Effect of ethylenediaminetetraacetic acid on the photocatalytic degradation of Rhodamine B under visible light irradiation using graphitic carbon nitride

Abstract

Graphitic carbon nitride (GCN) is a well-known visible light photocatalyst and it is widely used for the degradation of organic compounds. Melamine is the most commonly used precursor for preparing GCN. However, the photocatalytic efficacy of GCN prepared using melamine is very poor. To improve the efficiency, a mixture of melamine and ammonium chloride (1:4 ratio) was used as a precursor in this study to prepare the modified GCN, named as AGCN. Rhodamine B (Rh B) was chosen as a model pollutant. In addition, the study also aims at to evaluate the effect of addition of ethylenediaminetetraacetic acid (EDTA) on the extent of degradation of Rh B. The photocatalytic ability of AGCN for the degradation of Rh B under visible light irradiation was evaluated using a photoreactor with 140 W LED lamps (Wear and Friction Tech, Chennai). The concentrations of AGCN, Rh B and EDTA were kept constant at 100 mg, 10 ppm and 1 mM, respectively. The Rh B dye solution and AGCN mixture were ultrasonicated for 10 min to effectively disperse the catalyst. Before irradiation, the Rh B-AGCN solution mixture was kept in dark under mechanical agitation (500 rpm) for 30 min to enable them to reach an adsorption–desorption equilibrium. The photocatalytic degradation experiments were conducted for a period of 60 min. An aliquot of the solution mixture was drawn for every 15 min, centrifuged at 4000 rpm and analyzed for its absorbance at 554 nm. The study concludes that AGCN is an effective visible light photocatalyst for the degradation of Rh B and addition of 1 mM EDTA accelerates the rate of degradation. EDTA is a scavenger for photons (h+). However, when superoxide radicals (•O2–) are the main active species, addition of EDTA provides an additional supporting mechanism of suppressing the recombination of electron-hole pairs, thus enhancing the rate of degradation of Rh B.