Concept of complex processing of chlorinated hydrocarbons, involving catalytic decomposition of 1,2-dichloroethane on Ni–M alloys to obtain a carbon nanomaterial (CNM) showing high performance in adsorption treatment of water to remove 1,2-dichlorobenzene, was developed. A series of finely dispersed Ni–Pd (5 wt.%) and Ni–Mo (5 wt.%) alloys were synthesized and evaluated. The samples were studied as catalysts in decomposition of C2H4Cl2 vapor at 600°С to obtain a carbon nanomaterial. The addition of 5 wt.% second metal led to an increased carbon nanomaterial yield, from 20.1 to 25.4 (Ni–Pd) and 31.8 g/CNM(Ni–Mo). Analysis by electron microscopy and Raman spectroscopy showed that the carbon product consists of nanofibers of segmented structure, constituted by a poorly ordered graphite phase. The specific surface area of the carbon nanomaterial was 230–280 sq m/g>. The CNM/Ni, CNM/Ni–Pd, and CNM/Ni–Mo samples obtained were tested as adsorbents for water treatment to remove dissolved 1,2-dichlorobenzene (с0 = 73–880 ΜM) in the batch mode. The 1,2-dichlorobenzene adsorption isotherms were constructed. The degree of filling of the carbon nanomaterial surface with the adsorbate at equilibrium is 43%–47%, exceeding by a factor of more than 2 the utilization efficiency of AG-2000 activated carbon (SBET = 1230 m2 g–1).