Research Progress on Preparation of Black Titanium Dioxide and Utilization of Solar Energy

Titanium dioxide (TiO₂) has long been a key material in the fields of new energy and environmental protection, widely used in photocatalysis, solar energy conversion, and solar collectors. However, its application in solar energy utilization faces significant challenges. The main issues include a limited light absorption range—TiO₂ can only absorb about 5% of ultraviolet light from the solar spectrum—and a low efficiency in separating electron-hole pairs. Its intrinsic conductivity is very low (~10⁻¹⁰ S/cm), which hinders the movement and separation of charge carriers. These limitations have restricted the broader use of TiO₂ in energy and environmental applications, preventing it from fully harnessing solar energy. Recent collaborative research between the Shanghai Institute of Ceramics, Chinese Academy of Sciences, and Peking University's School of Chemistry has led to the development of several innovative preparation methods. Researchers such as Huang Fuqiang, Wang Zhou, Yang Zhongyi, and Lin Tianquan have introduced techniques like hydrogen plasma reduction, low-temperature aluminum reduction, and a two-step non-metallic doping method. These approaches significantly enhance the visible and near-infrared light absorption of TiO₂, showing remarkable improvements. The newly developed black titanium dioxide nanocrystals differ from traditionally high-temperature hydrogen-reduced black TiO₂. Instead, they feature a core-shell structure: the core remains crystalline TiO₂, while the outer shell is amorphous, containing oxygen vacancies or non-metallic doping (such as H, N, S, I). This unique structure enables sunlight absorption up to 85%, far surpassing previous reports of around 30%. With excellent solar absorption, chemical stability, and enhanced carrier concentration and electron mobility, these materials are well-suited for high-efficiency solar energy applications. For instance, nitrogen-doped nano-black TiO₂ has demonstrated a hydrogen production rate of 15 mmol·h⁻¹·g⁻¹ under visible light, making it one of the most efficient visible-light catalysts reported. Additionally, it degrades organic pollutants four times faster than commercial P25 TiO₂. When used as a photoelectrochemical (PEC) electrode, black TiO₂ nanotube arrays achieved a light-to-hydrogen conversion efficiency of 1.67%, the highest recorded for TiO₂-based PEC systems. These breakthroughs have been highlighted by Chemistry Views in an article titled "Titania: Black is the New White." The findings suggest promising applications in renewable energy, such as solar power generation and photocatalytic hydrogen production, as well as in environmental technologies like pollution degradation and antibacterial disinfection. International companies and universities have already started purchasing small batches of samples for environmental applications. Some of the research results have been published in top-tier journals including *J. Am. Chem. Soc.* (2013), *Adv. Funct. Mater.* (2013), *Energy Environ. Sci.* (2013, 2014), and *Chem. Eur. J.* (2013). Three invention patents have also been filed, marking a significant step forward in the development of advanced TiO₂-based materials for sustainable energy and environmental solutions.

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