Experimental investigation into the solidification effect of nano-TiO2 regulated microbially-induced calcium carbonate precipitation

As one of the most promising frontier materials in the 21st century, the action mechanism of nanomaterials on the microbial- induced calcium carbonate precipitation (MICP) system currently lacks systematic and in-depth research. In this study, three different incorporation methods were used to systematically explore the influence mechanism of nano-TiO2 on the MICP system from multiple aspects, including the amount of calcium carbonate generated, bacterial adhesion characteristics, urease activity, mechanical properties of soil, and microscopic structural morphology. The research results show that the influence of nano-TiO2 on the MICP process presents a dual mechanism of complex biological toxicity and physicochemical promotion. When nano-TiO2 are directly added to the bacterial culture medium (or nutrient solution), they will significantly inhibit the bacterial urease activity and the calcium carbonate precipitation process, ultimately leading to a decrease in the macroscopic mechanical strength of the improved soil. However, when nano-TiO2 are directly introduced into the soil, they can effectively promote the deposition of calcium carbonate and enhance the soil solidification and improvement effect to a certain extent. The research results of this study are expected to provide a theoretical basis and data support for the development and engineering application of nano-MICP strategy. The research elucidates the mechanisms by which nano-TiO2 affect the MICP process, filling a critical knowledge gap in this field. The influence of nano-TiO2 on MICP involves a complex competition between biotoxic inhibition and physicochemical promotion.