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Heatwaves have substantial but poorly quantified impacts on surface ozone photochemical regimes. As heatwaves of increasing severity occur, communities face more serious exposure to ozone, necessitating a more comprehensive understanding of the impact of heatwaves on the nonlinear response of ozone to its precursors for guiding policies in emission reductions. Here we estimate the spatiotemporal evolution of global ozone chemistry based on machine learning and in situ observations and show that emission changes and heatwaves alter ozone photochemical regimes, leading to diverse ozone changes across regions. Sustained emission reductions in East Asia decreased the ozone formation sensitivity to formaldehyde (HCHO) and fine particulate matter (PM 2.5 ), counteracting the adverse high-temperature effect. Quantified results reveal that heatwaves increased the sensitivity of ozone to HCHO and PM 2.5 , enhancing their positive contributions and causing increased ozone trends across most regions, with a global average anomaly of 9.4 μg/m 3 . Meanwhile, heatwave-induced PM 2.5 anomalies concentrated in wildfire-risk zones, coupled with increased HCHO, elevated downwind ozone levels. Specifically, the effects in wildfire-endangered western Canada and heatwave-exposed southeastern United States contributed to a chemically driven ozone increase of 0.18 μg/m 3 /month in Northern America. Our results demonstrate that more targeted and substantial regulation of volatile organic compounds will be beneficial in mitigating future intensifying climate penalty effects.

Organic contaminants with lower Hammett constants are typically more prone to being attacked by reactive oxygen species (ROS) in advanced oxidation processes (AOPs). However, the interactions of an organic contaminant with catalytic centers and participating ROS are complex and lack an in-depth understanding. In this work, we observed an abnormal phenomenon in AOPs that the degradation of electron-rich phenolics, such as 4-methoxyphenol, acetaminophen, and 4-presol, was unexpectedly slower than electron-deficient phenolics in a Mn(II)/nitrilotriacetic acid/peroxymonosulfate (Mn(II)/NTA/PMS) system. The established quantitative structure-activity relationship revealed a volcano-type dependence of the degradation rates on the Hammett constants of pollutants. Leveraging substantial analytical techniques and modeling analysis, we concluded that the electron-rich phenolics would inhibit the generation of both primary (Mn(III)NTA) and secondary (Mn(V)NTA) high-valent manganese species through complexation and competition effects. Specifically, the electron-rich phenolics would form a hydrogen bond with Mn(II)/NTA/PMS through outer-sphere interactions, thereby reducing the electrophilic reactivity of PMS to accept the electron transfer from Mn(II)NTA, and slowing down the generation of reactive Mn(III)NTA. Furthermore, the generated Mn(III)NTA is more inclined to react with electron-rich phenolics than PMS due to their higher reaction rate constants (8314 ± 440, 6372 ± 146, and 6919 ± 31 M -1 s -1 for 4-methoxyphenol, acetaminophen, and 4-presol, respectively, as compared with 671 M -1 s -1 for PMS). Consequently, the two-stage inhibition impeded the generation of Mn(V)NTA. In contrast, the complexation and competition effects are insignificant for electron-deficient phenolics, leading to declined reaction rates when the Hammett constants of pollutants increase. For practical applications, such complexation and competition effects would cause the degradation of electron-rich phenolics to be more susceptible to water matrixes, whereas the degradation of electron-deficient phenolics remains largely unaffected. Overall, this study elucidated the intricate interaction mechanisms between contaminants and reactive metal species at both the electronic and kinetic levels, further illuminating their implications for practical treatment.

Development of new technologies with strong selectivity for target pollutants and low sensitivity toward a water matrix remains challenging. Herein, we introduced a novel strategy that used chlorite as an activator for Mn(VII) at pH 4.8, turning the inert reactivity of the pollutants toward Mn(VII) into a strong reactivity. This paved a new way for triggering reactions in water decontamination. By utilizing sulfamethoxazole (SMX) as a typical pollutant, we proposed coupled pathways involving electron transfer across hydrogen bonds (TEHB) and oxidation by reactive manganese species. The results indicated that a hydrogen bonding complex, SMX-ClO 2 - *, formed through chlorite binding the amino group of SMX initially in the TEHB route; such a complex exhibited a stronger reduction capability toward Mn(VII). Chlorite, in the hydrogen bonding complex SMX-ClO 2 - *, can then complex with Mn(VII). Consequently, a new reactive center (SMX-ClO 2 - -Mn(VII)*) was formed, initiating the transfer of electrons across hydrogen bonds and the preliminary degradation of SMX. This is followed by the involvement of the generated Mn(V)-ClO 2 - /Mn(III) in the reduction process of Mn(VII). Such a process showed pH-dependent degradation, with a removal ratio ranging from 80% to near-stagnation as pH increased from 4.8 to 7. Combining with p K a analysis showed that the predominant forms of contaminants were crucial for the removal efficiency of pollutants by the Mn(VII)/chlorite process. The impact of the water matrix was demonstrated to have few adverse or even beneficial effects. With satisfactory performance against numerous contaminants, this study introduced a novel Mn(VII) synergistic strategy, and a new reactivity pattern focused on reducing the reduction potential of the contaminant, as opposed to increasing the oxidation potential of oxidants.

Colloidal activated carbon (CAC) is an emerging technology for the in situ remediation of groundwater impacted by per- and polyfluoroalkyl substances (PFAS). In assessing the long-term effectiveness of a CAC barrier, it is crucial to evaluate the potential of emplaced CAC particles to be remobilized and migrate away from the sorptive barrier. We examine the effect of two polymer stabilizers, carboxymethyl cellulose (CMC) and polydiallyldimethylammonium chloride (PolyDM), on CAC deposition and remobilization in saturated sand columns. CMC-modified CAC showed high mobility in a wide ionic strength (IS) range from 0.1 to 100 mM, which is favorable for CAC delivery at a sufficient scale. Interestingly, the mobility of PolyDM-modified CAC was high at low IS (0.1 mM) but greatly reduced at high IS (100 mM). Notably, significant remobilization (release) of deposited CMC-CAC particles occurred upon the introduction of solution with low IS following deposition at high IS. In contrast, PolyDM-CAC did not undergo any remobilization following deposition due to its favorable interactions with the quartz sand. We further elucidated the CAC deposition and remobilization behaviors by analyzing colloid-collector interactions through the application of Derjaguin-Landau-Verwey-Overbeek theory, and the inclusion of a discrete representation of charge heterogeneity on the quartz sand surface. The classical colloid filtration theory was also employed to estimate the travel distance of CAC in saturated columns. Our results underscore the roles of polymer coatings and solution chemistry in CAC transport, providing valuable guidelines for the design of in situ CAC remediation with maximized delivery efficiency and barrier longevity.

Humic acid (HA) is ubiquitous in natural aquatic environments and effectively accelerates decontamination by permanganate (Mn(VII)). However, the detailed mechanism remains uncertain. Herein, the intrinsic mechanisms of HA's impact on phenolics oxidation by Mn(VII) and its intermediate manganese oxo-anions were systematically studied. Results suggested that HA facilitated the transfer of a single electron from Mn(VII), resulting in the sequential formation of Mn(VI) and Mn(V). The formed Mn(V) was further reduced to Mn(III) through a double electron transfer process by HA. Mn(III) was responsible for the HA-boosted oxidation as the active species attacking pollutants, while Mn(VI) and Mn(V) tended to act as intermediate species due to their own instability. In addition, HA could serve as a stabilizer to form a complex with produced Mn(III) and retard the disproportionation of Mn(III). Notably, manganese oxo-anions did not mineralize HA but essentially changed its composition. According to the results of Fourier-transform ion cyclotron resonance mass spectrometry and the second derivative analysis of Fourier-transform infrared spectroscopy, we found that manganese oxo-anions triggered the decomposition of C-H bonds on HA and subsequently produced oxygen-containing functional groups (i.e., C-O). This study might shed new light on the HA/manganese oxo-anion process.

In this study, we introduce the count-based Morgan fingerprint (C-MF) to represent chemical structures of contaminants and develop machine learning (ML)-based predictive models for their activities and properties. Compared with the binary Morgan fingerprint (B-MF), C-MF not only qualifies the presence or absence of an atom group but also quantifies its counts in a molecule. We employ six different ML algorithms (ridge regression, SVM, KNN, RF, XGBoost, and CatBoost) to develop models on 10 contaminant-related data sets based on C-MF and B-MF to compare them in terms of the model's predictive performance, interpretation, and applicability domain (AD). Our results show that C-MF outperforms B-MF in nine of 10 data sets in terms of model predictive performance. The advantage of C-MF over B-MF is dependent on the ML algorithm, and the performance enhancements are proportional to the difference in the chemical diversity of data sets calculated by B-MF and C-MF. Model interpretation results show that the C-MF-based model can elucidate the effect of atom group counts on the target and have a wider range of SHAP values. AD analysis shows that C-MF-based models have an AD similar to that of B-MF-based ones. Finally, we developed a "ContaminaNET" platform to deploy these C-MF-based models for free use.

Despite decades of research on phenols oxidation by permanganate, there are still considerable uncertainties regarding the mechanisms accounting for the unexpected parabolic pH-dependent oxidation rate. Herein, the pH effect on phenols oxidation was reinvestigated experimentally and theoretically by highlighting the previously unappreciated proton transfer. The results revealed that the oxidation of protonated phenols occurred via proton-coupled electron transfer (PCET) pathways, which can switch from ETPT (electron transfer followed by proton transfer) to CEPT (concerted electron-proton transfer) or PTET (proton transfer followed by electron transfer) with an increase in pH. A PCET-based model was thus established, and it could fit the kinetic data of phenols oxidation by permanganate well. In contrast with what was previously thought, both the simulating results and the density functional theory calculation indicated the rate of CEPT reaction of protonated phenols with OH - as the proton acceptor was much higher than that of deprotonated phenols, which could account for the pH-rate profiles for phenols oxidation. Analysis of the quantitative structure-activity relationships among the modeled rate constants, Hammett constants, and p K a values of phenols further supports the idea that the oxidation of protonated phenols is dominated by PCET. This study improves our understanding of permanganate oxidation and suggests a new pattern of reactivity that may be applicable to other systems.

Recent research has primarily focused on the utilization of reductants as activators for Fe(VI) to generate high-valent iron species (Fe(IV)/Fe(V)) for the degradation of emerging organic contaminants (EOCs). However, a significant drawback of this approach arises from the reaction between reductants and ferrates, leading to a decrease in oxidation capacity. This study introduces a novel discovery that highlights the potential of the iron(III)-(1,10-phenanthroline) (Fe(III)-Phen) complex as an activator, effectively enhancing the degradation of EOCs by Fe(VI) and augmenting the overall oxidation capacity of Fe(VI). The degradation of EOCs in the Fe(VI)/Fe(III)-Phen system is facilitated through two mechanisms: a direct electron transfer (DET) process and electron shuttle action. The DET process involves the formation of a Phen-Fe(III)-Fe(VI)* complex, which exhibits a stronger oxidation ability than Fe(VI) alone and can accept electrons directly from EOCs. On the other hand, the electron shuttle process utilizes Fe(III)-Phen as a redox mediator to transfer electrons from EOCs to Fe(VI) through the Fe(IV)/Fe(III) or Fe(IV)/Fe(II)/Fe(III) cycle. Moreover, the Fe(III)-Phen complex can improve the utilization efficiency of Fe(V) by preventing its self-decay. This study's findings may present a viable option for utilizing an effective catalyst to enhance the oxidation of EOCs by Fe(VI) and Fe(V).

Fe(IV) and Fe(V) are promising oxidants for the selective removal of emerging organic contaminants (EOCs) from water under near-neutral conditions. The Fe(III)-assisted electrochemical oxidation system with a BDD anode (Fe(III)-EOS-BDD system) has been employed to generate Fe(VI), while the generation and contributions of Fe(IV) and Fe(V) have been largely ignored. Thus, we examined the feasibility and involved mechanisms of the selective degradation of EOCs in the Fe(III)-EOS-BDD system under near-neutral conditions. It was found that Fe(III) application selectively accelerated the electro-oxidation of phenolic and sulfonamide organics and made the oxidation system be resistant to interference from Cl - , HCO 3 - , and humic acid. Several lines of evidence indicated that EOCs were decomposed via direct electron-transfer process on the BDD anode and by Fe(IV) and Fe(V) but not Fe(VI), besides HO • . Fe(VI) was not generated until the exhaustion of EOCs. Furthermore, the overall contributions of Fe(IV) and Fe(V) to the oxidation of phenolic and sulfonamide organics were over 45%. Our results also revealed that Fe(III) was oxidized primarily by HO • to Fe(IV) and Fe(V) in the Fe(III)-EOS-BDD system. This study advances the understanding of the roles of Fe(IV) and Fe(V) in the Fe(III)-EOS-BDD system and provides an alternative for utilizing Fe(IV) and Fe(V) under near-neutral conditions.

Current techniques for identifying and quantifying sulfate radicals (SO 4 · - ) in SO 4 · - -based advanced oxidation processes (SR-AOPs) are unsatisfactory due to their low selectivity, poor reliability, and limited feasibility for real-time quantification. In this study, naproxen (NAP) was employed as a turn-on luminescent probe for real-time quantification of SO 4 · - in SR-AOPs. The chemiluminescence(CL) yield (Φ CL ) of the reaction of NAP with SO 4 · - was first determined to be 1.49 × 10 -5 E mol -1 with the bisulfite activation by cerium(IV) [Ce(IV)/BS] process. Then, the maximum peak concentrations of SO 4 · - in the Ce(IV)/BS-NAP process was quantified to be ∼10 -11 M based on the derived equation. Since Φ CL of the reaction of NAP with SO 4 · - was much greater than that with other reactive oxidizing species (ROS), the developed CL method worked well in selective quantification of SO 4 · - in various SR-AOPs (e.g., the activation of peroxymonosulfate and persulfate by iron processes). Finally, the electron transfer from NAP to SO 4 · - was proposed to be the critical step for CL production. This work provides a novel CL method for real-time quantification of SO 4 · - , which facilitates the development of SR-AOPs and their application in water and wastewater treatment.

Nanopesticides are considered to be a promising alternative strategy for enhancing bioactivity and delaying the development of pathogen resistance to pesticides. Here, a new type of nanosilica fungicide was proposed and demonstrated to control late blight by inducing intracellular peroxidation damage to Phytophthora infestans , the pathogen associated with potato late blight. Results indicated that the structural features of different silica nanoparticles were largely responsible for their antimicrobial activities. Mesoporous silica nanoparticles (MSNs) exhibited the highest antimicrobial activity with a 98.02% inhibition rate of P. infestans , causing oxidative stress responses and cell structure damage in P. infestans . For the first time, MSNs were found to selectively induce spontaneous excess production of intracellular reactive oxygen species in pathogenic cells, including hydroxyl radicals (•OH), superoxide radicals (•O 2 - ), and singlet oxygen ( 1 O 2 ), leading to peroxidation damage in P. infestans . The effectiveness of MSNs was further tested in the pot experiments as well as leaf and tuber infection, and successful control of potato late blight was achieved with high plant compatibility and safety. This work provides new insights into the antimicrobial mechanism of nanosilica and highlights the use of nanoparticles for controlling late blight with green and highly efficient nanofungicides.

Although intermediate manganese species can be generated during the reactions of permanganate (Mn(VII)) with organic pollutants in water, the role of the in situ generated MnO 2 colloids in the Mn(VII) oxidation process remained controversial and the contribution of Mn(III) was largely neglected. This study showed that the apparent second-order rate constants ( k app ) of Mn(VII) oxidation of methyl phenyl sulfoxide and carbamazepine remained constant with time. However, the degradation of four selected phenolic contaminants by Mn(VII) exhibited an autoaccelerating trend and a linear trend at pH 3.0-6.0 and pH 7.0-9.0, respectively. Multiple lines of evidence revealed that the occurrence of the autoaccelerating trend in the Mn(VII) oxidation process was ascribed to the oxidation of the phenolic organics by MnO 2 colloids. The influence of pyrophosphate on the oxidation of different organic contaminants by MnO 2 colloids suggests that Mn(III) was also responsible for the autoaccelerating oxidation of organic contaminants by Mn(VII) under specific reaction conditions. The kinetic models revealed that the overall contributions of MnO 2 colloids and Mn(III) ranged within 6.6-67.9% during the autoaccelerating oxidation of phenolic contaminants by Mn(VII). These findings advance the understanding of the roles of MnO 2 colloids and Mn(III) in the Mn(VII) oxidation process.

Novel brominated flame retardant (NBFR) and organophosphate ester (OPE) exposure may engender adverse effects on human health. However, present epidemiological information regarding the effects of such exposure is limited and controversial. In this case-control study, 481 serum samples were collected from patients with thyroid cancer ( n = 242) and healthy controls ( n = 239) in Shandong Province, eastern China. The levels of NBFRs and OPEs, thyroid hormones, and serum lipid parameters were measured in all the participants. Pentabromotoluene, 2,3-dibromopropyl 2,4,6 tribromophenyl ether, decabromodiphenylethane (DBDPE), tris (2-chloroethyl) phosphate (TCEP), and triphenyl phosphate (TPP) were widely detected (detection frequency > 60%) in all the participants. A significantly high risk association was found between exposure of NBFRs and OPEs (namely 1,2,3,4,5-pentabromobenzene, DBDPE, tri- n -propyl phosphate, tri[(2 R )-1-chloro-2-propyl] phosphate, tris (1,3-dichloro-2-propyl) phosphate, and tris (2-butoxyethyl) phosphate) and thyroid cancer in both males and females. In the females of the control group, TCEP levels exhibited a significantly positive association with thyroid-stimulating hormone and a negative association with triiodothyronine (T3), free triiodothyronine (FT3), and free thyroxine (FT4) levels. Weighted quantile sum regression evaluated the mixed effects of the compounds on thyroid hormones levels and thyroid cancer. As a result, TPP accounted for the majority of the T3, thyroxine, and FT3 amounts. Our results suggest that NBFR and OPE exposure contributes to alterations in thyroid function, thereby increasing thyroid cancer risk.

The poor oxidation capacity of the Fe(II)/S 2 O 8 2- [Fe(II)/PDS] system at pH > 3.0 has limited its wide application in water treatment. To unravel the underlying mechanism, this study systematically evaluated the possible influencing factors over the pH range of 1.0-8.0 and developed a mathematical model to quantify these effects. Results showed that ∼82% of the generated Fe(IV) could be used for pollutant degradation at pH 1.0, whereas negligible Fe(IV) contribution was observed at pH 7.5. This dramatic decline of Fe(IV) contribution with increasing pH dominantly accounted for the pH-dependent performance of the Fe(II)/PDS process. Unexpectedly, Fe(II) could consume ∼80% of the generated SO 4 •- non-productively under both acidic and near-neutral conditions, while the larger formation of Fe(III) precipitates at high pH inhibited the SO 4 •- contribution mildly. Moreover, the strong Fe(II) scavenging effect was difficult to be compensated for by slowing down the Fe(II) dosing rate. The competition of dissolved oxygen with PDS for Fe(II) was insignificant at pH ≤ 7.5, where the second-order rate constants for reactions of Fe(II) with oxygen were much lower than or comparable to that between Fe(II) and PDS. These findings could advance our understanding of the chemistry and application of the Fe(II)/PDS process.

Although periodate-based advanced oxidation processes have been proven to be efficient in abating organic contaminants, the activation properties of different periodate species remain largely unclear. Herein, by highlighting the role of H 4 IO 6 - , we reinvestigated the pH effect on the decontamination performance of the H 2 O 2 /periodate process. Results revealed that elevating pH from 2.0 to 10.0 could markedly accelerate the rates of organic contaminant decay but decrease the amounts of organic contaminant removal. This pH-dependent trend of organic contaminant degradation corresponded well with the HO · yield and the variation of periodate species. Specifically, although 1 O 2 could be detected at pH 9.0, HO · was determined to be the major reactive oxidizing species in the H 2 O 2 /periodate process under all the tested pH levels. Furthermore, it was suggested that only H 4 IO 6 - and H 2 I 2 O 10 4- could serve as the precursors of HO · . The second-order rate constant for the reaction of H 2 I 2 O 10 4- species with H 2 O 2 was determined to be ∼1199.5 M -1 s -1 at pH 9.0, which was two orders of magnitude greater than that of H 4 IO 6 - (∼2.2 M -1 s -1 at pH 3.0). Taken together, the reaction pathways of H 2 O 2 with different periodate species were proposed. These fundamental findings could improve our understanding of the periodate-based advanced oxidation processes.

Heavy metal(loid)s (HMs) such as Pb(II), Zn(II), Cd(II), and As(V) are ubiquitously present in co-contaminated soil and shallow groundwater, where the humic acid (HA)-rich environments can significantly influence their sequestration. In this study, sulfidated zero-valent iron (S-ZVI) was found to be able to simultaneously sequestrate these HA-complexed HMs. Specially, the HA-complexed Pb(II), Zn(II), Cd(II), and As(V) could be completely removed by S-ZVI within 60 min, while only 35-50% of them could be sequestrated within 72 h by unsulfidated ZVI. Interestingly, different from the S-ZVI corrosion behavior, the kinetics of HM sequestration by S-ZVI consisted of an initial slow reaction stage (or a lag phase) and then a fairly rapid reaction process. Characterization results indicated that forming metal sulfides controlled the HM sequestration at the first stage, whereas the enhanced ZVI corrosion and thus-improved adsorption and/or coprecipitation by iron hydroxides governed the second stage. Both metal-oxygen and metal-sulfur bonds in the solid phase could be confirmed by X-ray photoelectron spectroscopy and extended X-ray absorption fine structure analysis. Moreover, the transformation of S species from SO 4 2- , SO 3 2- , and S 2 2- to S 2- under reducing conditions could allow the sequestrated HMs to remain stable over a long period.

NO 3 - is an undesirable environmental pollutant that causes eutrophication in aquatic ecosystems, and its pollution is difficult to eliminate because it is easily converted into NH 4 + instead of N 2 . Additionally, it is a high-energy substance. Herein, we propose a novel denitrification fuel cell to realize the chemical energy recovery of NO 3 - and simultaneous conversion of total nitrogen (TN) into N 2 based on the outstanding ability of NH 4 + generation on a three-dimensional copper nanowire (CNW)-modified copper foam (CF) cathode (CNW@CF). The basic steps are as follows: direct and highly selective reduction of NO 3 - to NH 4 + rather than to N 2 on the CNW@CF cathode, on which negative NO 3 - ions can be easily adsorbed due to their double-electron layer structure and active hydrogen ([H]) can be generated due to a large number of catalytic active sites exposed on CNWs. Then, NH 4 + is selectively oxidized to N 2 by the strong oxidation of chlorine free radicals (Cl • ), which originate from the reaction of chlorine ions (Cl - ) by photogenerated holes (h + ) and hydroxyl radicals (OH • ) under irradiation. Then, the electrons from the oxidation on the photoanode is transferred to the cathode to form a closed loop for external power generation. Owing to the continuous redox loop, NO 3 - completely reduces to N 2 , and the released chemical energy is converted into electrical energy. The results indicate that 99.9% of NO 3 - can be removed in 90 min, and the highest yield of electrical power density reaches 0.973 mW cm -2 , of which the nitrate reduction rates on the CNW@CF cathode is 79 and 71 times higher than those on the Pt and CF cathodes, respectively. This study presents a novel and robust energy recycling concept for treating nitrate-rich wastewater.

The iron(II)-activated peroxymonosulfate [Fe(II)/PMS] process is effective in degrading organic contaminants with a rapid oxidation stage followed by a slow one. Nevertheless, prior studies have greatly underestimated the degradation rates of organic contaminants in the rapid oxidation stage and ignored the differences in the kinetics and mechanism of organic contaminants degradation in these two oxidation stages. In this work, we investigated the kinetics and mechanisms of organic contaminants in this process under acidic conditions by combining the stopped-flow spectrophotometric method and batch experiments. The organic contaminants were rapidly oxidized with rate constants of 0.18-2.9 s -1 in the rapid oxidation stage. Meanwhile, both Fe(IV) and SO 4 •- were active oxidants and contributed differently to the degradation of different organic contaminants in this stage. Additionally, the presence of Cl - promoted the degradation of both phenol and estradiol but the effects of Br - and humic acid on phenol degradation differed from those on estradiol degradation in the rapid oxidation stage. In contrast, the degradation of phenol and estradiol was slow and the amounts of Fe(IV) and SO 4 •- generated were small in the slow oxidation stage. This work updates the fundamental understanding of the degradation of organic contaminants in this process.

Reactions of core-shell iron nanoparticles with metal(loid)s in water can form an array of nanostructures such as Ag-seed/dendrite, As-subshell, U-yolk, Co-hollowshell, and Cs-spot. Nonetheless, there is a lack of profound understanding in the genesis of these amazing geometries. Herein, we propose a concept to unravel the interdiffusion between the core-shell iron nanoparticle and metal(loid)s, where several key interactions including the Kirkendall effect, metal(loid) character effect, and reaction condition effect are involved in determining the structure of the final solid reaction products. Particularly, the architectural growths of metal(loid)s with iron nanoparticles in water can be manipulated mutually or singly by the following factors: standard redox potential difference, magnetic property, electrical charge and conductivity, as well as the iron (hydr)oxide shell structure under different solution chemistry and operation conditions. This contribution provides a theoretical basis to rationalize the architectural genesis of various metal(loid)s with iron nanoparticles, which will benefit the real practice for synthesizing functional iron-based nanoparticles and recovering the rare/precious metal(loid)s by iron nanoparticles from water.

For the first time, this study showed that the apparent second-order rate constants ( k app ) of six selected emerging organic contaminants (EOCs) oxidation by Fe(VI) increased, remained constant, or declined with time, depending on [EOC] 0 /[Fe(VI)] 0 , pH, and EOCs species. Employing excess caffeine as the quenching reagent for Fe(V) and Fe(IV), it was found that Fe(V)/Fe(IV) contributed to 20-30% of phenol and bisphenol F degradation by Fe(VI), and the contributions of Fe(V)/Fe(IV) remained nearly constant with time under all the tested conditions. However, the contributions of Fe(V)/Fe(IV) accounted for over 50% during the oxidation of sulfamethoxazole, bisphenol S, and iohexol by Fe(VI), and the variation trends of k app of their degradation by Fe(VI) with time displayed three different patterns, which coincided with those of the contributions of Fe(V)/Fe(IV) to their decomposition with time. Results of the quenching experiments were validated by simulating the oxidation kinetic data of methyl phenyl sulfoxide by Fe(VI), which revealed that the variation trends of k app with time were significantly determined by the change in the molar ratio of Fe(V) to Fe(VI) with time, highlighting the key role of Fe(V) in the oxidative process. This study provides comprehensive and insightful information on the roles of Fe(V)/Fe(IV) during EOC oxidation by Fe(VI).

Recently, reactive iron species (RFeS) have shown great potential for the selective degradation of emerging organic contaminants (EOCs). However, the rapid generation of RFeS for the selective and efficient degradation of EOCs over a wide pH range is still challenging. Herein, we constructed FeN 4 structures on a carbon nanotube (CNT) to obtain single-atom catalysts (Fe SA -N-CNT) to generate RFeS in the presence of peroxymonosulfate (PMS). The obtained Fe SA -N-CNT/PMS system exhibited outstanding and selective reactivity for oxidizing EOCs over a wide pH range (3.0-9.0). Several lines of evidences suggested that RFeS existing as an FeN 4 ═O intermediate was the predominant oxidant, while SO 4 ·- and HO · were the secondary oxidants. Density functional theory calculation results revealed that a CNT played a key role in optimizing the distribution of bonding and antibonding states in the Fe 3d orbital, resulting in the outstanding ability of Fe SA -N-CNT for PMS chemical adsorption and activation. Moreover, CNT could significantly enhance the reactivity of the FeN 4 ═O intermediate by increasing the overlap of electrons of the Fe 3d orbital, O 2p orbital, and bisphenol A near the Fermi level. The results of this study can advance the understanding of RFeS generation in a heterogeneous system over a wide pH range and the application of RFeS in real practice.

Sulfate radical (SO 4 •- ) is widely recognized as the predominant species generated from the cobalt(II)-activated peroxymonosulfate (PMS) process. However, in this study, it was surprisingly found that methyl phenyl sulfoxide (PMSO) was readily oxidized to the corresponding sulfone (PMSO 2 ) with a transformation ratio of ∼100% under acidic conditions, which strongly implied the generation of high-valent cobalt-oxo species [Co(IV)] instead of SO 4 •- in the Co(II)/PMS process. Scavenging experiments using methanol (MeOH), tert -butyl alcohol, and dimethyl sulfoxide further suggested the negligible role of SO 4 •- and hydroxyl radical ( • OH) but favored the generation of Co(IV). By employing 18 O isotope-labeling technique, the formation of Co(IV) was conclusively verified and the oxygen atom exchange reaction between Co(IV) and H 2 O was revealed. Density functional theory calculation determined that the formation of Co(IV) was thermodynamically favorable than that of SO 4 •- and • OH in the Co(II)/PMS process. The generated Co(IV) species was indicated to be highly reactive due to the existence of oxo-wall and capable of oxidizing the organic pollutant that is rather recalcitrant to SO 4 •- attack, for example, nitrobenzene. Additionally, the degradation intermediates of sulfamethoxazole (SMX) in the Co(II)/PMS process under acidic conditions were identified to further understand the interaction between Co(IV) and the representative contaminant. The developed kinetic model successfully simulated PMSO loss, PMSO 2 production, SMX degradation, and/or PMS decomposition under varying conditions, which further supported the proposed mechanism. This study might shed new light on the Co(II)/PMS process.

Fe(VI) has received increasing attention since it can decompose a wide range of trace organic contaminants (TrOCs) in water treatment. However, the role of short-lived Fe(IV) and Fe(V) in TrOC decomposition by Fe(VI) has been overlooked. Using methyl phenyl sulfoxide (PMSO), carbamazepine, and caffeine as probe TrOCs, we observed that the apparent second-order rate constants ( k app ) between TrOCs and Fe(VI) determined with the initial kinetics data were strongly dependent on the initial molar ratios of TrOCs to Fe(VI). Furthermore, the k app value increases gradually as the reaction proceeds. Several lines of evidence suggested that these phenomena were ascribed to the accumulation of Fe(IV) and Fe(V) arising from Fe(VI) decay. Kinetic models were built and employed to simulate the kinetics of Fe(VI) self-decay and the kinetics of PMSO degradation by Fe(VI). The modeling results revealed that PMSO was mainly degraded by Fe(IV) and Fe(V) rather than by Fe(VI) per se and Fe(V) played a dominant role, which was also supported by the density functional theory calculation results. Given that Fe(IV) and Fe(V) have much greater oxidizing reactivity than Fe(VI), this work urges the development of Fe(V)/Fe(IV)-based oxidation technology for efficient degradation of TrOCs.

The application of nanoparticles (NPs) to soils, as either fertilizers or fungicides (e.g., CuO NPs), has been proposed to improve the sustainability of agriculture. The observed effects could result directly from the NP-plant interactions or indirectly through effects on the soil microbiome. The objective of this study was to assess the effects of CuO NPs on the changes in the bacterial community structure and nitrogen-cycling-associated functions in a high pH soil and to correlate these changes with nitrate accumulation, soil parameter changes, and plant growth over 28 days. Triticum aestivum seedlings were exposed to 50 mg/kg CuO NPs, 50 mg/kg CuSO 4 , or 0.5 mg/kg CuSO 4 in a standard soil (Lufa 2.1 soil, pH adjusted to 7.6). While Cu treatments reduced nitrate accumulation in the bulk soil, the effects were opposite in the rhizosphere (the soil influenced by root exudates). While nitrate accumulation in bulk soil negatively correlated with total Cu concentration, part of the nitrate concentration in the rhizosphere was explained by root uptake during plant growth, the rest being modulated by Cu treatments. The abundance of genes involved in the nitrogen cycle in the rhizosphere soil correlated with the ionic copper concentration. The increased nitrate concentration in the rhizosphere correlated with an increase of the gene abundance related to the nitrogen fixation and a decrease of denitrification gene abundance. Microbial diversity in bulk or rhizosphere soil under the different treatments alone could not explain these variations, while differences in the assemblages of bacteria associated with these functional gene abundances gave good insights. This study highlights the complexity of microbial N-related function in the rhizosphere and the need to characterize the rhizosphere soil, plant growth and root activity, NP (bio)transformations, along with microbial networks, to understand the impact of agrochemicals (here CuO NPs) on soil fertility.

Literature works reported that organic cocontaminants could be degraded during Cr(VI), a contaminant, reduction by sulfite (Cr(VI)/sulfite process). However, the role of Cr(V) and Cr(IV) intermediates in the Cr(VI)/sulfite process has been overlooked. In this study, we confirmed the generation of Cr(V) and proposed a new mechanism for the decomposition of coexisting organic contaminants during Cr(VI)/sulfite reactions occurring in oxygenated solutions at pH ini 4.0 with the molar ratio of sulfite to Cr(VI) of 10.0. UV-visible and electron paramagnetic resonance (EPR) spectra indicate that Cr(V) was the predominant Cr intermediates in oxygenated solutions, while Cr(IV) accumulated in deoxygenated solutions. The contribution of Cr(V) to the degradation of organic contaminants was verified by the EPR spectra collected at 2 K and using methyl phenyl sulfoxide as a probe compound. Both Cr(V) and SO 4 •- contributed to the decomposition of organic contaminants in oxygenated solutions, with the relative contributions from each species being strongly dependent on properties of the target organic cocontaminants. The key mechanisms responsible for Cr(V) accumulation were supported by DFT calculations, and the degradation kinetics of organic cocontaminants was simulated with the program Kintecus 6.51. This work advances the fundamental understanding of the oxidative transformation of coexisting organic contaminants in this process.

Both the reactivity and the removal capacity of zerovalent iron (ZVI) for the target contaminant are important for applying ZVI in wastewater treatment. In this study, the feasibility of combining sulfidation treatment and Fe 2+ dosing (S-ZVI/Fe 2+ ) to enhance the performance of ZVI for Se(VI) removal was comprehensively investigated under aerobic conditions. Se(VI) was first adsorbed on the surface of ZVI particles and then reduced to Se(IV) and Se(0) with Se(0) being the final product in S-ZVI/Fe 2+ system. This system bore the advantages of both sulfidation treatment (S-ZVI) and Fe 2+ dosing (ZVI/Fe 2+ ) for Se(VI) removal. The amounts and rate constants of Se(VI) removal in S-ZVI/Fe 2+ system were increased by 1.8-32.8 times and 11.7-194.0 times, respectively, compared to those in pristine ZVI system. Sulfidation significantly accelerated the corrosion of Fe 0 thus improved the removal rate of Se(VI). The promoting effect of Fe 2+ on Se(VI) sequestration by S-ZVI should be mainly associated with the following facts: Fe 2+ could maintain a relatively low pH level during Se(VI) removal by S-ZVI; Compared to S-ZVI alone, the consumption of Fe 0 in S-ZVI/Fe 2+ by O 2 /H + was slower, and thus the electron efficiency of S-ZVI was elevated; Fe 2+ dosing facilitated electron transfer by forming semiconductive Fe 3 O 4 .

Fertilization success is crucial for the population recruitment of an organism. However, little is known about the threat of nanoparticles (NPs) to the fertilization of broadcast spawners. Therefore, the effects of nTiO 2 on fertilization success, polyspermy rate, sperm velocity, gametic DNA damage, sperm-egg collision probability, gamete fusion, and oocyte ultrastructure were investigated in a broadcast spawning bivalve, Tegillarca granosa . The results obtained show that fertilization success significantly decreased, whereas polyspermy risk markedly increased upon nTiO 2 exposure. In addition, nTiO 2 exposure led to a significant reduction in sperm swimming velocity, which would subsequently constrain gamete collisions. In addition, nTiO 2 exposure resulted in a significant decline in gamete fusion per collision along with aggravated DNA damage in gametes. Furthermore, ultrastructural analysis illustrated the attachment of nTiO 2 to the oocyte surface, which subsequently resulted in microvillus disassociation and plasma membrane damage. In conclusion, the results obtained suggest a significant threat from NP pollution to the recruitment of broadcast spawning invertebrates.

The detection of soluble Mn(III) is typically accomplished using strong complexing agents to trap Mn(III), but the generation of soluble Mn(III) induced by strong complexing agents has seldom been considered. In this study, pyrophosphate (PP), a nonredox active ligand, was chosen as a typical Mn(III) chelating reagent to study the influence of ligands on soluble Mn(III) formation in reactions involving Mn oxides and Mn(VII). The presence of excess PP induced the generation of soluble Mn(III)-PP from α- and δ-MnO 2 and led to the conproportionation reaction of α-, β-, δ-, or colloidal MnO 2 with Mn(II) at pH 7.0. Compared to MnO 2 minerals, colloidal MnO 2 showed much higher reactivity toward Mn(II) in the presence of PP and the conproportionation rate of colloidal MnO 2 with Mn(II) elevated with increasing PP dosage and decreasing pH. The generation of Mn(III) was not observed in MnO 4 - /S 2 O 3 2- or MnO 4 - /NH 3 OH + system without PP while the introduction of excess PP induced the generation of Mn(III)-PP. Thermodynamic calculation results were consistent with the experimental observations. These findings not only provide evidence for the unsuitability of using strong ligands in quantification of soluble Mn(III) in manganese-involved redox reactions, but also advance the understanding of soluble Mn(III) generation in aquatic environment.

In this work, the kinetics and mechanisms of the reductive removal of BrO 3 - by sulfite in air atmosphere were determined. BrO 3 - could be effectively reduced by sulfite at pH ini 3.0-6.0, and the reduction rate of BrO 3 - increased with decreasing pH. The coexisting organic contaminants with electron-rich moieties could be degraded, accompanied with BrO 3 - reduction by sulfite. The reaction stoichiometries of -Δ[sulfite]/Δ[bromate] were determined to be 3.33 and 15.63 in the absence and presence of O 2 , respectively. Many lines of evidence verified that the main reactions in the BrO 3 - /sulfite system in air atmosphere included the reduction of BrO 3 - to HOBr and its further reduction to Br - , as well as the oxidation of H 2 SO 3 by BrO 3 - to form SO 3 · - and its further transformation to SO 4 · - . Moreover, SO 4 · - rather than HOBr was determined to be the major active oxidant in the BrO 3 - /sulfite system. SO 3 · - played a key role in the over-stoichiometric sulfite consumption because of its rapid reaction with dissolved oxygen. However, the formed SO 3 · - was further oxidized by BrO 3 - in the N 2 atmosphere. BrO 3 - reduction by sulfite is an alternative for controlling BrO 3 - in water treatment because it was effective in real water at pH ini ≤ 6.0.

Competition among oxidizing species in groundwater and wastewater for the reductive capacity of zerovalent iron (ZVI) makes the selectivity of ZVI for target contaminant degradation over other reduction pathways a major determinant of the feasibility of ZVI-based water treatment processes. The selectivity for reduction of contaminants over water is improved by sulfidation, but the effect of sulfidation on other competing reactions is not known. The interaction between these competing reactions was investigated using N -nitrosodimethylamine (NDMA) as the target contaminant, nitrate as a co-contaminant, and micrometer-sized ZVI with and without sulfidation. Unsulfidated ZVI reduced NDMA to dimethylamine via N , N -dimethylhydrazine, but the addition of nitrate decreased the rate of NDMA reduction and increased the quantity of intermediate observed. With sulfidated ZVI, the kinetics and products of NDMA reduction were similar to those with unsulfidated ZVI, but no inhibitory effect of nitrate was observed. Conversely, the reduction of nitrate-which dominated NDMA reduction in unsulfidated ZVI systems-was strongly inhibited by sulfidation. H 2 and Fe 2+ generation by sulfidated ZVI was almost independent of nitrate concentration. Therefore, sulfidation improved the efficiency of NDMA reduction by ZVI in the presence of nitrate mainly by inhibiting nitrate reduction. The shift in selectivity of ZVI for NDMA over nitrate upon sulfidation was due to replacement of Fe 0 /Fe x O y surface sites with FeS.

Although the Fe(VI)-sulfite process has shown great potential for the rapid removal of organic contaminants, the major active oxidants (Fe(IV)/Fe(V) versus SO 4 •- / • OH) involved in this process are still under debate. By employing sparingly soluble CaSO 3 as a slow-releasing source of SO 3 2- , this study evaluated the oxidation performance of the Fe(VI)-CaSO 3 process and identified the active oxidants involved in this process. The process exhibited efficient oxidation of a variety of compounds, including antibiotics, pharmaceuticals, and pesticides, at rates that were 6.1-173.7-fold faster than those measured for Fe(VI) alone, depending on pH, CaSO 3 dosage, and the properties of organic contaminants. Many lines of evidence verified that neither SO 4 •- nor • OH was the active species in the Fe(VI)-CaSO 3 process. The accelerating effect of CaSO 3 was ascribed to the direct generation of Fe(IV)/Fe(V) species from the reaction of Fe(VI) with soluble SO 3 2- via one-electron steps as well as the indirect generation of Fe(IV)/Fe(V) species from the self-decay of Fe(VI) and Fe(VI) reaction with H 2 O 2 , which could be catalyzed by uncomplexed Fe(III). Besides, the Fe(VI)-CaSO 3 process exhibited satisfactory removal of organic contaminants in real water, and inorganic anions showed negligible effects on organic contaminant decomposition in this process. Thus, the Fe(VI)-CaSO 3 process with Fe(IV)/Fe(V) as reactive oxidants may be a promising method for abating various micropollutants in water treatment.

The hydrogen evolution reaction (HER) that generates H 2 from the reduction of H 2 O by Fe 0 is among the most fundamental of the processes that control reactivity in environmental systems containing zerovalent iron (ZVI). To develop a comprehensive kinetic model for this process, a large and high-resolution data set for HER was measured using five types of ZVI pretreated by acid-washing and/or sulfidation (in pH 7 HEPES buffer). The data were fit to four alternative kinetic models using nonlinear regression analysis applied to the whole data set simultaneously, which allowed some model parameters to be treated globally across multiple experiments. The preferred model uses two independent reactive phases to match the two-stage character of most HER data, with rate constants ( k's) for each phase fitted globally by iron type and phase quantities ( S's) fitted as fully local (independent) parameters. The first, faster stage was attributed to a reactive mineral intermediate (RMI) phase like Fe(OH) 2 , which may form in all experiments during preequilibration, but is rapidly consumed, leaving the second, slower stage of HER, which is due to reaction of Fe 0 . In addition to providing a deterministic model to explain the kinetics of HER by ZVI over a wide range of conditions, the results provide an improved quantitative basis for comparing the effects of sulfidation on ZVI.

Large reductions of sulfur and nitrogen oxide emissions in the United States have led to considerable improvements in air quality, though recent analyses in the Southeastern United States have shown little response of aerosol pH to these reductions. This study examines the effects of reduced emissions on the trend of aerosol acidity in fine particulate matter (PM 2.5 ), at a nationwide scale, using ambient concentration data from three monitoring networks-the Ammonia Monitoring Network (AMoN), the Clean Air Status and Trends network (CASTNET) and the Southeastern Aerosol Research and Characterization Network (SEARCH), in conjunction with thermodynamic (ISORROPIA-II) and chemical transport (CMAQ) model results. Sulfate and ammonium experienced similar and significant decreases with little change in pH, neutralization ratio ( f = [NH 4 + ]/2[SO 4 2- ] + [NO 3 - ]), or nitrate. Oak Grove, MS was the only SEARCH site showing statistically significant pH changes in the Southeast region where small increases in pH (0.003-0.09 pH units/year) were observed. Of the five regions characterized using CASTNET/AMoN data, only California exhibited a statistically significant, albeit small pH increase of +0.04 pH units/year. Furthermore, statistically insignificant (α = 0.05) changes in ammonia were observed in response to emission and PM 2.5 speciation changes. CMAQ simulation results had similar responses, showing steady ammonia levels and generally low pH, with little change from 2001 to 2011.

When zerovalent iron (ZVI) is used in reductive removal of contaminants from industrial wastewater, where dissolved oxygen (DO) competes with target contaminant for the electrons donated by ZVI, both the reactivity and the electron selectivity (ES) of ZVI toward target contaminant are critical. Thus, the reactivity and ES of two sulfidated ZVI (S-ZVI) samples, synthesized by ball-milling with elemental sulfur (S-ZVI bm ) and reacting with Na 2 S (S-ZVI Na2S ), toward Cr(VI) under aerobic conditions were investigated. Sulfidation appreciably increased the reactivity of ZVI and the ratio of the rate constants for Cr(VI) removal by S-ZVI bm or S-ZVI Na2S to their counterparts without sulfur fell in the range of 1.4-29.9. ES of S-ZVI bm and S-ZVI Na2S toward Cr(VI) were determined to be 14.6% and 13.3%, which were 10.7- and 7.5-fold greater than that without sulfidation, respectively. This was mainly ascribed to the greater improving effect of sulfidation on the reduction rate of Cr(VI) than that of DO by ZVI. The improving effects of sulfidation on the performance of ZVI were mainly due to the following mechanisms: sulfidation increased the specific surface area of ZVI, the FeS x layer facilitated the enrichment of Cr(VI) anions on S-ZVI surface because of its anions selective property and favored the electron transfer from Fe 0 core to Cr(VI) at the surface because of its role as efficient electron conductor.

Sulfidation has gained increasing interest in recent years for improving the sequestration of contaminants by zerovalent iron (ZVI). In view of the bright prospects of the sulfidated ZVI (S-ZVI), this review comprehensively summarized the latest developments in sulfidation of ZVI, particularly that of nanoscale ZVI (S-nZVI). The milestones in development of S-ZVI technology including its background, enlightenment, synthesis, characterization, water remediation and treatment, etc., are summarized. Under most circumstances, sulfidation can enhance the sequestration of various organic compounds and metal(loid)s by ZVI to various extents. In particular, the reactivity of S-ZVI toward contaminants is strongly dependent on S/Fe molar ratio, sulfidation method, and solution chemistry. Additionally, sulfidation can improve the selectivity of ZVI toward targeted contaminant over water under anaerobic conditions. The mechanisms of sulfidation-induced improvement in contaminants sequestration by ZVI are also summarized. Finally, this review identifies the current knowledge gaps and future research needs of S-ZVI for environmental application.

Although the electron selectivity (ES) of zerovalent iron (ZVI) for target contaminant and its utilization ratio (UR) decide the removal capacity of ZVI, little effort has been made to improve them. Taking selenate [Se(VI)] as a target contaminant, this study investigated the coupled influence of aeration gas and Fe(II) on the ES and UR of ZVI. Oxygen was necessary for effective removal of Se(VI) by ZVI without Fe(II) addition. Due to the application of 1.0 mM Fe(II), the ES of ZVI was increased from 3.2-3.6% to 6.2-6.8% and the UR of ZVI was improved by 5.0-19.4% under aerobic conditions, which resulted in a 100-180% increase in the Se(VI) removal capacity by ZVI. Se(VI) reduction by Fe 0 was a heterogeneous redox reaction, and the enrichment of Se(VI) on ZVI surface was the first step of electron transfer from Fe 0 core to Se(VI). Oxygen promoted the generation of iron (hydr)oxides, which facilitated the enrichment of Se(VI) on the ZVI particle surface. Therefore, the high oxygen fraction (25-50%) in the purging gas resulted in only a slight decrease in the ES of ZVI. Fe(II) addition resulted in a pH drop and promoted the generation of lepidocrocite and magnetite, which benefited Se(VI) adsorption and the following electron transfer from underlying Fe 0 to surface-located Se(VI).

Acidity (pH) plays a key role in the physical and chemical behavior of PM 2.5 . However, understanding of how specific PM sources impact aerosol pH is rarely considered. Performing source apportionment of PM 2.5 allows a unique link of sources pH of aerosol from the polluted city. Hourly water-soluble (WS) ions of PM 2.5 were measured online from December 25th, 2014 to June 19th, 2015 in a northern city in China. Five sources were resolved including secondary nitrate (41%), secondary sulfate (26%), coal combustion (14%), mineral dust (11%), and vehicle exhaust (9%). The influence of source contributions to pH was estimated by ISORROPIA-II. The lowest aerosol pH levels were found at low WS-ion levels and then increased with increasing total ion levels, until high ion levels occur, at which point the aerosol becomes more acidic as both sulfate and nitrate increase. Ammonium levels increased nearly linearly with sulfate and nitrate until approximately 20 μg m -3 , supporting that the ammonium in the aerosol was more limited by thermodynamics than source limitations, and aerosol pH responded more to the contributions of sources such as dust than levels of sulfate. Commonly used pH indicator ratios were not indicative of the pH estimated using the thermodynamic model.

In this study, the effects of major anions (e.g., ClO 4 - , NO 3 - , Cl - , and SO 4 2- ) in water on the reactivity of zerovalent iron (ZVI) toward As(III) sequestration were evaluated with and without a weak magnetic field (WMF). Without WMF, ClO 4 - and NO 3 - had negligible influence on As(III) removal by ZVI, but Cl - and SO 4 2- could improve As(III) sequestration by ZVI. Moreover, the WMF-enhancing effect on As(III) removal by ZVI was minor in ultrapure water. A synergetic effect of WMF and individual anion on improving As(III) removal by ZVI was observed for each of the investigated anion, which became more pronounced as the concentration of anion increased. Based on the extent of enhancing effects, these anions were ranked in the order of SO 4 2- > Cl - > NO 3 - ≈ ClO 4 - (from most- to least-enhanced). Furthermore, the inhibitory effect of HSiO 3 - , HCO 3 - , and H 2 PO 4 - on ZVI corrosion could be alleviated taking advantage of the combined effect of WMF and SO 4 2- . The coupled influence of anions and WMF was associated with the simultaneous movement of anions with paramagnetic Fe 2+ to keep local electroneutrality in solution. Our findings suggest that the presence of anions is quite essential to maintaining or stimulating the WMF effect.

Scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) depth profiling were employed to characterize the aged zerovalent iron (AZVI) samples incubated in synthetic groundwater. The AZVI samples prepared under different conditions exhibited the passive layers of different morphologies, amounts, and constituents. Owing to the accumulation of iron oxides on their surface, all the prepared AZVI samples were much less reactive than the pristine ZVI for Se(IV) removal. However, the reactivity of all AZVI samples toward Se(IV) sequestration could be significantly enhanced by applying a uniform magnetic field (UMF). Moreover, the flux intensity of UMF necessary to depassivate an AZVI sample was strongly dependent on the properties of its passive layer. The UMF of 1 mT was strong enough to restore the reactivity of the AZVI samples with Fe3O4 as the major constituent of the passive film or with a thin layer of α-Fe2O3 and γ-FeOOH in the external passive film. The flux intensity of UMF necessary to depassivate the AZVI samples would increase to 2 mT or even 5 mT if the AZVI samples were covered with passive films being thicker, denser, and contained more γ-FeOOH and α-Fe2O3. Furthermore, increasing the flux intensity of UMF facilitated the reduction of Se(IV) to Se(0) by AZVI samples.

Novel iron-copper-carbon (FeCuC) aerogel was fabricated through a one-step process from metal-resin precursors and then activated with CO2 and N2 in environmentally friendly way. The activated FeCuC aerogel was applied in a heterogeneous electro-Fenton (EF) process and exhibited higher mineralization efficiency than homogeneous EF technology. High total organic carbon (TOC) removal of organic pollutants with activated FeCuC aerogel was achieved at a wide range of pH values (3-9). The chemical oxygen demand (COD) of real dyeing wastewater was below China's discharge standard after 30 min of treatment, and the specific energy consumption was low (9.2 kW·h·kg(-1)COD(-1)), corresponding to a power consumption of only ∼0.34 kW·h per ton of wastewater. The enhanced mineralization efficiency of FeCuC aerogel was mostly attributable to ultradispersed metallic Fe-Cu nanoparticles embedded in 3D carbon matrix and the CO2-N2 treatment. The CO2 activation enhanced the accessibility of the aerogel's pores, and the secondary N2 activation enlarged the porosity and regenerated the ultradispersed zerovalent iron (Fe(0)) with reductive carbon. Cu(0) acted as a reduction promoter for interfacial electron transfer. Moreover, activated FeCuC aerogel presented low iron leaching (<0.1 ppm) in acidic solution and can be molded into different sizes with high flexibility. Thus, this material could be used as a low-cost cathode and efficient heterogeneous EF technology for actual wastewater treatment.

Permanganate can be activated by bisulfite to generate soluble Mn(III) (noncomplexed with ligands other than H2O and OH(-)) which oxidizes organic contaminants at extraordinarily high rates. However, the generation of Mn(III) in the permanganate/bisulfite (PM/BS) process and the reactivity of Mn(III) toward emerging contaminants have never been quantified. In this work, Mn(III) generated in the PM/BS process was shown to absorb at 230-290 nm for the first time and disproportionated more easily at higher pH, and thus, the utilization rate of Mn(III) for decomposing organic contaminant was low under alkaline conditions. A Mn(III) generation and utilization model was developed to get the second-order reaction rate parameters of benzene oxidation by soluble Mn(III), and then, benzene was chosen as the reference probe to build a competition kinetics method, which was employed to obtain the second-order rate constants of organic contaminants oxidation by soluble Mn(III). The results revealed that the second-order rate constants of aniline and bisphenol A oxidation by soluble Mn(III) were in the range of 10(5)-10(6) M(-1) s(-1). With the presence of soluble Mn(III) at micromolar concentration, contaminants could be oxidized with the observed rates several orders of magnitude higher than those by common oxidation processes, implying the great potential application of the PM/BS process in water and wastewater treatment.

Premagnetization was applied to enhance the removal of various oxidative contaminants (including amaranth (AR27), lead ion (Pb(2+)), cupric ion (Cu(2+)), selenite (Se(4+)), silver ion (Ag(+)), and chromate (Cr(6+))) by zerovalent iron (ZVI) from different origins under well-controlled experimental conditions. The rate constants of contaminants by premagnetized ZVI (Mag-ZVI) samples were 1.2-12.2-fold greater than those by pristine ZVI (Pri-ZVI) samples. Generally, there was a linear correlation between the specific reaction rate constants (kSA) of one particular contaminant removal by various Pri-ZVI or Mag-ZVI samples and those of the other contaminant, which could be successfully employed to predict the kSA of one contaminant by one ZVI sample if kSA of the other contaminant by this ZVI sample was available. The specific rate constant of Fe(II) release at pH 4.0 was proposed in this study to stand for the intrinsic reactivity of a ZVI sample. All Mag-ZVI samples had higher intrinsic reactivity than their counterparts without premagnetization. There were strong correlations between the intrinsic reactivity of various Pri-ZVI/Mag-ZVI samples and the removal rate constants of a specific contaminant by these ZVI samples not only at pH 4.0 when the intrinsic reactivity was determined but also at other pH levels. This correlation could be employed to predict the removal rate constant of this contaminant by a ZVI sample that was not included in the original data set once the intrinsic reactivity of the ZVI sample was known.

MnO4(-) was activated by HSO3(-), resulting in a process that oxidizes organic contaminants at extraordinarily high rates. The permanganate/bisulfite (PM/BS) process oxidized phenol, ciprofloxacin, and methyl blue at pHini 5.0 with rates (kobs ≈ 60-150 s(-1)) that were 5-6 orders of magnitude faster than those measured for permanganate alone, and ∼5 to 7 orders of magnitude faster than conventional advanced oxidation processes for water treatment. Oxidation of phenol was fastest at pH 4.0, but still effective at pH 7.0, and only slightly slower when performed in tap water. A smaller, but still considerable (∼3 orders of magnitude) increase in oxidation rates of methyl blue was observed with MnO2 activated by HSO3(-) (MO/BS). The above results, time-resolved spectroscopy of manganese species under various conditions, stoichiometric analysis of pH changes, and the effect of pyrophosphate on UV absorbance spectra suggest that the reactive intermediate(s) responsible for the extremely rapid oxidation of organic contaminants in the PM/BS process involve manganese(III) species with minimal stabilization by complexation. The PM/BS process may lead to a new category of advanced oxidation technologies based on contaminant oxidation by reactive manganese(III) species, rather than hydroxyl and sulfate radicals.

Premagnetization was employed to enhance the reactivity of zerovalent iron (ZVI) toward As(III) sequestration for the first time. Compared to the pristine ZVI (Pri-ZVI), the rate of As(III) elimination by the premagnetized ZVI (Mag-ZVI) was greater over the pHini range of 4.0-9.0 and increased progressively with increasing intensity of the magnetic field for premagnetization. Mag-ZVI could keep its reactivity for a long time and showed better performance than Pri-ZVI for As(III) removal from synthetic groundwater in column tests. The Fe K-edge XAFS analysis for As(III)-treated ZVI samples unraveled that premagnetization promoted the transformation of ZVI to iron (hydr)oxides and shifted the corrosion products from maghemite and magnetite to lepidocrocite, which favored the arsenic sequestration. The arsenic species analysis revealed that premagnetization facilitated the oxidation of As(III) to As(V). ZVI pretreated with grinding was very different from Mag-ZVI with regard to As(III) removal, indicating that the improved reactivity of Mag-ZVI should not be associated with the physical squeezing effect of the ZVI grains during magnetization. The positive correlation between the remanence of Mag-ZVI and the rate constants of total arsenic removal indicated that the enhanced reactivity of Mag-ZVI was mainly ascribed to its magnetic memory, i.e., the remanence kept by Mag-ZVI.

In this study, a weak magnetic field (WMF), superimposed with a permanent magnet, was utilized to improve ZVI corrosion and thereby enhance As(V)/As(III) removal by ZVI at pHini 3.0-9.0. The experiment with real arsenic-bearing groundwater revealed that WMF could greatly improve arsenic removal by ZVI even in the presence of various cations and anions. The WMF-induced improvement in As(V)/As(III) removal by ZVI should be primarily associated with accelerated ZVI corrosion, as evidenced by the pH variation, Fe(2+) release, and the formation of corrosion products as characterized with X-ray absorption fine structure spectroscopy. The arsenic species analysis in solution/solid phases at pHini 3.0 revealed that As(III) oxidation to As(V) in aqueous phase preceded its subsequent sequestration by the newly formed iron (hydr)oxides. However, both As(V) adsorption following As(III) oxidation to As(V) in solution and As(III) adsorption preceding its conversion to As(V) in solid phase were observed at pHini 5.0-9.0. The application of WMF accelerated the transformation of As(III) to As(V) in both aqueous and solid phases at pHini 5.0-9.0 and enhanced the oxidation of As(III) to As(V) in solution at pHini 3.0.

The sequestration of Se(IV) by zero-valent iron (ZVI) is strongly influenced by the coupled effects of aging ZVI and the presence of a weak magnetic field (WMF). ZVI aged at pH 6.0 with MES as buffer between 6 and 60 h gave nearly constant rates of Se(IV) removal with WMF but with rate constants that are 10- to 100-fold greater than without. XANES analysis showed that applying WMF changes the mechanism of Se(IV) removal by ZVI aged for 6-60 h from adsorption followed by reduction to direct reduction. The strong correlation between Se(IV) removal and Fe2+ release suggests direct reduction of Se(IV) to Se(0) by Fe0, in agreement with the XANES analysis. The numerical simulation of ZVI magnetization revealed that the WMF influence on Se(IV) sequestration is associated mainly with the ferromagnetism of ZVI and the paramagnetism of Fe2+. In the presence of the WMF, the Lorentz force gives rise to convection in the solution, which narrows the diffusion layer, and the field gradient force, which tends to move paramagnetic ions (esp. Fe2+) along the higher field gradient at the ZVI particle surface, thereby inducing nonuniform depassivation and eventually localized corrosion of the ZVI surface.

Humic acid (HA) affects the oxidation of phenolic compounds by permanganate, but the role of HA in the oxidation of phenols by permanganate is far from clear. The mechanisms by which HA influences the oxidation of phenols by permanganate at pH 5.0-9.0 were systematically examined in this study. The presence of HA enhanced the oxidation of phenolic compounds by permanganate at pH ≤7.0, with greater enhancement at lower pH values. The presence of HA facilitated the in situ formation of MnO2, implying the importance of reductive moieties of HA in this reaction. This was supported by the finding that HA preoxidized by ozone showed enhancements in the oxidation of phenols by permanganate at pH 5.0-6.0 smaller than those seen with pristine HA. The good correlation between HA-induced improvement in the oxidation rates of phenols by permanganate and those by preformed colloidal MnO2 at pH 5.0 confirmed that contribution of MnO2 formed in situ for the oxidation of phenols under this condition. The differences in the influence of Na2S2O3 and HA on the oxidation of phenol by permanganate revealed the fact that the continuous generation of fresh MnO2 and stabilization of the MnO2 formed in situ by HA were crucial for the HA-induced enhancement of the oxidation of phenols by permanganate at pH ≤7.0. The consumption of permanganate by HA and the poor oxidation ability of in situ-generated MnO2 under alkaline conditions resulted in the slightly negative effect of HA on the degradation rates of phenols by permanganate at pH >7.0.

This study developed a heterogeneous catalytic permanganate oxidation system with ceria supported ruthenium, Ru/CeO2 (0.8‰ as Ru), as catalyst for the first time. The catalytic performance of Ru/CeO2 toward butylparaben (BP) oxidation by permanganate was strongly dependent on its dosage, pH, permanganate concentration and temperature. The presence of 1.0 g L(-1) Ru/CeO2 increased the oxidation rate of BP by permanganate at pH 4.0-8.0 by 3-96 times. The increase in Ru/CeO2 dosage led to a progressive enhancement in the oxidation rate of BP by permanganate at neutral pH. The XANES analysis revealed that (1) Ru was deposited on the surface of CeO2 as Ru(III); (2) Ru(III) was oxidized by permanganate to its higher oxidation state Ru(VI) and Ru(VII), which acted as the co-oxidants in BP oxidation; (3) Ru(VI) and Ru(VII) were reduced by BP to its initial state of Ru(III). Therefore, Ru/CeO2 acted as an electron shuttle in catalytic permanganate oxidation process. LC-MS/MS analysis implied that BP was initially attacked by permanganate or Ru(VI) and Ru(VII) at the aromatic ring, leading to the formation of various hydroxyl-substituted and ring-opening products. Ru/CeO2 could maintain its catalytic activity during the six successive runs. In conclusion, catalyzing permanganate oxidation with Ru/CeO2 is a promising technology for degrading phenolic pollutants in water treatment.