Non-conventional Adsorbents for Dye Removal - Green Chemistry for Dyes Removal from Wastewater - page 388

calix[n]arene moiety. Calix[n]arenes have been widely employed as build-
ing blocks in the design of novel host molecules. These macrocyclic com-
pounds are also attractive as a platform to develop novel host material for
entrapping pollutants. The preparation and characterization of a calix[4]
arene-based resin and its use for dye removal were reported by Kamboh
et al . [286]. Cucurbituril, a cyclic polymer of glycoluril and formaldehyde,
is another material also known to form host-guest complexes with aro-
matic compounds. This adsorbent presents interesting adsorption capaci-
ties for various types of textile dye [87]. However, because of its solubility,
cucurbituril is not feasible as an adsorbent in aqueous solutions unless it
is incorporated into fixed bed adsorption filters or covalently fixed onto a
suitable support material. Cost is also another disadvantage. Adsorption
mechanisms are explained by the formation of host-guest complexes and
the presence of hydrophobic interactions and the formation of insoluble
cucurbituril-dye-cation aggregates.
10.13 ConcludingRemarks
This chapter has attempted to cover a wide range of non-conventional
adsorbents so that the reader can get an idea about the various types of
materials used for the removal of dye molecules from aqueous solutions.
It is now accepted that inexpensive, locally available and effective non-
conventional adsorbents could be used in place of commercial activated
carbons and synthetic organic resins for dye removal [296]. It is impor-
tant to note that the adsorption capacity exhibited by each material relates
primarily to its textural and chemical properties. Other factors, however,
such as operation difficulty, practicability, regeneration potential and envi-
ronmental impact, need to be taken into consideration when selecting one
adsorbent over another. It is also important to point out that a particular
adsorbent is only applicable to a particular class of dye molecules. Thus,
using only one type of non-conventional adsorbent is difficult for the
treatment of the complicated composition of dye wastewaters. However,
undoubtedly non-conventional materials offer a lot of promising benefits
for commercial purposes in the future.
Although much has been accomplished from the use of new adsorbents
and their adsorption process studies, much work is, however, necessary
to predict the performance of dye removal from real industrial effluents
under a range of operating conditions and to demonstrate the applicability
of these materials on an industrial scale. Also, much work is still necessary
to clearly identify the adsorption mechanism. Another aspect concerns the