Ultrasonic-Assisted Adsorptive Uptake of Malachite Green Dye Onto Zn/Cu-Layered Double Oxide: Spectrophotometric and Smartphone-Based Detection

Abstract

In this work, efforts have been made to synthesize novel Zn/Cu-layered double oxide by performing calcination of Zn/Cu-layered double hydroxide, which was later used as an adsorbent for the uptake of toxic azo dye. Malachite green (MG) was used as a model cationic dye for assessing the practicability of dye wastewater treatment. From batch experiments study, it was evident that ultrasonication-assisted adsorption enables 90% of the MG to be removed from water within 30 min at neutral pH conditions. The ultrasound-assisted sorption process was driven by the acoustic cavitation process, which facilitated a homogeneous distribution of active adsorption sites on surface of the adsorbent resulting efficient removal of dye molecules. As predicted by the Langmuir isotherm model, the sorbent exhibited maximum adsorption capacity of 128.20 mg/g, and based on kinetic measurements, the pseudo-second-order adsorption model was found to be most accurate. The kinetic studies also revealed that intraparticle diffusion is the rate-limiting step of the adsorption process. The current study also demonstrates smartphone-assisted estimation of adsorbed MG dye in order to provide a simple, convenient, cost-effective, and instrument-free method to quantify dye concentration. A smartphone-based app called “ColorPicker” was used to calculate MG dye adsorption rate in real time based on RGB values and colorimetric responses. The percent removal obtained using smartphone app (87%) was in agreement with the data obtained using UV–vis spectroscopy (90%). As a result of its excellent properties, Zn/Cu-LDO appears to be a potential candidate for wastewater remediation.