Redox mechanisms of conversion of Cr(VI) to Cr(III) by graphene oxide-polymer composite

Abstract

was also confirmed by XPS (Fig. 2), and explained by the reactions in Eqs. (7) and (8). Furthermore, the peak of the C-H stretching at 2848 cm −1 became less visible in the used CS-PEI-GO due to the oxidation of the C-H of the chitosan (Eq. 9). When the C-H functional group was oxidized, the hydroxyl band observed in the ATR-FTIR (Figure S4) spectra became more intense.

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

“…On the other hand, the increase in C=O functionalities is noted for the exhausted carbons. This is affirmed by the elevated intensity of a peak at~287.1 eV (by~56% for CNP and by~42% for CNP PEI), assigned to carbonyl groups [48,53], and the appearance of a peak at~288.1 eV ascribed to C=O in carboxylic and carbonyl groups [50,54]. Furthermore, the increase in the intensity of C 1s peak at~289.1 eV is detected for CNP PEI.…”

“…For CNP PEI, just like in the case of the band at 1690 cm −1 , the band at 1580 cm −1 may also be associated with the N-H bend [48]. The overlap of multiple broad absorption bands happens in the region of~1400-1000 cm −1 , commonly attributed to C-O stretching in acid, alcohol, phenol, ether and/or ester groups, and phosphorous containing functionalities, P=O/P-O, due to the activation with phosphoric acid [41,48,50]. The bands at 1115, 1020 and 1430 cm −1 for CNP PEI may denote the C-N stretching vibration [19,41].…”

“…Thus, the broad band at~3300 cm −1 is characteristic of a stretching vibration of hydrogen-bonded (O-H) hydroxyl groups from carboxyl, phenol, alcohol, or surface bonded water [31,41,[48][49][50][51]. For CNP carbon grafted with PEI (CNP PEI) it is also associated with the N-H stretch [36,41,[49][50][51][52]. Two small bands at~2900 and 2800 cm −1 , especially visible on the spectra of PEI modified sample, correspond to C-H stretching vibrations [41,51].…”

“…The results of this analysis are presented in Table 2 and Figures 4-8. For C 1s spectrum (Figure 4), significant changes are observed in the region of~285.8 eV associated with C-O bonds in phenols, esters and ethers [48,53], and C-N bonds [41,50,54]. The amount of these groups increased by~22% after PEI grafting, supporting the appearance of C-N containing functionalities, and decreased after Cr (VI) removal (by~30% for CNP and by~40% for CNP PEI), indicating the involvement of C-O and C-N groups in the removal process.…”

Activated biochars derived from wood biomass liquefaction residues for effective removal of hazardous hexavalent chromium from aquatic environments

“…A similar mechanism was already reported for carbon‐based sorbents by several studies (Chen et al, 2018; Dong et al, 2011; Tytłak et al, 2015; Zhou et al, 2016). Interestingly, it seems that in the case of other types of materials, this mechanism can be assumed to be valid (Bandara et al, 2020; Kakavandi et al, 2014).…”