Synthesis and characterization of ZrO2-loaded rice husk ash-derived MCM-41 nanocomposites for boron adsorption from wastewater

Boron is essential for both plants and humans; however, it is toxic at high concentrations. Silica based composites can remove boron from wastewater. The potential of rice husk ash (RHA), an abundant and eco-friendly material, for synthesizing MCM-41, with or without ZrO2, has been explored. Small-angle X-ray diffraction patterns indicated that MCM-41 exhibits an amorphous structure. Morphological analyses revealed spherical structures with aligned mesopores, while residual channels and holes were observed in the RHA-based MCM-41. ZrO2 particles appeared highly agglomerated and irregularly shaped. Fourier transform infrared spectroscopy identified the characteristic Si-O vibrational bands, while thermogravimetric analysis confirmed the thermal stability and silica content in the nanocomposites. Si-O-Zr cation interactions were observed in MCM-41 loaded with ZrO2. The X-ray photoelectron spectroscopy revealed the presence of C, O, Si, and Zr, including CrO2-related signals, in the synthesized materials. According to Brunauer-Emmett-Teller (BET) surface area analysis, MCM-41 displayed a surface area of 1163.5 m2 g- 1, indicating its high potential for boron adsorption. The surface area of RHA-MCM-41 was 967.2 m2 g- 1, which decreased to 886.3 m2 g- 1 upon adding ZrO2. Inductively coupled plasma-optical emission spectrometry analysis indicated that boric acid and MCM-41 formed hydrogen bonds that enhanced adsorption. The equilibrium adsorption capacities (qe), where RHA-MCM-41@ZrO2 has the highest qe of 2711.2 ppm, suggesting a superior adsorption capacity. These results demonstrate the potential of the modified MCM-41 materials for high-efficiency adsorption applications.