Reproducible production of nanoporous carbon membranes

Abstract

Inorganic membranes offer significant potential advansubstrate. In the present study, a solution of poly(furfuryl) tages over polymer membranes, but only if they can be alcohol in acetone (30 wt.% PFA and balance acetone) fabricated readily and reproducibly [1–4]. Nanoporous loaded into a syringe pump is sprayed through the ulcarbons (NPC) or carbon molecular sieves (CMS) are trasonic nozzle onto a porous stainless steel support (0.2 good candidate materials for selective membrane formation mm SS316L, Mott Corporation (Farmington, CT) or 2.0 [5–8]. These can be prepared by the controlled pyrolysis of mm SS316L, Pall Process Filtration Company (East Hills, polymers such as poly(vinyl chloride) (PVC), poly(acrylNY). The ultrasonic spray system can accommodate onitrile) (PAN) and poly(furfuryl) alcohol (PFA) [9,10]. tubular supports ranging from 7.62 to 38.1 cm in length Although amorphous [11], they are endowed with a regular and from 3.175 to 19.05 mm in outside diameter. While the nanostructure that leads to a pore network with narrowly tubular support rotates with a constant frequency (from 0.1 distributed pore dimensions between 0.3 and 0.6 nm [12– to 10 Hz), the tube also moves independently in the 15]. In free standing form the materials are too friable to forward and reverse axial directions with a specified 21 be useful [16,17]. However they can be grown on porous translational velocity (from 0.254 to 25.4 mm s ). Thus, stainless steel support media by brush-coating, spray-coatmultiple coatings are possible with the number of spray ing [5,18], or preferably, ultrasonic deposition of the passes ranging between 1 and 100. polymer resin precursor [19]. Previously, membranes were Ultrasonic nozzles employ high-frequency sound waves prepared by manual control of the ultrasonic deposition of (25 to 120 kHz) to produce atomization of a liquid. They PFA on the support. As with any manual process, this step are ideally suited for spraying thin films because they can was somewhat variable with respect to the degree of dispense extremely small amounts of liquid onto a subcoverage of the support by polymer. Since uniform coverstrate precisely and reproducibly. Compared with convenage is needed to prepare a uniform film a new automated tional pressure spray nozzles, ultrasonic nozzles deliver a 21 unit was designed to do the ultrasonic deposition. Herein, low-velocity spray (,5 cm s ), which is approximately we describe the variability in performance of a group of one hundredth the velocity produced by a standard presseven supported nanoporous carbon membranes (SNPCM) sure nozzle. In an ultrasonically produced spray, drop size prepared in this way under nominally identical conditions. is governed primarily by the operating frequency at which The automated ultrasonic spray system was designed the nozzle vibrates, and to a lesser extent by the surface as-built by Sono-Tek Corporation (Milton, NY). The basic tension and density of the liquid being atomized. The system consists of a broadband ultrasonic generator, a higher the frequency, then the smaller will be the median syringe pump to control the flow of a polymer solution, an drop size. In the present study, we chose an ultrasonic ultrasonic nozzle, an electronic controller with operator nozzle (Sono-Tek, model 06-04029) operating at 60 kHz. interface, and a slide and rotator assembly for the coating This nozzle produced a number-mean droplet diameter of 40 mm for liquid water. To control the spray beam flux, the liquid flow rate was metered with a syringe pump. *Corresponding author. Tel.: 11-814-865-2574; fax: 11-814However, the adjustable flow rate range was limited for 865-7846. E-mail address: hankfoley@engr.psu.edu (H.C. Foley). producing a stable and uniform spray beam. The accept-