ADA Technologies (Littleton, CO) inventors Thomas A. Campbell and Kent D. Henry
Nanometrological validation of the success of purification and separation uses a pyroelectric detector and Raman spectroscopy in a single system, thus providing a critical aspect for the nanomanufacturing environment. The purification/separation and nanometrological validations may be performed in a feedback loop to provide a satisfactorily refined sample and optimized purification/separation settings.
ADA’s purification methods offer the ability to obtain nearly 100% carbonaceous impurity-free SWNT content from a given impure, as-prepared SWNT bundle without any destruction, defect creation or functionalization of the SWNTs. The separation methods offer the ability to obtain the desired range of chirality and diameter from a given non-separated, as-produced SWNT bundle. Nanometrological validation of the success of purification and separation uses a pyroelectric detector and Raman spectroscopy in a single system, thus providing a critical aspect for the nanomanufacturing environment. Additionally, the present invention offers the ability to avoid `wet` chemistry, as some embodiments process dry SWNTs (i.e. the SWNTs are not in solution). The SWNTs will thus be available as-is for a variety of applications without any further chemistry processing.
The following figure presents a flow chart for the ADA purification process and nanometrology for carbon nanotubes.
The Problem to Be Solved:
Carbon nanotubes (CNTs) are revolutionary materials having valuable electrical, optical, mechanical, and thermal characteristics due to their unique quasi-one-dimensional electron confinement. Despite more than 15 years of R&D, the nanomanufacturing environment for CNTs is still in an inchoate situation. Industrial companies claim they are expanding and refining their processes, yet if one purchases CNTs on the open market, more often than not one obtains a vial of unlabeled, uncharacterized material.
Accordingly, current manufacturing processes do not simply produce a single type of CNT. Instead, yields are a mixture of species, along with unwanted chemical impurities (3-50%). Yielding pure nanotubes of a particular species (type) is one of the principal barriers to significant adaptation of single walled nanotubes (SWNTs) in a wide range of industries, including, but not limited to, nanoelectronics, nanobiotechnology, and general nanomaterials (e.g., nanocomposites).
For industrial firms seeking to harness the amazing properties of CNTs, this is an intractable situation. Original Equipment Manufacturers (OEMs) must go to universities or national labs and spend significant time and money to characterize their purchased CNTs prior to end use. Technologies incorporating CNTs thus confront quality issues at every level, ranging from composite manufacturers integrating CNTs into high-strength structures, to the next generation of optical sources, detectors, and displays. Advanced, cost-effective analytical techniques are needed so that CNT manufacturers, product developers, and regulatory agencies can truly "see" what they have and obtain what they truly need.
Fundamental limitations encountered with off-the-shelf instrumentation applied to carbon nanotube metrology include: limits to information attainable; quantitativeness of results; cost, including capital, ownership, and training; complexity of measurement, including sample preparation; system reliability; sample matrices and sample destructiveness. Specifically, instrumentation can require a solution of SWNTs. Measurement repeatability can be a serious issue with solutions, as the SWNTs tend to fall-out of the solution after a single measurement.
Additionally, despite the high number of chemical, electrical and other processes for purification and separation, such as oxidation (e.g. thermal, wet, fixed air, mild), microwave treatment, chemical treatment (HNO3, HCL, mild acid), chromatography, magnetic purification, annealing, filtration, electrophoresis, sonication, centrifugation, there is no current technique that offers a nanomanufacturing-friendly nanotool to the general community.
For industrial firms seeking to harness the amazing properties of CNTs, this is an intractable situation. Original Equipment Manufacturers (OEMs) must go to universities or national labs and spend significant time and money to characterize their purchased CNTs prior to end use. Technologies incorporating CNTs thus confront quality issues at every level, ranging from composite manufacturers integrating CNTs into high-strength structures, to the next generation of optical sources, detectors, and displays. Advanced, cost-effective analytical techniques are needed so that CNT manufacturers, product developers, and regulatory agencies can truly "see" what they have and obtain what they truly need.
Fundamental limitations encountered with off-the-shelf instrumentation applied to carbon nanotube metrology include: limits to information attainable; quantitativeness of results; cost, including capital, ownership, and training; complexity of measurement, including sample preparation; system reliability; sample matrices and sample destructiveness. Specifically, instrumentation can require a solution of SWNTs. Measurement repeatability can be a serious issue with solutions, as the SWNTs tend to fall-out of the solution after a single measurement.
Additionally, despite the high number of chemical, electrical and other processes for purification and separation, such as oxidation (e.g. thermal, wet, fixed air, mild), microwave treatment, chemical treatment (HNO3, HCL, mild acid), chromatography, magnetic purification, annealing, filtration, electrophoresis, sonication, centrifugation, there is no current technique that offers a nanomanufacturing-friendly nanotool to the general community.
Most all of these techniques have thus far only been demonstrated on lab-scale CNT amounts (a few grams, with some allusion in the respective article that "scale-up should be trivial"), but none of the instruments come in a packaged system for implementation in a nanomanufacturing environment, and moreover many of these purification and separation techniques actually damage or destroy the CNTs during their processing.
Nevertheless, CNTs continue to have a significant allure for materials scientists. Their fundamental properties have been touted to be applicable in a wide range of industries, including chemical, aerospace, automotive, electronics, etc. SWNTs are of special interest to these communities for their prospective properties tunability. The challenge before the industry is to overcome the quality control issue now present at both the raw material supplier and OEM levels. Additionally, there is a challenge of doing this economically and efficiently if commercial manufacturing is to be achieved.
It is therefore desirable to provide systems and methods for quantifying, purifying and separating CNTs. It is also desirable for the systems and methods to be inexpensive and rapid in characterizing SWNTs for the parameters critical to the carbon nanotube industry.
Nevertheless, CNTs continue to have a significant allure for materials scientists. Their fundamental properties have been touted to be applicable in a wide range of industries, including chemical, aerospace, automotive, electronics, etc. SWNTs are of special interest to these communities for their prospective properties tunability. The challenge before the industry is to overcome the quality control issue now present at both the raw material supplier and OEM levels. Additionally, there is a challenge of doing this economically and efficiently if commercial manufacturing is to be achieved.
It is therefore desirable to provide systems and methods for quantifying, purifying and separating CNTs. It is also desirable for the systems and methods to be inexpensive and rapid in characterizing SWNTs for the parameters critical to the carbon nanotube industry.
ADA’s Solution
ADA purification methods offer the ability to obtain nearly 100% carbonaceous impurity-free SWNT content from a given impure, as-prepared SWNT bundle without any destruction, defect creation or functionalization of the SWNTs. The separation methods offer the ability to obtain the desired range of chirality and diameter from a given non-separated, as-produced SWNT bundle. Nanometrological validation of the success of purification and separation uses a pyroelectric detector and Raman spectroscopy in a single system, thus providing a critical aspect for the nanomanufacturing environment. Additionally,Ada offers the ability to avoid `wet` chemistry, as some embodiments process dry SWNTs (i.e. the SWNTs are not in solution). The SWNTs will thus be available as-is for a variety of applications without any further chemistry processing.
ADA separation method utilizes electromagnetic radiation to remove impurities. The electromagnetic radiation is transmitted at a resonance frequency of the nanotubes. For example, a SWNT exhibits a .pi.-plasmon frequency around 248 nm (5 eV), although other plasmon resonances and resonant frequencies may be used. For example, BN nanotubes, buckyballs, or other fullerenes will exhibit a different resonant frequency. The electrons in the fullerenes resonate when the resonant frequency equals the frequency of some outside force, e.g., the electromagnetic radiation, and momentum from the photons may be imparted to the impurities, which readily react with oxygen or ozone in the surrounding air and become oxidized. Thus, EM radiation at a plasmon resonance may be used to remove carbonaceous impurities from as-produced SWNTs using laser ablation.
FIG. 3 illustrates a purification system 300 according to an embodiment of the present invention. In one embodiment, a 248 nm laser 310 operating with a pulse width of approximately 20 ns and a pulse repetition frequency of 10 Hz is used. Other embodiments may use other laser wavelengths, pulse widths and/or repetition frequencies. The beam exiting the laser may be spatially homogenized by means of two lenses 320. In one aspect, each lens consisted of an array of cylindrical lenselets with the cylindrical axis of the first lens perpendicular to the second. In another aspect, the beam size is about 1 cm2. Each laser exposure may be defined by opening a manual shutter 330 for a set period of time, such as 30 s. Preferential oxidation and subsequent destruction of solely carbonaceous impurities may be achieved, leaving the CNTs 340 essentially intact after laser treatment. These results demonstrate a simple method for removing carbon impurities from bulk, as-produced single-walled carbon nanotubes.
Such laser ablation purification can also have important implications in removal of metallic catalysts from as-produced SWNTs. Although the laser treatment does not appear to remove metals, the laser purification might be useful for removing the carbon impurities that encapsulate the metals. The exposed metals may then be removed. Thus, removal of carbonaceous impurities may also aid later removal of metallic catalysts. These metallic catalysts and impurities may also be removed by the electromagnetic radiation directly.
Embodiments utilizing this purification technique, unlike other R&D techniques, do not: (1) destroy CNTs during the purification process, (2) create defects in the CNTs, or (3) functionalize with other atoms/molecules the CNTs. Moreover, a significant portion (greater than 90%) of the carbonaceous impurities are removed. In some embodiments, 100% or nearly 100% (e.g. >98%) of the carbonaceous impurities are removed. Additionally, the separation techniques offer the ability to avoid `wet` chemistry. The SWNTs will thus be available as-is for a variety of applications without any further chemical processing.
Embodiments utilizing this purification technique, unlike other R&D techniques, do not: (1) destroy CNTs during the purification process, (2) create defects in the CNTs, or (3) functionalize with other atoms/molecules the CNTs. Moreover, a significant portion (greater than 90%) of the carbonaceous impurities are removed. In some embodiments, 100% or nearly 100% (e.g. >98%) of the carbonaceous impurities are removed. Additionally, the separation techniques offer the ability to avoid `wet` chemistry. The SWNTs will thus be available as-is for a variety of applications without any further chemical processing.
