Capacitive deionization on-chip as a method for microfluidic sample preparation

Nanoscale Adsorption, Assembly, and Deionization Dynamics Recorded by Optical Fiber Sensors

Capacitive deionization in environmental decontamination has been widely studied and now requires intensive development to support large-scale deployment. Porous nanomaterials have been demonstrated to play pivotal roles in determining decontamination efficiency and manipulating nanomaterials to form functional architecture has been one of the most exciting challenges. Such nanostructure engineering and environmental applications highlight the importance of observing, recording, and studying basically electrical-assisted charge/ion/particle adsorption and assembly behaviors localized at charged interfaces. In addition, it is generally desirable to increase the sorption capacity and reduce the energy cost, which increase the requirement for recording collective dynamic and performance properties that stem from nanoscale deionization dynamics. Herein, we show how a single optical fiber can serve as an in situ and multifunctional opto-electrochemical platform for addressing these issues. The surface plasmon resonance signals allow the in situ spectral observation of nanoscale dynamic behaviors at the electrode-electrolyte interface. The parallel and complementary optical-electrical sensing signals enable the single probe but multifunctional recording of electrokinetic phenomena and electrosorption processes. As a proof of concept, we experimentally decipher the interfacial adsorption and assembly behaviors of anisotropic metal-organic framework nanoparticles at a charged surface and decouple the interfacial capacitive deionization within an assembled metal-organic framework nanocoating by visualizing its dynamic and energy consumption properties, including the adsorptive capacity, removal efficiency, kinetic properties, charge, specific energy consumption, and charge efficiency. This simple "all-in-fiber" opto-electrochemical platform offers intriguing opportunities to provide in situ and multidimensional insights into interfacial adsorption, assembly, and deionization dynamics information, which may contribute to understanding the underlying assembly rules and the exploring structure-deionization performance correlations for the development of tailor-made nanohybrid electrode coatings for deionization applications.

Diffusiophoretic exclusion of colloidal particles for continuous water purification

It has been observed that colloidal particles are anomalously repelled from the interface of nanoporous materials and water by up to hundreds of micrometers even if there is no additional external field present. Recently, the physical origin of this anomalous repulsion has turned out to be diffusiophoretic migration triggered by an ion exchange process through the interface. Since the repulsive force is induced by a salt gradient only, the phenomenon can be applied to a microscale water purification platform without the need for any external power sources. In this work, we suggest a micro/nanofluidic device for continuous water purification utilizing long-range diffusiophoretic migration around ion exchangeable surfaces. An ion concentration boundary layer was characterized by the Sherwood number (Sh) which is a key dimensionless number to describe the purification process. Depending on Sh, we have theoretically and experimentally demonstrated that long-range diffusiophoretic exclusion can be used for continuous water purification. Finally, our platform can be used as a highly energy-efficient and portable water treatment option for operations such as purification, disinfection, water softening, etc.

Gravity-assisted distillation on a chip: Fabrication, characterization, and applications

Distillation is widely used in industrial processes and laboratories for sample pre-treatment. The conventional apparatus of flash distillation is composed of heating source, distilling flask, condenser, and receiving flask. As disadvantages, this method shows manual and laborious analyses with high consumption of chemicals. In this paper, all these limitations were addressed by developing a fully integrated microscale distiller in agreement with the apparatus of conventional flash distillation. The main challenge facing the distillation miniaturization is the phase separation since surface forces take over from the gravity in microscale channels. Otherwise, our chip had ability to perform gravity-assisted distillations because of the somewhat large dimensions of the distillation chamber (roughly 900 μL) that was obtained by 3D-printing. The functional distillation units were integrated into a single device composed of polydimethylsiloxane (PDMS). Its fabrication was cost-effective and simple by avoiding the use of cleanroom and bonding step. In addition to user-friendly analysis and low consumption of chemicals, the method requires cost-effective instrumentation, namely, voltage supply and analytical balance. Furthermore, the so called distillation-on-a-chip (DOC) eliminates the use of membranes and electrodes (usually employed in microfluidic desalinations reported in the literature), thus avoiding drawbacks such as liquid leakage, membrane fouling, and electrode passivation. The DOC promoted desalinations at harsh salinity (NaCl 600.0 mmol L^-1) with high throughput and salt removal efficiency (roughly 99%). Besides, the method was used for determination of ethanol in alcoholic beverages to show the potential of the approach toward quantitative purposes.

On-line pre-treatment, separation, and nanoelectrospray mass spectrometric determinations for pesticide metabolites and peptides based on a modular microfluidic platform

In order to address time-consuming sample pre-treatment and separation prior to mass spectrometry (MS) identifications, highly integrated chips were developed, but damage to any functional unit in these chips would result in complete replacement. Herein, we propose a modular microfluidic platform comprising pre-treatment, liquid chromatography (LC) separation and nanoelectrospray ionization (nESI) chips for on-line enrichment, separation and nESI MS detection of pesticide metabolites and peptides. The pre-treatment chip is applicable in enriching pyridalyl and its metabolites, and it achieves optimal desalination efficiency, 98.5%, for polymerase chain reaction products. Additionally, the LC separation chip was fully characterised, and it demonstrated satisfactory separation efficiency, quantification ability and pressure durability. Finally, the modular microfluidic platform was used to identify the peptides in trypsin-digested casein. Four additional peptides were identified, indicating an improvement in detection ability compared with using off-line zip tips coupled with MS investigations. Because the proposed modular platform can significantly reduce manual work, it would be a potential tool to achieve high throughput and automatic MS identifications with low sample consumptions.

A microfluidic platform, composed of enrichment, separation and nanoelectrospray ionization modulations was developed to on-line-investigate pesticide metabolites and peptides.

The effect of surface transport on water desalination by porous electrodes undergoing capacitive charging

Capacitive deionization (CDI) is a technology in which water is desalinated by ion electrosorption into the electric double layers (EDLs) of charging porous electrodes. In recent years significant advances have been made in modeling the charge and salt dynamics in a CDI cell, but the possible effect of surface transport within diffuse EDLs on these dynamics has not been investigated. We here present theory which includes surface transport in describing the dynamics of a charging CDI cell. Through our numerical solution to the presented models, the possible effect of surface transport on the CDI process is elucidated. While at some model conditions surface transport enhances the rate of CDI cell charging, counter-intuitively this additional transport pathway is found to slow down cell charging at other model conditions.

Capacitive deionization in organic solutions: case study using propylene carbonate

We present a study of the performance of capacitive deionization (CDI) when applied to electrosorption in an organic solvent, finding enhanced cell charging voltages and improved salt sorption over electrosoprtion in aqueous solutions.

Microfluidic desalination techniques and their potential applications

In this review we discuss recent developments in the emerging research field of miniaturized desalination. Traditionally desalination is performed to convert salt water into potable water and research is focused on improving performance of large-scale desalination plants. Microfluidic desalination offers several new opportunities in comparison to macro-scale desalination, such as providing a platform to increase fundamental knowledge of ion transport on the nano- and microfluidic scale and new microfluidic sample preparation methods. This approach has also lead to the development of new desalination techniques, based on micro/nanofluidic ion-transport phenomena, which are potential candidates for up-scaling to (portable) drinking water devices. This review assesses microfluidic desalination techniques on their applications and is meant to contribute to further implementation of microfluidic desalination techniques in the lab-on-chip community.