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1Materials Science and Engineering Program and Department of Mechanical En-gineering, The University of Texas at Austin, Austin, TX 78712, USA. 2LockheedMartin Corporation, 1 Lockheed Boulevard, Fort Worth, TX 76108, USA.*These authors contributed equally to this work.†Corresponding author. Email: ghyu@austin.utexas.edu

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Architecting highly hydratable polymer networks totune the water state for solar water purificationXingyi Zhou1*, Fei Zhao1*, Youhong Guo1, Brian Rosenberger2, Guihua Yu1†

Water purification by solar distillation is a promising technology to produce fresh water. However, solar vapor gen-eration, is energy intensive, leading to a lowwater yield under natural sunlight. Therefore, developing newmaterialsthat can reduce the energy requirement of water vaporization and speed up solar water purification is highly de-sirable. Here, we introduce a highly hydratable light-absorbing hydrogel (h-LAH) consisting of polyvinyl alcohol andchitosan as the hydratable skeleton and polypyrrole as the light absorber, which can use less energy (<50% of bulkwater) for water evaporation. We demonstrate that enhancing the hydrability of the h-LAH could change the waterstate and partially activate the water, hence facilitating water evaporation. The h-LAH raises the solar vapor gener-ation to a record rate of ~3.6 kgm−2 hour−1 under 1 sun. Theh-LAH-based solar still also exhibits long-termdurabilityand antifouling functionality toward complex ionic contaminants.

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INTRODUCTIONRapid, energy-efficient water purification methods are urgently re-quired to address growing water scarcity (1, 2). Solar distillation is apromising technique that uses renewable energy to power the removalof contaminants in water, delivering fresh water to alleviate thefreshwater shortage (3, 4). However, solar vapor generation (SVG),the essential process of solar distillation to separate water and con-taminants, is energy intensive. Developing materials with an adaptivestructure that can efficiently convert solar irradiation to heat and boostwater vaporization creates a foundation for solar water purificationindependent of solar concentrators, opening up opportunities forcost-effective freshwater production. In particular, capillary structures,including porous structure (5–7), directional channel array (8–10), andtwo-dimensional network (11) as the means to regulate water distri-bution, have recently been explored using broadband light absorbers suchas plasmonic nanoparticles (8, 12–14), carbonmaterials (5, 6, 15, 16), andsemiconductor-based absorbers (17, 18). However, these designs exhibita limited range of SVG rate (vapor yield, ≤1.6 kg m−2 hour−1) undernatural sunlight (solar flux, ≤1 kW m−2). Whereas this drawback iscaused by the intrinsic energy demand of water vaporization, thehydrated solutes in water have a substantial impact on the phase changebehaviors of water by varying the water state (19, 20).

Owing to their tunable physicochemical properties, hydrogelmaterials consisting of highly hydratable polymer networks and swollenwater molecules are conducive to applications in flexible electronics(21, 22), biomedical technology (23, 24), and environmental sensing(25, 26). The hydration of this polymer network opens up possibilitiesto achieve an intriguing water state distinct from that of bulk water(19, 27, 28). Here, we introduce a light-absorbing hydrogel with highlyhydratable polymer networks (termed hydratable light-absorbing hy-drogel or h-LAH), made by infiltrating polypyrrole (PPy) absorbersinto a matrix consisting of polyvinyl alcohol (PVA) and chitosan.We provide fundamental insights into the links between the involvedpolymer-water interaction and the resultant variation of water phasechange behavior and demonstrate that h-LAH could significantly re-duce the energy demand of SVG. Because of the hydration effect, the

polymer chains in hydrogels could capture nearby water moleculesthrough strong interaction, such as hydrogen bonding, to form boundwater (Fig. 1, deep blue area). In contrast, the water molecules that areseparated from the polymer chains [termed as free water (FW)] exhibitidentical properties with those in bulk water (Fig. 1, light blue area).There is an intermediate region (Fig. 1, yellow area) between boundwater and FW, where the water molecules present relatively delicateinterplay with polymer chains and adjacent water molecules. Theintermediate water (IW) has been demonstrated as activated waterthat could be vaporized by less energy compared with bulk water(19, 20, 29, 30). On the basis of this design, the rate of 1-sun SVG couldbe increased up to 3.6 kg m−2 hour−1 at an energy efficiency of ~92%.The h-LAH–improved SVG enables highly efficient, scalable, and cost-effective solar water purification of various soluble ionic contaminateswith antifouling functionality, as well as long-term durability.

RESULTPreparation and characterization of h-LAHThe in situ cogelationmethod is used to construct the polymer networkthat consists of PVA and chitosan. The PPy was used as an additiveendowing the h-LAH with a light-absorbing functionality (see sec-tion S1 for details). The as-prepared h-LAHs were black and flexible(Fig. 2A). The configuration of h-LAHs, such as the size and shape,depends on the mold used for gelation, indicating desirable scalability.Scanning electron microscopy (SEM) imaging reveals the cross-sectionmorphology of the freeze-dried h-LAH (Fig. 2B). Pores with a diameterof several microns are uniformly distributed in the h-LAH, which is atypical structural feature, indicating homogeneous gelation throughoutthe resultant hydrogel. To analyze the chemical composition, we showthe Fourier transform infrared (FTIR) spectra of pure PVA, PPy, chito-san, and the h-LAH in Fig. 2C. In the spectrum of PVA (black curve),the peak at 1087 cm−1 represents the C—O stretching, which is acharacteristic peak of PVA (31). The spectrumof PPy (red curve) showsthe absorption signal at 1451 cm−1, corresponding to theC==C stretchingin the pyrrole rings (32). The blue curve represents the spectrum of chi-tosan inwhich the characteristic peaks are located at 1626 and 1374 cm−1,corresponding to the amide peak of chitosan (31). All the characteristicpeaks of PVA, PPy, and chitosan can be found in the spectrum of theh-LAH (purple curve), confirming the existence of PPy in the PVAand chitosan hybrid polymer network.

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As viscoelastic materials, hydrogels show energy storage and energydissipation characteristics. The corresponding storage modulus (G′)and loss modulus (G″) can be measured to reveal the structuraldifference of hydrogels (33). To confirm the cogelation of PVA and chi-tosan, we prepared a PVA/PPy hydrogel as the blank sample (i.e., con-

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trol sample without chitosan). The higher G′ values compared with G″values confirm the cross-linked polymeric skeleton of these hydrogels(Fig. 2D). The higher G′ value of the h-LAH compared with PVA/PPyindicates stronger mechanical strength due to the introduction of chi-tosan, while the higherG″ value reveals the steric hindrance of chitosan

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 canplay 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-LAHcan 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 inter-penetrated by the light-absorbing PPy. The containing water has three different water types—bound water, IW, and FW. Wherein, the IW can be effectively evaporatedwith 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 mechanicalanalysis 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.

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polymer chains (33). In addition, the comparison of G′ and G″ valuesbetween PVA/chitosan hydrogel and the h-LAH confirms that PPy isinterpenetrated in the polymer network composed of PVAand chitosan(fig. S1). These above results demonstrate that the PPy is interpene-trated in the PVA/chitosan hybrid polymer network.

Tunable water state in the h-LAHAccording to the difference of intermolecular hydrogen bonding, in-cluding water/polymer bonding, weakened water/water bonding, andnormal water/water bonding (Fig. 3A), the water in the hydrated poly-mer network has been classified into three types: FW (Fig. 3A, light bluecolor), IW (Fig. 3A, yellow color), and bound water (Fig. 3A, dark bluecolor), respectively. We analyze the Raman spectra in the region ofO—H stretching to show the hydrogen bonding distinction of watermolecules in the h-LAH (see details in section S2.3.1), revealing the wa-ter state in the h-LAH (Fig. 3B). The peaks at 3233 and 3401 cm−1 cor-respond to FW (Fig. 3B) with four hydrogen bonds (two protons andtwo lone electron pairs are involved in hydrogen bonding with adjacentwater molecules), while the peaks at 3514 and 3630 cm−1 are associatedwith weakly hydrogen-bonded IW (Fig. 3B) (19). Hence, the strongerIW peaks compared with FW peaks indicate a higher proportion of IWin the h-LAH.

Given that the water in each state shows characteristic phasechange behaviors (34), such as freezing and melting, the involvedenergy transfer could be monitored to further confirm that the h-LAHsinduced the differentiation of water state. To quantitatively de-scribe the water content (i.e., hydration level) of h-LAHs, we firstdefine a water fraction (WH2O) as

WH2O ¼ W=Ws

where the W and Ws are the weight of water in the h-LAH and thesaturated water content of a fully swollen h-LAH, respectively. We usethe differential scanning calorimetry (DSC) to reveal the phase changeof water (Fig. 3C). The h-LAHwith a lowWH2O of 1% (i.e., almost driedsample) presents a straight line without signals of endothermic process(black curve). It has been demonstrated that bound water, whichstrongly interacts with hydrophilic polymer chains, is nonfreezable wa-ter, while the IW and FW are freezable (34). Therefore, the water mo-

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lecules are captured by the polymer network of the h-LAH, formingbound water, when the WH2O is 1%. In contrast, there are two peakslocated at 0° and ~5°C corresponding to the melting of IW and FW,respectively, that could be observed in the fully hydrated h-LAH (i.e.,WH2O is 100%; green curve). In addition, the measured melting pointof FW is shifted to a higher temperature with the increase inWH2O (red,blue, and green curves), which could be attributed to the postponedheating of samples induced by endothermic melting. In contrast, thesteep signal of IW (purple curve) is independent of the water contentof the h-LAH, indicating that the generation of IW relies on the hydra-table polymer network. It should be mentioned that the melting pointsof IW and FW are close because of the almost similar melting enthalpyof ices with different crystal structures (35).

To obtain a tailored water state that is capable of providing high-proportioned IW, we constructed polymer networks consisting ofPVA and chitosan with a different proportion. Wherein, the h-LAHsamples with various PVA/chitosan weight ratios from 1:0 (i.e., no chi-tosan additive), 1:0.05, 1:0.1, and 1:0.175 to 1:0.25 are noted as h-LAH1to h-LAH5, respectively. Because of the similar carbon/oxygen ratio (i.e.,molar ratio of hydrophobic and hydrophilic groups) of PVA and chito-san (Fig. 4A), the obtained polymer networks in h-LAHs show a similarability to capture water molecules to form bound water (see details infig. S2, A and B). The amount of IW highly depends on the hydrabilityof polymer networks, which presents the ability of polymer networks toswellwater andcanbe indicatedby the saturatedwater contentofh-LAHs.The saturated water content (Qs) of h-LAHs is represented by

Qs ¼ W=Wd

whereW andWd are theweights of thewater in the fully swollen sampleand the corresponding dried aerogel sample, respectively. The Qs ofh-LAHs rises with the proportion of chitosan (Fig. 4B), indicating anincreased hydrability. This phenomenon could be attributed to thepresence of highly hydratable –NH2 groups on chitosan chains (36).

To systematically assess the influence of the hydrability of polymernetworks on the water state, we calculated the ratio of IW and FW infully swollen h-LAHs. According to the DSC data (fig. S2, C andD), theratios of IW to FW in h-LAH1 to h-LAH5 are 0.758, 0.933, 1.124, 1.284,and 1.339, respectively, indicating that h-LAHwith a higher hydrabilityfavors the formation of IW (Fig. 4C). These results are consistent with

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 calo-rimetry (DSC) curves of the h-LAH with different water fraction (i.e., swollen level, 100% refers to the fully swollen state).

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the estimation derived by Raman spectra (fig. S3, A to D). To evaluatethe benefits of IW to the SVG, we carefully measured the equivalentwater vaporization enthalpy through a comparison of h-LAH1to h-LAH5 and bulk water regarding the spontaneous evaporation(see details in fig. S3E). The equivalent water vaporization enthalpy(Eequ) of water in the h-LAHs can be estimated by assuming that thewater vaporization is powered by identical energy input (Uin), which has

Eequ ¼ E0m0=mg

where E0 andm0 are the vaporization enthalpy andmass change of bulkwater, respectively, and mg is the mass change of these h-LAHs. Asshown in Fig. 4D, the obtained equivalent water vaporization enthalpygradually decreases from h-LAH1 to h-LAH5, suggesting that the IWcan reduce the overall energy demand of water evaporation (also seefig. S3F). To systematically investigate this effect, we involved hydro-gels that consist of less hydratable polymer networks (see details in fig.S3, G to I).

DISCUSSIONSolar water purification based on the h-LAHThe SVG performance of h-LAHs upon pure water is representedby the mass change of water under 1-sun solar irradiation overtime (Fig. 5A). Note that all the h-LAHs are of optimized light ab-sorption (fig. S4A) and thermal management (Fig. 4, B to F) and

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the experimental data involved were calibrated with dark evapora-tion data. It is clear that the SVG rate based on the h-LAH is fasterthan that of pure water. On the basis of the optimized hydrophilicpolymer/water ratio (fig. S5, A and B), PPy absorber concentration(fig. S5, C and D), and cross-linking density (fig. S5, E and F), theh-LAH4 exhibited a high vapor generation rate of ~3.6 kg m−2 hour−1

with an energy efficiency of ~92% among all samples (fig. S5, G andH). The evaporation rate and energy efficiency gradually increasedfrom h-LAH1 to h-LAH4 due to decreasing equivalent vaporizationenthalpy. Despite the low water vaporization enthalpy, the h-LAH5exhibits high water content, hindering the effective energy utilizationand restricting the SVG rate (see detailed discussion in section S2.4.2),which shows the significance of balancing factors regarding water con-tent and state in design of hydratable polymer networks for SVG.

We used a real seawater sample (from the Gulf of Mexico) to showthe solar distillation based on the h-LAH and evaluated the quality ofcollected water using inductively coupled plasma mass spectroscopy(ICP-MS). As shown in Fig. 5B, the concentrations of four primary ions(Na+,Mg2+, K+, andCa2+) in seawater are significantly reduced by ~2 to3 orders after purification and were below the values obtained throughmembrane- and distillation-based seawater desalination techniques(13). To prove the durability of the h-LAH as an evaporator, we testedthe SVG rate under continuous 1-sun irradiation over 96 hours (Fig.5C). The stable evaporation rate shows that the h-LAH presents apromising performance for practical long-term solar desalination withantifouling functionality (fig. S6A). In addition, the salinities of threebrine samples (NaCl solution) with representative salinities of the Baltic

Fig. 4. Tunable water state and water vaporization enthalpy of the h-LAHs. (A) Schematic illustration of PVA and chitosan structure. (B) The saturated watercontent 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-LAH1to 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.

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Sea [lowest salinity, 0.8 weight % (wt %)], World Sea (average salinity,3.5 wt %) and Dead Sea (highest salinity, 10 wt %) were all significantlydecreased (about four orders of magnitude) after desalination, whichare about two orders below drinking water standards defined by theWorldHealthOrganization (1 permil; fig. S6, B to E) (13). These resultsdemonstrate effective solar desalination based on the h-LAH.

Figure 5D shows the steady evaporation rate of the h-LAH understrong acid (1 M H2SO4) and alkali (1 M NaOH) solutions, and thepH value of the purified water is close to 7 (Fig. 5, E and F). Moreover,we also conducted the solar purification of water containing mixedheavy metal ions with four representative ions, including Ni2+, Cu2+,

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Zn2+, and Pt2+, which are the most common heavy metal ions withrelatively high concentrations in industrial waste water, based on theh-LAH. As shown in Fig. 5G, the h-LAH exhibits a stable evapora-tion rate, and the concentrations of heavy metal ions dropped below1 mg liter−1 after purification (Fig. 5G, inset), which are comparablewith those of competitive purification techniques designed for thespecific ion (Fig. 5H) (37–39). Along with the unique advantages ofh-LAH–based solar water purification compared with other methodsin terms of core requirements of practical application, the h-LAHpresents a remarkable potential for the practical purification of industrialsewage containing multiple ionic contaminants (fig. S7).

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 asblank 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 solardesalination 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: Theconcentration of heavy metal ions in the solution before and after purification. (H) Ion residual in purified water compared with several competitive purificationtechniques designed for a specific ion.

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CONCLUSIONIn conclusion, we demonstrated the regulation of water state in hydro-gels via architecting the hydratable polymer network, as a new effectivemeans beyond the previous structural designs to endow materials withstronger ability to accelerate solar water evaporation. The hydrophilicfunctional groups, such as hydroxyl and amino groups, on the polymernetwork present strong interaction with water molecules. Hence, thehydrability of the polymer network determines the proportion of IW,thus influencing the overall energy demand of vapor generation. Themorphology of the polymer network (i.e., pore size), which depends onthe cross-linking density, significantly influences the water diffusionwithin the hydrogel, since those pores serve as water pathways whenthe water diffuses to the evaporating surface. Note that the “pores” hereare not themicroscopic scale pores but themolecular levelmeshes in thepolymer network. It is expected that these fundamental design princi-ples regardingmolecular engineeringwill spur the development of next-generation photothermal materials capable of managing the phasetransition of water and associated energy conversions.

We also demonstrated highly efficient solar water purificationenabled by the light-absorbing hydrogels with hydratable polymer net-works (h-LAH) under 1-sun irradiation. The h-LAH showed an ultra-fast water evaporation rate up to ~3.6 kgm−2 hour−1 and effective waterpurification removal of over 99.9% of ionic contaminants. Thepromising performance of h-LAH shows great potential as an antifoul-ing, long-term stable, and cost-effective vapor generator for solar waterpurification, and the introduction of IW-facilitated SVGprovides a newapproach for addressing growing challenges at the energy-water nexus.

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MATERIALS AND METHODSChemicals and materialsChemicals including PVA with an average molecular weight of 15,000,hydrochloric acid (37%), pyrrole, glutaraldehyde (50% aqueous so-lution), poly(ethylene glycol) diacrylate [number-average molecularweight (Mn), ~700], chitosan with low molecular weight, 2,2′-azobis(2-methylpropionitrile), and ammonium persulfate were purchased fromSigma-Aldrich. All thematerials were usedwithout further purification.

Preparation of h-LAHsIn a typical synthesis, PPy (100 ml, 10 wt%) solution and glutaraldehyde[12.5 ml, 50 wt % in deionized (DI) water] were added to 1 ml of PVA/chitosan precursor solution. The gelation was carried out for 24 hours.The obtained gel was immersed into DI water overnight to obtain thepure hydrogel. The purified hydrogel was frozen by liquid nitrogen andthen thawed inDIwater at a temperature of 30°C. The freezing-thawingprocess was repeated 10 times. Last, the obtained hydrogel sample wasfully swollen for testing.

SVG experimentsThewater evaporation performance experiments were conducted usinga solar simulator (M-LS Rev B, Abet Tech), outputting a simulated solarflux of 1 sun. The solar flux was measured using a thermopile (818SL,Newport) connected to a power meter (1916-R, Newport). h-LAHswith a thickness of ca. 0.5 cmwere floated on pure water (or unpurifiedfor purification tests) in a beaker with a solar flux of 1 sun. Themass ofthe water loss was measured by a lab balance with a 0.1-mg resolutionand calibrated to weights heavier than the total weight of the setup. Allevaporation rates were measured after a stabilization under 1 sun for30 min.

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CharacterizationsThe SEM images were implemented by SEM (S5500, Hitachi) to ob-serve the morphology and microstructure of the samples. The h-LAHswere freeze-dried for 24 hours before observation. The FTIR spectrawere conducted by the FTIR spectrometer (InfinityGold FTIR, ThermoMattson) equippedwith a liquid nitrogen cooled narrow-bandmercurycadmium telluride detector using an attenuated total reflection cellequipped with a Ge crystal. The mechanical properties of h-LAHs wereperformed by rheological experiments (AR2000EX, TA Instruments)using a parallel plate on a Peltier plate in the frequency sweep mode.Absorption spectra and reflectance were conducted using a UV-Vis-NIR spectrometer (Cary 5000) with an integrating sphere unit andautomation of reflectance measurement unit, and the measurementswere corrected by baseline/blank correction with dark correction. TheRaman spectraweremeasured via spectrometer (WITec alpha300). Theexcitation radiation for the Raman emissionwas produced using aYttriumaluminium garnet laser that had a single-mode operation at 532 nm.The evaporation andmelting behavior of h-LAHswere observed by adifferential scanning calorimeter (METTLER TOLEDODSC 3). Thetemperature and melting enthalpy were calibrated by indium. Theconcentration of ions was tracked by ICP-MS (Agilent 7500ce) withdilutions in 2% HNO3 to make the loaded ion concentration lower than10 parts per million.

SUPPLEMENTARY MATERIALSSupplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/6/eaaw5484/DC1Section S1. Supplementary methodsSection S1.1. Fabrication procedureSection S1.1.1. Preparation of PPy absorbersSection S1.1.2. Preparation of PVA and chitosan solutionSection S1.1.3. Preparation of PVA/chitosan hydrogelSection S1.1.4. Preparation of PEG/PPy hydrogel (l-LAH1, less hydratablelight-absorbing hydrogel)Section S1.1.5. Preparation of PEG/PVA/PPy hydrogel (l-LAH2)Section S1.2. Melting behavior of h-LAHs by DSC measurementSection S2. Supplementary figuresSection S2.1. Investigation of PPy penetrated in the PVA and chitosan polymer networkSection S2.2. Investigation of water state in h-LAHsSection S2.2.1. DSC measurement of bound water content in h-LAHsSection S2.2.2. Investigation of water state in fully swollen h-LAHsSection S2.3. Polymer network enabled activation of waterSection S2.3.1. Study of water-polymer interaction in h-LAHsSection S2.3.2. Observation of vapor generation under dark conditionsSection S2.3.3. DSC measurement of evaporation enthalpySection S2.3.4. Investigation of water state and SVG rate of less hydratable polymer networksSection S2.4. Investigation of photothermal behaviors of h-LAHsSection S2.4.1. Evaluation of light absorption of h-LAHsSection S2.4.2. Investigation of photothermal behavior of h-LAHsSection S2.5. Variables influencing the SVG of h-LAHsSection S2.5.1. Ratio of hydrophilic polymers (PVA and chitosan)/waterSection S2.5.2. Ratio of PPy/hydrophilic polymerSection S2.5.3. Cross-linker density of h-LAHsSection S2.5.4. Evaluation of 1-sun vapor generation performance of h-LAHsSection S2.6. Performance evaluation of h-LAHs in salt solutionsSection S2.6.1. Evaluation of the antifouling functionality of the h-LAHSection S2.6.2. Evaluation of purified simulating seawater based on the h-LAHSection S2.7. Comparison of techniques for purification of heavy metal ionsFig. 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.

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Fig. S7. Qualitative comparison of different techniques in terms of core requirements ofpractical 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 (40–46)

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AcknowledgmentsFunding: G.Y. acknowledges the financial support from the Lockheed Martin Corp., SloanResearch Fellowship, and Camille-Dreyfus Teacher-Scholar Award. Author contributions:G.Y. supervised the project. X.Z., F.Z., and G.Y. conceived the idea and cowrote the manuscript.X.Z. and F.Z. performed the materials fabrication, characterization, and carried out the dataanalysis. Y.G. assisted in the experimental work and data analysis. B.R. provided technicaladvice and helped edit the manuscript. All authors discussed the results and commented onthe manuscript. Competing interests: X.Z., F.Z., and G.Y. are inventors on a provisionalU.S. patent application related to this work (no. 15/941,080, filed 30 March 2018). The otherauthors declare that they have no competing interests. Data and materials availability: All dataneeded to evaluate the conclusions in the paper are present in the paper and/or the SupplementaryMaterials. Additional data related to this paper may be requested from the authors.

Submitted 4 January 2019Accepted 17 May 2019Published 28 June 201910.1126/sciadv.aaw5484

Citation: X. Zhou, F. Zhao, Y. Guo, B. Rosenberger, G. Yu, Architecting highly hydratablepolymer networks to tune the water state for solar water purification. Sci. Adv. 5, eaaw5484(2019).

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purificationArchitecting highly hydratable polymer networks to tune the water state for solar water

Xingyi Zhou, Fei Zhao, Youhong Guo, Brian Rosenberger and Guihua Yu

DOI: 10.1126/sciadv.aaw5484 (6), eaaw5484.5Sci Adv 

ARTICLE TOOLS http://advances.sciencemag.org/content/5/6/eaaw5484

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