The solutions used throughout the experimental work were prepared by using water purified in a Milli-Q Water System
from Millipore (Milford, MA, USA).
Reagents with analytical grade or higher were used as received.
Standard solutions of Cu(II) were daily prepared by suitable dilution of 1000 mg ml−1 stock solution, which was prepared by dissolving 2.5434 g of CuSO4•8H2O in 1000 ml of 0.2 mol l−1 HNO3 solution.
This solution was titrimetrically standardized