In Situ Growth of Self-Assembled ZIF-8-Aminoclay Nanocomposites with Enhanced Surface Area and CO 2 Uptake Anindita Chakraborty, Subhajit Laha, Kesavan Kamali, Chandrabhas Narayana, Muthusamy Eswaramoorthy,* and Tapas Kumar Maji* Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India * S Supporting Information ABSTRACT: Self-assembly of metal-organic framework (MOF) nanoparticles (NPs) with a functional material can result in MOF nanocomposites having new and advanced properties along with the fabrication of new nanoscopic structures. However, such assembly of MOFs has not been realized to date. Here we report self-assembled nano- composites of the zeolitic imidazolate framework (ZIF-8) and layered aminoclay (AC) for the first time, and the ZIF-8@ AC composites exhibit significantly enhanced adsorption properties in comparison to those of pristine ZIF-8 nano- particles. Four different composites denoted as ZIF-8@AC-1, ZIF-8@AC-2, ZIF-8@AC-3, and ZIF-8@AC-4 were synthe- sized by varying the clay content, and their AC contents were found to be 12.1, 18.3, 22.2, and 27.2 wt %, respectively. The composites were thoroughly characterized by PXRD, FTIR, Raman, and various microscopic techniques (FESEM, TEM, and STEM). The formation of the composites is driven by the specific interaction between unsaturated Zn(II) sites of ZIF-8 nanoparticles and NH 2 groups of the aminoclay, which was validated from ζ potential and Raman spectroscopic measurements. The adsorption studies of the desolvated composites were also carried out in detail. The best performance is achieved with one of the composites, which exhibits a 42% increase in BET surface area while CO 2 uptake at 298 K is doubled in comparison to the ZIF-8 nanoparticles. ■ INTRODUCTION The last two decades have witnessed tremendous growth in the synthesis, properties, and versatile applications of metal- organic frameworks (MOFs) having intriguing structures. 1 However, MOFs have certain drawbacks, such as moisture sensitivity, poor thermal and chemical stability, etc., which limit their applications. These shortcomings can be overcome by judicious integration of an MOF with other active species such as metal nanoparticles, organic polymers, graphene oxide, carbon nanotubes, boron nitride, biomolecules, etc. toward new composite materials. 2 Furthermore, the MOF composite materials can also have enhanced and new properties arising from the synergistic combination of the different functional components. 2 Recently, a number of MOF composites have been synthesized by coating nanoscale MOFs (NMOFs) with a suitable component for controlled drug delivery, enhanced in vivo performance, and improved mechanical properties. 3 However, enhanced gas adsorption properties in self-assembled composites obtained by coating of MOF nanoparticles (NPs) with a functional component has yet to be explored. The self- assembly of the colloidal Janus particles into intriguing hierarchical structures have been well-studied, while the self- assembly of MOF particles has been recently reported by applying an external electric field or by exploiting attractive van der Waals interactions between the MOF facets. 4 Self-assembly of MOF NPs with a suitable functional component would be interesting as well, as the composites can exhibit novel and enhanced properties. The prototypical ZIF-8 framework (Zn[MeIm] 2 ; MeIm = 2- methylimidazolate; ZIF = zeolitic imidazolate framework) has been well-studied for its high BET surface area (∼2000 m 2 g -1 ), unimodal micropores, and excellent thermal and chemical stability. 5 Nanosized ZIF-8 particles are particularly interesting, as the nanoscale regime opens up the opportunity of diverse applications, including drug delivery, due to better solution processability. 6 Syntheses of ZIF-8 NPs of various sizes and morphologies have already been reported, 7,8 and some of the reports involve facile synthesis of NPs in aqueous medium at room temperature. However, the reported ZIF-8 NPs (<100 nm) in general have significantly less surface area (∼800-1200 m 2 g -1 ) than the bulk ZIF-8 frameworks, 7-10 which eventually limits the applications of ZIF-8 NPs. The reason behind such reduced surface area of ZIF-8 NPs is not very clear. However, Kida and co-workers suggested that incomplete activation or the incorporation of a small amount of amorphous compounds can result in the smaller surface area in ZIF-8 NPs. 10 Recent experimental and simulation studies from Lively’s group have Received: June 22, 2017 Article pubs.acs.org/IC © XXXX American Chemical Society A DOI: 10.1021/acs.inorgchem.7b01601 Inorg. Chem. XXXX, XXX, XXX-XXX