Surface Functionalization of Zirconium Phosphate Nanoplatelets for the Design of Polymer Fillers Brian M. Mosby, AgustínDíaz, Vladimir Bakhmutov, and Abraham Clearfield* Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842, United States * S Supporting Information ABSTRACT: Inorganic-organic hybrid materials were synthesized by covalent attachment of epoxides to the surface of zirconium phosphate (ZrP) nanoplatelets. X-ray powder diffraction, FTIR, and TGA were utilized to confirm the presence of the modifiers and exclusive functionalization of the ZrP surface. NMR experiments were conducted to confirm the formation of P- O-C bonds between surface phosphate groups and epoxide rings. The applicability of the organically modified products was demonstrated by their use as fillers in a polymer matrix. Subsequently, a two step intercalation and surface modification procedure was utilized to prepare polymer nanocomposites that were imparted with functionality through the encapsulation of molecules within the interlayer of surface modified ZrP. KEYWORDS: surface modification, tetravalent metal phosphates, self-assembled monolayers, inorganic layered materials, polymer nanocomposites ■ INTRODUCTION Self-assembled monolayers (SAMs) have attracted much attention over the past three decades due to the simplicity of synthesis and broad range of applicability. Netzer and Sagiv originally found that reaction of trichlorosilanes with the hydroxyl terminated surface of SiO 2 led to addition of a monolayer, which greatly altered the properties of the material. 1 The smooth faces of silicon based platforms with Si-H and Si- OH bonds made them the initial platforms of choice; subsequently, SAMs have extended to a large number of platforms including gold and metal oxides. 2,3 SAMs are of interest due to the ability of the monolayer to alter the properties of the material. By carefully choosing the substrate and composition of the monolayer, SAMs have found applicability in a large number of fields such as chemical sensors, biosensors, cell adhesion, microelectronics, and thin film technology. 4,5 The principles of SAMs were soon applied to nanoparticles in which case surface modification is used to build monolayers. As is the case with SAMs, modification of nanoparticles can alter the properties of the material and dictate how they interact with their environment. Metal phosphates make up one of the largest families of inorganic layered materials. α-Zirconium hydrogen phosphate (Zr(O 3 POH) 2 ·H 2 O, ZrP) is one of these materials, which has been extensively studied since being reported by Clearfield and Stynes in 1964. 6 Single crystal X-ray diffraction data of the α phase showed that the Zr atoms lie in a plane, slightly below and above the layer, and are connected to each other by phosphate groups. Three of the oxygen atoms of each phosphate group are bonded to a different Zr atom, and the remaining hydroxyl group points away from the layer, either in the interlayer region or on the surface. 7 The arrangement of the layers forms a zeolitic cavity where a water molecule resides; this cavity has been utilized for intercalation chemistry, the reversible incorporation of guest molecules into the interlayer, and has given ZrP a large range of applications ranging from drug delivery to nanocomposites. 8-12 The introduction of organic functionality into ZrP was thought to be ideal as a means of producing hybrid materials with diverse applicability. Alberti found that organic derivatives of ZrP could be achieved by reaction of zirconium fluoro complexes with phosphonic acids or phosphoric acid esters. 13 Received: October 21, 2013 Accepted: December 6, 2013 Published: December 6, 2013 Research Article www.acsami.org © 2013 American Chemical Society 585 dx.doi.org/10.1021/am4046553 | ACS Appl. Mater. Interfaces 2014, 6, 585-592