Solar-powered gel composition for water purification and decontamination

Abstract

The present technology relates to materials, methods, processes, and systems for producing clean water, and in particular to unique hydrogels capable of purifying and decontaminating water, providing an effective and sustainable way to convert contaminated water into potable water. The present technology also contemplates methods for making such gels, methods for purifying water, and methods for producing purified water from contaminated water, and systems that achieve water purification in a rapid, cost-effective, and environmentally sustainable manner.

Description

[Technical Field]

[0001] This application is related to and claims priority to U.S. Provisional Patent Application No. 63 / 015,855, filed April 27, 2020, the entire disclosure of which is incorporated herein by reference.

[0002] The present technology relates to materials, methods, processes, and systems for producing clean water, and in particular to unique hydrogels capable of purifying and decontaminating water, which provide an effective and sustainable way to convert contaminated water into potable water, as well as methods, processes, and systems for achieving water purification. [Background technology]

[0003] The global demand for clean, safe water is ongoing and is expected to continue to grow in the 21st century. According to the World Health Organization (WHO), by 2025, over 50% of the world's population will live in water-scarce environments. Lack of access to clean water threatens human health on an enormous scale. Over one million people die each year from diarrhea worldwide due to unsafe drinking water. When supply cannot keep up with demand, scarce energy resources are strained, further exacerbating shortages.

[0004] Using renewable solar energy to generate clean water from contaminated water is an attractive and environmentally friendly approach to solving the long-standing clean water shortage crisis. Current technologies involve heating surface water using nanostructured solar absorbers to generate steam, followed by condensate collection. However, these methods and processes have significant drawbacks that make them inadequate to meet practical requirements. These include low water collection rates, a high dependency on solar radiation intensity (which can lead to unpredictable results based on location and weather conditions), reduced efficiency of treatment as the water becomes more contaminated, and the significant additional energy required to condense the steam. All of these drawbacks prevent these current technologies from being put to practical use.

[0005] Thus, there continues to be a need for materials and processes that can efficiently and predictably produce clean water from contaminated water, and those that can do so in a sustainable manner are particularly desirable. Summary of the Invention

[0006] In certain embodiments, the present technology comprises: (a) 3D microporous gel scaffold containing poly( N -isopropylacrylamide) (PNIPAm) and having an outer surface; (b) a plurality of polydopamine (PDA) nanoparticles attached to the outer surface of a 3D microporous gel scaffold and containing one or more catechol groups; and (c) A sodium alginate (SA) layer covering the 3D microporous gel scaffold and multiple PDA nanoparticles. The present invention relates to a gel composition comprising:

[0007] In certain embodiments, the gel compositions herein comprise: (a) 3D microporous gel scaffold containing poly( N -isopropylacrylamide) (PNIPAm) and having an outer surface; (b) Multiple polydopamine (PDA) nanoparticles containing one or more catechol groups attached to the outer surface of a 3D microporous gel scaffold; (c) a metal configured to coordinate with one or more catechol groups of the PDA; and (d) A 3D microporous gel scaffold and a sodium alginate (SA) layer coating multiple PDA nanoparticles.

[0008] In other embodiments, the present technology provides a method for producing a gel composition for water purification, comprising: (a) Preparing a 3D microporous gel scaffold; (b) immersing the 3D microporous gel scaffold in a solution containing dopamine to obtain a 3D microporous gel scaffold with attached polydopamine (PDA); (c) immersing the 3D microporous gel scaffold with the PDA attached in a solution containing sodium alginate to obtain a gel composition for water purification; The present invention is directed to a method, including:

[0009] In other embodiments, the present technology provides a method for purifying water, comprising: (a) obtaining a gel composition comprising: (i) a 3D microporous gel scaffold; (ii) a plurality of polydopamine (PDA) nanoparticles attached to the outer surface of the gel scaffold; and (iii) an outer layer comprising sodium alginate; (b) immersing the gel composition in a quantity of contaminated water, the contaminated water comprising water and a contaminant; (c) allowing the 3D microporous gel scaffold to absorb at least a portion of the remaining, less contaminated water while the outer layer of the gel composition repels at least a portion of the contaminants; (d) removing the gel composition from the contaminated water; (e) exposing the gel composition to sunlight such that the sunlight is converted into thermal energy, thereby raising the temperature of the gel composition to a temperature above the lower critical solution temperature of the gel composition and causing a hydrophilic to hydrophobic phase transition of the gel composition; (f) releasing the clean water absorbed in the gel framework from the gel composition; The present invention is directed to a method, including:

[0010] In other embodiments, the present technology is directed to a system for purifying water, the system comprising a gel composition comprising: (i) a 3D microporous gel scaffold; (ii) a plurality of polydopamine (PDA) nanoparticles attached to the outer surface of the gel scaffold; and (iii) an outer layer comprising sodium alginate. [Brief explanation of the drawings]

[0011] [Figure 1]Figure 1A illustrates exemplary steps in the water purification procedure discussed herein, including water adsorption, clean water production, and the resulting water in liquid and vapor forms. Figure 1B illustrates another aspect of the process herein, specifically the solar-assisted SAG technology for water production, which is based on the phase transformation (swelling and deswelling) of PNIPAm under natural or artificial sunlight. SAG harvests large volumes of clean water from contaminated water at or near atmospheric pressure. [Figure 2-1] Figure 2 details the embodiments herein as follows: Figure 2A illustrates the preparation of a 3D solar absorber gel at room temperature. [Figure 2-2] Figure 2B shows scanning electron microscopy (SEM) images of the polydopamine (PDA)-decorated gel under various magnifications, revealing the microporous structure and pore size distribution. Figure 2C shows SEM images and energy dispersive X-ray spectroscopy Cu, Na elemental mapping images of the 3D solar absorber gel prepared according to an embodiment of the present disclosure, demonstrating successful SA coating. [Figure 3-1] Figure 3 shows the generation of clean water from 3D gels under sunlight irradiation as follows: Figure 3A shows oil-contaminated water (cyclohexane-in-water emulsion), and Figure 3B shows bacteria-containing water (using yeast as a model). [Figure 3-2] Figure 3C shows the organic dye-containing wastewater (Rhodamine 6G), and Figure 3D shows the reusability of the 3D gel for water production from R6G-contaminated water. [Figure 4-1] Figure 4 shows the preparation and morphology of the SAG discussed herein: Figure 4A shows the preparation of SAG at room temperature; and Figure 4B shows the pore size distribution of PNIPAm-PDA hybrid gels. [Figure 4-2] Figure 4C shows scanning electron microscopy (SEM) images of the PDA-decorated gel under various magnifications, revealing the microporous structure. Figure 4D shows SEM images, energy dispersive X-ray spectroscopy elemental mapping images of C, O, Cu, and Na, and cross-sectional images of the SAG. [Figure 5-1] Figure 5 shows the mechanical, wetting, and component properties of the SAGs discussed herein. Figure 5A shows the results of non-cyclic fatigue tests of PNIPAm gels at 80% compressive strain. Figure 5B shows the reversible compressive stress-strain curves of the SAGs at 80% compressive strain. The inset shows a photograph of the compression-decompression test cycle. [Figure 5-2] Figure 5C shows optical images demonstrating the dynamic wetting behavior of a water droplet (approximately 30 μL) on SAG (top), PDA-modified PNIPAm gel (middle), and PNIPAm gel (bottom) at room temperature. Figure 5D shows the O1s, N1s, and C1s XPS spectra of the samples. [Figure 6-1] Figure 6 shows the photoinduced water release performance as follows: Figure 6A shows the DSC thermograms of swollen PNIPAm, PNIPAm-PDA, and SAG, and Figure 6B shows the UV-vis-NIR absorbance spectra of PNIPAm, PNIPAm-PDA, and SAG. [Figure 6-2] Figure 6C shows the surface temperature change over time for various gels under 1 sun illumination, and Figure 6D shows an IR image of a 3D porous gel under 1 sun illumination ("illumination" and "illumination" are used interchangeably herein). [Figure 6-3] Figure 6E shows the mass loss over time of the SAG herein relative to pure water, and Figure 6F shows the collection rate of the system herein in kg / m2 hr. [Figure 7-1] Figure 7 shows the results of wastewater purification evaluation. Figure 7A is a schematic diagram showing the exemplary SAG's clean water production from dye-contaminated water. Figure 7B shows the UV-vis adsorption of simulated R6G-contaminated water and SAG-produced water under 1 sun illumination. [Figure 7-2] Figure 7C shows the Pb2+ concentration in water purified with SAG herein. The inset image shows the change in Pb2+ concentration after a second SAG treatment. [Figure 7-3]7D and 7E show digital and photomicrographs of an SDS-stabilized cyclohexane-in-water emulsion (FIG. 7D) and a yeast solution (FIG. 7E) before and after treatment with the SAG herein. [Figure 8-1] Figure 8 illustrates natural sunlight-based clean water production according to embodiments herein. Figure 8A shows a SAG purification system floating on Lake Carnegie (Princeton, New Jersey). Figure 8B shows water collection for the SAG system under natural sunlight. [Figure 8-2] Figure 8C shows the surface temperature of an exemplary SAG under natural sunlight. Figures 8D and 8E show optical images of Lake Carnegie water (Figure 8D, showing microorganisms) and water purified by the methods herein (Figure 8E). [Figure 8-3] FIG. 8F shows the conductivity of Lake Carnegie water before and after purification by SAG herein. [Figure 9-1] Figure 9 illustrates the physical contrast between pure PNIPAm gels, which are completely or substantially transparent (e.g., Figures 9A, 9C, and 9E), and the final SAGs in certain embodiments, which are darker in visual appearance, e.g., black or substantially black, due to the deposition of PDA (e.g., Figures 9B, 9D, and 9F). After PDA and SAG overlay, the darker gels are able to at least substantially maintain the original shape of the PNIPAm gels, which is due to the gentle modification process described herein. Furthermore, the size and shape of the PNIPAm gels can be tailored by the mold used for gelation. For example, Figures 9A and 9C show substantially cylindrical gels with diameters of 1-4 cm and heights of 0.5-2.5 cm. Figure 9E also shows a substantially rectangular parallelepiped structure. [Figure 9-2]Figure 9 illustrates the physical contrast between pure PNIPAm gels, which are completely or substantially transparent (e.g., Figures 9A, 9C, and 9E), and the final SAGs in certain embodiments, which are darker in visual appearance, e.g., black or substantially black, due to the deposition of PDA (e.g., Figures 9B, 9D, and 9F). After PDA and SAG overlay, the darker gels are able to at least substantially maintain the original shape of the PNIPAm gels, which is due to the gentle modification process described herein. Furthermore, the size and shape of the PNIPAm gels can be tailored by the mold used for gelation. For example, Figures 9A and 9C show substantially cylindrical gels with diameters of 1-4 cm and heights of 0.5-2.5 cm. Figure 9E also shows a substantially rectangular parallelepiped structure. [Figure 10] Figures 10A and 10B show SEM images of an exemplary PNIPAm gel after freeze-drying, demonstrating a porous structure with an average pore diameter of around 50 μm and smooth polymer walls with a thickness of approximately 1 μm. Figures 10C-E show elemental distribution mapping by energy dispersive X-ray spectroscopy (EX), revealing a uniform distribution of C, N, and O elements in the PNIPAm gel. [Figure 11] FIG. 1 shows an SEM image of a PNIPAm-PDA sample according to embodiments herein, and a corresponding EDX image. [Figure 12] FIG. 10 shows a cross-sectional image of an SEM image of an exemplary SAG after cutting. [Figure 13] Figure 13A shows XPS of PDA, elastomeric PNIPAm, PNIPAm-PDA, and solar absorber gels, and Figure 13B shows FTIR of PNIPAm before and after PDA functionalization. [Figure 14] Figure 14A shows IR images of a SAG herein under 1 sun irradiation at 0, 10, 25, and 30 minutes, and Figure 14B shows water released from the SAG under optical radiation. [Figure 15-1] 1A-1C are sequential illustrations of the physical deformation and subsequent appearance upon release of a SAG herein, which shows that the SAG does not break and exhibits high resilience. [Figure 15-2] 1A-1C are sequential illustrations of the physical deformation and subsequent appearance upon release of a SAG herein, which shows that the SAG does not break and exhibits high resilience. [Figure 16] Figure 16A shows the UV-Vis absorption of solar-harvested water from 4-Nip solution (Figure 16A) and MO solution (Figure 16B). The solar absorber gels herein exhibited selective absorption behavior toward three organic contaminants. This is primarily due to two factors: the surface charge and molecular size of the dyes. Specifically, the size of MO is smaller than that of R6G and larger than that of 4-Nip. Smaller molecules diffuse more easily in and out of the gel. Meanwhile, electrostatic interactions may affect the mobility of contaminants. In certain embodiments, the PDA in the polymer network is overall charged. Therefore, although some dye molecules may enter the gel, they are generally trapped by the PDA, resulting in a higher concentration of negatively charged dyes than positively charged dyes in the gel-forming water. [Figure 17] Figure 17A shows the UV-Vis adsorption of product water from an R6G solution. Figure 17B shows the reusability of the gel to produce clean water from R6G-containing water. The inset in Figure 17B shows the shape recovery of the 3D porous gel after 10 swelling-deswelling cycles. These figures reveal that the regenerated solar absorber gel retains at least 90% of its original absorption capacity after 10 adsorption-desorption cycles. After the 10th cycle, the water released from the gel becomes significantly lighter in color, further confirming the high adsorption capacity and good cycling stability of the gel of the present invention. [Figure 18]This figure shows the stability test results of exemplary SAG (left) and PNIPAm-PDA gels (right) in water under 1.5 hours of sonication, as well as DLS measurements of the mixtures. PDA was attached to the polymer network and then chelated with a Cu2+-crosslinked SA polymer. The introduction of SA imparts excellent stability and high adsorption properties to PDA. As shown here, after removing the gel from water, virtually no leakage of PDA was observed, even with prolonged sonication. In contrast, the water after removing the PNIPAm-PDA gel without SA modification was not visibly transparent. DLS measurements suggested that PDA had leaked out of the gel framework, resulting in a light brown color even after 1.5 hours of sonication. Therefore, SA is shown to play an important role in maintaining the gel's high stability and adsorption. [Figure 19] Figure 19A shows the size distribution of a cyclohexane-in-water emulsion. Figure 19B shows DLS measurements of water collected from cyclohexane. The cyclohexane droplets in the original SDS-stabilized cyclohexane-in-water emulsion ranged from 1 to 20 μm. In the water-from-cyclohexane emulsion, the peak near 10 nm is due to water-soluble SDS, not cyclohexane droplets. This suggests that the gel described herein can effectively absorb water while filtering out all oil droplets and then release clean water under sunlight. [Figure 20] Figure 20A shows solar water collection from SDS-stabilized petroleum ester in water emulsion (Figure 20A) and hexane in water (Figure 20B) and their DLS measurements, respectively. [Figure 21]This figure shows the light-to-heat conversion of polymer chains in SAG under solar irradiation, including close-up images of swollen SAG, SAG exposed to sunlight, and shrunken SAG (after purified water has been released). In an exemplary SAG platform, the photothermogenic PNIPAm chains are hydrated and surrounded by water molecules at temperatures below the LCST, e.g., room temperature. When exposed to sunlight, the PDA on the PNIPAm chains can convert light energy into thermal energy, heating the system above the LCST of PNIPAm. The SA acts as an insulator to reduce heat loss and trap the thermal energy within the hydrogel. The heated PNIPAm chains then become hydrophobic, allowing them to squeeze out the absorbed water by volumetric contraction, resulting in unprecedentedly efficient pure water generation rates under sunlight. Unlike known methods that involve heating water to high temperatures to form steam, the method described herein directly heats the polymer network above the LCST via the PDA attached to the network. DETAILED DESCRIPTION OF THE INVENTION

[0012] All percentages expressed herein are by weight unless otherwise indicated. It should be noted that throughout this disclosure, references to any numbered items in the figures are for illustrative purposes only, and that embodiments herein are not limited to the depiction of such items in the figures.

[0013] In various embodiments, the present technology is directed to gels or gel compositions, including but not limited to 3D microporous gels. As used herein, "3D" or "3 dimensional" refers to an interconnected polar structure, as opposed to a simply flat structure such as a film.

[0014] As used herein, "gel" refers to a sol in which solid particles are networked to produce a rigid or semi-rigid mixture. Examples of gels include, but are not limited to, aerogels, hydrogels, or xerogels. As used herein, "hydrogel" refers to a gel prepared using water as a solvent. Hydrogels are water-swellable polymeric materials that maintain a distinct three-dimensional structure. As used herein, "gel composition" refers to any composition that contains, in whole or in part, a gel. As used herein, "gel scaffold" refers to the highly porous, underlying three-dimensional structure of a gel composition, with walls and spaces to which other compositions can adhere, adsorb, or be absorbed. As used herein, "microporous" refers to having small pores, e.g., 20-100 μm, 40-60 μm, or approximately 50 μm, as shown, for example, in Figures 2 and 4.

[0015] As used herein, "absorbed" refers to a combination of two materials such that one material is incorporated into another material. As used herein, "adsorbed" refers to a state in which one material adheres to the surface of another material such that one material coats the surface of the other material.

[0016] As used herein, "substantially" means within 10% of a quantitative value. For example, "substantially equal" means within 10% of the same value, and "substantially full" or "substantially empty" means within 10% of full or empty, respectively.

[0017] As used herein, "contaminated water" refers to water that contains one or more contaminants. As used herein, "purified" or "pure" water does not refer to water that is completely free of contaminants, but rather refers to water in which any amount of contaminants has been reduced, for example, through the processes discussed in this disclosure. Thus, in certain embodiments, a method, process, or system herein may refer to incoming "contaminated water" and outgoing "pure" or "purified" water, meaning that the second water contains fewer contaminants than the first. Similarly, in certain embodiments, a method of purifying water refers to a method that reduces contaminants in water to make it closer to potable, though not necessarily completely pure. Thus, in certain embodiments, the methods and processes herein may achieve even purer water after repeating the steps described herein multiple times.

[0018] As used herein, "contaminant" means any substance that can impure or contaminate water, and in various embodiments herein includes, but is not limited to, hydrocarbons, metals (e.g., heavy metals such as mercury or lead ions), salts, drugs, biological contaminants such as strains of bacteria, dyes, particulates, dirt, chemicals (e.g., nitrogen), or any naturally occurring organic matter.

[0019] As used herein, "solar" means solar energy and can include either natural sunlight (obtained from the sun) or artificial sunlight (obtained from a human-generated light source such as a light bulb or lamp).

[0020] As used herein, "phase change" or "conformational change" refers to a change from hydrophilic to hydrophobic, or vice versa.

[0021] As previously mentioned, current processes for purifying water have many drawbacks, including high cost, high energy input requirements, and limited end products. Embodiments herein are advantageous in that they are hydrogel-based systems that are environmentally friendly, have a small footprint, are scalable, and are modular.

[0022] In certain embodiments, poly(N-isopropylacrylamide) (PNIPAm) hydrogels are developed herein that can absorb and release water via hydrophilic / hydrophobic switching at their lower critical solution temperature (LCST) (approximately 33°C), a temperature readily achievable using natural sunlight. To enable solar energy harvesting, certain embodiments herein modify the PNIPAm hydrogels with efficient solar absorbers. In various embodiments, these utilize polydopamine (PDA). PDA is a melanin-based polymer that exhibits broadband solar absorption and high photothermal conversion efficiency. PDA offers additional properties useful for water purification, notably the presence of amino groups and aromatic rings, which endow PDA with the ability to remove heavy metal ions and organic dyes through chelation and hydrogen bonding.

[0023] In certain embodiments, the present technology is directed to hybrid hydrogels that are particularly useful for solar-powered water purification and decontamination. In certain embodiments, the hydrogels herein include 3D solar-powered absorber gels that can fully utilize renewable solar energy for highly efficient water purification and production. Exemplary materials can integrate desirable optical (polydopamine), thermal (PNIPAm), and wetting (alginate) properties to solve the long-standing clean water shortage crisis. Such solar-powered gels can significantly improve the efficiency of clean water production, unlocking new strategies for superior water treatment materials.

[0024] Photoresponsive solar absorber gel (SAG) In certain embodiments, the present technology is directed to a highly elastic, photoresponsive solar absorber gel (SAG) configured to enable repeated cycles of generating clean water from contaminated sources. Such SAGs can be fabricated, in certain embodiments, as follows: PDA and cross-linked sodium alginate (SA) can be deposited on top of a microporous PNIPAm hydrogel. The SA layer has been shown to improve the salt rejection rate of the SAG, i.e., repelling salt rather than absorbing it.

[0025] In certain embodiments, the terms "gel," "gel composition," "hydrogel," and "SAG" are used interchangeably herein to refer to embodiments of the technology herein, including the compositions of the present invention and associated methods, processes, and systems for use in disinfecting and purifying contaminated water.

[0026] In certain embodiments, the gels herein contain not only a layer of PDA but also sodium alginate (SA). In certain embodiments, the sodium alginate solution contains a metal, such as copper (e.g., Cu), that can coordinate with the catechol groups of polydopamine. 2+ ) is included.

[0027] In certain embodiments, sodium alginate (SA) is superhydrophilic, i.e., the contact angle of water is 0 degrees within 30 seconds, allowing water droplets to spread quickly across the sodium alginate (SA) film. This may further contribute to the effectiveness of the compositions discussed herein. In certain embodiments, the gel compositions herein have an SA layer that "coats" the microporous gel scaffold, although the terms "layer" and "coating" do not require that the entire surface of the microporous gel scaffold be completely covered with a uniform or continuous amount of any substance (e.g., including SA), but only that a portion of its surface be at least partially covered with another substance.

[0028] When immersed in polluted water, SAG was found to be able to absorb large amounts of water and release contaminants (including salts, biological matter, oil, and other pollutants). Furthermore, when exposed to natural or artificial sunlight, solar absorption by PDA can thermally heat SAG to temperatures above the LCST of PNIPAm. The hydrogel phase then transforms from a "swollen" hydrophilic state to a "collapsed" hydrophobic state at the LCST, allowing clean water (liquid water or a combination of liquid water and water vapor) to be released from SAG.

[0029] In certain embodiments, when contaminated water enters the gel and is then released as less contaminated (or "pure" or "purified") water, the concentration of the contaminant in the less contaminated water is less than 5%, or less than 2%, or less than 1% of the concentration of the contaminant originally present in the contaminated water.

[0030] In certain embodiments, the water becomes increasingly pure and less contaminated, and this process can be repeated as many times as necessary until a desired level of purity is achieved, i.e., the system can use the released, less contaminated water as a source of contaminated water in subsequent iterations of the step in a manner that provides water of higher purity than previous iterations of the step.

[0031] In certain embodiments, the SAG technology herein works well because it can integrate desirable optical, thermal, elastic, and wetting properties into a single material platform for solar-powered water purification: (i) PNIPAm can function as a flexible water collection vessel as well as a transport medium; (ii) PDA can function as a broad-spectrum light-to-heat conversion material as well as a pollutant filter; and (iii) SA can function as a hydrophilic insulator as well as a pollutant filter.

[0032] A further advantage of the methods and processes herein is the ability to produce liquid water without the need for either a steam generation or condensation step, i.e., in certain embodiments, the methods or processes herein can be powered entirely or substantially entirely by the power of the sun, without the need for any other inputs.

[0033] The aqueous-based fabrication process for SAGs in certain embodiments is shown in Figure 4A. As can be seen, conventional PNIPAm gels cross-linked with N,N'-methylenebisacrylamide (BIS) are weak and generally unsuitable for the multi-cycle use described herein. Instead, the SAGs developed herein, in certain embodiments, use PNIPAm microgels as a cross-linker to improve elasticity and mechanical stability.

[0034] Further details of the manufacturing processes and methods herein are provided in Example 1.

[0035] The power of the sun In certain embodiments, the methods and processes herein can be powered by light, including natural or artificial light, for example, by natural sunlight as shown in FIG. 1B.

[0036] In certain embodiments, the approaches herein can be used to purify and produce clean water at high rates from contaminated water sources, particularly by fully utilizing renewable solar energy. Given the high photothermal conversion efficiency and thermal responsiveness, the methods and systems herein may have great potential applications not only in various water treatments, but also in other potential photothermal catalysis, drug release, and desalination applications.

[0037] In certain embodiments, the 3D solar absorber gels discussed herein as solar-powered purification articles can exhibit several advantages, among which are the following:

[0038] (1) Among other reasons, the gel can be prepared at room temperature using water as a medium without any toxic solvents or complicated equipment, making the manufacturing process easy, environmentally friendly, time-saving, and cost-effective.

[0039] (2) In certain embodiments, the gels discussed herein can exhibit high purification performance because the outer sodium alginate (SA) layer can filter natural particulates, including dust, sand, or bacteria, in freshwater. In certain embodiments, the gels discussed herein can absorb large amounts of clean water after immersion in polluted water because the SA layer repels the contaminants (see, for example, Figure 1 , which illustrates an exemplary water purification procedure based on a 3D solar absorber gel under 1 sun irradiation). This property offers potential for contaminant filtration and antifouling functions, which are particularly useful for solar water production using turbid / polluted water sources.

[0040] (3) The water collection rate of the 3D solar absorber gel is much higher than any other conventional solar evaporation device known in the art. As established in the examples herein, in various embodiments, the methods, processes, and systems herein can collect water at least 5 kgm -2 time -1 (i.e., 5 kg per square metre per hour, or kg / m 2 (expressed as hours), at least 6 kgm -2 time -1 , or at least 7 kgm -2 time -1These excellent water collection rates can be attributed to the integration of PDA's excellent sunlight-to-heat conversion and PNIPAm's thermoresponsive hydrophilic switching function. When exposed to sunlight, PDA converts light into thermal energy through the photothermal effect. When the temperature rises above the LCST, our hybrid PNIPAm-PDA-SA hydrogel undergoes a phase transition from a hydrophilic "swollen" state to a hydrophobic "collapsed" state, resulting in a significant volume change. Therefore, during the shrinkage process, pure water can be generated not only by solar evaporation but also by water squeezed out by the considerable volume shrinkage of the swollen gel (see, for example, Figure 1).

[0041] Thus, as demonstrated herein, the methods and processes herein can function by immersion in contaminated water, absorbing pure (or substantially pure) water while keeping harmful impurities at bay. Subsequently, when irradiated in sunlight (e.g., irradiated at 1 sun or exposed to natural sunlight), purified water can be released from the SAG. In certain embodiments, capillary action drives water transport within the SAG, while the filter efficiency of the SA layer can also significantly reduce the likelihood of fouling.

[0042] In various embodiments, the methods and processes herein can function effectively in the substantial absence of water evaporation or condensation, or can include some water evaporation or condensation in conjunction with the hydrogel phase change mechanisms discussed herein.

[0043] In certain embodiments, the structure of the gels herein can be generally honeycomb-like. See, e.g., Figures 2 and 4. In certain embodiments, the SAGs herein exhibit high porosity as shown by SEM (see, e.g., Figure 10). This can provide a good structure for water transport by capillary flow. Following coating with PDA, in certain embodiments, the gels can maintain an interconnected porous structure, with average pore sizes of 20-100 μm, 30-90 μm, 40-80 μm, 40-75 μm, 40-60 μm, or 50-55 μm (see, e.g., Figures 4B-C).

[0044] In certain embodiments, the 3D solar absorber gels herein can be prepared by a convenient dip-coating method at or near room temperature, as detailed in the Examples below.

[0045] For at least the reasons discussed herein, the 3D porous hydrogels of the present technology, in certain embodiments, may not only favor the flow of water and steam, but may also be useful in removing particulates, dirt, bacteria, and naturally occurring organic matter from water.

[0046] In certain embodiments, the 3D hydrogels of the present technology can be easily prepared at or near room temperature, for example, by immersing the support gel in a dopamine solution and a sodium alginate solution, respectively. As used herein, "room temperature" refers to a temperature within the range of 20-25°C (68-77°F or 293-298K). This manufacturing process is simple and convenient, without requiring any complex or sophisticated equipment. Furthermore, all components are low-cost, non-toxic, and environmentally friendly materials that dissolve in aqueous solution without the use of expensive solvents, and there is no secondary contamination during the process. Furthermore, the 3D porous gels disclosed herein can rapidly produce high-quality clean water under 1 sun irradiation, which is advantageous for practical applications such as water harvesting from various wastewater sources.

[0047] For example, Figure 6F shows the collection rate in kg / m2 The comparative data, plotted over time, clearly demonstrates that the hydrogels herein exhibit a much higher rate than known materials.

[0048] Furthermore, in certain embodiments, the present technology is directed to a method for purifying water, as well as a system configured to produce purified water from contaminated water. In certain embodiments, the system herein is configured such that, when immersed in contaminated water, a hydrophilic 3D microporous gel absorbs water while repelling one or more contaminants in the water, becoming a hydrophilic swollen gel containing purified water. The swollen gel then transitions to a hydrophobic state when exposed to sunlight, thereby releasing purified water.

[0049] In various embodiments, the systems herein can further include one or more of the following: (a) a porous plate configured to contact the hydrophilic 3D microporous gel before and while the hydrophilic 3D microporous gel is in a hydrophilic swollen state, or (b) a container configured to receive purified water as it is released from the 3D microporous gel. For example, as exemplified later herein, in certain embodiments, the systems herein can include a water purification system including a gel piece described herein, held within a porous plate and floated in a contaminated body of water, such as a lake, river, or container vessel, such that the gel swells as the contaminated water is absorbed by the gel. The gel can then be removed from the water and allowed to absorb sunlight for a period of time (e.g., up to 2 hours, up to 4 hours, up to 12 hours, or up to 18 hours) to cause a phase change and release of purified water from the gel. In certain embodiments, the systems herein include a container for receiving purified water as it exits the gel, i.e., as it is released from the gel composition.

[0050] Considering the embodiments herein in more detail, further discussion is provided in the following examples.

[0051] [Example 1] SAG formation SAG according to one embodiment of the present disclosure was synthesized by polymerization of an aqueous solution of N-isopropylacrylamide monomer. To incorporate PDA nanoparticles onto the surface of the gel scaffold while maintaining the 3D porous structure, the PNIPAm hydrogel was immersed in a dopamine-Tris buffer solution (2 mg / mL) at room temperature (as shown in Figures 2A and 4A). A thin PDA layer formed on the surface of the gel scaffold. During this functionalization process, the color of the hydrogel changed to dark (black or nearly black), confirming successful coating and the robust deposition of cross-linked polydopamine homopolymer (see contrast in Figures 9A–F). PDA possesses uniformly distributed catechol groups, which can be easily oxidized and spontaneously coordinate with metal cations to form stable coordination bonds. Then, in the final step of SA film coating, the PDA-modified gel was immersed in a CuCl2 solution and sodium alginate solution for 5 min. Cross-linked SA was formed by coupling one or more catechol groups of PDA with Cu. 2+ was adsorbed onto the PDA layer via a coordinate bond between them.

[0052] The structure of the disclosed 3D porous gel was investigated using SEM. The results are shown in Figures 2 and 4. As revealed by SEM, the PNIPAm gel possessed a honeycomb-like structure with high porosity, providing a good platform for water transport via capillary flow. After coating with PDA, the hybrid gel maintained an interconnected porous structure with an average pore size of 50 μm (see Figures 4B-C). For example, as shown in Figure 2B, PDA nanoparticles firmly attached to the hydrogel backbone thanks to their catechol groups while maintaining the overall microporous structure as water transport channels and vapor pathways. Higher magnification revealed that PDA was indeed deposited on the PNIPAm structure in the form of nanoparticles.

[0053] Energy-dispersive X-ray (EDX) elemental mapping showed the presence of CK, NK, and OK edge elements in the PDA-modified PNIPAm gel. SA coating resulted in a dense and homogeneous polymer film on the hydrogel surface. For example, (Figure 2C) shows that both Cu and Na signals were uniformly distributed throughout the scanned area, and no large pores were observed on the hydrogel surface. N element in PDA and PNIPAm was not detected, and Cu was present on the surface of the entire hydrogel. 2+ This further confirmed the successful and well-controlled deposition of the SA / alginate layer. As another example, Figure 4D also shows EDX elemental mapping for the Cu L-edge, C-K-edge, Na K-edge, and O-K-edge elements. Notably, both Cu and Na signals were uniformly distributed throughout the entire scanned area, and no N element from PDA or PNIPAm was detected, further confirming the successful and well-controlled deposition of the SA / alginate layer to a thickness of 1.2 μm on the surface of the hybrid hydrogel.

[0054] The results further demonstrated that while conventional PNIPAm gels crosslinked with N,N'-methylenebisacrylamide (BIS) were not at all elastic and even shattered under compression, the PNIPAm gels obtained using the microgels formed here as crosslinkers were highly elastic and could recover to their original shape even after compression. Furthermore, the SAG formed here was able to maintain the elastic properties of PNIPAm after modification with PDA and SA. The gels formed here were found to be able to recover to their original state after being stretched to several times their original length.

[0055] [Example 2] Compression tests, wetting behavior, and XPS of SAG To demonstrate the resilience of SAGs formed according to embodiments herein, standard compression tests were performed.

[0056] As expected, the conventional BIS-crosslinked PNIPAm gel was brittle and unable to withstand compression. In contrast, the prepared microgel-crosslinked PNIPAm gel exhibited larger deformation under stress and fully recovered upon stress removal (see, for example, Figure 15A-D). After nine loading-unloading cycles at approximately 80% strain, the modified PNIPAm gel maintained good technical stability, an advantage of the crosslinked microgel nanostructure (Figure 5A).

[0057] After functionalization with PDA and SA, the gels maintained their elasticity. As shown in Figure 5A, the compressive stress-strain curves of SAG demonstrated that the recoverable compressive strain could reach at least 50%, at least 60%, at least 70%, or at least 80% in various embodiments. Furthermore, as the stress was removed, the strain was observed to gradually decrease to zero. Notably, SAG rapidly recovered to its original shape after high compression or large extension (see, for example, Figure 15D).

[0058] The effects of PDA and SA on the wetting properties of PNIPAm gels were investigated by recording the dynamic wetting behavior of water droplets at room temperature. As shown in Figure 5C, when placed on PNIPAm, the water droplet remained stable with a water contact angle of approximately 53°. In contrast, for PDA-modified PNIPAm, the water contact angle decreased to approximately 20° within 30 seconds due to the hydrophilic nature of polydopamine. Finally, with the SA / PDA composite layer, the water droplet was rapidly accepted by the SAG within 30 seconds. This suggests that SAG is hydrophilic, facilitating water transport within the membrane and useful for removing hydrophobic contaminants such as oil.

[0059] To confirm the chemical composition of the SAG, X-ray photoelectron spectroscopy (XPS) was also performed on the gels described herein along with Fourier transform infrared spectroscopy (FTIR). From the XPS of SAG (Figure 13), the peaks at 530, 400, and 285 eV were assigned to oxygen (O), nitrogen (N), and carbon (C). 2+A peak appeared around 950 eV, which corresponds to the binding energy of . The high-resolution spectra of each element further demonstrated the successful modification of PNIPAm with PDA and SA (see, for example, Figure 5D). The FTIR spectrum in Figure 13B showed a peak at approximately 3400 cm. -1 The broad band at 1643 cm can be attributed to the NH stretching vibration of PNIPAm and the OH stretching vibration of the hydroxyl groups of PDA. -1 and 1551 cm -1 The peaks represent the typical C=O and NH stretching of PNIPAm, respectively. Taken together, these results strongly suggest the formation of SAG, which is in good agreement with the SEM characterization.

[0060] Another observed advantage of SAG was the rapid water release triggered by a phase transition at the LCST of PNIPAm. The LCST was confirmed by differential scanning calorimetry (DSC), and the results are shown in Figure 6A. The LCST of PNIPAm was identified by an endothermic peak at approximately 34 °C and was unaffected by treatment with PDA and SA. The low-temperature LCST of SAG is beneficial for promoting water purification under conditions including natural sunlight. Another useful characteristic for solar water production is broadband and efficient light absorption. The total solar absorptance of SAG was measured by UV-vis-NIR spectroscopy in the wavelength range of 200–1800 nm. As shown in Figure 6B, SAG exhibited broad and efficient absorption.

[0061] Light-assisted water release from SAG at low temperatures was achieved at 1 kW / m 2The PDA was evaluated under simulated sunlight (1 sun). Under 1 sun illumination, the surface temperature of the SAG increased over time and reached the LCST within 300 seconds of illumination (as shown in Figure 6C). The final surface temperature of the SAG was approximately 39 °C, approximately 5 °C higher than the LCST. In contrast, illumination increased the surface temperature of pure PNIPAm to approximately 28 °C, significantly lower than the LCST. This comparison convincingly demonstrates the use of PDA as a photothermal conversion material. The heating effect of PDA was also revealed by infrared imaging; see Figure 14. The substantially homogeneous distribution of the hot areas again confirmed that PDA was distributed substantially uniformly on the PNIPAm.

[0062] [Example 3] water release rate To test the water release rate of water-swollen SAG, we exposed it to simulated sunlight. At the LCST, the hydrophilicity of PNIPAm is switched by a conformational change. Accordingly, any stored liquid was expected to be released. As shown in Figure 6D, exposure of the SAG formed herein to simulated sunlight was found to drive the release of liquid water. Furthermore, very small amounts of water vapor were collected by the evaporation-condensation process (see, for example, Figure 14). Therefore, we concluded that SAG combines two water release modes in a single material platform. SAG technology is a superior clean water production mechanism to previously reported solar-based water collection systems based solely on steam / vapor generation. In this regard, the materials, methods, and processes described herein can overcome two major drawbacks of known systems: (1) low water collection rate; and (2) high energy requirements for evaporation.

[0063] As shown in Figure 6E, when water-swollen SAG was irradiated with 1 sun, the mass loss increased with time, and the weight change was 80–90%, or approximately 87.4%, after 30 min. This indicates that almost all of the water absorbed in the SAG was released. In contrast, pure water showed negligible mass loss under the same conditions. More notably, the water collection rate of SAG was 7 kg / m under 1 sun irradiation. -2 h -2 reached over 7.18 kgm -2 h -2 , see Figure 4F). Because the purification mechanism in certain embodiments herein does not involve any or substantially no water evaporation (an energy-intensive process), the water collection rates found using the present technique can be higher than those that rely on evaporation: poly(vinyl alcohol) (PVA), alginate (SA), chitosan (CS), polyacrylamide (PAAm), poly(sodium acrylate) (PSA), silica gel, poly(ionic liquid) (PIL), poly(ethylene glycol) diacrylate (PEGDA), and agarose (see, e.g., Figure 6F for a comparison). The high water collection rates of the present technique may be at least partially due to the thermoresponsive phase transition of PNIPAm, which promotes liquid water release at the LCST.

[0064] [Example 4] Decontamination Capability A practical way to improve access to clean water is to obtain water after purification from various contaminated sources. The water decontamination ability of the present material was tested in several model wastewater sources containing small molecule dyes, heavy metals, oil, and yeast.

[0065] To initially test the solar-generated water of the SAG herein, three organic dyes with different sizes and surface charges, as well as lead (Pb), were selected as representative model contaminants: rhodamine 6G (R6G), methyl orange (MO), and 4-nitrophenol (4-Nip). R6G is a positively charged compound, MO is a negatively charged compound, and 4-Nip is essentially a neutral compound.

[0066] For R6G, after one treatment cycle, SAG removed more than 95% (approximately 97.1%), producing highly pure water, as evidenced by the color change (see Figure 7B).

[0067] The SAG removal rates for the MO and 4-Nip samples were greater than 85% (about 87.7%) and greater than 80% (about 84%), respectively, after one treatment cycle (see FIG. 16).

[0068] The high density of amine and catechol groups on PDA can strongly capture metals. As shown in Figure 7C, after one treatment with the SAG, the Pb in the contaminated water was significantly reduced. 2+ The concentration of ions was reduced from approximately 25 ppm to less than 5 ppm (approximately 3.7 ppm), demonstrating its effectiveness in decontaminating heavy metal-containing water. 2+ It has been observed that concentrations of PDA and SA are reduced from about 3.7 ppm to below the U.S. Environmental Protection Agency's (EPA) drinking water limit (15 ppm). Indeed, in certain embodiments, the reductions are so dramatic that they are below 15 ppm, below 10 ppm, below 5 ppm, and below 1 ppm, below 0.5 ppm (and even as low as about 0.012 ppm). These impressive results are believed to be due to the incorporation of PDA and SA into the porous gel network.

[0069] Another criterion for evaluating the practicality of materials for wastewater purification is their reusability. As shown in Figure 17, SAG showed almost no degradation in water purification after 10 cycles. This may be due to the SAG structure and the adhesion between different layers (see Figure 18).

[0070] Of further practical importance is the purification of water from emulsified oil / water mixtures during remediation and environmental remediation. The water purification properties and recyclability of the 3D porous gel were further tested as follows: To verify the application of the solar-powered purification device to wastewater purification, the 3D porous hydrogel was immersed in various simulated wastewaters, including wastewater contaminated with organic dyes, oil, and bacteria.

[0071] First, we evaluated the purification ability of the hybrid gel using a sodium dodecyl sulfonate (SDS)-stabilized oil-in-water emulsion composed of cyclohexane as a model. The original SDS-stabilized emulsion is milky white. After separation by the 3D gel, the water generated from the gel under sunlight irradiation became completely transparent and clean (see Figure 3A). Correspondingly, no oil droplets were observed in the collected water in optical microscope images, indicating that almost all oil droplets were removed by the hydrogel.

[0072] Considering that nearly 80% of known diseases are spread due to drinking unsafe water associated with bacteria, this study tested the bacteria-removal properties of the dried hybrid hydrogel using a 1 wt% yeast solution. As shown in Figures 3B and 7E, the yeast concentration was so high that the yeast cells aggregated to form a thick layer. For water samples produced from the gel, nearly all of the yeast was blocked, with only a few randomly dispersed yeast cells, indicating the likelihood of producing clean water free of bacteria. Thus, in certain embodiments, the SAG herein was found to produce substantially clean water substantially free of yeast cells.

[0073] As shown in Figure 3C, the gel also demonstrated strong purification performance against R6G-contaminated water, producing highly pure water. After 10 cycles of water production, only 5.8% R6G was present in the produced water (see Figure 3D). The 3D porous gel was also shown to be mechanically stable for reuse and recycling without any obvious deterioration in its water purification properties.

[0074] In further testing, SAG-decontaminated water from three different emulsions containing either hexane, cyclohexane, or petroleum ether was subjected to the following experiments. As shown in Figure 7D, the original cyclohexane-in-water emulsion was visually milky white, and the diameters of the cyclohexane droplets in the emulsion ranged from 1 to 30 μm (see Figures 19A and 20A-B). After one SAG treatment, clean water was produced (see Figure 7D) without any traces of oil droplets, as confirmed by DLS measurements (see Figure 19B).

[0075] For other oil-in-water emulsions tested, the SAG also produced purified water (see Figures 20A-B). Specifically, after adsorption and desorption by the solar absorber gel, the produced water was substantially clear and clean, with no oil droplets observed in the micrograph (see Figure 20A). For an SDS-stabilized oil-in-water emulsion composed of hexane, the gel was also able to effectively filter substantially all oil droplets from the emulsion and produce substantially clean water (see Figure 20B). This oil-fouling resistance property of the SAG herein is due to the strongly hydratable SA polymer surrounding the gel, which formed a strong and well-hydrated layer that prevented oil from adhering to the gel surface in an aqueous environment.

[0076] The ability of SAG to produce clean water from oil-in-water emulsions may be due to the superhydrophilicity of SAG, which appears to substantially hinder oil uptake.

[0077] [Example 5] Lake water testing Alternative water sources, such as lake water, are promising options for producing water safe for human consumption. A water purification system was fabricated from the materials described in this technology in a rectangular parallelepiped structure measuring 11 cm x 70 cm x 1 cm, placed on a porous plate, and floated on Lake Carnegie (see Figure 8A). The lake surface temperature was approximately 20-28°C, most typically approximately 25°C. During the process, the SAG system absorbed water and reached a swollen state. The swollen material was then removed from the lake, placed on a container, and exposed to natural sunlight. It was found that the surface temperature of the SAG rose above 30°C (over 2-6 hours in various embodiments), and once it exceeded 38°C, the purification system continuously produced clean water that flowed through the porous plate to the bottom of the container (see Figure 8B). In one embodiment, the system was exposed to sunlight for 2 hours, producing 40-60 mL of clean water. Microscopic images of lake water before and after treatment with the system revealed that various microorganisms (including coccoid, rod-shaped, spiral, and aggregated bacteria and other microorganisms) were successfully removed by the system to produce potable water (see Figures 8D-E). The quality of the purified water was compared to that of domestic and municipal water by measuring relative resistivity. The results are shown in Figure 8F. As can be seen, the resistivity values ​​of the lake water, SAG purified water, and domestic water were 0.16, 0.87, and 0.74 MΩ, respectively, indicating sufficiently effective purification at temperatures below 30-32°C. This indicates that the SA of the gel described herein is at a K + , Na + , Li + , Ca 2+ , and Mg 2+ It was speculated that this was the result of the excellent cation removal behavior of the SAG. Furthermore, it is highly likely that the formation of an SA membrane around the SAG blocked the migration path of fine particles. Some ions may enter the SAG, but will be adsorbed by the PDA.

[0078] While the present invention has been described in relation to its embodiments, these embodiments and examples are merely illustrative and are not intended to be limiting. Many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention should not be limited by the specific disclosure herein, and it may be embodied in other forms not expressly described herein without departing from its spirit. The inventions described in the original claims of this application are set forth below. [1] (a) A 3D microporous gel scaffold containing poly(N-isopropylacrylamide) (PNIPAm) and having an outer surface; (b) a plurality of polydopamine (PDA) nanoparticles attached to the outer surface of the 3D microporous gel scaffold, the polydopamine (PDA) nanoparticles comprising one or more catechol groups; (c) a sodium alginate (SA) layer coating the 3D microporous gel scaffold and the plurality of PDA nanoparticles; A gel composition comprising: [2] The gel composition according to [1], further comprising a metal configured to coordinate with one or more catechol groups of the PDA. [3] The gel composition according to [2], wherein the metal is copper. [4] (a) a 3D microporous gel scaffold containing poly(N-isopropylacrylamide) (PNIPAm) and having an outer surface; (b) a plurality of polydopamine (PDA) nanoparticles attached to the outer surface of the 3D microporous gel scaffold, the polydopamine (PDA) nanoparticles comprising one or more catechol groups; (c) a metal configured to coordinate with one or more catechol groups of said PDA; (d) a sodium alginate (SA) layer coating the 3D microporous gel scaffold and the plurality of PDA nanoparticles; The gel composition according to [1], comprising: [5] (a) Preparing 3D microporous; (b) immersing the 3D microporous gel scaffold in a solution containing dopamine to obtain a polydopamine (PDA)-attached 3D microporous gel scaffold; (c) immersing the PDA-attached 3D microporous gel scaffold in a solution containing sodium alginate to obtain a gel composition for water purification; A method for producing a gel composition for water purification, comprising: [6] The method according to [5], wherein the sodium alginate solution contains a metal capable of coordinating with the catechol group of the polydopamine. [7] (a) obtaining a gel composition comprising: (i) a 3D microporous gel scaffold; (ii) a plurality of polydopamine (PDA) nanoparticles attached to an outer surface of the gel scaffold; and (iii) an outer layer comprising sodium alginate; (b) immersing the gel composition in a predetermined amount of contaminated water, the contaminated water comprising water and a contaminant; (c) allowing the 3D microporous gel scaffold to absorb at least a portion of the remaining, less contaminated water while the outer layer of the gel composition repels at least a portion of the contaminants; (d) removing the gel composition from the contaminated water; (e) exposing the gel composition to sunlight such that the sunlight is converted into thermal energy, thereby raising the temperature of the gel composition above a lower critical solution temperature of the gel composition and causing a hydrophilic to hydrophobic phase transition of the gel composition; (f) releasing the less contaminated water absorbed in the gel framework from the gel composition; A method for purifying water, comprising: [8] The method according to [7], wherein the concentration of the contaminant in the less contaminated water is less than 5% of the concentration of the contaminant originally present in the contaminated water. [9] The method of [7], wherein the concentration of the contaminant in the less contaminated water is less than 1% of the concentration of the contaminant originally present in the contaminated water.

[10] The method according to [7], further comprising repeating steps (a) to (e).

[11] The method of

[10] , further comprising repeating steps (a) through (e) in a manner that provides water of higher purity than in a previous iteration, wherein in subsequent iterations of said steps, the released less contaminated water is used as a source of contaminated water.

[12] The method of [7], wherein the contaminant is a hydrocarbon, a bacterial strain, a metal, a pigment, a particulate, a dirt, a naturally occurring organic matter, or any combination thereof.

[13] A system for purifying water, comprising: (i) a 3D microporous gel scaffold; (ii) a plurality of polydopamine (PDA) nanoparticles attached to the outer surface of the gel scaffold; and (iii) a gel composition comprising an outer layer comprising sodium alginate.

[14] The system described in

[13] , wherein when the gel composition is immersed in contaminated water, it absorbs the water while repelling one or more contaminants in the water, becoming a hydrophilic, swollen gel composition containing purified water.

[15] The system described in

[14] , wherein the swollen gel composition transitions to a hydrophobic state when exposed to sunlight, thereby releasing the purified water.

[16] (a) a porous plate configured to contact the gel composition before and while the gel composition is in a hydrophilic swollen state; or (b) a container configured to receive the purified water as it is released from the gel composition;

[13] The system according to

[13] , further comprising one or more of:

Claims

1. (a) a 3D microporous gel scaffold comprising poly(N-isopropylacrylamide) (PNIPAm) and having an outer surface; (b) a plurality of polydopamine (PDA) nanoparticles attached to the outer surface of the 3D microporous gel scaffold, the polydopamine (PDA) nanoparticles comprising one or more catechol groups; (c) a sodium alginate (SA) layer coating the 3D microporous gel scaffold and the plurality of PDA nanoparticles; A gel composition comprising:

2. 10. The gel composition of claim 1, further comprising a metal configured to coordinate with one or more catechol groups of the PDA.

3. The gel composition of claim 2 wherein the metal is copper.

4. (a) a 3D microporous gel scaffold comprising poly(N-isopropylacrylamide) (PNIPAm) and having an outer surface; (b) a plurality of polydopamine (PDA) nanoparticles attached to the outer surface of the 3D microporous gel scaffold, the polydopamine (PDA) nanoparticles comprising one or more catechol groups; (c) a metal configured to coordinate with one or more catechol groups of said PDA; (d) a sodium alginate (SA) layer coating the 3D microporous gel scaffold and the plurality of PDA nanoparticles; 10. The gel composition of claim 1, comprising:

5. (a) providing a 3D microporous gel scaffold comprising poly(N-isopropylacrylamide) (PNIPAm) and having an outer surface; (b) immersing the 3D microporous gel scaffold in a solution containing dopamine to obtain a polydopamine (PDA)-attached 3D microporous gel scaffold; (c) immersing the PDA-attached 3D microporous gel scaffold in a solution containing sodium alginate to obtain a gel composition for water purification; A method for producing a gel composition for water purification, comprising:

6. The method of claim 5 , wherein the sodium alginate solution contains a metal capable of coordinating with the catechol group of the polydopamine.

7. (a) obtaining a gel composition comprising: (i) a 3D microporous gel scaffold comprising poly(N-isopropylacrylamide) (PNIPAm) and having an outer surface; (ii) a plurality of polydopamine (PDA) nanoparticles attached to the outer surface of the gel scaffold; and (iii) a sodium alginate (SA) layer coating the 3D microporous gel scaffold and the plurality of PDA nanoparticles; (b) immersing the gel composition in a predetermined amount of contaminated water, the contaminated water comprising water and a contaminant; (c) allowing the 3D microporous gel scaffold to absorb at least a portion of the remaining, less contaminated water while the outer layer of the gel composition repels at least a portion of the contaminants; (d) removing the gel composition from the contaminated water; (e) exposing the gel composition to sunlight such that the sunlight is converted into thermal energy, thereby raising the temperature of the gel composition above a lower critical solution temperature of the gel composition and causing a hydrophilic to hydrophobic phase transition of the gel composition; (f) releasing the less contaminated water absorbed in the gel framework from the gel composition; A method for purifying water, comprising:

8. 8. The method of claim 7, wherein the concentration of the contaminant in the less contaminated water is less than 5% of the concentration of the contaminant originally present in the contaminated water.

9. 8. The method of claim 7, wherein the concentration of the contaminant in the less contaminated water is less than 1% of the concentration of the contaminant originally present in the contaminated water.

10. The method of claim 7 further comprising repeating steps (a) through (e).

11. 11. The method of claim 10, further comprising repeating steps (a) through (e) in a manner that provides water of higher purity than in a previous iteration, wherein in subsequent iterations of said steps, the released less contaminated water is used as a source of contaminated water.

12. 8. The method of claim 7, wherein the contaminants are hydrocarbons, bacterial strains, metals, pigments, particulates, dirt, naturally occurring organic matter, or any combination thereof.

13. A system for purifying water, comprising a gel composition comprising: (i) a 3D microporous gel scaffold comprising poly(N-isopropylacrylamide) (PNIPAm) and having an outer surface; (ii) a plurality of polydopamine (PDA) nanoparticles attached to the outer surface of the gel scaffold; and (iii) a sodium alginate (SA) layer covering the 3D microporous gel scaffold and the plurality of PDA nanoparticles.

14. 14. The system of claim 13, wherein the gel composition, when immersed in contaminated water, absorbs the water while repelling one or more contaminants in the water, to become a hydrophilic, swollen gel composition containing purified water.

15. 15. The system of claim 14, wherein the swollen gel composition transitions to a hydrophobic state upon exposure to sunlight, thereby releasing the purified water.

16. (a) a porous plate configured to contact the gel composition before and while the gel composition is in a hydrophilic swollen state; or (b) a container configured to receive the purified water as it is released from the gel composition; The system of claim 13 , further comprising one or more of:

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