How does calcium carbonate enhance pollutants degradation under light illumination? Enhanced scattering and hydroxyl radical

Some trace pollutants exist extensively in the water, soil and other environment, as a result of unorganized emissions. The natural mineral CaCO₃ is also widely found in these environments. In this study, we studied the effect of CaCO₃ on the transformation of pollutants in water under light and the inactivation of bacteria in different environments. The photolysis of tetracycline (TC) under sunlight in the presence of CaCO₃ can be as high as about 77%, which was improved comparing with the pure photolysis under sunlight (15%) and adsorption (32%). The same trend was found when the natural minerals containing CaCO₃ (e.g. shell, oyster shell, limestone and marble) were adopted. It was determined that 1.10×10⁻⁵ mmol L⁻¹ of ∙OH can be produced under Xenon lamp light source (HID) illumination after 2 h of reaction, which was increased to 4.28×10⁻⁵ mmol L⁻¹ in the HID system with addition of CaCO₃. According to the calculation by projector-enhanced wave (PAW) method, it was found that the O-H bond length was increased after H₂O adsorption on CaCO₃. The O-H bond cleavage was easier for more ∙OH generation under light illumination. Based on ZEMAX software simulations, CaCO₃ can act as light scatterer and increase the residence time of light in solution.