What happens to dew each day when the sun rises?

Warmer air can hold more water than colder air. The air cools during the night due to lack of sunshine, and when it gets so cool that it can't hold any more water (called the dew point), dew forms (or frost if the temperature is below freezing). After sunrise, the air starts warming up. That makes it able to hold more water, so the dew evaporates.