Modification of MCM-41 based core-Shell for construction of a colorimetric gas sensor

A sol-gel method was employed to synthesize uniform micro-sized spheres of silica coated with MCM-41 or Ti-MCM-41 mesoporous shells. Some sensitive dyes including alizarin, phenolphthalein and malachite green were loaded into these core-shells to achieve a solid-state colorimetric gas sensor for ammonia sensing via tracking the emerged signals (change of color) by either naked eye or digital camera. Several analytical standard techniques were applied for characterization of the structure and texture of the prepared ammonia sensor. An instantaneous response was observed using alizarin-loaded core-shell for a low concentration of ammonia gas. The other two dyes were only responsive upon exposure to high concentrations of the gas. Using a six-element sensor array and applying a color analysis technique, a large range of ammonia gas concentrations from 10 to 1000 ppm were sensed and recorded. Although a digital approach was used to quantize the extent of responses to ammonia, but all changes were also detectable with naked eye even for low concentration of ammonia. A detection limit of 0.6 ppm was calculated for the produced sensor array.