Surface Electron Donor Research Articles

Shape controlled synthesis and crystal facet dependent gas sensitivity of tungsten oxide

Gas sensors can achieve remarkable functionality through the optimization of particle size, shapes, crystal facets, and oxygen defects, resulting in unsaturated coordination atoms, high charge densities, and enhanced bond energies. In this study, WO2.72 nanourchins, WO3-x nanowires, and WO3 nanorods/nanocube with (010), (001), (200), and (002) dominant crystal facets were synthesized and used as gas sensing materials. It was found that WO2.72 nanourchins exhibit an excellent response of Ra/Rg=21 to 100 ppm acetone with good selectivity among other sensors as-fabricated. First-principle calculations of Density Functional Theory were performed on acetone's adsorption on different crystal planes of tungsten oxide. The results verify spontaneous and fast adsorption on the (010) crystal plane than on the (001) and (200) planes. Further characterizations indicate that WO2.72 nanourchins with (010) crystal facets contain more reactive sites with high surface energy, facilitating charge separation, increasing charge carrier mobility, and enabling the redox reactions to occur independently at different rates. Moreover, their richer electron-donor surface oxygen defects, smaller feature sizes, and higher surface area (SBET) with hierarchical porous structures, all contribute to the enhanced acetone sensing. Our work provides a strategy for improved acetone sensing based on optimizing the particle shape with different crystal facets and oxygen vacancy density. We further expect our strategy to be applicable in designing other sensor materials with efficient charge separation and fast surface redox reactions to detect toxic gases.

Surface engineering and concentration-dependent emission activated flexible tunable fluorescence from lignin-based N-doped carbon dots

Achieving the flexible and tunable fluorescence of lignin-based N-doped carbon dots (LCDs) remains a win–win yet challenging strategy. In this study, combining the surface engineering and concentration regulation strategy enabled the flexible adjustment of LCDs fluorescence emission from blue to yellow regions (345 to 560 nm). The surface electron-donor –OH groups not only enhanced the photoluminescence quantum yield (PLQY) to 14.75 % but activated the spectral shift of reduced LCDs (RLCDs). These arose from the reinforced π-electron conjugation and generated new –OH-related extrinsic defects with elevating concentration. Conversely, the electron-withdrawing CO groups participated in the blue-to-green fluorescence modulation. Still, they drastically reduced the PLQY of oxidized LCDs (OLCDs) to 2.13 %, due to the larger particle size and more non-radiative transfer induced by CO groups. Based on these, CDs/PVA films and printed fluorescent patterns with multicolor fluorescence were realized for anti-counterfeiting, and the RLCDs@Al2O3 hybrid facilitated the precise fluorescence fingerprint tracking and recognition. This study provided a facile strategy for enriching and developing novel LCDs with flexible fluorescence for their advanced applications.

Kinetics of ferrihydrite reduction in a biofilm system

Microorganisms can exist in both suspended and attached forms in natural and engineered systems. While extensive research has been performed to investigate the bioreduction kinetics of iron oxides by suspended microorganisms, the kinetics of iron oxide reduction by biofilms has not been well studied. This study investigated the rates of ferrihydrite bioreduction by biofilms of Shewanella oneidensis MR-1 with variable concentration ratios of electron donor to acceptor, and different biofilm thickness. Results indicated that the bioreduction rate of ferrihydrite by biofilms increased with increasing biofilm surface area and was faster than that by suspended microorganisms for the same biomass amount, apparently as a result of the biofilm surface area facilitating the direct contact between ferrihydrite and microorganisms for electron transfer. Increasing biofilm thickness decreased bioreduction rate for the same total biomass as a result of the decrease of the ratio of the biofilm surface area to total biomass. The bioreduction rate increased with increasing electron donor and ferrihydrite inputs, consistent with the saturation type of kinetic models. The different rates of ferrihydrite reduction in the biofilm system resulted in different rates of Fe(II) production as a function of electron donor, acceptor, and biofilm surface area, which in turn affected the type and concentrations of the secondary iron minerals, such as lepidocrocite and goethite. A kinetic model was developed that integrates biofilm surface area, and electron donor and acceptor concentrations that well described the measured rates of ferrihydrite bioreduction. The results emphasized the importance of the biofilm surface area in understanding and modeling iron redox biogeochemistry and iron-related biogeochemical processes.

Indole-3-acetic acid regulating the initial adhesion of microalgae in biofilm formation

Regulating the microalgal initial adhesion in biofilm formation is a key approach to address the challenges of attached microalgae cultivation. As a type of phytohormone, Indole-3-acetic acid (IAA) can promote the growth and metabolism of microalgae. However, limited knowledge has been acquired of how IAA can change the initial adhesion of microalgae in biofilm formation. This study focused on investigating the initial adhesion of microalgae under different IAA concentrations exposure in biofilm formation. The results showed that IAA showed obvious hormesis-like effects on the initial adhesion ability of microalgae biofilm. Under exposure to the low concentration (0.1 mg/L) of IAA, the initial adhesion quantity of microalgae on the surface of the carrier reached the highest value of 7.2 g/m2. However, exposure to the excessively high concentration (10 mg/L) of IAA led to a decrease in the initial adhesion capability of microalgal biofilms. The enhanced adhesion of microalgal biofilms due to IAA was attributed to the upregulation of genes related to the Calvin Cycle, which promoted the synthesis of hydrophobic amino acids, leading to increased protein secretion and altering the surface electron donor characteristics of microalgal biofilms. This, in turn, reduced the energy barrier between the carriers and microalgae. The research findings would provide crucial support for the application of IAA in regulating the operation of microalgal biofilm systems.

Enhancing antibacterial properties of titanium implants through a novel Ag-TiO2-OTS nanocomposite coating: a comprehensive study on resist-killing-disintegrate approach

Titanium (Ti) implants are widely used in orthopedic and dental applications due to their excellent biocompatibility and mechanical properties. However, bacterial adhesion and subsequent biofilm formation on implant surfaces pose a significant risk of postoperative infections and complications. Conventional surface modifications often lack long-lasting antibacterial efficacy, necessitating the development of novel coatings with enhanced antimicrobial properties. This study aims to develop a novel Ag-TiO2-OTS (Silver-Titanium dioxide-Octadecyltrichlorosilane, ATO) nanocomposite coating, through a chemical plating method. By employing a ‘resist-killing-disintegrate’ approach, the coating is designed to inhibit bacterial adhesion effectively, and facilitate pollutant removal with lasting effects. Characterization of the coatings was performed using spectroscopy, electron microscopy, and contact angle analysis. Antibacterial efficacy, quantitatively evaluated against E. coli and S. aureus over 168 h, showed a significant reduction in bacterial adhesion by 76.6% and 66.5% respectively, and bacterial removal rates were up to 83.8% and 73.3% in comparison to uncoated Ti-base material. Additionally, antibacterial assays indicated that the ratio of the Lifshitz-van der Waals apolar component to electron donor surface energy components significantly influences bacterial adhesion and removal, underscoring a tunable parameter for optimizing antibacterial surfaces. Biocompatibility assessments with the L929 cell line revealed that the ATO coatings exhibited excellent biocompatibility, with minimal cytotoxicity and no significant impact on cell proliferation or apoptosis. The ATO coatings provided a multi-functionality surface that not only resists bacterial colonization but also possesses self-cleaning capabilities, thereby marking a substantial advancement in the development of antibacterial coatings for medical implants.

N-acyl homoserine lactone mediating initial adhesion of microalgal biofilm formation

While pioneering methods have demonstrated that bacterial N-acyl homoserine lactone (AHL) signaling molecules can influence the growth and self-aggregation of suspended microalgae, whether AHLs can affect the initial adhesion to a carrier has remained an open question. Here we revealed that the microalgae exhibited different adhesion potential under AHL mediation, where the performance was affiliated to both AHL types and concentrations. The result can be well explained by the interaction energy theory, where the energy barrier between the carriers and the cells varied due to AHL mediation. Depth analyses revealed that AHL acted through modifying the properties of the surface electron donor of the cells, which were dependent upon three major components, i.e., extracellular protein (PN) secretion, the PN secondary structure, and the PN amino acid composition. These findings expand the known diversity of AHLs mediation on microalgal initial adhesion and metabolisms, which may interface with other major cycles and become helpful to theoretically guide the application of AHLs in microalgal culture and harvesting.

A novel lithium ion-imprinted membrane with robust adsorption capacity and anti-fouling property based on the uniform multilayered interlayer

Effective modification strategies contribute to high adsorption capacity, separation efficiency and anti-fouling properties of ion-imprinted membranes. The design of a homogeneous and hydrophilic interlayer between the substrate membrane and ion-imprinted layer is crucial factor for the excellent performance of ion-imprinted membranes. In this study, a novel multilayered interlayer (SiO2@SP-PDA) was developed and uniformly coated on the substrate surface (PVDF membrane). The polydopamine (PDA) prepared via oxidation of sodium periodate (SP-PDA) increases the uniformity of SiO2@SP-PDA modification, which reduces the agglomeration of the ion-imprinted layer, and thereby boosts the adsorption capacity to 231.77 mg·g−1. The prepared ion-imprinted membrane (SiO2@SP-PDA-IIM) exhibits a favorable anti-fouling property due to the incremental hydrophilicity and the presence of SiO2 nano interlayer. Based on the XDLVO theory, it can be deduced that the SiO2 modification increases the membrane surface electron donor tension (γ−), which plays an essential role in enhancing the anti-fouling property of SiO2@SP-PDA-IIM. In this paper, the design of multilayered structure is of great significance to make the ion-imprinted membrane be a potential candidate for Li+ efficient separation in natural water.

Photocurrent quenching by competitive consumption of surface electron donor and light absorption for immunosensing

This work designs a competitive consumption strategy of surface electron donor and light absorption for quenching the photocurrent of ZnSnO3 nanocubes/BiOI nanoarrays/polydopamine (ZnSnO3 NCs/BiOI NAs/PDA) as a photoactive material. This material can be formed on electrode surface by successive coating and deposition to provide a substrate for immobilization of capture antibody, and producing strong photocurrent in the presence of ascorbate acid as a surface electron donor due to the well matching structure of band gaps between ZnSnO3 NCs and BiOI NAs, the excellent light absorption ability and high photo-electron conversion efficiency of BiOI NAs and PDA, and the accelerated electron transfer. Using ascorbate oxidase loaded dopamine-melanin nanosphere (DAM-AAO) as a label of the signal (secondary) antibody, the sandwich-type immunoreaction leads to dual photocurrent quenching of the label through the competitive consumption of ascorbate acid with enzymatic oxidation and the light absorption by DAM nanosphere. Thus, a sensitive “On-Off” photoelectrochemical (PEC) immunosensing method is constructed for the analysis of neuron specific enolase (NSE). The proposed method shows a detection range of 0.1 pg/mL −50 ng/mL and a detection limit of 0.03 pg/mL. The excellent performance and the recovery text demonstrated the practicability of the designed strategy and label in immunoassay of different protein biomarkers.

Grafting parameters and surface free energy components of photosensitive poly(methacrylated spiropyran) brushes

Poly(methacrylated spiropyran) (P(MMASP)) brushes on silicon wafers were synthesized using the interface-mediated RAFT polymerization of methacrylated spiropyran (MMASP) monomers to determine their grafting density and surface free energy changes during photoinitiation. The grafting parameters of P(MMASP) layers such as the grafting density (σ), the radius of gyration (Rg ) and average distance between polymer chains (D) were calculated. It is found that 1.25 P(MMASP) chains covered per nm2 area of wafers, and the distance between chains was 1.0 nm which is smaller than doubled Rg , 1.1 nm. Thus, P(MMASP) chains overlapped each other and forced themselves to stretch away from the interface. We evaluated the surface free energy components of P(MMASP) brushes during photo initiation. Van Oss-Good method was used to calculate the surface free energy components of brushes. It is found that spiropyran (SP)-merocyanine (MC) system significantly influenced the surface energy components of P(MMASP) brushes. The electron acceptor and electron donor surface free energies of SP and MC form of P(MMASP) brushes were found as and respectively. It is concluded that MC form of P(MMASP) brushes possess high base character; whereas, SP forms have low base character.

Exploring the electronic properties of Si-doped AlN (0001) surface with Cs adsorption layer for solar cell anode applications

The first-principles calculations are utilized to systematically investigate the adsorption behaviors of Cs on Si-doped AlN(0001) surfaces and its potential applications as anode material with low work function. Five Si substitution doping models and eight Cs adsorption surface models are established, respectively. Results show that Si atom tends to replace surface Al atom to form an n-type doping structure. Based on the most stable Si-doped surface, different Cs adsorption configurations with different adsorption sites and Cs coverage are analyzed. During Cs adsorption process, Cs acts as the electron donor and AlN surface is the electron acceptor. The large charge transfer at Cs adsorption interface induces a dipole moment pointing from Cs to AlN surface, which can effectively cut down the surface work function. Specifically, the 0.75 ML Cs-adsorbed surface shows the lowest work function of 0.62 eV, which has great potential application as the anode material of PETE devices. The findings in this work are generally applicable, which may shed new light on future exploration and development of low work function anode materials of PETE devices.

Oxygen vacancy engineering of vertically aligned NiO nanosheets for effective CO2 reduction and capture in Li-CO2 battery

The Li-CO2 battery with the concept of turning waste into treasure has aroused great scientific research enthusiasm recently, but unfortunately it is a long shot for the large-scale applications of Li-CO2 battery due to its huge overpotential and poor cycling life at current stage. Herein, NiO nanosheets engineered by oxygen vacancy growing vertically on carbon clothes (NiO-Vo@CC) was developed as viable catalyst for both CO2 reduction reaction (CO2RR) and CO2 evolution reaction (CO2ER) in Li- CO2 system. The oxygen vacancy decorated by surplus electron will not only work as electron donor (Lewis base) surface to activated the electron-deficient carbon atom in CO2 but also narrow the band gap of NiO, therefore optimized CO2 conversion kinetic can be obtained by using defective NiO-Vo@CC electrode. The utilization of defect engineering to achieve performance improvement in aprotic Li-CO2 battery is still in its infancy at current stage and thus our research initially corroborates that modulation of the surface property via defect engineering can serve as valid strategy to design high performance electrodes for Li-CO2 battery.

Synthesis of Surface-Porous Sorbents Based on Silicon Dioxide and Studying Their Adsorption Properties

Sorbents with a layer of silicon dioxide on the surface of a wide-pore Chromaton N-AW support have been synthesized. The dependence of the textural characteristics (specific surface area and pore size) of the obtained materials on the amount of tetraethoxysilane applied to Chromaton N-AW and on the pH of the synthesis medium was studied by the method of low-temperature nitrogen adsorption/desorption. The characteristics of the surface and the adsorption properties of the synthesized materials have been studied by methods of scanning electron microscopy, pH-metry, thermogravimetric analysis, and gas chromatography. It was found that during the synthesis of sorbents in an acidic medium, samples with a pore size of 2–4 nm are formed and in an alkaline medium, 13–16 nm. With a rise in the amount of tetraethoxysilane, a decrease in the polarity of the sorbents, the specific heat of adsorption with respect to the test compounds, and the number of electron-donor surface sites is observed, while the fraction of electron-acceptor surface sites increases significantly.

Antifouling mechanism of the additive-free β-PVDF membrane in water purification process: Relating the surface electron donor monopolarity to membrane-foulant interactions

Although the antifouling modification of polyvinylidene fluoride (PVDF) membrane has attracted much attentions recently, the underlying fouling/antifouling mechanism of the PVDF membranes having different polymorphs have rarely been mentioned. In this study, two PVDF membranes with similar pore structure but distinct polymorphs were prepared, and their antifouling performance was systematically investigated by using synthetic solutions containing complex foulants relevant to surface water sources (e.g., humic acid, bovine serum albumin and dextran). A remarkable correlation between PVDF polymorph, membrane surface chemistry and fouling resistance was observed, demonstrating the exceptional ability of β-PVDF phase (i.e., β-PVDF membrane) in fouling mitigations when compared to α-PVDF phase (i.e., α-PVDF membrane). In order to unravel the fouling mechanism of PVDF membrane having different polymorphs, interaction forces between foulant-coated particle probes, simulating foulant molecules, and each membrane surface were measured by AFM and theoretical calculated depended on surface energy components. It is clearly shown that the enhanced fouling resistance of β-PVDF membrane was mainly driven by the reduced adhesion tendency of foulants, which could further attribute to the strong electron donor monopolarity of β-PVDF phase (γAB− = 25.3 mJ/m2) compared to α-PVDF phase (γAB− = 3.3 mJ/m2). Moreover, for each SSW-fouled membrane, depth profiling of the external fouling layer and composition of the extracted internal foulants were carefully investigated by variable angle FTIR and UV–vis spectrometer, respectively, suggesting the strong relationship between membrane fouling behavior and membrane-foulant and foulant-foulant interactions. This work emphasized the selection of proper polymorph of PVDF membrane should be valued so as to mitigate membrane fouling, and we anticipate the advantage of β-PVDF phase in membrane fouling control can boost the development of additive-free and sustainable antifouling strategy in future.

Quantifying the influence of surface chemical composition on surface energy during powder flow

In this study, the dominant intermolecular interactions at powder surfaces were investigated using inverse gas chromatography. Silica beads coated with molasses, corn starch, butter, or wheat gluten were used as model powders to emulate the interactions of surface components present in common food powders. The flow properties of the powders were analyzed using a rotational shear cell device at ambient conditions (25 °C and 40% relative humidity). A positive correlation (r = 0.72, p < 0.05) between the acid-base ratio (accounting for the ratio between the number of electron acceptor to electron donor surface sites) and the flow factor (flowability indicator, ffc at 1 kPa pre-shear stress) was observed for all the size ranges of surface-modified silica beads and industry-grade powders (modified corn starch and palm oil powders). The results depict the importance of acid-base surface components in understanding the mechanistic influence of pre-load molecular dynamics on the bulk flowability.

Fate of NaClO and membrane foulants during in-situ cleaning of membrane bioreactors: Combined effect on thermodynamic properties of sludge

In this study, the fate of sodium hypochlorite (NaClO) and detached membrane foulants and their impacts on the thermodynamic properties of raw sludge were investigated in a membrane bioreactor (MBR). It was found that about 20.3% of the total NaClO was potentially released into the bulk sludge, which significantly altered the raw sludge surface properties, such as a reduction in the number of surface electron donor components (γ−) and an increase in surface hydrophobicity. After exposure to NaClO, the treated sludge had a higher adhesive and cohesive propensity compared to the raw sludge. Based on the extended Derjaguin-Landau-Verwey- Overbeek (XDLVO) theory and the batch filtration test results, the detached foulants potentially aggregated with the treated sludge and form the reconstructed sludge. The reconstructed sludge had a high protein (PN) level in the extracellular polymeric substances (EPS), with a higher membrane fouling potential compared with the raw sludge.

New insights into the rapid formation of initial membrane fouling after in-situ cleaning in a membrane bioreactor

Abstract In-situ chemical cleaning with sodium hypochlorite (NaClO) is often employed for maintaining constant permeability in a membrane bioreactor (MBR). In this study, the effect of NaClO shock on the rapid formation of initial membrane fouling was investigated over the course of the in-situ cleaning of a MBR. Variations of trans-membrane pressure (TMP) in the different runs indicated that the bulk sludge after NaClO-shock promotes the rapid formation of initial membrane fouling. After in-situ cleaning, the sludge had a high protein content in different extracellular polymeric substance layers and a substantial deterioration in sludge filterability compared to raw sludge. Based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, NaClO shock significantly changes the surface properties of raw sludge. It reduces the surface electron donor component ( γ − ) and increases surface hydrophobicity. The sludge after NaClO-shock exhibited a stronger adhesive energy with the membrane and higher self-cohesive ability, resulting in severe membrane fouling.

Reduction of bacterial adhesion on Ag-TiO2 coatings

Ag-TiO2 nano-composite coatings showed the synergistic effect on the anti-bacterial activity. However, little was known on the mechanism of the enhanced anti-bacterial effect. In this paper, a range of Ag-TiO2 nano-composited coating with different TiO2 contents were prepared on titanium substrate using an electroless deposition technique and the antibacterial performance of the coatings were evaluated with E. coli and S. aureus. This work demonstrated for the first time that the incorporation of TiO2 nano-particles into Ag matrix not only significantly promoted the Ag ion release, but also significantly increased the electron donor surface energy, which lead to the enhanced antibacterial effect of the Ag-TiO2 coatings.

Mechanisms of the enhanced antibacterial effect of Ag-TiO2 coatings

It has been demonstrated that Ag-TiO2 nanocomposite coatings with excellent antimicrobial activity and biocompatibility have the potential to reduce infection problems. However, the mechanism of the synergistic effect of Ag-TiO2 coatings on antibacterial efficiency is still not well understood. In this study, five types of Ag-TiO2 nanocomposited coatings with different TiO2 contents were prepared on a titanium substratum. Leaching tests indicated that the incorporation of TiO2 nanoparticles into an Ag matrix significantly promoted Ag ion release. Surface energy measurements showed that the addition of TiO2 nanoparticles also significantly increased the electron donor surface energy of the coatings. Bacterial adhesion assays with Escherichia coli and Staphylococcus aureus demonstrated that the number of adhered bacteria decreased with increasing electron donor surface energy. The increased Ag ion release rate and the increased electron donor surface energy contributed to an enhanced antibacterial efficiency of the coatings.

Reduction of bacterial adhesion on titanium-doped diamond-like carbon coatings

A range of titanium doped diamond-like carbon (Ti-DLC) coatings with different Ti contents were prepared on stainless steel substrates using a plasma-enhanced chemical vapour deposition technique. It was found that both the electron donor surface energy and the surface roughness of the Ti-DLC coatings increased with increasing Ti contents in the coatings. Bacterial adhesion to the coatings was evaluated against Escherichia coli WT F1693 and Pseudomonas aeruginosa ATCC 33347. The experimental data showed that bacterial adhesion decreased with the increases of the Ti content, the electron donor surface energy and surface roughness of the coatings, while the bacterial removal percentage increased with the increases of these parameters. The Ti-DLC coatings reduced bacterial attachment by up to 75% and increased bacterial detachment from 15 to 45%, compared with stainless steel control.

Controllable Evolution of Dual Defect Zni and VO Associate-Rich ZnO Nanodishes with (0001) Exposed Facet and Its Multiple Sensitization Effect for Ethanol Detection.

Building an effective way for finding the role of surface defects in gas sensing property remains a big challenge. In the present work, we synthesized the ZnO nanodishes (NDs) and first explored the formation process of rich electron donor surface defects by means of studying mechanism for the ZnO NDs synthesis. The test results revealed that ZnO-6, added by 6 mmol Zn powder, had the best gas-sensing properties with the excellent selectivity to ethanol than the others. Specially, the ZnO-6 sensor exhibited the best response (about 49) to 100 ppm ethanol at 230 °C among four as-synthesized samples, while noncustomized ZnO was only 28. It was mainly caused by the following two reasons: the exposure of target (0001) crystal facet and rich electron donor surface defects zinc interstitial (Zni) and oxygen vacancy (VO). As a guide, the formation process of surface defects was revealed by an ideal defect model. By the small-angle XRD and TEM patterns, we could conclude that ZnO NDs, changing stoichiometric ratio, increased the content of Zni by adding Zn powder, while excessive Zn powder promoted the growth of c axis of ZnO NDs in the self-assembly engineering. Besides, a depletion model has been provided to explain how the surface defects work on the sensors and the complex mechanism of gas sensing performance. These findings will develop the application of ZnO-based gas sensor in health and security.