Band-Edge Engineering at the Carbon Dot–TiO₂ Interface by Substitutional Boron Doping

Abstract

We investigated the heterostructures of pristine and boron-doped carbon dots (CDs) with TiO 2 using a first principles approach. Heterojunctions of CDs and TiO 2 demonstrated type II band alignments that promote spatial separation of charge carriers and were well suited for sensitizer configuration. However, large CD band gaps severely restricted their optical efficiencies. Substitutional boron doping of the CDs introduced new electronic states and pulled the CDs' conduction band minimum (CBM) down, resulting in dramatic reduction of CD band gaps (by 48− 57%). The resulting band alignment of the boron-doped CD− TiO 2 heterostructures were found to be type I, in which CBM and valence band maximum of TiO 2 straddled those of CDs and photoexcited carriers could migrate to CD side. This indicated better suitability for device configurations where conducting channel lies through the CDs but elevated the chance of recombination loss. However, the internal electric fields at these heterojunctions were found to selectively promote electron migration and hinder hole migration, which we postulate could counter the recombination loss in these systems. The obtained results offer insights into designing a new generation of watersplitting photocatalysts that would be able to utilize a broader spectrum of solar radiation than the current solutions.

Carbon Nanodots from an In Silico Perspective

“…Otyepka and co-workers, recently studied the effects of pure and B-doped CNDs at the interface with TiO 2 . DFT calculations were performed to analyze the optical absorption range and photocatalytic water-splitting performances of the TiO 2 /CNDs heterostructures.…”

“…Computational studies of the interactions of CDs with small molecules, ,,,,,,,,, surfaces ,,, and biological macromolecules or assembled structures, including proteins, − ,,,,,, nucleic acids, ,,, and lipid bilayers, ,,,,,,,,,,, generally make use of highly simplified or idealized CD models. The former two fields (interactions with small molecules or surfaces), which often employ computationally expensive electronic structure methods, specifically, DFT/TDDFT routinely models the CDs themselves as small molecules, e.g., pyrene or coronene derivatives.…”

“…The former two fields (interactions with small molecules or surfaces), which often employ computationally expensive electronic structure methods, specifically, DFT/TDDFT routinely models the CDs themselves as small molecules, e.g., pyrene or coronene derivatives. Recent examples reviewed in the preceding subsections include Wu et al's study of the oxygen photosensitization of N-doped CDs (GQDs) 43 and that of Otyepka and co-workers, 544 investigating the photocatalytic water splitting performance of B-doped CNDs at TiO 2 surfaces. Studies of CDs in biological environments, on the other hand, require the simulation of large to extremely large models, which are then necessarily described by approximate FFs or even further simplified by using CG models.…”

“…Figure 66. Side (left) and top (middle) views of the optimized geometries of TiO 2 −CDs heterostructures studied by Sen et al,544 with the CND modeled as (a) benzene, (b) pyrene, (c) boron doped coronene. Evaluated B doping sites (right).…”

Element‐Doped Mxenes: Mechanism, Synthesis, and Applications

“…TiO 2 is the most promising photocatalyst due to its wide bandgap (3.2 eV) and fast photogenerated carrier recombination speed (1-10 ps), [277,278] which limit its large-scale application in photocatalysis. [279,280] MXene materials optimized based on elemental doping are often used as precursor terminal functional groups for the synthesis of TiO 2 to effectively change the band position and bandgap while increasing the carrier concentration and lifetime.…”