Incorporation of phosphated tin oxide in mesoporous silica nanostructure for high-performance wastewater treatment and synthesis of pharmaceutically significant 14-aryl-14-alkyl-14-H-dibenzoxanthene

Purifying wastewater is critical for mitigating the expected clean water shortage and climate change. Herein, phosphated-SnO₂/mesoporous silica nanostructure (SnP₂O₇/MCM-41) was prepared by skillfully interacting pyrophosphate (P₂O₇^-4) with Sn(OH)₄ in the mesopores of MCM-41 via a simple sol-gel approach. TGA and XRD analysis revealed the high thermal stability and crystallinity of the SnP₂O₇/MCM-41 mesostructure. More importantly, the TEM images and acidity measurements indicated that the SnP₂O₇ species are homogeneously distributed over the MCM-41 surface, and the acid strength is maximized when the surface is saturated with 35 wt% SnP₂O₇/MCM-41. Benefiting from the high acidity and plenty of active sites, SnP₂O₇/MCM-41 catalyzed the conversion of benzaldehyde and β-naphthol to pharmaceutical-significant 14-Aryl-14-alkyl-14-H-dibenzoxanthene with an excellent yield of 97% after 2 h reaction progress under a gentle and solvent-free environment. Moreover, the zeta potential of SnP₂O₇/MCM-41 catalyst was measured at different pH values and the point of zero charges (PZC) were investigated to determine the best circumstances and make water purification more practicable. The PZC of SnP₂O₇/MCM-41 was found to be around pH 5.4, and SnP₂O₇/MCM-41 exhibits 96 % removal of 100 ppm BG dye, which is far higher than SnO₂/MCM-41 under the same conditions of pH 8, adsorption contact time (1 h), and adsorbent dosage (0.05 g). The experimental data follows a pseudo-second-order model, providing a good correlation coefficient (R² = 0.998). In terms of chemical stability, SnP₂O₇/MCM-41 was reused for 10 cycles without significant performance loss. From the application perspective, our results demonstrate that SnP₂O₇/MCM-41 has the desired chemical composition for wastewater purification and catalysis applications.