Synthesis, Characterization, and Application as a Chromium(VI) Adsorbent of Amine-Modified Polyacrylamide-Grafted Coconut Coir Pith

Abstract

The amine-modified polyacrylamide-grafted coconut coir pith carrying −NH3 +Cl- functional group at the chain end (PGCP−NH3 +Cl-) was investigated as an adsorbent for its possible application for the removal of chromium(VI) from aqueous solution and wastewater. The infrared spectroscopy results were used to confirm the graft copolymer formation and −NH3 +Cl- functional group. The grafting of polyacrylamide onto the coir pith improved the thermal stability of the adsorbent and enhanced the apparent activation energy for the thermal degradation of PGCP−NH3 +Cl-. X-ray diffraction pattern and scanning electron microscopy (SEM) studies were carried out to investigate the crystallinity and morphology of the adsorbent. The decrease in crystalline domains in PGCP−NH3 +Cl- results in the loss of tensile strength of the grafted chain and consequently enhances the free mobility of the grafted chain. Batch adsorption technique using PGCP−NH3 +Cl- was applied for the removal of chromium(VI) anion from aqueous solution and wastewater. The maximum adsorption of 99.4% (12.43 mg/g) took place from an initial concentration of 25.0 mg/L Cr(VI) at 30 °C, pH 3.0, and an adsorbent dosage of 2.0 g/L. The kinetics of sorption of Cr(VI) ions were described by a pseudo-second-order kinetic model. The temperature dependence indicates the exothermic nature of the process. Equilibrium isotherms were determined for different temperatures and the results are analyzed using the Langmuir and Freundlich isotherm equations. Adsorption isotherm experiments were also conducted for comparison using a commercial chloride form Dowex, a strong base (quaternary amine functionality) anion exchanger. Quantitative removal of 22.7 mg/L Cr(VI) in 50 mL of electroplating industry wastewater by 125 mg of PGCP−NH3 +Cl- was observed at pH 3.0. Alkali regeneration was also tried for several cycles with a view to recover the adsorbed metal ions and also to restore the sorbent to its original state.

Adsorption of Cr(VI) onto PEI immobilized acrylate-based magnetic beads: Isotherms, kinetics and thermodynamics study

“…Unnithan et al studied the amino modified polyacrylamide grafted coir pith for removal of Cr(VI) from wastewater. The maximum adsorption capacity was 12.43 mg/g under specified experimental conditions [24]. The crosslinked alginate and gelatin was used as adsorbents for the removal of chromium ions from wastewater.…”

“…Moreover, techniques employing magnetism are more amenable to automation and miniaturization [16][17][18]. Much attention has been paid to improve the adsorptive performance of the adsorbent and, the main effort focused on the introduction of a second functional polymer via coating to the adsorbent surfaces [19][20][21][22][23][24]. Unnithan et al studied the amino modified polyacrylamide grafted coir pith for removal of Cr(VI) from wastewater.…”

Development of Polymeric and Polymer‐Based Hybrid Adsorbents for Chromium Removal from Aqueous Solution

“…Among them, ion exchange is one of the most popular methods for the removal of chromium ion from wastewaters. A number of review articles have appeared on tertiary amine, quaternary ammonium and acrylic-based polymeric, adsorbents for the removal of chromium from wastewaters that are very stable in a range of buffers from pH 1.0 to 11.0 and were resistant to microbial degradation [20][21][22][23].…”

“…This is because they include not only strong adsorption properties, but also the feature of being easily separated by an external magnetic field. In scientific literature, adsorption capabilities of magnetite nanosized particles for heavy metal ions have also been reported [22,23]. Recently, there has been increased interest in the use of magnetic adsorbents in the magnetic separation technique, using magnetic particles, is fast, easy, nonlaborious and often highly scalable method for sensitive and reliable capture of inorganic or organic pollutants [21][22][23][24][25][26].…”

Synthesis and characterization of polyacrylamide‐grafted coconut coir pith having carboxylate functional group and adsorption ability for heavy metal ions

“…13 Any attempt to reutilize the CP will be worthwhile. Earlier workers 14,15 have developed anion exchangers from CP for the removal of anionic contaminants from wastewaters. Recently Parab et al 16 carried out an adsorption study on CP for the removal of uranium from aqueous solutions.…”