Charged Sites Research Articles

Investigation on Viscosity Behavior of Anionic Polyacrylamide Copolymer in Brine Solutions for Slickwater Fluids Applications at High Salinity and Hardness Conditions

Abstract Slickwater fluids, used to undertake fracturing in low-permeability reservoirs, may be derived from produced water consisting of a range of dissolved salts. The fluids are pumped downhole at high flowrates, and hence friction reducers, e.g., anionic polyacrylamides (APAMs) are added, which also impart viscosity to the fluid resulting in better proppant transport. The present work investigates the effect of an APAM copolymer on the viscosity of slickwater fluids; specifically, at high salinity and hardness conditions. The experimental part of this study demonstrated the impact of the parameters—APAM concentration and salt type/concentration—on slickwater fluid viscosity. In a freshwater–APAM fluid, as monovalent salt (salinity) is added incrementally, fluid viscosity decreased initially owing to the charge-shielding effect; and, then viscosity values were leveled off beyond a certain salinity level. However, a very peculiar behavior was observed for the addition of divalent salts (hardness) to fluid systems. Initially, as hardness increased up to 50k ppm (parts per million), as expected, fluid viscosity showed a significant decrease; on the contrary, as the hardness was raised beyond 50k ppm, the solution viscosity showed a distinctive increase up to 250k ppm. This phenomenon may be explained on the basis of the reverse charge-shielding effect, i.e., excessive divalent ionicity inducing repulsion between polymer charge sites. To model the above experimentally observed non-monotonous viscosity behavior, various machine learning models were employed; support vector regression (SVR)based models predicted the slickwater fluid viscosity with maximum accuracy. Sensitivity analysis was carried out to determine the prominence of the studied input parameters. The modeling work would assist in minimizing trial-and-error in designing/optimizing a slickwater fluid system.

Understanding Dual‐Polar Group Functionalized COFs for Accelerating Li‐Ion Transport and Dendrite‐Free Deposition in Lithium Metal Anodes

Lithium metal batteries (LMBs) have attracted wide attentions because of their high theoretical specific capacity and low electrochemical potential. However, the growth of lithium dendrites seriously affects the practical application of LMBs. Thus, the lithium‐philic carbonyl and carboxy dual‐group‐modified covalent organic framework (COF‐COOH) is designed to coat the polypropylene (PP) separator (COF‐COOH@PP separator), realizing the regulation of ion transport and uniform lithium deposition. The plentiful and negative charge sites in the COF‐COOH can suppress the diffusion of the freely movable lithium salt anion by the electrostatic interaction. Density functional theory (DFT) calculations demonstrate that the COF‐COOH possesses the function of anchoring anion and desolvation. Consequently, the Li+ transference number (0.7), ion conductivity (0.64 mS cm−1), and desolvating of Li+ are obviously improved by using the COF‐COOH@PP separator. The modified Li‐Li symmetric battery delivers stable cycle for more than 1000 h and lower voltage hysteresis (0.02 V). This dendrite‐free deposition strategy holds great promise for practical application of Li metal anodes.

Fabrication of highly mesoporous ZSM-48 zeolite by anionic surfactant-organosilane system for catalytic conversion of methanol to gasoline

A highly mesoporous ZSM-48 zeolite has been prepared using low-cost anionic surfactant sodium dodecylsulphate (SDS) as mesopore-generating agent and short-chain 3-aminopropyltrimethoxysilane (APTMS) as co-structure directing agent. The mesoporosity formation took place through the interaction between the silica species/APTMS and SDS molecules existing in the gel composition. In the synthesis solution with a pH slightly less than ten, the methoxysilyl moiety in APTMS was hydrolysed to the –SiO3 units and became incorporated inside the zeolite crystals while the positively charged ammonium site of APTMS interacted with the negatively charged head group of the SDS. Aggregation of aluminosilicate/APTMS species around the SDS micelles during the crystallization process, led to the formation of a mesoporous zeolite. In this study, a conventional ZSM-48 and seven ZSM-48 zeolites from different mixtures containing SDS, APTMS and SDS-APTMS with different APTMS/SiO2 molar ratios were synthesized. Changes in the properties of the synthesized samples were investigated by XRD, FTIR, SEM, TEM, nitrogen adsorption/desorption isotherms, NH3-TPD and TGA. The optimum ZSM-48/Sur/0.008OS zeolite prepared with APTMS/SiO2 molar ratio of 0.008 exhibited both bundled needle-like and spherical morphologies. The catalytic conversion of methanol to gasoline (MTG) was evaluated in a fixed-bed reactor, and the results revealed that mesoporosity development using Sur-OS system enhanced catalytic activity of ZSM-48/Sur/0.008OS catalyst compared to the other sample. The optimum zeolite showed long stable phase of 40 h and liquid hydrocarbon yield of 42% was achieved for 100% methanol conversion in 22 h of reaction. The proposed method opens a new and simple route for the synthesis of hierarchically porous ZSM-48 with tunable porosity using low-cost anionic surfactants.

Biosorption of acid brown 14 dye to mandarin-CO-TETA derived from mandarin peels

Several agronomic waste-materials are presently being widely used as bio-adsorbents for the treatment of toxic wastes such as dyes and heavy metals from industrial activities, which has resulted in critical global environmental issues. Therefore, there is a need to continue searching for more effective means of mitigating these industrial effluents. Synthetic aromatic dyes such as Acid Brown (AB14) dye are one such industrial effluent that is causing a serious global issue owing to the huge amount of these unsafe effluents released into the ecosystem daily as contaminants. Consequently, their confiscation from the environment is critical. Hence, in this study, Mandarin-CO-TETA (MCT) derived from mandarin peels was utilized for the removal of AB14 dyes. The synthesized biosorbent was subsequently characterized employing FTIR, TGA, BET, and SEM coupled with an EDX. The biosorption of this dye was observed to be pH-dependent, with the optimum removal of this dye being noticed at pH 1.5 and was ascribed to the electrostatic interaction between the positively charged sites on the biosorbent and the anionic AB14 dye. The biosorption process of AB14 dye was ideally described by employing the pseudo-second-order (PSO) and the Langmuir (LNR) models. The ideal biosorption capacity was calculated to be 416.67 mg/g and the biosorption process was indicative of monolayer sorption of AB14 dye to MCT biosorbent. Thus, the studied biosorbent can be employed as a low-cost activated biomass-based biosorbent for the treatment of AB14 dyes from industrial activities before they are further released into the environment, thus mitigating environmental contamination.

Structural Dynamics of Short Ligands on the Surface of ZnSe Semiconductor Nanocrystals.

ZnSe semiconductor nanocrystals (NCs) with a size comparable to their Bohr radius are synthesized, and the native capping agents with long hydrocarbon tails are replaced with short thiocyanate (SCN) ligands through a ligand exchange method. The structural dynamics of SCN ligands on the surface of ZnSe NCs in solution is investigated by ultrafast infrared spectroscopy. Vibrational population relaxation of SCN ligands is accelerated due to the specific interaction with the positively charged sites on the surface of NCs. The orientational anisotropy of the bound SCN ligands decayed at a rate much faster than that in the control solution containing Zn2+ cations. From the wobbling-in-the-cone model analysis, we found that the SCN ligand undergoes wobbling orientational diffusion with a relatively large cone semiangle on the surface of ZnSe NCs, and the overall orientational diffusion of bound SCN is found to be strongly dependent on the size of ZnSe NCs.

Aspartic Acid Stabilized Iron Oxide Nanoparticles for Biomedical Applications

Aspartic acid stabilized iron oxide nanoparticles (A-IONPs) with globular shape and narrow size distribution were prepared by the co-precipitation method in aqueous medium. A quantum-mechanical approach to aspartic acid optimized structure displayed negative charged sites, relatively high dipole moment, and hydrophilicity, which recommended it for interaction with iron cations and surrounding water electrical dipoles. A-IONPs were characterized by TEM, XRD, ATR-FTIR, EDS, DSC, TG, DLS, NTA, and VSM techniques. Theoretical study carried out by applying Hartree-Fock and density functional algorithms suggested that some aspartic acid properties related to the interaction can develop with nanoparticles and water molecules. The results of experimental investigation showed that the mean value of particle physical diameters was 9.17 ± 2.2 nm according to TEM image analysis, the crystallite size was about 8.9 nm according to XRD data, while the magnetic diameter was about 8.8 nm, as was determined from VSM data interpretation with Langevin’s theory. The A-IONP suspension was characterized by zeta-potential of about −11.7 mV, while the NTA investigation revealed a hydrodynamic diameter of 153.9 nm. These results recommend the A-IONP suspension for biomedical applications.

Adsorption of perfluorooctanoic acid from water by pH-modulated Brönsted acid and base sites in mesoporous hafnium oxide ceramics

SummaryPer- and polyfluoroalkyl substances (PFAS) are increasingly appearing in drinking water sources globally. Our work focuses specifically on the adsorption of the legacy perfluorooctanoic acid (PFOA) using mesoporous hafnium oxide (MHO) ceramic synthesized via a sol-gel process. Experiments were performed at varying pH to determine the effect of surface charge on adsorption capacity of PFOA by MHO, and to postulate adsorption behavior. At pH 2.3, the adsorption capacity of PFOA on MHO was 20.9 mg/g, whereas at a higher pH of 6.3, it was much lower at 9.2 mg/g. This was due to increased coulombic attractions at lower pH between the positively charged conjugate acid active sites on MHO surface and negatively charged deprotonated PFOA anion in solution. After adsorption, the solid MHO was regenerated via calcination, reducing the amount of toxic solid waste to be disposed since the adsorbent is regenerated, and the PFOA is completely removed.

Genetically engineered pH-responsive silk sericin nanospheres with efficient therapeutic effect on ulcerative colitis

Ulcerative colitis (UC) is one type of inflammatory bowel disease (IBD) and lactoferrin (LF) is a promising protein drug to treat UC. However, targeted LF delivery to optimize bioavailability, targeting and effectiveness remains a challenge. Here, we report an effective strategy to fabricate silk sericin nanospheres systems for the delivery of recombinant human lactoferrin (SS-NS-rhLF). The system is based on the use of optimized transgenic silkworms to generate genetically engineered silk fibers (rhLF-silks). The rhLF silks were used for fabricating SS-NS-rhLF by ethanol precipitation. The SS-NS-rhLF were stable with a spherical morphology with an average diameter of 123 nm. The negatively charged sericins in a pH ≥ 5.5 environment achieved specific targeting of the SS-NS-rhLF to positively charged colonic sites. The SS-NS-rhLF achieved efficient uptake by cells in the inflamed colon of mice when compared to free lactoferrin in solution (SOL-rhLF). Furthermore, oral administration of the SS-NS-rhLF with low dose of rhLF significantly relived symptoms of UC in mice and achieved comparable therapeutic effect to the high dose of SOL-rhLF by supporting the reformation of cell structure and length of colon tissue, reducing the release of inflammatory factors, inhibiting the activation of the NF-κB inflammatory pathway, and maintaining a stable intestinal microbial population in mice. These results showed that the SS-NS-rhLF is a promising system for colitis treatment. Statement of significanceTargeting and effective delivery of multiple biological functional protein human lactoferrin (rhLF) is a promising strategy to treat ulcerative colitis in the clinic. Here, rhLF-transgenic silk cocoons were used to fabricate a rhLF-sericin nanosphere delivery system (SS-NS-rhLF). The fabricated SS-NS-rhLF showed identical spherical morphology, stable structure, sustainable rhLF release, efficient cell uptake and negative charge in an environment of pH above 5.5, thus realized the specific targeting to the positively charged colonic sites to treat UC mice through oral administration. The therapeutic effect of SS-NS-rhLF with a low rhLF dose in the UC mice was comparable to the high dose of free rhLF treatment in solution form, suggesting that the SS-NS-rhLF is a promising system for colitis treatment.

Do not forget the Rydberg orbitals.

Within any molecule or cluster containing one or more positively charged sites, families of Rydberg orbitals exist. Free electrons can attach directly, and anionic reagents with low electron binding energy can transfer an electron into one of these orbitals to form a neutral Rydberg radical. The possibilities that such a radical could form a covalent bond either to another Rydberg radical or to a radical holding its electron in a conventional valence orbital are considered. This Perspective overviews two roles that Rydberg radicals can play, both of which have important chemical consequences. Attachment of an electron into excited Rydberg orbitals is followed by rapid (∼10-6s) relaxation into the lowest-energy Rydberg orbital to form the ground state radical. Although the excited Rydberg species are stable with respect to fragmentation, the ground-state species is usually quite fragile and undergoes homolytic bond cleavage (e.g., -R2NH dissociates into -R2N + H or into -RNH + R) by overcoming a very small barrier on its potential energy surface, thus generating reactive radicals (H or R). Here, it is shown that as a result of this fragility, any covalent bonds formed by Rydberg radicals are weak and the molecules they form are susceptible to exothermic fragmentations that involve quite small activation barriers. Another role played by Rydberg species arises when the Coulomb potentials provided by the (one or more) positive site(s) in the molecule stabilize low-energy anti-bonding orbitals (e.g., σ* orbitals of weak σ bonds or low-lying π* orbitals) to the extent that electron attachment into these Coulomb-stabilized orbitals is rendered exothermic. In such cases, the overlap of the Rydberg orbitals on the positive site(s) with the σ* or π* orbitals allows either a free electron or a weakly bound electron to an anionic reagent that is attracted toward the positive site by its Coulomb force to be guided/transferred into the σ* or π* orbital instead. After attaching to such an anti-bonding orbital, bond cleavage occurs again, generating reactive radical species. Because of the large radial extent of Rydberg orbitals, this class of bond cleavage events can occur quite distant from the positively charged group. In this Perspective, several examples of both types of phenomena are given for illustrative purposes.

Silver metal organic frameworks and copper metal organic frameworks immobilized on graphene oxide for enhanced adsorption in water treatment

In this study, copper metal organic frameworks (Cu-MOF) and silver metal organic frameworks (Ag-MOF) were synthesized and immobilized on and between GO sheets using an ultrasonication process. The GO-immobilized MOFs (GO-Ag-MOF and GO-Cu-MOF) showed enhanced physicochemical properties, including enhanced surface area, surface charge, and active adsorption sites confirmed with characterization techniques such as zeta potential, Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, the adsorption capacities of Ag-MOF, Cu-MOF, GO-Ag-MOF, and GO-Cu-MOF materials for methylene blue dye (MB), as an organic contaminant model, were thoroughly evaluated at different experimental conditions (pH (3–10), temperature (25–45 °C), and adsorbate concentrations (0–150 ppm)). The kinetics and thermodynamic behavior of the synthesized MOFs revealed that both GO-Ag-MOF and GO-Cu-MOF showed around 10% increase in adsorption capacity in comparison to the pristine Ag-MOF and Cu-MOF at all the tested conditions. GO-Ag-MOF exhibited more than 98 % dye removal, followed by Ag-MOF (90%), GO-Cu-MOF (75%), and Cu-MOF (65%). The main mechanism for adsorption was monolayer adsorption based on electrostatic interactions. All MOFs showed more than 80% re-generability after three regeneration cycles

In Situ Monitoring of Transmetallation in Electric Potential-Promoted Oxidative Coupling in a Single-Molecule Junction

In Situ Monitoring of Transmetallation in Electric Potential-Promoted Oxidative Coupling in a Single-Molecule Junction

Microwave-assisted synthesis of hybrid supercapacitors consisting of Ni, Co-layered double hydroxide shell assembled around wood-derived activated carbon fiber core

Activated carbon fibers (ACFs) are prepared from the discarded fir wood using two-step melt-spinning and CO2 activation post-treatment. Then, composites composed of these ACFs and Ni, Co-layered double hydroxides (NiCo-LDH@ACF) are synthesized by a microwave-assistant hydrothermal strategy. NiCo-LDHs agglomerated around ACFs, forming core-shell structures with sheet- or microsphere-like morphologies, which provide large surface area, hierarchical porosity, and numerous active sites for efficient charge and mass transfer. The NiCo-LDH@ACFs are used as an active material to construct the supercapacitors, the highest of capacitance and the corresponding rate performance of which are equal to 1453.3 F/g at 1 A/g and 78% at 10 A/g by microwave-assistant hydrothermal at 120 °C, respectively. We also use this material to assemble an asymmetric supercapacitor using activated carbon derived from fir bark as a negative electrode. The resulting device demonstrates excellent capacitance (equal to 146.9 F/g at 1.6 V), very high energy density (equal to 52.2 Wh/kg at 800 W/kg), and cycle life (judging by the 79.8% capacitance retention after 10000 cycles).

Ni–Zn Dual Sites Switch the CO2 Hydrogenation Selectivity via Tuning of the d-Band Center

Controlling the selectivity of CO2 hydrogenation by catalysis is a fundamental challenge. This study examines the interrelation between active sites and reaction pathways in Ni-catalyzed CO2 hydrogenation. The alloying of Ni with Zn to charged (Niσ––Znσ+) active sites modifies the electronic structure and d-band center, weakens the interaction with CO/H2, and preferentially catalyzes the reverse water gas shift to CO with the thermodynamically favored methanation pathway switched off. The charged dual sites can stabilize the activated CO2 species in a η2(C, O) bridge configuration, directly dissociate the C═O bond to *CO, and promote CO desorption. The mechanistic investigation has elucidated the reaction pathways in the Ni-catalyzed CO2 hydrogenation and identified the crucial intermediates that impacted the product selectivity, which can provide a theoretical guide for the Ni-based catalyst design.

Integrated Bayesian networks with GIS for electric vehicles charging site selection

Location selection of charging stations of electric vehicles (EVs) contributes to long-term sustainable urban development. This study proposes a hybrid approach integrated with the Geographical information system (GIS) and Bayesian network (BN) to deal with the location selection problem for EVs. GIS serves for capturing spatial and geographical data, which provides dynamic and visual information for selecting charging sites. BN is employed to process various criteria and demonstrate the cause-effect relationship in alternative site selection. A BN model consisting of nine criteria from three aspects is established to determine the most suitable locations for charging stations of EVs. A total of ten alternative locations in Singapore is used to verify the applicability and effectiveness of the developed hybrid approach. Results indicate that (1) Criteria, including the number of MRT stations, household units, and charging efficiency, are identified as the most sensitive factors to the location selection; (2) The transportation efficiency has the strongest linkage with the location selection (with an average value of the strength of 0.445), revealing that the transportation efficiency is more important than the social and economic efficiency. The novelty of this research lies in the development of the hybrid GIS-based BN approach that is more accurate and stable under noise interruption compared to the traditional decision-making method (e.g., TOPSIS). The developed approach can be used as a decision tool to identify the major contributing factors and update the optimal decisions given new observation data in GIS in an automatic manner.

Structure engineering of Zn-ZIF adsorbents for efficient and highly-selective phosphate removal from wastewater: Roles of surface mesopore and defect

The ability to purposely manipulate the material structure is vital in developing an efficient adsorbent for phosphate-selective removal from wastewater. Defects and mesopores play dominating roles in improving the adsorption performance of zinc-based zeolitic imidazolate frameworks (Zn-ZIF). In this work, nonporous leaf-like ZIF (ZIF-L) precursor was treated by a facile solvothermal method to successfully prepare defect-rich mesoporous Zn-ZIF materials. Among them, the optimized Zn-ZIF-72 exhibited the highest capacity of 102 ± 2 mg g−1 (only 75 ± 3 mg g−1 of ZIF-L) due to its strong electrostatic attraction from more positive surface charge (34.65 mV at pH = 5) and abundant available Zn-defect sites via well-developed mesopores. Yet the mass transfer resistance in newly-formed pores led to a slightly slow kinetics of 0.01 g mg−1 min−1 for Zn-ZIF-72. Moreover, >90% of phosphate-adsorbed efficiencies of Zn-ZIF-72 were achieved even under the interfering effect of seven common coexisting matters (e.g., CO32− and humic acid) of 100 times concentration, mainly attributing to specific inner-sphere complexation of surface Zn-defects with phosphate species. Furthermore, to achieve the effluent P < 0.5 mg L−1 in real wastewater treatment, about 885 bed volume (BV) by using Zn-ZIF-72 adsorbent was much higher than ∼710 BV by ZIF-L. Thus, this work offers a novel strategy for designing highly-effective phosphate adsorbents through structure engineering.

Inhibition of AdeB, AceI, and AmvA Efflux Pumps Restores Chlorhexidine and Benzalkonium Susceptibility in Acinetobacter baumannii ATCC 19606.

The management of infections caused by Acinetobacter baumannii is hindered by its intrinsic tolerance to a wide variety of biocides. The aim of the study was to analyze the role of different A. baumannii efflux pumps (EPs) in tolerance to chlorhexidine (CHX) and benzalkonium (BZK) and identify non-toxic compounds, which can restore susceptibility to CHX and BZK in A. baumannii. A. baumannii ATCC 19606 strain was tolerant to both CHX and BZK with MIC and MBC value of 32 mg/L. CHX subMIC concentrations increased the expression of adeB and adeJ (RND superfamily), aceI (PACE family) and amvA (MFS superfamily) EP genes. The values of CHX MIC and MBC decreased by eightfold in ΔadeB and twofold in ΔamvA or ΔaceI mutants, respectively, while not affected in ΔadeJ mutant; EPs double and triple deletion mutants showed an additive effect on CHX MIC. CHX susceptibility was restored in double and triple deletion mutants with inactivation of adeB gene. BZK MIC was decreased by fourfold in ΔadeB mutant, and twofold in ΔamvA and ΔaceI mutants, respectively; EPs double and triple deletion mutants showed an additive effect on BZK MIC. BZK susceptibility was recovered in ΔadeB ΔaceI ΔadeJ and ΔamvA ΔadeB ΔadeJ triple mutants. The structural comparison of AdeB and AdeJ protomers showed a more negatively charged entrance binding site and F-loop in AdeB, which may favor the transport of CHX. The carbonyl cyanide m-chlorophenylhydrazine protonophore (CCCP) EP inhibitor reduced dose-dependently CHX MIC in A. baumannii ATCC 19606 and in ΔadeJ, ΔaceI, or ΔamvA mutants, but not in ΔadeB mutant. Either piperine (PIP) or resveratrol (RV) at non-toxic concentrations inhibited CHX MIC in A. baumannii ATCC 19606 parental strain and EPs gene deletion mutants, and CHX-induced EP gene expression. Also, RV inhibited BZK MIC and EP genes expression in A. baumannii ATCC 19606 parental strain and EPs mutants. These results demonstrate that tolerance to CHX and BZK in A. baumannii is mediated by the activation of AdeB, AceI and AmvA EPs, AdeB playing a major role. Importantly, inhibition of EP genes expression by RV restores CHX and BZK susceptibility in A. baumannii.

Electrostatically Driven Protein-Protein Interactions: Quantitative Prediction of Second Osmotic Virial Coefficients to Aid Antibody Design.

Electrostatically driven attractions between proteins can result in issues for therapeutic protein formulations such as solubility limits, aggregation, and high solution viscosity. Previous work showed that a model monoclonal antibody displayed large and potentially problematic electrostatically driven attractions at typical pH (5-8) and ionic strength conditions (∼10-100 mM). Molecular simulations of a hybrid coarse-grained model (1bC/D, one bead per charged site and per domain) were used to predict potential point mutations to identify key charge changes (charge-to-neutral or charge-swap) that could greatly reduce the net attractive protein-protein self-interactions. A series of variants were tested experimentally with static and dynamic light scattering to quantify interactions and compared to model predictions at low and intermediate ionic strength. Differential scanning calorimetry and circular dichroism confirmed minimal impact on structural or thermal stability of the variants. The model provided quantitative/semiquantitative predictions of protein self-interactions compared to experimental results as well as showed which amino acid pairings or groups had the most impact.

Crystal engineering of novel MOF@iCOF composite as a multifunction platform for targeted monitoring and capturing of norfloxacin

The construction of novel multifunctional nanocomposites is of interest because of their excellent proven detection and capture performance. Herein, a new type of porous material, UiO-66-NH2@TpTGCl, is designed by combining a Zr-based metal organic framework, UiO-66-NH2, with a guanidine-based ionic covalent organic framework (iCOF), TpTGCl. The UiO-66-NH2@TpTGCl retains the high crystallinity and hierarchical pore structure of the MOF and iCOF, and has a surface rich in guanidine groups, and hence it has excellent hydrophilicity and is rich in positively charged sites; thus, the potential capacity of UiO-66-NH2@TpTGCl for the capture of antibiotics with polar functional groups, such as norfloxacin, is excellent. Tb3+ ions are then assembled onto the UiO-66-NH2@TpTGCl skeleton. With the addition of norfloxacin to the composite, strong coordination between the carboxyl group of norfloxacin and the Tb3+ ions in UiO-66-NH2@TpTGCl@Tb occurred, and the characteristic fluorescence emission of Tb3+ (5D4→7F5) is enhanced by antenna and spatial confinement effect. Consequently, ratiometric fluorescence detection and capture of norfloxacin are realized using UiO-66-NH2@TpTGCl@Tb. The linear detection range is 0.01–1 μM and the detection limit is 4 nM. Most importantly, UiO-66-NH2@TpTGCl@Tb exhibits high capture capacity (251 mg g−1) and favorable capture efficiency (80.5%). Meanwhile, the mechanism is detailed explored through XPS spectrum and DFT calculation. We believe that this work will trigger the study of new iCOF-functionalized MOF composites and that it presents a promising strategy for simultaneous ratiometric luminescence monitoring and capturing of antibiotics from water.

First-principles investigations into the effect of oxygen vacancies on the enhanced reactivity of NiO via Bader charge and density of states analysis

Vacancy defects are important parameters in determining the reactivity of metal oxides. Different areas such as catalysis, fuel cell, battery, and other energy conversion technologies (e.g., chemical looping combustion) can benefit from fundamental studies on the effect of vacancy defects on metal oxide reactivity. The effect of oxygen vacancies on the reactivity of NiO, which is a prominent and promising material in the aforementioned areas, is studied in this work. Using density functional theory, a comprehensive analysis of oxygen vacancy effect on the hydrogen chemisorbed state of NiO (100) is provided with Bader charge, charge redistribution, and density of states analyses. By inclusion of an oxygen vacancy, adsorption sites change from Ni and O sites on NiO to O and O vacant sites on NiO1−x. Adsorbed hydrogen on the positively charged oxygen vacant site has an enhanced interaction with two neighboring Ni atoms. As revealed by our analysis, change in the magnitude of H–Ni interaction is the main contributor to the enhanced reactivity of NiO by the addition of O vacancy. The results establish an understanding of the enhanced reactivity by the creation of O vacancies and elucidate the changes in the bonding nature as a result of the vacancy.

Embodying Violence, Manipulating Space: The Irony of Valloton's Police States

In the last decades of the nineteenth century, the visual and experiential character of the French capital was being reshaped as the urban street took on renewed social significance. Though considered a politically charged site of demonstration and insurrection since the Revolution, widespread social protests in the 1890s exacerbated the perceived danger of proletarian crowds. Propelled by heightened tensions between the bourgeois establishment and increasingly radical social reformers, the anarchist movement also reached a fever pitch around 1895. The arch of anarchism’s rise in France coincided with Vallotton’s arrival there and the height of his illustrious graphic career working for popular and fine art ventures alike. The candor and irony of Vallotton’s art has not been lost on art historians, though much of the scholarship has tended to focus on his uneasy relationship to the Nabis and his later painting career, which became the artist’s primary focus after 1899. When studies have addressed his graphic work, it has typically been in the context of his virtuosic handling of the woodcut medium or his prolific illustrations for the popular press. Recently, however, scholars like Richard Thomson and Bridget Alsdorf have undertaken more sustained examinations of Vallotton’s graphic interest in violence and the law. Building on and diverging from these studies, I argue that the seeming violence of Vallotton’s spatial interventions in his police prints—the transposition of space into form and back again—works not as hyperbole but rather as an astute expression of the unpredict-able and shifting experiences with police in the streets of Paris.