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Recovering chemical energy embedded in pollutants is significant in achieving carbon-neutral industrial wastewater treatment. Considering that industrial wastewater is usually treated in a decentralized manner, in situutilization of chemical energy to achieve waste-to-treasure should be given priority. Herein, the chemical energy released by the electroreduction of Cr(VI) was used to enhance on-site H2O2generation in a stacked flow-through electrochemical system. The driving force of water flow efficiently coupled O2evolution with 2-e O2reduction to facilitate H2O2generation by transporting anode-produced O2to the cathode. Meanwhile, the chemical energy released by Cr(VI) promoted O2evolution and impeded H2evolution by regulating the electrode potentials, accounting for the enhanced H2O2generation. The system could completely reduce 10–100 ppm of Cr(VI), reaching the maximum H2O2concentration of 2.41 mM. In particular, the H2O2concentrations in the Cr(VI)-containing electrolyte were 10.6–88.1% higher than those in the Cr(VI) free electrolyte at 1.8–2.5 V. A 24-day continuous experiment demonstrated the high efficiency and stability of the system, achieving a 100% reduction efficiency for 100 ppm of Cr(VI) and producing ∼1.5 mM H2O2at 1.8 V. This study presents a feasible strategy for Cr(VI) detoxification and synchronous on-site H2O2generation, providing a new perspective for innovative Cr(VI) wastewater treatment toward resource utilization.

Electrocatalytic nitrate (NO3–) reduction to N2via atomic hydrogen (H*) is a promising approach for advanced water treatment. However, the reduction rate and N2selectivity are hindered by slow mass transfer and H* provision–utilization mismatch, respectively. Herein, we report an open-framework cathode bearing electron-rich Co sites with extraordinary H* provision performance, which was validated by electron spin resonance (ESR) and cyclic voltammetry (CV) tests. Benefiting from its abundant channels, NO3–has a greater opportunity to be efficiently transferred to the vicinity of the Co active sites. Owing to the enhanced mass transfer and on-demand H* provision, the nitrate removal efficiency and N2selectivity of the proposed cathode were 100 and 97.89%, respectively, superior to those of noble metal-based electrodes. In addition, in situ differential electrochemical mass spectrometry (DEMS) indicated that ultrafast *NO2–to *NO reduction and highly selective *NO to *N2O or *N transformation played crucial roles during the NO3–reduction process. Moreover, the proposed electrochemical system can achieve remarkable N2selectivity without the additional Cl–supply, thus avoiding the formation of chlorinated byproducts, which are usually observed in conventional electrochemical nitrate reduction processes. Environmentally, energy conservation and negligible byproduct release ensure its practicability for use in nitrate remediation.

Hydroxyl radical (•OH) can hydroxylate or dehydrogenate organics without forming extra products and is thereby expediently applied in extensive domains. Although it can be efficiently produced through single-electron transfer from transition-metal-containing activators to hydrogen peroxide (H2O2), narrow applicable pH range, strict activator/H2O2ratio requirement, and byproducts that are formed in the mixture with the background matrix necessitate the need for additional energy-intensive up/downstream treatments. Here, we show a green Fenton process in an electrochemical cell, where the electro-generated atomic H* on a Pd/graphite cathode enables the efficient conversion of H2O2into •OH and subsequent degradation of organic pollutants (80% efficiency). Operando liquid time-of-fight secondary ion mass spectrometry verified that H2O2activation takes place through a transition state of the Pd–H*–H2O2adduct with a low reaction energy barrier of 0.92 eV, whereby the lone electron in atomic H* can readily cleave the peroxide bridge, with •OH and H2O as products (ΔGr= −1.344 eV). Using H+or H2O as the resource, we demonstrate that the well-directed output of H* determines the pH-independent production of •OH for stable conversion of organic contaminants in wider pH ranges (3–12). The research pioneers a novel path for eliminating the restrictions that are historically challenging in the traditional Fenton process.

Porous materials constructed from hierarchical pores are beneficial for the mass transport during the aqueous adsorption process. To achieve high performance, it is important to create adequate numbers of active centers to anchor the target ions in the solution. Synchronous construction of powerful bonding sites in the surface area amplification process should be a promising path for developing outstanding sorbents. By in situ evaporation of reductive soft organic templates, we successfully confined oxygen vacancies (VO) in porous La/Zr bimetallic oxides. For aqueous phosphate contaminants, the as-produced porous sorbent exhibited superior removal performance, with equilibrium adsorption capacities almost ∼2 times higher those that of the VO-free counterpart. Based on mass transfer model analysis, pore structure has the potential to buffer external influence on mass transfer. Under an adverse condition (pH 9.0), the mass transfer was ∼2.5 times higher than that in the pore-free one (0.10 min–1vs 0.04 min–1), ensuring the possibility of diffusing phosphate in further contact with these active sites. According to results of orbital interaction analysis and X-ray spectroscopy measurements, VO-dominated active sites not only enhanced attractive orbital bonding interaction toward phosphate but also converted repulsive interaction into attractive reaction, thereby eliminating this kinetics barrier and promoting the rate of phosphate chemisorption reaction.

Electrocatalytic hydrogen atom-hydroxyl radical (H*-·OH) redox system is a promising approach for contaminant removal and mineralization. However, its working mechanism, especially the effect of H*, remains unclear, hindering its practical application. Herein, we constructed an electrochemical reactor equipped with our self-made Pd-loaded Ti/TiO2nanotube cathode and a commercial boron-doped diamond anode. After fulfilling the electrode characterization and free radical detection, we employed coumarin and 7-azido-4-methylcoumarin as probes to confirm the participation of H* in the transformation of organic compounds. A comprehensive study on the degradation kinetics, reaction, and mineralization mechanisms using benzoic acid (BA) and 4-chlorophenol (4-CP) as model compounds was further conducted. The rate constants and total organic carbon removal of BA and 4-CP in the redox system increased compared with those of the individual oxidation and reduction processes. Theoretical calculations demonstrate that H* opens up alternative pathways for BA and 4-CP ring cleavage, forming quinones as reactive intermediates. Furthermore, H* facilitates the mineralization of the typical intermediates, maleic acid and fumaric acid, through C=C bond addition and H-abstraction from the 1,1-diol structure. The presence of H* provides alternative pathways for pollutant transformation, consequently reducing the treatment duration.

Long-term exposure to excessive iodine via drinking water presents health risks. Moderate oxidation of iodide (I–) to iodine (I2) has a better iodine removal effect than excessive oxidation to iodate (IO3–). This study combines computational and experimental methods to construct a heterogeneous interface with synchronous I–moderate oxidation and I2adsorption to increase the total iodine removal. Compared to other forms of crystal manganese dioxide (MnO2), theoretical calculations predict that MnO2with a γ-crystal structure has the lowest adsorption energy, that is, −1.20 eV, and a slight overlap between the conduction and valence bands, which favors electron transfer between I–and Mn(IV) and I2adsorption. Thus, γ-type MnO2was designed by adjusting the precursor Mn sources and hydrothermal reaction conditions. The liquid chromatography–inductively coupled plasma–mass spectrometry and high-performance liquid chromatography confirmed that the total iodine concentration in water decreased from 173.7 to 36.3 μg/L after 2 h, with 200 mg/L γ-MnO2dosage lower than the national standard of 0.1 mg/L. A minute proportion of I–in water was converted to IO3–(approximately 1.1 μg/L). The current I–adsorbent performed better than previously reported ones. During iodine removal, most of the I–migrated from water to the surface of γ-MnO2, and the ratio of I–to I2was determined to be 1:0.6 by X-ray photoelectron spectroscopy. This study evaluates iodine species transformation and an optimum strategy for heterogeneous interface design; it is promising for treating high-iodine groundwater.