Electron Back-donation Research Articles

Halogen Tailoring of Platinum Electrocatalyst with High CO Tolerance for Methanol Oxidation Reaction.

The catalytic activity of platinum for CO oxidation depends on the interaction of electron donation and back-donation at the platinum center. Here we demonstrate that the platinum bromine nanoparticles with electron-rich properties on bromine bonded with sp-C in graphdiyne (PtBr NPs/Br-GDY), which is formed by bromine ligand and constitutes an electrocatalyst with a high CO-resistant for methanol oxidation reaction (MOR). The catalyst showed peak mass activity for MOR as high as 10.4 A mgPt -1, which is 20.8 times higher than the 20 % Pt/C. The catalyst also showed robust long-term stability with slight current density decay after 100 hours at 35 mA cm-2. Structural characterization, experimental, and theoretical studies show that the electron donation from bromine makes the surface of platinum catalysts highly electron-rich, and can strengthen the adsorption of CO as well as enhance π back-donation of Pt to weaken the C-O bond to facilitate CO electrooxidation and enhance catalytic performance during MOR. The results highlight the importance of electron-rich structure among active sites in Pt-halogen catalysts and provide detailed insights into the new mechanism of CO electrooxidation to overcome CO poisoning at the Pt center on an orbital level.

Core-shell structured composite high-efficiency catalyst Co@Pd/TiO2 with a compressed-strain Pd shell for the direct synthesis of H2O2

Direct synthesis of H2O2 from H2 and O2 still faces the dilemma of low selectivity and productivity due to the O-O bond dissociation. To expedite the resolution of this issue, we introduce a core–shell structured catalyst Co@Pd/TiO2 with a compressed-strain Pd shell. The Co@Pd/TiO2 catalyst demonstrates a superior H2O2 productivity of 6.95 × 103 mmol·gPd-1·h−1 and H2O2 selectivity of 98.1 %, with enhancements of over 192 % and 139 %, respectively, when compared to Pd/TiO2. The construction of the compressed-strain Pd shell on the Co@Pd/TiO2 catalyst induces a winder width (wd) and a lower center (εd) of the Pd d-band, allowing the Co@Pd/TiO2 catalyst to achieve the following benefits for improving H2O2 selectivity and productivity: (1) Reducing the degree of electron back-donation to O2* (* denotes adsorbed state, the same below), thus inhibiting the cleavage of the O-O bond in O2*; (2) Showing a weaker Pd-O bond strength, which stabilizes the OOH* species and suppresses the breakage of the O-O bond therein; (3) Weakening the interaction between the catalyst and chemical substances, thereby restraining H2O2 degradation.

How Doping Regulates As(III) Adsorption at TiO2 Surfaces: A DFT + U Study.

The efficient adsorption and removal of As(III), which is highly toxic, remains difficult. TiO2 shows promise in this field, though the process needs improvement. Herein, how doping regulates As(OH)3 adsorption over TiO2 surfaces is comprehensively investigated by means of the DFT + D3 approach. Doping creates the bidentate mononuclear (Ce doping at the Ti5c site), tridentate (N, S doping at the O2c site), and other new adsorption structures. The extent of structural perturbation correlates with the atomic radius when doping the Ti site (Ce >> Fe, Mn, V >> B), while it correlates with the likelihood of forming more bonds when doping the O site (N > S > F). Doping the O2c, O3c rather than the Ti5c site is more effective in enhancing As(OH)3 adsorption and also causes more structural perturbation and diversity. Similar to the scenario of pristine surfaces, the bidentate binuclear complexes with two Ti-OAs bonds are often the most preferred, except for B doping at the Ti5c site, S doping at the O2c site, and B doping at the O3c site of rutile (110) and Ce, B doping at the Ti5c site, N, S doping at the O2c site, and N, S, B doping at the O3c site of anatase (101). Doping significantly regulates the As(OH)3 adsorption efficacy, and the adsorption energies reach -4.17, -4.13, and -4.67 eV for Mn doping at the Ti5c site and N doping at the O2c and O3c sites of rutile (110) and -1.99, -2.29, and -2.24 eV for Ce doping at the Ti5c site and N doping at the O2c and O3c sites of anatase (101), respectively. As(OH)3 adsorption and removal are crystal-dependent and become apparently more efficient for rutile vs. anatase, whether doped at the Ti5c, O2c, or O3c site. The auto-oxidation of As(III) occurs when the As centers interact directly with the TiO2 surface, and this occurs more frequently for rutile rather than anatase. The multidentate adsorption of As(OH)3 causes electron back-donation and As(V) re-reduction to As(IV). The regulatory effects of doping during As(III) adsorption and the critical roles played by crystal control are further unraveled at the molecular level. Significant insights are provided for As(III) pollution management via the adsorption and rational design of efficient scavengers.

Mixed ligand complexes of Pt(II) Tertiary phosphines and 1-(benzo[d]thiazol-2-yl)-3-phenylthiourea; Crystal structure and DFT of [Pt(C14H9N3S2)(dppe)].CH2Cl2

This paper describes a series of Pt(II) thiourea complexes (1–4). The complexes were synthesized by a reaction between [PtCl2(diphos)] and the ligand 1-(benzo[d]thiazol-2-yl)-3-phenylthioure in the presence of triethylamine, with all reactants present in equimolar amounts. The produced complexes exhibited square planar geometry, which was validated by FT-IR and 1HNMR . Single crystal XRD study revealed that the coordination geometry was distorted square planar in [Pt(Btzt)(dpppe)]. Hirshfeld surface analysis was used to delve deeper into the intermolecular interactions which showed that the combined contribution of H⋯H and H⋯C contacts in the stabilization of the supramolecular assembly was 81.3%. A void analysis was carried out which showed that there was no large cavity in the supramolecular assembly. Theoretical studies were also conducted on [Pt(Btzt)(dpppe)]. The DFT analysis was carried out using the B3LYP Hybrid method in combination with Def2-SVP. The theoretical findings indicated just 3% differences between the theoretical and experimental Figures. Furthermore, the computed HOMO-LUMO gap was 3.4 eV, which was close to the anatase photocatalyst's band gap. DFT predicted that all complexes are non-magnetic with μB=0. There are high electron donation and back-donation between heteroatoms and transition metals in the complexes.

Impact of ligand fields on Kubas interaction of open copper sites in MOFs with hydrogen molecules: an electronic structural insight.

We investigate hydrogen sorption on open copper sites in various ligand coordinations of metal-organic frameworks (MOFs), including the triangular T(CuL3) in MFU-4l, the linear L(CuL2) in NU2100, and the paddlewheel P(CuL4)2 in HKUST-1 from an electronic structure perspective using DFT calculations. The ligand-field-induced splitting of d states and spd hybridizations in copper are thoroughly examined. The hybridization between Cu s, p, and d orbitals occurs in various forms to optimize the Coulomb repulsion of different ligand fields. Despite the Cu+ oxidation state, which is typically conducive to strong Kubas interactions with hydrogen molecules, the vacant spd z 2 hybrid orbitals of the open copper site in the L(CuL2) coordination are unsuitable for facilitating electron forward donation, thereby preventing effective hydrogen adsorption. In contrast, the vacant spd z 2 hybrid orbitals in the T(CuL3) and P(CuL4)2 coordinations can engage in electron forward donations, forming bonding states between the Cu spd z 2 and H2 σ bonding orbitals. The forward donation in the T(CuL3) configuration is significantly stronger than in the P(CuL4)2 configuration due to both the lower energy of the vacant orbitals and the larger contributions of p and d z 2 characters to the hybrid orbital. Additionally, the occupied Cu pd xz/yz and pd x 2-y 2 hybrid orbitals in the T(CuL3) configuration promote electron back donation to the H2 σ* antibonding orbital, leading to the formation of π bonding states. In the P(CuL4)2 coordination, the repulsion from the electron density distributed over the surrounding ligands prevents the H2 molecule from approaching the copper center closely enough for the back donation to occur. The complete Kubas interaction, involving both forward and back electron donations, results in a large dihydrogen-copper binding energy of 37.6 kJ mol-1 in the T(CuL3) coordination. In contrast, the binding energy of 10.6 kJ mol-1 in the P(CuL4)2 coordination is primarily driven by electrostatic interactions with a minor contribution of the Kubas-like forward donation interaction. This analysis highlights the pivotal role of coordination environments in determining the hydrogen sorption properties of MOFs.

Main-Group Metal-Nonmetal Dynamic Proton Bridges Enhance Ammonia Electrosynthesis.

The electrochemical nitrogen reduction reactionis a crucial process for the sustainable production of ammoniafor energy and agriculture applications. However, the reaction's efficiency is highly dependent on the activation of the inert N≡N bond, which is hindered by the electron back-donation to the π* orbitals of the N≡N bond, resulting in low eNRR capacity. Herein, we report a main-group metal-non-metal (O-In-S) eNRR catalyst featuring a dynamic proton bridge, with In-S serving as the polarization pair and O functioning as the dynamic electron pool. In-situ spectroscopic analysis and theoretical calculations reveal that the In-S polarization pair acts as asymmetric dual-sites, polarizing the N≡N bond by concurrently back-donating electrons to both the πx* and πy* orbitals of N2, thereby overcoming the significant band gap limitations, while inhibiting the competitive hydrogen evolution reaction. Meanwhile, the O dynamic electron pool acts as a "repository" for electron storage and donation to the In-S polarization pair. As a result, the O-In-S dynamic proton bridge exhibits exceptional NH3 yield rates and Faradaic efficiencies (FEs) across a wide potential window of 0.3 V, with an optimal NH3 yield of 80.07 ± 4.25 μg h-1 mg-1 and an FE of 38.01 ± 2.02%, outperforming most previously reported catalysts.

Constructing Pd@Layered-CoOx/MFI Bifunctional Catalyst for Efficient Ethyl Acetate Oxidation: Boosted C═O Activation and *O Species Transformation.

Oxygenated volatile organic compounds (OVOCs), emitted in large quantities by the chemical industry, are a major contributor to the formation of ozone and subsequent particulate matter. For the efficient catalytic oxidation of OVOCs, the challenges of molecular activation and intermediate inhibition remain. The construction of bifunctional active sites with specific structures offers a promising way to overcome these problems. Here, the Pd@Layered-CoOx/MFI bifunctional catalyst with core-shell active sites was rationally fabricated though a two-step ligand pyrolysis method, which exhibits a superb oxidation efficiency toward ethyl acetate (EA). Over this, 13.4% of EA (1000 ppm) can be oxidized at just 140 °C with a reaction rate of 13.85 mmol·gPd-1·s-1, around 176.7 times higher than that of the conventional Pd-CoOx/MFI catalyst. The electronic coupling of the Pd-Co pair promotes the electron back-donation from Pd nanoparticles to the layered CoOx shell and facilitates the formation of Pd2+ species, which greatly enhances the adsorption and activation of the electron-rich C═O bond of the EA molecules. In addition, the synergy of these core-shell Pd@Layered-CoOx sites accelerates the activation and transformation of *O species, which inhibit the formation of acetaldehyde and ethanol byproducts, ensuring the rapid total oxidation of EA molecules via the Mars-van Krevelen mechanism. This work established a solid foundation for exploring robust bifunctional catalysts for deep OVOC purification.

Bisgermylene-Stabilized Stannylone: Catalytic Reduction of Nitrous Oxide and Nitro Compounds via Element-Ligand Cooperativity.

This study describes the synthesis, structural characterization, and catalytic application of a bis(germylene)-stabilized stannylone (2). The reduction of digermylated stannylene (1) with 2.2 equiv of potassium graphite (KC8) leads to the formation of stannylone 2 as a green solid in 78% yield. Computational studies showed that stannylone 2 possesses a formal Sn(0) center and a delocalized 3-c-2-e π-bond in the Ge2Sn core, which arises from back-donation of the p-type lone pair electrons on the Sn atom to the vacant orbitals of the Ge atoms. Stannylone 2 can serve as an efficient precatalyst for the selective reduction of nitrous oxide (N2O) and nitroarenes (ArNO2) with the formation of dinitrogen (N2) and hydrazines (ArNH-NHAr), respectively. Exposure of 2 with N2O (1 atm) resulted in the insertion of two oxygen atoms into the Ge-Ge and Ge-Sn bonds, yielding the germyl(oxyl)stannylene (3). Moreover, the stoichiometric reaction of 2 with 1-chloro-4-nitrobenzene afforded an amido(oxyl)stannylene (4) through the complete scission of the N-O bonds of the nitroarene. Stannylenes 3 and 4 serve as catalytically active species for the catalytic reduction of nitrous oxide and nitroarenes, respectively. Mechanistic studies reveal that the cooperation of the low-valent Ge and Sn centers allows for multiple electron transfers to cleave the N-O bonds of N2O and ArNO2. This approach presents a new strategy for catalyzing the deoxygenation of N2O and ArNO2 using a zerovalent tin compound.

Promoting intermediates transformation by boosting H2O dissociation over core-shell Pd@CoO Janus for acetone efficacious oxidation

Reactivity loss by intermediates aggregation and water vapor inhibition are two major and longstanding challenges for the noble-metal-based catalysts in oxygenated volatile organic compounds (OVOCs) oxidation. Herein, the core-shell Pd@CoO Janus sites are creatively designed and stabilized over the HSAPO-34 support. Quasi in situ XPS spectra reveal that the strong interactions in Pd@CoO Janus sites promote the charge redistribution and electron back-donation through Pd-O-Co coordination. Therefore, abundant positively charged Pd2+ sites are formed and oxygen species transformation is facilitated, which significantly promote the low-temperature efficiency of acetone oxidation. Furthermore, the Pd@CoO/HSAPO-34 catalyst facilitates H2O molecules dissociation and produce reactive OHTer and OHTri species, which considerably promotes the rapid decomposition of aldehyde intermediate via attacked CH2O* group, ensuring low-temperature oxidation of acetone. This work provides valuable guidance to develop specific catalysts with functional active sites for rationally utilizing H2O molecules to improve low-temperature performance and modulate reaction pathways during OVOCs oxidation.

Polarized Ultrathin BN Induced Dynamic Electron Interactions for Enhancing Acidic Oxygen Evolution.

Developing ruthenium-based heterogeneous catalysts with an efficient and stable interface is essential for enhanced acidic oxygen evolution reaction (OER). Herein, we report a defect-rich ultrathin boron nitride nanosheet support with relatively independent electron donor and acceptor sites, which serves as an electron reservoir and receiving station for RuO2, realizing the rapid supply and reception of electrons. Through precisely controlling the reaction interface, a low OER overpotential of only 180 mV (at 10 mA cm-2) and long-term operational stability (350 h) are achieved, suggesting potential practical applications. In situ characterization and theoretical calculations have validated the existence of a localized electronic recycling between RuO2 and ultrathin BN nanosheets (BNNS). The electron-rich Ru sites accelerate the adsorption of water molecules and the dissociation of intermediates, while the interconnection between the O-terminal and B-terminal edge establishes electronic back-donation, effectively suppressing the over-oxidation of lattice oxygen. This study provides a new perspective for constructing a stable and highly active catalytic interface.

Asymmetric empty orbitals in ZrO2-BCN for enhancing electrocatalytic hydrogenation of nitrogen to ammonia

Electrocatalytic nitrogen reduction reaction (NRR) provides an environment-friendly and sustainable approach for nitrogen fixation at ambient conditions. However, simultaneously activating N≡N triple bond and suppressing the competitive hydrogen evolution reaction (HER) in aqueous electrolytes remain challenges. Herein, we construct ZrO2-BCN hetero-catalyst with tunable Zr-B-N interfacial structure for efficiently improving selectivity of the NRR. The asymmetric electron acceptance and back-donation capacity of the empty orbitals of Zr and B favors the activation of the N≡N triple bond during the NRR. The optimal ZrO2-BCN catalyst exhibits excellent NRR performance with a high ammonia yield of 17.8 μg mg-1cat. h−1 at −0.65 V vs. reversible hydrogen electrode (RHE) and a faradaic efficiency of 23.1 % at −0.45 V vs. RHE in 0.1 M HCl electrolyte, surpassing most previous reports. In-situ electrochemical attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy demonstrates the effect of the Zr-B-N interface on activating N2. This study paves a new way for hetero-interface catalyst design that would accelerate the implementation of NRR technology.

Unraveling the mechanism of modulating external electric fields for regulating nitrogen fixation and activation on three-atom metal clusters

Efficient N2 fixation and activation under mild conditions are critical for green ammonia synthesis. Coupling external electric fields with three-atom transition metal clusters is a promising approach to realizing this vision. Herein, we report an effective strategy by modulating external electric fields to regulate the adsorption and activation of N2 on Sc3. The mechanism is further elucidated through DFT calculations. The most favorable adsorption site for N2 is the hollow site of Sc3. Although external electric fields inhibit the adsorption process of N2 on Sc3, the adsorbing performance of Sc3 is still very superior. Positive fields promote the activation and polarization of the adsorbed dinitrogen on the three-atom cluster, and negative fields have the opposite effect. The synergistic effect of positive/negative electric fields and Sc3 regulates the charge distribution of NN* in different ways. Furthermore, the d-band center (relative to the Fermi level), which determines the adsorption strength of N2, is affected by both positive and negative fields, resulting from the electron donation and back-donation mechanism between the NN* and the Sc3. This work provides guidelines for designing surface-anchored three-atom clusters with superior ammonia synthesis performance under electric fields in the future.

Computational understanding of the structural characteristics of Sm-based endohedral metallofullerenes

Endohedral metallofullerenes (EMFs) containing samarium (Sm) are rich and cover all kinds of conventional endofullerene types. Herein, an exhaustive density functional theory study was conducted to understand the structural characteristics of all 21 Sm-based EMFs characterized by single-crystal X-ray diffraction. The mono-, di- and tri-EMFs have open-shell septet, 13-et and 19-et electronic states, respectively. The internal Sm atoms hold all the unpaired spins (six for each), which are completely shielded by carbon cages. A formal divalent state can be assigned to each metal but with obvious electron backdonation from cage orbitals, rendering the metal-metal and metal-cage interactions mainly ionic. Thus, their Sm positions can be easily located by the electrostatic potentials inside negatively charged hollow cages and also affected by intramolecular covalent interactions. All Sm-based EMFs are stable with large encapsulation energies and SOMO-LUMO gap energies. Interestingly, although the two Sm2+ cations are repulsive, the limited cage cavity of Sm2@D2(35)-C88 may push them to have obvious covalent interactions. While for Sm3@Ih(7)-C80, the three Sm2+ cations exhibit markedly reduced positive charges to effectively alleviate the intermetallic repulsions. Our findings rationalize the structural characteristics and favorable formation of all Sm-based EMFs, and could deepen the understanding for more types of EMFs.

Transforming graphdiyne-like boron nitride monolayer into single-atom adsorbent for CO2 adsorption

Developing an efficient adsorbent with optimal absorption capacity for carbon dioxide (CO2) has always been a significant issue. Recently, single-atom adsorbents (SAAs) have been highlighted with special interest as a promising material with a wide range of applications. Nevertheless, comprehending the intricate mechanisms of gas adsorption on SAAs remains an enormous challenge. Herein, we have systematically evaluated the adsorption mechanisms over the transition metals (Fe, Co, Ni, Cu, and Zn) embedded onto the graphdiyne-like boron nitride monolayer using density functional theory calculations. Results show that SAAs exhibit a promoted capacity compared to the pristine graphdiyne-like boron nitride monolayer, mainly ascribed to the electron donation and back-donation mechanism between metal and CO2. Further, BNene/Fe is favorable for CO2 adsorption with the strongest interaction energy (−20.7 kcal mol−1). We hope this work will facilitate the design of SAAs in the field of gas adsorption.

Atomic high-spin cobalt(II) center for highly selective electrochemical CO reduction to CH3OH

In this work, via engineering the conformation of cobalt active center in cobalt phthalocyanine molecular catalyst, the catalytic efficiency of electrochemical carbon monoxide reduction to methanol can be dramatically tuned. Based on a collection of experimental investigations and density functional theory calculations, it reveals that the electron rearrangement of the Co 3d orbitals of cobalt phthalocyanine from the low-spin state (S = 1/2) to the high-spin state (S = 3/2), induced by molecular conformation change, is responsible for the greatly enhanced CO reduction reaction performance. Operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy measurements disclose accelerated hydrogenation of CORR intermediates, and kinetic isotope effect validates expedited proton-feeding rate over cobalt phthalocyanine with high-spin state. Further natural population analysis and density functional theory calculations demonstrate that the high spin Co2+ can enhance the electron backdonation via the dxz/dyz−2π* bond and weaken the C-O bonding in *CO, promoting hydrogenation of CORR intermediates.

Insights into the geometrical parameters, charge distribution, and reactivity of Ca, Mg, Sr, and Bi complexes of piroxicam and meloxicam: A quantum chemical study

DFT studies have been used to calculate the geometrical parameters of optimized structures, along with the charge distribution and reactivity of the respective compounds. The gas-phase optimization of the recently synthesized Ca, Mg, Sr, and Bi complexes of piroxicam and meloxicam were carried out using B3LYP functional in the Gaussian program and 6-31G(d,p), LanL2DZ, and SDD basis set in a sequel. The charge distribution around metal atoms was analyzed using the same basis set. The reactivity descriptors were calculated from the frontier molecular orbitals (FMOs) energy calculations. The relationship between geometrical parameters, the dipole moment of the complexes, and the type of metal were established in this study. The charge analysis study dictated the less electron-back donation with the increased size of the metal atom. The theoretical calculations concluded that the studied complexes are soft, more polarizable, and prefer to act as electrophiles during chemical reactions with nucleophiles.

The mechanism of the oxidation of narceine by means of selenous acid -sulphuric acid

The chemistry of selenous acid was misunderstood for many years, being explained by electron back donation. In this communication we disclose the reaction mechanism of the interaction of narceine with selenous acid in sulphuric acid. Narceine is a complex molecule that displays a carboxylic acid, a tertiary amine, a ketone, three methoxy groups and a benzodioxole; so, it was necessary select the principal reaction site. Although a methoxy group can be demethylated with the employed reagent since codeine gives the same violet colour obtained with morphine. The chemical deportment of the methylenedioxy ring in the presence of methoxy groups needed revision. It was found that the five-member ring is cleaved preferentially. Thus, a sustained reaction mechanism could be advanced. The reactive species is protonated selenous acid, which reacts with an oxygen of the cyclic group, water being eliminated. The oxonium ion is neutralized by ring opening in a concerted mechanism involving water reaction at the methylene. An organometallic intermediate is obtained, a selenite, and a hemiacetal. Finally, protonation of the selenium-oxygen double bond produces an acidolysis via a synchronous mechanism involving five electron shifts. This way selenium (II) hydroxide, an ortho-quinone and formaldehyde are obtained.

Identifying and clearing individual oxygen impurities on graphene through the use of NO2 as a radical scavenger

We present a novel method to detect and eliminate oxygen adatoms on a graphene basal plane, which can be observed as individual single-electron transfer (SET) events through graphene Hall measurements. The central idea, supported by first-principles calculations, is to use NO2 as a radical scavenger, effectively targeting and removing oxygen impurities on graphene. The reaction between NO2 and the oxygen adatom produces a negatively charged NO3− species and creates a hole carrier in graphene. Subsequently, NO3− reacts with NO2 to form N2O5, accompanied by an electron back-donation to graphene. The thermal decomposition of N2O5 produces neutral NO3, which can accept an electron from graphene and return to the NO3− state. Under conditions of low oxygen impurity levels and NO2 partial pressures, these SET reactions induce intermittent, step-like changes in the graphene's Hall resistivity ρxy at room temperature. Notably, the simulated ρxy patterns during NO2 adsorption closely resemble previously observed patterns [Schedin et al., Nat. Mater. 6 (2007) 652–655], suggesting a connection to the proposed SET reactions for unintentionally introduced oxygen impurities. Furthermore, we find that NO2 also reacts with hydroxyl and peroxide groups on the graphene basal plane, removing them by forming HNO3 and N2O5, respectively. Our findings offer a promising approach to remove oxygen-containing functional groups from graphene, paving the way for obtaining high-quality graphene from reduced graphene oxide.

The effective and sustainable application of a green amino acid-based corrosion Inhibitor for Cu metal

The human body is a remarkably aggressive medium and applied materials must be extremely resistant to corrosion and destruction, so copper, which is a biological material and is widely used in medicine, is being considered. Copper corrosion may be associated with inflammation in body because it releases ions that are toxic to humans. In aggressive solutions, biomolecules called amino acids act as corrosion inhibitors. In the present research, the purpose is to study the inhibitory action of l-alanine (L-Ala) and l-Leucine (L-Leu) amino acids on the corrosion of Cu. By density functional theory (DFT), inhibition behavior of l-Ala-and l-Leu-and their conformers against Cu corrosion have been investigated. According to values of back-donation of electrons (Eback-d), fraction of electron transferred (ΔN), electrophilicity (ω), electronegativity (χ), softness (σ), hardness (η), energy gap (Eg), ELUMO, and EHOMO computed reactivity factors between copper surface and inhibitors are studied. l-Leu's theoretical indicators confirm its tendency towards adsorption. l-Leu-activity against corrosion has been investigated and favorable results have been obtained.

Evidence of electronic influence in the adsorption of cationic and zwitterionic dyes on zeolites

The adsorption of a cationic dye, Methylene blue (MB), and a zwitterionic dye, 8-Hydroxyquinoline (8-HQ), onto zeolites synthesized from different clays has been investigated. The presence of certain metals and the Si/Al ratio of the parent clay has an overall effect on the type of zeolites produced. Zeolites LTA and FAU Y were obtained using the hydrothermal method. X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) spectral analysis was used to study the adsorption phenomena of the adsorbates on the adsorbents. The adsorption profile of MB (Topological Polar Surface Area (TPSA) 43.9 Å2 and 8-HQ (TPSA 33.1 Å2) compared favourably with a Freundlich isotherm with R2 > 0.9 for all the zeolitic materials synthesized. Adsorption capacities of zeolite FAU was significantly different from zeolite LTA for MB removal. The higher adsorption capacity of zeolite FAU was attributed to geometric effects resulting in greater shrinkage in the inter lattice spacing of zeolite LTA leading to a reduction in surface area. Adsorption of the relatively smaller 8-HQ however, did not show significant difference in the two zeolite types. Surface and structural characterization showed that adsorbates/adsorbents interactions were driven by both geometric (inter lattice spacing which imparts higher surface area of the adsorbent) and electronic (electrostatic repulsions through electron back donation from metals in the zeolitic structure) considerations.