Strong Adsorption Interactions Research Articles

New insights into selective depression mechanism of Tamarindus indica kernel gum in flotation separation of fluorapatite and calcite

The similar floatability of fluorapatite (FAp) and calcite (Cal) lead to difficulty in their separation using fatty acid collectors alone. To effectively recover FAp from Cal, a biodegradable polysaccharide, called Tamarindus indica kernel gum (TIKG), was introduced as an efficient Cal depressant in this study, and its depression mechanisms were elucidated. Flotation tests suggested that in sodium oleate (NaOl) system, TIKG strongly depressed Cal but hardly affected FAp, significantly widening the difference in their floatability. Infrared spectroscopy (IR), zeta potential, and wettability analyses indicated that TIKG had strong adsorption interaction with Cal, hindered NaOl adsorption on Cal, and significantly weakened the hydrophobicity of Cal, while the opposite effect was observed for FAp. X-ray photoelectron spectroscopy (XPS) proved that intense interactions of TIKG with Ca sites of Cal enhanced its adsorption on Cal rather than FAp. Extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) calculations confirmed that TIKG reduced the hydrophobic attraction between Cal and bubbles and enhanced the electrostatic repulsion between them, thereby weakening Cal adhesion to bubbles and depressing Cal flotation. Consequently, TIKG achieved effective separation of FAp and Cal, in which 90.21% of Cal was efficiently removed in addition to 83.58% of FAp recovered. Based on these findings, TIKG serves as a Cal depressant for the purification of Cal-bearing phosphate ores by flotation.

Study on the effects of a novel imidazoline siliconophilic collector in the desilication process of magnesite: Separation experiments, adsorption mechanisms, and separation model

This study innovatively introduced heptadecenyl amine ethyl imidazoline quaternary ammonium salt (ODD) as a siliconophilic flotation collector, effectively facilitating the achievement of high-efficiency separation of magnesite from quartz. ODD exhibits unique properties such as high selectivity and environmental friendliness. Through a comprehensive series of experiments, including flotation tests, zeta potential characterization, atomic force microscopy (AFM) imaging, Fourier-transform infrared (FTIR) spectroscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS), the flotation performance and selective adsorption mechanisms of ODD were thoroughly investigated. The experiments demonstrated that at a pH of 7.00 and an ODD concentration of 40 mg/L, quartz achieved a flotation recovery rate of 95.16 %, while magnesite was only 2.99 %, underscoring the high selectivity of ODD in mineral separation. Zeta potential measurements indicated that ODD exhibits strong adsorption interactions with quartz over magnesite. AFM observations confirmed that ODD forms significant adsorption structures on quartz surfaces, in contrast to weaker interactions with magnesite. FTIR analysis further revealed the robust interactions between ODD and quartz through hydrogen bonds and electrostatic forces, which were significantly diminished on magnesite surfaces. ToF-SIMS analysis provided direct evidence of ODD’s selective adsorption on quartz, contributing to a better understanding of the flotation mechanisms involved. This research not only offers a novel approach for the purification of magnesite and effective removal of quartz but also demonstrates the potential of ODD as an eco-friendly collector in mineral processing, potentially advancing a green transformation in the industry. The findings provide a solid theoretical and experimental basis for future industrial applications and innovative development of flotation collectors.

COF/MXene composite membranes compact assembled by electrostatic interactions: A strategy for H2/CO2 separation

H2 and CO2 separation in processes such as reforming hydrocarbons or gasifying fossil fuels using membranes has gained attention as an energy-efficient separation method. Covalent organic frameworks (COFs) are a promising class of organic porous crystalline materials, but their pore sizes (typically >0.5 nm) exceed the kinetic diameters of H2 (0.289 nm) and CO2 (0.33 nm). Herein, we aimed to improve the H2/CO2 selectivity of COF (TpPa-1) membranes by fabricating a two-dimensional composite membrane. This strategy involved the compact assembly of mesoporous COF (TpPa-1) nanosheets facilitated by non-porous MXene (Ti3C2Tx), driven by electrostatic interactions. The objective was to reduce the pore sizes of gas transport channels, enabling molecular sieving for H2/CO2 separation. Additionally, strong adsorptive interactions between CO2 and the COF/MXene composite membranes were leveraged to impede the transport of CO2 molecules. The results demonstrated that the 2D COF/MXene composite membranes with a Ti3C2Tx doping amount of 65 wt% achieved the highest H2/CO2 selectivity of 64.0 at 298 K, which was 5.67 times that of the pristine COF (TpPa-1) membrane. The H2 permeance reached 2.35 × 10−7 mol m−2 s−1 Pa−1, surpassing the latest Robeson upper bound. This innovative strategy not only presents a high-performance candidate for H2/CO2 separation but also provides inspiration for pore regulation of COF compactly assembled with non-porous MXene through electrostatic interactions.

PtZn/ZnO intermetallic catalyst prepared by reactive metal-support interaction for the semi-hydrogenation of 1,4-butynediol

The continuous flow selective hydrogenation of 1,4-butynediol to 2-butene-1,4-diol places high demands on the activity and stability of the catalyst. Herein, an intermetallic PtZn/ZnO catalyst is designed by using the coupling strategy of strong electrostatic adsorption and subsequent reactive metal-support interaction. The TOF value of the Pt/ZnO-H500 catalyst, including PtZn intermetallic compound with electron-rich Ptδ- active sites, reaches 1421.6 h−1, which is almost 8 times higher than that of Pt/ZnO-H200 catalyst with monometallic Pt as active sites. The activation energy of Pt/ZnO-H500 catalyst (35.5 kJ mol−1) is significantly lower than that of Pt/ZnO-H200 catalyst with 49.9 kJ mol−1. In addition, the Pt/ZnO-H500 presents high stability in the continuous flow selective hydrogenation of 1,4-butynediol to 2-butene-1,4-diol for 75 h. These results suggest the intermetallic PtZn/ZnO presents as an alternative Pt-based catalyst without modification by toxic metals or organic matter and is a promising catalyst for directional hydrogenation in fine chemical synthesis.

TiN as Radical Scavenger in Fe─N─C Aerogel Oxygen Reduction Catalyst for Durable Fuel Cell.

Fe─N─C is the most promising alternative to platinum-based catalysts to lower the cost of proton-exchange-membrane fuel cell (PEMFC). However, the deficient durability of Fe─N─C has hindered their application. Herein, a TiN-doped Fe─N─C (Fe─N─C/TiN) is elaborately synthesized via the sol-gel method for the oxygen-reduction reaction (ORR) in PEMFC. The interpenetrating network composed by Fe─N─C and TiN can simultaneously eliminate the free radical intermediates while maintaining the high ORR activity. As a result, the H2O2 yields of Fe─N─C/TiN are suppressed below 4%, ≈4 times lower than the Fe─N─C, and the half-wave potential only lost 15mV after 30 kilo-cycle accelerated durability test (ADT). In a H2─O2 fuel cell assembled with Fe─N─C/TiN, it presents 980mAcm-2 current density at 0.6V, 880mWcm-2 peak power density, and only 17mV voltage loss at 0.80Acm-2 after 10 kilo-cycle ADT. The experiment and calculation results prove that the TiN has a strong adsorption interaction for the free radical intermediates (such as *OH, *OOH, etc.), and the radicals are scavenged subsequently. The rational integration of Fe single-atom, TiN radical scavenger, and highly porous network adequately utilize the intrinsic advantages of composite structure, enabling a durable and active Pt-metal-free catalyst for PEMFC.

Exploring separation mechanism of graphene slit-pore for N2/CH4 in coalbed methane via DFT and MD simulations approaches

A combination of molecular dynamic (MD) simulation and first-principles calculations (DFT) is utilized to explore the separation performance of N2/CH4 in different graphene slit-pore sizes. By performing MD simulations, the absorption selectivity and diffusion coefficients of N2/CH4 are determined, facilitating the analysis of the separation mechanism. The highest selectivity of N2/CH4 is achieved at a slit-pore size of 6.2 Å, attributing to the sieve effect. As increasing pore-size (6.3–7.0 Å), the slit-pore exhibits preferential N2 permeation, determined by strong adsorptive interactions. However, as the pore-size expands further (7.0–10.0 Å), a higher diffusion coefficient indicates that the system is converted to preferential permeation of CH4. Moreover, the separation mechanism of larger slit-pore (>10.0 Å) size is not a mere selective mechanism but a synergistic interplay between adsorption and diffusion. Notably, we demonstrate that the dominant separation mechanism can be transitioned sequentially from size sieving to thermodynamic adsorption and dynamic diffusion by adjusting bilayer graphene slit-pores. This various mechanism determines the crossover preferential permeation for N2 to CH4. Our work primarily focuses on investigating the separation mechanisms of N2/CH4 at different graphene slit-pores, providing theoretical insights and understanding for the experimental separation of coalbed methane using carbon-based materials.

Selective depression of marmatite by sodium alginate in flotation separation of galena and marmatite

In this study, sodium alginate (SA) is proposed as a flotation depressant for the selective separation of galena and marmatite. The effect of SA on the flotation performance of galena and marmatite was investigated using sodium butyl xanthate (SBX) as the collector. The adsorption behavior of SA on the mineral surface was theoretically analyzed. The micro-flotation results demonstrated that the flotation of marmatite could be selectively depressed through the addition of SA before SBX at pH = 11. The contact angle, FTIR, XPS, and zeta potential results demonstrated that SA could be selectively adsorbed on the marmatite surface, thereby hindering the subsequent adsorption of the collector and affecting its flotation. A coordination theory analysis further confirmed that Fe2+ was the active site on the marmatite surface. SA can form π-backbonding with Fe2+ on the surface of the marmatite, resulting in strong adsorption but weaker interactions with Zn2+ and Pb2+. Overall, the high selectivity and environmental compatibility of SA make it an effective green depressant for the flotation separation of marmatite.

How solid–liquid adsorption affects the liquid–vapor interface in pores

AbstractThe augmented Young–Laplace (AYL) equation has been widely used to describe the liquid–vapor interfaces affected by capillarity and adsorption, particularly in nanoporous or clay minerals where strong adsorptive interaction prevails. Still, how adsorption ultimately shapes the liquid–vapor interface in pores remains elusive. All current forms of the AYL equation only consider the attractive van der Waals interaction for complete wetting surface and are mostly an extension of the general equation based on thermodynamic principles without rigorous derivation. In this paper, closed forms of the AYL equations are derived by variational calculus method for two typical pore models considering effects of capillarity and adsorption, based on the minimization of free energy for the equilibrium system. The van der Waals, electrical, and structural forces are incorporated as disjoining pressure into the proposed AYL equations to quantify effects of both attractive and repulsive interactions (hence complete and partial wetting conditions) on interfacial geometry and equilibrium matric potential. Numerical calculation algorithms are established to solve the interfacial geometric profiles and characteristics. The proposed model illustrates a transition region on the interface where geometry and physical characteristics are drastically altered under adsorption compared with sole capillarity. Different surface wettabilities are examined for interface profiles and curvature distributions. An apparent contact angle on the partial wetting surface is identified that is approaching complete wetting as the adsorption dominates when pore size reduces. Water retention and interparticle force demonstrate clear distinctions in their evolution, with different particle sizes and varying half‐filling angles under adsorptive conditions as water volume changes.

Constructing high-performance N-doped carbon nanotubes anode by tuning interlayer spacing and the compatibility mechanism with ether electrolyte for sodium-ion batteries

The graphitic carbon nitride (g-C3N4) as a promising high-nitrogen carbon material has attracted abundant attentions in energy storage field. In this work, the N-doped carbon nanotubes (N-CNTs) are synthesized through a facile one-step pyrolysis of g-C3N4 precursor assisting by Ni catalyst. The obtained N-CNTs possess unique one-dimensional (1D) nanotubular structure, high conductivity, suitable N-doping around 8.73 ∼ 14.72 at.% and tunable interlayer distance up to 0.462 nm which can accommodate sufficiently Na+. Serving as anodes for sodium-ion batteries (SIBs), the resultant N-CNTs exhibit a promising specific capacity of 290.3 mAh⋅g−1 at 0.05 A⋅g−1 and superior rate capability of 164.5 mAh⋅g−1 at 10 A⋅g−1, as well as excellent long-term cycling performance at 0.5 A⋅g−1 for 1000 cycles. Further kinetic analysis and ex-situ Raman reveal the sodium storage mechanism of N-CNTs, which simultaneously combines the diffusion and the dominated capacitive mechanisms together. According to the first principles, density functional theory (DFT) calculations from the perspective of atomic structure further demonstrate that the superior electrochemical performance of N-CNTs is attributed to the strong adsorption interaction between Na+ in ether-based electrolyte and pyrrolic N site. This work provides a facile method to synthesize N-doped carbon nanotube with remarkable electrochemical performance, which is a promising nanotube-structured anode material for the practical application of SIBs.

Cationic covalent organic nanosheets for rapid and effective detection of phenoxy carboxylic acid herbicides residue emitted from water and rice samples

Development of efficient and sensitive adsorbent for capturing phenoxy carboxylic acids (PCAs) from environmental and food samples is necessary because PCAs could threaten human health. Designing nanoparticle with multiple functional groups is beneficial to achieve the strong adsorption interaction and the specific recognition for target compound. In this paper, TpTGCl as an ionic covalent organic framework (ICOF), that could offer plenty of positive charges and hydrogen-bonding sites, was fabricated. TpTGCl achieved quicker, more sensitive enrichment for anionic PCAs. The analysis of binding affinity by density functional theory (DFT) demonstrated that PCAs bonded to TpTGCl primarily via electrostatic attraction, N H···O and O H···O, and C H···π interaction. The quantitative approach indicated low limits of detection (0.016–0.036 ng·g−1 for rice and 0.43–0.78 ng·L-1 for water). Furthermore, successfully determining PCAs emitted from real samples indicated the applicability of TpTGCl.

Theoretical Study of CO Adsorption Interactions with Cr-Doped Tungsten Oxide/Graphene Composites for Gas Sensor Application.

The present study explores the CO adsorption properties with graphene, tungsten oxide/graphene composite, and Cr-doped tungsten oxide/graphene composite using density functional theory (DFT) calculations. The results of the study reveal the Cr-doped tungsten oxide/graphene composites, g-CrWn–1O3n (n = 2 to 4), to have a lowered highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap, high surface reactivity, and a strong cluster–graphene binding energy, hence exhibiting a strong adsorption interaction with CO. The CO adsorption interaction shows physisorption properties by having a greater tendency for Mulliken and natural bond orbital (NBO) charge transfer supported by a strong physisorption interaction toward the g-CrWn–1O3n (n = 2 to 4) composite with HOMO–LUMO energy gaps of −0.638, −0.486, and −0.327 eV, respectively. The calculated photoelectron spectroscopy (PES) and infrared spectra combined with the visualized electrostatic potential and contour line confirm the population density of the physisorption interaction. The calculated results show that the g-CrWn–1O3n composite achieves a greater sensing ability by possessing the highest sensitivity, adsorption, and desorption characteristics for n = 2 (g-CrWO6 composite). In conclusion, Cr-doped tungsten oxide/graphene has high sensitivity toward CO gas.

Intermetallic PdZn nanoparticles catalyze the continuous-flow hydrogenation of alkynols to cis-enols

Designing highly active and stable lead-free palladium-based catalysts without introducing surfactants and stabilizers is vital for large-scale and high-efficiency manufacturing of cis-enols via continuous-flow semi-hydrogenation of alkynols. Herein, we report an intermetallic PdZn/ZnO catalyst, designed by using the coupling strategy of strong electrostatic adsorption and reactive metal-support interaction, which can be used as a credible alternative to the commercial PdAg/Al2O3 and Lindlar catalysts. Intermetallic PdZn nanoparticles with electron-poor active sites on a Pd/ZnO catalyst significantly boost the thermodynamic selectivity with respect to the mechanistic selectivity and therefore enhance the selectivity towards cis-enols. Based on in situ diffuse reflectance infrared Fourier-transform spectra as well as simulations, we identify that the preferential adsorption of alkynol over enol on PdZn nanoparticles suppresses the over-hydrogenation of enols. These results suggest the application of fine surface engineering technology in oxide-supported metal (particles) could tune the ensemble and ligand effects of metallic active sites and achieve directional hydrogenation in fine chemical synthesis.

Epoxy coating as effective anti-corrosive polymeric material for aluminum alloys: Formulation, electrochemical and computational approaches

In this work, a formulation based on epoxy coating composed of DGEBA cured with polyaminoamide has been used as anti-corrosive material for aluminum alloys (2024-T3, 5086 and 7075-T6) substrates for accelerated corrosion assays. The epoxy coating on aluminum alloys samples was tested in 3.0 wt% NaCl solution using salt spray test chamber. The anticorrosive behavior of the aluminum alloys samples under these conditions was monitored by impedance diagrams Bode and Nyquist plots and theoretical studies by DFT, MC and MD. The results showed that the evolution of the impedance modulus plots |Z|0.01 Hz values of the epoxy coating applied on AA2024-T3, AA5086 and 7075-T6 samples began from 2.63, 1.46 and 0.43 MΩ.cm2 after 1 h of immersion and finally reached 0.27, 0.26 and 0.24 MΩ.cm2 after 4392 h of immersion, respectively. The lessening of impedance with submersion time means that the electrolyte scatters into the epoxy coating and diminishes the boundary properties of the film. DFT calculations were used to determine the coatings adsorption centers. Additionally, the Monte Carlo and Molecular Dynamics calculations support the coatings strong adsorption interaction with the metal surface, providing molecular evidence for the epoxy molecule's adsorption behavior (geometry) and adsorption energy on the aluminum surface. Theoretical results (DFT, MC, and MD) corroborate the experimental results.

Preparation of a biomimetic Cu(II) protoporphyrin magnetic nanocomposite and its application for the selective adsorption of angiotensin I

In this study, a novel Cu(II) protoporphyrin polymer-based magnetic nanocomposite, CuPPIX@MNPs, is obtained by electropolimerization of metalloporphyrin IX dimethyl ester onto Fe3O4 nanoparticles in organic medium. CuPPIX@MNPs are proposed as a biomimetic magnetic solid-phase extraction sorbent with high selectivity toward peptides containing histidine residues. The nanocomposite was characterized by SEM/EDX, TEM and FTIR. Magnetic saturation values for magnetic nanoparticles (MNPs), naked MNPs (74 emu g−1) and CuPPIX@MNPs (43 emu g−1), were obtained at 300 K.At pH 7, CuPPIX@MNPs show selective adsorption toward angiotensin, about 90% adsorption vs 49 % adsorption for naked MNPs. In order to evaluate the mechanisms involved in angiotensin adsorption onto CuPPIX@MNPs, different adsorption–desorption conditions and the model that describes the adsorption isotherm for both sorbents were determined. The parameters of fitting analyses were qm = 2.55 mg g−1 and b = 0.012 L mg−1 by Langmuir model for naked MNPs, and KF = 0.4105 mg g−1 and n = 2.09 by Freundlich model for CuPPIX@MNPs. This indicates that CuPPIX@MNPs have heterogenous adsorption surface and different adsorption sites. The Freundlich exponent greater than 1 suggests strong adsorption interactions between angiotensin and this magnetic solid-phase extraction (MSPE) nanomaterial. The selectivity the CuPPIX@MNPs toward angiotensin was evaluated in an aqueous mixture composed of four peptides by capillary electrophoresis.Finally, the intrinsic characteristics of the magnetic substrate, the stable inclusion of the copper in an environment that favors the interaction with histidine residues, in addition to easy and reproducible preparation of the nanocomposite offer a very interesting strategy for the design of the MSPE sorbents.

Enhancing Selective Adsorption in a Robust Pillared-Layer Metal-Organic Framework via Channel Methylation for the Recovery of C2-C3 from Natural Gas.

Here, we reported a strategy for channel methylation to construct a robust ultramicroporous metal-organic framework (MOF) Ni(TMBDC)(DABCO)0.5 through hydrothermal synthesis method and investigated its adsorption performance for recovering ethane (C2) and propane (C3) from natural gas. The as-synthesized Ni(TMBDC)(DABCO)0.5 featured ultramicroporosity with a uniform pore size of 0.5 nm. The resulting sample showed a strong adsorption interaction with C3H8 and C2H6, and its C3H8 adsorption capacity at a low pressure of 1 kPa was up to 2.80 mmol/g and its C2H6 adsorption capacity at a low pressure of 10 kPa reached as high as 2.93 mmol/g, exhibiting strong binding affinity for ethane and propane. The enhanced adsorption can be attributed to the presence of the dense and accessible methyl and methylene groups in the channels of the sample. Grand Canonical Monte Carlo (GCMC) simulations also confirmed that the methylene groups from the DABCO pillar and the methyl groups from the TMBDC ligand play an important role in enhancing the adsorption of ethane and propane. Its ideal adsorbed solution theory (IAST)-predicted selectivity of C2H6/CH4 reached unprecedentedly 29, much higher than most of the reported data for MOFs. The stability test confirmed that the crystal structure of Ni(TMBDC)(DABCO)0.5 still remained intact after it was exposed to moist air with a relative humidity of 100% for days. The breakthrough experiment demonstrated that the CH4/C2H6/C3H8 ternary mixture was completely separated using a fixed bed of Ni(TMBDC)(DABCO)0.5 at ambient temperature, showing a great potential for recovering the low content of ethane and propane from natural gas.

DFT study of gas adsorbing and electronic properties of unsaturated nanoporous graphene

ABSTRACT The interaction sensitivity of unsaturated nanoporous graphene toward a series of gas molecules (O2, NO, NO2 and CO) was investigated by the first-principle calculation based on density functional theory. The most stable geometry configuration, adsorption energy, charge transfer, and electronic density of states of the complexes were thoroughly investigated, in which the gases were adsorbed on the unsaturated nanoporous graphene. It was found that all the gas molecules are strongly chemisorbed on the unsaturated nanoporous graphene. The enhanced adsorption energy and large charge transfer demonstrated a strong chemical adsorption interaction of gas molecules with the nanoporous graphene sheet. However, the electronic properties of the unsaturated nanoporous graphene are not very sensitive to all the gas molecules. It is suggested that the unsaturated nanoporous graphene might be suitable for sensing O2 and CO, while it could not be used for the NO and NO2.

Investigation of 2,2′-diaminodiethyl disulfide for mild steel protection in acid solution

Inhibition performance of 2,2′-diaminodiethyl disulfide (DA) was studied against mild steel (MS) corrosion in 0.5 M HCl. Electrochemical impedance spectroscopy (EIS), potentiodynamic (PD) polarization measurements were utilized to investigate the influence of inhibitor concentration and temperature on efficiency, as well as explanation of inhibition mechanism. Scanning electron microscopy (SEM) analysis was utilized to investigate the surface damages due to corrosion, in the absence and presence of inhibitor molecules. PD data revealed that the studied molecule exhibits mixed type inhibitor behavior on steel surface. Moreover, the calculated free adsorption energy (ΔGadso) value is 38.45 kJ mol−1, which indicates to strong adsorptive interaction by both physical and chemical means. UV–Visible study results supported the idea that there is strong interaction between the surface with the molecule, via its –S and –N atoms. As a consequence, 91.7% inhibition efficiency was determined in presence of 1.0 mM DA.

Controlled-synthesis of alumina-graphene oxide nanocomposite coupled with DNA/ sulfide fluorophore for eco-friendly “Turn off/on” H2S nanobiosensor

Hydrogen sulfide (H2S) is a toxic environmental pollutant and crucial gas-signaling agent of human physiology. There is an urgent need for developing a sensitive and selective detection approach for H2S. Herein, a novel turn off/on response approach using γ-Al2O3 nanorods anchored on the surface graphene oxide (GO) nanosheets and coupled with DNA/sulfide fluorophore (SF) for H2S detection at room temperature was developed. The fluorescent fluorophore, DNA/SF, remains quenched on the super quencher γ-Al2O3–GO hybrid surface. In the existence of H2S, DNA/SF fluorophore was detached from γ-Al2O3–GO hybrid surface because of the strong physical adsorption interaction between H2S molecules and γ-Al2O3–GO surface. The recovered fluorescence intensity gave direct insight about H2S concentration in the medium. The developed γ-Al2O3–GO/DNA/SF nanobiosensor shows high sensitivity with 75 to 2.5 μM linear detection range of H2S, and a high binding constant of 9.8 × 103 M−1. The nanobiosensor is very selective toward H2S in the presence of various interfering anions and thiols and used for H2S detection in real water samples. γ-Al2O3–GO/DNA/SF nanobiosensor provides a cheap, simple, and highly selective H2S detection method at room temperature.

Hierarchically structured hollow bimetallic ZnNi MOF microspheres as a sensing platform for adenosine detection

This work reported a label-free electrochemical aptasensor based on bimetallic ZnNi metal–organic framework (MOF) microspheres for highly efficient detection of adenosine (AD). Three ZnNi MOFs with different morphologies were prepared by regulating the molar ratio of Zn2+ to Ni2+ (1:1, 1:2, and 1:3) in the preparation processes. The ZnNi MOF (1:2)-based aptasensor displayed excellent sensing performance toward AD compared with ZnNi MOF (1:1) and ZnNi MOF (1:3)-based ones due to its higher electrochemical activity and stronger binding interaction between the aptamer strands and hierarchically nanostructured hollow microspheres. The proposed aptasensor exhibited a low detection limit of 20.32 fg·mL−1 for AD within a wide linear range from 0.0001 to 100 ng·mL−1. This aptasensor also showed excellent selectivity, acceptable reproducibility, high stability, good regenerability, and favorable applicability for AD detection in human serum. The remarkable biosensing performance was primarily attributed to the strong adsorption interactions of Ni2+ to aptamers, special morphology of materials, and the synergistic effect of Zn2+/Ni2+ in MOF matrixes. The rational construction of bimetallic ZnNi MOFs provided a promising sensing platform for sensitive detection of AD and further, showed great potentials in clinic diagnosis.

Theoretical Investigation on the Single Transition-Metal Atom-Decorated Defective MoS2 for Electrocatalytic Ammonia Synthesis.

Using density functional theory calculations, we explored the potential of defective MoS2 sheets decorated with a series of single transition-metal (TM) atoms as electrocatalysts for the N2 reduction reaction (NRR). The computed reaction free-energy profiles reveal that the introduction of embedded single TM atoms significantly reduces the difficulty to break the N≡N triple bond and thus facilitates the activation of inert nitrogen. Onset potential close to -0.6 V could be achieved by anchoring various TMs, such as Sc, Ti, Cu, Hf, Pt, and Zr, and the formation of the second ammonia molecule limits the overall process. The Ti-decorated nanosheet possesses the lowest free-energy change of -0.63 eV for the potential determining step. To better predict the catalysis performance, we introduced a descriptor, φ, which is the product of the number of valence electron and electronegativity of the decorated TM. It shows a good linear relationship between the d-band center and binding energy of nitrogen, except for those metals with less than half-filled d-band. Although the metals in Group IIIB and IVB have strong adsorption interactions with N atoms, the Gibbs free-energy changes for desorption of the second ammonia are unexpectedly low. The selectivity of these systems toward nitrogen reduction reaction (NRR) is also significantly improved. Therefore, those defective MoS2 decorated with Sc, Ti, Zr, and Hf are suggested as promising electrocatalysts for NRR, for their both high efficiency and selectivity.