Microwave hydrothermal synthesis and characterization of aluminum substituted tobermorite

In tackling the sustainability challenges encountered in conventional hydrothermal synthesis, the microwave hydrothermal synthesis emerges as a promising approach, offering various advantages such as accelerated heating and energy efficiency owing to its unique volumetric heating property. This method presents a potential solution to the limitations inherent in conventional hydrothermal synthesis techniques. The synthesis of aluminum substituted tobermorite (Al-tobermorite) was conducted by using conventional and microwave hydrothermal methods, the experimental results were compared and the mechanism of microwave heating was revealed. Results show the optimal Al/Si ratio for synthesizing Al-tobermorite was identified as 0.15. Microwave hydrothermal synthesis of Al-tobermorite demonstrated a notable advantage in efficiency, requiring only about one-seventh of the time needed for conventional hydrothermal synthesis. At the same time, the Al-tobermorite produced via microwave hydrothermal synthesis exhibited a larger specific surface area and pore volume compared to its conventionally synthesized counterpart. Fourier Transform Infrared Spectrometer (FTIR) spectroscopy results consistently indicate that in the structure of Al-tobermorite, regardless of the synthesis method, aluminum substitutes silicon at the Q2 and Q3 positions. The findings can provide valuable insights for the efficient processing of materials containing aluminum and serve as a practical reference in applications and waste management, conforming to the contemporary policy requirements for sustainable development.