Microwave-Assisted Conversion of Walnut Shells into Carbonaceous Adsorbents-Toward Efficient Removal of Organic Dyes, Polymers, and Surfactants from Aqueous Media.

Abstract

A new set of carbonaceous adsorbents is synthesized via direct physical or chemical activation of walnut shells using microwave-assisted heating. Their ability to remove various classes of organic contaminants-including dyes, surfactants, and polymers-from aqueous media has been comprehensively investigated. In the activation process, CO₂ and H₃PO₄ are used as activating agents under microwave-induced thermal treatment. The obtained biocarbons are systematically tested for their chemical composition, surface characteristics, textural features, and electrokinetic behavior. Variations in the activation method resulted in distinct differences among the produced biocarbons with respect to their elemental composition, surface acidity-basicity, specific surface area development, and pore size distribution. Adsorption tests show that the efficiency of organic pollutants removal from aqueous media depends significantly on the type of adsorbent prepared and the chemical properties of the adsorbate applied. The sample obtained via microwave-assisted chemical activation proved to be very effective in terms of all the tested organic pollutants' adsorption. The maximum sorption capacity toward poly(ethylene glycol), methylene blue, Triton X-100 and poly(acrylic acid) reached the levels of 722.6, 339.7, 63.4 and 49.9 mg g^-1, respectively.