Earthworm excrete derived-enzyme enriched SnO2/g-C3N4 nanocomposite for near complete decomposition of toxic dye molecules

Abstract

Enzymes derived from earthworm (Eudrilus eugeniae) excretes (vermiwash) were used as supporting bio-catalysts with SnO2/g-C3N4 nanocomposites for photocatalytic dye degradation of toxic organic dyes. The results were compared to those of the composite partners SnO2 and g-C3N4. The enzyme supported nanocomposite has superior photocatalytic efficiency of 95 %, 93 %, 83 % and 97 % against the test dyes Methylene Blue (MB), Malachite Green (MG), Methyl Orange (MO) and Rose Bengal (RB) whereas the partners SnO2 (62 %, 81 %, 36 % & 73 %) and g-C3N4 (76 %, 84 %, 80 % & 89 %) exhibited lower efficiencies. The enzymes phosphatase, amylase, urease and protease present in the synthesized nanocomposite play supporting role as co-catalyst in enhancing the photocatalytic ability of the nanocomposite. The mechanism involving the charge carrier recombination delay due to the formation of g-C3N4 sheets beneath the SnO2 particles is illustrated. The partnering mechanism with g-C3N4 having lower bandgap (2.8 eV) leads to a reduction in the bandgap from 3.5 eV for SnO2 to 2.6 eV for the nanocomposite making the nanocomposite as visible light responsive photocatalyst. The XRD, FTIR, SEM-EDX, UV–vis–NIR, XPS and DFT results support the discussion on photocatalytic mechanism. The near complete dye degradation is confirmed by phenotypic test on earthworm (Eudrilus eugeniae).