Preparation, Characterization and Surface Free Energy of Nickel-Doped Silica Organic-Inorganic Hybrid Membrane for H₂/CO₂ Separation.

Abstract

Nickel-doped silica organic-inorganic hybrid (Ni/SiO₂) membranes based on tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) were prepared via a sol-gel process for H₂/CO₂ separation. The influence of calcination temperature and Ni-doping amount on the microstructure and surface free energy of Ni/SiO₂ materials was investigated. The permeance of H₂ and CO₂ and vapor stability of the membranes were tested. For the Ni/SiO₂ membrane, the optimal calcination temperature should be 350 °C and Ni/TEOS molar ratio is 0.1. After calcination at 350 °C, nickel element exists in form of Ni-O-Si structure and crystalline NiO with small grain size. At this temperature, the water contact angle of Ni/SiO₂ film achieved a maximum of (96.1±0.4)° and the surface free energy reached the minimum. The H₂ and CO₂ permeance of freshly-prepared the Ni/SiO₂ membrane was 7.86×10-6 and 1.50×10-6 mol m-2 Pa-1 s-1, respectively, at 25 °C and a pressure difference of 0.4 MPa. Compared with the pure SiO₂ membrane, the H₂ permeance and H₂/CO₂ selectivity of Ni/SiO₂ membrane increased by 20.9% and 15.9%, respectively. After aging in the moist condition for 7 d, the H₂ permeance of Ni/SiO₂ membrane was reduced by 6.9% and the H₂/CO₂ selectivity increased by 4.7%. The Ni/SiO₂ membrane showed higher H₂ permeance, H₂/CO₂ selectivity and vapor stability than pure SiO₂ membrane.