Low-cost and high-wet-strength paper-based lignocellulosic adsorbents for the removal of heavy metal ions

Abstract

Paper-based lignocellulosic adsorbents with high wet strength, high adsorption capacity and good separation and recycling performance were prepared from polar chemimechanical pulp by simple papermaking and one-step dip coating. Green crosslinking agent of citric acid, which can react with the hydroxyl groups of cellulose under the catalysis of sodium hypophosphite, was used to increase the wet strength as well as the carboxyl content of the paper-based adsorbents. Both the wet strength and carboxyl content increase upon increasing the beating degree and the dosage of citric acid. The wet strengths reach 40∼50 % of their dry strengths and the carboxyl contents are tuned in the range of 0.07∼ 0.66 mmol/g. Pseudo-second-order equation was found to fit the kinetics data best, indicating the adsorption is chemisorption process. The good agreement of equilibrium data with Langmuir model confirm the monolayer coverage of Cu(II) and Pb(II) onto adsorbents. The maximum adsorption capacities of Cu(II) and Pb(II) are high up to 61.96 and 138.11 mg/g, respectively. Good regeneration stability and more than 90% of its initial adsorption capacity are achieved even after four adsorption-regeneration cycles, and the adsorbents are basically unaffected during the desorption process. In addition, the paper-based adsorbents with micron pores are able to effectively separate particles with the size larger than 50 μm. Combined with the filtration device, the paper-based adsorbents are easy to realize the continuous adsorption process and can be simply recycled from water without separation difficulty. The synthetic strategy of multifunctional paper-based adsorbents from polar chemimechanical pulp provides new ideas and methods for the full and high-value utilization of lignocellulose.