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To obtain a magnetically separable, low-cost and highly efficient reduction catalyst, microbial carbon-loaded bimetallic palladium/iron nanoparticles (MC-FePd3 NPs) were synthesized in this study by using waste yeast residue doped with iron during the preparation process of microbial carbon-loaded monometallic palladium nanoparticles (MC-Pd NPs). The morphology, crystal structure, magnetic properties and catalytic performance of MC-FePd3 NPs for the reduction of p -nitrophenol (p-NP) were investigated by various characterization techniques, such as SEM-EDS, TEM, XRD, PPMS-9 and UV–vis spectroscopy. The catalytic experiments showed that the MC-FePd3 NPs prepared under pyrolysis conditions at 700 °C had an apparent rate constant of 1.85 × 10−1 s−1 which is better than the rate constants of MC-Pd NPs and other palladium-based nanocatalytic materials reported so far. The amount of palladium used in the synthesis of MC-FePd3 NPs was half that of MC-Pd NPs. The catalyst exhibited soft magnetic ordering behavior and still showed a catalytic efficiency of 97.4% after five consecutive reaction cycles. Furthermore, employing MC-FePd3 NPs reduces the costs of catalyst preparation and use in production. MC-FePd3 NPs with efficient catalytic properties, facile magnetic separation and recyclability, and low costs of preparation and use have considerable potential for industrial applications. [ABSTRACT FROM AUTHOR]

In recent years, the pyrolysis of microbial biomasses that adsorb various metal ions has enabled the preparation of carbon-based polymetallic nanomaterials with excellent electrocatalytic and electrical energy storage properties. However, the preparation of ozone catalysts by this technique and the corresponding catalytic oxidation mechanism are still unclear. In this study, an Escherichia coli strain (BL21) was used for tetra-metal (Cu, Fe, Mn and Al) absorption and the obtained microbial biomass was pyrolyzed under the protection of a nitrogen flow at 700 °C and activated at 900 °C to prepare a microbial-char-based tetra-metal ozone catalyst (MCOC). This was used to degrade phenol and coking wastewater and exhibited a strong catalytic capability for coking wastewater, whose chemical oxygen demand removal efficiency of 70.86% is 16.7% higher than that of pure ozone and 14.67%, 7.21% and 3.58% higher than that of three commercial catalysts, respectively. It also improved the efficiency of ozonation for phenol by 33%. The MCOC was characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy–energy-dispersive spectroscopy, transmission electron microscopy and other methods. The results demonstrated that the spherical metal nanoparticles had sizes ranging from 3 nm to 7 nm and that crystals of Fe2O3 and Fe3P were observed. The study showed that the MCOC promoted the production of more hydroxyl radicals and superoxides from ozone, which attack organics. The oxygen vacancies of the catalyst were also investigated. It was proved that the Lewis acid sites on the surface of metal oxides are the active centers of ozone decomposition. Therefore, this work provides a new method for the synthesis of multi-metal nanocomposites and expands the application of biosynthetic nanomaterials. [ABSTRACT FROM AUTHOR]