Adsorption of Phenoxyacetic Herbicides from Water on Carbonaceous and Non-Carbonaceous Adsorbents

Abstract

The increasing consumption of phenoxyacetic acid-derived herbicides is becoming a major public health and environmental concern, posing a serious challenge to existing conventional water treatment systems. Among the various physicochemical and biological purification processes, adsorption is considered one of the most efficient and popular techniques due to its high removal efficiency, ease of operation, and cost effectiveness. This review article provides extensive literature information on the adsorption of phenoxyacetic herbicides by various adsorbents. The purpose of this article is to organize the scattered information on the currently used adsorbents for herbicide removal from the water, such as activated carbons, carbon and silica adsorbents, metal oxides, and numerous natural and industrial waste materials known as low-cost adsorbents. The adsorption capacity of these adsorbents was compared for the two most popular phenoxyacetic herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA). The application of various kinetic models and adsorption isotherms in describing the removal of these herbicides by the adsorbents was also presented and discussed. At the beginning of this review paper, the most important information on phenoxyacetic herbicides has been collected, including their classification, physicochemical properties, and occurrence in the environment.

Waste-Based Adsorbents for the Removal of Phenoxyacetic Herbicides from Water: A Comprehensive Review

“…In general, the adsorption capacities of the activated carbons were very high when compared with other waste-based adsorbents, i.e., unmodified/modified materials, ashes, and biochars. Additionally, their adsorption capacities were not inferior to commercial activated carbons derived from fossil coals, for which the values of the parameter q m towards 2,4-D and MCPA were in the range of 8.11-555.5 mg g −1 and 105.3-599.9 mg g −1 , respectively [33]. A significant share of micropores in the pores' structure caused the overall adsorption rate to be pore volume diffusion-dependent.…”

“…Among the above-mentioned techniques for water treatment, adsorption seems to be the most suitable because it is characterized by low cost and low energy consumption; moreover, it is highly selective and effective. There are various groups of adsorbents, i.e., (i) carbonaceous materials (commercial activated carbons, activated carbons from solid waste, carbon blacks, carbon nanotubes, graphene, reduced graphene oxide, and ordered mesoporous carbons); (ii) inorganic materials (silica gels, activated alumina, zeolites, molecular sieves, and metal oxides); (iii) advanced materials (inorganic-organic composites, doped materials); and (iv) low-cost materials (agricultural and household waste-based materials, natural materials, biosorbents, industrial by-products) [33,34]. Due to the low cost of production for most of them, and the renewability and availability of the raw material, adsorbents based on agricultural and household waste are considered to be one of the most promising types.…”

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

“…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]. An estimated 2.7 million tons were used annually in agriculture in 2020, with approximately 52% of that amount being attributed to herbicides, 23% being attributed to fungicides, 18% being attributed to insecticides, and 7% being attributed to other pesticides [7].…”

“…The use of agricultural biomass wastes as ecological, cheap, and renewable sources can reduce greenhouse gas emissions while achieving sustainability in AC production [24]. The preparation of AC from biomass waste is considered necessary as it offers various environmental, economic, and sustainability benefits, such as waste valorization, resource efficiency, carbon sequestration, circular economy practices, reduced dependency on fossil fuels, environmental impact reduction, water and air purification, green chemistry and sustainable industry, diversification of feedstock sources, community and rural development, and maximization of benefits from agricultural residues [10]. Therefore, AC obtained from sustainable biomass resources has the advantages of low cost and eco-friendliness compared to that obtained from non-renewable sources such as coal.…”

“…Moreover, the chemical speciation of both the adsorbate and the adsorbent is influenced by the solution pH. Changes in the solution pH can alter the forms of the adsorbate present in the solution, affecting their adsorption behavior [10]. Furthermore, ionic strength is a critical parameter in the adsorption processes, particularly in aqueous solutions [34].…”