The authors would like to acknowledge the support from the Department of Earth Sciences, Uppsala University for supporting part of this research.

1. Functionalization of Multiwalled Carbon Nanotubes
<ol>
	<li>Perform the entire functionalization step inside a fume hood, using safety eye glasses, gloves and lab coat. Measure 24 ml of sulfuric acid and 8 ml of nitrate acid using a graduated cylinder, and then transfer them into a beaker. Add 32 mg of untreated MWCNTs into a beaker using tin foil container at an analytical balance (final concentration should be 1 mg/ml of acid mixture).</li>
	<li>First, keep the beaker with MWCNT and acid mixture in the ultrasonic cleaner (bath) for 2 hr at RT. Then, heat and stir the MWCNT-acid solution for 5 hr at 90 &#176;C using a hot plate.</li>
	<li>Filter the CNT suspension with a 0.2 &#181;m pore diameter PTFE filter membrane placed on a filter holder, and use vacuum to help filtration. Perform the filtration portion by portion and use several filter membranes (approximately 1/4th of above mixture per portion for one filter). Add boiling water during filtration process to filter out the acid solution until the pH of the mixture becomes greater than 5.</li>
	<li>Always break the vacuum before it is turned off and not to introduce anything into the vacuum system. Use a conical beaker to collect the waste liquid.</li>
	<li>Pour filtrated acid into a waste container (send the waste container to a waste handling facility or dilute the liquid before dumping it into the sink by adding at least ten times of tap water).</li>
	<li>Transfer the filter membranes with retained MWCNTs into evaporating dishes and put the dishes into the desiccator (contains approximately 100 g of silica gel) and create a vacuum environment (leave the vacuum on for about 1 hr) for CNT to complete drying (about 24 hr).
	<ol>
		<li>Scrape the CNTs out of the membranes carefully using spatula and transfer the particles into a clean container. Weigh the MWCNTs powder and label the container for future use.</li>
	</ol>
	</li>
</ol>
2. Porous Media for Transport Experiments
<ol>
	<li>Prepare 0.1 M HCl solution for acid washing of silica sand.
	<ol>
		<li>Perform all these steps inside a fume hood with safety eye glasses, gloves, and lab coat. Add 1 L de-ionized water to a 2 L flask. Measure 8 ml of 37% HCl using a graduated cylinder.</li>
		<li>Add the HCl into the de-ionized water carefully. Shake the flask carefully to help mixing.</li>
	</ol>
	</li>
	<li>Wash the sand with the prepared HCl solution.
	<ol>
		<li>Weigh about 1,000 g sand. Add 1/3 of sand into the flask with the HCl solution and shake the flask twice to help mixing then add rest of the sand (1/3 of the sand each time).</li>
		<li>Shake the flask three times and leave the acid with sand for 30 min.</li>
		<li>Pour the liquid out of the flask to acid waste container and rinse the sand with de-ionized water at least 8 times.</li>
	</ol>
	</li>
	<li>Wash the sand with a H2O2 solution.
	<ol>
		<li>Add 700 ml of de-ionized water into the flask with sand then measure 40 ml of 30% H2O2 solution using a graduated cylinder.</li>
		<li>Add the H2O2 solution into flask with sand and shake twice to help mixing. Then add another 40 ml of 30% H2O2 solution 3 times until there is 160 ml H2O2 total in the flask.</li>
		<li>Shake and mix the solution and sand each time and leave the H2O2 solution with sand for 40 min to allow the reaction to be completed. Shake the flask and stir the sand with a plastic rod every 10 min.</li>
		<li>Decant the liquid down to the sink and run tap water for 30 sec.</li>
	</ol>
	</li>
	<li>Rinse and dry the sand.
	<ol>
		<li>Rinse sand with de-ionized water at least 8 times to get rid of any solution or left over reaction products. Shake and stir thoroughly when rinsing.</li>
		<li>Put flask with rinsed sand into an oven (105 &#176;C) for 24 hr to dry, then take sand out of the oven using oven-mitten and leave at the counter for 2 hr for the sand to cool down.</li>
		<li>Transfer the clean sand into a plastic container. Mark the container and place it in an appropriate shelf to be ready for use.</li>
	</ol>
	</li>
</ol>
3. Column Experiments
<ol>
	<li>Preparation of background solution.
	<ol>
		<li>Prepare appropriate background solution chemistry for the column experiment.</li>
		<li>Use 0.1 M HCl and 0.1 M NaOH solutions to adjust the pH and NaCl salt to achieve appropriate ionic strength for the following experiment.</li>
	</ol>
	</li>
	<li>Column selection.
	<ol>
		<li>Choose a glass column of 2.5 cm diameter and 15 cm length for this experiment (pH: 5 and ionic strength: 2 mM in the current study). Use a steel mesh filter (0.2 mm) on both sides of the glass column.</li>
		<li>Flush the tubes connected to the column and fill with background solution (or MWCNTs solution until the 3-way valve to control the type of liquid flow (MWCNTs solution or background solution) as shown in Figure 1.</li>
	</ol>
	</li>
	<li>Wet-packing of the column.
	<ol>
		<li>Weigh the clean sand on a scale and take 124 g of clean sand for the selected column size.</li>
		<li>Use a high precision peristaltic pump. Calibrate the pump to achieve 2 ml/min of liquid flow.</li>
		<li>Start the pump to fill the column from the bottom until the water level is a couple of centimeters above the bottom of the column. Put approximately 1/10th of the measured sand at a time into the column but make sure that the sand level doesn&#8217;t come above the water level in the column. Continue the water flow to the column continuously to stay above the sand level.</li>
		<li>Close the column cap with appropriate filter mesh after complete filling.</li>
		<li>Allow the packed column to flow for at least 1 hr. The individual parameters of the column are indicated in Table 1.</li>
	</ol>
	</li>
	<li>Tracer test.
	<ol>
		<li>Start the column experiment with a tracer test prior to the MWCNT solution experiments.</li>
		<li>Switch the 3-way valve to the tracer solution (using food color tracer at 20 mg/L) to start the experiment.</li>
		<li>Collect the outflow samples from the column at every 2 min (i.e., 4 ml/samples in each sampling tube) using the connected fraction collector as shown in Figure 1.</li>
		<li>Continue to inject the tracer solution for a 4.32 pore volume (i.e., solution passes 4.32 times of the total empty pore space in the sand packed column), which is also called phase I of the experiment.</li>
		<li>Switch the 3-way valve to flow background solution (DI water in the case of tracer experiment) for another 4.32 pore volume.</li>
	</ol>
	</li>
	<li>Preparation of MWCNT solution.
	<ol>
		<li>Make a dispersed, functionalized MWCNTs solution by placing 15 mg of functionalized MWCNTs in a 300 ml beaker containing 200 ml of aqueous solution (with desired solution chemistry i.e., pH 5 and 2 mM ionic strength in the current experimental condition) and using an ultrasonic homogenizer probe placed in the beaker (with 40% power output for 15 min). Mix the dispersed MWCNTs solution with another 800 ml of the same aqueous solution to achieve the MWCNT concentration of 15 mg/L.</li>
		<li>Perform scanning electron microscopy (SEM) image analysis of stock solution for their size and shape of the nanoparticle after functionalization.</li>
	</ol>
	</li>
	<li>MWCNT transport experiment.
	<ol>
		<li>Switch the 3-way valve to MWCNT solution to start the column experiment.</li>
		<li>Collect the outflow samples from the column at every 2 min using the connected fraction collector.</li>
		<li>Inject the MWCNT solution for a 4.32 pore volume (phase I of the experiment).</li>
		<li>Switch the 3-way valve to flow background solution for another 4.32 pore volume, which is called phase II of the experiment.</li>
		<li>Change the injection tube of background solution into DI water bottle (after stopping the pump for a moment to avoid the entrance of air from the tube) and continue the flow for another 4.32 pore volume, which is called phase III of the experiment.</li>
	</ol>
	</li>
	<li>Sample analysis.
	<ol>
		<li>Transfer all the tube samples from fraction collector into a tube rack.</li>
		<li>Prepare a UV/VIS spectrophotometer for sample analysis, i.e., find out the appropriate scanning wavelength for the quantification of the collected samples. Use 400 nm for a MWCNT solution and a 333 nm wavelength for tracer solution.</li>
		<li>Scan all the samples collected from the column during phases I, II, and III using a cuvette at 400 nm wavelength (or a different wavelength if deemed more appropriate in the previous step) and store the data.</li>
		<li>Collect the data from the spectrophotometer and plot them vs time or pore volume to obtain breakthrough curves as shown in the representative results (for example, Figure 3).</li>
		<li>Perform size analysis (hydrodynamic diameter) of inflow and outflow samples using zeta sizer and conduct the visualization studied for both inflow and outflow samples using scanning electron microscopy.</li>
	</ol>
	</li>
</ol>

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The authors declare that they have no competing financial interests.

Effect of MWCNT Functionalization
As Figure 2 confirms the stability of functionalized MWCNTs, the observed difference in eluted volume of MWCNT was due to functionalization and particularly due to the addition of carboxyl (-COOH) groups to the surface of the MWCNTs (Figures 3 and 4). In the similar functionalization process, the presence of oxygen was confirmed by X-ray photoelectron spectroscopy14. It has been fou...

With the recent development in nanotechnology that uses various types of nanoparticles to improve a number of technologies in industries such as information technology, energy, environmental science, medicine, homeland security, food safety, and transportation; a thorough understanding of the&#160;transport&#160;and&#160;retention&#160;of nanoparticles in soil and groundwater is critical for risk assessment as well as environmental applications of engineered nanoparticles1-3. Carbon nanotubes (CNTs) are one of the most produced carbon-based nanoparticles2,4. CNTs are the long and cylindrical form of graphene with a diameter typically below 100 nm and a length in the range of 100 nm to 50 &#181;m. They have unique properties, which have accelerated their use in many applications, such as electronics, optics, cosmetics, and biomedical technology (e.g., composite materials)5. With increased use, there is also an increased risk to human exposure and effect on health as well as adverse ecological consequences following CNT and other carbon based nanomaterials disposal to the environment5-8.
With no surface modifications (unfunctionalized), CNTs are extremely hydrophobic and tend to aggregate in an aqueous solution. Functionalized CNTs can, however, remain dispersed and stable in aqueous solutions and are used for biomedical purposes such as drug delivery9. Here it is essential that the CNTs remain dispersed and mobilized, so the drug can be delivered within the human body10. On the other hand, to reduce environmental risks, there is a need for studies focusing on how to immobilize the CNTs in order to avoid their entrance into aquifers and drinking water resources11. Recent studies have reported the toxic effect of CNTs on living organisms and also risks to ecosystems in terms of CNTs entering and accumulating in the food chains, since CNTs are hard to biodegrade5,8. Even with barrier systems in landfills containing CNTs, it may be possible for CNTs to pass through the barriers. In such cases CNTs could enter into groundwater reservoirs and surface water bodies. As CNT disposal regulations are not well defined and transport mechanisms are poorly understood, an improved understanding of mobility of CNTs is necessary to formulate and design appropriate disposal systems12. Therefore, it is important to study and understand the fate and transport of CNTs in porous media and the effect of physical and chemical factors commonly present in the subsurface environment on surface modified CNT retention.
A number of research has been carried out about the effect of collector grain size13-15, flow rate16, and surface properties of the grains17 on transport of nanoparticles in porous media. However, systematic investigations on the effect of solution chemistry (such as pH and ionic strength) on possible deposition onto the collector surfaces are still limited18-20. Additionally, the combined impact of physical factors, solution chemistry of the medium, and surface properties of carbon nanotubes is not well understood and vary in different literature. In this study, a preparation method for surface modification of MWCNTs will be demonstrated along with a systematic laboratory-scale column packed with acid-cleaned quartz sand will be used to investigate the transport, retention and remobilization of surface-modified CNTs in saturated porous media.

<table border="0" cellpadding="0" cellspacing="0" width="750">
	<tbody>
		<tr height="43">
			<td height="43" style="height:43px;width:183px;">Name of Material/ Equipments</td>
			<td style="width:228px;">Company</td>
			<td style="width:169px;">Catalog Number</td>
			<td style="width:171px;">Comments/Description</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:183px;">MWCNT</td>
			<td style="width:228px;">Cheap Tubes Inc., USA</td>
			<td style="width:169px;">sku-03040304</td>
			<td style="width:171px;">Purchased as semi-functionlized powder</td>
		</tr>
		<tr height="148">
			<td height="148" style="height:148px;width:183px;">Quartz sand</td>
			<td style="width:228px;">Sibelco Nordic, Baskarp, Sweden</td>
			<td style="width:169px;">B44</td>
			<td style="width:171px;">Purchased with more than 91% silica sand</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:183px;">H2SO4</td>
			<td style="width:228px;">VWR</td>
			<td style="width:169px;">1.01833.2500</td>
			<td style="width:171px;">95-97% purity</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:183px;">HNO3</td>
			<td style="width:228px;">VWR</td>
			<td style="width:169px;">1.00441.1000</td>
			<td style="width:171px;">70% purity</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:183px;">HCl</td>
			<td style="width:228px;">VWR</td>
			<td style="width:169px;">1.00317.2500</td>
			<td style="width:171px;">37-38% purity</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:183px;">H2O2</td>
			<td style="width:228px;">VWR</td>
			<td style="width:169px;">23615.248</td>
			<td style="width:171px;">30% purity</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:183px;">NaCl</td>
			<td style="width:228px;">VWR</td>
			<td style="width:169px;">1.06404.0500</td>
			<td style="width:171px;">99.5% purity</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:183px;">NaOH</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:169px;">S8045-500G</td>
			<td style="width:171px;">99.99% pur pellets&#160;</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:183px;">Ultrasonic Homogenizer</td>
			<td style="width:228px;">Biologics Inc. Manassas, Virginia</td>
			<td style="width:169px;">Model 3000, 0-127-0002</td>
			<td style="width:171px;">Operated for fix time interval</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:183px;">Sonicator (bath)</td>
			<td style="width:228px;">Kerry Ultrasonic Ltd</td>
			<td style="width:169px;">1808</td>
			<td style="width:171px;">Common bath sonicator</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:183px;">Peristaltic pump</td>
			<td style="width:228px;">Ismantec, Glattbrugg, Switzerland</td>
			<td style="width:169px;">ISM931</td>
			<td style="width:171px;">Work with tygon tubing in the pump</td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:183px;">Spectrophotometer</td>
			<td style="width:228px;">Hach Lange</td>
			<td style="width:169px;">DR500, LPV408.99.0001</td>
			<td style="width:171px;">Operate with manual cuvette as well as automated sampling</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:183px;">pH meter</td>
			<td style="width:228px;">Metrohm</td>
			<td style="width:169px;">781</td>
			<td style="width:171px;">pH analysis</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:183px;">Glass column</td>
			<td style="width:228px;">Chromaflex</td>
			<td style="width:169px;">420830-1510</td>
			<td style="width:171px;">Column with adjustable cap</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:183px;">Fraction collector</td>
			<td style="width:228px;">Spectrum Labs Europe</td>
			<td style="width:169px;">CF-2, 124846</td>
			<td style="width:171px;">Fixed at regular interval of time</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:183px;">Fraction collector tubes</td>
			<td style="width:228px;">VWR</td>
			<td style="width:169px;">212-9599</td>
			<td style="width:171px;">6 ml volume glass tube</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:183px;">Hot plate stir</td>
			<td style="width:228px;">Thermo Scientific</td>
			<td style="width:169px;">SP131320-33</td>
			<td style="width:171px;">Adjustable tempurature</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:183px;">Oven</td>
			<td style="width:228px;">Elektro Helios</td>
			<td style="width:169px;">259</td>
			<td style="width:171px;">For oven dry of sand</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:183px;">Balance</td>
			<td style="width:228px;">Mettler Toledo</td>
			<td style="width:169px;">AE 160</td>
			<td style="width:171px;">For accurate weight</td>
		</tr>
	</tbody>
</table>

transport of surface-modified carbon nanotubes through a soil column

Carbon nanotubes (CNTs) are widely manufactured nanoparticles, which are being utilized in a number of consumer products, such as sporting goods, electronics and biomedical applications. Due to their accelerating production and use, CNTs constitute a potential environmental risk if they are released to soil and groundwater systems. It is therefore essential to improve the current understanding of environmental fate and transport of CNTs. The transport and retention of CNTs in both natural and artificial media have been reported in literature, but the findings widely vary and are thus not conclusive. There are a number of physical and chemical parameters responsible for variation in retention and transport. In this study, a complete procedure of selected multiwalled carbon nanotubes (MWCNTs) is presented starting from their surface modification to a complete set of laboratory column experiments at critical physical and chemical scenarios. Results indicate that the stability of the commercially available MWCNTs are critical with their attached surface functional group which can also influence the transport and retention of MWCNT through the surrounding medium.

Effect of MWCNT Functionalization
The functionalized and dispersed MWCNT solution was sealed in the beaker to allow the solution to reach equilibrium. There was neither sedimentation nor aggregation observed in the stock solution after sonication, as the hydrodynamic diameter of MWCNT (1,619 &#177; 262 nm) in the solution remained the same for six months of sonication (Figure 2). To investigate the effect of functionalization of MWCNTs on their mobility, two s...

Watch this Scientific Journal Video about Transport of Surface-modified Carbon Nanotubes through a Soil Column at JoVE.com

Transport of Surface-modified Carbon Nanotubes through a Soil Column

Surface properties of a nanoparticle are important for their interaction with the surrounding medium. Therefore the surface modification of carbon nanotubes can be critical for their transport and retention through porous media. Here, lab scale column experiments are used to understand the possible transport and retention of these nanoparticles.

Carbon nanotubes (CNTs) are widely manufactured nanoparticles, which are being utilized in a number of consumer products, such as sporting goods, ...

transport-of-surface-modified-carbon-nanotubes-through-a-soil-column

Research

JoVE Journal

Chemistry

9.4K Views.  Nalanda University. Surface properties of a nanoparticle are important for their interaction with the surrounding medium. Therefore the surface modification of carbon nanotubes can be critical for their transport and retention through porous media. Here, lab scale column experiments are used to understand the possible transport and retention of these nanoparticles. 

Video: Transport of Surface-modified Carbon Nanotubes through a Soil Column

Dependence of Laser-induced Breakdown Spectroscopy Results on Pulse Energies and Timing Parameters Using Soil Simulants

The dependence of some LIBS detection capabilities on lower pulse energies (&lt;100 mJ) and timing parameters were examined using synthetic silicate samples. These samples were used as simulants for soil and contained minor and trace elements commonly found in soil at a wide range of concentrations. For this study, over 100 calibration curves were prepared using different pulse energies and timing parameters; detection limits and sensitivities were determined from the calibration curves. Plasma temperatures were also measured using Boltzmann plots for the various energies and the timing parameters tested. The electron density of the plasma was calculated using the full-width half maximum (FWHM) of the hydrogen line at 656.5 nm over the energies tested. Overall, the results indicate that the use of lower pulse energies and non-gated detection do not seriously compromise the analytical results. These results are very relevant to the design of field- and person-portable LIBS instruments.

LIBS detection capabilities on soil simulants were tested using a range of pulse energies and timing parameters. Calibration curves were used to determine detection limits and sensitivities for different parameters. Generally, the results showed that there was not a significant reduction in detection capabilities using lower pulse energies and non-gated detection.

The  dependence of some LIBS detection capabilities on lower pulse energies (&lt;100  mJ) and timing parameters were examined using synthetic silicate ...

An Inverse Analysis Approach to the Characterization of Chemical Transport in Paints

The ability to directly characterize chemical transport and interactions that occur within a material (i.e., subsurface dynamics) is a vital component in understanding contaminant mass transport and the ability to decontaminate materials. If a material is contaminated, over time, the transport of highly toxic chemicals (such as chemical warfare agent species) out of the material can result in vapor exposure or transfer to the skin, which can result in percutaneous exposure to personnel who interact with the material. Due to the high toxicity of chemical warfare agents, the release of trace chemical quantities is of significant concern. Mapping subsurface concentration distribution and transport characteristics of absorbed agents enables exposure hazards to be assessed in untested conditions. Furthermore, these tools can be used to characterize subsurface reaction dynamics to ultimately design improved decontaminants or decontamination procedures. To achieve this goal, an inverse analysis mass transport modeling approach was developed that utilizes time-resolved mass spectroscopy measurements of vapor emission from contaminated paint coatings as the input parameter for calculation of subsurface concentration profiles. Details are provided on sample preparation, including contaminant and material handling, the application of mass spectrometry for the measurement of emitted contaminant vapor, and the implementation of inverse analysis using a physics-based diffusion model to determine transport properties of live chemical warfare agents including distilled mustard (HD) and the nerve agent VX.

In this paper, a procedure for quantifying the mass transport parameters of chemicals in various materials is presented. This process involves employing an inverse-analysis based diffusion model to vapor emission profiles recorded by real-time, mass spectrometry in high vacuum.

The ability to directly characterize chemical transport and interactions that occur within a material (i.e., subsurface dynamics) is a vital component in ...

Tuning a Parallel Segmented Flow Column and Enabling Multiplexed Detection

Active flow technology (AFT) is new form of column technology that was designed to overcome flow heterogeneity to increase separation performance in terms of efficiency and sensitivity and to enable multiplexed detection. This form of AFT uses a parallel segmented flow (PSF) column. A PSF column outlet end-fitting consists of 2 or 4 ports, which can be multiplexed to connect up to 4 detectors. The PSF column not only allows a platform for multiplexed detection but also the combination of both destructive and non-destructive detectors, without additional dead volume tubing, simultaneously. The amount of flow through each port can also be adjusted through pressure management to suit the requirements of a specific detector(s). To achieve multiplexed detection using a PSF column there are a number of parameters which can be controlled to ensure optimal separation performance and quality of results; that is tube dimensions for each port, choice of port for each type of detector and flow adjustment. This protocol is intended to show how to use and tune a PSF column functioning in a multiplexed mode of detection.

Here, we present a protocol for the operation and tuning of parallel segmented flow chromatography columns to enable multiplexed detection.

Active flow technology (AFT) is new form of column technology that was designed to overcome flow heterogeneity to increase separation performance in terms ...

Curtain Flow Column: Optimization of Efficiency and Sensitivity

Active Flow Technology (AFT) is a form of column technology that increases the separation performance of a HPLC column through the use of a specially purpose built multiport end-fitting(s). Curtain Flow (CF) columns belong to the AFT suite of columns, specifically the CF column is designed so that the sample is injected into the radial central region of the bed and a curtain flow of mobile phase surrounding the injection of solute prevents the radial dispersion of the sample to the wall. The column functions as an 'infinite diameter' column. The purpose of the design is to overcome the radial heterogeneity of the column bed, and at the same time maximize the sample load into the radial central region of the column bed, which serves to increase detection sensitivity. The protocol described herein outlines the system and CF column set up and the tuning process for an optimized infinite diameter 'virtual' column.

Here, we present a protocol for the operation and optimization of Active Flow Technology (AFT) column in Curtain flow (CF) mode for enhanced separation performance.

Active Flow Technology (AFT) is a form of column technology that increases the separation performance of a HPLC column through the use of a specially ...

Facile Preparation of Internally Self-assembled Lipid Particles Stabilized by Carbon Nanotubes

We present a facile method to prepare nanostructured lipid particles stabilized by carbon nanotubes (CNTs). Single-walled (pristine) and multi-walled (functionalized) CNTs are used as stabilizers to produce Pickering type oil-in-water (O/W) emulsions. Lipids namely, Dimodan U and Phytantriol are used as emulsifiers, which in excess water self-assemble into the bicontinuous cubic Pn3m phase. This highly viscous phase is fragmented into smaller particles using a probe ultrasonicator in presence of conventional surfactant stabilizers or CNTs as done here. Initially, the CNTs (powder form) are dispersed in water followed by further ultrasonication with the molten lipid to form the final emulsion. During this process the CNTs get coated with lipid molecules, which in turn are presumed to surround the lipid droplets to form a particulate emulsion that is stable for months. The average size of CNT-stabilized nanostructured lipid particles is in the submicron range, which compares well with the particles stabilized using conventional surfactants. Small angle X-ray scattering data confirms the retention of the original Pn3m cubic phase in the CNT-stabilized lipid dispersions as compared to the pure lipid phase (bulk state). Blue shift and lowering of the intensities in characteristic G and G&#39; bands of CNTs observed in Raman spectroscopy characterize the interaction between CNT surface and lipid molecules. These results suggest that the interactions between the CNTs and lipids are responsible for their mutual stabilization in aqueous solutions. As the concentrations of CNTs employed for stabilization are very low and lipid molecules are able to functionalize the CNTs, the toxicity of CNTs is expected to be insignificant while their biocompatibility is greatly enhanced. Hence the present approach finds a great potential in various biomedical applications, for instance, for developing hybrid nanocarrier systems for the delivery of multiple functional molecules as in combination therapy or polytherapy.

We report on a smart application of carbon nanotubes for kinetic stabilization of lipid particles that contain self-assembled nanostructures in their cores. The preparation of lipid particles requires rather low concentrations of carbon nanotubes permitting their use in biomedical applications such as drug delivery.

We present a facile method to prepare nanostructured lipid particles stabilized by carbon nanotubes (CNTs). Single-walled (pristine) and multi-walled ...

Preparation of Carbon Nanosheets at Room Temperature

Amphiphilic molecules equipped with a reactive, carbon-rich "oligoyne" segment consisting of conjugated carbon-carbon triple bonds self-assemble into defined aggregates in aqueous media and at the air-water interface. In the aggregated state, the oligoynes can then be carbonized under mild conditions while preserving the morphology and the embedded chemical functionalization. This novel approach provides direct access to functionalized carbon nanomaterials. In this article, we present a synthetic approach that allows us to prepare hexayne carboxylate amphiphiles as carbon-rich siblings of typical fatty acid esters through a series of repeated bromination and Negishi-type cross-coupling reactions. The obtained compounds are designed to self-assemble into monolayers at the air-water interface, and we show how this can be achieved in a Langmuir trough. Thus, compression of the molecules at the air-water interface triggers the film formation and leads to a densely packed layer of the molecules. The complete carbonization of the films at the air-water interface is then accomplished by cross-linking of the hexayne layer at room temperature, using UV irradiation as a mild external stimulus. The changes in the layer during this process can be monitored with the help of infrared reflection-absorption spectroscopy and Brewster angle microscopy. Moreover, a transfer of the carbonized films onto solid substrates by the Langmuir-Blodgett technique has enabled us to prove that they were carbon nanosheets with lateral dimensions on the order of centimeters.

We present the synthesis of an amphiphilic hexayne and its use in the preparation of carbon nanosheets at the air-water interface from a self-assembled monolayer of these reactive, carbon-rich molecular precursors.

Amphiphilic molecules equipped with a reactive, carbon-rich "oligoyne" segment consisting of conjugated carbon-carbon triple bonds self-assemble into ...

Functionalization of Single-walled Carbon Nanotubes with Thermo-reversible Block Copolymers and Characterization by Small-angle Neutron Scattering

We demonstrate a protocol for single-walled carbon nanotube functionalization using thermo-sensitive PEO-PPO-PEO triblock copolymers in an aqueous solution. In a carbon nanotube/PEO105-PPO70-PEO105 (poloxamer 407) aqueous solution, the amphiphilic poloxamer 407 adsorbs onto the carbon nanotube surfaces and self-assembles into continuous layers, driven by intermolecular interactions between constituent molecules. The addition of 5-methylsalicylic acid changes the self-assembled structure from spherical-micellar to a cylindrical morphology. The fabricated poloxamer 407/carbon nanotube hybrid particles exhibit thermo-responsive structural features so that the density and thickness of poloxamer 407 layers are also reversibly controllable by varying temperature. The detailed structural properties of the poloxamer 407/carbon nanotube particles in suspension can be characterized by small-angle neutron scattering experiments and model fit analyses. The distinct curve shapes of the scattering intensities depending on temperature control or addition of aromatic additives are well described by a modified core-shell cylinder model consisting of a carbon nanotube core cylinder, a hydrophobic shell, and a hydrated polymer layer. This method can provide a simple but efficient way for the fabrication and in-situ characterization of carbon nanotube-based nano particles with a structure-tunable encapsulation.

A method for the functionalization of carbon nanotubes with structure-tunable polymeric encapsulation layers and structural characterization using small-angle neutron scattering is presented.

We demonstrate a protocol for single-walled carbon nanotube functionalization using thermo-sensitive PEO-PPO-PEO triblock copolymers in an aqueous ...

Characterizing Electron Transport through Living Biofilms

Here we demonstrate the method of electrochemical gating used to characterize electrical conductivity of electrode-grown microbial biofilms under physiologically relevant conditions.1 These measurements are performed on living biofilms in aqueous medium using source and drain electrodes patterned on a glass surface in a specialized configuration referred to as an interdigitated electrode (IDA) array. A biofilm is grown that extends across the gap connecting the source and drain. Potentials are applied to the electrodes (ES and ED) generating a source-drain current (ISD) through the biofilm between the electrodes. The dependency of electrical conductivity on gate potential (the average of the source and drain potentials, EG = [ED + ES]/2) is determined by systematically changing the gate potential and measuring the resulting source-drain current. The dependency of conductivity on gate potential provides mechanistic information about the extracellular electron transport process underlying the electrical conductivity of the specific biofilm under investigation. The electrochemical gating measurement method described here is based directly on that used by M. S. Wrighton2,3 and colleagues and R. W. Murray4,5,6 and colleagues in the 1980&#39;s to investigate thin film conductive polymers.

A protocol for measuring electrical conductivity of living microbial biofilms under physiologically relevant conditions is presented.

Here we demonstrate the method of electrochemical gating used to characterize electrical conductivity of electrode-grown microbial biofilms under ...

Grafting Multiwalled Carbon Nanotubes with Polystyrene to Enable Self-Assembly and Anisotropic Patchiness

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a free-radical polymerization strategy to enable the modulation of the nanotube surface properties and produce supramolecular self-assembly of the nanostructures. First, a selective hydroxylation of the pristine nanotubes through a biphasic catalytically mediated oxidation reaction creates superficially distributed reactive sites at the sidewalls. The latter reactive sites are subsequently modified with methacrylic moieties using a silylated methacrylic precursor to create polymerizable sites. Those polymerizable groups can address further polymerization of styrene to produce a hybrid nanomaterial containing PS chains grafted to the nanotube sidewalls. The polymer-graft content, amount of silylated methacrylic moieties introduced and hydroxylation modification of the nanotubes are identified and quantified by Thermogravimetric Analysis (TGA). The presence of reactive functional groups hydroxyl and silylated methacrylate are confirmed by Fourier Transform Infrared Spectroscopy (FT-IR). Polystyrene-grafted carbon nanotube solutions in tetrahydrofuran (THF) provide wall-to-wall collinearly self-assembled nanotubes when cast samples are analyzed by transmission electron microscopy (TEM). Those self-assemblies are not obtained when suitable blanks are similarly cast from analogous solutions containing non-grafted counterparts. Therefore, this method enables the modification of the nanotube anisotropic patchiness at the sidewalls which results into spontaneous auto-organization at the nanoscale.

A procedure for the synthesis of polystyrene-grafted multiwalled carbon nanotubes using successive chemical modification steps to selectively introduce the polymer chains to the sidewalls and their self-assembly via anisotropic patchiness is presented.

We demonstrate a straightforward protocol to graft pristine multiwalled carbon nanotubes (MWCNTs) with polystyrene (PS) chains at the sidewalls through a ...

Electrochemical Impedance Spectroscopy as a Tool for Electrochemical Rate Constant Estimation

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). In the case of fast reversible electrochemical processes, current is predominantly affected by the rate of diffusion, which is the slowest and limiting stage. EIS is a powerful technique that allows separate analysis of stages of charge transfer that have different AC frequency response. The capability of the method was used to extract the value of charge transfer resistance, which characterizes the rate of charge exchange on the electrode-solution interface. The application of this technique is broad, from biochemistry up to organic electronics. In this work, we are presenting the method of analysis of organic compounds for optoelectronic applications.

Electrochemical impedance spectroscopy (EIS) of species that undergo reversible oxidation or reduction in solution was used for determination of rate constants of oxidation or reduction.

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). ...