Preparation of a nano-MnO2 surface-modified reduced graphene oxide/PVDF flat sheet membrane for adsorptive removal of aqueous Ni(ii)

Abstract

In this paper, nanoscale MnO₂ particles were attached onto the surface of a PVDF flat sheet membrane, step by step, first through dispersion of graphene oxide (GO) in the PVDF membrane, then reduction of immobilized GO by hydroiodic acid and further micro-wave assisted oxidation of RGO (reduced graphene oxide) by KMnO₄ and formation of MnO₂ on GO. The SEM observation revealed an asymmetric structure with a finger-like transition layer dominating the membrane of PVDF/MnO₂. The uniform distribution of MnO₂ on the membrane is revealed by EDX and XPS analysis. The attached MnO₂ endowed the membrane with high adsorption capacity for aqueous Ni(II). The adsorption was spontaneous and endothermic, fitting a pseudo-first-order kinetic model and Freundlich isotherm model well. The pure water flux and stable permeation flux of the PVDF/MnO₂ membrane reached 31.2 L m⁻² h⁻¹ and 9.0 L m⁻² h⁻¹ under 0.1 MPa, which were 2.3 and 2.6 times those of the PVDF membrane. The analysis of the fouling resistance and flux recovery ratio indicated that the PVDF/MnO₂ membrane had better antifouling properties than the PVDF membrane, attributed to the changes of membrane morphologies and surface hydrophilicity. The PVDF/MnO₂ membrane had a high removal ratio (≥87.4%) of Ni²⁺ in dynamic adsorption. Meanwhile the Ni(II) adsorbed membrane could be easily regenerated by a 0.1 M HNO₃ solution.