Characterization of sulfonated poly(styrene–divinylbenzene) and poly(divinylbenzene) and its application as catalysts in esterification reaction

Carbon-Based Electrocatalysts for Efficient Hydrogen Peroxide Production

Hydrogen peroxide (H₂ O₂ ) is an environment-friendly and efficient oxidant with a wide range of applications in different industries. Recently, the production of hydrogen peroxide through direct electrosynthesis has attracted widespread research attention, and has emerged as the most promising method to replace the traditional energy-intensive multi-step anthraquinone process. In ongoing efforts to achieve highly efficient large-scale electrosynthesis of H₂ O₂ , carbon-based materials have been developed as 2e^- oxygen reduction reaction catalysts, with the benefits of low cost, abundant availability, and optimal performance. This review comprehensively introduces the strategies for optimizing carbon-based materials toward H₂ O₂ production, and the latest advances in carbon-based hybrid catalysts. The active sites of the carbon-based materials and the influence of coordination heteroatom doping on the selectivity of H₂ O₂ are extensively analyzed. In particular, the appropriate design of functional groups and understanding the effect of the electrolyte pH are expected to further improve the selective efficiency of producing H₂ O₂ via the oxygen reduction reaction. Methods for improving catalytic activity by interface engineering and reaction kinetics are summarized. Finally, the challenges carbon-based catalysts face before they can be employed for commercial-scale H₂ O₂ production are identified, and prospects for designing novel electrochemical reactors are proposed.

Electrochemical CO2 reduction to high-concentration pure formic acid solutions in an all-solid-state reactor

Electrochemical CO₂ reduction reaction (CO₂RR) to liquid fuels is currently challenged by low product concentrations, as well as their mixture with traditional liquid electrolytes, such as KHCO₃ solution. Here we report an all-solid-state electrochemical CO₂RR system for continuous generation of high-purity and high-concentration formic acid vapors and solutions. The cathode and anode were separated by a porous solid electrolyte (PSE) layer, where electrochemically generated formate and proton were recombined to form molecular formic acid. The generated formic acid can be efficiently removed in the form of vapors via inert gas stream flowing through the PSE layer. Coupling with a high activity (formate partial current densities ~450 mA cm⁻²), selectivity (maximal Faradaic efficiency ~97%), and stability (100 hours) grain boundary-enriched bismuth catalyst, we demonstrated ultra-high concentrations of pure formic acid solutions (up to nearly 100 wt.%) condensed from generated vapors via flexible tuning of the carrier gas stream.

Electrochemical CO₂ reduction to liquid fuels is limited by low product concentrations and formation of mixtures with traditional liquid electrolytes. Here the authors report an all-solid-state system for a continuous generation of high-purity and high-concentration formic acid vapors and solutions.

The SPE-assisted europium (III) based complex fluorometric assay for the highly selective and sensitive detection of manganese (II) in water

Detection of trace manganese (Ⅱ) ion (Mn²⁺) is crucial to water safety. Here, commercially available PS-DVB microspheres were sulfonated and then filled into the SPE column in order to separate Mn²⁺ from complex matrices. Meanwhile, europium (III) complex was prepared with a simple "one pot" method, and its fluorescence intensity was quenched gradually with the increase of Mn²⁺ concentration. Europium (III) complex combined with home-made SPE column was utilized for highly selective and sensitive measurement of Mn²⁺. The detectable concentrations of Mn²⁺ can be low as 0.2 μM, which was less than the drinking water guidelines. Consequently, this new method is promising to assess the content of Mn²⁺ rapidly and accurately in real-world water samples.

Direct electrosynthesis of pure aqueous H2O2 solutions up to 20% by weight using a solid electrolyte

Hydrogen peroxide (H2O2) synthesis generally requires substantial postreaction purification. Here, we report a direct electrosynthesis strategy that delivers separate hydrogen (H2) and oxygen (O2) streams to an anode and cathode separated by a porous solid electrolyte, wherein the electrochemically generated H+ and HO2– recombine to form pure aqueous H2O2 solutions. By optimizing a functionalized carbon black catalyst for two-electron oxygen reduction, we achieved >90% selectivity for pure H2O2 at current densities up to 200 milliamperes per square centimeter, which represents an H2O2 productivity of 3.4 millimoles per square centimeter per hour (3660 moles per kilogram of catalyst per hour). A wide range of concentrations of pure H2O2 solutions up to 20 weight % could be obtained by tuning the water flow rate through the solid electrolyte, and the catalyst retained activity and selectivity for 100 hours.

Resinas poliméricas reticuladas com ação biocida: atual estado da arte

ResumoCopolímeros reticulados à base de divinilbenzeno vêm sendo extensivamente empregados como suportes de catalisadores e complexantes de íons metálicos, adsorventes de compostos orgânicos e fases estacionárias em separações cromatográficas. A introdução de grupos biocidas a estes materiais é relatada em patentes desde a década de 1970, contudo apenas a partir do ano 2000 estes copolímeros passaram a ser aplicados também como suportes para grupos biocidas. A presente revisão apresenta as principais combinações de suportes poliméricos e grupos biocidas estudados com o objetivo de preparar resinas biocidas reticuladas. Procura-se estabelecer relação entre as características dessas resinas e seu mecanismo de ação biocida.

Atomistic simulations of the structure of highly crosslinked sulfonated poly(styrene-co-divinylbenzene) ion exchange resins

The microscopic structures of highly crosslinked sulfonated poly(styrene-co-divinylbenzene) resins have been modeled by generating atomistic microstructures using stochastic-like algorithms, which are subsequently relaxed using molecular dynamics. Two different generation algorithms have been tested. The relaxation of the microstructures generated by the first algorithm, which is based on a homogeneous construction of the resin, leads to a significant overestimation of the experimental density as well as to an unsatisfactory description of the porosity. In contrast, the generation approach that combines algorithms for the heterogeneous growing and branching of the chains enables the formation of crosslinks with different topologies. In particular, the intrinsic heterogeneity observed in these resins is efficiently reproduced when the topological loops, which are defined by two or more crosslinks closing a cycle, are present in their microscopic description. Thus, the apparent density, porosity and pore volume estimated using microstructures with these topological loops, called super-crosslinks, are in very good agreement with the experimental results. Although the backbone dihedral angle distribution of the generated and relaxed models is not influenced by the topology, the number and type of crosslinks affect the medium- and long-range atomic disposition of the backbone atoms and the distribution of sulfonic groups. An analysis of the distribution of the local density indicates that super-crosslinks are responsible for the heterogeneous homogenization observed during the MD relaxation. Finally the π-π stacking interactions have been analyzed. Results indicate that those in which the two rings adopt a T-shaped disposition are considerably more abundant as compared to those with the co-facially oriented rings, independently of the resin topology.

Time-resolved chromatographic analysis and mechanisms in adsorption and catalysis

The main object of this review is the study of fundamentals of adsorption and heterogeneous catalysis, a benefit for the understanding of adsorptive and catalytic properties. This work aims to define and record, with the utmost accuracy, the phenomena and the possible reactions. A new methodology for the study of the adsorption is presented, which is a version of the well-known inverse gas chromatography. This reversed-flow inverse gas chromatography (RF-IGC) is technically very simple, and it is combined with a mathematical analysis that gives the possibility for the estimation of various physicochemical parameters related to adsorbent or catalyst characterization, under conditions compatible with the operation of real adsorbents and catalysts. On this base, this methodology has been successfully applied to the study of the impact of air pollutants, volatile organic and/or inorganic, on many solids such as marbles, ceramics, oxide-pigments of works of art, building materials, authentic statues of the Greek Archaeological Museums. Moreover, this methodology proved to be a powerful tool for studying the topography of active sites of heterogeneous surfaces in the nano-scale domain. Thus, some very important local quantities for the surface chemistry have been determined experimentally for many solids including thin films. These physicochemical local quantities (among which adsorption energy and entropy, surface diffusion coefficient, probability density function) have been determined from the experimental pairs of height of extra chromatographic peaks and time by a nonlinear least-squares method, through personal computer programs written in GW BASIC and lately in FORTRAN. Through the time-resolved analysis the surface characterization of the examined materials took place. In addition, the kinetic constants responsible for adsorption/desorption and surface chemical reactions have also been calculated. Thus, important answers have been provided to the following essential questions: (1) Can RF-IGC define the gnostic regions of adsorption/desorption, surface diffusion, surface reaction? Yes, irrefutably and undeniably. (2) Can RF-IGC deal with issues of catalysis, the existence of more than one reaction? Certainly yes. Indeed, it is impressive to observe the reactions "on line". (3) Can RF-IGC identify peaks of products and reactants simultaneously? Certainly yes. (4) Can RF-IGC be applied to thin films in a nano-scale domain? The answer is "definitely yes". (5) Can it kinetically follow the above? Yes, again.