This book provides a comprehensive look at titanium dioxide (TiO₂) semiconductor nanomaterials, covering their synthesis, unique properties, and applications across energy, environmental, and biomedical fields. From fundamental optical and electronic properties to the design of hybrid TiO₂ materials, it explores their role as multifunctional photocatalysts, pivotal in solar cells, hydrogen production, and lithium-ion batteries. Environmental applications are emphasized through TiO₂'s effectiveness in pollutant degradation, CO₂ reduction, and water purification, while biomedical uses include antibacterial functions and biosensing technologies relevant to diagnostics and even COVID-19 studies. With a focus on current advancements and future potential, this book is an essential resource for researchers and industry professionals exploring TiO₂ nanomaterials' diverse scientific and technological impacts.