Graphene Oxide Nanocomposite Hydrogel Beads for Removal of Selenium in Contaminated Water

Abstract

Selenium in water is becoming of increasing risk to human exposure because only recently serious health effects have been associated with their presence in water resources. The present study investigated the development and optimization of the composition of graphene oxide polymeric nanocomposite hydrogel beads by using response surface methodology. The use of polymers such as chitosan and polyethylenimine, which are rich in amine and alcoholic functional groups, provided enhanced removal of anionic selenium species from the water. Experimentally validated polymeric beads were used to perform batch adsorptions of selenium under different conditions such as pH, bead dosage, and diverse selenium concentrations to investigate their potential use, adsorption kinetics, and selenium removal mechanisms. Acidic conditions were found to best remove negatively charged selenium ions from aqueous solutions via −OH, −COOH, and amine functional groups present in the beads. The adsorption kinetic mechanism was better described by the pseudo-second-order adsorption kinetics, indicating that the beads remove selenium via chemisorption mechanisms. The isotherm studies showed an adsorption capacity of 1.62 mg/g based on the Langmuir isotherms at 25 °C. Regeneration studies showed loss of available adsorption sites after the first desorption treatment with different concentrations of NaOH and HCl. The mathematically optimized nanocomposite was further used to treat selenium spiked in real environmental water samples, which confirmed that the best removal of selenium occurs in acidic conditions.

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

“…These conditions were also previously described to be the best conditions for adsorption of Chromium [17][18][19] . Using a higher initial concentration of Cr(VI) (100 ppm) allowed us to achieve enough adsorption in the beads to be able to observe better peaks in the XPS spectra and characterize with higher accuracy the conversion of Cr(VI) to Cr(III) 7,20 .…”

“…While the intensity of the -OH peak in CS reduced to 46%, the peak attributing to the C=O, which is at 288.2 eV, increased from 5% to 10% indicating the occurrence of oxidation reactions suggested in Eqs. (7) and (8) 24 .…”

“…This material was selected since it was shown to remove Cr (VI) and convert to Cr (III) and because these beads contain diverse functional groups, such as amine, hydroxyl, carboxyl, carbonyl and alkyl groups, which were previously suggested to be playing a significant role in this conversion of Cr (VI) to Cr(III). The polymer beads were synthesized according to a previously reported method 3,7,8 .…”

“…GO used in this study was synthesized using the modified Hummer's method, and successful synthesis of GO was confirmed through characterization techniques: Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM). Further information about GO and polymer beads synthesis and detailed characterizations are available in our previously published work 3,7,8 . In the present study, the synthesized CS-PEI-GO beads were characterized in detail with XPS and ATR-FTIR in order to identify the successful synthesis and functional variability of the beads before and after adsorption to Cr(VI) that could lead to the Cr species uptake and reduction.…”

Techno-Economic Evaluation of Iron and Aluminum Coagulants on Se(IV) Removal

“…Purification of polluted waters has been studied by applying various treatment processes, such as physical, biological, and chemical, including adsorption with inorganic [11,12] or organic adsorbents [13] that mostly demonstrate low sorption capacities or weak chemical affinity. Biological removal [14] is a time-consuming process and not compatible with potable water.…”