Preparation of STT zeolite membranes with outstanding helium extraction performance by gradient induction method

STT zeolite membranes were attractive for gas separation. Zeolite membranes generally grew from the substrate towards the precursor solution together with the particle formation in the bulk precursor solution. It is still challenging to achieve highly selective zeolite membranes for He/CH₄ separation. In this study, we proposed a gradient induction method to prepare highly selective STT zeolite membranes. The substrate was coated with the underlying calcined (slow-induction) seed layer, followed by the upper original (fast-induction) seed layer. The fast-induction seed led to a rapid formation of the STT zeolite membranes by consuming silica from the bulk precursor solution. Meanwhile, the slow-induction seed acted as a nutrient source to heal the non-selective defects of the membranes from the other side. The as-synthesized STT zeolite membrane demonstrated a He permeance of 1.0 × 10⁻⁷ mol m⁻² s⁻¹·Pa⁻¹ (∼300 GPU) and a He/CH₄ selectivity of 208, far surpassed the 2019 upper bound.