Mitigating Water Pollution Using a Sustainable Biobased Low-Cost Adsorbent Derived From Mustard Straw

The present work is focussed on treating dye-laden polluted water by using a mustard straw-based activated carbon prepared using ZnCl₂ and H₃PO₄ activation methods. The activation conditions based on the parameters reported in the literature are taken as follows: 700 °C activation temperature, impregnation ratio 2.0, and heating time 2 h. The textural and surface properties of mustard stalk activated carbon (MSAC) were studied by using SEM, nitrogen adsorption, and FT-IR, whereas its adsorption capacity was obtained using the methylene blue (MB) adsorption method. Activation of ZnCl₂ and H₃PO₄ resulted in a BET surface area of 402 and 496 m²/g, respectively. The average pore diameter of the MSAC was found to be 2.13 and 2.59 nm for ZnCl₂ and H₃PO₄ activation respectively. The Langmuir and Freundlich models were applied to evaluate the equilibrium parameters of MB adsorption. The monolayer adsorption capacity of MSAC by ZnCl₂ and H₃PO₄ for MB removal from the Langmuir model were 122.25 and 213.21 mg/g respectively. Activation with H₃PO₄ was found to be more effective in modifying the structure of the mustard straw when compared with ZnCl₂ and also it resulted in a higher adsorption capacity of MB. The present work highlights that the MSAC produced using H₃PO₄ activation is a low-cost bio-based adsorbent using abundant agricultural by-product namely mustard straw, and this adsorbent can be used in numerous industrially important applications.