Simultaneous removal of phenoxy herbicides, 2-methyl-4-chlorophenoxyacetic acid and 2.4-dichlorophenoxyacetic acid from aqueous media by magnetized MgAl-LDH@Fe 3 O 4 composite: Application of partial least squares and Doehlert experimental design

Abstract

Phenoxy herbicides are families of chemicals that have been developed as commercially important herbicides, widely used in agriculture. Excessive consumption and increasing use of these pesticides to control pests of agricultural products and the continued entry of these pollutants into the environment due to their lack of biodegradability as well as their toxicity and carcinogenicity, has become one of the most challenging environmental problems today. Hormonal-like herbicides 2-Methyl-4-chlorophenoxyacetic acid (MCPA) and (2,4-Dichlorophenoxy)acetic acid (2.4-DCPA) are among the phenoxy herbicides that in mixed form, provide essential tools for modern farming for control of undesirable vegetation on grazing land, in crop, and non-crop lands. Natural clay minerals, especially layered double hydroxides (LDHs), are among the various materials that are used for pesticide adsorbents. LDHs have received special attention, mainly due to the large specific surface area associated with their layered structure, ease of synthesis, and the possibility of modifying their surfaces. In this work, a magnetized MgAl-LDH@Fe3O4 composite was prepared by co-precipitation method and used for the simultaneous removal of MCPA and 2.4-DCPA herbicides from aqueous solution by adsorption process. It should be noted that after the adsorption process, the magnetized MgAl-LDH@Fe3O4 nanocomposite can be separated and collected from the aqueous solution by an external magnet. Characterizations of the adsorbent were performed by various techniques, including Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and thermal analysis. The partial least square method was used to determine the concentration of each individual herbicide and in the mixture of them in the aqueous solution. Next, simultaneous adsorption of MCPA and 2.4-DCPA by LDH was optimized using Doehlert experimental design. The optimum conditions for adsorption were obtained as, adsorbent dosage 40.20 mg L−1, pH 6.8 and initial concentration 28.35 mg L−1. The equilibrium adsorption data were obtained using the Langmuir, Freundlich, Temkin and Dubinin-Radush-Kevich isotherms models. The results indicated that the experimental adsorption data were controlled by Freundlich models. The maximum adsorption capacity of MCPA and 2.4-DCPA herbicides on the MgAl-LDH@Fe3O4 adsorbent was obtained as, 134.50 and 131.30 mg g-1, respectively. The kinetic data of adsorption process were evaluated as pseudo-first order, pseudo-second order and intraparticle diffusion; the obtained results were well described by the pseudo-second-order model. Adsorption thermodynamic studies were also investigated. The positive ΔH◦ and negative values of ΔG° at various indicated that adsorption process is endothermic and spontaneous in nature respectively. The positive ΔS° value indicates the increase of disorder at the solid-solution interface during adsorption.

Activated Carbon Fabricated from Biomass for Adsorption/Bio-Adsorption of 2,4-D and MCPA: Kinetics, Isotherms, and Artificial Neural Network Modeling

“…The increase in pesticide application is beneficial in controlling weeds, killing insects, staving off fungi, preventing hazardous crop diseases, improving crop yields, and preserving the financial sustainability of agriculture [3]. Although pesticides work on their intended targets, they have harmful impacts on the wider ecosystem [4]. The increase in pesticide application raises the possibility of human exposure, which could lead to health problems including respiratory, neurological, and cancerous effects [5].…”

“…Herbicides are considered the most common pesticides, representing approximately 80% of total pesticide use [9]. They are chemicals that are used to prevent unwanted plant growth, including the growth of invasive species and weeds in homes or farms [4]. Over the years, the consumption of crop products protected by pesticides has increased significantly [10].…”

“…They are categorized as human carcinogens (Group 2B) by the International Agency for Research on Cancer (IARC) and are identified as relatively toxic by the World Health Organization (WHO) [13]. Due to their increasing use and their serious effects on human health and the environment, their effective removal from the environment is essential and important [4].…”

“…The removal of hazardous compounds from polluted water using clean and feasible technologies represents an important issue in research on water treatment [14]. Several methods can be used for herbicide removal from aqueous solutions, including biodegradation, photocatalytic degradation, adsorption, and electrochemical methods [4,[15][16][17]. Adsorption is considered an attractive option for the depletion of phenoxy acetic herbicides because it is a simple, eco-friendly, and economical method [14].…”

“…Adsorption is considered an attractive option for the depletion of phenoxy acetic herbicides because it is a simple, eco-friendly, and economical method [14]. The adsorption process is a surface phenomenon which depends on various factors such as the specific surface area and porosity of the adsorbent, the interaction types, and the number of active sites for adsorption [4]. Moreover, adsorption has advantages over other techniques for the treatment and reuse of polluted water due to its simplicity and flexibility in design, ease of operation, low initial cost, and insensitivity to toxic pollutants, and because it does not cause the formation of harmful materials [18].…”