Disclosed herein are modified zeolites and methods for making modified zeolites. In one or more embodiments disclosed herein, a modified zeolite may include a microporous framework including a plurality of micropores having diameters of less than or equal to 2 nm. The microporous framework includes at least silicon atoms and oxygen atoms. The modified zeolite may further include organometallic moieties each bonded to bridging oxygen atoms. The organometallic moieties include a hafnium atom. The hafnium atom is bonded to a bridging oxygen atom, and bridging oxygen atom bridges the hafnium atom of the organometallic moiety and a silicon atom of the microporous framework.