No abstract

The conversion of biomass into value-added products has recently received much attention for a broad range of applications. In this work, water lettuce was converted into calcium carbonate (CaCO3)/carbon via hydrothermal carbonization (HTC) and pyrolysis at 900 °C. The HTC temperature and time varied in the range of 160–200 °C for 6–18 h, respectively. X-ray diffraction analysis indicated that the samples consisted of a mixture of calcite and vaterite phases of CaCO3 and amorphous carbon. The ratio of calcite and vaterite phases varied with HTC time. The Fourier transform infrared spectroscopy (FTIR) result showed the characteristic absorption bands confirming the presence of CaCO3. Scanning electron microscopy (SEM) images revealed the large crystal of CaCO3 and fine carbon particles. From the N2 sorption analysis, the sample prepared from the HTC at 200 °C for 6 h had the highest specific surface area of 95 m2/g due to the development of micropores. The results presented in this work demonstrated that both HTC temperature and time play critical roles in altering the surface area and phase structure of CaCO3/carbon. The CaCO3/carbon derived from water lettuce can potentially be used and adapted for many applications.