Sonicating for the Uptake of Paracetamol from Solution by Activated Carbon from Oak: Kinetics, Thermodynamics, and Isotherms

This inquiry used ultrasonic waves to uptake paracetamol (PA) by using oak-based activated carbon (ACO). The surface of ACO was explored based on FT-IR, SEM, and XRD before and after the adsorption. The kinetic data for PA adsorption onto ACO corresponds to a pseudo-second-order kinetic model. Isothermal models of the Langmuir, Freundlich, D-R, and Temkin were used. The adsorption of PA onto ACO was found to be a monolayer with 96.03% uptake, which corresponds to Langmuir. The thermodynamic experiments revealed the endothermic nature of PA adsorption onto ACO. Under the investigated optimal conditions, the adsorption capacity of PA onto ACO was found to be 97.1 mg. L-1. ACO could be recycled after six regenerations. Ultimately, sonicating has adequate performance for the uptake of PA by ACO.


Introduction
Hazardous material pollution has recently grown into a significant concern throughout the world.Recent research has focused on the efficient removal of such contaminants to reduce the threat that they pose to living organisms [1].Diverse forms of organic pollutants, such as pharmaceuticals, were detected in a wide range of water supplies.Since pharmaceuticals are essential to preserving human and animal health, their production has grown significantly in recent decades.These pharmaceutical compounds are regularly released in enormous quantities into the environment, mainly through water and soil, from a diversity of sources, including anthropogenic activities, the pharmaceutical industry, and hospitals [2].Due to its efficacy in relieving pain and fever, paracetamol, also known as acetaminophen (Scheme 1), is one of the most used medications globally.Because of its solubility and hydrophilicity, paracetamol concentrates readily in water.Paracetamol decomposes gradually in the environment since it is not biodegradable [2].Paracetamol is particularly toxic to the liver, posing a risk of hepatitis development [3].In the past, significant efforts were made to improve water treatment processes.As a result, many effective techniques for discarding pharmaceutical micropollutants from polluted water were developed.
Various techniques were employed for removing pollutants from water, such as filtration, chemical precipitation, coagulation, ion exchange, ozonation, advanced oxidation, reverse osmosis, biodegradation, and adsorption processes [4].Adsorption is a broadly used technique for removing pollutants from water due to its exceptional efficiency, low toxicity, modesty, environment-friendly, nondestructiveness, and insignificant cost [5].The most prominent adsorbent for extracting contaminants, specifically from water, is activated carbon due to its adaptability and attractive characteristics, such as its high surface area, porosity, and distinct chemical properties, which enable interaction with various chemical substances [6].Activated carbon has been prepared using a variety of precursors in frequent studies.Among these precursors is oak fruit.Oak (Quercus calliprinos) is a prevalent plant in the Eastern Mediterranean, growing on rocky hillsides.It is indigenous to Jordan and can be found in Salt, Ajlun, Jerash, Amman, Tafila, and Shobak.The fruit of the oak is a nut called an acorn that grows in a cup-like structure (called a cupule).In many investigations, the uptake of paracetamol from aqueous solutions by adsorption onto activated carbon was performed based on the shaking technique assisted with sonication.Also, numerous studies used modified activated carbon such that modified by aminoterphthalic acid [7].Sonication boosted the migration of pollutants into activated carbon pores, causing higher efficiency [8].
The aim of this study is to prove the effectiveness of using just sonication in removing paracetamol from an aqueous solution and simulated samples.Numerous variables, including adsorbent dose, initial concentration, contact time, and pH, were examined for their effectiveness.The equilibrium and mechanism of the adsorption process were examined by kinetic and isothermal investigations.

Reagents and Instruments.
Paracetamol with a purity of >99% (Scheme 1) was acquired from Sigma Aldrich and used without any more cleansing.This analgesic was chosen for its widespread production and consumption around the world.Calculated amounts of powder standards from PA were dissolved in distilled water to prepare stock solutions (250 mg.L -1 ).The prepared solutions were kept out of the light at 4 °C.Operative concentrations (10-100 mg L -1 ) were prepared from stock solutions by dilution.Solutions of 0.1 M NaOH and 0.1 M HCl were employed for pH adjustment.FT-IR instrument (TENSOR from Bruker) was employed for the functional groups evident on the activated carbon surface and their implications in the adsorption.The LEO 1550 scanning electron microscopy (SEM) was employed to obtain images of the adsorbent surface.X-ray diffraction patterns were obtained from an XRD D5005 diffractometer (Siemens, Munich, Germany).

Preparation and Characterization of Adsorbent.
The abundant oak cupule was collected as waste from the north of Jordan in the summer.Subsequently, the oak cupule was repeatedly rinsed with distilled water, dried at 80 °C for 48 hours, and then crushed.The crushed sample was used to prepare activated carbon according to the method [9].The prepared activated carbon was ground and sieved to obtain particles of 180 μm particle size.Finally, the prepared activated carbon was stored in a desiccator and employed for paracetamol uptake.

Bach Adsorption Experiment.
All experiments were performed using a laboratory ultrasonic water bath (Branson 5800, USA).Each experiment was performed three times.A 50.0 mL of PA solution at different concentrations was added to a weighed amount of ACO into a 250 ml of the Erlenmeyer flask.The mixtures were sonicated for a particular time.The mixtures were filtered and subjected to absorbance measurements to determine the concentration.The effects of sonication time, initial PA concentration, adsorbent dose, solution pH, and temperature were investigated.A UV-6100 PC double-beam spectrophotometer was used to investigate the PA concentrations at a wavelength of 244 nm.The adsorbed amount of PA onto the ACO, q e (mg.g -1 ), was calculated using Equation (1) [10,11].
q e (mg.g -1 ) is the adsorbed PA amount at equilibrium, C i (mg.L -1 ) is the initial Pa concentration, C eq (mg.L -1 ) are the equilibrium PA concentration, and V (L) is the volume of working solution.
The removal percentage was calculated based on Equation (2).

Results and Discussion
3.1.Characterization of Adsorbent 3.1.1.FT-IR Analysis.FT-IR analysis (Figure 1) was performed for ACO adsorbent and ACOPA (the coated ACO with paracetamol after the adsorption process).The results revealed the existence of various functional groups.Results were summarized in Table 1 [9].As a result, there are obvious shifts in absorbance and changes in intensity confirm the adsorption of PA onto ACO.  3 Adsorption Science & Technology 10 to 100 mg.At 25 ± 1 °C for 60 minutes, a volume of 50.0 ml of 50 mg/L L -1 PA solution with a pH of 7.0 was sonicated with a specific dose of ACO. Figure 4 shows that the proportion of paracetamol removed increases when the ACO dose is increased due to the plentiful presence of active sites at the initial stages of the adsorption process.At 50.0 mg, the increments in the uptake become very slight, signifying that the optimum dose of ACO for the removal of PA from an aqueous solution by sonication has already been achieved.

Influence of Sonication Time.
Contact time (sonicating) was one of the factors that had a significant impact on the effectiveness of the adsorption process.The batch adsorption experiments were conducted by sonication of 50 mg ACO with 50 ml of 50 mg, L -1 PA concentration at 7.0 pH, and 25 ± 1 °C for 15-120 minutes.Figure 5 shows the adsorption equilibrium of PA onto the ACO surface was reached after 60 min, and then the uptake becomes approximately constant.In this study, the initial concentration of PA varied from 10 to 90 mg.L -1 .In the first stages, the change in adsorption is likely to be negligible until it reaches 50 mg.L -1 due to the availability of achievable active sites.After the optimal initial concentration (50 mg.L -1 ), the uptake starts to drop due to the saturation of active sites with PA molecules.

Influence of pH.
The pH of the solution is a crucial parameter in the adsorption process.Firstly, the value of pHpzc was determined by shaking 150 mg of ACO adsorbent with 50.0 ml of 0.1 M NaOH solution for 24 hours at a pH of 2, 4, 6, 8, 10, and 12. Figure 7 shows the pHpzc is equal to 6.39.For pH values exceeding pHpzc, the adsorbent surface of ACO becomes negative, whereas, for values beneath pHpzc, it becomes positive [12].
In this study, the impact of pH on the adsorption of PA onto ACO was investigated at a temperature of 25 ± 1 °C, an initial concentration of 50 mg.L -1 and ACO dosage of 50 mg, sonication time for 60 min, and pH ranged from 3-11.Scheme 2 illustrates the protonated and deprotonated structures of PA.
The optimal adsorption of PA onto ACO was recorded at pH 5.0, as Figure 8 shows.Adsorption was maximal at an acidic pH because the phenols continued to remain undissociated, and the interactions between the ACO adsorbent and the PA were issued.Equilibrium was achieved at pH 7.0, then rapidly deteriorated beyond pH 9.0 as a result of the repulsion between the negatively charged ACO surface and the anionic (deprotonated) paracetamol [13].The kinetics and the mechanism of PA adsorption onto ACO were investigated using pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetics models.Plotting kinetic data according to Equations ( 3) and (4) [14] determines whether the PA adsorption onto ACO was first or second order.Results in Figure 9 indicate that the process is of pseudosecond order with an R 2 of 0.9928 and a rate constant (k 1 ) of 0.0287 g. mg -1 .min -1 .
q e is the equilibrium amount of adsorbate per unit mass of adsorbent (mg.g -1 ), q t is the equilibrium amount of adsorbate per unit mass of adsorbent at time t (mg.g -1 ), and k 1 and k 2 are the rate constant in min -1 and g. mg -1 .min -1 , respectively.
The intraparticle diffusion model represented by Equation ( 5) was employed for the demonstration of PA adsorption onto the ACO mechanism [15].where q t is the adsorbate amount g -1 ), K id is the rate constant (mg.g -1 .min -0.5 ), and t 1/2 is the square root of time (min 0.5 ).It is anticipated that if the intercept C equals zero, intraparticle diffusion would be the only rate-limiting step.The effect of surface adsorption rises in significance when the C constant is raised.According to Figure 10, the rate-limiting step is surface adsorption, not intra-particle diffusion.

Intra-particle diffusion model Experimental
q e = q m e −B D ε 2 : ð9Þ q e is the equilibrium adsorbate amount (mg.g -1 ), q e is the equilibrium adsorbate amount (mg.g -1 ), C e is the equilibrium adsorbate concentration (mg.L -1 ), k L , the Langmuir isotherm constant, is associated to adsorption energy and utilized to determine adsorbate affinity to the adsorbent surface, q m is the adsorption capacity (mg.g - 1 ), K F is the Freundlich isotherm constant (mg.g -1 ), n is the adsorption intensity, A is the binding constant in g -1 at equilibrium, B is constant associated to the adsorption heat, B D is the D-R constant mol 2 /KJ 2 , and Ɛ (Polanyi potential) in D-R isotherm and the mean energy of the adsorption (KJ.Mol -1 ) could be obtained using Equations (10) and (11), respectively.
Figure 11 demonstrates the results of the fourth isotherms.Correlation coefficients (R 2 ), dimensional factors, and associated constants were presented in Table 3. R 2 values determined that the Langmuir isotherm properly appropriately characterized the PA adsorption onto ACO, indicating monolayer and homogenous adsorption.The value of the Temkin constant (B) (Table 3), reveals that the PA adsorption onto the ACO adsorbent is endothermic.In accordance with the D-R isotherm, the predicted energy values, 1.3 KJ<8.0 KJ.Mol -1 imply the physisorption nature of PA onto ACO [16].
K L is a dimensionless and represent the adsorption equilibrium constant according to the best-fitted model.R is the universal constant of ideal gases, 8.314 J•K -1 mol - 1 .For PA adsorption onto ACO, positive values of Gibb's free energy (ΔG °) indicate that the process is not spontaneous.The positive value of enthalpy (ΔH o ) confirms the endothermic nature of the adsorption process.Enthalpy magnitude indicates physisorption through the van der Waals if less than 20 kJ mol -1 or electrostatic forces between PA and ACO if between 20 and 80 kJ mol -1 [17].Positive entropy change (ΔS o ) values suggest adsorbate/adsorbent interface unpredictability and ACO adsorbent affinity [18].Thermodynamic experiments were performed under the same experimental conditions previously applied in the adsorption equilibrium; thus, under temperature variation (25 ± 1 °C, 35 ± 1 °C, and 45 ± 1 °C) and sonication for 60 min.
3.6.Simulated Sample.A tablet of three commercial medicines containing PA was dissolved in tap water and soni-cated with 50 mg ACO for 60.0 min under optimal conditions.The PA uptake was found to be 81.78%,84.27%, and 83.12%, confirming the effectiveness of ACO in the uptake of PA by sonication.

Comparison with Other Activated Carbon Adsorbents
The maximum PA uptake capacities by ACO based on sonication was compared to other activated carbon adsorbent based on the shaking technique (Table 5).The comparison shows that ACO has an adsorption capacity of 97.91 mg g - 1 near to many of the other reported adsorbents.

Desorption and Regeneration Study
Sodium hydroxide is found to be the best for the regeneration of PA adsorbed [28].1.0 M of NOH was used for the elution of PA from the ACO surface.The percentage of desorption was calculated using Equation (14).

Conclusion
This study revealed that the PA is successfully uptake from an aqueous and simulated sample by activated carbon prepared from an oak cupule (ACO) by solely sonication.The experimental results demonstrated that the adsorption potential of PA onto ACO adsorbent is adversely impacted by operative factors such as sonication time, pH, adsorbent dose, temperature, and PA initial concentration.Maximum uptake (96.03%) of 50 mg g -1 PA was achieved after 60 minutes of sonication with 50 mg ACO at 45 °C and 5.0 pH.The adsorption isotherm data best fit the Langmuir model.Information from the kinetic studies indicated that the pseudo-second-order kinetic model was in better agreement compared to the pseudofirst-order kinetic.Thermodynamically, the adsorption of PA onto ACO was found to be endothermic and nonspontaneous.ACO could be reused after six cycles with decrease in efficiency by 14.89%.
Figure 6 demonstrates how the initial concentration of the adsorbate substantially impacts the adsorption of PA onto ACO.

Table 4 :
Thermodynamic parameters of PA adsorption onto ACO.

Table 5 :
Comparison of PA adsorption onto ACO with other reported adsorbents.