Multi-response optimization of ultrasound assisted competitive adsorption of dyes onto Cu (OH)2-nanoparticle loaded activated carbon: Central composite design

Abstract

This paper focuses on the development of an effective methodology to obtain the optimum removal conditions assisted by ultrasonics to maximize the simultaneous removal of dyes, eosin Y (EY), methylene blue (MB) and phenol red (PR), by Cu(OH)2-NP-AC in aqueous solution using response surface methodology (RSM). The effects of variables such as pH, initial dyes concentrations (mg L−1), and amount of sorbent (mg) and sonication time (min) on the dyes removal were studied. A central composite design (CCD) was applied to evaluate the interactive effects of adsorption variables. A good correlation (with R2 > 0.940) between the statistical model and experiment was found for dyes removal from aqueous wastewater using the adsorbent. The optimum removal (99.20% ± 1.48) was thus obtained at pH 6.0, ultrasound time 2.5 min, adsorbent mass 20 mg and initial dye concentration at 5 mg L−1 for MB and EY and 12.5 mg L−1 for PR. The maximum adsorption capacity (Qmax) was calculated from the Langmuir isotherm as 32.9, 26.4 and 38.5 mg g−1 for the MB, EY and PR, respectively for the 0.015 g of sorbent. The adsorption kinetic data of the dyes were analyzed and was found fitting well in a pseudo-second-order equation. Adsorption isotherms and separation factors showed that the adsorbent displays a high selectivity toward one dye in a three-component system with an affinity order of PR > MB > EY. On the other hand, acoustic waves emitted by the cavitation bubbles render a direct effect on the process. This is attributed to the discrete nature and high pressure amplitude of the waves, which creates excessively high convection in the medium, causing adsorption of the pollutants. The chemical nature of the pollutants influences the enhancement effect of ultrasound.