It should be emphasized that the pH range that produces pure
copper against copper oxide varies in the presence of various surface
capping agents. For example, the optimum pH has been obtained
~10.3[28], in which only polyacrylic acid was used as capping agent
of copper nanoparticles. The obtained optimum pH value in the present
study (pH ~ 11)was slightly higher. This difference can be attributed to
the presence of cross linking agent and the formation of the copper
nanoparticles into the hydrogel network in the present study. The red
color of the hydrogel–copper nanocomposite scarcely changed even
after three months, indicating extra protection of the copper nanoparticles into the hydrogel network against oxidation