370
batch mode showed that ECP materials are efficient adsorbents for the removal of
fungicides present in polycontaminated solutions (Crini et al. 2017). Interesting
affinities were found toward the mixture propiconazole + tebuconazole + epoxiconazole + bromuconazole + difenoconazole, five triazole fungicides. These contaminants are commonly used in the wood industry, vegetable cultivation, horticulture,
and agriculture to protect various products against fungal decay.
8.4.5 Mechanisms of Sorption
In spite of the abundance of literature and conclusive results, interpreting the mechanisms of pollutant removal by ECP materials remains a source of debate and sometimes contradiction (Morin-Crini and Crini 2013; Gidwani and Vyas 2014; Cova
et al. 2018; Morin-Crini et al. 2018a; Sikder et al. 2019; Liu et al. 2020). Recently,
we published a review summarizing the different mechanisms proposed in the literature (Morin-Crini et al. 2018a).
Mechanisms are still being debated because they involve various interactions that
can occur simultaneously, making it difficult to interpret the results. Until the 2000s,
the literature reported a consensus on the adsorption/sorption mechanism which was
mainly a chemical mechanism (chemisorption) via the formation of inclusion complexes (complexation concept introduced by Professor Cramer in the 1950s), as first
suggested by Professor Solms in the 1960s to interpret its adsorption results, particularly the adsorption mechanism. At the same time, this concept was also taken
up by Professors Wiedenhof and Hoffman. It was only demonstrated in the 1980s by
Professor Szejtli (Crini 2005a; Morin-Crini and Crini 2013). Professor Szejtli also
used the notion of association complexes (also suggested by Professor Cramer in the
1950s), i.e., the cooperation effect between cyclodextrin cavities during the adsorption process, in addition to the formation of inclusion complexes to interpret the
adsorption mechanism (Crini 2014). Since the mid-2000s, studies have also highlighted the role played by the macromolecular network formed by the cross-linking
agent. The performance of an ECP material depended not only on the presence of
cyclodextrin units but also on its structure and therefore on the cross- linking step.
Since the 1980s, to explain the chemical effectiveness of ECP materials in water
treatment, the concept of inclusion complex or more simply complexation was used
by all researchers working on this subject, demonstrating the predominant role of
the cyclodextrin molecules in the performance of an ECP material. This concept is
mainly the formation of inclusion complexes between cyclodextrin and pollutant
molecules. Our first studies also confirmed it (Crini et al. 1998b; Bertini et al. 1999;
Janus et al. 1999). Kinetic studies have indicated longer contact times required to
achieve equilibrium independently of polymer structure, suggesting chemisorption
mechanism such as molecular encapsulation or complexation. During synthesis, the
parameter that must be followed the most closely to obtain a material efficient for
forming complexes was the quantity of cyclodextrin present per gram of material
used. The greater this quantity (for a constant amount of adsorbent), the greater the
complexing capacity of the material (Bertini et al. 1999). This first led to an important notion, namely, that a molecule of cyclodextrin corresponds to a guest
G. Crini
batch mode showed that ECP materials are efficient adsorbents for the removal of
fungicides present in polycontaminated solutions (Crini et al. 2017). Interesting
affinities were found toward the mixture propiconazole + tebuconazole + epoxiconazole + bromuconazole + difenoconazole, five triazole fungicides. These contaminants are commonly used in the wood industry, vegetable cultivation, horticulture,
and agriculture to protect various products against fungal decay.
8.4.5 Mechanisms of Sorption
In spite of the abundance of literature and conclusive results, interpreting the mechanisms of pollutant removal by ECP materials remains a source of debate and sometimes contradiction (Morin-Crini and Crini 2013; Gidwani and Vyas 2014; Cova
et al. 2018; Morin-Crini et al. 2018a; Sikder et al. 2019; Liu et al. 2020). Recently,
we published a review summarizing the different mechanisms proposed in the literature (Morin-Crini et al. 2018a).
Mechanisms are still being debated because they involve various interactions that
can occur simultaneously, making it difficult to interpret the results. Until the 2000s,
the literature reported a consensus on the adsorption/sorption mechanism which was
mainly a chemical mechanism (chemisorption) via the formation of inclusion complexes (complexation concept introduced by Professor Cramer in the 1950s), as first
suggested by Professor Solms in the 1960s to interpret its adsorption results, particularly the adsorption mechanism. At the same time, this concept was also taken
up by Professors Wiedenhof and Hoffman. It was only demonstrated in the 1980s by
Professor Szejtli (Crini 2005a; Morin-Crini and Crini 2013). Professor Szejtli also
used the notion of association complexes (also suggested by Professor Cramer in the
1950s), i.e., the cooperation effect between cyclodextrin cavities during the adsorption process, in addition to the formation of inclusion complexes to interpret the
adsorption mechanism (Crini 2014). Since the mid-2000s, studies have also highlighted the role played by the macromolecular network formed by the cross-linking
agent. The performance of an ECP material depended not only on the presence of
cyclodextrin units but also on its structure and therefore on the cross- linking step.
Since the 1980s, to explain the chemical effectiveness of ECP materials in water
treatment, the concept of inclusion complex or more simply complexation was used
by all researchers working on this subject, demonstrating the predominant role of
the cyclodextrin molecules in the performance of an ECP material. This concept is
mainly the formation of inclusion complexes between cyclodextrin and pollutant
molecules. Our first studies also confirmed it (Crini et al. 1998b; Bertini et al. 1999;
Janus et al. 1999). Kinetic studies have indicated longer contact times required to
achieve equilibrium independently of polymer structure, suggesting chemisorption
mechanism such as molecular encapsulation or complexation. During synthesis, the
parameter that must be followed the most closely to obtain a material efficient for
forming complexes was the quantity of cyclodextrin present per gram of material
used. The greater this quantity (for a constant amount of adsorbent), the greater the
complexing capacity of the material (Bertini et al. 1999). This first led to an important notion, namely, that a molecule of cyclodextrin corresponds to a guest
G. Crini