Synthesis and application of carbon nanotubes grown directly on pozzolanic clay

This study reports the high-yield “in situ” growth of carbon nanotubes (CNT) on pozzolanic clay (P-Clay) and its application as a substitute for Portland cement in mortar. Initially, iron chloride hexahydrate (FeCl3·6H2O) and cobalt nitrate hexahydrate (Co(NO3)2·6H2O) supported on magnesium oxide (MgO) we used as catalysts, and the production of CNT over time was studied. The same catalyst was then employed for CNT synthesis on clay particles, resulting in an impressive 1700% yield in carbon mass. Various characterization techniques such as scanning electron microscopy, transmission electron microscopy, X-ray dispersive energy, thermogravimetry analyses, Raman spectroscopy, and X-ray diffraction were employed to assess the morphology and properties of the new material. The nanostructured pozzolanic clay (NP-Clay) was used to produce mortar. The dispersion of carbon nanotubes supported on clay particles proved to be easier compared to dispersing individual CNT, which can be attributed to the size of the supporting particles. Consequently, NP-Clay could be simply mixed with other mortar ingredients without the need for prior dispersion procedures such as ultrasound treatment. Nanostructured mortar samples with varying concentrations of CNT were prepared, and mechanical tests demonstrated show improvement of the flexural and compressive strength (up to 20% achieved using 0.2% CNT concentration). The results obtained after varying the water/cement ratio (0.48, 0.55, and 0.65) for the optimal CNT concentration in mortar are also presented. The method presented for the in situ production of nanostructured materials as a substitute for Portland cement is scalable and contributes to social and environmental development by reducing the reliance on conventional cement, thus aiding in the reduction of CO2 emissions.