Membranes for diffusion dialysis (DD) purpose have been mostly based on organic polymer materials up to now. Here, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-SiO2 hybrid membranes, which are produced from hydroxylation, quaternization and sot-gel reaction of brominated PPO, have been successfully applied for DD recovery of hydrochloride acid (HCl) from the mixture of HCl and ferrous chloride (FeCl2). The temperature for DD process is ranged from 15 degrees C to 65 degrees C and the results show that the hybrid membranes can have better separation performances under higher temperature. Separation factor (S) of hybrid membranes increases to as high as 41 as the temperature increases. The commercial polymer membrane DF-120, as a comparison membrane, exhibits much lower S values as the temperature changes. The physico-chemical structure and properties of the hybrid membranes are investigated and related with DD results, indicating that the inorganic silica network contributes much to the enhanced selectivity, especially at higher temperatures. Findings here show the success of organic-inorganic hybrid membranes in DD application field and may provide clues for their further explorations. (C) 2009 Elsevier B.V. All rights reserved.