Cation-exchange Method Research Articles

Preparation, characterization of mixed-valence antimony-tin phosphomolybdic polyoxometalates and application in the cyclohexanone oxidation in the presence of hydrogen peroxide

In this work, a series of polyoxometalates (POMs), as soluble salts of formula Sn1.5PMo12O40, SbPMo12O40 and H 3-x Sn x1 Sb x2 PMo 12 O 40 (x=2x 1 +3x 2 and x 1 , x 2 = 0–0.75) were synthesized using the cationic exchange method under stoichiometric conditions. They were characterized and tested in the oxidation of cyclohexanone using hydrogen peroxide in the absence of organic solvent, co-catalyst phase transfer compounds or surfactants. UV–Visible and X-ray photoelectron spectroscopic analyses showed a partially reduced state of POM with coexistence of the couples Mo(VI)/Mo(V), Sb(V)/Sb(III) and Sn(IV)/Sn(II), without affecting their structure, results confirmed by FT-IR and Raman spectroscopies. The reversible cyclic voltammetry analysis evidenced the valence change of the Mo species, Mo(VI)/Mo(V). The POMs are found to be active in the cyclohexanone oxidation reaction and among them the most efficient is H 0.75 Sb 0.75 PMo 12 O 40 with 49% of adipic acid yield.

Phase-separated CuAg alloy interfacial stress induced Cu defects for efficient N2 activation and electrocatalytic reduction

The electrochemical nitrogen reduction reaction (eN2RR) to produce ammonia represents a promising approach to substitute the traditional Haber-Bosch process. However, it remains challenging due to the low ammonia yield caused by low Faradic Efficiency over the target intermediates. Herein, the adjacent Cu defect formed at the interface of phase-separated CuAg alloy was successfully prepared by using the cation-exchange method and identified as the most active electrocatalytic center for efficient N2 reduction. The phase-separated CuAg alloy with rich interfacial Cu defective sites exhibited excellent eN2RR performance with an ammonia production rate (38.35 µg h−1 cm−2) and a Faradaic efficiency of 12.72 % at − 0.60 V versus reversible hydrogen electrode. Our work unravels fundamental principles for the rational design of electrocatalysts, and provides a strategy for fabricating the CuAg-PS alloy with rich interfacial Cu defective sites for eN2RR.

Calcium-organic frameworks cathode for high-stable aqueous Zn/organic batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) are attracting tremendous attention because of their intrinsic merits such as high safety and low cost. Cathode plays a critical role in enhancing the electrochemical performance of AZIBs. However, it is difficult to design a robust and high-efficiency cathode material and further implement the commercialization of AZIBs. Metal-organic frameworks (MOFs) electroactive compounds are attractive to serve as the cathode of AZIBs due to their unique porosity and crystal structures, resource renewability and structural diversity. In this work, a calcium-pure terephthalates acid framework (Ca-PTA·3H2O) was synthesized by facile hydrolysis and cationic exchange method, then explored as a novel cathode for AZIBs. The results highlight a high specific capacity of 431 mAh/g (0.51 mAh/cm2) at a current density of 50 mA/g, and excellent cycle performance with capacity retention of ∼90% after 2700 cycles at 500 mA/g. The following up characterizations investigate the reversible zinc storage mechanism in detail. This experiment made a specific contribution to the exploration of the new MOF as a competitive cathode for AZIBs.

Microfluidic Chromatography for Enhanced Amino Acid Detection at Ocean Worlds.

Increasing interest in the detection of biogenic signatures, such as amino acids, on icy moons and bodies within our solar system has led to the development of compact in situ instruments. Given the expected dilute biosignatures and high salinities of these extreme environments, purification of icy samples before analysis enables increased detection sensitivity. Herein, we outline a novel compact cation exchange method to desalinate proteinogenic amino acids in solution, independent of the type and concentration of salts in the sample. Using a modular microfluidic device, initial experiments explored operational limits of binding capacity with phenylalanine and three model cations, Na+, Mg2+, and Ca2+. Phenylalanine recovery (94–17%) with reduced conductivity (30–200 times) was seen at high salt-to-amino-acid ratios between 25:1 and 500:1. Later experiments tested competition between mixtures of 17 amino acids and other chemistries present in a terrestrial ocean sample. Recoveries ranged from 11% to 85% depending on side chain chemistry and cation competition, with concentration shown for select high affinity amino acids. This work outlines a nondestructive amino acid purification device capable of coupling to multiple downstream analytical techniques for improved characterization of icy samples at remote ocean worlds.

Designing hierarchical iron doped nickel-vanadium hydroxide microsphere as an efficient electrocatalyst for oxygen evolution reaction

Exploring highly active and inexpensive electrocatalysts for oxygen evolution reaction (OER) is considered to be one of the preconditions for the development of energy and environment-related technologies. Nickel-based layered double hydroxides (LDHs) are extensively-studied OER electrocatalysts, but they still require relatively high overpotentials to achieve threshold current densities. In this work, iron-doped nickel-vanadium hydroxide microspheres (Fe-doped NiV HMS) were synthesized by doping iron ions into the NiV HMS through a facile cation-exchange method. The Fe-doped NiV HMS are hollow hierarchical structure stacked by high-density perpendicularly-lying nanosheets, which provide enough space for electrolyte penetration and diffusion. Owing to optimized composition and hollow hierarchical structure, the Fe-doped NiV HMS exhibits excellent electrocatalytic performance, which possessed a very low running overpotential (255 mV at 10 mA cm−2) and a smallest Tafel slope (56 mV dec−1) compared with hierarchical NiV HMS toward OER. Electrochemical results and density functional theory (DFT) manifest that Fe doping could regulate the electronic structure of NiV HMS, thus improving its electrical conductivity and electron transfer rate, and thus enhancing its catalytic activity. This research provides a convenient way to prepare Ni-based hydroxides as promising OER catalysts.

Intraband Transitions of Nanocrystals Transforming from Lead Selenide to Self-doped Silver Selenide Quantum Dots by Cation Exchange.

In search of heavy metal-free mid-IR active colloidal materials, self-doped silver selenide colloidal quantum dots (CQDs) can be an alternative offering tunable mid-IR wavelength with a narrow bandwidth. One of the challenges in the study of the intraband transition is developing a method to widen the intraband transition energy range as well as reducing the toxicity of the materials. Here, we present AgxSe (x > 2) CQDs exhibiting an intraband transition up to 0.39 eV, produced by the cation exchange (CE) method from PbSe CQDs. The major electronic transition efficiently changes from the SWIR band gap of PbSe CQDs to the mid-IR intraband transition of the AgxSe CQDs by the CE. The intraband exciton is verified by examining the absorption and emission of the CE AgxSe CQDs as well as their applications on electrochemical mid-IR luminescence and mid-IR intraband photodetectors.

Construction of CdS@Cu2-xS core−shell p-n heterojunction with enhanced charge separation for wide spectrum photocatalytic H2 evolution

Development of wide spectrum photocatalysts have become research hotspot in efficient solar energy-chemical conversion. In this work, a novel CdS@Cu2-xS core-shell p-n heterojunction was designed by cation exchange method for photocatalytic H2 evolution. The formation of built-in electric field on CdS@Cu2-xS core-shell p-n heterojunction effectively accelerates the separation efficiency of photogenerated carriers. The highest photocatalytic hydrogen evolution rate is 8176.5 μmol g−1h−1 over optimized CdS@1%Cu2-xS-2 p-n heterojunction, which is 3.85 times higher than hexagonal CdS. And the highest AQE of 2.60% is acquired at 475 nm. The enhanced photocatalytic activity of the CdS@Cu2-xS p-n heterojunction is mainly attributed to the effect of the built-in electric field generated by p-n heterojunction, which improves the separation efficiency of photogenerated carriers. More importantly, the formed CdS@Cu2-xS p-n heterojunction with built-in electric field steering photogenerated carrier separation was certified by in-situ XPS. This work provides effective strategy to construction of p-n heterojunction for wide spectrum photocatalysis.

Compositionally Tuning Electron Transfer from Photoexcited Core/Shell Quantum Dots via Cation Exchange.

It is critical to find methods to control the thermodynamic driving force for photoexcited charge transfer from quantum dots (QDs) and explore how this affects charge transfer rates, since the efficiency of QD-based photovoltaic and photocatalysis technologies depends on both this rate and the associated energetic losses. In this work, we introduce a single-pot shell growth and Cu-catalyzed cation exchange method to synthesize CdxZn1-xSe/CdyZn1-yS QDs with tunable driving forces for electron transfer. Functionalizing them with two molecular electron acceptors─naphthalenediimide (NDI) and anthraquinone (AQ)─allowed us to probe nearly 1 eV of driving forces. For AQ, at lower driving forces, we find that higher Zn content results in a 130-fold increase of electron transfer rate constants. However, at higher driving forces electron transfer dynamics are unaltered. The data are understood using an Auger-assisted electron transfer model and analyzed with computational work to determine approximate binding geometries of these electron acceptors. Our work provides a method to tune QD reducing power and produces useful metrics for optimizing QD charge transfer systems that maximize rates of electron transfer while minimizing energetic losses.

Controlled Synthesis and Photoelectrochemical Performance Enhancement of Cu2−xSe Decorated Porous Au/Bi2Se3 Z-Scheme Plasmonic Photoelectrocatalyst

In this paper, uniform Cu2−xSe-modified Au/Bi2Se3 hybrid nanoparticles with porous shells have been prepared through a cation exchange method. Bi2Se3/Cu2−xSe Z-scheme heterojunction is introduced onto Au nanocube by replacing Bi3+ with Cu2+. Owing to the effective coupling between Au core and semiconductor shells, Au/Bi2Se3/Cu2−xSe hybrids present a broad and strong plasmon resonance absorption in the visible band. More intriguingly, the carrier lifetime of Au/Bi2Se3/Cu2−xSe hybrid photoelectrodes can be further tailored with corresponding Cu2−xSe content. Through parameter optimization, 0.1-Au/Bi2Se3/Cu2−xSe electrode exhibits the longest electron lifetime (86.03 ms) among all the parallel samples, and corresponding photoelectrochemical performance enhancement is also observed in the tests. Compared with that of pure Bi2Se3 (0.016% at 0.90 V vs. RHE) and Au/Bi2Se3 (0.02% at 0.90 V vs. RHE) nanoparticles, the maximum photoconversion efficiency of porous Au/Bi2Se3/Cu2−xSe hybrid photoanodes increased by 5.87 and 4.50 times under simulated sunlight illumination, attributing to the cooperation of Z-scheme heterojunction and plasmon resonance enhancement effects. All the results indicate that Au/Bi2Se3/Cu2−xSe porous hybrids combine eco-friendliness with excellent sunlight harvesting capability and effectively inhibiting the charge recombination, which provide a new idea for efficient solar-driven water splitting.

Porous Pb-Doped ZnO Nanobelts with Enriched Oxygen Vacancies: Preparation and Their Chemiresistive Sensing Performance

Among various approaches to improve the sensing performance of metal oxide, the metal-doped method is perceived as effective, and has received great attention and is widely investigated. However, it is still a challenge to construct heterogeneous metal-doped metal oxide with an excellent sensing performance. In the present study, porous Pb-doped ZnO nanobelts were prepared by a simply partial cation exchange method, followed by in situ thermal oxidation. Detailed characterization confirmed that Pb was uniformly distributed on porous nanobelts. Additionally, it occupied the Zn situation, not forming its oxides. The gas-sensing measurements revealed that 0.61 at% Pb-doped ZnO porous nanobelts exhibited a selectively enhanced response with long-term stability toward n-butanol among the investigated VOCs. The relative response to 50 ppm of n-butanol was up to 47.7 at the working temperature of 300 °C. Additionally, the response time was short (about 5 s). These results were mainly ascribed to the porous nanostructure, two-dimensional belt-like morphology, enriched oxygen vacancies and the specific synergistic effect from the Pb dopant. Finally, a possible sensing mechanism of porous Pb-doped ZnO nanobelts is proposed and discussed.

Large Stokes Shifts over Visible–Infrared Wavelengths from Multicore/Shell Quantum Dots for Solar-Harvesting Applications

Multicore/shell PbCdS quantum dots (QDs) with an extraordinarily large Stokes shift of more than 550 nm are reported in this study. The QDs were prepared from a Pb–Cd cation-exchange method at an elevated reaction temperature for an extended reaction time, resulting in PbS–CdS domain separation within the core/shell PbS/CdS QD matrix. As a result, the QDs with the multidomain structure possess the first exciton absorption and photoluminescence wavelengths of 450 and 1002 nm, respectively, leading to an unusually large Stokes shift. The unique QDs are considered promising in some applications such as a down-shifting layer for solar harvesting.

Iron‐Doped Ni−Al Layered Double Hydroxide as an Efficient Oxygen Evolution Reaction Electrocatalyst

AbstractTwo‐dimensional (2D) layered double hydroxide (LDH) is a good alternative to precious metals in terms of oxygen evolution electrocatalysis. The doping of various elements into LDH has been widely investigated in order to further minimize the oxygen evolution overpotential. Herein, by using the cation exchange method, we design and construct a Fe‐doped Ni−Al LDH nanoplatelets (NAF LDH‐25). Fe3+ enter the nickel and aluminum vacancies smoothly as a result of the dual action of corrosion and cation exchange, and iron ion activity is optimized. Meanwhile, strong interaction of Ni and Fe, effect of Al on electronic structure and the structural advantages of two‐dimensional nanoplatelets, as a result, the as‐prepared NAF LDH‐25 exhibits extremely low overpotential (288 mV) at high current density of 100 mA cm−2. The NAF LDH‐25 also showed excellent stability in the 72 h chronopotentiometry test. Therefore, cation exchange strategy provides a new option for the preparation of practical OER catalysts.

A zero-dimensional/two-dimensional Ag–Ag2S–CdS plasmonic nanohybrid for rapid photodegradation of organic pollutant by solar light

Herein, the two synthesis strategies are employed for rational design of 0D/2DAg-Ag2S–CdS heterojunctions towards photocatalytic degradation of methyl orange (MO) under simulated solar light. As the first strategy, a ternary Ag–Ag2S–CdS nanosheet (NS) heterojunction was fabricated via combined cation exchange and photo-reduction (CEPR) method (Ag–Ag2S–CdS/CEPR). The second strategy employed coprecipitation (CP) method (Ag–Ag2S–CdS/CP). Strikingly, SEM, TEM and HR-TEM images are manifested the first strategy is beneficial for retaining the original thickness (20.2 nm) of CdS NSs with a dominant formation of metallic Ag, whereas the second strategy increases the thickness (33.4 nm) of CdS NSs with a dominant formation of Ag2S. The Ag–Ag2S–CdS/CEPR exhibited 1.8-fold and 3.5-fold enhancement in photocatalytic activities as compared to those of Ag–Ag2S–CdS/CP and bare CdS NSs, respectively. This enhanced photocatalytic activity could be ascribed to fact that the first strategy produces a high-quality interface with intimate contact between the Ag–Ag2S–CdS heterojunctions, resulting in enhanced separation of photo-excited charge carriers, extended light absorption, and enriched active-sites. Furthermore, the degradation efficiency of Ag–Ag2S–CdS/CEPR was significantly reduced to ∼5% in the presence of BQ (•O2− scavenger), indicating that •O2− is the major active species that can decompose MO dye under simulated solar light.

Effect of Cation Exchange Time on the Morphology and Photoactivity of CdS/Ag2S Composites for Ciprofloxacin Degradation

Herein, the effect of reaction time in the cationic exchange method on the CdS/Ag2S structure and photocatalytic activity is investigated. A hydrothermal approach is used to produce CdS nanorods, and then a cation exchange method is applied to synthesize CdS/Ag2S composites. The heterostructure between CdS and Ag2S is determined by the X‐ray diffraction and transmission electron microscopy studies. Comparing pure CdS NRs and CdS/Ag2S by the UV–vis diffuse reflection spectra data, the introduction of Ag2S is proven to enhance the light absorption in visible region. The Brunauer–Emmett–Teller method indicates that CdS and CdS/Ag2S are mesopore materials and the specific surface areas of CdS, CdS/Ag2S‐15, CdS/Ag2S‐30, and CdS/Ag2S‐60 samples without and with a cation‐exchange reaction time of 15, 30, and 60 min are 305, 900, 187, and 52 m2 g−1, respectively. The photocatalytic activity of CdS/Ag2S is examined through the ciprofloxacin photodegradation. The ciprofloxacin degradation rate increases with the introduction of CdS and reached a maximum value of 60% within 180 min for CdS/Ag2S‐15 under simulated sunlight irradiation, which is 1.5 times greater than that of pure CdS. The ciprofloxacin degradation rate decreases as the cation‐exchange reaction time is increased to 60 min (26% after 180 min illumination).

Synthesis and characterization of poly(3,4-ethylenedioxythiophene)/ Montmorillonite nanocomposites using surfactants modified clay

Nanocomposites of Poly (3,4-ethylenedioxythiophene) (PEDOT) and surfactant modified Maghnite clay have been successfully synthesized by in situ polymerization of EDOT monomer in the interlayer space of the organoclay. The synthesis has been assisted by ultrasonic method to improve the dispersion of PEDOT polymer between the Maghnite clay sheets. The surfactant modified clay is synthesized via cation exchange method with Hydrogenure Tetrabutylammonuim (TBAHS) and cetyltrimethylammonium (CTAB). Two types of organo-modified clays are obtained namely the Mag-TBA and Mag-CTA according to the template used. Various physico-chemical techniques are used for nanocomposites characterization such as XRD, FTIR, AFM, TGA/DTA, SEM and TEM. The results prove the formation of intercalated / exfoliated upon increasing the content of organoclay in the nanocomposites , consequently, different morphologies and structures in which the exfoliated and intercalated forms were obtained. Both nanocomposites display significant enhancement in the thermal stabilities compared to the PEDOT polymer. However, a decrease in conductivity values is observed for all samples compared to pure conducting polymer. This feature can be improved in view of desired application in electrochemical devices.

Enhanced solar water splitting of BiVO4photoanodes byin situsurface band edge modulation

In this work, the surface band edge of the BiVO4photoanode is modulated by anin situgas-phase cation exchange method, in which some of the Bi atoms on the surface are replaced by V atoms to form a V-rich surface.

Layered Clay-Graphene Oxide Nanohybrids for the Reinforcement and Fire-Retardant Properties of Polyurea Matrix.

Nanostructures are more and more evolved through extensive research on their functionalities; thus, the aim of this study was to obtain layered clay–graphene oxide nanohybrids with application as reinforcing agents in polyurea nanocomposites with enhanced thermal–mechanical and fire-retardant properties. Montmorillonite (MMT) was combined with graphene oxide (GO) and amine functionalized graphene oxide (GOD) through a new cation exchange method; the complex nanostructures were analyzed through FTIR and XPS to assess ionic interactions between clay layers and GO sheets by C1s deconvolution and specific C sp3, respective/ly, C-O secondary peaks appearance. The thermal decomposition of nanohybrids showed a great influence of MMT layers in TGA, while the XRD patterns highlighted mutual MMT and GO sheets crystalline-structure disruption by the d (002) shift 2θ = 6.29° to lower values. Furthermore, the nanohybrids were embedded in the polyurea matrix, and the thermo-mechanical analysis gave information about the stiffness of MMT–GO nanocomposites, while GOD insertion within the MMT layers resulted in a 30 °C improvement in the Tg of hard domains, as shown in the DSC study. The micro CT analysis show good dispersion of inorganic structures within the polyurea, while the SEM fracture images revealed smooth surfaces. Cone calorimetry was used to evaluate fire-retardant properties through limiting the oxygen index, and MMT–GOD based nanocomposites showed a 35.4% value.

Versatile Synthesis of Hollow Metal Sulfides via Reverse Cation Exchange Reactions for Photocatalytic CO2 Reduction

AbstractHerein, we explore a general Cu2−xS nanocube template‐assisted and reverse cation exchange‐mediated growth strategy for fabricating hollow multinary metal sulfide. Unlike the traditional cation exchange method controlled by the metal sulfide constant, the introduction of tri‐n‐butylphosphine (TBP) can reverse cation exchange to give a series of hollow metal sulfides. A variety of hollow multinary metal sulfide cubic nanostructures has been demonstrated while preserving anisotropic shapes to the as‐synthesized templates, including binary compounds (CdS, ZnS, Ag2S, PbS, SnS), ternary compound (CuInS2, ZnxCd1−xS), and quaternary compound (single‐atom platinum anchored ZnxCd1−xS; ZnxCd1−xS‐Pt1). Experimental and density functional theory (DFT) calculations show that the hollow metal sulfide semiconductors obtained could significantly improve the separation and migration of photogenerated electron‐hole pairs. Owing to the efficient charge transfer, the ZnxCd1−xS‐Pt1 exhibited outstanding photocatalytic performance of CO2 to CO, with the highest CO generation rate of 75.31 μmol h−1.

Versatile Synthesis of Hollow Metal Sulfides via Reverse Cation Exchange Reactions for Photocatalytic CO2 Reduction.

Herein, we explore a general Cu2-x S nanocube template-assisted and reverse cation exchange-mediated growth strategy for fabricating hollow multinary metal sulfide. Unlike the traditional cation exchange method controlled by the metal sulfide constant, the introduction of tri-n-butylphosphine (TBP) can reverse cation exchange to give a series of hollow metal sulfides. A variety of hollow multinary metal sulfide cubic nanostructures has been demonstrated while preserving anisotropic shapes to the as-synthesized templates, including binary compounds (CdS, ZnS, Ag2 S, PbS, SnS), ternary compound (CuInS2 , Znx Cd1-x S), and quaternary compound (single-atom platinum anchored Znx Cd1-x S; Znx Cd1-x S-Pt1 ). Experimental and density functional theory (DFT) calculations show that the hollow metal sulfide semiconductors obtained could significantly improve the separation and migration of photogenerated electron-hole pairs. Owing to the efficient charge transfer, the Znx Cd1-x S-Pt1 exhibited outstanding photocatalytic performance of CO2 to CO, with the highest CO generation rate of 75.31 μmol h-1 .

Structure design of Prussian blue analogue derived CoFe@C composite with tunable microwave absorption performance

Manufacturing microwave absorbers with controllable microstructure is appealing continuous interest. Here, tunable structure of cobalt hexacyanoferrate submicrocubes (CoHCF) are fabricated via cation exchange method. Subsequently, porous cobalt iron alloys and carbon (CoFe@C) composites are obtained through annealed the CoHCF precursors at 500 °C. By simply adjust the reaction solvent of precursors, the CoHCF submicrocubes with yolk-shell, hollow, and mesoporous structure are obtained. The results show that the morphology and structure are important for enhancing the microwave absorption properties. Typically, the optimal reflection loss of CoFe@C submicrocubes with mesoporous structure is −73.63 dB at the absorber thickness of 2.6 mm, and the effective absorption bandwidth (EAB, RL < -10 dB) is 5.0 GHz. This strategy provides a novel approach for the structural control of Prussian blue analogous (PBAs), which may be greatly helpful for the wide application of PBAs and their derivatives.