Adsorption Conformation Research Articles

A Stealthiness Evaluation of Main Chain Carboxybetaine Polymer Modified into Liposome.

Background: Acrylamide polymers with zwitterionic carboxybetaine (CB) side groups have attracted attention as stealth polymers that do not induce antibodies when conjugated to proteins. However, they induce antibodies when modified onto liposomes. We hypothesized that antibodies are produced against polymer backbones rather than CB side groups. Objectives: In this study, we designed and synthesized a polymer employing CB in its main chain, poly(N-acetic acid-N-methyl-propyleneimine) (PAMPI), and evaluated the blood retention of PAMPI-modified liposomes in mice. Results: The non-fouling nature of PAMPI-modified liposomes estimated from serum protein adsorption was found to be not inferior to PCB- and PEG-modified liposomes. However, to our surprise, the PAMPI-modified liposomes showed an instantaneous clearance less than 1 h post-injection, comparable to the naked liposomes. Conclusions: The extent of the blood retention of polymer-modified liposomes cannot be predicted by their susceptibility to serum protein adsorption and semi-flexible conformation.

Rapid synthesis of solid polycarboxylate superplasticizers via photoinitiated radical polymerization

The synthesis and performance optimization of solid polycarboxylate superplasticizers (PCEs) present significant challenges. In our study, a rapid synthesis of a solid polycarboxylate superplasticizer (IPCE10) was achieved using photoinitiated free radical polymerization. IPCE10 exhibited good dispersibility and improved compressive strength in concrete. Dynamic light scattering tests and molecular dynamics simulations demonstrated that the adsorption conformation of IPCE10 on the calcium silicate hydrate surface was relatively dispersed, with a thicker adsorption layer. This indicates that IPCE10 has stronger steric hindrance, resulting in superior dispersibility. Additionally, density functional theory calculations of the reaction energy barriers for radical generation by photoinitiated and azo-initiated monomers revealed that the energy barrier in the photoinitiated system was significantly lower than that in the azo-initiated system, indicating that photoinitiated polymerization is more feasible. This study proposes a simple and rapid method for the preparation of solid polycarboxylate superplasticizers, providing valuable insights for the development of high-value-added construction materials.

Effect of protonation and deprotonation on oxygen-containing groups functionalized graphene for boron adsorption removal

This study investigated the adsorption mechanisms of boron on protonated and deprotonated graphene with oxygen-containing functional groups. Six representative adsorption conformations of boron predominant species (B(OH)3 (B3) and B(OH)4− (B4)) on graphene were proposed. Protonation and deprotonation of graphene had significant effects on boron adsorption. Deprotonation of hydroxyl-modified (G20-OH) and carboxyl-modified graphene (G20-COOH) with 20 carbon rings decreased B3 and B4 adsorption. Protonation of G20-OH enhanced B3 adsorption. The adsorption interface, mainly around hydrogen atoms associated with protonated groups, exhibited a sharp gradient, due to the increased electron density from OH bond formation. B3 showed stronger electron sharing, emphasizing robust interactions. Hydrogen bonding dominated G20-OH2-B3, while G20-O-B4 exhibited more substantial hydrogen bond interactions. In summary, hydrogen bond strength was crucial in B3 adsorption, while electrostatic repulsion hindered B4 adsorption on deprotonated graphene. These findings highlight the importance of graphene protonated and deprotonated states in effectively removing various pKa contaminants.

Molecular-level explanation of interactions of random and block polycarboxylic acid dispersants with bituminous coal in coal–water slurry through experiments and simulations

The adsorption conformations of random-structure polycarboxylic acid (PCR) and block-structure polycarboxylic acid (PCB) on coal surfaces were analyzed from a microscopic perspective. This analysis involved a combination of molecular dynamics (MD) simulations and experiments. The saturation adsorption amount of PCB was found to be significantly much larger than that of PCR. Additionally, observations from the contact angle and X-ray photoelectron spectroscopy confirmed that PCB exhibited superior wetting performance on coal compared to PCR and had a greater adsorption layer thickness. The relative concentration changes and the mean square displacement (MSD) of water indicate that the better adsorption of PCB on the coal surface makes the water molecules more evenly distributed, which improves hydration, increases the thickness of the “adsorption layer”, and enhances the mobility of water molecules. The interaction energy suggests the block structure of PCB is more favorable for molecular extension due to its well-defined structure. This provides a theoretical and experimental basis for expanding the molecular sequence structure design of polycarboxylic acid dispersants.

A molecular level-based parametric study on the capture of hydrogen sulfide and carbon oxides from flue gas mixtures using Au nanopores

ABSTRACT Identifying a means of effectively separating and adsorbing the harmful constituents from flue gas emissions is always crucial for the protection of human health and the environment. All-atom molecular dynamics were employed to analyze the dynamic behaviour of flue gas molecules in Au nanopores. The influences of various system temperatures, gas concentrations, and pore sizes on the adsorption conformation, diffusion coefficient, average adsorption energy, and adsorption probability of the flue gases inside an Au nanopore were examined. Results showed that when the temperature rose to 300∼400 K, the gaseous H2S constituent in the flue gas was swiftly adsorbed to the nanopore walls due to the strong H2S-Au interactions, enabling an effective separation of H2S from the flue gas. In addition, increases in pore size (d ≥ 40 Å) reduced the adsorption probability of CO2 and CO on the nanopore surfaces, which also promoted constituent separations of H2S from the flue gas. When the concentration of flue gas exceeded 6.6 mol/L, hydrogen bonds of H2O clusters and their networks entangled, impeding molecular diffusion and thereby reducing the functionality of nanopore-trapping molecules. The results presented in this paper provide a valuable reference for filter material design for flue gas depuration.

Mechanism insights into low-temperature oxidation of n-heptane on CeO2 surface: A DFT study

The low-temperature oxidation (LTO) mechanism of n-heptane on CeO2 surfaces was investigated in this study employing density functional theory (DFT). Firstly, the adsorption conformations of relevant species were optimized, and the main reaction steps' energy barriers and reaction-rate coefficients were calculated. The results show that the hydroxyl groups of fuel radicals strengthen the adsorption of fuel radicals on CeO2 surfaces. Furthermore, the energy barriers associated with the low-temperature (LT) chain branching pathway of n-heptane on the CeO2 surface exhibit lower values compared to those observed in the gas phase. The presence of CeO2 is also observed to mitigate the detrimental impact of competing reactions on the low-temperature branching pathway of n-heptane. It should be noted that the energy barrier for the decomposition of H2O2 on the CeO2 surface is 32.575 kcal/mol, 33.2 % lower than that in the gas phase, which allows H2O2 to be decomposed much easier at low temperatures. The resultant OH radicals desorb to the intimated gas phase, accelerating the oxidation of fuel molecules in the gas phase. Therefore, n-heptane transitioned to high-temperature ignition more easily and rapidly in the presence of CeO2. The calculation's findings adequately explain the experimental finding that adding CeO2 improves diesel fuel combustion.

Electrical property-selective noncovalent dispersion of carbon nanotubes by poly(perylene diimide-thiophene): a molecular dynamics study

ABSTRACT Thiophene polymers have been widely used to selectively disperse semiconducting single-walled carbon nanotubes (sc-SWNTs). Important questions concern the influence of the solvent on the adsorbability and adsorption-conformation of such polymers, along with the relation between the thiophene polymer structure and selectivity to SWNTs. These concerns about the behaviour of poly(perylene diimide (PDI)-thiophene) have been addressed in this study via molecular dynamics simulation. It is observed that the polymer does not adsorb to SWNTs in a solvent with strong polarity and shows an effective adsorbability in a solvent with moderate polarity or non-polarity. Its selectivity turns from metallic SWNTs to semi-conducting SWNTs in a solvent with a decreasing polarity. In addition, the rigid part in the polymer backbone (PDI) enlarges adsorbability significantly, and the flexible part (two thiophene units) adjusts its adsorption conformation onto SWNTs, which offers the selectivity. The study offers theoretical clues for designing the structure of thiophene polymers with respect to SWNTs-extraction.

Molecular dynamics simulations of adsorption behavior of mixtures of surfactant and polymer at C3A/water and Ettringite/water interfaces

In cementitious system, surfactant is used as air-entraining agents, which is often incompatible with other chemical admixtures, such as superplasticizers. The adsorption of surfactants at solid–liquid interface is critical for the bubble stability. The measurement of adsorption properties of surfactant in fresh cement or concrete is very difficult. In this study, classical molecular dynamics simulations is used to analysis the influence of two polymers (call as HPMC and PCA, respectively) on the adsorption behaviors of the two anionic surfactants (call as HSO4 and HPO4, respectively) at the C3A/water and ettringite/water interfaces. At solid/water interface, both of HSO4 and HPO4 molecules form a monolayer with hydrophilic head groups adsorbed on the solid surfaces. After adding polymers, the adsorption conformations are changed to spherical micelle or multilayer. The electrostatic interaction between oxygen atoms of hydrophilic head groups and calcium atoms of solid surface plays a decisive role. Therefore, the value of adsorption energy of HPO4 with more negatively charged hydrophilic head groups is greater than that of HSO4. The adsorption energies of the two surfactants are weakened by the two polymers, but the adsorption energy value of HPO4 is always greater. The influence mechanism of HPMC and PCA is different. The negatively charged PCA has a strongly competitive adsorption with the surfactants. The neutral HPMC has a weak adsorption capacity but it carries many hydroxyl groups to interact with the hydrophilic head groups of surfactants.

Understanding of the flocculating performance in varying salinity solutions of Chi-g-CPAM and CPAM

In this work, the adsorption performance of a novel chitosan-based flocculant (Chi-g-CPAM) and a cationic flocculant (CPAM) onto the kaolinite surface as well as the interaction mechanisms have been investigated by settling tests, atomic force microscopy (AFM) and quartz crystal microbalance with dissipation (QCM-D). When the KCl concentration of the solution altered from 1 mM to 100 mM, the settling rate of kaolinite suspension using CPAM deteriorated from 2.73 m/h to 1.97 m/h. However, the Chi-g-CPAM exhibited salt resistance as the settling rate changed slightly from 2.34 m/h to 2.44 m/h. From the QCM-D results, the Δf of CPAM onto silica sensor changed from − 3.6 Hz to − 33.6 Hz and -ΔD/Δf × 106 increased from 0.167 to 0.223, confirming that the CPAM layer adsorbed on the silica surface was thicker and more dissipative in 100 mM KCl solution. Meanwhile, the Δf of Chi-g-CPAM onto silica sensor changed from − 14.3 Hz to − 33.9 Hz. The conformation of Chi-g-CPAM layer changed slightly as the -ΔD/Δf × 106 increased from 0.174 to 0.186. From the AFM measurements in 1 mM and 100 mM KCl solution, the distance of adhesion forces between the silica probe and CPAM expanded from approximately 20 nm to around 50 nm, and the adhesion force changed from 1.9 nN± 0.1 nN to 21.3 nN± 0.1 nN. The interaction forces with a long range (∼100 nm) maintained at about 3 nN between the silica probe and Chi-g-CPAM. Such difference was mainly attributed to the steric hindrance effect originating from the shorter molecular chain of Chi-g-CPAM. In 100 mM KCl solution, the CPAM molecules with long chains had a more coiled conformation than Chi-g-CPAM, which resulted a train-like flat adsorption conformation and larger adhesion, and formed a loose and thick polymer layer of CPAM in high salinity. The insights into the flocculating performance in varying salinity solutions of CPAM and Chi-g-CPAM will contribute to the molecular design of chitosan-based flocculants for efficient wastewater treatment.

In situ adsorption study of carboxymethylcellulose and sodium oleate on quartz using a quartz crystal microbalance with dissipation (QCM-D)

Adsorption kinetics and conformation of sodium oleate and carboxymethylcellulose (CMC) on the quartz surface in real time remain a challenge in the flotation system of CMC /sodium oleate/quartz. In this work, in situ adsorption characteristics of CMC and sodium oleate on quartz surface was investigated by using quartz surface crystal microbalance with dissipation (QCM-D). QCM-D data showed that the conformations and kinetics were critically dependent on pH and degree of substitution (DS) of CMC. As the degree of substitution of CMC increases, the adsorption layer on the quartz surface becomes looser. There was only one adsorption stage at pH 8 and 12, and the adsorption layer was rigid at pH 12. At pH= 10, the conformation of the adsorbed layer changes from loose to rigid and then to loose again. CMC adsorbs less in the early adsorption stage, and the adsorbed layer is loose. As the adsorption proceeds, the adsorption increases, and the adsorbed layer becomes more rigid. At stage III, the adsorbed layer becomes loose, which is considered to be the formation of a hydrated layer. Under different pH conditions, the adsorption of sodium oleate on the quartz surface had only one stage, and when CMC and sodium oleate were adsorbed one after the other on the surface of the quartz surface, two distinguishable adsorption stages appeared, and the conformation of the adsorbed layer gradually changed from rigid to loose. The change of surface free energy of quartz surface before and after CMC adsorption was also calculated by Washburn kinetic equation and the van Oss - Chaudhuri-Good theory. The results showed that the surface free energy reduced and the hydrophobicity increased after the adsorption of CMC on the quartz surface.

Density Functional Theory Study on the Interaction between Aflatoxin B1/M1 and Gold Substrate.

Aflatoxin M1 (AFM1) and its precursor, Aflatoxin B1 (AFB1), are highly pathogenic and mutagenic substances, making the detection and sensing of AFB1/M1 a long-standing focus of researchers. Among various detection techniques, surface-enhanced Raman spectroscopy (SERS) is considered an ideal method for AFB1/M1 detection due to its ability not only to enhance characteristic frequencies but also to detect shifts in these frequencies with high repeatability. Therefore, we employed density functional theory in conjunction with surface-enhanced Raman spectroscopy to investigate the interaction between AFB1/M1 and a Au substrate in the context of the SERS effect for the first time. To predict the potential binding sites of AFB1/M1 and Au within the SERS effect, we performed calculations on the molecular electrostatic potential of AFB1/M1. Considering the crucial role of the binding energy in molecular docking studies, we computed the binding energy between two molecules interacting with Au at different binding sites. The molecular frontier orbitals and related chemical parameters of AFB1/M1 and "molecular-Au" complexes were computed to elucidate the alterations in AFB1/M1 molecules under the SERS effect. Subsequently, the theoretical Raman spectra of AFB1/M1 and the complexes were compared and analyzed, enabling determination of the adsorption conformation of AFB1/M1 on the gold surface based on SERS surface selection rules. These findings not only provide a deeper understanding of the interaction mechanism between molecules and substrates in the SERS effect but also offer theoretical support for developing novel aflatoxin SERS sensors.

Molecular Structure and Conformation of Biodegradable Water-Soluble Polymers Control Adsorption and Transport in Model Soil Mineral Systems.

Water-soluble polymers (WSPs) are used in diverse applications, including agricultural formulations, that can result in the release of WSPs to soils. WSP biodegradability in soils is desirable to prevent long-term accumulation and potential associated adverse effects. In this work, we assessed adsorption of five candidate biodegradable WSPs with varying chemistry, charge, and polarity characteristics (i.e., dextran, diethylaminoethyl dextran, carboxymethyl dextran, polyethylene glycol monomethyl ether, and poly-l-lysine) and of one nonbiodegradable WSP (poly(acrylic acid)) to sand and iron oxide-coated sand particles that represent important soil minerals. Combined adsorption studies using solution-depletion measurements, direct surface adsorption techniques, and column transport experiments over varying solution pH and ionic strengths revealed electrostatics dominating interactions of charged WSPs with the sorbents as well as WSP conformations and packing densities in the adsorbed states. Hydrogen bonding controls adsorption of noncharged WSPs. Under transport in columns, WSP adsorption exhibited fast and slow kinetic adsorption regimes with time scales of minutes to hours. Slow adsorption kinetics in soil may lead to enhanced transport but also shorter lifetimes of biodegradable WSPs, assuming more rapid biodegradation when dissolved than adsorbed. This work establishes a basis for understanding the coupled adsorption and biodegradation dynamics of biodegradable WSPs in agricultural soils.

Probing the adsorption configuration of methanol at a charged air/aqueous interface using nonlinear spectroscopy.

Investigating the effects of electrolyte ions on the adsorption configuration of methanol at a charged interface is important for studying the interface structure of electrolyte solutions and the oxidation mechanism of methanol in fuel cells. This study uses sum frequency generation (SFG) and heterodyne-detected second harmonic generation (HD-SHG) to investigate the adsorption configuration of methanol at the air/aqueous interface of 0.1 M NaClO4 solution, 0.1 M HClO4 solution and pure water. The results elucidate that the ion effect in the electrolyte solution affects the interface's charged state and the methanol's adsorption conformation at the interface. The negatively charged surface of the 0.1 M NaClO4 solution and the positively charged surface of the 0.1 M HClO4 solution arise from the corresponding specific ionic effects of the electrolyte solution. The orientation angle of methyl with respect to the surface normal is 43.4° ± 0.1° at the 0.1 M NaClO4 solution surface and 21.5° ± 0.2° at the 0.1 M HClO4 solution surface. Examining these adsorption configurations in detail, we find that at the negatively charged surface the inclined orientation angle (43.4°) of methanol favors the hydroxymethyl production by breaking the C-H bond, while at the positively charged surface the upright orientation angle (21.5°) of methanol promotes the methoxy formation by breaking the O-H bond. These findings not only illuminate the intricate ion effects on small organic molecules but also contribute to a molecular-level comprehension of the oxidation mechanism of methanol at electrode interfaces.

Dependence of lactose adsorption on the exposed crystal facets of metals: a comparative study of gold, silver and copper.

In this theoretical work, we investigated the adsorption of a lactose molecule on metal-based surfaces, with a focus on the influence of the nature of the metal and of the type of exposed crystal facet on the adsorbed structures and energetics. More precisely, we considered three flat crystallographic facets of three face-centered cubic metals (gold, silver, and copper). For the global exploration of the energy landscape, we employed a multi-stage procedure where high-throughput searches, using a stochastic method that performs global optimization by iterating local searches, are followed by a refinement of the most probable adsorption conformations of the molecule at the ab initio level. We predicted the optimal conformation of lactose on each of the nine metal-surface combinations, classified the many low-energy minima into possible adsorption modes, and analyzed the structural, electronic and energetic aspects of the lactose molecule on the surface, as well as their dependence on the type of metal and exposed crystal facet. We observed structural similarities between the various minimum-energy conformations of lactose in vacuum and on the surface, a rough correlation between adsorption and interaction energies of the molecule, and a small charge transfer between molecule and surface whose direction is metal-dependent. During adsorption, an electronic reorganization occurs at the metal-molecule interface only, without affecting the vacuum-pointing atoms of the lactose molecule. For all types of surfaces, lactose exhibits the weakest adsorption on silver substrates, while for each coinage metal the adsorption is strongest on the (110) crystal facet. This study demonstrates that the control of exposed facets can allow to modulate the interaction between metals and small saccharides.

The effect of amphiphilic monomer on the interaction between amphiphilic polyacrylamide and crude oil on the solid surface

Hydrophobically modified polyacrylamide (HMPAM) is one of most used amphiphilic polymers for polymer flooding in oilfield. The interaction between HMPAM and crude oil is key to the oil displacement efficiency of HMPAM. However, due to the lack of experimental research method, there is little research on this aspect. In this work, HMPAMs containing different types of amphiphilic monomers were prepared, their interactions with crude oil were studied by dual polarization interferometry (DPI) for the first time, and their adsorption conformations on the surface of crude oil were discussed. The DPI results directly shown that the influence of amphiphilic monomer type on the interaction strength was as follows: nonionic type > cationic type ≈ anionic type. This order was consistent with the adsorption capacity of amphiphilic monomer on the surface of crude oil, indicating that the interaction strength between HMPAM and crude oil mainly depended on the type of amphiphilic monomers. In addition, the DPI results indirectly shown that the effect of amphiphilic monomer type on the HMPAM molecular coiled conformation on the surface of crude oil was also determined by the adsorption capacity of amphiphilic monomer. The research results of this paper can provide useful information for the amphiphilic monomer selection from the perspective of improving oil displacement efficiency of HMPAM.

Revealing Adsorption Conformation and Electro-oxidation Mechanism of Urea on the Ni Film Catalyst by In Situ ATR-SEIRAS

Revealing Adsorption Conformation and Electro-oxidation Mechanism of Urea on the Ni Film Catalyst by In Situ ATR-SEIRAS

The effect of pre-corrosion on corrosion inhibition performance and mechanism of quinoline quaternary ammonium salts

The influence of pre-corrosion on the corrosion inhibition performance and corrosion inhibition mechanism of quinoline quaternary ammonium salt (QQAS) on Q235 carbon steel in 1 wt% HCl solution at 60 °C were investigated by weight loss experiment, molecular dynamics simulation. The results of IR vibrational spectra and NMR hydrogen spectra indicate the successful synthesis of QQAS. The results of weight loss experiments show that the corrosion inhibition performance of the synthesized QQAS increase with the increasing of the concentration under the condition of Q235 carbon steel with and without pre-corrosion. But the pre-corrosion obviously decreases the corrosion inhibition efficiency by 17.28% when the concentration is 50 mg·L−1. Analysis of thermodynamic parameters shows that the adsorption of QQAS on the steel surface is a spontaneous and exothermic process, which conforms to the Langmuir isothermal formula and is mainly based on chemical adsorption. The results of molecular dynamics simulation indicate that pre-corrosion changes the equilibrium adsorption conformations of QQAS molecules, and decreases the adsorption energies, and decreases the density of the film for the different oxidization extent of Q235 carbon steel. As a result, the corrosion inhibition performance of QQAS is decreased by the pre-corrosion. The results are in good agreement with the results of weight loss experiments. The corrosion inhibition performance of QQAS is the best when the number of QQAS molecules is 18. The corrosion inhibition mechanism is a single molecular layer adsorption mechanism. The results of this study can provide a reference for studying the corrosion inhibition performance and corrosion inhibition mechanism of corrosion inhibitors under the action of pre-corrosion.

Mechanistic insight into the adsorption and interaction of lignite, organic ingredients, and dispersant in coal wastewater slurry

The conversion of coal gasification wastewater into coal wastewater slurry (CWWS) for combustion and gasification fuels is a promising approach that combines resource recovery with effective wastewater management. In this work, the influence of organic ingredients derived from coal gasification wastewater on the slurrying capabilities of lignite, particle dispersion/aggregation behavior, and adsorption characteristics between lignite and sodium methylene dinaphthalene sulfonate (NNO) in CWWS was thoroughly investigated. The interaction mechanism of lignite, NNO, and the organic ingredients in the slurry systems revealed subsequently by molecular dynamics (MD) simulations. Results indicated that the maximum solid concentration for coal gasification wastewater simulated by organic ingredients increased by 1.64% with a decrease in pseudo-plasticity and stability. The presence of dodecane, phenolic and heterocyclic nitrogen compounds caused the dissociation and coalescence of particles in the CWWS and further formation of creaming or clarifying layer. The adsorption processes of NNO and the organic ingredients on lignite particles exhibited competitive adsorption, following the pseudo-second-order kinetic and the Freundlich thermodynamic models. The adsorbed organic ingredients enhanced the hydrophobicity and electrostatic repulsion of the particle surface in CWWS, increasing the hydrophobic C-C/C-H content from 64.73% to 71.27%. Moreover, the MD simulation results revealed that the adsorption conformations at the lignite-water interface in CWWS changed from “single-point and single-layer” adsorption of NNO to “multi-point and multi-layer” adsorption of NNO and organic ingredients driven by hydrophobic effect, van der Waals force, π-π stacking effect, and hydrogen bonding.

Molecular dynamics simulation of the influence of doping on the water absorption characteristics of kaolinite

The large amount of water adsorbed by clay minerals in argillaceous rocks upsets the balance of the microstructure, causing large deformation and failure of the rock surrounding deep mining roadways when they encounter water. The many impurities in natural clay minerals, and the electronegativity of the system caused by doping, greatly promote the adsorption of water. Grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) methods were both used to simulate the water adsorption characteristics of kaolinite to study the effects of doping elements of different valency and the pressure on water molecules in kaolinite particles, and the extent to which these affect the adsorption conformation, relative concentration distribution, adsorptive capacity, adsorption site, the heat of adsorption and adsorption energy of the water molecules on the surface of kaolinite particles. The molecular mechanism of microscopic interactions between doped kaolinite and water molecules is illustrated. It was found that at a temperature of 25 °C and a pressure of 10 MPa, water molecules are adsorbed on the surface of kaolinite in two layers. The heat of adsorption is 1.899–2.128 kJ/mol, which is far below the critical value of 42 kJ/mol for chemical adsorption. The interaction between kaolinite and water molecules is typical of physical adsorption. The absorption energy is negative, and the system is thermodynamically stable after kaolinite absorbs water. The variation of adsorption energy values is similar to the variation pattern of absorptive capacity, and both increase logarithmically with increasing pressure; doping causes both to decrease. Doping enhances the interaction between the kaolinite surface and water molecules, promoting the adsorption of water molecules on the kaolinite surface. This work explores the adsorption behavior of water molecules on the doped kaolinite surface from a microscopic perspective, and provides a theoretical foundation for further research on the deterioration of engineering properties of kaolinite-like clay minerals in contact with water.

Promoting CO2 and H2O activation on O-vacancy regulated In-Ti dual-sites for enhanced CH4 photo-production

Engineering the specific active sites of photocatalysts for simultaneously promoting CO2 and H2O activation is important to achieve the efficient conversion of CO2 to hydrocarbon with H2O as a proton source under sunlight. Herein, we delicately design the In/TiO2-VO photocatalyst by engineering In single atoms (SAs) and oxygen vacancies (VOs) on porous TiO2. The relation between structure and performance of the photocatalyst is clarified by both experimental and theoretical analyses at the atomic levels. The In/TiO2-VO photocatalyst furnish a high CH4 production rate up to 35.49 μmol g−1 h−1 with a high selectivity of 91.3% under simulated sunlight, while only CO is sluggishly generated on TiO2-VO. The combination of in situ spectroscopic analyses with theoretical calculations reveal that the VO sites accelerate H2O dissociation and increase proton feeding for CO2 reduction. Furthermore, the VO regulated In-Ti dual sites enable the formation of a stable adsorption conformation of In-C-O-Ti intermediate, which is responsible for the highly selective reduction of CO2 to CH4. This work demonstrates a new strategy for the development of effective photocatalysts by coupling metal SA sites with the adjacent metal sites of support to synergistically enhance the activity and selectivity of CO2 photoreduction.