Method for sulfonating sawdust to form modified sorbent

A method of sulfonating sawdust to form a modified sawdust sorbent comprising:

• mixing the sawdust with sulfuric acid to form a sulfonating mixture,
• heating the sulfonating mixture at 100 to 200° C. to form a mixture comprising a liquid and a sulfonated sawdust,
• filtering and/or decanting the mixture to isolate the sulfonated sawdust,
• washing and drying the sulfonated sawdust at 50 to 150° C. to form a dried sawdust,
• treating the dried sawdust with a hydrogen peroxide solution to form a peroxide-treated sawdust,
• washing and drying the peroxide-treated sawdust at 50 to 150° C. to form a sulfonated and oxidized sawdust, and
• milling and sieving the sulfonated and oxidized sawdust to form the modified sawdust sorbent,
• wherein the modified sawdust sorbent has a dye adsorption capacity of 20 to 25 mg of dye per g of sorbent at 25 to 45° C.