Remediation of TCE-contaminated groundwater using KMnO4 oxidation: laboratory and field-scale studies.

The objectives of this study were to (1) conduct laboratory bench and column experiments to determine the oxidation kinetics and optimal operational parameters for trichloroethene (TCE)-contaminated groundwater remediation using potassium permanganate (KMnO4) as oxidant and (2) to conduct a pilot-scale study to assess the efficiency of TCE remediation by KMnO4 oxidation. The controlling factors in laboratory studies included soil oxidant demand (SOD), molar ratios of KMnO4 to TCE, KMnO4 decay rate, and molar ratios of Na2HPO4 to KMnO4 for manganese dioxide (MnO2) production control. Results show that a significant amount of KMnO4 was depleted when it was added in a soil/water system due to the existence of natural soil organic matters. The presence of natural organic material in soils can exert a significant oxidant demand thereby reducing the amount of KMnO4 available for the destruction of TCE as well as the overall oxidation rate of TCE. Supplement of higher concentrations of KMnO4 is required in the soil systems with high SOD values. Higher KMnO4 application resulted in more significant H+ and subsequent pH drop. The addition of Na2HPO4 could minimize the amount of produced MnO2 particles and prevent the clogging of soil pores, and TCE oxidation efficiency would not be affected by Na2HPO4. To obtain a complete TCE removal, the amount of KMnO4 used to oxidize TCE needs to be higher than the theoretical molar ratio of KMnO4 to TCE based on the stoichiometry equation. Relatively lower oxidation rates are obtained with lower initial TCE concentrations. The half-life of TCE decreased with increased KMnO4 concentrations. Results from the pilot-scale study indicate that a significant KMnO4 decay occurs after the injection due to the reaction of KMnO4 with soil organic matters, and thus, the amount of KMnO4, which could be transported from the injection point to the downgradient area, would be low. The effective influence zone of the KMnO4 oxidation was limited to the KMnO4 injection area (within a 3-m radius zone). Migration of KMnO4 to farther downgradient area was limited due to the reaction of KMnO4 to natural organic matters. To retain a higher TCE removal efficiency, continuous supplement of high concentrations of KMnO4 is required. The findings would be useful in designing an in situ field-scale ISCO system for TCE-contaminated groundwater remediation using KMnO4 as the oxidant.

Using poly-glutamic acid as soil-washing agent to remediate heavy metal-contaminated soils.

The extraction efficiency of heavy metals from soils using three forms of gamma poly-glutamic acid (γ-PGA) as the washing agents was investigated. Controlling factors including agent concentrations, extraction time, pH, and liquid to soil ratio were evaluated to determine the optimum operational conditions. The distribution of heavy metal species in soils before and after extraction processes was analyzed. Up to 46 and 74% of heavy metal removal efficiencies were achieved with one round and a sequential extraction process using H-bonding form of γ-PGA (200 mM) with washing time of 40 min, liquid to solid ratio of 10 to 1, and pH of 6. Major heavy metal removal mechanisms were (1) γ-PGA-promoted dissolution and (2) complexation of heavy metal with free carboxyl groups in γ-PGA, which resulted in heavy metal desorption from soils. Metal species on soils were redistributed after washing, and soils were remediated without destruction of soil structures and productivity.

Electrically tunable transmission of gold binary-grating metasurfaces integrated with liquid crystals.

Planar photonics using metasurfaces is of great interest because a metasurface can control the flow of light beyond that attainable with natural materials. The resonance wavelength of a binary-grating metasurface is adjustable by changing the width and thickness of the nanostructure. We propose a novel combination of nematic liquid crystals and a binary-grating metasurface with which the diffraction efficiency can be controlled by adjusting the applied voltage.

Hybrid contact and interfacial adhesion on well-defined periodic hierarchical pillars.

Herein, we describe a simple fabrication procedure for creating artificial hierarchical micro/nanopillars on silicon substrates that allows an effective, precise control of the interfacial adhesion and surface hydrophobicity. These well-defined hierarchical micro/nanostructures have four possible wetting states: Cassie-Cassie (C-C), Cassie-Wenzel (C-W), Wenzel-Cassie (W-C) and Wenzel-Wenzel (W-W). By controlling the critical height of the micro/nanopillars, it is possible to fabricate hierarchical micro/nanostructures in these four states. Thus, the hierarchical superhydrophobic surfaces proposed and fabricated in this study are promising for mimicking either lotus leaves with low adhesion or rose petals with high adhesion.

Exploring the formation of focal adhesions on patterned surfaces using super-resolution imaging.

The formation of focal adhesions on various sizes of fibronectin patterns, ranging from 200 µm to 250 nm, was systematically investigated by total internal reflection fluorescence microscopy and super-resolution imaging. It was found that cells adhered to and spread on these micro/nanopatterns, forming focal adhesions. On a micrometer scale the shape of the focal adhesions was elongated. However, on the nanometer scale, the shape of focal adhesions became dotlike. To further explore the distribution of focal adhesion proteins formed on surfaces, a localization-based super-resolution imaging technique was employed in order to determine the position and density of vinculin proteins. A characteristic distance of 50 nm was found between vinculin molecules in the focal adhesions, which did not depend on the size of the fibronectin nanopatterns. This distance was found to be crucial for the formation of focal adhesions. In addition, the density of vinculin at the focal adhesions formed on the nanopatterns increased as the pattern size decreased. The density of the protein was found to be 425 ± 247, 584 ± 302, and 703 ± 305 proteins µm(-2) on the 600, 400, and 250 nm fibronectin patterns respectively. Whereas 226 ± 77 proteins µm(-2) was measured for the matured focal adhesions on homogeneous fibronectin coated substrates. The increase in vinculin density implies that an increase in mechanical load was applied to the focal adhesions formed on the smaller nanopatterns.

Investigation of the growth of focal adhesions using protein nanoarrays fabricated by nanocontact printing using size tunable polymeric nanopillars.

Here we describe a simple approach to create various sizes of protein nanoarrays for the investigation of cell adhesion. Using a combination of nanosphere lithography, oxygen plasma treatment, deep etching and nanomolding processes, well-ordered polymeric nanopillar arrays have been fabricated with diameters in the range of 50-600 nm. These nanopillar arrays were used as stamps for nanocontact printing to create fibronectin nanoarrays, which were used to study the size dependent formation of focal adhesion. It was found that cells can adhere and spread on fibronectin nanoarrays with a fibronectin pattern as small as 50 nm. It was also found that the average size of focal adhesion decreased as the size of the fibronectin pattern was reduced.

Conversion of surface energy and manipulation of a single droplet across micropatterned surfaces.

To clarify a driving mechanism for the self-movement of a droplet across hydrophobic textured surfaces in series and to develop applications for a microfluidic device, we report a theoretical model, a microfabrication technique, and experimental measurements. The contact angle of a droplet on a composite surface, the stable surface energy level, and the energy barrier caused by hysteresis were investigated. With increasing patterned density of the microstructure, the contact angle and stable surface energy decreased gradually, but the energy barrier increased. Both the analytical results and the experimental measurements show that the surface energy for a suspended status is greater than that for a collapsed status, which produces increased energy to generate the movement of a droplet. An analysis of interactions between actuation force, resistive force, and viscous force during the motion of a droplet is based on the equilibrium between forces. From the perspective of energy conversion, the difference in surface energy between a higher state and a lower state would drive a single droplet and make it move spontaneously if it could overcome the static friction force resulting from hysteresis and the kinetic friction force under droplet movement. The mean velocity in the present device, measured to be 62.5 mm s (-1), agrees satisfactorily with the theoretical prediction. The model developed for the energy levels enables us to assess the contact mode of a droplet placed on the patterned surface. For a prediction of the transport capability of the designed devices, a theoretical interpretation of the conversion between the surface energy and the kinetic energy of the droplet establishes a criterion that the pattern density of a textured surface should be less than 0.76. The effective rate of energy conversion is estimated to be 20.6%.