Cary 100 scan uv vis spectrophotometer

Ultraviolet/visible (UV/vis) absorption
spectra were recorded for wavelengths of 200 to 800 nm using a Cary
100 Scan UV/vis spectrophotometer (Agilent, US). One ml of sample
solution was filled into a semimicro UV cuvette and spectra were taken
directly after sample preparation as well as after 1, 2, and 7 days
of aging. The latter helped to access the colloidal stability of the
samples. More information is given in the Supporting Information. The method of continuous variations, also known
as Job’s plot (details in the Supporting Information), was applied in order to resolve the stoichiometry
of ion pair formation between SSY and C₁₆TAB. Job’s
plots have been used in previous work for the investigation of dye-surfactant
binding interactions.^{6 (link),38 (link)−41 (link)} For a description of the working
principle and experimental results from the application of the Jobs
method the reader is referred to the Supporting Information.

The equilibrium MB uptake capacity
of GO and GO-LCTS composites was
evaluated by batch mode using fixed amounts of adsorbent in sealed
glass vials. The adsorption isotherms obtained by such batch mode
conditions used a dosage of 5 mg adsorbent with 7 mL MB solution (pH
= 7) at variable initial MB (100–1000 μM). Samples were
mixed on a horizontal shaker (SCILOGEX SK-O330-Pro) for 24 h to ensure
equilibrium. A 1 mM stock solution of MB in water was prepared, and
other solutions were obtained by appropriate dilution. Absorption
measurements were carried out at λ = 664 nm, and a linear calibration
curve for MB absorbance at variable concentration was obtained with
a slope of 0.0615 = Abs_664nm/[MB]. After 24 h shaking to
achieve equilibrium, the sample powders were separated from the solution
by centrifugation and the residual (MB) was measured using UV–vis
spectroscopy (Varian Cary 100 Scan UV–vis spectrophotometer).
The equilibrium uptake of MB was calculated using eq 2. where Q_e (mg g^–1) is the MB adsorbed per unit mass of adsorbent, C₀ (mM) is the initial dye concentration, C_e (mM) is the residual amount of MB, V (L) is the volume of the MB solution, and m (g) is the weight of the adsorbent.
The GO composite was tested
for its regeneration properties over several adsorption–desorption
cycles with MB, as described in further detail in the Supporting Information.