A new and efficient nanozero-valent iron based trimetallic catalyst immobilized on bentonite clay for anionic dyes reduction

چکیده مقاله

Background: Nanozero-valent iron (nZVI) based materials have been used as tunable reducing composite because of their unique properties e.g. large surface area, high reactivity, strong reductive capacity, eco-friendly, and cost-effective. NZVI is a potential reductive composite because of its sufficient mobility and low toxicity. It can instantaneously adsorb anionic dyes on its surface. Though, the aggregation tendency of nZVI refers to intrinsic magnetic interactions and high surface energy. This limits its dispersibility. Also, in aqueous media, reductive property of nZVI decrease significantly due to quick formation of a Fe oxide and hydroxide layer on its surface. Supporting nZVI on some clays such as kaolin, hematite and bentonite results efficient dispersion of nZVI which prevents its aggregation causing greater reduction performance. On the other hand, oxidation rate and aggregation tendency of nZVI could be reduced depositing Pd as second catalytic metal onto its surface. Also, the activation energy of reduction reaction could be decreased using catalytic property of second metal. It also improves the reduction rate. Recently, it is presented that depositing third catalytic metal on the surface of nZVI based bimetallic catalyst results better performance. Methods: In this study, nanozero-valent iron (nZVI) based trimetallic nanoparticle immobilized on bentonite was synthesized based on literature [1, 2], and characterized by TEM, FT-IR, XRD, SEM, EDS and BET. The simultaneous reduction of methyl orange and congo red, as two model anionic dyes, by the proposed nanocatalyst was investigated and the dose of nanocatalyst, initial pH, and contact time as parameters which affecting the reduction efficiency were modeled and optimized by response surface methodology. Results: The characterization results of the synthesized Be@Fe/Cu/Ag nanocatalyst showing successful synthesis of trimetallic immobilized on bentonite. Under the defined optimum value of parameters, the kinetic data for nanocatalyst were fitted well with the pseudo-second order model. The rate constants increase with the increase in temperature, time and dosage of proposed nanocatalyst, but decrease with the increase in initial dyes concentration and pH. The proposed Be@Fe/Cu/Ag system would be a promising process for the removal of the dyes from food industrial wastewater. Conclusion: The experimental results of the present research indicated that the presence of bentonite clay as support could decrease the aggregation of nZVI besides increasing of their adsorption and reactivity. The structure of Fe/Cu/Ag could improve the electron transport and create active sites with high electron density at the surface enhancing the generation of surface-bonded atomic hydrogen ([H]ads) or the direct reduction of pollutant.