Archive for the ‘Hot Articles’ Category

Prolonging the Lifetimes of Dye-Sensitized Solar Cells by Positioning Dyes

Dye-sensitized solar cells (DSSCs) are electrochemical devices that can convert solar energy into electricity. The critical component of a DSSC is its dye molecules which are covalently adsorbed on the electrodes of the DSSC. These molecules are responsible for light absorption and energy conversion in the device. DSSCs are more economical than commercial Si-based solar cells, but their lifetimes are limited (~6 years vs. 20-30 years of Si-based counterparts).

A research team from Xiamen University, China, recently demonstrated in Chemical Science (DOI: 10.1039/D0SC00588F) that the anchoring stability of the dyes determined the longevity of DSSCs. They specifically studied N719, a Ru-containing dye, adsorbed on three different crystal facets of rutile TiO2 (electrode). N719 adsorbed on the TiO2(111) facets was the most stable among all the facets studied.

The researchers adopted surface-enhanced Raman spectroscopy (Fig.1) in their research, the setup of which involved two laser beams. One 405-nm laser excited the dye molecules to initiate energy conversion, and another 638-nm laser collected the Raman scattering signals at the dye/TiO2 interface. The obtained Raman spectra showed the peaks associated with the vibrations of N719.

Figure 1. The experimental setup. The 405-nm laser excites N719 dye molecules adsorbed on rutile TiO2. The 638-nm laser probed the Raman scattering signals of N719. The Au nanoparticle (yellow sphere) enhances the Raman signal intensity.

The Raman spectra revealed that the adsorption stability of N719 depended on the crystal facet of TiO2. For TiO2(001), after illumination for 36 min, the Raman peaks of N719 gradually diminished (Fig. 2a), indicating that the dye molecules were either detached from TiO2 or decomposed. A similar trend was observed for N719 on TiO2(110) (Fig. 2b). Mass spectroscopy detected that the electrolytes after 36-min illumination contained N719 molecules missing an S atom. This result indicated that the C=S bond of N719 was broken, leading to the loss of the dye. In contrast, N719 on TiO2(111) exhibited stable Raman signals during the identical illumination duration (Fig. 2c).

The different stability was ascribed to variation in the dissociation energy of the C=S bond. Density functional theory (DFT) simulation proved that the cleavage of the C=S bond on TiO2(111) had an energy barrier of 3.5 eV, about 1.0 eV and 1.5 eV higher than those on TiO2(110) and TiO2(001), respectively. The higher energy barrier suppresses bond dissociation and stabilizes the adsorption of N719.

Figure 2. Raman spectra of N719 adsorbed on (a) TiO2(001), (b) TiO2(110), and (c) TiO2(111). Spectra were collected with an interval of 4 min. Peaks highlighted in yellow and blue are from TiO2 and N719, respectively. The schemes on the right show the simulated structures of dye-adsorbed (top) and desorbed (bottom) TiO2 facets. Ph–N=C=S represents N719 in simulation. The yellow spheres are S.

This work highlights the importance of dye positioning in promoting long-lasting performance of DSSCs.

For expanded understanding, please read:

In Situ Raman Study of the PhotoInduced Behavior of Dye Molecules on TiO2(hkl) Single Crystal Surfaces

Sheng-Pei Zhang, Jia-Sheng Lin, Rong-Kun Lin, Petar M. Radjenovic, Wei-Min Yang, Juan Xu, Jin-Chao Dong, Zhi-Lin Yang, Wei Hang, Zhong-Qun Tian, and Jian-Feng Li

Chem. Sci., 2020, DOI: 10.1039/D0SC00588F

 

Tianyu Liu acknowledges Zacary Croft at Virginia Tech, U.S., for his careful proofreading of this post.

 

About the blogger:

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

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Real World data for protein modeling

It should go without saying that NMR is an incredibly important characterization technique with profoundly broad applicability across the entirety of chemistry. Rarely do you find something that people who work on proteins and wacky main-group synthesis both consider crucial to their work. Given powerful enough magnets and high-quality samples, rich structural information can be obtained for all manner of molecules large and small. Large molecules do pose a problem with the sheer volume of information contained within a single spectrum. Because of this, there exists a need to develop computational programs that can translate spectra into detailed structural models. Currently, existing methods predict NMR spectra based on a combination of experimentally based databases with chemical shift heuristics. These simulations, while useful, lack high predictive rigor and often have difficulty simulating the messiness of real world data. This is particularly challenging because experimental spectra can often have significant chemical shift deviations from predicted values, with those peaks discarded as outliers.

Figure 1. The overall design of the novel UCBShift chemical shift prediction algorithm, combining both a transfer prediction module a machine learning module.

To face these challenges and generate more accurate results, researchers in the US developed a new algorithm that uses both machine learning and transfer prediction (Figure 1). Transfer prediction has been widely used and relies on the similarities of NRM peak sequences between known data, typically clean datasets, and the experimental sample in question. The advantage of the new approach is that it allows for data that would previously have been dismissed as anomalous to be utilized and to give more accurate predictions. The researchers used high-quality datasets that they modified for accuracy. In particular, they retained the water and ligand molecules that co-crystallized with the proteins that would likely be associated with the solvated forms of the proteins. As the interactions of these small molecules can alter the spectral shifts of NMR peaks, their inclusion increases the likelihood that peaks previously considered outliers will be incorporated and analyzed.

Figure 2. Difference between UCBShift-Y and SHIFTY+ (previous method) showing that overall the new algorithm is making better predictions.

Initial analysis with the new dataset produced some anomalous results, which were then mitigated by removing paramagnetic and other outlier proteins that would bias the results against the earlier algorithms. Once those were removed, the new algorithm still outperformed prior methods (Figure 2). While these advances are extremely useful for current researchers, they are approaching the limit of accuracy for systems that rely heavily on transfer predictions. In order to generate fully accurate models and structures intense work on combining deep learning with human expertise is necessary.

To find out more, please read:

Accurate prediction of chemical shifts for aqueous protein structure on “Real World” data

Jie Li, Kochise C. Bennett, Yuchen Liu, Michael V. Martin and Teresa Head-Gordon

Chem. Sci., 2020,11, 3180-3191

About the blogger:

Dr. Beth Mundy is a recent PhD in chemistry from the Cossairt lab at the University of Washington in Seattle, Washington. Her research focused 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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HOT articles: April

We are pleased to share a selection of our referee-recommended HOT articles for April. We hope you enjoy reading these articles and congratulations to all the authors whose articles are featured! As always, Chemical Science is free to read & download. You can find our full 2020 HOT article collection here.

 

What is the role of acid–acid interactions in asymmetric phosphoric acid organocatalysis? A detailed mechanistic study using interlocked and non-interlocked catalysts
Dennis Jansen, Johannes Gramüller, Felix Niemeyer, Torsten Schaller, Matthias C. Letzel, Stefan Grimme, Hui Zhu, Ruth M. Gschwind and Jochen Niemeyer
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC01026J

10.1039/D0SC01026J

 

Structural properties of ultra-small thorium and uranium dioxide nanoparticles embedded in a covalent organic framework
Liane M. Moreau, Alexandre Herve, Mark D. Straub, Dominic R. Russo, Rebecca J. Abergel, Selim Alayoglu, John Arnold, Augustin Braun, Gauthier J. P. Deblonde, Yangdongling Liu, Trevor D. Lohrey, Daniel T. Olive, Yusen Qiao, Julian A. Rees, David K. Shuh, Simon J. Teat, Corwin H. Booth and Stefan G. Minasian
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC06117G

 

Iron porphyrin catalysed light driven C–H bond amination and alkene aziridination with organic azides
Yi-Dan Du, Cong-Ying Zhou, Wai-Pong To, Hai-Xu Wang and Chi-Ming Che
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC00784F

 

The assemble, grow and lift-off (AGLO) strategy to construct complex gold nanostructures with pre-designed morphologies
Xin Luo, Christophe Lachance-Brais, Amy Bantle and Hanadi F. Sleiman
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC00553C

 

Geometric Landscapes for Material Discovery within Energy-Structure-Function Maps
Seyed Mohamad Moosavi, Henglu Xu, Linjiang Chen, Andrew Cooper and Berend Smit
Chem. Sci., 2020, Accepted Manuscript
DOI: 10.1039/D0SC00049C

 

Expedient synthesis of conjugated triynes via alkyne metathesis
Idriss Curbet, Sophie Colombel-Rouen, Romane Manguin, Anthony Clermont, Alexandre Quelhas, Daniel S. Müller, Thierry Roisnel, Olivier Baslé, Yann Trolez and Marc Mauduit
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC01124J

 

Transferring Axial Molecular Chirality Through a Sequence of On-Surface Reactions
Néstor Merino-Díez, Mohammed S. G. Mohammed, Jesus Castro, Luciano Colazzo, Alejandro Berdonces-Layunta, James Lawrence, Jose Ignacio Pascual, Dimas G. de Oteyza and Diego Peña
Chem. Sci., 2020, Accepted Manuscript
DOI: 10.1039/D0SC01653E

 

Chemical Science, Royal Society of Chemistry

Submit to Chemical Science today! Check out our author guidelines for information on our article types or find out more about the advantages of publishing in a Royal Society of Chemistry journal.

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Seeing is Believing: Is Your Polymerization Working?

If you are a polymer chemist, you may have dreamt of having a pair of eyes that can directly tell whether your polymerization reaction is working or not. Good news! Randall H. Goldsmith of the University of Wisconsin-Madison, U.S. and coworkers have developed an optical technique to monitor the course of a polymerization reaction in real-time. This breakthrough has been published in Chemical Science (DOI: 10.1039/C9SC05559B).

This technique relies on two parameters, fluorescence polarization anisotropy and aggregation-induced emission, to examine molecular weights. The authors specifically studied a well-controlled polymerization of norbornene (NB) into polynorbornene. Besides monomer, they added small amounts of two fluorescent probes, perylene diimide-functionalized norbornene (PDI-NB) and tetraphenylethylene-linked norbornene (TPE-NB), to the polymerization system. These NB derivatives were co-polymerized with NB (Fig.1).

Figure 1. Polymerization of norbornene (NB) catalyzed by a ruthenium-based Grubbs Generation II catalyst (Grubbs Gen II). PDI-NB and TPE-NB are two probes co-polymerized with NB to monitor the growth of polynorbornene.

The technique temporally resolved the evolution of polynorbornene molecular weight. The polymerization incorporated the probe molecules into the backbones of polynorbornene. As polymer chains grew, the rotational freedom of PDI-NB became increasingly limited, giving rise to an enhanced anisotropy signal during the first 200 min of polymerization (Fig. 2a, top panel and Fig. 2b, red curve). Further polymerization brought the incorporated TPE-NB together, triggering the aggregation-induced fluorescence emission of TPE-NB (Fig. 2a, bottom panel and Fig. 2b, blue curve). Importantly, the rise of the emission intensity from TPE-NB immediately followed the saturation of anisotropy signal from PDI-NB, making the two molecules complementary for monitoring the polymer growth in different time scales. Critically, the anisotropy signal intensity of PDI-NB correlated positively with the weight-average molecular weight of polynorbornene (Fig. 2c), demonstrating the capability of this technique to track the progression of polymer growth.

Figure 2. (a) (top) Color-scale images of anisotropy values of PDI-NB and (bottom) emission intensities of TPE-NB over time. Dots are top-view toluene microdroplets where polymerization happens. Scale bar: 250 µm. (b) Time-evolution of average anisotropy values of PDI-NB (red) and aggregation-induced-emission (AIE) intensity of TPE-NB (blue) throughout a polymerization. (c) The correlation between measured anisotropy values and the weight-average molecular weights of polynorbornene. The red dashed line provides a visualization of the trend.

The reported technique is applicable to other ring-opening metathesis polymerizations (ROMPs) involving monomers such as norbornadiene.

 

For expanded understanding, please read:

Optical Monitoring of Polymerizations in Droplets with High Temporal Dynamic Range

Andrew C. Cavell, Veronica K. Krasecki, Guoping Li, Abhishek Sharma, Hao Sun, Matthew P. Thompson, Christopher J. Forman, Si Yue Guo, Riley J. Hickman, Katherine A. Parrish, Alán Aspuru-Guzik, Leroy Cronin, Nathan C. Gianneschi, and Randall H. Goldsmith

Chem. Sci., 2020, 11, 2647-2656.

 

The blogger acknowledges Zac Croft at Virginia Tech, U.S., for his careful proofreading of this post.

 

About the blogger:

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

 

 

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HOT articles: February

We are pleased to share a selection of our referee-recommended HOT articles for January. We hope you enjoy reading these articles and congratulations to all the authors whose articles are featured! As always, Chemical Science is free to read & download. You can find our full 2020 HOT article collection here.

 

Metal complexes as a promising source for new antibiotics
Angelo Frei, Johannes Zuegg, Alysha G. Elliott, Murray Baker, Stefan Braese, Christopher Brown, Feng Chen, Christopher G. Dowson, Gilles Dujardin, Nicole Jung, A. Paden King, Ahmed M. Mansour, Massimiliano Massi, John Moat, Heba A. Mohamed, Anna K. Renfrew, Peter J. Rutledge, Peter J. Sadler, Matthew H. Todd, Charlotte E. Willans, Justin J. Wilson, Matthew A. Cooper and Mark A. T. Blaskovich
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC06460E
10.1039/C9SC06460E

 

 

A clustering-triggered emission strategy for tunable multicolor persistent phosphorescence
Qing Zhou, Tianjia Yang, Zihao Zhong, Fahmeeda Kausar, Ziyi Wang, Yongming Zhang and Wang Zhang Yuan
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC06518K

10.1039/C9SC06518K

 

 

Time-resolved luminescence detection of peroxynitrite using a reactivity-based lanthanide probe
Colum Breen, Robert Pal, Mark R. J. Elsegood, Simon J. Teat, Felipe Iza, Kristian Wende, Benjamin R. Buckley and Stephen J. Butler
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC06053G
10.1039/C9SC06053G

 

Electron-enriched thione enables strong Pb–S interaction for stabilizing high quality CsPbI3 perovskite films with low-temperature processing
Xiaojia Xu, Hao Zhang, Erpeng Li, Pengbin Ru, Han Chen, Zhenhua Chen, Yongzhen Wu, He Tiana and Wei-Hong Zhu
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC06574A
10.1039/C9SC06574A

 

Accurate chiral pattern recognition for amines from just a single chemosensor
Yui Sasaki, Soya Kojima, Vahid Hamedpour, Riku Kubota, Shin-ya Takizawa, Isao Yoshikawa, Hirohiko Houjou, Yuji Kubo and Tsuyoshi Minami
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC00194E

10.1039/D0SC00194E

 

Tackling the chemical diversity of microbial nonulosonic acids – a universal large-scale survey approach
Hugo B. C. Kleikamp, Yue Mei Lin, Duncan G. G. McMillan, Jeanine S. Geelhoed, Suzanne N. H. Naus-Wiezer, Peter van Baarlen, Chinmoy Saha, Rogier Louwen, Dimitry Y. Sorokin, Mark C. M. van Loosdrecht and Martin Pabst
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC06406K

10.1039/C9SC06406K

 

 

Chemical Science, Royal Society of Chemistry

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HOT articles: January

We are pleased to share a selection of our referee-recommended HOT articles for January. We hope you enjoy reading these articles and congratulations to all the authors whose articles are featured! As always, Chemical Science is free to read & download. You can find our full 2020 HOT article collection here.

 

Breaking scaling relations for efficient CO2 electrochemical reduction through dual-atom catalysts
Yixin Ouyang, Li Shi, Xiaowan Bai, Qiang Li and Jinlan Wang
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC05236D

Breaking scaling relations for efficient CO2 electrochemical reduction through dual-atom catalysts

 

Unexpected monolayer-to-bilayer transition of arylazopyrazole surfactants facilitates superior photo-control of fluid interfaces and colloids
Christian Honnigfort, Richard A. Campbell, Jörn Droste, Philipp Gutfreund, Michael Ryan Hansen, Bart Jan Ravoo and Björn Braunschweig
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC05490A

Unexpected monolayer-to-bilayer transition of arylazopyrazole surfactants facilitates superior photo-control of fluid interfaces and colloids

 

Type 3 porous liquids based on non-ionic liquid phases – a broad and tailorable platform of selective, fluid gas sorbents
John Cahir, Min Ying Tsang, Beibei Lai, David Hughes, M. Ashraf Alam, Johan Jacquemin, David Rooney and Stuart L. James
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC05770F

Type 3 porous liquids based on non-ionic liquid phases – a broad and tailorable platform of selective, fluid gas sorbents

 

A programmable chemical switch based on triggerable Michael acceptors
Jiaming Zhuang, Bo Zhao, Xiangxi Meng, Jessica D. Schiffman, Sarah L. Perry, Richard W. Vachet and S. Thayumanavan
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC05841A

 

Simulating protein–ligand binding with neural network potentials
Shae-Lynn J. Lahey and Christopher N. Rowley
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC06017K

Simulating protein–ligand binding with neural network potentials

 

Efficient white polymer light-emitting diodes (WPLEDs) based on covalent-grafting of [Zn2(MP)3(OAc)] into PVK
Guorui Fu, Yani He, Wentao Li, Tiezheng Miao, Xingqiang Lü, Hongshan He, Li Liu c and Wai-Yeung Wong
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC05288G

Efficient white polymer light-emitting diodes (WPLEDs) based on covalent-grafting of [Zn2(MP)3(OAc)] into PVK

 

Chemical Science, Royal Society of Chemistry

Submit to Chemical Science today! Check out our author guidelines for information on our article types or find out more about the advantages of publishing in a Royal Society of Chemistry journal.

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For catalysis, do you need one gold or two?

Doesn’t everyone love gold? Not only is it shiny and pretty in macroscopic form, but it’s one of the best-behaved nanoscale systems and the focus of extensive catalysis study. While much is known about the mechanisms of many gold-catalyzed reactions, a question of whether a number of organogold complexes are actual intermediates or off-cycle sinks remains. Catalysis of the nucleophilic addition of water to alkynes via gold complexes is a reaction with multiple hypothesized active intermediates and reaction pathways. Initially thought to occur via monoaurated species, subsequent work proposed activation by multiple gold catalysts. The problem, as seen in figure 1, is that the two pathways are connected and the presence of any specific intermediates can’t rule either pathway out.

Figure 1. Reaction scheme with potential intermediates for nucleophile addition to an alkyne via a gold-catalyzed pathway.

To solve this problem, researchers in the Czech Republic and the Netherlands developed a method to probe solution-phase intermediates with electrospray ionization mass spectrometry (ESI-MS) called Delayed Reactant Labeling. To do this, one of the reactants must be a mixture of isotopically labeled and unlabeled molecules, added separately with a time delay. This helps eliminate ionization artifacts and moves the reaction away from steady state conditions to allow for kinetic modeling. Using this technique, combined with other more standard characterization methods like NMR and infrared (IR) spectroscopy, the researchers studied gold-catalyzed water addition to alkynes. The catalyst is known to form digold hydroxides in the presence of water, which lends credence to the idea that a digold species is involved in the catalysis. Based on kinetic restrictions, they studied the addition of water to 1-phenylpropyne, which produces a mixture of regioisomers of intermediates that was a bit challenging to deconvolute. The initial ESI-MS spectra show the presence of both mono- and diaurated species and the different fragments were isolated, analyzed by IR photodissociation, and the spectra compared to theoretical models to corroborate their identity.

These results set the stage for the Delayed Reactant Labeling studies using deuterated 1-phenylpropyne. After the reaction reached equilibrium, in this case about 40 minutes, the labeled reactant was added to then allow for kinetic fitting of the intermediates. They determined that under standard conditions the monoaurated species has a half life of approximately 9 minutes and the diaurated species has a half life of 7 minutes. These decay constants could be altered by adding organic acids to degrade the complexes faster, while attempts to trap the species as salts were unsuccessful. Upon reaction with D2O a kinetic isotope effect doubling the lifetimes was observed and suggests that the mechanism is likely the same for all intermediates and that it involves a hydrogen/proton transfer. The two types of species also have slightly different rates of formation, with the diaurated species likely having a higher turn-over frequency. However, there isn’t a dramatic difference between the kinetics of these two types of intermediates.

Figure 2. Example of a) spectra obtained from the delayed reactant labeling method and b) fits of peak intensities over time used to extract kinetic information.

In order to determine which of the intermediates is catalytically relevant, the researchers changed the substrate to 3-hexyne. The symmetric alkyne has no regioisomeric intermediates to convolute the data, but the reaction kinetics are much faster and therefore not suited to the prior mechanistic studies. By adding an excess of acid, the rate determining step was moved from protodeauration.  Under these conditions, the rate has a linear dependence on the gold complex and likely proceeds primarily via monoaurated intermediates. This approach combining multiple analytical techniques elucidated the role of various gold-containing intermediates and demonstrated the utility of ESI-MS as a tool for determining reaction kinetics.

To find out more, please read:

Monoaurated vs. diaurated intermediates: causality or independence?

Mariarosa Anania, Lucie Jašková, Jan Zelenka, Elena Shcherbachenko, Juraj Jašk and Jana Roithová

Chem. Sci., 2020, Advance Article

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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HOT articles: December

We are pleased to share a selection of our referee-recommended HOT articles for December. We hope you enjoy reading these articles and congratulations to all the authors whose articles are featured! As always, Chemical Science is free to read & download. You can find our full 2019 HOT article collection here.

 

Interplay between intrinsically disordered proteins inside membraneless protein liquid droplets
Yongsang Jo and Yongwon Jung
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC03191J

https://doi.org/10.1039/C9SC03191J

 

 

 

 

 

 

 

 

Single-molecule nanopore sensing of actin dynamics and drug binding
Xiaoyi Wang, Mark D. Wilkinson, Xiaoyan Lin, Ren Ren, Keith R. Willison, Aleksandar P. Ivanov, Jake Baum and Joshua B. Edel
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC05710B

10.1039/C9SC05710B

 

 

 

 

 

 

 

Uncommon structural and bonding properties in Ag16B4O10
Anton Kovalevskiy, Congling Yin, Jürgen Nuss, Ulrich Wedig and Martin Jansen
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC05185F
10.1039/C9SC05185F

 

 

 

 

 

 

 

 

 

 

Rational synthesis of interpenetrated 3D covalent organic frameworks for asymmetric photocatalysis
Xing Kang, Xiaowei Wu, Xing Han, Chen Yuan, Yan Liu and Yong Cui
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC04882K

10.1039/C9SC04882K
 

 

 

 

 

 

 

 

 

Serine is the molecular source of the NH(CH2)2 bridgehead moiety of the in vitro assembled [FeFe] hydrogenase H-cluster
Guodong Rao, Lizhi Tao and R. David Britt
Chem. Sci., 2020, Advance Article
DOI: 10.1039/C9SC05900H

10.1039/C9SC05900H
 

 

 

 

 

 

 

 

Chemical Science, Royal Society of Chemistry

Submit to Chemical Science today! Check out our author guidelines for information on our article types or find out more about the advantages of publishing in a Royal Society of Chemistry journal.

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How Does Nano-Confinement Boost Oxygen-Reduction Electrocatalytic Activity?

Why do biological enzymes exhibit superior catalytic activity? Well, this is mainly because they can firmly anchor reactants into catalytically active pockets using their three-dimensional structures. Inspired by this nano-confinement effect, scientists have developed “nanozymes,” a family of artificial enzymes.

A group of scientists from the University of New South Wales (Australia), University of Utah (USA), and Ruhr-Universität Bochum (Germany) investigated the interplay between the degree of nano-confinement and oxygen reduction reaction (ORR) activity. They discovered that ORR activity only scaled proportionally to the degree of confinement at low overpotentials (ORR theoretical potential: 1.23 V vs. RHE). The results have been published in Chemical Science (doi: 10.1039/C9SC05611D).

Synthesized by etching Ni from Pt-Ni alloy nanoparticles, metallic Pt nanoparticles possessing channels of different opening sizes served as the nanozymes with different confinement degrees. When the Ni content increased, the channel of the etched nanoparticles widened. Specifically, Pt nanozymes prepared from Pt-Ni nanoparticles with Pt/Ni = 1/1.5 (NZsmall) contained 69% channel openings smaller than 2 nm (Fig. 1a); Whereas those from the precursors with Pt/Ni = 1/2.5 (NZmedium) and 1/3 (NZlarge) had 52% (Fig. 1b) and 34% (Fig. 1c) <2-nm-wide channels, respectively. Therefore, the nano-confinement degrees of the three nanozymes followed the sequence of NZsmall>NZmedium>NZlarge.

Figure 1. High-resolution transmission electron microscopy images (left) and channel diameter distribution profiles (right) of (a) NZsmall, (b) NZmedium, and (c) NZlarge.

The ORR activity of the three nanozymes strongly depended on the magnitude of the overpotential. With the outer surfaces passivated by surfactants, the ORR activities of the nanozymes were only associated with O2 reduction within their channels. At low overpotentials (Fig. 2, inset), NZsmall had the highest ORR activity among all the catalysts evaluated by the authors, as indicated by its lowest kinetic current. At high overpotentials or low applied biases; however, the ORR activity of NZmedium and NZlarge rapidly increased (Fig. 2). NZmedium and NZlarge became more active than NZsmall at potentials lower than 0.82 V (vs. RHE) and 0.80 V (vs. RHE), respectively.

Figure 2. The potential (E)-dependence of kinetic current density (jk). Inset: low-overpotential (high potentials) region. Legends: solid black – NZsmall; solid blue – NZmedium; solid red – NZlarge; open black – mesoporous Pt nanoparticles without nano-channels. The consistently small absolute jk of the mesoporous nanoparticles reflected its relatively low ORR activity.

The finite element simulation revealed the underlying mechanism of the experimental results. At low overpotentials, the ORR activity was governed by the kinetics of O2-reduction. Due to high charge density, the local proton concentration inside the channels of NZsmall was the highest, leading to the fastest reaction and the highest ORR activity. At high overpotentials, the ORR activity became mass-transport limited. Nanozymes with wide channel openings, that is, NZmedium and NZlarge, allowed a large amount of O2 to diffuse into the channels, which enhanced O2 supply and augmented ORR activity.

This work unveiled the potential-dependence of the ORR catalytic activities of porous Pt nanoparticles under different degrees of nano-confinement. This insight could rationalize and further enable the design of nanozymes with tailorable ORR activities.

 

To find out more, please read:

The Importance of Nanoscale Confinement to Electrocatalytic Performance

Johanna Wordsworth, Tania M. Benedetti, Ali Alinezhad, Richard D. Tilley, Martin A. Edwards, Wolfgang Schuhmann, and J. Justin Gooding

Chem. Sci., 2019, DOI: 10.1039/C9SC05611D

 

Tianyu Liu acknowledges Zac Croft at Virginia Tech, U.S., for his careful proofreading of this post.

 

About the blogger:

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

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Looking Inside Nanocomposites with Tomography

As a nanocrystal chemist, it pains me to say that sometimes nanoparticles aren’t enough. One strategy for engineering materials with complex functionalities is to embed nanoparticles into a larger host matrix structure. This has been widely studied for polymer-nanoparticle assemblies, but challenges abound for inorganic host matrices. Difficulties stem from problems controlling the microstructure of the host, as nanoparticles tend to accumulate at the borders of individual crystals in polycrystalline materials. Even when higher quality inorganic materials are made in the presence of nanocrystals loadings are below 1 wt%. A possible route to address these issues is by combining inorganic matrices with polymer-functionalized nanoparticles. The polymers can also form into vesicle structures that contain the nanoparticles which are larger and more compatible with characterization techniques.

One of those techniques is cryo-ptychographic X-ray computed tomography (cryo-PXCT), a fascinating and literally cool characterization method to image the internal structure of crystals. This is a variation on imaging techniques used heavily in medicine archeology to non-destructively visualize the interior of humans or artifacts. Cryo-PXCT cools the sample to -180 oC and has spatial resolution on the order of 50-70 nm. The researchers synthesized polymer vesicles and worms of approximately 232 nm in diameter and over 1 micron in length, respectively. The nanocomposites were made via an ammonia diffusion method with a solution of calcium chloride containing the polymer nano-structure exposed to gaseous ammonia and carbon dioxide to form CaCO3 crystals with nano-structure occlusions. The morphology of the nanocomposite crystal altered based on the type of occlusion – the vesicle/calcite combination retained a traditional calcite rhombohedral structure, while the worm/calcite composite crystals featured several rounded sides, an elongated shape, and only three flat faces. These composites possessed 15 – 25 wt% occlusions, significantly higher than prior work with pure nanoparticle incorporation.

Figure 1. SEM images of vessicle/calcite (left) and worm/calcite (right) nanocomposite single crystals.

Once prepared, the researchers examined the crystals by cryo-PXCT to determine the locations of the occlusions within the composites. In the vesicle/calcite composite the vesicles are non-uniformly distributed, with several layers of vesicle density, starting with a vesicle poor core, followed by a vesicle rich region, surrounded by another vesicle poor layer, with a slight vesicle enrichment near the surface. On average the vesicles are 300 nm apart and they maintain their shape, with the larger vesicles preferentially occluding in regions of higher occlusion densities.

Figure 2. Rendering of slice through the vesicle/calcite nanocomposite colored to show both components.

The worm/calcite composite crystals show a very different distribution of occlusions, with an hourglass of low density in the center of the crystal, surrounded by a worm rich zone, and an exterior worm poor layer. These zoning effects are likely determined by the interactions between the polymers and the growing crystal surfaces or the calcium cations in the solution. Cryo-PXCT offers a fascinating way to probe the internal structure of novel multicomponent crystals in three dimensions with nanoscale resolution, providing valuable information to eventually help determine structure-function relationships.

Figure 3. Tomographs of worm/calcite nanocomposites showing the localization of worms in an hourglass shape in the center of the crystal.

To find out more, please read:

Ptychographic X-ray tomography reveals additive zoning in nanocomposite single crystals

Johannes Ihli, Mark A. Levenstein, Yi-Yeoun Kim, Klaus Wakonig, Yin Ning, Aikaterini Tatani, Alexander N. Kulak, David C. Green, Mirko Holler, Steven P. Armes and Fiona C. Meldrum

Chem. Sci., 2020, 11, 355-363.

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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