Nitrate Adsorption Research Articles

Interfacial Defect Engineering Triggered by Single Atom Doping for Highly Efficient Electrocatalytic Nitrate Reduction to Ammonia

Electrochemical reduction of nitrate (NO3RR), a widespread water pollutant, to high-valued ammonia is encouraging for sustainable artificial nutrient recycling and environmental-friendly pollution management. However, the limited available catalytic active sites and competitive hydrogen evolution make the catalytic performance still unsatisfactory. In this work, interfacial defect engineering via single atom doping was conducted to achieve highly efficient electrocatalytic NO3RR. Upon introduction of isolated Fe atoms, abundant oxygen vacancies are generated over atomic interface of TiO2, and the induced charge redistribution triggers the formation of considerable active sites for nitrate reduction, which plays a crucial role in inhibiting the proton reduction and promoting the adsorption and activation of nitrate. As expected, single atom Fe modified TiO2 exhibits a maximum ammonia yield rate of 137.3 mg h–1 mgcat.–1 and a Faradaic efficiency of 92.3% at −1.4 V (vs RHE), which are among the best of all the reported values yet. This work provides valuable insights into the exploration of highly efficient electrocatalysts toward nitrate reduction through the heteroatom doping and defect engineering over atomic interface.

In Situ Reconstruction of Metal Oxide Cathodes for Ammonium Generation from High-Strength Nitrate Wastewater: Elucidating the Role of the Substrate in the Performance of Co3O4-x.

In situ electrochemical reconstruction is important for transition metal oxides explored as electrocatalysts for electrochemical nitrate reduction reactions (ENRRs). Herein, we report substantial performance enhancement of ammonium generation on Co, Fe, Ni, Cu, Ti, and W oxide-based cathodes upon reconstruction. Among them, the performance of a freestanding ER-Co3O4-x/CF (Co3O4 grown on Co foil subjected to electrochemical reduction) cathode was superior to its unreconstructed counterpart and other cathodes; e.g., an ammonium yield of 0.46 mmol h-1 cm-2, an ammonium selectivity of 100%, and a Faradaic efficiency of 99.9% were attained at -1.3 V in a 1400 mg L-1 NO3--N solution. The reconstruction behaviors were found to vary with the underlying substrate. The inert carbon cloth only acted as a supporting matrix for immobilizing Co3O4, without appreciable electronic interactions between them. A combination of physicochemical characterizations and theoretical modeling provided compelling evidence that the CF-promoted self-reconstruction of Co3O4 induced the evolution of metallic Co and the creation of oxygen vacancies, which promoted and optimized interfacial nitrate adsorption and water dissociation, thus boosting the ENRR performance. The ER-Co3O4-x/CF cathode performed well over wide ranges of pH and applied current and at high nitrate loadings, ensuring its high efficacy in treating high-strength real wastewater.

Enhanced electrocatalytic nitrate reduction to ammonia on cobalt oxide nanosheets via multiscale defect modulation

The traditional Haber-Bosch process synthesizes ammonia subjecting to harsh process conditions and high energy consumption, and the nitrate pollution is a common environmental issue due to the excessive use of fertilizers. A sustainable and moderate nitrate electrocatalytic reduction to ammonia (NO3RR) was employed to achieve N-cycle, turning waste into treasure. Pre-density functional theory calculations forecast that Co3O4 will display optimal NO3RR performance among all the spinel cobalt-based catalysts. In this work, Co3O4/Co with unique interlaced nanosheets was fabricated through electrodeposition and calcination. Benefitting from the open-pore, defective nanosheet structure and modulated oxygen vacancy, the Co3O4/Co catalyst can accumulate more nitrate on activated sites and display excellent NO3RR properties in the neutral electrolyte (ammonia yield rate: 4.43 mg h−1 cm−2, Faradaic efficiency: 88.7 %). Theoretical calculations reveal that oxygen vacancy could enhance nitrate adsorption energy, suppress hydrogen evolution reaction, and weaken the rate-determining step of *NO → *HNO. Furthermore, the continuous NO3RR flow electrolyzer has been customized with Co3O4/Co electrocatalyst and it highly enlarges ammonia yield over one day, which could accelerate the NO3RR to commercial application.

Nitrate adsorption towards ultrasound-assisted modified oil palm frond: Characterization and performance investigation using response surface methodology

Nitrate is known as one of the nutrients contributing towards eutrophication condition, when its concentration exceeds threshold. Adsorption of nitrate had been studied extensively, and lignocellulosic adsorbent has been favourable of many researchers. In Malaysia, oil palm biomass is a readily available lignocellulosic material in high volume, specifically oil palm frond (OPF). However, the potential of OPF for nitrate adsorption is still not vastly explored. Hence, this study aims to determine the structural properties of ultrasound-assisted modified OPF and to investigate the performance as an adsorbent for the adsorption of nitrate via response surface methodology (RSM). Batch adsorption experiment was carried out according to the parameters set by central composite design (CCD) under RSM via Design Expert software. A steady state nitrate recovery of 65.0 % and adsorption capacity of 1.65 mg/g were achieved at pH 7.0, initial concentration of 15 mg/L, adsorbent dosage of 5.5 g/L, contact time of 12 hours and temperature of 32.5℃ Meanwhile, optimization condition was conducted with at pH 5.12, initial concentration of 25.0 mg/L, adsorbent dosage of 1.0 g/L, and contact time of 5 hours at 25℃ resulted to an average of 65.28 % nitrate removal percentage and 16.25 mg/g of adsorption capacity. FESEM, BET and FTIR showed successful grafting of quaternary amine ions on ultrasound-assisted modified OPF. This shows that the modified OPF is a potential adsorbent for nitrate.

Assessment of the Feasibility of Modified Chitosan Beads for the Adsorption of Nitrate from an Aqueous Solution

Assessment of the Feasibility of Modified Chitosan Beads for the Adsorption of Nitrate from an Aqueous Solution

Nitrate adsorption using green iron oxide nanoparticles synthesized by Eucalyptus leaf extracts: Kinetics and effects of pH, KCl salt, and anions competition

This research investigated the colloidal stability and reactivity of green iron oxide nanoparticles for removing NO3– ions from polluted water. These nanoparticles were synthesized by Eucalyptus globulus leaf extract (EL-Fe NPs). Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and dynamic light scattering (DLS) were utilized to characterize EL-Fe NPs. The effect of contact time, different pH, KCl salt, and anions (PO43−, SO42−, HCO3–, Cl−), on NO3– adsorption using EL-Fe NPs were evaluated. Based on the results, Fe3O4 and α-Fe2O3 nanoparticles were encapsulated by polyphenols and have irregular nano-particulate structures. After 30 min, the maximum adsorption capacity of 1.5 g L−1 EL-Fe NPs dispersed in 50 mg L−1 NO3– solution with a pH of 3.7 was acquired at about 12.91 mg/g. Adsorption of NO3– on EL-Fe NPs was strongly pH dependent, and at pH > 6.6 no significant adsorption occurred. KCl salt by agglomeration of EL-Fe NPs, the mean particle size varied between 25.6 nm and 63 nm, and NO3– adsorption decreased dramatically. It was observed that EL-Fe NPs significant affinity to adsorb PO43− ions. As a result, no significant adsorption of NO3– ions onto EL-Fe NPs was detected in the presence of phosphate ions. The experimental data were reasonably fit to a pseudo-second-order kinetic model (R2 = 0.992), which can be concluded that the primary mechanism of NO3– adsorption is electrostatic. This work indicated that the removal of NO3– using EL-Fe NPs was influenced by the type and concentration of accompanying cations and anions.

Revealing the activity origin of ultrathin nickel metal–organic framework nanosheet catalysts for selective electrochemical nitrate reduction to ammonia: Experimental and density functional theory investigations

The electrochemical nitrate reduction reaction (NitRR) affords a sustainable way for nitrate mitigation and ammonia synthesis, but there are still some problems such as poor nitrate conversion, low ammonia selectivity, and slow reaction kinetics. A clear structure-performance relationship is essential for designing efficient catalysts and understanding the reaction mechanisms. Herein, ultrathin nickel metal–organic framework (Ni-MOF) nanosheets supported on Ni foam featuring a well-defined stable structure, large electrochemically active surface area, and low electron transport resistance were prepared by a one-step solvothermal process. At −1.4 V, the nitrate reduction, rate constant, ammonia selectivity, and yield reached 96.4%, 0.448 h−1, 80%, and 110.13 ug·h−1·cm−2, respectively. Experimental and theoretical studies demonstrated that the hydroxyl-ligated Ni atoms exhibited higher nitrate adsorption properties and lower activation energy towards NitRR compared to carboxylic acid-ligated Ni atoms. Mechanism investigations revealed a nitrate-to-ammonia reaction pathway involving multiple intermediate species on Ni-MOF nanosheet catalysts. This work offers a new avenue to construct highly efficient electrocatalysts for the selective transformation of nitrate to valuable ammonia.

Study on adsorption of ammonium and nitrate in wastewater by modified biochar

This study investigates the prepared rice husk biochar (RHB) and Mg/Ca-LDHs@RH biochar (MCB) microstructural, morphological, and nitrate adsorption capacity, owing to the increased concentration of nitrate ions in industrial wastewater that lead to serious environmental problems. In this study, biochar was prepared from agricultural waste, and the co-precipitation method was integrated to prepare Mg/Ca-rich layered double hydroxides (Mg/Ca-LDHs). The prepared biochar physicochemical characteristics were analyzed using XRD, FESEM, EDS, BET, and IC. Here we further investigated the influence of pyrolysis temperature and different concentrations (Mg, Ca) LDHs coatings. This study found that the pyrolysis temperature reduces the biochar yield percentage from 44.5 to 30.2 %. The biochar pores are shown in a honeycomb shape, and the diameter of the pores is about 3–5 μm. In addition, the obtained biochar pores seemed to be more fragmented as the Mg/Ca ratio gradually increased. The surface area of biochar increased with the increase in the Mg/Ca ratio, and the specific surface area of 3:1 and 4:1 Mg/Ca-LDHs ratio was the highest, reaching about 288–308 cm2/g. The biochar LDHs with a 3:1 Mg/Ca-LDHs ratio can effectively adsorb nitrate ions in water, and the LDHs maintain a stable state during the adsorption process.

Facile fabrication of nano zerovalent iron and granular activated carbon for enhanced nitrate removal from water

ABSTRACT Nitrate contamination of groundwater has become a serious threat to the environmental health. In this study, nano zerovalent iron (nZVI) and granular activated carbon (GAC) were fabricated and characterized by some advanced analytical techniques including SEM, BET, XRD, and FTIR to investigate their structural properties. Batch experiments were conducted for the adsorption of nitrate from water. The effect of various parameters including pH, adsorbent dose, initial nitrate concentration, and contact time was investigated. The nZVI showed maximum adsorption capacity (qmax) of 104.20 mg/g for nitrate at optimum conditions (pH 2, initial concentration 50 ppm, adsorbent dose 3.75 g/L at room temperature), while GAC has shown qmax 81.07 mg/g at optimum conditions (pH 6, initial concentration 50 ppm, adsorbent dose 3.75 g/L at room temperature). Equilibrium data of nitrate adsorption by nZVI and GAC followed the Langmuir isotherm (R2 = 0.999) and pseudo-second-order kinetic model. ANOVA and RCBD approaches were used to evaluate and check the significant level of various parameters.

Achieving reaction pathway separation for electrochemical nitrate fixation on triatomic catalysts: A new mechanism

As the continuous development of electrocatalytic technique, the degradation of toxic nitrate wastewater into green fuel ammonia has become the goal of researcher’s unremitting efforts by electrochemical method. Particularly, a high performance catalyst for electrochemical process is regarded as an indispensable tool for sustainable cycle. Although existing designed electrodes may effectively advance nitrate reduction reaction, they remain unsatisfactory due to elusive reaction processes. Here, a brand-new reaction mechanism has been proposed via density functional theory (DFT) and ab initio molecule dynamic (AIMD) methods, which breaks the bottleneck of linear scaling in atomic scale catalyst design. It is found that triple Mn atoms anchored on graphdiyne (Mn 3 -GDY) can drive nitrate adsorption and ammonia desorption on its surface with weak binding strength and strong activation by the spin polarization of active site. In addition, the powerful adsorption capacity of triatomic active site prevents the thermodynamic barrier from rising due to the transformation of the intermediates *NO 3 H and *NO 2 H into *NO 2 *OH and *NO*OH, respectively. More importantly, in accordance with the “weak-strong-weak” principle, Mn 3 -GDY has rapid response to ammonia desorption that is conducive to boost the turnover frequency. Anyway, this work may provide a new insight into atomic catalysts for improving reaction mechanisms. • Electrocatalytic reduction of nitrate into ammonia is realized on triatomic catalysts • A new mechanism breaks the bottleneck of linear scaling in atomic catalyst design • This mechanism perfectly matches the “weak-strong-weak” design principles • Mn 3 -GDY is an excellent candidate for NO 3 RR with an low limiting potential of 0.23 V

Durable Electrocatalytic Reduction of Nitrate to Ammonia over Defective Pseudobrookite Fe2 TiO5 Nanofibers with Abundant Oxygen Vacancies.

We propose the pseudobrookite Fe2 TiO5 nanofiber with abundant oxygen vacancies as a new electrocatalyst to ambiently reduce nitrate to ammonia. Such catalyst achieves a large NH3 yield of 0.73 mmol h-1 mg-1 cat. and a high Faradaic Efficiency (FE) of 87.6 % in phosphate buffer saline solution with 0.1 M NaNO3 , which is lifted to 1.36 mmol h-1 mg-1 cat. and 96.06 % at -0.9 V vs. RHE for nitrite conversion to ammonia in 0.1 M NaNO2 . It also shows excellent electrochemical durability and structural stability. Theoretical calculation reveals the enhanced conductivity of this catalyst and an extremely low free energy of -0.28 eV for nitrate adsorption at the presence of vacant oxygen.

Durable Electrocatalytic Reduction of Nitrate to Ammonia over Defective Pseudobrookite Fe2TiO5Nanofibers with Abundant Oxygen Vacancies

AbstractWe propose the pseudobrookite Fe2TiO5nanofiber with abundant oxygen vacancies as a new electrocatalyst to ambiently reduce nitrate to ammonia. Such catalyst achieves a large NH3yield of 0.73 mmol h−1 mg−1cat.and a high Faradaic Efficiency (FE) of 87.6 % in phosphate buffer saline solution with 0.1 M NaNO3, which is lifted to 1.36 mmol h−1 mg−1cat.and 96.06 % at −0.9 V vs. RHE for nitrite conversion to ammonia in 0.1 M NaNO2. It also shows excellent electrochemical durability and structural stability. Theoretical calculation reveals the enhanced conductivity of this catalyst and an extremely low free energy of −0.28 eV for nitrate adsorption at the presence of vacant oxygen.

Effects of ecological roofs in water quality: an experimental study over a humid tropical climate

Although ecological roofs (vegetated or non-vegetated) provide many benefits, it can also leach substances such as nutrients and metals that can affect downstream aquatic ecosystems. Therefore, this work aims to investigate the rainwater quality from ecological roofs in Recife, located in the Northeast Brazil, using local species in a tropical and humid climate. Using four test cells of 1 m2 (one non-vegetated filled with expanded clay aggregate, two vegetated with cactus “Coroa-de-Frade” and grass “Grama Esmeralda”, and one control roof), we analyzed thirteen water quality variables regarding irrigation parameters: pH, electrical conductivity, turbidity, nitrate, ammonia, phosphate, bicarbonate, carbonate, calcium, magnesium, sulfate, potassium, boron, sodium, and sodium adsorption ratio. We simulated rain events controlling its intensity and analyzed a sample of natural rainwater event. All roofs neutralized the pH. Control and clay roofs were source of bicarbonate and calcium, responsible for more alkaline effluents. Carbonate and ammonia were below the recommended limits for irrigation purposes for all roofs. Green roofs were source of nitrate, ammonia, and boron. Neither roofs were source or sink for sulfate and chloride for all analyzed samples. Regarding the natural rainwater experiment, only green roof with Coroa-de-Frade exceeded the recommend irrigation parameters for potassium and phosphate. A post-treatment is required for irrigation purposes. We recommend a first-flush system followed by a filter with sand and activated carbon.

Atomic catalyst supported on oxygen defective MXenes for synergetic electrocatalytic nitrate reduction to ammonia: A first principles study

The constant downscaling of catalysts to atomic catalyst with maximized atomic utilization efficiency provides a way for cost-efficient catalysis using a minimum amount of metals. However, the current studies are insufficient in the understanding of feasibility and mechanism of atomic catalyst on nitrate electroreduction toward ammonia (NRA). Herein, using first-principles calculations, we systematically explore the NRA mechanism of MXenes-based atomic catalysts TMn@M3C2O2 (TM = non-noble transition metal; M = Ti, V, Cr, Nb and Mo; n = 1, 2, and 3, which represents single-, double-, and triple-atom catalysts on MXenes). Nb3- and Nb2-modified V3C2O2 (Nb3@V3C2O2 and Nb2@V3C2O2) shows high NRA activity with low potential determination steps (−0.22 and −0.26 eV, respectively) and suppression to hydrogen evolution reaction (HER). The doping of Nb atoms causes a negatively upshift of the MXenes d-band center and creates more electron-deficient sites, which regulates the strong adsorption of nitrate and weaken the adsorption of *NHx (x = 1–3), thereby facilitating easy deoxidation and hydrogenation. This study not only theoretically verified the feasibility of atomic catalyst for NRA, but also provided a new idea for rational design of MXenes-based non-noble metal atomic catalyst.

Investigation of the interaction between adsorbed water and various morphologies of boehmite nanoparticles prepared by continuous supercritical hydrothermal synthesis

Boehmite applications are often subject to specific characteristics in terms of morphologies and surface properties. The versatile continuous supercritical hydrothermal method allows synthesizing various boehmite morphologies from rhombic to hexagonal platelet-like nanoparticles depending on the preferential adsorption of part of the precursor after transformation species on the (020) surface resulting in a preferential growth along [001] and mostly [100] directions. This adsorption on surface free sites plays the role of morphology stabilizer and results in the reduction of adsorbed water. The interaction between adsorbed water and the boehmite morphology depends on various parameters: 1) the structure order of boehmite as exhibited by XPS analysis associated with 1H Solid-State NMR spectroscopy and, 2) the number of available free sites, which tend to be filled by the adsorption of nitrates as observed by Raman spectroscopy.

Adsorption of nitrate in water by CTAB-modified MgFe layered double hydroxide composite biochar at low temperature: Adsorption characteristics and mechanisms

In this study, for the purpose of improving the removal effect of biochar on nitrate in wastewater at lower temperature, MgFe layered double hydroxides (MgFe-LDHs) were precipitated on the surface and in the pores of corn stover biochar (BC) in the presence of surfactant cetyltrimethylammonium bromide (CTAB) to prepare a novel adsorbent MgFe-CTAB-LDHs/BC. The result shows that BC has abundant pore structure and MgFe-LDHs has been uniformly loaded on the surface of BC and in the pores, which greatly reduced the agglomeration of LDHs. Part of CTAB was on the surface of BC, making it more positively charged, and the other part entered the interlayer of LDHs, changing the interlayer spacing, which is beneficial to adsorption. Meanwhile, the hydroxyl groups and metal hydroxides in LDHs and numerous active groups of BC enhanced the adsorption capacity through synergistic effect. The successful preparation of MgFe-CTAB-LDHs/BC was proved by various characterization analyses and the adsorption mechanism of nitrate on MgFe-CTAB-LDHs/BC was investigated through experimental demonstration and characterization analysis. The adsorption kinetics and isotherm studies also showed that the adsorption rate of MgFe-CTAB-LDHs/BC for nitrate was improved, and it still had a good adsorption effect at lower temperature. This study aims to provide a novel environmentally friendly adsorbent for nitrate adsorption at lower temperature.

A novel ion-imprinted polymer based on the principle of ion exchange by bulk polymerization for specific recognition and adsorption of nitrate in polluted groundwater

A novel NO3− ion imprinted polymer (IIP-NO3−) was successfully synthesized based on the principle of “ion exchange” and the method of “bulk polymerization”. The NO3− anions, cationic monomers dimethyldiallylammonium chloride (DMDAAC) and acrylamide (AM) was used as template ions and functional monomers respectively. The material characterization showed that IIP-NO3− has an irregular porous structure. The maximum nitrate adsorption capacity of IIP-NO3− on NO3− was 48.486 mg/g under an optimal preparation condition. The isothermal adsorption (R2 = 0.9947) of IIP-NO3− for NO3− basically conformed to the Langmuir model. The adsorption process followed with the pseudo-secondary order kinetic model (R2 > 0.99), and it can reach equilibrium within 5 min. The IIP-NO3− had an obviously lower adsorption capacity for another common anion NO2−, HCO3−, SO42− ions in groundwater pollution than NO3− ions. The recognition selectivity coefficient of IIP-NO3− for NO3− ions were 2.839, 6.450, 1.773 respectively due to the imprinted effect. And this ion imprinted polymers with high selectivity to nitrate can be combined with the chemical reduction and the electrochemical reduction method, so as to improve the nitrate chemical reduction efficiency and reduce the regeneration cost of the IIP-NO3−.

Nitrate adsorption by fired clay in fixed bed column

Excessive use of nitrogen fertilizers has increased nitrate concentrations in groundwater, which poses a health hazard from nitrate-contaminated drinking water and contributes to eutrophication. Nitrate removal from water systems has been carefully studied; However, new, low-cost solutions are urgently needed. Clay and terracotta minerals are commonly used in environmental applications due to their non-toxicity, global availability, low cost, and physical and chemical properties (ion-exchange capacity, high surface area, high adsorption, and catalytic properties). Although most are used to reduce cationic pollutants, depending on the method of modification or the materials with which they are mixed, they can be equally effective in removing anionic contamination. The goal of the study is to treat water containing excessive concentrations of nitrates to produce water of acceptable environmental specifications and to evaluate the performance of fired clay as a low-cost and environmentally friendly water treatment material.

Role of oxide support in electrocatalytic nitrate reduction on Cu

AbstractThe electrochemical nitrate reduction reaction (NO3RR) has the potential for distributed water treatment and renewable chemical synthesis. Cu is an active monometallic electrocatalyst for the NO3RR in acidic and alkaline electrolytes, where activity is limited by the reduction of adsorbed nitrate to nitrite. Oxygen‐vacancy forming metal‐oxide supports provide sites for N‐O bond activation in thermal reduction, impacting product distribution as well. Here we compare the electrochemical NO3RR activity of Cu deposited on two metal‐oxide supports (cerium dioxide [Cu/CeO2‐δ] and fluorine‐doped tin dioxide [Cu/FTO]) to a Cu foil benchmark. Considering activity in phosphate‐buffered neutral media, nitrate and adsorbed hydrogen compete for surface sites under NO3RR conditions. The less‐cathodic overpotential on Cu/CeO2‐δ compared to Cu/FTO is attributed to stronger nitrate adsorption, similar to thermal nitrate reduction. Utilization of CeO2‐δ as an electrocatalyst support slightly shifting product distribution toward more oxidized products, either by enhancing nitrate affinity or by a more dynamic process involving the formation and healing of oxygen vacancies (𝑣O••). These results suggest supporting catalysts on metal oxides may enhance activity by promoting the adsorption of anionic reactants on cathodic electrocatalysts.

Preparation of inhalable N-acetylcysteine-loaded magnetite chitosan microparticles for nitrate adsorption in particulate matter

Airborne particulate matter has been designated as a class 1 carcinogen by the World Health Organization. Nitrate is a toxic substance that accounts for a large proportion of particulate matter, and nitrate toxicity has long been reported.In this study, we aimed to optimize the adsorption and removal of particulate matter containing nitrate for effective elimination by the lungs. To this end, particles were designed to optimize the inhalation and removal efficiencies. These particles were prepared as chitosan-based particles containing N-acetylcysteine by using emulsion diffusion methods. Chitosan adsorbs nitrate, while N-acetylcysteine dissolves mucus. This removal mechanism has been found to occur in various in vitro models that mimic respiratory environments and in vivo models.In particular, the removal of exogenous substances, such as particulate matter, by the motility of respiratory cilia through mucolytic effect was investigated. This new approach for the adsorption and elimination of toxic substances entering the lungs represents an alternative defense mechanism against exposure to nitrates from air pollution.