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Deep brain stimulation (DBS) of the anterior nucleus of the thalamus (ANT) has been widely used as an effective treatment for refractory temporal lobe epilepsy. Despite its promising clinical outcome, the exact mechanism of how ANT-DBS alleviates seizure severity has not been fully understood, especially at the cellular level. To assess effects of DBS, the present study examined electroencephalography (EEG) signals and locomotor behavior changes and conducted immunohistochemical analyses to examine changes in neuronal activity, number of neurons, and neurogenesis of inhibitory neurons in different hippocampal subregions. ANT-DBS alleviated seizure activity, abnormal locomotor behaviors, reduced theta-band, increased gamma-band EEG power in the interictal state, and increased the number of neurons in the dentate gyrus (DG). The number of parvalbumin- and somatostatin-expressing inhibitory neurons was recovered to the level in DG and CA1 of naïve mice. Notably, BrdU-positive inhibitory neurons were increased. In conclusion, ANT-DBS not only could reduce the number of seizures, but also could induce neuronal changes in the hippocampus, which is a key region involved in chronic epileptogenesis. Importantly, our results suggest that ANT-DBS may lead to hippocampal subregion-specific cellular recovery of GABAergic inhibitory neurons.

International audience; In this study, changes in the reactivity of nanoscale zerovalent iron (NZVI) in five different groundwater (GW) systems under anoxic and oxic conditions were examined over a wide range of aging time (0−60 d). p-nitrophenol (p-NP) was used as a redox-sensitive probe, whereas nalidixic acid (NA), a typical antibiotic found in the natural environment, was used as a sorbing compound. Investigation of the p-NP reduction in pure water systems showed that NZVI lost 41% and 98% of its reductive activity under anoxic and oxic conditions after 60 d, while enhancement of its reactivity was observed after short-term aging in GW (1−5 d), followed by a further decline. This behavior has been ascribed to the formation of secondary Fe(II)-bearing phases, including magnetite and green rust, resulting from NZVI aging in GW. Adsorption experiments revealed that GW-anoxic-aged NZVI samples exhibited a good affinity toward NA, and a greater NA adsorption (∼27 µmol g−1) than that of pristine NZVI (∼2 µmol g−1) at alkaline pH values. Surface complexation modeling showed that the enhanced adsorption of NA onto secondary minerals can be attributed to the Fe(II)-NA surface complexation. This considerable change in the reductive ability and the adsorption capacity of NZVI arising from groundwater corrosion calls for greater attention to be paid in assessment studies, where NZVI is injected for long-term remediation in groundwater.

Herein, we report the significant effects of natural organic matter contained in natural zeolite (Z-NOM) on the physicochemical characteristics of a Ni/Fe@natural zeolite (NF@NZ) catalyst and its decontamination performance toward the dechlorination of trichloroethylene (TCE). Z-NOM predominantly consists of humic-like substances and has demonstrable utility in the synthesis of bimetallic catalysts. Compared to NF@NZ

Understanding the neurovascular coupling (NVC) underlying hemodynamic changes in epilepsy is crucial to properly interpreting functional brain imaging signals associated with epileptic events. However, how excitatory and inhibitory neurons affect vascular responses in different epileptic states remains unknown. We conducted real-time in vivo measurements of cerebral blood flow (CBF), vessel diameter, and excitatory and inhibitory neuronal calcium signals during recurrent focal seizures. During preictal states, decreases in CBF and arteriole diameter were closely related to decreased γ-band local field potential (LFP) power, which was linked to relatively elevated excitatory and reduced inhibitory neuronal activity levels. Notably, this preictal condition was followed by a strengthened ictal event. In particular, the preictal inhibitory activity level was positively correlated with coherent oscillating activity specific to inhibitory neurons. In contrast, ictal states were characterized by elevated synchrony in excitatory neurons. Given these findings, we suggest that excitatory and inhibitory neurons differentially contribute to shaping the ictal and preictal neural states, respectively. Moreover, the preictal vascular activity, alongside with the γ-band, may reflect the relative levels of excitatory and inhibitory neuronal activity, and upcoming ictal activity. Our findings provide useful insights into how perfusion signals of different epileptic states are related in terms of NVC.

Nitrate (NO3−) contamination has dramatically increased owing to extensive human activities, which may cause severe problems on human health and the environment. Recently, catalytic denitrification of NO3− to N2 has attracted much attention owing to its highly fast reaction with high N2 selectivity. However, only a few studies have investigated the effect of natural substances in real groundwater on catalytic denitrification, particularly the type of natural organic matter (NOM) and combined effect of NOM and ionic ions. Herein, we investigated the effects of natural dissolved inorganic and organic matter on catalytic denitrification of contaminated groundwater using a novel Pd–In bimetallic catalyst supported on kaolin-derived zeolite (ZK). Pd–In/ZK showed a highly enhanced performance for denitrification, resulting in a high turnover frequency (18.9 × 10−3 s−1) and N2 selectivity (98%). Various surface analyses confirmed that the rejuvenation of In by active H on Pd sites is the key factor that controls the enhanced NO3− reduction and high N2 selectivity. Applying the optimized Pd–In/ZK catalyst to NO3− contaminated groundwater revealed that its catalytic activity was significantly affected by various constituents in groundwater. Particularly, the results from fluorescence excitation emission matrix spectroscopy showed that humic-like and fulvic-like organic substances potentially inhibited the catalytic NO3− reduction owing to their adsorption onto the catalyst surface. Furthermore, some inorganic ions inhibited the catalytic NO3− reduction via different inhibitory mechanisms, i.e. the competitive adsorption of Cl− and SO42− with NO3− and catalyst fouling induced by formation of CaCO3(s). The novel findings from this study highlight the potential applicability of ZK as a value-adding support material for catalytic denitrification and emphasize the effect of dissolved organic and inorganic matters in groundwater on the catalytic activity of bimetallic catalysts.

A novel and sustainable Pd–Sn bimetallic catalyst supported by fly ash-derived zeolite Na-X (Zeolite-XF) was developed for highly reactive and N2-selective reduction of nitrate in water. The surface characteristics of Zeolite-XF and Pd–Sn/Zeolite-XF were identified via various surface analyses, which showed formation of zeolite Na-X crystals with high purity and uniform dispersion of Pd and Sn nanoparticles on the surfaces of Pd–Sn/Zeolite-XF. Pd–Sn/Zeolite-XF showed a 43.1 × 10−3 s−1 turnover frequency (TOF) with almost 90% N2 selectivity under optimal conditions, which is 4–92 times higher than those of previously reported Pd based bimetallic catalysts. The great catalytic activity was elucidated by XPS and H2-pulse chemisorption analysis, demonstrating that Zeolite-XF enhanced metal dispersion and increased the active metallic sites of Pd and Sn nanoparticles. Furthermore, the optimized Pd–Sn/Zeolite-XF catalyst was tested for reduction of nitrate in real groundwater, which showed the complete removal with 94% N2 selectivity. The experimental results obtained from this study can provide a new insight that discarded solid waste can be converted to value-added environmental materials for synthesis of highly active catalysts, which surpass other freshly synthesized and commercially produced materials.

Quasi-solid-state electrolytes in dye-sensitized solar cells (DSSCs) prevent solvent leakage or evaporation and stability issues that conventional electrolytes cannot; however, there are no known reports that use such an electrolyte based on fly ash SiO

In this study, NaOH-assisted H

Various biological, chemical, and physical technologies have been studied to effectively remove total phosphorus (T-P) from wastewater. Among them, some mineral suspensions and cations in the aqueous phase have shown great potential for promoting phosphorus removal via chemical precipitation. Herein, we investigated the efficiency of T-P removal using various chemical-based cations (Fe2+, Fe3+, Mg2+, and Al3+); ferric ions (Fe3+) showed the highest T-P-removal efficiency (33.1%), regardless of the type of anion (Cl−, NO3−, and SO42−). To prepare natural Fe3+-rich solutions, three different Fe(III)-rich minerals (hematite, lepidocrocite, and magnetite) were treated with various HCl concentrations to maximize the dissolved Fe3+ amounts. Lepidocrocite in 2 N HCl showed the most effective Fe3+-leaching ability (L-Fe dissolved solution). Almost no significant difference in Fe3+ leaching was observed between HCl and H2SO4, whereas lepidocrocite-2 N H2SO4 showed the highest T-P-removal ability (91.5%), with the formation of amorphous Fe(III)-P precipitates. The L-Fe dissolved solution exhibited a higher T-P-removal efficiency than polyammonium chloride under real wastewater conditions. Our results can provide fundamental knowledge about the effect of cations on T-P removal in wastewater treatment and the feasibility of using the Fe3+ leaching solution prepared from Fe(III)-containing minerals for efficient T-P removal via chemical precipitation.

In this study, a dye pollutant (methyl orange, MO) was effectively oxidized in a hydroxylamine (HA)-assisted Fenton system using various Al/Si/Fe- and Fe-containing minerals. The fastest degradation kinetics of MO were observed in the olivine-HA Fenton system, whereas other Al/Si/Fe and Fe-rich minerals (magnetite and lepidocrocite) demonstrated much slower degradation kinetics. The degradation rate constants were proportional to dissolved Fe(II) quantities in mineral suspensions (R

Conventional acoustic brain stimulators that transmit low frequency (

Wastewater contaminated with organic compounds is a serious problem; therefore, many catalysts, especially copper catalysts, have been developed to treat it and remove contaminants before discharge. However, such separation and reuse of these catalysts is often challenging. Steel slag (SS), a by-product of steel production, is produced in large quantities and requires careful disposal. Therefore, in this study, we developed a magnetically recyclable copper catalyst utilizing pre-treated magnetic steel slag (MSS) as a support. First, magnetic separation was carried out to remove calcium silicate impurities such as alite and belite in MSS up to five times, thus increasing the Fe content of the MSS. We synthesized the Cu catalyst supported by MSS (donated as Cu@MSS) and characterized the catalyst by various surface analysis techniques, showing the presence of CuO and CuCO3 nanoparticles on the MSS surface. In catalytic reduction tests of para-nitrophenol using sodium borohydride in the presence of Cu@MSS, the reaction was accelerated when using the five-times pre-treated MSS because of the removal of inhibitors such as calcium compounds, as well as the high content of iron oxides leading to a synergetic effect with metallic Cu in this study. In addition, we investigated the effects of various factors, including Cu loading, sodium borohydride concentration, and catalyst dosage, on the catalytic activity of Cu@MSS. The catalyst was found to be stable and reusable. In summary, these results suggest that treated SS can be used as a support material for copper catalysts for the treatment of contaminated wastewater and the easy separation and reuse of the catalyst.

In this study, a magnetically recyclable Pd catalyst was developed by using the novel support of iron-rich coal fly ash/silica (IRFA@SiO2) for highly efficient reduction of p-nitrophenol (p-NP). IRFA microspheres were coated with amorphous SiO2 synthesized from non-magnetic coal fly ash (NMFA) and then loaded with Pd by impregnation method for the synthesis of Pd/IRFA@SiO2. Various surface analyses demonstrated that amorphous SiO2 was well deposited on the surface of IRFA, providing a unique three-dimensionally structured SiO2 layer to suppress aggregation of IRFA and enhance dispersion of Pd nanoparticles. Pd/IRFA@SiO2 exhibited a significantly enhanced p-NP reduction than those of Pd/IRFA, Pd/Al2O3, and Pd/SiO2. Compared to other Pd- and metal-loaded catalysts, Pd/IRFA@SiO2 showed ˜4000× enhancements in kobs-p-NP/CM (L min−1 gM−1, M = precious metals) values and ˜3800× increases in price-normalized kobs-p-NP values, indicating that Pd/IRFA@SiO2 is a highly efficient and cost-effective alternative catalyst. The catalyst was successfully recycled five times without significant leaching of Pd, Si, and heavy metals because of the magnetic property of Pd/IRFA@SiO2. The experimental results suggest the applicability of the surface-modified IRFA support for the development of novel magnetically recoverable catalysts without severe toxicity problems.

We successfully synthesized three zeolites (i.e., zeolite-XF7, zeolite-X&AF, and zeolite-XF12) by new synthesis methods using acetic acid treatment of non-magnetic coal fly ash (FA). The synthesized zeolites were characterized by various surface analysis and used as quasi-solid-state electrolytes for dye-sensitized solar cells (DSSCs). Compared to nano-gel electrolytes based DSSCs showing almost 3.8% of cell efficiency, the enhanced cell efficiencies were obtained from zeolite-XF12 (6.0%), XF7 (5.0%) and X&A (4.8%), respectively. The enhanced performance by zeolite-XF12 was resulted from effective light harvesting properties of quasi-solid-state electrolyte, reduction of resistance at photoanode/electrolyte interface, and decrease in charge recombination.

We firstly developed a novel synthesis method of nanoscale zerovalent iron (NZVI) using Fe sources in coal fly ash (CFA) for the oxidative degradation of methyl orange by Fenton reaction. Hydrochloric acid (HCl) and methyl isobutyl ketone (MIBK) were used for Fe dissolution from CFA and selective Fe(III) chelation, respectively. Among varied HCl concentrations, 7 N HCl showed the best performance for the oxidation of aqueous Fe(II) to Fe(III) and efficient chelation of Fe(III) with MIBK. The NZVI-CFA was synthesized by adding NaBH4 to a solution of Fe(III)-chelated MIBK, yielding NZVI transformation >95% from Fe(III) in HCl. Various surface analyses were performed to characterize the NZVI-CFA, which was almost identical to typical NZVI-Bare. HCl and MIBK could be reused several times, indicating potential reusability of chemicals used in the synthesis. Remarkable >96% decolorization of methyl orange was obtained by the NZVI-CFA-induced Fenton reaction at pH 3, with a ∼22% decrease in total organic carbon in 7 min. The heterogeneous Fenton reaction initiated by NZVI-CFA with H2O2 showed reactivity similar to that of the homogeneous Fenton reaction (i.e., aqueous Fe(II) with H2O2), indicating the importance of homogeneous reaction for the oxidative degradation of methyl orange.

We developed a novel solidification and stabilization process using a nanoscale zerovalent iron (NZVI)-cement system for reductive immobilization of hexavalent uranium (U(VI)) in a soil–cement matrix. The NZVI suspension without cement demonstrated high removal efficiency (100% in 2 h) and fast removal kinetics (53.7 Lm−2d−1), which surpassed those of other Fe-containing minerals (i.e., green rust, mackinawite, magnetite, and pyrite). Significant removal of aqueous U(VI) was observed in NZVI-cement slurries and minimal adsorbed U was desorbed by a bicarbonate/carbonate (CARB) solution. Surface analysis using scanning electron microscopy and X-ray photoelectron spectroscopy revealed U distributed homogeneously on the surface of the NZVI-cement and transformed considerably from U(VI) to reduced U species by coupled oxidation of Fe(0)/Fe(II) to Fe(III). Furthermore, the increase in pH and NZVI concentration, and presence of humic acid resulted in the enhanced U(VI) reduction in NZVI-cement slurries. The NZVI-cement system was tested with a soil matrix, resulting in successful immobilization of aqueous U(VI) in both batch and column experiments. Moreover, the U(VI) removed in the NZVI-cement system was not leached out by the CARB solution during long-term experiments. The results suggest an NZVI-cement system could represent a promising remediation alternative for effective and stable immobilization of U(VI) in contaminated sites.

Recently, graphitic carbon nitride (g-C

In this study, novel green nano-zerovalent iron (G-NZVI) is synthesized for the first time using onion peel extract for the prevention of rapid surface oxidation and the enhancement of particle dispersibility with a high reductive capacity. The results from various surface analyses revealed that the spherical shape of G-NZVI was fully covered by the onion peel extract composed of polyphenolic compounds with CC–CC unsaturated carbon, CC, C–O, and O–H bonds, resulting in high mobility during column chromatography. Furthermore, the obtained G-NZVI showed the complete removal of 50 mg L−1 of bromate (BrO3−) in 2 min under both aerobic (k = 4.42 min−1) and anaerobic conditions (k = 4.50 min−1), showing that G-NZVI had outstanding oxidation resistance compared to that of bare NZVI. Moreover, the observed performance of G-NZVI showed that it was much more reactive than other well-known reductants (e.g., Fe and Co metal organic frameworks), regardless of whether aerobic or anaerobic conditions were used. The effects of G-NZVI loading, the BrO3− concentration, and pH on the BrO3− removal kinetics using G-NZVI were also investigated in this study. The results provide the novel insight that organic onion peel waste can be reused to synthesize highly reactive anti-oxidative nanoparticles for the treatment of inorganic chemical species and heavy metals in water and wastewater.

This study investigated the competitive adsorption mechanisms of pharmaceuticals (i.e., naproxen, diclofenac, and ibuprofen) toward the pristine and NaOH-activated biochars from spent coffee wastes (SCW) in lake water and wastewater effluent. The kinetic and isotherm studies revealed that the improved physicochemical characteristics and physically homogenized surfaces of the pristine SCW biochar through the chemical activation with NaOH were beneficial to the adsorption of pharmaceuticals (competitive equilibrium adsorption capacity (Qe, exp): NaOH-activated SCW biochar (61.25–192.07 μmol/g) > pristine SCW biochar (14.81–20.65 μmol/g)). The adsorptive removal of naproxen (Qe, exp = 14.81–18.81 μmol/g), diclofenac (Qe, exp = 15.73–20.00 μmol/g), and ibuprofen (Qe, exp = 16.20–20.65 μmol/g) for the pristine SCW biochar showed linear correlations with their hydrophobicity (log D at pH 7.0: ibuprofen (1.71) > diclofenac (1.37) > naproxen (0.25)). However, their Qe, exp values for the NaOH-activated SCW biochar (naproxen (176.39–192.07 μmol/g) > diclofenac (78.44–98.74 μmol/g) > ibuprofen (61.25–80.02 μmol/g)) were inversely correlated to the order of their log D values. These results suggest that the reinforced aromatic structure of the NaOH-activated SCW biochar facilitated the π-π interaction. The calculated thermodynamic parameters demonstrated that the competitive adsorption of pharmaceuticals on the NaOH-activated SCW biochar compared to pristine SCW biochar occurred more spontaneously over the entire pH (5.0–11.0) and ionic strength (NaCl: 0–0.125 M) ranges. These observations imply that the NaOH-activated SCW biochar might be potentially applicable for the removal of pharmaceuticals in lake water and wastewater effluent.

Although it has recently been reported that notable amounts of rare earth elements (REEs) are present in the residual coal ash, little is currently known regarding the association of these elements with the coal ash matrix, thereby limiting the potential for extraction of REEs from coal ash. In this study, we analyzed the binding characteristics of REEs within coal ash via sequential extraction and examined REE recovery during a coal ash recycling process. Major components of coal ash were found to be mineral oxides, mainly composed of Si, Fe, Al, and Ca, and residual carbons. Bottom and fly ashes were found to contain 185.8 mg/kg and 179.2 mg/kg of REEs, respectively. Tessier sequential extraction confirmed that 85 % of REEs are included in the residual fraction of both bottom and fly ashes. Furthermore, BCR sequential extraction revealed that 60-70 % of REEs are contained within the residual fraction, thereby indicating that REEs are strongly bound in both bottom and fly ashes and the use of very strong acids is required for the thorough extraction of REEs from coal ash. Additionally, it was found that 46.3 % of REEs can be recovered from the wastewaters produced during the process of coal ash-derived zeolite synthesis.

A systematic study was conducted to investigate the effect of major groundwater ions (i.e., Ca

Recently, an increasing number of pharmaceutical compounds has become fluorinated. Owing to their pharmacological efficacy, the use of these fluorinated pharmaceuticals continues to grow, and they constitute 20% of the drugs on the current market. However, only a few studies have investigated the fate and transformation of these emerging contaminants in natural and engineered aquatic environments. In the present study, the H

Supplemental material, sj-pdf-1-jcb-10.1177_0271678X20934071 for Differential contribution of excitatory and inhibitory neurons in shaping neurovascular coupling in different epileptic neural states by Hyun-Kyoung Lim, Nayeon You, Sungjun Bae, Bok-Man Kang, Young-Min Shon, Seong-Gi Kim and Minah Suh in Journal of Cerebral Blood Flow & Metabolism

Despite the extensive use of nanoscale zerovalent iron (NZVI) in water and soil remediation, no data exist on the reactivity of secondary iron minerals formed upon the NZVI corrosion. Herein, we investigated the oxidation kinetics of NZVI by monitoring the variations of pH, oxidation–reduction potential (ORP) and dissolved Fe(II) concentration, and then examined the reactivity of resulting oxidized particles for the adsorption of an emerging contaminant (nalidixic acid (NA)). NA adsorption was found the greatest on oxidized particles and negligible on the fresh NZVI. Interestingly, the formed secondary mineral phases exhibited an unusual pH adsorption curve with an unexpected great adsorption at alkaline pH values. X-ray photoelectron spectroscopy and high resolution-transmission electron microscopy revealed a gradual increase in the Fe(II) content at the surface of the magnetite phase over the reaction time. Additional experiments and surface complexation modeling showed that the enhanced adsorption of NA onto the secondary magnetite is due to the formation of surface bound Fe(II). Fe(II) is released into the solution because, for instance, of the presence of organic buffer molecules, decreased surface Fe(II) and NA adsorption at alkaline pH values. This work sheds light on an overseen aspect of the reactivity of secondary iron minerals resulting from NZVI passivation, which can bind co-existing emerging contaminants and then affect their fate in the environment.

International audience; In this study, a novel peroxymonosulfate (PMS) activation method, which combines a solid waste (i.e., red mud, RM) and a reducing agent (i.e., hydroxylamine, HA), for the oxidative degradation of fluoroquinolones (FQs; i.e., flumequine (FLU) and ciprofloxacin (CIP)) in hospital wastewater (HW) was developed. The addition of HA into the PMS/RM suspension significantly enhanced FLU removal, owing to its ability to enhance the Fe(III)/Fe(II) cycle on the RM surface. The results of the quenching experiments suggested the predominance of SO over OH in the PMS/RM/HA system. Moreover, owing to the greater reactivity between CIP and SO, CIP removal was more effective than FLU removal. Additionally, the liquid chromatography-mass spectroscopy (LC-MS) analysis revealed that the oxidation of CIP and FLU by PMS/RM/HA occurred via sequential and separate processes, involving ring cleavage, hydroxylation, decarbonylation, and defluorination. Surprisingly, the wastewater components exhibited contrasting effects on FLU removal in HW. Natural organic matter, nitrate and sulfate showed a slight impact on the removal performance of FLU, whereas chloride improved the oxidation extent. However, phosphate significantly inhibited the FLU removal because of its competitive binding at the RM surface and its scavenging effect towards SO. This inhibitory effect was overcome by increasing the PMS concentration and its sequential addition, thus guaranteeing successful mineralization of FLU in HW. These results show that the RM/HA system can be utilized to activate PMS for the removal of antibiotics in wastewater.

Recently, graphitic carbon nitride (g-C3N4) has received significant attention as a non-metallic, visible-light-activated photocatalyst for treating water and wastewater by degrading contaminants. Accordingly, previous review articles have focused on the photocatalytic properties of g–C3N4–based materials. However, g-C3N4 has several other notable features, such as high adsorption affinity towards aromatic substances and heavy metals, high thermal and chemical resistances, good compatibility with various materials, and easily scalable synthesis; therefore, in addition to simple photocatalysis, it can be widely used in other decontamination systems based on activation of oxidants and electrocatalysis. This critical review provides a comprehensive summary of recent advancements in g–C3N4–based materials and their use in treating polluted water and wastewater via the following routes (1) activation of oxidizing agents (e.g., hydrogen peroxide, ozone, peroxymonosulfate, and persulfate): and (2) photoelectrocatalysis using fabricated g–C3N4–based photocathodes and photoanodes. For each route, we briefly summarize the primary mechanisms, distinctive features, and performances of various water treatment systems using g–C3N4–based catalysts. We also highlight the specific roles of g-C3N4 in improving the efficiencies of these treatment processes. The advantages and limitations of previously reported water treatment systems using g–C3N4–based materials are also described and compared in this review. Finally, we discuss the challenges and prospects of improving g–C3N4–based water purification applications.

The use of red mud as a support material was evaluated in this study to develop a novel bimetallic catalyst for highly reactive and selective nitrate removal from water and wastewater. The catalyst was optimized for the selection of promoter metal (i.e., Sn, Cu, In, and Zn) and then for noble metal (i.e., Pd, Pt, and Au). Sn-Pd-red mud and In-Pd-red mud catalysts achieved a complete nitrate removal. Sn-Pd-red mud showed 5.1 times higher removal kinetics (k = 11.57 × 10−2 min−1) than that of In-Pd-red mud (k = 2.27 × 10−2 min−1). The results from characterization study confirmed that the enhanced nitrate removal kinetics of Sn-Pd-red mud was mainly attributed to 1) its high affinity towards nitrate, 2) low alloying effect of Sn on Pd, 3) high reduction potential of Sn, and 4) high H2 activation by Pd, as compared to those of other red mud supported bimetallic catalysts. We also found that the interaction between CaO and Fe2O3 was the driving force for the enhanced nitrate reduction and high N2 selectivity in this study. A complete nitrate removal with high N2 selectivity (>88%) was preserved during the 11 times of recycling tests with consistent reduction kinetics (k = 10.87 ± 0.48 × 10−2 min−1), indicating that red mud could be an excellent support material for efficient and durable bimetallic catalyst for the enhanced selective nitrate reduction.

Metal-free oxidative degradation by persulfate (PS) is an emerging process as green chemistry without any toxic metal leaching to aquatic environments but has never been explored for natural organic matter (NOM) removal to date. In this study, nitrogen-doped reduced graphene oxide (NrGO) was applied as a catalyst first to investigate the degradation behavior of NOM. A parallel system was also examined without PS for non-oxidative interaction. For three tested NOM, the extent of the removal increased with the addition of NrGO, and the removal rates were consistently higher for the systems with versus without PS (by 25–102%). Specific ultraviolet absorbance (SUVA) exhibited declining trends with NrGO for both oxidative and non-oxidative systems. Up to 86.9%, 59.9%, and 60.3% reduction in SUVA values were found for the oxidative removal of Suwannee River natural organic matter, Suwannee River humic acid, and Suwannee River fulvic acid, respectively. The excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC) decomposed fluorescent NOM into two fulvic-like (C1 and C2) and two humic-like (C3 and C4) components. Results implied that more hydrophobic and more condensed aromatic NOM constituents might be preferably removed by both oxidation and adsorption with the greater removal tendency shown for the humic versus the fulvic-like components. Size exclusion chromatography (SEC) demonstrated that large size molecules were more effectively removed by the oxidative versus the non-oxidative interactions with NrGO. Comparative results revealed that adsorption likely played a critical role in determining the preferential removal tendency of the metal-free oxidation toward heterogeneous NOM structures.