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The efficiency of saturated Activated Carbon (AC) electrochemical regeneration was evaluated. Reactor configurations in cathodic/anodic process, applied current effect on the properties of AC and Methylene Blue MB-AC interactions and adsorption/desorption mechanisms were studied. The efficiency was measured by adsorption capacity adsorption/regeneration cycles and changes in the adsorbent characteristic were analyzed through FTIR, BET, Optical Microscopy (OM) and SEM before and after the regeneration. The energy consumption was analyzed to assess the economic feasibility. It was found that the electrochemical treatment was efficient in returning the AC adsorption capacity, maximum efficiencies of approximately 79% and 84% were reached when the Carbon Fiber Cloth-AC electrode was subjected to anodic and cathodic currents, respectively, at a current of 0.1 A. In addition, the material demonstrated good stability through adsorption-regeneration cycles by cathodic process, with the material's adsorption capacity being almost totally recovered for 8 consecutive cycles. The removal percentage around 80% was kept after the cycles, with optimal conditions when the electrode was subjected to cathodic currents, NaCI as electrolyte at a current of 0.1 A for 2 h. The characterization techniques provided results that allow to explain the higher and prolonged efficiency of the cathodic current. Furthermore, these reactor configurations achieved an electrical energy consumption of 2.3 and 2.1 kWh kg-1 of material for cathodic and anodic, respectively. These results indicate that the electrochemical is an economical and environmental suitable technique capable of restore carbon adsorbents to be reusable for several water treatment cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] The efficiency of saturated Activated Carbon (AC) electrochemical regeneration was evaluated. Reactor configurations in cathodic/anodic process, applied current effect on the properties of AC and Methylene Blue MB-AC interactions and adsorption/desorption mechanisms were studied. The efficiency was measured by adsorption capacity adsorption/regeneration cycles and changes in the adsorbent characteristic were analyzed through FTIR, BET, Optical Microscopy (OM) and SEM before and after the regeneration. The energy consumption was analyzed to assess the economic feasibility. It was found that the electrochemical treatment was efficient in returning the AC adsorption capacity, maximum efficiencies of approximately 79% and 84% were reached when the Carbon Fiber Cloth-AC electrode was subjected to anodic and cathodic currents, respectively, at a current of 0.1 A. In addition, the material demonstrated good stability through adsorption-regeneration cycles by cathodic process, with the material's adsorption capacity being almost totally recovered for 8 consecutive cycles. The removal percentage around 80% was kept after the cycles, with optimal conditions when the electrode was subjected to cathodic currents, NaCl as electrolyte at a current of 0.1 A for 2 h. The characterization techniques provided results that allow to explain the higher and prolonged efficiency of the cathodic current. Furthermore, these reactor configurations achieved an electrical energy consumption of 2.3 and 2.1 kWh kg −1 of material for cathodic and anodic, respectively. These results indicate that the electrochemical is an economical and environmental suitable technique capable of restore carbon adsorbents to be reusable for several water treatment cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • The roles of specific N-containing groups on HCHO removal were comprehensively studied. • The ACN-600 exhibited the superior HCHO adsorption capacity (16.37 mg/g). • DFT calculation results indicated that pyrrolic-N exhibited the highest HCHO adsorption energy (−32.83 kJ/mol). • Pyridinic-N could trigger the Cannizzaro-type disproportionation reaction. Inserting nitrogen (N) heteroatoms into the carbonaceous adsorbents has been confirmed to be one of efficient strategies for enhancing HCHO removal. However, the essential promotion mechanisms of specific N-containing groups (such as pyridinic-N, pyrrolic-N, and quaternary-N) remain blurred. Herein, a series of N-doped activated carbons were prepared by annealing the melamine impregnated activated carbons at 600–900 °C and used for HCHO elimination. It manifested that the HCHO elimination performance of samples was remarkably improved after N-doping and their HCHO adsorption capacities were in the order of ACN-600 (16.37 mg/g) > ACN-750 (9.87 mg/g) > ACN-900 (7.28 mg/g) > AC (5.09 mg/g). DFT calculation results revealed that there existed stronger attractive noncovalent interactions between pyrrolic-N doped carbon and HCHO due to the formation of stronger H-bonds. Therefore, the HCHO physisorption energy on pyrrolic-N doped carbon was the highest (−32.83 kJ/mol). Compared with the single physisorption mechanism of previous studies, the in-situ DRIFTS results manifested that the pyridinic-N atom (as a typical strong Lewis base) could trigger the Cannizzaro-type disproportionation reaction, which would transform toxic HCHO into relatively less toxic methanol and formic acid. Benefiting from the dual enhanced mechanisms of attractive noncovalent interactions and Cannizzaro-type disproportionation reaction, the ACN-600 manifested excellent HCHO removal performance. This study not only intrinsically discloses the promotion mechanism of specific N-containing groups on HCHO removal at molecular level but also provides guidelines for rational design and development of carbonaceous materials for effective HCHO elimination. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) holds great promise for phosphorus adsorption and recovery from wastewater, while current electrodes exhibit poor salt adsorption capacity (SAC) and selectivity due to co-ion effect and interference of co-existed ions with high concentration. Herein, to overcome these issues, a facile route was proposed to prepare a covalent organic framework-membrane coating electrode (COF-MCE) by depositing polyvinyl alcohol/polyethyleneimine membrane onto activated carbon fiber (ACF) followed by the in-situ growth of COF-LZU1. Compared to ACF and MCE, COF-MCE, with abundant functional groups and specific sites, facilitated electrical double layer (EDL)-based adsorption and induced hydrogen-bond interaction with phosphorus, contributing to a higher SAC of phosphorus (10.5 mg/g) in treating 1 mM NaH 2 PO 4. When treating different mixtures of NaH 2 PO 4 /NaCl, NaH 2 PO 4 /NaNO 3 , and NaH 2 PO 4 /Na 2 SO 4 with molar ratio of 1:5, COF-MCE exhibited the high phosphorus selectivity of 3.62, 5.98 and 7.01, respectively, which was attributed to the synergistic effects of EDL-based adsorption, hydrogen-bond and pseudocapacitance. Desorption experiments revealed that high reversal voltage and alkaline condition can weaken the hydrogen-bond interaction and strengthen the electrostatic repulsion between COF-MCE and phosphorus, thus improving the desorption and recovery of phosphorus. These findings confirmed the high potential of COF-MCE in the effective electrosorption and recovery of phosphorus from wastewater. • COF-MCE was prepared by casting followed by in-situ growth of COF powders. • Inhibited co-ion effect and enhanced EDL formation led to superb P adsorption. • Hydrogen-bond and redox-reaction interaction contributed to high selectivity for P. • A reversal voltage and high pH weakened the interaction and favored P recovery. [ABSTRACT FROM AUTHOR]

• The effect of operating conditions on the desalination rate was studied. • Under various conditions, ion adsorption follows a quasi-first order kinetic model effectively. • MCDI outperforms other CDI methods in desalination rate and ion adsorption. • Optimal conditions: 1.6 V voltage, 30 mL/min flow rate, 1000 mg/L initial concentration. Membrane Capacitive Deionization (MCDI) is an efficient desalination technology using ion-selective membranes and capacitive principles to remove ions. Highly mineralized water flows through parallel electrode plates separated by ion-selective membranes. An applied electric field adsorbs ions onto electrodes, creating an electric double layer, and periodic field reversals release enriched ions back into the water while discharging ions on the electrode surfaces, enabling continuous deionization. This study aims to investigate the feasibility of using MCDI technology with Prussian blue analog (PBA)/carbon electrodes to treat highly mineralized water in oilfields. The desalination rate under different operating conditions is experimentally analyzed and compared. A comparison is made between the Capacitive De-Ionization (CDI) systems in terms of changes in conductivity, desalination rate, ion adsorption capacity, and ion adsorption rate. Results showed that compared to conventional CDI and Hybird-CDI (HCDI), MCDI demonstrates the highest desalination rate, ion adsorption capacity, and ion adsorption rate. It indicates that MCDI has significant advantages in treating highly mineralized water. At a voltage of 1.6 V, a flow rate of 30 mL·min−1, and an initial concentration of 1000 mg·L−1, the MCDI system exhibited the highest desalination efficiency. Under these conditions, the desalination rate was 43.4%, the electrosorption capacity was 54.75 mg·g−1, and the electrosorption rate was 0.018 mg·g−1·s−1. The study provides a viable solution for the treatment of highly mineralized water in oilfields and serves as a reference for further improvement and application of MCDI technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitric acid oxidation promotes moderate dissociation of petroleum pitch. • Preparation Multi cavity Carbon Microsheets by using NaCl and Modified pitch. • Multi cavity carbon microsheets have excellent NO 3 – removal performance of CDI. • DFT calculations indicate carbon cavity is beneficial for NO 3 – electron enrichment. Capacities deionization (CDI) denitrification technology has attracted considerable attention, and electrode materials with nitrate adsorption properties have become a research hotspot. In this study, a multi cavity carbon microsheets (MCCM-5) was prepared using a hard template method and low-cost nitrated pitch as a carbon source. The results of the electrosorption experiments showed that the material had an excellent capacity of NaNO 3 (45 mg g−1). Furthermore, although the actual specific surface area and specific capacitance of MCCM-5 are lower than those of hierarchical porous carbon materials (HPCM-1), MCCM-5 exhibit lower diffusion and charge-transfer resistances, resulting in a better denitrification performance. The adsorption capacity of MCCM-5 for NaNO 3 was twice that HPCM-1 and 11.8 times that of commercial activated carbon, which is superior to the material properties reported thus far. Our analysis indicated that the material combined the advantages of both a layered structure and hierarchical pores. First, the uniformly distributed hierarchical pores in the layered structure enhanced the ion concentration potential. Second, the layered structure provided good ion diffusion channels, thereby increasing the effective adsorption area of the material. DFT calculation shows that the carbon cavity structure enriched in the material shows a stronger adsorption capacity for NO 3 –, which can promote the electron transfer process during NO 3 – adsorption. This study shows that a precise regulation of the carbon material structure can be achieved by adjusting the size of the template material and carbonization conditions to obtain a higher adsorption capacity and provides a new idea for the structural optimization of electrode materials. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Electrosorption performance of activated carbons was examined for the desalination. • The effect of pore structure on capacitive characteristics was investigated. • High specific capacitance suggested high salt adsorption capacity. • CDI Ragone provided comprehensive view on desalination capacity and rate. • Single-pass mode CDI was desirable to estimate desalination performance. Abstract In the present work, the electrosorption performance of activated carbon-base capacitive deionization (CDI) was evaluated by batch and single-pass mode experiments. Two commercial activated carbon electrodes with raw materials of coal (AC1) and wood (AC2) were selected and their physical and electrochemical characteristics were determined by Brunauer–Emmett–Teller (BET) and cyclic voltammetry experiments. The results indicated that micropores and mesopores are well-balanced in both AC1 and AC2. The specific surface of AC1 (940 m2/g) was higher than that of AC2 (662 m2/g), and the AC1 showed a higher specific capacitance from cyclic voltammetry curves. CDI characteristics could be determined from the batch-mode and single-pass experiment, both AC1 and AC2 showed good electrosorption performance. The batch-mode, however, can only serve as evaluation of basic CDI performance. As evidenced in single-pass experiments with 2 mM NaCl at 1.0 V, AC1 exhibited a higher salt adsorption capacity of 5.08 mg/g-carbon than that of AC2 (2.39 mg/g-carbon). The CDI Ragone plot from single-pass experiments was further used as a functional tool to provide the key performance indicators: salt adsorption capacity and mean deionization rate. In the CDI Ragone plot, AC1 appeared towards the top and right side, showing that AC1 was more well-developed than AC2. In addition, the impact of pore structure on electrosorption performance was clearly observed. Overall, this study can provide a fundamental basis for understanding the estimation of CDI performance. [ABSTRACT FROM AUTHOR]

Polysaccharide-based hydrogel adsorbents become popular because of their high adsorption capacity and fast adsorption rate, but their low removal rate and poor pH resistance have always been fatal shortcomings. Herein, a feasible strategy was proposed to strengthen the ability of hydrogel adsorbent to remove organic pollutants (i.e., dye) by incorporating natural rectorite (REC) into chitosan- g -poly (2-acrylamido-2-methyl-propane-sulfonic-acid) hydrogel network to form a rectorite-in-polymer network structure. The introduction of less dosage of REC (1.2 wt%) into the hydrogel facilitates to improve its adsorption capacities toward methylene blue (MB) in deionized water, tap water, seawater, Yangtze River water, and Yellow River water (1083.39–1303.49 mg/g); while incorporating higher content of REC (15.8 wt% REC) helps to improve the removal rate (99.6% for MB in real waters), which are greatly superior to commercial activated carbons. The adsorbent keeps high adsorption efficiency in a broad pH range (2–11), and can be reused for >4 times. [Display omitted] • Synthesized chitosan-based hydrogel has a rectorite-in-polymer composite network. • The hydrogel shows high adsorption capacity (1303.49 mg/g) and removal rate (99.6 %). • Removal efficiency keeps high in real waters (Yangtze River, Yellow River, seawater). • The hydrogel's adsorption capacity far exceeds that of commercial activated carbon. • This method is universal to enhance the removal efficiency of hydrogel adsorbent. [ABSTRACT FROM AUTHOR]

Flow electrode capacitive deionization (FCDI) has great advantages in high salinity wastewater desalination. However, due to the limited adsorption capacity of electrode material, membrane concentration polarization would form and increase energy consumption, and affect the continuity of desalination. In this work, milling technology was used to modify original activated carbon (AC), the obtained ball milled activated carbon (BAC) was used as FCDI electrode material. The milling process modified multiple physical and electrochemical characteristics of original AC. The highest average salt removal rate (ASRR) of BAC was 2.2 times of that of AC, which was attributed to the modified surface properties including more oxygenated functional group, larger electrostatic gravitation characteristics and better hydrophilicity. The reduced concentration polarization during the desalination was responsible for the increased adsorption capacity, which was due to larger electrolyte contact area, enhanced ions capacity by more suitable pore structures, and 5 times higher energy normalized removal salt (ENRS) of BAC flow electrode than that of AC. Because of its simple operation and remarkable modification effect, ball milling technology shows great potential in large scale modification of electrode materials. [ABSTRACT FROM AUTHOR]

Cadmium (Cd2+) is the main toxic heavy metal in desulphurisation wastewater for coal-fired power plants. Here, a novel carbon skeleton/molybdenum disulphide composite material (MoS 2 /AC) with expanded layer spacing was synthetized in one step for Cd2+ removal through the capacitive deionization method. As the results showed, the Cd2+ removal capacity of the MoS 2 /AC cell was 22.15 mg g−1, and the concentration of Cd2+ in the simulated wastewater was effectively reduced from 10 ppm to <0.1 ppm. According to the characterisation, the layer spacing of MoS 2 nanosheets in MoS 2 /AC increased by 58.06% compared with the original commercial MoS 2 , which could provide more active sites for Cd2+ adsorption. Moreover, the XPS results showed that electrosorption and complexation on the surface of MoS 2 /AC were the main routes for Cd2+ removal, especially the complexation between Cd2+ and metal-sulphur. In addition, the selective adsorption efficiency of MoS 2 /AC was more than 98% under the coexistence of other ions, such as Na+, Mg2+, and Ca2+. The regenerated MoS 2 /AC also had a high adsorption capacity for Cd2+ even after 5 cycles. The MoS 2 /AC material also exhibited excellent removal capability for heavy metal ions in the actual desulphurisation wastewater from coal-fired power plants (<1 ppb). The results indicated that MoS 2 /AC may be a prospective material for heavy metal ion removal from wastewater. [Display omitted] • MoS 2 /AC was developed as an effective CDI electrode material. • High Cd2+ absorption capacity of 22.15 mg g−1 and excellent recyclability. • The obtained MoS 2 /AC possess enlarged interlayer spacing to expose S adsorption sites. • The exposed sulphur atoms complexed with cadmium ions to remove Cd2+. [ABSTRACT FROM AUTHOR]

Capacitive deionization (CDI) technology is a high-efficiency, energy-saving, green and environmentally friendly new water treatment technology, which will have potential in the field of low-salinity seawater desalination. Current carbon-based electrode materials have limited desalination capacity and rate due to insufficient ion-accessible specific surface area and slow ion transmission rate. Here, we demonstrate layered porous carbon (CHPC) derived from Chitosan, colloidal SiO 2 and polytetrafluoroethylene (PTFE) mixed carbonization for efficient CDI desalination. CHPC has abundant macropores that are connected with mesopores. This layered porous structure enables CHPC to have a faster ion migration rate. The salt removal capacity of CHPC reaches 26.5 ± 1.5 mg/g, and the average adsorption rate is 8.8 ± 0.5 mg/g/min, which are about 1.6 and 10 times than that of commercial activated carbon, respectively. In addition, CHPC has extremely strong anti-interference performance against organic macromolecules, which could maintain more than 95% adsorption capacity after 30 cycles. Our work helps to promote the practical application of hierarchical porous structures based on typical biomass in large-capacity and fast-rate CDI desalination technology. [Display omitted] • CHPC forms a macroporous-mesoporous hierarchical carbon network framework through a multi-step etching reaction. • CHPC achieves an ultra-fast adsorption efficiency of 8.8 ± 0.5 mg/g/min due to fast ion/electron transport. • CHPC has excellent cycle stability and resistance to interference from macromolecular substances. [ABSTRACT FROM AUTHOR]

Activated-carbon-electrodes are widely used in capacitive deionization (CDI). However, the desalination capacity of most activated carbons remains to be improved, which makes it necessary to explore activated carbons with special structure and improved desalination capacity. In this context, we studied the desalination performance of super activated carbons with ultra-high total pore volume (V Tot). This carbon showed a salt adsorption capacity of 27.2 mg/g in 500 mg/L NaCl solution at 1.2 V, which ranked among the highest value ever reported for activated carbons. The high adsorption capacity was due to the large V Tot caused by the abundant presence of both micropores and mesopores in the material. The adsorption capacity of the carbon after 10 adsorption-desorption cycles (saturated adsorption capacity) was as high as 67.6 mg/g, which was dominated by V Tot and water contact angle. The sample also showed excellent desalination rate and superior charge efficiency (76.5%). This study indicated that superior desalination performance could be obtained by using super activated carbon with high pore volume as a CDI electrode material. [Display omitted] • SAC with high pore volume (AC-P-CO 2) showed excellent desalination performance. • The salt adsorption capacity of AC-P-CO 2 was 27.2 mg/g. • The salt adsorption capacity ranked among the highest values for activated carbons. • The salt adsorption capacity after 10 cycles of AC-P-CO 2 was 67.6 mg/g. • AC-P-CO 2 showed superior desalination rate and charge efficiency (76.5%). [ABSTRACT FROM AUTHOR]

• The first high entropy oxides based multifunctional electrode material is synthesized by simple grinding technique. • Nano-sized (< 10 nm) high entropy oxides are incorporated in surface functionalized biowaste derived activated carbon. • High salt adsorption capacity of 241 mg g−1 and cycle repeatability upto 20 cycles is demonstrated. • The excellent desalination capacity is attributed to the combined electric-double layer and pseudocapacitive mechanism. Nano-sized high entropy oxides (particle size < 10 nm) are expected to possess enhanced stability, electrochemical properties and increased potential in versatile applications than bulk metal oxides. In this study, nano-sized high entropy oxides incorporated surface functionalized coconut shell derived activated carbon (HEO/f-CSAC) is synthesized, characterised and used as an advanced multifunctional material for electrochemical energy storage and desalination. Attributed to its unique microstructure and extraordinary properties, HEO/f-CSAC shows an excellent salt adsorption capacity of 241 mg g−1 at 1.2 V in 500 mg L−1 concentration of NaCl solution, which is very high as compared to previous reports. The reason behind high salt adsorption capacity is its outstanding specific capacitance of 147.5 F g−1 at current density 1 A g−1. Moreover, the assembled lab-scale CDI unit demonstrates extremely good performance upto 20 adsorption-desorption cycles due to the long cycle life with good capacitance retention of fabricated HEO/f-CSAC based two-electrode supercapacitor. Additionally, a red light-emitting diode illumination by connecting three supercapacitors in series, indicates the high efficiency and potential of HEO/f-CSAC for real life energy-related application. These results prove that HEO/f-CSAC can be implemented for water desalination with enhanced supercapacitive performance manifesting its multifunctionality for energy and environmental applications. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • QRAC electrodes selectively adsorb NO 3 – due to the difference in binding energy. • The selectivity coefficient of QRAC-5 to NO 3 – reaches 2.7 at 0.4 V. • The electrosorption behavior of QRAC depends on physical adsorption and ion exchange adsorption. Nitrate pollution has become an increasingly serious water pollution problem worldwide. Capacitive deionization (CDI) technology is an emerging water treatment technology that can efficiently remove nitrate in water with advantages of simple process, high water recovery rate, low cost and energy consumption. In this work, we engineer a covalently bonded quaternized activated carbon (QRAC) material by silanization and investigate its selective adsorption of nitrate in mixed solution with extended voltage capacitive deionization (eV-CDI) mode. The results show that (1) the QRAC electrodes achieve selective adsorption due to the different adsorption binding energies of the quaternary ammonium group with Cl- and NO 3 –. The selectivity coefficient of QRAC-5 to NO 3 – reaches 2.7 at 0.4 V and the electrosorption capacity is 140% higher than that of AC in 5/5 mM KCl/KNO 3 solution. (2) The electrosorption of QRAC electrodes are dominated by two aspects: physical adsorption by external electric field which occurs in the incipient stage and ion exchange adsorption by quaternary ammonium groups occurring in the following stage. (3) CDI experiments in simulated municipal wastewater show that SO 4 2- had a negative effect on the adsorption capacity of NO 3 –, but QRAC electrode can still achieve separation effect in Cl-/NO 3 – solution system. These results show that covalently bonded quaternized activated carbon can achieve the effective separation and removal of NO 3 – in polluted water, and our work provides new insights into the selective electrosorption of CDI technology. [ABSTRACT FROM AUTHOR]

In this study, the activated graphene (AG) was applied to remove a malachite green (MG) as an adsorbent. The AG with fractal structure was synthesized at high temperature under a nitrogen (N 2) environment. The fractal structure is shaped like a branch that extends apart because the AG is created by the rGO with a thin sheet. The fractal structure allows AG to have a high surface area. The surface area of AG was found to be 1885.7 m2 g−1. Also, it makes many pores of micro, meso-size which improves the quality as compared to traditional activated carbon (AC). Due to these features, the maximum MG adsorption capacity was 791.27 mg L−1 within the contact time at 40 min. Freundlich isotherm and pseudo-second-order were fitted to AG. Moreover, after cleaning with ethanol and deionized water, the recycled AG maintained a 99.44% removal efficiency which suggesting a good reusability. The AG showed better adsorption capacity than commercial AC showing that AG could be utilized as an excellent adsorbent for next-generation owing to its high removal efficiency, eco-friendly nature, and the long-lasting ability for adsorption of MG. [Display omitted] • Activated graphene (AG) was successfully synthesized under N 2 atmosphere. • The AG has the fractal structure owing to the edge. • The fractal structure of AG has micro, meso-size pores with high surface area. • The maximum adsorption capacity of AG is 791.27 mg L−1 for malachite green. [ABSTRACT FROM AUTHOR]

Pb2+ adsorption onto activated carbon was studied as a function of the different liquid medium during batch adsorption process without shaking/agitation of flasks (where adsorbate and adsorbent coexist). As liquid medium deionized water (DW) enhanced with gases bulk nanobubbles (bNBs) was used. The adsorbent material used was activated carbon from potato peels. The maximum Pb2+ adsorption capacity (Q m) was 9 mg/g in the case of adsorption process in DW without agitation, whereas the respective Q m was 94 mg/g by using DW-bNBs as medium without agitation. It was also found that Q m increased to 171 mg/g in the adsorption process with DW-bNBs and agitation (150 rpm). This finding was the start point of a new experimental design where after re-agitation (intense shaking of 225 rpm) of the respective experimental case (94 mg/g), the final Q m was 163 mg/g i.e. very close to the one corresponding to simultaneous adsorption and agitation from the beginning. The results are analyzed and discussed intensively to lead in several important implications on the influence of bNBs to the bulk solute mass transfer. Based on our experimental equilibrium data a modified-Langmuir equation was developed, applied and proposed so as to better simulate the whole (complicated) process. [ABSTRACT FROM AUTHOR]

• Freundlich model can well describe the phosphate electroadsorption behavior. • CDI electroadsorption is an endothermic process according to thermodynamics. • pH was determined by water electrolysis and forms transformation of phosphate. • Surface charge can reflect the amount of ions adsorbed by GCS model. The advanced treatment for phosphate (P) has been focused on in the wastewater treatment field in recent years. Developing an innovative P removal technology with high efficiency, low cost, and low energy consumption has become an imperative requirement. Capacitive deionization (CDI) is an emerging environmentally friendly technology for removing charged ions from aqueous solutions. In this study, we investigated the performances of P removal by CDI with homemade activated carbon electrodes. Furthermore, kinetics, thermodynamics and the equilibrium Gouy-Chapman-Stern (GCS) double-layer model were studied to reveal the mechanism of P adsorption. It was observed that the adsorption capacity was positively correlated with the voltage. The pH first increased and then decreased during the adsorption because of water electrolysis and forms transformation of phosphate. The experimental results were validated by pseudo-first-order adsorption kinetics and Freundlich isotherms. The adsorption rate increased with increasing temperature, voltage, and concentration. The adsorption capacity decreased with increasing temperature, and the maximum adsorption capacity was 8.53 mg/g. Thermodynamic analysis confirmed that the electrosorption of P on the activated carbon electrode was an endothermic process, and the high temperature was conducive to reducing the adsorption potential of P on the activated carbon electrode. The theoretical results of the double layer model were in agreement with the experimental data, which showed that the ion adsorption can be reflected by surface charge. This study can help to understand the adsorption mechanism of P on activated carbon electrodes and provide a theoretical basis for the application of P removal by CDI. [ABSTRACT FROM AUTHOR]

Introduction of new nanomaterials with conductivity, salt adsorption capacity (SAC) and rate (SAR) exceeding that of carbon electrodes may greatly improve capacitive deionization of water. However, those materials show a different electrochemical behavior, which must be studied and optimized for practical use. Here, effects of operating conditions on desalination performance of pre-conditioned Ti 3 C 2 T x -MXene-based electrodes in a symmetric membrane capacitive deionization (MCDI) system were investigated. Specifically, influences of discharge potential, half-cycle length (HCL), and flow rate were systematically studied. Results showed different degrees of performance dependence on operating conditions. For instance, lower discharge potentials increased SAC and SAR by 152%. However, longer HCL increased SAC by 32% while decreasing SAR by 54%. Finally, faster flow rates decreased both SAC and SAR by 20%. Desalination performances of symmetric pre-conditioned MXene and activated carbon cloth (ACC) electrodes were gravimetrically and volumetrically compared in MCDI system. Pre-conditioned MXene electrodes gravimetrically performed 30% lower than ACC due to their notably higher density. Yet, pre-conditioned MXene electrodes volumetrically outperformed ACC by 162%. Results suggest that although MXenes offer high electrochemical activity and hydrophilicity, making them promising candidates for CDI applications, the strong dependence of desalination performance of MXenes on operating conditions requires in-depth understanding and warrants further research. Unlabelled Image • Pre-conditioned MXene outperforms ACC by 162% due to bulk volume ion storage. • Pre-conditioned MXene MCDI system has shown steady SAC for 100 cycles. • Lower discharge potentials enable more effective ion deintercalation. • Improved ion deintercalation leads to up to 152% increase in SAC and SAR. • Longer half-cycle length increases SAC by 32% and decreases SAR by 54%. [ABSTRACT FROM AUTHOR]