Grantee Research Project Results

Final Report: Development of High Surface Area Material and Filter Media

EPA Contract Number: 68D02021
Title: Development of High Surface Area Material and Filter Media
Investigators: Doshi, Jayesh
Small Business: eSpin Technologies Inc.
EPA Contact: Richards, April
Phase: I
Project Period: April 1, 2002 through September 1, 2002
Project Amount: $69,995
RFA: Small Business Innovation Research (SBIR) - Phase I (2002) RFA Text |  Recipients Lists
Research Category: SBIR - Air Pollution , Small Business Innovation Research (SBIR) , Air Quality and Air Toxics

Description:

Atmospheric concentrations of volatile organic compounds (VOCs) from engine exhaust, power generators, and low-level emissions in indoor air are of significant concern. Additionally, during chemical manufacturing, many VOCs are generated and enter important water streams. Therefore, the efficient collection, careful handling, and disposal or recovery of these organic compounds is a major environmental issue. Granular activated carbons are routinely used as one of the methods to adsorb impurities from air and water because of their high surface area and large adsorption capacity. In recent years, nanotechnology and nanomaterials have received a great deal of attention from the industrial and scientific communities due to their potential impact on these types of applications.

This Phase I research project involved the development of activated carbon nanofibers to be used as filter media for VOC remediation. The main features of activated carbon nanofiber webs are: high surface area, very high porosity, and tight pore size. These features address the problems associated with adsorbing gaseous pollutants, thereby reducing (or eliminating in certain applications) VOCs and their effects.

The major task for the Phase I research project was to design and develop a process to produce a prototype activated carbon nanofiber web with high surface area and demonstrate its capability as filter media. During Phase II, eSpin Technologies, Inc., will tailor the surface area for specific applications and develop a scaled-up version of an activated carbon nanofiber web.

Summary/Accomplishments (Outputs/Outcomes):

eSpin Technologies, Inc., was successful in designing and developing a process to produce a prototype activated carbon nanofiber web. Polyacrylonitrile-based nanofibers were produced under different processing conditions using an electrospinning process. Nanofiber webs of different thickness and fiber diameter were produced. Polyacrylonitrile nanofiber webs then were stabilized, carbonized, and activated.

Physical properties and fiber morphology of the web were evaluated using numerous instruments. Three separate instruments were used to evaluate the surface area of the web and its efficacy to adsorb molecules. A nitrogen Brunauer, Emmett, and Teller (BET) surface area analyzer was used to obtain the surface area of the web. Using a porosimeter, pore size and pore volume distributions of the pores within the webs were determined. eSpin's industrial partner evaluated the samples; surface area measurements and iodine numbers were compared with commercially available powdered activated carbon.

In the case of activated carbon nanofibers, the diameters of the fibers were determined to be in the range of 50 nm, whereas multipoint BET surface area measurements were found to be in the range of 650 m²/g. The average micropore area and volume for activated carbon nanofiber web were in the range of 600 m²/g and 0.3 cc/g, respectively, and porosity was determined to be 56 percent. The iodine number and ash content provided by eSpin's industrial partner were in the range of 800 m²/g and 5 percent, respectively.

The affinity of activated carbon nanofiber web in a concentrated methylene blue solution was tested by immersing the nanofibers into the solution and observing that 89 percent of the dye molecules were adsorbed to the carbon.

Conclusions:

The most desired outcome of Phase I research was the demonstration of activated carbon nanofiber with large surface area (i.e., 850 m²/g) and improvement in filtration efficiency for removal of VOC gases and particles smaller than 3 µm while keeping the pressure drop within an acceptable range.

Although the sample media is non-uniform in mass-per-unit area and thickness in a given lot, a clear trend in increasing gas adsorption was observed compared with large-diameter carbon nanofibers. This supports the original expectation that small-fiber diameters can be put to use to capture a large quantity of VOCs and particulates. It appears likely that activated carbon nanofiber-based filters will have higher VOC gas adsorption efficiency-suggesting that nanofibers' high surface area can be utilized effectively in a practical system.

eSpin has greatly increased the understanding of various challenges facing the manufacture of activated carbon filter media and its use in filters. Although it appears that the material in "thin" sheet form has been brittle, the fragility of nanofibers is an issue to be resolved in Phase II.

Supplemental Keywords:

nanofilter, adsorption, powdered activated carbon, activated carbon nanofiber, electrospinning, electrospun nanofibers, filter media, indoor air, drinking water, nanoweb, sick building, nanocomposite filter, nanotechnology, SBIR., Sustainable Industry/Business, RFA, Scientific Discipline, Waste, Water, Remediation, Technology for Sustainable Environment, Sustainable Environment, Environmental Chemistry, Engineering, Chemistry, & Physics, Chemistry and Materials Science, New/Innovative technologies, Environmental Engineering, nanoparticle remediation, biotechnology, aquifer remediation design, wastewater, groundwater contamination, contaminated aquifers, environmental sustainability, innovative technologies, bio-engineering, groundwater remediation, remediation technologies, environmentally applicable nanoparticles, bioremediation, biodegradation, nanotechnology, decontamination, nanoparticle based remediation