Abstract
In this study, orthophosphoric acid-modified activated char was prepared from Eucalyptus camaldulensis bark (EBAC), and used for removing traces of [N-(phosphonomethyl)glycine] (glyphosate) herbicide from aqueous solution. The adsorption capacity was characterized by zero-point-charge pH, surface analysis, and Fourier transform infrared spectroscopy. Batch mode experiments were conducted to observe the effects of selected variables, namely dose, contact time, pH, temperature, and initial concentration, on adsorption capacity. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models were generated to describe the mechanisms involved in the multilayer adsorption process. The results show that high temperature enhanced the adsorption capacity of EBAC, with a temperature of 373 K yielding adsorption capacity (qmax) and Freundlich parameter (KF) of 66.76 mg g−1 and 9.64 (mg g−1) (L mg−1)−n, respectively. The thermodynamics study revealed entropy and enthalpy of −5281.3 J mol−1 and −20.416 J mol−1, respectively. Finally, glyphosate adsorption was optimized by the Box–Behnken model, and optimal conditions were recorded as initial concentration of 20.28 mg L−1, pH 10.18, adsorbent dose of 199.92 mg/50 mL, temperature of 303.23 K, and contact time of 78.42 min, with removal efficiency of 98%. Therefore, it can be suggested that EBAC could be used as an efficient, low-cost adsorbent for removal of glyphosate from aqueous solutions.
Highlights
Contamination of agricultural fields by the release of toxic chemicals remains a significant problem in the agricultural sector (Abbasi et al 2014)
The peak at 1729.11 cm−1 is attributed to the presence of a C–O–P linkage, while peaks at 1178.10 cm−1, 1027.78 cm−1, and 1292.40 cm−1 are attributed to organophosphorus (P=O stretching), C–O stretching, and C–NH2 stretching vibrations before and after glyphosate loading of Eucalyptus camaldulensis bark‐activated char (EBAC) (Coates 2000; Smidt et al 2011)
The results clearly show that glyphosate adsorption gradually increased with increasing temperature, with maximum adsorption of 97.84% recorded at 373 K
Summary
Contamination of agricultural fields by the release of toxic chemicals remains a significant problem in the agricultural sector (Abbasi et al 2014). The extensive use of chemical fertilizers can reduce soil fertility and microbial diversity (Trivedi et al 2016; Ermakova et al 2010). Various studies have reported a tremendous impact of different pesticides, including glyphosate, napropamide, metam sodium, methyl bromide, and copper, in terms of changes to soil microbial community composition and ecosystems and reduced crop tolerance (Lancaster et al 2010; Cycon et al 2013; Locke et al 2008; Berg et al 2012; Cosgrove et al 2019). Glyphosate (C3H8NO5P) is an aminophosphonic analog of the natural amino acid glycine and, like all amino acids, exists in different ionic states depending on pH, showing zwitterionic form with a phosphonate proton by delocalization of the amino nitrogen (Borggaard and Gimsing 2008).
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