A robust and accurate tight-binding quantum chemical method was performed to study adsorption process of dichlorodiphenyltrichloroethane (DDT) on graphitic carbon nitride (g-C3N4) and  g-C3N4 modified with nickel cluster (Ni2). The adsorption energy, charges on atoms, bond orders have been calculated and analysed. The obtained results indicate that the adsorption of DDT on the pristine g-C3N4 is physical of nature. Ni2 cluster can be easily doped on g-C3N4 due to the formation of chemical bonds. The Ni2-g-C3N4 system exhibits enhanced adsorption ability for DDT.