Divalent heavy metal ions removal from contaminated water using positively charged membrane prepared from a new carbon nanomaterial and HPEI

In this work, for the first time a new carbon nanomaterial (CNM) with was synthesized from charcoal and characterized using SEM, TEM, EDX, CHNS, FTIR, XRD and Raman analysis. The obtained characterization results showed that the synthesized CNM has two-dimentional morphology (layer structure with nanometeric thickness), high oxygen and nitrogen contents (with carbon to oxygen atomic ratio of about 2.11) and interlayer spacing of about 0.8 nm. The synthesized CNM was used to prepare a positively charged membrane via vacuum-filtration method for removal of divalent heavy metal ions from contaminated water. Hyperbranched polyethyleneimine (HPEI) was used as crosslinking agent. Structure and properties of the prepared membranes without and with HPEI crosslinking were characterized using SEM and WCA analysis. The WCA of the prepared membranes without and with HPEI crosslinking is about 51 degrees and 60 degrees, respectively. Performance and separation mechanism of the prepared membranes were investigated. The prepared HPEI crosslinked membrane with positively charged surface showed superior performance for removal of divalent heavy metal ions from aqueous solutions with rejection sequence of R (Zn2+: 95.65%) > R (Cd2+: 94.10%) > R (Cu2+: 92.56%) > R (Ni2+: 92.34%) > R (Pb2+: 90.51%). The obtained results showed that performance of the prepared HPEI crosslinked membrane is based on steric hindrance and Donnan electrostatic exclusion. Performance of the prepared crosslinked membrane during four cycles of regeneration was also evaluated. The prepared membrane with high structural stability and durability can be employed repeatedly for divalent heavy metal ions removal from contaminated water.