A Highly Stable Two‐Dimensional Copper(II) Organic Framework for Proton Conduction and Ammonia Impedance Sensing

Abstract

This work reports the design and fabrication of a proton conductive 2D metal-organic framework (MOF), [Cu(p-IPhHIDC)] (1) (p-IPhH IDC=2-(p-N-imidazol-1-yl)-phenyl-1 H-imidazole-4,5-dicarboxylic acid) as an advanced ammonia impedance sensor at room temperature and 68-98 % relative humidity (RH). MOF 1 shows the optimized proton conductivity value of 1.51×10 S cm at 100 °C and 98 % RH. Its temperature-dependent and humidity-dependent proton conduction properties have been explored. The large amount of uncoordinated carboxylate groups between the layers plays a vital role in the resultant conductivity. Distinctly, the fabricated MOF-based sensor displays the required stability toward NH , enhanced sensitivity, and notable selectivity for NH gas. At room temperature and 68 % RH, it gives a remarkable gas response of 8620 % to 130 ppm NH gas and lower detection limit of 2 ppm towards NH gas. It is also found that the gas response of the ammonia sensor increases linearly with the increase of NH gas concentration under 68-98 % RH and room temperature. Moreover, the sensor indicates excellent reversibility and selectivity toward NH versus N , H , O , CO, CO , benzene, and MeOH. Based on structural analyses, activation energy calculations, water and NH vapor absorptions, and PXRD determinations, proton conduction and NH sensing mechanisms are suggested.

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

“…Under 98 %R H, the conductivityi ncreases from 3.06 10 À6 Scm -1 (25 8C) to 5.26 10 À5 Scm -1 (70 8C) and finally obtains the best value of 8.95 10 À4 Scm -1 (100 8C) (Figure 4b). [12,20,28,53] Obviously,t he conductivity increased significantly with the increaseo ft emperature, and the conditions also occurred at 75 %, 85 %a nd 93 %R Hs (FiguresS8-10). The optimum conductivity (8.95 10 À4 Scm -1 )o fZZU-1 is distinctly higher than that of conventional MOFs, [9,18,52] but slightly lower than that of other conductive materials.…”

“…[10,20] The responses of both materials wered efined following the ratio = R 0 /R a ,w here R 0 and R a are the resistanceo fs ensors after detecting pure Chem. [10,20] The responses of both materials wered efined following the ratio = R 0 /R a ,w here R 0 and R a are the resistanceo fs ensors after detecting pure Chem.…”

“…[9][10][11][12][13] Kanda et al first reported ap rotonc onductive MOFs in 1979, [14] and since then, these materials have becomeanew field of research, making significant progress. [15][16][17][18][19][20][21][22][23][24] Unlike semicrystalline or amorphousp olymers, the high crystallinity of MOFs is very suitable for studying protont ransport pathway and the conductionm echanism, demonstrating that protonc an transit through modified groups on the surfaceo ft he cavity (e.g., H 2 O, -SO 3 Ha nd -PO 3 H 2 )a nd guests in the cavity (e.g.,i midazole, histamine and ionic liquids). [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.…”

“…[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.…”

“…Sensitive and selective detection of formic acid has great practical value, such as monitoring air quality,e nabling automatic pest control, and diagnosing health status, etc. [10,20] Also, the sensing properties towards ammonia and amine gases of an ovel 3D ionic Cd II MOF were investigated by proton conduction methoda tr oom temperature. [42][43][44] It is very important to detect the concentration of HCOOH in aqueous solution,b ut in direct detection process, the formic acid solution is highly corrosive, which limits the application of the detection method.…”