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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]

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]

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]