Chelating Interaction Research Articles

Efficient metal-organic framework adsorbents for removal of harmful heavy metal Pb(II) from solution: Activation energy and interaction mechanism

Because of its irreversible toxicity and harm to people's health, lead contamination has gotten a lot of attention. As a result, the development of low-cost, high-performance removal approaches has become a popular issue. In this work, novel metal-organic framework (AMO-MOF) was developed to selectively adsorb Pb(II) from water. AMO-MOF perfectly inherits the structural characteristics of mesoporous materials and its specific surface area is 255.251 m2/g. The adsorption reached equilibrium at 180 min and the maximum adsorption capacity of AMO-MOF for Pb(II) was 472.73 mg/g. The adsorption of Pb(II) on AMO-MOF was fitted with pseudo-second-order kinetics and Langmuir isotherm models, indicating that the adsorption was monolayer chemisorption process. Thermodynamic and activation energy (Ea) analyses indicate that the monolayer chemisorption of Pb(II) on AMO-MOF was an endothermic process. When multiple cations coexist, AMO-MOF exhibits excellent selectivity for Pb(II). Meanwhile, after repeated used for 5 times, the removal rate can still reach more than 80 %. The adsorption mechanism is mainly the chelation and electrostatic interaction of N and O-containing functional groups on the adsorbent with Pb(II). The excellent adsorption performance of AMO-MOF for Pb(II) makes it have great application potential in practical environmental remediation.

Adsorption behaviors of heavy metal ions by different hydrazone-modified sodium alginate in aqueous medium: Experimental and DFT studies

Herein the hydrazone-modified sodium alginate, being prepared with aldimine condensation through dihydrazide and dialdehydes sodium alginate, possessed extremely effective and selective removal of Pb2+, Cd2+, and Cu2+. Equilibrium adsorption data of biphthalate dihydrazidemodified sodium alginate was obeyed the Freundlich isotherm and pseudo-second-order kinetics models, which reflected that the adsorption process was mainly via the chemisorption, and the maximum adsorption capacities for Pb2+, Cd2+, and Cu2+ were found to be 668.42, 472.37, and 200.10 mg g−1, respectively. The thermodynamic parameter for the sorption demonstrated the process was endothermic and spontaneous. Fourier Transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses revealed combination of chelation interactions coordination and ion exchange of nitrogen and oxygen atoms with heavy metal ions, and the density functional theory (DFT) calculations confirmed that heavy metal ions formed a stable five membered ring coordination structure with the nitrogen and oxygen atoms in hydrazone groups. Moreover, the adsorption efficiency was not significantly reduced after 10 adsorption–desorption recycles. To sum up, this study provides a new strategy for the removal of heavy metal ions by hydrazone-modified sodium alginate with great potential for wastewater treatment.

Adsorption of Sodium of Polyaspartic Acid on Serpentine and Its Effects on Selective Pyrite/Serpentine Flotation

Due to the optimum dissolution of the hydroxyl ion, serpentine is positively charged and tends to cover the sulfide mineral surface as a slime coating through electrostatic attraction, which intensively worsens sulfide flotation. To handle this problem, the sodium of polyaspartic acid (PASP) was employed as the selective depressant for the flotation of pyrite from serpentine in this work. Micro-flotation results showed that the fine serpentine of −10 µm could intensively hinder pyrite flotation, with a maximum decrease of about 75.8% in pyrite recovery at pH 9. However, at this pH, pyrite recovery remarkably increased from 20.17% to 92.68% when 15 mg/L PASP was introduced. Zeta potential results depicted that the addition of PASP overcompensated the positive charge on the serpentine surface and rendered it negative, while it had little impact on that of pyrite. Hence, the hetero-coagulation between serpentine and pyrite was broken due to the electrostatic repulsion, which was further confirmed by turbidity results. After that, the adsorption of PAX on the pyrite surface was restored, and the selective flotation of pyrite from serpentine was obtained. XPS analyses revealed that the chelation interaction between the carboxylate groups in PASP and the magnesium cations that remained on the serpentine surface were the main driving forces for the adsorption of PASP on the serpentine surface.

Novel magnetic covalent organic framework for the selective and effective removal of hazardous metal Pb(II) from solution: Synthesis and adsorption characteristics

The removal of lead(II) from wastewater is conducive to reduce the risk of harmful metals to the environment and people. A magnetic organic framework adsorbent (Ni0.6Fe2.4O4-HT-COF) with high selectivity, repeatability and facile solid–liquid separation was devised through the condensation process of hexachlorocyclo-triphosphazene, trithiocyanuric acid and Ni0.6Fe2.4O4. At 298 K and pH = 5.0, the adsorbent showed remarkable Pb(II) adsorption capability. The removal rate reached 95.64 % at 10 min and the maximum adsorption capacity was 411.80 mg/g. The partition coefficient (KQ) of Pb(II) among the seven coexisting ions was 34079 mL/g and the adsorption efficiency was 97.15 %, indicating that the adsorbent can accurately capture Pb(II) from wastewater containing multiple ions. The PSO kinetic and the Langmuir isotherm models agreed with Pb(II) adsorption on Ni0.6Fe2.4O4-HT-COF, demonstrating that Pb(II) was removed by monolayer chemisorption. The adsorption was a spontaneous exothermic process using thermodynamic analysis. In addition, the adsorbent was able to maintain 91.77 % adsorption efficiency for Pb(II) after four adsorption–desorption cycles. Zeta potential and XPS analysis revealed that Ni0.6Fe2.4O4-HT-COF removed Pb(II) by electrostatic attraction and chelation. Density functional theory (DFT) was utilized to simulate the adsorption process, and the effects of different types of atoms on adsorption were discussed. The results demonstrate that the chelation and electrostatic interaction between Ni0.6Fe2.4O4-HT-COF and lead(II) ions were involved in the selective adsorption. The novel magnetic COF has a lot of potential for removing heavy metal Pb(II).

Computational and Experimental Investigation of the Selective Adsorption of Indium/Iron Ions by the Epigallocatechin Gallate Monomer.

Selective recovery of indium has been widely studied to improve the resource efficiency of critical metals. However, the interaction and selective adsorption mechanism of indium/iron ions with tannin-based adsorbents is still unclear and hinders further optimization of their selective adsorption performance. In this study, the epigallocatechin gallate (EGCG) monomer, which is the key functional unit of persimmon tannin, was chosen to explore the ability and mechanism of selective separation/extraction of indium from indium-iron mixture solutions. The density functional theory calculation results indicated that the deprotonated EGCG was easier to combine with indium/iron cations than those of un-deprotonated EGCG. Moreover, the interaction of the EGCG-Fe(III) complex was dominated by chelation and electrostatic interaction, while that of the EGCG-In(III) complex was controlled by electrostatic interactions and aromatic ring stacking effects. Furthermore, the calculation of binding energy verified that EGCG exhibited a stronger affinity for Fe(III) than that for In(III) and preferentially adsorbed iron ions in acidic or neutral solutions. Further experimental results were consistent with the theoretical study, which showed that the Freundlich equilibrium isotherm fit the In(III) and Fe(III) adsorption behavior very well, and the Fe(III) adsorption processes followed a pseudo-second-order model. Thermodynamics data revealed that the adsorption of In(III) and Fe(III) onto EGCG was feasible, spontaneous, and endothermic. The adsorption rate of the EGCG monomer for Fe(III) in neutral solution (1:1 mixed solution, pH = 3.0) was 45.7%, 4.3 times that of In(III) (10.7%). This study provides an in-depth understanding of the relationship between the structure of EGCG and the selective adsorption capacity at the molecular level and provides theoretical guidance for further optimization of the selective adsorption performance of structurally similar tannin-based adsorbents.

Strengthened versatile organic adsorption films of double antibiotic scaffold-included branched compounds on copper surface for highly efficient antiagal, antibacterial and anticorrosive effects

• Target double norfloxacin or ciprofloxacin scaffolds included compounds were synthesized. • The formed organic adsorption layers of the target compounds on copper surface were demonstrated. • The organic adsorption layers displayed super resistance effect on Chlorella and E. coli as well as corrosion. New double antibotic skeleton-based branched target molecules were synthesized and purified under mild conditions, which could be efficiently adsorbed on copper surface by the strong chemistry chelation interaction between the target molecules and metal atoms. It was firstly demonstrated that the organic adsorption films of the target compounds on copper surface displayed super inhibition effects on biofouling as well as corrosion in aqueous media.

Thermal response of CuO/polydopamine nanospheres under NIR laser irradiation

Composite nanostructures with enhanced photothermal conversion (PTC) play an important role in near infrared (NIR) light-mediated photothermal therapy (PTT) and cancer theranostic applications. However, the diversity and multiplicity of assembled components in a single nanostructured particle produce complexity, so the integrated effects of such a formulation product are difficult to predict and control. In this study, novel composite nanospheres were synthesized by combining only two components with inherent multifunctional properties, i.e., small copper oxide nanoparticles (CuO-NPs) and polydopamine (PDA). The CuO-NPs embedded PDA nanospheres (CuO/PDA-NS) were subjected to material analysis demonstrating strong chelating interactions between the catechol groups of PDA and CuO-NPs surface. This behavior apparently suppresses the release of the embedded CuO-NPs in water, consequently giving the composite nanospheres remarkable stability in aqueous solution (19% copper release in 78 days, pH 7.2). The heating efficiency of CuO/PDA-NS versus water was found to be 66%, which is significantly higher than the heating efficiency of CuO-NPs and PDA-NS (i.e., 50% and 55%, respectively). Additionally, CuO/PDA-NS showed a good thermal stability after consecutive NIR irradiations. Taken together, these results confirm that CuO/PDA-NS exhibit an enhanced thermal effect under NIR laser irradiation, which is expected to lead to great advantages in the treatment of cancer diseases with a minimally invasive approach.

Synthesis of Superhydrophobic/Superoleophilic stearic acid and Polymer-modified magnetic polyurethane for Oil-Water Separation: Effect of polymeric nature

The superhydrophobic/superoleophilic materials based on polyurethane foams have been layered with three different polymers and extensive modification with iron/magnetic nanocomposite. The general desires are to study the effect of the polymer layer and to eliminate the oil contaminant from the oil–water system which is crucial due to the development of environmental technologies. These materials were generated by facile dip-coating two-step method on the polyurethane foams (PUF) surface. PUF was directly layered with polydopamine/polypyrrole/polyaniline (PDA/PPy/PANI) and incorporated with Fe-SA (stearic acid) nanocomposites by ultrasonication and refluxing. In addition, characterization by FTIR, SEM/EDX, XRD, and TGA presented that the polymer layer and Fe-SA nanocomposites successfully covered the PUF surface caused by the chelating interaction between the carboxylates and active sites on iron particles due to intermolecular hydrogen bond interaction. Interestingly, the water contact angle (WCA) measurement of the nanocomposites displayed that the contact angle significantly improved up to 164°. After 20 cycles of oil absorption capacity, the WCA steadily remained up to 153° indicating powerful superhydrophobic properties of the materials. Furthermore, the oil absorption capacity of the materials was evaluated using typical oil–water separation methods such as reusability, separation efficiency, and oil permeate flux. The results exhibited that the modified PUFs have enhanced the absorption capacity up to 44 times the foam weight, 99 % separation efficiency, and about 8000 L.m−2.h−1 oil flux. For oil removal, the dyed oil phase was rapidly absorbed within 2 s confirming the highly used products for a wide area of oil–water separation. PDA-coated PUF nanocomposites obtained the most outstanding results due to their remarkable interfacial adhesion properties which provide larger active functional groups for hydrogen bonding interaction on PUF surface and Fe-SA nanocomposites.

Electrospinning preparation of nylon-6@UiO-66-NH2 fiber membrane for selective adsorption enhanced photocatalysis reduction of Cr(VI) in water

The environmental problem caused by Cr(VI) need to be solved urgently. Fiber membranes have been widely utilized for pollutants removal owing to their high surface area and easy recovery property. Inspiredly, a nylon-6@UiO-66-NH2 fiber membrane was prepared using electrospinning and subsequent in-situ crystal growth process. In the process, UiO-66-NH2 crystals grew on the nylon-6 fiber uniformly and continuously through in-situ solvothermal treatment. The unique structure exhibits selective adsorption enhanced photocatalysis performance towards Cr(VI) reduction under visible light irradiation. The nylon-6 fiber resists aggregation of UiO-66-NH2 crystals and provides nitrogen-containing functional groups for the composite membrane, which shows selectively high adsorption capacity for Cr(VI) (202.79 mg·g−1) based on electrostatic and chelation interactions. Such excellent adsorption behavior is beneficial for photocatalytic reduction of toxic Cr(VI) into Cr(III). More importantly, the photocatalytic capacity of nylon-6@UiO-66-NH2 fiber membrane for Cr(VI) is 27.1 mg·g−1 of UiO-66-NH2, almost twice that of pure UiO-66-NH2 powder (15.5 mg·g−1), exhibiting selective adsorption enhanced photocatalysis performance. This work not only offers a novel strategy for in-situ fabrication of polymer@MOF composite membrane but also gives insight into adsorption enhanced photocatalysis Cr(VI) reduction behavior.

Label-free dynamic light scattering assay for C-reactive protein detection using magnetic nanoparticles

In this work, we present a simple method for label-free detection of C-reactive protein (CRP) in diluted saliva samples without the use of specific molecules against CRP. We use the dynamic light scattering (DLS) technique and silica-coated Fe3O4 nanoparticles (∼50 nm in diameter) functionalized with amino carboxylate moieties (Fe3O4@SiO2/COOH) as probes. After contact with the sample, the particles could be easily separated with a handy magnet and redispersed for DLS analysis simply by vortex shaking. The variation of the hydrodynamic diameter of the nanoparticles (Z-average size) could be correlated with the concentration of CRP up to concentrations of 10 mg L−1. The detection limit (LOD) in diluted saliva samples that were spiked with CRP was 0.205 mg L−1, which is below salivary levels of CRP detected in unhealthy individuals. The coefficient of variation was found to be less than 1.5% in the entire detection range. The variation of Z-average size of non-functionalized silica coated nanoparticles (Fe3O4@SiO2) also correlated well with CRP concentration. Nevertheless, the Fe3O4@SiO2/COOH nanoparticles were less susceptible to interference from other biomolecules present in saliva and adsorbed more CRP, indicating higher selectivity toward CRP than nonfunctionalized nanoparticles. This higher affinity was attributed to the chelating interaction between the aminocarboxylate groups of the organosilane N-[3-(trimethoxysilyl)propyl]ethylenediaminetriacetic acid trisodium salt (EDTA-TMS) grafted onto the surface of the Fe3O4@SiO2/COOH nanoparticles and the Ca2+ ions of CRP. LC-MS/MS analyses allowed identification of the proteins adsorbed on the nanoparticles and confirmation of the presence of CRP, which is involved in several biological processes, including immune response, response to stress and transport.

An ultrasensitive sandwich-type electrochemical aptasensor using silver nanoparticle/titanium carbide nanocomposites for the determination of Staphylococcus aureus in milk.

A novel sandwich-type electrochemical aptasensor for the detection ofStaphylococcus aureus (S. aureus) was developed. S. aureus aptamers were self-assembled onto the surface of a glassy carbon electrode (GCE) modified with nanocomposites comprising titanium carbide embedded with silver nanoparticles (AgNPs@Ti3C2) through hydrogen bonds and the chelation interaction between phosphate groups and Ti ions. In addition, the self-assembled aptamers were immobilized on CuO/graphene (GR) nanocomposites via π-π stacking interactions to serve as a signal probe. In the presence of the target S. aureus, the sandwich-type recognition system reacted on the surface of GCE, and the CuO/GR nanocomposites catalyzed the hydrogen peroxide + hydroquinone reaction producing a strong current response. Under the optimal experimental conditions, the current response of the aptasensor was linearly correlated with the concentration of S. aureus (52-5.2 × 107CFUmL-1) with a low detection limit of 1CFUmL-1. The aptasensor displayed good repeatability and excellent selectivity for S. aureus detection. Moreover, this aptasensor was applied to the detection of S. aureus in cow, sheep, and goat milk samples, affording recoveries ranging from 92.64 to 109.58%. This research provides a new platform for the detection of pathogenic bacteria and other toxic and harmful substances in food.

Selective adsorption and mechanism of Au (III) onto thiourea functionalized cuprous oxide

Thiourea-modified Cu2O (Cu2O-TU) was prepared by a facile route and used for the selective recovery of gold in acidic solution. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis elucidated that Au (III) ions were adsorbed onto the surface of Cu2O-TU via the electrostatic attraction of surface protonated amines groups (-NH3+) with AuCl4- and the chelating interaction of pyrrole-type nitrogen as well as CS groups in the pH range of 1.0 – 5.0. Subsequently, partial adsorption of Au (III) was reduced to Au (I) and Au (0), while pyridine-type nitrogen was oxidized to -NO, which accelerated the adsorption rate of Au (III). The adsorption equilibrium time was about 2 min and the adsorption capacity was 79.7 mg·g−1 at a pH value of 2.0 in 40 mg·L−1 Au (III) solution. The fitted result of gold adsorption by the Langmuir model was 1529.4 mg·g−1 at 318 K. The experimental data conformed to the pseudo-second-order model, indicating that the adsorption process was chemisorption. After 5 cycles, the capability of adsorption only decreased by 7.43%, which provided a great possibility for its application in solutions. Besides, Cu2O-TU showed specific and selective adsorption ability for Au (III) in the outdoor environment.

A β-ray irradiation resistant MOF-based trap for efficient capture of Th(IV) ion

Efficient capture of radionuclides from aqueous solution is highly essential for environment safety and resource recycling, but still faces large challenge. In this study, a stable aluminum-based metal–organic framework (MOF-303) with high-density ion traps was used to selectively capture thorium (Th) ion from aqueous solution. The features of aluminum center endow this material with excellent resistance from β-ray irradiation even with a high dose of 1000 kGy. Further, due to the special chelation interaction from the ion trap, MOF-303 exhibits a large adsorption capacity for Th(IV) ion (461.7 mg g−1) and excellent separation coefficients up to 97.6, 97.3 and 81.3 for Th(IV)/Pr(III), Th(IV)/Eu(III) and Th(IV)/Nd(III) respectively. The adsorption equilibrium was reached at ∼ 420 min. Besides, the regeneration of MOF-303 as well as the elution of Th(IV) ion can be achieved via an acid-wash process. Experimental and theoretical calculation results indicate Th(IV) ion can be tightly anchored in the ion trap surrounded by six active atoms, via the chemical bonding mode.

The Role of Antioxidant Structure in Mitigating Oxidation in Ti3C2Tx and Ti2CTx MXenes

AbstractThe oxidation of 2D MXenes jeopardizes their shelf life, both in colloidal dispersions and in functional devices. Certain compounds have been shown to effectively mitigate oxidation of MXenes (such as sodium L‐ascorbate, ascorbic acid, and polyanions), but the nature of interaction between these antioxidants and MXene remains unknown, which impedes the future selection and design of improved protection. This work systematically examines the interactions between three classes of organic antioxidant candidates, α‐hydroxy acids, polycarboxylic acids, and phenols with Tin+1CnTx MXenes, specifically Ti3C2Tx and Ti2CTx. Interestingly, while some antioxidants provide no protection for the MXenes, and some antioxidants even accelerate their degradation, three antioxidants (e.g., citric acid, tartaric acid, and oxalic acid) protect the MXene nanosheets exceptionally well, showing minimum MXene degradation after the 14‐day storage period. Analysis of the antioxidants’ molecular structure and efficacy suggests that chelation interactions with the transition metal atoms of the nanosheets play a key role in effective protection of MXenes from oxidation.

Reactive Inhibition Strategy for Triple‐cation Mixed‐halide Perovskite Ink with Prolonged Shelf‐life

AbstractSolution processing of perovskite solar cells (PSCs) is highly promising for the high‐throughput production of cost‐effective devices. Although PSCs have achieved great advances in power conversion efficiency, challenges still remain in the reproducibility of high‐quality perovskite thin film with simultaneously improved precursor solution stability. Here, a reactive inhibition strategy by introducing diethyl (hydroxymethyl) phosphonate (DHP) in perovskite precursor solution is successfully employed to improve the stability of precursor solution and the performance of corresponding device. DHP inhibits the reactivity of the iodide and formamidinium ions through multiple chemical bonds, ensuring the stability of the precursor solution. In addition, due to chelation interaction of Pb2+ with the oxygen of PO in DHP, the DHP in the perovskite film improves the film quality with desired stoichiometry by reducing the defects and the content of lead iodide. The DHP‐doped precursor solution and corresponding devices show excellent performance reproducibility and super stability under ambient conditions for more than 50 days, which illustrates the commercial feasibility for scalable fabrication.

Pharmacophore-Oriented Discovery of Novel 1,2,3-Benzotriazine-4-one Derivatives as Potent 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is a functional protein existing in almost all aerobic organisms. In the field of agricultural chemicals, HPPD is acknowledged to be one of the crucial targets for herbicides at present due to its unique bio-function in plants. In the Auto Core Fragment in silico Screening (ACFIS) web server, a potential HPPD inhibitor featuring 1,2,3-benzotriazine-4-one was screened out via a pharmacophore-linked fragment virtual screening (PFVS) method. Molecular simulation studies drove the process of "hit-to-lead" optimization, and a family of 1,2,3-benzotriazine-4-one derivatives was synthesized. Consequently, 6-(2-hydroxy-6-oxocyclohex-1-ene-1-carbonyl)-5-methyl-3-(2-methylbenzyl)benzo[d][1,2,3]triazin-4(3H)-one (15bu) was identified to be the best HPPD inhibitor (IC50 = 36 nM) among the 1,2,3-benzotriazine-4-one derivatives, which had over 8-fold improvement of enzyme inhibition compared with the positive control mesotrione (IC50 = 289 nM). Crystallography information for the AtHPPD-15bu complex revealed several important interactions of the ligand bound upon the target protein, i.e., the bidentate chelating interaction of the triketone motif with the metal ion of AtHPPD, a tight π-π stacking interaction consisting of the1,2,3-benzotriazine-4-one moiety and two benzene rings of Phe-424 and Phe-381, and the polydirectional hydrophobic contacts consisting of the ortho-CH3-benzyl group of the core scaffold and some hydrophobic residues. Furthermore, compound 15bu displayed 100% inhibition against the five species of target weeds at the tested dosage, which was comparable to the weed control of mesotrione. Collectively, the fused 1,2,3-benzotriazine-4-one-triketone hybrid is a promising chemical tool for the development of more potent HPPD inhibitors and provides a valuable lead compound 15bu for herbicide innovation.

Excellent performance separation of trypsin by novel ternary magnetic composite adsorbent based on betaine-urea- glycerol natural deep eutectic solvent modified MnFe2O4-MWCNTs

The effective trypsin purification methods should be established since trypsin plays a crucial role in biosome. In this work, a novel ternary magnetic composite adsorbent (MnFe2O4-MWCNTs@B–U-G) with the features of strong specific selectivity, good adsorption effect, simple and efficient separation process, no secondary pollution brought in was prepared by integrating the superior physicochemical properties of ternary based natural deep eutectic solvent, multi-walled carbon nanotubes and MnFe2O4. The property, composition and microtopography structure of MnFe2O4-MWCNTs@B–U-G were characterized in detail. Combined with magnetic solid-phase extraction, MnFe2O4-MWCNTs@B–U-G was utilized to adsorb trypsin. Response surface methodology experiment was prepared under Box-Behnken design to optimize the adsorption conditions and the results showed that the practical maximum adsorption capacity for trypsin was 1020.1 mg g−1. Besides, the adsorption isotherms, adsorption kinetics, regeneration studies and method validation studies were investigated systematically to evaluate the established adsorption separation system. Mechanism exploration proved that electrostatic interaction, hydrogen bonding interaction and chelation interaction were the dominant forces for the high-performance adsorption of trypsin. The activity of trypsin after elution had been analyzed by UV–vis spectrophotometer and CD spectrometer with three methods, which illustrated that the enzyme activity, conformation and secondary structure of trypsin did not change significantly during the adsorption-desorption process. In addition, the proposed method was successful and practical applicability to isolation trypsin from crude bovine pancreas. As a result, due to the superiority of the MnFe2O4-MWCNTs@B–U-G, the proposed method not only exhibites high-performance adsorption of trypsin, but also provides a green and sustainable potential value in the adsorption of biomacromolecule.

Construction of sodium alginate/konjac glucomannan/chitosan oligosaccharide/Zeolite P hydrogel microspheres loaded with potassium diformate for sustained intestinal bacterial inhibition

Owing to their non-toxicity and non-resistance to bacteria, potassium diformate (KDF) bacterial inhibitors may act as antibacterials in the intestinal tract and are good alternatives to antibiotics; however, KDF has low intestinal utilization rate when used directly. We prepared pH-sensitive sodium alginate (ALG)/konjac glucomannan (KGM)/chitosan oligosaccharide (COS)/Zeolite P hydrogel microspheres for the slow release of KDF using a complex coalescence method to ensure better bacterial inhibition and balance of the gut flora in the intestine. We found that the hydrogen bonding interaction between ALG and KGM, chelating interaction between ALG and Ca2+, and electrostatic interaction of COS together build a three-dimensional porous network structure. Notably, Zeolite P contributes to the formation of a dense three-dimensional network structure to avoid premature release of KDF in the stomach, improve the stability of KDF and prolong its release in the intestine. In vitro bacterial inhibition experiments showed that the maximum antibacterial rates of the hydrogel microspheres were 92 ± 3%, 86 ± 4%, and 88 ± 4% against Escherichia coli, Staphylococcus aureus, and Bacillus subtilis, respectively, indicating that they can effectively inhibit bacterial growth and balance the bacterial flora. In addition, hydrogel antibacterial microspheres are biodegradable and non-cytotoxic. Thus, ALG/KGM/COS/Zeolite P hydrogel microspheres may be used for colon-targeted delivery of drugs.

Polymer-chelation approach to high-performance Fe-Nx-C catalyst towards oxygen reduction reaction

Pyrolyzed Fe-Nx-C with atomically dispersed Fe-Nx sites are hailed as the most promising alternative to the noble metal Pt-based catalysts towards oxygen reduction reaction (ORR). However, the conventional micropore-confinement synthetic approach usually causes the insufficient utilization of active sites and mass transport resistance as the sites are located inside the micropore. We herein report a polymer-chelation strategy to directly disperse the Fe-Nx active sites onto the carbon surface. The N-rich monomer was in-situ polymerized on the carbon support and then chelated with Fe. The strong Fe-N chelating interaction is crucial to suppress Fe aggregation when undergoing the high-temperature pyrolysis. Due to the enriched surface sites, hierarchically porous structure and excellent conductivity of carbon support, the optimal catalyst (denoted as Fe-Nx-C@C-900) exhibits impressive ORR activity of onset and half-wave potential of 1.02 and 0.87 V, respectively, superior to the Pt/C benchmark.

Effects of chemical inhibitors on the scaling behaviors of calcite and the associated surface interaction mechanisms

HypothesisIt is hypothesized that the performance of a chemical inhibitor to interfere with the precipitation and scaling of calcite (calcium carbonate, CaCO3) is achieved through its chelating interaction with calcium ions. The effectiveness of a chemical inhibitor in removing existing scales from the mineral surfaces is proposed to rely on its ability to modify the calcite crystal structures. ExperimentsBulk scaling tests and dynamic adsorption experiments using a quartz crystal microbalance with dissipation monitoring were conducted to systematically investigate the scaling behaviours (i.e., buildup and breakup processes) of calcite crystals, in the absence and presence of chemical inhibitors, that include polyacrylic acid, sodium hexametaphosphate, 2-phosphonobutane-1,2,4-tricarboxylic acid, and diethylenetriamine penta(methylene phosphonic acid). Scanning electron microscope imaging and thermodynamic characterization using isothermal titration calorimetry were further applied to reveal the surface interactions that contributed to the differences among the effects of the four additives. FindingsThe results indicate that sodium hexametaphosphate is most efficient in alleviating the amount of CaCO3 deposited by reducing the concentration of free Ca2+, and diethylenetriamine penta(methylene phosphonic acid) shows an outstanding ability to clean the mineral surface by destroying the ordered crystal layers of the scales so that they can be washed away with water. This work provides useful insights into the fundamental interactions of chemical inhibitors and calcite, with implications for the development of effective chemical solutions for anti-scaling and descaling applications.