Influence of Functionalization on the Textural Properties and Photocatalytic Performance of ZnO-Modified Metakaolin Based-Geopolymer

Metakaolin-based geopolymers modified with ZnO and surface-functionalized ZnO were developed and investigated in terms of structure, morphology, textural properties, and photocatalytic performance. ZnO, ZnO@AS(zinc oxide functionalized with steric acid), and ZnO@PEG(zinc oxide functionalized with polyethylene glycol) were incorporated into the geopolymer matrix and characterized by XRD(X-ray diffraction), ATR–FTIR(Fourier transform infrared spectroscopy in attenuated total reflectance, SEM–EDS (scanning electron microscopy coupled with spectroscopy with energy-dispersive X-ray spectroscopy), and BET(Brunauer–Emmett–Teller) analysis. The results showed that ZnO incorporation did not significantly modify the amorphous aluminosilicate network but affected the morphology and porosity depending on the functionalization method. ZnO@AS induced matrix densification and reduced accessible porosity, while ZnO@PEG improved particle dispersion and preserved the porous structure. Among the ZnO-modified metakaolin-based geopolymers, GP/ZnO@PEG(geopolymer with ZnO@PEG particles) exhibited the highest photocatalytic performance, characterized by a BET surface area of 17.22 m2/g, an apparent kinetic constant of 0.01668 min−1, and a half-life of approximately 41 min, achieving approximately 90% methylene blue removal after 120 min of UV-A irradiation. The study demonstrates that ZnO surface functionalization controls the interfacial interaction with the geopolymer matrix and plays a key role in the performance of geopolymer-based photocatalytic materials.