Ion-selective asymmetric carbon electrodes for enhanced capacitive deionization

With the development of capacitive deionization technology, charge efficiency and electrosorption capacity have become some of the biggest technical bottlenecks. Asymmetric activated carbon electrodes with ion-selective functional groups inspired by membrane capacitive deionization were developed to conquer these issues. The deionization capacity increased from 11.0 mg g⁻¹ to 23.2 mg g⁻¹, and the charge efficiency increased from 0.54 to 0.84, due to ion-selective functional groups minimizing the co-ion effect. The charge efficiency and electrosorption capacity resulting from better wettability of these electrodes are effectively enhanced by grafting ion-selective functional groups, which are propitious to ion movement. In addition, asymmetric deionization capacitors show better cycling stability and higher desalination rates. These experimental results have demonstrated that the modification of the ion-selective (oxygen-containing) functional groups on the surfaces of activated carbon could greatly minimize the co-ion effects and increase the salt removal from the solution. These results have indicated that the ion-selective asymmetric carbon electrodes can promote well the development of deionization capacitors for practical desalination.

Ion-selective asymmetric carbon electrodes are developed for capacitive deionization to minimize the co-ion effects.     

Novel mesoporous Co3O4–Sb2O3–SnO2 active material in high-performance capacitive deionization

Capacitive deionization (CDI), as an emerging eco-friendly electrochemical brackish water deionization technology, has widely benefited from carbon/metal oxide composite electrodes. However, this technique still requires further development of the electrode materials to tackle the ion removal capacity/rate issues. In the present work, we introduce a novel active carbon (AC)/Co₃O₄–Sb₂O₃–SnO₂ active material for hybrid electrode capacitive deionization (HECDI) systems. The structure and morphology of the developed electrodes were determined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Brunauer–Emmett–Teller (BET)/Barrett–Joyner–Halenda (BJH) techniques, as well as Fourier-transform infrared (FT-IR) spectroscopy. The electrochemical properties were also investigated by cyclic voltammetry (CV) and impedance spectroscopy (EIS). The CDI active materials AC/Co₃O₄ and AC/Co₃O₄–Sb₂O₃–SnO₂ showed a high specific capacity of 96 and 124 F g⁻¹ at the scan rate of 10 mV s⁻¹, respectively. In addition, the newly-developed electrode AC/Co₃O₄–Sb₂O₃–SnO₂ showed high capacity retention of 97.2% after 2000 cycles at 100 mV s⁻¹. Moreover, the electrode displayed excellent CDI performance with an ion removal capacity of 52 mg g⁻¹ at the applied voltage of 1.6 V and in a solution of potable water with initial electrical conductivity of 950 μs cm⁻¹. The electrode displayed a high ion removal rate of 7.1 mg g⁻¹ min⁻¹ with an excellent desalination–regeneration capability while retaining about 99.5% of its ion removal capacity even after 100 CDI cycles.

Capacitive deionization (CDI), as an emerging eco-friendly electrochemical brackish water deionization technology, has widely benefited from carbon/metal oxide composite electrodes.     

Properties of amorphous iron phosphate in pseudocapacitive sodium ion removal for water desalination

Capacitive deionization (CDI) is an energy saving and environmentally friendly technology for water desalination. However, classical CDI is challenged by a low salt removal capacity. To improve the desalination capacity, electrode materials utilizing the battery mechanism for salt ion removal have emerged as a new direction more recently. In this work, we report a study of amorphous iron phosphate (FePO₄) as a promising electrode material for pseudocapacitive sodium ion removal. Sodium ions can be effectively, reversibly intercalated and de-intercalated upon its electrochemical reduction and oxidation, with an excellent sodium ion capacity under half-cell testing conditions. By assembling a hybrid CDI (HCDI) system utilizing the FePO₄ electrode for pseudocapacitive sodium ion removal and active carbon electrode for capacitive chloride ion removal, the cell exhibited a high salt removal capacity and good reversibility and durability, which was attributed to the advantageous features of amorphous FePO₄. The HCDI system achieved a high deionization capacity (82 mg g⁻¹) in 10 mM NaCl, a fast deionization rate (0.046 mg g⁻¹ s⁻¹), and good stability and cyclability.

Amorphous iron phosphate (FePO₄) exhibits excellent capacity, reversibility and stability in pseudocapacitive sodium ion removal for water desalination.     

Chitin derived biochar for efficient capacitive deionization performance

The selection and preparation of an electrode material is the core of capacitive deionization. In order to obtain a material with a good deionization properties, we have designed an environmentally-friendly and simple way of preparing biochar. In this work, biochar was prepared by a thermal-deposition method and after chemical modification it was characterized with a scanning electron microscope (SEM), Fourier transform infrared spectrophotometer (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The specific surface area of biochar modified by KOH is as high as 833.76 m² g⁻¹, but the specific surface area of the unmodified electrode material is only 126.43 m² g⁻¹. The electrochemical analysis (CV and EIS) of the biochar indicates that HC-800 has a lower charge transfer resistance and a higher specific capacitance, where the specific capacity of HC-800 reaches 120 F g⁻¹. A CDI property analysis of HC-800 shows a better electrosorption capacity of 11.52 mg g⁻¹ and better regeneration and cycling stability than CS-800. The desalination amount remains 87.23% after several cycles.

Schematic illustration of the fabrication of chitin derived biochar and KOH-activated chitin derived biochar electrodes for capacitive deionization.     

Three-dimensional honeycomb-like porous carbon derived from corncob for the removal of heavy metals from water by capacitive deionization

In this study, porous carbon (3DHPC) with a 3D honeycomb-like structure was synthesized from waste biomass corncob via hydrothermal carbonization coupled with KOH activation and investigated as a capacitive deionization (CDI) electrode material. The obtained 3DHPC possesses a hierarchal macroporous and mesoporous structure, and a large accessible specific surface area (952 m² g⁻¹). Electrochemical tests showed that the 3DHPC electrode exhibited a specific capacitance of 452 F g⁻¹ and good electric conductivity. Moreover, the feasibility of electrosorptive removal of chromium(vi) from an aqueous solution using the 3DHPC electrode was demonstrated. When 1.0 V was applied to a solution containing 30 mg L⁻¹ chromium(vi), the 3DHPC electrode exhibited a higher removal efficiency of 91.58% compared with that in the open circuit condition. This enhanced adsorption results from the improved affinity between chromium(vi) and the electrode under electrochemical assistance involving a non-faradic process. Consequently, the 3DHPC electrode with typical double-layer capacitor behavior is demonstrated to be a favorable electrode material for capacitive deionization.

A porous carbon electrode with a 3D honeycomb-like structure demonstrates a high removal efficiency for the removal of chromium(vi) from water.     

Chitosan-based activated carbon as economic and efficient sustainable material for capacitive deionization of low salinity water

Capacitive deionization (CDI) is a novel low-energy green desalination technology that has attracted much attention in recent years, especially for the desalination of low salinity water. One of the key issues in CDI is the electrode materials, and many efforts have been devoted to developing materials with high specific surface areas, appropriate pore distributions, and good electronic conductivity, in order to obtain a high salt adsorption capacity. In this study, chitosan was selected as a precursor for the preparation of high-performance chitosan-based activated carbon (CTS-AC) for use in CDI electrodes via pyrolysis and KOH activation. The results show that CTS-AC800 (activated at 800 °C) has the largest BET specific surface area (2727 m² g⁻¹), and exhibits an appropriate pore size distribution (<10 nm), nitrogen doping (2.0%) and good electronic conductivity (2.09 S cm⁻¹). The CDI performance results show that the CTS-AC800 electrode has a saturated salt adsorption capacity of 14.12 mg g⁻¹ in a 500 mg L⁻¹ NaCl solution and retains 95% capacity after 150 adsorption–desorption cycles. Thus, chitosan is a promising, sustainable precursor for CDI electrode materials.

Chitosan was selected as a carbonaceous precursor to prepare high-performance chitosan-based activated carbon (CTS-AC) for CDI electrode.     

Nitrogen-doped graphene–TiOxNy nanocomposite electrode for highly efficient capacitive deionization

In this work, the first-ever reported nanocomposite electrode of nitrogen-doped graphene–titanium oxynitride (NG–TiO_xN_y) for capacitive deionization (CDI) was synthesized via hydrothermal reaction and a high-temperature nitridation process. The physiochemical characterizations revealed that the nitrogen was doped in the graphene structure mainly in the form of graphitic nitrogen and the TiO_xN_y was successfully formed via TiO₂ nitridation process. The layered NG nanosheets facilitated the diffusion of ions in saline water and formed electrical double layer on the surface of the electrode material, while the presence of TiO_xN_y enhanced the electrochemical performance by increasing surface area and generating surface vacancies via nitridation. The CDI cell employed NG–TiO_xN_y electrode delivered a breakthrough salt adsorption capacity of 26.1 mg g⁻¹ in 500 mg L⁻¹ saline water, and retained over 90% of its initial salt removal efficacy after 12 regeneration cycles. Such high CDI performance exhibits the promising application of NG–TiO_xN_y as a novel CDI electrode candidate.

A nanocomposite electrode of nitrogen-doped graphene and titanium oxynitride is applied as an effective and efficient electrode to deliver outstanding salt adsorption capacity in a flow-by capacitive deionization (CDI) cell.     

Low voltage operation of a silver/silver chloride battery with high desalination capacity in seawater

Technologies for the effective and energy efficient removal of salt from saline media for advanced water remediation are in high demand. Capacitive deionization using carbon electrodes is limited to highly diluted salt water. Our work demonstrates the high desalination performance of the silver/silver chloride conversion reaction by a chloride ion rocking-chair desalination mechanism. Silver nanoparticles are used as positive electrodes while their chlorination into AgCl particles produces the negative electrode in such a combination that enables a very low cell voltage of only Δ200 mV. We used a chloride-ion desalination cell with two flow channels separated by a polymeric cation exchange membrane. The optimized electrode paring between Ag and AgCl achieves a low energy consumption of 2.5 kT per ion when performing treatment with highly saline feed (600 mM NaCl). The cell affords a stable desalination capacity of 115 mg g⁻¹ at a charge efficiency of 98%. This performance aligns with a charge capacity of 110 mA h g⁻¹.

The silver/silver chloride conversion reaction allows for a high desalination capacity of saline media with high molar strength.     

Investigation of electrolytic flocculation for microalga Scenedesmus sp. using aluminum and graphite electrodes

Electrolytic flocculation using non-sacrificial electrodes with flocculants added was studied on harvesting Scenedesmus sp. In order to optimize the operating conditions of the electrolytic flocculation process and to quantify the amount of flocculants added, aluminum electrodes were first used in the process. It was found that under optimal conditions, the microalgae removal efficiency using aluminum electrodes could reach 98.5%, while 34.2 mg L⁻¹ of aluminum ions were released during the process. Different metal electrodes were also studied, but high microalgae removal efficiency was witnessed only using aluminum electrodes, indicating the influence of the aluminum ion in flocculation. When non-sacrificial graphite electrodes were used in the electrolytic flocculation process, the corresponding amount of aluminum sulfate was added so that the aluminum ion concentration in water was also equal to 34.2 mg L⁻¹. The result showed that the microalgae removal efficiency of graphite electrodes could reach above 90% after aluminum sulfate was added. In contrast, using graphite electrodes alone and using the metal salt alone only yielded 22.9% and 7.1% of microalgae removal efficiency, respectively. These results indicated that the presence of metal ions is necessary in the electrolytic flocculation process. The energy consumption of the process was found to be 0.3 kW h m⁻³ or 0.88 kW h kg⁻¹, which is considered to be low energy consumption. The total cost of the process, including energy and chemicals, was found to be $ 0.21 m⁻³, proving a cost competitive method in microalgae harvesting.

Electrolytic flocculation of microalgae using aluminum and graphite electrodes.     

Intact mangrove root electrodes for desalination

Through the benefit of billions of years of evolution, biology has developed tremendous strategies on how to co-exist in high salinity and water scarce environments. Biologically-inspired abiotic systems are becoming a central pillar in how we respond to critical grand challenges that accompany exponential population growth, uncontrolled climate change and the harsh reality that 96.5% of the water on the planet is saltwater. One fascinating biologic adaptation to saltwater is the growth of mangrove trees in brackish swamps and along the coasts. Through a process of salt exclusion, the mangrove maintains a near freshwater flow from roots to leaves to survive. One abiotic approach to water desalination is capacitive deionization, which aims to desalinate low-salinity water sources at energy costs below current technologies, such as reverse osmosis and thermal distillation. In this work, we use one-step carbonization of a plant with developed aerenchyma tissue to enable highly-permeable, freestanding flow-through capacitive deionization electrodes. We show that carbonized aerenchyma from red mangrove roots reduces the resistance to water flow through electrodes by 65-fold relative to carbonized common woody biomass. We then demonstrate the practical use of the intact carbonized red mangrove roots as electrodes in a flow-through capacitive deionization system. These findings have implications in a range of fields including water desalination, bioinspired materials, and plant functionality.

Biological adaptation in mangrove root enables freestanding carbonized architecture to be used as a highly permeable flow-through capacitive deionization electrode.     

N-Doped carbon nanoparticles on highly porous carbon nanofiber electrodes for sodium ion batteries

Nitrogen doped carbon nanoparticles on highly porous carbon nanofiber electrodes were successfully synthesized via combining centrifugal spinning, chemical polymerization of pyrrole and a two-step heat treatment. Nanoparticle-on-nanofiber morphology with highly porous carbon nanotube like channels were observed from SEM and TEM images. Nitrogen doped carbon nanoparticles on highly porous carbon nanofiber (N-PCNF) electrodes exhibited excellent cycling and C-rate performance with a high reversible capacity of around 280 mA h g⁻¹ in sodium ion batteries. Moreover, at 1000 mA g⁻¹, a high reversible capacity of 172 mA h g⁻¹ was observed after 300 cycles. The superior electrochemical properties were attributed to a highly porous structure with enlarged d-spacings, enriched defects and active sites due to nitrogen doping. The electrochemical results prove that N-PCNF electrodes are promising electrode materials for high performance sodium ion batteries.

Nitrogen doped carbon nanoparticles on highly porous carbon nanofiber electrodes were successfully synthesized via combining centrifugal spinning, chemical polymerization of pyrrole and a two-step heat treatment.     

Boosting the electrochemical properties of carbon materials as bipolar electrodes by introducing oxygen functional groups

Carbon materials are often used as both positive and negative electrodes (bipolar electrode materials) in energy storage devices, which significantly reduces the preparation complexity of the electrode. Herein, oxygen-modified carbon nanotubes mounted on carbon cloth (CCC) present a high areal capacitance as both positive and negative electrodes in a safe neutral electrolyte. The introduction of oxygen functional groups facilitates the formation of many electrochemical active sites and defects conducive to ion diffusion. When carbon materials are utilized as negative electrodes, the charge storage characteristics are mainly dependent on the adsorption and desorption of the ions (corresponding to the electric double layer capacitance). Whereas, when utilized as positive electrodes, the charge storage characteristics come from the intercalation and de-intercalation of the electrolyte ions in the multi-defect carbon material. The maximum areal capacitance measured at the positive electrode and negative electrode was 336 mF cm⁻² and 158 mF cm⁻², respectively. The measured areal capacitance of the assembled symmetrical supercapacitors was 93.6 mF cm⁻², and the areal energy density reached 33 μW h cm⁻² at a power density of 793 μW cm⁻². It is believed that the efficient preparation method and electrochemical mechanism elucidated in this work can guide the practical applications of carbon cloth in supercapacitors.

Carbon materials with effective oxygen functional groups as positive and negative electrodes and their special energy storage mechanism.     

N-doped porous carbons derived from Zn-porphyrin-MOF

N-doped porous metal–organic framework (MOF)-derived carbons (MDCs) were directly synthesized from a new Zn-DpyDtolP-MOF (ZnDpyDtolP·1/2DMF, H₂DpyDtolP = 5,15-di(4-pyridyl)-10,20-di(4-methylphenyl)porphyrin) containing a 3D hexagonal network through a self-templated carbonization method. KOH-activated MDC derivatives denoted as MDC-700-nKOH were also prepared with different weight ratios of KOH activator to MDC (MDC : KOH = 1 : n, where n = 1, 2). Compared to bare MDC, MDC-700-nKOH showed effective improvements of both gas sorption and electrochemical capacitive properties. More developed microporosity by KOH activation might induce great enhancement of high operating capacitive performances. The N-doped MDC-700-2KOH had high maximum gravimetric specific capacitance (555.6 F g⁻¹) and specific energy (40.4 W h kg⁻¹) at 0.1 A g⁻¹ in 1 M H₂SO₄. Even at a high current density of 190 A g⁻¹ in 6 M KOH, it exhibited high capacitive performance with a large specific power of 80 423 W kg⁻¹. MDC-700-nKOH electrodes also showed good recycling properties of electrochemical capacitance up to 30 000 cycles.

The porphyrin-based Zn-MOF is directly carbonized and activated by KOH for the generation of N-doped porous carbons acting as high performance supercapacitor electrode materials.     

An ultrasound-assisted approach to bio-derived nanoporous carbons: disclosing a linear relationship between effective micropores and capacitance

Ultrasound irradiation is a technique that can induce acoustic cavitation in liquids, leading to a highly interactive mixture of reactants. In pursuit of high-performance and cost-effective supercapacitor electrodes, pore size distributions of carbonaceous materials should be carefully designed. Herein, fruit skins (mango, pitaya and watermelon) are employed as carbon precursors to prepare nanoporous carbons by the ultrasound-assisted method. Large BET specific surface areas of the as-prepared carbons (2700–3000 m² g⁻¹) are reproducible with pore diameters being concentrated at about 0.8 nm. Among a suite of the bio-derived nanoporous carbons, one reaches a maximum specific capacitance of up to 493 F g⁻¹ (at 0.5 A g⁻¹ in 6 M KOH) in the three-electrode system and achieves high energy densities of 27.5 W h kg⁻¹ (at 180 W kg⁻¹ in 1 M Na₂SO₄) and 10.9 W h kg⁻¹ (at 100 W kg⁻¹ in 6 M KOH) in the two-electrode system. After 5000 continuous charge/discharge cycles, the capacitances maintain 108% in 1 M Na₂SO₄ and 98% in 6 M KOH, exhibiting long working stability. Moreover, such high capacitive performance can be attributed to the optimization of surface areas and pore volumes of the effective micropores (referred to as 0.7–2 nm sized pores). Notably, specific capacitances have been found linearly correlated with surface areas and pore volumes of the effective micropores rather than those of any other sized pore (i.e., <0.7, 2–50 and 0.5–50 nm). Consequently, the fit of electrolyte ions into micropore frameworks should be an important consideration for the rational design of nanopore structures in terms of supercapacitor electrodes.

There is a linear relationship between the effective micropore volume (surface area) and the specific capacitance of bio-derived nanoporous carbons, regardless of biomass type and activation temperature employed.     

Green and sustainable zero-waste conversion of water hyacinth (Eichhornia crassipes) into superior magnetic carbon composite adsorbents and supercapacitor electrodes

Troublesome aquatic weed, water hyacinth (Eichhornia crassipes) was converted into solid and liquid fractions via green and energy-saving hydrothermal carbonization (HTC). The solid product, hydrochar, was employed as a precursor to prepare magnetic carbon materials by simple activation and magnetization using KOH and Fe³⁺ ions, respectively. The obtained magnetic adsorbent possessed good magnetic properties and presented outstanding capacities to adsorb methylene blue (524.20 mg g⁻¹), methyl orange (425.15 mg g⁻¹) and tetracycline (294.24 mg g⁻¹) with rapid adsorption kinetics even at high concentrations (up to 500 mg L⁻¹), attributed to high specific surface area and mesopore porosity. Besides the solid hydrochar, the water-soluble liquid product was used to fabricate carbon-based supercapacitors through facile KOH activation with a considerably lower KOH amount in comparison to conventional activation. The supercapacitor electrode made from activated liquid product possessed an extremely high specific surface area of 2545 cm² g⁻¹ and showed excellent specific capacitance (100 F g⁻¹ or 50 F cm⁻³ at 1 A g⁻¹) and good retention of capacitance (92% even after 10 000 cycles). This work demonstrated that both solid and liquid HTC fractions from this bio-waste can serve as effective sources to prepare functional carbon materials, making this approach a sustainable zero-waste biomass conversion process.

Our facile approach converts embarrassing weed to value-added products through environmentally friendly routes towards zero-waste scheme.     

One-pot mechanochemical exfoliation of graphite and in situ polymerization of aniline for the production of graphene/polyaniline composites for high-performance supercapacitors

Graphene/polyaniline composites have attracted considerable attention as high-performance supercapacitor electrode materials; however, there are still numerous challenges for their practical applications, such as the complex preparation process, high cost, and disequilibrium between energy density and power density. Herein, we report an efficient method to produce graphene/polyaniline composites via a one-pot ball-milling process, in which aniline molecules act as both the intercalator for the exfoliation of graphite and the monomer for mechanochemical polymerization into polyaniline clusters on the in situ exfoliated graphene sheets. The graphene/polyaniline composite electrode delivered a large specific capacitance of 886 F g⁻¹ at 5 mV s⁻¹ with a high retention of 73.4% at 100 mV s⁻¹. The high capacitance and rate capability of the graphene/polyaniline composite can contribute to the fast electron/ion transfer and dominantly capacitive contribution because of the synergistic effects between the conductive graphene and pseudocapacitive polyaniline. In addition, a high energy density of 40.9 W h kg⁻¹ was achieved by the graphene/polyaniline-based symmetric supercapacitor at a power density of 0.25 kW kg⁻¹, and the supercapacitor also maintained 89.1% of the initial capacitance over 10 000 cycles.

Efficient ball-milling production of graphene/polyaniline composites as supercapacitor electrodes with enhanced capacitive contribution, rate capability, and specific capacitance.     

Homogeneous coating of carbon nanotubes with tailored N-doped carbon layers for improved electrochemical energy storage

The combination of activity-enriched heteroatoms and highly-conductive networks is a powerful strategy to craft carbon-based electrodes for high-efficiency electrochemical energy storage. Herein, N-doped carbon (N-C) coated carbon nanotubes (N-CNTs) were fabricated via a facile in situ synthesis of polyimide in the presence of carbon nanotubes (CNTs), followed by carbonization. The polyimide-divided N-C layers were uniformly covered on the surface of CNTs with a tailored layer thickness. The as-fabricated N-CNTs were further used as electrode active materials for energy storage. When employed as the electrodes for supercapacitors, the N-CNTs exhibited a specific capacitance of 63 F g⁻¹ at 0.1 A g⁻¹ (an energy density of 1.4 W h kg⁻¹ at a power density of 20 W kg⁻¹), which was much higher than that of pure N-C (5 F g⁻¹) and CNTs (13 F g⁻¹). The supercapacitor also retained 66.7% of its initial capacitance (42 F g⁻¹ at 10 A g⁻¹) after a 100-fold increase in the current density and nearly 100% of its initial capacitance after running 10 000 cycles. Furthermore, functioning as an anode material for a Li-ion battery, the N-CNTs also delivered a larger reversible capacity (432 mA h g⁻¹ at 50 mA g⁻¹), higher rate capability, and better cycling stability compared to pure CNTs. The electrochemical performances of the N-CNTs were improved overall due to the synergistic effects of interconnected 3D networks and core–shell structures capable of facilitating electrolyte percolation and charge transportation, enhancing conductivity and surface/interface wettability, and contributing additional pseudocapacitance.

Polyimide-derived N-doped carbon layers were coated onto carbon nanotubes for high-rate electrodes with enhanced energy storage.     

Insights into the production of extracellular polymeric substances of Cupriavidus pauculus 1490 under the stimulation of heavy metal ions

Three different methods (a sulfuric acid method, sodium chloride method and vibration method) were used to extract extracellular polymeric substances (EPS) from Cupriavidus pauculus 1490 (C. pauculus 1490) in the present study. The sodium chloride method was able to extract the maximum amount of EPS (86.15 ± 1.50 mg g⁻¹-DW), and could ensure minimum cell lysis by detecting glucose-6-phosphate dehydrogenase activity and using scanning electron microscopy. This method was therefore selected as the optimal extraction method and used in subsequent experiments. On this basis, the tolerance of C. pauculus 1490 and variations in EPS secretion after the addition of different metal ions was investigated. The tolerance levels of C. pauculus 1490 to Cd(ii), Ni(ii), Cu(ii) and Co(ii) were 300 mg L⁻¹, 400 mg L⁻¹, 400 mg L⁻¹ and 400 mg L⁻¹, respectively. Low concentrations of these heavy metal ions could promote bacterial growth, while increased concentrations were found to inhibit it. The results show that metal ions, especially Cd(ii), stimulate the secretion of EPS, with an EPS yield reaching 956.12 ± 10.59 mg g⁻¹-DW at 100 mg L⁻¹. Real-time polymerase chain reaction (PCR) analysis showed that the key EPS synthetic genes, epsB, epsP and Wzz, were up-regulated. Fourier transform infrared spectroscopy analysis suggested that abundant functional groups in EPS play an important role in heavy metal ion complexation. These results will contribute to our understanding of the tolerance mechanism of microorganisms in the presence of different types and concentrations of metal ions.

Metal ions are shown to stimulate the secretion of EPS components of Cupriavidus pauculus 1490, especially Cd(II).     

Effective screen-printed potentiometric devices modified with carbon nanotubes for the detection of chlorogenic acid: application to food quality monitoring

All-solid state screen-printed electrodes were fabricated for chlorogenic acid (CGA) detection. The screen-printed platforms were modified with multi-walled carbon nanotubes (MWCNTs) to work as a lipophilic solid-contact transducer. The sensing-membrane was plasticized with a suitable solvent mediator and incorporating [Ni^II(bathophenanthroline)₃][CGA]₂ complex as a sensory material. In a 30 mM phosphate solution (buffer, pH 6), the sensor revealed a Nernstian-response towards CGA ions with a slope of −55.1 ± 1.1 (r² = 0.9997) over the linear range 1.0 × 10⁻⁷ to 1.0 × 10⁻³ (0.035–354.31 μg mL⁻¹) with a detection limit 7.0 × 10⁻⁸ M (24.8 ng mL⁻¹). It revealed a stable potentiometric response with excellent reproducibility and enhanced selectivity over several common ions. Short-term potential stability and the interfacial sensor capacitance was estimated using both electrochemical-impedance spectroscopy (EIS) and chronopotentiometry techniques. The presented electrochemical platform revealed the merits of design simplicity, ease of miniaturization, good potential-stability, and cost-effectiveness. It is successfully applied to CGA determination in different coffee beans extracts and juice samples. The data obtained were compared with those obtained by liquid chromatography reference method (HPLC).

All-solid state screen-printed electrodes were fabricated for chlorogenic acid (CGA) detection.     

Determination of cesium ions in environmental water samples with a magnetic multi-walled carbon nanotube imprinted potentiometric sensor

A potentiometric sensor, based on the glassy carbon electrode (GCE) modified with a magnetic multi-walled carbon nanotubes/cesium ion-imprinted polymer composite (MMWCNTs@Cs-IIP), is introduced for the detection of cesium(i). The IIP was synthesized using cesium ions as the template ions, chitosan as the functional monomer and glutaraldehyde as the cross-linking agent. The membrane, which was coated on the surface of the GCE, was prepared using MMWCNTs@Cs(i)-IIP as the modifier, PVC as the neutral carrier, 2-nitrophenyloctyl ether as the plasticizer and sodium tetraphenylborate as the lipophilic salt. The proposed sensor exhibited a Nernstian slope of 0.05954 V dec⁻¹ in a working concentration range of 1 × 10⁻⁷ to 1 × 10⁻⁴ M (mol L⁻¹) with a detection limit of 4 × 10⁻⁸ M. The sensor exhibited high selectivity for cesium ions and was successfully applied for the determination of Cs(i) in real samples.

A Cs(i)-selective potentiometric microsensor based on the glassy carbon electrode (GCE) modified with a magnetic multi-walled carbon nanotubes/cesium ion-imprinted polymer has been developed.