Insights into adsorbent tortuosity across aqueous adsorption systems

Pore network, pore connectivity and the resulting effective adsorbate pore diffusivity within an adsorbent are critical physical considerations in mass transport modelling of aqueous adsorption. Tied to these three adsorbent features are the adsorbent tortuosity and tortuosity factor concepts. These concepts encompass the collective hindrance to intra-adsorbent adsorbate transport arising because of a disorderly adsorbent porous topology. It is crucial to the materials scientist, chemist, chemical engineer and water treatment specialist to understand the complex and variable connections among adsorbate chemistry, adsorbent chemistry, adsorbent porosity, pore shape, size and tortuosity, pore wall effect, adsorbate-adsorbent and adsorbate-adsorbate interactions in competitive contaminated aqueous environments. Adsorbent tortuosity has been sporadically studied in aqueous adsorption models. Despite the slim population of these studies, insightful observations and inferences have been reported. However, as it appears, no review has been published to compile, compare and contrast these aspects. Hence, this review concisely brings up those observations and interpretations around adsorbent tortuosity for aqueous adsorption systems. The notion of an adsorbent’s tortuosity being single-valued is argued to be imprecise. Finally, perspectives are aired on possible research and development directions for elucidating the dynamic attributes of adsorbent tortuosity and applying them in real-scale adsorption-oriented water purification. The data acquired by filling in these research gaps can enable the design of adsorbents more adapted for real-scale water purification.