Straightforward single-step generation of microswimmers by bipolar electrochemistry

Autonomous microswimmers are of enormous interest not only from an academic point of view, but also for future practical applications ranging from miniaturized motors to nanomedicine. A key step for the generation of such objects is their dissymmetric modification with a catalyst particle that activates the chemical conversion of a fuel molecule, leading ultimately to the propulsion of the object. So far it has been quite difficult to synthesize such dissymmetric objects and most approaches are based on using interfaces to break the symmetry. We demonstrate here that a very simple approach based on bipolar electrochemistry allows the bulk generation of carbon microtubes that are modified selectively at one end with a Pt cluster. The presence of this metal cluster allows the catalytic decomposition of hydrogen peroxide and the resulting oxygen bubbles trigger the propulsion of the object. The type of motion can be switched from linear to circular as a function of the exact position of the Pt cluster.     

Butanol and ethanol production from tapioca starch wastewater by Clostridium spp

Total (TWW) and tapioca starch wash wastewater (TSWW) from a cassava processing plant in Thailand were analyzed for their composition with a view to evaluate their potential as substrates for solvent production by ABE fermentation with Clostridium spp. Starch was detected at a 1.63-fold higher level in the TWW than that in the TSWW (24.4% and 15.0% (w/w), respectively). The chemical oxygen demand (COD) was broadly similar (20,093 and 20,433 mg/L), but the biological oxygen demand (BOD) was 1.84-fold higher (18,000 and 9,750 mg/L) in the TWW than that in the TSWW. Thus, the TSWW was selected as a substrate to evaluate its potential for butanol and ethanol production by two Clostridium spp. The combined ethanol plus butanol production in the TSWW at pH 6.5 was higher than that at pH 4.5, being around 27.8- and 3.4-fold higher in C. butyricum TISTR 1032 and C. acetobutylicum ATCC 824, respectively. In both strains, the butanol (and combined butanol plus ethanol) production level was improved at pH 5.5. The addition of yeast extract increased the bacterial cell production, but did not significantly improve solvent productivity in C. acetobutylicum, and even decreased butanol production by C. butyricum.     

Dissymmetric carbon nanotubes by bipolar electrochemistry

Short carbon nanotubes have been modified selectively on one end with metal using a bulk technique based on bipolar electrochemistry. A stabilized suspension of nanotubes is introduced in a capillary containing an aqueous metal salt solution, and a high electric field is applied to orientate and polarize the individual tubes. During their transport through the capillary under sufficient polarization (30 kV), each nanotube is the site of water oxidation on one end and the site of metal ion reduction on the other end with the size of the formed metal cluster being proportional to the potential drop along the nanotube.     

The versatile synthesis method for hierarchical micro‐ and mesoporous zeolite: An embedded nanocarbon cluster approach

In this work, we are reporting for the first time the synthesis of hierarchical micro‐ and mesoporous zeolite using silica–carbon (SiO₂/C) composites prepared by pyrolysis of carbonaceous gases in the presence of silica gel. The pyrolysis effectively yielded carbon deposited onto the raw silica material. The obtained SiO₂/C composites were utilised as a bifunctional material, mesoporous template and silica source, for the zeolite synthesis. Tetrapropylammonium hydroxide (TPAOH) was used as a microporous template. The combination of the obtained composites and the TPAOH for the hydrothermal synthesis resulted in the formation of hierarchical micro‐ and mesoporous ZSM‐5. The results from the SEM, TEM, and N₂ adsorption/desorption isotherms, and ²⁷Al MAS NMR characterisations of the synthesised samples obtained after the removal of the templates confirmed the successful formation of the micro‐ and mesoporous zeolites. The mesoporosity of the zeolites could be controlled by adjusting the carbon content in the SiO₂/C composites while the carbon content could be controlled by varying the deposition time and the concentration of the carbonaceous gases used. This controllable and efficient synthesis method is considered to be a promising method for creating hierarchical micro‐ and mesoporous zeolites. © 2011 Canadian Society for Chemical Engineering     

Production and characterization of a novel hierarchical porous silica adsorbent for removal of methylene blue dye from wastewaters

Adsorption of methylene blue (MB) dye by hierarchical porous silica (HPS) is reported as a means of removing the dye from wastewater. HPS was produced through a sol–gel process by templating on rubber particles in skimmed natural rubber latex. The silica precursor was tetraethyl orthosilicate and the costructure directing agent was 3-aminopropyltriethoxysilane. Based on nitrogen-sorption, the HPS had a total pore volume of 1.0?cm³/g, a specific surface area of 237?m²/g, and a peak pore size of 4?nm. Larger pores (sizes >100?nm to 1?µm) were observed by scanning electron microscopy. The pores had an ink-bottle morphology of narrow necks connected to large cavities. The adsorption obeyed the Langmuir isotherm and was endothermic. Pseudo-second-order adsorption kinetics were observed. The specific adsorption of MB on HPS was 0.225?mmol/g at equilibrium. HPS was superior to many adsorbents reported for removing MB from aqueous media.     

Thermal stabilization of thin gold nanowires by surfactant-coating: a molecular dynamics study

The thermal stabilization of thin gold nanowires with a diameter of about 2 nm by surfactants is investigated by means of classical molecular dynamics simulations. While the well-known melting point depression leads to a much lower melting of gold nanowires compared to bulk gold, coating the nanowires with surfactants can reverse this, given that the attractive interaction between surfactant molecules and gold atoms lies beyond a certain threshold. It is found that the melting process of coated nanowires is dominated by surface instability patterns, whereas the melting behaviour of gold nanowires in a vacuum is dominated by the greater mobility of atoms with lower coordination numbers that are located at edges and corners. The suppression of the melting by surfactants is explained by the isotropic pressure acting on the gold surface (due to the attractive interaction) which successfully suppresses large-amplitude thermal motions of the gold atoms.     

Single point electrodeposition of nickel for the dissymmetric decoration of carbon tubes

Dissymmetric micro- and nanoobjects are of enormous interest in many areas ranging from molecular electronics to targeted drug delivery. So far it has been quite difficult to synthesize dissymmetric objects at these scales and most approaches are based on using interfaces to break the symmetry. Only a few bulk procedures are known so far to produce the so-called Janus-type objects. We report here a simple approach for the bulk generation of dissymmetric micro- and nanoobjects, especially carbon tubes (CTs), based on a known, but so far underestimated electrochemical principle, namely bipolar electrodeposition. A suspension of CTs is introduced in a capillary containing an aqueous nickel salt solution and a high electric field is applied to orientate and polarize the individual tubes. During their transport through the capillary under sufficient polarization, each tube is the site of water oxidation at one end, and of Ni²⁺ reduction at the other one. The resulting nickel deposit at one end of the tube allows manipulation of the objects with the help of a magnetic field.