The preparation of functional materials of controlled architectures is still demanding using the currently available methods and is the cornerstone in experimental materials chemistry. The main focus is to develop well-defined materials (e.g. catalysts) with homogenously dispersed nanoparticles of the active phases with controlled surface coverage, size, and shape.
The aim of the study was to develop and optimize an innovative method for the deposition of nanoparticles (NPs) of catalytically active phases on structural oxide supports (monoliths and foams) using the bacterias’ ability to colonize porous surfaces. The working hypothesis consists in using bacteria as size and shape-selective microcarriers of inorganic nanoparticles and for their subsequent homogeneous dispersion over the catalytic supports. Such conjecture is based on the ability of the bacteria to selective adsorption of nanoparticles, and owing to ‘race for the surface’ phenomenon, to seize the available surface area. Since bacteria strains exhibit different sizes (100 nm – 5 μm), shapes (coccoid round, rod-shaped, filamentous, and appendaged) and surface charges (both: positive and negative) they can be individually selected for the given type of nanoparticles. Additionally, by controlling the bacteria concentration, the exposition time and the number of the deposition cycles, the active phase loading can be precisely engineered.
The overall strategy of the proposed method of catalyst preparation can be divided into the following interlaced tasks: preparation of the active phase nanoparticles, adsorption of nanoparticles onto the bacteria walls, evaluation of bacterial nanoparticle uptake, bacteria–mediated deposition of active phase nanoparticles on the supports, final evaluation of the new catalytic material. Four non-pathogenic bacteria strains were selected for this purpose (Pseudomonas putida, Neisseria subflava, Bacillus subtilis, and Staphylococcus carnosus), and the main criteria for their selection include not only the morphological and surface properties, but also the possibility to apply them in the large scale practice. As a model active phases: metal (Au, Ag, Pt) and oxide (Fe3O4) nanoparticles were used. The typical results are summarized in graphical scheme in the Figure (Au deposition on cordierite with the use of S. carnosus as a cargo).
The proposed novel method presents the original, unprecedented and versatile approach for preparation of the state-of-the-art functional surfaces (patent applications P.424760).