Green synthesis of Ag ultra-fine nano-catalyst supported on layered double oxide and chitosan: Accelerated reduction of 4-nitrophenol to 4-aminophenol

Abstract

In this research, the green synthesis of a silver nanoparticle (Ag NPs) based nano-catalyst for reducing 4-nitrophenol (4-NP) pollutants were explained. Hence, instead of using chemical reductant, natural extract of green tea was utilized as reducing agent to prepare Ag NPs. The obtained Ag NPs had uniform size and shape. The small size of Ag NPs helps exited electron to be stabilized and extends lifespan during a reduction reaction. Then, layered double hydroxides (LDHs) was prepared, and after calcination was added to Ag NPs. The calcination of LDH leads to a significant increase in the number of catalytic active sites, thereby enhancing catalyst function. Besides, chitosan (CS) was chosen as a natural polymer matrix. Ag-LDH hybrids can remain immobilized and well-dispersed on CS matrix. The CS matrix also facilitates the separation process. More importantly, it enhances reusability of the nano-catalyst noticeably and accordingly plays an important role in the synthesis of the reusable high-performance nano-catalyst. Finally, the prepared CS/Ag-LDH NC film reduced 4-NP to 4–aminophenol in 5 min with a conversion percentage of 99.01% ± 0.13. The effect of various parameters like pH, catalyst amount, NaBH4 concentration, and 4-NP concentration was evaluated. Based on the obtained findings, reaction kinetics is pseudo-first-order with an apparent rate constant of 1.65 × 10−2 (s−1), and the activation energy was calculated to be 13.93 kJ mol−1. Presence of CS enhanced reusability of the nano-catalyst noticeably so that, performance of the nano-catalyst remained unchanged after five reuse cycles.