Metal-organic frameworks-derived 3D yolk shell-like structure Ni@carbon as a recyclable catalyst for Cr(VI) reduction

Metal-organic framework (MOFs)-derived [email protected] composites with three-dimensional (3D) yolk shell-like structure have been successfully synthesized by a self-template strategy. After continuous carbonization treatment, the metallic Ni was uniformly embedded in the carbon matrix that could effectively protect Ni from corrosion and subsequent leaching. Carbon layers in [email protected] composites mainly existed in the form of graphene structure according to high-resolution transmission electron microscopy and powder X-ray diffraction pattern. As-prepared materials inherited superior properties of Ni-MOFs, such as large specific surface area, layered 3D yolk shell-like structure and abundant Ni content. As a consequence, among all synthetic materials, the [email protected] exhibited the most excellent catalytic activity towards Cr(VI) reduction in the presence of HCOOH. Impressively, highly toxic Cr(VI) in aqueous solution can be completely reduced to hypotoxic Cr(III) by [email protected] within 30 min. The catalytic efficiency was much higher than that of other Ni-based and some precious metal catalysts. In addition, the reusability experiment showed that the [email protected] had good stability and high catalytic activity after 10 cycles of utilization. Ni also gave [email protected] catalyst ferromagnetism, and composites obtained were easily separated under the external magnetic field. The catalytic reduction mechanism of [email protected] for Cr(VI) was also described and discussed in detail. More importantly, this study is expected to provide a new idea for the synthesis of non-noble metal catalysts from MOFs by self-template carbonization.