In Situ and Ex Situ Immobilization of Nano Gold Particles in Zeolite Framework and a Comparison of Their Photocatalytic Activities

Gold nano particles-zeolite hybrids (Au-NPs/zeolite) have been prepared in previous works by either of the two approaches, in situ and ex situ and have been studied for their catalytic properties. But a rational comparison of performance of such materials prepared by both the techniques is still lacking. The present work comprises development of zeolite from coal fly ash, a solid waste pollutant, and its conversion into visible light active photocatalyst through immobilization of Au-NPs by both in situ and ex situ techniques. All the catalysts were characterized by Fourier transform infrared, X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscopy and diffuse reflectance spectroscopy techniques. They were employed for photocatalytic degradation of p-nitrophenol (p-NP) and phenol. Under optimized condition (catalyst dose = 250 mg/L, [phenolics] = 20 mg/L, pH 4), Au-NPs/zeolite in situ and ex situ materials exhibited 80.8 and 73.7% degradation for p-NP and 78.4 and 63.9% degradation for phenol respectively. On recycling and repeated use in 3rd/4th run, the efficiency decreased slightly from those of fresh and the difference in efficiency between in situ and ex situ catalysts prevailed on reuse also. The configurational arrangement in immobilization of Au-NPs in zeolite framework appeared to be more favorable for activity only in in situ loading. [GRAPHICS]