Palladized cells as suspension catalyst and electrochemical catalyst for reductively degrading aromatics contaminants: Roles of Pd size and distribution

Abstract

a b s t r a c tThe palladized cell (Pd-cell) could be used as an efficient catalyst in catalyzing the degradations of a wide variety of environmental contaminants. Nevertheless, when the Pd NPs associate with the bacteria, the catalytic activity likely significantly affected by the biomass. Quantitative indicators that characterize of Pd-cell are necessary and little attention has been paid to investigate how the catalytic efficiency of Pdcell is affected by the size and distribution of Pd NPs. To fill this gap, we explored the roles of the abovementioned key factors on the performance of Pd-cell in catalyzing the degradations of two aromatic contaminants (nitrobenzene and p-chlorophenol) in two commonly used scenarios: (1) using Pd-cell as suspended catalyst in solution and (2) using Pd-cell as electrocatalyst directly coated on electrode. In scenario (1), the relationship of exposing area to Pd particle size and distribution factors was established. Based on theoretical estimation and catalytic performance analysis, the results indicated that adjusting the exposing area to a large value (9.3 ± 0.1 Â 10 5 nm 2 mg À1 Pd) was extremely effective for improving the catalytic activity of Pd-cell used as a suspension catalyst. In scenario (2), our results showed that the best electrocatalytic performances were achieved on the electrode decorated with Pd-cells with the largest NP size (54.3 ± 16.4 nm), which exerted maximum electrochemical active surface area (10.6 m 2 g À1 ) as well as favorable conductivity. The coverage of deposited Pd NPs (>95%) on the cell surface played a crucial role in boosting the conductivity of biocatalyst, thus determining the possibility of Pd-cell as an efficient electrocatalyst. The findings of this study provide a guidance for the synthesis and application of Pd-cell, which enables the design of Pd-cell to be suitable for different catalysis systems with high catalytic performance.

Engineered Nanoenzymes with Multifunctional Properties for Next‐Generation Biological and Environmental Applications

“…Conversely, the best electrocatalytic effect was achieved on electrodes covered with Pd@cells with nanoparticles of size greater than 50 nm. [ 81 ] Following the results obtained in the previous study, Cheng and colleagues demonstrated that the electrocatalytic activity of S. oneidensis @Pd biofilm formed on the surface of an electrode can be increased 68 times upon hybridization with carbon nanotubes (in a 1: 10 ratio Pd /CNT). The hybridized CNT acts as an electron bridge improving the electron transfer throughout the growing biofilm, thus increasing the current density from 0.02 mA cm −2 (Pd@cells) to ≈0.1 mA cm −2 (Pd@cell@CNTs10).…”

Biotechnological synthesis of Pd-based nanoparticle catalysts

“…These particles possessed a larger average size of 25.8 nm, but with high exposed surface area, extracellular distribution, and cell surface coverage, indicating that these properties were more favourable than size. 96 At lower CDW : Pd ratios there were fewer cell nucleation sites and the cells were exposed to more metal toxicity. The particles were larger and more often extracellular, as they nucleated in the periplasm then grew beyond the cell surface; in addition damaged cells would release enzymes providing additional extracellular nucleation sites, and abiotic reduction would occur.…”

“… 95 Hou et al also showed that the CDW : Pd ratio affected the extracellular distribution of bio-Pd, which in turn impacted the catalytic activity of bio-Pd nanoparticles. 96 Pd/ S. oneidensis nanoparticles were synthesised using formate as the electron donor at five different CDW : Pd ratios: 6 : 1, 3 : 1, 1 : 1, 1 : 3 and 1 : 6, which increased the average particle size from <10 nm to >50 nm. When tested as a suspension catalyst for the reduction of nitrobenzene and 4-chlorophenol, the smallest nanoparticles gave some of the lowest rates of reaction.…”

“…113 Shewanella species perform the recovery and formation of nanoparticles of precious metals such as Au, Ag, Pt, Rh and In, 108,114–117 and have produced catalytically active bio-Pd nanoparticles. 30,96,118–120 A key model Shewanella species for study is Shewanella oneidensis MR-1, which utilises lactate, formate and hydrogen most effectively as electron donors for metal reduction, via reasonably well-understood metabolic pathways (Fig. 1B).…”

Activating electrochemical catalytic activity of bio-palladium by hybridizing with carbon nanotube as “e− Bridge”

“…To date, the feasibility of Pd NPs production has been demonstrated in a number of bacteria, including Shewanella 9 , Geobacter 10 , Desulfovibrio 11 , Enterococcus 12 , etc. Efforts to improve the catalytic activity of bio-Pd have been made by controlling the size and distribution of Pd NPs or by introducing another metal to form Pd based bimetal NPs 13 , 14 . In addition, to avoid the loss of bio-Pd, magnetite was proved to be co-deposited with Pd on the cell and facilitated the its recovery 6 .…”