorbate and be used to categorize the adsorbing site?. The distribution of the amount of adsorbing sites according to their adsorbing energy level (similar to a probability density function) could hc a quantitative description of the heterogeneity of the surface in the respect of adsorption tendency
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
