Chitosan-Bentonite composite adsorption of herbicide glyphosate from water solution

This study highlights the use of Chitosan-Bentonite composites as an eco-friendly and cost-effective alternative to traditional adsorbents, which are often expensive and less accessible. Chitosan-Bentonite composite (CBC) samples with various chitosan/bentonite ratios (2/1, 2/2, 2/4, 2/8, and 2/10) were developed to remove glyphosate, one of the most widely used herbicides globally, from contaminated aqueous solutions. The CBC samples were characterized using complementary techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses were performed. FTIR revealed OH vibrations at 3630 cm⁻¹ and -NH₂ and -NH₃⁺ at 1517 cm⁻¹, indicating electrostatic interactions between chitosan and bentonite. The NH₂ band at 1514 cm⁻¹ was absent in CBC 2/8 and CBC 2/10 due to low chitosan content. XRD analysis showed that the interaction between chitosan and bentonite significantly altered crystalline characteristics, reducing bentonite crystallinity and shifting reflection peaks, indicating effective chitosan intercalation. SEM images showed a non-porous lamellar structure for chitosan and reduced porosity in the composites, indicating exfoliation after interaction. The adsorption study revealed that the mass ratio influenced glyphosate adsorption capacity, with CBC 2/8 showing the best performance. Adsorption parameter analysis showed that the 2/8 Chitosan-Bentonite ratio, with an equilibrium adsorption capacity of 1.18 mg/g, was the most effective for glyphosate removal. Optimal conditions were found at pH 3.76, using 50 mg of CBC adsorbent, an initial glyphosate concentration of 10 mg/L, and a contact time of 8 h. Adsorption on the CBC 2/8 composite increased with concentration, reaching 2.8 mg/g at equilibrium (C_e = 10.98 mg/L). The S-type isotherm suggested that glyphosate is monofunctional with moderate intermolecular interactions. The Langmuir model indicated a maximum adsorption capacity (q_m) of 133 mg/g with moderate affinity (K_L = 0.0018 L/mg). The Freundlich model, with an adsorption intensity coefficient (n) of 0.912, showed favorable adsorption, while low χ² (0.450) and SSE (0.330) values indicated a slightly better fit to the data. Compared to costly synthetic materials, the CBC composite provides an economical and non-toxic option for wastewater decontamination, offering moderate but promising results for glyphosate removal. This study highlights the potential of chitosan-based composites to provide viable and sustainable solutions for managing agricultural pollutants.