3.1.4. Preparation of Mixed Oxides by Coprecipitation Using Synthesized Binary Oxides

General Procedure: Cu2O was deposited on the nanoparticles of the second oxide with formation of core-shell In2O3 or Fe2O3 particles covered with Cu2O. We have attempted to produce Cu2O core shell covered with In2O3 or Fe2O3 but so far substantial oxidation of Cu(I) to Cu(II) was observed during the dehydration of In- or-Fe-hydroxides. In 20 mL of a 0.5 M CuSO4 aqueous solution, weighted (see below) amounts of the nano-sized powder for the *n-type* partner oxide were dispersed. 40 mL of a 0.5 M NaOH aqueous solution were dropwise added to such solution under stirring. When the addition was completed, an adequate amount of a 0.1 M L-ascorbic acid aqueous solution was added dropwise as a reductant (glucose has also been used, but with lower yield) to produce Cu2O that deposited on the *n-type* semiconductor. Particles were separated by centrifugation (6000 rpm, 15 min), washed with deionized water, and dried at 80 ◦C overnight.

