Enhanced electrochemical nitrate reduction on copper nitride with moderate intermediates adsorption.

Nitrate in surface and underground water caused systematic risk to the ecological environment. The electrochemically reduction of nitrate into ammonia (NO3RR), offering a sustainable route for nitrate containing wastewater treatment and ammonia fertilizer conversion. Exploration of catalyst with improved catalytic activity with lower energy barriers is still challenging. Here, we report a copper nitride (Cu3N) catalyst with moderate *NOx and *H2O intermediates adsorptions showed enhanced NO3RR performance. Density functional theory calculations reveals that the unique electronic structure of Cu3N provides efficient active sites for NO3RR, thus enabled balanced adsorption of *NO3 and *H2O (ΔE descriptor), sufficient active hydrogen, and moderate intermediate (*NO3 â†’ HNO3, *NH2→*NH3) adsorption energy. Notably, the in-situ analysis technology revealed potential-driven reconstruction and rehabilitation of Cu3N, forming possible nitrogen vacancy, thus implied for better mechanism understanding. The NO3RR activity of Cu3N surpasses that of most recent catalysts and demonstrates superior stability and implies the application for NH4+ fertilizer recovery, which maintaining an NH3 Faradaic efficiency of 93.1 % and high yield rate of 2.9 mg cm2h-1 at -0.6 V versus RHE. These findings broaden the application scenarios of Cu3N catalyst for ammonia synthesis and provide strategy on improving NO3RR performance.

In Situ Implanting ZrW2O7(OH)2(H2O)2 Nanorods into Hierarchical Functionalized Metal-Organic Framework via Solvent-Free Approach for Upgrading Catalytic Performance.

Host-guest catalyst provides new opportunities for targeted applications and the development of new strategies for preparing host-guest catalysts is highly desired. Herein, an in situ solvent-free approach is developed for implanting ZrW2O7(OH)2(H2O)2 nanorods (ZrW-NR) in nitro-functionalized UiO-66(Zr) (UiO-66(Zr)-NO2) with hierarchical porosity, and the encapsulation of ZrW-NR enables the as-prepared host-guest catalyst remarkably enhanced catalytic performance for both for oxidative desulfurization (ODS) and acetalization reactions. ZrW-NR@UiO-66(Zr)-NO2 can eliminate 500 ppm sulfur within 9 min at 40 °C in ODS, and can transform 5.6 mmol benzaldehyde after 3 min at room temperature in acetalization reaction. Its turnover frequencies reach 72.3 h-1 at 40 °C for ODS which is 33.4 times higher than UiO-66(Zr)-NO2, and 28140 h-1 for acetalization which is the highest among previous reports. Density functional theory calculation result indicates that the W sites in ZrW-NR can decompose H2O2 to WVI-peroxo intermediates that contribute to catalytic activity for the ODS reaction. This work opens a new solvent-free approach for preparing MOFs-based host-guest catalysts to upgrade their redox and acid performance.

Copper-based electro-catalytic nitrate reduction to ammonia from water: Mechanism, preparation, and research directions.

Global water bodies are increasingly imperiled by nitrate pollution, primarily originating from industrial waste, agricultural runoffs, and urban sewage. This escalating environmental crisis challenges traditional water treatment paradigms and necessitates innovative solutions. Electro-catalysis, especially utilizing copper-based catalysts, known for their efficiency, cost-effectiveness, and eco-friendliness, offer a promising avenue for the electro-catalytic reduction of nitrate to ammonia. In this review, we systematically consolidate current research on diverse copper-based catalysts, including pure Cu, Cu alloys, oxides, single-atom entities, and composites. Furthermore, we assess their catalytic performance, operational mechanisms, and future research directions to find effective, long-term solutions to water purification and ammonia synthesis. Electro-catalysis technology shows the potential in mitigating nitrate pollution and has strategic importance in sustainable environmental management. As to the application, challenges regarding complexity of the real water, the scale-up of the commerical catalysts, and the efficient collection of produced NH3 are still exist. Following reseraches of catalyst specially on long term stability and in situ mechanisms are proposed.

H2O2 treatment boosts activity of NiFe layered double hydroxide for electro-catalytic oxidation of urea.

Urea oxidation reaction (UOR) provides a method for hydrogen production besides wastewater treatment, but the current limited catalytic activity has prevented the application. Herein, we develop a novel H2O2 treatment strategy for tailoring the surface oxygen ligand of NiFe-layered double hydroxides (NiFe-LDH). The sample after H2O2 treatment (NiFeO-LDH) shows significant enhancement on UOR efficiency, with the potential of 1.37 V (RHE) to reach a current density of 10 mA/cm2. The boost is attributed to the richness adsorption O ligand on NiFeO-LDH as revealed by XPS and Raman analysis. DFT calculation indicates formation of two possible types of oxygen ligands: adsorbed oxygen on the surface and exposed from hydroxyl group, lowered the desorption energy of CO2 product, which lead to the lowered onset potential. This strategy is further extended to NiFe-LDH nano sheet on Ni foam to reach a higher current density of 440 mA/cm2 of UOR at 1.8 V (RHE). The facile surface O ligand manipulation is also expected to give chance to many other electro-catalytic oxidations.

Insight into the key role of oxygen dopants over ball-milled boron nitride for efficient degradation of PFOS alternative 6:2 fluorotelomer sulfonic acid.

6:2 Fluorotelomer sulfonic acid (6:2 FTS) has been identified as an alternative to perfluorooctane sulfonic acid but has been proven to cause potential threats to humans and the environment. In this study, boron nitride (BN) photocatalysis was explored for 6:2 FTS degradation with 100% removal (kobs=1.8 h-1) and desulfurization rate of 100% as well as the defluorination rate of 57.3%. The superior performance of BN was primarily related to oxygen dopants defects (O-dopants). In addition, O-dopants contribution was confirmed by ball-milled BN (B-BN), which introduced more O-dopants and exhibited an increased 6:2 FTS degradation rate of 2.88 h-1. The decomposition of 6:2 FTS was attributed to holes (h+), hydroxyl radicals (•OH), and superoxide (•O2-) and proceeded via two pathways, the hydrogen abstraction from ethyl carbons by •OH and the C-S bond activation by h+ and •OH. To the best of our knowledge, this is the first study demonstrating that h+, •OH, and •O2- played significant roles in the heterogeneous photocatalytic degradation of 6:2 FTS.

In Situ Implanting of Single Tungsten Sites into Defective UiO-66(Zr) by Solvent-Free Route for Efficient Oxidative Desulfurization at Room Temperature.

Design of single-site catalysts with catalytic sites at atomic-scale and high atom utilization, provides new opportunities to gain superior catalytic performance for targeted reactions. In this contribution, we report a one-pot green approach for in situ implanting of single tungsten sites (up to 12.7 wt.%) onto the nodes of defective UiO-66(Zr) structure via forming Zr-O-W bonds under solvent-free condition. The catalysts displayed extraordinary activity for the oxidative removal of sulfur compounds (1000 ppm S) at room temperature within 30 min. The turnover frequency (TOF) value can reach 44.0 h-1 at 30 °C, which is 109.0, 12.3 and 1.2 times higher than that of pristine UiO-66(Zr), WO3 , and WCl6 (homogeneous catalyst). Theoretical and experimental studies show that the anchored W sites can react with oxidant readily and generate WVI -peroxo intermediates that determine the reaction activity. Our work not only manifests the application of SSCs in the field of desulfurization of fuel oil but also opens a new solvent-free avenue for fabricating MOFs based SSCs.

Catalytic ozonation for metoprolol and ibuprofen removal over different MnO2 nanocrystals: Efficiency, transformation and mechanism.

Manganese dioxide has been widely recognized as catalyst in catalytic ozonation for organic pollutants removal from wastewater in recent decades. However, few studies focus on the structure-activity relationship of MnO2 and catalytic ozonation mechanism in water. In the present study, the oxidative reactivity of three different crystal phases of MnO2 corresponding to α-MnO2, ß-MnO2 and γ-MnO2 towards metoprolol (MET) and ibuprofen (IBU) were evaluated. α-MnO2 was found to contain the most abundant oxygen vacancy and readily reducible surface adsorbed oxygen (O2-, O-, OH-), which facilitated an increase of ozone utilization and the highest catalytic performance with 99% degradation efficiency for IBU and MET. α-MnO2 was then selected to investigate the optimum key operating parameters with a result of catalyst dosage 0.1 g/L, ozone dosage 1 mg/min and an initial pH 7. The introduction of α-MnO2 promoted reactive oxygen species (O2-, O-, OH-) generation which played significant roles in IBU degradation. Probable degradation pathways of MET and IBU were proposed according to the organic intermediates identified and the reaction sites based on density function theory (DFT) calculations. The present study deepened our understanding on the MnO2 catalyzed ozonation and provided reference to enhance the process efficiency.

Lead removal from water using organic acrylic amine fiber (AAF) and inorganic-organic P-AAF, fixed bed filtration and surface-induced precipitation.

Granular porous sorbents were normally used for heavy metals removal from water. To search for the new commercial sorbent and treatment strategy, an organic acrylic amine fiber (AAF) and phosphorus loading inorganic-organic AAF (P-AAF) were prepared and used for lead (Pb) removal from water. A new strategy of inorganic-organic coupling technology was proposed for Pb removal, based on the hypothesis of surface-induced precipitation mechanism. The AAF showed a Pb adsorption capacity of 417 mg/g from the Langmuir fitting, while the column filtration technology was further applied to measure the adsorption edge and applications. Effects of different initial Pb concentrations, hydraulic retention time, and co-existing P were considered in the filtration experiments. The presence of 0.8 mg/L P in water significantly improved the Pb breakthrough point from 15,000 to 41,000 bed volumes of water spiked with 85 µg/L Pb, while the P-AAF fixed bed showed better removal of Pb than AAF SEM/EDX and XRD spectra were employed for determining the surface functional groups and the formation of surface-induced precipitation of pyromorphite (Pb5(PO4)3OH) on AAF. This study verified the application of AAF sorbent for Pb removal and the enhanced effect of coating P on AAF, thus improved our fundamental understanding and application of the surface chemistry process of Pb with P.

Selenium and arsenic removal from water using amine sorbent, competitive adsorption and regeneration.

Selenium (Se) and arsenic (As) are toxic contaminants in surface water and drinking water. The human body needs little quantity of Se, but too high dose is not allowed. Metal oxides such as iron oxides were used for adsorption or co-precipitation removal of As from water. However, the regeneration and stability problems of metals oxides sorbents are unsatisfactory , and there is not enough adsorbent for Se removal from water also. We developed the acrylic amine fiber (AAF) for adsorption reomval of Se and As from water and systematically studied the influenced factors. Batch experiments were conducted for investigating the adsorption edges, while column filtration tests were employed for dynamic application edges. At neutral pH, the Langmuir isotherm fittings gave the maximum adsorption capacities of As(V), As(III), Se(VI) and Se(IV) are 270.3, 40.5, 256.4, and 158.7 mg/g, respectively. Effects of co-existing inorganic anions on As(V) and Se(VI) adsorption using AAF gave the order of PO43- > SO42- > NO3- > SiO32-, while different organic acids obey the order of citric acid > oxalic acid > formic acid. Fourier transform infrared analysis showed the PO43- and SO42- competition mechanisms are electrostatic repulsions, while the competition of organic acids derived from acid-base reaction between the carboxyl group and the amino group. Column filtration and regeneration results showed that the spent AAF can be regenerated using 0.5 mol/L HCl solution and reused with no much decrease of adsorption capacity.

Lead immobilization by phosphate in the presence of iron oxides: Adsorption versus precipitation.

As a commonly used corrosion inhibitor, phosphate (PO4) has a complicated effect on the fate and transport of lead (Pb) in drinking water systems. While the formation of pyromorphite has been recognized to be the major driving force of the Pb immobilization mechanism, the role of adsorption on iron oxides is still not clear. This study aims to clarify the contributions of adsorption and precipitation to Pb removal in a system containing both iron oxides and PO4. A combination of batch experiments, X-ray absorption spectroscopy, infrared spectroscopy, and electron spectroscopy was employed to distinguish the adsorbed and precipitated Pb species. The results indicated that the adsorption of Pb on iron oxides still occurred even when the solution was supersaturated to pyromorphite (i.e., 5 mg/L P with 0.1-30 mg/L Pb in 0.01 M NaCl solution at neutral pH). In the tap water containing 0.92 mg/L P and 1 mg/L Pb, adsorption on iron oxides contributed more (62-67%) than precipitation (33-38%) in terms of Pb removal. Surprisingly, the pre-formed pyromorphite is transformed to adsorbed species after mixing with iron oxides in water for 24 h. The illustration of this transformation is important to understand the immobilization mechanisms and transport behaviors of Pb in drinking water systems after the utilization of PO4.

Surface mole-ratio method to distinguish surface precipitation and adsorption on solid-liquid interface.

The enhancement effects of phosphate (P) on Pb removal by adsorbents have been attributed to co-adsorption of P and Pb, the formation of P-Pb surface ternary surface complexes, and surface precipitation of P and Pb. However, distinguishing adsorption from surface precipitation in multi-adsorbate systems has been a challenge. For the first time, a surface mole-ratio (SMR) method was established and applied for delineating Pb-P precipitation and Pb adsorption on an acrylic amine fiber (AAF) adsorbent. In elaborating the SMR method, we developed Pb removal experiments by mixing solutions containing 0.2 g/L of AAF, 6 and 12 µmol/L P, and 0-35 µmol/L Pb. When the removed Pb/P (µmol/µmol) was plotted as a function of the equilibrium Pb (µmol/L), the SMR diagram exhibited a turning-point similar to the Pb/P mole ratio of 5/3 = 1.67 in pyromorphite (Pb5(PO4)3OH) precipitate. The SMR diagram indicated that when the Pb concentration increased, the precipitate formed first; after all P formed precipitates, Pb was removed by adsorption. The precipitation and adsorption processes were further confirmed by other SMR diagrams, FTIR, SEM-EDX, and XRD analysis. The SMR method will have broad applications in determining the removal mechanisms of multi-adsorbates by adsorbents and coagulants, and stabilization mechanisms of heavy metals in soils. With the development and application of more modern in-situ characterization techniques, SMR method will be more effective.

Challenges of arsenic removal from municipal wastewater by coagulation with ferric chloride and alum.

Discharge of treated municipal wastewater containing arsenic (As) may cause adverse effects on the environment and drinking water sources. Arsenic concentrations were measured throughout the treatment systems at two municipal wastewater plants in New Jersey, USA. The efficiency of As removal by ferric chloride and alum coagulants were evaluated. Besides, the effects of suspended solids in the mixed liquor, pH, and orthophosphate (PO43-) on As removal were investigated. The total recoverable As (TAs) concentrations in the influent and effluent of Plant A were in the ranges of 2.00-3.00 and 1.50-2.30 µg/L, respectively. The results indicated that <30% of the As was removed by the conventional biological wastewater treatment processes. The influent and effluent TAs concentrations at Plant B was below 1.00 µg/L. The bench-scale coagulation results demonstrated for the first time that the coagulation treatment could not effectively remove As from the municipal wastewater to <2.00 µg/L. Very high doses of the coagulants (8 and 40 mg/L of Fe(III) or Al(III)) were required to reduce the TAs from 2.84 and 8.61 µg/L in the primary clarifier effluent and arsenate-spiked effluent samples to <2.00 µg/L, respectively, which could be attributed to the high concentrations of PO43- and dissolved organic matters (DOM) in the wastewater. The protein DOM in wastewater may negatively impact removal efficiencies more than the DOM in natural water, which mainly consists of humic substances. Furthermore, an artificial neural network was constructed to determine the relative importance of different parameters for As removal. Under the experimental conditions, the importance followed the order: coagulant dose>dissolved PO43- > initial As concentration > pH. The findings of this study will help develop effective treatment processes to remove As from municipal wastewater.

Adsorption and recovery of phosphate from water by amine fiber, effects of co-existing ions and column filtration.

A weak-base adsorption fiber, acrylic amine fiber (AAF), was prepared for removal and recovery of phosphate from water. The adsorption properties of the AAF for phosphate and effects of co-existing ions were investigated using batch and column filtration experiments, scanning electron microscope, and Fourier transform infrared techniques. Experimental results showed that AAF had a high phosphate adsorption capacity of 119 mg/g at pH 7.0. The effects of calcium, sulfate, carbonate, nitrate, and fluoride showed that sulfate and calcium inhibited phosphate adsorption. However, AAF showed higher binding affinity toward phosphate than sulfate. Column filtration results showed that AAF could filter 1420 bed volumes of tap water containing 1.0 mg-P/L of phosphate. The saturated AAF could be regenerated using 0.5 mol/L hydrochloric acid solution and reused. After desorption, phosphate was recovered through precipitation of hydroxyapatite (Ca5(PO4)3OH). The easy of regeneration, good adsorption performance, and the fiber morphology of AAF make it an attractive alternative for phosphate recovery from multiple water sources.