# Surface Stabilization of High-Pressure TiO2 Polymorph via High-Energy Ball Milling: Boosting Noble-Metal-Free CO2 Photoreduction

## TL;DR

High-energy ball milling creates a stable titanium dioxide structure that efficiently converts CO2 to methanol without noble metals.

## Contribution

A novel method using high-energy ball milling to stabilize TiO2-II polymorph for CO2 photoreduction is introduced.

## Key findings

- TiO2–II nanocrystallites anchored to anatase surfaces enhance CO2 photoreduction to CH3OH.
- Defect-rich configurations provide high-affinity CO2 adsorption and activation sites.
- HEBM restructures TiO2 under ambient conditions, mimicking high-pressure pathways.

## Abstract

High-energy ball milling (HEBM) is employed to stabilize
the high-pressure
TiO2–II polymorph as nanocrystallites anchored to
anatase surfaces, producing a controllable polymorphic mixture that
markedly enhances CO2 photoreduction to CH3OH
in aqueous media without noble metals or cocatalysts. The resulting
architecture features TiO2–II intimately interfaced
with strained anatase and a high density of extended defects (grain
boundaries, phase interfaces, and dislocation terminations) hosting
reactive surface species with modified electronic properties. This
defect-rich configuration provides high-affinity CO2 adsorption
and activation sites. Both bulk and surface are profoundly restructured
under the extreme nonequilibrium conditions of HEBM, which reproduce
high-pressure transformation pathways at ambient conditions. These
results highlight a green, scalable strategy for defect and polymorph
engineering in TiO2, enabling targeted surface chemistry
design to improve photocatalytic CO2 conversion.