Surface- and Structural-Dependent Reactivity of Titanium Oxide Nanostructures with 2‑Chloroethyl Ethyl Sulfide under Ambient Conditions

Robust materials capable of heterogeneous reactivity are valuable for addressing toxic chemical clean up. Synthetic manipulations for generating titanium oxide nanomaterials have been utilized to alter both photochemical (1000 nm > λ > 400 nm) and chemical heterogeneous reactivity with 2-chloroethyl ethyl sulfide (2-CEES). Synthesizing TiO₂ nanomaterials in the presence of long-chain alkylphosphonic acids enhanced the visible light-driven oxidation of the thioether sulfur of 2-CEES. Photooxidation reaction rates of 99 and 168 μmol/g/h (quantum yields of 5.07 × 10^–4 and 8.58 × 10^–4 molecules/photon, respectively) were observed for samples made with two different alkylphosphonic acids (C₁₄H₂₉PO₃H₂ and C₉H₁₉PO₃H₂, respectively). These observations are correlated with (i) generation of new surface defects/states (i.e., oxygen vacancies) as a result of TiO₂ grafting by alkylphosphonic acid that may serve as reaction active sites, (ii) better light absorption by assemblies of nanorods and nanowires in comparison to individual nanorods, (iii) surface area differences, and (iv) the exclusion of OH groups due to the surface functionalization with alkylphosphonic acids via Ti–O–P bonds on the TiO₂. Alternatively, nanowire-form H₂Ti₂O₅·H₂O was produced and found to be capable of highly efficient hydrolysis of the carbon–chlorine (C–Cl) bond of 2-CEES in the dark with a reaction rate of 279.2 μmol/g/h due to the high surface area and chemical nature of the titanate structure.