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Methylene blue is a cationic dye used for dyeing cotton, wool, and silk. This dye can cause impacts when reaching water resources due to the reduction of sunlight infiltration, besides the health problems if ingested. Therefore, the complete removal of this contaminant in industrial effluents is indispensable. Currently, soybean hulls residues are used in animal feed supplementation; however, since soybean oil production is large, expressive quantities is discarded in landfills. Thus, the present study aim is to evaluate the adsorption capacity of methylene blue onto soybean hulls as an alternative use of this agroindustrial residue. The material was characterized through morphological and chemical analysis which showed porosity, heterogeneity, and functional groups that favor the adsorption. Due to the mainly negative charge of the surface, the pH did not affect the cationic dye uptake, enabling a wide pH range. After the adsorption studies, the best experimental conditions were at temperatures of 298 K, mass of 0.025 g, and contact time of 180 min, resulting in the maximum adsorption capacity of 169.90 mg g−1. When compared with other low‐cost biosorbent and activated carbons, it can be perceived a potential applicability of soybean hulls in wastewater treatment as an alternative use.

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Considering the need for new technologies for the removal of pesticides from the aqueous environment, the Moringa oleifera seed husks (h-MO) were investigated for the diuron adsorption from contaminated water at different temperatures and solute concentrations. The biosorbent used in this study was characterized by chemical, structural and textural analyses. The best experimental condition for the biosorption was determined by evaluating the mass of the biosorbent and the pH solution. We found a good adsorption capacity for the herbicide where the maximum adsorption capacity was 14.74 mg/g at pH 5 and 45°C. In addition, the adsorption process of diuron by the h-MO occurred spontaneously, in which, ΔG° values increased as the temperature increased, meaning that the process tends to a more energetically favourable process at higher temperatures. Both Langmuir and Sips isotherm models presented satisfactory adjustment at all temperatures and the pseudo-second-order model presented the best fit for the experimental results. The application of the intra-particle diffusion model showed that the adsorption process started instantaneously through the boundary layer of the adsorbent and that the pore diffusion step was a limiting step in the process. Finally, the capacity of the h-MO was compared with other adsorbents that had been used for diuron removal from contaminated where it was found that the adsorption capacity of the h-MO is much higher than other natural adsorbents.