Agar based bimetallic nanoparticles as high-performance renewable adsorbent for removal and degradation of cationic organic dyes

• Agar-based adsorbent was synthesized using monometallic/bimetallic nanoparticles.
• The agar-based adsorbent was used for adsorption, removal and degradation of dyes.
• Rate of degradation of MB and RhB on agar@Fe/Pd nanoparticles was also studied.
• Rate constants were found as 3.16 × 10−2 and 4.82 × 10−2 s−1 for MB and RhB.
• The adsorbent could be reused for at least 20 cycles with 90% dye removal capacity.

Removal of toxic organic compounds from the industrial wastewater is currently one of the most important subjects in water pollution control. A highly efficient, effective and rapid polysaccharide (agar)-based adsorbent was synthesized by modifying monometallic/bimetallic nanoparticles (Fe, Cu, Pd, Fe/Cu and Fe/Pd) to remove cationic dyes (methylene blue, MB and rhodamine B, RhB). The effects of different parameters like initial contact time, solution pH value, temperature and amount of adsorbent on the adsorption capacity as well as dye removal capacity of the adsorbent were investigated. The maximum adsorption capacities of the agar@Fe/Pd nanoparticles based adsorbent for both MB and RhB were found 875.0 mg g−1 and 780.0 mg g−1, respectively. On the optimized parameter, the adsorbent shows a very high efficiency and rapid removal property for both the dyes. The adsorption follows the Freundlich isotherm model for the equilibrium process. The kinetic studies revealed that the adsorption of both the dyes followed the pseudo-first order kinetic model. Additionally, two different models, i.e. intraparticle diffusion and elovich model were also studied for adsorption of both the dyes. Similarly, the rate of degradation of MB and RhB on agar@Fe/Pd nanoparticles was also studied and their rate constants were found as 3.16 × 10−2 s−1 and 4.82 × 10−2 s−1, respectively. Furthermore, the regeneration experiments showed that the adsorbent could be reused for at least 20 cycles with very efficient dye removal capacity (90%) even in complex systems containing mixture of dyes, salt, and surfactant. Thus, the agar-based adsorbent has the potential in the fast and effective adsorption, removal and degradation of toxic dyes from industrial textile wastewater.

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