Metal nanoparticles decorated sodium alginate‑carbon nitride composite beads as effective catalyst for the reduction of organic pollutants

Abstract

Herein, a simple method is used for fabrication of carbon nitride (g-C3N4) incorporated sodium alginate (Alg) beads. The alginate carbon nitride beads (Alg-CNBs) were prepared by introducing the g-C3N4 dispersed Alg aqueous solution to a divalent Ca2+ ions solution. Alg-CNBs were further treated with different transition metal salt solutions. The surface coated transition metal ions on Alg-CNBs were reduced to zero-valent state (M0), through strong reducing agent NaBH4, and used for the catalytic reduction of different organic dyes. The surface morphology of all catalysts was investigated by FE-SEM and metal uptake capacity was investigated by ICP-OES. The prepared M0/Alg-CNBs (where M0 = Ag0, Ni0, Fe0 and Cu0) catalysts were tested against the reduction of 4-nitrophenol (4-NP) to recognize the fastest one. Among all the catalysts, the Cu0/Alg-CNBs efficiently reduced 4-NP to 4-aminophenol (4-AP). Cu0/Alg-CNBs was used further for the reduction of methyl orange (MO), congo red (CR), 2-nitrophenol (2-NP) and 2,6-dinitrophenol (2,6-DNP). The MO, CR and 4-NP was reduced with rate constant of 0.135, 0.077 and 0.384 min−1, respectively. For large scale and continuous reduction of 4-NP to 4-AP, the column was packed with 0.15 g catalyst and the reducible reactants were passed through it. A reduction of 4-NP up to 97–99% was achieved by simply passing it through column packed with catalyst under gravity. Similarly, effects of changing initial dye concentration, catalytic dosage and NaBH4 performance has been investigated for the reduction process. Also, the prepared catalyst beads can be easily prepared, recovered simply by discarding the dye after completion of the reaction, recyclable and its good catalytic activity.