Archive for the ‘Subject Areas’ Category

1+1>2: Bridging Constituents in Hetero-Structured Hydrogen Evolution Photocatalysts

Solar-driven water reduction is a sustainable method to acquire hydrogen fuel. An indispensable component of this reaction is the photocatalyst which drives spontaneous hydrogen gas evolution from water when illuminated. Hetero-structured materials consisting of two or more catalysts stand out as promising hydrogen evolution catalysts, due to the combined advantages of their constituents (e.g. enhanced light-absorption capability). Unfortunately, the weak adhesion between different components is the Achilles heel of conventional hetero-structured photocatalysts. It impedes electron transport from the photocatalysts to the nearby water molecules, hindering the catalytic activity.

A research group led by Xiao Xiao and Jian-Ping Zou from Nanchang Hangkong University of China has demonstrated a solution to the aforementioned challenge. They firmly connected two photocatalysts – Pt-loaded carbon nitride (CN) and the covalent organic framework CTF-1 – via amide bonds, resulting in a new type of hetero-structured photocatalyst, CN/CTF-1, which exhibited a hydrogen evolution rate approximately 3 times faster than those of conventional hetero-structured photocatalysts made of weakly bound CN and CTF-1.

The researchers adopted a two-step method to synthesize CN/CTF-1. They first reacted CTF-1 sheets with 4-aminobenzoic acid to graft carboxylic groups onto the surfaces of the CTF-1 sheets. A subsequent amide condensation between the amine groups of the CN and the carboxyl groups on the CTF-1 bridged the two components. The amide groups serve as electron transport pathways and facilitate the movement of photo-excited electrons from CTF-1 to CN (Figure 1a) which liberates hydrogen gas.

The covalent amide “bridges” gave CN/CTF-1 a fast hydrogen production rate. Quantitatively, when irradiated with a 300 W Xe lamp at 160 mW/cm2, CN/CTF-1 produced ~4 mmol H2 per gram of CN/CTF-1 after 4 h (0.85 mmol H2 h-1 gcatalyst-1), whereas under identical conditions, weakly adhered CN and CTF-1 sheets as well as a physical mixture of CN and CTF-1 all achieved H2 evolution rates of ~1 mmol H2 per gram of photocatalyst (0.30 mmol H2 h-1 gcatalyst-1) (Figure 1b).

Figure 1. (a) (Pt-loaded) CN sheets are covalently bound to CTF-1 sheets via amide bonds. These covalent bonds serve as electron transport “bridges” that facilitate the diffusion of photo-excited electrons from CTF-1 to CN. (b) H2 evolution rates of four photocatalysts: 1 – covalently bound CN/CTF-1; 2 and 3 –  weakly adhered CN and CTF-1; 4 – a physical mixture of CN and CTF-1.

The covalent bonding strategy is applicable to other coupling reactions such as the Friedel-Crafts reaction. This general method could create a new paradigm for designing and synthesizing high-performance hetero-structured photocatalysts.

 

To find out more please read:

A General Strategy via Chemically Covalent Combination for Constructing Heterostructured Catalysts with Enhanced Photocatalytic Hydrogen Evolution

Gang Zhou, Ling-Ling Zheng, Dengke Wang, Qiu-Ju Xing, Fei Li, Peng Ye, Xiao Xiao, Yan Li, and Jian-Ping Zou

Chem. Commun., 2019, 55, 4150-4153

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the United States. He is passionate about scientific communication to introduce cutting-edge research to both the general public and scientists with diverse research expertise. He is a blog writer for Chem. Commun. and Chem. Sci. More information about him can be found at http://liutianyuresearch.weebly.com/.

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Using Carbon to Make a Better Solar Cell

Maybe I’m stating the obvious, but solar cells are incredibly complex devices with more components than just the light absorber.

While the focus on the active layer by chemists looking to develop new materials is understandable, in order to truly create next-generation solar cells the other components of the architecture must be improved.  Creating the crack-resistant or resilient layers necessary for functional flexible solar cells is a major challenge currently being addressed. These new materials and approaches also need to work within the general framework of fabrication techniques used for the other layers – ideally at low temperature and solution processible.

An often-neglected piece of the puzzle is the electrode. Electrodes are traditionally composed of a thin metal layer, which is often vapor deposited at high temperatures and low pressures. This class of electrodes is expensive, susceptible to degradation, and can damage the critical hole transport or active layers. One emerging alternative is carbon-based electrodes, applied as pastes. These low-cost, highly stable, and hydrophobic materials are attractive given their compatibility with emerging photovoltaic technologies, particularly perovskites. Their broad application has been limited by the necessity of toxic solvents to create the pastes, but researchers in China have developed a low-temperature, highly conductive carbon paste that can be screen printed onto perovskite solar cells without using toxic solvents.

Fabrication schematic and cross sectional SEM for a perovskite solar cell with a carbon electrode

Figure 1. (a) Fabrication schematic for perovskite solar cells with carbon electrodes and hole transport layers. (b) Cross sectional SEM image of a device.

Not only are the solvents more environmentally friendly compared to those previously used, they also increase the mechanical strength of the final film and, under fabrication conditions, do not damage the perovskite active layer or organic hole transport layer. While the hole transport layer isn’t strictly necessary to create a working device, it has been shown to increase the champion efficiency from 11.7% to 14.55%. This is likely due to poor contact between the perovskite and carbon electrode, which the thin hole transport layer (PEDOT:PSS) helps remedy.

Carbon-based electrode undergoing a bending test and sheet resistivity data

Figure 2. (a) A sample undergoing a bending test. (b) The electrode sheet resistance before and after 100 bends.

The most exciting aspect of these electrodes is their resilience when subjected to a bending test. After 100 bends, the researchers saw no visible film damage or increase in the sheet resistance when compared to the initial sample. Actual flexible solar cells fabricated and studied did show a decrease in performance after 1,000 bends, but this was attributed to known robustness issues in the base ITO layer. This work with carbon-based electrode materials could lead to simpler manufacturing for fabricating perovskite solar cells at a commercial level.

 

To find out more please read:

A low-temperature carbon electrode with good perovskite compatibility and high flexibility in carbon based perovskite solar cells

Shiyu Wang, Pei Jiang, Wenjian Shen, Anyi Mei, Sixing Xiong, Xueshi Jiang, Yaoguang Rong, Yiwen Tang, Yue Hu & Hongwei Han

Chem. Commun., 2019, 55, 2765-2768

This article is also part of the Chemical CommunicationsPerovskites‘ themed collection.

About the blogger:

 

Beth Mundy is a PhD candidate in chemistry in the Cossairt lab at the University of Washington in Seattle, Washington. Her research focuses on developing new and better ways to synthesize nanomaterials for energy applications. She is often spotted knitting in seminars or with her nose in a good book. You can find her on Twitter at @BethMundySci.

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A Battery Cathode with a Bee Pupa-Filled Honeycomb Structure

Increasing the volumetric energy densities of batteries is essential for improving the durability of portable electronics and the operating ranges of electric vehicles. One way to improve energy density is to enlarge the mass fraction of active materials in battery electrodes; however, the degree of enhancement remains limited. This limitation results from the densification of the electrodes when the mass fraction increases, making electron transport and ion diffusion throughout the electrodes sluggish. These drawbacks lower the utilization efficiency of the overall electrode materials.

A team of scientists from China and the United States has recently addressed the aforementioned challenges. Specifically, they synthesized a 3D cathode of carbon-coated Li2MnSiO4 (Li2MnSiO4/C) with a structure mimicking a honeycomb filled with bee pupas (Fig. 1). This lithium-ion battery cathode possesses a high mass fraction of 90% (of overall electrode mass) as well as a volumetric energy density as high as 2443 Wh/dm3.

The uniquely structured electrodes were prepared through a hard-template method (Fig. 1). Using polystyrene particles, silica surface coating, and Li2MnSiO4 precursor infiltration, the authors synthesized a carbon-coated Li2MnSiO4 honeycomb scaffold with each cavity filled with a carbon-coated Li2MnSiO4 particle. This architecture differed from previously reported 3D structures, which typically had a large portion of voids, and enabled an ultrahigh active-material mass loading of 90 wt.%. Additionally, the gaps between the scaffold and the particles functioned as ion-diffusion channels, and the carbon coatings served as electron-transport expressways. These characteristics effectively addressed the problem of sluggish ion diffusion and electron transport.

Figure 1. The synthesis procedures of the BPFH-shaped Li2MnSiO4/C electrode. The green particles and yellow scaffold represent polystyrene spheres and the silica coating, respectively.

Due to the facilitated electron transport and ion diffusion, the Li2MnSiO4/C electrode with a bee pupa-filled honeycomb (BPFH) structure (Fig. 2a) exhibited an outstanding charge-storage performance. Specifically, it delivered a high volumetric capacity of 643 mAh/cm3 at a current density of 0.1 C, corresponding to a volumetric density of 2443 Wh/dm3. This volumetric capacity was approximately two times higher than that of a Li2MnSiO4/C honeycomb lattice without any Li2MnSiO4 particles (Fig. 2b). After 100 consecutive charge-discharge cycles, the BPFH-shaped Li2MnSiO4/C electrode retained a volumetric capacity of 328 mAh/cm3 (Fig. 2c).

Figure 2. (a and b) Scanning electron microscopy images of (a) the BPFH-shaped Li2MnSiO4/C electrode and (b) the Li2MnSiO4/C scaffold. (c) The capacities and the Coulombic efficiencies of the two electrodes during 100 charge-discharge cycles.

The demonstrated BPFH architecture could be extended to other materials for the synthesis of battery electrodes with both high mass fractions of active materials and outstanding volumetric energy densities.

 

To find out more please read:

A Bee Pupa-Infilled Honeycomb Structure-Inspired Li2MnSiO4 Cathode for High Volumetric Energy Density Secondary Batteries

Jinyun Liu, Xirong Lin, Huigang Zhang, Zihan Shen, Qianqian Lu, Junjie Niu, Jinjin Li and Paul V. Braun

Chem. Commun., 2019, 55, 3582-3585

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the United States. He is passionate about scientific communication to introduce cutting-edge research to both the general public and scientists with diverse research expertise. He is a blog writer for Chem. Commun. and Chem. Sci. More information about him can be found at http://liutianyuresearch.weebly.com/.

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Saving Organic Electrodes in Lithium-Ion Batteries

Organic compounds with conjugated electron structures are emerging as promising Li-ion battery cathodes due to their high capacity and environmental benignity. To make these cathodes practically feasible, organic electrodes are typically incorporated with metal ions to boost their energy densities. The addition of metal ions, however, usually jeopardizes the structural integrity of the electrodes and shortens battery lifetime.

Recently, three groups of Chinese researchers demonstrated that increasing the electrolyte concentration could effectively prolong the lifespan of metal-incorporated organic cathodes. The researchers studied cuprous tetracyano-quinodimethane (CuTCNQ), a Cu2+-containing organic Li-ion battery cathode, and observed its significantly improved cycling stability in a 7 M LiClO4 electrolyte compared to a 1 M electrolyte. This work was published recently in ChemComm.

CuTCNQ in a typical diluted electrolyte of 1 M LiClO4 exhibited unsatisfactory stability. Its first-cycle charging capacity reached ~180 mAh/g, but it dropped appreciably to 23 mAh/g after the first discharging process (Figure 1a). Concurrently, the electrolyte turned from clear to yellow (Figure 1b), due to the dissolution of TCNQ. These observations unequivocally showed the rapid disintegration of CuTCNQ in diluted electrolytes.

Figure 1. (a) The first-cycle charge-discharge profile of CuTCNQ in a liquid electrolyte containing ethylene carbonate (EC), propylene carbonate (PC) and 1 M LiClO4 (1 M LiClO4-EC/PC). (b) Photographs showing the electrolyte color before and after the first charge-discharge cycle.

CuTCNQ was found to be more stable in electrolytes with concentrations higher than 1 M. When the LiClO4 concentration increased to 3 M, 5 M and 7 M, the specific capacities of CuTCNQ retained after 50 consecutive charge-discharge cycles were ~25 mAh/g, ~70 mAh/g, and ~110 mAh/g, respectively (Figure 2a). All of these capacities were higher than that of CuTCNQ in 1 M LiClO4 after the same cycle number (<10 mAh/g). Additionally, the electrolytes experienced nearly no color change, suggesting little TCNQ was dissolved (Figure 2b).

The elevated stability of CuTCNQ correlates to the formation of Li+-ClO4 ion pairs in concentrated electrolytes (Figure 2c). With increasing LiClO4 concentration, Li+ and ClO4 tend to form ion pairs that coordinate with solvent molecules. Solvent-coordination reduces the number of free solvent molecules that can dissolve TCNQ, thus minimizing the dissolution of TCNQ.

Figure 2. (a) The cycling stability performances of CuTCNQ with electrolytes with different LiClO4 concentrations. (b) Photographs showing the electrolyte color before and after 50 charge-discharge cycles at different LiClO4 concentrations. (c) Li+ and ClO4- form solvent-coordinated ion pairs in super-concentrated electrolytes (e.g., 7 M).

This work provides a facile approach to mitigate the capacity fading of CuTCNQ. The strategy may be extended to stabilize other metal-incorporated organic cathodes in Li-ion batteries.

To find out more please read:

Sustainable Cycling Enabled by A High-Concentration Electrolyte for Lithium-Organic Batteries

Ying Huang, Chun Fang, Wang Zhang, Qingju Liu and Yunhui Huang

Chem. Commun., 2019, 55, 608-611

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the United States. He is passionate about scientific communication to introduce cutting-edge research to both the general public and scientists with diverse research expertise. He is a blog writer for Chem. Commun. and Chem. Sci. More information about him can be found at http://liutianyuresearch.weebly.com/.

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Shrinking the Size of Hydrogen Evolution Catalysts by Carbon Coating

Hydrogen gas is a zero-emission energy resource promising to replace diminishing fossil fuels. The electrolysis of water is a sustainable way to acquire hydrogen gas, but this non-spontaneous process demands electricity to proceed. Therefore, hydrogen evolution reaction (HER) catalysts are used to reduce the energy cost or overpotential of the electrolysis.

Researchers are pursuing ultrafine nanoparticles as HER catalysts due to their high catalytic activity. For example, the HER catalytic activities of Ru nanoparticles are reportedly 100-200% higher than those of bulk Ru catalysts. Unfortunately, the preparation of well-dispersed nanoparticles is challenging because nanoparticles are prone to aggregate together.

Recently in ChemComm, Fuqiang Chu, Yong Qin and coworkers from Changzhou University, China addressed the challenge. They utilized a Ru-based coordination complex and cyanuric acid as the reactants, and synthesized high-performance HER catalysts composed of ~2 nm Ru nanoparticles uniformly dispersed on graphene sheets. During the thermal annealing step in the synthesis, the ligands of the complex and the cyanuric acid both decompose to nitrogen-doped carbon shells covering the as-formed Ru nanoparticles. These shells serve as spacers that prevent particle aggregation (Figure 1).

Figure 1. An illustration of the synthesis of carbon-coated Ru ultrafine nanoparticles on graphene sheets. Tris(2,2′-bipyrindine) ruthenium dichloride is the precursor of the Ru nanoparticles.

In both the acidic and the alkaline electrolytes, the 2 nm Ru particles (RuNC-2) display lower overpotentials and higher current densities than the 5 nm Ru particles (Figure 2) without the carbon coating (RuNC-5). Remarkably, the 2 nm particles showed comparable performance to the benchmark Pt catalyst in the acidic electrolyte (the red and black curves in Figure 2a).

Figure 2. Linear sweep voltammograms of ~3 nm Pt nanoparticles (PtNC), 2 nm Ru nanoparticles (RuNC-2) and 5 nm Ru nanoparticles (RuNC-5) in (a) 0.5 M H2SO4 and (b) 1 M KOH aqueous solutions.

The concept of the in-situ generation of protective coatings could inspire the synthesis of other ultra-small nanoparticles to potentially push the HER catalytic performance to new heights.

 

To find out more please read:

An Ultrafine Ruthenium Nanocrystal with Extremely High Activity for the Hydrogen Evolution Reaction in Both Acidic and Alkaline Media

Yutong Li, Fuqiang Chu, Yang Liu, Yong Kong, Yongxin Tao, Yongxin Li and Yong Qin

Chem. Commun., 2018, DOI: 10.1039/c8cc08276f

 

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the United States. He is passionate about scientific communication to introduce cutting-edge research to both the general public and scientists with diverse research expertise. He is a blog writer for Chem. Commun. and Chem. Sci. More information about him can be found at http://liutianyuresearch.weebly.com/.

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Copper A3 Coupling using a Switchable Homogeneous/Heterogeneous Catalyst

A MOC, I learned this week, is a metal-organic cage. I was familiar with MOMs, MOFs and MOBs, but MOCs were a new one. A MOM (metal-organic material) is a coordination-driven assembly constructed from metal nodes linked by organic ligands. MOMs encompass both MOFs (metal-organic frameworks) and MOCs (metal-organic cages). A MOF is an extended network with the potential for inner porosity, and a MOC is a discrete metal-ligand cluster. And that’s just about as far down the nomenclature rabbit hole I’m willing to go. If you’re keeping up you’ll realise that I forgot one! A MOB is a crowd of graduate students competing for free coffee at the public seminar.

Dong and co-workers at Shandong Normal University designed and prepared a MOM catalyst constructed from copper(II) nodes and a tripodal ligand consisting of a phenylic wheel functionalised with diketones. In chloroform these two components arrange into discrete MOC assemblies containing two tripodal ligands and three copper ions. The copper ions in the cluster are each coordinated to two diketone moieties (in a acetylacetonate-like fashion) in a quasi-square planar arrangement.

Synthesis of the tripodal ligand functionalised with diketone coordinating moieties.

Synthesis of the tripodal ligand functionalised with diketone coordinating moieties.

An interesting property of the material is that it can switch between the MOC form, soluble in halogenated solvents, and an insoluble MOF that assembles upon addition of 1,4-dioxane. 1,4-Dioxane is both an anti-solvent and a ligand; coordination between copper and 1,4-dioxane binds the discrete MOC cages to each other, arranging them into the extended MOF structure. This behaviour can be exploited to prepare a practical catalyst that combines the benefits of both homogeneous and heterogeneous catalysis, namely that homogeneous catalysts are generally more efficient, selective and easier to study, but heterogeneous catalysis are easier to recover and recycle. What better way to solve this problem than with a catalyst that is homogeneous during the reaction conditions, but heterogeneous when it comes to product separation?

Reversible metal-organic cage MOC(top left)-MOF(top right) metal-organic framework transition mediated by the addition of 1,4-dioxane. Coordination bonds between 1,4-dioxane shown (bottom image).

Reversible MOC(top left)-MOF(top right) transition mediated by the addition of 1,4-dioxane. Coordination bonds between 1,4-dioxane shown (bottom image).

The authors used the A3 coupling reaction to demonstrate this concept in a catalytic reaction. The A3 reaction is a transition metal-catalysed, multi-component coupling reaction between aldehydes, alkynes and amines. The products are propargylamines, practical synthetic intermediates for the synthesis of nitrogen heterocycles. The A3 reaction has been extensively studied and can be effected by a wide range of transition metal catalysts. Its versatility makes it a popular choice as a model catalytic reaction to demonstrate innovative ideas in catalytic design – as the authors have done here.

Coordination-driven assemblies have a unique potential for the synthesis of differentially soluble materials, used by the authors for novel catalytic design. Whether this particular metal-ligand combination can be applied to other copper catalysed reactions remains to be seen, nevertheless the principle offers an innovative approach that augments the range of methods striving to bridge the gap between homogeneous and heterogeneous catalysis.

To find out more please read:

Cu3L2 metal-organic cages for A3-coupling reactions: reversible coordination interaction triggered homogeneous catalysis and heterogeneous recovery

Gong-Jun Chen, Chao-Qun Chen, Xue-Tian Li, Hui-Chao Ma and Yu-Bin Dong.
Chem. Commun., 2018, 54, 11550-11553
DOI: 10.1039/c8cc07208f

About the author

Zoë Hearne is a PhD candidate in chemistry at McGill University in Montréal, Canada, under the supervision of Professor Chao-Jun Li. She hails from Canberra, Australia, where she completed her undergraduate degree. Her current research focuses on transition metal catalysis to effect novel transformations, and out of the lab she is an enthusiastic chemistry tutor and science communicator.

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The Birth of a Semiconducting Metal Organic Framework by Sulfur Coordination

Metal organic frameworks (MOFs) are crystalline nanomaterials composed of metal ions or clusters coordinated with organic ligands. Owing to the versatility of their building blocks, MOFs have multiple functionalities and can serve as gas separators, sensors, catalysts, electrode materials etc. Now the structure diversity of MOFs is further enriched by Wu and coworkers from Soochow University, China. Specifically, the researchers synthesized a semiconducting MOF with tetra-coordinated sulfur units. This breakthrough was recently published in ChemComm.

The uniqueness of the synthesized semiconducting MOF (MCOF-89) is its square-planar tetra-coordinated metal-sulfur structure, which is observed in MOFs for the first time. It was believed that putting a sulfur atom next to a metal node of MOFs was extremely difficult, because of the large discrepancy in bonding energy between metal-sulfur bonds and conventional metal-carboxylate bonds. Incorporating sulfur atoms thereby could undermine the structural stability of MOFs.

The authors addressed this challenge by designing a tetra-coordination environment as illustrated in Figure 1. The four manganese-sulfur bonds effectively reinforced the unstable S coordination. MCOF-89 was synthesized via a solvothermal reaction with Mn(CH3COO)2 and thiourea as the Mn and S sources, respectively.

Figure 1. The structure of MCOF-89. The illustration on the left is a three-dimensional lattice structure (the red, green and yellow balls represent oxygen, manganese and sulfur), and the structure on the right shows the Mn-S square-planar tetra-coordination configuration (M = manganese).

The synthesized S-incorporated MOF is a semiconductor with a bandgap of 2.82 eV. Additionally, this MOF is photoactive and is able to generate a photocurrent of ~1.9 µA/cm2 upon light irradiation.

This work exemplifies how molecular design can lead to the discovery of novel MOFs with extraordinary structures. It could also inspire other synthesis protocols toward various metal-chalcogenide-containing MOFs with unexpected properties.

 

To find out more please read:

A Semiconducting Metal-Chalcogenide–Organic Framework with Square-Planar Tetra-Coordinated Sulfur

Huajun Yang, Min Luo, Zhou Wu, Wei Wang, Chaozhuang Xue and Tao Wu

Chem. Commun., 2018, 54, 11272-11275

 

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the United States. He is passionate about scientific communication to introduce cutting-edge research to both the general public and scientists with diverse research expertise. He is a blog writer for Chem. Commun. and Chem. Sci. More information about him can be found at http://liutianyuresearch.weebly.com/.

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How do Anions Fight Indoor Organic Contaminants?

Indoor air quality is critical to public health. Chronic exposure to indoor organic contaminants (IOCs), including aldehydes and benzene homologues, substantially increases the risk of having respiratory diseases. In recent years, negative air ions (NAIs) have emerged as promising materials to decompose IOCs. NAIs are negatively charged ions generated via ionizing air. However, the limited understanding of the decomposition reaction mechanisms hinders the safety evaluation and wide adoption of NAI-cleaning.

A group of Chinese researchers led by Jin-Ming Lin of Tsinghua University recently demonstrated in ChemComm a powerful tool to unveil the reaction mechanisms. They built a system integrated with an NAI generator, an IOC sprayer and a mass spectrometer (Figure 1). NAIs containing mostly CO3 were produced by the ionization of air. These anions then mixed and reacted with the sprayer-delivered IOCs in front of the mass spectrometer inlet. All species generated during the reactions were directly brought into the mass spectrometer by inert N2 for characterization.

Figure 1. The experimental set-up of the integrated system.

This device revealed real-time reaction kinetics by identifying the reaction intermediates. The mass spectrum of a common IOC, formaldehyde, when reacted with CO3 is presented in Figure 2a. Two pronounced peaks with mass to charge ratios (m/z) of 45.10 and 60.10 were assigned to HCOO and CO3, respectively. Additionally, the 45.10 peak was only detected when formaldehyde was present (Figure 2b). On the basis of these observations, the authors concluded that the major pathway of formaldehyde degradation by CO3was the reaction between CO3 and the α-H atom of the aldehyde group. With identical instrumentation, the authors also proposed how the reactions between CO3 and benzene homologues or esters may proceed.

Figure 2. (a) The mass spectrum of reaction intermediates between CO3 and 10 ppm formaldehyde. (b) The change of peak intensities of m/z = 60.10 and 45.10 peaks with the operation time. Formaldehyde was present during 7.0-14.0 min.

The results obtained by this study could greatly deepen the understanding of NAI-based chemistry. It could also be useful to investigate kinetics of a broad range of other chemical reactions involving charged reactants.

 

To find out more please read:

Real-Time Characterization of Negative Air Ion-Induced Decomposition of Indoor Organic Contaminants by Mass Spectrometry

Ling Lin, Yu Li, Mashooq Khan, Jiashu Sun and Jin-Ming Li

Chem. Commun., 2018, DOI: 10.1039/c8cc05795h

 

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the United States. He is passionate about scientific communication to introduce cutting-edge research to both the general public and scientists with diverse research expertise. He is a blog writer for Chem. Commun. and Chem. Sci. More information about him can be found at http://liutianyuresearch.weebly.com/.

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MOFS, ZMOFS and Automobiles

Mohamed Eddaoudi and co-workers at KAUST have synthesised a porous metal organic framework (MOF) constructed from carboxylic acid-functionalised imidazole linkers coordinated to yttrium and potassium cations. The researchers classified this material as a zeolite-like MOF (ZMOF) due to its topological resemblance to the naturally occurring zeolite mineral analcime.

The material’s architecture, with cylindrical channels and a pore aperture measuring 3.8 x 6.2 Å, promised utility as a molecular sieve, and the authors showed the ZMOF could be used to sort small chain alkanes based on their level of branching. Linear and mono-branched pentanes and butanes were adsorbed by the material for different lengths of time (linear isomers were retained longer than their branched counterparts) allowing kinetic separation, while the di-branched alkane 2,2,4-trimethylpentane was excluded entirely. The authors anticipate that this material could have practical applications in crude oil refining, to upgrade petroleum into more energy-efficient fuels with reduced emissions.

ZMOF zeolite-like metal organic framework crystal structure with analcime (ana) topology showing channels and pore aperture.

ZMOF crystal structure with analcime (ana) topology showing channels and pore aperture.

The petroleum used to power internal combustion engines consists of a mixture of low molecular weight, linear and branched alkanes. The research octane number (RON) is a standard measure of petroleum performance, and indicates how much pressure a fuel can withstand before self-igniting (knocking) in the engine. High compression engines, which are more energy efficient and release less emissions than regular engines, require high RON fuels.

The RON increases with the proportion of branched alkanes, so can be improved by supplementing fuels with branched isomers obtained by catalytic isomerisation. This process generates a mixture of linear and branched alkanes, so the desired products must be isolated via fractional distillation, which is energy intensive. This creates a dilemma: high RON fuels are more energy efficient, but their energy-intensive production reduces the net benefit.

The authors envisaged an energy-efficient strategy for increasing the RON of petroleum fuels: A low RON fuel is pumped into the engine, where it encounters a separation chamber consisting of ZMOF-based membranes. The membrane excludes and redirects di-branched alkanes, which have a very high RON, to the internal combustion engine. The low RON fraction, consisting of mono-branched and linear alkanes, passes through the ZMOF pores to undergo further reforming processes downstream. In other words: low RON fuels go in, but high RON fuels are combusted.

Scheme showing how ZMOF materials could be used to upgrade gasoline by separating alkanes based on their level of branching. zeolite-like metal organic framework petroleum reforming

Scheme showing the RON of common small-chain alkanes and the use of ZMOF membranes in upgrading gasoline by separating alkanes based on their level of branching

In this work the authors show the potential of ZMOFs to maximise the energetic potential and reduce emissions of petroleum based fuels, while also offering a glimpse of the more general strategy of energy-efficient separations of chemically-similar molecules using tailored materials.

To find out more please read:

Upgrading gasoline to high octane number using zeolite-like metal organic framework molecular sieve with ana-topology

M. Infas H. Mohideen, Youssef Belmabkhout, Prashant M. Bhatt, Aleksander Shkurenko, Zhijie Chen, Karim Adil, Mohamed Eddaoudi.
Chem. Commun., 2018, 54, 9414-9417
DOI: 10.1039/c8cc04824j

About the author

Zoë Hearne is a PhD candidate in chemistry at McGill University in Montréal, Canada, under the supervision of Professor Chao-Jun Li. She hails from Canberra, Australia, where she completed her undergraduate degree. Her current research focuses on transition metal catalysis to effect novel transformations, and out of the lab she is an enthusiastic chemistry tutor and science communicator.

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Marbles, Microreactions and Magic Tricks

The reaction vessel is a fixed variable behind every innovative chemical synthesis, material or catalyst. It may be as simple as a round bottom flask or as complex as a single cell, as large as an industrial batch reactor or as small as a test tube.

Yujun Feng and co-workers, at Sichuan University in China, study a different kind of reaction vessel: water droplets. The droplets are ‘liquid marbles’, composed of microlitre volumes of water with fine hydrophobic particles covering their surface. Liquid marbles can be used as reaction vessels to manipulate small liquid volumes, avoiding the use of specialised microfluidics equipment. In this communication the authors show that carbon dioxide can trigger coalescence of droplets containing multiple reagents, in order to perform microscale chemistry. This research could be useful for developing high-throughput assays for procedures that would benefit from remotely controlled induction such as very fast or hazardous reactions.

The authors synthesised CO2-responsive particles composed of a mixture of polystyrene and PDEA: a methacrylate polymer bearing tertiary amine ancillary groups. The amine is vital to the properties of the polymer: when deprotonated the powder is hydrophobic, but exposure to carbon dioxide renders the polymer hydrophilic by transforming the amine into an ammonium bicarbonate salt. Liquid marbles were synthesised with a patch of CO2-responsive polymer powder. The rest of the marble was coated in lycopodium, a moss spore with hydrophobic properties that is not CO2-responsive (trivia: the high fat content of lycopdoium makes it a great flash powder, used by magicians since the middle ages).

A) Liquid marbles with white hydrophobic/hydrophilic CO2-responsive patches and pink (dyed) lycopodium powder. B) Coalescence of two liquid marbles upon CO2 carbon dioxide exposure within one minute. C) Coalescence schematic

A) Liquid marbles with white CO2-responsive patches and pink (dyed) lycopodium powder. B) & C) Photos and schematic of coalescence between two liquid marbles upon CO2 exposure

To realise CO2-induced chemistry, two liquid marbles containing different chemical reagents are placed side by side with the CO2-responsive powder positioned at the interface of the two marbles. Upon exposure to CO2 the responsive powder becomes hydrophilic and disperses into the aqueous solution within the two marbles, causing them to coalesce and the reagents to react within a single vessel. The authors performed several reactions using this method, all with distinct colour changes for rapid analysis: redox (persulfate and iodide, permanganate and persulfate), complexation (starch and iodine), substitution (bromine water and phenol) and chemiluminescence (luminol, peroxide and ferricyanide).

The authors show in this paper that innovations in chemistry needn’t be limited to reactions themselves; the vessel we choose can broaden what is possible on a practical level. On a completely impractical note, remotely controlled microreactions in liquid marbles sounds like a magic trick, resonant with the lycopodium flash powder covering their surface.

To find out more please read:

CO2-triggered microreactions in liquid marbles 

Xinjie Luo, Hongyao Yin, Xian’e Li, Xin Su, Yujun Feng.
Chem. Commun., 2018, Advance Article
DOI: 10.1039/c8cc01786g

About the author

Zoë Hearne is a PhD candidate in chemistry at McGill University in Montréal, Canada, under the supervision of Professor Chao-Jun Li. She hails from Canberra, Australia, where she completed her undergraduate degree. Her current research focuses on transition metal catalysis to effect novel transformations, and out of the lab she is an enthusiastic chemistry tutor and science communicator.

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