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

Abstract

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.

Ni-Doped Ordered Nanoporous Carbon Prepared from Chestnut Wood Tannins for the Removal and Photocatalytic Degradation of Methylene Blue

“…The crystalline structure of TPNi was studied by XRD in the range of 2 θ Bragg angles of 5 to 80°. The XRD diffractogram of TPNi is presented in Figure 2 c. Here, the broad diffraction peak between 15° and 30° indicates the presence of amorphous carbon [ 20 , 22 , 46 ]. Furthermore, the reflections at 37.3°, 43.3°, 44.4°, 51.8°, 62.8°, and 76.3° reveal the presence of different nickel species.…”

“…The deconvolution of C 1 s spectrum revealed the nature of these functionalities, denoting the existence of C–C (284.5 eV), C–O (285.8 eV), C=O (287.0 eV), and O–C=O (288.3 eV) groups, and π−π* transitions (290.0 eV). Here, C–O groups (phenols and ethers [ 2 , 28 , 46 ]) are predominant, followed by C=O (carbonyls, quinones [ 2 , 28 , 44 ]), O–C=O (carboxylic [ 2 , 28 , 46 ]), and π−π* transitions (HOMO−LUMO transitions coming from the ring excited by the exciting photoelectrons for unsaturated carbon in aromatic rings [ 47 ]). Furthermore, the deconvolution of O 1 s spectrum showed the presence of peaks at 530.5, 532.1 and 533.7 eV, which can be related to O 2- in nickel oxide [ 48 ], O=C in carbonyl and carboxylic groups [ 46 ], and O–C in phenols, ethers, and lactones [ 46 ], respectively.…”

“…Here, C–O groups (phenols and ethers [ 2 , 28 , 46 ]) are predominant, followed by C=O (carbonyls, quinones [ 2 , 28 , 44 ]), O–C=O (carboxylic [ 2 , 28 , 46 ]), and π−π* transitions (HOMO−LUMO transitions coming from the ring excited by the exciting photoelectrons for unsaturated carbon in aromatic rings [ 47 ]). Furthermore, the deconvolution of O 1 s spectrum showed the presence of peaks at 530.5, 532.1 and 533.7 eV, which can be related to O 2- in nickel oxide [ 48 ], O=C in carbonyl and carboxylic groups [ 46 ], and O–C in phenols, ethers, and lactones [ 46 ], respectively. Interestingly, the amount of O=C functionalities in the O 1 s spectrum is higher than the amount of O–C, which contradicts the results of the C 1 s spectrum.…”

Enhanced photocatalytic reduction of hexavalent chromium by using piezo-photo active calcium bismuth oxide ferroelectric nanoflakes

“…3,4 According to World Health Organization regulations, the highest permitted concentration of residential sewage is 0.05 mg L À1 . 5 Because its reduced product, Cr(III), is an essential nutrient for a living being, the conversion of Cr(VI) to Cr(III) is critical in terms of remediation. 6 As a result, extensive research is underway to develop an effective technique for converting potentially dangerous Cr(VI) to Cr(III) in wastewater.…”

Facile Synthesis and Characterization of a Bromine-Substituted (Chloromethyl)Pyridine Precursor towards the Immobilization of Biomimetic Metal Ion Chelates on Functionalized Carbons

“…Indeed, Radi and coworkers linked a bis(2-pyridylmethyl)amine chelate to functionalized silica for applications in heavy metal extractions [27]. Furthermore, one of us recently reported the grafting of polyethyleneimine (PEI) onto activated carbons for the removal of Cr(VI) ions from water at pH values ranging from 2 to 5 [28]. Extension of this activated carbon work includes linking the biomimetic pyridine ligand scaffolds onto activated carbon surfaces to study catalytic activity and recyclability of these activated carbon supported heterogeneous systems.…”