Abiotic humification of phenolic pollutant to form a hybrid adsorbent for toxic metals by LDH based composite

Abstract

As a novel method for recycling phenolic compound from wastewater, a hybrid adsorbent has been synthesized through chemical catalytic humification. The results show that the heterogeneous catalyst for humification contains a lamellar Zn2Al-NO3 layered double hydroxide (LDH) matrix in which nanostructural Fe3O4 is embedded. Based on this catalyst, the catechol, a typical phenolic compound can be effectively transformed into humic-like substance (HLS) and almost all of them are in-situ attached on the LDH matrix to form a hybrid adsorbent. The conversion ratio of humification can reach up to 65% and loading amount of HLS can reach around 668 mg/g solid. Both the substrate concentration and pH have little effect on the properties of HLS whose molecule weight are around 1000 g/mol and total contents of carboxyl and phenolic hydroxyl are approximately 8.5 mmol/g. The hybrid adsorbent whose surface and part of interlayer are both loaded with HLS presents a good performance on adsorption of toxic metals. The adsorption isotherms of Pb2+, Cu2+, Ni2+ and Cd2+ fit with monolayer adsorption models and the adsorption capacity can reach up to 1.34, 1.31, 0.98 and 0.50 mmol/g respectively with an adsorption preference order of Pb2+ > Cu2+ > Ni2+ > Cd2+.