A new perspective on the photocatalytic action of titanium dioxide on phenol elucidated using comprehensive multiphase NMR

Abstract

First application of CMP-NMR to heterogeneous catalysis, we discover a region where organics experience restricted diffusion and are preferentially degraded.

SASSY NMR: Simultaneous Solid and Solution Spectroscopy

“…At the same time, the local dynamics that reduce the CP efficiency also narrow the 1 H linewidth allowing low power 1 H decoupling to become more efficient, and as such a signal appears in the “solution‐state”. Ultimately, it is clear that SASSY can be used to distinguish the degree of rigidity and may appeal to those investigating biological tissue (tissue stiffness, hard scaffolds), [19] or solid–liquid interactions such as substrate–catalyst binding/fouling, [20, 21] protein immobilization at interfaces [22, 23] and other processes involving changes in multiple phases such as swelling or drying.…”

Improved Photocatalytic Performance of TiO2–Nitrogen-Doped Graphene Quantum Dot Composites Mediated by Heterogeneous Interactions

“…Our group recently published a report monitoring photocatalysis using Comprehensive MultiPhase Nuclear Magnetic Resonance (CMP-NMR). 11 CMP-NMR creates a series of NMR spectra of individual phases defined by their diffusion (solutions, gels) and dipolar interactions (solids). These include the solution phase (bulk solution molecules far from colloidal surface), the solid phase (molecules tightly bound or adsorbed to the colloidal surface), and a restricted diffusion phase (molecules at the interface between the previous phases which are interacting with the colloid but not tightly bound).…”

“…12−14 A detailed description of the origin and interpretation of these spectra in photocatalytic systems has been provided in previous studies. 11 This previous work identified that molecules in a diffusion restricted phase, which were distinct from those bound to the colloidal surface, were preferentially targeted by reactive oxygen species (ROS) generated at the catalyst surface.…”

“…This is an improvement over P25 TiO 2 whose surface was found to foul under similar conditions. 11 The restricted diffusion phase is perhaps the most interesting, as it is not observable by other standard analytical techniques. The signals in this phase arise from molecules whose microscopic diffusion is limited relative to purely dissolved molecules but retain the relaxation properties of solvated molecules from the perspective of the NMR.…”

“…With increased irradiation the solid signals are reduced, suggesting that the catalyst is capable of regenerating the surface with sufficient time and light. This is an improvement over P25 TiO 2 whose surface was found to foul under similar conditions …”