Hydroxyl groups (- OH) can exhibit acidity or alkalinity on the surface of metal oxides in the form of proton reception or supply. By adjusting the quantity and distribution of hydroxyl groups, precise control of surface acidity and alkalinity can be achieved, thereby affecting the activation pathway and selectivity of catalytic reactions.
On unsaturated metal sites of metal oxides or semiconductor oxides (such as Ti4+, Fe3+), water molecules first adsorb in molecular form, followed by O-H bond cleavage, resulting in bridge or terminal hydroxyl groups (M-OH) and surface hydrogen atoms. The thermodynamic driving force of this process comes from the strong Lewis acidity of metal ions, making water molecules easy to dissociate. Both experiments and DFT calculations indicate that surfaces covered with low oxygen tend to dissociate and adsorb, while surfaces covered with high oxygen tend to adsorb molecules.
Surface hydroxyl engineering refers to the targeted regulation of the number, distribution, and chemical activity of hydroxyl (- OH) groups on the surface of materials through physical, chemical, or plasmonic means, in order to achieve precise adjustment of surface properties. Hydroxyl groups are the most common polar functional groups that can form hydrogen bonds, coordination bonds, or covalent bonds with water, metal ions, polymer chains, or biomolecules, significantly altering the hydrophilicity, surface energy, adsorption/catalytic activity, and biocompatibility of materials.
Infrared spectroscopy: It looks at how much light has been consumed. When a molecule absorbs light of a specific wavelength, we know what functional groups are inside it. Raman spectroscopy: It looks at how much light has been deflected. A laser beam is applied to analyze how much the light bounced back has changed, in order to determine the molecular structure.
The basic characterization techniques of catalysts are powerful tools for gaining a deeper understanding of their physical, chemical, and structural properties. Through comprehensive application, the catalytic reaction mechanism can be revealed, providing a theoretical basis for the design and development of high-performance catalysts. With the advancement of technology, this technology continues to innovate and develop towards higher resolution, more accurate quantification, and better simulation of real reaction conditions.
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