(Invited) Surface and Structural Dependent Reactivity of Alkylphosphonic Acids-Modified Titanium Oxide Nanostructures with 2-Chloroethyl Ethyl Sulfide Under Visible Light Excitation

Abstract

Synthesizing novel TiO2 nanomaterials are valuable for heterogeneous reactivity to address toxic chemical remediation. Titanium oxide nanoflowers (comprising assemblies of nanorods) and nanowires have been synthesized in which photocatalytic reactivity with 2-chloroethyl ethyl sulfide (2-CEES) has been significantly enhanced under visible light (1000 nm > λ > 400 nm) excitation. Enhancement of photooxidation with reaction rates of 99 and 168 µmol/g/h (quantum yields of 5.07 x 10-4 and 8.58 x 10-4 molecules/photon) were observed for TiO2 synthesized in the presence of two different alkylphosphonic acids (C14H29PO3H2 and C9H19PO3H2). Additionally, H2Ti2O5‧H2O nanowires were synthesized and capable of highly efficient hydrolysis of the carbon-chlorine (C-Cl) bond of 2-CEES without light at a reaction rate of 279.2 µmol/g/h due to high surface area and chemical nature of the titanate structure. These observations are correlated with: 1) generation of new surface defects/states (i.e. oxygen vacancies) as a result of TiO2 grafting by alkyl phosphonic acid that may serve as reaction active sites; 2) better light absorption by assemblies of nanorods in comparison to individual nanorods, 3) surface area differences, and 4) the exclusion of OH groups due to the formation surface functionalization with alkylphosphonic acids via Ti-O-P bonds on the TiO2. These robust materials can be used for highly efficient surface decontamination.