Hot water has more kinetic energy than cold water, meaning the molecules in the water move around more quickly.

When the water is heated, its surface tension decreases. So hot water can remove particulate matter more efficiently from its surface by spreading over more surface area than cold water.

Surface tension is a property of a fluid surface.

 The tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area.