Walnut Shell Modified by Maleic Anhydride: Synthesis and Characterisation

A novel modified walnut shell (MWNS) was prepared by the reaction between maleic anhydride and raw walnut shell (WNS) in ethyl acetate. MWNSs with different carboxylic acid groups values (MWNS1 and MWNS2) are obtained and characterised by Fourier transform infrared (FTIR). The effects of reaction temperature, reaction time and maleic anhydride concentration on the carboxylic acid groups value of MWNS have been investigated. The results show that the carboxylic acid groups value of MWNS is positively correlated with the temperature of the reaction and the concentration of maleic anhydride, and it increases with the increase of reaction time until the equilibrium was reached. When the reaction temperature is 77°C, the reaction time is 180 min, and maleic anhydride concentration is 2.0 mol/L, the carboxylic acid groups value of MWNS is up to 2.80 mmol/g. The obtained product has a higher adsorption capacity for metal ions (e.g., Pb2+, Ni2+) and can be used in the wastewater treatment.