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Superb Dye Adsorption and Dye-Sensitized Change in Cu2O–Ag Crystal Faces in the Dark

Sasmal, Anup Kumar, Pal, Jaya, Sahoo, Ramkrishna, Kartikeya, Prashant, Dutta, Soumen, Pal, Tarasankar
The Journal of Physical Chemistry C 2016 v.120 no.38 pp. 21580-21588
Raman spectroscopy, adsorption, azo dyes, copper, crystallization, cuprous oxide, kinetics, methyl orange, nanoparticles, nanosheets, p-nitrophenol, photocatalysis, pollutants, porosity, remediation, silver nitrate, sodium, sorption isotherms, toxicity
Hybrid Cu₂O–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 Cu₂O–Ag. Cu₂O–Ag has been found to exhibit excellent anionic dye adsorption properties together with organic transformation for effective water remediation. Cu₂O–Ag was prepared through a facile but controlled galvanic reaction between cuprous oxide (Cu₂O) and silver nitrate (AgNO₃), rendering stability and porosity. The experimental results of adsorption showed that Cu₂O–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 Cu₂O–Ag happens because of the definite chemical interaction between Cu(I) and the SO₃– functionality of MO. A kinetic study revealed that the MO adsorption on Cu₂O–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 Cu₂O–Ag is the transformation of the 3-D morphology of Cu₂O–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 Cu₂O–Ag nanoparticles. This unique recrystallization of Cu₂O–Ag due to the chemisorption of MO is reported for the first time. Cu₂O–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, Cu₂O–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 Cu₂O–Ag in the presence of sodium borohydride (NaBH₄) exhibited a high rate constant value (k = 0.38 min–¹). Thus, two novel properties, adsorption and catalytic reduction on organic pollutants, of Cu₂O–Ag have been ascertained for water remediation.