Heavy metals widely exist in wastewater, which is a serious threat to human health or water environment. Highly efficient removal of heavy metal ions from wastewater is a major challenge to wastewater treatment. In this work, capacitive removal of heavy metal ions from wastewater via an electro-adsorption and electro-reaction coupling process was originally demonstrated. The removal efficiency of heavy metal ions in the binary-component solutions containing metal nitrate (10 mg/L) and NaCl (100 mg/L) can reach 99%. Even the removal efficiency of heavy metal ions can be close to 99% in the multi-component solution containing all the seven metal nitrates (10 mg/L for each) and 100 mg/L NaCl. Meanwhile, the electro-adsorption and electro-reaction coupling process maintained excellent regeneration ability even after 20 cycles. Furthermore, the heavy metal ions removal mechanism was proven to be the pseudocapacitive intercalation of heavy metal ions into the layered structure of the employed W18O49/graphene in the electro-adsorption and electro-reaction coupling process. This work demonstrates great potential for general applicability to wastewater treatment.

Water pollution has become an environmental hazard. Diverse metal cations exist in wastewater; lead is the most common heavy metal pollutant among them. Selective removal of highly toxic and ultradiluted lead ions from wastewater is a major challenge for water purification. Here, selective capacitive removal (SCR) of lead ions from wastewater over redox-active molybdenum dioxide/carbon (MoO2/C) electrodes was developed by an environment-friendly asymmetric capacitive deionization (CDI) method. The MoO2/C spheres act as cathodes of an asymmetric CDI device and effectively reduce the concentration of Pb2+ from 50 ppm to <0.21 ppb. Moreover, the SCR efficiency of lead ions over redox-active MoO2/C electrodes is >99% in mixtures of 100 ppm Pb­(NO3)2 and 100 ppm NaCl solutions. In addition, the electrodes exhibit high regeneration performance in mixtures of NaCl and Pb­(NO3)2 and high SCR efficiency for lead ions from mixtures of heavy metal ions. The tetrahedral structure of the [MoO4] lattice is shown to be more favorable for the intercalation of lead ions. In situ Raman spectroscopy further shows that the transition of the crystal interface between [MoO6] and [MoO4] cluster lattice could be electrochemically controlled during SCR. Therefore, this study provides a new direction for the SCR of lead ions from wastewater.

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.

During the design and construction of an efficient iron–nitrogen–carbon (Fe–N–C) electrocatalyst, it was difficult to avoid the formation of iron oxides along with the hierarchical carbon frameworks containing dispersed FeN x sites. As a result, a slow oxygen reduction reaction (ORR) occurred, making it difficult to improve the electrocatalytic property. Herein, we have successfully synthesized the Fe, N-doped hierarchically porous carbon architectures from FeTe-trapped ZIF-8 coated with polydopamine by heat treatment. During the pyrolysis process, the evaporation of tellurium could inhibit the formation of iron oxides, promote the formation of more FeN x active species, and facilitate the formation of mesoporous structure to accelerate mass transfer and increase the approachability of active species. The resulting Fe, N-doped porous carbon architectures possessed excellent ORR catalytic performance, and the half-wave potential was 10 mV more than that of the precious Pt/C catalysts. Besides, the obtained catalysts present a superb methanol tolerance and long-term durability compared to precious Pt/C catalysts in alkaline media. This work opens up new avenues for the construction of the uniformly dispersed FeN x sites catalysts for ORR.

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