Showing papers on "Chemisorption published in 2020"

Isotopic and in situ DRIFTS study of the CO2 methanation mechanism using Ni/CeO2 and Ni/Al2O3 catalysts

Abstract: The CO2 methanation mechanism was studied for Ni/CeO2 and Ni/Al2O3 catalysts. The higher methanation activity and selectivity of Ni/CeO2 is attributed to: i) Ni/CeO2 combines two types of active sites efficient for CO2 dissociation at the NiO-Ceria interface and for H2 dissociation on Ni0 particles; ii) water desorption is the slowest mechanism step, and, due to the high oxygen mobility throughout the ceria lattice, water is not necessarily formed on the same active sites that chemisorb CO2, i.e., the CO2 chemisorption sites are not blocked by water molecules; iii) the Ni/CeO2 surface does not accumulate carbon-containing species under reaction conditions, which allows faster chemisorption and dissociation of CO2. The Ni/Al2O3 catalyst handicaps are that all the steps of the mechanism take place on the same active sites, and the slow release of water and the accumulation of surface formates on these sites delay the chemisorption of further CO2 molecules.

Evaluation of corrosion inhibition performance of phosphorus polymer for carbon steel in [1 M] HCl: Computational studies (DFT, MC and MD simulations)

Abstract: Pentaglycidyl ether pentabisphenol A of phosphorus (PGEPBAP) phosphorus polymer was investigated as corrosion inhibition for carbon steel in aggressive solution using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), weight loss (WL), scanning electron microscope (SEM), density functional theory (DFT), electrostatic potential (ESP), radial distribution function (RDF), molecular dynamics (MD) and Monte Carlo (MC) simulations. The higher inhibition efficiencies for PDP, EIS and WL studies at 10−3 M concentration of PGEPBA phosphorus polymer are 94.18 %, 91.79 % and 91.3 %, respectively. ΔEcorr (23.7 mV) value of PGEPBAP phosphorus polymer is lower than 85 mV has been assigned to mixed type inhibitor. PGEPBAP formed protective film on carbon steel surface by adsorption according to Langmuir adsorption isotherm. SEM morphology suggested that PGEPBAP could effectively block acid attack by chemisorption on metal surface. To evaluate the polymer inhibitor and potential mechanism were especially realized DFT, ESP, RDF, MD and MC simulations.

Chemically induced transformation of chemical vapour deposition grown bilayer graphene into fluorinated single-layer diamond

Abstract: Notwithstanding the numerous density functional studies on the chemically induced transformation of multilayer graphene into a diamond-like film carried out to date, a comprehensive convincing experimental proof of such a conversion is still lacking. We show that the fluorination of graphene sheets in Bernal (AB)-stacked bilayer graphene grown by chemical vapour deposition on a single-crystal CuNi(111) surface triggers the formation of interlayer carbon-carbon bonds, resulting in a fluorinated diamond monolayer ('F-diamane'). Induced by fluorine chemisorption, the phase transition from (AB)-stacked bilayer graphene to single-layer diamond was studied and verified by X-ray photoelectron, UV photoelectron, Raman, UV-Vis and electron energy loss spectroscopies, transmission electron microscopy and density functional theory calculations.

Multidimensional insights into the corrosion inhibition of 3,3-dithiodipropionic acid on Q235 steel in H2SO4 medium: A combined experimental and in silico investigation.

Abstract: 3,3-Dithiodipropionic acid (DDA) as a potential corrosion inhibitor for Q235 steel in 0.5 M H2SO4 solution was examined. A variety of research approaches including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), scanning electron microscopy (SEM), atomic force microscopy (AFM), and computational techniques were employed. The toxicity and solubility of DAA were reasonably assessed. Its inhibition efficiency can reach approximately 93% when the optimal concentration is 5 mM. The results of PDP curves manifest that DDA is a mixed type corrosion inhibitor. EIS data indicate that the charge transfer resistance increases with increasing concentration of DDA. Gibbs free energy obtained from the Langmuir isotherm model suggests that DDA molecules hinder the acid attack mainly by chemisorption. Surface topography analysis strongly confirmed the electrochemical findings. Moreover, the simulation results based on density functional theory (DFT) calculation and molecular dynamics (MD) simulations supported the successful interfacial adsorption of DDA on Fe(1 1 0) surface.

Molybdenum Carbide-Oxide Heterostructures: In Situ Surface Reconfiguration toward Efficient Electrocatalytic Hydrogen Evolution.

Abstract: Heterostructured Mo2 C-MoOx on carbon cloth (Mo2 C-MoOx /CC), as a model of easily oxidized electrocatalysts under ambient conditions, is investigated to uncover surface reconfiguration during the hydrogen evolution reaction (HER). Raman spectroscopy combined with electrochemical tests demonstrates that the MoVI oxides on the surface are in situ reduced to MoIV , accomplishing promoted HER in acidic condition. As indicated by density functional theoretical calculations, the in situ reduced surface with terminal Mo=O moieties can effectively bring the negative ΔGH* on bare Mo2 C close to a thermodynamic neutral value, addressing difficult H* desorption toward fast HER kinetics. The optimized Mo2 C-MoOx /CC only requires a low overpotential (η10 ) of 60 mV at -10 mA cm-2 in 1.0 m HClO4 , outperforming Mo2 C/CC and most non-precious electrocatalysts. In situ surface reconfiguration are shown on W2 C-WOx , highlighting the significance to boost various metal-carbides and to identify active sites.

Redox-Active Two-Dimensional Covalent Organic Frameworks (COFs) for Selective Reductive Separation of Valence-Variable, Redox-Sensitive and Long-Lived Radionuclides.

Abstract: We report the first example of 2D covalent organic framework nanosheets (Redox-COF1) for the selective reduction and in situ loading of valence-variable, redox-sensitive and long-lived radionuclides (abbreviated as VRL nuclides). Compared with sorbents based on chemical adsorption and physical adsorption, the redox adsorption mechanism of Redox-COF1 can effectively reduce the impact of functional group protonation under the usual high-acidity conditions in chemisorption, and raise the adsorption efficiency from the monotonous capture by pores in physisorption. The adsorption selectivity for UO2 2+ reaches up to unprecedented ca. 97 % at pH 3, more than for any analogous adsorbing material.

Investigation of imidazole derivatives as corrosion inhibitors of copper in sulfuric acid: Combination of experimental and theoretical researches

Abstract: Levamisole (LMS) and 4-phenylimidazole (PIZ), used as corrosion inhibitors of copper in sulfuric acid solution were explored by electrochemical tests, morphology analysis and theoretical calculation. At the concentration of 8 mM, the maximum corrosion inhibition efficiencies of LMS and PIZ are 99.03% and 95.84%, respectively. All test data found that LMS had better corrosion inhibition performance than PIZ. LMS is a cathodic corrosion inhibitor, while PIZ belongs to a mixed-type corrosion inhibitor. Electrochemical results indicate that the corrosion inhibition efficiency has the same trend when the concentration of corrosion inhibitor increases. Scanning electron microscope and atomic force microscope were applied to research the surface morphology of copper samples under different conditions. X-ray photoelectron spectroscopy and Langmuir adsorption isotherm model were utilized to explain adsorption means. What is more, Langmuir adsorption isotherm model indicates the coexistence of physisorption and chemisorption for the two inhibitors. Besides, the adsorption between LMS and copper is more prone to chemical adsorption. The mechanism of metallic copper and corrosion inhibitors was explored through quantum chemistry studies and molecular dynamics simulation.

Refining Energy Levels in ReS 2 Nanosheets by Low‐Valent Transition‐Metal Doping for Dual‐Boosted Electrochemical Ammonia/Hydrogen Production

Abstract: Electrocatalytic nitrogen reduction reaction (NRR) and hydrogen evolution reaction (HER) are intriguing approaches to nitrogen fixation and hydrogen production under ambient conditions, given the need to discover efficient and stable catalysts to light up the “green chemistry” future. However, bottlenecks are often found during N2/H2O activation, the very first step of NRR/HER, due to energetic electron injection from the surface of electrocatalysts. It is reported that the bottlenecks for both NRR and HER can be tackled by engineering the energy level via low‐valent transition‐metal doping, simultaneously, where rhenium disulfide (ReS2) is employed as a model platform to prove the concept. The doped low‐valent transition‐metal domains (e.g., Fe, Co, Ni, Cu, Zn) in ReS2 provide more active sites for N2/H2O chemisorption and electron transfer, not only weakening the NN/OH bonds for easier dissociation through proton coupling, but also elevating d‐band center toward the Fermi level with more electron energy for N2/H2O reduction. As a result, it is found that iron‐doped ReS2 nanosheets wrapped nitrogen‐doped carbon nanofiber (Fe‐ReS2@N‐CNF) catalyst exhibits superior electrochemical activity with eightfold higher ammonia production yield of 80.4 µg h−1 mg−1cat., and lower onset overpotential of 146 mV and Tafel slope of 63 mV dec−1, when comparing with the pristine ReS2.

The fabrication of 3D hierarchical flower-like δ-MnO2@COF nanocomposites for the efficient and ultra-fast removal of UO22+ ions from aqueous solution

Abstract: Herein, interpenetrating 3D flower-like δ-MnO2@TpPa-1 composites were suitably constructed though the integration of δ-crystal manganese dioxide (δ-MnO2) nano-flowers with a covalent organic framework (COF, TpPa-1) via adopting a simple ultrasonication process. The physicochemical properties of δ-MnO2@TpPa-1 were characterized via SEM, TEM-EDX, XRD, FT-IR, pHpzc, XPS, and N2 adsorption–desorption studies. The kinetics of UO22+-ion adsorption onto δ-MnO2 and δ-MnO2@TpPa-1 confirmed the existence of a pseudo-second-order model. The results of isothermal experiments showed that the Langmuir model provided a better fit, illustrating a spontaneous, endothermic, and monolayer chemisorption process for UO22+ ions onto δ-MnO2 and δ-MnO2@TpPa-1. The maximum adsorption levels of UO22+ ions onto δ-MnO2 and δ-MnO2@TpPa-1 were 499.41 mg g−1 and 1147.773 mg g−1, respectively, at pH 6.5 and 298 K, owing to electrostatic attraction and inner-sphere surface complexation. Oxygen-containing groups played essential roles in the formation of U–O bonds and covalent Mn–O–U bonds, making δ-MnO2@TpPa-1 an excellent adsorbent for radionuclide elimination from solution.

Azo dye adsorption on an industrial waste-transformed hydroxyapatite adsorbent: Kinetics, isotherms, mechanism and regeneration studies

Abstract: Nanocrystalline hydroxyapatite (HAp) with high surface area was synthesized by surfactant-assistant hydrothermal method from an industrial waste phosphogypsum. X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen sorption characterizations revealed that HAp crystals grow as needle-like particles along the c direction with surface area of 86 and 135 m2/g for the samples synthesized without and with Brij-93 surfactant, respectively. Adsorption of anionic azo dye Congo Red (CR) were conducted on both samples, taking into account the influence of initial dye concentration (100–500 mg/L), adsorbent dosage (0.5–30 g/L), contact time (5–180 min) and solution pH (2–12). Kinetic studies showed that the adsorption of CR followed pseudo-second-order model, i.e., chemisorption is the rate controlling step. Freundlich isotherm was found to be most suitable model for the adsorption of CR, i.e. adsorption is multilayer process. The calculated maximum adsorption capacity of synthesized B93-HAp adsorbent using Brij-93 surfactant was found to be 139 mg/g at pH 5.5 and dosage of 2 g/L. Two predominant mechanisms were observed for CR adsorption, electrostatic attraction and hydrogen bonding as revealed by Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) studies. The multi-cycle sorption/desorption tests indicated that waste-transformed adsorbent could be regenerated and reused up to 6 cycles. Therefore, this work shows that the conversion of waste materials into adsorbents has a two-fold environmental benefit for both waste management and wastewater treatment.

Engineered tea-waste biochar for the removal of caffeine, a model compound in pharmaceuticals and personal care products (PPCPs), from aqueous media

Abstract: This study aimed to synthesize engineered tea-waste biochar, pyrolyzed at 700 °C using steam activation (TWBC-SA) for caffeine (CFN) removal from aqueous media. The morphological features and available functional groups on the surface of biochar were characterized using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Adsorption batch experiments were carried out at various pH values (3–10), contact time (up to 24 h), and initial concentration of CFN (10–300 mg L−1) using 1 g L−1 of TWBC-SA at 25 °C. SEM images showed the distribution of well-developed pores on the surface of biochar. FTIR spectra revealed that the surface of TWBC-SA provided extra aromatic character, which was further confirmed by XPS analysis. pH-adsorption edge data showed a maximum adsorption capacity of 15.4 mg g − 1 at pH 3.5. The experimental data were best-fitted to the non-linear Elovich kinetic model, demonstrating the contribution of chemical forces for adsorption of CFN onto the heterogeneous surface of TWBC-SA (initial rate of adsorption = 55.6 mg g − 1 min−1). Non-linear forms of Freundlich and Temkin isotherm models were fitted with the experimental data, describing favorability of chemical interactions between CFN and TWBC-SA. Finally, it is demonstrated that the adsorption of CFN by TWBC-SA is mainly governed by the chemisorption mechanism via electrostatic interactions and nucleophilic attraction. Thus, the engineered steam-activated tea-waste biochar has a high potential for adsorbing CFN from water.

Efficient Sm modified Mn/TiO2 catalysts for selective catalytic reduction of NO with NH3 at low temperature

Abstract: A series of Sm modified Mn/TiO2 catalysts were proposed for selective catalytic reduction of NO with NH3 and their catalytic activity was evaluated at low temperature. The effect of Sm on the catalytic activity of Mn-Sm/TiO2 was comprehensively studied using XRD, low-temperature N2 adsorption, XPS, NH3-TPD and H2-TPR. The results showed that the 20Mn-10Sm/TiO2 catalyst, prepared by ultrasonic impregnation, exhibited NOx conversion of higher than 80 % at the temperature range of 110–250 °C with a gas hourly space velocity of 80,000 h−1. The weak Lewis acid site and redox ability may be crucial properties for catalytic performance as a result of the increase of Mn4+ and surface chemisorption oxygen as well as weak acid sites due to the enhanced interaction among Mn, Sm and Ti after addition of Sm. The in situ DRIFTS experiments were conducted to investigate the adsorption of NH3 and NO with their surface reaction. The results revealed that the SCR reactions on the surface of Mn/TiO2 catalyst follow both Langmuir-Hinshelwood and Eley-Rideal mechanism and bridging nitrate is the important intermediate. While, that on surface of 20Mn-10Sm/TiO2 catalyst comply with only Eley-Rideal mechanism, as the introduction of Sm changes the reaction path by inhibiting the adsorption of NO in the presence of NH3. Besides, SCR reaction rate over 20Mn-10Sm/TiO2 catalyst is fast as a result of large amount of -NH2 species formed on the surface of 20Mn-10Sm/TiO2 catalyst for the breaking of N H bonds become easier over the Sm modified catalyst, which is beneficial for SCR activity of 20Mn-10Sm/TiO2 catalyst at low temperature. The TG-DSC-MS results revealed that the addition of Sm reduce the sulfation of Mn/TiO2 catalyst.