Name: probe type ii band alignment in one-dimensional van der waals heterostructures using first-principles calculations
Uploaded: 2019-10-12T13:00:00
Description: Watch this Scientific Journal Video about Probe Type II Band Alignment in One-Dimensional Van Der Waals Heterostructures Using First-Principles Calculations at JoVE.com

This work was supported from China Postdoctoral Science Foundation (Grant No. 2017M612348), Qingdao Postdoctoral Foundation (Grant No. 3002000-861805033070) and from the Young Talent Project at Ocean University of China (Grant No. 3002000-861701013151). The authors thank Miss Ya Chong Li for preparing the narration.

1. Optimize the atomic structure.
<ol>
	<li>Prepare four input files for structure relaxation calculation by VASP: INCAR, POSCAR, POTCAR, and KPOINTS. 
	NOTE: There are specified parameters in the INCAR file that define the calculation. The line &#34;EDIFFG = 0.02&#34; in the INCAR file indicates that all atoms are relaxed until the force on each atom is &#60;0.02 eV/&#197;. The POSCAR file contains the atomic geometry information. The initial lattice parameters in the POSCAR file can be chosen from theoretical<su...

<ol>
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The calculations for electronic properties in sections 2, 3, and 4 would be similar among various nanoscale materials. The initial atomic model in step 1 should be carefully designed to extract meaningful information. For example, the factor for selecting the model could be the size or chirality of the materials. Also, the initial atomic model in step 1.1 should be reasonably prepared for low-cost structure relaxation. Taking the nanocomposite in the protocol as an example, the NR should be encapsulated inside the NT in ...

The worldwide demand for clean and sustainable energy has spurred research for promising materials to reduce dependence on finite petroleum resources. Simulations are more efficient and economical than experiments in accelerating the search for new functional materials1. Material design from a theoretical perspective2,3,4 is now more and more popular due to rapid advances in computational resources and theory developments, making computational simulations more reliable5. The density functional theory (DFT) calculations implemented in many codes are becoming more robust and yield reproducible results6.
The Vienna Ab initio Simulation Package&#160;(VASP)7 presents one of the most promising DFT codes for predicting molecular and crystalline properties and more than 40,000 studies making use of this code have been published. Most work is performed at the Perdew-Burke-Ernzerhof (PBE) functional level8, which underestimates the band gap sizes, but captures the essential trends in band alignment and band offsets3. This protocol aims to outline the details of investigating the band edge profiles and bandgaps of nanoscale materials for clean and renewable energy using this computational tool. More examples using VASP are available at https://www.vasp.at.
This report presents the computational screening of one-dimensional (1D) vdW heterostructures with type II band alignments9 for a promising application in photocatalytic water splitting4. Specifically, nanoribbons (NRs) encapsulated inside nanotubes (NTs) are examined as an example10. To address noncovalent interactions, vdW corrections using the DFT-D3 method are included11. The DFT calculations in steps 1.2, 2.2, 3.2, 3.5.2, and section 4 by VASP are performed using a Portable Batch System (PBS) script by the high-performance research computers in the CenTOS system. An example of a PBS script is shown in the Supplementary Materials. The data postprocessing by the P4VASP software in step 3.3 and the figure plot by the xmgrace software in step 3.4 are carried on a local computer (laptop or desktop) in the Ubuntu system.

<table>
	<tbody>
		<tr>
			<td>Nanotube Modeler</td>
			<td>Developed by Dr. Steffen Weber</td>
			<td>NanotubeModeler1.8</td>
			<td>http://www.jcrystal.com/products/wincnt/NanotubeModeler.exe</td>
		</tr>
		<tr>
			<td>P4VASP</td>
			<td>Orest Dubay</td>
			<td>p4vasp 0.3.30</td>
			<td>Open source, available at www.p4vasp.at</td>
		</tr>
		<tr>
			<td>v2xsf</td>
			<td>Developed by Dr. Jens Kunstmann</td>
			<td>v2xsf</td>
			<td>http://theory.chm.tu-dresden.de/~jk/software.html</td>
		</tr>
		<tr>
			<td>VASP software</td>
			<td>Computational Materials Physics, Dept. of Physics, University of Vienna</td>
			<td>vasp.5.4.1</td>
			<td>https://www.vasp.at</td>
		</tr>
		<tr>
			<td>VMD software</td>
			<td>Theoretical and Computational Biophysics Group, University of Illinois at Urbana-Champaign</td>
			<td>vmd1.9.3</td>
			<td>https://www.ks.uiuc.edu/Research/vmd</td>
		</tr>
		<tr>
			<td>xcrysden</td>
			<td>Dept. of Physical and Organic Chemistry, Jozef Stefan Institute</td>
			<td>XCrySDen1.5.60</td>
			<td>http://www.xcrysden.org/</td>
		</tr>
		<tr>
			<td>Xmakemol</td>
			<td>Developed by M. P. Hodges</td>
			<td>xmakemol5.16</td>
			<td>https://www.nongnu.org/xmakemol/XmakemolDownloads.html</td>
		</tr>
		<tr>
			<td>Xmgrace software</td>
			<td>Grace Development Team under the coordination of Evgeny Stambulchik</td>
			<td>xmgrace5.1.25</td>
			<td>http://plasma-gate.weizmann.ac.il/Grace/</td>
		</tr>
	</tbody>
</table>

probe type ii band alignment in one-dimensional van der waals heterostructures using first-principles calculations

Computational tools based on density-functional theory (DFT) enable the exploration of the qualitatively new, experimentally attainable nanoscale compounds for a targeted application. Theoretical simulations provide a profound understanding of the intrinsic electronic properties of functional materials. The goal of this protocol is to search for photocatalyst candidates by computational dissection. Photocatalytic applications require suitable band gaps, appropriate band edge positions relative to the redox potentials. Hybrid functionals can provide accurate values of these properties but are computationally expensive, whereas the results at the Perdew-Burke-Ernzerhof (PBE) functional level could be effective for suggesting strategies for band structure engineering via electric field and tensile strain aiming to enhance the photocatalytic performance. To illustrate this, in the present manuscript, the DFT based simulation tool VASP is used to investigate the band alignment of nanocomposites in combinations of nanotubes and nanoribbons in the ground state. To address the lifetime of photogenerated holes and electrons in the excited state, nonadiabatic dynamics calculations are needed.

Zigzag BN-NRs encapsulated inside armchair BN-NTs (11,11) were chosen as representative examples for a 1D vdW heterostructure. The lattice parameters were taken from Sahin et al.20. For convenience, zigzag NRs are abbreviated Zn, where n represents the III&#8211;V dimers along the width14. The encapsulation energy EL from step 2.3 was used as a rough estimate for the energetic stability of the nanocomposite. The EL values of Z2, Z...

Watch this Scientific Journal Video about Probe Type II Band Alignment in One-Dimensional Van Der Waals Heterostructures Using First-Principles Calculations at JoVE.com

Probe Type II Band Alignment in One-Dimensional Van Der Waals Heterostructures Using First-Principles Calculations

Calculations performed by the Vienna Ab initio Simulation Package can be used to identify the intrinsic electronic properties of nanoscale materials and predict the potential water-splitting photocatalysts.

Computational tools based on density-functional theory (DFT) enable the exploration of the qualitatively new, experimentally attainable nanoscale ...

This protocol reports a computational screening of photo catalyst with type two bond alignment by first principles Softwire vast expressive Calais, boron nitrite nanoribbons encapsulated inside nanotubes. And taking other examples. Step one, optimize the atomic structure.Prepare for input files for structure relaxation calculation by vast, INCAR, POSCAR, POTCAR, and KPOINTS. There are specified parameters in the file INCAR that define the calculation. The line in the file INCAR enclosed by blue box, in case that all atoms are relaxed until the force on each atom is less than 0.028 per atom.The file POSCAR contains the atomic geometry information. The initial lattice parameters in the file, POSCAR can be chosen from the radical or experimental references. As indicated by orange box.KPOINTS defines a KPOINT mesh and POSCAR is still the potential file generates the initial structure of boron nitrites nanoribbon for POSCAR. First download POSCAR for boron nitrites box unit from the website of The Materials Project. They used V2SXF to convert POSCAR to a file with SXF format.The SXF file can be right expression. Type V2SXF POSCAR onto no in band two system. And output POSCAR SXFGZ tab gunzi POSCAR, delta SXF-GZ.And output POSCAR SXF. We'll use xcrysden to build supercell of boron nitrite. Type xcrysden-sxf POSCAR.Xsf.Select the menu, modifying number of illness drawn and extend the style in X and Y direction. Select the menu, file. Save XSF structure to export the super cell structure.Use xmakemol to open the super cell by typing xmakemol-f supercell. Select the menu, and add it visible. Click toggle to delay the atoms inside the ranging and cast nanoribbon with desired width and chirality.Boron nitrites nanotube can be constructed by nanotube modeler, open nanotube modeler EXC in Window system. Select the menu, select type B-N. And specify the chirality.Select the menu, file, save XYZ table to export this structure. Use VMD Southwire to check the atomic structure before start making the calculation job. Type VMD onto internal VMD system.In the opened VMD main window. Select the menu, file, molecule, and find the POSCAR through the browse window. Load POSCAR by the type MAGE and the score POSCAR.Display the structure by different styles in the graphical representations drawing methods window. For example, choose CPK. Each atom is represented by a sphere and each bond is represented by a stake.Type qsub job. pbs to submit the job to the computer. Class to a portable batch systems script.This is a example of the script which named job.pbs. After the job finished, if ratio requires accuracy stopping structure energy minimization appears at the end of output lock. The converging result is a pend.The resulting POSCAR will be used as an input file POSCAR for the following calculations. For analyzing electronic properties of materials. Step two.Calculate the encapsulation energy. Type mkdir nanocomposite isolated-nanoribbon isolated-nanotube to create qsub folders for nanocomposite, nanoribbon and nanotube internal in Linux system. Prepare one PBS script, job.pbs and four input files INCAR, POSCAR, POTCAR and KPOINTS. For energy, calculation in each folder. The input file POSCAR in the same way that relaxes structure and count CAR forms that one.Go to each folder and type qsub job. pbs onto internal Linux system. The series of mated jobs will perform the static self consistent energy calculations of nanocomposites, isolates nanoribbon, isolates nanotube respectively.Next track the total energy from the file OUTCAR for each system back up command. After finishing the static self-consistent calculations then compute the encapsulation energy as shown in this formula. The periodic interaction of the nanocomposite is allow Z axis and L is the lattice constant of the unit cell, along Z.The encapsulation energy can be used as an estimate for the energetic stability of nanocomposite.Step three, extract the electronic properties from the band structure. Prepare one PBS, script job. pbs and the six input files.INCAR, POSCAR, POTCAR, KPOINTS, CHGCAR, and CHG. For band-calculations, said ICHARG equals 11 in INCAR. The pre-conversion CHGCAR and CHG files are from static self-consistent calculations.The KPOINT sampling in KPOINTS is in line-mode. Type qsub job. pbs onto internal Linux system to submit the job.Use p4vasprun to generate the projected band. Load vasprun. xml by typing p4v vasprun.xml on terminal. Select the menu, electronic local DOS bands. Control and then select bands.Specify the atomic numbers of nanotube in the label atoms selection. Get the atomic number by pointing to the corresponding atoms using VMD. Specify the color, type, and size of symbol for the projected band structure.Those menus symbol and the symbol size. Press the menu, add new line. The graph will show the band structure with the contributions from nanotube.Then repeat the same procedure to gather projected band with contributions from nanoribbon. Select the menu graph export. Export the graph into the file with agr format.For example, saved as 11-4.agr. Use XM grades to ID the projected bands. Type xmgrace11-4.agr on terminal to start xmgrace in menu system. Select the menu, plot access properties to ID the label and the range of the axes. Select the manual plot set appearance to read the energy value as specified band number and key point.Release band maximum and the conduction band minimum of nanotube or nanoribbon can be right from the projected band with the contributions of nanotube or nanoribbons respectively. Then calculate the valence band offset, conduction band offset and the band gap. Select the menu, file, point to export the graph with APS formats.Calculate the band decompose to charge density for VBM and CBM. Prepare one pbs, script job. pbs and seven input files, INCAR, POSCAR, POTCAR, KPOINTS, WAVECAR, CHGCAR, and CHG.Specify the band numbers for CBM and VBM. Then type IBAND in INCAR. Use the single corresponding KPOINT for each band edge.The point converges CHGCAR, CHG. And the WAVECAR files, are from static self-consistent calculations. Type qsub job.pbs onto internal Linux system to submit the job. Use VMD to plot VBM and CBM in real space after the job finished. Start a VMD session and load POSCAR.Select the menu, file, new molecule in the VMD main window. Find the PARCHG through the browse window. Load the PARCHG by the type, press and score PARCHG.Select the menu, draw solid surface and show a solid surface in the graphical representations window. Change the ISO value to an appropriate value, for example 0.02. Change the color of the ISO surface though the menu coloring method.Step four, modulate the electronic properties of the nanocomposite by external fields. Add a transverse electric field to the nanocomposite. Prepare one PBS, script job.pbs and the four input files, INCAR, POSCAR, POTCAR, and KPOINTS. Define the strength of the electric field by the tag e-field in units of eV Astrum. Set LDIPOL equals T, set IDIPOL equals 2.And the electric field will be applied allow Y axis. Perform static self-consistent calculations and band structure calculations, following steps two and three without structure optimization. Add a longitudinal test of strength to the nanocomposite, chain the lattice parameter along the periodical direction to consider the string effect.For example, to optimize the lattice parameter of nanocomposite along the axis is 2.5045 Astrum If applied 1%and the axial tensile strength along the Z through action. Change the lattice parameter in POSCAR to 2.529545 Astrum. Relax the modify structure following step one, perform static self-consistent calculations and band structure calculations, following steps two and three.Representative results. The encapsulation energy can be used as a rough estimate for the energetic stability of the nanocomposite. The encapsulation energy of boron nitrite nanoribbons, a 2, a 3, and a 4 encapsulated inside the boron nitrite nanotube 11, 11 are 0.033 eV Astrum, 0.068 eV Astrum and 0131 eV Astrum respectively.Although the encapsulation energy varies by an order of magnitude with the nanoribbon size, all three nanocomposites present type two band alignment. This is a band structure of boron nitrite and nanoribbons, a four encapsulated inside the boron nitrite nanotube, 11, 11. Valence band maximum and the conduction band minimum located at nanotube and nanoribbon respectively.The staggered band alignment is beneficial for light currents to the main mechanism of charge transport is as follows. The photo generates electric ad hull in nanoribbons at the X point. Then the whole dissociates from nanoribbons to nanotube.The calculated valence band offset is 317 micro eV. It is larger than the thermal energy at 300 Kelvins which is about 13 micro eV. This effectively decreases the recombination rate of photo-generated carriers.To enhance light harvest through a wide spectrum, this transfers electric field and longitudinal tensile strength are applied to boron nitrite nanoribbons, a four encapsulated inside the boron nitrite nanotube, 11, 11. This is the evolution of band edges relative to the vacuum level, and reacts to no field. A substantial gap reduction up to near 0.95 eV is observed in this nanocomposite by both external fields.More importantly, the staggered band alignment is preserved against the diffuse. The redox potentials of water are marked by the blue dashed lines. The band edges are relative to the redox potentials indicate that such a nanocomposite may be promising for water splitting.Conclusion.It is rapid and efficient to use a computational screening approach to discover low dimensional materials that possess properties suitable for solo water splitting. Such a one dimensional system can propose to integrate a photo-catalated hydrogen generation and safe capsule style reach. The photo-generated electrons could be collected by nanoribbon, protons penetrate through the nanotube to generate hydrogen molecule joined by electrostatic attraction.The produced hydrogen is completely isolated within the nanotube to avoid unwanted reverse reaction or explosion. The first principles calculations will underestimate the gap status using the PPE functional. But they can capture the essential trends in band alignment and band offsets.More accurate values of valence band offset, conduction band offset and the band gap are needed if compared with experimental work, operate functional would be rather employed, which will be time consuming than PPE function. Besides to address the lifetime of photo generated hulls and electric in static states nano diabetics deny me some calculations that are needed. This is important to design photo-catalysts with long lifetime careers.

probe-type-ii-band-alignment-one-dimensional-van-der-waals

Research

JoVE Journal

Chemistry

Preparation and Use of Samarium Diiodide (SmI2) in Organic Synthesis: The Mechanistic Role of HMPA and Ni(II) Salts in the Samarium Barbier Reaction

Although initially considered an esoteric reagent, SmI2 has become a common tool for synthetic organic chemists. SmI2 is generated through the addition of molecular iodine to samarium metal in THF.1,2-3 It is a mild and selective single electron reductant and its versatility is a result of its ability to initiate a wide range of reductions including C-C bond-forming and cascade or sequential reactions. SmI2 can reduce a variety of functional groups including sulfoxides and sulfones, phosphine oxides, epoxides, alkyl and aryl halides, carbonyls, and conjugated double bonds.2-12 One of the fascinating features of SmI-2-mediated reactions is the ability to manipulate the outcome of reactions through the selective use of cosolvents or additives. In most instances, additives are essential in controlling the rate of reduction and the chemo- or stereoselectivity of reactions.13-14 Additives commonly utilized to fine tune the reactivity of SmI2 can be classified into three major groups: (1) Lewis bases (HMPA, other electron-donor ligands, chelating ethers, etc.), (2) proton sources (alcohols, water etc.), and (3) inorganic additives (Ni(acac)2, FeCl3, etc).3
Understanding the mechanism of SmI2 reactions and the role of the additives enables utilization of the full potential of the reagent in organic synthesis. The Sm-Barbier reaction is chosen to illustrate the synthetic importance and mechanistic role of two common additives: HMPA and Ni(II) in this reaction. The Sm-Barbier reaction is similar to the traditional Grignard reaction with the only difference being that the alkyl halide, carbonyl, and Sm reductant are mixed simultaneously in one pot.1,15 Examples of Sm-mediated Barbier reactions with a range of coupling partners have been reported,1,3,7,10,12 and have been utilized in key steps of the synthesis of large natural products.16,17 Previous studies on the effect of additives on SmI2 reactions have shown that HMPA enhances the reduction potential of SmI2 by coordinating to the samarium metal center, producing a more powerful,13-14,18 sterically encumbered reductant19-21 and in some cases playing an integral role in post electron-transfer steps facilitating subsequent bond-forming events.22 In the Sm-Barbier reaction, HMPA has been shown to additionally activate the alkyl halide by forming a complex in a pre-equilibrium step.23
Ni(II) salts are a catalytic additive used frequently in Sm-mediated transformations.24-27 Though critical for success, the mechanistic role of Ni(II) was not known in these reactions. Recently it has been shown that SmI2 reduces Ni(II) to Ni(0), and the reaction is then carried out through organometallic Ni(0) chemistry.28
These mechanistic studies highlight that although the same Barbier product is obtained, the use of different additives in the SmI2 reaction drastically alters the mechanistic pathway of the reaction. The protocol for running these SmI2-initiated reactions is described.

Preparation and Use of Samarium Diiodide SmI2 in Organic Synthesis: The Mechanistic Role of HMPA and NiII Salts in the Samarium Barbier Reaction

A straightforward procedure for the preparation of samarium diiodide (SmI2) in THF is described. The role of two main additives namely hexamethylphosphoramide (HMPA) and Ni(acac)2 in Sm mediated reactions is demonstrated in the Sm-Barbier reaction.

Although initially considered an esoteric reagent, SmI2 has become a common tool for synthetic organic chemists. SmI2 is generated through the addition of ...

Analyzing Protein Dynamics Using Hydrogen Exchange Mass Spectrometry

All cellular processes depend on the functionality of proteins. Although the functionality of a given protein is the direct consequence of its unique amino acid sequence, it is only realized by the folding of the polypeptide chain into a single defined three-dimensional arrangement or more commonly into an ensemble of interconverting conformations. Investigating the connection between protein conformation and its function is therefore essential for a complete understanding of how proteins are able to fulfill their great variety of tasks. One possibility to study conformational changes a protein undergoes while progressing through its functional cycle is hydrogen-1H/2H-exchange in combination with high-resolution mass spectrometry (HX-MS). HX-MS is a versatile and robust method that adds a new dimension to structural information obtained by e.g. crystallography. It is used to study protein folding and unfolding, binding of small molecule ligands, protein-protein interactions, conformational changes linked to enzyme catalysis, and allostery. In addition, HX-MS is often used when the amount of protein is very limited or crystallization of the protein is not feasible. Here we provide a general protocol for studying protein dynamics with HX-MS and describe as an example how to reveal the interaction interface of two proteins in a complex. &#160;&#160;

Protein conformation and dynamics are key to understanding the relationship between protein structure and function. Hydrogen exchange coupled with high-resolution mass spectrometry is a versatile method to study the conformational dynamics of proteins as well as characterizing protein-ligand and protein-protein interactions, including contact interfaces and allosteric effects.

All cellular processes depend on the functionality of proteins. Although the functionality of a given protein is the direct consequence of its unique ...

Quantitative and Qualitative Examination of Particle-particle Interactions Using Colloidal Probe Nanoscopy

Colloidal Probe Nanoscopy (CPN), the study of the nano-scale interactive forces between a specifically prepared colloidal probe and any chosen substrate using the Atomic Force Microscope (AFM), can provide key insights into physical interactions present within colloidal systems. Colloidal systems are widely existent in several applications including, pharmaceuticals, foods, paints, paper, soil and minerals, detergents, printing and much more.1-3 Furthermore, colloids can exist in many states such as emulsions, foams and suspensions. Using colloidal probe nanoscopy one can obtain key information on the adhesive properties, binding energies and even gain insight into the physical stability and coagulation kinetics of the colloids present within. Additionally, colloidal probe nanoscopy can be used with biological cells to aid in drug discovery and formulation development. In this paper we describe a method for conducting colloidal probe nanoscopy, discuss key factors that are important to consider during the measurement, and show that both quantitative and qualitative data that can be obtained from such measurements.

Colloidal probe nanoscopy can be used within a variety of fields to gain insight into the physical stability and coagulation kinetics of colloidal systems and aid in drug discovery and formulation sciences using biological systems. The method described within provides a quantitative and qualitative means to study such systems.

Colloidal Probe Nanoscopy (CPN), the study of the nano-scale interactive forces between a specifically prepared colloidal probe and any chosen substrate ...

Iridium(III) Luminescent Probe for Detection of the Malarial Protein Biomarker Histidine Rich Protein-II

This work outlines the synthesis of a non-emissive, cyclometalated Ir(III) complex, Ir(ppy)2(H2O)2+ (Ir1), which elicits a rapid, long-lived phosphorescent signal when coordinated to a histidine-containing protein immobilized on the surface of a magnetic particle. Synthesis of Ir1, in high yields,is complete O/N&#160;and involves splitting of the parent cyclometalated Ir(III) chloro-bridged dimer into two equivalents of the solvated complex. To confirm specificity, several amino acids were probed for coordination activity when added to the synthesized probe, and only histidine elicited a signal response. Using BNT-II, a branched peptide mimic of the malarial biomarker Histidine Rich Protein II (pfHRP-II), the iridium probe was validated as a tool for HRP-II detection. Quenching effects were noted in the BNT-II/Ir1 titration when compared to L-Histidine/Ir1, but these were attributed to steric hindrance and triplet state quenching. Biolayer interferometry was used to determine real-time kinetics of interaction of Ir1 with BNT-II. Once the system was optimized, the limit of detection of rcHRP-II using the probe was found to be 12.8 nM in solution. When this protein was immobilized on the surface of a 50 &#181;m magnetic agarose particle, the limit of detection was 14.5 nM. The robust signal response of this inorganic probe, as well as its flexibility of use in solution or immobilized on a surface, can lend itself toward a variety of applications, from diagnostic use to imaging.

IridiumIII Luminescent Probe for Detection of the Malarial Protein Biomarker Histidine Rich Protein-II

Robust detection reagents are of increasing necessity for developing new malaria diagnostic tools. An iridium(III) probe was designed that emits long-lasting luminescent signal in the presence of a histidine-rich malarial protein biomarker. Detection of the protein either in solution or immobilized on a magnetic particle affords flexibility in application.

This work outlines the synthesis of a non-emissive, cyclometalated Ir(III) complex, Ir(ppy)2(H2O)2+ (Ir1), which elicits a rapid, long-lived ...

Post Column Derivatization Using Reaction Flow High Performance Liquid Chromatography Columns

A protocol for the use of reaction flow high performance liquid chromatography columns for methods employing post column derivatization (PCD) is presented. A major difficulty in adapting PCD to modern HPLC systems and columns is the need for large volume reaction coils that enable reagent mixing and then the derivatization reaction to take place. This large post column dead volume leads to band broadening, which results in a loss of observed separation efficiency and indeed detection in sensitivity. In reaction flow post column derivatization (RF-PCD) the derivatization reagent(s) are pumped against the flow of mobile phase into either one or two of the outer ports of the reaction flow column where it is mixed with column effluent inside a frit housed within the column end fitting. This technique allows for more efficient mixing of the column effluent and derivatization reagent(s) meaning that the volume of the reaction loops can be minimized or even eliminated altogether. It has been found that RF-PCD methods perform better than conventional PCD methods in terms of observed separation efficiency and signal to noise ratio. A further advantage of RF-PCD techniques is the ability to monitor effluent coming from the central port in its underivatized state. RF-PCD has currently been trialed on a relatively small range of post column reactions, however, there is currently no reason to suggest that RF-PCD could not be adapted to any existing one or two component (as long as both reagents are added at the same time) post column derivatization reaction.

A protocol for the use of reaction flow high performance liquid chromatography columns for methods employing post column derivatization (PCD) is presented.

A protocol for the use of reaction flow high performance liquid chromatography columns for methods employing post column derivatization (PCD) is ...

On-line Analysis of Nitrogen Containing Compounds in Complex Hydrocarbon Matrixes

The shift to heavy crude oils and the use of alternative fossil resources such as shale oil are a challenge for the petrochemical industry. The composition of heavy crude oils and shale oils varies substantially depending on the origin of the mixture. In particular they contain an increased amount of nitrogen containing compounds compared to the conventionally used sweet crude oils. As nitrogen compounds have an influence on the operation of thermal processes occurring in coker units and steam crackers, and as some species are considered as environmentally hazardous, a detailed analysis of the reactions involving nitrogen containing compounds under pyrolysis conditions provides valuable information. Therefore a novel method has been developed and validated with a feedstock containing a high nitrogen content, i.e., a shale oil. First, the feed was characterized offline by comprehensive two-dimensional gas chromatography (GC &#215; GC) coupled with a nitrogen chemiluminescence detector (NCD). In a second step the on-line analysis method was developed and tested on a steam cracking pilot plant by feeding pyridine dissolved in heptane. The former being a representative compound for one of the most abundant classes of compounds present in shale oil. The composition of the reactor effluent was determined via an in-house developed automated sampling system followed by immediate injection of the sample on a GC &#215; GC coupled with a time-of-flight mass spectrometer (TOF-MS), flame ionization detector (FID) and NCD. A novel method for quantitative analysis of nitrogen containing compounds using NCD and 2-chloropyridine as an internal standard has been developed and demonstrated.

A method combining comprehensive two-dimensional gas chromatography with nitrogen chemiluminescence detection has been developed and applied to on-line analysis of nitrogen containing compounds in a complex hydrocarbon matrix.

The shift to heavy crude oils and the use of alternative fossil resources such as shale oil are a challenge for the petrochemical industry. The ...

Non-equilibrium Microwave Plasma for Efficient High Temperature Chemistry

A flowing microwave plasma based methodology for converting electric energy into internal and/or translational modes of stable molecules with the purpose of efficiently driving non-equilibrium chemistry is discussed. The advantage of a flowing plasma reactor is that continuous chemical processes can be driven with the flexibility of startup times in the seconds timescale. The plasma approach is generically suitable for conversion/activation of stable molecules such as CO2, N2 and CH4. Here the reduction of CO2 to CO is used as a model system: the complementary diagnostics illustrate how a baseline thermodynamic equilibrium conversion can be exceeded by the intrinsic non-equilibrium from high vibrational excitation. Laser (Rayleigh) scattering is used to measure the reactor temperature and Fourier Transform Infrared Spectroscopy (FTIR) to characterize in situ internal (vibrational) excitation as well as the effluent composition to monitor conversion and selectivity.

This article describes a flowing microwave reactor that is used to drive efficient non-equilibrium chemistry for the application of conversion/activation of stable molecules such as CO2, N2 and CH4. The goal of the procedure described here is to measure the in situ gas temperature and gas conversion.

A flowing microwave plasma based methodology for converting electric energy into internal and/or translational modes of stable molecules with the purpose ...

Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films

Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, we present a protocol for the fabrication of this material via the low-pressure vapor assisted solution process (LP-VASP) method, which yields ~19% power conversion efficiency in planar heterojunction perovskite solar cells. First, we report the synthesis of methylammonium iodide (CH3NH3I) and methylammonium bromide (CH3NH3Br) from methylamine and the corresponding halide acid (HI or HBr). Then, we describe the fabrication of pinhole-free, continuous methylammonium-lead halide perovskite (CH3NH3PbX3 with X = I, Br, Cl and their mixture) films with the LP-VASP. This process is based on two steps: i) spin-coating of a homogenous layer of lead halide precursor onto a substrate, and ii) conversion of this layer to CH3NH3PbI3-xBrx by exposing the substrate to vapors of a mixture of CH3NH3I and CH3NH3Br at reduced pressure and 120 &#176;C. Through slow diffusion of the methylammonium halide vapor into the lead halide precursor, we achieve slow and controlled growth of a continuous, pinhole-free perovskite film. The LP-VASP allows synthetic access to the full halide composition space in CH3NH3PbI3-xBrx with 0&#160;&#8804; x&#160;&#8804; 3. Depending on the composition of the vapor phase, the bandgap can be tuned between 1.6 eV&#160;&#8804; Eg&#160;&#8804; 2.3 eV. In addition, by varying the composition of the halide precursor and of the vapor phase, we can also obtain CH3NH3PbI3-xClx. Films obtained from the LP-VASP are reproducible, phase pure as confirmed by X-ray diffraction measurements, and show high photoluminescence quantum yield. The process does not require the use of a glovebox.

Here, we present a protocol for the synthesis of CH3NH3I and CH3NH3Br precursors and the subsequent formation of pinhole-free, continuous CH3NH3PbI3-xBrx thin films for the application in high efficiency solar cells and other optoelectronic devices.

Organo-lead halide perovskites have recently attracted great interest for potential applications in thin-film photovoltaics and optoelectronics. Herein, ...

A Closed-Type Wireless Nanopore Electrode for Analyzing Single Nanoparticles

Measuring the intrinsic features of single nanoparticles by nanoelectrochemistry holds deep fundamental importance and has potential impacts in nanoscience. However, electrochemically analyzing single nanoparticles is challenging, as the sensing nanointerface is uncontrollable. To address this challenge, we describe here the fabrication and characterization of a closed-type wireless nanopore electrode (WNE) that exhibits a highly controllable morphology and outstanding reproducibility. The facile fabrication of WNE enables the preparation of well-defined nanoelectrodes in a general chemistry laboratory without the use of a clean room and expensive equipment. One application of a 30 nm closed-type WNE in analysis of single gold nanoparticles in the mixture is also highlighted, which shows a high current resolution of 0.6 pA and high temporal resolution of 0.01 ms. Accompanied by their excellent morphology and small diameters, more potential applications of closed-type WNEs can be expanded from nanoparticle characterization to single molecule/ion detection and single-cell probing.

Here, we present a protocol for fabrication of a closed-type wireless nanopore electrode and subsequent electrochemical measurement of single nanoparticle collisions.

Measuring the intrinsic features of single nanoparticles by nanoelectrochemistry holds deep fundamental importance and has potential impacts in ...

Early Detection of Cyanobacterial Blooms and Associated Cyanotoxins using Fast Detection Strategy

Fast detection of cyanobacteria and cyanotoxins is achieved using a Fast Detection Strategy (FDS). Only 24 h are needed to unravel the presence of cyanobacteria and related cyanotoxins in water samples and in an organic matrix, such as bivalve extracts. FDS combines remote/proximal sensing techniques with analytical/bioinformatics analyses. Sampling spots are chosen through multi-disciplinary, multi-scale, and multi-parametric monitoring in a three-dimensional physical space, including remote sensing. Microscopic observation and taxonomic analysis of the samples are performed in the laboratory setting, which allows for the identification of cyanobacterial species. Samples are then extracted with organic solvents and processed with LC-MS/MS. Data obtained by MS/MS are analyzed using a bioinformatic approach using the online platform Global Natural Products Social (GNPS) to create a network of molecules. These networks are analyzed to detect and identify toxins, comparing data of the fragmentation spectra obtained by mass spectrometry with the GNPS library. This allows for the detection of known toxins and unknown analogues that appear related in the same molecular network.

A fast-multidisciplinarystrategy for early detection of cyanobacterial blooms and associated cyanotoxins is described here. It allows for the detection of cyanobacteria and related cyanotoxins in water samples and in organic matrices, such as bivalve samples, in 24 h.