Preparation of polyvinyl alcohol reinforced with microcrystalline cellulose to function as test strips immobilized with a hydrazone chromophore for colorimetric identification of toxic ammonia

Ammonia is a colorless gas that has been known as one of the most toxic gases. It may cause irritations to nose, eyes, as well as organ failure and even death. Hence, it is of high significance to assemble an onsite detection device for aqueous and gaseous ammonia. Herein, we develop a highly sensitive and inexpensive microporous composite test strip for ammonia. An easy-to-prepare colorimetric tricyanofuran-hydrazone (TCFH) dye was synthesized and encapsulated into microporous polyvinyl alcohol/microcrystalline cellulose (PVOH-MCC) composite. PVOH-MCC-TCFH demonstrated bathochromic shift of 126 nm with increasing the concentration of ammonia. The colorimetric changes of PVOH-MCC-TCFH after exposure to methanolic solution (pH ∼7.0) of ammonia were monitored. This color shifts can be attributed to delocalization of electrons in the tricyanofuran-hydrazone molecular structure. The hydrazone binding sites was found to selectively sense ammonia over a sequence of other aliphatic and aromatic amines. The color shifts of PVOH-MCC-TCFH depended on the total content of ammonia in aqueous solution. The determination limit of NH3(aq) was observed between 5 and 200 ppb. The morphology, thermal stability and fibrous crystallinity of the produced PVOH-MCC-TCFH sensor strips were explored by different spectral techniques. The microporous structure of PVOH-MCC immobilized with TCFH demonstrated highly porous scaffolds with pore diameters of 25–35 to 50–100 μm depending on the total content of TCFH. The mechanical performance of the prepared PVOH-MCC-TCFH sensor strips was also explored. •Portable and biodegradable microporous sensor for toxic ammonia was developed.•Hydrazone probe was physically embedded in-situ into PVOH-MCC composite.•Vapochromic test strip demonstrated real-time color change from pink to purple.•Limit of detection for aqueous ammonia was monitored in the range of 5–200 ppb.•High reversibility was observed without fatigue.