*4.1.1. Physical properties of an adsorbent*

Many studies were carried out to find the correlation between specific surface area of sorbent and uptake of phenolic compounds. It is clear that as higher is the value of specific surface area, the higher are microporosity and the larger number of active sites available to interact with adsorbate. Consequently, extraction efficiency increases [23]. That is why, for hypercrosslinked polymers, higher sorption capacity is observed in comparison with traditional polymeric sorbents [18, 21].

On the other hand, there are many works indicating lack of correlation between the value of specific surface area and ability to adsorb phenols [16, 24, 25, 27, 33, 41]. However, specific surface area is still put into characteristic in order to define the morphology of the adsorbent and for comparative purposes.

In general, an adsorption process consists of three following steps:


Consequently, adsorption of phenols is controlled by diffusion processes which are the slowest stage of the overall process. Therefore, characteristic features of porous structure like type of pores, their shape, size, a way of their connection and a size distribution are the most important factors determining the adsorption process and deciding on proper application [31, 44].

In case of sorption processes realized in a dynamic mode (e.g. chromatography, solid phase extraction), size, shape and uniformity of sorbent particles also play significant role. These parameters have an impact on a length of diffusional path, availability of pores for adsorbed molecules, mass transfer resistance and contact time. Not meaningless is the geometry of a device (e.g. column, cartridge, sampler) as its length and diameter decide on the rate and efficiency of the process.
