Optical Ammonia Sensors Based on Spray-Coated Polyaniline Complexes with Polysulfonic Acids

Area of Science:

• Materials Science
• Chemical Sensing
• Polymer Chemistry

Background:

• Polyaniline (PANI) is a conductive polymer with potential for chemical sensing.
• Polysulfonic acids influence PANI's properties, affecting its use in sensor applications.
• Optimizing PANI-based sensors for ammonia detection requires understanding material structure and processing.

Purpose of the Study:

• To compare the optical ammonia-sensing properties of water-dispersible PANI complexes synthesized with various polysulfonic acids.
• To investigate the effect of different polysulfonic acid structures (flexible, semi-rigid, rigid) on PANI sensor performance.
• To evaluate post-synthesis treatments for improving sensor response, stability, and accuracy.

Main Methods:

• Synthesis of PANI complexes with flexible (PSSA, PAAc) and rigid (t-PASA) polysulfonic acids.
• Fabrication of sensor films using spray coating of aqueous PANI complex solutions.
• Optical characterization of sensor response (time, amplitude) to varying ammonia concentrations (5-200 ppm).
• Post-treatment of sensor films with NaCl, CaCl2, and BaCl2 solutions to mitigate humidity and proton interference.

Main Results:

• Treatment with 1 M CaCl2 significantly enhanced response time, amplitude, and reproducibility for all PANI complexes.
• PANI complexes with flexible polyacids showed higher response amplitude at low ammonia concentrations (5-25 ppm).
• PANI-t-PASA films exhibited superior sensing properties at higher ammonia concentrations (>50 ppm).
• FTIR analysis indicated CaCl2 treatment induces cross-linking via Ca2+ ions, reducing swelling and neutralizing excess protons.

Conclusions:

• Post-synthesis CaCl2 treatment is crucial for optimizing PANI-based optical ammonia sensors.
• The choice of polysulfonic acid structure dictates the optimal operating range for PANI ammonia sensors.
• CaCl2 treatment improves sensor performance by stabilizing the PANI complex structure and reducing environmental interference.