Highly efficient catalytic degradation of organic dyes using in situ synthesized silver nanoparticles on bioscaffolds of natural eggshell

Dyes and pigments as a major class of synthetic organic compounds are widely used in variety of industrial applications. In the most cases, nearly 15% of dyes are wasted after the completion of their use [1].Therefore, discharge of hazardous dyes can lead to serious environmental and health problems due to their high toxicity, chemical stability, slow biodegradation, and potential carcinogenicity. Thus, the control and abatement of residual dyes is a required section of wastewater treatment. Traditional biological and physical treatments have been proven slow, expensive and inefficient to remove some dyes from wastewater. Metal nanostructures due to their relatively large surface-to-volume ratios and the unique chemical properties show an enhanced catalytic activity for the degradation of organic dyes. Among diverse metallic nanostructures, the noble metal/metaloxide nanoparticles such as Ag, Pd, Au and TiO2 nanoparticles are able to gain tremendous significance in catalytic dye degradation because of their good electron relaying capability arising from their appropriate redox potentials [2]. In each case, immobilizing noble-metal nanoparticles with specific shape on various solid supports, such as carbon materials, metal oxides, polymers, and so on, it is regarded as an effective strategy. Foregoing facts revealed that the use of novel metal nanocomposits is an exciting possibility that is relatively underexploited, which aroused our motivation in the present investigation [2]. In this study, catalytic treatment of silver nanoparticles for the degradation of some toxic dyes, methylene blue (MB), methyl red (MR) and methyl orange (MO) was evaluated. for this purpose, we developed an efficient and facile route for the in situ growth of silver nanoparticles (AgNPs) through the reduction of aqueous solution on porous bioscaffolds of natural eggshell at the presence of ascorbic acids as reducing and stabilizing agent. The results of spectroscopic [X-ray diffraction (XRD)] and imaging [scanning electron microscopy (SEM) transmission electron microscopy (TEM)] measurements confirm the successful synthesis of Ag-eggshell nanocomposite. The in-question nanohybrids show superior catalytic activity toward MB, MR and MO with high degradation efficiency above 94%, 93% and 88.4%, respectively. Different parameters such as nanoparticle content, time and sample pH that affect the results of nanocomposite behavior are studied. The catalyst was recycled over six times without showing a significant loss in its activity. However, it should be noted that mere color change may sometimes be deceptive to judge the effectiveness of dye removal [3]. Therefore, systematic studies are necessary to draw any reasonable consensus. The degradation reaction followed pseudo-first-order kinetics with respect to the concentration of the studied dyes.