Research ArticleAPPLIED SCIENCES AND ENGINEERING

Architecting highly hydratable polymer networks to tune the water state for solar water purification

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Science Advances  28 Jun 2019:
Vol. 5, no. 6, eaaw5484
DOI: 10.1126/sciadv.aaw5484
  • Fig. 1 Schematic illustration of SVG based on the h-LAH.

    The h-LAH is made by infiltrating PPy absorbers into a matrix consisting of PVA and chitosan. As PVA can play the role of surfactant, the PPy chains are dispersed uniformly in the cross-linked PVA and chitosan polymer network. Upon exposure to the solar irradiation, h-LAH can generate water vapor using solar energy. The floating h-LAH consists of the hydratable polymer network based on cross-linked PVA and chitosan, which is interpenetrated by the light-absorbing PPy. The containing water has three different water types—bound water, IW, and FW. Wherein, the IW can be effectively evaporated with significantly reduced energy demand.

  • Fig. 2 Chemical and structural characterization of the h-LAH.

    (A) Photograph of as-prepared h-LAH sample. (B) SEM image of the micron-sized pores in the freeze-dried h-LAH. (C) FTIR spectra of PVA (black curve), PPy (red curve), chitosan (blue curve), and the h-LAH (purple curve). a.u., arbitrary units. (D) Dynamic mechanical analysis showing storage modulus (G′) and loss modulus (G″) of PVA/PPy hydrogel and the h-LAH. Photo credit: Xingyi Zhou, The University of Texas at Austin.

  • Fig. 3 Water state in the h-LAH.

    (A) Schematic of the water in the hydratable polymer network of the h-LAH, showing water/polymer bonding, weakened water/water bonding, and normal water/water bonding. (B) Raman spectra showing the fitting peaks representing IW and FW in the h-LAH. (C) Differential scanning calorimetry (DSC) curves of the h-LAH with different water fraction (i.e., swollen level, 100% refers to the fully swollen state).

  • Fig. 4 Tunable water state and water vaporization enthalpy of the h-LAHs.

    (A) Schematic illustration of PVA and chitosan structure. (B) The saturated water content of h-LAH samples, where the h-LAHs with PVA/chitosan weight ratios of 1:0 (i.e., no chitosan additive), 1:0.05, 1:0.1, 1:0.175, and 1:0.25 are noted as h-LAH1 to h-LAH5, respectively. (C) The ratio of IW to FW in h-LAHs. (D) The equivalent water vaporization enthalpy of bulk water and water in h-LAH1 to h-LAH5.

  • Fig. 5 Solar water purification based on the h-LAH.

    (A) The mass loss of pure water for different h-LAH samples under 1 sun compared with the bare pure water as blank control experiment. (B) The primary ions in a seawater sample before and after desalination. (C) The duration test of the h-LAH4 based on continuous solar desalination for 96 hours. Insets: The mass loss of water with the h-LAH4 as a solar evaporator at the 1st hour and 96th hour. (D to G) Evaluation of corrosion resistance (D) in acid or alkali solutions. (E and F) Comparison of the pH of the solution before and after purification. (G) Purification of heavy metal polluted water. Inset: The concentration of heavy metal ions in the solution before and after purification. (H) Ion residual in purified water compared with several competitive purification techniques designed for a specific ion.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/6/eaaw5484/DC1

    Section S1. Supplementary methods

    Section S1.1. Fabrication procedure

    Section S1.1.1. Preparation of PPy absorbers

    Section S1.1.2. Preparation of PVA and chitosan solution

    Section S1.1.3. Preparation of PVA/chitosan hydrogel

    Section S1.1.4. Preparation of PEG/PPy hydrogel (l-LAH1, less hydratable light-absorbing hydrogel)

    Section S1.1.5. Preparation of PEG/PVA/PPy hydrogel (l-LAH2)

    Section S1.2. Melting behavior of h-LAHs by DSC measurement

    Section S2. Supplementary figures

    Section S2.1. Investigation of PPy penetrated in the PVA and chitosan polymer network

    Section S2.2. Investigation of water state in h-LAHs

    Section S2.2.1. DSC measurement of bound water content in h-LAHs

    Section S2.2.2. Investigation of water state in fully swollen h-LAHs

    Section S2.3. Polymer network enabled activation of water

    Section S2.3.1. Study of water-polymer interaction in h-LAHs

    Section S2.3.2. Observation of vapor generation under dark conditions

    Section S2.3.3. DSC measurement of evaporation enthalpy

    Section S2.3.4. Investigation of water state and SVG rate of less hydratable polymer networks

    Section S2.4. Investigation of photothermal behaviors of h-LAHs

    Section S2.4.1. Evaluation of light absorption of h-LAHs

    Section S2.4.2. Investigation of photothermal behavior of h-LAHs

    Section S2.5. Variables influencing the SVG of h-LAHs

    Section S2.5.1. Ratio of hydrophilic polymers (PVA and chitosan)/water

    Section S2.5.2. Ratio of PPy/hydrophilic polymer

    Section S2.5.3. Cross-linker density of h-LAHs

    Section S2.5.4. Evaluation of 1-sun vapor generation performance of h-LAHs

    Section S2.6. Performance evaluation of h-LAHs in salt solutions

    Section S2.6.1. Evaluation of the antifouling functionality of the h-LAH

    Section S2.6.2. Evaluation of purified simulating seawater based on the h-LAH

    Section S2.7. Comparison of techniques for purification of heavy metal ions

    Fig. S1. Dynamic mechanical analysis of storage modulus (G′) and loss modulus (G″) of PVA/chitosan hydrogel and the h-LAH4.

    Fig. S2. DSC analysis of different samples.

    Fig. S3. Investigation of water-polymer interaction in h-LAHs.

    Fig. S4. Photothermal behaviors of h-LAHs.

    Fig. S5. Factors influencing the SVG of h-LAHs.

    Fig. S6. Performance evaluation of h-LAHs in salt solutions.

    Fig. S7. Qualitative comparison of different techniques in terms of core requirements of practical purification of heavy metal ions.

    Table S1. Bound water content of h-LAHs from the DSC measurement.

    Table S2. The fraction of free, intermediate, and bound water in h-LAHs.

    Table S3. Comparison of evaporation enthalpy from DSC measurement and dark experiment.

    References (4046)

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Supplementary methods
    • Section S1.1. Fabrication procedure
    • Section S1.1.1. Preparation of PPy absorbers
    • Section S1.1.2. Preparation of PVA and chitosan solution
    • Section S1.1.3. Preparation of PVA/chitosan hydrogel
    • Section S1.1.4. Preparation of PEG/PPy hydrogel (l-LAH1, less hydratable light-absorbing hydrogel)
    • Section S1.1.5. Preparation of PEG/PVA/PPy hydrogel (l-LAH2)
    • Section S1.2. Melting behavior of h-LAHs by DSC measurement
    • Section S2. Supplementary figures
    • Section S2.1. Investigation of PPy penetrated in the PVA and chitosan polymer network
    • Section S2.2. Investigation of water state in h-LAHs
    • Section S2.2.1. DSC measurement of bound water content in h-LAHs
    • Section S2.2.2. Investigation of water state in fully swollen h-LAHs
    • Section S2.3. Polymer network enabled activation of water
    • Section S2.3.1. Study of water-polymer interaction in h-LAHs
    • Section S2.3.2. Observation of vapor generation under dark conditions
    • Section S2.3.3. DSC measurement of evaporation enthalpy
    • Section S2.3.4. Investigation of water state and SVG rate of less hydratable polymer networks
    • Section S2.4. Investigation of photothermal behaviors of h-LAHs
    • Section S2.4.1. Evaluation of light absorption of h-LAHs
    • Section S2.4.2. Investigation of photothermal behavior of h-LAHs
    • Section S2.5. Variables influencing the SVG of h-LAHs
    • Section S2.5.1. Ratio of hydrophilic polymers (PVA and chitosan)/water
    • Section S2.5.2. Ratio of PPy/hydrophilic polymer
    • Section S2.5.3. Cross-linker density of h-LAHs
    • Section S2.5.4. Evaluation of 1-sun vapor generation performance of h-LAHs
    • Section S2.6. Performance evaluation of h-LAHs in salt solutions
    • Section S2.6.1. Evaluation of the antifouling functionality of the h-LAH
    • Section S2.6.2. Evaluation of purified simulating seawater based on the h-LAH
    • Section S2.7. Comparison of techniques for purification of heavy metal ions
    • Fig. S1. Dynamic mechanical analysis of storage modulus (G′) and loss modulus (G″) of PVA/chitosan hydrogel and the h-LAH4.
    • Fig. S2. DSC analysis of different samples.
    • Fig. S3. Investigation of water-polymer interaction in h-LAHs.
    • Fig. S4. Photothermal behaviors of h-LAHs.
    • Fig. S5. Factors influencing the SVG of h-LAHs.
    • Fig. S6. Performance evaluation of h-LAHs in salt solutions.
    • Fig. S7. Qualitative comparison of different techniques in terms of core requirements of practical purification of heavy metal ions.
    • Table S1. Bound water content of h-LAHs from the DSC measurement.
    • Table S2. The fraction of free, intermediate, and bound water in h-LAHs.
    • Table S3. Comparison of evaporation enthalpy from DSC measurement and dark experiment.
    • References (4046)

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