The Role of Surface Chemistry and Polyethylenimine Grafting in the Removal of Cr (VI) by Activated Carbons from Cashew Nut Shells

Activated carbons prepared from cashew nut shells and modified by grafting polyethylenimine onto the surface were tested for removal of Cr (VI). The removal efficiency of carbons without and with polyethylenimine decreased with an increase in pH, with maximum efficiency found at pH 2. The average ma...

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Bibliographic Details
Published inC (Basel) Vol. 7; no. 1; p. 27
Main Authors Smith, Victoria A., Rivera, Juster F. A., Bello, Ruby, Rodríguez-Aguado, Elena, Elshaer, Mohammed R., Wodzinski, Rebecca L., Bashkova, Svetlana
Format Journal Article
LanguageEnglish
Published Basel MDPI AG 01.03.2021
Subjects
Activated carbon
Adsorption
adsorption capacity
Amides
cashew nut shells
chromium (VI) removal
Drinking water
Efficiency
Equilibrium
Fourier transforms
Grafting
Membrane separation
Polyethyleneimine
polyethylenimine
Steric hindrance
Surface chemistry
Surface properties
Trivalent chromium
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Summary:Activated carbons prepared from cashew nut shells and modified by grafting polyethylenimine onto the surface were tested for removal of Cr (VI). The removal efficiency of carbons without and with polyethylenimine decreased with an increase in pH, with maximum efficiency found at pH 2. The average maximum adsorption capacities of carbons were calculated to be 340 ± 20 mg/g and 320 ± 20 mg/g for unmodified and modified carbons, respectively. Surface characterization of carbons revealed that C–O functionalities are actively involved in both polyethylenimine grafting and Cr (VI) removal. Moreover, lactone groups and amides, formed by polyethylenimine grafting, seemingly undergo acid hydrolysis with formation of phenol and carboxylic groups. Considering that Cr (III) is the only form of chromium found on the surface of both carbons, the reduction mechanism is deduced as the predominant one. Here Cr (VI), majorly present as HCrO4¯, is attracted to the positively charged carbon surface, reduced to Cr (III) by phenol groups, and adsorbed inside the pores. The mechanism of Cr (VI) removal appears to be similar for unmodified and modified carbons, where the smaller adsorption capacity of the latter one can be related to steric hindrance and pore inaccessibility.
ISSN:2311-5629
2311-5629
DOI:10.3390/c7010027