Structural evolution and photocatalytic behaviour of CaO-Modified Ti-MCM-41 mesoporous materials

Abstract

This work investigates the influence of CaO incorporation on the structural, textural, optical, surface chemical, and photocatalytic properties of mesoporous Ti-MCM-41. CaO derived from waste eggshells was incorporated into the Ti-MCM-41 framework through a sol-gel method. X-ray diffraction and Raman analyses reveal that increasing CaO loading induces a gradual phase transformation of TiO₂ from anatase to rutile, accompanied by the formation of crystalline CaO domains. Low-angle XRD and nitrogen adsorption–desorption analyses confirm that the ordered mesoporous structure is retained after modification, although the specific surface area decreases from 208.8 to 26.7 m² g^− 1 owing to partial pore filling and blockage by CaO species. HRTEM further confirms the preservation of the mesoporous framework together with the coexistence of crystalline CaO and TiO₂ phases. UV-Vis diffuse reflectance spectroscopy shows a gradual increase in the optical band gap from 3.04 to 3.39 eV, while photoluminescence analysis demonstrates progressive suppression of charge carrier recombination with increasing CaO loading. X-ray photoelectron spectroscopy confirms the successful incorporation of CaO and reveals modifications in the surface chemical states and electronic environment of the Ti-MCM-41 framework. Zeta potential measurements show that CaO modification shifts the surface charge towards more negative values, indicating enhanced colloidal stability and favourable electrostatic interactions with cationic dye molecules. The CaO-modified materials exhibit enhanced photocatalytic degradation of organic dyes under UV irradiation following pseudo-first-order kinetics. The improved photocatalytic performance is attributed to the synergistic effects of structural evolution, interfacial charge transport, increased surface basicity, and enhanced charge separation within the mesoporous framework.

Graphical Abstract