WO2022250797A2

WO2022250797A2 - Nanocomposite aerogel

Info

Publication number: WO2022250797A2
Application number: PCT/US2022/024363
Authority: WO
Inventors: Nasrullah SHAH; Dong Lin; Halil TETIK
Original assignee: Kansas State University Research Foundation
Priority date: 2021-04-13
Filing date: 2022-04-12
Publication date: 2022-12-01
Also published as: WO2022250797A3

Abstract

A biocompatible nanocomposite aerogel is provided that is relatively non- conductive in its dry form, but rendered conductive when wetted or moistened, making it suitable for use in a variety of sensors, including vapor sensors. The high porosity of the nanocomposite aerogel also renders it a good adsorbent for purposes such as environmental remediation of pollutants.

Description

NANOCOMPOSITE AEROGEL

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of U.S. Provisional Patent Application No. 63/174,147, filed April 13, 2021, which in incorporated by reference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH This invention was made with government support under Contract No. 80NSSC19M0153 awarded by the NASA EPSCoR CAN. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

Field of the Invention

Embodiments of the present invention are directed toward a biocompatible 3D- magnetic agar nanocomposite aerogel (3D-MANCA) that exhibits little to no electrical conductance in its dry form but becomes conductive in its wet or moist form making the aerogel suitable for use in vapor sensor fabrication. Embodiments of the 3D-MANCA can also exhibit good adsorption capabilities, especially as dye adsorbents.

Description of the Prior Art

Aerogels are the world’s lightest known materials that were first introduced in 1931, and after that demand for these materials has continuously increased due to their outstanding characteristics and suitability for many applications. These airy materials offer several applications including adsorption, catalysis, electromagnetic absorption, enzyme immobilization, drug delivery systems, scaffolds, energy storage, electronics, environmental and analytical applications (Pierre atid Pajonk. 2002. Aeaerter et ah. 2011. Baetens et al. 2011, Biener et al., 2011, Stergar and Maver, 2016, Cheng et al. 2020, Flusing and Schubert. 1998. Akimov. 2003). However, to make them more applicable some modifications are often needed. To reduce the net cost and improve the final characteristics of the aerogel, the fabrication process was wisely developed. One approach was to avoid agglomeration of additive nanoparticles within the polymer matrix and achieve uniform dispersion within the matrix as it would affect the efficiency and reproducibility of results (Ma et al. .

The detection of water vapors is important from different perspectives starting with simple heating and cooling systems for households and other building sectors, to weather stations, irrigation control, and other industrial applications such as textile, printing, paper, wood, and agricultural materials-based industries. The use of water vapordetection in the electronics, household appliances, pharmaceutical, environmental sector, and automobile industries is also increasing. Due to the wide array of applications, there is a need for humidity sensors with rapid response, which are capable of generating reliable results, and providing long term stability.

Attempts were made in the past to develop water vapor sensors, with response time, stability, compatibility, and application areas being important considerations. A chemically modified carbon nanotube-based vapor sensor based on measuring the increase in electrical resistance on exposure with water vapors was reported by Zahab et al. (Zahab ¾t al., 2000). However, they found that the sensor was very slow and took several hours to show a response. Similarly, regenerating the sensor was hard to achieve without heating. Other gas or vapor sensors have been made from organic conducting polymers and inorganic materials. The shortcoming of the organic polymer sensor is its low conductivity and stability. Sensors made with inorganic metal oxides nanoparticles have been reported as quality sensors for detections of vapors. However, at high temperature, the efficiency is greatly affected which make them restricted in application.

Due to the toxic and carcinogenic nature of dyes, their adsorption from an aqueous medium is one of the most important aspects of environmental remediation. The efficiency, adsorption time, stability, and reusability of the adsorbent are a primary consideration. Accordingly, a need exists for an adsorptive material that can remove and dyes, and which are easily recovered and regenerated.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention there is provided a nanocomposite aerogel comprising a matrix in which iron oxide nanoparticles, copper oxide nanoparticles, and graphene powder are dispersed. The matrix comprises agar and nanocellulose. The nanocomposite aerogels according to the present invention may be used in the fabrication of numerous products including sensors, adsorbent materials, and chromatography media, for example.

According to another embodiment of the present invention there is provided a method of producing a nanocomposite aerogel. The method comprises dissolving a quantity of agar and a quantity of nanocellulose in water to create an agar/nanocellulose solution. A metal oxide/graphene suspension also is prepared by suspending respective quantities of iron oxide nanoparticles, copper oxide nanoparticles, and graphene nanopowder in water. The agar/nanocellulose solution and the metal oxide/graphene suspension are mixed together to form a nanocomposite suspension. The nanocomposite suspension is solidified, such as by freezing the suspension, to form a solid nanocomposite. Water is then removed from the solid nanocomposite to form the nanocomposite aerogel.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure l is a photograph of a magnetic agar nanocomposite aerogel (3D-MANCA) made in accordance with an embodiment of the present invention;

Figs. 2A-C are SEM images showing top views of the 3D-MANCA;

Figs. 2D-F are SEM images showing cross section views of the 3D-MANCA;

Figs. 3A and B depict the attraction of the composite to a standard permanent magnet;

Fig. 3C depicts the attraction of the composite to an electromagnet;

Fig. 4 is a thermal image of the 3D-MANCA when placed on a hot plate heated to

200°C;

Fig. 5 is a chart of the thermal curves measured on the top and bottom surface of the 3D-MANCA sample placed on a hot plate;

Figs. 6A and B are stress-strain curves of the 3D-MANCA under single step and (B) periodic conditions, respectively;

Fig. 7 is a schematic depiction of a vapor sensor fabricated using the 3D-MANCA;

Figs. 8A-C are charts depicting the response of 3D-MANCA under (A) open conditions with direct vapor exposure from humidifier, (B) close cabinet conditions with indirect vapor exposure from humidifier, and (C) open condition vapor exposure from boiling water, all plots depict the response during vapor exposure and after removing the vapor source; and

Figs. 9A-C are charts depicting humidity values during experiments with the 3D- MANCA with respect to time under (A) open conditions with direct vapor exposure, (B) closed system indirect vapor exposure, and (C) boiling conditions vapor exposure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Aerogels are the lightest known materials and possess unique properties of high porosity, large surface area, insulation, and thermal stability while in some cases also possessing demerits of high brittleness and cost. In one or more embodiments, biocompatible 3D magnetic agar nanocomposite aerogel (3D-MANCA) was fabricated with outstanding characteristics and analytical applications.

In one or more embodiments, the nanocomposite aerogel comprises a matrix that comprises, consists of, or consists essentially of agar and nanocellulose. Preferably, the agar is the majority component of the matrix, with the nanocellulose being present in minor quantities. Generally, the agar comprises, as the primary components the polysaccharides agarose and agaropectin, with agarose making up approximately 70% of the mixture.

In certain embodiments, the weight ratio of agar to nanocellulose present within the matrix is from about 1:1 to about 8:1, or from about 2:1 to about 6:1, from about 3:1 to about 5:1, or about 4:1. In certain embodiments the matrix comprises from 40 to 90% by weight (preferably 55 to 85% by weight, more preferably 65 to 75% by weight) on a dry basis of the total weight of the nanocomposite aerogel. In certain embodiments, the nanocomposite aerogel comprises from 30 to 80% (preferably 40 to 70%, more preferably 50 to 60%) by weight agar on a dry basis. In certain embodiments, the nanocomposite aerogel comprises from 20 to 70% (preferably 30 to 60 %, more preferably 40 to 50 %) by weight nanocellulose on a dry basis.

Dispersed within the matrix are respective quantities of one or more (and preferably all) of iron oxide nanoparticles, copper oxide nanoparticles, and graphene powder. The aforementioned components preferably have particle sizes (as measured along the greatest dimension of the particle) of less than one micron, less than 500 nm, less than 200 nm, or less than 100 nm. In certain embodiments, the particle sizes for these components range from about 1 nm to about 100 nm, from about 5 nm to about 75 nm, or from about 10 nm to about 50 nm.

In one or more embodiments, the iron oxide nanoparticles may be iron (II) and/or iron (III) oxide and are present within the nanocomposite aerogel at a level of from about 50 to about 300 mg/g, from about 80 to about 250 mg/g, or from about 120 to about 200 mg/g on a dry basis.

In one or more embodiments, the copper oxide nanoparticles are present within the nanocomposite aerogel at a level of from about 50 to about 180 mg/g, from about 60 to about 120 mg/g, or from about 70 to about 90 mg/g on a dry basis.

In one or more embodiments, the graphene powder is present with the nanocomposite aerogel at a level of from about 50 to about 150 mg/g, from about 60 to about 120 mg/g, or from about 70 to about 90 mg/g on a dry basis.

In certain embodiments, the weight of the iron oxide nanoparticles present in the nanocomposite aerogel is greater than the amount by weight of either the copper oxide nanoparticles or graphene powder, but this need not always be the case depending upon the desired characteristics for the nanocomposite aerogel. In particular embodiments, the iron oxide nanoparticles are present at a level of at least 1.25, at least 1.5, at least 1.75, or at least 2.0 times that of either of the copper oxide nanoparticles or graphene powder. In one preferred embodiment the weight ratio of the iron oxide nanoparticles to copper oxide nanoparticles to graphene powder is about 1:0.5:0.5.

In one or more embodiments, the nanocomposite aerogel has a very low density and is highly porous. In certain embodiments, the nanocomposite aerogel has a density that is less than 0.2 g/cm³, less than 0.175 g/cm³, or less than 0.15 g/cm³. In still other embodiments, the nanocomposite aerogel has a density than is from about 0.125 to about 0.2 g/cm³, from about 0.135 to about 0.175 g/cm³, or from about 0.14 to about 0.15 g/cm³. In certain embodiments, the nanocomposite aerogel has a porosity of 80% or more, 85% or more, or 90% or more.

In one or more embodiments, the nanocomposite aerogel has a low electrical conductivity (or high resistance) in its dry state. However, when the nanocomposite aerogel adsorbs a polar liquid, such as water or an alcohol, its electrical conductivity increases (or resistance decreases). In certain embodiments, the nanocomposite aerogel exhibits a conductivity of greater than 10⁴ S/cm, greater than 10³ S/cm, or greater than 10² S/cm when the nanocomposite aerogel comprises at least 20% (or at least 30%, or at least 40%, or at least 50%) by weight moisture. In the same or similar embodiments, the nanocomposite aerogel exhibits a conductivity of less than 10⁵ S/cm, or less than 10⁷ S/cm, or less than 10⁹ S/cm when the nanocomposite aerogel comprises less than 2% (or less than 1.5%, or less than 1%) by weight moisture.

In one or more embodiments, the nanocomposite aerogel is highly absorbent and is capable of absorbing at least 4 times, at least 6 times, at least 8 times, or about 9 times its weight with water, or other liquid of similar density. This equates to a swelling ratio of at least 400%, at least 600%, at least 800% or about 900%.

In one or more embodiments, the nanocomposite aerogel exhibits superparamagnetic behavior. Thus, the nanocomposite aerogel can be attracted to various permanent magnets and electromagnets. This feature is useful, for example, in helping to recover the aerogel following its use in certain applications.

In one or more embodiments, the nanocomposite aerogel exhibits excellent thermal insulating characteristics. For example, when one surface of the aerogel is exposed to a heat source, a heat gradient can be maintained across the aerogel in a direction that is normal to the heat source. In certain embodiments, a temperature difference between opposed surfaces (one facing and one facing away from the heat source) of four to five times the temperature of the cool surface can be maintained. For example, if one surface is permitted to heat up to 200°C, the opposed surface may heat up only to 40°C to 60°C, even though the heat is applied for a period of at least 1 hour, at least 5 hours, at least 10 hours, or at least 15 hours.

In one or more embodiments, the nanocomposite aerogel is highly compressible, but not brittle. Therefore, the aerogel can be compressed through application of stress without permanently or irreversibly damaging the porous structure of the aerogel. In certain embodiments, the compressed aerogel can be returned to its original size and shape after being soaked in a liquid medium, such as water or ethanol. Moreover, the nanocomposite aerogel is highly insoluble in these liquid media. In one or more embodiments, the nanocomposite aerogel is made according to a simple, fast, and economical process. A solution of agar and nanocellulose in a solvent, e.g., water, aqueous ethanol or aqueous acidic solution is prepared. In certain embodiments, the agar is added to the solvent in an amount of from about 10 to about 80 g/1, or from about 20 to about 60 g/1, or from about 40 to about 50 g/1 of solvent. In certain embodiments, the nanocellulose is added to the solvent in an amount of from about 5 to about 60 g/1, or from about 8 to about 40 g/1, or from about 10 to about 20 g/1 of solvent. The mixture is thoroughly and vigorously mixed using, for example a vortex mixer followed by sonication, until the agar and nanocellulose are fully dissolved. The agar/nanocellulose solution becomes the matrix for the nanocomposite aerogel.

Separately, a suspension comprising the iron oxide nanoparticles, copper oxide nanoparticles, and/or graphene powder is prepared by dispersing the particles within a liquid medium, preferably the same medium used to create the agar/nanocellulose solution, although this need not always be the case. In certain embodiments, the iron oxide nanoparticles are added to the liquid medium in an amount of from about 5 to about 60 g/1, or from about 10 to about 40 g/1, or from about 10 to about 20 g/1 of the liquid medium. In certain embodiments, the copper oxide nanoparticles are added to the liquid medium in an amount of from about 3 to about 60 g/1, or from about 4 to about 40 g/1, or from about 5 to about 15 g/1 of the liquid medium. In certain embodiments, the graphene powder is added to the liquid medium in an amount of from about 3 to about 40 g/1, or from about 4 to about 30 g/1, or from about 5 to about 10 g/1 of the liquid medium. The mixture of nanoparticles and powder is thoroughly mixed until the particles are uniformly dispersed and suspended.

Next, the agar/nanocellulose solution and nanoparticle suspension are mixed together in a similar manner as described above for the solution and suspension, individually. In one or more embodiments, the solution and suspension are combined in a weight ratio of from about 5:1 to about 3:1, or from about 3:1 to about 2:1, or from about 2:1 to about 1:1. The net suspension containing all the components is then heated, such as using a water bath, to a temperature of at least 75°C, at least 80°C, at least 85°C, or at least 90°C. In certain embodiments, the net suspension is heated to a temperature of from about 75°C to about 110°C, from about 85°C to about 105°C, or from about 90°C to about 100°C, preferably under constant stirring, to achieve a uniform, sticky -viscous suspension. The obtained suspension is then solidified, such as by freezing the suspension, to form a solid nanocomposite. In one or more embodiments, the suspension is poured into a mold or other container of desired size and shape and freeze cast. In certain embodiments, the solidification by freezing comprises cooling the suspension at a cooling rate of from 5°C/min to 20°C/min, or from 7.5°C/min to 15°C/min, or about 10°C/min until a final temperature of less than -40°C, less than -50°C, less than -60°C, or about -70°C is achieved. The solidified nanocomposite may be kept at the final temperature for a predetermined period of time, e.g., at least 1, 2, or 3 hours, to permit further crystallization to occur within the nanocomposite.

Finally, the solvent or liquid medium, e.g., water, is then removed from the solid nanocomposite to form the nanocomposite aerogel. In one or more embodiments, freeze drying is used to remove the solvent or liquid from the nanocomposite. For example, freeze-drying may be carried out using a commercial freeze dryer operating at -35°C and 0.02 mbar. The nanocomposite aerogel can then be processed into any desired form or shape, including a powder form.

The combination of useful characteristics of the nanocomposite aerogel makes it suitable for use in a wide range of applications. These applications include, but are not limited to sensors, adsorbents, biomedical applications (e.g., scaffolds for drug delivery, wound dressing, enzyme immobilization, and cancer therapy), electromagnetic radiation protection, catalysis, environmental remediation, and other electronics and analytical applications.

As described above, in one or more embodiments, one property of the nanocomposite aerogel is its low (or no) electrical conductance in dry form, but when wetted, it becomes conductive. This particular feature renders the nanocomposite aerogel suitable for use in the fabrication of vapor sensors, especially water sensors. In certain embodiments, the change in conductivity due to vapor absorption is rapid (e.g., response in less than 60 seconds, less than 30 seconds, or less than 10 seconds) and linear with respect to time. Generally, sensor fabrication comprises placing a quantity of the nanocomposite aerogel in between two electrodes and measuring the resistance and/or conductivity between the electrodes. An exemplary vapor sensor is described in the Example below. The vapor sensors are also capable of being easily regenerated by removing the vapor source and/or drying of the sensor to desorb the vapor material.

Specific applications for vapor sensors constructed with the nanocomposite aerogel include sensors for the detection of water or steam leaks in industrial processing equipment or underground piping. The sensors can also be configured to detect and/or differentiate other types of vapors including ethanol, methanol, and other polar compounds, as the conductivity of the nanocomposite aerogel is affected by the vapor make up. Sensor can also be fabricated for biomedical use such as in the detection/measurement of perspiration or sweat generated from a human body, especially if the nanocomposite aerogel is fabricated in the form of sheets. In addition to analyzing types of vapors, sensors can be fabricated to analyze the nature of various types of liquids or solvents due to the affect that such liquids have on the conductivity of the nanocomposite aerogel.

As described above, in one or more embodiments, the nanocomposite aerogel may exhibit excellent adsorbent characteristics. Thus, the nanocomposite aerogel may be useful in creating adsorbent and/or absorbent materials. The adsorbent materials can be useful in environmental remediation applications in which pollutants such as dyes, oils, and heavy metals, can be adsorbed from water. The adsorbents can be placed into filters, packed columns, or the like and the water being remediated can be circulated through the media constructed from the nanocomposite aerogel. Alternatively, the adsorbent materials can be dispersed into the body of water to be treated, and then after remediation is completed, collected, and removed through use of magnets and/or induced magnetic fields because of the magnetic properties of the nanocomposite aerogel. In one or more embodiments, the adsorbent materials can be regenerated by passing one or more liquid media, such as ethanol followed by water, through the material comprising the adsorbed pollutant that can desorb the pollutant therefrom.

Embodiments of the nanocomposite aerogel may also be used as a stationary phase chromatography medium. In one or more embodiments, the nanocomposite aerogel may be pulverized into a powder and placed into a chromatography column as a bed of packed powder. EXAMPLE

The following example sets forth an exemplary nanocomposite aerogel, and methods of making and using the same. It is to be understood, however, that this example is provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention.

Chemicals and reagents

Agar (extra pure, Merck), cellulose nanocrystals (CelluForce NCC), Iron(II, III) oxide (nanopowder 50-100nm, Sigma-Aldrich), copper(II) oxide (nanopowder <50nm, Sigma-Aldrich), graphene nanopowder, polydimethylsiloxane (PDMS) (Dow Corning, Sylgard 184).

Fabrication of 3D magnetic agar nanocomposite aerogel (3D-MANCA)

To fabricate the 3D-MANCA with uniformly dispersed additives, the physico- thermomechanical dispersion process was used followed by freeze-casting and freeze- drying. First, the agar and nanocellulose were taken in the percent mass ratio of (4:1) and dissolved in distilled water. In particular, 4 g of agar and 1 g of nanocellulose were dissolved in 100 ml of distilled water. Similarly, a suspension was prepared by adding Fe3C>4, CuO, and graphene nanopowder in the percent mass ratio of 1:0.5:0.5 in distilled water. In particular, 1 g of Fe304 nanoparticles, 0.5 g of CuO nanoparticles and 0.5 g of graphene powder were dispersed in 100 ml of water. Both the solution and the suspension were thoroughly and vigorously mixed separately by vortexing for 15 min using Four E’s vortex mixer, ultra-stirring (4000 rpm) for 3 min with an IKA ultra-turax stirrer, and sonication for 2 min utilizing a high voltage probe sonicator. Then, the two suspensions (100 ml of each) were mixed together by applying the same procedure. The net suspension containing all the components was heated in the water bath at 96°C under constant stirring for 5-10 min to achieve a uniform sticky -viscous suspension. The obtained suspension was freeze cast by pouring the suspension inside a cubic wall structure (10 mm x 10 mm) made of the PDMS, that was placed on top of a cold plate (Instec, Mk2000). The suspension was solidified by freezing at a cooling rate of 10°C/min with a final temperature of -70°C for 15 min. After cooling to -70°C, the frozen samples were shifted to an ultra-freezer set at - 70°C for few hours for further crystallization followed by freeze-drying at -35°C and 0.02mbar using a commercial freeze dryer (Labconco, Freezone Triad).

Characterization of 3D-MANCA

A thermal camera (FLIRR) connected to a PC was used to check the thermal insulation behavior and thermal stability of the 3D-MANCA. A square mass (10x10 mm) of 3D-MANCA was put on the pre-heated hot plate adjusted with 200°C temperature and difference in lower (touching the hot plate) and upper surface temperatures of the 3D- MANCA was recorded. A digital Universal Testing Machine (Shimadzu)was used to measure the stress-strain curve in two different modes (one-step direct compression and periodic compression).

The swelling ratio was calculated by using the following equation:

Ww - Wd

Swellinq = - — — - x 100

Wd

Where Ww and Wd are the weights (g) of wet and freeze-dried 3D-MANCA samples, respectively.

The magnetic property was studied with an ordinary magnet while for further evaluation electrical magnet was also used to determine the superparamagnetic behavior of the prepared 3D-MANCA.

The porosity was determined by liquid displacement method using ethanol as a solvent (Xiong et al., 2002).

The surface and cross-sectional morphology and porosity was investigated with a scanning electron microscope (SEM) (FEI Versa3D Dual Beam). The SEM images were used for determining the approximate pores size as well.

Developing a vapor sensor

A special assembly comprising two inert plastic plates layered with copper foils was developed. There was no connection between the two plastic plates except the as prepared 3D-MANCA (9x9 mm) cubic mass put in between them touching the copper foils which were in turn connected with clips from the digital multimeter(Fluke 287)for measuring the resistance. The sensor set up was firmly held in a stand-in such a way to expose the in-between put 3D-MANCA mass to the vapors. The sensor was tested in three different conditions including in the presence of vapors from humidifier (in open conditions with direct vapors exposure, and closed system with indirect vapors exposure) and direct vapors exposure from boiling water in open conditions.

Characterization

The newly prepared 3D-MANCA (Fig. 1) showed excellent characteristics in different aspects. The density, porosity, thermal and mechanical properties of the 3D- MANCA were determined as these are the key features for any aerogel that defines its application areas. Various properties of the as-prepared 3D-MANCA as shown in Fig. 1 are summarized in Table 1, below. The 3D-MANCA had low density (0.145 g.cm ³) and high porosity (-90%) which makes it suitable for any important application as a porous material. The highly porous structure with almost uniform pores structure was confirmed from SEM study as shown in Figs. 2A-F which are showing the surface (Fig. 2A-C) and cross-section views (Fig. 2D-F) of the prepared 3D-MANCA. This study further indicates the effect of vertical freezing conditions on the shapes of the pores of the as-prepared 3D-MANCA.

Table l.Various properties of the prepared 3D-MANCA fabricated by physico-mechanical incorporation of FeiCri, CuO, and graphene nanopowders in agar-nanocellulose matrix.

The magnetic property makes the aerogel suitable for several important purposes. The uniform dispersion of magnetic nanoparticles resulted in providing high magnetic property to the resultant 3D-MANCA. Two types of magnets, permanent and electromagnetic, were used to test the superparamagnetic behavior of the 3D-MANCA. In both cases, it was attracted and held by the magnets as shown in Figs. 3 A-C. Figs. 3 A and B depict the attraction of the composite to a standard permanent magnet, and Fig. 3C depicts the attraction of the composite to an electromagnet.

As can be seen in Fig. 4, the 3D-MANCA (encircled) showed high thermal stability. During the heating process, it was observed that while heating just 9x9 mm diameter 3D cubic structure of the as-prepared 3D-MANCA maintained four to five times the temperature difference between the upper and lower surfaces even though it was put on the open hot plate where the heat was equally distributed to the material. The thermal curve obtained by using the thermal camera is represented as Fig. 5 and fully supports the discovery of high thermal insulation and stability as it indicates a clear difference between the temperatures of the two surfaces of the 3D-MANCA.

The mechanical stability studied in terms of compressibility was determined and the stress-strain curve was plotted. The curves are given as Figs. 6A and B and show the linear change in strain with applied stress. The applied stress did not break the 3D-MANCA cubic mass but instead caused its compression. This mechanical stability was due to the strength provided by the additives inside the matrix. Hence, the 3D-MANCA was found to be non-brittle and highly compressible with complete reversible recovery to its original shape and size after soaking into water or ethanol with no solubility during soaking.

In terms of electrical conductivity, the 3D-MANCA showed interesting behavior. It was nonconductive in a dry state, but when wet or exposed to vapors it showed electrical conductance. Applications as vapors sensor and dye adsorbent

A vapor sensor, schematically illustrated in Fig 7, was developed to take advantage of the unique electrical behavior of the developed 3D-MANCA. The sensor comprised a sample of the 3D-MANCA 10 mounted in between plastic plates 12, 14, which were fastened together with knobs 16. A space 18 permitting air between plates 12, 14 was provided. A copper strip 20 was placed in contact with the 3D-MANCA 10 and probes 22, 24 were attached to respective ends of the strip 20. The probes 22, 24 were then connected to a multimeter 26. When dry, the 3D-MANCA was a bad conductor with very high resistance or zero resistance, but when it was wetted it showed good electrical conductivity (-3.24 x 10⁴ S.cm ¹ ) and was able to light an LED when the potential was applied to it in a wet state or during exposure of vapors as shown in Figs. 8A-C.

The developed 3D-MANCA vapors sensor device was exposed to water vapors in three different conditions, in open conditions to water vapors from humidifier (Fig. 8A), in a closed box to vapors from humidifier (Fig. 8B), and to boiling vapors from boiling water (Fig. 8C). It is clear from the figures that in all the three conditions the sensors showed a linear decrease in resistance with an increase in time. The response was very rapid and within seconds its response was varied as the humidity changed with respect to time. The resistance to the time curve for all three conditions was similar in trend with a slight difference in resistance values due to the variation in humidity or extent of exposure to vapors. Along with each exposure experiment, the linear reverse trend of resistance after removing the water vapors source was observed. In all the three conditions after removing the source of the vapors, the resistance started to increase and within few minutes it reached its original state of resistance that make it fast, effective, and a very sensitive sensor.

The possible reason for the change in the resistance value of 3D-MANCA is the physical adsorption of water vapors to the matrix material through weak intermolecular interactions. The 3D-MANCA matrix made of agar and cellulose have hydroxyl groups at their surfaces which have strong tendency to interact with water molecules through van der Waals forces. The adsorbed water molecules filled the porous structure and eased the movement of electrons and as a result, the resistance decreased with an increase in time or vapors concentration. The adsorption of vapors in the 3D-MANCA is rapid due to the highly porous structure and friendly matrix nature for establishing interaction with water vapors that caused a rapid response of the sensor to vapors. Some other possible reasons for surface and bulk modification of the 3D-MANCA due to the adsorbed water vapors can also be considered for change in the resistance. The Fe304and CuO nanoparticles present in the 3D-MANCA matrix also show interaction to water molecules without changing their structures that causing a change in the net electrical property of 3D-MANCA. The p electrons of graphene are directly exposed to molecules for interactions. Hence, water molecules in vapors withdraw electrons from graphene which is favored more by the nano-sized structure of graphene. The decrease in resistance of the 3D-MANCA sensor after exposure with vapors is also greatly contributed by the interaction of water vapors with graphene nanopowder. Hence, it is believed that all the components of 3D-MANCA, including the matrix, and the incorporated additives had contributed to the sensing process and caused a rapid and linear response of the developed water vapors sensor. After removing the source of the vapors, the adsorbed vapors tended to leave the 3D-MANCA and escaped to the atmosphere due to weak nature and low energy of van der Waals interactions and, hence, caused the loss of conductivity or increase in the resistance. During the exposure process, the concentration of the vapors with respect to time was measured and plotted as shown in Fig. 9. Therefore, it can be correlated with the response of the 3D- MANCA sensor. In other words, the decrease in resistance was due to the increase in vapors concentration with respect to time. Moreover, in order to make the sensor more applicable its response with different types of solvents was studied, and it was observed that the resistance values (data not shown) were varied with variation in nature and concentration of the solvents. This property indicated its applicability as an analytical tool for multiple purposes.

Considering the high porosity and composition of the 3D-MANCA, it was tested for the adsorption of methylene blue dye. A dye solution of 50 ppm was completely decolorized just in a few seconds by its pressurized instant passage through a 3D-MANCA bed packed in a syringe. The adsorbed dye was recovered with few ml of ethanol and was successfully re-used. The efficient and rapid adsorption of methylene blue dye by 3D- MANCA was obtained due to the highly adsorbing nature of the matrix and additive materials. The high surface area, porosity, and hydrophilicity of the 3D-MANCA provided a good medium for adsorption of dye which caused fast and efficient adsorption. The magnetic property further broadens its applicability as an adsorbent as it is easily recoverable after use.

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Claims

We claim:

1. A nanocomposite aerogel comprising a matrix in which iron oxide nanoparticles, copper oxide nanoparticles, and graphene powder are dispersed, the matrix comprising agar and nanocellulose.

2. The nanocomposite aerogel of claim 1, wherein the agar is the majority component of the matrix.

3. The nanocomposite aerogel of claim 1, wherein the weight ratio of agar to nanocellulose present within the matrix is from about 1 : 1 to about 8:1.

4. The nanocomposite aerogel of claim 1, wherein the iron oxide nanoparticles are present within the nanocomposite at a level of from about 50 to about 300 mg/g.

5. The nanocomposite aerogel of claim 1, wherein the copper oxide nanoparticles are present within the nanocomposite at a level of from about 50 to about

180 mg/g.

6. The nanocomposite aerogel of claim 1, wherein the graphene powder is present with the nanocomposite at a level of from about 50 to about 180 mg/g.

7. The nanocomposite aerogel of claim 1, wherein the amount by weight of the iron oxide nanoparticles present in the aerogel is greater than the amount by weight of either the copper oxide nanoparticles or graphene powder.

8. The nanocomposite aerogel of claim 1, wherein the nanocomposite aerogel has a density that is less than 0.2 g/cm³.

9. The nanocomposite aerogel of claim 1, wherein the nanocomposite aerogel has a porosity of greater than 80%.

10. The nanocomposite aerogel of claim 1, wherein the nanocomposite aerogel exhibits a conductivity of greater than 10⁵ S/cm when the nanocomposite aerogel comprises at least 20% by weight moisture, and wherein the nanocomposite aerogel exhibits a conductivity of less than 10⁶ S/cm when the nanocomposite aerogel comprises less than 2% by weight moisture.

11. The nanocomposite aerogel of claim 1, wherein the nanocomposite aerogel is capable of absorbing at least 4 times its weight with water.

12. A sensor comprising the nanocomposite aerogel of any of claims 1-

11

13. The sensor of claim 12, wherein the sensor is a vapor sensor.

14. An adsorbent material comprising the nanocomposite aerogel of any of claims 1-11.

15. The adsorbent material of claim 14, wherein the adsorbent material is capable of absorbing dyes.

16. A chromatography medium comprising the nanocomposite aerogel of any of claims 1-11.

17. The chromatography medium of claim 16, wherein the nanocomposite aerogel is a packed powder.

18. A method of producing a nanocomposite aerogel comprising: a. dissolving a quantity of agar and a quantity of nanocellulose in water to create an agar/nanocellulose solution; b. preparing a metal oxide/graphene suspension by suspending respective quantities of iron oxide nanoparticles, copper oxide nanoparticles, and graphene nanopowder in water; c. mixing the agar/nanocellulose solution and the metal oxide/graphene suspension together to form a nanocomposite suspension; d. solidifying the nanocomposite suspension to form a solid nanocomposite; and e. removing water from the solid nanocomposite to form the nanocomposite aerogel.

19. The method of claim 18, wherein the weight ratio of agar to nanocellulose present within the agar/nanocellulose solution is from about 1 : 1 to about 8:1.

20. The method of claim 18, wherein the iron oxide nanoparticles are present within metal oxide/graphene suspension at a level of from about 5 to about 60 mg/1.

21. The method of claim 18, wherein the copper oxide nanoparticles are present within the metal oxide/graphene suspension at a level of from about 3 to about 60 mg/1.

22. The method of claim 18, wherein the graphene powder is present with the metal oxide/graphene suspension at a level of from about 3 to about 40 mg/1.

23. The method of claim 18, wherein step c comprises heating the nanocomposite suspension to a temperature of at least 75°C while stirring.

24. The method of claim 18, wherein step d comprises cooling the nanocomposite suspension to a temperature of less than -40°C to form the solid nanocomposite.

25. The method of claim 18, wherein step e comprises freeze drying the solid nanocomposite to form the nanocomposite aerogel.