Adsorption Reaction Mechanism Research Articles

Reaction mechanisms of α,ω-bifunctional molecules toward atomic layer deposition versus molecular layer deposition

Atomic layer deposition (ALD) and molecular layer deposition (MLD) are key techniques used to fabricate high-quality thin films. Organic α,ω-bifunctional precursors often exhibit different growth behaviors depending on the functional groups as well as the chain length of the molecular backbone, so that some organic precursors produce thin films of organic-inorganic hybrid materials, while others may deposit purely inorganic thin films without incorporation of the hydrocarbon moiety. In this study, we investigated the surface reaction mechanisms of α,ω-bifunctional molecules (X(CH2)nX, n = 2, 3, 4, 5, 6, and X = OH, SH, NH2) with diethylzinc toward MLD and ALD using density functional theory (DFT) calculations. It was found that the length of the aliphatic alkyl chain and the terminal functional groups of bifunctional organic precursors significantly influences their reactivity, resulting in the possibility toward removal or incorporation of the organic moiety in the product. Bifunctional reactants with longer alkyl backbones (n > 4) showed higher reactivity for removal of the hydrocarbon chain, facilitated by a ω-2 hydrogen transfer reaction. Furthermore, a reactivity trend of SH > OH > NH2 for removal of the hydrocarbon chains was observed. Our study provides in-depth theoretical insights into the adsorption reaction mechanisms occurring when bifunctional molecules are employed as organic reactants in ALD and MLD processes.

(Invited) Novel Surface Reactions in Low-Temperature Regime for High-Aspect-Ratio Dielectric Etching

The most critical issue to achieve High-Aspect-Ratio (HAR) dielectric etching is the transport of both radicals and ions to the bottom of a feature [1]. Current HAR dielectric etching uses fluorocarbon and hydrofluorocarbon gases combined with high applied bias power. However, the etch rate drastically decreases at high depth due to the decline of radicals being supplied to the etch front. Alternative methods have long been required to solve this problem. To address the radical transport issue, we propose adopting a novel precursor with low molecular weight to enhance Knudsen transport. In addition, cryogenic temperature regimes are also known to enhance etch rates [2][3] but have not yet been implemented for HAR dielectric etching. In this work we evaluated a novel precursor in cryogenic temperature regime for HAR dielectric etching. For the first time, we demonstrate a synergy effect between cryogenic temperature and this novel precursor by successfully developing an innovative HAR dielectric etch process. We confirmed that this process is capable of etching beyond a ten-micron depth for a 3D-NAND channel hole with a hundred nanometer critical dimension in diameter, thus an aspect ratio of over one hundred to one. The key to enabling high etch rate is strongly correlated with the adsorption of the precursor on the surface, which is enhanced at cryogenic temperature. Detailed surface adsorption reaction mechanisms will be described in the conference. This new process not only enables higher etch rate, higher selectivity and higher aspect ratio etching capability, but also significantly shortens the process time with 84% carbon footprint reduction of greenhouse gas emissions.[1] K. Ishikawa, et al., Jpn. J. Appl. Phys. Vol. 57, No. 6S2, 06JA01, (2018).[2] T. Ohiwa, et al., Jpn. J. Appl. Phys. Vol.31, p.405, (1992).[3] R Dussart, et al., J. Phys. D: 47, 123001, (2014).

Biowaste Valorization to Produce Advance Carbon Material-Hydrochar for Potential Application of Cr (VI) and Cd (II) Adsorption in Wastewater: A Review

The dramatic increase in the use of biomass waste has caused a serious environmental pollution phenomenon. Biowaste valorization to produce advanced material-hydrochar is regarded as a promising carbon neutrality technology for biomass waste recycling and utilization. Hydrochar obtained by hydrothermal carbonization has attracted much attention due to its regular morphology, good physical and chemical stability, and abundant oxygen-containing functional groups on the surface. This reviews the preparation of hydrochar and the basic methods of modified hydrochar and expounds on the related reaction mechanism of adsorption. The adsorption and recovery of heavy metals, Cr (VI) and Cd (II), in wastewater by hydrochar were focused on. The experimental conditions of hydrochar, such as synthesis temperature, synthesis time, modified condition, adsorption capacity, adsorption isotherm, and adsorption kinetics, were compared. The adsorption conditions of hydrochar for Cr (VI) and Cd (II) in wastewater, including the adsorption pH value, the adsorption time, the adsorption temperature, and so on, have been summarized. The review develops a better understanding of Cr (VI) and Cd (II) adsorption by hydrochar in wastewater, making an innovative perspective for the improvement and large-scale application of hydrochar as an advanced carbon material as well as biowaste utilization.

Corrosion inhibition of copper in sulfuric acid by Leonurus japonicus Houtt. extract as a green corrosion inhibitor: Combination of experimental and theoretical research

BackgroundBased on the consideration of green and safety in industrial production, the demand and desire for green corrosion inhibitors are increasingly strong. MethodsIn this study, we selected Leonurus japonicus Houtt. leaves extract (LLE) extracted by water. Electrochemistry experiments and morphology characterization showed excellent anti-corrosion performance of LLE for copper in 0.5 mol∙L1 H2SO4. The chemical bond information measured by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) indicated that LLE adsorbed on Cu/H2SO4 interface by chemical bonding. Through quantum chemical calculation and molecular dynamics simulation analysis, the adsorption reaction mechanism was profoundly studied. Significant findsElectrochemical test data showed that the inhibition efficiency of 400mg/L LLE arrived at 90% at 298 K, 308K and 318 K. After processing the data, it is concluded that LLE protective film belonged to Langmuir adsorption. By calculating thermodynamic and kinetic parameters of corrosion, it is found that the activation complex is formed by the binding of Cu+ and LLE in the adsorption layer.

Releasing Si[sbnd]O tetrahedron and Al[sbnd]O octahedron from montmorillonite to enhance the adsorption performance of carbon@chitosan@montmorillonite nanosheet for cationic dyes: Coupling quantum chemistry simulations with experiments

A novel adsorbent of carbon@chitosan@montmorillonite nanosheet (C@CS@ MTN) was successfully fabricated layer-by-layer assembly method to deal with cationic dye wastewater. Batch adsorption experiments showed that the adsorption capacities of MB and RhB were higher than 325 mg·g−1 and 236 mg·g−1, respectively, indicating that C@CS@MTN exhibited an excellent adsorption performance. Through quantum chemistry simulations, the molecular electrostatic potential, electron density, differential charge density, molecular orbital distribution and adsorption binding energy were analyzed to reveal the adsorption reaction mechanism between C@CS@MTN and cationic dyes. The results indicated that SiO tetrahedron ring and AlO octahedron ring released from montmorillonite with inherent periodic structure was beneficial to electrostatic attraction, while cation-π interaction benefitted from the interaction between Al atoms of AlO octahedron ring and benzene ring. It was noteworthy that the electron transfer direction of electrostatic attraction was from O atoms of SiO tetrahedron ring to the benzene ring of dye molecules, but the electron transfer direction of cation-π interaction was from benzene ring of dye molecules to Al atoms of AlO octahedron ring. These results provide fundamental theoretical support for the functional design of mineral-based adsorbents and the efficient removal of cationic dyes.

A density functional theory study on the adsorption reaction mechanism of double CO2 on the surface of graphene defects.

Much research has been done on reactions of a single CO2 molecule with a graphene surface. In this paper, density functional theory calculations are used to investigate the adsorption and reaction of double CO2 on the surface of single vacancy (SV) and divacancy (DV) defect graphene. The study found that due to the mutual repulsion between CO2 and the size of the SV defect, it is difficult for two CO2 molecular to be adsorbed directly above the SV defect at the same time. Regardless of SV or DV, the adsorption of the first CO2 in the defect center will have a beneficial effect on the adsorption of the second CO2. In addition, the transition state calculation of the CO2 reaction on the DV plane was carried out, and the adsorption behavior was analyzed and studied. This in-depth study is helpful to the understanding of the reaction behavior of CO2 on graphene, and further exploration in the direction of the effective application of graphene to the reaction and adsorption of CO2. Our work explores the adsorption behavior of CO2 on graphene surfaces, the physical and chemical adsorption of double CO2 at the defect was studied and analyzed.

Effects of carbon nanomaterials on the migration and fate of organic pollutants in the ecological environment

The purpose of this study was to investigate the mechanism of adsorption reaction between heterocyclic organic compounds with different number of ring atoms and different atoms replacing carbon atoms and carbon nanotubes with different surface functional groups. Based on the current situation of research on adsorption of carbon nanomaterials adsorbing organic pollutants, the existing problems and limitations were analyzed by studying the properties and characterization of single-walled carbon nanotubes, oxidized single-walled carbon nanotubes and non-porous graphite powder, such as elemental analysis, transmission electron micrograph, zero charge point, etc. The three adsorption materials were investigated by batch experiment. Six compounds of thiophene, pyrimidine, benzene, aniline, 2-aminopyrimidine and 4,6-diaminopyrimidine were selected as the adsorbate for detecting adsorption capacity. The results showed that the affinity of different adsorbents on different adsorbents varied greatly. The adsorption capacity of heterocyclic compounds containing N and S was greatly enhanced by non-hydrophobic action. And the degree of oxidation of the adsorbent and the ph of the solution determined the adsorption capacity of the adsorbent for nitrogen-containing heterocyclic compounds. Therefore, in the ecological environment, the migration of hydrophilic organic pollutants in the environment can be reduced by the preparation of appropriate carbon nanotubes.

Methylene Blue and Malachite Green Removal From Aqueous Solution Using Waste Activated Carbon

In the present investigation, Waste Activated Carbon (WAC) collected from domestic water filter has been used for the removal of two cationic dyes methylene blue (MB) and malachite green (MG) from synthetic solution. The surface of WAC is characterized to know the mechanism of adsorption reaction and the effect of different adsorption parameters like pH, temperature, contact period, adsorbate and adsorbent doses are also studied for the said adsorption study. The optimum contact times for MB and MG adsorption on WAC are 60 and 120 minutes respectively, whereas pH is having no significant effect on adsorption. However, % adsorption increases slowly with the increase of pH from 2.5 to 7. Adsorption of both the dyes on WAC is exothermic, spontaneous, and favorable in nature. Langmuir isotherm and pseudo-second-order kinetics are obeyed well. Langmuir’s maximum monolayer adsorption capacities are found to be 15.38 and 18.87mg/g for MB and MG, respectively. Temkin isotherm, and Morris-Weber equations are also obeyed well. Temkin’s isotherm concludes the physicochemical nature of adsorption, and Morris Weber equation indicates possibilities of intraparticle diffusion. The interaction between these two cationic dyes and WAC can be explained through electrostatic force of attraction or by hydrogen bonding.

The pivotal effects of oxygen vacancy on Bi2MoO6: Promoted visible light photocatalytic activity and reaction mechanism

Bi2MoO6, a typical Bi-based photocatalyst, has received increasing interests and been widely applied in various fields. However, the visible light photocatalytic activity of Bi2MoO6 is still restricted by some obstacles, such as limited photo-response and low charge separation efficiency. In this work, we developed a facile method to introduce artificial oxygen vacancy into Bi2MoO6 microspheres, which could effectively address these problems and realize highly efficient visible light photocatalysis. The experimental and theoretical methods were combined to explore the effects of oxygen vacancy on the electronic structure, photocatalytic activity and the reaction mechanism toward NO removal. The results showed that the addition of NaBH4 during catalyst preparation induced the formation of oxygen vacancy in Bi2MoO6, which plays a significant role in extending the visible light absorption of Bi2MoO6. The visible light photocatalytic activity of Bi2MoO6 with oxygen vacancy was obviously enhanced with a NO removal ratio of 43.5%, in contrast to that of 25.0% with the pristine Bi2MoO6. This can be attributed to the oxygen vacancy that creates a defect energy level in the band gap of Bi2MoO6, thus facilitating the charge separation and transfer processes. Hence, more reactive radicals were generated and participated in the photocatalytic NO oxidation reaction. The in situ FT-IR was used to dynamically monitor the photocatalytic NO oxidation process. The reaction intermediates were observed and the adsorption-reaction mechanism was proposed. It was found that the reaction mechanism was unchanged by introducing the oxygen vacancy in Bi2MoO6. This work could provide new insights into the understanding of the oxygen vacancy in photocatalysis and gas-phase photocatalytic reaction mechanism.

Kinetics of the photocatalysed oxidation of NO in the ISO 22197 reactor

Abstract The photocatalytic reactor described in the NOx removal ISO 22197-1:2007 is used to study the kinetics of the process, using a film of P25 TiO2 which has either been conventionally pre-irradiated in a stream of air, or unconventionally in a stream of NO (1 ppmv). In the former case it is shown that the system does not achieve steady state exit levels of NO, probably due to the gradual accumulation of HNO3 on the surface of the photocatalyst. The NO-preconditioned TiO2 film demonstrated excellent steady-state levels when monitored as a function of NO concentration, [NO] and UV irradiance, ρ. However, in this case the photocatalytic reaction under study is NOT NOx removal, but the conversion of NO to NO2. It is shown that the kinetics of this steady state process fit very well to a kinetic expression based on a disrupted adsorption reaction mechanism, which has also been used by others to fit their observed (non-steady state) kinetics for NOx removal on conventionally-(air) preconditioned films of P25. The appropriateness of this model for either system is questioned, since in both systems the kinetics appear to have a significant mass transport element. These findings suggest that mass transport and non-steady-state kinetics are likely to be significant features for most active photocatalytic samples, where the %NO conversion is >7%, and so limits the usefulness of the NOx removal ISO 22197-1:2007.

Catalytic oxidation of hydrogen on platinum

Using the thermochemical approach to interpret the kinetics of heterogeneous reactions and the mechanism of congruent dissociative decomposition of solids developed in the 1980s and (re)analyzing the experimental data available in the literature over the last 90 years, a novel mechanism for the catalytic oxidation of H2 by PtO2 is proposed. In place of the conventional Langmuir–Hinshelwood and Eley–Rideal adsorption reaction mechanisms, our model is based on the reactions: PtO2(s) + 2H2 ↔ Pt(g) + 2H2O and Pt(g) + O2 ↔ PtO2(g) → PtO2(s). The first reaction determines the kinetics of H2 oxidation and the second determines the kinetics of restoration of the PtO2 layer. Thermochemical consideration of kinetic features of this model enables (for first time in the history of this reaction) the enthalpy and equilibrium constants for H2 oxidation on platinum to be calculated. The results are in good agreement with experimental data. In addition, the proposed mechanism explains the origin of the surface-retexturing effect, the impact of autocatalysis, the influence of H2O vapor on oxidation rate, and the three-fold variation of the Arrhenius E parameter with temperature. This all convincingly demonstrates the value of the thermochemical approach in interpreting heterogeneous reactions.

Density functional study of Hg adsorption mechanisms on α-Fe2O3 with H2S

First-principle calculations based on the density functional theory are performed to clarify the Hg0 adsorption reaction mechanism on an α-Fe2O3 surface with H2S in coal-utilizing facilities. Theoretical calculations based on the various adsorption mechanisms of H2S and Hg0 on α-Fe2O3 are performed to investigate a realistic reaction pathway. The results demonstrate that the Eley–Rideal mechanism with Hg0 adsorption on H2S/α-Fe2O3 surface is the most suitable reaction process, whereas the Mars–Maessen, Langmuir–Hinshelwood, and Eley–Rideal mechanisms with H2S adsorption on Hg0/α-Fe2O3 surface are not possible in real reaction mechanisms. In addition, the potential energy diagram of H2S dissociation on α-Fe2O3 surface is provided.

Removal of phosphorus and sulfur from yellow phosphorus off-gas by metal-modified activated carbon

In order to provide comprehensive utilization of high concentration CO for mono-carbon (C1) chemical industry, the purification of yellow phosphorus off-gas is of great concern. In this research, activated carbon (AC) modified by different impregnants were used for removal of PH 3, H 2S, SO 2, COS, and CS 2 in yellow phosphorus off-gas. For the removal of PH 3, AC impregnated with 0.10 mol L −1 CuAc 2 was proved to be the best adsorbent. And removal efficiency of H 2S could be significantly enhanced by AC impregnated with 7% Na 2CO 3. The results of plant experiments suggested that the total concentration of the impurities in yellow phosphorus off-gas was less than 1 mg Nm −3 after purification operation. The metal-modified activated carbon (MMAC) was systematically characterized in terms of XPS, TGA, and DTA. The adsorption reaction mechanism was also investigated. As a result, the yellow phosphorus off-gas purified in this study can be used as a raw material gas in the C1 chemical industry.

Adsorption of uranium on halloysite

SummaryAdsorption of uranium (U(VI)) from aqueous solutions on halloysite type clay was studied as a function of amount of adsorbent, initial concentration and pH. The values of adsorption data were fitted to Freundlich, Langmuir and Dubinin–Radushkevich (D–R) adsorption isotherms. The mean energy of adsorption was calculated as 5.91 kJ/mol from D–R adsorption isotherm. Lagergren and Bangham equation has been used for dynamic modelling of process and the rate constants of adsorption of uranium on halloysite type clay were calculated at 293, 313 and 333 K. In order to explain the mechanism of adsorption reaction, the rate constants were calculated at high and low uranium concentrations. Adsorption reaction was studied at 293, 303, 313, 323 and 333 K for halloysite type clay and also thermodynamic constants have been calculated. The results show that the adsorption reaction was endothermic and more spontaneous at high temperature.

Competitive Adsorption Reaction Mechanism of Ni/Yttria-Stabilized Zirconia Cermet Anodes in H 2 ­ H 2 O Solid Oxide Fuel Cells

The reaction mechanism of the most commonly used anode material, Ni/yttria-stabilized zirconia (YSZ) cermets, in solid oxide fuel cells (SOFCs) was investigated. Because the reaction mechanism for the Ni/YSZ anode in has not been conclusively determined, we investigated the detailed dependence of dc polarization and interfacial conductivity of Ni/YSZ cermet anode on the partial pressure of hydrogen Based on our experimental results, we developed a model that links the chemical reactions on the anode with the electrical characteristics of the anode such as the dc polarization and the interfacial conductivity. In our model, we assumed competitive adsorption equilibrium of and O on Ni surfaces at the three-phase boundary, and assumed the rate-determining step to be Langmuir-type reactions of H with O. In SOFCs with Ni/YSZ anodes, reported dependencies of the current and interfacial conductivity on and differ among previous studies. Both our measured dependencies and previously published dependencies were successfully reproduced by our Langmuir reaction model. Furthermore, possible reasons for these different observed dependencies include the different adsorption equilibrium constants. © 2001 The Electrochemical Society. All rights reserved.

Influence of oxygen concentration in the carrier gas on the response of tin dioxide sensor under hydrogen and methane

A SnO 2 sensor has been tested under hydrogen or methane pollutant gases with varying the oxygen concentration in the supporting gas (nitrogen). The oxidation reactivity of the SnO 2 material has been evaluated by the use of a hygrometer, which in the dynamic flow system beyond the sensor cell, measures the water evolved when the H 2 (or CH 4)/SnO 2 interaction takes place. The results, expressed by the electrical response as a function of oxygen and hydrogen (or methane) concentrations, give information about the detection mechanism. For hydrogen gas detection, two different processes seem to occur, an adsorption-reaction mechanism when the oxygen concentration is high in comparison with the hydrogen one and an electrochemical response in the reverse case. For methane gas, the sensor response mechanism is probably independent over the range of oxygen and methane concentrations investigated.

Effect of diffusion on stationary states for a spherical catalyst with a three-stage adsorption reaction mechanism

In this work a study is made of the multiplicity of stationary points for a kinetic Langmuir-Hinshelwood model of the oxidation reaction of CO on a platinum spherical catalyst taking account of diffusion of reagents towards the surface. Analysis shows the existance of additional arms of the stationary reaction rate connected with the occurence of the external diffusion process itself (central diffusion schedule). The lesser the catalyst grain radius, the closer is the upper diffusion arm to the upper kinetic arm, and the central diffusion arm to the lower kinetic arm. The changeover from one diffusion arm to another and analysis of stationary state stability is examined in another paper.