Capacitive Removal of Heavy Metal Ions from Wastewater via an Electro-Adsorption and Electro-Reaction Coupling Process

Supramolecular hyperbranched polymer gels based on pillar[5]arene and their applications in removal of micropollutants from water

Two kinds of pillar[5]arene-based supramolecular hyperbranched polymer gels were constructed and applied to efficiently remove micropollutants from water.

Efficient and selective removal of Pb(ii) from aqueous solution by a thioether-functionalized lignin-based magnetic adsorbent

The effective and selective removal of heavy metal ions from sewage is a major challenge and is of great significance to the treatment and recovery of metal waste. Herein, a novel magnetic lignin-based adsorbent L@MNP was synthesized by a thiol-ene click reaction under ultraviolet (UV) light irradiation. Multiple characterization techniques, including Fourier transform infrared (FT-IR) spectrometry, X-ray diffraction (XRD), elemental analysis, vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), confirmed the formed nano-morphology and structure of L@MNP. The effects of pH, contact time, initial metal concentration and temperature on the batch adsorption of Pb(ii) by L@MNP were investigated. Due to the existence of sulfur and oxygen-containing sites, the maximum adsorption capacity of L@MNP for Pb(ii) could reach 97.38 mg g^-1, while the adsorption equilibrium was achieved within 30 min. The adsorption kinetics and isotherms were well described by the pseudo-second-order model and Langmuir model, respectively, suggesting a chemical and monolayer adsorption process. In addition, L@MNP showed a high adsorption selectivity (k _Pb = 0.903) toward Pb(ii) in the presence of other co-existing metal ions. The experimental results also revealed that L@MNP displayed structural stability, ease of recovery under an external magnetic field, and acceptable recyclability after the fifth cycle. Considering its facile preparation, low cost and high adsorption efficiency, the developed L@MNP adsorbent demonstrated great potential in removing heavy metal ions from wastewater.

Potential Oscillated Electrochemical Metal Recovery System with Improved Conversion Kinetics and High Levelized Quality

Electrodeposition, which is an eco-friendly process with high efficiency, is one of the most promising technologies for metal recovery. However, the kinetics are often limited by the polarization and uncontrollable quality of deposits during the electrodeposition process, which restrict the efficiency and controllability of metal recovery. To ameliorate the limitations of the deposition rate and as-formed deposit quality, transient electrodeposition was introduced to control the microinterfacial reaction by regulating the relationship between charge and mass transfer. The Cu²⁺ removal efficiency and kinetic coefficient during 1 kHz transient electrodeposition were 17.4 and 17.7% higher than those under the conventional steady electric stimulus, respectively. Based on the combined results of X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS), it was found that the chemical composition of the deposits from transient electrodeposition was more homogenous, as indicated by the low content of metal oxides. The in situ Raman spectra explained the homogenous composition based on the weak interaction of the electrode with the anions during the transient electrodeposition, which was mainly due to the enhanced dehydration under the oscillating or alternating electric field. The potential oscillation induced by the transient electric field also facilitated dehydration, charge transport, and mass transfer, which led to rapid and high-quality metal recovery. Transient electrodeposition will have a great guidance value in the field of metal electroplating and heavy metal recovery from wastewater by electrodeposition.

Adsorption Performance of Amino Functionalized Magnetic Molecular Sieve Adsorbent for Effective Removal of Lead Ion from Aqueous Solution

Lead ion (Pb²⁺) has high toxicity and brings great harm to human body. It is very important to find an effective method to address lead ion pollution. In this work, amino functionalized CoFe₂O₄/SBA–15 nanocomposite (NH₂–CoFe₂O₄/SBA–15) was prepared for the effective removal of Pb²⁺ from aqueous solution. The prepared NH₂–CoFe₂O₄/SBA–15 adsorbent was manifested by using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectrum (FTIR), X-ray powder diffraction (XRD), and Brunauer-Emmett-Teller (BET) analysis. In the meantime, the adsorption conditions, including pH, adsorbent dosage, and adsorption time, were studied. The investigation of adsorption kinetics revealed that the adsorption results conform to the pseudo-first-order kinetic model. The adsorption isotherms research displayed that the adsorption was consistent with the Freundlich model, demonstrating that the adsorption for Pb²⁺ with the prepared adsorbent was a multimolecular layer adsorption process. In addition, the thermodynamic investigations (ΔG < 0, ΔH > 0, ΔS > 0) demonstrated that the adsorption for Pb²⁺ with the prepared adsorbent was endothermic and spontaneous. Moreover, the prepared adsorbent showed superior anti-interference performance and reusability, implying the potential application of the adsorbent in actual water treatment. Furthermore, this research may provide a reference and basis for the study of other heavy metal ions.

Capacitive Removal of Fluoride Ions via Creating Multiple Capture Sites in a Modulatory Heterostructure

Fluoride pollution has become a major concern because of its adverse effects on human health. However, the removal capacity of defluorination agents in traditional methods is far from satisfactory. Herein, capacitive removal of F^- ions via creating multiple capture sites in a modulatory heterostructure has been originally demonstrated. The heterostructure of uniformly dispersed Al₂O₃ coating on hollow porous nitrogen-doped carbon frameworks was precisely synthesized by atomic layer deposition. An exceptional F^- ion removal efficiency at 1.2 V (95.8 and 92.9% in 5 and 10 mg/L F^- solutions, respectively) could be finally achieved, with a good regeneration ability after 20 consecutive defluorination cycles. Furthermore, we investigated the removal mechanisms of F^- ions by in situ Raman, in situ X-ray diffraction, and ex situ X-ray photoelectron spectroscopy measurements. The promotional removal capacity was realized by the multiple capture sites of the reversible conversion of Al-F species and the insertion of F^- ions into the carbon skeleton. This work offers an important new pathway and deep understanding for efficient removal of F^- ions from wastewater.

Magnetic and electric field accelerate Phytoextraction of copper Lemna minor duckweed

In accordance with the opinion of the World Health Organization and the World Water Council the development of effective technologies for the treatment of wastewater from heavy metals for their discharge into water bodies or reuse is an urgent task nowadays. Phytoremediation biotechnologies is the most environmentally friendly and cheapest way of the treatment of wastewater, suitable for sustainable development principals. The main disadvantage of the phytoremediation is the slow speed of the process. A method for accelerating the process of phytoremediation by the combined effect of magnetic and weak electric fields is proposed. The purpose of this study is to determine the values of the parameters of the magnetic and weak electric fields that are most suitable for extracting cuprum ions from wastewater using the higher aqua plants (Lemna minor). A corresponding technological process based on the results of the study is proposed. The results have shown that the removal of copper cations from sulfate solutions effectively occurs in the initial period of time (1–5 hours) under the influence of a magnetic field with an intensity of H = 2 kA/m. Under the combined influence of an electrical current with density j = 240 μA/cm² and a magnetic field (H = 2 kA/m) the highest rate of copper extraction by duckweed leaves is achieved. Under these conditions, the greatest growth and development of plant leaves occurs. The paper presents the results of determining of the parameters of the electrochemical release from the eluate of the spent phytomass of duckweed. It has been determined that the release of metal occurs at E = 0.32 V. An original scheme for wastewater treatment from copper with subsequent separation of copper from the spent phytomass of duckweed is proposed. In general, the presented results are a scientific justification of wastewater treatment technologies and a contribution to resolving the crisis in the field of fresh water supply. An important contribution in the circular economy is a technology recommendation proposed for recovering copper from duckweed after wastewater treatment.

Electrochemical recovery and high value-added reutilization of heavy metal ions from wastewater: Recent advances and future trends

Wastewater treatment for heavy metals is currently transitioning from pollution remediation towards resource recovery. As a controllable and environment-friendly method, electrochemical technologies have recently gained significant attention. However, there is a lack of systematic and goal oriented summarize of electrochemical metal recovery techniques, which has inhibited the optimized application of these methods. This review aims at recent advances in electrochemical metal recovery techniques, by comparing different electrochemical recovery methods, attempts to target recycling heavy metal resources with minimize energy consumption, boost recovery efficiency and realize the commercial application. In this review, different electrochemical recovery methods (including E-adsorption recovery, E-oxidation recovery, E-reduction recovery, and E-precipitation recovery) for recovering heavy metals are introduced, followed an analysis of their corresponding mechanisms, influencing factors, and recovery efficiencies. In addition, the mass transfer efficiency can be promoted further through optimizing electrodes and reactors, and multiple technologies (photo-electrochemical and sono-electrochemical) could to be used synergistically improve recovery efficiencies. Finally, the most promising directions for electrochemical recovery of heavy metals are discussed along with the challenges and future opportunities of electrochemical technology in recycling heavy metals from wastewater.

Selective Capacitive Removal of Heavy Metal Ions from Wastewater over Lewis Base Sites of S-Doped Fe-N-C Cathodes via an Electro-Adsorption Process

The pollution of toxic heavy metals is becoming an increasingly important issue in environmental remediation because these metals are harmful to the ecological environment and human health. Highly efficient selective removal of heavy metal ions is a huge challenge for wastewater purification. Here, highly efficient selective capacitive removal (SCR) of heavy metal ions from complex wastewater over Lewis base sites of S-doped Fe-N-C cathodes was originally performed via an electro-adsorption process. The SCR efficiency of heavy metal ions can reach 99% in a binary mixed solution [NaCl (100 ppm) and metal nitrate (10 ppm)]. Even the SCR efficiency of heavy metal ions in a mixed solution containing NaCl (100 ppm) and multicomponent metal nitrates (10 ppm for each) can approach 99%. Meanwhile, the electrode also demonstrated excellent cycle performance. It has been demonstrated that the doping of S can not only enhance the activity of Fe-N sites and improve the removal ability of heavy metal ions but also combine with heavy metal ions by forming covalent bonds of S^- clusters on Lewis bases. This work demonstrates a prospective way for the selective removal of heavy metal ions in wastewater.