Understanding structure of small \({\hbox {TiO}}_2\) nanoparticles and adsorption mechanisms of PbS quantum dots for solid-state applications: a combined theoretical and experimental study

A combined theoretical and experimental study on a series of \({\hbox {TiO}}_{2}\), lead sulfide (PbS) and PbS@TiO\(_{2}\) nanocomposites was performed. \({\hbox {TiO}}_{2}\) structures were stabilized with simulated annealing using molecular dynamics at the ReaxFF level. A density functional theory study elucidated relevant electronic structure properties. We performed the study for a series of \({\hbox {TiO}}_2\))\(_{n}\), where \(n =18\), 28, 38, 76 and 114. Band gaps ranging from 1.2 to 2.2 eV were found. This range was attributed to the size of the \({\hbox {TiO}}_2\) cluster models used in the calculations, and some models became metallic at smaller sizes. We synthesized \({\hbox {TiO}}_2\) nanoparticles of anatase (101) facet, which were characterized with pair distribution functions, in excellent agreement with the theoretical results. We explored the possibility to anchor a PbS quantum dot with a \({\hbox {TiO}}_2\) model system. This intermolecular interaction was relevant, since the composite material could be used in solid-state devices' applications, in which stability in the formation of the \({\hbox {PbS}}/{\hbox {TiO}}_{2}\) interface plays an important role for the device performance. The possibility to form a PbS@TiO\(_{2}\) composite material was evidenced, via a covalent interaction, with contributions of the van der Waals type.