In this article, Cr(OH) nanoparticle-modified cellulose nanocrystal (CNC) as a novel hybrid nanocomposite (Cr(OH)-NPs-CNC) was prepared by a simple procedure and used as a sorbent for adsorptive removal of methylene blue (MB) and malachite green (MG) from aqueous solution. Different kinetic models were tested, and the pseudo-second-order kinetic model was found more suitable for the MB and MG adsorption processes. The BET and Langmuir models were more suitable for the adsorption processes of MB and MG. Thermodynamic studies suggested that the adsorption of MB and MG onto Cr(OH)-NPs-CNC nanocomposite was a spontaneous and endothermic process. The maximum adsorption capacities for MB and MG were reached 106 and 104 mg/g, respectively, which were almost two times higher than unmodified CNC. The chemical stability and leaching tests of the Cr(OH)-NPs-CNC hybrid nanocomposite showed that only small amounts of chromium were leached into the solution.
A new method was developed for the efficient spectrophotometric determination of methylene blue (MB) dye in solutions. The method is based on a combined dispersive solid phase and cloud point extraction using Cu(OH) nanoflakes (as an adsorbent). Cu(OH) nanoflakes were synthesized by facile and fast methods and characterized using various techniques. The developed method is based on the adsorption of MB on the Cu(OH) nanoflakes and transfer into a surfactant-rich phase using Triton X-114 as a nonionic surfactant. Subsequently, MB dye is desorbed from Cu(OH) nanoflakes using a mixture of nitric acid and methanol solution and determined by UV-Vis spectrophotometry. The effects of pH, amount of Cu(OH) nanoflakes, volume (concentration of Triton X-114), and temperature were investigated by designing experiments using response surface methodology (RSM). A quadratic model was utilized to predict the variables. Analysis of variance (ANOVA) was applied for the analysis of variables and their interactions, and optimal conditions were established. The results demonstrated logical agreement between experimental and predicted values of the response owing to high F value, low P value, and low lack-of-fit. The calibration graph was linear in the range of 2.0-350.0 μg L of MB dye with a correlation coefficient (R) of 0.9996. The limits of detection and quantification were found to be 0.65 and 2.05 μg L, respectively. The developed method was successfully applied to different water samples, thereby confirming the applicability of the approach. Graphical Abstract Proposed procedure.
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