A Highly Proton-Conductive 3D Ionic Cadmium–Organic Framework for Ammonia and Amines Impedance Sensing

Abstract

Lately, the progressive study of metal−organic frameworks (MOFs) for the detection of ammonia and amines has made infusive achievements. Nevertheless, the investigation of proton-conductive MOFs used to detect the low concentrations of ammonia and amine gases at different relative humidities (RHs) at room temperature is relatively restricted. Herein, by solvothermal reaction of Cd(NO 3 ) 2 with 2-methyl-1H-imidazole-4,5-dicarboxylic acid (H 3 MIDC), a three-dimensional ionic MOF {Na[Cd(MIDC)]} n (1) bearing ordered one-dimensional channels was successfully synthesized. Our research indicates that the uncoordination carboxylate sites are beneficial to proton transfer and the recognition of ammonia and amine compounds. The optimized proton conductivity of 1 reaches a high value of 1.04 × 10 −3 S•cm −1 (100 °C, 98% RH). The room temperature sensing properties of ammonia and amine gases were explored under 68, 85, and 98% RHs, respectively. Satisfactorily, the detection limits of MOF 1 toward ammonia, methylamine, dimethylamine, trimethylamine, and ethylamine are 0.05, 0.1, 0.5, 1, and 4 ppm, respectively, which is one of the best room-temperature sensors for ammonia among previous sensors based on protonconductive MOFs. The proton conducting and sensing mechanisms were highlighted as well.

Two Highly Stable Proton Conductive Cobalt(II)–Organic Frameworks as Impedance Sensors for Formic Acid

“…At 25 8C, the data from the Nyquist plots reveal that the low protonc onductivity of 1 (2) ranges from 1.19 10 À7 (2.13 10 À8 )t o4 . 47 1 (2), the protonc onductivity increased from 6.54 10 À5 (5.18 10 À5 )Scm at 68 %R Ht o1 .31 10 À4 (1.16 10 À4 )Scm at 85 % RH, then reached the highest proton conductivity of 1.04 10 À3 (7.02 10 À4 )Scm at 98 %RH (Figures 3c and S20, Table S7 in the Supporting Information). As denoted in Table S8 (in the Supporting Information), these conductivity values of 1 and 2 can be compared with that of several renowned MOFs under similar testing conditions, [12,13,[38][39][40] such as {[Co 3 (m-ClPhID-C) 2 (H 2 O) 6 ]·2H 2 O} n (m-ClPhH 3 IDC = 2-(m-chlorophenyl)imidazole-4,5-dicarboxylic acid; s = 7.62 10 À4 Scma t1 00 8C), [13] Mg-BPTC (BPTC = 2,2',6,6'-tetracarboxybiphenyl; s = 2.6 10 À4 Scm at 100 8Ca nd 98 %R H), [12]…”

Proton‐Conductive 3D LnIII Metal–Organic Frameworks for Formic Acid Impedance Sensing

“…It is speculated that the rich hydrogen bonding interaction between the imidazole Na toms,w ater molecules and formic acid molecule plays ac rucial role in selectivity.H ydrogen bonds are ubiquitous in various chemicals and biological systems, [56][57][58][59] where ploargroups, [60,61] such as -CO-NH 2 and -COOH groups, can be very close to each other and undergo exceptionally strong electrostatic interactions. [10,20,33,35] A large number of literatures have found that the employment of hydrogen bond interaction to perform chemical selectivity in the field of molecular identification and sensingh as been extensively researched. Based on the investigation of proton conductivity of impedances ensing for ammonia and amine, it is found that the structurec haracteristics of MOF and detection gas have a great influenceo nt he recognition performance.…”

“…[5,16,[25][26][27][28] On the other hand, based on the outstanding advantagesofMOFs, the exploration of the practical application of electrically conductive MOFs has received extensive attention, especially in the field of chemoresistive sensors. [29][30][31][32][33][34] Representatively,D incǎ et al demonstrated an array of cross-reactive sensor for the identification of different typeso fv olatile organic compounds (VOCs). [34] Nevertheless, the studies on proton conductingM OFs as sensors are very limited.…”

“…[34] Nevertheless, the studies on proton conductingM OFs as sensors are very limited. [10,20,33,35] Formic acid (HCOOH) as one of the most significant VOCs has aw ide range of practical applications,such as preservative, antibacterial agent,a nd as ap recursor for the synthesis of quite af ew compounds. [36] Formica cidh as strong irritation and causticity,a nd excessive exposure and accumulationc an lead to chemical pneumonitis, nerve injury and dermatosis.…”

“…[36,37] Although people have carried out many methods to detectf ormic acid, such as, mass spectrometry or liquid and gas chromatography, [37][38][39][40][41] limitede xamples of selectives ensors for the formic acidv apor can be found in literature. [33] Considering the harmfulness of formic acid vapor,w ea re committed to finding as ensorw ith universal applicability under mild conditions. It is advantageous to measure the concentration of HCOOHi na queous solutioni ndirectly by detecting the concentration of formic acid vapor.T herefore, the potential applicationso fp roton conductingM OFs in this field have attracted our attention.…”