TiO 2 ‑Integrated Carbon Prepared via Pyrolysis of Ti-Loaded Metal- Organic Frameworks for Redox Catalysis Mithun Sarker, Biswa Nath Bhadra, Subin Shin, and Sung Hwa Jhung* Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University, Daegu 41566, Republic of Korea * S Supporting Information ABSTRACT: By suitably selecting metal-organic frame- works (MOFs) and solvents (to dissolve Ti precursors) applied for double solvent method (based on the hydro- philicity 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 hydro- philic and hydrophobic solution onto hydrophobic and hydrophilic MOF, respectively. TiO 2 -integrated carbons (TiO 2 @M-6, TiO 2 @M-74, M-6@TiO 2 , and M-74@TiO 2 ) were further prepared by pyrolysis of Ti-loaded-MAF-6 and MOF-74, where particle size of TiO 2 depends on the position of loaded Ti precursor, or the TiO 2 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 TiO 2 size might be due to the residence of Ti-precursor inside of MOFs. In order to estimate the possible applications of the obtained TiO 2 -integrated carbons in redox catalysis, those materials, together with synthesized TiO 2 (rutile and anatase), commercial P-25, and TiO 2 -loaded activated carbon, were applied as catalyst in oxidative desulfurization (ODS) and reduction of 4-nitrophenol (4-NP). The catalytic result shows that TiO 2 -integrated carbons obtained from pyrolysis of Ti- precursors@MOF have higher catalytic activity than those from pyrolysis of MOF@Ti-precursors (because of smaller TiO 2 size and higher porosity). Finally, the TiO 2 @M-6, prepared from pyrolysis of TiCl 4 @MAF-6, could be suggested as a highly effective catalyst for ODS and the reduction of 4-NP. KEYWORDS: double solvent method, hydrophilicity-hydrophobicity, oxidative desulfurization, reduction of 4-nitrophenol, titania-carbon composite 1. INTRODUCTION Metal-organic frameworks (MOFs) 1-3 with or without modification are an advanced class of porous materials 4,5 that have received much attention because of their simple synthesis, excellent porosity, and several potential applications. 6-8 Recently, MOFs have been employed as support materials for loading various materials including metallic precursors or nanoparticles. 9-11 There are several approaches 12 such as chemical vapor deposition, 13 solution infiltration or incipient wetness impregnation, 14 and solid grinding 15 to introduce metal precursors onto MOFs. Recently, double solvent (DS) method 16-21 has attracted much attention to introduce metal precursors inside the cavities of MOFs because of the possibility to minimize the aggregation of metal precursors on the external surface, 16 which is beneficial for catalysis. 16 In contrast, in the typical single-solvent impregnation process, metal precursors can be deposited on the outer surfaces of MOF after drying, producing aggregated nanoparticles on the external surfaces which may lead to reduction in catalytic activity/durability during a reaction. 12,16 In DS method, hydrophilic and hydrophobic solvent were employed to avoid aggregation of metal precursors on external surfaces of MOF. So far, usually hydrophilic MOFs such as MIIL-101 16-18 and UiO-66 19,20 have been employed in DS method using hydrophilic solvent containing the metal precursor with a volume less than the pore volume of the MOF, which finally can be introduced inside of the pores of hydrophilic MOF by capillary force. 16 However, the DS method is an emerging technology that needs more study for various applications. Further research such as the effect of hydrophilicity and hydrophobicity of MOFs (these properties of MOFs might be controlled or selected because of designable and rich chemistry of MOFs) and solvents on the products is, therefore, required to understand details of DS method including mechanism. On the other hand, metallic or metal oxide nanoparticles, especially when dispersed well on nanostructured material, Received: October 15, 2018 Accepted: December 21, 2018 Published: December 21, 2018 Article www.acsanm.org Cite This: ACS Appl. Nano Mater. XXXX, XXX, XXX-XXX © XXXX American Chemical Society A DOI: 10.1021/acsanm.8b01841 ACS Appl. Nano Mater. XXXX, XXX, XXX-XXX Downloaded via 196.52.65.21 on January 10, 2019 at 13:04:11 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.