The present disclosure discloses a preparation method of an organosilica/ceramic composite membrane with a gradient pore structure. The preparation method comprises: (1) selecting a porous ceramic material as a membrane support layer; (2) gradually replacing a solvent with water to prepare zirconium colloidal sols with different particle sizes, and successively coating the prepared zirconium colloidal sols onto a ceramic support from large to small so as to form a membrane transition layer with a gradient pore structure; and (3) catalytically synthesizing an organosilica polymeric sol using hydrochloric acid, coating the prepared organosilica sol onto the preheated transition layer through ultrasonic thermal spraying to undergo heat treatment, so as to prepare the organosilica/ceramic composite membrane with the gradient pore structure. According to the present disclosure, the transition layer with the gradient pore structure is prepared by using the zirconium colloidal sols with different particle sizes. An ultrathin defect-free organosilica separation layer is prepared through ultrasonic thermal spraying. As a result, the obtained organosilica/ceramic composite membrane can be applied to the fields of salt-containing dye wastewater treatment and polypeptide bioactive substance separation.

The present invention relates to a process for the preparation of a green multilayer sol-gel ceramic membrane for the separation of gaseous CO.sub.2 from natural gas. For being composed solely of ceramic materials (silica and alumina), the ceramic membrane developed by the proposed process has high chemical, physical and mechanical stability as its main characteristics. These characteristics ensure its usefulness in the process of separating CO.sub.2 from natural gas, even in streams having high CO.sub.2 concentrations and under high pressure; the developed membrane further enables backwashing operations to be carried out, when needed.