Ir spectroscopy grade

The crushed hydrogel samples were mixed with potassium bromide (Merck IR spectroscopy grade) in 1:100 proportions and dried at 45 °C. The mixtures were compressed to a 12 mm semitransparent disk by a pressure of 65 kN (Pressure gauge, Shimadzu) for 1 min. The FTIR spectra were recorded over the wavelength range 4,000–400 cm⁻¹ using FTIR spectrometer (FTIR 8400 S, Shimadzu).

Fourier transform infrared spectroscopy (FTIR) of unloaded and loaded hydrogel samples was recorded in transmission mode by using a Bomem MB 100 FTIR spectrophotometer, as KBr pellets. Before recordings, xerogels were crumbled into powder and mixed with potassium bromide (Merck IR spectroscopy grade) in the proportion of 1:100 and then compressed into a 12 mm semi-transparent disk under pressure (Pressure gage, Shimadzu). The morphology of the hydrogel samples before and after nickel adsorption was observed on a scanning electron microscope (SEM) instrument, JEOL JSM-5800. The surface topography changes before and after adsorption were observed and recorded by atomic force microscopy (AFM) in the contact mode bt using Auto Probe CP Research (TM Microscopes—Veeco Instruments, Santa Barbara, CA, USA). For an estimation of the roughness of the samples by the determination of the arithmetic average of the absolute (Ra) roughness parameters, the software SPMLab (SPMLab NT Ver. 6.0.2., Veeco Instruments, Santa Barbara, CA, USA) was used.
The ICP-OES Thermo iCAP 6500 system, equipped with the Thermo iTEVA software, a concentric nebulizer and a Cyclonic Spray Chamber, was used for the determination of the concentration of Ni²⁺ ions in the solution.