Synthesis of functionalized PET fibers by grafting and modification and their application for Cr(VI) ion removal

Development of recoverable adsorbents for Cr(VI) ions by grafting of a dimethylamino group-containing monomer on polyethylene substrate and subsequent quaternization

A polymeric adsorbent for removal of hexavalent chromium (Cr(VI)) ions was developed by the photografting of 2-(dimethylamino)ethyl methacrylate (DMAEMA) to a polyethylene (PE) mesh and subsequent quaternization with iodoalkanes of different alkyl chain lengths. The grafting of DMAEMA and subsequent quaternization were verified by the FT-IR and XPS measurements. The Cr(VI) ion adsorption capacity of the DMAEMA-grafted PE meshes had the maximum value at the grafted amount of 2.6 mmol/g in a 0.20 mM K₂Cr₂O₇ solution at pH 3.0 and 30°C. The adsorption behaviour obeyed the pseudo-second order kinetic model and well expressed by Langmuir isotherm. These results suggest that the Cr(VI) ion adsorption occurs through the electrostatic interaction mainly between protonated dimethylamino groups and hydrochromate (HCrO₄^-) ions. The adsorption capacity of the quaternized PE-g-PDMAEMA meshes increased with an increase in the degree of quaternization and/or the alkyl chain length of the iodoalkanes used and the maximum adsorption ratio was obtained at the degree of quaternization of 54.2% for the iodoheptane-quaternized PE-g-PDMAEMA (PE-g-QC₇PDMAEMA) mesh. This value was about 1.86 times higher than that of the PE-g-PDAMEMA mesh. Cr(VI) ions were successfully desorbed from the PE-g-PDMAEMA and PE-g-QC₇PDMAEMA meshes in eluents such as NaOH, NaCl, and NH₄Cl. In 0.50 M NaCl, 0.10 M NH₄Cl, and 0.50 mM NaOH, the adsorption and desorption process was repeatedly performed without any considerable decrease and the desorption behaviour obeyed the pseudo-second order kinetic model. These results emphasise that the PE-g-PDMAEMA meshes and their quaternized products can be applied as an adsorbent for Cr(VI) ions.

Enhancement of Cr(VI) ion adsorption by two-step grafting of methacrylamide (MAAm) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) onto polyethylene plate

Polyethylene (PE) plates grafted with a neutral hydrophilic monomer, methacrylamide (MAAm), and a cationic monomer, 2-(dimethylamino)ethyl methacrylate (DMAEMA), (PE-g-PMAAm)-g-PDMAEMA plates, were prepared by the two-step photografting. The Cr(VI) ion adsorption of the resultant (PE-g-PMAAm)-g-PDMAEMA plates was investigated as a function of the initial pH value, temperature, and grafted amounts of PMAAm and PDMAEMA. The adsorption capacity of the (PE-g-PMAAm)-g-PDMAEMA plates had the maximum at the initial pH value of 3.0 and the initial adsorption rate increased with the temperature and increased with the amount of grafted DMAEMA. This result suggests that protonated dimethylamino groups present in the inside of the grafted layer are increasingly involved in the Cr(VI) ion adsorption by the increase in the water absorptivity through the formation of the intermediate grafted layer of PMAAm. The maximum adsorption ratio of 0.510 was obtained for a (PE-g-PMAAm)-g-PDMAEMA plate with G_MAAm = 30 μmol/cm² and G_DMAEMA = 1.7 μmol/cm². The maximum adsorption capacity obtained in this study was comparable to or higher than those of other adsorbents for Cr(VI) ions. The adsorption behaviour obeyed the pseudo-second order kinetic model and was well described by the Langmuir isotherm model, suggesting that the adsorption of Cr(VI) ions occurs through the electrostatic interaction between protonated dimethylamino groups and HCrO4- ions. Cr(VI) ions were successfully desorbed in such eluents as NaCl, NaCl containing NaOH, NH₄Cl, NH₄Cl containing NaOH, and NaOH and (PE-g-PMAAm)-g-PDMAEMA plates were repeatedly used without considerable loss in the adsorption capacity.

Pentaclethra macrophylla stem bark extract anchored on functionalized MWCNT-spent molecular sieve nanocomposite for the biosorption of hexavalent chromium

nsufficient innovative research on the sequestration of Cr(VI) from the aquatic ecosystem has made Cr(VI) a recalcitrant water contaminant that often affects water sources. In this work, a novel plant anchor-nanocomposite was fabricated from the spent molecular sieve, multi-walled carbon nanotubes, and the extract from the stem bark of Pentaclethra macrophylla. It was envisaged that due to the phytochemical constituent of the modifier, this nanocomposite could also act as potent adsorbents for the treatment of Cr(VI) polluted water. To the best of our knowledge, the application of Pentaclethra macrophylla stem bark extract as a modifier for the green fabrication of nanocomposite has not been reported. The resulting composites showed good uptake capacity for Cr(VI) as well as efficient reusability.

Facile Synthesis of Luffa Sponge Activated Carbon Fiber Based Carbon Quantum Dots with Green Fluorescence and Their Application in Cr(VI) Determination

Carbon quantum dots (CQDs) were prepared by a chemical oxidation method using luffa sponge based activated carbon fiber as the raw material. The obtained CQDs were well characterized. The fluorescence quenching effect of Cr(VI) ion on CQDs was investigated. The results show that the addition of Cr(VI) changes the intensity of the ultraviolet characteristic absorption peak of CQDs, and causes static quenching of the fluorescence of CQDs. With the increase in the Cr(VI) concentration, the fluorescence of CQDs was gradually extinguished linearly.

Structure-enhanced removal of Cr(vi) in aqueous solutions using MoS2 ultrathin nanosheets

Molybdenum disulfide (MoS₂) ultrathin nanosheets with enlarged interlayer spacing and defects enables the structure-enhanced removal of Cr(vi), in which the synergistic effects of adsorption and reduction not only captured Cr(vi) from aqueous solutions, but also alleviated the toxicity of chromium to some degree.