Exploring the Iron Oxide Functionalized Biobased Carbon-silica-polyethyleneimine Composites for Hexavalent Chromium Removal from Dilute Aqueous Solutions

Mpho Cynthia Qhubu,Vusumzi Emmanuel Pakade,Philiswa Nosizo Nomngongo

doi:10.3390/w13213081

Mpho Cynthia Qhubu, Vusumzi Emmanuel Pakade + Show 1 more

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https://doi.org/10.3390/w13213081

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Abstract

The contamination of water resources by toxic hexavalent chromium remains a challenge. In this study, amino-functionalized iron oxide biobased carbon-silica composites were prepared through co-precipitation of Fe(II) and Fe(III) over Macadamia activated carbon and explored as feasible adsorbents for the removal of Cr(VI) from dilute aqueous solutions. The energy dispersive spectroscopy (EDS) elemental analysis confirmed the existence of Fe, Si, O, and C atoms, which form the backbone of the composite. The FTIR also showed the presence of Fe-O and Si-O-Si and Si-OH spectral bands, affirming the backbone of the adsorbents. Cr(VI) adsorption efficiency (5.76 mg/g) was achieved at pH 1 when an initial concentration of 2.5 mg/L, contact time of 90 min, and dosage concentration of 1.7 g/L were used. The data were best described by the Langmuir adsorption model and pseudo-second-order rate model. ΔG° (−3 to −12 kJ/mol) and ΔH° (46, 12 and 5 kJ/mol) values affirmed that the adsorption of Cr(VI) was spontaneous and endothermic and dominated by chemical interactions.

Highlights

Chromium, similar to other heavy metals, is a menace to the environment as it persists and is non-biodegradable [1]
Compared to activated carbons (ACs)-Fe3O4, new bands appeared in AC-Fe3O4-SiO2 at 1054.45 cm−1 assigned to the stretching vibrations of Si-O-Fe [21] and/or C-O-C [28], while those at 948.73 and 791.46 cm−1 were assigned to the asymmetric and symmetric stretches of Si-O-Si of the SiO2
The AC-Fe3O4-SiO2PEI exhibited a peak at 3289 cm−1 assigned to the –OH stretch which overlaps with the NH-stretch of the amine groups of PEI and the peaks at 2932.34 and 2816.03 cm−1 were assigned to the asymmetric and symmetric –CH2- stretching vibrations of the ethyl groups on PEI branches [32]

Summary

Introduction

Similar to other heavy metals, is a menace to the environment as it persists and is non-biodegradable [1]. Chromium can be present in both anionic and cationic forms in aqueous media depending on the pH/Eh conditions. In cationic form, Cr(III) is the most stable oxidation state. The major sources of Cr(VI) in the environment are through anthropogenic activities because the kinetic reactions governing the conversion of natural Cr(III) to Cr(VI) are very slow [3,4]. Cr(VI) is a major element for the electroplating and stainless-steel production industries [5]. These industries use lots of water during their production, the probability of Cr(VI) compounds leaching to the environment is too high [6]. The World Health Organization put stringent regulations to limit the amount of Cr(VI) in drinking water and surface water to 0.05 mg/L and 0.1 mg/L, respectively [6]

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