Materials with function of producing negative ions effection,containing valency-variable rare earth elements and semiconductor oxide,were fabricated.Free radicals produced by the materials were tested.The result shows that the materials can produce quite a few free radicals as·O-2 no matter whether they are under illumination of ultraviolet radiation or under visible light radiation,or under no light radiation, demonstrating semiconductor oxide can be catalysed under the visible light radiation.At the same time the result shows there is direct relation between the number of free radicals and of the negative ion produced by the materials,which meant that during photo-catalyzed and redox process of valency-variable rare earth elements free radicals translate into negative ions. A circular model is presented involving circulating change of valency-variable rare earth elements and water and oxygen absorbed on the surface of materials under the condition of photocatalysis.
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