Research paperThe modification of rectorite with carbon layers and trisodium trimetaphosphate for the removal of Pb2Â +

•Carbon layer with oxygen containing groups formed on REC layers.•RECC reacted with STMP to introduce phosphate ester groups.•The adsorption process of Pb2 + was investigated.•Phosphate ester groups contributed to the Pb2 + advantageous selectivity and trace Pb2 + removal.

At the presence of rectorite (Rec), starch was treated with hydrothermal carbonization to fabricate carbon layer with many oxygen containing groups on the surface of Rec layer, which were further reacted with trisodium trimetaphosphate (STMP) to introduce phosphate ester groups on Rec. The obtained RecCPN were used to remove heavy metal ions from aqueous solution. The adsorption kinetics and isotherms could be described with the pseudo- second-order model and the Langmuir model. The maximum monolayer adsorption capacities could reach 258.40 mg/g for RecCPN at pH 5 and 303 K, in which the Pb2 + adsorption processes was spontaneous. The positive values of ΔH0 indicated that the interaction of Pb2 + with phosphate ester groups was endothermic. RecCPN still exhibited the good adsorption capacity in the adsorption-desorption cycles. In addition, RecCPN showed advantageous selectivity towards Pb2 + over other metal ions (Cu2 +, Ni2 +, Co2 + and Cd2 +) and still removed above 90% Pb2 + at the initial trace Pb2 + concentration (0.5 mg/L).