Superb Dye Adsorption and Dye-Sensitized Change in Cu 2 O–Ag Crystal Faces in the Dark

Hybrid Cu 2 O–Ag is attractive because of its many applications in the fields of photocatalysis, surface-enhanced Raman scattering (SERS), and optical features. In this article, we have presented a newer application of Cu 2 O–Ag. Cu 2 O–Ag has been found to exhibit excellent anionic dye adsorption properties together with organic transformation for effective water remediation. Cu 2 O–Ag was prepared through a facile but controlled galvanic reaction between cuprous oxide (Cu 2 O) and silver nitrate (AgNO 3 ), rendering stability and porosity. The experimental results of adsorption showed that Cu 2 O–Ag bears an exceptionally high adsorption capacity toward methyl orange (501.23 mg g –1 ), which is higher than most reported results. The adsorption of MO on Cu 2 O–Ag happens because of the definite chemical interaction between Cu(I) and the SO 3 – functionality of MO. A kinetic study revealed that the MO adsorption on Cu 2 O–Ag primarily followed the pseudo-second-order kinetic model. The kinetic model followed the Langmuir adsorption isotherm. A very significant feature that emerged during MO adsorption by Cu 2 O–Ag is the transformation of the 3-D morphology of Cu 2 O–Ag into 2-D nanosheets under ambient and dark conditions. This morphology change corroborates that the adsorption occurred through chemical interaction, i.e., the chemisorption process. This feature, a morphology change in the dark, presumably happened through the participation of the highly interactive exposed high-index facet of spherical Cu 2 O–Ag nanoparticles. This unique recrystallization of Cu 2 O–Ag due to the chemisorption of MO is reported for the first time. Cu 2 O–Ag was also found to have a high adsorption capacity (976.30 mg g –1 ) even for Congo red (an anionic azo dye), which is also higher than the reported adsorption capacities of various materials. In another water remediation aspect, Cu 2 O–Ag has also been applied to the transformation of organic toxic pollutant, 4-nitrophenol (4-NP), into its nontoxic and medicinally important amino derivative through catalytic reduction. The catalysis of 4-NP reduction by Cu 2 O–Ag in the presence of sodium borohydride (NaBH 4 ) exhibited a high rate constant value ( k = 0.38 min –1 ). Thus, two novel properties, adsorption and catalytic reduction on organic pollutants, of Cu 2 O–Ag have been ascertained for water remediation.