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.

In view of environmental protection and the need for early prediction of major diseases, it is necessary to accurately monitor the change of trace ammonia concentration in air or in exhaled breath. However, the adoption of proton-conductive metal-organic frameworks (MOFs) as smart sensors in this field is limited by a lack of ultrasensitive gas-detecting performance at high relative humidity (RH). Here, the pellet fabrication of a water-stable proton-conductive MOF, Ba( o-CbPhHIDC)(HO)] (1) ( o-CbPhHIDC = 2-(2-carboxylphenyl)-1 H-imidazole-4,5-dicarboxylic acid) is reported. The MOF 1 displays enhanced sensitivity and selectivity to NH gas at high RHs (>85%) and 30 °C, and the sensing mechanism is suggested. The electrochemical impedance gas sensor fabricated by MOF 1 is a promising sensor for ammonia at mild temperature and high RHs.

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.

By reaction of a newly designed organic ligand, [3-(naphthalene-1-carbonyl)-thioureido] acetic acid (CHC(O)NHC(S)NHCHCOOH; HL), with Cu(OAc), a metal-organic framework [(CuCuL)·3HO] (1) containing unique mixed-valence [CuCuL] subunits has been successfully synthesized and structurally characterized. MOF 1 displays a three-dimensional open framework bearing one-dimensional channels. Consequently, a new derivative MOF [CuCuL] -NH (2) is procured upon exposure of 1 to NH vapors from 28 wt % aqueous NH solution, which bears 2 NH and 4 HO molecules in accordance with the elemental and thermal analyses. Both 1 and 2 exhibit relatively high water stability, whose proton conduction properties under water vapor have been researched. Notably, 2 shows an ultrahigh proton conductivity of 1.13 × 10 S cm, which is 2 orders of magnitude larger than that of MOF 1 (4.90 × 10 S cm) under 100 °C and 98% RH. On the basis of the structural data, E values, HO and ammonia vapor absorptions, and PXRD measurements, the proton transfer mechanisms were suggested. This is an efficient and convenient way to obtain suitable and highly proton-conducting materials by attaching NH molecules.

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