Abstract
In this work, we reported the synthesis, characterization and adsorption study of two β-cyclodextrin (βCD) cross-linked polymers using aromatic linker 2,4-toluene diisocyanate (2,4-TDI) and aliphatic linker 1,6-hexamethylene diisocyanate (1,6-HDI) to form insoluble βCD-TDI and βCD-HDI. The adsorption of 2,4-dinitrophenol (DNP) on both polymers as an adsorbent was studied in batch adsorption experiments. Both polymers were well characterized using various tools that include Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller analysis and scanning electron microscopy, and the results obtained were compared with the native βCD. The adsorption isotherm of 2,4-DNP onto polymers was studied. It showed that the Freundlich isotherm is a better fit for βCD-TDI, while the Langmuir isotherm is a better fit for βCD-HMDI. The pseudo-second-order kinetic model represented the adsorption process for both of the polymers. The thermodynamic study showed that βCD-TDI polymer was more favourable towards 2,4-DNP when compared with βCD-HDI polymer. Under optimized conditions, both βCD polymers were successfully applied on various environmental water samples for the removal of 2,4-DNP. βCD-TDI polymer showed enhanced sorption capacity and higher removal efficiency (greater than 80%) than βCD-HDI (greater than 70%) towards 2,4-DNP. The mechanism involved was discussed, and the effects of cross-linkers on βCD open up new perspectives for the removal of toxic contaminants from a body of water.
Highlights
To date, a lot of new adsorbents based on natural and polymeric materials have been developed in order to remove organic and inorganic pollutants from water distribution networks
The chemical structures of bCD-TDI and bCD-HDI were analysed by Fourier transform infrared (FTIR) spectrometry and their FTIR spectra were compared with native b-CD as shown in figure 3
No significant degradation was observed in the sorbent performance and the removal efficiency was still well above 80% for bCD-TDI and 70% for bCD-HDI. These results showed that the adsorbents can be recycled for 2,4-DNP adsorption, and demonstrated that both polymers are stable and there is no carryover of the targeted analytes occurring during the removal process
Summary
A lot of new adsorbents based on natural and polymeric materials have been developed in order to remove organic and inorganic pollutants from water distribution networks. Numerous approaches have been studied for the development of cheaper and more effective adsorbents, for example activated carbon, which is the most widespread adsorbent being used in water treatment. They have several deficiencies, including slow pollutant uptake and poor removal of hydrophilic pollutants. The three smallest CDs, aCD, bCD and gCD, which consist of six, seven and eight a-1,4 linked D(C)-glucopyranose units with numerous available hydroxyl groups, are active sites for forming different types of linkages and derivatives [3 – 5]
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