Polymer composite membranes containing mesoporous particles which function in part as reinforcing agents, modifiers of polymer surface polarity, and membrane structure modifiers are provided. The composites provide superior resistance to internal damage and pore compaction, increased permeability to water with retention of separation fidelity, and resistance to chemical degradation and mechanical wear, along with minimal shedding of the reinforcing particles under applied pressure. These improvements in properties are particularly desirable for the water purification by membrane filtration methods.