The excellent photocatalytic properties of titanium oxide (TiO₂) under ultraviolet light have long motivated the search for doping strategies capable of extending its photoactivity to the visible part of the spectrum. One approach is high-pressure and high-temperature hydrogenation, which results in reduced ‘black TiO₂’ nanoparticles with a crystalline core and a disordered shell that absorbs visible light. Here we elucidate the formation mechanism and structural features of black TiO₂ using first-principles-validated reactive force field molecular dynamics simulations of anatase TiO₂ surfaces and nanoparticles at high temperature and under high hydrogen pressures. Simulations reveal that surface oxygen vacancies created upon reaction of H₂ with surface oxygen atoms diffuse towards the bulk material but encounter a high barrier for subsurface migration on {001} facets of the nanoparticles, which initiates surface disordering. Besides confirming that the hydrogenated amorphous shell has a key role in the photoactivity of black TiO₂, our results provide insight into the properties of the disordered surface layers that are observed on regular anatase nanocrystals under photocatalytic water-splitting conditions.

长期以来，氧化钛（TiO ₂）在紫外光下的优异光催化性能促使人们寻求能够将其光活性扩展到光谱可见部分的掺杂策略。一种方法是高压和高温氢化，这导致还原的“黑色TiO ₂ ”纳米颗粒具有晶状芯和吸收可见光的无序外壳。在这里，我们使用第一原理验证的锐钛矿型TiO _2的反作用力场分子动力学模拟来阐明黑色TiO ₂的形成机理和结构特征。表面和纳米颗粒在高温和高氢气压下。模拟表明，H ₂与表面氧原子反应生成的表面氧空位向本体材料扩散，但是在纳米粒子的{001}面上遇到了次表面迁移的高障碍，从而引发了表面无序化。除了确认氢化非晶壳在黑色TiO ₂的光活性中起关键作用外，我们的结果还提供了对在光催化水分解条件下在常规锐钛矿型纳米晶体上观察到的无序表面层性质的了解。