Exploring effective catalytic degradation of organic pollutant dyes using environment benign, green engineered gold nanoparticles

Hazardous organic dyes both cationic (rhodamine-B (RhB), methylene blue (MB)) and anionic (congo red (CR), methyl orange (MO)) found in industrial waste water creates huge environmental pollution. An active catalyst gold nanoparticle (AuNps) is engineered here in order to decrease the dye toxicity. After characterization of green engineered gold nanoparticles by microscopy and spectroscopy, time dependent catalytic activity is explored in the reduction of these four dyes by sodium borohydride. The selective toxicity of gold nanoparticles evaluated by performing antimicrobial assay against Gram’s positive and Gram’s negative microorganisms. Electron microscopy found < 24 nm sized nanoparticles. The presence of elemental gold proved by 4f5/2 and 4f7/2 BE peaks in X ray photon spectroscopy (XPS) which is supported by 2.1 eV signal peak in energy-dispersive X-ray spectroscopy (EDS). Additionally, the functionalization of –OH and –C = O functional groups around nanoparticles confirmed by XPS and EDS study. The use of engineered AuNp in traditional dye removal approaches, improved the catalytic activity along with pseudo first order reaction kinetics. The improved degradation efficiency towards cationic rhodamine B reported 87% in 7 min., methylene blue 97% in 9 min, while anionic congo red found 92% in 9 min. and methyl orange 95% in 11 min., within separate reactions. After recovery XRD study indicated the 38.2 (1 1 1), 44.4 (2 0 0), 64.8 (2 2 0) and 78.3 (3 1 1) peak with their respective planes. TEM study indicated up to 20 nm sized nanoparticles were present. In this nanoparticle based reduction reaction, gold nanoparticles acted as an electron relaying system contributing to fasten the degradation process. Appreciably, AuNp toxicity study against living bacteria like Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa elucidated less toxicity which clearly indicated significant environment benign property.