Imperfection in Cu foil consists of surface contaminations (particles) and grooves. High-purity, expensive Cu foils have a low concentration of particles and have been reported to synthesize graphene after simple solvent washing. They are also free of large grooves and scratches. However, their cost is prohibitive for membrane application (Table ). For low-cost Cu, contamination particles are present on the surface of the Cu foil and are likely deposited during the process of rolling Cu foils. Another source of contamination, irrespective of Cu foil, is the reaction between Cu vapor and the reactor wall made of a fused quartz tube, where SiOx particles are formed. These particles eventually deposit on the Cu foil, affecting graphene quality (Figure ). These could be largely eliminated by placing a high-purity (99.7%) alumina tube (f16 cm) inside the quartz tube, which screened off the quartz tube from Cu vapor (Figure ). We chose a low-cost Cu foil (10 $/m 2 at scale, Table ) and developed a simple protocol for removing contamination, grooves, and scratches. Micron-sized particles formed by several elements (Ca, K, Al, or Cl) could be observed on the as-received Cu foils (Figure ). A facile protocol involving submerging Cu foil in a dilute nitric acid solution was developed. Dissolution of the Cu surface in the nitric acid effectively detached the particles from the surface of the Cu foil.