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An absorber with lightweight, low-cost, high absorption and broad frequency bandwidth is highly expected to design an electromagnetic wave absorber application. In this paper, the carbon materials based agricultural waste from oil palm empty fruit bunch (OPEFB) were studied to investigate the electromagnetic wave, especially the microwave absorption properties within the range from 8 to 12 GHz (X-band). The carbon-based OPEFB is prepared by hydrothermal carbonization (at 180 oC for 8 hours) followed by chemical (using KOH activating agent) and physical (at 800 oC for 2 hours) of carbonization processes. We studied the microwave absorption properties of the porous carbon-based OPEFB with 20 % of KOH concentration. A vector network analyzer (VNA) takes the microwave absorption properties within the X-band frequency range. The results indicate the ability to absorb electromagnetic waves in all X-band frequencies for porous activated carbon-based OPEFB samples. The reflection loss is reach -32.21 dB at 10.64 GHz. The enhancement of EM wave absorption in activated carbon-based OPEFB compared to that of raw OPEFB material is correlated to the formation of porous stracture inducing the multiple reflection to enhance the interfacial polarization of EM wave. This research show that the porous carbon-based OPEFB can be a promising candidate for a lightweight, green, and renewable of electromagnetic waves absorber in the future. [ABSTRACT FROM AUTHOR]

Activated carbon is an amorphous material that is widely used as a filter, adsorbent, electrode material, etc. However, conventional activated carbon is non-eco-friendly material due to its unsustainable issue, therefore, biomass-based activated carbon (AC) has become popular research in order to replace fossil-based activated carbon. In this study, we used oil palm waste as our raw materials from different parts of the oil palm tree such as Oil Palm Empty Fruit Bunches (OPEFB), and Oil Palm Shells (OPS). The different structures of activated carbon from oil palm waste will be investigated through OPEFB and OPS while the differences in carbonization methods between hydrothermal and pyrolysis were performed on OPS and OPS-char. These materials were activated using solid KOH and FeCl2.H2O, followed by pyrolysis at 800oC in an N2 atmosphere. Physical characterization was carried out by proximate analysis to determine the quality of activated carbon using ASTM standards. Meanwhile, the structural characterization was carried out using XRD, BET, and FESEM methods to observe the structural morphology of each activated carbon. The proximate analysis results show good results that meet ASTM standards D 3172-3175 with low moisture, ash content, volatile matter, and high fixed carbon values. The highest value in the methylene blue adsorption test was found in AC OPEFB. XRD analysis showed that our samples have an amorphous structure while BET analysis presents our samples have high surface area namely, AC OPEFB (775.58 m2/g), AC OPS (733.04 m2/g), and AC OPS-char (594.093 m2/g). The FESEM images show the formed AC pores depending on the natural structure and type of carbonization method. In general, these material properties can be applied to pore-based applications such as adsorbents in wastewater treatment or electrodes in energy storage. [ABSTRACT FROM AUTHOR]