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The carbon content of biomass waste makes it usable as a precursor in the production of activated carbon. The purpose of this work was to investigate the influence of lignocellulosic composition (i.e., lignin, cellulose, hemicellulose) in biomass waste on the microstructure and dye adsorption characteristics of microwave-assisted ZnCl2 activated carbon. Three biomass wastes with significant differences in lignocellulosic composition (i.e., pineapple leaf, cocoa shell, and coconut shell) were used as model substances. Carbonization experiments were conducted at 500 °C for two hours in a muffle furnace while the activation process was carried out at 600 W for 6 min in a microwave oven. The results showed that the composition of hemicellulose, cellulose, and lignin in biomass has an effect on the character of activated carbon. It was also found that cellulose is responsible for the formation of porosity so the high cellulose content in the biomass increases the specific surface area of the activated carbon obtained. It is in contrast with lignin which is responsible for the presence of functional groups and pore size. Activation using ZnCl2 coupled with microwave heating creates a template effect, resulting in uniform pores in activated carbon. As a result, the adsorption of dye increases with an increase in the impregnation ratio. The best adsorption ability was found in activated carbon with the highest cellulose content. Under the conditions of pH 3, an adsorption time of 180 min, and an adsorbent dose of 0.3 g per 50 mm−3 dye solution, the adsorption ability of all activated carbons was the best (adsorption rate reached 99% for the initial concentration of methyl violet dye of 100 mg.dm−3). All activated carbons exhibited the best fit with the Langmuir isotherm model. [ABSTRACT FROM AUTHOR]