Patent Application
20240254013
Provided herein are novel foam composites comprising a chitosan-cellulose-MXene hydrogel adsorbed into a foam. Hydrophilic surface-modified two-dimensional MXenes nanosheets integrated into one-dimensional activated cellulose microfibers and three-dimensional neutralized chitosan hydrogel are adsorbed into a foam, for example polyurethane foam, to create the foam composites. Also described herein are the use of the foam composites for the purification of water, including the removal of at least one heavy metal.
MXenes are a class of 2-D transition metal carbide, nitride, or carbonitride inorganic compounds that were first discovered in 2011. MXenes, which have the general formula Mn+1XnTx where M is an early transition metal, X is carbon and/or nitrogen, and T is a functional group (typically O, OH, and/or F) on the surface of the MXene, are a few layers thick and have the appearance of fine, flaky pastry dough under a scanning electron microscope. The conductive carbide core means that MXenes have high metallic conductivity, but unlike other 2-D materials, they are also hydrophilic because of their hydroxyl- and oxygen-functionalized surfaces. The first MXene discovered was Ti3C2 (Naguib, M. et al. ACS Nano 2012, 6, 1322), and in the last several years, over two dozen MXenes have been synthesized (Anasori et al. Nature Reviews Materials, 2017, 2, 16098) for various applications, including electrochemical capacitors, sensors, energy storage, electronics, and catalysis.
While various MXene-based materials have also been used individually or with other composites as adsorbents for the removal of toxic pollutants, including lead, copper, barium, chromium, cadmium, mercury, uranium, and phosphate, these composites take a long-time (from several minutes to several hours) to achieve complete adsorption. Also, their use typically requires multiple preparation steps, and they can only be used in small quantities, which precludes their use in large-scale applications. The use of MXene-based hydrogels for water purification is described in U.S. Pat. No. 11,311,843 assigned to Qatar University.
Alternative technologies for water purification or treatment include physical adsorption, photocatalytic degradation, electrocoagulation, membrane filtration, and electrochemical techniques. However, these often require complicated steps and/or special laboratory techniques. They are also often high cost-operations (i.e., heating, pressure, and electricity, etc.), especially in large-scale applications.
Given that water is the most important natural resource and 97% of water is saline, it would be useful to provide new compositions for water treatment that can be easily prepared in a high yield from abundant, green, and inexpensive resources. It would also be beneficial to provide porous foam compositions that are capable of the complete removal of toxic metals at ambient temperature and zero pressure in a minimal amount of time.
Described herein are foam composites comprising a chitosan-cellulose-MXene hydrogel adsorbed into a polymer-based foam. Hydrophilic two-dimensional MXenes nanosheets surface distributed in between one-dimensional activated cellulose microfibers and three-dimensional neutralized chitosan hydrogel are adsorbed into the foam, for example, polyurethane foam, to form the foam composites. In one embodiment, polyurethane foam is soaked in a composite gel comprising cellulose, chitosan and MXene. The foam easily absorbs the gel because the foam contains pores with sizes of about 1-5 mm, while the size of the MXene is about 200 nm, the cellulose is about 200 nm diameter/3 mm in length, and the chitosan flakes are about 5 μm. The foam composites described herein combine the unique physiochemical merits of hybrid hydrophilic (metal carbide) and hydrophobic (chitosan, cellulose, and polyurethane foam) materials in combination with porous form. The foam composites are advantageous for green water treatment, and the foam in particular allows for the efficient removal of toxins and heavy metals of various sizes.
Also described herein is a simple one-step method for water purification that occurs within a few seconds at room temperature, zero-electricity, and atmospheric pressure using the novel foam composites described herein. Unlike previous approaches that need several hours to remove toxic metals, under certain embodiments, and as described below, water purification using the foam composites described herein results in the complete removal of Cd and/or Zn within about 20 to 30 seconds at room temperature, atmospheric pressure, and using zero-electricity. The method of purifying water using the foam composites described herein can be used to purify, for example, industrial wastewater, agricultural wastewater, or household waste water.
Also described herein is a method for the synthesis of the foam composites that comprises adding dropwise an aqueous solution of the MXenes nanosheets and cellulose microfibers into an aqueous solution of chitosan to form the chitosan-cellulose-MXene hydrogel that is then adsorbed into a foam to afford the foam composites.
It is, in part, this simple synthesis that renders the foam composites described herein easy to use and cost effective. The simple synthesis and the use of cost-effective, green, and abundant materials makes these foam composites highly practical for general utilization in the industrial, agriculture, and household sectors.
Described herein are novel foam composites comprising a chitosan-cellulose-MXene hydrogel adsorbed into a foam. The chitosan-cellulose-MXene hydrogel of the foam composite comprises hydrophilic two-dimensional MXenes nanosheets surface modified with hydroxyl-, oxygen-, and fluorine-terminated groups integrated into one-dimensional activated cellulose microfibers and three-dimensional neutralized chitosan hydrogel. The chitosan-cellulose-MXene hydrogel is then mixed with polyurethane foam prior to annealing to form the foam composites.
In certain embodiments, the foam composites as described herein can be directly used as adsorbents for prompt, for example in about 30 seconds or less, and efficient removal of toxic metals (including, but not limited to, Cd, Zn, and Co, mixed or individualized), and inorganic pollutants from wastewater. Importantly, the treatment can be conducted at room temperature, under zero-pressure, and with zero-electricity.
The current approaches for water treatment, such as adsorption, photocatalytic degradation, chemical oxidation, membrane filtration, and electrochemical techniques involve multiple steps, and can require heating, pressure, and electricity in addition to special laboratory equipment or skills. This is in contrast to the foam composites described herein that, in certain embodiments, can treat wastewater in a simple one-step process at room temperature, zero-pressure, and zero-electricity without the need for special laboratory technique. In certain embodiments, the foam composites as described herein can be easily integrated or combined with other techniques such as electrocoagulation (to remove organic and inorganic pollutants) and capacitive deionization (to remove soluble salts, phosphates, and carbonates).
The terms “a” and “an” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The term “or” means “and/or”. Recitation of ranges of values merely intend to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. The endpoints of all ranges are included within the range and independently combinable. All processes described herein can be performed in a suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of example, or exemplary language (e.g., “such as”), is intended merely to better illustrate the invention and does not pose a limitation on the scope of the invention on unless otherwise claimed.
As used herein, “independently” refers to the relationship among multiple instances of the same variable when selected from the same set of possibilities (e.g., a Markush group). For example, if the variable X is selected independently from the group consisting of a, b, and c, each instance of X in a structure can be the same as (e.g., all “a”) or be different from any other instance of X (e.g., for three “X,” one “b” and two “a” or any other combination of a, b, and c). Typically, for at least some embodiments of a group as disclosed herein (e.g., “A, B, or C”; “the member selected from the group consisting of A, B, and C”), members of the group are (1) independently selected from the alternatives and (2) groups do not exclude the possibility of embodiments comprising combinations of the individual group members.
As used herein, “or” is not exclusive (i.e., “or” may be equivalent to “and/or”). For example, an aspect comprising “A, B, or C” may present embodiments with A, B, C, A in combination with B, B in combination with C, A in combination with C, or all three (A, B, and C) in combination.
The term “MXene” refers to a hydrophilic two-dimensional nanosheet that consists of metal carbides, nitrides, or carbonitrides. In certain embodiments, the MXene is approximately 200 nm×100 nm with a thickness between about 1 nm and 2 nm.
As used herein, “activation” or “activated” refers to treatment of a chemical substance to improve the chemical properties of the chemical substance compared to the chemical properties of the chemical substance before such treatment. For example, an activated chemical substance has chemical properties that are better and/or more useful than the corresponding chemical substance or educt in unactivated form.
As used herein, “nanosheets” refers to nanoscale particles (particles having a size of less than 100 nm) arranged in the form of sheets or layers of the nanoscale particles.
As used herein, “hydrogel” refers to cross-linked hydrophilic polymers that maintain structural integrity when dispersed in water.
As used herein, “halogen” refers to fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).
As used herein, “industrial wastewater” refers to water waste derived from industrial scale (e.g., metric ton) oil, gas, and petroleum processing.
As used herein, “domestic wastewater” or “household wastewater” refers to water waste derived from, for example, household use.
As used herein, “heavy metals” refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations. Examples of heavy metals include, without limitation, mercury (Hg), cadmium (Cd), zinc (Zn), arsenic (As), chromium (Cr), thallium (TI), and lead (Pb).
As used herein “one-dimensional” nanomaterials (e.g., nanosheets) refer to nanomaterials where at least one dimension is outside of the nanoscale. For example, in certain embodiments, when one dimension of the nanomaterial is larger than 100 nm. In certain embodiments, one-dimensional nanomaterials are nanosheets.
As used herein “two-dimensional” nanomaterials (e.g., nanosheets) refer to nanomaterials where at least two dimensions are outside the nanoscale. For example, in certain embodiments, when two dimensions of the nanomaterial are larger than 100 nm. In certain embodiments, two-dimensional nanomaterials are plate-like shapes. In certain embodiments, two-dimensional nanomaterials include, without limitation, nanofilms, nanolayers, and nanocoatings.
As used herein, “three-dimensional” materials refer to materials where each dimension is outside the nanoscale. For example, in certain embodiments, three-dimensional materials include, without limitation, chitosan.
The foam composites described herein comprise a chitosan-cellulose-MXene hydrogel adsorbed into a foam, for example a polymer-based foam. The chitosan-cellulose-MXene hydrogel of the foam composites comprises hydrophilic two-dimensional MXenes nanosheets surface modified with hydroxyl-, oxygen-, and fluorine-terminated groups integrated into one-dimensional activated cellulose microfibers and three-dimensional neutralized chitosan hydrogel.
The foam composites described herein combine the unique physiochemical merits of functionalized Mxenes, activated 1D cellulose, chitosan hydrogel and a porous foam, and the foam in particular is advantageous because it provides feasibility for a large-scale operation, is low in cost, has high adsorption affinity, and is easy to recycle. The functionalized MXenes provide high surface area, electrical conductivity, hydrophilicity, abundant OH groups, and abundant adsorption sites. These MXenes help to promote ion exchange, diffusion rate, swelling properties, and provide massive adsorption for the pollutants. The activated 1D cellulose is electron-rich, has a high aspect ratio, provides accessible active adsorption sites, and is hydrophobic. Activation of the cellulose provides massive adsorption or exchange sites for toxic/heavy metals and organic/inorganic pollutants. The chitosan hydrogel is antimicrobial, hydrophobic, is composed of abundant amino/hydroxyl/ether groups that provide for strong intercalation with metals, and is safe. The strong cation exchange of chitosan induces the quick and efficient adsorption of various pollutants at room temperature, while the antimicrobial activity allows for disinfection of water and the removal of pollutants. Importantly, the porous foam with high porosity volume and a wide range of pore sizes allows for the efficient removal of toxins and heavy metals of various sizes.
The foam composite is porous. In one embodiment, the average pore size is between about 1 mm and 5 mm. In one embodiment, the average pore size is between about 1 mm and 3 mm. In one embodiment, the average pore size is between about 2 mm and 4 mm. In one embodiment, the average pore size is at less than about 5 mm, less than about 4 mm, less than about 3 mm, less than about 2 mm, less than about 1 mm, or less than about 0.5 mm.
In one embodiment, the average pore diameter of the foam is between about 500 μm and 50 μm. In one embodiment, the average pore diameter of the foam is between about 450 μm and 100 μm. In one embodiment, the average pore diameter of the foam is between about 400 μm and 150 μm. In one embodiment, the average pore diameter of the foam is between about 350 μm and 200 μm. In one embodiment, the average pore diameter of the foam is between about 300 μm and 250 μm. In one embodiment, the average pore diameter of the foam is less than about 500 μm, less than about 400 μm, less than about 300 μm, less than about 250 μm, less than about 200 μm, less than about 150 μm, less than about 100 μm, or less than about 50 μm. In certain embodiments, the average pore diameter may vary by ±10 μm.
In one embodiment, the pore volume is between about 70% and 95%. In one embodiment, the pore volume is between about 75% and 90% or about 80% and 90%. In one embodiment, the pore volume is at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, or at least about 95%.
In certain embodiments, the average pore diameter of the foam composite is between about 210 μm and 190 μm. In one embodiment, the average pore diameter of the foam composite is about 200 μm.
The foam composites described herein are degradable, green, and easy to handle. Additionally, the foam composites described herein can be in synthesized in high yield under both small-scale (several centimeters) and large scale (several meters) conditions. Further, they can be easily prepared from a wide variety of natural, abundant, and inexpensive material.
The MXene of the foam composite is characterized by the formula Mn+1XnTx where M is an early transition metal selected from scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo), mercury (Hf), and tantalum (Ta); X is carbon and/or nitrogen; and, Tx is a functional group on the surface of the MXene (typically oxygen-, hydroxyl- and fluorine-terminating groups).
In one embodiment, the MXene of the foam composite has the formula M2XTx. In one embodiment, the MXene of the foam composite has the formula M3X2Tx. In one embodiment, the MXene of the foam composite has the formula M4X3Tx.
In a preferred embodiment, the MXene of the foam composite has the formula Ti3C2Tx.
In one embodiment, the MXene of the foam composite is modified with functional groups selected from hydroxyl-, oxygen-, and fluorine-terminated groups. In one embodiment, the MXene of the foam composite is modified with hydroxyl-, oxygen-, and fluorine-terminated groups. In one embodiment, the MXene of the foam composite is modified with hydroxyl-terminated groups. In one embodiment, the MXene of the foam composite is modified with oxygen-terminated groups. In one embodiment, the MXene of the foam composite is modified with fluorine-terminated groups. In one embodiment, the MXene of the foam composite is not modified and has the formula Mn+1Xn, for example Ti2C.
The MXene of the foam composite can be solid, porous, or mesoporous. The MXene is between about 1 nm and 2 nm thick. In one embodiment, the MXene is between about 1.5 and 2 nm thick.
In one embodiment, the cellulose of the foam composite is natural. In one embodiment, the cellulose is synthetic.
In certain embodiments, the chitosan of the foam composite can be further modified with a polymer or a cross-linker. In one embodiment, the polymer is a hydrophilic or hydrophobic polymer. Alternatively, the polymer can be an ionic or nonionic polymer. Non-limiting examples of cross-linking agents include glutaraldehyde, epoxy chloropropane, epoxy propyl trimethylammonium chloride, trimesoyl chloride, phthaloyl chloride, isophthaloyl dichloride, paraphthaloyl chloride, or hexanedioyl chloride.
In one embodiment, a carbon-based material, including, but not limited to, carbon-nitride, carbon-dots, carbon nanotubes, a metal organic framework, zeolite, or graphene can be used with the foam nanocomposites described herein.
The chitosan-cellulose-MXene hydrogel is mixed with foam prior to annealing to form the foam composite. In certain embodiments, the foam is polyurethane foam. In alternative embodiments, the foam is another polymer-based foam, including, but not limited to polyethylene (PE)-, polystyrene (PS)-, and polypropylene (PP)-based foam.
The foam composites can be characterized by high annular dark-field SEM imaging and/or EDS elemental mapping analysis. The foam composites can also be analyzed by EDX (energy dispersive X-ray analysis). In one embodiment, the atomic ratio of carbon:titanium:oxygen:fluorine (C:Ti:O:F) of the foam composite as measured by EDX is about 80:14:5:1.
In one embodiment, the foam composite is characterized by an atomic percentage of carbon as measured by EDX between about 90% and about 70%. In one embodiment, the foam composite is characterized by an atomic percentage of carbon as measured by EDX of at least about 70%, at least about 75%, at least about 80%, at least about 85%, or at least about 90%. In one embodiment, foam composite is characterized by an atomic percentage of carbon as measured by EDX of about 80%.
In one embodiment, the foam composite is characterized by an atomic percentage of titanium as measured by EDX of at least about 10%, at least about 15%, or at least about 20%. In one embodiment, the foam composite is characterized by an atomic percentage of titanium as measured by EDX of about 14%.
In one embodiment, the foam composite is characterized by an atomic percentage of oxygen as measured by EDX of at least about 10%, at least about 8%, at least about 5%, or at least about 3%. In one embodiment, the foam composite is characterized by an atomic percentage of oxygen as measured by EDX of about 5%.
In one embodiment, the foam composite is characterized by an atomic percentage of fluorine as measured by EDX of at least about 3%, at least about 2%, at least about 1%, or at least about 0.5%. In one embodiment, the foam composite is characterized by an atomic percentage of fluorine as measured by EDX of about 1%.
In one embodiment, the foam composite is amorphous as measured by X-ray diffraction analysis (XRD).
Also described herein is a method for the synthesis of the foam composite that comprises:
In one embodiment, the etching in step 1 is conducted at room temperature.
In one embodiment, step 1 further comprises modifying the MXene Ti3C2T nanosheet by dissolving the powder in aqueous NaOH solution stirring and drying the subsequent powder to be used in step 2.
In one embodiment, the nanosheet powder and the cellulose powder are mixed in water in step 3.
In one embodiment, the foam is a polyurethane foam. In one embodiment, the annealing is conducted between about 50° C. and 120° C. In one embodiment, the annealing is conducted between about 60° C. and 110° C. In one embodiment, the annealing is conducted between about 70° C. and 100° C. In one embodiment, the annealing is conducted at 80° C.
Another aspect of the current invention is a simple one-step method for the removal of toxic metals, such as heavy metals, mixed or individualized, within a few seconds at room temperature, zero-electricity, and atmospheric pressure using the foam composites described herein. For example, in one embodiment, the use of the foam composites described herein for wastewater treatment results in the complete removal of toxic metals within about 30 seconds at room temperature without heating, pressure, or electricity. In one embodiment, the use of the foam composites described herein for wastewater treatment results in the complete removal of heavy metals, mixed or individualized, within about 20-40 seconds at room temperature without heating, pressure, or electricity. The foam composites described herein can also be used for the removal of other organic (i.e., dyes, hydrocarbons, etc.) and inorganic pollutants (i.e., phosphate, sulfate, carbonate, etc.). In one embodiment, the foam composites described herein are used for the removal of zinc and/or cadmium.
The foam composites as described herein can also be used for water desalination under ambient conditions.
In one embodiment, the purification process is carried out for a solution of one heavy metal. In one embodiment, the purification process is carried out for a solution of more than one heavy metal.
In one embodiment, the foam composites described herein are used for the purification of water solution, wastewater, industrial wastewater, agricultural wastewater, or household water. The pH of the water can be acidic, alkaline, or neutral.
In certain embodiments, the water purification process is carried out simultaneously with disinfection.
In certain embodiments, including any of the foregoing, the foam composites described herein adsorb at least about 60% of the heavy metal from a water solution within less than about 5 minutes, less than about 4 minutes, less than about 3 minutes, less than about 2 minutes, less than about 1 minute, less than about 45 seconds, less than about 30 seconds, or less than about 15 seconds.
In certain embodiments, including any of the foregoing, the foam composites described herein adsorb at least about 65% of the heavy metal from a water solution within less than about 5 minutes, less than about 4 minutes, less than about 3 minutes, less than about 2 minutes, less than about 1 minute, less than about 45 seconds, less than about 30 seconds, or less than about 15 seconds.
In certain embodiments, including any of the foregoing, the foam composites described herein adsorb at least about 70% of the heavy metal from a water solution within less than about 5 minutes, less than about 4 minutes, less than about 3 minutes, less than about 2 minutes, less than about 1 minute, less than about 45 seconds, less than about 30 seconds, or less than about 15 seconds.
In certain embodiments, including any of the foregoing, the foam composites described herein adsorb at least about 75% of the heavy metal from a water solution within less than about 5 minutes, less than about 4 minutes, less than about 3 minutes, less than about 2 minutes, less than about 1 minute, less than about 45 seconds, less than about 30 seconds, or less than about 15 seconds.
In certain embodiments, including any of the foregoing, the foam composites described herein adsorb at least about 80% of the heavy metal from a water solution within less than about 5 minutes, less than about 4 minutes, less than about 3 minutes, less than about 2 minutes, less than about 1 minute, less than about 45 seconds, less than about 30 seconds, or less than about 15 seconds.
In certain embodiments, including any of the foregoing, the foam composites described herein adsorb at least about 85% of the heavy metal from a water solution within less than about 5 minutes, less than about 4 minutes, less than about 3 minutes, less than about 2 minutes, less than about 1 minute, less than about 45 seconds, less than about 30 seconds, or less than about 15 seconds.
In certain embodiments, including any of the foregoing, the foam composites described herein adsorb at least about 90% of the heavy metal from a water solution within less than about 5 minutes, less than about 4 minutes, less than about 3 minutes, less than about 2 minutes, less than about 1 minute, less than about 45 seconds, less than about 30 seconds, or less than about 15 seconds.
In certain embodiments, including any of the foregoing, the foam composites described herein adsorb at least about 95% of the heavy metal from a water solution within less than about 5 minutes, less than about 4 minutes, less than about 3 minutes, less than about 2 minutes, less than about 1 minute, less than about 45 seconds, less than about 30 seconds, or less than about 15 seconds.
In certain embodiments, including any of the foregoing, the foam composites described herein adsorb at least about 99% of the heavy metal from a water solution within less than about 5 minutes, less than about 4 minutes, less than about 3 minutes, less than about 2 minutes, less than about 1 minute, less than about 45 seconds, less than about 30 seconds, or less than about 15 seconds.
In certain embodiments, including any of the foregoing, the foam composites described herein adsorb about 100% of the heavy metal from a water solution within less than about 5 minutes, less than about 4 minutes, less than about 3 minutes, less than about 2 minutes, less than about 1 minute, less than about 45 seconds, less than about 30 seconds, or less than about 15 seconds.
In certain embodiments, including any of the foregoing, the water is acidic. In certain embodiments, including any of the foregoing, the water is alkaline. In certain embodiments, including any of the foregoing, the water is basic.
In certain embodiments, including any of the foregoing, the water comprises at least one heavy metal selected from zinc, cadmium, lead, chromium, copper, mercury, and barium. In one embodiment, including any of the foregoing, the water comprises zinc. In one embodiment, including any of the foregoing, the water comprises cadmium. In certain embodiments, including any of the foregoing, the water comprises both zinc and cadmium.
In one embodiment, the foam composites described herein adsorb at least about 75% of the heavy metal from an acidic water solution within less than about 20 seconds.
In one embodiment, the foam composites described herein adsorb at least about 95% of the heavy metal from an alkaline water solution within less than about 35 seconds.
In one embodiment, the foam composites described herein adsorb about 100% of the heavy metal from an alkaline water solution within less than about 20 seconds.
In one embodiment, the foam composites described herein adsorb about 100% of the heavy metal from a neutral water solution within less than about 20 seconds.
Aluminum titanium carbide powder MAX-phase ((Ti3AlC2), 98%) was purchased from Carbon-Ukraine Ltd and dimethyl sulfoxide (DMSO, C2H6OS, 99.7%) was obtained from Fisher Scientific International, Inc. Hydrofluoric acid, (HF, 48%) was obtained from VWR Chemicals BDH. Sodium hydroxide (NaOH, 99.9%), cellulose microcrystalline powder, (0.6 g/mL (25° C.)), acetic acid (≥99%), sodium hydroxide (≥97%) and chitosan (medium molecular weight) were purchased from Sigma-Aldrich Chemie GmbH (Munich, Germany). Ethanol solution (99%), cadmium chloride hydrated (99%), and polyurethane foam sheet, (0.08 g/cm3) were obtained from DongGuan Gao Yuan Shoes Material Co., Ltd. DongGuan, P.R. China.
For the typical preparation of modified two-dimensional Ti3C2T (T=F, O, OH) nanosheets, Ti3C2Al (1 g) was dispersed in 10 mL HF (48%) and stirred for 24 hours at room temperature followed by five centrifugation/washing cycles at 4000 rpm until the pH reached 5. The resulting powder was stirred with 12 mL of DMSO for 24 hours at room temperature before being centrifuged/washed with water at 3500 rpm five times to afford a powder. The powder was redispersed in H2O under ultrasonic treatment at room temperature for 5 hours and then purified by centrifugation/washing cycles at 3500 rpm with H2O five times to afford a powder that was freeze-dried at 50° C. for 5 hours.
To prepare the MXene with modified —OH groups, Ti3C2 (3 g) powder was mixed with 5% NaOH under stirring at room temperature for 4 hours and freeze-dried at 50° C. for 5 hours.
Cellulose powder (10 g) was dissolved in a solution of 10 mL H2O and 2 mL NaOH for 2 hours at room temperature followed by centrifugation/washing with H2O and drying at 60° C. under vacuum. The resulting powder was mixed with the Ti3C2T powder and dispersed (0.6 g/mL) in water and then added dropwise to the chitosan solution. In an alternative embodiment, the power is dispersed in an inorganic solvent, an organic solvent, or a mixture thereof.
Chitosan hydrogel was prepared by dissolving 4 g of chitosan in an aqueous solution of 100 mL acetic acid (20% v/v) under mechanical stirring at room temperature. Next, the aqueous solution of the 2D Ti3C2T nanosheets (2 g in 5 mL H2O) and 1D cellulose fiber (1.2 gm in 2 mL H2O) was added dropwise into the chitosan hydrogel under mechanical stirring and sonicated to afford a chitosan-cellulose-Ti3C2T hydrogel.
For the preparation of the composite foam, the chitosan-cellulose-Ti3C2T hydrogel was adsorbed onto polyurethane foam (10 cm2) via the impregnation approach, dried at 80° C. under air, and then neutralized in NaOH solution (1 M) until the pH was 7. The foam was left to dry in air at 80° C. and kept for further utilization.
The foam composite was characterized by scanning electron microscope (SEM, Hitachi S-4800, Hitachi, Japan) equipped with an energy dispersive spectrometer (EDS). X-ray diffraction pattern (XRD) was investigated on an X-ray diffractometer (X Pert-Pro MPD, PANalytical Co., Netherland). The Fourier Transform Infrared (FTIR) was recorded on (FTIR, Shimadzu IR-Prestige21).
As shown in the low-magnification SEM images
The high-magnification SEM image showed the 3D multi-layered structure of the composite inside the wall of pores (
A high annular dark-field SEM and EDS elemental mapping analysis showed the composition of the formed composite. Elements titanium (Ti), carbon (C), oxygen (O), and fluorine (F) were coherently resolved and distributed within the composite. The atomic ratios of C, Ti, O, and F were about 79.8, 14.2, 4.9, and 1.1, respectively. This corresponded to the EDX analysis (
The composite foam was dipped in 200 mL aqueous solutions containing H2CdCl2O(100 ppm) and (CH3CO2)2Zn (100 ppm) at 25° C. Standard buffer solutions were used to make solutions with pH values of about 4, 7.4, and 9. Every 10 seconds, an aliquot of the water solution (1 mL) was withdrawn and analyzed using inductively coupled plasma (ICP-OES & ICP-AES, PerkinElmer, USA). The removal efficiency was determined using the following equation:
Under acidic conditions (pH=4), 78% of both metals were adsorbed by the composite foam within 18 seconds (
When the composite foam was modified with —OH groups, the foam was also efficient at removing Zn and Cd. Under alkaline conditions (pH=9), 100% of the both metals were adsorbed within 18 seconds (
The previous detailed description is of a small number of embodiments for implementing the invention and is not intended to be limiting in scope. One of skill in this art will immediately envisage the methods and variations used to implement this invention in other areas than those described in detail. The following claims set forth a number of the embodiments of the invention disclosed with greater particularity.
