Functionalized 2D Nano Materials for Selective Separation and Related Interfacial Interaction Mechanisms

• Author / Creator

  Hu,Wenjihao

• The functionalized 2D nanomaterials have attracted increasing attention due to their promising selective interfacial separation performance, including oil-water separation, desalination, ion extraction, wastewater treatment and ionic sieving. To help understand the separation performance or transport phenomena within the nanopores or channels formed by the functionalized 2D materials, the surface properties and interaction mechanisms between transport species and these nanomaterials have been investigated. In this study, the 2D materials, such as graphene oxide (GO), molybdenum disulfide (MoS2) and Nb2CTx MXene, were modified and assembled as the composite or crosslinked materials for selective separation. Some chemical or physical methods such as hydrothermal synthesis, centrifugation, ultrasonication, vacuum filtration and spin coating were used to exfoliate the 2D materials and prepare surface-modified 2D nanosheets.
  The separation performance of the above-mentioned materials was evaluated by using several complementary experimental techniques. The atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscope (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), zeta potential and size distribution, contact angle measurement and Fourier-transform infrared spectroscopy (FTIR) were applied to characterize the synthesized functionalized 2D materials in terms of surface structure, heterogeneity, electrochemical properties and hydrophobicity. The ion rejection and permeation properties were studied by using inductively coupled plasma mass spectrometry (ICP-MS), while dye concentration was detected by using ultraviolet-visible (UV-Vis) spectroscopy. The transport behavior of ion selective separation within the functionalized 2D nanosheet channels is highly dependent on the interaction between transported ions and surface functional groups of the 2D nanosheets.
  In this work, a series of 2D nanosheet materials such as graphene oxide (GO), molybdenum disulfide (MoS2) and Nb2CTx MXene incorporated with guest materials have been synthesized as functionalized materials (e.g., membrane, and hydrogel) in order to achieve highly selective separation performance. The resulted LA/F/rGO hydrogel owns selective permeation of oil or water flow depending on the pre-soaking condition. The intriguing bouncing performance of the LA/F/rGO hydrogel suggests that it has signficant potential application as new oil fence material.
  Another surface modified 2D-based material TAMoS2 (tannic acid-modified, water-stabilized MoS2 (MoSe2) nanosheets) has been successfully synthesized through a two-stage, L-ascorbic acid (LA)-assisted exfoliation method with a high yield of 90% ± 5%. The as-prepared vacuum-filtered membranes from the resultant TAMoS2 nanosheets shows fast water flux around 32 L m-2 h-1 (LMH) and >97% rejection of various cations under osmosis pressure static diffusion mode. In addition, under vacuum-driven filtration conditions, such a hybrid membrane demonstrates ultrafast water flux of 15,000 ± 100 L/(m²h.bar) and 99.87 ± 0.1% rejection of various model organic dyes, e.g., basic blue, toluidine blue and rhodamine 6g. The superior performance of TA-modified MoS2 membranes demonstrates their significant potential for practical applications in water desalination, purification and ion/dye separation.
  Furthermore, sodium alginate modified Nb2CTx Mxene (NbSA) nanosheets have been successfully synthesized through one-step ultrasonication method. The NbSA nanosheet membrane with a thickness of 5 µm shows ultrahigh rejection rates (>95%) towards multiple cations while maintaining high water flux of 1.7-2.2 LMH under forward osmosis process. In terms of vacuum filtration, the NbSA nanosheet membrane demonstrates ultrahigh rejection rates (~100%) towards multiple target dyes including basic blue, toluidine blue and rhodamine 6g while possesses high water flux of ~2200 LMHB.
  This work provides novel and instructive methods to fabricate 2D nanosheet-based materials (e.g., hydrogel and membrane) with high separation performance toward oil/water mixture, multiple ions and dyes at the nanoscale. The built-up concepts of designing 2D nanosheet membrane provide constructive strategies for surface modification of 2D nanosheets. The selective separation results for oil/water mixture or ion-water exchange process as demonstrated in this work provide valuable and quantitative information for analyzing and understanding the nanoscale transport phenomena between wanted and unwanted species within the membrane matrix.

• Subjects / Keywords

  • 2D Nano Materials
  • Selective Separation

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-pgf6-p869

• License

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