Periodate and TEMPO sequential oxidations of cellulose fabrics: Exploration of a multiple and synergistic adsorption mechanism

Abstract

Oxidized cellulose fabrics were fabricated by means of periodate and TEMPO sequential two-step oxidations and were employed as a highly efficient filter for dye adsorption with a multiple and synergistic adsorption mechanism. The mechanical properties, yields, and molecular weights of the oxidized cellulose fabrics depend on the content balance between carboxylate and aldehyde groups distributed either in or on the fiber surface where the oxidized cellulose fabrics with high adsorption sites (e.g., carboxylate and aldehyde groups) and high tensile strength were optimized through TEMPO oxidation that was first enhanced by periodate oxidation. The oxidized cellulose fabrics with both carboxylate and aldehyde groups exhibited remarkable adsorption capability, specifically in the adsorption of amino-containing molecules such as chrysoidine dye and hydrazine. A multiple and synergistic adsorption mechanism based on chemical reaction (e.g., Schiff base reaction between the aldehyde and amino groups) and electrostatic interaction (e.g., carboxyl and amino) was proposed and verified by adsorption kinetics, isotherms, thermodynamics as well as dynamic adsorption, while the maximum adsorption capacities of the oxidized cellulose fabrics against chrysoidine and hydrazine were as high as 118.34 mg/g and 92.76 mg/g, respectively, due to the synergistic adsorption of both carboxylate and aldehyde groups. A spiral wound filtration cartridge (made by 3.6 g of oxidized cellulose fabrics) was fabricated and the removal capability against hydrazine and chrysoidine was investigated. It was impressive that when 18.3 L of hydrazine and 28.8 L of chrysoidine solutions with 3.0 mg/L of concentration were purified separately, the rejection ratios remained as high as 98% and 94%, respectively, with a pressure drop as low as 0.3 kPa. This indicated that the oxidized cellulose fabrics could be employed as highly efficient filters for industrial wastewater treatment through a multiple and synergistic adsorption mechanism.