Ions In Sites Research Articles

Spin-orbital mechanisms for negative thermal expansion in Ca2RuO4

The phenomenon of negative thermal expansion (NTE) deals with the increase of the lattice parameters and the volume of the unit cell when the material is thermally cooled. The NTE is typically associated with thermal phonons and anomalous spin-lattice coupling at low temperatures. However, the underlying mechanisms in the presence of strong electron correlations in multiorbital systems are not yet fully established. Here, we investigate the role of Coulomb interaction in the presence of lattice distortions in setting out the NTE effect, by focusing on the physical case of layered ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ with the ${d}^{4}$ configuration at each Ru ion site. We employ the Slater-Koster parametrization to describe the electron-lattice coupling through the dependence of the d-p hybridization on the Ru-O-Ru bond angle. The evaluation of the minimum of the free energy at finite temperature by fully solving the multiorbital many-body problem on a finite-size cluster allows us to identify the regime for which the system is prone to exhibit NTE effects. The analysis shows that the nature of the spin-orbital correlations is relevant to drive the reduction of the bond angle by cooling, and in turn the tendency toward a NTE. This is confirmed by the fact that a changeover of the electronic and orbital configuration from ${d}^{4}$ to ${d}^{3}$ by transition metal substitution is shown to favor the occurrence of a NTE in ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$. This finding is in agreement with the experimental observations of a NTE effect which is significantly dependent on the transition metal substitution in the ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ compound.

Cascade energy reemission after inner-shell ionization of atomic gold. Role of photo- and cascade-produced electrons in radiosensitization using gold-containing agents

A method of straightforward construction and analysis of the cascade decay trees is applied to calculate photon and electron spectra emitted upon the cascade de-excitation of single inner-shell vacancies in the gold atom produced by photoionization. The energy acquired by the gold atom upon photoionization is split into the following channels: i) energy absorbed by the gold atom itself, ii) energy carried away by the cascade electrons, and iii) energy carried away by the cascade photons. The energies absorbed through channels i–iii are analyzed for the cascade decay of each single vacancy in O to K shells, and presented as functions of incident photon energies based on calculated partial photoionization cross sections. Energy reemitted through channels ii and iii in the cases of O-, N-, M-, L-, and K-ionization make, respectively, 47–60%, 55–69%, 85–89%, 94–96%, and 99% of the initially acquired energy. Cascade-produced electrons and photons eventually transfer their energy to the medium which lays the base for using gold-containing compounds and gold nanoparticles as radiosensitizing agents in radiotherapy. Cascade-produced electrons, as well as photoelectrons, are found to be the principal transmitters of energy to atoms of the environment in the vicinity of the sites of initial ionization. Their relative role in possible radiosensitizing effect is analyzed on the incident photon energy range of 0.01–1000 keV.

The influence of spin state of the Cr ions on the structural and magnetic behavior of orthorhombic LaFe1−xCrxO3 Perovskites (0.0

Herein, we report, for the first time, the influence of the state of spin of the Cr3+ ions on the structure and magnetic behavior of LaFe1−xCrxO3 (0.0 < x < 0.5) perovskite crystal structures to improve their magnetic properties for memory storage and magneto-optical application potential. A series of LaFe1−xCrxO3 (0.0 < x < 0.5) nanocrystals was prepared using the citrate-nitrate auto-combustion route. The influence of the Cr3+ ions on the structure and morphology of the LaFe1−xCrxO3 nanostructures was emphasized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), the selected area of electron diffraction (SAED), and scanning electron microscopy (SEM). The results revealed that the inclusion of the Cr3+ ions into the Fe3+ sites leads to an increase in the crystallite size of the LaFe1−xCrxO3 (0.0 < x < 0.5) nanocrystals, from 16.12 to 57.29 nm, to preserve their orthorhombic crystal symmetry. The phase stability and the electron density mapping of the prepared orthoferrite nanocrystals were verified using the Goldschmidt tolerance factor and Rietveld refinement. The magnetic properties were evaluated and discussed based on Kanamori–Goodenough (KG) regulations and Heisenberg Hamiltonian notation. The results showed that the inclusion of the 20 mol% of Cr3+ ions in the Fe sites results in an enhancement of the magnetic parameters. The enhancement of the magnetic behavior was argued to the tendency of the Cr3+ ions to be in the high spin state when included in the Fe3+ ions site. This improvement in the magnetic performance of the LaFe1−xCrxO3 (x = 0.2) nanocrystals will open a new avenue for using this nanomagnetic material in the fields of memory storage and magneto-optical devices.

Sodium‐Coordinated Polymeric Phthalocyanines as Stable High‐Capacity Organic Anodes for Sodium‐Ion Batteries

Sodium‐ion batteries (SIBs) have attracted considerable interest as an alternative to lithium‐ion batteries owing to their similar electrochemical performance and superior long‐term cycle stability. Organic materials are regarded as promising anode materials for constructing SIBs with high capacity and good retention. However, utilization of organic materials is rather limited by their low energy density and poor stability at high current densities. To overcome these limitations, we utilized a novel polymeric disodium phthalocyanines (pNaPc) as SIB anodes to provide stable coordination sites for Na ions as well as to enhance the stability at high current density. By varying the linker type during a one‐pot cyclization and polymerization process, two pNaPc anodes with O‐ (O‐pNaPc) and S‐linkers (S‐pNaPc) were prepared, and their structural and electrochemical properties were investigated. The O‐pNaPc binds Na ions with a lower binding energy compared with S‐pNaPc, which leads to more facile Na‐ion coordination/dissociation when engaged as SIB anode. The use of O‐pNaPc significantly improves the redox kinetics and cycle stability and allows the fabrication of a full cell against Na3V2(PO4)2F3/C cathode, which demonstrates its practical application with high energy density (288 Wh kg−1) and high power density (149 W kg−1).

Ion-Induced Polysaccharide Gelation: Peculiarities of Alginate Egg-Box Association with Different Divalent Cations.

Structural aspects of polysaccharide hydrogels based on sodium alginate and divalent cations Ba2+, Ca2+, Sr2+, Cu2+, Zn2+, Ni2+ and Mn2+ was studied using data on hydrogel elemental composition and combinatorial analysis of the primary structure of alginate chains. It was shown that the elemental composition of hydrogels in the form of freezing dried microspheres gives information on the structure of junction zones in the polysaccharide hydrogel network, the degree of filling of egg-box cells by cations, the type and magnitude of the interaction of cations with alginate chains, the most preferred types of alginate egg-box cells for cation binding and the nature of alginate dimers binding in junction zones. It was ascertained that metal-alginate complexes have more complicated organization than was previously desired. It was revealed that in metal-alginate hydrogels, the number of cations of various metals per C12 block may be less than the limiting theoretical value equal to 1 for completely filled cells. In the case of alkaline earth metals and zinc, this number is equal to 0.3 for calcium, 0.6 for barium and zinc and 0.65-0.7 for strontium. We have determined that in the presence of transition metals copper, nickel and manganese, a structure similar to an egg-box is formed with completely filled cells. It was determined that in nickel-alginate and copper-alginate microspheres, the cross-linking of alginate chains and formation of ordered egg-box structures with completely filled cells are carried out by hydrated metal complexes with complicated composition. It was found that an additional characteristic of complex formation with manganese cations is the partial destruction of alginate chains. It has been established that the existence of unequal binding sites of metal ions with alginate chains can lead to the appearance of ordered secondary structures due to the physical sorption of metal ions and their compounds from the environment. It was shown that hydrogels based on calcium alginate are most promising for absorbent engineering in environmental and other modern technologies.

Structural and magnetic properties of gadolinium substituted Mn0.6Zn0.4GdxFe2−xO4 (x = 0–0.1) spinel ferrite

Soft magnetic ferrites Mn0.6Zn0.4GdxFe2-xO4 (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) have been synthesized using a solvothermal method. X-ray diffraction analysis revealed the structure of Gd3+ doped Mn-Zn ferrite was spinel structure. In response to an increase in Gd3+ content, the lattice constant of the sample increased and then decreased, and the largest lattice constant was 8.452 Å with x = 0.04. The crystallite size varied between 14.7 and 18 nm. M−H data revealed that all samples are soft magnetic and characterized by the larger saturation magnetization, low remnant magnetization and coercively. We found that the Gd3+ ions substituted into Fe3+ ion sites and resulted an increase in Gd3+ content from x = 0 to x = 0.1, which lead to the saturation magnetization first increased then decreased. The maximum saturation magnetization value of Mn0.6Zn0.4GdxFe2-xO4 was 90.1 emu/g with x = 0.04, which suggested the Mn0.6Zn0.4Gd0.04Fe1.96O4 was magnetically responsive, and could be used in hyperthermia tumor applications.

Two Stable Sodalite-Cage-Based MOFs for Highly Gas Selective Capture and Conversion in Cycloaddition Reaction.

Stable metal-organic frameworks, containing periodically arranged nanosized cages or pores and active Lewis acid-base sites, are considered ideal candidates for efficient heterogeneous catalysis. Herein, based on the light of reticular chemistry design principles, the ingenious assembly of two pyridine N-rich multifunctional triangular linkers, H3TBA [3,5-di (1h-tetrazol-5-yl) benzoic acid] and H2TZI [5-(1H-tetrazol-5-yl)isophthalic acid], with MnII formed PCP-33(Mn) and PCP-34(Mn), respectively. PCP-33(Mn) and PCP-34(Mn) are typical sod topology zeolitic metal-organic frameworks (ZMOFs) with hierarchical tetragonal micropores and metal organic polyhedral sodalite-like cages. The inner walls of these cages are modified by open metal sites MnII and Lewis acid-base sites of halide ions and N pyridine atoms. The characteristics of the cages' structures make two MOFs exhibit high surface area and a small window, which promote their outstanding gas capture ability (C2H2, 131.8 cm3 g-1; CO2, 77.9 cm3 g-1 at 273 K) and selective separation performance (C2H2/CH4, 226.2, CO2/CH4, 50.3 at 298 K), and are also suitable as catalytic reactors for metal/solvent-free chemical fixation of CO2 with epoxides to achieve high-efficiency CO2 conversion. Furthermore, they are greatly recyclable for several cycles while retaining their structural rigidity and catalytic activity.

Perylene Diimide-Containing Dynamic Hyper-crosslinked Ionic Porous Organic Polymers: Modulation of Assembly and Gas Storage

A strategy to synthesize hyper-crosslinked polymers with strong visible-light absorption and abundant ionic sites is discussed. This is achieved in a one-pot reaction via the simultaneous Friedel–Crafts alkylation and quaternization reaction between α,α′-dibromo-p-xylene (DBX) and perylene diimide (PDI) substituted with N,N-dimethyl ethylene to result in hyper-crosslinked ionic polymers (HIPs). These HIPs display good surface areas with strong visible-light absorption (400–650 nm) and dispersibility in polar solvents like water and DMSO. Importantly, our experimental and theoretical studies indicate that PDI-HIPs possess a dynamic network with good uptake of water up to seven times their weight. Notably, PDI in PDI-HIPs is not only responsible for visible-light absorption but also acts as a probe to study their dynamic nature. Moreover, the presence of ultramicropores and CO2-philic functional groups in PDI-HIPs renders good CO2 uptake up to 2.11 mmol/g at 273 K despite their relatively low surface area.

Engineering the Pore Structure and Functionality of Ionic Porous Polymers for Separating Acetylene over Carbon Dioxide

AbstractPrecise engineering of organic porous polymers to realize the selective separation of structurally similar gases presents a great challenge. In this study, a new class of ionic porous polymers P(Ph3Im‐Br‐nDVB) with a high ionic density and microporous surface area are constructed through a facile copolymerization strategy, providing an efficient path to rational control over pore structure and functionality. The first example of ionic porous organic polymers is reported to address the challenge of discriminating the subtle difference of C2H2 and CO2, which have almost identical molecular sizes and similar physicochemical properties, which achieve the highest C2H2/CO2 selectivity (17.9) among porous organic polymers. These ionic porous polymers exhibit high stability and excellent dynamic breakthrough performance for binary C2H2/CO2 mixtures, indicating their practical feasibility. Modeling studies reveal that anions are the specific binding sites for preferential C2H2 capture because of Br−···HCCH interactions. This study not only demonstrates an efficient strategy to build novel ionic porous polymers integrating abundant micropores and ionic sites but also sheds some light on the development of functionalized materials for the separation of structurally similar gas molecules.

Fabricating Robust Pt Clusters on Sn-Doped CeO2 for CO Oxidation: A Deep Insight into Support Engineering and Surface Structural Evolution.

The size effect on nanoparticles, which affects the catalysis performance in a significant way, is crucial. The tuning of oxygen vacancies on metal-oxide support can help reduce the size of the particles in active clusters of Pt, thus improving catalysis performance of the supported catalyst. Herein, Ce-Sn solid solutions (CSO) with abundant oxygen vacancies have been synthesized. Activated by simple CO reduction after loading Pt species, the catalytic CO oxidation performance of Pt/CSO was significantly better than that of Pt/CeO2 . The reasons for the elevated activity were further explored regarding ionic Pt single sites being transformed into active Pt clusters after CO reduction. Due to more exposed oxygen vacancies, much smaller Pt clusters were created on CSO (ca. 1.2 nm) than on CeO2 (ca. 1.8 nm). Consequently, more exposed active Pt clusters significantly improved the ability to activate oxygen and directly translated to the higher catalytic oxidation performance of activated Pt/CSO catalysts in vehicle emission control applications.

Revisiting Lithium- and Sodium-Ion Storage in Hard Carbon Anodes.

The galvanostatic lithiation/sodiation voltage profiles of hard carbon anodes are simple, with a sloping drop followed by aplateau. However, a precise understanding of the corresponding redox sites and storage mechanisms is still elusive, which hinders further development in commercial applications. Here, a comprehensive comparison of the lithium- and sodium-ion storage behaviors of hard carbon is conducted, yielding the following key findings: 1) the sloping voltage section is presented by the lithium-ion intercalation in the graphitic lattices of hard carbons, whereas it mainly arises from the chemisorption of sodium ions on their inner surfaces constituting closed pores, even if the graphitic lattices are unoccupied; 2) the redox sites for the plateau capacities are the same as those for the closed pores regardless of the alkali ions; 3) the sodiation plateau capacities are mostly determined by the volume of the available closed pore, whereas the lithiation plateau capacities are primarily affected by the intercalation propensity; and 4) the intercalation preference and the plateau capacity have an inverse correlation. These findings from extensive characterizations and theoretical investigations provide a relatively clear elucidation of the electrochemical footprint of hard carbon anodes in relation to the redox mechanisms and storage sites for lithium and sodium ions, thereby providing a more rational design strategy for constructing better hard carbon anodes.

Theoretical and Experimental Investigation of Autoxidation Propensity of Selected Drugs in Solution State.

The C-H bond dissociation energy (BDE) of drug molecules is often used to estimate their relative propensities to undergo autoxidation. BDE calculations based on electronic structures provide a convenient means to estimate the risk for a given compound to degrade via autoxidation. This study aimed to verify the utility of calculated C-H BDEs of a range of drug molecules in predicting their autoxidation propensities, in the solution state. For the autoxidation study, 2,2'-azobis (2-methylpropionitrile) was employed as the solution state stressor, and the experimental reaction rate constants were determined employing ultraperformance liquid chromatographic (UPLC) methods. Reaction rates in the solution state were compared to the calculated C-H BDE values of the respective compounds. The results indicated a poor correlation for compounds in the solution state, and their relative stabilities could not be explained with C-H BDE. On the other hand, a favorable relationship was observed between the relative extent of ionization and the autoxidation rates of the selected compounds. In the solution state, factors such as the type and extent of drug ionization, degree and type of solvation have been shown to contribute to differences in reactivity. By applying the computational method involving the effect of H-atom abstraction and potential ionization sites in the molecule, the calculated C-H BDE should relate better to the experimental autoxidation rates.

Construction of multifunctional histidine-based hypercrosslinked hierarchical porous ionic polymers for efficient CO2 capture and conversion

Several novel multifunctional histidine-based hypercrosslinked ionic polymers (HIPs) were constructed via a one-pot copolymerization strategy. The resultant HIPs were characterized by various technologies and investigated for the CO2 adsorption and conversion. Plentiful hydrogen bond donors, nucleophilic ionic sites, and Lewis bases were successfully integrated into the HIPs skeletons. As-prepared histidine-based HIPs possess excellent hierarchical pore structure. The optimal HIP-Br-His exhibits a high CO2 capture capacity of 2.90 mmol/g at 273 K and 1 bar, much higher than that of corresponding hypercrosslinked polymer HCP-Br without histidine units. Meanwhile, the HIP-Br-His achieves an excellent catalytic activity of 95 % product yield with 99 % product selectivity in CO2 cycloaddition to propylene oxide under metal-, cocatalyst- and solvent-free and mild conditions (70 °C and 1.0 MPa). Particularly, HIP-Br-His can efficiently capture and convert dilute CO2 into cyclic carbonates with a satisfactory catalytic performance. The excellent catalytic activity associating with the confirmed good stability, recyclability, and substrate compatibility make the developed histidine-based HIPs a promising heterogeneous catalyst for efficient CO2 capture and conversion.

Aluminum Porphyrin-Based Ionic Porous Aromatic Frameworks Having High Surface Areas and Highly Dispersed Dual-Function Sites for Boosting the Catalytic Conversion of CO2 into Cyclic Carbonates.

Multifunctionalization of porous organic polymers toward synergistic CO2 catalysis has drawn much attention in recent decades, but it still faces many challenges. Herein, we develop a facile, simple, and efficient strategy to obtain a series of aluminum porphyrin-based ionic porous aromatic frameworks (iPAFs), which are considered excellent bifunctional catalysts for converting CO2 into cyclic carbonates without any cocatalyst under mild and solvent-free conditions. By increasing the amounts of tetraphenylmethane fragments in the porphyrin backbones, the cooperative effect between Lewis acidic metal centers and nucleophilic ionic sites has been enhanced and then the significant improvement of catalytic activity can be achieved owing to the high surface areas (up to 719 m2·g-1), abundant hierarchical micro-mesopores, and prominent CO2 adsorption capacities (up to 1.8 mmol·g-1 at 273 K) as well as highly dispersed dual-function sites. More fascinatingly, high-active AlPor-iPAF-3 enables CO2 cycloaddition to perform with diluted CO2 (15% CO2 in 85% N2, v/v) or under ambient conditions. Therefore, this postsynthetic modification procedure in combination with the framework dilution strategy provides a new approach to fabricating high-surface-area metalloporphyrin-based porous ionic polymers (PIPs) with hierarchical structures, which is conducive to improving the accessibility of multiple active sites around substrates.

The morphology modulation of graphene to produce wrinkles and folds for effective electrochemical determination of Hg(II)

AbstractA highly efficient electrode material, three‐dimensional reduced graphene oxide with varying wrinkles and folds (WRGO), applicable for electrochemical determination of Hg(II) was obtained by treating graphene oxide (GO) with KOH aqueous solution. After alkaline etching, the relatively flat graphene was altered and its self‐aggregation was significantly alleviated, producing more wrinkles and folds, which provided more active adsorption sites for heavy metal ions. WRGO‐5 modified electrode system herein offers a highest sensitivity of (31.83 μAμM−1) and a lowest LOD of (16.28 nM). Moreover, the electrode sensor possesses good stability and reproducibility.

NMR-assisted crystallography of the tryptophan synthase α-aminoacrylate intermediate: Proton positions and role in inhibition.

NMR-assisted crystallography - the integrated application of solid-state NMR, X-ray crystallography, and first-principles computational chemistry - holds significant promise for mechanistic enzymology: by providing atomic-resolution characterization of stable intermediates, including hydrogen atom locations and tautomeric equilibria, NMR crystallography offers insight into structure and chemical dynamics. Here, we make use of this combined approach to characterize the tryptophan synthase α-aminoacrylate intermediate, a defining species for pyridoxal-5′-phosphate-dependent enzymes that catalyze β-elimination and replacement reactions. For this intermediate, NMR-assisted crystallography identifies the protonation states of the ionizable sites on the cofactor, substrate, and catalytic side chains, and the location and orientation of crystallographic waters within the active site. From this, a detailed three-dimensional picture of structure and reactivity emerges, highlighting the fate of the substrate L-serine hydroxyl leaving group and the reaction pathway back to the preceding transition state. Reaction of the α-aminoacrylate intermediate with benzimidazole, an isostere of the natural substrate, indole, shows benzimidazole bound in the active site and poised for, but unable to initiate, the subsequent bond formation step. Here, the chemically detailed, three-dimensional structure from NMR-assisted crystallography is key to understanding why benzimidazole does not react.

Improving stability and reversibility of manganese dioxide cathode materials via nitrogen and sulfur doping for aqueous zinc ion batteries

Manganese based oxides are one of the most promising cathode materials for secondary aqueous zinc ion batteries. However, its structural instability and slow reaction kinetics have hampered its large-scale application. Here, a rational nitrogen and sulfur diatomic doping strategy is suggested to enhance the electrochemical activity and reversibility of manganese dioxide. The nitrogen and sulfur-doped manganese dioxide (N-MnxOy-S) electrode material is synthesized by a simple hydrothermal approach combined with a low temperature vulcanization treatment. The electrode exhibits an excellent initial discharge capacity of 178 mA h g−1 at 1 A g−1. Even at a high rate of 2 A g−1, the capacity retention rate exceeds 90% for 3000 cycles. The large number of oxygen defects increases the storage sites for zinc ions, resulting in the excellent electrochemical properties of N-MnxOy-S. Additionally, the Mn-S and Mn-N bonds in N-MnxOy-S boost the interfacial dynamics of manganese dioxide, which can effectively reduce the dissolution of manganese and efficiently improve the electronic conductivity. The current study demonstrates that nitrogen and sulfur co-doping is a successful method for enhancing the electrochemical performance of manganese-based oxide cathodes, which serves as an important benchmark for the development of cathode materials appropriate for aqueous zinc ion batteries.

Construction of Aluminum‐Porphyrin‐Based Hypercrosslinked Ionic Polymers (HIPs) by Direct Knitting Approach for CO2 Capture and In‐Situ Conversion to Cyclic Carbonates

AbstractHypercrosslinked polymers (HCPs) constructed by Friedel‐Crafts reaction have drawn increasing attention in recent decades, but their multifunctionalization remains a huge challenge. Herein, a series of aluminum‐porphyrin‐based hypercrosslinked ionic polymers have been successfully synthesized by direct knitting approach without additional electrophilic comonomers, which involves the copolymerization of neutral porphyrin monomers and ionic building. By increasing the connected nodes numbers of ionic monomers, the introduction of abundant tetraphenylmethane fragements into the porphyrin backbones endows them with high‐density ionic active sites. Accordingly, the well‐matched molar ratios of aluminum sites to nucleophilic chloride anions that work synergistically for CO2/epoxide coupling can be achieved. Al‐HIP‐2 with flexible ionic pendants and a high Al/Cl ratio allows CO2 cycloaddition to be performed at ambient conditions or with diluted CO2; while Al‐HIP‐3 with rigid ionic moieties and a relatively low Al/Cl ratio exhibits higher specific surface area and stronger CO2 capture ability. Therefore, this co‐condensation strategy provides a simple and feasible pathway for adjusting the reactivity ratios of comonomers via simple structural changes in the knitting process, thus achieving the rational construction of multifunctionalized HCPs for CO2 capture and in‐situ conversion to cyclic carbonates.

Adsorption/desorption behavior of ionic dyes on sintered bone char

The aim of this study was to investigate the regularity and differences in the adsorption/desorption behavior of bovine rib char (BC) as an adsorbent material for the cationic Malachite Green (MG) and anionic Sunset Yellow (SY) dyes. The effects of pyrolysis temperature, adsorbent dosage, solution pH, initial concentration, contact time, and adsorption temperature were investigated. The pore characteristics of BC were determined by the Brunauer-Emmett-Teller (BET) method. The changes in functional groups before and after the adsorption of BC were analyzed by Fourier transform infrared spectroscopy. And the chemical composition and surface morphology of BC were characterized by X-ray diffraction and scanning electron microscopy. The experimental data were further analyzed using different isotherm models, kinetic models, and thermodynamic equations, and an understanding of the adsorption studies was carried out. The results show that BC is 90% mesoporous with a BET specific surface area of approximately 150 m2/g. BC is rich in active sites at 700 °C and performs best in the adsorption process. The adsorption of MG increases with increasing pH, while the opposite is true for SY, with optimum pH values of 7 and 3, respectively. Ionic dyes bind to BC easily (the fitted values for the Freundlich model 1/n are all less than 0.5, R2 > 0.748). The maximum adsorption capacity (Qmax) of MG was much higher than that of SY (the Langmuir model indicated Qmax of 1168.4 mg/g and 47.0 mg/g, respectively, R2 > 0.830). The adsorption of ionic dyes on BC was mainly non-homogeneous surface chemisorption, which was spontaneous (ΔG<0, ΔH>0). The desorption of BC after adsorption of MG and SY in HCl and NaOH solutions, respectively, was better. Analysis of the adsorption contribution of the BC fraction showed that the mineral fraction played an important role in the adsorption process (about 94%), while the organic fraction contributed about 6%. The experimental results indicate that the adsorption mechanism of MG and SY on BC can be attributed to the filling of mesopores, electrostatic interaction between the ionic polar sites of BC and the different charged dyes, the formation of chemical bonds between the oxygen-containing functional groups on the surface of BC and the dyes, and the ionic exchange between the polar sites of BC such as Ca2+, PO43−, CO32− and OH−.

N-doped porous polymer with protonated ionic liquid sites for efficient conversion of CO2 to cyclic carbonates

A N-doped porous polymer with protonated ionic liquid sites was fabricated by a solvent-free self-assembly synthesis of resorcinol/formaldehyde resin, followed by modification with hydrobromic acid (HBr) to introduce ionic sites. Compared with the parent polymer PIP-HP, polymer PIP-HP-HBr maintains a high specific surface area after ion site construction, and the elevated activity was also acquired under metal/solvent/cocatalyst-free conditions with up to 99% yield of cyclic carbonates. Furthermore, the PIP-HP-HBr as a heterogeneous catalyst can be readily recovered and demonstrate excellent cycling stability. In addition, a plausible catalytic mechanism had been proposed that the high catalytic activity originates from the synergistic effect of hydrogen bond donor –OH and nucleophilic anion Br−.