Adsorption Of Small Molecules Research Articles

Adsorption and activation of small molecules on boron nitride catalysts.

Hexagonal boron nitride possesses a unique layered structure, high specific surface area and similar electronic properties as graphene, which makes it not only a promising catalyst support, but also a highly effective metal-free catalyst in the booming field of green chemistry. Reactions involving small molecules (e.g., oxygen, low carbon alkanes, nitrogen and carbon dioxide) have always been a hot topic in catalytic research, especially associated with the adsorption and activation regime of different forms of small molecules on catalysts. In this review, we have investigated the adsorption of different small molecules and the relevant activation mechanisms of four typical chemical bonds (OO, C-H, NN, CO) on hexagonal boron nitride. Recent progress on approaches adopted to enhance the activation capacity such as doping, defect engineering and heterostructuring are summarized, highlighting the potential applications of nonmetallic hexagonal boron nitride catalysts in various reactions. This comprehensive investigation offers a reference point for the enhanced mechanistic understanding and future design of effective and sustainable catalytic systems based on boron nitride.

Optimized Adsorption of Small and Medium Molecules by a Biosorbent Based on Hevea Hulls

Optimized Adsorption of Small and Medium Molecules by a Biosorbent Based on Hevea Hulls

Electro-oxidation of alcohols over electrochemically activated nickel alloys for energy-saving hydrogen production

High-valence metal species generated via in situ electrochemical activation effectively enhance the adsorption of small organic molecules on the alloy surface.

Probing the role of surface termination in the adsorption of azupyrene on copper.

The role of the inorganic substrate termination, within the organic-inorganic interface, has been well studied for systems that contain strong localised bonding. However, how varying the substrate termination affects coordination to delocalised electronic states, like that found in aromatic molecules, is an open question. Azupyrene, a non-alternant polycyclic aromatic hydrocarbon, is known to bind strongly to metal surfaces through its delocalised π orbitals, thus yielding an ideal probe into delocalised surface-adsorbate interactions. Normal incidence X-ray standing wave (NIXSW) measurements and density functional theory calculations are reported for the adsorption of azupyrene on the (111), (110) and (100) surface facets of copper to investigate the dependence of the adsorption structure on the substrate termination. Structural models based on hybrid density functional theory calculations with non-local many-body dispersion yield excellent agreement with the experimental NIXSW results. No statistically significant difference in the azupyrene adsorption height was observed between the (111) and (100) surfaces. On the Cu(110) surface, the molecule was found to adsorb 0.06 ± 0.04 Å closer to the substrate than on the other surface facets. The most energetically favoured adsorption site on each surface, as determined by DFT, is subtly different, but in each case involved a configuration where the aromatic rings were centred above a hollow site, consistent with previous reports for the adsorption of small aromatic molecules on metal surfaces.

Effect of pore structure in bismuth metal-organic framework nanorod derivatives on adsorption and organic pollutant degradation.

This study explores the synthesis, characterization, and photocatalytic properties of bismuth metal-organic framework (Bi-MOF) nanorods and their derivatives such as Ag/Bi-MOF and Ag/Bi2O3. Bi-MOF nanorods exhibit significant photocatalytic activity under visible light, with the addition of silver (Ag) enhancing electron-hole pair separation and reducing their recombination. This leads to improved photocatalytic performance, particularly in the degradation of organic pollutants such as Rhodamine B (RhB) and Methylene Blue (MB). The results show that Bi-MOF and its derivatives demonstrate excellent chemical stability and high performance in photocatalytic applications, even when subjected to high temperatures and tested across a wide pH range. The large surface area and microporous structure facilitate selective adsorption of small organic molecules like MB. The pores and large surface area not only provide numerous active sites but also enhance the interaction between reactants and the catalyst surface, improving photocatalytic efficiency. Bi-MOF and its derivatives perform optimally across a broad pH range, from acidic to alkaline environments, where strong oxidizing hydroxyl radicals (·OH) are easily formed, aiding in the effective degradation of organic compounds. The study also shows that Bi-MOF and its derivatives can be reused multiple times without significant loss in performance. This research contributes to the development of advanced materials for environmental remediation, highlighting the potential of Bi-MOF-based nanocomposites in practical applications.

Two-dimensional Janus X2STe (X = B, Al) monolayers: the effect of surface selectivity and adsorption of small gas molecules on electronic and optical properties.

This investigation delves into the adsorption characteristics of CO, NO, NO2, NH3, and O2 on two-dimensional (2D) Janus group-III materials, specifically Al2XY and B2XY. The examination covers adsorption energies and heights, diverse adsorption sites, and molecular orientations. Employing first-principles analysis, a comprehensive assessment of structural, electronic, and optical properties is conducted. The findings highlight NO2 as a prominent adsorbate, emphasizing the Te surface of 2D Al2STe and B2STe materials as particularly adept for NO2 detection, based on considerations of adsorption energy, height, and charge transfer. Additionally, the study underscores the heightened sensitivity of work function changes in the B2STe material. The adsorption properties of all gas molecules, except for NO2, on both materials were determined to be physical. Upon adsorption of the NO2 gas molecule onto the B2STe Janus material, it was observed that the material exhibited weak chemical adsorption behavior, which was confirmed by the adsorption energy, larger band gap change, electron localization function, work function changes and charge transfer from the material. This research provides valuable insights into the gas-sensing potential of 2D Janus materials.

Cooperativity between coordinative unsaturated Fe(iii) and aryl-π electrons in MIL-100(Fe) for adsorption of small molecules

Coordinatively unsaturated sites and aryl-π electrons coorperatively affect the adsorption of aromatics with polar groups.

Capturing Acidic CO2 Using Surface-Active Difunctional Core-Shell Composite Polymer Particles via an Aqueous Medium.

Multifunctional surface-active polymeric composites are attractive materials for the adsorption of various small molecules. Herein, dual-functionalized micron-sized surface-active composite polymer particles were prepared by a three-step process for CO2 adsorption. First, polystyrene (PS) seed particles were prepared via the dispersion polymerization of styrene. PS/P(MMA-AAm-EGDMA) composite polymer particles were then synthesized by aqueous seeded copolymerization of methyl methacrylate (MMA) and acrylamide (AAm) in the presence of an ethylene glycol dimethacrylate (EGDMA) cross-linker. Finally, the amide moieties of PS/P(MMA-AAm-EGDMA) composite particles were converted into an amine-functionalized composite by using the Hofmann degradation reaction. The presence of primary amine groups on the surface of aminated composite particles was confirmed by some conventional chemical routes, such as diazotization and Schiff's base formation reactions. The formation and functionality of the PS seed, PS/P(MMA-AAm-EGDMA), and aminated PS/P(MMA-AAm-EGDMA) composite polymer particles were confirmed by Fourier transform infrared (FTIR) spectra analyses. Scanning electron microscopy (SEM) analysis revealed spherical shape, size, and surface morphologies of the PS seed, reference composite, and aminated composites. The elemental surface compositions, surface porosity, pore volume, pore diameter, and surface area of both composite particles were evaluated by energy-dispersive X-ray (EDX) mapping, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) analyses. Dynamic light scattering (DLS) and ζ-potential measurements confirmed the pH-dependent surface properties of the functionalized particles. The amount of the adsorbed anionic emulsifier, sodium dodecyl sulfate (SDS), on the surface of aminated PS/P(MMA-AAm-EGDMA) is higher at pH 4 than that at pH 10. A vice versa result was found in the case of cationic surfactant, hexadecyltrimethylammonium bromide (HTABr), adsorption. Synthesized aminated composite particles were used as an adsorbent for CO2 adsorption via bubbling CO2 in an aqueous medium. The changes in dispersion pH were monitored continuously during the adsorption of CO2 under various conditions. The amount of CO2 adsorption by aminated composite particles was found to be 209 mg/g, which is almost double that of reference composite particles.

Zeolitic imidazolate framework-8 nanosheet assemblies for high-efficiency small molecule adsorption

Metal-organic frameworks (MOFs) have gained tremendous attention based on the prospect of application-oriented structural tuning. In this study, the surfactant (SDS)-directed hydrothermal synthesis route was adopted for a one-pot, bottom-up synthesis of ZIF-8 spherical assemblies, stacked with externally oriented and intergrown two-dimensional (2D) nanosheets. The as-obtained nanosheet assemblies exhibited good crystallinity, a large surface area, and excellent thermal stability, as shown by XRD, BET, and TGA, respectively. More importantly, the ZIF-8 nanosheet assemblies displayed excellent small molecule adsorption characteristics, especially for the negatively charged dyes, including rose bengal (RB), uni-blue A (UA), and methyl orange (MO). Furthermore, samples showed a pseudo-second-order adsorption mechanism for dye molecules and presented a good fit for Langmuir's and Temkin's adsorption isotherms with an R2 value of 0.98 and 0.94, respectively. Adsorbent–adsorbate electrostatic interaction, nanosheet structures, molecular size and structural aromaticity of the dye, and the presence of SDS functionalities were found as the essential components for the high-capacity dye adsorption as compared with previous studies.

DFT study on adsorption of small gas molecules on Pt-capped armchair and zigzag single-walled carbon nanotubes

The adsorption of small gas molecules (CO, O2 and N2) on Pt-capped armchair and zigzag single-walled carbon nanotubes (SWCNT) has been investigated by density functional theory (DFT) method to determine the potential for gas sensor detection. Results indicated that O2 and N2 molecules with lower adsorption energies (1.66 eV and 1.00 eV) exhibited weak chemical adsorption on SWCNT(4,4)-Pt. However, CO demonstrates strong chemical adsorption with a high adsorption energy of 2.23 eV on SWCNT(4,4)-Pt. The adsorption energy of CO on SWCNT(7,0)-Pt shows the chemical adsorption between CO and SWCNT(7,0)-Pt. In addition, these findings also implied Pt-capped SWCNT could act as small gas molecule sensors to detect CO toxic gas at room temperature. In this system, CO is the electron donor and SWCNT-Pt is the electron receptor. The interaction of Pt and carbon nanotube backbone delocalized π electrons could not only increases the conductivity of SWCNT-Pt, but also enhances the conductivity of SWCNT-Pt-CO. The HOMO-LUMO gap (Δε) of Pt-capped SWCNT(7,0) reduced from 0.43 eV to 0.39 eV after CO adsorption, and the Δε value of Pt-capped SWCNT(4,4) decreased by 0.08 eV. The electrical conductivity of Pt-capped armchair and zigzag SWCNT has increased after the adsorption of CO molecule. The results may be helpful for designing a promising Pt-capped SWCNT-based CO sensors.

Small-Molecule Adsorption Energy Predictions for High-Throughput Screening of Electrocatalysts.

Predicting adsorption energies of small molecules (e.g., OH, OOH, CO) on electrocatalysts involved in electrochemical reactions aids in accelerating the design and screening of electrocatalysts. Avoiding computationally expensive electronic structure calculations increases the speed of such predictions. Geometric and electronic descriptors have been reported to characterize the environment around surface active sites and predict adsorption energies. However, these descriptors cannot be used to predict adsorption energies of small molecules on various substrates, e.g., metal-oxide and nonmetal electrocatalysts. We compare the performance of these descriptors in predicting adsorption energies of small molecules on various electrocatalysts with adsorption energies calculated from density functional theory. We show that two recently developed machine learning algorithms, Crystal Graph Convolutional Neural Network (CGCNN) and Atomistic Line Graph Neural Network (ALIGNN), outperform the reported descriptors based on geometric (coordination number of the active site and its nearest neighbors) and electronic (the bond-energy-integrated orbitalwise coordination number, the electronegativity, and the number of valence electrons of the active site) properties in predicting the adsorption energies. Our results suggest that ALIGNN is almost always more accurate than CGCNN in adsorption energy predictions. The improvement ranges from 0.02 to 1.0 eV in the mean absolute errors (MAEs). We also compare the performance of CGCNN and ALIGNN algorithms in predicting the overpotentials of the oxygen evolution reaction occurring on various electrocatalysts with MAEs of 0.06 and 0.05 V, respectively.

Computational study on the adsorption of small molecules to surface-supported Ni-porphyrins

With their flexible oxidation and spin states, surface-supported metalloporphyrins are attractive building blocks for tuneable, periodic spin interfaces. A technique to manipulate the spin in such systems is based on the adsorption of external gas ligands to the chelated metal center. In the search for promising interfaces, computational studies allow for a convenient scan through potential ligand candidates. In this contribution, we perform density functional theory calculations to investigate the coordination of six exemplary gases (CH4, H2O, NH3, CO, NO and NO2) to nickel tetraphenylporphyrin interfaces. Analyzing the formed complexes, we distinguish four major interaction mechanisms between metal center and ligand: non-interacting, weak field d-splitting, competing surface trans-effect and redox reaction. We find that a surface-mediated redox reaction between a strong π-acceptor (e.g.: NO2) and an unusually reduced metal (e.g.: Ni d9) has the strongest potential to induce spin changes at ambient conditions. Furthermore, we demonstrate how commonly chosen theoretical approximations may influence the interpretation of DFT calculations for metalloporphyrins and their complexes. By highlighting the limitations and possibilities of theoretical approaches, we hope to contribute to a better understanding and more selective harnessing of the special properties of surface-supported metalloporphyrins.

Understanding polymer-porous solid interactions based on small gas molecule adsorption behavior

Understanding the interactions between molten polymers and inorganic porous solids is critical for the heterogeneous catalytic conversion of waste polymers into useful chemicals and the fabrication of nanocomposites and nanostructured polymers. Developing experimental and theoretical approaches to quantify and understand polymer-surface interactions would be extremely useful for the design of new catalysts and composites. Here, we demonstrate that the interfacial energy between molten polystyrene (PS) or polyethylene (PE) and various inorganic surfaces prepared via atomic layer deposition (ALD) such as SiO2, TiO2, WO3, and CaCO3 are correlated with the adsorption of small molecules that bear structural similarity to the repeat unit of the two polymers. The interfacial energy inferred from the dynamics of polymer infiltration into ALD-modified porous solids is compared with the heats of adsorption of small molecules on mesoporous silica (SBA-15) modified with ALD. Both our experimental and computational results suggest a strong correlation between the polymer-solid interfacial energy and the adsorption strengths of their respective small molecules on the same surface. These results highlight that even though there are no specific modes of interaction between the polymers and the inorganic surfaces, their interaction energies vary significantly and are dominated by differences in the enthalpic interactions between each repeat unit and the solid surface. Besides providing a novel method for measuring the polymer-solid interaction, this work bridges the gap between the behavior of macromolecules on solid surfaces and the adsorption properties of small gas molecules. This understanding will have important implications for designing new catalysts for polymer upcycling and composite membranes for gas and potentially polymer separation.

Fabrication of granular MOF@γ-Al2O3 composites as promising dual-function adsorbents for the efficient capture of iodine and dyes

As reported herein, we have designed an effective way to achieve in-situ loading of metal-organic frameworks (MOFs) into the pores of activated γ-Al2O3 particles to prepare low-cost, easy-to-obtain and high-yield granular MOFs composites (GMCs). MOF-5, ZIF-8, Ni-BTC, and Co-BTC have been selected to prepare GMCs via in-situ synthesis methods, thereby leading to the GMCs MOF-5-X@γ-Al2O3, ZIF-8-X@γ-Al2O3, Ni-BTC-X@γ-Al2O3, and Co-BTC-X@γ-Al2O3 (X = NO3 or OAc), respectively. The physical and chemical properties of the as-prepared MOF@γ-Al2O3 GMCs were characterized in detail. The results show that MOF-5-X@γ-Al2O3 and ZIF-8-X@γ-Al2O3 exhibit selective adsorption behavior for anionic dye. The adsorption capacities of MOF-5-X@γ-Al2O3 are 1388.01 mg g−1 (for CR and X = NO3), 1431.25 mg g−1 (for CR and X = OAc), 406.50 mg g−1 (for MO and X = NO3), and 234.16 mg g−1 (for MO and X = OAc), respectively, while the adsorption capacities of ZIF-8-X@γ-Al2O3 are 1426.85 mg g−1 (for CR and X = NO3), 1543.91 mg g−1 (for CR and X = OAc), 477.03 mg g−1 (for MO and X = NO3), and 451.02 mg g−1 (for MO and X = OAc), respectively. Moreover, ZIF-8-X@γ-Al2O3 has high adsorption performance for iodine molecules in solution, and the adsorption capacity reaches 630.63 mg g−1 for ZIF-8-NO3@γ-Al2O3 and 583.92 mg g−1 for ZIF-8-OAc@γ-Al2O3, respectively. This method is universal and can be used as an effective approach to prepare GMCs. In addition, the materials prepared by this method can be widely used in the adsorption of small molecules.

Adsorption of a photoresponsive surfactant at the water–quartz interface: The role of UV irradiation and cucurbit[7]uril

It is a challenge to develop a method of controlling the adsorption of small molecules at different interfaces. Here, we report the photocontrolled adsorption of a surfactant containing an azobenzene group (AZO) at the aqueous solution–quartz interface. The adsorption of the surfactant decreases at the interface and the corresponding adsorption layer becomes more rigid after UV irradiation. In addition, the adsorption of the surfactant at the interface is also decreased by addition of cucurbit[7]uril (Q[7]) due to the host–guest interaction between Q[7] and the surfactant. Adsorption of surfactant is stronger at the aqueous solution–quartz interface than at the aqueous solution–air one. The aqueous solution–quartz interfacial tension (γsl) of the surfactant is decreased by using UV irradiation or Q[7]. The adsorption mechanisms of the surfactant were investigated. Our study provides the methods to control the adsorption of the small molecules at the aqueous solution–solid interface.

Nickel–cobalt oxides decorated Chitosan electrocatalyst for ethylene glycol oxidation

A composite of NiCo2O4 modified electrocatalyst is prepared to enhance the ethylene glycol electrooxidation. Chitosan matrix is used to improve the activity and adsorption ability of the surface to enhance ethylene glycol conversion. A Comparative study is investigated between pristine NiCo2O4 and Chitosan-modified spinel oxide to evaluate the synergistic effect between spinel oxide and chitosan. The composite is studied in an alkaline solution using electrochemistry techniques. The electrochemical activity towards ethylene glycol electrooxidation is studied as a function of anodic oxidation current density. Thus, the oxidation current values for NiCo2O4 and NiCo2O4@Chitosan in 1.0 M EG and 1.0 M KOH are 36 and 42 mA cm−2, respectively. The long-term stability of the electrode is measured by constant potential chronoamperometry. Kinetic parameters like diffusion coefficient, Tafel slope, surface coverage, and transfer coefficient are calculated. The density-functional theory estimates the adsorption of small molecules like ethylene glycol, urea, and carbon monoxide. The adsorption energy is studied on the top site of Ni and Co atoms of NiCo2O4. Forcite model is used to study the interaction between spinel oxide and chitosan. The energy calculation assumes that chitosan is adsorbed on the spinel oxide surface and enhances chitosan's ability for the adsorption of small molecules.

Adsorption of small gas molecules onto the two-dimensional Janus SnSSe monolayer

First-principles electronic structure calculations under density functional theory (DFT), carbon monoxide (CO), nitrogen monoxide (NO), nitrogen dioxide (NO2), ammonia (NH3), and oxygen gas (O2) has been studied to explain the small gas detection capabilities onto the two-dimensional (2D) Janus SnSSe monolayer considering for each different sites. By including van der Waals (vdW) interactions between gas molecules and SnSSe, we have found that NO, NO2 and NH3 from these proposed molecules could be strongly adsorbed on the SnSSe monolayer with large adsorption energies. The charge transfer variation of electronic structures and the partial density of states are discussed. Thus, our results for the potential applications of the SnSSe monolayer in gas sensing provide a theoretical basis as well as an important explanation for the experimental findings.

Dispersion interactions with analytes at the center of graphene nanoflakes turn into electrostatic at the edge

Adsorption of small gaseous molecules on the center and edges of polycyclic aromatic hydrocarbons is studied through density functional theory calculations. The choice of selected functional for the study is based on a benchmarking, where 37 functionals are evaluated at low cost basis set against high level DFT SAPT calculations for adsorption of water molecule on coronene and hexabenzocoronene. After benchmarking, the detailed analysis is performed for the adsorption of H2S, H2O, NH3, CH3OH, HCN, H2O2 and NH2NH2 on coronene at its center and edges. The coronene is chosen to better elucidate the edge effect on the adsorption of analytes. All of the studied analytes are physiosorbed on coronene with adsorption energies ranging from 1 to 6 kcal mol−1. These complexes are stabilized by X-H---π interactions between analytes and coronene surface. The SAPT0 analysis reveals that the X-H---π interactions at the center (non-edge) position of coronene are dominated by dispersion interaction whereas the similar interactions at the edges are dominated by electrostatic interactions. The change from dispersion to electrostatic on edges is attributed to polarization of the systems by C–H polarity differences. The complexes having lone pair---π interactions have unexpectedly repulsive electrostatic interactions in H2S@GNF and NH3@GNF complexes. Electronic properties reveal that coronene surface is highly selective for hydrazine whereas adsorption of other analytes does not bring any significant changes in the electronic structure of coronene. The high selectivity of coronene for NH2NH2 is also evident from the redistribution of densities in frontier molecular orbitals. For NH2NH2@GNF complexes, the HOMOs are present on hydrazine whereas LUMOs are present in coronene. For other analytes, HOMOs and LUMOs are present merely on graphene nanoflake. This high sensitivity of coronene for hydrazine is due to better overlap of frontier molecular orbitals of analyte with coronene.

Photo-Enhanced Chemo-Transistor Platform for Ultrasensitive Assay of Small Molecules.

Compared with traditional assay techniques, field-effect transistors (FETs) have advantages such as fast response, high sensitivity, being label-free, and point-of-care detection, while lacking generality to detect a wide range of small molecules since most of them are electrically neutral with a weak doping effect. Here, we demonstrate a photo-enhanced chemo-transistor platform based on a synergistic photo-chemical gating effect in order to overcome the aforementioned limitation. Under light irradiation, accumulated photoelectrons generated from covalent organic frameworks offer a photo-gating modulation, amplifying the response to small molecule adsorption including methylglyoxal, p-nitroaniline, nitrobenzene, aniline, and glyoxal when measuring the photocurrent. We perform testing in buffer, artificial urine, sweat, saliva, and diabetic mouse serum. The limit of detection is down to 10-19 M methylglyoxal, about 5 orders of magnitude lower than existing assay technologies. This work develops a photo-enhanced FET platform to detect small molecules or other neutral species with enhanced sensitivity for applications in fields such as biochemical research, health monitoring, and disease diagnosis.

Weakened crystalline SnNb2O6 for enhanced performance in photocatalytic H2 production and CO2 reduction.

Low crystalline photocatalysts with the unsaturated active site, such as oxygen vacancy (Ov), is reported to exhibit enhanced adsorption and activation of oxygen-containing small molecules, such as H2O and CO2, thus boosting the activity in photocatalytic H2 evolution and CO2 reduction. However, numerous low-crystalline photocatalysts show unsatisfactory stability due to the easily repaired surface Ov. Herein, three SnNb2O6 with different crystallinity were prepared by hydrothermal approach with similar precursors. Compared with bulk SnNb2O6 and ultra-thin layered SnNb2O6, low-crystalline SnNb2O6 (SNA) exhibits optimal visible-light-driven evolution rates of H2 (86.04 μmolg-1h-1) and CO from CO2 (71.97 μmolg-1h-1), which is mainly ascribed to the fast separation of the photogenerated carriers and enhanced photoreduction power caused by the surface Ov. More importantly, the sharp decrease of photocatalytic activity of SNA after seven cycles is well restored by the hydrothermal treatment of recycled SNA, ascribed to the reactivated surface Ov with the recovered low-crystalline structure. These works thus offer a promising strategy for developing low-crystalline and amorphous photocatalysts with high activity and stability.