An investigation on adsorption of carbamazepine with adsorbents developed from flax shives: Kinetics, mechanisms, and desorption

Highlights

• Flax shive adsorbents were used to adsorb carbamazepine (CBZ).

• The adsorption kinetics was investigated at various temperatures and times.

• The mechanisms of CBZ adsorption were elucidated.

• Desorption of CBZ from CBZ-loaded adsorbents was investigated with various organic solvents and water at different pH.

Abstract

In this work, adsorbents based on hydrochars and steam activated hydrochars developed from flax shives were used to adsorb carbamazepine (CBZ) from simulated contaminated water. The adsorption kinetics was investigated at various temperatures (293–313 K) and times (2–96 h). Four different kinetic models were used to analyze the experimental CBZ adsorption kinetic data. Among the tested various models, the pseudo-second-order kinetic model provided the best simulation to the kinetic data of both adsorbents with R² of being 0.98 and above, and activation energy of 31.8 and 16.45 kJ/mol, respectively. The determined adsorption rate constant of the steam activated hydrochars ((5.88–9.09) × 10⁻⁵) was much higher than that of the hydrochars ((2.81–6.44) × 10⁻⁶). Further, X-ray photoelectron spectra and Near-Edge X-Ray Absorption Fine Structure (NEXAFS) Spectroscopy analysis were done before and after loading with CBZ. The results show π-π electron donor-acceptor interaction played an important role on the adsorption mechanism of CBZ on the above-mentioned adsorbents. Hydrophobic interaction also contributed while the roles of hydrogen bonding and electrostatic attraction between CBZ and adsorbents with opposite charges is insignificant. Pore filling may contribute. Desorption of CBZ from CBZ-loaded adsorbents was investigated with various organic solvents, and water at different pH (2, 6 and 10), among which ethanol was the most effective solvent to desorb CBZ. Overall, the results demonstrated that flax shives are promising feedstocks to be made into adsorbents for treatment of wastewater contaminated by antibiotics and additional pharmaceuticals.

Introduction

The widespread uses of pharmaceuticals from different sources of agricultural and veterinary practices along with human consumption result in pharmaceutical pollution in the environment. In the past few years, trace pollutants have received attention. The pharmaceutical pollutants are present in wastewater effluents, surface, and ground waters, and research has been carried on by adsorbing the pollutants from aqueous phase (Aghababaei et al., 2021a, Aghababaei et al., 2021b, Yu et al., 2008, Nikolaou et al., 2007, Fent et al., 2006). In addition, irrigation of plants with water containing pharmaceuticals causes an uptake of pharmaceuticals by plants. This results in exposure of pharmaceuticals to food chain (Ahmad et al., 2020; Barrett, 2015). Moreover, the amounts of pharmaceuticals emitted into the environment increases which is a world-wide problem. Pharmaceuticals cannot be completely metabolized in human or animal body and significant amounts are discharged with feces and urine. The existence of pharmaceuticals in the environment with different toxicity has achieved great attention of regulatory organizations because of the existing and potential adverse effects, such as being toxic for aquatic organisms and developing genes of antibiotic resistance in pathogens.

Carbamazepine (CBZ) is a kind of pharmaceutical in the epileptic category, widely used for the treatment of some diseases or symptoms such as alcoholism (Zeghioud et al., 2022: Chen et al., 2017b; Sternebring et al., 1992), opiate withdrawal (Montgomery et al., 2000), relieve depressant (Bertschy et al., 1997), and epileptic (Tixier et al., 2003). While using CBZ, around 72% of orally administered dosage is metabolized, whereas 28% is unchanged and consequently leaves the body with feces (Zhang et al., 2008). According to the dose, the elimination half-life varies in the range of 25–65 h (Zhang et al., 2008; Wishart et al., 2006). It was estimated that about 30 ton CBZ is released into the aqueous worldwide environment each year (Chen et al., 2017a; Naghdi et al., 2016).

According to several reports, CBZ cannot be totally eliminated during wastewater treatment using current technologies (Heberer et al., 2002, Ternes, 1998); therefore, it may cause a risk to human health through contaminated drinking water. According to the challenges in treating the contaminated water, developing efficient and cost-effective removal methods is becoming a crucial necessity. Several methods such as chemical precipitation and ion exchange, advanced oxidation, and bioremediation (Aghababaei et al., 2017) are applied for wastewater treatment in order to eliminate the pollutants (Ahmad et al., 2022). Among them, adsorption is one of the most effective methods (Ayub et al., 2022; Abdoli et al.,2015). Flax shives are abundantly generated agricultural byproducts and they have been used for wastewater treatment to remove CBZ from simulated wastewater. Effects of solution pH and temperature on equilibrium CBZ adsorption, key factors, characterization of the adsorbent, site energy, and thermodynamic studies and comparison between two treatment methods with two different acid and base were investigated in the previous studies of the authors of this work (Aghababaei et al., 2021a, Aghababaei et al., 2021b). However, that work did not provide information on CBZ adsorption's kinetics, mechanisms, and desorption, which are the fundamentals of pharmaceutical adsorption and important to understand. It was reported that mechanisms of CBZ adsorption by nanotube (Lerman et al., 2013) and biochar (Chen et al., 2017b), and phenol compounds adsorption by nanoporous silica aerolgel (Abdoli et al.,2015) were associated with electron donor-acceptor interaction, hydrophobic attraction, and so on. However, the adsorption mechanisms of the systems containing CBZ and hydrochars and steam activated hydrochars developed from flax shives are not well understood.

In this work, the effects of key operation parameters on adsorption kinetics were investigated. The experimentally obtained kinetic data were analyzed with the aid of four different kinetic models of Pseudo-first-order kinetic, Pseudo-second-order kinetic, Elovich, and Intraparticle diffusion models. Furthermore, the mechanisms of CBZ adsorption were analyzed in aid of Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS: C1s., O1s. and N1s. spectra), and Near-edge X-ray absorption fine structure spectroscopy (NEXAFS).

Moreover, the desorption of CBZ from hydrochars and steam activated hydrochars was investigated with various organic solvents and water at different pH values. Reuse of the selected hydrochars and steam activated hydrochars were studied.