TiO2 nanomaterials have been widely studied for various photocatalytic and photoelectrochemical reactions in environmental pollution removal and renewable energy production (hydrogen production, CO2 reduction, fuel production, etc.). Their performances in those areas largely depend on the interaction with the electromagnetic radiation. Therefore, revealing those interactions is very important to many applications and may also open new applications. In this work, we will present our effort in studying the absorption of such electromagetic radition across various energy ranges with TiO2 nanomaterials and modified TiO2 nanomaterials. Mechanisms of such absorption are proposed and discussed, along with possible applications.