Regenerable Kiwi Peels as an Adsorbent to Remove and Reuse the Emerging Pollutant Propranolol from Water

Abstract

This work aims to characterize the adsorption process of propranolol HCl, an emerging pollutant and a widely used β-blocker, onto kiwi peels, an agricultural waste. The use of UV-vis spectroscopy was considered to obtain information about the pollutant removal working in the in-batch mode. In a relatively short time, the adsorption process could remove the pollutant from water. A kiwi peel maximum adsorption capacity of 2 mg/g was obtained. With the perspective of scaling up the process, preliminary in-flux measurements were also performed. The investigation of the whole in-batch adsorption process was conducted by studying the effect of ionic strength (adopting salt concentrations from 0 to 0.4 M), pH values (from 2 to 12), adsorbent/pollutant amounts (from 25 to 100 mg and from 7.5 to 15 mg/L, respectively), and temperature values (from 289 to 305 K). The thermodynamics, the adsorption isotherms, and the kinetics of the adsorption process were also carefully investigated. The Langmuir model fitted the experimental data well, with an R2 of 0.9912, restituting KL: 1 L/mg and Q0: 1.8 mg/g. The temperature increase enhanced the pollutant removal due to the endothermic adsorption characteristics. Accordingly, a ΔH°298K of +70 KJ/mol was obtained. The pseudo-first-order kinetic model described the process. Due to the results observed during the study of the effects of pH and ionic strength, the prominent presence of electrostatic interactions, working in synergy with hydrophobic forces and H-bonds between the pollutant and kiwi peel surfaces, was successfully demonstrated. In particular, FTIR-ATR measurements confirmed the latter findings. Finally, desorption experiments for recycling 100% of propranolol for each cycle were performed using 0.1 M MgCl2. Ten cycles of adsorption/desorption were obtained and indicated that the percentage of propranolol removal was not affected during each run, increasing the maximum adsorption from 2 to 20 mg/g.

Kiwi peel waste as a recyclable adsorbent to remove textile dyes from water: Direct Blue 78 removal and recovery

“…Indeed, some authors of this paper recently have reported the use of this waste/adsorbent for the removal of emerging pollutants, presenting for the first time the chemical and physical features of kiwi peels. 34,35 In particular, Gubitosa et al, 34,35 by the synergistic use of different techniques (such as SEM investigation, FTIR-ATR, and TG analyses), showed that the adsorbent is characterized by particular morphological features, irregular domains, and filaments on both sides of peels' surfaces, and it is mainly constituted by lignin, cellulose, and hemicellulose. Furthermore, it was demonstrated that the main morphological and chemical features of kiwi peels were also retained after their use and reuse during the adsorption/ desorption processes, enabling kiwi peels as a long-lasting adsorbent material.…”

“…Furthermore, it was demonstrated that the main morphological and chemical features of kiwi peels were also retained after their use and reuse during the adsorption/ desorption processes, enabling kiwi peels as a long-lasting adsorbent material. 34,35 This work aims to widen the kiwi peels' applicability, proposing that this waste can also be used for the anionic textile dye removal from water. Indeed, about this concern, only one work is reported in the literature, and it refers to methylene blue and rhodamine B removal.…”

“…36 On the other hand, kiwi peels, to our knowledge, were employed in the past to remove Cd 2+ , Cr 3+ and Zn 2+ ions, 37 nitrate, 38 and oil, 39 sequester Pb 2+ , 40 and, as previously said, to remove emerging pollutants. 34,35 Therefore, a deep scientific research activity should be developed to promote the sustainable management of kiwi peels' wastes to address environmental problems related to dye pollution. Moreover, an important aspect of this paper is related to the eco-friendly kiwi peel pre-treatment, avoiding hard experimental conditions and hazardous materials, as already reported by Gubitosa et al 34,35 Furthermore, the adsorbent recycling was proposed under safe conditions, demonstrating the dyestuff reuse.…”

“…34,35 Therefore, a deep scientific research activity should be developed to promote the sustainable management of kiwi peels' wastes to address environmental problems related to dye pollution. Moreover, an important aspect of this paper is related to the eco-friendly kiwi peel pre-treatment, avoiding hard experimental conditions and hazardous materials, as already reported by Gubitosa et al 34,35 Furthermore, the adsorbent recycling was proposed under safe conditions, demonstrating the dyestuff reuse. More specifically, kiwi peels (i) were only washed with hot water, avoiding the use of toxic chemicals, leading to the development of an eco-design in accordance with an eco-innovation model, especially for a potential future perspective to implement the process on a large-scale; (ii) hot water was used to desorb the color, regenerating the adsorbent, dyeing cotton fibers again.…”

“…Novel horizons in the environmental field are thus opened, considering that this adsorbent is also able to adsorb emerging pollutants from water and desorb them in salt solutions. 34,35 On the other hand, the removal of color was observed in a completely reversed situation: adsorption in salt solutions and desorption in water. So, kiwi peels, compared with other adsorbents, could be potentially considered ''on-demand'' adsorbents, being able to remove different classes of pollutants, according to the working conditions.…”