Preparation and characterization of a novel modified system: polyaniline/1,5-naphthalene disulfonic acid as a novel photocatalyst for H2 production

The semiconducting properties of the system Polyaniline (PANI)/1,5-naphthalene disulfonic acid (NDSA) were investigated to assess its photocatalytic performance for the hydrogen evolution under visible light irradiation. PANI/NDSA is thermally stable up to ~ 300 °C, above which a weight loss of ~ 1.2% occurs. The X-ray diffraction pattern showed broad peaks with a particle size of ~ 7 nm. A direct optical transition at 1.96 eV, was determined from the diffuse reflectance spectrum. The electrical conductivity of PANI/NDSA follow an exponential law with an activation energy of 0.24 eV. The p -type conduction was demonstrated from the (capacitance −2 —potential) characteristic; a flat band potential (E fb ) of 0.82 V SCE and a holes density (N A ) of 8.43× 10 24 m −3 were determined in neutral solution (Na 2 SO 4 0.1 M). The electrochemical impedance spectroscopy, measured over an extended frequency domain (1 mHz—10 10 Hz), indicated the contribution of both the bulk and grain boundaries with a constant phase element (CPE). As application, PANI/NDSA was successfully tested for the hydrogen production under visible light owing to the potential of its conduction band (− 0.75 V SCE ), more cathodic than that of H 2 O/H 2 (~− 0.30 V SCE ). The H 2 liberation rate of 3840 µmol h −1 (g catalyst) −1 and a quantum efficiency of 0.34% were obtained under full light (29 mW cm −2 ) using Fe(CN) 6 4− as reducing agent. The photoactivity was completely restored during the second cycle.