Biochar-supported magnetic noble metallic nanoparticles for the fast recovery of excessive reductant during pollutant reduction.

The catalytic reduction of diverse pollutants by noble metal catalysts in the presence of reductants is a highly effective and widely used method. However, the considerable cost of noble metal catalysts impedes the practical application of this method, and the recovery of excessive reductants has not been reported previously. In this work, we prepared inexpensive biochar-supported magnetic noble metallic nanoparticles (NPs) and efficiently recovered the excessive reductants in the form of H2. The as-synthesized biochar-supported noble metallic NPs exhibited high H2 recovery during the 4-nitrophenol reduction reaction. Results showed that the catalysts with low noble metallic content have higher H2 recovery rate than commercial Pd/C, Ag/C, and Pt/C. The catalytic mechanism of magnetic biochar-supported noble metallic NPs was demonstrated to be a "synergetic effect", where biochar and Fe3O4 acted as accelerants that enable noble metallic NPs to produce active hydrogen for the reduction reaction, and the excess active hydrogen atoms combined to form H2.