The supply of energy from the Sun to the Earth is 3 x 10^24 joules a year, which is about 10,000 times higher than the current global energy consumption. This solar energy is distributed across different regions of the electromagnetic spectrum. Approximately 5% of the solar energy falls within the ultraviolet (UV) range (100 - 400 nm), while the visible range (400 - 700 nm) accounts for approximately 43%. The majority, about 52%, is in the near-infrared (NIR) region (700 - 2500 nm). Utilizing the full spectrum of solar energy for driving photocatalytic processes, such as water decontamination and hydrogen production, has been a long-standing goal. To achieve this goal, it is essential to find the material that is capable of absorbing and converting the entire solar spectrum into chemical or electrochemical energy. In the first section of my research, I focused on studying the photocatalytic decomposition of ammonia and pure water using sulfur-doped carbon nanodots. This research aimed to develop efficient methods for ammonia decomposition and water splitting, which are crucial for various industrial processes and environmental applications. The second part of my PhD study was dedicated to exploring near-infrared (NIR)-driven photocatalysis using upconversion lanthanide nanocrystals as the core material. These nanocrystals were then coated with SiO2 and TiO2 to create a core-shell-shell structure. Additionally, I investigated the tuning of these core-shell structures by varying the surfactants used in the synthesis process. In the last section of my research, I focused on the development of a photothermal-based water desalination device using glycerol-derived nanocarbons. Specifically, I synthesized porous nanocarbon composites (PNCs) that exhibited excellent light absorption properties, making them highly efficient for solar-evaporator-based water desalination. Overall, my research encompasses the decomposition of ammonia using carbon nanodots, the exploration of NIR-driven photocatalysis, and the development of a photothermal water desalination device. These investigations contribute to the advancement of sustainable energy technologies and provide insights into the utilization of full solar energy for various applications.