Layer‐by‐Layer Assembled Conductive Metal–Organic Framework Nanofilms for Room‐Temperature Chemiresistive Sensing

Abstract

The utility of electronically conductive metalorganic frameworks (EC-MOFs) in high-performance devices has been limited to date by alackofhigh-quality thin film. The controllable thin-film fabrication of an EC-MOF,C u 3 -(HHTP) 2 ,( HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), by as prayl ayer-by-layer liquid-phase epitaxial method is reported. The Cu 3 (HHTP) 2 thin film can not only be precisely prepared with thickness increment of about 2nmper growing cycle,but also shows asmooth surface,good crystallinity,and high orientation. The chemiresistor gas sensor based on this high-quality thin film is one of the best room-temperature sensors for NH 3 among all reported sensors based on various materials.

Near‐Room‐Temperature Ethanol Gas Sensor Based on Mesoporous Ag/Zn–LaFeO3 Nanocomposite

“…Figure a,b shows good linearity relationship in the plot between the sensing response and ethanol concentrations in the range of 5–10 and 10–100 ppm, respectively, which is in accordance with typical chemiresistor gas sensor and suitable for detection of ethanol in practical applications . Meanwhile, the responses of other three senors decline into negligible values.…”

Origin of the Chemiresistive Response of Ultrathin Films of Conductive Metal–Organic Frameworks

“…In summary,o ur results indicate that the origin of the chemiresistive response of this family of conductive MOFs is linked to the direct interaction of gas molecules with the Cu II sites.This results in slight distortions of the internal structure of the layer or more acute changes in the coordination geometry of the metal node for concomitant modifications of the band gap of the solid. Our findings are also consistent with previous reports [27][28][29] that suggest ap ossible relationship between the nature of the metal nodes and the coordination ability of the analytes with the intensity and selectivity of the turn-on response.W eare confident this information will be of use to help guiding the design of advanced sensory platforms based on the rational optimization of the chemical functionality and electronic structure of MOFs.…”

“…[6,7,15,[24][25][26] Thelarge bulk conductivity and processability of this family of 2D MOFs has enabled the development of solid-supported devices based on micro and nanometric thick films of M 3 (HITP) 2 and M 3 -(HHTP) 2 (M = Fe,C o, Ni, or Cu, HITP = 2,3,6,7,10,11hexaiminotriphenylene) for selective and fast chemiresistive sensing of ammonia (NH 3 )a nd volatile organic compounds. [27][28][29] Thec oordination of the metal center in the network is for most cases square planar, but also octahedral for HHTP (2,3,6,7,10,11-hexahydroxytriphenylene) and M = Co or Ni, [15] which have two axial water molecules.T hese early works confirm ad irect dependence of the electrical response with host-guest interactions that can be also modified for different metal nodes.H owever,f urther information that would help to unveil the exact mechanism controlling this phenomenon is still missing.We recently reported ab ottom-up approach to fabricate very thin (10 nm), highly oriented, semiconductive Cu 3 -(HHTP) 2 films (Cu-CAT-1; Figure 1). [23] Thes equential transfer of Cu-CAT-1l ayers pre-assembled in aL angmuir-Blodgett (LB) trough over as ubstrate modified with as elfassembled monolayer (SAM) allowed to integrate Cu-CAT-1f ilms into FET-type devices with high consistencya nd comparability.…”

Bottom‐Up Fabrication of 1D Cu‐based Conductive Metal–Organic Framework Nanowires as a High‐Rate Anode towards Efficient Lithium Storage

“…[6] Meanwhile, conductive MOFs,r elying on post-synthetic introductiono fe xternal guest molecules, which promote the through-bond charge transport between neighboring molecular building blocks, exhibit improved electric conductivitya nd retain the inherenta dvantages of conventional MOFs, including abundant active sites and open diffusion channels. [10] Generally,t he conductive mechanism of conductive MOFs are similar to those of organic and inorganic semiconductors, including hopping, through-space, through-bond, and band transport. [8] Strikingly,t he Ni 3 (HITP) 2 exhibits ah igh bulk electricalc onductivity,e ven greater than holey graphite.…”

“…ers to form the p-stacked and p-conjugated network, resulting in highly enhanced electrical conductivity. [10] Generally,t he conductive mechanism of conductive MOFs are similar to those of organic and inorganic semiconductors, including hopping, through-space, through-bond, and band transport. [1] As for the M-CAT, both the metallic nodes and organic linkersa re the sources of charge carriers, but it mainly relies on the electron-donating or electron-withdrawing nature of additional substituents, which can be employed to modulate the density and distribution of charges within the organic ligands.…”