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. 2022 Feb 28;14(5):984.
doi: 10.3390/polym14050984.

Ionic Liquid Agar-Alginate Beads as a Sustainable Phenol Adsorbent

Nihal Yasir  1 , Amir Sada Khan  1   2 , Muhammad Faheem Hassan  1 , Taleb H Ibrahim  1 , Mustafa I Khamis  3 , Paul Nancarrow  1
Affiliations

Ionic Liquid Agar-Alginate Beads as a Sustainable Phenol Adsorbent

Nihal Yasir et al. Polymers (Basel). .

Abstract

Cleaning wastewater containing low concentrations of phenolic compounds is a challenging task. In this work, agar-alginate beads impregnated with trihexyltetradecylphosphonium bromide ([P66614][Br]) ionic liquid adsorbent were synthesized as a potential adsorbent for such applications. FTIR, TGA, SEM, EDX and PZC studies were performed to characterize and understand the physicochemical properties of the adsorbent. The Fourier transformation infrared spectroscopy (FTIR) study showed that [P66614][Br] ionic liquid was effectively incorporated into the agar-alginate structure. TGA and SEM confirmed comparative enhanced thermal stability and porous surface, respectively. Chemical reaction rate-altering parameters, i.e., pH, contact time, initial phenol concentration and temperature, are optimized at highest phenol removal. It was found that the maximum phenol adsorption capacity and highest removal efficiency by the adsorbent occurred at pH 2, initial phenol concentration of 150 mg/L, beads dosage of 6 mg/mL and contact time of 2 h with values of 16.28 mg/g and 65.12%, respectively. The pseudo-second order model fitted the adsorption kinetics well, and the Freundlich isotherm model gave the experimental data the best fit. Analysis of thermodynamic data demonstrated that the adsorption process is fundamentally exothermic in nature, and low temperature favors spontaneity of the chemical reaction. Regeneration studies indicated that the adsorbent can at least be used for four cycles in such applications without any considerable loss in adsorption efficiency.

Keywords: adsorption; agar; alginate; ionic liquids; isotherms; kinetic study; phenol; wastewater.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1
Figure 1
Total number of entries in web of science for phenol adsorption articles from year 2016 to 2022.
Figure 2
Figure 2
Schematic diagram for IL–agar–alginate beads preparation.
Figure 3
Figure 3
The prepared IL–agar–alginate beads (a) wet and (b) dry.
Figure 4
Figure 4
FTIR spectra of (a) IL, alginate and agar (b) Phenol and IL–agar–alginate bead before and after phenol adsorption.
Figure 4
Figure 4
FTIR spectra of (a) IL, alginate and agar (b) Phenol and IL–agar–alginate bead before and after phenol adsorption.
Figure 5
Figure 5
TGA curve for agar and agar–alginate-IL beads.
Figure 6
Figure 6
SEM images for adsorbent bead at two different magnifications (a) 100 µm and (b) 50 µm. (c) EDX analysis of adsorbent bead.
Figure 7
Figure 7
pHpzc analysis of agar–alginate-IL beads study at room temperature.
Figure 8
Figure 8
Effect of IL–agar–alginate beads dosage on the adsorption capacity and on the removal efficiency of phenol (Ci = 150 mg/L, pH of 2, 150 rpm, 2 h and at 25 °C).
Figure 9
Figure 9
The effect of initial pH of phenol solution on the adsorption capacity by IL–agar–alginate beads (Ci = 100 mg/L, 150 rpm, 24 h, beads dosage = 1 mg/mL and at 25 °C).
Figure 10
Figure 10
Effect of time on phenol adsorption onto the IL–agar–alginate beads (Ci = 150 mg/L, pH of 2, 150 rpm, 2 h, beads dosage = 1 mg/mL and at 25 °C).
Figure 11
Figure 11
Effect of initial phenol concentration on the adsorption capacity (pH of 2, 150 rpm, 2 h, beads dosage = 1 mg/mL and at 25 °C).
Figure 12
Figure 12
Effect of temperature on phenol adsorption capacity of IL–agar–alginate beads (Ci = 150 mg/L, pH of 2, 150 rpm, 2 h and beads dosage = 1 mg/mL).
Figure 13
Figure 13
Kinetics plots for adsorption of phenol by IL–agar–alginate beads at 25.0 °C (using pseudo-first order model (PFO) (a) and pseudo-second order model (PSO) (b)) at different initial concentrations of phenol.
Figure 14
Figure 14
Adsorption isotherm plots for phenol adsorption on IL–agar–alginate beads using (a) Langmuir and (b) Freundlich models at 25 °C.
Figure 14
Figure 14
Adsorption isotherm plots for phenol adsorption on IL–agar–alginate beads using (a) Langmuir and (b) Freundlich models at 25 °C.
Figure 15
Figure 15
Van’t Hoff plot for the adsorption of phenol on the IL–agar–alginate beads.
Figure 16
Figure 16
Regeneration and reusability of IL–agar–alginate beads.
Figure 17
Figure 17
Proposed interaction forces between sodium alginate and IL and agar–IL–alginate beads with phenol.
See this image and copyright information in PMC

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