Adsorption Step Research Articles

Adsorption characteristics of S-Metolachlor onto the sawdust biochar derived from Acacia auriculiformis

The adsorption mechanism of S-Metolachlor in an aqueous solution by sawdust biochar derived from Acacia auriculiformis (SAB) was studied. SAB was manufactured at 500 °C for 4 h under oxygen-limited conditions and characterized for SEM, EDS, pHpzc, BET, and FTIR. The adsorption kinetics, isotherm, and diffusion studies of S-Metolachlor and SAB were further explored. Moreover, the effects of the solution pH were examined on the adsorption of S-Metolachlor by SAB. The BET analysis of SAB was achieved at 106.74 m2.g − 1 and the solution pH did not significantly influence the S-Metolachlor adsorption. The adsorption data were fitted into a Langmuir isotherm and the PSO model. The film diffusion coefficient Df (4.93 × 10 − 11 to 8.17 × 10 − 11 m2.s − 1) and the particle diffusion coefficient Dp (1.68 × 10 − 11 to 2.65 × 10 − 11 m2.s − 1) were determined and the rate-limiting step of S-Metolachlor adsorption and SAB was governed by liquid film diffusion. The S-Metolachlor adsorption process onto SAB was controlled by multiple mechanisms, including pore filling, H-bonding, hydrophobic interaction, and π-π EDA interactions. H-bonding is the main interaction for the adsorption of S-Metolachlor and SAB. Conclusively, the study illustrates that biochar produced from Acacia auriculiformis sawdust possessed effective adsorption properties for S-Metolachlor herbicide.

Molecular driving forces for water adsorption in MOF-808: A comparative analysis with UiO-66.

Metal-organic frameworks (MOFs), with their unique porous structures and versatile functionality, have emerged as promising materials for the adsorption, separation, and storage of diverse molecular species. In this study, we investigate water adsorption in MOF-808, a prototypical MOF that shares the same secondary building unit (SBU) as UiO-66, and elucidate how differences in topology and connectivity between the two MOFs influence the adsorption mechanism. To this end, molecular dynamics simulations were performed to calculate several thermodynamic and dynamical properties of water in MOF-808 as a function of relative humidity (RH), from the initial adsorption step to full pore filling. At low RH, the μ3-OH groups of the SBUs form hydrogen bonds with the initial water molecules entering the pores, which triggers the filling of these pores before the μ3-OH groups in other pores become engaged in hydrogen bonding with water molecules. Our analyses indicate that the pores of MOF-808 become filled by water sequentially as the RH increases. A similar mechanism has been reported for water adsorption in UiO-66. Despite this similarity, our study highlights distinct thermodynamic properties and framework characteristics that influence the adsorption process differently in MOF-808 and UiO-66.

Isolation and identification of olive tree leaf phenols through a resin adsorption/desorption process

Agricultural by-products contain substantial amounts of phenolics with significant antioxidant properties. In this work, a method to recover high concentrations of phenolic substances from a typical agricultural by-product, such as olive tree leaves, was investigated. Phenolic compounds previously separated through extraction and fractionated on a membrane array: Ultrafiltration (UF)-Nanofiltration (NF)-Reverse Osmosis (RO), were examined, alongside standard compounds. More specifically, the NF concentrate fraction, which contained the low molecular weight organics (simple phenols, carbohydrates) was treated by sorption/desorption processes in a cylindrical column packed with XAD16 N resin. The aim of this study was to optimize the isolation and the enrichment of phenolic compounds through their selective adsorption on resin grains. Standard compounds such as gallic acid and glucose were tested to study the sorption and desorption kinetics of phenol and carbohydrate families and the sorption parameters were estimated using the Thomas model. The results showed that XAD16 N resin selectively adsorbed phenolic compounds over carbohydrates. This was evident by the adsorption capacity exhibited by the resin when treating the glucose and gallic acid solutions. Regarding the NF concentrate fraction of olive leaf phenols, after the adsorption step, the adsorbed hydrophilic carbohydrates were removed by desorption using pure water. Immediately afterwards, an alcohol/water mixture was introduced to recover and extract the phenolic compounds. To identify the distinct phenols, a thorough liquid chromatography study was performed on the sorption and desorption samples collected at the outlet of the packed column, identifying the different time frame each phenol left the system.

Evaluation of adsorption characteristics of HFO-1234yf refrigerant with different adsorbents

The adsorption refrigerator system with HFO-1234yf refrigerant (2,3,3,3-tetrafluoropropene) has a global warming potential of less than 4 and activated carbons (MaxsorbIII, MH-00), mesoporous silica (TMPS-2), and metal organic frameworks (MOF-177). We measured the adsorption isotherm under diverse temperature and pressure conditions experimentally, and evaluated the adsorption characteristics of these adsorbents. In this study, we designed an experimental apparatus using a volumetric method and measured the adsorption equilibrium uptake. The MaxsorbIII/HFO-1234yf pair has an adsorption uptake as high as 1.30 g-HFO-1234yf/g-ads at 40 °C and 300 kPa. The adsorption uptake is approximately equivalent to that of the MaxsorbsIII/HFC-134a pair. The experimental data of the adsorption/desorption isotherms show that there is no hysteresis for the studied pair. The experimental results were reproduced using the Dubinin–Astakhov model (D–A model). The D–A model fits the experimental results precisely within 7%. A diagram of the relationship between HFO-1234yf and MaxsorbsIII also generated the D–A model, and the adsorption uptake capacity between the adsorption and desorption steps was obtained as 0.07 kg-HFO-1234yf/kg-ads at 40 and 80 °C. The adsorption capacities of MOF-177, MaxsorbIII, TMPS-2, and MH-00 were evaluated under similar operating conditions to be 0.19, 0.08, 0.11, and −0.03 kg/kg respectively.

Entropic Effects on Diamine Dynamics and CO2 Capture in Diamine-Appended Mg2(dopbdc) Metal-Organic Frameworks.

Recent measurements [Xu, J.; J. Phys. Chem. Lett. 2019, 10 (22), 7044-7049] have reported temperature-dependent rates of detachment of diamine from Mg sites in diamine-appended Mg2(dobpdc) [dobpdc4- = 4,4'-dihydroxy(1,1'-biphenyl)-3,3'-dicarboxylic] metal-organic frameworks, a process hypothesized to be a precursor for cooperative CO2 adsorption, leading to step-shaped isotherms or isobars. Here, we compute the rate of diamine exchange in this system for different diamines using metadynamics simulations based on a density functional theory-derived neural network potential. Reanalyzing recent measurements accounting for entropic effects, we find a positive correlation between the previously reported CO2 adsorption step pressure and the free energy at room temperature and show that the experiments and simulations are in good qualitative and quantitative agreement. The rates obtained here provide new insight into the chemical dynamics of CO2 adsorption in a class of materials that are promising for carbon capture and a lower bound on the time scale of cooperative adsorption.

Comparison of H2O2 and H2O oxidations on TDMAT absorbed on silicon(100) surface during reaction step of ALD–TiO2 process: A DFT study

Atomic layer deposition (ALD) is a thin film technology with high potential in nano fabrication. There is industrial demand to produce an ALD–TiO2 thin film using a low temperature process for applications of bending electronic devices and biomaterials. TDMAT has gained the most attention as a suitable titanium source to grow an ALD–TiO2 film at extremely low temperatures. In this process, almost all published reports have focused on metal-oxide precursors. The current work investigates the effects of oxidizing agents. For the first time, a theoretical investigation was carried out on the oxidation of H2O2 and H2O on TDMAT absorbed on a silicon (100) surface during the reaction step of the ALD–TiO2 process. We simulated the oxidation process, which continued from the adsorption step of the ALD–TiO2 process, where the TDMAT was used as a titanium precursor. The cluster of the Si9H12 =O2 =Ti[N(CH3)]2 surface model was used to represent the remaining TDMAT molecule absorbed on the Si(100) substrate. The reaction mechanisms of H2O2 oxidizing on this surface were evaluated based on their reaction pathways. The reaction pathway of H2O oxidizing on this surface was calculated at the same level to compare the effect of oxidizers. The DFT at the B3LYP 6–311 G+ (2d,p) and 6–31 G(d,p) theoretical levels were used to calculate the potential energy surface and to optimize the electronic structures in this process. It was found that the reaction mechanism depended on the nature of chemical bond dissociation within the oxidizer molecules during the oxidation process. In the oxidation of H2O2, the H2O2 molecule contained O–O and O–H bonds, which were dissociated during the oxidation process, resulting in different product structures. Only the O–O bond dissociation pathway produced the TiO2 structure. The two species of TDMAT ligands at the surface were completely oxidized using a single H2O2 molecule. The H2O2 oxidation produced more –OH groups (double) compared to H2O oxidation. In H2O oxidation, the H2O molecule contained only the O–H bond within its molecule and required activation energies significantly less than for all pathways of H2O2. The HOMO–LUMO properties and IR frequency characteristics (cm−1) of the plausible product structures were discussed. The results should be useful in guiding the selection of suitable precursors for use in the co–reactant system of the ALD–TiO2 process.

Enhancing Initial Surface Adsorption for Doped Lead‐Free Copper(I) Halide Microcrystals Through a Moderate Lewis Base Ligand

AbstractDoping Mn2+ in newly emerged lead‐free metal halides to access versatile optoelectronic applications is highly desired. However, understanding the chemical pathway of Mn2+ doping and precisely controlling it remains challenging. Here, the crucial role of the initial surface adsorption of Mn2+ in doping kinetics is demonstrated, and the adsorption step is effectively optimized by a moderate Lewis base ligand. The results show that not only the doping concentration of Mn2+ in Cs3Cu2I5 is modulated flexibly but also the produced Cs3Cu2I5:Mn2+ microcrystals exhibit tuned photoluminescence/radioluminescence properties, indicating their applicability in anti‐counterfeiting and X‐ray imaging. Systematic experimental and theoretical outcomes reveal that the moderate Lewis base ligand dually links Mn2+ (hard acid) and Cu+ (soft acid) on the matrix surface, which improves the initial surface adsorption of the dopant and further promotes the doping step. This study contributes a simple strategy for simply controlling Mn2+ doping in Cu(I)‐based halides and also opens a new avenue for understanding the fundamentals of doping dynamics in metal halide systems.

In Situ Infrared Spectroscopic Evidence of Enhanced Electrochemical CO2 Reduction and C-C Coupling on Oxide-Derived Copper.

The reaction mechanism of CO2 electroreduction on oxide-derived copper has not yet been unraveled even though high C2+ Faradaic efficiencies are commonly observed on these surfaces. In this study, we aim to explore the effects of copper anodization on the adsorption of various CO2RR intermediates using in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) on metallic and mildly anodized copper thin films. The in situ SEIRAS results show that the preoxidation process can significantly improve the overall CO2 reduction activity by (1) enhancing CO2 activation, (2) increasing CO uptake, and (3) promoting C-C coupling. First, the strong *COO- redshift indicates that the preoxidation process significantly enhances the first elementary step of CO2 adsorption and activation. The rapid uptake of adsorbed *COatop also illustrates how a high *CO coverage can be achieved in oxide-derived copper electrocatalysts. Finally, for the first time, we observed the formation of the *COCHO dimer on the anodized copper thin film. Using DFT calculations, we show how the presence of subsurface oxygen within the Cu lattice can improve the thermodynamics of C2 product formation via the coupling of adsorbed *CO and *CHO intermediates. This study advances our understanding of the role of surface and subsurface conditions in improving the catalytic reaction kinetics and product selectivity of CO2 reduction.

MnCoFe-LDH/Ni-MOF nanocomposite-coated hollow fiber membrane for solid phase extraction of amaranth dye from water and food samples followed by spectrophotometric analysis

In the present study, the new composite based on MnCoFe-LDH nanoflower/Ni-MOF/ hollow fiber membrane (HFM) was synthesized in such a way that first MnCoFe-LDH and Ni-MOF nanoparticles were synthesized separately, then converted into a composite and finally coated on the surface of the HFM. The final composite was characterized using FT-IR, XRD, SEM, and EDX analysis and applied as a promising and effective sorbent for the solid-phase microextraction of amaranth dye (as a model analyte) in various water and food samples, followed by spectrophotometric analysis. It should be noted that two main driving forces for conducting the extraction process are the electrostatic and π-π interactions between the surface of the adsorbent and the analyte molecule. By using this proposed adsorbent, the requirement for using a centrifuge for phase separation was eliminated. Furthermore, there was no necessity to use the vortex or the stirrer to carry out the adsorption and desorption steps, and only by hand-shaking of the sample solution, high extraction recovery was achieved. These advantages made the extraction process greener, quicker, and easier. Optimizations of all parameters affecting the proposed method (such as pH, sample solution, HFM size, adsorption time, and desorption time) were done using the central composite design methodology. The findings indicate that the calibration graphs exhibited linearity in the range of 20.0–1000 µg/L, with the limit of detection of 5.6 µg/L, the limit of quantification of 17.2 µg/L, and the correlation coefficient of 0.9981 for the model analyte. Furthermore, the relative recovery was obtained in the range of 93.6–101 %. In addition, intra-day RSD, inter-day RSD, and preconcentration factor (PF) were achieved at 3.8, 6.9, and 30, respectively. The suggested sorbent was successfully synthesized and applied for effective solid-phase microextraction of amaranth dye in different real samples.

Probing Ti–doped (Al–Ga) surface as Nanosensor for adsorbing the S- & N-containing heterocyclic compounds

Aluminum–Gallium doped with titanium by using ONIOM method through structural, electrical, and thermodynamic properties was studied in detail. Crystal structure of Ti–(Al–Ga) surface was coated by S- & N-heterocyclic carbenes of benzotriazole (BTA), 2-mercaptobenzothiazole (2MBT), 8-hydroxyquinoline (8HQ) and 3-amino-1,2,4-triazole-5-thiol (ATR). The “NMR” spectroscopy of the adsorption of BTA, 2MBT, 8HQ, and ATR on the Ti–doped Al–Ga nanoalloy surface represents that this surface can be employed as the magnetic S- & N-heterocyclic carbene sensors. In fact, “Ti” site in “Ti–(Al–Ga)” nanoalloy surface has bigger interaction energy amount from “Van der Waals’ forces” with BTA, 2MBT, 8HQ, and ATR that might cause them large stable towards coating data on the nanosurface. It has been estimated that the criterion for choosing the surface linkage of “S” and “N” atom in BTA, 2MBT, 8HQ, and ATR in adsorption sites can be impacted by the existence of close atoms of aluminum and gallium in the “Ti–(Al–Ga)” surface. The fluctuation of “NQR” has estimated the inhibiting role of BTA, 2MBT, 8HQ, and ATR for Ti–doped Al–Ga alloy nanosheet due to “S” and “N” atoms in the benzene cycle of heterocyclic carbenes being near the monolayer surface of ternary “Ti–(Al–Ga)” nanoalloy. Moreover, “IR” spectroscopy has exhibited that Ti–doped Al–Ga alloy nanosheet with the fluctuation in the frequency of intra–atomic interaction leads us to the most considerable influence in the vicinage elements generated due to inter–atomic interaction. Comparison to amounts versus dipole moment has illustrated a proper accord among measured parameters based on the rightness of the chosen isotherm for the adsorption steps of the formation of BTA @Ti–(Al–Ga), 2MBT @Ti–(Al–Ga), 8HQ @Ti–(Al–Ga), and ATR @Ti–(Al–Ga) complexes. Thus, the interval between sulfur, nitrogen and oxygen atoms in BTA, 2MBT, 8HQ, and ATR during interaction with transition metal of “Ti” in “Ti–(Al–Ga)” nanoalloy, (N→Ti, O→Ti, S→Ti), has been estimated with relation coefficient of R² = 0.9509. Thus, the present has exhibit the influence of “Ti” doped on the “Al–Ga” surface for adsorption of S- & N-heterocyclic carbenes of BTA, 2MBT, 8HQ, and ATR by using theoretical methods. Furthermore, the “partial electron density” or “PDOS” has estimated a certain charge assembly between Ti–(Al–Ga) and S– & N–heterocycles of BTA, 2MBT, 8HQ, and ATR which can remark that the complex dominant of metallic features and an exact degree of covalent traits can describe the augmenting of the sensitivity of “Ti–(Al–Ga)” surface as a potent sensor for adsorption of BTA, 2MBT, 8HQ, and ATR heterocycles.

Catalytic insights into perhydro-benzyltoluene dehydrogenation: Probing surface characteristics revealed by DRIFTS study

The enhancement of dehydrogenation activity in liquid organic hydrogen carriers (LOHC), such as perhydro-benzyltoluene (H12-BT), has been attributed to the addition of various promoters and support modifications into platinum (Pt)-based heterogeneous catalysts. Comprehensive understanding of surface sites predominantly catalyzing the dehydrogenation process is crucial for further enhancing catalytic performance. In this contribution, an in-depth quantitative CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) study on Pt-based catalysts with varying contents of sulfur, known to be effective in dehydrogenation reactions, is performed to unveil the active sites involved in the H12-BT dehydrogenation. Furthermore, while challenges associated with the adsorption step of reactants and products potentially deteriorate catalytic activity, these processes remain open questions for H12-BT dehydrogenation. To shed light on these aspects, we conducted in situ DRIFTS experiments utilizing H12-BT and H0-BT, its dehydrogenated counterpart, to determine the adsorption strength between these molecules and the different catalyst surfaces, influenced by the electron-deficiency effect due to the addition of sulfur. Additionally, our study investigates the correlation between sulfur-induced catalyst surface characteristics and the formation of methane through the demethylation process.

Surface chemical reactions of etch stop prevention in plasma-enhanced atomic layer etching of silicon nitride

Molecular dynamics (MD) simulations were performed to examine the influence of oxygen (O) ion irradiation at the end of each cycle of plasma-enhanced atomic layer etching (PE-ALE) of silicon nitride (SiN). The main concern during the SiN PE-ALE process is that it can lead to an etch stop due to excessive hydrofluorocarbon (HFC) polymer accumulation, which hinders ion impact in the desorption step. Such an etch stop can be avoided by incorporating an oxygen (O2) plasma irradiation step after the desorption step of a conventional two-step PE-ALE process of SiN. In this study, the differences between the two- and three-step PE-ALE processes of SiN with and without O2 plasma irradiation are discussed. In the simulations of this study, low-energy CH2F radicals are deposited on a SiN surface in the adsorption step, and the modified surface is then irradiated with energetic Ar+ ions and removed in the desorption step. In the O2 plasma irradiation step, the resulting surface is irradiated with low-energy O species, and excess carbon (C) atoms are removed. It has been found that the O irradiation step effectively prevents the accumulation of C atoms by promoting the formation of volatile CO molecules.

Understanding the rate-limiting step adsorption kinetics onto biomaterials for mechanism adsorption control

Biomaterials are a class of porous materials that have been widely exploited over the past two decades. However, the implications of controlling adsorption by rate-limiting steps are still not adequately established. Identifying the rate-limiting step is a promising approach for the design of adsorption systems. In this review, we study in detail the rate-limiting step of the adsorption of dyes in aqueous media on biomaterials to rationalize the factors governing the rate-limiting step involved in the adsorption process using empirical kinetics and mass transfer models. This knowledge is then applied to identify the best fit of these models to study the rate-controlling step involved in the adsorption process, which is crucial for the design of the adsorption system. This review first studies the limiting step of adsorption of dyes in an aqueous medium on biomaterials. Kinetic modeling is used to better understand the rate control step involved in biosorption. Generally, the equations used are empirical models of kinetics and mass transfer and the biomaterials come from the following categories: agricultural and industrial waste, algae, fungi, bacteria, and plants. In most adsorption studies reported in this review, the pseudo second-order model was found to be best suited for fitting the kinetic data of dyes on biomaterials, indicating that chemisorption is the rate-limiting step that controls adsorption. Concerning the diffusion effects of mass transfer, intraparticle diffusion is among the most often used models to examine the rate-limiting step which is controlled by both film diffusion and intraparticle diffusion. The first takes place when the external transfer is greater than the internal transfer while the opposite occurs in the case of porous diffusion. However, the majority of works do not study the real step of controlling the overall adsorption kinetics, namely, film diffusion or intraparticle diffusion.

Diluting the Resistance of Built-in Electric Fields in Oxygen Vacancy-enriched Ru/NiMoO4-x for Enhanced Hydrogen Spillover in Alkaline Seawater Splitting.

Recently, hydrogen spillover based binary (HSBB) catalysts have received widespread attention due to the sufficiently utilized reaction sites. However, the specific regulation mechanism of spillover intensity is still unclear. Herein, we have fabricated oxygen vacancies enriched Ru/NiMoO4-x to investigate the internal relationship between electron supply and mechanism of hydrogen spillover enhancement. The DFT calculations cooperate with in situ Raman spectrum to uncover that the H* spillover from NiMoO4-x to Ru. Meanwhile, oxygen vacancies weakened the electron supply from Ru to NiMoO4-x , which contributes to dilute the resistance of built-in electric field (BEF) for hydrogen spillover. In addition, the higher ion concentration in electrolyte will promote the H* adsorption step obviously, which is demonstrated by in situ EIS tests. As a result, the Ru/NiMoO4-x exhibits a low overpotential of 206 mV at 3.0 A cm-2 , a small Tafel slope of 28.8 mV dec-1 , and an excellent durability of 550 h at the current density of 0.5 A cm-2 for HER in 1.0 M KOH seawater.

Diluting the Resistance of Built‐in Electric Fields in Oxygen Vacancy‐enriched Ru/NiMoO4‐x for Enhanced Hydrogen Spillover in Alkaline Seawater Splitting

AbstractRecently, hydrogen spillover based binary (HSBB) catalysts have received widespread attention due to the sufficiently utilized reaction sites. However, the specific regulation mechanism of spillover intensity is still unclear. Herein, we have fabricated oxygen vacancies enriched Ru/NiMoO4‐x to investigate the internal relationship between electron supply and mechanism of hydrogen spillover enhancement. The DFT calculations cooperate with in situ Raman spectrum to uncover that the H* spillover from NiMoO4‐x to Ru. Meanwhile, oxygen vacancies weakened the electron supply from Ru to NiMoO4‐x, which contributes to dilute the resistance of built‐in electric field (BEF) for hydrogen spillover. In addition, the higher ion concentration in electrolyte will promote the H* adsorption step obviously, which is demonstrated by in situ EIS tests. As a result, the Ru/NiMoO4‐x exhibits a low overpotential of 206 mV at 3.0 A cm−2, a small Tafel slope of 28.8 mV dec−1, and an excellent durability of 550 h at the current density of 0.5 A cm−2 for HER in 1.0 M KOH seawater.

Illuminating Oxygen Reduction Reaction Kinetics in High Temperature Polymer Electrolyte Membrane Fuel Cells Using EIS

Owing to their notable power efficiency and zero greenhouse emissions, High Temperature Polymer Electrolyte Membrane Fuel Cells (HTPEMFCs) hold immense promise as a prospective candidate for generating clean energy. However, their commercialization is still impeded by the cathodic Oxygen Reduction Reaction (ORR) kinetics, which after almost half a century not only remain elusive, but constitute the most energy-intensive process, requiring large amounts of the expensive Pt catalyst to mitigate.In this work we provide solid experimental evidence, that the simple three elementary step Dissociative Adsorption Pathway (DAP) with two intermediate species (Oad and OHad), can accurately capture both the steady state (IV) and the Electrochemical Impedance Spectra (EIS) as well.Detailed EIS and IV experimental data were recorded at 180 °C under differential conditions, using a single serpentine HTPEMFC with a 4 cm2 active area. The fuel cell operated at the activation regime, where ORR potential losses dominate but mass transport limitations are negligible. The experimental data were successfully fitted with the derived analytic IV and EIS microkinetic model.The use of the DAP in accordance with the Transitions State Theory (TST), allowed the extraction and analysis of ORR kinetics and energetics. The deconvoluted EIS outlined the important role of the intrinsic kinetic inertia , i.e. the outcome of the competitive nature of the elementary reaction steps on the adsorbed intermediate species. Kinetic inertia not only dominated EIS and the polarization resistance, but demonstrated that the commonly used Butler Volmer and apparent Tafel slope kinetic approach is incapable of describing the multistep ORR kinetics. With the help of the Degree of Rate Control (DRC) analysis, we successfully identified the O2(g) dissociative adsorption as the rate limiting step.Finally, from an energetics perspective, by employing the TST kinetics formulation, we were able to calculate the free Gibbs’ transition states activation (kinetics) and reaction steps’ energies (thermodynamics). These results clarified that, the high ORR overpotential losses stem from the combined strength of both kinetically and thermodynamically imposed barriers, which originate from the high bonding strength of Oad on the Pt surface and the rather high activation energy of the O2(g) adsorption step.

Investigating the Electrochemical CO2 Reduction Mechanism on Oxide-Derived Copper Using in Situ FTIR Spectroscopy

Oxide-derived copper (OD-Cu) electrocatalysts have been extensively used for CO2 reduction reaction (CO2RR) applications in recent years due to their capability to selectively produce valuable C2 compounds. The mechanism of CO2 reduction on these surfaces, however, is still not clearly understood. Using in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), we show how the copper pre-oxidation process can significantly influence the adsorption of various CO2RR intermediates. Upon mildly anodizing a Cu thin film, we observed a redshift on the *CO2 – band, indicating that the initial CO2 adsorption and activation step is promoted on the oxide-derived surface. Additionally, we observed a faster growth of the *COatop band for the anodized copper film at low overpotentials, which demonstrates how a high *CO coverage can be achieved on OD-Cu. Finally, for the first time, we observed the simultaneous formation of two bands at 1327 cm–1 and 1425 cm–1 on the anodized Cu thin film. Using DFT calculations, we show that these bands match the theoretical vibrational frequencies of the *COCHO dimer, a key intermediate of the C2 pathway. Furthermore, our calculations show that the thermodynamics of *CO and *CHO coupling can be improved in the presence of the subsurface oxygen sites in OD-Cu. Our findings reveal the different aspects through which the CO2 reduction mechanism can be improved on OD-Cu electrocatalysts as compared to metallic copper.This work was financially supported by the Research Grants Council (16310419, 16309418, and 16304821) and the Innovation and Technology Commission (grant no. ITC-CNERC14EG03).

Interplay between surface structure, reaction condition and mechanism for ammonia decomposition on Ru catalyst

Ammonia decomposition provides a potential route for the production of COx-free hydrogen. Despite numerous studies, the active sites and reaction mechanism remain in debate. To date, only N-N recombination mechanism, in which N2* is formed by the N* atoms recombination, is investigated on the archetypical Ru catalyst and Ru B5 site has been identified as the active site. Combined density functional theory calculation and microkinetic modeling, we show that the N2Hy* (y > 0) dehydrogenation mechanism, which involves the stepwise N2Hy* dehydrogenation to N2*, is important and even dominant on Ru defect sites at low temperatures, elevated PNH3 or PH2 where the coverage of vacant sites is low so that the NHx (x = 1–3) dehydrogenation is suppressed. Regardless of reaction conditions, Ru A4 and kink sites show higher activity than the conventional B5 site, with the rate-determining steps of NH3 adsorption and H2 desorption. Inhibition of the ammonia decomposition rate by the hydrogen produced originates from the low dissociation barrier of hydrogen. This work reveals the interplay between surface structure, reaction condition and mechanism for ammonia decomposition on Ru catalyst, and the insights can enrich the design principles of catalysts for the ammonia decomposition and other important reactions of technological interest.

Enhanced Adsorptive Removal of Tetracycline by Phosphomolybdic Acid-Modified Low-Temperature Sludge Biochar.

Increasing the adsorption capacity and reducing the energy consumption of sludge biochar during preparation is important. In this study, a new modification method was developed to prepare phosphomolybdic acid-modified sludge biochar through the low-temperature pyrolysis of sewage sludge using phosphomolybdic acid as a modifier. Tetracycline was used to assess the adsorption performance of sludge biochar, and phosphomolybdic acid-modified sludge biochar was prepared at different temperatures. The results showed that the adsorption capacity of sludge biochar improved from 84.49 to 120.86 mg/g through modification with phosphomolybdic acid at 200 °C. The maximum adsorption capacities of phosphomolybdic acid-modified sludge biochar (200 °C pyrolysis temperature) at 298, 308, and 318 K were 283.87, 421.39, and 545.48 mg/g, respectively. Both liquid film and intraparticle diffusion were the main rate-limiting steps of tetracycline adsorption by phosphomolybdic acid-modified sludge biochar. Furthermore, the adsorption of tetracycline by phosphomolybdic acid-modified sludge biochar was mainly attributed to π-π interactions, electrostatic interactions, hydrogen bonding, and pore filling.

The Inhibitory Effect of KerraTM, KSTM, and MinozaTM on Human Papillomavirus Infection and Cervical Cancer.

Background and Objectives: Cervical cancer is one of the most common types of frequently found cancers in Thailand. One of the causative agents is the infection of the high-risk human papillomavirus (HPV) type 16 and 18. Traditional medicines are rich sources of bioactive compounds which are a valuable source for the development of novel cancer therapies. In this study, the therapeutic effects of 3 traditional medicines, KerraTM, KSTM, and MinozaTM, were studied on HeLa and CaSki cells. Materials and Methods: The effects of KerraTM, KSTM, and MinozaTM on cancer cells were evaluated through cytotoxicity and cell death assays. The infection assay using HPV-16 pseudovirus was also carried out. Results: All traditional medicines efficiently suppressed cell growths of HeLa and CaSki, with KerraTM being the most potent anticancer agent followed by KSTM and MinozaTM. KerraTM at 158 µg/mL and 261 µg/mL significantly increases the percentage inhibition of the HPV-16 pseudovirus infection in a pre-attachment step in a dose-dependent manner, while KSTM at 261 µg/mL efficiently inhibited viral infection in both pre-attachment and adsorption steps. However, KerraTM, KSTM, and MinozaTM at subtoxic concentrations could not reduce the viral E6 mRNA expressions of HPV-16 and HPV-18. Cell death assay by acridine orange/ethidium bromide showed that KerraTM increased population of dead cells in dose-dependent manner in both CaSki and HeLa. The percentage of secondary necrosis in KerraTM-treated CaSki was higher than that of HeLa cells, while the percentage of late apoptotic cells in HeLa was higher than that of CaSki, indicating that HeLa was more susceptible to KerraTM than CaSki. For KSTM and MinozaTM, these extracts at 250 µg/mL promoted autophagy over cell death. At 500 µg/mL, the percentage of dead cells in KerraTM was higher than that of KSTM and MinozaTM. Conclusions: KerraTM is a potent traditional medicine for promoting cancer cell death. KerraTM is possibly useful in the prevention and treatment of cervical cancer. Further investigation will be carried out to gain a better understanding of the biochemical mechanism and the pharmacological activity underlying this effect.