Synergistic effects of ionic and nonionic surfactants treatment on activated carbon electrodes for inverted capacitive deionization

Aggregation of Mixed (Cationic + Anionic) and (Cationic + Nonionic) Surfactant Systems within a (Lanthanide Salt:Urea) Deep Eutectic Solvent

Deep eutectic solvents (DESs) are emerging as versatile media to support and facilitate various molecular aggregation processes, including surfactant self-assembly. The effect of a type IV DES consisting of La(NO3)3·6H2O and urea in a 1:3.5 molar ratio named (La:U) as a solubilizing medium on the self-aggregation of (cationic + anionic) and (cationic + nonionic) surfactant mixtures with N-dodecyltrimethylammonium bromide (DTAB), sodium dodecyl sulfate (SDS), and Triton X-100 (TX-100) as cationic, anionic, and nonionic surfactants, respectively, is investigated. The surfactant mixtures are found to readily self-aggregate within the (La:U) DES across the complete composition range under ambient conditions. The critical aggregation concentrations (CACs) of both (DTAB + SDS) and (DTAB + TX-100) surfactant mixtures lie between the CACs of the respective surfactants in the mixture, indicating that, owing to its ionic nature, the (La:U) DES effectively screens the charges present on the surfactant headgroups. While for the (DTAB + SDS) mixture, this observation is in contrast to that in aqueous media, it is similar to that in water for the (DTAB + TX-100) mixture. Both investigated surfactant mixtures exhibit a mostly negative interaction parameter (β) within the DES, implying the presence of predominantly attractive interactions between DTAB and SDS/TX-100. The thermodynamic parameters estimated for both surfactant mixtures within the (La:U) DES indicate aggregation to be a spontaneous process. While it appears to be both enthalpically and entropically driven, it is predominantly entropically driven. Using fluorescence spectroscopic methods, the aggregation number (Nagg) of the self-assembly of mixed surfactant systems is estimated and the solute solvation microenvironment afforded by these aggregates within the (La:U) DES is also ascertained. The outcomes will help expand the application potential of such polar DESs by establishing them as alternate and effective media for mixed surfactant aggregation.

A novel asymmetric CDI device for targeted removal of cation in water desalination

A novel asymmetric capacitive deionisation (CDI) device was home-made for the removal of cations from an aqueous solution through the structural innovation in this experiment. The adsorbent materials were characterised by Scanning Electron Microscope and BET as well as performing cyclic voltammetry curve tests. The results showed that the materials exhibited excellent performance (the specific surface area is 321.14 m²/g) and the maximum specific capacitance of the adsorbent material can reach 60 F/g at the 5 mV/s. The optimal operating conditions of the asymmetric CDI device were obtained using an orthogonal test method analysis and response surface methodology: the best desalination efficiency of CDI obtained at the concentration is 455.82 mg/L, the potential is 1.18 V and the flow rate is 46.54 mL/min. After the analysis of first-order kinetic model, it can be obtained that the fastest adsorption efficiency for Ca²⁺, followed by Mg²⁺, and the slowest for Na⁺, and the CDI device had a better adsorption effect on divalent cations. Simulation by Comsol software showed that the adsorption efficiency was better at a high flow rate. In addition, the CDI device has good stability and the mechanism of targeted cation removal and mass transfer process of the CDI were discussed in detail.

Upgrading Waste Activated Carbon by Equipping Micro-/Mesopore-Dominant Microstructures from the Perspective of Circular Economy

Equipping wastes with interesting properties in response to the circular economy could release environmental burdens by reducing resource exploitation and material manufacturing. In this study, we demonstrated that the waste regenerated activated carbon (RAC) could become micro-/mesopore-dominant through a simple surfactant/gel modification. This was achieved by associating carbon precursors, such as commercially available low-cost surfactants/methyl cellulose thickening reagents, with the pores of RAC. Following heat treatment, associated carbon precursors were carbonized, hence modifying the microstructure of RAC to be micro-/mesopore-dominant. The surfactant modification gave rise to a micropore-dominant RAC by increasing the micropore volume (PVmicro) together with significantly decreasing the mesopore volume (PVmeso) and macropore volume (PVmacro). In contrast, gel modification led to mesopore-rich RAC by blocking micropores with carbonized methyl cellulose and a surfactant matrix. Interestingly, both surfactant/gel modifications were insensitive to the properties of the surfactant applied, which provided a new alternative for waste/low-grade surfactant mixture disposal. Our results provide an important demonstration that waste could be effectively upgraded with a rational design by exhibiting new properties in response to the circular economy.

Agricultural waste buckwheat husk derived bifunctional nitrogen, sulfur and oxygen-co-doped porous carbon for symmetric supercapacitors and capacitive deionization

A practical strategy for the value-added utilization of agricultural waste was provide. The buckwheat husk derived N, S, O-co-doped porous carbon was used as bifunctional electrode materials for symmetric supercapacitor and capacitive deionization.