Preparations of nano/micro structured polyaniline membranes for pH sensing

Effect of acidity on the growth of polyaniline nanostructures was investigated in various acidic media, such as 0.1 mol/L H₂SO₄, phosphate buffer solutions (PBS) at pH=4 and pH=7, and 0.1 mol/L ammonium hydroxide. PANI nanostructures, such as nanocactus, micromats, microflakes, microroses and interconnected three-dimensional networks, microdendrimers, microbranches, etc., were synthesized using ammonium persulfate as oxidant under frozen condition in solution and on dipped substrates, respectively. A possible mechanism for forming those PANI nanostructures, ascribed to pH effect and the crystalline aniso-tropy of ice to direct growth, was proposed. In addition, induction of dipped substrates and diffusion-limited growth play key roles in forming dendritic morphology on them. Moreover, pH responses of those four nanostructured PANI membranes in-situ deposited on glass substrates were further examined in the range of pH=3-9, which resulted in a high sensitivity.