Heterobimetallic Ru(II)/M (M = Ag(+), Cu(2+), Pb(2+)) Complexes as Photosensitizers for Room-Temperature Gas Sensing

This work is devoted to the investigation of heterobimetallic Ru(II) complexes as photosensitizers for room-temperature photoactivated In(2)O(3)-based gas sensors. Nanocrystalline In(2)O(3) was synthesized by the chemical precipitation method. The obtained In(2)O(3) matrix has a single-phase bixbyite structure with an average grain size of 13–14 nm and a specific surface area of 72 ± 3 m(2)/g. The synthesis of new ditope ligands with different coordination centers, their ruthenium complexes, and the preparation of heterobimetallic complexes with various cations of heavy and transition metals (Ag(+), Pb(2+), or Cu(2+)) is reported. The heterobimetallic Ru(II) complexes were deposited onto the surface of the In(2)O(3) matrix by impregnation. The obtained hybrid materials were characterized by X-ray fluorescent analysis, FTIR spectroscopy, and optical absorption spectroscopy. The elemental distribution on the hybrids was characterized by energy-dispersive X-ray spectroscopy (EDS) mapping. The gas sensor properties were investigated toward NO(2), NO, and NH(3) at room temperature under periodic blue LED irradiation. It was identified that the nature of the second binding cation in Ru(II) heterobimetallic complexes can influence the selectivity toward different gases. Thus, the maximum sensor signal for oxidizing gases (NO(2), NO) was obtained for hybrids containing Ag(+) or Pb(2+) cations while the presence of Cu(2+) cation results in the highest and reversible sensor response toward ammonia. This may be due to the specific adsorption of NH(3) molecules on Cu(2+) cations. On the other hand, Cu(2+) ions are proposed to be active sites for the reduction of nitrogen oxides to N(2). This fact leads to a significant decrease in the sensor response toward NO(2) and NO gases.