MgO-CdWO4: A visible-light-active heterojunction photocatalyst for Bismark brown dye degradation

The photocatalytic activity of magnesium oxide coupled with cadmium tungstate was observed in this study. Magnesium oxide was coupled with cadmium tungstate as using leave extract of the Brassica rapa plant. The prepared samples were characterized by various spectroscopic and microscopic techniques. As a result, it was found that the particles of the prepared sample were in the nano range. The individual crystallite sizes of magnesium oxide and cadmium tungstate in the prepared composite sample were 15 nm and 25 nm, respectively. The energy band gap for the prepared sample was found to be narrow (Eg = 2.4 eV) in comparison to the energy band gap of bare cadmium tungstate (Eg = 3.6). The zero-point charge of the prepared sample was estimated to be 6.5. The photoluminescence analysis suggested the lowering in the recombination of electron and hole heterojunction formation between magnesium oxide and cadmium tungstate in the prepared sample. The measured band edge (valence and conduction band) positions of individual semiconductors in the prepared sample suggested the formation of staggered gap (type II) heterojunction material. The heterojunction material was utilized as a photocatalyst for the photodegradation of Bismarck brown dye in water under natural sunlight irradiation. Photodegradation results suggested that the 2 g/L of sample was capable to remove ∼94% of the Bismarck brown dye from its a 20 mg/L aqueous solution within 90 minutes. The first-order chemical kinetics is reported for this study. It was found that this photocatalyst works efficiently at higher temperature and basic pH condition. The free radical scavenging and quenching experiments was also conducted. The results of the free radical scavenging experiment showed that superoxide free radicals, hydroxyl free radicals, and holes were majorly responsible for the current photodegradation process. The detailed interfacial charge transfer mechanism for the photodegradation of Bismarck brown (BBR) is also delved. Reusability and stability analysis suggested high efficiency and stability of the present photocatalyst even after five reusability cycles. The trend of the photocatalysts for Bismarck brown dye degradation under the similar condition was found to be MgO-CdWO4>MgO> CdWO4> Dark> without catalyst. The mineralization study suggested that after 280 min of sunlight irradiation only 52% mineralization could be achieved. The comparative study revealed that the efficiency of MgO-CdWO4 photocatalyst is observed better than previous reported literature.