TiO2-Integrated Carbon Prepared via Pyrolysis of Ti-Loaded Metal–Organic Frameworks for Redox Catalysis

By suitably selecting metal–organic frameworks (MOFs) and solvents (to dissolve Ti precursors) applied for double solvent method (based on the hydrophilicity or hydrophobicity of both MOF and solvent), the position of loaded Ti precursors could be controlled (inside or outside of MOFs). For example, hydrophobic solution of Ti precursors loaded on hydrophobic MOF (MAF-6) or hydrophilic solution of Ti precursors loaded on hydrophilic MOF (MOF-74) leads to MOFs with Ti precursors selectively inside of the MOFs. On the contrary, Ti precursors loaded outside of MOFs could be obtained by introducing hydrophilic and hydrophobic solution onto hydrophobic and hydrophilic MOF, respectively. TiO2-integrated carbons (TiO2@M-6, TiO2@M-74, M-6@TiO2, and M-74@TiO2) were further prepared by pyrolysis of Ti-loaded-MAF-6 and MOF-74, where particle size of TiO2 depends on the position of loaded Ti precursor, or the TiO2 obtained by pyrolysis of Ti precursor-loaded inside of MOF has smaller particle size compared with the particle prepared similarly from Ti precursor-loaded outside of MOF. The reduced TiO2 size might be due to the residence of Ti-precursor inside of MOFs. In order to estimate the possible applications of the obtained TiO2-integrated carbons in redox catalysis, those materials, together with synthesized TiO2 (rutile and anatase), commercial P-25, and TiO2-loaded activated carbon, were applied as catalyst in oxidative desulfurization (ODS) and reduction of 4-nitrophenol (4-NP). The catalytic result shows that TiO2-integrated carbons obtained from pyrolysis of Ti-precursors@MOF have higher catalytic activity than those from pyrolysis of MOF@Ti-precursors (because of smaller TiO2 size and higher porosity). Finally, the TiO2@M-6, prepared from pyrolysis of TiCl4@MAF-6, could be suggested as a highly effective catalyst for ODS and the reduction of 4-NP.