Synthesis of Aminopropyl-Functionalized Mesoporous Silica Derived from Geothermal Silica for an Effective Slow-Release Urea Carrier

Abstract

An effective method to prepare slow-release urea was developed with aminopropyl-functionalized mesoporous silica (MS) to achieve enhanced urea adsorption and slow-release properties. As a novel study, mesoporous silica was developed using treated geothermal silica as the silica source, cetyltrimethylammonium bromide (CTAB) as the surfactant, and 3-aminopropyl trimethoxy silane (APTMS) as the surface modification agent. Mesoporous silica with the most desirable properties of uniform micromorphology containing 38.55 wt % silica particles, 668.849 m2/g surface area, 149.33–353.28 mL/g adsorption–desorption range, and 0.26 mL/g adsorption pore volume was achieved using 0.05 mol of CTAB. The synthesized mesoporous silica showed type-IV hysteresis, which corresponds to mesoporous materials. Differential scanning calorimetry (DSC)–thermogravimetric analysis (TGA) thermograms showed that mesoporous silica is more reactive, with peaks at 82.3 and 159.5 °C, has good thermal stability, and undergoes only 17.61% weight loss until 124 °C. Scanning electron microscopy (SEM) showed that functionalization and urea adsorption to mesoporous silica resulted in no significant morphological changes. In the Fourier transform infrared (FTIR) spectra, MS/APTMS/U26.74 was observed to have higher intensities of C═O, N–H, C–N, and C–H groups compared with other samples. The cumulative urea release during 7 days was 184.5 ppm (92.4%) for commercial urea and 124.6 ppm (64.4%) for MS/APTMS/U26.74. The Higuchi kinetic model yielded the best fit predicting MS/APTMS/U26.74 release kinetics, with an R2 of 0.9979 and a Higuchi constant of 24.4964%/day. Finally, MS/APTMS/U26.74 synthesized using geothermal silica, CTAB, and APTMS was noted to possess a potential composition for slow-release urea with enhanced efficiency.