the present invention discloses a new type of high selectivity uv - cross - linked tetrazole group functionalized polymer nanosieve membranes , their preparation , as well as their use for gas and liquid separations . the uv - cross - linked tzpim membrane showed more than 50 % improvement in co 2 / ch 4 selectivity and more than 30 % improvement in co 2 / n 2 selectivity compared to the uncross - linked tzpim membrane for co 2 / ch 4 and co 2 / n 2 separations , respectively .