Electron-rich Area Research Articles

Boosting peracetic acid activation with Cu single-atom catalysts for sulfamethoxazole abatement: A nonradical pathway and ‘double engine’ driving mechanism

Herein, a Cu single-atom catalyst with ultrahigh loading of Cu-pyridinic N4 sites on carbon nanosheets (CuSA-N-C) is successfully designed and synthesized as an activator for peracetic acid (PAA). The CuSA-N-C showed the most powerful capacity for PAA activation among the Cu-based catalysts, and even a 48-fold enhancement on sulfamethoxazole (SMX) degradation compared to homogeneous Cu2+. The scavenging experiments and ESR analysis indicated that singlet oxygen (1O2) but not conventional radicals play a dominant role in SMX degradation. Theoretical calculations further insights into the generation of 1O2 in PAA activation. Furthermore, a ‘double engine’ driving mechanism was proposed, where the electron-rich area around Cu site and the electron-poor area around C site in the saturated Cu-N4 configuration could efficiently adsorb and activate PAA. The CuSA-N-C/PAA process exhibited high tolerance towards the common water matrices (e.g., CO32−/HCO3− and Cl-), and thus showed excellent performance in the real wastewater. This study advances the understanding of non-radical PAA activation process and provides guidance for the design of smart PAA-active catalysts.

Synergetic effects of catalyst-surface dual-electric centers and microbes for efficient removal of ciprofloxacin in water

Antibiotics and antibiotic resistance genes (ARGs) are still a problem in biological treatment. Herein, we propose a synergetic strategy between microbes and dual-electric centers catalysts (CCN/Cu-Al2O3/ceramsite) for Ciprofloxacin (CIP)-contained (5 mg/L) water treatment in an up-flow biological filter. CIP was cleaved into small molecules by the catalyst, bringing a 57.6% removal and reducing 10.5% ARG. The characterization results verified that a Cu-π electrostatic force occurs on the catalyst surface, forming electron-rich areas around Cu and electron-poor areas at the carbon-doped g-C3N4 (CCN) aromatic ring. Thus, the electrons of adsorbed CIP were delocalized and then captured by the adsorbed extracellular polymeric substance at the electron-rich areas. Therefore, the synergetic process weakened the stress of CIP on bacteria and reduced ARG accumulation. It also enriched more electro-active bacteria on the surface of CCN/Cu-Al2O3/ceramsite, promoting the expression of extracellular electron transfer-related genes and reconstructing the energy metabolism mode. This result provides an opportunity for refractory antibiotic treatment in the biological process.

Rational design of NiO/NiSe2@C heterostructure as high-performance anode for Li-ion battery

Biphasic or multiphase heterostructures have promising futures in advanced electrode materials for energy-related applications because of their desirable synergistic effects. Here we prepared a rational NiO/NiSe2@C heterostructure microsphere through carbonization, selenization, and oxidation using Ni-MOF as a precursor. Electrochemical studies were conducted to examine the Li+ storage characteristics, and density functional theory (DFT) was utilized to comprehend the underlying mechanism. When employed as the anode for LIBs, the NiO/NiSe2@C showed a high specific capacity and long-term cyclic stability, with a specific capacity of 992 mAh g−1 for 600 cycles at a current density of 0.2 A g−1. The NiO/NiSe2@C exhibits a significantly enhanced lithium-ion diffusion coefficient (DLi+) value. The DFT results show that an electron-rich area forms at the NiO/NiSe2 heterointerface, where the metalloid selenium transfers electrons to the oxygen atoms. The lithiation reactions were improved dramatically by redistributing interfacial charges, which can trigger a built-in electric field that dramatically promotes the capacitance contribution of electrode materials, enhances the lithium storage capacity, and accelerates the ion/electron transmission. The rational synthesis of NiO/NiSe2@C heterostructure can provide an idea for designing novel heterostructure anode materials.

Insights into singlet oxygen generation and electron-transfer process induced by a single-atom Cu catalyst with saturated Cu-N4 sites

SummaryPersulfate-based nonradical oxidation processes are appealing in water treatment for the efficient and selective degradation of trace contaminants in complex water matrices. However, there is still lacking of systematic understanding of the relationship between multiple nonradical pathways and the active sites of catalyst. Herein, a single-atom Cu catalyst with saturated Cu-N4 sites on a carbon substrate (SA-Cu-NC) was constructed to activate peroxymonosulfate (PMS), which exhibited high catalytic performance and selectivity for pollutant degradation in different water conditions. Combined with the results of density functional theory (DFT) calculations, the electron-rich area around Cu site and the electron-poor area around C site in the saturated Cu-N4 configuration could efficiently adsorb and activate PMS, which promoted pollutant degradation through the oxidation of singlet oxygen (1O2) and electron transfer process, respectively. This study advances the understanding of the saturated coordination structure of metals and the superiority of multiple nonradical pathways in wastewater treatment.

Electronic Structure and External Electric Field Modulation of Polyethylene/Graphene Interface.

Polymer nanocomposites can serve as promising electrostatic shielding materials; however, the underlying physical mechanisms governing the carrier transport properties between nanofillers and polymers remain unclear. Herein, the structural and electronic properties of two polyethylene/graphene (PE/G) interfaces, i.e., type-H and type-A, have been systematically investigated under different electric fields using first principle calculations. The results testify that the bandgaps of 128.6 and 67.8 meV are opened at the Dirac point for type-H and type-A PE/G interfaces, respectively, accompanied by an electron-rich area around the graphene layer, and a hole-rich area around the PE layer. Moreover, the Fermi level shifts towards the valence band maximum (VBM) of the PE layer, forming a p-type Schottky contact at the interface. Upon application of an electric field perpendicular to the PE/G interface, the Schottky contact can be transformed into an Ohmic contact via the tuning of the Schottky barrier height (SBH) of the PE/G interface. Compared with the A-type PE/G interfaces, the H-type requires a lower electric field to induce an Ohmic contact. All these results can provide deeper insights into the conduction mechanism of graphene-based polymer composites as field-shielding materials.

Electron-rich ketone-based covalent organic frameworks supported nickel oxyhydroxide for highly efficient peroxymonosulfate activation and sulfadiazine removal: Performance and multi-path reaction mechanisms

NiOOH/PMS system suffers from relative lower catalytic performance of PMS activation on the degradation of extremely recalcitrant organic pollutants and potential high risk of leaching Ni(II) ions. To address these, ketone-based covalent organic frameworks (COFs) with electron-deficient and electron-rich areas and large surface area was employed as a novel 2D carbon supporter to synthesize NiOOH@COFs composite. It turned out that the reaction rate constant of sulfadiazine in the NiOOH@COFs/PMS (0.1221 min−1) was 2.06 and 2.39 times than that in the NiOOH/PMS (0.0594 min−1) and COFs/PMS system (0.0509 min−1), respectively. This was attributed from the efficient synergic effect of NiOOH and COFs on the PMS activation, resulting in faster and more production of multiple reactive oxygen species (ROS) (SO4−, OH, O2− and 1O2). Specifically, the PMS could be reduced around the electron-rich oxygen atom of the ketone for radical (SO4−, OH) generation, and could be oxidized over the electron-deficient carbon atom of the ketone for the non-radical (1O2) generation. Moreover, NiOOH can active PMS to simultaneously generate non-radical (1O2) and radicals (SO4−, OH, and O2−). 1O2 is distinguished as the dominant ROS contributing to the degradation of sulfadiazine. Furthermore, the leaching of total Ni ions is reduced by 72% than counterparts from NiOOH, demonstrating improved stability and reusability. Hence, this study provides new insights into the multi-path mechanism of the synergistic PMS activation by NiOOH and ketone-COFs, and sheds new light on the development of efficient metal-free catalysts with rich-electronic structure for peroxymonosulfate-mediated environmental remediation.

Congregated-electrons-strengthened anchoring and mineralization of gaseous formaldehyde on a novel self-supporting Cu2-xSe/Cu2O heterojunction photocatalyst under visible lights: A viable mesh for designing air purifier

Reinforced adsorption enabled efficient degradation of formaldehyde was investigated with a unique flower-like Cu2−xSe/Cu2O heterojunction photocatalyst. Nonstoichiometric Cu2−xSe crystals are grown from a pliable Cu mesh through a self-sacrifice template strategy. Sintering Cu2−xSe in O2/N2 atmosphere enables the formation of Cu2−xSe/Cu2O heterojunction. The implantation of Cu2O lowers the work function of Cu2−xSe and boosts the gathering of electrons, qualifying the heterojunction as electron-rich area with those shared Cu atoms being active sites. Under illumination, abundant electrons on Cu2−xSe/Cu2O delocalize to attract formaldehyde molecules and convert them into semi-stable carbonates. Simultaneously, these electrons react with adsorbed oxygen to produce active •O2-. With a continuous-flow operation mode, 100% removal percentage and 99.5% CO2 conversion rate are achieved when eliminating formaldehyde. By virtue of its integrity and pliability, the Cu mesh bearing Cu2−xSe/Cu2O can be applied in air purifier directly.

Accelerating the Activation of NO x − on Ru Nanoparticles for Ammonia Production by Tuning Their Electron Deficiency

Accelerating the Activation of NO _x ⁻ on Ru Nanoparticles for Ammonia Production by Tuning Their Electron Deficiency

Theoretical insight on antioxidant potency of kanzakiflavone-2 and its derivatives

Functional groups in flavonoids always act as deciding factors in making a particular flavonoid to be active. They possess the capability to enhance or diminish the structural activity of flavonoids. The idea about conjugated functional units and their role over structural activity alteration still seems to be less explored. In the present work, kanzakiflavone and its derivatives possessing the structural activity directors –OH, -OCH3, and –O-CH2-O- are analyzed using density functional theory with help of global hybrid meta GGA correlation functional (M06-2X) under the basis set 6-311++G(d,p). Energy surface analysis (frontier molecular orbitals and electrostatic potential) based on charge distribution shows that the studied flavonoids prefer to act as potential electron donors. Interestingly, the electron rich area (A-ring) is profound to be altered with B-ring in comparison with other flavones. All the studied flavonoids prefer to act as potential radical scavengers in aqueous phase which is witnessed via antioxidant mechanisms. Absorption, digestion, metabolism, and excretion (ADME) analysis was carried out to understand the nominal role of flavonoids to meet medicinal applications. Kanzakiflavone and its derivatives prefer to act as possible leads based on physiological, pharmacological, and lipophilic properties.

Notable light-free catalytic activity for pollutant destruction over flower-like BiOI microspheres by a dual-reaction-center Fenton-like process

BiOI is widely used as photocatalysts for pollutant removal, water splitting, CO2 reduction and organic transformation due to its excellent photoelectric properties. Here, we report for the first time that a light-free catalyst consisting of the flower-like BiOI microspheres (f-BiOI MSs) exposing (1 0 1) and (1 1 0) crystal planes prepared by a hydrothermal method in ethylene glycol environment can rapidly eliminate the refractory BPA within only ∼3 min through a Fenton-like process. The reaction activity is ∼190 times higher than that of the conventional Fenton catalyst Fe2O3. A series of characterizations and experiments reveal the formation of the dual reaction centers on f-BiOI MSs. The electron-rich O centers efficiently reduce H2O2 to OH, while the electron-poor oxygen vacancies capture electrons from the adsorbed pollutants and divert them to the electron-rich area during the Fenton-like reactions. By these processes, pollutants are degraded and mineralized quickly in a wide pH range. Our findings address the problems of the classical Fenton reaction and are useful for the development of efficient Fenton-like catalysts through constructing dual reaction centers.

Efficient Destruction of Pollutants in Water by a Dual-Reaction-Center Fenton-like Process over Carbon Nitride Compounds-Complexed Cu(II)-CuAlO2.

Carbon nitride compounds (CN) complexed with the in-situ-produced Cu(II) on the surface of CuAlO2 substrate (CN-Cu(II)-CuAlO2) is prepared via a surface growth process for the first time and exhibits exceptionally high activity and efficiency for the degradation of the refractory pollutants in water through a Fenton-like process in a wide pH range. The reaction rate for bisphenol A removal is ∼25 times higher than that of the CuAlO2. According to the characterization, Cu(II) generation on the surface of CuAlO2 during the surface growth process results in the marked decrease of the surface oxygen vacancies and the formation of the C-O-Cu bridges between CN and Cu(II)-CuAlO2 in the catalyst. The electron paramagnetic resonance (EPR) analysis and density functional theory (DFT) calculations demonstrate that the dual reaction centers are produced around the Cu and C sites due to the cation-π interactions through the C-O-Cu bridges in CN-Cu(II)-CuAlO2. During the Fenton-like reactions, the electron-rich center around Cu is responsible for the efficient reduction of H2O2 to •OH, and the electron-poor center around C captures electrons from H2O2 or pollutants and diverts them to the electron-rich area via the C-O-Cu bridge. Thus, the catalyst exhibits excellent catalytic performance for the refractory pollutant degradation. This study can deepen our understanding on the enhanced Fenton reactivity for water purification through functionalizing with organic solid-phase ligands on the catalyst surface.

4-Phenoxyphenol-Functionalized Reduced Graphene Oxide Nanosheets: A Metal-Free Fenton-Like Catalyst for Pollutant Destruction.

Metal-containing Fenton catalysts have been widely investigated. Here, we report for the first time a highly effective stable metal-free Fenton-like catalyst with dual reaction centers consisting of 4-phenoxyphenol-functionalized reduced graphene oxide nanosheets (POP-rGO NSs) prepared through surface complexation and copolymerization. Experimental and theoretical studies verified that dual reaction centers are formed on the C-O-C bridge of POP-rGO NSs. The electron-rich center around O is responsible for the efficient reduction of H2O2 to •OH, while the electron-poor center around C captures electrons from the adsorbed pollutants and diverts them to the electron-rich area via the C-O-C bridge. By these processes, pollutants are degraded and mineralized quickly in a wide pH range, and a higher H2O2 utilization efficiency is achieved. Our findings address the problems of the classical Fenton reaction and are useful for the development of efficient Fenton-like catalysts using organic polymers for different fields.

Crystal structure of bis-{μ2-2,2'-[(4,10-dimethyl-1,4,7,10-tetra-aza-cyclo-dodecane-1,7-di-yl)bis(meth-yl-ene)]bis-(4-oxo-4H-pyran-3-olato)}dicobalt-calcium bis-(perchlorate) 1.36-hydrate.

The title compound, [CaCo2(C22H30N4O6)2](ClO4)2·1.36H2O or {Ca[Co(H-2L1)]2}·2ClO4·1.36H2O {where L1 is 4,10-bis-[(3-hy-droxy-4-pyron-2-yl)meth-yl]-1,7-dimethyl-1,4,7,10-tetra-aza-cyclo-dodecane}, is a trinuclear complex whose asymmetric unit comprises a quarter of the {Ca[Co(H-2L1)]2}2+ trinuclear complex, half of a perchlorate ion and 0.34-water mol-ecules. In the neutral [Co(H-2L1)] moiety, the cobalt ion is hexa-coordinated in a trigonal-prismatic fashion by the surrounding N4O2 donor set. A Ca2+ cation holds together two neutral [Co(H-2L1)] moieties and is octa-coordinated in a distorted trigonal-dodeca-hedral fashion by the surrounding O atoms belonging to the deprotonated oxide and carbonyl groups of two [Co(H-2L1)] units. The coordination of the CoII cation preorganizes L1 and an electron-rich area forms, which is able to host hard metal ions. The comparison between the present structure and the previously published ones suggests a high versatility of this ligand; indeed, hard metal ions with different nature and dimensions lead to complexes having different stoichiometry (mono- and dinuclear monomers and trinuclear dimers) or even a polymeric structure. The heterotrinuclear CoII-CaII-CoII complexes are connected in three dimensions via weak C-H⋯O hydrogen bonds, which are also responsible for the inter-actions with the perchlorate anions and the lattice water mol-ecules. The perchlorate anion is disordered about a twofold rotation axis and was refined giving the two positions a fixed occupancy factor of 0.5. The crystal studied was refined as a two-component inversion twin [BASF parameter = 0.14 (4)].

Selective H2O2 conversion to hydroxyl radicals in the electron-rich area of hydroxylated C-g-C3N4/CuCo–Al2O3

Twice the amount of ˙OH as that of the reacted H2O2 is produced via two electron transfer processes from the electron-rich Cu centers to H2O2 and from H2O to the N atom of the OH–CCN/CuCo–Al2O3 composite, which results in extremely high activity for pollutant degradation with a high utilization efficiency of H2O2.

Electron emission in a source-collector sheath system: A kinetic study

The classical source-collector sheath system describes a plasma that forms between a Maxwellian source and an absorbing wall. The plasma is assumed to be collisionless and without ionization. Two distinct areas are being formed: the collector sheath, an ion-rich region in contact with the absorbing boundary, and the source sheath, which is an electron-rich area near the Maxwellian source. In this work, we study a modified version of the classical source-collector sheath system, where the wall is no longer absorbing but emits electrons. As a result, we have two different types of collector sheath, one where a potential well is formed and one without a potential well. We examine the effect of electron emission for a range of conditions for the plasma and the emitted electrons. In the first part of this work, we study the problem analytically, and in the second, using our kinetic Vlasov code, Yggdrasil. The simulation results are in very good agreement with the predictions of our theoretical model.

A preorganized metalloreceptor for alkaline earth ions showing calcium versus magnesium selectivity in water: biological activity of selected metal complexes.

The N,N'-bis[(3-hydroxy-4-pyron-2-yl)methyl]-N,N'-dimethylethylendiamine (Malten = L) forms the highly stable [CuH(-2)L] species in water, in which the converging maltol oxygen atoms form an electron-rich area able to host hard metal ions. When considering the alkaline earth series (AE), the [Cu(H(-2)L)] species binds all metal ions, with the exception of Mg(2+), exhibiting the relevant property to discriminate Ca(2+) versus Mg(2+) at physiological pH 7.4; the binding of the AE metal is visible to the naked eye. The stability constant values of the trinuclear [AE{Cu(H(-2)L)}2](2+) species formed reach the maximum for Ca(2+) (log K=7.7). Ca(2+) also forms a tetranuclear [Ca{Cu(H(-2)L)}]2(4+) species at a high Ca(2+) concentration. Tri- and tetranuclear calcium complexes show blue- and pink-colored crystals, respectively. [Cu(H(-2)L)] is the most active species in inducing DNA alterations. The DNA damages are compatible with its hydrolytic cleavages.

Conducting poly(azomethine)esters: synthesis, characterization and insight into the electronic properties using DFT calculations

Electrostatic potential map, PI; yellow colour around ‘N’ and ‘O’ atoms indicate electron rich area prone to the electrophilic attack.

A kinetic study of the source–collector sheath system in a drifting plasma

The source–collector sheath system describes a plasma that forms between a Maxwellian source and an absorbing wall. The plasma is assumed to be collisionless and without ionization. Two distinct areas are being formed: the collector sheath, an ion-rich region in contact with the absorbing boundary, and the source sheath, which is an electron-rich area near the Maxwellian source. Our work examines the effect that shifted Maxwellian distributions at the plasma source have on the characteristics of such a system. This is studied for a range of drift velocities and ratios of ion and electron temperatures. We study the problem both analytically and using our kinetic Vlasov code, Yggdrasil. The simulation results are in very good agreement with the predictions of our theoretical model.

Preorganizing binding side-arms on a cyclen scaffold: the choice of a suitable metal ion

The binding properties of 4,10-bis[(3-hydroxy-4-pyron-2-yl)methyl]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L1) and 4,10-bis[(2-hydroxy-5-nitrophenyl)methyl]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (L2) towards Cu(II) and Co(II) transition metal ions in aqueous solution and in the solid state were studied and compared. Each system consists of a cyclen scaffold bearing two different side-arms; the role of the two transition metal ions to involve side-arms in coordination was investigated. Each metal ion is coordinated in a similar way by both ligands although a different side-arm arrangement occurs. The Me2Cyclen base is always involved in the coordination of the transition metal cation with the four amine functions; both side-arms bind Co(II) while only one of them binds Cu(II). As a consequence, Co(II) forms only mononuclear species with both ligands; the main [Co(H−2L)] species exhibits both side-arms on the same part with respect to the macrocyclic plane. In the case of L1, this allows the formation of an electron rich area, formed by the four converging oxygen atoms of the two maltol functions, able to lodge one hard metal ion such as sodium. On the other hand, L1 forms a dinuclear Cu(II)-species using the remaining unbound maltolic function which affords a Cu(II)-tetranuclear species in the solid state. This behavior is attributed to the different coordination requirements of the two metals, thus providing information for the choice of a suitable metal to preorganize side-arms on a polyamine macrocyclic scaffold. Potentiometric and UV-Vis solution studies as well as four crystal structures of metal-complexes support this conclusion.

Experimental electron density distribution of dopamine hydrochloride

Careful high-resolution x-ray diffraction measurements at 90 K have been used to map the electron density distribution in a single crystal of dopamine hydrochloride, a neurotransmitter. A least-squares refinement procedure has been used in which multipole parameters are added to describe the distortions of the atomic electron distributions from spherical symmetry. The refinement also yields improved estimates of the x-ray phases, which have been used to plot maps of the electron distribution. The most electron-rich areas of the molecule are the hydroxyl groups that show large buildups of electron density at the position of the nonbonded lone pairs. The sum of the net atomic charges for the ammonium group is +0.2(2). The net atomic charge for the chloride ion is −0.1(1).