This research constitutes a relatively new area that has emerged from the synthesis of carbon nanotubes (CNTs) from hydrochars of agricultural wastes. The unwanted sugarcane bagasse (SCB), black liquor (BL), and mature beech pinewood sawdust (MW) waste in Egypt are used for CNTs preparation. SEM, TEM, and Raman spectra showed that the type of agricultural waste precursor affects the degree of wall graphitization and the number of tubes. Multiwalled carbon nanotubes (MWCNTs) with diameters of 5.39 - 19.78, 2.95 - 7.98, and 4.59 - 10.35 nm were prepared from the hydrochars of SCB, BL, and MW, respectively. CNT from SCB and BL consists of a small number of tubes and graphene (G) nanosheets. In comparison, that MW provided a larger number of tubes. The Ni2+ adsorption efficiency by CNTs under processing conditions was investigated. Our findings hinted that the adsorptions of Ni2+ to CNTs/SCB and CNTs/MW (R% = 81.85 and 79.78 respectively) were found to be much higher than that CNTs/BL (R%= 32.70). Our findings also hinted that the interaction between Ni2+ and CNTs/MW is an exothermic process (with a negative value of ΔH) while the adsorption between Ni2+ and CNTs/SCB and CNTs/BL is an endothermic process (with a positive value of ΔH).