Adsorption Of Urea Research Articles

Nutrient recovery from urine: Urea adsorption onto biochar integrated with Na-chabazite as urease inhibitor

This study presents an innovative technical integration for concomitant nutrient recovery from source-separated urine. While cation exchange is known for efficient K+ recovery, it faces competition due to the high molarity of NH4+ in hydrolyzed urine. This study proposes inhibiting urease activity to facilitate the recovery of K⁺ and urea from fresh urine. Na-chabazite was first proposed as a urease inhibitor in this study, reducing urease activity by 50 %. Wood biochar, with its high porosity (308.0 m²/g) and polar functional groups, shows a urea adsorption capacity of 25.4 mg/g, which can be further improved by steam activation. The isotherm analysis suggests that urea adsorption onto biochar follows a multi-layer adsorption process. Finally, an integrated process is suggested: "Na-chabazite and Biochar adsorption → urea hydrolysis → struvite precipitation + ammonia stripping-acid scrubbing", ensuring efficient recovery of urea, NH4+, PO43-, and K+ from source-separated urine.

Adsorption Study of Uremic Toxins (Urea, Creatinine, and Uric Acid) Using Modified Clinoptilolite

The development of materials for uremic toxin removal is under continuous research. In this work, a natural zeolite (clinoptilolite) was modified using tartaric acid through two different methods: conventional reflux heating and ultrasound energy. The resulting materials were used as an adsorbent material for the removal of uremic toxins such as urea, creatinine, and uric acid. In the uremic toxin removal study, it was observed that the material modified using ultrasound for 100 min had the highest removal values (74.49%, 40.31%, and 51.50% for urea, creatinine, and uric acid, respectively), while unmodified zeolite removed 30.57%, 18.07%, and 22.84% of the same toxins. The best results for conventional heating modification were 67.08%, 31.97%, and 32.39%, respectively. Therefore, acid group incorporation considerably improved the adsorption properties of the clinoptilolite. Regarding adsorption kinetics, it was found that the pseudo-second-order model better described the behavior of all the modified materials. Equilibrium adsorption data were adjusted to the Langmuir and Freundlich models. The Freundlich model (multilayer adsorption) described urea adsorption, while the Langmuir model (monolayer adsorption) described creatinine and uric acid.

Urea adsorption and detection using silicon nanowires doped with B, Al, C, Ge, N, and P: A DFT investigation

Urea can serve as a biomarker for the detection of various illnesses, including renal and hepatic failure. Consequently, the development of novel devices and materials capable of adsorbing and identifying urea is a crucial objective for the scientific community. This study theoretically investigates the adsorption and detection capabilities of doped silicon nanowires (SiNWs) for urea using Density Functional Theory (DFT). Doping involves substituting a silicon atom on the surface with a dopant atom; B, Al, C, Ge, N, and P were employed for this purpose. This study presents an innovative method for enhancing urea adsorption and detection by doping SiNWs with group XIII elements, specifically aluminum and boron atoms. The results indicate that this doping significantly improves urea adsorption on SiNWs compared to undoped SiNWs. Notable changes in the bandgaps and work functions of the doped nanowires following urea adsorption suggest their potential use as diagnostic tools for uremia.

Photo-Excited High-Spin State Ni (III) Species in Mo-Doped Ni3S2 for Efficient Urea Oxidation Reaction.

Designing robust catalystsfor increasing the sluggish kinetics of the urea oxidation reaction (UOR) is challenging. Herein, the regulation of spin states for metal active sites by photoexcitation to facilitate the adsorption of urea and intermediates is demonstrated. Mo-doped nickel sulfide nanoribbon arrays (Mo-Ni3S2@NMF) with excellent light-trapping capacity are successfully prepared. Under AM 1.5G illumination, the activity of the Mo-Ni3S2@NMF exhibits a 50% improvement in the UOR current. Compared with those under dark conditions, Mo-Ni3S2@NMF achieve 10mA cm-2 at 1.315 VRHE for UOR and 1.32 Vcell for urea electrolysis, which are decreases of 15 and 80mV, respectively. The electron spin resonance, in situ Fourier transform infrared spectroscopy analysis and density functional theorycalculations reveal that illumination led to the formation of Ni3+ active sites in a high-spin state, which strengthens the d-p orbital hybridization of Ni-N, hence facilitating the adsorption of urea. C─N cleavage of the *CONN intermediate is further inhibited, which promotes the oxidation of urea molecules via the active N2 pathway, thereby accelerating the UOR rate.

Improved Urea Oxidation Performance via Interface Electron Redistributions of the NiFe(OH)x/MnO2/NF p-p Heterojunction.

The development of highly efficient urea oxidation reaction (UOR) electrocatalysts is the key to simultaneously achieving green hydrogen production and the treatment of urea-containing wastewater. Ni-based electrocatalysts are expected to replace precious metal catalysts for UOR because of their high activity and low cost. However, the construction of Ni-based electrocatalysts that can synergistically enhance UOR still needs further in-depth study. In this study, highly active electrocatalysts of NiFe(OH)x/MnO2 p-p heterostructures are constructed on nickelfoam (NF) by electrodeposition (NiFe(OH)x/MnO2/NF), illustrating the effect of electronic structure changes at heterogeneous interfaces on UOR and revealing the catalytic mechanism of UOR. The NiFe(OH)x/MnO2/NF only needs 1.364V (vs Reversible Hydrogen Electrode, RHE) to reach 10mA cm-2 for UOR. Structural characterizations and theoretical calculations indicate that energy gap leads to directed charge transfer and redistribution at the heterojunction interface, forming electron-rich (MnO2) and electron-poor (NiFe(OH)x) regions. This enhances the catalyst's adsorption of urea and reaction intermediates, reduces thermodynamic barriers during the UOR process, promotes the formation of Ni3+ phases at lower potentials, and thus improves UOR performance. This work provides a new idea for the development of Ni-based high-efficiency UOR electrocatalysts.

Effect of functional groups on the adsorption of urea on activated carbon

The recovery of urea, present in the urine of mammals, has the potential of converting a current wastewater pollutant into an energy source due to its high hydrogen content, in alignment with the waste-to-energy principles. Carbon-based materials enable this approach due to their relatively high urea adsorption capacities. This work reveals that the adsorption of urea from aqueous solutions on activated carbon is a combination of weak van der Waals interactions such hydrogen bonds with the aromatic structure of the pristine carbon surface and also with carboxyl groups on the functionalised carbon, showing no appreciable interaction with hydroxyl or lactone groups. The selective introduction and quantification of different oxygen functional groups on activated carbon reveals their independent effect on the urea adsorption capacity, bringing an end to previous discrepancies in the literature. It also demonstrates that the optimisation of carbon materials must balance the increase of carboxyl groups and the decrease of the surface area associated to functionalisation treatments, providing guidance for future developments of carbon-based materials for circular economy applications.

Linker-induced hollow MOF embedded into arginine-modified montmorillonite for efficient urea removal: Adsorption behavior and mechanism analysis

The precise regulation of hollow metal–organic framework (HMOF) and the effective assembly with excellent guest materials present limitless potential for pollutant removal. In this work, the arginine-modified montmorillonite (AMMT) was preferentially prepared via room temperature impregnation approach, and then the AMMT-HMOF composite was effectively constructed through a one-pot method. During this process, linker-induced MOF to MOF route was proposed, i.e., solid ZIF-67 transformed into hollow MOF-74 (thicknesses: ∼25 nm). Of note, this route involves the transition from solid to hollow structures, as well as the change between different topologies. Next, the AMMT-HMOF composite was evaluated for adsorption experiments with urea in aqueous solution as the target molecule. Further speaking, the optimization experiments were conducted to analyze the impact of pH, contact time, adsorbent mass and original urea concentration towards the adsorption process. The as-fabricated absorbent presented a maximum adsorption capacity of 298.5 mg/g within 1 h, demonstrating adherence to pseudo-second-order kinetics and the Langmuir model. The excellent adsorption performance can be ascribed to the enlarged layer spacing of AMMT, as well as the fast mass transport and abundant diffusion channels in HMOF. Additionally, the mechanistic analyses revealed the existence of hydrogen bonding interactions between the adsorbent and urea. Meanwhile, the adsorbent displayed the outstanding morphological and structural stability after usage. According to our survey, this is the first time to use this linker-induced MOF-to-MOF strategy and predictably assemble with functionalized montmorillonite to construct the hollow MOF composite for urea adsorption.

Conjugated molecularly imprinted polymers based on covalent organic frameworks: Fluorescent sensing platform for specific capture of urea and elimination of ethyl carbamate

This study described the preparation of an azide covalent organic framework-embedded molecularly imprinted polymers (COFs(azide)@MIPs) platform for urea adsorption and indirect ethyl carbamate (EC) removal from Chinese yellow rice wine (Huangjiu). By modifying the pore surface of COFs using the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, COFs(azide) with a high fluorescence quantum yield and particular recognition ability were inventively produced. In order to selectively trap urea, the COFs(azide) were encased in an imprinted shell layer via imprinting technology. With a detection limit (LOD) of 0.016 μg L-1 (R2 = 0.9874), the COFs(azides)@MIPs demonstrated a good linear relationship with urea in the linear range of 0–5 μg L-1. Using real Huangjiu samples, the spiking recovery trials showed the viability of this sensing platform with recoveries ranging from 88.44 % to 109.26 % and an RSD of less than 3.40 %. The Huangjiu processing model system achieved 38.93 % EC reduction by COFs(azides)@MIPs. This research will open up new avenues for the treatment of health problems associated with fermented alcoholic beverages, particularly Huangjiu, while also capturing and removing hazards coming from food.

Expression of Concern: Molecular dynamics simulation of Urea adsorption on various nanoparticles in a spiral Microfluidic system

Expression of Concern: Molecular dynamics simulation of Urea adsorption on various nanoparticles in a spiral Microfluidic system

Surface reconstruction and synergistic electrocatalysis of perovskite K-Ni-Zn-F for efficient urea-based energy conversion

Urea oxidation reaction (UOR) is hindered by poor catalytic activity, sluggish kinetics, and complex catalytic mechanism of electrocatalysts. Herein, we develop a novel perovskite K-Ni-Zn-F catalyst (KNZF-31) towards efficient UOR, showing a low potential of 1.348 V vs. RHE at 10 mA cm−2. The designed direct urea-hydrogen peroxide fuel cell (DUHPFC) provides superior open circuit voltages and power densities (0.99 V, 11.41 mW cm−2). Ex situ technology verifies amorphous electro-active/inert NiOOH/ZnO derived from surface conversion of crystalline KNZF-31, which synergistically drive the UOR. Theoretical calculation indicates that Zn-doping in KNiF3 promotes the OH− adsorption and charge transfer of Ni2+-site and formation of surface NiOOH electroactive species, which optimizes subsequent urea adsorption and charge transfer of Ni3+-site and desorption of CO2 on NiOOH/ZnO hetero-interface. This study reveals catalytic mechanism and activity origin of KNZF-31 catalyst towards UOR, offering a bright prospect for energy-sustainable developments.

Vertical Cross-Alignments of 2D Semiconductors with Steered Internal Electric Field for Urea Electrooxidation via Balancing Intermediates Adsorption.

Single-component electrocatalysts generally lead to unbalanced adsorption of OH- and urea during urea oxidation reaction (UOR), thus obtaining low activity and selectivity especially when oxygen evolution reaction (OER) competes at high potentials (>1.5 V). Herein, a cross-alignment strategy of in situ vertically growing Ni(OH)2 nanosheets on 2D semiconductor g-C3N4 is reported to form a hetero-structured electrocatalyst. Various spectroscopy measurements including in situ experiments indicate the existence of enhanced internal electric field at the interfaces of vertical Ni(OH)2 and g-C3N4 nanosheets, favorable for balancing adsorption of reaction intermediates. This heterojunction electrocatalyst shows high-selectivity UOR compared to pure Ni(OH)2, even at high potentials (>1.5 V) and large current density. The computational results show the vertical heterojunction could steer the internal electric field to increase the adsorption of urea, thus efficiently avoiding poisoning of strongly adsorbed OH- on active sites. A membrane electrode assembly (MEA)-based electrolyzer with the heterojunction anode could operate at an industrial-level current density of 200 mA cm-2. This work paves an avenue for designing high-performance electrocatalysts by vertical cross-alignments of active components.

Tailoring competitive adsorption sites of hydroxide ion to enhance urea oxidation-assisted hydrogen production

Alloys with bimetallic electron modulation effect are promising catalysts for the electrooxidation of urea. However, the side reaction oxygen evolution reaction (OER) originating from the competitive adsorption of OH− and urea severely limited the urea oxidation reaction (UOR) activity on the alloy catalysts. This work successfully constructs the defect-rich NiCo alloy with lattice strain (PMo-NiCo/NF) by rapid pyrolysis and co-doping. By taking advantage of the compressive strain, the d-band center of NiCo is shifted downward, inhibiting OH− from adsorbing on the NiCo site and avoiding the detrimental OER. Meanwhile, the oxygenophilic P/Mo tailored specific adsorption sites to adsorb OH− preferentially, which further released the NiCo sites to ensure the enriched adsorption of urea, thus improving the UOR efficiency. As a result, PMo-NiCo/NF only requires 1.27 V and −57 mV to drive a current density of ±10 mA cm−2 for UOR and hydrogen evolution reaction (HER), respectively. With the guidance of this work, reactant competing adsorption sites could be tailored for effective electrocatalytic performance.

Uremic Toxins Elimination from Simulated Intestinal Serum with Mesopo-rous Silica Nanoparticles Coupled with Molecularly Imprinted Polymers and Amino Linker

Background: One of the most researched issues is the elimination of uremic toxins from the human body. These toxins can build up and lead to catastrophic issues including renal failure. To get rid of them, absorbents like activated carbon, zeolites, and other minerals are frequently utilized. Methods: Mesoporous silica nanoparticles functionalized with (3-Aminopropyl) triethox-ysilane (APTES) linker (MSN-NH2) and mesoporous silica nanoparticles grafted with molec-ularly imprinted polymers (MSN-MIP) from the previous study were examined in this study to determine how well they absorbed urea, creatinine, and uric acid in a simulated intestinal serum. Results: MSN-MIP's large surface area (879.12 (m2/g)) and volume of pores (0.8475 (cm3/g)) made removal results that were satisfactory in the simulated serum. Additionally, MSN-MIP demonstrated a high urea adsorption capacity (qm = 1836.45 mg/g). Creatinine (qm = 1529.5 mg/g) and uric acid (qm = 1210.6 mg/g) were absorbed via NH-MSN2, which demonstrated a noticeable potential for absorption. The results of cell viability test for the first 72 hours, showed that the use of these absorbents in hemodialysis systems is acceptable. Conclusion: Synthesized adsorbents can be utilized in the hemodialysis system since the results of the cell viability test also showed that the percentage of cell viability was extremely high up to 72 hours.

Towards an industrial perspective for urea-to-hydrogen valorization by electro-oxidation on nickel(III): Real effluents and pilot-scale proof of concept

This paper presents an investigation into urea-to-hydrogen valorization through electro-oxidation on nickel(III). The study has dual objectives: (i) to gain a better understanding of the effects of organic compounds (other than urea) in human urine on UEO and (ii) to upscale the process to pilot-scale. Initial voltammetric studies at lab-scale using real human urine showed that urea adsorption on nickel(III) sites, followed by its electro-oxidation, competes with molecules such as creatinine, histidine, and creatine. Notably, creatinine reduced the nickel(II) oxidation signal by up to 20 %, indicating its reaction precedence over urea. Additionally, the oxidation rate of urea by nickel(III) in urine exhibited a much lower partial order (0.1), as opposed to 0.3 in KOH solution, confirming the impact of competitive adsorption. Subsequently, UEO experiments were upscaled using a specially designed 1 L undivided tubular EC reactor operating in multi-pass mode. Potentiostatic electrolysis of a urea synthetic solution was conducted over 70 h, achieving nitrogen and carbon species mass balances of over 97 %—a milestone previously unreported at this scale. The study further examined the influence of operating parameters such as anode surface area, flow rate and applied potential on the EC process. This investigation underscored the impact of factor like reactor geometry, controlled potential and temperature on process efficiency. Parameters for optimal N2 production, highest urea conversion rate, etc., were also defined. Finally, the electrolysis of human urine at pilot-scale unveiled new challenges distinct from those encountered with urea synthetic solutions.

Preparation of a honeycomb-like magnetically controlled release straw-based fertilizer

It is significant to improve fertilizers utilization efficiency (UE), realize the recycling of straw, and transform the traditional fertilization mode for fruit trees (ditch or hole). Therefore, a honeycomb-like magnetically controlled-release fertilizer (HMCRF) was prepared by combining corn straw (CS), urea, Fe3O4, modified starch adhesive (MSA), and amino silicone oil (ASO) in this work. CS served as a carrier for urea, MSA was an environmentally friendly adhesive, and Fe3O4 acted as a magnetic-sensitive material. The hydrogen bonds that exist among CS (-OH), urea (-NH2), and Fe3O4 (-FeO) played an essential role in urea adsorption. The magnetic field could effectively control the release of urea and improve urea UE. Thus, fertilizers could be provided to fruit trees according to their nutrient requirements at different growth stages to reduce waste. What's more, HMCRF could be applied directly on the soil surface, which not only saved labor but also differed from the traditional application method. The honeycomb-like structure was also favorable for rainwater storage and urea release in practice. Notably, HMCRF had a high biosafety on earthworms and could significantly boost the amount of beneficial microorganism in soil. The study offers a novel controlled-release fertilizer to promote urea UE, reduce labor, and achieve CS recycling.

Barium-induced lattice expansion of Ni(OH)2: enhancing catalytic urea oxidation activity for energy-saving H2 production.

Constructing an environmentally friendly and efficient electrocatalyst holds important and profound significance for energy-efficient hydrogen production. Replacing the oxygen evolution reaction with a lower potential urea oxidation reaction (UOR) may save energy in water electrolysis to produce hydrogen. The UOR is characterized by its high energy barrier, which results in slow reaction kinetics. In this study, we introduced Ba(OH)2 into Ni(OH)2 to form uniform nanosheets. Due to the introduction of Ba2+, the lattice expansion of Ni(OH)2 was triggered, leading to significant improvement in UOR activity. The catalyst achieved a current density of 100 mA cm-2 at only 1.316 V and exhibited remarkable stability over time. Density functional theory (DFT) calculations demonstrate that the Ba-Ni(OH)2 site significantly reduces the energy barrier for urea adsorption, intermediate steps, and desorption. This work provides a novel and environmentally friendly strategy for constructing energy-efficient and highly efficient catalysts through the doping of alkaline earth metals.

Optimized carbonization of coffee shell via response surface methodology: A circular economy approach for environmental remediation

The disposal of coffee shell waste on farmland, is a common practice that can causing the environmental and waste valuable resources. Carbonization has been identified as an effective method for transforming coffee shells into useful products that mitigate environmental pollution. Through the response surface methodology, the carbonization conditions of the coffee shells were optimized and its potential as a biochar-based slow-release urea fertilizer was explored. Experiments were conducted on coffee shell performance under varying carbonization conditions such as temperature (600–1000 °C), time (1–5 h), and heating rate (5–20 °C/min). The results indicated that the ideal urea adsorption was 56.3 mg/g, achieved under carbonization conditions of 2.83 h, 809 °C, and 15.3 °C/min. The optimal nutrient release rate within seven days was 45.4% under carbonization conditions of 3.19 h, 813 °C, and 15.0 °C/min. The infrared spectroscopy analysis indicates that carbonization conditions influenced the absorption peak intensity of coffee shell biochar, while the functional group types remain unchanged. The biochar exhibits diverse functional groups and abundant pores, making it a promising candidate for use as a biochar-based fertilizer material. Overall, the findings demonstrate an effective waste management approach that significantly reduces environmental pollutants while remediating pollution.

Ferric Oxide Nanocrystals-Embedded Co/Fe-MOF with Self-Tuned d-Band Centers for Boosting Urea-Assisted Overall Water Splitting.

A novel semiconductive Co/Fe-MOF embedded with Fe2 O3 nanocrystals (Fe2 O3 @CoFe-MOF) is developed as a trifunctional electrocatalyst for the urea oxidation reaction (UOR), oxygen evolution reaction (OER), and hydrogen evolution reaction for enhancing the efficiency of the hydrogen production via the urea-assisted overall water splitting. Fe2 O3 @CoFe-TPyP-MOF comprises unsaturated metal-nitrogen coordination sites, affording enriched defects, self-tuned d-band centers, and efficient π-π interaction between different layers. Density functional theory calculation confirms that the adsorption of urea can be optimized at Fe2 O3 @CoFe-TPyP-MOF, realizing the efficient adsorption of intermediates and desorption of the final product of CO2 and N2 characterized by the in situ Fourier transform infrared spectroscopy. The two-electrode urea-assisted water splitting device-assembled with Fe2 O3 @CoFe-TPyP-MOF illustrates a low cell voltage of 1.41V versus the reversible hydrogen electrode at the current density of 10mA cm-2 , attaining the hydrogen production rate of 13.13µmol min-1 in 1m KOH with 0.33m urea. The in situ electrochemical Raman spectra and other basic characterizations of the used electrocatalyst uncover that Fe2 O3 @CoFe-TPyP-MOF undergoes the reversible structural reconstruction after the UOR test, while it demonstrates the irreversible reconstruction after the OER measurement. This work redounds the progress of urea-assisted water spitting for hydrogen production.

Stable light-emitting bionic antibody-conjugated covalent organic frameworks for the adsorption of urea and control of ethyl carbamate

In this paper, a novel azide-modified covalent organic framework conjugated bionic antibody microspheres (COFs(azide)@BAs) were prepared for the adsorption of urea and indirect control of ethyl carbamate (EC) in the processing of Huangjiu. To improve the fluorescence properties and specific binding ability to target, COFs(azides) were synthesized using post-modification of copper-catalyzed azide-alkyne cycloaddition (CuAAC). The aggregation-induced enhancement (AIE) interaction between COFs(azides)@BAs and urea induced an enhanced fluorescence behavior. The detection limit of urea was as low as 13 ng L−1 (R2 = 0.9896) in the linear range of 0.05–5 μg L−1. In addition, a satisfactory control rate for the removal of EC was achieved by COFs(azide)@BAs in the simulated system of Huangjiu processing. Therefore, this research broadened the path for the application of optical sensing systems in food safety control, which had important food safety implication and great economic value.

Superfast adsorption of small and uncharged urea from water using post-sonicated iron-based metal-organic framework

Urea is widely used in fertilizer production for agricultural purposes which risks runoff into soil and water sources. An excess of urea can result in algal or toxic blooms which can poison wildlife or even humans by accumulation in food sources. The removal of urea from water is challenging due to the small size (0.254 nm) and uncharged surface of urea. Intensive research has been conducted on a variety of methods to remove environmental concentrations of urea using adsorbents, but most of them lack effective removal, require long (>2 h) process time, and lack re-generability. Metal-organic frameworks (MOFs) are the new generation of adsorbents with excellent structural and functional group tunability. In this study, we synthesized MIL-100 (Fe), an iron-based MOF, as an efficient adsorbent for the removal of uncharged urea from water. The urea adsorption capacity of MIL-100 (Fe) was tested under varying experimental conditions such as pH (2–10), temperature (25–65 °C), MOF concentration (25–400 ppm), and urea concentration (25–1000 ppm). The results showed the superfast adsorption (more than 85% removal within 2 min) of neutrally charged urea molecules on MIL-100 (Fe). The MOF was able to reach a maximum adsorption efficiency of around 85% with a maximum uptake capacity of 3321 mg/g. The MIL-100 (Fe) showed acceptable re-generability by retaining up to 90% removal efficiency after four regeneration cycles. The urea adsorption followed pseudo 2nd-order adsorption kinetics and dipole-dipole interactions and π-NH bonding were the primary adsorption mechanism.