In most cases, there is a time lag (hence a negative y-axis intercept) in the initial stage of the adsorption, which indicates that pyridine adsorption on both adsorbents experiences external film diffusion resistance.
In addition, two different regimes for pyridine adsorption are observed, each of them showing linear behaviour, attributing to
the intraparticle adsorption of pyridine into the adsorbent pores.
This type of behaviour has been frequently observed for adsorption of organic pollutants from water on various porous carbon materials [58–60] and functionalised hypercrosslinked polymers [61,62].