Adsorption equilibrium, kinetics and thermodynamics of Malachite Green onto Silver nano particle loaded on activated carbon

This study investigates the adsorption potential of Silver nano particle loaded on activated carbon (SN-AC) to remove Malachite Green (MG) from its aqueous solution. (MG), a triphenylmethane dye, is used as an antifungal, anti-bacterial, and anti-parasitical therapeutic agent in aquacultures and animal husbandry. It has detrimental effects on intestine and gonads of aquatic organisms. When it was inhaled by human, it may cause even cancer. Contact of malachite green with skin causes irritation with redness and pain. Therefore, the use of it was banned in many countries. To this end, the effect of operational parameters including initial pH, adsorbent dose, contact time, initial dye concentration and temperature were studied in batch adsorption experiments. Silver nanoparticle preparation is also being experimented upon and studied to find the most cost-efficient and effective way to synthesize them. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis were used to characterize the adsorbent material. The experimental equilibrium data were tested by three widely used isotherm models namely, Langmuir, Freundlich and Dubinin–Radushkevich (D–R). It was found that adsorption of (MG) on (SN-AC) well with the Langmuir isotherm model, implying monolayer coverage of dye molecules onto the surface of the adsorbent. More than 90% removal efficiency was obtained within 30 min at adsorbent dose of 0.04 g/50ml for initial dye concentration of 10-15ppm in pH=5. Kinetics of the adsorption process was tested by pseudo-first-order and pseudo-second-order kinetics, and intraparticle diffusion mechanism. Pseudo-second-order kinetic model provided a better correlation for the experimental data studied in comparison to the pseudo-first-order model. Intraparticle diffusion was not the sole rate-controlling factor. A thermodynamic study showed spontaneous nature and feasibility of the adsorption process. The results indicate that Silver nano particle loaded on activated carbon can be used as an effective and low-cost adsorbent to remove Malachite Green from aqueous solution rather than various conventional methods of removing dyes including coagulation and flocculation, oxidation or ozonation and membrane separation

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