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Abstract
Capacitive deionization (CDI) is a promising desalination technique that gains more and more attentions worldwide in recent years due to its high efficiency and feasibility. In this work, the sulfuric acid functionalized activated carbon (FAC) is proposed as electrode for CDI. By compared to pristine AC, FAC electrode shows an improved microspores volume from 0.17 to 0.22 m3 g-1 and therefore a high electrosorption capacity of 3.54 mg g-1 as well as a charge efficiency of 0.21. Furthermore, the FAC electrode follows the Langmuir isotherm, indicating the monolayer adsorption. Besides, the pseudo-first-order can describe the adsorption kinetics of FAC electrode as compared to other kinetics models. Additionally, the FAC electrode can be regenerated very well.
... Surface modification of carbons is also used to inhibit co-ion expulsion [23,24]. Acids [25], tetraethyl orthosilicates [26], fluoride [27], sodium dodecyl sulfate [28] and permanganate ions [29] are some of the materials used to modify the surface of carbon electrodes. The modification of carbon surface significantly contributes to improvement of the CDI electrodes resulting to the enhanced charge efficiency [30]. ...
... Furthermore, literature indicates that most CDI studies test the electrosorption performance of materials using high ionic strength solutions as in Refs. [25,32,34,35] and as reviewed by [36]. This may become a challenge to generalize the performance of these materials in the desalination of solutions with low ionic strength to obtain DI water as it is more difficult to remove ions in highly dilute solutions. ...
... The broad peaks of carbon are observed in the binding energy range from 282 to 296 eV. High resolution of the C1s XPS spectra generate four peaks at 284.6, 286.5, 289.0 and 291.2 eV, which corresponds to CeC, C]C, CeC]O and ππ* respectively [25]. Table 2 summarizes the intensities of various binding energy peaks of corresponding carbon components. ...
The deionized water (DI) of high purity standards is used in several industrial processes to manufacture products and technologies for high end applications. Currently, DI water is produced by either reverse osmosis or continuous electrodeionization systems, however; both of them are facing several limitations. Therefore there is an urgent need for the alternative technologies for DI water production. This study investigated suitability of producing DI water by using capacitive deionization (CDI) with nitric acid treated activated carbon electrodes (NTAC). Activated carbon (AC) was etched in nitric acid solution to introduce various oxygen functional groups on its surface. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to confirm the increased surface oxygen containing groups on AC after nitric acid treatment that enhanced its salt adsorption capacity. CDI experiments were conducted using water solution of 12.0 μS/cm as a result DI water with the conductivity of 1.6 μS/cm (DI water grade III, according to International Organization of Standards) was produced. Also, electrochemical tests revealed good capacitive behavior due to improved conductivity with NTAC having highest specific capacitance of 381.7 F/g compared to 106.6 F/g of AC electrode. This study provides an insight of the electrosorption performance of materials in desalination of solutions of low ionic strength.
... Also, Niu et al. [98], used sulfuric acid to modify AC by hydrothermal method. After acid treatment, N 2 adsorption-desorption isotherms were used to study pore size distribution. ...
... It is worth noting that H 2 SO 4 treatment increased specific capacitance by 175% while carbon materials treated in HNO 3 increased capacitance by 155%. Recently, Niu et al. [98] studied AC treated by H 2 SO 4 and confirmed the electrode to exhibit the highest capacitance of 232 F/g compared to untreated AC with a specific capacitance of 219 F/g at the scan rate of 1 mV/s. Though both studies complement each other in increasing capacitance there is a large difference in the percentage of improvement (175% vs 6%). ...
... Though both studies complement each other in increasing capacitance there is a large difference in the percentage of improvement (175% vs 6%). This might be caused by use of too high concentrated H 2 SO 4 by Niu et al. [98] which caused a large reduction of surface area and total pore volume. Electrosorption result indicates that HNO 3 treated electrodes exhibit higher electrosorption capacity due to introduced functional groups which increase ion capacitance of the ACC electrodes. ...
Capacitive deionization (CDI) is the competitive technology for water desalination which appears to become an alternative to conventional methods such as ion exchange resins, reverse osmosis, and electrodeionization. Variety of materials including, carbide-derived carbon, activated carbons, carbon nanotubes, carbon aerogels and mesoporous carbons have been studied for CDI applications most of them being porous carbons. However, materials such as carbon
nanotubes are highly expensive and hinder applications at large industrial scale. Activated carbon is a cheap and commercially available electrode material for CDI though its desalination
capacity is limited by factors such as low electrical conductivity, inability to selectively remove specific ions, co-ion expulsion, poor wettability, inappropriate pore size distribution and lack of
inter-pore connectivity to enable ion diffusion. These factors have raised a concern to most researchers and try to find a way to modify the surface of porous materials. Some strategies have been used to modify activated carbons including dip-coating in dopamine solution, mixing with quaternized poly (4-vinylpyridine), combining with graphenes and carbon nanotubes, direct fluorination and etching in acid solution to mention few. This review highlight factor(s) that
cause low performance of activated carbon and modification strategies used to treat activated carbon to enhance its adsorption performance. Furthermore, characterization methods used to
confirm whether the modification was successful and the practical application of modification methods have been discussed. To our view this work will provide an understanding of the contribution offered by modified activated carbon electrodes in the development of CDI technology.
... Activated carbons mostly have weak functional groups, like -OH, -NH2, and -COOH, spontaneously bond with carbon atoms through chemical oxidations. These groups cause weak pseudo reactions that actually benefit the performance of carbon electrodes in CDI [9]. In order to develop functional groups on the surface of ACs, there are commonly used chemical activation techniques including chloride-dipping [10], sulfuric acid functionalization [9], activation with iron(III) chloride [11] and zinc chloride [12] as well as potassium hydroxide (KOH) activation [13][14][15]. ...
... These groups cause weak pseudo reactions that actually benefit the performance of carbon electrodes in CDI [9]. In order to develop functional groups on the surface of ACs, there are commonly used chemical activation techniques including chloride-dipping [10], sulfuric acid functionalization [9], activation with iron(III) chloride [11] and zinc chloride [12] as well as potassium hydroxide (KOH) activation [13][14][15]. Using KOH as the activating agent for chemically activating different carbon sources holds great promise due to its lower activation temperature, higher yields, and the resulting porous carbons with a well-defined micropore size distribution and high specific surface area [14]. ...
Process parameters of Capacitive Deionization (CDI) was investigated and optimized in this study. The effect of adsorption period (7–13 min), flow rate (5–20 ml min⁻¹), and NaCl concentration (2–22 mM) on salt adsorption capacity was examined via Box-Behnken experimental design approach. A quadratic regression model (R² = 0.9987) was developed, revealing significant individual and binary effects between process parameters and salt adsorption capacity. The ANOVA results demonstrated its high significance with the p-value<0.0001. Optimal conditions varied with salt concentration, indicating significant interactions between the parameters. Maximum salt adsorption capacity occurred at 5 ml min⁻¹ flow rate and 13 min adsorption period for 22 mM NaCl, whereas for 12 mM and 2 mM NaCl concentrations, maximum adsorption capacity was obtained at the flow rate of 20 ml min⁻¹ and duration of 13 min. This study provided deep insights into CDI modelling and optimization, crucial for water treatment advancements.
... (3) and (4): where q * was the voltammetric charge, q s,out was the "outer" capacity, and q s was the surface-controlled capacity. q s,out was calculated to be 154.1 mF cm −2 , constituting 43.2% of q s , which was a relatively very high value [79]. ...
Despite the promising potential of transition metal oxides (TMOs) as capacitive deionization (CDI) electrodes, the actual capacity of TMOs electrodes for sodium storage is significantly lower than the theoretical capacity, posing a major obstacle. Herein, we prepared the kinetically favorable Zn x Ni 1 − x O electrode in situ growth on carbon felt (Zn x Ni 1 − x O@CF) through constraining the rate of OH ⁻ generation in the hydrothermal method. Zn x Ni 1 − x O@CF exhibited a high-density hierarchical nanosheet structure with three-dimensional open pores, benefitting the ion transport/electron transfer. And tuning the moderate amount of redox-inert Zn-doping can enhance surface electroactive sites, actual activity of redox-active Ni species, and lower adsorption energy, promoting the adsorption kinetic and thermodynamic of the Zn 0.2 Ni 0.8 O@CF. Benefitting from the kinetic-thermodynamic facilitation mechanism, Zn 0.2 Ni 0.8 O@CF achieved ultrahigh desalination capacity (128.9 mg NaCl g ⁻¹ ), ultra-low energy consumption (0.164 kW h kg NaCl ⁻¹ ), high salt removal rate (1.21 mg NaCl g ⁻¹ min ⁻¹ ), and good cyclability. The thermodynamic facilitation and Na ⁺ intercalation mechanism of Zn 0.2 Ni 0.8 O@CF are identified by the density functional theory calculations and electrochemical quartz crystal microbalance with dissipation monitoring, respectively. This research provides new insights into controlling electrochemically favorable morphology and demonstrates that Zn-doping, which is redox-inert, is essential for enhancing the electrochemical performance of CDI electrodes.
... It was employed as the electrode material in one of the groundbreaking studies in CDI [11]. More recent CDI studies that used activated carbon as electrode performed some modifications in the pristine carbon material to improve its deionization efficiency [12][13][14][15][16][17]. ...
Activated carbon-nickel (II) oxide (AC-NiO) electrodes were studied as materials for the capacitive deionization (CDI) of aqueous sodium chloride solution. AC-NiO electrodes were fabricated through physical mixing and low-temperature heating of precursor materials. The amount of NiO in the electrodes was varied and its effect on the deionization performance was investigated using a single-pass mode CDI setup. The pure activated carbon electrode showed the highest specific surface area among the electrodes. However, the AC-NiO electrode with approximately 10 and 20% of NiO displayed better deionization performance. The addition of a dielectric material like NiO to the carbon material resulted in the enhancement of the electric field, which eventually led to an improved deionization performance. Among all as-prepared electrodes, the AC-NiO electrode with approximately 10% of NiO gave the highest salt adsorption capacity and charge efficiency, which are equal to 7.46 mg/g and 90.1%, respectively. This finding can be attributed to the optimum enhancement of the physical and chemical characteristics of the electrode brought by the addition of the appropriate amount of NiO.
... From the XPS measurement spectrum, it can be seen that the broad peaks of carbon were observed in the binding energy range of 282 ~ 296 eV. The high-resolution XPS spectra of C1s produced three peaks at 284.8 eV, 286.3 eV, and 288.8 eV, corresponding to C-C, C-O, and C-C = O, respectively (Lang et al. 2012;Niu et al. 2015). In comparison, it was found that the surface group composition of AC (Fig. 6a) and AC-HNO 3 (Fig. 6b) did not change after nitric acid treatment. ...
In this paper, nitric acid-modified activated carbon was used as an electrode in the electrosorption process for the removal of Co²⁺, Mn²⁺, and Ni²⁺ from wastewater. The effects of applied voltage, initial pH, and coexisting ions on removal efficiency were investigated. The adsorption process was evaluated by adsorption isotherm models. The results indicated that the electrosorption process was consistent with the Langmuir model, proving that the electrosorption process was a monolayer adsorption process. The maximum adsorption capacities of Co²⁺, Mn²⁺, and Ni²⁺ were 131.58 mg/g, 102.04 mg/g, and 103.09 mg/g. Electrochemical tests revealed that the specific capacitance of AC-HNO3 was 54.11 F/g when the scanning rate was 5 mV/s, while the specific capacitance of AC was 36.51 F/g. The Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) confirmed that the content of oxygen groups on the surface of activated carbon increased after modification, which provided more adsorption sites for electrosorption. When the selected concentration of HCl was used as the eluent, the elution efficiency of Co²⁺, Mn²⁺, and Ni²⁺ could reach 94.23%, 93.65%, and 90.61%. The removal efficiency could reach more than 95% after three cycles. The results of the study can be used as a reference significance for the removal of cobalt, manganese, and nickel ions from heavy metal wastewater by electrosorption.
... Research is calculated to be 22 F·g -1 ·cm -2 , constituting 50% of q s , which is comparable to modified carbon electrodes [59] and notably higher than CuAl-LDH@rGO [53]. This indicates that hollow Co(OH) 2 electrode provides rapid, capacitorlike charge transfer and ion removal (Figures 6(c) and 6(d)). ...
Faradaic electrode materials have significantly improved the performance of membrane capacitive deionization, which offers an opportunity to produce freshwater from seawater or brackish water in an energy-efficient way. However, Faradaic materials hold the drawbacks of slow desalination rate due to the intrinsic low ion diffusion kinetics and inferior stability arising from the volume expansion during ion intercalation, impeding the engineering application of capacitive deionization. Herein, a pseudocapacitive material with hollow architecture was prepared via template-etching method, namely, cuboid cobalt hydroxide, with fast desalination rate (3.3 mg (NaCl)·g ⁻¹ (h-Co(OH) 2 )·min ⁻¹ at 100 mA·g ⁻¹ ) and outstanding stability (90% capacity retention after 100 cycles). The hollow structure enables swift ion transport inside the material and keeps the electrode intact by alleviating the stress induced from volume expansion during the ion capture process, which is corroborated well by in situ electrochemical dilatometry and finite element simulation. Additionally, benefiting from the elimination of unreacted bulk material and vertical cobalt hydroxide nanosheets on the exterior surface, the synthesized material provides a high desalination capacity ( 117 ± 6 mg (NaCl)·g ⁻¹ (h-Co(OH) 2 ) at 30 mA·g ⁻¹ ). This work provides a new strategy, constructing microscale hollow faradic configuration, to further boost the desalination performance of Faradaic materials.
... For these MCDI processes, the experimental data was fitted by using pseudo-first-order model presented as follows and pseudo-second-order kinetic model shown in the Supporting Information. [36,37] ln C t À C e C 0 À C e ¼ Àkt ...
To achieve a fluid uniform distribution, novel liquid distributors were introduced into the MCDI cell. Here were proposed three fluid distributors with different structures, primarily including flow channels and distributed baffles. Also, the effects of each liquid distributor on the fluid distribution were evaluated through CFD software. As a result, the Liquid distributor‐3 was demonstrated to be optimal, which can facilitate the fluid uniform distribution and relieve the impact of inlet flow rate on the fluid distribution. Correspondingly, the adsorption capacity reached up to 23.8 mg·g⁻¹ for this novel MCDI cell under the 2000 mg·L⁻¹ NaCl solution. To find a trade‐off between desalination performance and energy‐efficient, a modified MCDI system based on two novel MCDI cells and three valves was established by analyzing three adsorption/desorption processes, including Process 1 (both adsorption and desorption in parallel), Process 2 (adsorption in series and desorption in parallel) and Process 3 (both adsorption and desorption in series). The best performance was obtained by Process 1, where the current efficiency increased by about 25% in adsorption process and by about 37% during desorption process compared with Process 3. This study lays a foundation for the commercial application of multi‐component MCDI technology.
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... shows the FTIR spectra obtained from undoped ACC and N and F doped ACC. Characteristic absorption at 3084, 1496, 1332, 1064 and 981 cm -1 assigned to O-H stretching, C=C stretching in aromatic ring, O-H deformation, C-O stretching and C-O-C stretching vibrations, respectively can be observed in the ACC electrodes[37][38][39][40]. Upon doping with nitrogen, two adsorption bands at 1318 and 1212 cm -1 , assigned to C=N and C-N stretching vibrations are observed[41,42]. ...
Capacitive deionization (CDI) is an emerging technology as a sustainable low energy process for desalination of brackish water. Activated carbon electrodes are often used in the CDI devices. Electrosorption capacity was found to be improved on asymmetric electrode configuration using activated carbon cloth doped with fluorine due to redistribution of electric potential. This led to improvement in desalination performance up to 12.4 mg/g for a desalination cycle of 6 minutes employing an asymmetric fluorinated electrode as cathode (ACC//F-ACC). A relatively high charge efficiency of 77 % was obtained representing 92 % charge efficiency neglecting the leakage currents. Furthermore, the ion adsorption rate was found to improve substantially due to an increased surface conductivity of the fluorinated electrode confirmed by Mott-Schottky analysis. Energy consumption during desalination of 1000 ppm sodium chloride solution of 0.71kWh/m3 for symmetric electrode configuration was found to reduce by 36 % upon employing asymmetric configuration. This study shows some of the benefits of asymmetric configuration to achieve an optimal operation of CDI device, as well as improvements related to energy consumption.
... Very low intensity of broadband (~287.9 eV) suggested the minor presence of C=O, suggesting that most of the oxygenated groups of citric acid had been removed during thermal treatment [38,39]. N1s spectra (Fig. 2f) could be fitted into three N species: pyridine N (~398.3 ...
Pore hierarchy facilitates the mass transportation/exchange between the interior surface and bulk solution, which is critical for the enhancement of capacitive performance. Herein, by applying in situ foamed Mg chelates as precursors, we managed the scalable fabrication of hierarchically porous carbon (HPC) materials and explored their capacitive applications. Particularly, citric acid first reacted with magnesium nitrate to form Mg chelate while the generated gaseous HNO3 molecules bubbled the intermediate carbon framework to produce abundant open pores. The as-made precursors were then submitted to potassium hydroxide activation for a high carbonization degree and rich meso-/micropores. The optimized sample (HPC-2) exhibited very high specific capacitance of 213.5 F g−1 in neutral NaCl solution and a high rate capability of ~ 67.5% at 10.0 A g−1. Furthermore, it showed impressive capacitive deionization performance regarding high removal efficiency (67.1%), large capacity of 1810.1 mg g−1 (in 2200 mg L−1 NaCl solution), and robust cycling stability.
... Desalination technology is commonly believed as one of the most effective pathways to solve the water crisis [1,2]. Traditional seawater desalination methods generally include reverse osmosis (RO) [3,4], distillation [5,6], and electrodialysis [7,8]. ...
In this study, a nitrogen and sulfur co-doped sodium titanium phosphate/hole graphene (N,S-NTP/rHGO) was synthesized by one-step hydrothermal method using thiourea as N/S source. The microstructure characterization confirms that N and S heteroatoms have been integrated into the graphene skeleton. The electrochemistry and electrosorption properties of the N,S-NTP/rHGO electrodes were investigated for hybrid capacitor deionization (HCDI). The results indicate that the specific capacitance of N,S-NTP/rHGO electrodes can reach 530.46 F g⁻¹ at a scan rate of 0.2 mV s⁻¹, which is 33.8% higher than that of the sample without doping. Moreover, the HCDI cell based on the N,S-NTP/rHGO-2 shows a high desalination capacity of 36.87 mg g⁻¹ and a rapid ion removal rate of 0.66 mg g⁻¹ s⁻¹, which is more than twice as high as the sample without doping (0.3 mg g⁻¹ s⁻¹) at an initial NaCl concentration of 800 mg L⁻¹ and applied voltage of 1.4 V. Further, the N,S-NTP/rHGO electrode exhibits excellent regeneration ability. Therefore, this study suggests that as-prepared N,S-NTP/rHGO composite exhibits a great potential application for high-performance HCDI systems.
... Among processes of introducing S into carbon, the most common S-doping method consists on handling carbon material with sulfuric acid. However, this method is extremely destructive and most cases leads to a significant reduction in specific surface area and pore volume [18,[22][23][24]. Therefore, under the conditions of less corrosive reactants, other mild approaches could be suitable for introducing S functionalities without damaging the porous structure of the CSiO 2 material. ...
... To investigate the salt removal capacity of the electrodes, the batch mode CDI experiments were carried out at different initial concentrations of the NaCl solutions, as can be seen from Fig.10, the salt retention capacity increases from 6.87 to 17.8 mg/g for ACP900 and from 4.7 to 14.8 mg/g for CP1000 with increasing NaCl concentration from 0.5 to 10 mol/L. After literature survey, we found that our values are better than those obtained by the sulfuric acid functionalized activated carbon (3.54mg/g) [41], the RAC-1-2 electrode (2.10 mg/g) [42] and the ordered mesoporous carbon (0.52-0.93 mg/g) [43], not far from those for coconut shell-based activated carbon electrodes (9.72-20.91 mg/g) [44], but lesser than those for Ligninderived carbon (18.5 mg/g in 0.5g/L) [45], 3D graphene sheet-sphere (22.09 mg/g in 0.5g/L) [46], ZIF-8@PZS-C electrodes (22.19mg/g) [47] and graphene frameworks (19.1mg/g) [48]. ...
Microporous activated carbon pellets have been prepared from date stone without the use of a binder. These pellets were tested as electrodes for capacitive deionization. The activation process involved two steps. First, a pyrolysis of the date stone was conducted to a temperature of 1000 °C under nitrogen flow. Then, the obtained carbon monoliths were physically activated at 900 °C under CO2 flow. Elemental analysis, BET, SEM, mercury porosimetry, conductivity measurement and electrochemical performance testing carried out to characterize the structure and the properties of activated carbon pellets. The activated carbon exhibited predominant microporosity with a specific surface area of 896 m² g⁻¹ which leads to the highest specific capacitance 270.90 F/g. The performance of activated carbon electrode at 900 °C in capacitive deionization (CDI) test was also examined.
... A schematic illustration of the preparation and activation phases for activated carbons is presented in Figure 1. The formulated course of activations of SPB materials with H 2 SO 4 concentrations has been attained, resulting in activation of agent-to-precursor impregnation ratios of around 151/ (Niu, Li, Ma, He, & Li, 2015) at a 700 o C temperature over a 2-hour holding period. ...
Unprocessed sago palm bark (SPB) is a material that has been newly utilised for preparations of activated carbons (AC), using physicochemical activation techniques comprising dual carbonisation and activation phases. Activations have been conducted utilising three agents: sulphuric acid (H2SO4), potassium hydroxide (KOH), and zinc chloride (ZnCl2). Characterisations of the porosities of AC preparations were performed using N2 adsorption-desorption to ascertain BET and micropore surface areas as well as micropore volumes and pore-size distributions. Existing groups on the AC surfaces were resolved using Fourier Transform Infrared Spectroscopy (FTIR) analyses. The morphologies of the activated carbons were assessed via scanning-electron microscopic methods (SEM) combined with energy-dispersive X-ray spectroscopic techniques (EDX). The maximal surface areas (1639.34 m2/g), pore volume (0.649 cm3/g), micropore volume (0.335 cm3/g), and micropore surface area (1,148.58 m2/g) of the prepared AC using sago palm bark were discovered at activation temperatures of 700oC and with chemical impregnation ratios of 1.51/ zinc chloride to precursors. In the instance of KOH and H2SO4 utilisation, the surface areas of the AC preparations corresponded to 970.38 m2/g and 630.73 m2/g with pore volume of 0.458 and 0.196 cm3/g, respectively.
... IR analysis also shows enhancement in the peaks attributed to C-O/C=N/C-S due to the involvement of C-SO 3 H or C-OSO 3 H. In some works, reduction in the intensity of the O-C=O peak (at 289.1 eV, 1729 cm −1 ) confirms its conversion into -O-SO 3 H (Liu et al. 2012, Niu et al. 2015, Santos et al. 2015. ...
Biochar (BC) generated from thermal and hydrothermal cracking of biomass is a carbon-rich product with the microporous structure. The graphene-like structure of BC contains different chemical functional groups (e.g. phenolic, carboxylic, carbonylic, etc.), making it a very attractive tool for wastewater treatment, CO 2 capture, toxic gas adsorption, soil amendment, supercapacitors, catalytic applications, etc. However, the carbonaceous and mineral structure of BC has a potential to accept more favorable functional groups and discard undesirable groups through different chemical processes. The current review aims at providing a comprehensive overview on different chemical modification mechanisms and exploring their effects on BC physicochemical properties, functionalities, and applications. To reach these objectives, the processes of oxidation (using either acidic or alkaline oxidizing agents), amination, sulfonation, metal oxide impregnation, and magnetization are investigated and compared. The nature of precursor materials, modification preparatory/conditions, and post-modification processes as the key factors which influence the final product properties are considered in detail; however, the focus is dedicated to the most common methods and those with technological importance.
... First carbon precursors such as wood [81], coconut shell [82], oil palm wood [83], and coal [84] are pyrolysed under inert atmosphere at temperatures of 600-800°C to eliminate noncarbon elements and produce char [85,86]. Then, the produced char is either physically activated by gasification with steam [87,88], carbon dioxide [89,90] or chemically activated using strong acids [91,92] or bases [93,94]. ...
... Conc. H 2 SO 4 triggered acid activation was adopted for achieving rapid thermal decomposition as reported in earlier researches (Gomes et al., 2010;Vithanage et al., 2015;Niu et al., 2015;Zhang et al., 2015) in a single phase treatment. Conc. ...
Alachlor, a globally used aniline herbicide, has great agronomic interest for controlling the development of broadleaved weeds and grasses. This research aspires to evaluate the sorption attributes of Alachlor through batch equilibrium method and its successive removal through biomass based activated carbon prepared from Sawdust (Cedrus deodara). Six soil samples were collected from selected regions of Pakistan to assess the adsorption and removal phenomena. Adsorption capacity for Alachlor varied in soils depending upon their physicochemical properties. Adsorption coefficient (Kd) values ranged from 12 to 31 µg ml⁻¹ with the highest Kd value observed in soil sample with highest organic content (1.4%) and least pH (5.62). The Gibbs free energy values ranged from −17 to −20 kJ mol⁻¹ proposing physio-sorption and exothermic interaction with soils. Values of R² (0.96–0.99) exhibited the best fit to linear adsorption model. Adsorption coefficient displayed a negative correlation (r = −0.97) with soil pH and positive correlation with organic matter (r = 0.87). The effect of contact time and pesticide concentration on the removal efficiency by activated carbon was investigated. The highest removal percentages observed through activated carbon were 66% and 64% at concentrations of 5 and 7.5 ppm respectively. Activated carbon from sawdust (Cedrus deodara) was investigated as a suitable adsorbent for the removal of Alachor from selected soils. Biomass based activated carbon can prove to be an effective and a sustainable mean to remove pesticides from soil.
... Desalination is envisioned to be one of the most effective ways to challenge the water crisis [1,2]. For the past few decades, various de- salination technologies, such as reverse osmosis, thermal distillation and multiple-effect distillation, have been developed in many areas. ...
Asymmetrical capacitive deionization (A-CDI) is expected to be a promising desalination technique with high salt removal capacity. In this work, the novel A-CDI are proposed where the negative and positive electrode are Na4Ti9O20 (NTO) and activated carbon (AC), respectively. Basically, the NTO nanotubes with the specific surface area of 142.43 m²/g have been prepared by hydrothermal reaction. The electrochemical test shows that the specific capacitance of optimum NTO electrode can reach 120.45 F/g in 1 M Na2SO4 solution with the scan rate of 1 mV/s by employing three-electrodes method. Moreover, the electrosorption capacity of AC/NTO asymmetrical electrodes is approach to 23.35 mg/g in NaCl solution with an initial concentration of 250 ppm. To improve the conductivity of NTO, reduced graphene oxide (rGO) is proposed to couple with NTO, named as [email protected], to constitute the AC/[email protected] A-CDI. As a result, the AC/[email protected] A-CDI exhibited an ultrahigh desalination capacity of 41.8 mg/g in NaCl solution with an initial concentration of 250 ppm under 1.4 V, which is almost twice higher than that of AC/NTO electrodes and the highest value among all reported data anywhere. Besides, the charge efficiency of AC/[email protected] approaches to 1, implying the co-ions impaction has been successfully restricted.
... Figure 7 shows the FTIR spectrum, which was carried out to investigate the structural features of the AC, TiO 2 /ZrO 2 NFs, and the significant changes that were observed in NACTZ after their interaction. The FTIR spectra of the AC show peaks at 1129 cm −1 (C-O stretching vibration) 47 , 1560 cm −1 (C = C bonding in aromatic carbons) 48 and 3324 cm −1 (OH group) 49 . On the other side, the vibration band at 465-672 cm −1 in the TiO 2 /ZrO 2 NFs was attributed to a Ti-O vibration and the bands at 3443, 2887, 2334 and 1631 cm −1 were assigned to O-H bending of the absorbed water molecules, C-H stretch, O = C = O and C = C (skeletal vibration of unoxidized graphitic domains), respectively 50,51 . ...
Capacitive deionization, as a second generation electrosorption technique to obtain water, is one of the most promising water desalination technologies. Yet; in order to achieve high CDI performance, a well-designed structure of the electrode materials is needed, and is in high demand. Here, a novel composite nitrogen-TiO2/ZrO2 nanofibers incorporated activated carbon (NACTZ) is synthesized for the first time with enhanced desalination efficiency as well as disinfection performance towards brackish water. Nitrogen and TiO2/ZrO2 nanofibers are used as the support of activated carbon to improve its low capacitance and hydrophobicity, which had dramatically limited its adequacy during the CDI process. Importantly, the as-fabricated NACTZ nanocomposite demonstrates enhanced electrochemical performance with significant specific capacitance of 691.78 F g-1, low internal resistance and good cycling stability. In addition, it offers a high capacitive deionization performance of NACTZ yield with electrosorptive capacity of 3.98 mg g-1, and, good antibacterial effects as well. This work will provide an effective solution for developing highly performance and low-cost design for CDI electrode materials.
... For instance, 600-NS-DCM with 1.6 V applied voltage has a desalination capacity of 32.3 mg g -1 and a maximum ion removal rate of 0.56 mg g -1 min -1 , which exceed most of the currently reported values for CDI applications as listed in Table S2. 20,33,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] Even with 1.4 V applied voltage, the desalination capacity still reaches 30.9 mg g -1 and the maximum ion removal rate is 0.51 mg g -1 min -1 . Secondly, the cycling stability of 600-NS-DCM was measured by monitoring the conductivity changes over five adsorption/desorption cycles with 1.4 or 1.6 V ( Figure 6C). ...
Doped carbon materials (DCM) with multiple heteroatoms hold broad interests in electrochemical catalysis and energy storage but require several steps to fabricate, which greatly hinder their practical applications. In this study, a facile strategy is developed to enable the fast fabrication of multiply doped carbon materials via room-temperature dehalogenation of polyvinyl dichloride (PVDC) promoted by KOH with the presence of different organic dopants. A N, S-codoped carbon material (NS-DCM) is demonstratively synthesized using two dopants (dimethylformamide for N doping and dimethylsulfoxide for S doping). Afterwards, the precursive room-temperature NS-DCM with intentionally overdosed KOH is submitted to inert annealing to obtain large specific surface area and high conductivity. Remarkably, NS-DCM annealed at 600 °C (named as 600-NS-DCM), with 3.0 at.% N and 2.4 at.% S, exhibits a very high specific capacitance of 427 F g-1 at 1.0 A g-1 in acidic electrolyte and also keeps ~60% of capacitance at ultrahigh current density of 100.0 A g-1. Furthermore, capacitive deionization (CDI) measurements reveal that 600-NS-DCM possesses a large desalination capacity of 32.3 mg g-1 (40.0 mg L-1 NaCl), and very good cycling stability. Our strategy of fabricating multiply doped carbon materials can be potentially extended to the synthesis of carbon materials with various combinations of heteroatom doping for broad electrochemical applications.
... As it is shown in Fig. 1, salty ions which are the minority one are immobilized in the double layer between the surface of electrodes and solution. On the contrary, other methods extract the majority phase, the water, from the seawater then much additional energy would be wasted [5]. At present, the key feature of CDI is to design new electrode's material, which performs high specific area, conductivity and reasonable pore size distribution. ...
In this work, the capacitive deionization (CDI) behavior of mesoporous carbons (MCs) through direct carbonization of ZIF-8 at 1000 °C under Ar + 4%H2 atmosphere has been explored. The obtained MCs exhibit a well-defined mesoporous structure, with a high specific surface area of 723.41 m²·g− 1 and average pore diameter of 3.2 nm. The specific electrochemical capacitance of MCs was evaluated in a three-electrode configuration with 1 M NaCl electrolyte, showing that the capacitance reached as high as 215.72 F·g− 1 at the scan rate of 5 mV·s− 1 and 186 F·g− 1 with current density of 100 mA·g− 1, respectively. Moreover, it is found that the electrosorption capacity of MCs was 4.8 mg·g− 1 in NaCl solutions with an initial concentration of 250 mg·L− 1 and cell voltage of 1.2 V. Remarkably, the theoretical maximum electrosorption capacity was estimated at 17 mg·g− 1 from Langmuir isotherm when the cell voltage was fixed at 1.2 V. Finally, the well regeneration of MCs electrode was demonstrated, indicating the great potential application of MCs in desalination.
Емкостная деионизация воды (ЕДВ) привлекает пристальное внимание как перспективная, недорогая и энергоэффективная технология опреснения воды. Невысокая стоимость устройства, в первую очередь, обусловливается возможностью использования углеродных материалов из природного сырья. Одна из последних концепций развития ЕДВ подразумевает применение инвертированного профиля потенциала в процессе работы (сорбция при 0 В, десорбция при небольшом значении потенциала), что дополнительно снижает энергопотребление системы. Для работы такой системы необходимо использование углеродных материалов, несущих поверхностный заряд, который обеспечит сорбцию при отсутствии внешнего потенциала. В данной работе авторы представляют простую двухстадийную методологию создания высокопористых углеродных материалов из рисовой шелухи и их последующую химическую функционализацию азотсодержащими группами –NO2 и –NH2, несущими отрицательный и положительный заряды, соответственно. За счет использования модифицированных материалов удалось достичь высоких значений удельной емкости в 253 Ф/г. Применение полученных материалов в качестве электродов в мембранных и инверсионных ячейках ЕДВ продемонстрировало их высокую эффективность, увеличив на 15% (до 16,91 мг/г) максимальную удельную адсорбционную емкость (УАЕ) по сравнению с симметричными мембранными ячейками с использованием немодифицированных углей.
Herein, the integral technology process including the production, doping and tail gas recovery systems is constructed to realize the S doping modification with the excellent universality for arbitrary carbon materials. S-doped porous carbon (SPC) and S-doped carbon nanotubes (SCNTs) obtained by the developed doping methodology are employed as anode material and conductive additives of cathode and anode in lithium ion capacitor (LIC), respectively. The great alleviation of the kinetics mismatch between cathode and anode in LIC is benefited from S doping modification on anode and the construction of efficient conductive network inside electrodes. Besides, the excellent rate capability and durability can still be afforded by the fabricated LIC even at low temperature environment. This work not only develops a scalable, green and universal S doping methodology for arbitrary carbon materials, but also provides a reasonable design for the construction of high-performance LIC device.
Capacitive deionization (CDI) is a promising membraneless technology being widely-explored for water desalination and selective separations. The active elements in CDI are often inexpensive activated carbon electrodes, which store ions...
W18O49 has been demonstrated to be a promising candidate for efficient electrochemical applications. To further improve the electrical conductivity of W18O49 and make it suitable for hybrid capacitive deionization (HCDI), highly stable three-dimensional (3D) interconnected network architectures assembled from W18O49 and Ti3C2 MXene composites with different Ti3C2 contents have been synthesized via a facile and effective electrostatic attraction self-assembly strategy and used as a novel HCDI electrode material. Compared to single-component electrodes, the synergistic effect between W18O49 and Ti3C2 enabled high specific surface area (SSA), fast ion diffusion, and dual pseudocapacitance effect. These multiple advantages of the W18O49/Ti3C2 electrode achieved a preponderant salt adsorption capacity (SAC) as high as 29.25 mg g⁻¹ in 500 mg L⁻¹ NaCl solution at an applied voltage of 1.2 V. An excellent capacitance (153 F g⁻¹ at 2 mV s⁻¹) and high cycling stability (maintaining 98.3% of the initial capacity after 10 cycles) were also observed. This work could provide some insights for rational design of 3D electrode architectures for electrochemical applications and water desalination.
It is evident that high consumption of several kind of products around the world increases the presence of pollutants in different water sources. For example, caffeine is an alkaloid widely used in foods, beverages, and commercial analgesic medicines as a central nervous system stimulant. Caffeine is an anthropogenic pollutant, and it is part of emergent contaminants. In addition, nickel (II) has been found in industrial effluents such as mining, oil refining, mineral processing, electroplating, silver refining, paint formulation, battery manufacturing, and steam electric power plants. This metal is toxic and it bio-accumulates, thus it has been classified as a priority pollutant. Thus, it is necessary to use innovative techniques to remove pollutants of water. In this sense, adsorption is an option to deal with this problem; therefore, carbonaceous materials could be a good alternative. Moreover, magnetic carbon composites obtained from carbonaceous materials have been widely studied for environmental applications, as it makes easy the process of separation from aqueous solutions.
The development of high-performance electrode materials is the main factor in improving the efficiency of the capacitive deionization (CDI) process. Activated carbon is the most extensively used electrode material because of its excellent physicochemical properties and low cost; however, its desalination application has been largely limited owing to its poor wettability. In this study, we prepared a ZnO nanoparticle-incorporated activated carbon/graphene hydrogel composite via ultrasonication and freeze-drying, followed by a hydrothermal treatment. As the hydrophilicity, electrical conductivity, and electrosorptive capacity were improved owing to the presence of the graphene hydrogel and ZnO nanoparticles, the as-fabricated nanocomposite showed excellent specific capacitance (746.5 F g⁻¹ at 10 mV s–1), salt removal efficiency (83.65%), and electrosorptive capacity (9.95 mg g⁻¹). Thus, the nanocomposite design devised in this study has potential in realizing the practical CDI applications of activated carbon.
Capacitive deionization (CDI), in which electrode materials play an important role, is considered a novel desalination technology because of its advantages of low energy consumption, low cost and low pollution. Porous electrode materials with a high accessible surface area, hydrophilic surfaces and excellent electrochemical performance have proved to be ideal. Carbons derived from metal-organic frameworks (MOFs) are most suitable for this purpose because of their controllable morphology and microstructure, suitable pore size distribution, and excellent electrical conductivity. The preparation and of MOF-derived carbon materials and their performance for the use as CDI electrode materials are reviewed. These include MOF-derived carbons, modified MOF-derived carbons, doped MOF-derived carbons and MOF-derived carbon composites with graphene, carbon nanofibers and carbon nanotubes. The advantages and challenges of these carbon electrode materials for CDI are summarized and future development is proposed.
Capacitive deionization (CDI) is a fast-emerging technology typically applied to brackish water desalination and ion selective separations. In a typical cell, feedwater is desalinated via ion electrosorption into micropore electric double layers (EDLs) of charging porous carbon electrodes. Several studies have previously demonostrated that oxidizing the cathode via a nitric acid pretreatment enhances the cell’s salt adorption capacity (SAC). It was recently reported that oxidized cathodes can degrade rapidly during cell cycling, yet the mechanisms and mitigation strategies remain unknown. Here, we experimentally characterize the performance and degradation of nitric acid-oxidized commercial carbon cloth cathodes. For a full cycle time (FCT) of 100 min and 1 V applied, we observed a 42.5% reduction of SAC by the 100th cycle, and measured a reduction in cathode micropore chemical charge concentration at pH = 7 from -1.5 M to -0.25 M after cycling. We further found that cell charging time and electrode mass are major determinants of degradation rate, for example, reducing FCT to 30 min and 10 min allows for SAC decay of only ∼14% and <2%, respectively, over 100 cycles. The insights provided here allow us to posit degradation mechanisms, and develop long-lasting, high performance CDI cells with oxidized cathodes.
Activated carbon particle electrodes modified by oxygen or nitrogen groups could be promising electrode candidates for capacitive deionization (CDI) processes. In this work, activated carbon particle electrodes were modified by phosphoric acid, nitric acid, urea, melamine, and zinc chloride to enhance desalination of an aqueous electrolytic solution. The modified activated carbon particles were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier-transformed infrared spectroscopy, Brunner − Emmet − Teller measurements and electrochemical scanning. The electrodes with oxygen or nitrogen groups on the surface exhibited a much higher desalination capacity and charge efficiency than those without any surface modification. Particularly, the activated carbon particle electrode modified by phosphoric acid exhibited a desalination capacity of 15.52 mg/g at 1.4 V in 500 mg/L NaCl solution, which was approximately eight times that of the unmodified electrode (2.46 mg/g). The enhancement was attributed to a higher specific capacitance, a lower electrochemical impedance and an increase in oxygen or nitrogen-containing groups on the surface.
Designing novel nanostructured materials is very significant to enhance the desalination capacity enabled by capacitive deionization (CDI). In this work, the vertical-aligned CuAl-layered double oxide grown on reduced graphene oxide (CuAl-LDO/rGO) is proposed as high-performance anode for hybrid CDI (HCDI). It is found that the morphology of CuAl-LDO is ultimately dependent on the loading mass of urea. As a result, the optimized CuAl-LDO/rGO exhibits relatively high specific surface area, 3D porous structure and electrochemical behavior. When employed as anode for HCDI, it demonstrated high salt removal capacity of 64.0 mg/g at cell voltage of 1.2 V in NaCl solution with an initial concentration of 1000 mg/L. After 20 cycles, the capacity still remains at 58.0 mg/g which is ～90% of initial value, suggesting the superior cycling ability. Moreover, the phase transformation of CuAl-LDO/rGO at various stages indicates that the formation of Cu(OH,Cl)2•2H2O may responsible for the capacity decay upon the cycling. However, the morphology characterization realizes that the aggregation of Cu(OH,Cl)2•2H2O nanoparticles can be effectively inhibited within CuAl-LDO/rGO by compared to that of random oriented CuAl-LDO nanoflakes, which is accounted for superior salt removal capacity retention. Besides, a comparison is performed on HCDI performance among different anodes, highlighting the advances of CuAl-LDO/rGO. It is attributed to the unique structure of CuAl-LDO/rGO which is beneficial to provide as much as tunnels for diffusion of salty ions and active sites for intercalation.
Capacitive deionization (CDI) is considered as a simple, robust, and environmentally favorable technology for water treatment. High performance electrode materials beyond commercial activated carbons (AC) should be developed for the practical application of CDI. Herein, we demonstrate hierarchically open-porous nitrogen-incorporated activated nanoporous carbon polyhedron (A-NCP) derived from metal-organic frameworks (MOFs) for high performance CDI electrodes. Owing to the 3D morphology with open nanoporous surface, macroporous channels by interlinked polyhedron particles, and electric conductivity by doped nitrogen, A-NCP delivers a high desalination capacity of 24.4 mg/g with a low concentration of 100 mg/mL at 1.2 V, revealing faster kinetic performance than that of commercial AC in the batch-mode CDI. Varying operating conditions such as applied voltage, concentration, and feed rate of saline water in a single-pass experiment, high salt adsorption capacity and fast ion removal of A-NCP are obtained, achieving high position of CDI Ragone plot.
Capacitive deionization (CDI) technology has attracted wide attention since its advent and is considered as one of the most promising technologies in the field of desalination and ion recycling. It is constructed with an electric field by applying a low voltage of direct-current to make ions migrate directionally in solution to achieve the purpose of ion separation and removal. The performance of CDI is heavily dependent on the electrode material. Carbon is widely used as CDI electrode material because of its lower price and better stability. To enhance the adsorption capacity, extensive research efforts have been made for the modification of carbon material. In this review, we enumerate and analyze four modification methods of carbon material including element doping, metal oxide modification, chemical treatment and surface coating. The influence of each modification method on CDI performance is concluded in the perspective mechanism and some constructive advice is put forward on how to effectively enhance the performance of CDI by the decoration of carbon materials.
In order to enhance the desalting performance of electrode in the capacitive deionization process (CDI), a novel sulfobutyl ether β-cyclodextrin polymer with multi-sulfonic groups and multi-hydroxyl groups (SBE-β-CDP) was successfully synthesized and attached on the surface of carbon nanotubes (CNT) by non-covalent bond. The as-prepared [email protected]β-CDP electrode possesses significantly improved capacitance property and hydrophilicity (60.9 F/g, 65.5°) as compared to the CNT electrode (51.7 F/g, 103.6°), which indicates that the multi-sulfonic groups and multi-hydroxyl groups on the [email protected]β-CDP electrode surface can provide efficient ion transfer pathway by the synergistic effect. The symmetric and asymmetric CDI cells, named as R‖R, R(+)‖R-CDP(−) and R-CDP(+)‖R(−), were assembled with the CNT electrode (R) and [email protected]β-CDP electrode (R-CDP). Based on the electroneutrality principle of electrode, the theoretical analysis about the adsorption process of these CDI cells by balancing the ionic charge, electronic charge and chemical charge in the electrode demonstrates that when the [email protected]β-CDP electrode is used as cathode, the theoretical charge efficiency reaches a maximum in the asymmetric R(+)‖R-CDP(−). In the desalting experiments, the average salt adsorption capacity and charge efficiency for R(+)‖R-CDP(−) (6.37 mg/g, 36.9%) surpass those of R‖R (4.17 mg/g, 25.8%) and R-CDP(+)‖R(−) (3.11 mg/g, 17.3%). These facts confirm the good cation selectivity of [email protected]β-CDP electrode that strengthens the desalting performance of asymmetric CDI process.
In the capacitive deionization (CDI) process, the degradation of desalting performance is predominantly due to the co-ions expulsion effect and electrode oxidation. To overcome these complications, carbon nanotubes grafted with amine and sulfonic functional groups respectively were prepared and used as the CDI electrodes. The structural characterizations and performance tests confirmed that a uniform functional layer was formed on the surface of the modified electrodes and it enhanced the ion selectivity and wettability of the electrode surface. Moreover, the effects of the functional layer on the electrode stability were investigated by circulating CV tests and desalination tests. The positive shift value of the potential of zero charge (PZC) for the as-prepared electrodes was tested as a quantitative indication for their possible surface oxidation during cyclic tests. Analysis of the PZC variation and desalting performance demonstrated that the excellent desalting stability was achieved by the Cell N-S assembled with the ammoniated CNTs electrode as anode and sulfonated CNTs electrode as cathode. Because the functional layer could preserve the pores system on the modified electrodes and diminish the parasitic reactions that exacerbate the electrode oxidation. This work provides an effective strategy for promoting the electrode performance and prolonging the life of the electrode.
We demonstrate hierarchical porous carbons derived from rice husk (RH) through the combination of carbonization and two post-processing methods for the electrode material of capacitive deionization (CDI). The carbonized RHs, consisting of carbon/inorganic composite materials, are used to control hierarchical porous structures, depending on the existence of silicon domains. Hierarchical porous carbons denoted as RHC-A, which is comprised of dominant micropores and small fraction mesopores, are synthesized by steam activation to react with the carbon fraction in the presence of silicon components. On the other hand, mesopore-dominant porous carbons denoted as RHC-H are obtained selectively removing silicon components acting as a natural template from carbonized RH using hydrofluoric acid treatment. In order to understand the effect of pore structure on CDI performance, two RH-derived porous carbons are compared for the performances of water purification. In the batch-mode experiment, the microporous activated carbon (AC) exhibits the highest maximum electrosorption capacity of 17.7 mg/g, which is mainly determined by the specific surface area. Under the same condition, however, the RHC-A is verified to have enhanced kinetic performance from the Langmuir isotherm and the Pseudo-second-order kinetic model. The hierarchical porous structures with the continuous mesopores interconnected by micropores contribute to the enhanced kinetic performance of the RHC-A, facilitating effective ion transport and adsorption. In a continuous mode similar to the practical CDI, the kinetically improved RHC-A achieves the higher salt-removal capacity of 8.09 mg/g than 5.40 and 1.63 mg/g of the commercial activated carbon and RHC-H, respectively, at 1.5 V and a feed rate of 20 mL/min in 100 ppm of NaCl solution.
Zeolitic imidazolate framework (ZIF) composite derived carbon, exhibiting large surface area and high micropore volume, is demonstrated to be promising electrode material for capacitive deionization (CDI) application. However, some inherent serious issues (e.g. low electrical conductivity, narrow pore size, relatively low pore volume, etc.) still remain in the nitrogen-doped porous carbon particles, which restrict their CDI performance. In order to solve the above-mentioned problems, herein we prepared gold-nanoparticle-embedded ZIF-8-derived nitrogen doped carbon calcined at 800 C (Au@NC800) and PEDOT doped-NC-800 (NC800-PEDOT). With the notably increased conductivity, the new-generated NC800-PEDOT and Au@NC800 electrode achieve high electrosorption capacities of 16.18 mg/g and 14.31 mg/g, respectively, which is much higher than that of NC800 (8.36 mg/g). The Au@NC800 and NC800-PEDOT should be promisingly applicable as highly efficient CDI electrode materials.
Revalorization of an agricultural waste from olive oil industry was performed by transforming it into activated carbon. In such a way, a material with excellent textural properties (high surface area and large micro and mesopore volumes) was obtained by carbonization and chemical activation of solid residues from olive oil industry. Moreover, this activated carbon was solvothermally treated in order to improve its electrochemical properties by adding sulphur and oxygen functionalities on its surface. The treatment was able to introduce a great proportion of sulphur and oxygen, mainly located on the external surface of sample. This modification led to functionalized materials with not only larger capacitance (325 versus 158 F g⁻¹ at 0.125 A g⁻¹ in H2SO4 1 M), but also with a greater retention at higher current densities (large capacitance even at current densities as high as 30 A g⁻¹), due to their lower electrical resistance. Furthermore, the amount of electric energy stored by these materials was largely increased (from 21.8 to 37.0 Wh kg⁻¹ in H2SO4 1 M) as well as their power density (from 7393 to 34360 W kg⁻¹ in H2SO4 1 M). Several charge/discharge cycles were performed in order to test the cyclability of these materials, showing not significant reduction on their electrochemical properties after 12,500 cycles.
Herein, nitrogen-doped tin oxide intercalated activated carbon nanocomposite (N-AC/SnO2) were prepared using hydrothermal strategy and explored as an electrode for capacitive desalination and disinfection. Although tin oxide (SnO2) has good characteristics, the nitrogen must be carefully considered for modifying the characteristics of the carbonaceous materials to improve the performance as an electrode in the CDI process. The characterization of the proposed materials which investigated by XRD, TEM, FE-SEM, XPS and FT-IR affirmed the formation of the nanocomposite. The electrosorption behavior investigated by electrochemical techniques demonstrates that, compared to the specific capacitance of the AC and AC/SnO2 (207.46 F g⁻¹ and 233.21 F g⁻¹), that of the N-AC/SnO2 is higher at 408.8 F g⁻¹, and N-AC/SnO2 exhibits better electrical conductivity. The CDI performance evaluated by batch mode experiments through an applied voltage of 1.2 V in a 50 mg L⁻¹ NaCl aqueous solution shows that the N-AC/SnO2 electrode introduces a higher electrosorptive capacity of 3.42 mg g⁻¹, an enhanced desalination efficiency of 61.13%, and good antibacterial performance. Overall, the present study demonstrates that N-AC/SnO2 has considerable potential as an electrode material for CDI application.
Although many studies suggested that aluminum (Al) induced programmed cell death (PCD) in plants, the mechanism of Al-induced PCD and its effects in Al tolerance is limited. This study was to investigate the mechanism and type of Al induced PCD and the relationship between PCD and Al tolerance.
In this study, two genotypes of peanut 99–1507 (Al tolerant) and ZH2 (Al sensitive) were used to investigate Al-induced PCD. Peanut root growth inhibition induced by AlCl3 was concentration and time-dependent in two peanut varieties. AlCl3 at 100 μM could induce rapidly peanut root tip PCD involved in DNA cleavage, typical apoptotic chromatin condensation staining with DAPI, apoptosis related gene Hrs203j expression and cytochrome C (Cyt c) release from mitochondria to cytosol. Caspase3-like protease was activated by Al; it was higher in ZH2 than in 99–1507. Al increased the opening of mitochondrial permeability transition pore (MPTP), decreased inner membrane potential (ΔΨm) of mitochondria. Compared with the control, Al stress increased O2
•- and H2O2 production in mitochondria. Reactive oxygen species (ROS) burst was produced at Al treatment for 4 h.
Al-induced PCD is earlier and faster in Al-sensitive peanut cultivar than in Al-tolerant cultivar. There is a negative relationship between PCD and Al resistance. Mitochondria- dependence PCD was induced by Al and ROS was involved in this process. The mechanism can be explained by the model of acceleration of senescence under Al stress.
As one of the forms and shapes of modern furniture design, folding furniture is a reflection of increasing aestheticism and daily life, being the inevitable trend of the variety of furniture design. Folding dining table is mainly for the young in the city, displaying its fashion and novelty from its shape and interior structure; projecting its perfect combination of traditional material and modern craftmanship from selecting the proper material; presenting the concept of creating the need to boost consumption by studying the products aesthetic value and human value. This article is to predict the future trend of modern funiture design through the above-mentioned three aspects.
One of the most pervasive problems afflicting people throughout the world is inadequate access to clean water and sanitation. Problems with water are expected to grow worse in the coming decades, with water scarcity occurring globally, even in regions currently considered water-rich. Addressing these problems calls out for a tremendous amount of research to be conducted to identify robust new methods of purifying water at lower cost and with less energy, while at the same time minimizing the use of chemicals and impact on the environment. Here we highlight some of the science and technology being developed to improve the disinfection and decontamination of water, as well as efforts to increase water supplies through the safe re-use of wastewater and efficient desalination of sea and brackish water.
The effect of oxidation on the structural integrity of multiwalled carbon nanotubes through acidic (nitric acid and a mixture of sulfuric acid and hydrogen peroxide) and basic (ammonium hydroxide/hydrogen peroxide) agents has been studied. In order to purify the as-received material, a non-oxidative treatment (with hydrochloric acid) was also applied. Electron microscopy and thermogravimetric analysis clearly revealed that the nitric acid-treated material under reflux conditions suffered the highest degree of degradation, such as, nanotube shortening and additional defect generation in the graphitic network. Basic oxidative treatment led to the complete removal of amorphous carbon and metal oxide impurities but the structural integrity was found to be intact. X-ray photoelectron spectroscopy was employed to confirm the different functionalities produced for each oxidation agent, whereas titration measurements determined the relative concentration of carboxylic functions onto the graphitic surface. Moreover, a general relationship between the chemical treatment and the amount of non-graphitic carbon was established by means of Raman spectroscopy measurements. The possibility of controlling the required amount of functionality, carboxylic and hydroxyl, via these oxidation procedures is discussed.
Supercapacitors, also called ultracapacitors or electrochemical capacitors, store electrical charge on high-surface-area conducting materials. Their widespread use is limited by their low energy storage density and relatively high effective series resistance. Using chemical activation of exfoliated graphite oxide, we synthesized a porous carbon with a Brunauer-Emmett-Teller surface area of up to 3100 square meters per gram, a high electrical conductivity, and a low oxygen and hydrogen content. This sp(2)-bonded carbon has a continuous three-dimensional network of highly curved, atom-thick walls that form primarily 0.6- to 5-nanometer-width pores. Two-electrode supercapacitor cells constructed with this carbon yielded high values of gravimetric capacitance and energy density with organic and ionic liquid electrolytes. The processes used to make this carbon are readily scalable to industrial levels.
We report the synthesis of ultra-low-density three-dimensional macroassemblies of graphene sheets that exhibit high electrical conductivities and large internal surface areas. These materials are prepared as monolithic solids from suspensions of single-layer graphene oxide in which organic sol-gel chemistry is used to cross-link the individual sheets. The resulting gels are supercritically dried and then thermally reduced to yield graphene aerogels with densities approaching 10 mg/cm(3). In contrast to methods that utilize physical cross-links between GO, this approach provides covalent carbon bonding between the graphene sheets. These graphene aerogels exhibit an improvement in bulk electrical conductivity of more than 2 orders of magnitude (∼1 × 10(2) S/m) compared to graphene assemblies with physical cross-links alone (∼5 × 10(-1) S/m). The graphene aerogels also possess large surface areas (584 m(2)/g) and pore volumes (2.96 cm(3)/g), making these materials viable candidates for use in energy storage, catalysis, and sensing applications.
Carbon supercapacitors, which are energy storage devices that use ion adsorption on the surface of highly porous materials to store charge, have numerous advantages over other power-source technologies, but could realize further gains if their electrodes were properly optimized. Studying the effect of the pore size on capacitance could potentially improve performance by maximizing the electrode surface area accessible to electrolyte ions, but until recently, no studies had addressed the lower size limit of accessible pores. Using carbide-derived carbon, we generated pores with average sizes from 0.6 to 2.25 nanometer and studied double-layer capacitance in an organic electrolyte. The results challenge the long-held axiom that pores smaller than the size of solvated electrolyte ions are incapable of contributing to charge storage.
Metal-free, heteroatom functionalized carbon-based catalysts have made remarkable progress in recent years in a wide range of applications related to energy storage and energy generation. In this study, high surface area mesoporous ordered sulphur doped carbon materials are obtained via one-pot hydrothermal synthesis of carbon/SBA-15 composite after removal of in-situ synthesized hard template SiO2. 2-thiophenecarboxy acid as sulphur source gives rise to sulphur doping level of 5.5 wt%. Comparing with pristine carbon, the sulphur doped mesoporous ordered carbon demonstrates improved electro-catalytic activity in the oxygen reduction reaction in alkaline solution.
Objective: To investigate serotype/serogroup distribution of S. pneumoniae in children with community-acquired pneumonia in Shenzhen, understand possible vaccine coverage of the serotypes and the bacterial resistance to 8 antibiotics. Methods: S. pneumoniae strains were isolated from the sputum, cerebrospinal fluid, blood and pleural effusion of children with community-acquired pneumonia in Shenzhen during February 2006 and February 2007. The isolates were serotyped by capsular swelling technique. Susceptibility to 8 antibiotics was determined by E-test. Results: Ninety strains of S. pneumoniae were isolated from 1 011 specimens. The prevalence was 8.9%. Of these isolates, 89 were from sputum, 1 from pleural effusion. Serotype 19F was the most frequently isolated type (62.2%, 56/90), followed by 23F (15.6%, 14/90), 6B (10.0%, 9/90), 4 (6.7%, 6/90). These 4 serotypes accounted for 94.4% of all isolates. About 94. 4% of these isolates were covered by the 7-valent pneumococcal conjugate vaccine (PCV7). The additional serotypes contained in 9, 10 and 11-valent pneumococcal conjugate vaccines were not identified. The coverage of 13-valent pneumococcal conjugate vaccine was 97.8%, showed no significant difference from that of PCV7 (χ 2 = 1.34, P>0.05). Of the serotypes in PCV7, 14.1% were resistant to penicillin. About 13.3% of all S. pneumoniae isolates were resistant to penicillin. No resistant strain was found to vancomycin, levofloxacin or imipenem. About 98.9%, 64.4% and 4.4% of the isolates were resistant to erythromycin, cefuroxime and ceftriaxone respectively. Conclusions: The 19F, 23F, 6B and 4 serotypes are the most frequently isolated pneumococcal strains in children with community-acquired pneumonia in Shenzhen area. PCV7 can cover 94.4% of these S. pneumoniae strains. These S. pneumoniae strains are highly sensitive to vancomycin, levofloxacin, amoxicillin and imipenem, but relatively resistant to penicillin, erythromycin and cefuroxime.
Sulfur-doped ordered mesoporous carbons (OMC-S-X) (X=1, 2 and 3) with different sulfur contents were synthesized as metal-free electrocatalyst for oxygen reduction reaction (ORR). Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectra (EDX), nitrogen adsorption-desorption, X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) were employed to confirm the characterizations of OMC and OMC-S. The prepared OMC-S-3 exhibits high electrocatalytic activity, good stability and excellent tolerance to crossover effect for ORR. The high electrocatalytic activity of OMC-S-3 for ORR can be mainly ascribed to the doping of sulfur especially the existence of sulfide groups (-C-S-C-) which play an important role in promoting the ORE.
Ordered mesoporous carbon CMK-3 was successfully prepared by a hard template nanocasting method followed by carbonization at temperatures from 700 to 900 degrees C. The values of specific surface area, pore diameter and pore volume were found to increase with the rise of carbonization temperatures. After chemical activation by 6 M HNO3, the specific surface areas decreased significantly, but the specific capacitances increased remarkably in both alkaline (3 M KOH) and neutral (0.5 M Na2SO4) electrolytes. Analysis of the surface structure and composition showed that the chemical activation introduced oxygen-containing functional groups on carbon surface, which are responsible for the enhancement of supercapacitive performances revealed by electrochemical tests. The best achieved specific capacitance is 182.1 F/g in 0.5 M Na2SO4, and 223.5 F/g in 3 M KOH, both at the current density of 0.5 A/g. The specific capacitance retentions after 500 cycles are 95.6% and 86.3% in 0.5 M Na2SO4 and 3 M KOH, respectively. The higher specific capacitance in KOH electrolyte is due to the lower faradic charge transfer resistance and better electrochemical surface area utilization than in Na2SO4 electrolyte.
It is necessary to determine camera postures in inertial coordinate systems, when the mapping camera is used in a photogrammetry for a transport stereo mapping satellite. In determining the camera postures, the postures of star sensor measuring system in the inertial coordinate system were measured by star sensors, then, the postures of the mapping camera measuring system in the inertial coordinate system were obtained by the transition matrix between star sensor measuring system and the cubic prism in star sensor and the transition matrix between the two cubic prisms in the star sensor and mapping camera. This paper introduces the definition of coordinate systems. By using the measuring systems of four theodolites, we establish coordinate systems on two cubic prisms respectively and a transition matrix for the coordinate systems. The calibration method of two coordinate systems is presented. The measuring results from many experiments show that the maximum calibration error is 1.011 6″, which is better than 2″(1σ) and satisfies the precision requirement of the stereoscopic mapping.
Sulphonated reduced graphene oxide (SRGO) is self-assembled onto carbon fibre cloth (CFC) by electrophoresis deposition as a composite (CFC–SRGO) electrode for high-performance capacitive deionization (CDI). The resulting CFC–SRGO composite shows a cross-linked nanotubular structure and the individual carbon fibre is fully encapsulated by SRGO nano-sheets, forming a cylindrical-shell microstructure. The electrosorption performance of the CFC–SRGO composite electrode is determined by carrying out a batch-mode electrosorption experiment, showing a great improvement in charge efficiency of more than twice that of a bare CFC electrode. Remarkably, this result is comparable with that of membrane enhanced capacitive deionization. Further, the low exponential decay constant of the CFC–SRGO composite electrode derived from the electrosorption kinetics demonstrates that the deposited SRGO favors a decrease in the internal electrode resistivity and therefore improves the ion electrosorption rate which contributed to the enhanced charge efficiency significantly. Another possible reason accounting for the high charge efficiency of the CFC–SRGO electrode is that the functionalized SRGO is analogous to a cation-exchange membrane which can block the co-ions during electrosorption. In addition, the electrosorption isotherm of the CFC–SRGO film follows Langmuir adsorption, indicating the monolayer adsorption mechanism. Meanwhile, the thermodynamic analyses imply that the electrosorption of salt ions onto the CFC–SRGO electrode is driven by a physisorption process.
Long-term performance of capacitive deionization (CDI) and membrane-assisted capacitive deionization (MCDI) single cells equipped with the same pristine carbon xerogel (CX) electrodes configured as the anode and cathode was investigated. Unlike CDI, which was subject to performance degradation in a short period of time, MCDI showed performance preservation during the 50 hours of operation due to its ability to mitigate charge leakage from parasitic electrochemical reactions that result in carbon oxidation. Differential capacitance measurements of the used CDI and MCDI electrodes revealed shifting of the potential of zero charge (EPZC) of the CDI anode from 0.1 to 0.4 V, but only to 0.1 V for the MCDI anode. CDI and MCDI cells tested with electrodes having EPZCs at -0.1 and 0.5 V showed strongly contrasting results depending on the anode-cathode EPZC configuration. The MCDI cell configured with a 0.5 V EPZC cathode and -0.1 V EPZC anode displayed the best performance of all the tested cells, benefiting from increased counter-ion excess within the potential window, and the membrane in-place to reject expelled co-ions from accessing the bulk.
N-doped activated carbons for electric double-layer capacitors were prepared from waste medium density fiberboard using K2CO3 activation. The effects of carbonization temperature, activation temperature, activation time and K2CO3/coke mass ratios on surface chemical compositions, pore structure and electrochemical performance of the resulting activated carbons were investigated. Results indicated that the activated carbons had nitrogen contents from 0.93-2.86%, Brunauer-Emmett-Teller specific surface areas from 569 to 1 027 m2/g and specific capacitances from 147 to 223 F/g, depending on carbonization and activation conditions. The maximum specific capacitance was attributed to a high surface area, optimum pore size, large pore volume and high N-5 (the pyrrolic nitrogen and pyridinic nitrogen in association with oxygen functionality) content.
This manuscript spans over 180 years of ideas, discoveries, inventions, breakthroughs and research in Capacitive Deionisation (CDI) and Membrane CDI (MCDI) desalination. Starting with the first discovery of the dissociation of ions in solution under an electric field by M. Faraday (1833), through the pioneering work of carbon aerogel flow through capacitors by J. Farmer's group (1996) at Lawrence Livermore National Laboratory (LLNL), to the utilization of novel graphene and carbon nanotube (CNT) materials as electrodes, the CDI and MCDI technologies are progressively making its path to the desalination industry. Through this review various deficiencies of this technology have been identified, first and far most was the need for low cost and efficient electrode materials. The review identified that a low cost and high efficiency electrode capable of processing high salinity (seawater) stream still does not exists and is considered important if the technology is to make it to the industry. Furthermore, the lack of long term reliability, operation demonstrations and experience meant that information about scaling and fouling are rather scarce. Taking a step further, no comprehensive environmental assessment such as Life Cycle Assessment (LCA) or Environmental Impact Assessment (EIA) has been performed yet.
In this work an activated carbon modified by nitric acid has been used as the electrodes in capacitive deionization (CDI) process for the desalination of an aqueous electrolytic solution. The experimental results have shown that the modification could greatly increase the salt removal from the solution. The desalination efficiency was increased about 15%, and the desalination kinetics was improved in the form of rate constant from 0.09208 to 0.09922. It has been found that the modification greatly increased the oxygen-containing functional groups on the surfaces of activated carbon, leading to the increases of the capacitance and the reduction of the charging resistance, which might be attributed to the improvement of the desalination.
The unusual electronic structure of graphene characterized by linear energy dispersion of bands adjacent to the Fermi level underpins its remarkable transport properties. However, for practical device integration, graphene will need to be interfaced with other materials: 2D layered structures, metals (as ad-atoms, nanoparticles, extended surfaces, and patterned metamaterial geometries), dielectrics, organics, or hybrid structures that in turn are constituted from various inorganic or organic components. The structural complexity at these nanoscale interfaces holds much promise for manifestation of novel emergent phenomena and provides a means to modulate the electronic structure of graphene. In this feature article, we review the modifications to the electronic structure of graphene induced upon interfacing with disparate types of materials with an emphasis on iterative learnings from theoretical calculations and electronic spectroscopy (X-ray absorption fine structure (XAFS) spectroscopy, scanning transmission X-ray microscopy (STXM), angle-resolved photoemission spectroscopy (ARPES), and X-ray magnetic circular dichroism (XMCD)). We discuss approaches for engineering and modulating a bandgap in graphene through interfacial hybridization, outline experimental methods for examining electronic structure at interfaces, and overview device implications of engineered interfaces. A unified view of how geometric and electronic structure are correlated at interfaces will provide a rational means for designing heterostructures exhibiting emergent physical phenomena with implications for plasmonics, photonics, spintronics, and engineered polymer and metal matrix composites.
Controlled surface functionalization is demonstrated by nitric acid hydrothermal oxidation on multiwall carbon nanotubes (MWCNTs). The formation and evolution of oxygen functional groups were systematically investigated as a function of the HNO3 concentration on MWCNTs with different structural and morphological characteristics, employing temperature-programmed desorption coupled with mass spectrometry, thermogravimetry and differential scanning calorimetry, Raman spectroscopy and N2 porosimetry analysis. Hydrothermal treatment provides controlled MWCNT modification by specific oxygen functionalities at amounts determined by the morphology, texture and crystallinity of the pristine materials. Hydrothermal oxidation competes well with the harsh boiling nitric acid treatment regarding the total amount of oxygen functionalities, while requiring much lower amounts of oxidizing agent and, most importantly, reducing amorphous carbon deposits on the MWCNT surface, a major drawback of aggressive liquid phase oxidation methods. Detailed pore structure analysis revealed a progressive increase of the surface area upon hydrothermal functionalization, whereas the mesopore structure varied consistently with the intrinsic MWCNT properties related to the packing of the nanotube bundles and the reduction of amorphous carbon. These advantageous features render nitric acid hydrothermal oxidation an efficient functionalization process to fine tune and optimize the surface chemistry of MWCNTs for target applications, circumventing the need for additional purification post-processing.
Multi-walled carbon nanotubes (MWCNTs) were simultaneously fluidized and oxidized with gaseous ozone in a vertical reactor. Two different varieties of MWCNTs were compared to determine the versatility of the treatment and to elucidate the effect of defects on the oxidation behavior of MWCNTs. The extent of oxidation and nature of functional groups introduced on the nanotube surfaces were determined using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Boehm titration, and structural changes were monitored with Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). After only a few minutes of treatment, non-graphitic impurities were removed from the MWCNTs and significant levels of oxidation (~8 at% O) were achieved with very little damage to the nanotube sidewalls. Short O3 exposure resulted in primarily hydroxyl functionalities while longer exposure led to the formation of mainly carboxylic acid groups. Aliphatic defects present in the commercially-produced MWCNTs were found to play an important role in the oxidation mechanism. Because of its ability to remove impurities and evenly oxidize the sidewalls of nanotubes without the use of any solvents, the fluidized O3 reaction developed in this study was found to be an attractive option for industrial-scale MWCNT functionalization.
In this study, we applied the capacitive deionization (CDI) technology to develop a process that efficiently and economically removes one of the impurities, ZnCl2, during the purifying process of insulin. The main process parameters of the CDI process were also optimized. The removal of ZnCl2 increased as the applied electric potential (voltage) increased. The applied electric potential of 1.2 V obtained the best removal of ZnCl2. The removal of ZnCl2 increased as the initial ZnCl2 concentration (10, 20, 45, 90, 180, 360, 540 mg/L) decreased. There was almost no change in the removal of acid for the initial ZnCl2 concentration below 45 mg/L while there was a high removal of ZnCl2 of 93% or above. A longer operation time led to less adsorption at the electrode. After 3 min of operation time, the amount adsorbed started to decline after 3 min and a sharp drop occurred after 10 min. When a sample with insulin (0.4 g/L insulin, 360 mg/L ZnCl2) was used in the process under the optimal operation condition (applied electric potential: 1.2 V, adsorption time: 3 min, flow rate: 20 mL/min), 75% of ZnCl2 was removed and most (>99%) of the insulin was recovered.
Ordered mesoporous carbon-reduced graphene oxide (OMC-RGO) composites are prepared through organic-organic self-assembly method. The conductivity of OMC-RGO (32.5 S m−1) is higher than that of OMC (0.76 S m−1), while the pore structure is reduced and the BET surface area and pore volume of OMC-RGO (361 m2 g−1, 0.23 cm3 g−1) are lower than OMC (670 m2 g−1, 0.40 cm3 g−1). Furthermore, the presence of RGO in OMC-RGO is favorable to load more Ag nanoparticles due to the oxygen-containing groups on the surface of RGO and the Raman signal intensity of OMC-RGO–Ag is greatly increased comparing with OMC–Ag, showing surface-enhanced Raman scattering (SERS) activity.
The novel biacidic carbon has been synthesized via one-step hydrothermal carbonization of glucose, citric acid, and hydroxyethylsulfonic acid at 180 °C for only 4 h. The novel carbon had an acidity of 1.7 mmol/g with the carbonyl to sulfonic acid groups molar ratio of 1:3, which was confirmed by IR, XPS, TPD, SEM, and BET analyses. The catalytic activities of the carbon were investigated through esterification and oxathioketalization. The results showed that the carbon owned the comparable activities to sulfuric acid, which indicated that the carbon holds great potential for the green processes.
In this work, functional graphene nanocomposite (reduced graphite oxidate‐resol like material, named RGO-RF) was successfully synthesized and used as electrode in capacitive deionization (CDI) process. The porosity, morphology and electrochemical characteristics of RGO-RF were confirmed by N2 adsorption–desorption curve, transmission electron microscopy and cyclic voltammetry, respectively. Further, the deionization performances of the RGO-RF electrode, reduced graphite oxidate (RGO) and activated carbon (AC) were examined for comparison by a lab-scale CDI experimental system. It is found that the RGO-RF shows the best deionization performance among the three target materials, indicating that it is a novel electrode material which has a great potential as effective electrode for CDI. Besides, the electrosorption isotherms and electrosorption kinetics were studied, and it is found that the ion sorption behaviour of RGO-RF follows a Langmuir adsorption isotherm, implying monolayer adsorption.
A novel pyridine–thermal strategy for successive exfoliation and reduction of graphite oxide with the use of pyridine as the intercalating agent and dispersant is reported, and the obtained graphene exhibits a good performance in capacitive deionization.
This paper presents a comparative study on electrosorptive behavior of commercial single walled and double walled carbon nanotubes (CNTs) and as-prepared graphene as potential electrode materials for capacitive deionization (CDI). Their electrosorptive behaviors are evaluated under the same experimental conditions and described by various adsorption isotherms and kinetics models. It was found that the electrosorptive capacity of CNTs (single walled or double walled)-based CDI is higher than that of graphene-based CDI, which is related to their specific surface area, pore structure and hydrophilic functional groups. Electrosorptive kinetics analysis further confirms that CNTs are more suitable as electrode materials than graphene.
The dependence of the voltammetric surface charge q* on solution pH and potential scan rate has been investigated using a set of RuO2 electrodes prepared by thermal decomposition of RuCl3 at temperatures in the range 300–500°C. The systematically higher charge in KOH than in HClO4 in the same potential range (vs rhe) is attributed to the stabilization of higher oxidation states of surface Ru atoms in the alkaline environment. The variation of q* with v, the potential scan rate, is shown to be linearizable as a function of v. It is thus possible to extrapolate the values of q* to v=0 and v=∞, respectively. The extrapolation enables an “inner” surface to be discriminated from an “outer” surface. The former is pointed out to be composed by the regions of difficult accessibility for the proton-donating species assisting the surface redox reactions. Reasons why the “screened” surface appears to be higher in alkaline than in acid solutions, are discussed. It is stressed that only working with a set of RuO2 electrodes prepared at different temperatures it is possible to discover meaningful correlations.
It is very important to increase the wetted surface area of a carbon electrode for high capacitive deionization performance. To increase the wettability of a carbon electrode, we fabricated carbon electrodes by using water-soluble polymer binder, polyvinyl alcohol (PVA). The electrochemical properties of the PVA-bonded carbon electrode were compared with another that was prepared using hydrophobic binder, polyvinylidene fluoride (PVdF). Electrochemical methods – cyclic voltammetry, chronoamperometry, and electrical impedance spectroscopy – were used to characterize the electrochemical properties of the electrodes. As might be expected, it was confirmed that the PVA-bonded electrode was more wettable than the PVdF-bonded one, based on contact angle measurements. From the cyclic voltammetric analysis, we found that the specific capacitance was 74.4–80.3Fg−1 for the PVdF-bonded electrode and 89.6–99.8Fg−1 for the PVA-bonded electrode, depending on the potential, indicating a 13.3–30.1% increase in specific capacitance. It was observed that the ac-signal penetrated micropores of the PVA-bonded carbon electrode more deeply than the PVdF-bonded one, resulting in a higher capacitance. This was attributed to the fact that the ac-signal was able to charge more inner surface sites because micropores in the PVA-bonded electrode could be wetted due to the PVA binder.
We fabricated nitrate-selective composite carbon electrodes (NSCCEs) for use in capacitive deionization to remove nitrate ions selectively from a solution containing a mixture of anions. The NSCCE was fabricated by coating the surface of a carbon electrode with the anion exchange resin, BHP55, after grinding the resin into fine powder. BHP55 is known to be selective for nitrate ions. We performed desalination experiments on a solution containing 5.0 mM NaCl and 2.0 mM NaNO(3) using the NSCCE system constructed with the fabricated electrode. The selective removal of nitrate in the NSCCE system was compared to a membrane capacitive deionization (MCDI) system constructed with ion exchange membranes and carbon electrodes. The total quantity of chloride and nitrate ions adsorbed onto the unit area of the electrode in the MCDI system was 25 mmol/m(2) at a cell potential of 1.0 V. The adsorption of nitrate ions was 8.3 mmol/m(2), accounting for 33% of the total. In contrast, the total anion adsorption in the NSCCE system was 34 mmol/m(2), 36% greater than the total anion adsorption of the MCDI system. The adsorption of nitrate ions was 19 mmol/m(2), 2.3-times greater than the adsorption in the MCDI system. These results showed that the ions were initially adsorbed by an electrostatic force, and the ion exchange reactions then occurred between the resin powder in the coated layer and the solution containing mixed anions.
a b s t r a c t The carbon nanotubes and carbon nanofibers composite films (CNTs–CNFs) were fabricated by chemical vapor deposition. The electrosorption performance of CNTs–CNFs films at different solution temperatures was studied. It is found that the salt removal decreases from 45.4% to 33% due to hydrophobic–hydro-philic transition taking place on the surface of CNTs–CNFs films, when solution temperature ranges from 281 to 295 K. The electrosorption isotherm investigation shows Langmuir isotherm can better describe experimental data. Meanwhile, the kinetics and thermodynamics analyses indicate that the electrosorp-tion of NaCl onto CNTs–CNFs electrodes follows first-order kinetics model and is driven by a physisorp-tion process.
To examine whether acid treatment of a non-graphitizing hard carbon influences positively or negatively its electrochemical ano-dic performance, this study reports the effects of sulfuric acid treatment on the microstructural changes and electrochemical per-formance of PAN-based hard carbons prepared at various temperatures. It was found that PAN-based hard carbons heat treated at 900 °C (TAN9) exhibit an increased reversible capacity by up to 8% following the sulfuric acid treatment (TAN9S series). Since small changes in microstructure, except for slight reductions in surface area and crystallite size (L a) value, were observed after sulfuric acid treatment, it was speculated that the capacity responses of samples in series TAN9S were due to the introduction of new functional groups such as ASO 3 H and ASO 4 H. As the newly intro-duced functional groups are strong acids but their conjugates (ASO À 3 and ASO À 4) are weak bases, those conjugates were thus con-sidered to be able to react with Li + ion relatively weakly and reversibly. For PAN-based hard carbons heat treated at 1100 °C (TAN11), there were much smaller changes, as compared with series TAN9S samples, in surface chemistry and microstructure by sulfuric acid treatment. Consequently, we observed an analogous but smaller influence of sulfuric acid oxidation on electrochem-ical performance. The samples from series TAN11S exhibited very stable cycling behavior. It was suggested that the acidity/basicity of surface functional groups may be an influential factor for improving the electrochemical performance of hard carbon-based ano-dic materials for lithium ion batteries.
Carbon functionalized with sulfonic acid groups has been synthesized using the one-step hydrothermal carbonization of furaldehyde and hydroxyethylsulfonic acid aqueous solution at 180 °C for 4 h. The carbon exhibited high acidity and comparable activities to sulfuric acid for the traditional acid-catalyzed reactions, which indicated that it has great potential for environment-friendly processes. The copolymerization method provides an efficient procedure for the synthesis of various functionalized carbons by one-step hydrothermal carbonization.
Reduction of a colloidal suspension of exfoliated graphene oxide sheets in water with hydrazine hydrate results in their aggregation and subsequent formation of a high-surface-area carbon material which consists of thin graphene-based sheets. The reduced material was characterized by elemental analysis, thermo-gravimetric analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, NMR spectroscopy, Raman spectroscopy, and by electrical conductivity measurements. (c) 2007 Elsevier Ltd. All rights reserved.
In capacitive deionization (CDI), an electrical potential difference is applied across oppositely placed electrodes, resulting in the adsorption of ions from aqueous solution and a partially ion-depleted product stream. CDI is a dynamic process which operates in a sequential mode; i.e., after a certain ion adsorption capacity has been reached, the applied voltage is reduced, and ions are released back into solution, resulting in a solution concentrated in ions. The energetic input of CDI is very small, while there are no ion-exchange materials involved that need to be replaced regularly. Here we present a dynamic process model for CDI which includes the storage and release of ions in/from the polarization layers of the electrodes. The charge and ion adsorption capacity of the polarization layers is described using the equilibrium Gouy¿Chapman¿Stern (GCS) model, while the charge transfer rate from bulk solution into the polarization layer is modeled according to Ohm¿s law, i.e., depends solely on an electric field term across a mass-transfer layer. An important element in the model is the differential charge efficiency: the effective salt removal rate relative to the electronic current, for which an analytical expression is derived based on the GCS model. We present results for the effluent salt concentration and electron current, both as function of time, based on a process model that assumes ideal mixing in the CDI unit cell. The theoretical results are in very good agreement with an example data set.
Porous electrodes are important in many physical−chemical processes including capacitive deionization (CDI), a desalination technology where ions are adsorbed from solution into the electrostatic double layers formed at the electrode/solution interface inside of two juxtaposed porous electrodes. A key property of the porous electrode is the charge efficiency of the double layer, Λ, defined as the ratio of equilibrium salt adsorption over electrode charge. We present experimental data for Λ as a function of voltage and salt concentration and use this data set to characterize the double-layer structure inside of the electrode and determine the effective area for ion adsorption. Accurate experimental assessment of these two crucial properties of the electrode/solution interface enables more structured optimization of electrode materials for desalination purposes. In addition, detailed knowledge of the double-layer structure and effective area gives way to the development of more accurate dynamic process models describing CDI