Strong Physisorption Research Articles

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.

Molecular Modeling Study to the Relation between Structure of LPEI, Including Water-Induced Phase Transitions and CO2 Capturing Reactions

A molecular modeling study was carried out on linear polyethyleneimine (LPEI) to determine the CO2 capturing process taking into account structural changes of the material at various amounts of H2O. Until now, CO2 capture by LPEI was described as a combination of carbamic and carbonic acid formation. It was found that humidification below the melting point of LPEI leads to the formation of an LPEI/0.5H2O type of phase. Such a type of phase leads to CO2 capture exclusively via carbonic acid formation, stabilized by secondary amines via ammonium bicarbonate and H-bridged amine carbonic acid complexes. Both the strong physisorption CO2 complex and the low activation barrier for carbonic acid formation contribute to the overall process. Only in the absence of H2O, carbamic acid formation is possible. Thus, under CO2 capturing process conditions, carbonic acid formation seems to be the only option as H2O will be present in flue gas.

Research on CO2 adsorption performances of metal-doped (Ca, Fe and Al) MgO

Capturing CO2 from the atmosphere is key to solving the global warming problem/transforming it into chemical products. Therefore, in this study, CO2 adsorption features of Ca/Fe/Al doped MgO are investigated via density functional theory (DFT) calculations. With adsorption structures, adsorption energies, partial density of states (PDOS), electron cloud distribution and transition state (TS) processes, CO2 adsorption mechanisms of doped MgO for sustainable and recyclable utilization are clearly demonstrated. According to calculation results, the average CO2 adsorption energies of doped MgO increase in sequence of Ca-doping, Fe-doping and Al-doping, which corresponds to relevant chemical valence (+2 for Ca, +2/+3 for Fe and +3 for Al). In the meantime, it is discovered that the more doping atoms are embedded in MgO, the higher average CO2 adsorption energies of doped MgO are, which further verifies the adsorption enhancement effects of doping atoms. What is more, TS energy barriers of CO2 adsorbing on some sites of Al-doped MgO are calculated to investigate chemisorption structures being transformed into strong physisorption, which could help to cut down energy consumption during cyclic use of adsorbents. The results of this study would supply significant information for realizing massive and sustainable CO2 adsorption application of MgO in some industries.

DFT study of CO2 adsorption properties on pristine, vacancy and doped graphenes

Through DFT calculation, the adsorption properties, geometry changes and charge transfer of CO2 molecule on pristine graphene (PG), vacancy defect graphene (VG) and doped graphene (DG) are investigated. The results show that different adsorption forms of CO2 on PG and VG are physisorption through van der Waals force with few charge transfer. On PG, it shows weak physisorption. On VG, it is strong physisorption. Therefore, the appearance of defect can increase adsorption ability for CO2. When CO2 parallel to the H-site of PG and monoatomic vacancy graphene (M-VG), the adsorption structure is the most stable, which is similar with literature. On DG, N-doped can not enhance the adsorption and charge transfer ability, and this result is consistent with co-doped system of Cu/N-DG and Ni/N-DG. While Cu or Ni-doped can increase adsorption and charge transfer ability, and decrease the adsorption distance. When CO2 on Cu-DG, Cu/N-DG, Ni-DG and Ni/N-DG, these adsorption processes are chemisorption process in which new chemical bonds are formed. Adding defects and Cu/Ni atoms to graphene can serve as an excellent adsorption material for the preparation of catalysts to activate CO2. Among them, Cu-DG has the best performance. Moreover, through electronic band structures and density of states analysis, we find that vacancy and Cu/Ni-doped can open the band gap, increase the width of the pseudo-gap, and strengthen the adsorption and activation ability of CO2 gas molecular in heterogeneous catalytic reaction based on graphene support.

Significant Enhancement of the Polarization Holographic Performance of Photopolymeric Materials by Introducing Graphene Oxide.

Relying on various defects and functional oxygen-containing groups on the basal planes, graphene oxide (GO) is commonly unitized for intimate mixing with a polymer matrix to fabricate high-performance nanocomposite polymeric materials with the characteristics of graphene. Herein, by introducing GO nanosheets in a phenanthraquinone-doped polymethyl methacrylate (PQ/PMMA) photopolymer, we demonstrate that the polarization holographic diffraction efficiency of nanocomposite materials can be dramatically enhanced up to nearly 10 times and the photosensitivity can also be enhanced by more than 3 times. Experimental observations reveal that the incorporation of GO nanosheets serves as a polymerization initiator not only to promote the polymerization of MMA monomers and induce the drafting behavior of the PMMA polymer on its surface but also to effectively modulate the molecular weight of the PQ/PMMA photopolymer by adjusting the doping concentration of GO nanosheets. The current study, for the first time, demonstrates that the modulation of molecular weight for PQ/PMMA photopolymers here exerts a significant impact on their holography performance. In addition, due to the strong physisorption of PQ photosensitizers onto GO nanosheets, the aggregation of PQ around GO-graft-PMMA also facilitates the formation of GO-graft-PMMA/PQ and is beneficial to the enhancement of holographic performance. The emergence of GO-graft-PMMA/PQ nanocomposite materials here is expected to fulfill the requirement of high-performance polarization-sensitive materials in the field of polarization holographic data storage and provide a facile but effective nanocomposite doping strategy to modulate the holographic performance of photopolymers from micro- and mesoscopic levels.

Comprehensive investigations of interaction properties of polylactic Acid‒Attapulgite composite by reactive molecular dynamics simulations and dispersion corrected DFT calculations

We have evaluated the interactive nature of attapulgite (ATB) and PLA (Poly (lactic acid)) by dispersion corrected density functional theory (DFT‒D2) calculations and reactive molecular dynamic (MD) simulations. Our DFT‒D2 findings revealed that PLA interacted strongly with pristine and calcined ATB surface with interaction energies of -4.706 and -10.101 eV, respectively. The accuracy of obtained interaction energies has been validated against the advanced second order Møller–Plesset level. Atom‒in‒molecule (AIM) analysis illustrated that the interactive nature was typical for the chemisorption (high polar and partially covalent) in PLA/calcined ATB and strong physisorption (hydrogen bonding) in PLA/pristine ATB system. Finally, reactive MD simulations at room temperature showed that as result of strong attraction between PLA and ATB surface a clear approaching and bonding procedure between O atom from PLA and H/Al atom of ATB was observed in pristine/calcined crystal.

SO2 absorption in highly efficient chemical solvent AChBr + Gly compared with physical solvent ChBr + Gly

Deep eutectic solvents (DESs) have been identified as optimal gas absorbents. A tertiary amine-containing task-specific DES AChBr+Gly and a conventional DES ChBr+Gly have been designed, prepared and used to capture SO2. It is found that absorption capacity of 3.74 and 2.97 mol of SO2 per mole of DES can be obtained by AChBr+Gly and ChBr+Gly, respectively, at 293.2 K and 1 bar. When SO2 partial pressure was decreased to 0.01 bar, the capacity decreased to 0.93 and 0.13 mol SO2 of per mole of AChBr+Gly and ChBr+Gly, respectively. Mechanism and thermodynamic studies show that absorption by former absorbent includes physisorption, quasi-chemisorption (a strong physisorption) and chemisorption, while absorption by later absorbent only includes physisorption and quasi-chemisorption. Two equations were first proposed for the description of SO2 absorption. In these equations, the physisorption capacity is correlated with Henry's law, and the quasi-chemisorption and chemisorption are correlated with the quasi-chemical equilibrium constant of halogen···SO2 interaction and the chemical equilibrium constant of tertiary amine···SO2 interaction, respectively. In addition, the corresponding enthalpy change, entropy change, and Gibbs energy change have been calculated and discussed.

Theoretical studies on the electronic and optoelectronic properties of DNA/RNA hybrid-metal complexes

The electronic and optoelectronic properties of DNA/RNA functionalized conductive metal adatoms were studied using DFT and TDDFT methods. Four hybrid structures were selected from the experimental work on RNA microchips. The occupied number of states by the system at each energy level were studied by Density of States (DOS). Atom-in Molecules (AIM) analysis and Noncovalent Interaction (NCI) PLOT were used to study the interaction in these complexes. Results indicated that HOMO-LUMO (HL) Gap is larger for C1–C4 complexes as compared to the HL gap for DNA/RNA hybrid-metal interacted complexes. This clearly indicates strong DNA/RNA-metal interaction, which is also observed in NCIPLOT analysis. Al and Au are chemically bonded to DNA/RNA hybrids, while the adsorption of Cu is between weak chemisorption and strong physisorption. The interacted bond distance of DNA/RNA-(Al, Cu) complexes are smaller than the bond distance of DNA/RNA-Au complexes. AIM analysis predicts noncovalent interaction for the studied complexes. TDDFT results indicate that few complexes can be used as fluorescent biomarkers as the absorption and emission wavelength lies in the visible region.

Quantitative analysis of the formation mechanism of tightly bound rubber by using carbon-coated alumina nanoparticles as a model filler

Using carbon-coated alumina nanoparticles as a model filler for styrene-butadiene rubber (SBR), rubber composites with different carbon surface chemistry were prepared and the bound rubber thus formed in each composite was analyzed in relation to the carbon surface chemistry. The present approach provides quantitative understanding of the rubber-carbon interface at the molecular level and thereby the formation mechanism of tightly bound rubber during a mixing process with SBR is proposed as follows. At first, the strong physisorption of SBR occurs and almost all the filler surface (99.8% of the total surface) is covered with a single-molecule layer of physisorbed SBR. The polymer radicals formed in the process are then gradually allowed to react with the H-terminated edge sites on the exposed carbon surface (0.2% of the total surface) and the resulting free edge sites are chemically-bonded to the other polymer radicals to form the chemisorbed polymer. Moreover, the unique structure of the present composites makes it possible to analyze the state of tightly bound rubber with the conventional differential scanning calorimetry, which strongly suggests that the tightly bound rubber is indeed in a glassy state.

Puffed carbon/titanium carbide matrix to improve the electrochemical performance of sulfur cathode

Conductive titanium carbide (TiC) nanoparticles implanted into puffed rice carbon (PRC), forming a highly porous TiC/PRC host, is reported. Typically, PRC possesses cross-linked nano/microsheets with three-dimensional (3D) structure and large surface area, prepared by a puffing strategy. Moreover, TiC is further introduced into the carbon matrix (TiC/PRC) with excellent compatibility. TiC plays a dual role for not only enhancement of conductivity but also adsorption of soluble lithium polysulfides. When employed as a host of sulfur in LSBs, the designed TiC/PRC-S cathode exhibits improved rate capability, high reversible capacity of 1223.0 mA h g−1 at 0.1 C, and long cycling life of 884.5 mA h g−1 after 200 cycles. The excellent electrochemical performance is ascribed to the synergetic work of porous PRC architecture and polar conductive TiC with strong physisorption and chemisorption of soluble polysulfide simultaneously.

Relevance of metal (Ca versus Mn) embedded C2N for energy-storage applications: Atomic-scale study

The suitability of embedding metal atoms (Ca versus Mn) in the pores of C2N to be employed as the anode material for metal-ion battery applications is studied using density-functional theory. The effect of single-atom catalyst (SAC) versus dimer-atom catalyst (DAC) on the uptake catalyst capacity is put under focus. Our results show that both metal atoms exhibit very strong interactions with the pyridinic-nitrogen pore and show the ability of the pore to accommodate either a single Ca atom or a dimer of Mn atoms within its membrane-plane. While the theoretical irreducible capacitance in case of SAC Ca catalyst is limited to about 200 mAhg−1, it can exceed this value in case of DAC-Mn catalyst to reach 1110 mAhg−1. Regarding the adsorption, the H2 molecule exhibits strong physisorption on Ca-catalyst and moderate chemisorption on Mn-catalyst, with an adsorption energy increasing from SAC to DAC cases. The SAC of Mn is found not only concurrent candidate to Ca for energy-storage applications but further promising for platform of reusable hydrogen gas-sensors with very low recovery time (i.e., τ « 1 s). Our findings are in good agreement with the available experimental data and theoretical results.

A Hybrid Metal-Organic Framework-Reduced Graphene Oxide Nanomaterial for Selective Removal of Chromate from Water in an Electrochemical Process.

Hexavalent chromium Cr(VI) is a highly toxic groundwater contaminant. In this study, we demonstrate a selective electrochemical process tailored for removal of Cr(VI) using a hybrid MOF@rGO nanomaterial synthesized by in situ growth of a nanocrystalline, mixed ligand octahedral metal-organic framework with cobalt metal centers, [Co2(btec)(bipy)(DMF)2]n (Co-MOF), on the surface of reduced graphene oxide (rGO). The rGO provides the electric conductivity necessary for an electrode, while the Co-MOF endows highly selective adsorption sites for CrO42-. When used as an anode in the treatment cycles, the MOF@rGO electrode exhibits strong selectivity for adsorption of CrO42- over competing anions including Cl-, SO42-, and As(III) and achieves charge efficiency (CE) >100% due to the strong physisorption of CrO42- by Co-MOF; both electro- and physisorption capacities are regenerated with the reversal of the applied voltage, when highly toxic Cr(VI) is reduced to less toxic reduced Cr species and subsequently released into brine. This approach allows easy regeneration of the nonconducting Co-MOF without any chemical addition while simultaneously transforming Cr(VI), inspiring a novel electrochemical method for highly selective degradation of toxic contaminants using tailor-designed electrodes with high affinity adsorbents.

Adsorption of toxic gas molecules on the pre-oxidized Cu2Si nanosheet – A DFT study

Using first principles calculation, we investigated the adsorption mechanism of small toxic gas molecules (NO, NO2, NH3, CO, CO2, and SO2) by employing van der Waals (vdW) corrections to study the structural, electronic, magnetic and gas sensing properties of pre-oxidized Cu2Si nanosheet. The sensing mechanism was explored in practical oxygen-rich condition to understand its possibility as a gas sensor. All gas molecules except NO were weakly physisorbed on the pre-oxidized Cu2Si nanosheet, while NO gas molecule shows strong physisorption. It is fascinating to see that all the gas molecules except O2 act as charge donors, and also adsorption of NO and NO2 induces small magnetic moments on the non-magnetic pre-oxidized Cu2Si nanosheet. The value of total magnetic moment for NO is 0.56 μB/cell and for NO2 is 0.01 μB/cell, respectively. It is observed that the work function increases by about 2.8% for pre-oxidized condition. Further, the adsorption of gas molecules on the pre-oxidized Cu2Si nanosheet indicates a drop in the work function for NO, CO, CO2 and rise for NO2, NH3, SO2. Admissible values of adsorption energy assure short recovery time making pre-oxidized Cu2Si nanosheet as an effective nano sensor for harmful toxic gases.

Phosphorene: A promising candidate for H2 storage at room temperature

Owing to the existence of periodic channels in phosphorene, this 2D material can be a good candidate for room temperature reversible hydrogen storage. The density functional theory calculations (DFT), including van der Waals interactions (vdW-DF2) coupled with the cooper exchange functional (C09), has been applied to study the potential of phosphorene as a new 2D material for hydrogen storage. Our results show that the adsorption energy (−292 to −277 meV) of H2 on phosphorene is appropriate for storage. The analysis of diffusion pathways between different physisorbed states on phosphorene shows that a single hydrogen molecule diffuses very easily along the open channel (less than 1 meV along the zigzag direction), as compared to 14 meV for diffusion across the channels (along the armchair direction). The potential energy surfaces for the dissociative chemisorption of H2 was computed on highly symmetric sites of phosphorene and the highest activation barrier was found to be 2.77 eV. The very large dissociation energy coupled with a strong physisorption of H2 on phosphorene and facile diffusion, makes this 2D material a promising candidate for H2 storage at room temperature.

Molecular Interactions of MeOH and EtOH with Black Phosphorus Monolayer: A Periodic Density Functional Study

The adsorption properties of black phosphorus monolayer (BPML) nanostructure toward methanol and ethanol were investigated using periodic density functional theory calculations. Despite the subtle in-plane distortions, the integrity of the BPML nanostructure was preserved. All complexes revealed interactions of pure electrostatic nature as evinced by the LOL and QTAIM data. The band gap was slightly enlarged, and both valence and conduction bands moved upward upon the detection of both alcohols. These observations implied that the perfect surface of the semiconductor could be considered a work function sensor for the alcohol molecules. The adsorption energy ranged from –0.13 to –0.36 eV, with ethanol presenting relatively stronger physisorption.

Molecular Dynamics Simulation to Investigate the Adhesion and Diffusion of Asphalt Binder on Aggregate Surfaces

Asphalt-aggregate interface properties are considered to play a crucial role in asphalt mixture. To better understand the detailed binding mechanism, the present study analyzed the adhesion and diffusion of asphalt binder on mineral surfaces at a nanoscale based on molecular dynamics simulation. A 12-component AAA-1 asphalt model and five oxide models were generated to represent asphalt binder and mineral aggregates, respectively. The effectiveness of these models was validated by comparing the physical properties of the model with the values reported in the literature. The binding energy and diffusion coefficient obtained were examined to characterize the adhesion and diffusion of asphalt on different mineral surfaces. The results indicated that van der Waals energy played the main role in forming the strong physisorption of asphalt on the mineral surface. Among all four fractions of asphalt, asphaltene made a great contribution to the adhesion of asphalt on the mineral surface. It was also found that the work of adhesion between asphalt and five oxides ranked MgO > CaO > Al2O3 > Fe2O3 > SiO2. The content of MgO and CaO in mineral aggregates can be further adopted as an index to evaluate and classify mineral aggregates during asphalt mixture design. Meanwhile, asphalt mobility does not entirely rely on the molecular mass but also depends strongly on the medium it adsorbed into and interaction energy. This work provides a fundamental understanding of the adhesion and diffusion of asphalt binder on the mineral aggregate surface at the atomistic scale.

Area-Selective Atomic Layer Deposition of ZnO by Area Activation Using Electron Beam-Induced Deposition

Area-selective atomic layer deposition (ALD) of ZnO was achieved on SiO2 seed layer patterns on Hterminated silicon substrates, using diethylzinc (DEZ) as the zinc precursor and H2O as the coreactant. The selectivity of the ALD process was studied using in situ spectroscopic ellipsometry and scanning electron microscopy, revealing improved selectivity for increasing deposition temperatures from 100 to 300 °C. The selectivity was also investigated using transmission electron microscopy and energy-dispersive X-ray spectroscopy. Density functional theory (DFT) calculations were performed to corroborate the experimental results obtained and to provide an atomic-level understanding of the underlying surface chemistry. A kinetically hindered proton transfer reaction from the H-terminated Si was conceived to underpin the selectivity exhibited by the ALD process. By combining the experimental and DFT results, we suggest that the trend in selectivity with temperature may be due to a strong DEZ or H2O physisorption on the H-terminated Si that hampers high selectivity at low deposition temperature. This work highlights the deposition temperature as an extra process parameter to improve the selectivity.

Two-dimensional delafossite cobalt oxyhydroxide as a toxic gas sensor

To the chain of development of 2D materials, recently synthesized ultrathin cobalt oxy-hydroxide (CoOOH) nano sheets gain potential interest due to its structural, electronic and other properties. We have studied the interaction mechanism of two toxic gases hydrogen peroxide (H2O2) and ammonia (NH3) adsorbed over 2D CoOOH to understand the role of 2D CoOOH as a toxic gas sensor. We employ first principles based dispersion corrected density functional calculations to study the sensing behavior of 2D CoOOH towards H2O2 and NH3 by calculating adsorption energy, electronic band structure, density of states (DOS) and work function. The electronic band structure, DOS and work function of 2D CoOOH are modulated after adsorption of H2O2 and NH3 molecules. Adsorption of gas molecules confirms the sensing behavior of 2D CoOOH towards these molecules and depicts its use in a sensing device. The full phonon dispersion curves and phonondensity of states reveal the dynamical stability of 2D CoOOH. The calculated adsorption energy of H2O2 and NH3 molecules is −0.532 and −0.460 eV respectively which indicates the strong physisorption of these gases over 2D CoOOH. The ultrafast recovery time of 1239 and 1203 ns respectively were found for H2O2 and NH3 on 2D CoOOH. The work function which is 6.29 eV found for 2D CoOOH, decreases to 5.63 eV for H2O2 as it follows the reduction process on 2D CoOOH, and increases to 6.44 eV for NH3 molecules as it acts as oxidation gas on CoOOH. Our study reveals that the 2D CoOOH can be a better sensor for the H2O2 and NH3 gases than some traditional two-dimensional materials.

Competing adsorption mechanisms of pyridine on Cu, Ag, Au, and Pt(110) surfaces.

We explore the adsorption of pyridine on Cu, Ag, Au, and Pt(110) surfaces using density functional theory. To account for the van der Waals interaction, we use the optB86b-vdW, optB88-vdW, optPBE-vdW, revPBE-vdW, and rPW86-vdW2 functionals. For comparison, we also run calculations using the generalized gradient approximation-PBE (Perdew-Burke-Ernzerhof) functional. We find the most stable adsorption site to depend on both metal and functional, with two energetically favorable adsorption sites, namely, a vertically oriented site and a flat pyridine site. We calculate that every functional predicts pyridine to lie in the vertical configuration on the coinage metals at a low coverage. On Pt(110), by contrast, we calculate all the functionals-except rPW86-vdW2-to predict pyridine to lie flat at a low coverage. By analyzing these differences for these adsorption configurations, along with various geometric and electronic properties of the adsorbate/substrate system, we access in detail the performance of the 6 functionals we use. We also characterize the nature of the bonding of pyridine on the coinage metals from weak to strong physisorption, depending on the functional used. On Pt(110), we characterize the nature of the bonding of pyridine as ranging from strong physisorption to strong chemisorption depending again on the functional used, illustrating both the importance of the van der Waals interaction to this system and that this system can make a stringent test for computational methods.

Strong physisorption and superb thermal stability of carbon nanofibers carried CuxO-V2O5 enabling the flexible and long-cycling supercapacitor

Carbon nanofibers supported the vanadium and copper bimetallic oxide composite electrode material has been developed successfully in this study, as the outstanding electrode materials in supercapacitors. In electrospunning and calcination processes, the organic salt of vanadium underwent high temperature decomposition to form V2O5 in situ. The various ratios of CuxO-V2O5/CNFs composite electrode material were used to apply in the electrochemical performance testing through the vacuum impregnation method. Because of the copper doping, CuxO-V2O5/CNFs (10:1) composites exhibited a specific capacitance of 867.2 F g−1 at 0.5 A g−1 over a potential range of 0–0.51 V, which surpassed those of their individual counterparts (682.5 F g−1 and 507.1 F g−1 at 0.5 A g−1 for V2O5/CNFs and CuCl2/CNF, respectively). The addition of trace copper oxide greatly improves the electrochemical performance of vanadium-based carbon fibers composites. The composites also showed good cycling stability due to the unique structure of the V2O5 and synergies with copper oxide. The preparation route provided a novel strategy to synthesize composites of transition bimetallic oxide with improving electrochemical performance for applications in supercapacitors.