Probing Environmental Remediation of RhB Organic Dye Using alpha-MnO2 under Visible- Light Irradiation: Structural, Photocatalytic and Mineralization Studies

Abstract

Photocatalytic activity of alpha-MnO2 nanorod synthesized through a low temperature (90 degrees C) single step precipitation route in the absence of surfactant and template is reported. Dependence of precipitation time on morphology of the synthesized alpha-MnO2 has been investigated and the photocatalyst has been tested for the degradation of organic cationic and anionic dyes. Detailed study on the degradation of Rhodamine B (RhB) has been carried out. The lower precipitation time (of 6 h) is found to be ideal for the synthesis of the photocatalyst. The mechanism of RhB photodegradation under visible light using alpha-MnO2 nanorods has been established through mass spectra analysis. The intermediate products during degradation ex-hibits de-ethylation and mineralisation steps. Experimental results suggest that both super oxide and hydroxyl radicals are the main active species in the process. Total organic carbon (TOC) analysis of treated RhB reveals complete mineralisation. The photodegradation efficiency of alpha-MnO2 for cationic and anionic dyes are found to be 95-100% under visible light irradiation. The excellent photocatalytic activity of alpha-MnO2 can be correlated with its 1-D morphology of high aspect ratio and low photoluminescence intensity. The complete dye discoloration within 10 min and total mineralisation of RhB in 25 min is quite significant especially under visible light irradiation and has never been reported earlier.