Improvement of heavy metal separation performance by positively charged small-sized graphene oxide membrane

ABSTRACT

Multilayered graphene oxide (GO) membranes are promising to be widely applied to purify water effectively. However, the performance of most membranes prepared at present is not ideal, which may be related to the pore diameter of the substrate (determining the real loading amount of GO) and the size of the GO nanosheets (determining the number of channels on the unit area), which has not been fully studied. In this study, a rotating dip-coating reactor were firstly developed to ensure the uniform deposition of reactants on the surface of the substrate. Then, the preparation method for the membrane was improved. Microfiltration membranes were used as the supporting substrate, polydopamine was deposited as the adhesive layer, ethylenediamine was used to restrict the layer spacing to strengthen the size exclusion effect, and positively charged polyethyleneimine (PEI) was used to strengthen the Donnan effect. Finally, the effects of the pore size of the substrate and the size of the GO nanosheets on the membrane performance were investigated. Compared with the substrates with a pore size of 0.22 μm in most literatures, substrates of 0.1 μm can retain more small GO (SGO) nanosheets, thereby improving the performance. The performance of the SGO membrane was much better than that of the large-sized GO membrane. With a water permeability of no less than 7.9 L/(m²·h·bar), rejection rates for Pb²⁺ and Cd²⁺ of the SGO membrane could reach more than 97%. These findings are constructive to separate heavy metals from water effectively.

GRAPHICAL ABSTRACT

KEYWORDS:

• Graphene oxide
• nanofiltration
• ethylenediamine
• polyethyleneimine
• heavy metal

Disclosure statement

No potential conflict of interest was reported by the author(s) .

Supporting information

The detailed information on the RDCR (Figure S1), schema of the reaction between GO and EDA (Figure S3), schema of the effect of the real concentration at the dead-end filtration (Figure S7), and some supplementary experiment data are shown in the supporting information.

Data availability statement

The data that support the findings of this study are available from the corresponding author, YM Tian, upon reasonable request.

Additional information

Funding

This work was supported by Talent Introduction Project of Hebei Agricultural University [grant number YJ201921]; Basic Scientific Research Business Expenses Program of Hebei Provincial Colleges and Universities [grant number KY2022022].