EFFECT OF COPPER PRECURSOR ON THE STABILIZATION OF TITANIA PHASES, AND THE OPTICAL-PROPERTIES OF CU TIO2 PREPARED WITH THE SOL-GEL TECHNIQUE/

In the sol-gel Cu/TiO2 system, nanocrystalline brookite, which was sta ble even after annealing the sample at 400 degrees C, was generated in high concentrations. This was achieved with copper chloride as copper precursor. The respective samples had a light absorption band at 562 nm that corresponded to an energy bandgap of 2.30 eV, which is smaller than the values reported for titania. When copper sulfate was the pre cursor, brookite was absent, but nanocrystalline anatase, the main pha se, was stabilized even at 800 degrees C by sulfate ions. After anneal ing the samples at low temperatures, copper was well dispersed for 1 w t % copper, but part of it segregated forming copper compounds when th e copper concentration was 10 wt %. By annealing the samples at 800 de grees C, copper oxidized to CuO; except in the 10 wt %-copper sample p repared with copper sulfate, where it formed antlerite.