Electrostatic Adsorption Interaction Research Articles

Straightforward synthesis of novel chitosan bio-based flame retardants and their application to epoxy resin flame retardancy

Epoxy resin (EP) is widely used in various industries. However, its inherent flammability characteristics limit its application, so there is an urgent need to develop bio-based flame retardants for efficient flame retardant EP. Chitosan (CS) is one of the most commonly used bio-based raw materials, but most chitosan-based flame retardants are synthesised using large amounts of organic solvents, with low yields and not in line with the theme of green and sustainable development. In this paper, we report a facile, eco-friendly, and solvent-free approach to chitosan-based flame retardants. A novel full biomass flame retardant, chitosan-based ammonium phytate (PUCS), was synthesised without the organic solvent by using chitosan and phytanic acid as raw materials and the electrostatic adsorption interaction between them and urea, and it was used as a flame retardant additive for EP. The results showed that the EP samples with 7.5 wt% PUCS added increased the limiting oxygen index from 22.2 % to 32.2 % and the vertical burning rating from no rating to V-0. Moreover, the cone calorimeter test results showed that the EP/PUCS composites with adding PUCS showed a significant decrease in the peak heat release rate, and it has excellent flame retardancy. It is worth mentioning that the mechanical property test results showed that the mechanical properties of EP/PUCS composites with adding PUCS could still reach the scope of the needs for engineering applications. This work provides an economical, convenient, and eco-friendly feasible route for bio-based flame retardants.

Development of a rhodamine-based fluorescent probe for ATP detection for potential applications in meat freshness assessment

Adenosine triphosphate (ATP) plays a vital role in physiological processes and is an essential indicator of microbial content in food. Herein, a new sensitive, rapid and water-soluble probe for ATP detection was developed. Rhodamine B and pentaethylenehexamine were employed to design and synthesise the probe rhodamine-pentaethylenehexamine (RP) for selective ATP detection. The synthesised probe RP was characterized using Fourier transform infrared, NMR and dynamic light scattering size distributions. Upon the addition of ATP, the probe exhibited a distinct change in fluorescence intensity, with fluorescence emission at 580 nm. A linear relationship was observed between fluorescence intensity and ATP concentrations at 0–50 μmol/L, with a limit of detection of 10.97 × 10−9 mol/L. The results of the zeta potential and molecular dynamics simulation demonstrated that the detection mechanism of the probe RP is associated with the electrostatic adsorption interaction between the multi-positively charged sites of RP and the negatively charged triphosphate structure of ATP. Our study provides new insights into improving charge site identification in small molecule detection. Furthermore, the successful detection of ATP on meat surfaces indicates that RP has the potential to assess meat freshness.

Tetraphenylethylene fluorophore based AIE-fluorescent probe for detection of ATP in mitochondria

A tetraphenylethylene fluorophore based on D-π-A structure was employed to design and synthesize the TPE-Py-FP probe for selective detection of ATP. TPE-Py-FP had the advantages of large Stokes shift, great hydrophilicity and good selectivity. Especially, the pyridine portion and quaternary ammonium structure of TPE-Py-FP had positively charged sites, which could be used as recognition groups to interact with the negatively charged triphosphate structure of ATP. Then the fluorescence emission of TPE-Py-FP at 580 nm showed a “turn-on” response after adding ATP. Moreover, this probe could rapidly respond to ATP over a wide linear range of 10–120 μM and the limit of detection (LOD) was 2.76 μM. The zeta potential and dynamic light scattering experiments revealed that the detection mechanism was mainly the electrostatic adsorption interaction between the dual positively charged sites of TPE-Py-FP and the negatively charged triphosphate structure of ATP. Additionally, TPE-Py-FP could localize in mitochondria specifically with a Pearson's coefficient of 0.81, and show great utility in monitoring the fluctuation of mitochondrial ATP level.

Remediation of heavy-metal-contaminated soil with two organic acids: Washing efficiency, recovery performance, and benefit analysis

There remains a need to develop efficient and recoverable washing reagents to repair heavy metal-contaminated soil. However, the past study of recovery only considered conventional chelating agents, hindering the sustainable development of new reagents. In this study, two new-reagents, organic phosphonic acid (DTPMPA) and polycarboxylic acid (AA/AMPS/HPA), simultaneously investigated their ability to remove heavy metal and recover by electrochemical to improve reagent sustainability. Results indicated that the metal removals were influenced by the washing solution concentrations, pH, and contact time. The maximum removal by DTPMPA was 72% Cd and 33% Zn, were higher than those of AA/AMPS/HPA (concentration, 5%; pH, 3.0; and contact time, 120 min). The strong chelation of the phosphonic acid group of DTPMPA binds more metal ions. Characterization results demonstrated that both reagents were successfully recovered using electrochemical methods. While AA/AMPS/HPA had a better recovery performance because of electrostatic adsorption interactions with the metal ions, the rewashing ability of Cd and Zn was 88% and 64% of the fresh solution. Moreover, in benefit analysis, AA/AMPS/HPA showed better circular economy and long-term sustainability properties. Therefore, AA/AMPS/HPA is a feasible remediation reagents of the heavy-metal-contaminated soil with both efficiency and sustainability. The development of reagent takes into account efficiency and reuseable simultaneously, showing great economic benefits.

Electrostatic interaction and surface S vacancies synergistically enhanced the photocatalytic degradation of ceftriaxone sodium

ZnIn2S4 ultrathin 2D nanosheets with a positive surface charge are synthesized by a hydrothermal method and different contents of surface S vacancies are induced via heat treatment of as-prepared ZnIn2S4 (ZIS). As the S vacancies contents increased, the photocatalytic degradation efficiency of ceftriaxone (CTRX) sodium is promoted. Especially, ZIS-300 shows the best degradation efficiency (88.8%) for an initial CTRX concentration of 10 mg L−1 in 2 h. It is found that S vacancies cause the electron density of surface metal atoms (Zn, In) to be decreased, which makes the effective adsorption and activation of ceftriaxone anions through electrostatic adsorption interactions. Meanwhile, S vacancies also serve as active centers to promote the absorption of O2 and gather electrons to form •O2− species. The photogenerated holes quickly transfer to the surface of the catalyst to directly degrade the adsorbed CTRX. Thus, the photocatalytic CTRX degradation efficiency is significantly improved. Finally, a possible mechanism for over defective ZIS is proposed. This work provides a feasible strategy for the efficient degradation of antibiotics from the perspective of electrostatic adsorption and molecule activation.

A Neuron-specific Enolase Electrochemical Immunosensor Based on rGO/Cu8Ni2 Nanocomposite with Enhanced Catalytic Activity

Neuron-specific enolase (NSE) is a reliable biomarker for the diagnosis of small cell lung cancer (SCLC). Effective detection of NSE plays an important role in the clinical diagnosis, treatment, and prediction of disease recurrence of SCLC. Herein, a simple label-free electrochemical immunosensor based on reduced graphene oxide/Cu8Ni2 (rGO/Cu8Ni2) nanocomposite was reported to detect the neuron-specific enolase (NSE). The rGO/Cu8Ni2 nanocomposite was prepared by loading optimized CuNi (8:2) alloy on the reduced graphene oxide through electrostatic-adsorption interactions and in situ simultaneous reductions. As a noble-metal-free alloy, Cu8Ni2 exhibits favorable catalytic activity. Combining the CuNi alloys with graphene can effectively keep off the aggregation of the alloy and further maintain its high catalytic activity. Simultaneously with the huge surface area and conductivity of rGO, rGO/Cu8Ni2 showed increased bound antibodies and enhanced catalytic activity, which makes the fabricated immunosensor exhibit enhanced performance. Under the optimal conditions, the designed electrochemical immunosensor for detecting NSE showed a wide linear range from 500 fg ml−1 to 50 ng ml−1 and the low detection limit was 137 fg ml−1. The proposed immunosensor in this study provides an effective method for the detection of NSE and may be expected to be applied in clinical diagnosis and treatment.

Insight into the KOH/KMnO4 activation mechanism of oxygen-enriched hierarchical porous biochar derived from biomass waste by in-situ pyrolysis for methylene blue enhanced adsorption

A high-performance hierarchical porous carbon enriched in oxygen-containing functional groups was prepared by using pine as the raw material, KOH and KMnO4 as a green activator via cost-effective one-step or two-step in-situ pyrolysis processes. The adsorption performance, kinetics and thermodynamics of activated biochar were evaluated using methylene blue (MB) as a model pollutant. Biochar structure was investigated by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), N2 adsorption/desorption isotherms (BET) and scanning electron microscopy (SEM) to explore its morphological, physical, and chemical properties. A possible adsorption mechanism and pathway were also proposed. The results showed that a two-step process, higher activation (KOH and KMnO4) to biomass ratio led to excellent adsorption performance. AC-KOH-1-1 and AC-KMnO4-1-3 presented the maximum equilibrium adsorption capacities of 637.5 mg/g and 439.5 mg/g, respectively. The adsorption isotherm fit well with the Freundlich isotherm model and pseudo-second-order kinetic model, which exhibited better monolayer adsorption and chemical adsorption control. In addition, the adsorption was dominated by pore diffusion and π-π stacking interactions for KOH activation due to the well-developed pore volume (0.04990 mg/L), pore channel (18.65 nm), aromatized structure (66.03 %) and surface defective structure. However, the adsorption capacity was controlled by hydrogen bonding, electrostatic adsorption interactions, cation exchange and the donor-receptor-effect for AC-KMnO4 due to it having the highest proportion of O- and N-containing functional groups. Therefore, this cost-efficient biochar preparation technology for the efficient removal of organic pollutants has great potential for practical application.

‘Plug and play’ microelectrode assisted with Y-motif-mediated primer-free cyclic signal amplification for sensitive quantitation of DNA methyltransferase activity

DNA methyltransferase (MTase), modulating the level of genomic DNA methylation, harbors both a pharmacological target for clinical therapy and a potential biomarker for genetic disorders and tumorigenesis. Typical homogeneous electrochemical approaches, employing solution phase probes, have been considered simple, efficient, and economical method, yet these architectures usually require electroactive molecules labeling, rely on weak electrostatic adsorption interaction, and possess low sensitivity. For circumventing the above drawbacks, herein, we devise a ‘plug and play’ microelectrode featuring microminiaturization, rapid response time and enhanced mass transport to quantify MTase activity through monitoring the variation of diffusion current of methylene blue (MB) induced by the less-mobile G-quadruplex framework. By coupling the unique signal-transduction approach with Y-motif-mediated primer-free cyclic signal amplification (YPCSA), the miniaturized biosensor possesses low detection limit (down to 2.5 × 10−4 U mL−1), high specificity, good stability and satisfying reusability, and has been successfully applied to the screening of MTase inhibitors, holding great potential in clinical diagnosis and pharmacological research.

Marine sponge spicules-inspired magnesium oxychloride cement with both enhanced water resistance and compressive strength via incorporating acid-activated palygorskite

The high energy consumption, large CO2 emission and mass pollutant release during the preparation process of Ordinary Portland cement (OPC) promote the development of sustainable magnesium oxychloride cement (MOC), which can increase the potash industrial waste utilization and alleviate ecological problems. However, MOC is limited by the poor water resistance, and integrating high water resistance with compressive strength for the MOC still remains a challenge. Herein, inspired by marine sponge spicules, acid-activated palygorskite (APal) was introduced into MOC to construct the inorganic fiber reinforced structure, thus both the water resistance (enhanced from 0.37 to 0.71 in water resistance coefficient) and compressive strength (37.1% increase) were improved. This improvement can be due to the physical filling, surface complexation, electrostatic adsorption interaction and fiber reinforcement of APal, as well as the transformation to gel-like phase 5. Especially, this strategy offers a new and effective approach to enhance the water resistance of MOC that although phase 5 content exhibit a reduction trend in soaked MOC-APal, the composite still present enhanced water resistance. This may be attributed to the sponge spicules-inspired fibrous structure serving as an effective supporting skeleton to provide a certain mechanical strength for soaked MOC-APal.

Cationic and temperature-sensitive liposomes loaded with eugenol for the application to silk

Silk has been widely used in the clothing industry due to their soft and smooth features, good biocompatibility, good heat dissipation, warmth and ultraviolet resistance. The application of fragrance to silk can significantly improve the performance of silk. However, there are two key scientific problems that need to be solved: slowing down the release rate of fragrances and increasing the scent lasting time of silk. In this study, cationic and temperature-sensitive liposomes were designed and prepared to encapsulate eugenol. These fragrance-loaded liposomes significantly slowed down the release rate of the fragrance and controlled the release rate of the fragrance in a thermo-sensitive manner. The liposomes adhered to the silk through electrostatic adsorption interaction. The positive charge on the fragrance-loaded liposomes neutralized much negative charge on silk and thereby increasing the adhesion efficiency.

Research of desulfurization of dibenzothiophene with SO3H-functionalized morpholine heteropolyacid ionic liquid catalyst

In this work, several SO3H-functionalized strong Brønsted acidic morpholine phosphotungstic acid ionic liquid catalyst was synthesized and applied for oxidative removal of dibenzothiophene (DBT) from fuel. Chemical structure of the aforementioned catalyst was successfully characterized by FT-IR, 1H NMR, XRD, and TGA. Meanwhile, the catalytic activity of the synthesized catalyst was also evaluated by investigating the removal of DBT from model fuel. The investigated results reveal that the optimal removal rate of DBT was 99.4 wt%, which was obtained under the optimum experimental conditions ([C3SO3Hnhm]3PW12O40 was chosen as catalyst, the mass ratio of catalyst to model oil was 2 wt%, molar ratio of O/S was 15, reaction time of 105 min and reaction temperature of 50 °C). Moreover, this catalyst could be recycled at least six time without any decrease in catalytic activity. It was also found that the DBT was adsorbed to the cation through an electrostatic adsorption interaction between the morpholine ring (N+ position) and the S atom of DBT and the structure of DBT can be distorted by the acidity of the SO3H group, which makes it more susceptible to oxidization. Combined with the kinetic study, results suggested that oxidation of DBT was attributed to a pseudo-first-order kinetic reaction.

Removal of fluoride from zinc sulfate solution by in situ Fe(III) in a cleaner desulfuration process

The desulfuration of fume gas using ZnO slurry is a cleaner process because the SO2 from exhaust is transformed to a valuable ZnSO4 solution, and the ZnSO4 solution can then be reused in industrial processes. However, the existence of fluoride (F) in the cleaner process severely hinders the reuse of the ZnSO4 solution. In this study, an innovative, targeted and simple technique using in situ Fe(III) in the actual ZnSO4 waste liquid for the removal of F was proposed. The results indicated that in situ Fe(III) exhibited a good performance in the removal of F and an increase of Fe concentration is beneficial to the removal of F. The active component in the removal of F was identified as a type of hydroxylation ferric sulfate, schwertmannite, which formed under the strong acidic condition. The removal mechanism of F was recognized as an ionic-exchange with the OH− groups from coordinated FeOH−1/2 and Fe2OH0 and SO42− groups in schwertmannite as well as electrostatic adsorption interactions. Based on above principle, the concentration of F in the actual ZnSO4 solution was successfully reduced to below 50 mg/L, bringing the ZnSO4 solution up to the recycling standard. This research can be used to guide the effective removal of F from the waste liquid with high acidity, salinity and heavy metals, in the practice.

High efficient and selective removal of Pb2+ through formation of lead molybdate on α-MoO3 porous nanosheets array

2D hand-like structured α-MoO3 porous nanosheets were grown in-situ onto a capillary by a simple hydrothermal route, on which titanium dioxide seed layer was sol-dip-coated in advance. The α-MoO3 porous nanosheets array exhibits an exceptional lead ion uptake capacity up to 1450.0mg·g−1, and can effectively reduce Pb2+ concentration from 20mg·L−1 to a low level of smaller than 3μg·L−1, well below the acceptable limits in drinking water standards (10μg·L−1) and can efficiently remove 99.9% lead ion within a few minutes at room temperature. Furthermore, α-MoO3 porous nanosheets array also has high selectivity toward Pb2+ better than Cu2+, Zn2+, Cr3+ and Cd2+. The mechanism for adsorption was discussed according to the results of Zeta potential, IR, XPS and XRD analyses. The excellent removal performance of the array to Pb2+ is resulted from the electrostatic adsorption interaction and the formation of new species lead molybdate.

Electrolyte effect on gelation behavior of oppositely charged nanocrystalline cellulose and polyelectrolyte

The electrolyte (NaCl) influences on the sol–gel transition of the complex solution composed of oppositely charged nanocrystalline cellulose (NCC) and polyelectrolyte (quaternized hydroxyethylcellulose ethoxylate, QHEC) were investigated by the rheological means in the present paper. Winter and Chambon theory was applicable to describe the sol–gel transition, and the critical gel points have been successfully determined. When increasing the NaCl concentration, more NCC were needed to form a critical gel due to the screening of the electrostatic interaction, and the larger loss tangent and relaxation exponent (n) values at the gel point demonstrated a less elastic nature of the complex solution with more NaCl. The results indicated the gel network was composed of entanglements and association of QHEC (as polymer network), as well as the electrostatic adsorption interaction between QHEC chains and NCC rods (as cross-linking). With the addition of NaCl, the screening effect led to the enhancement of the entanglements and weakening of the electrostatic adsorption, however, the gel strength decreased with increasing the NaCl amount, suggesting the electrostatic adsorption interaction played a more dominant role than the entanglements when the gel was formed. Moreover, the exponents of the scaling law η0∝ɛ−γ and Ge∝ɛz of the QHEC/NCC/NaCl solution revealed that the scaling law n=z/(z+γ) between n, γ, and z was only feasible at the highest NaCl concentration, as a result of that the intermolecular electrostatic interaction was completely screened, indicating the scaling law was only feasible when intermolecular interaction was small enough to be neglected.

Investigation of the scaling law on gelation of oppositely charged nanocrystalline cellulose and polyelectrolyte

The sol–gel transition in the mixture system of oppositely charged polyelectrolyte (quaternized hydroxyethylcellulose ethoxylate, QHEC) and nanocrystalline cellulose (NCC) induced by electrostatic adsorption interaction was investigated by rheological means. Winter and Chambon theory was validated to be applicable for the critical gel point determination, and critical gel point have been successfully determined. With QHEC concentration increasing, more NCC were needed to form a critical gel, and smaller loss tangent and relaxation exponent (n) values at the gel point were observed, indicating the elastic nature of mixture was enhanced with QHEC increase. Gel strength behaved as a function of both QHEC and NCC concentrations, suggesting the gel network at the critical point was composed of entanglements and association of QHEC macromolecular chains, as well as the electrostatic adsorption interaction between QHEC chains and NCC rods. The calculated number of NCC rods per junction decreased from 0.30 to 0.01 when the QHEC concentration increased from 1.0wt% to 3.0wt%, indicating the electrostatic adsorption interaction between the NCC rods and QHEC chains was less significant to gel formation at higher QHEC concentrations. Therefore, the exponents of scaling law η0∝ϵ–γ and Ge∝ϵ z for the QHEC/NCC mixtures revealed that the scaling law n=z/(z+γ) between n, γ, and z was only feasible at highest QHEC concentration, since the intermolecular interaction (electrostatic adsorption interaction in this article) was so weak that can be neglected and the critical gel network was dominated by QHEC chain entanglements and association.

Role of electrostatic interactions in particle adsorption

The role of the electrostatic double-layer interactions in adsorption of colloid particles at solid/liquid interface was reviewed. The phenomenological formulation of the governing PB equation was presented with the expressions for the pressure tensor enabling one to calculate forces, torques and interaction energies between particles in electrolyte solutions. Then, the limiting analytical results for an isolated double-layer (both spherical and planar) were discussed in relation to the effective surface potential concept. The range of validity of the approximate expression connecting the surface potential and the effective surface potential with surface charge for various electrolytes was estimated. The results for double-layer systems were next presented including the case of two planar double-layers and two dissimilar spherical particles. Limiting solutions for short and long distances as well as for low potentials (linear HHF model) were discussed. The approximate models for calculating interactions of spheres, i.e., the extended Derjaguin summation method and the linear superposition approach (LSA) were also introduced. The results stemming from these models were compared with the exact numerical solution obtained in bispherical coordinate system. Possibilities of describing interactions of nonspherical particles (e.g., spheroids) in terms of the Derjaguin and the equivalent sphere methods were pointed out. In further part of the review the role of these electrostatic interactions in adsorption of colloid particles was discussed. Theoretical predictions were presented enabling a quantitative determination of both the initial adsorption flux for low surface coverages and the surface blocking effects for larger surface coverages. Possibility of bilayer adsorption for dilute electrolytes was mentioned. The theoretical results concerning both the adsorption kinetics and structure formation were then confronted with experimental evidences obtained in the well-defined systems, e.g., the impinging-jet cells and the packed-bed columns of monodisperse spherical particles. The experiments proved that the initial adsorption flux was considerably increased in dilute electrolytes whereas the monolayer coverages were considerably decreased due to lateral interactions among particles. It was then concluded that the good agreement between experimental and theoretical data confirmed the thesis of an essential role of the electrostatic interactions in adsorption phenomena of colloid particles.