Adsorption of diclofenac on mesoporous activated carbons: Physical and chemical activation, modeling with genetic programming and molecular dynamic simulation

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Highlights

  • AC successfully prepared from a low-cost bio-adsorbent and agro-industrial waste.

  • ACs were modified by chemical (three types) and physical (two types) activations.

  • Operational parameters of adsorption were optimized using ACs for DCF removal.

  • GP modelling and MD simulation performed for selected AC in adsorption process.

Abstract

This work aims at the preparation of AC from chemical activation (H3PO4, KOH, and HCl) and physical activation (thermal treatment under N2 atmosphere at 500 and 700 °C) of Astragalus Mongholicus (AM) (a low-cost bio-adsorbent and agro-industrial waste), used as carbon precursor. The obtained materials were further applied in the adsorption of diclofenac (DCF) from water/wastewater. The physicochemical properties of the as-prepared ACs and commercial activated carbons (CAC) were evaluated by SEM, XRD, FT-IR, and BET analyses, revealing the high surface area and mesoporous proportion of AC when compared to CAC . Adsorption results showed that the efficiency of AC-700 °C (774 m2 g−1) for DCF removal (92.29%) was greater than that of AC-500 °C (648 m2 g−1, 83.5%), AC-H3PO4 (596 m2 g−1, 80.8%), AC-KOH (450 m2 g−1, 59.3%), AC-HCl (156 m2 g−1, 29.8%) and CAC (455 m2 g−1, 67.8%). The optimization of effective parameters in adsorption was examined at a laboratory-scale using the selected AC-700 °C. The Langmuir isotherm and the pseudo-second-order model fitted well the experimental data. The regeneration efficiency was maintained at 96% (DI-water) and 97% (heating) after three cycles. Besides, genetic programming (GP) and molecular dynamics (MD) simulations were applied to predict the adsorption behavior of DCF from aqueous phase as well as in the ACs structure. It was found that the adsorption mechanisms involved were electrostatic interaction, cation–π interaction, and π–π electron interaction.

Introduction

Pharmaceutical and personal care products (PPCPs) are the largest groups of micro-pollutants widely used in human and veterinary medical applications. Non-steroidal anti-inflammatory drugs (NSAIDs) is isis an important pharmaceutical group detected in the environmental matrix, including water bodies (Bhadra et al., 2016; Stülten et al., 2008). Among NSAIDs, Diclofenac [2-(2, 6-dichlorophenyl amino) phenyl acetic acid)] (DCF) is used mostly in the inflammation and pain treatment of animals and humans. Physico-chemical properties, chemical formula and structure of DCF are depicted in Table S1. The estimated average world consumption of pharmaceutical products is about 15 g per capita per year, but in industrialized countries, annual use was reported up to 50–150 g per capita and the annual worldwide consumption of DCF for human health purposes averaged 1443 ± 58 t (Vieno and Sillanpää, 2014; Lonappan et al., 2016; Acuña et al., 2015; Zhao et al., 2019). Several studies reported adverse effects of DCF as an endocrine disrupter including oxidative stress, DNA damage, cyto-genotoxicity and teratogenic potential on non-target organisms in aquatic environments (Noorimotlagh et al., 2020a; Guiloski et al., 2015; Islas-Flores et al., 2013). Due to its extensive usage and inherent properties, DCF is classified as “dangerous for the aquatic environment” (Coll et al., 2015; Földényi et al., 2017; Guiloski et al., 2015; Martínez-Alcalá et al., 2017; Tiwari, 2015). During the past few decades, the PPCPs have been detected in water resources, including surface and ground waters, at low levels (below μg/L). It is reported the occurrence of DCF in surface waters (between 1030 ng/L and 1.2 μg/L), in sewage treatment effluents (4.7 μg/L), in drinking water wells in ten Mediterranean regions (2 ng/L) and in groundwater in Berlin (0.38 μg/L) (Álvarez-Torrellas et al., 2016; Bhadra et al., 2016; Poirier-Larabie et al., 2016; Heberer, 2002; de Oliveira et al., 2016; Heberer et al., 2002; Jux et al., 2002; Rabiet et al., 2006). In general, the occurrence of DCF in freshwater was reported in 38 countries with a median concentration of 21 ± 722 ng/L (Acuña et al., 2015). Therefore, the removal of these types of micro-pollutants from water/wastewater is of utmost importance.

Several techniques such as ozonation, catalytic wet oxidation, coagulation-flocculation, biological degradation, ultrasonic irradiation, electro-oxidation, and adsorption technology were previously used for the removal of micro-pollutants from aqueous phases (Alavi et al., 2017; Bernardo et al., 2016; Bhadra et al., 2017; de Luna et al., 2017). Among the above-mentioned treatment processes, the adsorption technology is widely used due to its advantages of ease in the design, convenient use, reliability, possibility of regeneration, absence of by-products and sludge generation, high efficiency, and low cost (Bhadra et al., 2017; Zhang et al., 2016). Therefore, more attention has been devoted to the research on the synthesis and development of new adsorbents with high adsorptive capacity.

The production of activated carbons (ACs) from low-cost and waste materials as precursors is gaining popularity (Paraskeva et al., 2008; Gholami et al., 2018). Several reports have focused on DCF removal from aqueous wastes using ACs obtained from low-cost agricultural waste materials due to high efficiency for dilute solutions, non-hazardous to the environment and low energy demand (Baccar et al., 2012; Bernardo et al., 2016; Gottipati and Mishra, 2016; Tan et al., 2015; Omo-Okoro et al., 2018). Thus, in the present study, the application of Astragalus Mongholicus (AM), a locally available plant in Ilam province in the southwest of Iran, with about 3000 species of small shrubs and herbs, has been considered for the production of ACs. AM can be used as an inexpensive precursor for AC production due to its high lignocellulosic content, renewability and environmental-friendly nature (Yin et al., 2008). Chemical and physical activation methods have been reported as methods for the synthesis of ACs from organic compounds (Álvarez-Torrellas et al., 2017; Jaafarzadeh et al., 2019; Noorimotlagh et al., 2019, Noorimotlagh et al., 2020b; Noorimotlagh et al., 2014). In physical activation, the raw material is converted to char under high temperatures (carbonization) and then activation of the char is done in the presence of an oxidizing gas such as carbon dioxide, N2, or steam. Chemical activation firstly consists of the impregnation of the carbonaceous precursor with chemical agents such as KOH, H3PO4, H2SO4, NaOH and HCl, followed by thermal activation under various temperatures (Álvarez-Torrellas et al., 2017; Jaafarzadeh et al., 2019; Noorimotlagh et al., 2014). Recent studies have highlighted thermal activation as a great physical activation methodology, due to the production of higher-grade carbons, porosity and finally the development of high surface areas in the synthesized ACs (Álvarez-Torrellas et al., 2017; Nowicki et al., 2016; Wiśniewska et al., 2017).

To investigate each system, an adsorption process for example, its model is needed and the accuracy of the model affects the investigation of the system directly. The number of parameters and their relationship in a system shows the degree of complexity of the system and the more complex the system, the harder it is to model. From the industrial application point of view, the application of simple models can help to predict the effect of different operating parameters on adsorption efficiency (Rostami et al., 2017). Because of the exponential increase in the available data, it is impossible to manipulate these data by previous techniques, such as least square fitting (Duong et al., 2018).In this sense, soft computing can be a good solution for this challenge. In chemical engineering, this challenge is complicated because most of the systems are multi-dimensional and nonlinear. Soft computing such as Artificial Neural Networks (ANNs), Fuzzy Logic, and Evolutionary Algorithms (EA) that are nonlinear have been introduced and can be used. Genetic Programming (GP) that is proposed by Koza (Koza, 1990) is one of the well-known types of EA that is used in this research. On the other hand, Molecular dynamics (MD) simulations have also been used to predict forces near the surface of the molecules, as well as the attractive and repulsive mobility forces between adsorbent and adsorbate and to understand the molecular structure and interaction (Peng et al., 2017; Tang et al., 2011). MD simulation is used to study the microscopic phenomena of the research object by accurately describing the motion of atoms in a defined system based on the classical Newtonian laws of motion. Besides, the molecular simulations are very important to study the adsorption in situations in which the experiment is difficult to perform (Khanmohammadi et al., 2019; Tirjoo et al., 2019). Therefore, the simulation of the adsorption of DCF on the ACs can provide useful information and have a better understanding of its mechanism.

To the best of our knowledge, there is little information about the comparison of physical and chemical activating agents for the production of ACs from organo-carbonaceous materials and the evaluation of its application for the removal of DCF from waste-waters. Besides, the application of relatively simple derived models as well as molecular simulation based on experimental results to study adsorption has been gaining great interesting. Therefore, the aims of the present study are: (1) preparation of ACs from low-cost AM through chemical activating agents (H3PO4, KOH and HCl) and physical activation (thermal treatment under N2 atmosphere) for application in the removal of DCF (as representative PPCPs) from aqueous solutions, (2) comparative adsorption efficiency of ACs yields for removing DCF with commercial AC (CAC) and choosing the best synthesized AC with the highest DCF removal, (3) optimization of effective parameters, such as initial DCF concentration, dosage of the selected AC, pH and reaction time, (4) investigation of the equilibrium isotherms, kinetics, and reusability of the selected AC, (5) study of GP model and molecular simulation for determining the correlation between experimental data and algorithm results, and (6) discussion of the possible mechanism of DCF adsorption onto the selected AC.

Section snippets

Chemicals

DCF (C14H10Cl2NNaO2, purity ≥98%) was purchased from Sigma (Sigma–Aldrich Chemical Co. USA). AM wood was collected from Ilam Mountains (33.2958° N, 46.6705° E), Iran. Powdered DCF was dissolved in deionized water (DI-water) for the preparation of DCF synthetic stock solution. Analytical grade chemicals and CAC were purchased from Merck (Germany) and used without further purification throughout the experiments. Hydrochloric acid and sodium hydroxide solutions (0.1N each one) were used for

XRD and FT-IR characterization

The XRD patterns of the five synthesized ACs are shown in Fig. 3a for the investigation of the microcrystalline structure of the adsorbents. Strong and weak bands are observed in the XRD patterns at 2Ɵ = 26.5° and 44.13° corresponding to (002) and (101) of the crystal planes, respectively. The existence of graphite crystallites in each of the ACs can be clearly seen. The diffraction peaks of CAC, AC-700 °C and AC-500 °C are sharper than AC-H3PO4, AC-KOH, and AC-HCl (Girgis et al., 2007; Wang et

Conclusions

This work describes the preparation of ACs from AM as a low-cost bio-adsorbent and agro-industrial waste with chemical and physical activations. Three types of ACs were prepared through chemical activating agents with H3PO4, KOH, and HCl and two types of ACs with physical activations (thermal treatment under N2 atmosphere in 500 °C and 700 °C) to remove DCF as a representative PPCPs from aqueous solutions. After the activations, the physicochemical properties of the ACs were evaluated by SEM,

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgments

This research project was submitted to Ilam University of Medical Sciences, Ilam, Iran (Grant No.: 99R001/25). The authors would like to thank Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran.

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