Malachite nanoparticle: A potent surface for the adsorption of xanthene dyes

•Malachite nanoparticles have been used for the first time for the effective adsorption of dyes.•Three xanthene dyes (Fluorescein, Rhodamine B, Rhodamine 6G) were taken for the adsorption study.•Malachite nanoparticles showed high sorption capacity.•Reusability accounted up to many cycles without significant deterioration.

The ability of the Malachite nanoparticles (NPs) for differential adsorption of dye with differential functionality was explored. Fluorescein (with COOH and OH), Rhodamine B (with COOH) and Rhodamine 6G each having same xanthene moiety but differing in their functionality was taken for the study. Fluorescein was adsorbed more followed by other two dyes at pH ∼ 7. Electrostatic interaction was sought to play a major role in the adsorption process. Batch studies were conducted to evaluate the effects of regulating parameters viz. contact time, temperature, adsorbent dosage, and solution pH. Experimental results showed that a steady state was achieved at ∼6 h after which the adsorption seemed constant for all the three dyes. Temperature range of 10–40 °C was taken for the study and the adsorption was found to increase with the temperature. The concentration of dye was varied from 10 to 500 mg L−1 and the maximum adsorption was obtained for Flu with qe value ∼29.54 mg g−1 followed by RB qe value ∼20.74 mg g−1. R6G was least adsorbed with qe value ∼6.4 mg g−1. The experimental data found to follow the Langmuir isotherm preferentially and followed second order kinetics. Furthermore effective desorption was carried out using 50% ethanol. Flu was desorbed to ∼99.5% whereas complete extraction of RB and R6G were obtained. The multi-cycle efficiency was also investigated. Overall, the work substantiates the possible use of Malachite NPs as an effective adsorbent for removal of dye from aqueous solution.