Impregnated Fibrous Chemisorbents for the Colorimetric Detection of Ammonia

Abstract

The paper presents research results on the colorimetric behavior of impregnated fibrous chemisorbents (IFCS) of basic gases with visual identification of the dynamic absorption capacity “response” moment (IFCS-I) during the absorption of ammonia. Chemisorbents were obtained by impregnation of fibrous carriers with polybasic hydroxyl acid aqueous solutions with adding acid-base indicators (Ind). IFCS-I based on oxyethylenediphosphonic (IFCS-OEDPA-I), citric (IFCS-CA-I), and malic (IFCS-MA-I) acids were used. Azolithine (Az), lakmoid (LA), methyl orange (MO), methyl red (MR), Tropeolin OOO (TrOOO), Congo red (CoR), bromocresol green (BCG), broxylenol blue (BXB), bromophenol blue (BPB), bromophenol red (BPR), thymol blue (TB), xylenol orange (XO), and phenol red (PR) were used as acid-base indicators. The specificity of the changes in the colorimetric functions of IFCS-I during the absorption of NH3 by them was revealed. It was found that the color of the initial IFCS-I samples significantly depended not only on the structure of Ind, but also on the nature of the polybasic hydroxy acid being part of them. The colors of the samples based only on OEDPA (Ind = CoR, BCG, BPB), CA (Ind = CoR, TrOOO, BCG, BPB, BPR, XO) and some MA (TrOOO, BCG) are similar to the colors of aqueous solutions of Brönsted acids. The difference in the colors of the other samples from the colors of strong acid aqueous solutions with the same Ind is apparently due to specific interactions between hydroxy acid anions and neutral dye forms. During “response” to NH3 only some IFCS-I samples based on OEDPA (Ind: MO, TrOOO, Az and BPR), CA (Ind: CoR, MR, MO, TrOOO, BXB, BPR, TB, PR) and MA (Ind: LA, MR, MO, Az, BXB, XO, TB, PR) are discolored in contrast to the behavior of SO2 indicator chemisorbents.