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Heteroatom doping, involving the introduction of atoms with distinct electronegativity into carbon materials, has emerged as an effective approach to optimize their charge distribution. In this study, we designed a strategy to synthesize in-situ Mn, N co-doped carbon nanospheres (Mn-NC) through the polycondensation of 2,6-diaminopyridine and formaldehyde in synchronization with Mn2+ chelation to form Mn-polytriazine precursor, followed by calcination to form carbonaceous solid. Then Mn-NC was fabricated into a capacitive deionization (CDI) electrode for the selective removal of uranium ions (U (VI)), which is commonly found in radioactive water. Interestingly, Mn-NC exhibited good selectivity for UO 2 2+ capture with a demonstrated adsorption capacity of approximately 194 mg/g @1.8 V. The systematic analysis of the adsorption mechanism of UO 2 2+ revealed that N dopants within Mn-NC can coordinate with the U (VI) ions, thereby facilitating the removal process. Our study presents a straightforward and convenient strategy for removing UO 2 2+ ions by harnessing the coordination effect, eliminating the requirement for pore size control. [Display omitted] • Trace Mn in N doped carbon can boost charge density and adsorption energy. • Mn–N–C adsorbs UO 2 2+ ions by coordination interaction with high selectivity. • This material has a good adsorption capacity of 194 mg/g @1.8 V. [ABSTRACT FROM AUTHOR]

With the continuous development of society, industrialization, and human activities have been producing more and more pollutants. Fluoride discharge is one of the main causes of water pollution. This review summarizes various commonly used and effective fluoride removal technologies, including ion exchange technology, electrochemical technology, coagulation technology, membrane treatment, and adsorption technology, and points out the outstanding advantages of adsorption technology. Various commonly used fluoride removal techniques as well as typical adsorbent materials have been discussed in published papers, however, the relationship between different adsorbent materials and adsorption models has rarely been explored, therefore, this paper categorizes and summarizes the various models involved in static adsorption, dynamic adsorption, and electrosorption fluoride removal processes, such as pseudo-first-order and pseudo-second-order kinetic models, Langmuir and Freundlich isotherm models, Thomas and Clark dynamic adsorption models, including the mathematical equations of the corresponding models and the significance of the models are also comprehensively summarized. Furthermore, this comprehensive discussion delves into the fundamental adsorption mechanisms, quantification of maximum adsorption capacity, evaluation of resistance to anion interference, and assessment of adsorption regeneration performance exhibited by diverse adsorption materials. The selection of the best adsorption model not only predicts the adsorption performance of the adsorbent but also provides a better description and understanding of the details of each part of the adsorption process, which facilitates the adjustment of experimental conditions to optimize the adsorption process. This review may provide some guidance for the development of more cost-effective adsorbent materials and adsorption processes in the future. [Display omitted] • Overview of commonly used effective fluoride removal technologies. • The various models involved in different fluoride removal modes by adsorption are classified and summarized. • Combining models to describe the adsorption process and mechanism of different materials. • The adsorption capacity, anion resistance, and adsorption regeneration performance of different materials are discussed. [ABSTRACT FROM AUTHOR]

Abstract Hexavalent chromium is highly toxic and elaborate technology is necessary for ensured removal during drinking water production. The present study aimed at estimating the potential of a micro-sized iron hydroxide (μGFH] adsorbent for chromate removal in competition to ions presents in drinking water. Freundlich and Langmuir models were applied to describe the adsorption behaviour. The results show a high dependency on the pH value with increasing adsorption for decreasing pH values. The adsorption capacity in deionized water (DI) at pH 7 was 5.8 mg/g Cr(VI) while it decreased to 1.9 mg/g Cr(VI) in Berlin drinking water (DW) at initial concentrations of 1.2 mg/L. Desorption experiments showed reversible adsorption indicating ion exchange and outer sphere complexes as main removal mechanisms. Competing ions present in DW were tested for interfering effects on chromate adsorption. Bicarbonate was identified as main inhibitor of chromate adsorption. Sulfate, silicate and phosphate also decreased chromate loadings, while calcium enhanced chromate adsorption. Adsorption kinetics were highly dependent on particle size and adsorbent dose. Adsorption equilibrium was reached after 60 min for particles smaller than 63 μm, while 240 min were required for particles from 125 μm to 300 μm. Adsorption kinetics in single solute systems could be modelled using the homogeneous surface diffusion model (HSDM) with a surface diffusion coefficient of 4∙10 −14 m2/s. Competitive adsorption could be modelled using simple equations dependent on time, adsorption capacity and concentrations only. Graphical abstract Image 1 Highlights • Micro-seized ferric hydroxide (μGFH) useful as adsorbent for chromate. • Decreased capacities in drinking water due to the competition by carbonate species. • Improved kinetics in contrast to conventional GFH due to small particle size. • Modelling of chromate adsorption onto μGFH with the homogeneous surface diffusion model in single solute systems. • Modelling of competitive adsorption using a model dependent only on time, adsorption capacity and concentrations. [ABSTRACT FROM AUTHOR]

The resin-activated carbon composite (RAC) electrodes were fabricated and applied in capacitive deionization for recovery of V(V) from complex vanadium solution. The adsorption capacity of the RAC electrode for V(V) is extremely low and the reduction of V(V) is significant in low pH solution, but the adsorbed V(V) on the electrode increases obviously and the reduction of V(V) gradually diminishes with the rise of pH. However, as the pH is increased to 10, the adsorbed V(V) on the RAC electrode declines. The higher applied potential is beneficial to the adsorption of V(V) and 1.0 V is appropriate for the adsorption. The impurities ions (Al, P and Si) are mainly adsorbed in the electric double layers on the RAC electrode and V(V) is dominantly adsorbed by the resins in the electrode. The adsorbed impurity ions can be easily removed by diluted H 2 SO 4 and V(V) can be effectively eluted by 10% NaOH solution. The vanadium-bearing eluent can be recycled to recover and enrich vanadium from the complex solution. The performance of the RAC electrode keeps stable during the cyclic operation. This study may provide a promising and novel method for the recovery and separation of metals from aqueous solution. [ABSTRACT FROM AUTHOR]

Polyethersulfone (PES) is a widely used polymer for ultrafiltration (UF) membrane fabrication. In the current study, carbide-derived carbon (CDC) oxidized by acid treatment was utilized as a filler to fabricate a novel PES composites UF membranes. The successful oxidation of CDC was validated from presence of oxygen containing functional groups and improved oxygen content, from 5.08 at.% for CDC to 26.22 at.% for oxidized CDC (OCDC). The OCDC PES UF membranes were prepared at different loadings of OCDC between 0.5 and 3.0 wt%. The membrane porosity, pore size and surface free energy found to be improved while a noticeable reduction in water contact angle was observed with OCDC loading implying the improved hydrophilicity of PES membranes. Consequently, the pure water flux found to improve from 151.6 to 569.6 (L/(m2. h)) for the 3.0 wt% modified OCDC membrane (M−3) which is 3.8 folds of the bare PES membrane. The antifouling characteristics were evaluated by humic acid (HA) filtration. The results revealed a significant enhancement in HA rejection with OCDC loading, the highest rejection was 96.8% for M−3 membrane. Additionally, the adsorption capacity of OCDC modified membranes found to decrease with OCDC loading indicating improved rejection of HA from the membrane surface. Moreover, M−3 demonstrated the maximum flux recovery ratio (FRR) of 92.3%. Reusability of the fabricated membranes was evaluated by deionized water/humic acid cycling filtration. The FRR was higher than 86.7% over three cycles of pure water/HA filtration for 140 min, indicated the excellent stability and reusability of the membranes. Overall, the OCDC was an effective filler for enhancing the PES UF membranes antifouling and permeability properties. [Display omitted] • Oxidized carbide-derived carbon (OCDC) was synthesized by acid treatment. • PES UF membrane porosity, contact angle and hydrophilicity were improved with OCDC addition. • Humic acid rejection and antifouling properties were improved with OCDC loading. • Long term filtration experiments of pure water and humic acid were considered. • The OCDC found to be an effective and compatible filler for PES UF membranes. [ABSTRACT FROM AUTHOR]

The performance of the membrane capacitive deionization (MCDI) system was evaluated during the removal of three selected pharmaceuticals, neutral acetaminophen (APAP), cationic atenolol (ATN), and anionic sulfamethoxazole (SMX), in batch experiments (feed solution: 2 mM NaCl and 0.01 mM of each pharmaceutical). Upon charging, the cationic ATN showed the highest removal rate of 97.65 ± 1.71%, followed by anionic SMX (93.22 ± 1.66%) and neutral APAP (68.08 ± 5.24%) due to the difference in electrostatic charge and hydrophobicity. The performance parameters (salt adsorption capacity, specific capacity, and cycling efficiency) and energy factors (specific energy consumption and recoverable energy) were further evaluated over ten consecutive cycles depending on the pharmaceutical addition. A significant decrease in the specific adsorption capacity (from 24.6 to ∼3 mg−NaCl g−1) and specific capacity (from 17.6 to ∼2.5 mAh g−1) were observed mainly due to the shortened charging and discharging time by pharmaceutical adsorption onto the electrode. This shortened charging time also led to an immediate drop in specific energy consumption from 0.41 to 0.04 Wh L−1. Collectively, these findings suggest that MCDI can efficiently remove pharmaceuticals at a low energy demand; however, its performance changes dramatically as the pharmaceuticals are present in the target water. [Display omitted] • The performances of the MCDI system were evaluated during pharmaceutical removal. • Neutral APAP, cationic ATN, and anionic SMX were tested. • Neutral APAP was removed ∼68% while ionic ATN and SMX were removed >93%. • A significant decrease in SAC and SC were observed. • The shorter operation time of the pharmaceutical addition led to lower SEC and E R. [ABSTRACT FROM AUTHOR]