Clean Technology (청정기술)

The Korean Society of Clean Technology (한국청정기술학회)
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Capping Intercrystalline Defects of Polycrystalline UiO-66 Membranes by Polydimethylsiloxane Coating

폴리다이메틸실록산 코팅을 통한 다결정성 UiO-66 분리막의 비선택적 결정립계 결함 캡핑

  • Ik Ji Kim (Department of Chemical Engineering, Pukyong National University) ;
  • Hyuk Taek Kwon (Department of Chemical Engineering, Pukyong National University)
  • 김익지 (부경대학교 화학공학과) ;
  • 권혁택 (부경대학교 화학공학과)
  • Received : 2023.02.02
  • Accepted : 2023.03.03
  • Published : 2023.03.31
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Abstract

In general, the presence of non-selective intercrystalline (grain boundary) defects in polycrystalline metal-organic framework (MOF) or zeolite membranes, which are known to be ca. 1 nm in size, causes lower membrane performance (selectivity) than the intrinsically expected. In this study we show that applying a thin polymeric coating of polydimethylsiloxane (PDMS) on a polycrystalline MOF membrane is effective to cap the non-selective intercrystalline defects and therefore improve membrane performance. To demonstrate the concept, first, polycrystalline UiO-66, one of Zr-based MOFs, membranes were prepared by an in-situ solvothermal growth. By controlling membrane growth condition with respect to growth temperature, we were able to obtain polycrystalline UiO-66 membranes at 150 ℃ with intercrystalline defects of which the quantity is not significant, so it can be plugged by the suggested PDMS deposition. Second, their performances were compared before and after the PDMS deposition. As expected, the PDMS deposition ended up with a noticeable increase in CO2/N2 ideal selectivity from 6 to 14, indicating successful intercrystalline defect plugging. However, the enhancement in CO2/N2 selectivity was accompanied by a significant reduction in CO2 permeance from 5700 to 33 GPU because the PDMS deposition not only plugs defects but also forms a continuous coating on membrane surface, adding an additional transport resistance.

다공성 결정물질(예: 금속유기골격체(Metal-Organic Framework, MOF), 제올라이트(zeolite))로 만들어진 다결정성 분리막의 선택도는 일반적으로 크기가 1 nm 혹은 그 이상으로 알려진 비선택적 결정 간 결함, 즉 결정립계의 존재 때문에 저하된다. 본 논문에서는 다결정성 MOF 분리막 위에 폴리다이메틸실록산(polydimethylsiloxane, PDMS)의 코팅이 결정립계를 캡핑하여 분리막의 선택도를 향상시키는데 효과적임을 증명하였다. 제안된 개념을 증명하기 위해서 in-situ 용매열 합성법을 통해 제조된 지르코늄 기반의 MOF의 일종인 UiO-66 분리막 위에 PDMS를 코팅한 후, 코팅 전후의 성능변화를 관찰하였다. PDMS 코팅 후 UiO-66 분리막의 CO2/N2 단일 기체 분리 선택도는 6에서 14로 증가하였고, 동시에 CO2 투과도는 5700 GPU에서 33 GPU로 감소하였다. 선택도의 증가는 PDMS 코팅이 결정립계 결함을 효과적으로 메웠음을 의미하며, 동반된 투과도의 감소는 PDMS 코팅이 결함을 메우는 동시에 분리막 위에 연속적인 층을 형성하여 추가된 투과 저항에서 비롯되었다고 판단된다.

Keywords

Acknowledgement

이 논문은 부경대학교 자율창의학술연구(2021년)에 의하여 연구되었음.

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