Novel halochromic hydrazonal chromophore immobilized into rice-straw based cellulose aerogel for vapochromic detection of ammonia

Cellulose aerogel has been characterized as a light weight biopolymer that could be applied for a range of prospective applications in various areas. A feature of an aerogel is a result of its porous structure. In the current study, a simple and reversible colorimetric detection tool was developed for ammonia by incorporating a novel halochromic hydrazonal (Ha) chromophoric compound into the matrix of carboxymethyl cellulose (CMC). The collected wastes of rice straw were employed to extract cellulose, which was then subjected to carboxymethylation. The hydrazonal spectroscopic probe guest was incorporated into a freeze-dried and crosslinked regenerated CMC aerogel host. The morphologies of the synthesized cellulose aerogel were explored utilizing Fourier-transform infrared (FT-IR) spectroscopy and scanning electron microscope (SEM) to display porous structures with an average pore diameter of 80–120 μm. The generated aerogel demonstrated significant sensitivity to gaseous ammonia. The vapochromic aerogel delivered an immediate color change from yellow to blue due to contacting with aqueous or gaseous ammonia as measured by the absorbance spectra, CIE Lab coordinates and colorimetric strength (K/S). The detection of NH3(g) took place through proton transfer from the hydrazonal NH to the nitrogen atom of ammonia to generate the corresponding hydrazone anion isomer. The visible colorimetric changes of the sensor aerogel was found to change from yellow to blue in proportionate with rising the concentration of NH3(aq). Furthermore, the aerogel sensor demonstrated a limit of detection (LOD) at 1–250 ppb for NH3(aq), and excellent reversibility. The cytotoxic properties of the prepared aerogel were also explored.