Metal-Organic Framework Co-MOF-74-Based Host-Guest Composites for Resistive Gas Sensing.

Ina Strauss,Seungtaik Hwang,Karsten Lange,Jürgen Caro,Pascal Rusch,Marvin Treger,Alexander Mundstock,Hidetsugu Shiozawa,Thomas Pichler,Nadja C Bigall,Christian Chmelik

doi:10.1021/acsami.8b22002

Abstract

Increasing demands in the field of sensing, especially for gas detection applications, require new approaches to chemical sensors. Metal–organic frameworks (MOFs) can play a decisive role owing to their outstanding performances regarding gas selectivity and sensitivity. The tetrathiafulvalene (TTF)-infiltrated MOF, Co-MOF-74, has been prepared following the host–guest concept and evaluated in resistive gas sensing. The Co-MOF-74-TTF crystal morphology has been characterized via X-ray diffraction and scanning electron microscopy, while the successful incorporation of TTF into the MOF has been validated via X-ray photoemission spectroscopy, thermogravimetric analysis, UV/vis, infrared (IR), and Raman investigations. We demonstrate a reduced yet ample uptake of CO2 in the pores of the new material by IR imaging and adsorption isotherms. The nanocomposite Co-MOF-74-TTF exhibits an increased electrical conductivity in comparison to Co-MOF-74 which can be influenced by gas adsorption from a surrounding atmosphere. This effect could be used for gas sensing.

Highlights

Metal−organic frameworks (MOFs) are a class of crystalline and porous organic−inorganic hybrid materials.[1,2] A MOF consists of metal ions or metal-oxide clusters as inorganic building units which are connected by organic ligands acting as linkers
The major bottle neck for the construction of MOF-based resistive gas sensors is the development of electrically conductive or semiconductive MOFs.[17−22] In 2014, Allendorf and co-workers published an electrically conductive MOF based on HKUST-1 doped with the organic semiconductor 7,7,8,8-tetracyanoquinodimethane (TCNQ).[23−25] This was the first conductive MOF following the Guest@MOF concept which is based on the idea that the combination of MOFs and guest molecules can promote new materials with new properties.[25,26]
We showed that Co-MOF-74, with its hexagonal honeycomb-like lattice and open metal sites, is a potential material for gas sensing.[32]

Summary

■ INTRODUCTION

Metal−organic frameworks (MOFs) are a class of crystalline and porous organic−inorganic hybrid materials.[1,2] A MOF consists of metal ions or metal-oxide clusters as inorganic building units which are connected by organic ligands acting as linkers. Co-MOF-74, known as CPO-27-Co or Co2(dobdc), contains CoII as metal ions connected through 2,5-dioxido-1,4benzenedicarboxylate as organic ligands. Following the Guest@ MOF concept, we infiltrated Co-MOF-74 powder with the organic semiconductor tetrathiafulvalene (TTF).[33] Subsequently, resistive gas sensing experiments with pressed tablets were performed. The MOF powders were infiltrated with the organic semiconductors TCNQ or TTF via the gas phase by storing them in a previously evacuated flask over the respective organic semiconductor molecules at 70 °C overnight, followed by a stepwise increase of the temperature up to 170 °C within 4 h. The resulting solid composites were washed with MeOH, dried under reduced pressure, and activated before gas sensing under vacuum at 160 °C over 4 h. Conductivity measurements were performed in a three-necked glass flask with a home-built electrode setup under atmospheric pressure of the respective gases. The glass flask was evacuated for 30 min

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES