Zinc oxide functionalized biochar from rambutan wood as a novel material to utilize an agricultural waste in Thailand

Abstract

Zinc oxide-functionalized biochar (biochar-ZnO) from rambutan wood, an agricultural waste, was prepared to increase a value of biochar from rambutan, an important economic fruit crop in Thailand, for the first time. Biochar-ZnO was synthesized by a sol-gel process. X-ray diffraction (XRD) spectra suggest that the biochar consists of amorphous carbon mainly and confirm the success of zinc oxide functionalization on the biochar surface. The crystal structure of zinc oxide is hexagonal Wurtzite. The diameter of zinc oxide particles is 20 nm. Thermogravimetric (TGA) thermograms indicate the success of biochar-ZnO preparation. A weight percentage of zinc oxide in the composite is 20. Their Fourier transform infrared (FTIR) spectra confirm, again, the success of ZnO functionalization on the biochar surface and indicate both carboxylic and hydroxyl groups on the biochar and biochar-ZnO surface. The iodine numbers of the biochar and biochar-ZnO are 570 and 555 mg·g⁻¹, respectively. These numbers suggest that the biochar without an activation has a surface area that is comparable to that of activated carbon. Also, a decrease in the iodine numbers after the sol-gel process suggest a coverage of zinc oxide particles on the biochar surface. Lastly, biochar-ZnO is a promising material to be used for further applications such as a filler in rubber industry, an important industry in Thailand.