Panel Discussion

Toxic pollutants like reactive dyes and hexavalent chromium (Cr^VI) presented in water streams have attracted significant research attention because of their toxicity, slow self-degradation in nature, and huge volume of production from various industries. Thus, it has become a challenge in the development of effective materials and/or methods with an excellent performance to capture and remove these toxic species from waters. In this paper, novel “sea urchin”-like Ni nanoparticles embedded in N-doped carbon nanotubes (CNTs) supported on porous carbon (Ni@N-C) 3D materials derived from waste biomass were prepared via pyrolysis and employed as an environmentally friendly, easy available and cost-effective catalyst for removal of toxic pollutants. The characterizations indicated that Ni⁰ catalyzed the growth of intertwined CNTs on carbon layers, affording abundant porous materials and larger specific surface area. With the synergistic effect of embedded Ni⁰ nanoparticles, nitrogen doping, hierarchical micro-mesopores, and interconnected CNTs, Ni@N-C displayed a superior catalytic capability for the oxidation of organic pollutants using peroxymonosulfate as an oxidant, and catalytic reduction of toxic Cr^VI to nontoxic Cr^III by formic acid as a reducing agent. It was found that the pyrolysis temperature affected the composition, morphologies, and catalytic properties of Ni@N-C. Inactive oxidized N species have transformed to the highly active graphitic N, pyridinic-N, and Ni-O-N clusters, thereby improving the catalytic activity. Moreover, Ni@N-C maintained good physicochemical structure and stable activity even after several cycles of reactions. The simple synthetic strategies, 3D structure, and remarkable performance of Ni@N-C composites make them serve as alternative environmentally friendly catalysts for removal of pollutants.