Guidelines to Study the Adsorption of Pesticides onto Clay Minerals Aiming at a Straightforward Evaluation of Their Removal Performance

Abstract

Natural and modified clay minerals have been extensively used for the adsorption/desorption of organic substances, especially pesticides, from waters and wastewater, aiming at pollution control and more efficient use of the herbicides through controlled release. While natural clay minerals efficiently remove organic cations such as paraquat and diquat, the adsorption of anionic or neutral species demands surface chemical modification with, for instance, quaternary ammonium salts containing long alkyl chains. Basic pesticides, on the other hand, are better absorbed in clay minerals modified with polycations. Kinetic studies and adsorption/desorption isotherms provide the parameters needed to evaluate the clay mineral’s adsorptive performance towards the pollutant target. However, the direct comparison of these parameters is complicated because the experimental conditions, the analytical techniques, the kinetic and isotherm models, and the numerical fitting method differ among the various studies. The free-energy-related Langmuir constant depends on the degree of site occupation; that is, it depends on the concentration window used to construct the adsorption isotherm and, consequently, on the analytical technique used to quantify the free concentrations. This paper reviews pesticides’ adsorption on natural and modified clay minerals and proposes guidelines for designing batch adsorption/desorption studies to obtain easily comparable and meaningful adsorption parameters. Articles should clearly describe the experimental conditions such as temperature, contact time, total concentration window, the solution to adsorbent ratio, the analytical technique, and its detection and quantification limits, besides the fitting models. Research should also evaluate the competitive effects of humic substances, colloidal inorganic particles, and ionic strength to emulate real-world adsorption experiments.

Soil Organic Matter Composition and pH as Factors Affecting Retention of Carbaryl, Carbofuran and Metolachlor in Soil

“…Based on the constants obtained from the Freundlich approximation of the experimental data, a thermodynamic parameter determining the spontaneity of the adsorbate–adsorbent interactions, namely, standard Gibb’s free energy (ΔG°), can be calculated: ΔG°= −RT ln K c , where T is the temperature (K), R is the gas constant (8.314 J mol −1 K −1 ) and K c is the standard equilibrium constant (dimensionless), which can be obtained by K f conversion using the proposed equation [ 54 , 55 , 56 ]: where is the density of pure water (1.0 g/mL). For other experimental equilibrium constants K L , K f and K D , the strategies for converting them into K c were adapted [ 101 , 102 , 103 , 104 ] and must not be omitted when elaborating ΔG° calculations.…”

“…Freundlich K f parameters, which revealed the highest variation when comparing both studied soils, were used for the calculation of the standard Gibb's free energy change (∆G • ) of the tested pesticides (Table 2). Prior to ∆G • calculations, K f parameters were converted to the dimensionless standard equilibrium constants using the appropriate equations, as suggested in the literature [54][55][56]. The negative ∆G • values obtained for all studied pesticides on soils L and C point to the spontaneous character of the sorption.…”

The efficacy of Acorus calamus L. crude extract formulated in bentonite nanoparticles against Crocidolomia pavonana (Lepidoptera:Pyralidae)

“…It is well known that bentonite's porous nature and ionic charge allow it to absorb chemicals. Bentonite, or smectites, can absorb several naturally occurring organic substances, such as which have pesticidal properties (Masini & Abate, 2021)…”

“…A.calamus extract was released by Bentonite more slowly than by other Na bentonite adsorbents. The physiochemical characteristics of bentonite, such as its chemical composition, selectivity, porosity, cation exchange capacity, and surface area, increased the material's ability to adsorb substances (Masini & Abate, 2021)…”

Application of Viscose-Based Porous Carbon Fibers in Food Processing—Malathion and Chlorpyrifos Removal

“…In terms of pesticide remediation, adsorption is a process of removing pesticide molecules from various samples by attaching them to an adsorbent material [ 20 ]. The adsorbent materials most commonly used for pesticide removal include activated carbon materials [ 20 , 21 ], mesoporous monetite [ 22 ], porous metal–organic frameworks [ 23 ], mineral surfaces [ 24 ], organohydrotalcite [ 25 ], zeolites [ 26 ], materials from the graphene family [ 27 ], metal nanoparticles [ 28 ], and others. Activated carbon materials have an excellent potential for removing pesticides during food processing.…”