To find a more stable adsorbent for the selective removal of mercury ions, a new mesoporous adsorbent is developed and compared with a number of carefully selected mesoporous silica adsorbents described in literature. This new adsorbent is based on a pure trans-ethene bridged periodic mesoporous organosilica (PMO) which is subsequently modified to obtain a suitable adsorbent. The outcome is a new thiol-containing ethene bridged PM which combines the adsorption efficiency of the thiol group toward mercury ions with the stability of ethene bridged PMOs. During the adsorption process, this material not only maintains its mesoporous structure and ordering, it also completely preserves the amount of organic functionalities, allowing recycling and reuse of the adsorbent. Additionally, this PMO is able to reduce the Hg2+ amount in aqueous solutions below 0.5 mu g/L, and the adsorbent has a maximal adsorption capacity of 64 mg/g which means an apparent 1:1 ratio mercury(II) ion to thiol.