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.
The imperative need for efficient and selective adsorption of Ni(II) and Mo(VI) is crucial for resource utilization and environmental protection. However, this process faces a challenge due to the scarcity of adsorbents that can adeptly adsorb both metal ions simultaneously. To address this, this study introduces a novel composite adsorbent material, denoted as BECZN, achieved through composite cross-linking of waste orange peel biochar with in situ aminated cobalt/zinc-zeolitic imidazolate frameworks (Co/Zn-ZIF-NH 2 ). The incorporation of Co/Zn-ZIF-NH 2 enhances the availability of active groups within BECZN. The aerogel structure of BECZN prevents ZIF material collapse and agglomeration, thereby improving active site exposure. BECZN exhibits notable adsorption capacities, reaching 151.84 mg/g for Ni(II) at pH = 7 and 842.54 mg/g for Mo(VI) at pH = 3. Further investigations indicated that the adsorption of Ni(II) and Mo(VI) obeys the Langmuir isotherm model, while exhibiting pseudo-second-order kinetics and intraparticle diffusion characteristics. Notably, BECZN selectively adsorbs Ni(II) and Mo(VI) efficiently under acidic and neutral conditions, respectively. It can maintain high capacity under the interference of various cations and anions. Meanwhile, this excellent selective adsorption of Ni(II) and Mo(VI) by Co/Zn-ZIF-NH 2 is revealed at the atomic level using density functional theory (DFT) calculations. This study offers a theoretical basis and experimental reference for the design and synthesis of ZIF and biomass-based composite adsorbents.
Wei-Ye Zhang,Si-Qing Ye,Xin-Tao Yang,Bao-Shi Zhu,Wei-Li Li,Hong-Xing He,Xiu-Jun Deng
A novel magnetic graphene oxide-based surface imprinted polymer (Fe3O4@GO@IIP) was synthesized using the surface imprinting technology to selectively adsorb Ni(II) from aqueous solution. The imprinted polymer was characterized by FT-IR, XRD, SEM, TEM, VSM, TGA and XPS. The results showed that the sorbent exhibited good thermal and mechanical stability, and can be quickly separated from the solution by applying an external magnetic field. The adsorption performance indicated that the prepared imprinted material had a short adsorption equilibrium time (16 min) and a high adsorption capacity (35.31 mg g−1) for Ni(II) at an optimal pH of 6.0. The selectivity coefficients of the imprinted material were 17.57, 16.27, 10.86, 14.27 and 17.65 for Ni(II)/Co(II), Ni(II)/Cu(II), Ni(II)/Pb(II) Ni(II)/Cd(II), and Ni(II)/Zn(II), respectively. Reusability studies indicated that the adsorption capacity of the prepared polymer did not decrease significantly after repeated use ten times. Moreover, the adsorption mechanism of Ni(II) by the imprinted polymer was also studied. The adsorption process was spontaneous and endothermic, and followed the pseudo-secondary kinetic model and the Langmuir model. The results of the Scatchard model indicated the presence of two Ni(II) strong binding sites on Fe3O4@GO@IIP, where the single-bond O atom of the sulfonic acid group and the N atom of the –N–CO group in AMPS played a dominant role in Ni(II) adsorption, as conformed by both DFT calculations and XPS.
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