Competitive coadsorption of ammonia with water and sulfur dioxide on metal-organic frameworks at low pressure

Abstract

Purification of ammonia in semiconductor cleanrooms is crucial to improve semiconductor yields and ensure standardized production. In this study, adsorption isotherms for ammonia on HKUST-1, UIO-66, and MIL-100(Fe) were acquired. Density functional theory (DFT) calculations for ammonia illustrated the adsorption mechanism at low pressure. Adsorption isotherms and DFT calculations for water and sulfur dioxide (SO2) were used to investigate the effect of water and SO2 on ammonia adsorption.The ammonia adsorption capacity of HKUST-1 exceeded that of UIO-66 from 1.0 × 10−6 to 1.0 × 10−5 P/P0. The UIO-66 ammonia adsorption capacity was superior to that of MIL-100(Fe) at low pressure. The water adsorption capacity at 45% relative humidity followed an order of MIL-100(Fe) (24.040 mmol/g) > UIO-66 (16.300 mmol/g) > HKUST-1 (14.200 mmol/g). The SO2 adsorption capacity of MIL-100(Fe) exceeded that of HKUST-1 at low pressure.The order of interaction energies was HKUST-1 (−147.890 kJ/mol) > MIL-100(Fe) (−80.280 kJ/mol) > UIO-66 (−47.080 kJ/mol) for ammonia, ammonia (−147.890 kJ/mol) > SO2(O) (−78.890 kJ/mol) > SO2(S) (−74.790 kJ/mol) > water (−64.070 kJ/mol) on HKUST-1, ammonia (−80.280 kJ/mol) > SO2(O) (−64.910 kJ/mol) > water (−46.940 kJ/mol) > SO2(S) (−40.920 kJ/mol) on MIL-100(Fe), and SO2(O) (−71.670 kJ/mol) > SO2(S) (−65.720 kJ/mol) > ammonia (−47.080 kJ/mol) > water (−30.000 kJ/mol) on UIO-66. Ammonia is likely to displace preadsorbed SO2 and water due to ammonia's higher affinity for HKUST-1. Preadsorbed ammonia could be more difficult to displace with SO2 or water on MIL-100(Fe) and with water on UIO-66.