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[Display omitted] Porous carbon materials have been regarded as a promising alternative to activated carbon for desalination via capacitive deionization (CDI) due to refined architectures and functionalities. However, it is still challenging to obtain a controlled hierarchical pore structure and considerable nitrogen-doped content by convenient method. Herein, nitrogen-doped hierarchical porous carbon foams (NHCFs) with different microstructural features, nitrogen contents and nitrogen species were successfully fabricated via a stepwise pyrolysis carbonization strategy using easily available melamine foam. Due to the synergistic effect of hierarchical porous structure and doped nitrogen, the optimized NHCF sample carbonized at 800℃ (NHCF-800) exhibited a maximum desalination capacity of 30.1 mg g−1 at the optimal operating parameters (500 mg/L NaCl solution, 1.2 V) and an excellent regeneration performance after 50 continuous adsorption–desorption cycles. Furthermore, density functional theory (DFT) was also conducted to elaborate the disparity of sodium adsorption energy among the nitrogen species for in-depth understanding, and it mainly benefits from the ascendency of the pyrrolic-N and pyridinic-N over the graphitic-N dopant. This work paves the way of rational regulation of nitrogen-doped process and hierarchical porous structure carbon as CDI electrode materials for desalination. [ABSTRACT FROM AUTHOR]

• An efficient method is presented for the recovery of In3+ from acidic solution. • The activated carbon electrode shows good capability for electrosorption of In3+. • The recovery of In3+ is mainly based on electrical double-layer charging. • In3+ ions are preferentially electrosorbed in a competitive environment. High-efficiency recycling technology for endangered elements effectively mitigates the risk of resource shortages and promises the sustainability of supply chains, which is significant to the industry. In this study, an activated carbon (AC)-based capacitive deionization (CDI) for the selective electrosorption and recovery of indium ions (In3+) from acidic aqueous solution is proposed. The effects of applied voltage, pH, and initial concentration of indium were investigated to optimize the operation parameters for In3+ electrosorption. The results of cyclic voltammetry and the galvanostatic charge/discharge measurements indicate that the AC electrode shows good capability for the electrosorption of In3+ based on electrical double-layer capacitance. As demonstrated, In3+ can be successfully removed by CDI without deposition when the pH < 4, as confirmed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The deionization capacity of In3+ is 7.95 mg/g with an energy consumption of 0.84 kWh/mol in single-pass mode CDI with an initial concentration of 50 mg/L (pH = 3) at 1.2 V. However, the removal of In3+ is affected by the solution pH since hydrogen ions (H+) compete for electrosorption. Note that In3+ ions with high valence are preferentially electrosorbed on the electrode surface over H+ ions, exhibiting a selectivity coefficient of 2.12. Herein, in the charging step, a large number of H+ ions in solution are rapidly electrosorbed onto the electrode, while these H+ ions are gradually replaced by a small number of In3+ ions in solution. Therefore, this electrosorption process shows great potential for effectively recovering indium ions from acidic aqueous solutions. [ABSTRACT FROM AUTHOR]

Membrane capacitive deionization (MCDI) as a promising approach was developed to simultaneously conduct water desalination and metal recovery by using activated carbon fiber (ACF) as electrodes. The removal performance of two metal ions (Cu2+, Zn2+) was firstly investigated at different voltages. Experiments showed that the adsorption amount of Cu2+ was higher than that of Zn2+ under the voltage of 0.4–0.6 V. However, inverse result was obtained at the voltage of 0.8–1.2 V that the adsorption amount of Cu2+ was lower than that of Zn2+. The analysis of scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) showed that Cu2+ removal involved the adsorption and electrodeposition, and the reduction potential of Cu2+ was found to be 0.6 V. At a higher voltage, Cu2+ was reduced and the reduction product consisting of Cu/Cu 2 O would decrease the effective surface area and cause serious degradation of electrode properties, which inhibited Cu2+ adsorption. Comparatively, Zn2+ reduction was only observed at the voltage of 1.2 V. FTIR showed that the difference of the reduction potential was partly attributed to the type of functional groups of ACF and its affinity towards ions. Considering the gap of the reduction potential, the feasibility of selective reduction and recovery of Cu(0) from CuCl 2 /ZnCl 2 mixed solution was studied by controlling the applied voltage and the optimal voltage was determined to be 0.8 V. The recovery efficiency of Cu(0) in the competitive environment could reach to 42.8% at the voltage of 0.8 V. Moreover, the electrode regeneration was investigated and it was found that the performance of fouled electrode could be effectively recovered for further reuse via cleaning methods. [ABSTRACT FROM AUTHOR]

Abstract The authors tailored coconut-based activated carbons with a quaternary ammonium epoxide (QAE) surfactant that greatly increased the carbon's capacity for sorbing nitrate from water. This QAE-tailored carbon processed deionized water spiked with 50 mg/L NO 3 − through rapid small scale column tests; and achieved half-breakthrough at 477 bed volumes. This favorably compared to 52 bed volumes for the pristine coconut activated carbon. The QAE employed herein was QUAB 360. Most favorable pretreatment of the carbon was achieved via NaOH immersion, which created extensive phenolic functionality on the carbon's graphene edges, and raised the carbon's slurry pH to 9.3–9.6. These phenolics served as the anchor for the QUAB's epoxide reactions. This pretreatment offered the highest QUAB loading onto the carbon, which in turn netted the most nitrate removal. Per X-ray photoelectron spectroscopy, favorable QUAB360 preloading incurred a 1.62% increase in the quaternary N content of these activated carbons. The phenolic functionality that followed pretreatment was discerned by Boehm titrations; and these mathematically matched with Gaussian-based models that were fitted to incremental titration data. The most favorable QUAB-loaded variants were the ones whose pretreated precursors had exhibited the highest peak of functionality in the 9.3–10.4 pH range—corresponding to the pK a of phenolics. If the precursor pH was below the 9.3–9.6 range—as induced by acids or H 2 O 2 , then the QUAB's epoxide intermediate apparently over-reacted with the hydroxylated functionality of other QUAB molecules, rather than with phenolic functionality of the carbon's graphene edge sites. Graphical abstract Image 1 Highlights • QAE preloading onto GAC can be able to remove the low concentrations of contaminants as well as the higher one. • mechanismThe carbon slurry pH influenced the pathway of the QAE epoxide-forming reactions and the anchoring mechanism. • pK distribution with Gaussian-based models for characterizing the surface acidity of pretreated activated carbon variants. • The proportion of functional groups calculated by pK distribution are close to the ones obtained by the Boehm titration. [ABSTRACT FROM AUTHOR]

The main objective of this study was to banana waste-derived activated carbon (BWAC) make a high pore surface area was prepared and composited with Fe 3 O 4 via a facile hydrothermal method. Various physiochemical characteristics of the prepared samples were evaluated using XRD, FTIR, FESEM, Raman Spectroscopy and XPS analysis. In addition, cyclic voltammetry and electrochemical impedance spectroscopy analyses were performed to determine the electrochemical properties of the prepared samples. The Fe 3 O 4 /BWAC sample showed a higher capacitance (285 F g−1) than BWAC at the same scan rate of 10 mV s−1. The capacitive deionization (CDI) cell configuration was varied, and its electro-sorption and defluoridization efficiencies were analyzed during the lead (Pb2+) removal 90%. An asymmetric combination of electrodes in the CDI cell exhibited better heavy metal removal performance, possibly due to the synergistic effect of the high surface area and the balance between the active adsorption site and the overlapping effect of the EDL. As a result, Fe 3 O 4 /BWAC could be a potential resource for supercapacitors and CDI electrodes, and the novel Fe 3 O 4 /BWAC nanocomposites outstanding performance suggests that they could be helpful for future energy storage and environmental applications. [Display omitted] • Fe 3 O 4 /BWAC nanocomposite was fabricated via a facile hydrothermal method. • The Fe 3 O 4 /BWAC nanocomposite showed a higher capacitance of 285 F g−1 was obtained. • The results proved high electrochemical kinetics and defluoridization ability. • Fe 3 O 4 /BWAC nanocomposite is promising electrode for removing Pb2+. [ABSTRACT FROM AUTHOR]

Currently, efficient and cost-effective recycling of waste capacitors is a pressing issue. In this study, the recovery of electrode powder from waste supercapacitors and enabling the reuse of the prepared samples are reported. The recovered powder is directly activated by mixing it with KOH using chemical activation to regenerate the waste-activated carbon. The regenerated activated carbon's specific surface area could be restored to a level similar to that of the original commercial powder, reaching 1803.15 m2/g. The regenerated activated carbon has a high proportion of microporous, which played a crucial role in its electrochemical performance. The samples' capacity in the organic system reached 125.96 F/g at 0.2 A/g and 111.77 F/g at 20 A/g, with a retention rate of 88.74%. Furthermore, the capacitance was maintained at 91.18% after 10,000 cycles, showing good cycling performance. Additionally, the supercapacitor assembled from the regenerated activated carbon delivered a high energy density of 31.83 Wh/kg and a power density of 269.76 W/kg, indicating great application potential. Overall, this study offers a useful and low-cost approach for recycling activated carbon from waste electrodes, which would be possible for supercapacitors recycling. [Display omitted] • The waste electrode carbon powder is regenerated into activated carbon. • The electrochemical properties of 21RAC-3 are superior than 21KSN. • 21RAC-3 organic supercapacitor exhibits an energy density of 31.83 Wh/kg. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) is an alternative, effective and environmentally friendly technology for desalination of brackish water. The performance of the CDI device is highly determined by the electrode materials. In this paper, a composite of carbon nanotubes (CNTs) embedded in activated carbon nanofiber (ACF) was prepared by a direct co-electrospinning way and subsequent CO 2 activation. The introduction of CNTs can greatly improve the conductivity while the CO 2 -mediated activation can render the final product with high porosity. As such, the hybrid structure can provide an excellent storage space and pathways for ion adsorption and conduction. When evaluated as electrode materials for CDI, the as-prepared CNT/ACF composites with higher electrical conductivity and mesopore ratios exhibited higher electrosorption capacity and good regeneration performance in comparison with the pure ACF. [ABSTRACT FROM AUTHOR]

The combined effect of resorcinol/catalyst (100≤R/C≤800) and resorcinol/water (0.04≤R/W≤0.13) molar ratio on the textural and capacitive properties of carbon aerogels with potential application for capacitive deionization has been evaluated. Activated and pyrolyzed aerogels were synthesized by the sol-gel polymerization of resorcinol-formaldehyde mixtures and dried in supercritical conditions. Data show that high R/C and R/W molar ratios lead to materials with large pores in the mesopore range, whereas the surface area and micropore volumes remain somewhat the same. The activation of the aerogels increased the differences in the specific surface and micropore volumes due to the development of microporosity. This effect was more remarkable for the samples with low R/C whatever the R/W ratio, indicating that the carbon aerogel obtained using high amounts of catalyst are more prone to be activated. Regarding the electrochemical features of the aerogels, low capacitance values were measured in aerogels combining low R/W and high R/C and reciprocally low R/C and high R/W molar ratios, due to their higher resistance. Polarization resistances were found to be slightly higher for the pyrolyzed than for activated aerogels, and followed a decreasing trend with the mesoporosity, indicating the outstanding contribution of the mesoporous network to provide a good kinetic response. The desalting capacity of monolithic aerogels showed a simultaneous dependence with the surface area and the resistivity of the electrodes, pointing out the importance of performing electrochemical measurements in adequate cell configurations (i.e., desalting units) upon the intended application. [ABSTRACT FROM AUTHOR]

Developing technological solutions that use yerba mate waste as precursors is key to reducing the environmental impact caused by the lack of treatment and its accumulation in landfills. Due to their physicochemical properties, these residues can be used to develop activated carbons. Activated carbon is a versatile material with a high surface area that can be used for energy storage. In this work, yerba mate residues were valued by producing chemically activated carbon to be used as electrode material in supercapacitors. Activated carbons were developed through chemical activation in two steps with KOH. Variables such as impregnation ratio and activation temperature are studied. The developed carbons were characterized by physicochemical and electrochemical techniques. They were found to have high surface areas, up to 1800 m2 g-1, with a hierarchical porous distribution. A maximum specific capacitance of 644 F g-1 at 0.1 A g-1, and power values of ca 32,000 W kg-1, at 33 A g-1 were found. All the synthesized carbons have excellent electrochemical properties and are suitable for use as active material in supercapacitors. [Display omitted] • Activated carbons are successfully synthesized using yerba mate as a precursor. • The activated carbons have high surface areas and hierarchical pore distribution. • The maximum specific capacitance reach is 644 F g-1 at 0.1 A g-1. • The maximum capacitance retention is 91% at 7.5 A g-1, after 1000 cycles. • The synthesized carbons are suitable as active materials in supercapacitors. [ABSTRACT FROM AUTHOR]

The integrated high-efficiency treatment technology for dye industry wastewater is one of the current research hot topic in industrial wastewater treatment area. This article reports a new fluidized three-dimensional electrochemical treatment process integrating activated carbon adsorption, direct electro-oxidation and ·OH oxidation. In the process, activated carbon is polarized in a fluidized bed electrochemical reactor to enhance the direct electro-oxidation and ·OH oxidation, and there is a synergistic effect of effective adsorption and electrochemical oxidation to strengthen the treatment efficiency. When 200 mg/L methyl orange is processed, its removal rate reaches 99.9% in 30min, and the synergistic efficiency is 57.3%. After 8 cycles of activated carbon reusage in the process, the removal rate of methyl orange still kept at 89.2%. It is also founded that the activated carbon maintains 64.5% of its original adsorption capacity during the cycle. These results shows its interesting application potential in the fields of high-efficiency, low-cost and green treatment of various industrial organic wastewaters. Further improvements should focus on the development of continuous operation model and the improvement of the activated carbon electro-catalytic performance and the practical regeneration ways of the activated carbon particle electrodes. [Display omitted] • Study on three-dimensional electrode integrated process of fluidized activated carbon. • The synergistic effect of adsorption and electrochemical oxidation was observed. • It can remove 99.9% of 200 mg/L methyl orange, obtain 57.3% synergistic efficiency. • Activated carbon can maintain 64.5% adsorption capacity in 10 cycles. • Polarized activated carbon improve the direct electro-oxidation and ·OH oxidation. [ABSTRACT FROM AUTHOR]

This study's aim was to compare biochar and steam activated biochar functionalized with iron for removal of selenium as selenate from solutions also containing nitrate and sulfate. The Fe-biochar composites were made impregnating iron (ferric nitrate) onto regular biochar (RB) and steam activated biochar (SAB), forming the Fe-biochar composites FeRB and FeSAB. Iron oxyhydroxide deposits were observed on the surface of FeRB using Raman spectroscopy analysis, but not on the FeSAB surface. Unmodified biochar samples did not remove selenium, as Se(VI), from solution, whereas FeRB and FeSAB recovered 8.3 mg-Se⋅g-composite−1 and 5.9 mg-Se⋅g-composite−1, respectively. Higher Se uptake was achieved at higher Fe-loads and lower acetone:biochar ratio, to a maximum of 17.3 mg-Se⋅g-composite−1 (FeRB). Washing after Fe-impregnation using deionized water diminished nitrate and Fe-leaching from the Fe-biochar composites while removing selenium. Se(VI) and sulfate uptake were observed when washed composites were tested in the presence of possible competing ions at environmentally relevant concentrations ([Se] t=0 = 1.01 ± 0.03 mg⋅L−1; [N–NO 3 - t=0 = 40.2 ± 0.2 mg⋅L−1; and [SO 4 2− t=0 = 496 ± 25 mg⋅L−1). One of the possible mechanisms of removal might be the complexation of Se with the iron oxyhydroxide deposits (goethite and hematite) found on the FeRB surface. Image 1 • Iron oxide deposits were found on the surface of the Fe-biochar composites. • Modifying the biochar surface by steam activation results in less Fe-leaching. • Fe-biochar composites using non-activated biochar have higher Se uptake. • Leaching of N–NO 3 and Fe can be eliminated by continuous washing the composites prior use. • Washed composites removed simultaneously Se and SO 4 at environmental conditions. [ABSTRACT FROM AUTHOR]