Scratch test for immobilization of photocatalytic ZnO nanopowders synthesized by solution combustion method Original Research Article

Four kinds of organic binders and three kinds of inorganic binders were prepared. All of the binding materials are commercially available except zinc phosphate. The zinc phosphate was synthesized by the reaction of ZnO powders and phosphoric acid. All of these binders were used to immobilize the solution combustion method (SCM) ZnO powders on the glass substrates. Scratch test result showed that the zinc phosphate has the best overall adhesion properties such as high cohesive force with the ZnO powders and high adhesive force with the glass substrate. Furthermore, it showed the highest photocatalytic efficiency among organic and inorganic binders. Its photocatalytic efficiency reached to about 80% of the powder-type photocatalytic reaction. In general, organic binders have good adhesion properties but they could be decomposed by photocatalytic reaction. Inorganic binders, however, have poor adhesion properties but they are not decomposed by photocatalytic reaction. Contrary to general aspect, the zinc phosphate inorganic binder synthesized in this work showed good adhesion properties, high photocatalytic efficiency and good mechanical stability. This surprising result might be due to the chemical reaction between ZnO powders and the zinc phosphate binder.