Decrease In Adsorption Energy Research Articles

Nitrogen doped compound defect in black phosphorene for enhanced gas sensing

Point defects are widely recognized for their ability to fine-tune the surface reactivity and chemical selectivity of two-dimensional materials. This study delves into the surface adsorption of five environmentally detrimental gas molecules, namely NO2, SO2, CO, CO2, and NH3, on black phosphorene, employing first-principles calculations to explore the compound effect of two distinct point defects, specifically, P vacancy and N dopant. Our calculations unveil that the existence of dangling bonds in BP monolayers disrupts the N-O bond in the NO2 molecule, leading to an increase in adsorption energies to -5.74 eV and -4.40 eV. Interestingly, the monolayer with compound defect demonstrates promising results for detecting SO2 gas molecules but exhibits a decrease in adsorption energy by 44% and 76% when only one type of defect is present. In contrast, for CO, CO2, and NH3 molecules, insignificant changes near the Fermi level suggests that both systems, the one with the compound defect and those with a single defect, remain entirely insensitive. This nontrivial and distinctive study of a BP gas sensor incorporating compound point defect could provide ample insights into revealing its sensitivity and reliability in detecting environmentally harmful, toxic gases.

Construction of core–shell structured CrOx/NiCoxO4 catalyst for low temperature catalytic oxidation of toluene: Understanding the reactivity promotion mechanism of the core–shell interactions

Bimetallic-based spinels are potential materials for toluene oxidation ascribing to their remarkable stability and oxidation activity. However, the insufficient toluene adsorption capacity and limited reactive oxygen species severely restrict their low-temperature catalytic reactivity. This study reports a facile two-step solvothermal strategy for the synthesis of core–shell structured CrOx/NiCoxO4 catalyst, which exhibits excellent toluene oxidation performance with T50 and T90 values of 187 and 218 °C, respectively, and the toluene conversion remains above 90 % at 218 °C for 20 h. The in-situ DRIFTs indicate that the oxidation of toluene to CO2 and H2O follows Mars-van Krevelen (MvK) mechanism, and the rate limiting step is the oxidation of maleic anhydride. The strong interaction between core NiCo2O4 and shell Cr2O3 regulates the morphology of Cr2O3 from particles to porous flocculent structure, which increases the porosity of catalyst and promotes the adsorption of toluene for further oxidation. Moreover, the interaction promotes the charge transfer from NiCo2O4 to Cr2O3, which increases the adsorbed oxygen species contents and the redox capability of the catalyst. A further density functional theory (DFT) calculation confirms that the core NiCo2O4 is the main active component, where the oxygen vacancy formation energy of NiCo2O4 and Cr2O3 decrease from 2.43 and 3.85 eV to 0.31 and 1.52 eV, while the toluene adsorption energy decrease from −0.04 and −0.94 eV to −5.29, and −4.48 eV, respectively, which evidently demonstrates that the formation of core–shell structured CrOx/NiCoxO4 would significantly promote the adsorption and oxidation of toluene, thereby exhibiting excellent low temperature toluene oxidation reactivity.

Cavitands based nanocapsule as smart and highly effective vehicle for 5-fluorouracil anti-cancer drug delivery: DFT insights

The nanomaterials have been widely investigated as drug delivery system for a variety of anticancer drugs to limit their adverse effects while transporting to the target site. In the current study, we report the cavitand-based nanocapsules as a drug delivery vehicle for nitrosourea (NU) and fluorouracil (FU) anti-cancer drugs. FU and NU drugs interact with the nanocapsules with the interaction energies in gas phase (solvent) −24.78 kcal/mol (–22.39 kcal/mol) and −21.58 kcal/mol (-20.45 kcal/mol), respectively. The results of Quantum theory of atoms in molecules (QTAIM) and noncovalent index (NCI) analyses indicate that the FU@Capsule and NU@Capsule complexes are mainly stabilized through hydrogen bonding and van der Waals interactions. Electron density difference (EDD) and natural bond order (NBO) analyses reveal that significant amount of charge is transferred from the nanocapsule to drug molecules. Frontier molecular orbital (FMO) analysis also reveals slight reduction in the energy gap. AIMDS analysis shows that cavitand capsules can efficiently carry the anti-cancerous drug to their target site without distorting complexes. The dipole moments and pH effect are studied to understand the drug release mechanism of considered anticancer drugs. The decrease in adsorption energy and increase in interaction distances indicate that anticancer drugs can easily be off-loaded from the carrier (nanocapsule) at the target site due to the low pH of cancerous cells compared to the normal cells. Therefore, cavitand nanocapsule can be employed as an excellent drug delivery carrier in smart targeted drug delivery.

Hydrodeoxygenation of mixtures of biomass-derived model compound oxygenates over Pt/HY catalysts

In this study, a systematic analysis of the effect of three biomass pyrolysis oxygenates, viz., acetic acid, cyclopentanone and furfural, on the hydrodeoxygenation (HDO) of guaiacol is performed. Bifunctional Pt/HY catalysts with different Si/Al ratios were screened for the HDO of guaiacol. Guaiacol conversion and the cyclohexane yield increased with the concentration of acid sites in the zeolites. The presence of acetic acid and cyclopentanone did not affect the guaiacol conversion and the product selectivity, while guaiacol conversion decreased significantly in the presence of furfural. The effects of temperature, reaction time, and the guaiacol-furfural molar ratio on the HDO of guaiacol were studied. The time evolution of products showed that the furan ring opening influences the conversion of guaiacol.Quantum chemicaldensity functional theorycalculations using individual and binary model compounds revealed the decrease in adsorption energy of guaiacol over Pt (111) in the presence of furfural.

Theoretical evidence of enhanced interaction between H2O and O3 leads to improved performance of catalytic ozonation with copper doping α-FeOOH

The catalytic performance of copper doped α-FeOOH in ozonation process for wastewater treatment was explored through both experimental method and DFT calculations. The results revealed that when Cu was doped to α-FeOOH, part of the Fe atoms in crystal lattice were replaced by Cu atoms. As the Cu mole content increased from 3% to 10%, the doped compounds was gradually transformed into oxides of Fe2O3 and CuO. 5%Cu-α-FeOOH/ozone achieved the highest naproxen removal of 79.6% in water, which was more effective than ozone alone or α-FeOOH/ozone system. The main active species in the catalytic ozonation system were found to be hydroxyl radicals, the accumulative hydroxyl radical amount could reach 14.2 μmol in 15 min in 5%Cu-α-FeOOH catalyzed ozonation. According to the characterization of catalysts and the detection of active species, it could be conjectured that during copper doping a certain amount of oxygen vacancy were formed in the condensed hydroxyl oxides, resulting in the increase of surface oxygen species. Based on density functional theory (DFT) calculation, the enhanced performance with Cu doping in α-FeOOH might be attributed to the decrease in adsorption energy of H2O & O3 as well as the increase in formation energy of free radicals.

Cu- and Al-Decorated Monolayer TiSe2 for Enhanced Gas Detection Sensitivity: A DFT Study.

The rapid industrial development has contributed to worsening global pollution, necessitating the urgent development of highly sensitive, cost-effective, and portable gas sensors. In this work, the adsorption of CO, CO2, H2S, NH3, NO, NO2, O2, and SO2 gas molecules on pristine and Cu- and Al-decorated monolayer TiSe2 has been investigated based on first-principles calculations. First, the results of the phonon spectrum and ab initio molecular dynamics simulations demonstrated that TiSe2 is dynamically stable. In addition, compared to pristine TiSe2 (-0.029 to -0.154 eV), the adsorption energy of gas molecules (excluding CO2) significantly decreased after decorated with Cu or Al (-0.212 to -0.977 eV in Cu-decorated TiSe2, -0.438 to -2.896 eV in Al-decorated TiSe2). Among them, NH3 and NO2 have the lowest adsorption energies in Cu and Al-decorated TiSe2, respectively. Further research has shown that the decrease in adsorption energy of gas molecules is mainly due to orbital hybridization and charge transfer between decorated Cu and Al atoms and gas molecules. These findings suggest that TiSe2 decorated with Cu and Al can effectively improve its sensitivity to NH3 and NO2, respectively, making it promising in gas sensing applications.

A dual-balance strategy via phosphate modification on MnO2-CeO2 for NOx and chlorobenzene synergistic catalytic control

Traditional MnO2-CeO2 (MnCe) exhibits efficient synergistic-control performance for selective catalytic reduction of NOx and chlorobenzene (CB) oxidation. However, the issues of N2O formation and chlorine-deposition remain challenges. Herein, a phosphate-modified MnCe exhibits both higher NOx and CB conversions than MnCe: N2O formation decreases by 23%, while HCl selectively increases by 10% at 300 ℃. Phosphate widens the band gap of Mn 3d of MnCe and recovers the bond length of Ce-O back to that of ceria, restricting the electrons transfer from surface cations to chlorine ions by the orbital polarization effect. Meanwhile, phosphate also provides more Brønsted and weakly Lewis acid sites, favoring CB nucleophilic substitutions rather than polychlorinated species accumulation. Both the chlorine adsorption energy and HCl formation barrier decrease after phosphate modification. This work provides a novel modulation strategy of dual-balance (reducibility vs. total acidity; Lewis vs. Brønsted) on the design of multi-pollutant control catalysts.

Enhanced uranium separation by charge enabling γ-MnO2 with oxygen vacancies

Numerous efforts have been devoted to understanding the electron transfer process of uranium (UO22+) on adsorbent materials, whereas the potential oxygen vacancies (OVs) in metal oxides have long been overlooked. Once these interactions are taken into account, the emerging molecular orbital effects undoubtedly affect the adsorption process. Here, we synthesized CC/γ-MnO2 by growing MnO2 on carbon cloth (CC), followed by the creation of oxygen vacancies (OVs) through electrochemical methods to form CC/γ-MnO2-OVs. The CC/γ-MnO2-OVs shows significantly enhanced selectivity and durability for UO22+, with the maximum adsorption capacity increasing from 456.8 to 1648.1 mg/g (by a factor of 3.6). Theoretical calculations suggest that the generation of OVs leads to an increase in charge transfer and a decrease in adsorption energy between UO22+ and CC/γ–MnO2, due to the interaction between Mn 3d orbital in CC/γ–MnO2 and O 2p orbital in UO22+. The OVs in CC/γ–MnO2 provide a spatial structure for anchoring the OU=O moiety of UO22+, while the surface van der Waals forces and the formation of chemical bonds between Mn-U contribute to charge interactions. This synergistic effect allows CC/γ-MnO2-OVs to exhibit favorable selectivity, a large adsorption capacity, and rapid adsorption kinetics towards uranyl ions. This work achieves enhanced UO22+ separation by introducing OVs in CC/γ–MnO2 through a facile electrochemical strategy, highlighting the great potential for nuclear waste processing.

Efficient separation of strontium in different environments with novel acid-resistant silica-based ion exchanger

Radioactive strontium (90Sr) is widespreadly concerned due to its high biochemical toxicity, relatively long half-life, high fission yield and potential special applications in heat source and medical field. Herein, a novel acid-resistant silica-based adsorbent Sb2O5/SiO2 was prepared by a two-step method, i.e. vacuum impregnation followed by oxidation. The adsorbent was characterized by XRD, SEM, TEM, EDS, BET, FT-IR and XPS techniques, which revealed its characterization of small particle size (75–150 μm), abundant functional groups and well-crystallized structure. The experimental results revealed Sb2O5/SiO2 exhibited good adsorption selectivity for Sr in pH 9–3 M HNO3 solution, the adsorption equilibriums were obtained within 5 min in pH 6 solution and 30 min in 1 M HNO3 solution with the adsorption capacities of 160.6 mg/g and 51.8 mg/g, respectively. Moreover, it also demonstrated good application potential in medical isotope preparation area as efficient strontium-yttrium (Sr-Y) separation was achieved with the separation factor over 7769 in pH 6 solution. Furthermore, the column experiments confirmed that Sr could be effectively removed both in seawater and simulated high level liquid waste (HLLW), and the purity of Y could reach to 99.7 % in Sr-Y separation. Finally, density functional theory (DFT) calculations confirmed that the adsorption mechanism was ion exchange between Sr(II) and H+ (in Sb-OH), and the adsorption was accompanied by the transfer of charge and the decrease of adsorption energy.

Copper content effects on passive film of modified 00Cr20Ni18Mo6CuN super austenitic stainless steels in acidic environment

To provide a theoretical basis for the design of super austenitic stainless steel used in flue gas desulfurization environment, by changing the Cu content in 00Cr20Ni18Mo6CuN super austenitic stainless steel to explore the influence of Cu on its corrosion resistance, by electrochemical methods, XPS and first-principle computational simulations. The results show that Cu promotes the selective dissolution of Fe, Cr and Mo in stainless steel, and the copper content changes the proportion of compounds in the passive film, as well as its surface quality, resistance and defect density. The addition of one Cu atom increases the adsorption energy and work function of NH3 on Cr2O3 surface, reduces the charge transfer and hybridization. However, when the Cu content exceeds 1 wt%, the surface of the passive film is loose and has many defects. The appearance of oxygen vacancy and two Cu atoms leads to the decrease of adsorption energy and work function, and enhances the charge transfer and hybrid effect. The optimal Cu content is obtained through research, which not only improves the corrosion resistance of 00Cr20Ni18Mo6CuN super austenitic stainless steel in flue gas desulfurization environment, prolonging the service life of 00Cr20Ni18Mo6CuN super austenitic stainless steel, but also has practical application value.

Covalent Organic Framework (C6N6) as a Drug Delivery Platform for Fluorouracil to Treat Cancerous Cells: A DFT Study.

Continuous studies are being carried out to explore new methods and carrier surfaces for target drug delivery. Herein, we report the covalent triazine framework C6N6 as a drug delivery carrier for fluorouracil (FU) and nitrosourea (NU) anti-cancer drugs. FU and NU are physiosorbed on C6N6 with adsorption energies of -28.14 kcal/mol and -27.54 kcal/mol, respectively. The outcomes of the non-covalent index (NCI) and quantum theory of atoms in molecules (QTAIM) analyses reveal that the FU@C6N6 and NU@C6N6 complexes were stabilized through van der Waals interactions. Natural bond order (NBO) and electron density difference (EDD) analyses show an appreciable charge transfer from the drug and carrier. The FU@C6N6 complex had a higher charge transfer (-0.16 e-) compared to the NU@C6N6 complex (-0.02 e-). Frontier molecular orbital (FMO) analysis reveals that the adsorption of FU on C6N6 caused a more pronounced decrease in the HOMO-LUMO gap (EH-L) compared to that of NU. The results of the FMO analysis are consistent with the NBO and EDD analyses. The drug release mechanism was studied through dipole moments and pH effects. The highest decrease in adsorption energy was observed for the FU@C6N6 complex in an acidic medium, which indicates that FU can easily be off-loaded from the carrier (C6N6) to a target site because the cancerous cells have a low pH compared to a normal cell. Thus, it may be concluded that C6N6 possesses the therapeutic potential to act as a nanocarrier for FU to treat cancer. Furthermore, the current study will also provide motivation to the scientific community to explore new surfaces for drug delivery applications.

First-principle study of CO sensing properties on Pt-doped SnO2(1 1 0) surface with oxygen defect

For SnO2 (110) surface, one bridge lattice oxygen was removed and then one oxygen molecule perpendicular to the oxygen vacancy position was absorbed. Based on the density functional theory, the electronic structure and gas sensing property of CO on different Pt concentration doped SnO2 (110) surface is studied. The results show that the adsorption energy decreases and the electron concentrations at the Fermi level increase after Pt doping, in which the minimum adsorption energy is −2.71 eV and the biggest electron value is 12.64 eV. Combined with The charge density difference (CDD) analysis, the SnO2(110) surface may have the best gas sensing property when Pt doping concentration is 4.17%. From the charge population, it is found that the pure SnO2(110) surface loses 0.10e electrons to CO, and the SnO2(110) surface gets electrons from CO after Pt doping, which means Pt doping can enhance the oxidation capacity of SnO2(110) surface.

Effect of CO2 on the As2O3 adsorption over carbonaceous surface: Experiment and quantum chemistry study

The adsorption characteristics of the As2O3 over carbonaceous surface in the presence of CO2 were systematically studied by experiment and density functional theory (DFT). The experimental results show that CO2 has a negative effect on the adsorption of arsenic by activated carbon. In addition, quantum chemistry calculations were employed to study the mechanism for CO2 influence on arsenic adsorption. Calculation results show that carbonaceous surface tends to react with CO2 compared to As2O3 in the flue gas. Compared to the As2O3 adsorption over the complete carbonaceous surface, there is a noticeable decrease for the adsorption energy over the defective carbonaceous surface. Besides, with the pre-assembled CO2 adsorption over the carbonaceous surface, the As2O3 adsorption energy decreases, indicating CO2 has the negative effect on As2O3 adsorption. By means of Hirshfeld atomic charges analysis, CO2 adsorbed on carbonaceous surface would weaken the activity of adsorption sites and inhibit the As2O3 adsorption. The experiment and theoretical study figured out the influences mechanism of CO2 on the As2O3 adsorption and provide a theoretical foundation for gaseous arsenic removal using carbonaceous surface.

Synergistic effect of oxygen defects and hetero-phase junctions of TiO2 for selective nitrate electroreduction to ammonia

Electrocatalytic nitrate reduction to ammonia (NH3) has been received increasing attention due to the potential of both decontaminating nitrogen oxide (NOx) from industrial exhaust gas and providing an option for NH3 synthesis. However, their related catalytic process and mechanism dominated by the active phase structure and active sites of nitrate to ammonia electrocatalyst still remain unclear. To this end, in this study TiO2 nanomaterials with constructed hetero-phase junctions and oxygen defects were used to study the catalytic mechanism and make a clear of the function of hetero-phase junctions and defects. Combined with EPR and FT-IR methods, oxygen defects acted as the adsorption sites of NO3- are experimentally confirmed. Systematic characterizations further demonstrate that enhanced performance with the highest NH3 Faradaic efficiency (78.0%) and selectivity (81.9%) for NITRR can be attributed to the Ti3+- Odef pairs and hetero-phase junctions induced strong interface interactions between anatase and rutile phases. The online differential electrochemical mass spectrometry (DEMS) and density functional theory (DFT) calculations demonstrate that both Ti3+ - Odef pairs and hetero-phase junctions lead to the decrease of adsorption energy of NO3- and promote the formation of *NOH intermediates, revealing the reaction mechanism for NH3 synthesis from NO3-.

Ab Initio Study of the C–O Bond Dissociation in CO2 Reduction by Redox and Carboxyl Routes on 3d Transition Metal Systems

The C–O bond dissociation of the CO2 molecule via the reverse water gas shift reaction is crucial for several reactions used as renewable alternatives for fuel synthesis. However, our atomistic understanding of this process on transition metal (TM) clusters, where quantum-size effects might play a significant role, is far from complete. Here, we addressed the C–O bond dissociation by redox and carboxyl routes on 13-atom TM (Fe, Co, Ni, Cu) clusters using density functional theory calculations and the climbing image nudged elastic band algorithm. From the potential energy profiles, we found that CO2 is prone to dissociate into adsorbed CO via the redox route with lower activation energies, Ea’s, than the carboxyl route on all studied TM13 systems. Our results suggested that the smaller activation barrier found on the Co13 cluster is due to the stronger adsorption exhibited for both CO2 and O. By increasing the d-state occupation (from Fe to Cu), the Ea differences between CO2 dissociation and COOH formation decrease. We associated this behavior with a decrease in the (CO2 + H) adsorption energy from Fe13 to Cu13 that facilitates the COO–H bond formation and H–TM bond cleavage, i.e., favoring the carboxyl route. Also, our analyses indicate that the adsorption energies of the CO2 and trans-COOH species are the best descriptors for the C–O bond dissociation via the redox and carboxyl routes, respectively.

First‐principles study on the methane adsorption properties by Ti‐modified graphyne

AbstractGraphyne (GY) is an allotrope composed of sp and sp2 hybridized carbon atoms. In this paper, the adsorption performance of Ti‐modified GY (Ti‐GY) system on the adsorption of CH4 molecules is studied based on first principles. The study found that the most stable adsorption site for Ti atoms is the six‐membered carbon ring pore site. There is a strong ionic interaction between the two, and the Ti‐GY system structure remains stable during the adsorption of CH4 molecules. A single Ti‐modified GY can adsorb 7 CH4 molecules on one side, and the adsorption structure is stratified, with average adsorption energy of −0.298 eV, and an adsorption capacity of 0.369 g g−1; two Ti‐modified GY adsorbs 14 CH4 molecules on double‐sided, the average adsorption energy is about −0.300 eV, and the adsorption capacity reaches 0.484 g g−1. The first layer of CH4 molecules is adsorbed, which is mainly affected by the Ti atoms. There is a strong Coulomb interaction between it and Ti. With the increase of CH4 molecules, the adsorption energy decreases; While the second layer of CH4 molecules is due to the distance Ti atoms are far away, At this time, the interaction between the CH4 molecules and the substrate is mainly the electrostatic interaction between the positively charged CH4 molecules and the negatively charged GY and the van der Waals interaction between the CH4 molecules. The adsorption performance of CH4 molecules is closely related to the pore size of the two‐dimensional adsorbent. When the pore size is small, the interaction between molecules is enhanced and the average adsorption energy is larger. On the contrary, the larger the pore size, the higher the adsorption capacity.

Methane adsorption properties of N-doped graphdiyne: a first-principles study

N-doped graphdiyne (N-graphdiyne) is a new kind of alkynyl carbon material whose structure resembles graphdiyne. This study describes the Mn-modified N-graphdiyne (Mn-N-graphdiyne) system on methane (CH4) adsorption properties based on first principles. We found that the modifications of the Mn atom could significantly improve the adsorption of CH4 by N-graphdiyne. Two Mn atoms can adsorb 36 CH4 molecules upon double-sided modification, with average adsorption capacity and storage capacities of approximately − 0.158 eV and 0.585 g g−1, respectively. The adsorption of the first CH4 molecule by the Mn-N-graphdiyne system, which is mainly affected by the Mn atoms, involves a strong Coulomb interaction with Mn accompanied by the highest adsorption energy. Subsequently, an increase in the distance between CH4 molecules and Mn atoms increases leads to a weakened Coulomb interaction. The adsorption of CH4 molecules is then mainly affected by the van der Waals force between the substrate N-graphdiyne, and the adsorption energy decreases. The N-graphdiyne system has a larger acetylene chain macroporous position than GDY owing to the doping of N atoms, which provides sufficient adsorption space and adsorption sites for CH4.

Ultra-stable ZnO nanobelts in electrochemical environments

The In-ZnO nanobelts present ultrahigh stability of morphology and electrical properties in the electrochemical environment. It can be attributed to the adsorption energy decrease in the unique lattice structure with doped indium atoms.

Wettability and hydrolytic stability of 3-aminopropylsilane coupling agent and phenol-urea-formaldehyde binder on silicate surfaces and fibers

The stability of phenol-urea-formaldehyde (PUF) binder and 3-aminopropylsilane (APS) on composite silicate materials (fibers and wafers) was studied with surface sensitive techniques (X-ray photoelectron spectroscopy (XPS) and streaming potential) through a wide range of humidity and temperature and ab initio modelling complemented the results. Behavior was compared for wettability properties, determined by vapor adsorption and contact angle analysis. APS and PUF, deposited on the silicate surfaces, decrease surface energy and wettability but water adsorption remains high, facilitating hydrolytic decomposition of the composite material. Deposited APS is unstable at T>50°C and 75% RH, while PUF is less sensitive to high humidity and temperature. Molecular dynamics confirmed APS sensitivity to humidity. Water adsorption and surface energy decrease, and material stability increases when a hydrophobization agent is applied to APS/PUF treated surfaces. The direct correlation between wettability and stability of PUF/APS/fiber composites can contribute in designing new materials with controlled hydrophobic properties.

Adsorption of acetylene on Sn-doped Ni(111) surfaces: a density functional study.

First-principle density functional theory calculations have been performed to investigate the adsorption of C2H2 on Ni(111) and Sn@Ni(111) at different coverages. At low coverage, the C2H2 molecule is strongly adsorbed on Ni(111) and the dissociation of the H atom is not favorable. Furthermore, the more the H atom dissociated, the more unstable the system is. However, the dissociation structure of C2H+H has the largest adsorption energy on Sn@Ni(111), indicating that the dissociation structure is more stable than molecular adsorbed C2H2. At moderate coverage, there is some repulsive interaction between two C2H2 molecules, inducing the decrease in adsorption energy. On Ni(111), the two C2H2 tend to adsorb separately, however, the dimer C4H4 has the largest adsorption energy on Sn@Ni(111). At high coverage, the trimer derivative benzene has the largest adsorption energy on both Ni(111) and Sn@Ni(111) surfaces. The adsorption energies of the formed benzene are very high on the two systems, even larger than those of three individual adsorbed C2H2.