NANOCOMPOSITE PRODUCTION INCLUDING DEPOSITION OF NANOP ARTICLES ON NANOFIBERS

CONTRACTUAL ORIGIN

The United States Government has rights in this invention under Contract No. DE-AC36- 99GO10337 between the United States Department of Energy and the National Renewable Energy Laboratory, a Division of the Midwest Research Institute.

BACKGROUND

Recently, there has been interest in nanotechnology including the generation and use of nanomaterials. The term nanomaterial refers to nearly any material or "nanostructure" that has at least one dimension that is roughly between 1 and 100 nanometers. For example, a nanoparticle has a diameter that is between 1 and 100 nanometers, and a nanofiber has a diameter between about 1 and 100 nanometers but a much larger length (e.g., a length of up to 100 to 200 or more times the diameter). Nanomaterials are unique when compared with structures larger than the nanoscale because the properties of nanomaterials actually depend on and vary with their size. In other words, the fundamental properties or functions such as chemical, electrical, and physical properties of a particular material can be changed and, in some cases, enhanced in a desired manner by synthesizing or producing the material on the nanoscale.

Nanoparticles, nanofibers, and other nanomaterials are used in numerous applications and incorporated in devices to utilize their fundamental properties or functionalities. For example, nanoparticles and nanofibers are used to produce "smart" materials that are engineered to perform a specific task such as by using a photorefractive polymer provided on the nanoscale that can be added to glass to make it self-tinting. Nanomaterials are frequently used to fabricate ultrasensitive sensors such as sensors that function to provide molecular recognition or to trap particular target molecules. Another focus of nanotechnology is to use nanomaterials to form nanoscale biostructures that have particular functions including affecting a biological process or interacting with a biological entity (e.g., forming artificial bone, recognizing/attacking particular viruses, assisting in drug production and delivery, etc.). Nanomaterials are also attracting interest in the

areas of electronics, optics, magnetism, energy (such as for their catalysis properties important for fabrication and design of fuel cells), and filtration (e.g., filters formed with nanofϊbers or a nanoflber matrix to filter air or water with enhanced capability to trap one or more targeted molecules).

The nanotechnology industry continues to search for new and better ways to manufacture or produce nanomaterials. For example, significant research effort continues to be spent on developing nanomaterials with enhanced functionality. To this end, nanomaterials have been produced that try to combine the functionality or fundamental properties of two or more nanomaterials. The production methods have generally involved physically mixing different nanoparticles, mixing different nanofibers, or mixing nanoparticles of one material with nanofibers of another material. The resulting nanomaterial mixtures have sometimes provided desired properties, but, often, the function of the nanomaterials are not significantly improved and other challenges such as obtaining desired ratios of the materials has led to these mixtures not being widely adopted or used in devices such as filters, sensors, etc. Hence, there remains a need and strong demand for an improved method of producing nanomaterials with enhanced functionality or with particular fundamental properties that can be used alone or as part of a device such as a sensor or filter.

The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.

SUMMARY

The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods that are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements.

This is achieved, in part, by providing a method of producing composites of nanoparticles of a first material bound to nanofibers of a second material (such as a polymer, an inorganic, carbon, or other material). A composite is formed by synthesizing the nanoparticles in the presence of the

nanofibers. For example, the method may include providing a synthesis aid or additive for a particular nanoparticle in a reaction vessel and also adding a quantity of the nanofibers to the reaction vessel. In some cases, the synthesis aid or additive is a solvent such as an organic solvent or water, and a suspension of the nanofibers in the water is created in the vessel. The method may further include adding a quantity of a precursor for the nanoparticle into the suspension formed in the vessel. In other cases, the nanofiber may be formed concurrently in the vessel by providing precursors for the nanofibers in the vessel. The contents of the vessel are then placed in the proper conditions for synthesizing nanoparticles such as by a particular type of chemical synthesis or by heating the contents to a temperature in a synthesis temperature range for a time (i.e., a synthesis time). The formed nanocomposite is then separated such as through use of centrifugation and/or filtration, and the separated nanocomposite may be dried to further remove remaining solvent or other remnants of the wet chemistry process.

A nanocomposite and not a mere physical mixture is formed in the vessel as the synthesized nanoparticles chemically interact with the nanofibers and become bound to the surfaces of the nanofibers. The formation of the nanocomposite is typically done for active reasons such as to enhance or add functionality to the nanofiber matrix such as providing or enhancing a direct chemical function or photochemical function to the nanofiber matrix. For example, the addition of the nanoparticles to the nanofiber matrix may result in enhanced filtration of air, water, or other fluid with a filter that includes the nanocomposite (e.g., a filter effective in filtering bacteria and nanosize particles such as viruses, microbes, and colloidal particles), improved catalysis such as in fuel cells or improved accuracy of a sensor that incorporates the nanocomposite (e.g., such as on a support structure or using the nanocomposite by themselves to form a mat). In other words, nanoparticles of a particular material or compound that are known to be catalytic, photocatalytic, sensitive to a particular atmospheric or biological agent, or to have another function or property on their own or in the presence of another material (e.g., the material of the nanofiber) can be combined with nanofibers of a particular material to enhance or modify the function of the nanofiber. In some cases, for example, nanofibers of a first material may be used for catalysis or absorbing, but the addition of nanoparticles of a second material may result in a nanocomposite that is more effective for the desired catalysis or absorbing (or other function). In some cases, the

chemical reactivity of the nanofibers can be tuned by binding nanoparticles of one or more materials onto the nanofibers to form a particle/fiber nanocomposite.

By way of example, but not limitation, an embodiment includes a method for producing nanocomposites that include nanoparticles of one material chemically bound to nanofibers of another material (e.g., zinc oxide nanoparticles bound to boehmite or sodium titanate nanofibers). The method includes providing a reaction vessel and adding a synthesis aid for a particular nanopaiticle to the reaction vessel such as adding a solvent for the nanoparticle material (such as water when the nanoparticle material is one of a number of metal oxides). The method continues with adding a quantity of nanofibers of a first material to the reaction vessel and adding a precursor for nanoparticles of a second material, which typically differs from the first material, to the reaction vessel. The synthesis aid, nanofibers, and precursor may be mechanically agitated or mixed to form a mixture in the vessel. These contents or the mixture is then placed under conditions conducive to synthesis of the nanoparticles of the second material. For example, hydrothermal synthesis may be used to form the particles and, in this case, the conditions may include heating the vessel contents to a temperature within a particle synthesis range for a particle synthesis time (such as heating between 30 to 120 °C for a few minutes up to 1 to 3 hours or longer), hi the method, a quantity of the nanoparticles of the second material are synthesized or formed in the reaction vessel and are chemically bound to the nanofibers of the first material to form the nanocomposite. The method may further include separating the nanocomposite such as by centrifugation and/or filtration and then drying the separated nanocomposite.

In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions.

BRIEF DESCRIPTION OF THE DETAILED DRAWINGS

Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting.

Fig. 1 illustrates an exemplary representation of a nanocomposite showing nanoparticles of a first material chemically bound to nanofibers of a second material;

Fig. 2 illustrates another an exemplary representation of a nanocomposite showing nanoparticles of two different materials bound to nanofibers of a third material;

Fig. 3 illustrates still another exemplary representation of a nanocomposite in which nanoparticles of a first material are bound to nanofibers formed from two different materials;

Fig. 4 is a functional block diagram illustrating an exemplary nanocomposite production system in which particles are synthesized in a reaction vessel in the presence of nanofibers such that the nanoparticles are chemically bound to the fibers;

Fig. 5 illustrates an exemplary method of preparing nanocomposites such as those shown in Figures 1-3 and 6-9;

Fig. 6 is a transmission electron microscopy (TEM) image of a ZnO/boehmite composite formed using an implementation of a method of preparing nanocomposites described herein such as the method of Fig. 5;

Fig. 7 illustrates an X-ray diffraction (XRD) characterization of the composite shown in Fig. 6 illustrating the presence of both ZnO and boehmite in the composite;

Fig. 8 is an scanning electron microscope (SEM) image of a ZnO/sodium titanate composite formed using an implementation of a method of preparing nanocomposites described herein such as the method of Fig. 5; and

Fig. 9 is a highly magnified image of a nanocomposite formed using an implementation of an exemplary method of preparing nanocomposites described herein such as the method of Fig. 5 and, particularly, a nanocomposite in which TiO ₂ nanoparticles are deposited on carbon nanofibers to form a TiO ₂ /C composite.

DESCRIPTION

The following provides a description of an exemplary method for preparing nanoscale materials with enhanced functionality and with functions that can be tuned or modified to meet certain uses or needs. More specifically, an exemplary production method is illustrated for forming nanocomposites that include a matrix of nanofibers upon which nanoparticles have been

chemically bound. The function of the nanocomposite can be selected or tuned by choosing a nanofiber that provides a desired fundamental property such as a particular ability to absorb another material or target or to facilitate catalysis, by next selecting an additional material or additive that acts to enhance that particular function or property or that provides a second desired function or property, and by then synthesizing the nanoparticles of the selected material or additive in the presence of a matrix of the nanofibers. Generating the nanoparticles in the presence of the nanofibers results in the nanoparticles being deposited upon the surfaces of the fibers and, more specifically, results in forming a nanocomposite by causing the particles to chemically react with the material of the nanofiber (i.e., chemically bonding to the nanofibers).

The exemplary nanocomposite production or preparation method differs from mere mixing of nanofibers with nanoparticles because the two materials interact chemically. The nanoparticles also typically tend to form or deposit relatively uniformly throughout the fiber matrix (e.g., have a tendency to deposit on available surfaces of the nanofibers). The resulting nanocomposite can then be used alone or within a device such as sensors, filters, absorption materials, catalysis materials, etc. For example, but not as a limitation, the nanocomposites may be designed to provide functions that are utilized for environmental remediation, for trapping and photo-destruction of viruses and/or bacteria, for fabricating elements of solar cells (e.g., cells based on semiconductor nanoparticle absorbers with the nanocomposite used to supplement or replace the nanoparticles), etc.

Figure 1 illustrates an exemplary nanocomposite 110 formed with nanocomposite production methods described herein. As shown, the nanocomposite 110 is a matrix of nanofibers 120 of a particular material upon which a plurality of nanoparticles 130 of a different material have become chemically bound. A "nanoparticle" is typically any particle that is between about 1 and about 100 nm in size or diameter. A "nanofiber" typically is an elongated structure with a cross sectional dimension or diameter in this same range of about 1 to about 100 nm. The length of the nanofiber, however, is typically much larger than the diameter such as up to 100 to 200 times as large. Hence, a nanofiber may be described as having an aspect ratio (or length/diameter) of up to about 200:1 and more typically 100:1 or less. Of course, the size of the nanoparticles and the nanofibers will vary with the particular materials selected for each part of the nanocomposite. As shown, the nanoparticles 130 are deposited on the surface of the nanofibers 120 and, in the case of

nanoparticles 134, a nanoparticle may be bound to two or more of the nanofϊbers 120 (e.g., similar to cross-linking found in other structures creating a link between two or more nanofibers 120).

The method described with reference to Figures 4 and 5 and elsewhere is believed to be general in nature and useful with a wide variety of materials. In other words, the nanocomposite production method can be utilized with nearly any nanofiber and nanoparticle combination with one of the only limitations being that the two materials be compatible such that the nanoparticles and nanofibers chemically react such that the nanoparticles are chemically bound to the nanofibers and not merely physically mixed within the nanofiber matrix. Additionally, the technique used to provide or prepare the nanofibers is generally not limiting of the nanocomposite production method. For example, the nanofibers may be grown or synthesized according to any well-known process or in a process yet discovered, and these techniques can be used, in some cases, to control the dimensions of the nanofϊbers.

Examples of materials useful for the nanofibers include polymers, carbon, glass, ceramics, metals, cellulose, boehmite, titanate, titanium dioxide, and metal oxides, etc., and the specific examples provided below include boehmite nanofibers, sodium titanate nanofibers, and carbon fibers. Examples of materials useful for the nanoparticles may be nearly any element found in Groups HA to VILA of the periodic table of elements and/or compounds including such elements, and the specific examples provided below utilize metal oxide and semiconductor nanoparticles including zinc oxide and titanium dioxide. Metal oxides may include transition metal oxides and, specifically, metal oxides such as ZnO, TiO ₂ , Fe ₂ O ₃ , SnO ₂ , Ga ₂ O ₃ , In ₂ O ₃ , etc. Semiconductor nanoparticles may be formed from the following non-exclusive or exhaustive list: GaN, GaP, GaAs, InN, InP, InAs, Si, Ge, CdS, CdSe, and CdTe. Metal nanoparticles may include, but are not limited to: Ag, Cu, Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, Os, and compounds including these and other metals.

Figure 2 illustrates another exemplary nanocomposite 210 which may be formed by an embodiment of the nanocomposite production methods described herein. The nanocomposite 210 is similar to nanocomposite 110 in that it includes a matrix or plurality of fibers or nanofibers 220 such as carbon fibers or boehmite or titanate nanofibers. The nanocomposite 210 differs from nanocomposite 110, however, because it includes nanoparticles 230 of a first material and

nanoparticles 240 of a second material that are both chemically bound to the nanofibers 220. The nanoparticles 230, 240 differ in their chemical make up and, for example, may provide two differing functionalities or may provide a single functionality that is achieved by the presence of both particles (with or without the addition of the nanofibers 220). The nanoparticles 230, 240 may be of a similar size or diameter or differ significantly as shown in Figure 2. Similarly, the amount of each of the nanoparticles 230, 240 may vary to achieve desired properties. For example, an equal amount as measured by weight may be bound to the nanofibers 220 of each of the nanoparticles 230, 240 or a particular weight ratio may be chosen (e.g., such as 2:1, 3:1 of particle 230 to particle 240 or vice versa) to achieve a particular function or property. The nanoparticles 230, 240 may be synthesized concurrently in the presence of the nanofibers 220 or the two nanoparticles 230, 240 may be synthesized in series, with the selection of the particular particle generation step and order depending upon the chemical make up of the materials chosen for the nanoparticles and their interaction with each other and the material of the nanofibers 220.

Some examples of the combined functionality of these nanocomposites include photocatalytic TiO ₂ nanoparticles combined with chemically absorptive boehmite nanofibers. Here the boehmite nanofibers can absorb organic materials, bacteria, and viruses in close proximity to TiO ₂ nanoparticles which, when exposed to light, will oxidize the organic or biological materials to CO ₂ and water. Thus, the functionality of this composite includes absorption and destruction of organic and biological materials combined in a self-cleaning structure. Another example is ZnO nanofibers combined with TiO ₂ nanoparticles for electrode structures in organic electronics. Here, ZnO has the useful properties that it is highly conductive and nanofiber arrays can be grown easily on a variety of substrates. However, it suffers because it does not form a good interface with organic conductors, which is crucial for charge transport in these devices. The addition of TiO ₂ nanoparticles, which couple well to both the ZnO surface and the organic conductors, forms an interfacial layer that effectively mediates charge transfer from the organic conductor to the ZnO nanofiber and produces a more functional device. Another example is Fe ₂ O ₃ and/or MnO ₂ nanoparticles in a composite with boehmite or Al ₂ O ₃ nanofibers for absorption and neutralization of chemical contaminants in water. These materials are useful, an one example, for removal of arsenic from water.

Figure 3 illustrates yet another exemplary embodiment of a nanocomposite 310 that may be formed by the exemplary production methods described herein. The nanocomposite 310 differs from those shown in Figures 1 and 2 in that the matrix of nanofibers includes nanofibers 320 and 325 of first and second materials. The first and second materials typically differ to provide different functions or properties desired in the nanocomposite 310. In some cases, though, the nanofibers 320, 325 are formed of the same basic material that is provided from differing sources or formed in differing manners that causes the nanofibers 320, 325 to differ in some aspect such as differing diameter, length, and/or surface characteristics (e.g., surface roughness). The nanofibers 320, 325 may be of similar or differing size and/or have differing aspect ratios. The materials selected for the nanofibers 320, 325 do not necessarily have to be chemically compatible because they do not generally bind or react with each other.

The nanocomposite 310 is shown to include a plurality of nanoparticles 330 that are chemically bound to both the nanofibers 320 and the nanofibers 325, and, hence, the nanoparticles 330 are generally a material that is chemically compatible with the materials of both nanofibers 320, 325. In other embodiments of the nanocomposite 310, the nanoparticles 330 are formed from two or more materials. As will be understood by those skilled in the art, the nanocomposite 310 is not limited to only two materials for the nanofibers 320, 330 or a single material for the nanoparticles 330 but, instead, nanocomposites may be formed with nanofibers of 1, 2, or more materials and nanoparticles synthesized in the presence of the nanofibers that are formed from 1, 2, or more materials. Further, while it is generally the case that the nanoparticles 330 will bind with all the nanofibers 320, 325, there are certain applications where it is acceptable for the nanoparticles 330 only chemically interact with one of the nanofibers 320 or 325 (such as when nanoparticles 330 of two differing materials are utilized in the nanocomposite 310).

Figure 4 illustrates in functional block form an exemplary nanocomposite production system 400 that may be implemented for forming nanocomposites including nanoparticles deposited on or bound to nanofibers. The particular equipment utilized for the system 400 is not limiting (e.g., is relatively well-known in the chemical and nanotechnology fields) and, hence, the higher-level description provided with reference to Figure 4 is believed adequate to allow those skilled in the art to practice the exemplary production method.

The system 410 is shown to include a particle synthesis vessel 420, which may also be thought of as a composite reactor or reaction vessel. The particle synthesis vessel 420 is significant because it is selected and configured to provide the conditions, such as temperature, pressure, mixing, vibration, etc., that are useful for forming nanoparticles of a selected material. To form a composite this particle synthesis is performed with nanofibers also being present or provided in the vessel 420. For example, the conditions for synthesizing zinc oxide (ZnO) nanoparticles include providing water as a synthesis aid or additive (e.g., a synthesis solvent) and a Zn particle precursor to the vessel or reactor 420, mixing the combination, and heating the mixture for a time (e.g., to 80 to 90 °C for up to about 3 hours or longer). The vessel 420 may be configured to provide a desired amount of mixing automatically prior to and/or during heating or such mixing may be performed manually. The contents of the vessel 420 are heated to a desired temperature or range of temperatures to provide synthesis conditions by heater 422 and as measured by thermometer or gauge 426, and operation of the heater 422 may be controlled by a control circuit (not shown) to maintain the vessel contents within desired temperature ranges for a desired amount of time to produce nanoparticles.

To obtain a nanocomposite, exemplary embodiments of system 400 include a synthesis aid source 410 which may be a supply for a particular solvent or combination of materials (in solid, gas, or liquid form) to facilitate generation of a nanoparticle (such as water when the nanoparticle is TiO ₂ , ZnO, etc.). The synthesis aid or additive may be added to the vessel 420 in a metered fashion or in a single step using flow and/or supply control devices appropriate for the additive such as piping and control valves for metering a desired volume of flow when the additive is a liquid solvent. The system 400 further includes a nanofiber source 414 for providing an amount (typically measured by weight and/or volume) of a nanofiber of one or more materials to the particle synthesis vessel 420. Again, the technique used for forming the nanofibers is not limiting of the system 400 and the mechanisms used to implement the nanofiber source 414 may vary, too, to practice the system 400 and may even be manual (e.g., physically pouring a quantity or amount of nanofibers into the vessel 420). Further, exemplary embodiments of system 400 include a source 418 of nanoparticle precursor(s) that functions to provide a quantity of material(s) useful when combined with the synthesis aid and processed in the conditions provided by the synthesis vessel 420 to create nanoparticles of a particular material. Again, the particular source of the precursor is not limiting

and the mechanisms used to deliver the precursor to the vessel 420 is not limiting and may even involve manual addition of the nanoparticle precursor to the vessel 420.

After or during the addition of the inputs from the sources 410, 414, 418, the synthesis vessel 420 is operated to create the conditions useful for generating nanoparticles from the one or more precursor materials. The nanoparticles are deposited upon or are formed on the nanofibers from the source 414, and this results in a chemical bond between the materials of the nanofibers and the nanoparticles. After a time (i.e., a synthesis time or particle generation time), all or a portion of the mixture is processed to separate the composite made up of the synthesized nanoparticles in the matrix of the nanofibers. For example, the mixture may be transferred to a stand-alone separator 430 for processing that separates the composite from the synthesis aid or remaining liquid. Such separation may be achieved with filters and/or with a centrifuge provided in the separator 430. Alternatively, these separation processes may be provided in or by operation of the synthesis vessel 420. Once the composite is separated, it is typically further processed such as with a drier or other finishing processor 440 and the output of this device 440 is a prepared nanocomposite including a matrix of nanofibers with nanoparticles chemically bound to the nanofibers. The system 400 further is illustrated to show that the prepared nanocomposites 450 may be used directly in a standalone use 460 (e.g., such as a mat for absorbing a target material ) or as a component in a device/material such as in a sensor, a filter, a semiconductor device, a solar cell, etc.

Figure 5 illustrates an exemplary method 500 of producing nanocomposites, and it may be useful to understand the general method of forming nanocomposites and then to provide more specific working examples with reference to Figures 6-9. The exemplary method 500 begins at 510 with the identification of one or more desired functions or properties for a nanocomposite. For example, the function desired may be to provide a nanocomposite that is able to act as a catalysis for a particular reaction, to act as a sensor for a particular material, to filter a target chemical or virus, etc. At 520, the method 500 includes selecting materials that in nanofibers provide the identified function or that provide a related function or property (e.g., can be modified by the addition of a nanoparticle to provide the identified function). At 526, the method 500 includes identifying one or more materials that in nanoparticle form can be deposited upon the nanofibers selected at 520 to enhance the functionality of the nanofibers or to create a nanocomposite with the nanofibers that provides the desired functionality or properties. The range of materials for these nanoparticles may

be quite large (e.g., a significant portion of the elements found in the periodic table of elements and their compounds), but the material selected may be one that can be synthesized in the presence of the nanofibers and that will chemically bind to the nanofibers during or as part of such synthesis.

At 530, a solvent or other synthesis additive is added to a reaction vessel. At 540, nanofibers are produced or otherwise obtained and are added to the reaction vessel. The method 500 may include mixing the solvent and the nanofiber material at this point and performing some pre-processing such as some heating of the mixture. At 548, a quantity of precursor for the selected nanoparticles is added to the reaction vessel 548. At 550, the reaction vessel is heated and other steps may be taken to establish particle formation conditions. For example, the solvent, nanofiber material, and the precursor may be blended physically such as with stirring or other mechanical agitation to mix the inputs to the reaction vessel, and then other parameters may be established such as a desired temperature and/or pressure. In many cases, nanoparticles can be formed by combining a precursor with a solvent or other synthesis aid and then heating the mixture for a time (with or without additional agitation/mixing).

At 560, the method 500 continues with determining whether the synthesis time for the particular solvent/precursor combination has been reached. If not, the method 500 continues maintaining the combination in the temperature range (or above a particular temperature), and in some cases, more than one temperature setting for the vessel may be utilized (such as when two or more precursors are used to form the nanocomposite). If the synthesis time has elapsed, the method 500 continues at 570 with cooling of the nanocomposite/solvent mixture and with separating the nanocomposite from the solvent at 574. At 580, the nanocomposite 580 is optionally dried. At 590, the nanocomposite made up of a matrix of nanofibers of one or more material with nanoparticles (of one or more materials/compounds) is supplied to an end use (e.g., as one material for forming a device having a desired function such as a sensor or filter). The produced nanocomposite from step 580 may also include a quantity of nanoparticles that have not reacted with the nanofibers or have reacted with other nanoparticles such as when surface area of the nanofibers available for reaction is substantially utilized or saturated. The method 500 ends at 598 or is repeated beginning at 510, e.g., with a different nanocomposite being formed.

In one implementation of a nanocomposite production method, a composite of ZnO nanoparticles and boehmite nanofibers was produced. In this representative implementation, it was first determined that it would be desirable to enhance the function or properties of boehmite nanofibers (i.e., nanofibers of aluminum oxide hydroxide (AlO(OH)) mineral nanofibers) with zinc oxide nanoparticles. A solvent suitable for generation of the desired nanoparticles was chosen, and, specifically in this example, water was selected as a suitable solvent or synthesis additive or aid for creating particles of ZnO. A volume of water was added to a reaction vessel, and boehmite nanofibers were obtained and added to the water in the vessel to form a suspension of the nanofibers in the water. The suspension was then treated with a precursor of ZnO nanoparticles by adding zinc nitrate and hexamethylenetetramine to the reaction vessel and mixing the precursor and the suspension (although mixing may not be necessary in many cases).

The resulting mixture in the vessel was then heated to a synthesis temperature range and maintained at a temperature within this range for a synthesis time. In the specific implementation, the synthesis temperature range was selected to be about 80 to about 90 °C and the synthesis time was selected to be about 3 hours. However, it is believed that lower and higher temperatures can be used as well as shorter and longer synthesis times, with the temperature range and synthesis time being acceptable if they result in a useful amount of nanoparticle synthesis and may vary with the precursor and additive/solvent chosen to form the nanoparticles. In the specific implementation, for example, a temperature in a much larger range such as 30 to 120 °C may be used and a synthesis time of 15 minutes to 4 hours or more may be chosen based on the chosen synthesis temperature. Further, in some implementations, the precursor and synthesis additives may be selected such that their mixture at room temperature or without adding heat provides the "synthesis conditions" in the reaction vessel useful for creating nanoparticles in the presence of the nanofibers that produces a nanocomposite.

In exemplary embodiments of the production method, the mixture was then cooled to about room temperature and the particle/fiber composite material was harvested by first separating and then drying the separated material. The separating was performed by centrifugation, but, of course, other techniques such as filtration may also be used to isolate the nanocomposite or to remove unwanted portions of the synthesis aid (or solvent in this example). An energy dispersive X-ray (EDX) analysis was performed on the dried composite, and the results showed that only Al, Zn,

and O were present in the nanocomposite. Figure 6 illustrates a TEM image of the ZnO/boehmite nanocomposite 610, and under this magnification it is evident that the nanoparticles 630 are deposited upon the nanofibers 620 in the nanocomposite. Analysis of the image 610 showed that the composite 610 includes ZnO nanoparticles 630 in the range of about 10 to about 60 nm in size and boehmite fibers with exemplary dimensions of about 5 nm wide by about 100 nm long. Further analysis was performed of the dried nanocomposite using XRD characterization and the results are shown in Figure 7 with the graph 700. As can be seen, the XRD characterization of the ZnO/boehmite composite indicates that both crystalline ZnO and boehmite are present in the composite.

Formation of the ZnO/boehmite composite, in one implementation, was prepared by obtaining or providing 50 mL portions of 0.2 M solutions of zinc nitrate and hexamethylenetetramine in water, and then filtering these two solutions through 0.45 micron syringe filters. The two filtered solutions were combined in a round bottom flask. A suspension of boehmite fibers in water (5 mL, -1.0 g boehmite) was added, and the flask was immersed in a hot oil bath at 80-90°C for 3 hours. During the reaction time, a white solid gradually precipitated. The product was isolated by filtration, washed with water, and dried. The TEM image in Figure 6 and the XRD scan in Figure 7 show that the product of this reaction is a composite of boehmite and ZnO nanoparticles.

In an additional exemplary embodiment of the nanocomposite production method a nanocomposite of ZnO particles and titanate nanofibers was produced. In this embodiment, the synthesis aid or additive for the ZnO precursor was again selected to be water (e.g., a solvent comprising water was chosen) and added to the reaction vessel. A quantity of metal titanate nanofibers, and, more specifically for this embodiment, sodium titanate nanofibers, were obtained and placed in the reaction vessel. The vessel contents were mixed to form a suspension and a ZnO precursor (i.e., zinc nitrate and hexamethylenetetramine) was added to the reaction vessel. The contents were then again mixed, and the mixture was heated under conditions where ZnO nanoparticles were formed, i.e., in one embodiment the mixture was heated to a temperature in the range of about 80 to about 90 °C for about 3 hours. The mixture was then cooled and particle/fiber composite was isolated or separated by centrifugation and dried. Evidence that the dried material is a nanocomposite was found by producing SEM images of the material such as the SEM image 810 shown in Figure 8 that shows a matrix of sodium titanate nanofibers 820 with ZnO nanoparticles 830 bound to the

fibers 820. Analysis of the SEM image 810 indicates that the ZnO nanoparticles 830 are generally hexagonal and about 10 to about 100 nm in size and are bound to the titanate nanowires 820.

In an exemplary embodiment, a composite of ZnO nanoparticles with sodium titanate nanofibers was prepared. In this exemplary embodiment, separate 50 mL portions of 0.2 M solutions of zinc nitrate and hexamethylenetetramine in water were filtered through 0.45 micron syringe filters and combined in a round bottom flask. A 1 cm ² piece of Ti-metal gauze coated with Na ₂ Ti ₃ O ₇ nanowires was placed in the solution, and the flask was immersed in a hot oil bath at 80-90°C for 3 hours. During the reaction time, the solution became cloudy white and a white solid gradually precipitated. The Ti gauze supporting the composite was removed from the solution, washed thoroughly with water, and allowed to dry in air. The SEM image in Figure 8 was taken of the product and shows the ZnO nanoparticles bound to the titanate nanofibers in a nanocomposite.

In another exemplary embodiment of a nanocomposite production method, carbon fibers (e.g., up to about 8 microns in diameter) were chosen for the nanofiber or fiber matrix and were added to a reaction vessel containing a solvent (e.g., water acting as the synthesis additive for a precursor for TiO ₂ ). A precursor for TiO ₂ nanoparticles was then added to the reaction vessel and a mixture formed of the three input materials. The mixture was heated to a synthesis temperature range and the mixture's temperature was maintained in this range for a synthesis time. This resulted in the hydrothermal synthesis of TiO ₂ nanoparticles in the presence of the carbon fibers, which generated a TiO ₂ /carbon nanocomposite in the vessel. Further processing again included cooling the mixture, separating the nanocomposite, and drying the separated nanocomposite. A highly magnified (e.g., 1 micrometer at 20000X) image 910 of the nanocomposite is shown in Figure 9 that shows TiO ₂ nanoparticles 930 deposited on and bound to carbon fibers 920.

hi particular implementation of this method, a nanocomposite of TiO2 nanoparticles with carbon fiber was formed by placing a mixture of carbon fibers (ALFA # 10450, diameter 8 micron, ~1 g) and sodium titanate (Na ₂ Ti ₃ O ₇ , 2.0 g) in 100 mL of water was placed in a glass lined, 600 mL Parr pressure reaction vessel. The vessel was sealed and placed in a temperature controlled heating jacket where it was heated to 240°C and maintained at that temperature for 5 hours. The heater was then turned off, and the vessel was allowed to cool to room temperature. During the reaction interval, the titanate dissolved and converted to TiO ₂ nanoparticles, which deposited on the carbon

fibers. When the reaction vessel had cooled to room temperature, it was opened, and the fibers were separated by filtration, washed with water, and dried. The resulting composite was characterized by SEM analysis, with the image presented in Figure 9 showing a nanocomposite with TiO ₂ nanoparticles bound to the carbon fiber surface.

While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions, and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include modifications, permutations, additions, and sub-combinations to the exemplary aspects and embodiments discussed above as are within their true spirit and scope. The three exemplary embodiments of the nanocomposite production method are useful for demonstrating that the method is broad in its scope and use with a wide variety of nanoparticle material and nanofiber material to product a range of nanocomposites. For example, a wide variety of metal oxide or semiconductor nanoparticles may readily be combined according to the teaching herein with carbon, boehmite, and metal oxide nanofibers to produce a variety of nanocomposites with a range of desirable properties and functions.