Enhanced quality of transfer-free graphene membrane for He/CH4 separation

• Published in: Separation and purification technology 2020-02, Vol.232, p.115972, Article 115972
• Main Authors: Nikkho, Sepehr, Mirzaei, Maryam, Karimi Sabet, Javad, Moosavian, Mohammad Ali, Hedayat, Seyed Mahdi
• Format: Article
• Language: English
• Subjects: Chemical vapor deposition; Gas separation; Graphene membrane; Intrinsic defects; Photolithography; Transfer-free
• ISSN: 1383-5866; 1873-3794
• DOI: 10.1016/j.seppur.2019.115972

[Display omitted] •Graphene membrane quality was improved and the tears/cracks were decreased.•Small holes were introduced into the copper foil via photolithography process.•The selectivity of 3.5 was achieved through the transfer-free graphene membrane.•The helium permeation through the graphene membrane was 1.19 × 10-5 mol/m2.pa.s. Atomically thin porous graphene as a selective layer is believed to be a promising candidate to exhibit superior gas separation performance. While small-area graphene membranes have been successfully fabricated, crack-free and large-area graphene transfer onto the porous substrate remains a great challenge. Large defects, up to micron-scale, can emerge during the conventional graphene transfer techniques. In this work, we improved transfer-free graphene membrane fabrication through small pore introduction into copper foil. We apply the typical photolithography process to establish a patterned mask on the backside of the graphene-covered copper foil followed by a chemical etching process to drill small-sized pores into the copper foil, with pore sizes varying between 200 nm and 4 µm. To measure the membrane performance, He/CH4 separation is carried out. The observed selectivity ~3.5 shows 28% enhancement in comparison to the membrane prepared through the transfer step (~2.5). The maximum measured selectivity achieved in this work is higher compared to the Knudsen selectivity (2), which can confirm the molecular-sieving-based selective gas transport through the angstrom-size intrinsic defects of the graphene film. In addition to the high permeance (1.19 × 10−5 mol/m2·s·Pa) achieved through the graphene-based membrane, its selectivity also exceeds the Robeson upper bound for polymeric membranes, proving the higher performance acquired compared to other polymeric membranes. The enhancement in transfer-free graphene membrane quality can bring us one step closer to realizing graphene’s full potential and developing large-area and crack-free graphene membranes.