We discuss our recent progress in the design and architectural control of complex nanostructured photocatalytic systems and their applications. We first review the synthesis, crystallinity control, and photocatalysis of titania porous nanostructures by discussing several methods for changing the structures from amorphous to crystalline and subsequently ways for enhancing the crystallinity. We also discuss the photocatalytic applications of the nanoshells and the methods for improving their catalytic activities. We will also report a new color switching system based on the reversible redox reaction that could be initiated by the photocatalytic response of semiconductor oxide nanocrystals. The excellent performance of the new color switching system promises their potential applications as attractive rewritable media to meet our society’s increasing needs for sustainability and environmental conservation. We further discuss the use of such photocatalytic systems for heavy metal removal from the wastewater.