Bio-Templating: An Emerging Synthetic Technique for Catalysts. A Review

In the last few years, researchers have focused their attention on the synthesis of new catalyst structures based on or inspired by nature. Biotemplating involves the transfer of biological structures to inorganic materials through artificial mineralization processes. This approach offers the main advantage of allowing morphological control of the product, as a template with the desired morphology can be pre-determined, as long as it is found in nature. This way, natural evolution through millions of years can provide us with new synthetic pathways to develop some novel functional materials with advantageous properties, such as sophistication, miniaturization, hybridization, hierarchical organization, resistance, and adaptability to the required need. The field of application of these materials is very wide, covering nanomedicine, energy capture and storage, sensors, biocompatible materials, adsorbents, and catalysis. In the latter case, bio-inspired materials can be applied as catalysts requiring different types of active sites (i.e., redox, acidic, basic sites, or a combination of them) to a wide range of processes, including conventional thermal catalysis, photocatalysis, or electrocatalysis, among others. This review aims to cover current experimental studies in the field of biotemplating materials synthesis and their characterization, focusing on their application in heterogeneous catalysis.

Self-supporting hybrid silica membranes with controlled porous architectures

Transferrable, self-supporting membranes with controlled and ordered pore architectures have been developed for potential applications in the fields of filtration, sensing, separation and catalysis.

Bacteria-Assisted Synthesis of Nanosheet-Assembled TiO2 Hierarchical Architectures for Constructing TiO2-Based Composites for Photocatalytic and Electrocatalytic Applications

Synthesis and application of three-dimensional TiO₂ hierarchical architectures are one of the major priorities in the research and development of TiO₂ catalysts. Using bacteria as a template and a reactor, a bioinspired strategy was developed in the present study to synthesize nanosheet-assembled TiO₂ hierarchical architectures (N-TiO₂-HA) and relative composites for photocatalytic and electrocatalytic applications. In the first part of this work, three kinds of bacteria were used for the synthesis of N-TiO₂-HA with satisfactory monodispersity, and the growth mechanism was investigated. In the second part, porous TiO₂ hollow spheres (P-TiO₂-HS), which were obtained by calcining N-TiO₂-HA at 750 °C in air, were incorporated with MIL-101(Fe) to improve the visible-light photocatalytic efficiency. The results of the photo-Fenton-assisted degradation of rhodamine B and ciprofloxacin indicate that the synthesized composites have excellent visible-light photocatalytic activity. In the third part, the nanosheet-assembled TiO₂-carbon hollow spheres (N-TiO₂-C-HS), which were obtained by calcining N-TiO₂-HA at 750 °C in argon atmosphere, were electrodeposited with Pt for electrocatalytic oxidation of methanol. The electrochemical measurements show that Pt-deposited N-TiO₂-C-HS have better electrocatalytic activity, stability, and tolerance to CO poisoning than commercial Pt/C catalysts.

Controllable alignment of elongated microorganisms in 3D microspace using electrofluidic devices manufactured by hybrid femtosecond laser microfabrication

This paper presents a simple technique to fabricate new electrofluidic devices for the three-dimensional (3D) manipulation of microorganisms by hybrid subtractive and additive femtosecond (fs) laser microfabrication (fs laser-assisted wet etching of glass followed by water-assisted fs laser modification combined with electroless metal plating). The technique enables the formation of patterned metal electrodes in arbitrary regions in closed glass microfluidic channels, which can spatially and temporally control the direction of electric fields in 3D microfluidic environments. The fabricated electrofluidic devices were applied to nanoaquariums to demonstrate the 3D electro-orientation of Euglena gracilis (an elongated unicellular microorganism) in microfluidics with high controllability and reliability. In particular, swimming Euglena cells can be oriented along the z-direction (perpendicular to the device surface) using electrodes with square outlines formed at the top and bottom of the channel, which is quite useful for observing the motions of cells parallel to their swimming directions. Specifically, z-directional electric field control ensured efficient observation of manipulated cells on the front side (45 cells were captured in a minute in an imaging area of ~160×120 μm), resulting in a reduction of the average time required to capture the images of five Euglena cells swimming continuously along the z-direction by a factor of ~43 compared with the case of no electric field. In addition, the combination of the electrofluidic devices and dynamic imaging enabled observation of the flagella of Euglena cells, revealing that the swimming direction of each Euglena cell under the electric field application was determined by the initial body angle.

Self-supporting hybrid silica membranes with 3D large-scale ordered interconnected pore architectures

Transferrable, self-supporting membranes with unique hierarchical, interconnected pore architectures over a large length scale, have been developed.

Size and Shape Control of Gold Nanodeposits in an Array of Silica Nanowells on a Gold Electrode

Ordered arrays of hemispherical nanowells were formed in a sol-gel-derived silica film on a gold electrode using 500 nm diameter polystyrene latex spheres as templates. The conductive domain located at the bottom of each nanowell upon template removal was enlarged via electroless deposition from a gold plating solution. The structured electrodes thus formed were characterized using scanning electron microscopy and atomic force microscopy. Depending on the method used to make the films, the extent of the long-range packing and the size of the conductive domain changed. Electroless deposition in the nanowells produced (near) sphere-like nanostructures of gold, the size of which depended on the incubation time in the plating solution and the size of the conductive domain. Longer exposure times yielded nanostructures that filled the nanowell, whereas smaller exposure time yielded much smaller structures. Significantly larger, rougher deposits were formed in nanowells with large conductive domains. The electrochemical response observed at these electrodes was strongly dependent on the extent of long-range packing, the presence of defect sites in the film and their relative spacing, and the redox species in solution.

3-dimensional electrode patterning within a microfluidic channel using metal ion implantation

The application of electrical fields within a microfluidic channel enables many forms of manipulation necessary for lab-on-a-chip devices. Patterning electrodes inside the microfluidic channel generally requires multi-step optical lithography. Here, we utilize an ion-implantation process to pattern 3D electrodes within a fluidic channel made of polydimethylsiloxane (PDMS). Electrode structuring within the channel is achieved by ion implantation at a 40 degrees angle with a metal shadow mask. The advantages of three-dimensional structuring of electrodes within a fluidic channel over traditional planar electrode designs are discussed. Two possible applications are presented: asymmetric particles can be aligned in any of the three axial dimensions with electro-orientation; colloidal focusing and concentration within a fluidic channel can be achieved through dielectrophoresis. Demonstrations are shown with E. coli, a rod shaped bacteria, and indicate the potential that ion-implanted microfluidic channels have for manipulations in the context of lab-on-a-chip devices.