Hydrothermal Carbonization of Coconut Pulp and the Adsorption Activity toward Methylene Blue

This study aimed to investigate alterations in the physical and chemical properties resulting from hydrothermal carbonization process applied to dried coconut pulp samples. The samples were passed through a 50-mesh sieve, immersed in demineralized water, and subjected to heating in an autoclave soaked in silicone oil at 200 °C for 5 hours. Hydrochar product (HTC-coconut pulp) of the treatment is a black powder characterized using several instruments. The results of X-ray diffraction (XRD) analysis showed that the peaks in coconut pulp occurred at 2θ: 16.1°, 20.3°, and in the corresponding HTC-coconut pulp at 2θ: 20.2°, 21.2°. Meanwhile, analysis using FTIR showed a significant change where the peaks were at wavenumber (cm-1) 3603, 2926, 2855, 1746, 1462, 1372, and 1155. The peaks detected in HTC-coconut pulp were at wavenumber (cm-1) 2929, 2849, 1713, 1468, 1290, 1117, and 1057. The results of X-ray fluorescence (XRF) analysis showed several elements such as Al, P, S, Cl, K, and Ca, while HTC-coconut pulp showed Al, Si, P, S, Cl, K, and Ca. A simple application of the two types of materials was as an adsorbent for a simulated methylene blue (MB) solution. According to UV-Vis spectrophotometry absorbance before and after treatment, HTC-coconut pulp showed a slightly higher absorbency compared to normal coconut pulp.