Plasma and radiation mediated green synthesis of gold Nanoparticles-immobilized bio-template based catalytic reactor ‘AuNICaR’: Mechanistic insights, catalytic performance and reusability analysis

Abstract

The present work reports a green, non-thermal plasma-based approach for efficient synthesis of a gold nanoparticles (Au NPs) Immobilized Catalytic Reactor “AuNICaR” via a novel, efficient, indigenously developed process termed “Plasma Assisted Synthesis and Simultaneous Immobilization (PASSI)”, using isopropanol to enhance the reducing plasma environment. Au NPs were synthesized and simultaneously immobilized onto a cellulose based bio-template pre-functionalized via radiation induced grafting of 2,3-epoxypropylmethacrylate (EPMA) onto a nonwoven cellulose (NWC) substrate. The process entails minimal wastage of expensive gold precursor and eliminates use of external chemicals (reducing and stabilizing agents). Samples were characterized by 13C NMR, FTIR, XPS, TGA, DSC, SEM-EDS, BET, and EDXRF analysis. Catalytic activity was assessed by spectrophotometrically monitoring the reduction of p-nitroaniline (PNA) in presence of NaBH4. DFT calculations established the interaction between Au NPs and EPMA groups of the bio-template to be occurring in ratios of 1:1 and 1:2, with 1:1 being more stable. ANN modelling was also invoked to investigate the effect of simultaneous variation of plasma process parameters on the catalytic performance. AuNICaR was demonstrated for catalytic reduction of pollutants: PNA, p-nitrophenol (PNP) and methyl orange (MO) azo dye in both batch and continuous flow mode. Over 25000 mL of cumulative pollutant feed with concentrations ranging from 0.06 mM − 2 mM was treated at a flow rate of 540 mL.h−1, using a single catalyst batch after intermittent washing with water. With excellent storage stability of > 12 months and > 92 % retention in catalytic activity post multiple cycles, AuNICaR certifies as a potentially inexhaustible catalytic system for cost-effective pollutant treatment.