Internal electric field induced photocarriers separation of nickel-doped pyrite/pyrite homojunction with rich sulfur vacancies for superior Cr(VI) reduction.

Improving the separation efficiency and transfer ability of photoinduced electrons/holes in pyrite (FeS)-based photocatalytic materials is significant for the photoreduction of hexavalent chromium (Cr(VI)) but still remains a challenge. Herein, a novel homojunction was prepared through in-situ growth of nickel (Ni) doped FeS nanoparticles on FeS nanobelts (denoted as Ni-FeS/FeS). Systematical characterizations revealed that Ni doped FeS nanoparticles have been successfully in situ grown along the lattice of FeS nanobelts. Photoreduction experiments demonstrated that the Ni-FeS/FeS homojunction with 2 mmol Ni doping contents (denoted as 2Ni-FeS/FeS) exhibited the optimum Cr(VI) reduction efficiency among the studied catalysts. Density Functional Theory (DFT) calculated results verified that Ni doping could not only be advantageous for the formation of sulfur vacancies but also modify the band gap and band structure of FeS nanoparticles. Moreover, several doping energy levels caused by Ni doping have also appeared near the Fermi level of FeS nanoparticles. The migration paths of electrons and the existence of internal electric field (IEF) in homojunction were further verified by the calculation of work function. To sum up, the doping energy levels and IEF that produced by homojunction played important roles in accelerating the separation efficiency of its photogenerated carriers.