Experimental and theoretical investigation of Crassostrea gigas (gigas) shells based CaO nanoparticles as a photocatalyst for the degradation of bromocresol green dye (BCGD) in an aqueous solution

Contamination of water by dyes is prevalent in several industries and the application of some management strategies has compounded results such as the toxicity of the materials employed in the removal process. The present study seeks to degrade bromocresol green dye using calcium oxide nanoparticles (synthesized from gigas shells) as a photocatalyst. The catalyst was synthesized through a sol-gel process involving the conversion of the CaCO3 in the shells to CaO nanoparticles. The catalysts absorbed maximally at 306 nm and exhibited a band gap of 5.898 eV. The X-ray diffraction of the nanoparticle showed a major peak at 2 theta= 29.40 degrees, average crystallite size = 57.18 nm, d-spacing = 1.21 to 3.53 angstrom, density = 2.71 g/cm(3), and cell volume = 3.807 x 10(-4) pm(3). Photodegradation experiments were conducted using the sun as a source of UV radiation, and results were obtained under variable conditions (such as variation in particle size, catalyst load, period of contact, ionic strength, pH) with percentage degradation efficiencies ranging from 68 to 89%. Best-fitted kinetic models for the photodegradation of the dye were the Langmuir-Hinshelwood, pseudo-second-order, and parabolic diffusion models. Regeneration of the catalyst recorded huge success with high re-use efficiency. Analysis of the band potentials toward redox degradation indicated that the valence band potential the (- 3.145 eV) is more negative than the potential of OH- / H2O(2.27V) while the conduction band potential (0.43 eV) is more positive than the potential of O-2 / O-2(-) (- 0.282 eV) which suggested that the degradation process was facilitated by superhydroxide. DFT data for the frontier molecular orbital energies of the dye were E-HOMO = - 6.070 eV, E-LUMO = - 2.560 eV, and energy gap = 3.71 eV. Adsorption is established to be a limiting factor in the photodegradation process and the evaluated adsorption energy (- 47.55 eV) confirmed that the initial mechanism of photocatalyzed degradation of the dye is spontaneous. Also, the HOMO-LUMO diagram and Fukui function calculations (at DFT/BLYP/6-31G*) gave evidence that supported the adsorption of the dye as a limiting factor in the photodegradation, which primarily involved superoxide and superhydroxide.

Automated summary

Water contamination by dyes is a common issue in various industries, but some management strategies have resulted in the toxicity of removal materials. This study aims to degrade bromocresol green dye using calcium oxide nanoparticles synthesized from gigas shells as a photocatalyst. Photodegradation experiments under variable conditions achieved degradation efficiencies of 68% to 89%. The best-fitted kinetic models were Langmuir-Hinshelwood, pseudo-second-order, and parabolic diffusion models.