Questo lavoro è stato supportato dalla Rowland Fellows Program presso l'Università di Rowland Institute di Harvard. Quest'opera è stata eseguita in parte al centro per sistemi su scala nanometrica (CNS), un membro della nanotecnologia infrastruttura rete nazionale, che è sostenuto dalla National Science Foundation sotto Premio no. ECS-0335765. Il CNS è parte dell'Università di Harvard.

1. preparazione del catalizzatore di Ni singolo atomo (NiN-GS)
<ol><li>Preparazione della soluzione di precursore di elettrofilatura<ol>
<li>Prendere un flacone di scintillazione 20ml, sciogliere 0,5 g di poliacrilonitrile (Mw= 150.000), 0,5 g di usato (Mw= 1.300.000), 0,5 g di Ni (NO3)2·6H2O e 0,1 g di diciandiammide (DCDA) in 10 mL di dimetilformammide (DMF).</li>
		<li>La miscela DMF a 80 ° C di calore e mantenere la miscela ad 80 ° C mescolando costantemente fino a quando tutti i polimeri e sale si dissolvono e si osserva una soluzione chiara.</li>
	</ol>
</li>
	<li>Elettrofilatura per produrre fibre polimeriche<ol>
<li>Impostare i parametri di elettrofilatura convenzionali come: 15 kV di tensione elettrica statica, 15 cm di aria gap di distanza, un substrato di raccolta di 8 carta di × 8 cm di fibra di carbonio (PCP) con - 4 kV di tensione elettrica.</li>
		<li>Estratto 5 mL di soluzione di precursore in una siringa da 5 mL, avviare la pompa a siringa ad una portata di 1,2 mL h−1, quindi iniziare l'elettrofilatura. Nota: Un'ad alta tensione viene utilizzata per elettrofilatura. Anche se molto bassa corrente passa attraverso il sistema durante il processo di filatura, è suggerito un cabinet in legno coibentato.</li>
		<li>Estrarre il substrato di PCP, una volta completato il processo di elettrofilatura. Un film di fibra di polimero ricopre la superficie di PCP.</li>
	</ol>
</li>
	<li>Ricottura di fibre polimeriche in nanotubi di carbonio<ol>
<li>Preparato come polimero fibra film/PCP a 300 ° C in 1,5 h in una fornace di casella di calore e mantenere la temperatura per 0,5 h ossidare i polimeri. Nota: Dopo il processo di ossidazione, le nanofibre (NFs) sono auto-staccate dalla carta carbone risultanti nel film indipendente.</li>
		<li>Utilizzare un paio di forbici per tagliare quei nanofibre in pezzi più piccoli (~ 0,5 cm × 2 cm) e inserirli in una barca di quarzo.</li>
		<li>Mettere la barca al quarzo in un forno tubolare e disareare esso all'interno formando atmosfera di gas (5% H2 in Ar). Mantenere il tasso di flusso di gas come sccm 100 e la pressione come 1 Tor.</li>
		<li>Riscaldarli entro 10 min in rampa a 300 ° C e 2 h rampa a 750 ° C, dove viene mantenuta per un altro h 1 e seguito dal raffreddamento naturale.</li>
	</ol>
</li>
	<li>Ball mill come sintetizzato NiN-GS catalizzatore per 5 min a nanopolveri per catalisi e caratterizzazioni.</li>
</ol>2. misure di riduzione di CO elettrochimica2
<ol><li>Cella e gli elettrodi<ol>
<li>Per preparare dell'elettrolito 0,1 M KHCO3 per le seguenti misure, prima sciogliere 2,5 g di KHCO3 in 250 mL di acqua ultrapura, quindi purificare l'elettrolita per elettrolisi tra due barre di grafite a 0.1 mA per 24 h per rimuovere qualsiasi traccia quantità di metallo ioni.</li>
		<li>Prendere un fresco carbonio vetroso (elettrochimicamente) lucido (1 × 2cm) e coprire la sua parte posteriore con una cera elettrochimicamente inerte, idrofobica, come il substrato di elettrodo di lavoro.</li>
		<li>Prendere un flacone di scintillazione 4 mL, mescolare 5 mg di preparato come catalizzatore di NiN-GS con 1 mL di etanolo e 100 µ l di soluzione ionomero (5% in 2-proponal) all'interno del flacone e Sonicare per 20 min ottenere una sospensione di inchiostro di catalizzatore omogeneo.</li>
		<li>Dispensare 80 µ l di inchiostro catalizzatore sulla superficie di 2cm2 carbonio vetroso (0,2 mg cm-2 la massa di caricamento) e il vuoto a secco il catalizzatore dell'elettrodo rivestito in un essiccatore prima dell'uso.</li>
		<li>Utilizzare una lamina di platino e un elettrodo al calomelano saturo (SCE) come il contatore e l'elettrodo di riferimento, rispettivamente.</li>
		<li>Utilizzare una tenuta di gas H-tipo vetro cella personalizzata, separata da membrana a scambio protonico, per i sopra 3 elettrodi assemblaggio, nonché le prove elettrochimiche in esecuzione.</li>
		<li>Posizionare l'elettrodo di lavoro ed elettrodo di riferimento SCE in uno scomparto della H-cella ed elettrodo di Pt foglio in altra camera. Iniettare ~ 25 mL di elettrolita in ogni vano del H-cell.</li>
		<li>Collegare gli 3 elettrodi in H-cella della stazione di lavoro elettrochimico per controllo potenziale.</li>
		<li>Bolla dell'elettrolito con N2 a 50.0 sccm (monitorata da controllore di flusso di massa) per 30 min verso N2-saturi 0,1 M KHCO3.</li>
		<li>Selezionare la tecnica di voltammetria ciclica (CV) in CE-Lab software, impostare "E gamma (potenziale)" come "-10 V a 10 V", "gamma (corrente)" come "Auto", eseguire 5 continuo CV scansioni da -0.5 V a -1,8 V (vs SCE) a una velocità di scansione di 50 mV/s a N2-saturi 0,1 M KHCO3.</li>
		<li>Cambiare 50 sccm CO2 flusso di gas, attendere 30 min verso CO2-saturi dell'elettrolito 0,1 M KHCO3 e mantenere lo stesso flusso di CO2 durante l'elettrolisi seguente.</li>
		<li>Selezionare la tecnica di CV in CE-Lab software, impostare "E gamma (potenziale)" come "-10 V a 10 V", "gamma (corrente)" come "Auto", eseguire 5 continuo CV scansioni da -0.5 V a -1,8 V (vs SCE) a una velocità di scansione di 50 mV/s in CO2-saturi 0,1 M KHCO3.</li>
		<li>Utilizzare un misuratore di pH per determinare i valori di pH degli elettroliti, cioè., 0,1 M KHCO3 saturata con N2 o CO2.</li>
		<li>Convertire tutti i potenziali misurati contro SCE per la scala di elettrodo (RHE) idrogeno reversibile in questo lavoro utilizzando E (vs RHE) = E (vs SCE) + 0,244 V + 0.0591 × pH.</li>
		<li>Determinare la soluzione resistenza (Ru) in CE-Lab software selezionando la tecnica di spettroscopia di impedenza elettrochimica potenziostatica (PEIS), quindi la gamma di frequenza impostata da 0,1 Hz a 200 kHz, registrare il valore di resistenza.</li>
		<li>Compensare manualmente iR-drop come E (correzione iR vs RHE) = E (vs RHE) - ×u R I (amp di corrente media).</li>
	</ol>
</li>
	<li>Analisi di prodotti di CO2 riduzione di on-line gascromatografo (GC)<ol>
<li>Impiegare un GC, dotato di una combinazione di setaccio molecolare 5A e micropacked colonne, per analisi di gas prodotti durante la CO2RR. Nota: I tipi di colonna GC dettagliati è reperibile in allegato Tabella materiali.</li>
		<li>Utilizzare un rivelatore a conducibilità termica (TCD) per quantificare la concentrazione di2 H e un rivelatore a ionizzazione di fiamma (FID) con un methanizer a tenore di CO di analisi quantitativa e/o di qualsiasi altra specie di alcano.</li>
		<li>Utilizzare due diversi tipi di gas standard per le curve di calibrazione di H2 e concentrazione di CO (H2: 1042 e 100 ppm; CO: 496.7 e 100 ppm; bilanciato con Argon).</li>
		<li>Durante l'elettrolisi, mantenere CO2 portata gas a 50.0 sccm, consegnare CO2 nel vano catodico contenenti CO2-saturi 0,1 M KHCO3 elettrolito e sfiato del gas di scarico in GC.</li>
		<li>Tune graduale la tensione sull'elettrodo di lavoro, che vanno da -0,3 a -1,0 V vs RHE, mantenere ~ 15 min per ogni potenziale e registrare la corrispondente curva di chronoamperimetric.</li>
		<li>Determinare H2 e CO contenuti nei gas di scarico dai segnali di TCD e FID, rispettivamente. Nota: I prodotti di gas vengono campionati dopo un'elettrolisi continua di ~ 10 min sotto ogni potenziale. Il 50 sccm CO2 gas, mescolato con continuamente prodotto H2 e CO, scorreva attraverso il ciclo di campionamento (1 mL) di GC durante l'elettrolisi.</li>
		<li>Calcolare la densità di corrente parziale per un prodotto dato gas come qui sotto: <img alt="Equation" src="/files/ftp_upload/57380/57380eq2.jpg"> dove xho è la frazione di volume di determinato prodotto determinato dal GC online a cui fa riferimento alle curve di calibrazione da due campioni di gas standard (Scott e Airgas), v è la portata di 50 sccm, n è il numero di elettroni coinvolti, p0 = 101.3 kPa e F è la costante faradica e R è la costante dei gas.</li>
		<li>Calcolare l'efficienza faradica corrispondente (FE) presso ogni potenziale come <img alt="Equation" src="/files/ftp_upload/57380/57380eq7.jpg"> </img>. Nota: L'efficienza generale faradica potrebbe essere all'interno di una gamma di 90-110% a causa di errori da portata gas, densità di corrente e l'analisi di concentrazione di gas su GC.</li>
	</ol>
</li>
</ol>

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Nel processo di elettrofilatura sopra, due passi importanti dovrebbero essere notate in procedure di sintesi materiale: 1) la miscela DMF (punto 1.1.2) e 2) il tasso di pompa regolazione (passo 1.2.2) per adeguarsi alla velocità di filatura di riscaldamento. L'immagine di SEM in Figura 1A Mostra le nanofibre di carbonio ottenuta interconnesse tra loro (~ 200 nm di diametro). Essi sono stati suddivisi in piccoli pezzi da palla di fresatura per caratterizzazioni come mostrato in <strong class...

Converting CO2 in sostanze chimiche o combustibili utilizzando energia elettrica pulita sta diventando sempre più importante come un potenziale mezzo per prevenire ulteriori CO2 emissioni1,2,3,4, 5,6. Tuttavia, questa pratica applicazione attualmente è sfidata dalla bassa attività e selettività di CO2 riduzione reazione (CO2RR) dovuto le alte barriere cinetiche e la concorrenza con reazione di evoluzione di idrogeno (HER) a acquosa mezzi di comunicazione. La maggior parte del catalizzatore tradizionali metalli di transizione, come Fe, Co e Ni, esibiscono CO2RR selettività bassa a causa della loro superba HER attività7,8. Ottimizzazione efficacemente loro proprietà per modificare i percorsi di reazione su questi catalizzatori di metalli di transizione diventa fondamentale per migliorare la loro selettività di2RR CO. Tra vari metodi per modificare le proprietà elettroniche dei catalizzatori, disperdendo atomi del metallo in una morfologia di singolo-atomo attira attenzioni intensivi recentemente a causa dei loro comportamenti catalitici radicalmente mutati rispetto alla loro controparte alla rinfusa 9 , 10 , 11. Tuttavia, a causa l'elevata mobilità degli atomi non vincolati, è abbastanza difficile ottenere singoli atomi di metallo senza la presenza di materiali di supporto. Pertanto, un materiale di matrice ospite con difetti creato per confinare e coordinare con atomi di metalli di transizione è necessario. Questo potrebbe aprire nuove opportunità per: 1) ottimizzare le proprietà elettroniche dei metalli di transizione come siti attivi di CO2RR e 2) allo stesso tempo mantenere relativamente semplice coordinamento atomico per gli studi di meccanismo fondamentale. Inoltre, quegli atomi di metalli di transizione intrappolati in un ambiente confinato, non possono essere facilmente spostati durante la catalisi, che impedisce la nucleazione o ricostruzioni degli atomi di superficie osservati in molti casi12,13 ,14.
Bidimensionale grafene a strati è di particolare interesse come host per metallo singoli atomi a causa della loro conducibilità alta dell'elettrone, la stabilità chimica e l'inerzia sia riduzione di CO2 e le sue reazioni catalitiche. Ancora più importante, Fe, Co e Ni metalli erano noti per essere in grado di catalizzare il processo di grafitizzazione di carbonio sulla loro superficie15. In breve, quei metalli di transizione in lega con il carbonio durante la termica ad alta temperatura processo di ricottura. Quando la temperatura scende, carbonio inizia a precipitare fuori la fase lega ed è catalizzato da strati di grafene forma sulla superficie del metallo di transizione. Durante questo processo, con difetti di grafene generati, metallo singoli atomi sarebbero intrappolati in quei difetti di grafene come i siti attivi per CO2RR16,17,18,19. Qui, segnaliamo questo protocollo dettagliato con l'intenzione di aiutare nuovi praticanti nel campo della catalisi di singolo atomo, così da fornire una dimostrazione esplicita di on-line CO2 analisi del prodotto di riduzione. Ulteriori informazioni possono essere trovati nel nostro articolo recentemente pubblicato19 e una serie di opere relative al20,21,22,23.

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		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">gas chromatograph</td>
			<td style="width:164px;">Shimadzu</td>
			<td style="width:151px;">GC-2014</td>
			<td>a combined seperation system consisting of molecular sieve 5A, Hayesep Q, Hayesep T, and Hayesep N</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">mass flow controller</td>
			<td>Alicat Scientific&#160;</td>
			<td style="width:151px;">MC-50SCCM-D/5M</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">ultrapure water system</td>
			<td>Millipore</td>
			<td>Synergy</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">vacuum desiccator&#160;</td>
			<td>PolyLab</td>
			<td>55205</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">polyacrylonitrile</td>
			<td style="width:164px;">Sigma-Aldrich</td>
			<td style="width:151px;">181315</td>
			<td>Mw=150,000</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">polypyrrolidone</td>
			<td style="width:164px;">Sigma-Aldrich</td>
			<td style="width:151px;">437190</td>
			<td>Mw=1,300,000</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Ni(NO3)26H2O</td>
			<td style="width:164px;">Sigma-Aldrich</td>
			<td style="width:151px;">244074</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">dicyandiamide</td>
			<td style="width:164px;">Sigma-Aldrich</td>
			<td style="width:151px;">D76609</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">dimethylformamide</td>
			<td style="width:164px;">Sigma-Aldrich</td>
			<td style="width:151px;">227056</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">carbon fiber paper&#160;</td>
			<td style="width:164px;">AvCarb</td>
			<td style="width:151px;">MGL370</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Nafion 117 membrane</td>
			<td style="width:164px;">Fuel Cell Store</td>
			<td style="width:151px;">117</td>
			<td>used as proton exchange membrane in H-cell</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">KHCO3</td>
			<td style="width:164px;">Sigma-Aldrich</td>
			<td style="width:151px;">431583</td>
			<td>further purified by electrolysis</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">platinum foil&#160;</td>
			<td style="width:164px;">Beantown Chemical</td>
			<td style="width:151px;">126580</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">saturated calomel electrode</td>
			<td style="width:164px;">CH Instruments</td>
			<td style="width:151px;">CHI150</td>
			<td></td>
		</tr>
		<tr height="27">
			<td height="27" style="height:27px;width:216px;">glassy carbon electrode</td>
			<td style="width:164px;">HTW GmbH</td>
			<td style="width:151px;">SIGRADUR</td>
			<td>1 cm &#215; 2 cm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">wax</td>
			<td>Apiezon</td>
			<td style="width:151px;">W-W100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Nafion 117 solution</td>
			<td>Sigma-Aldrich</td>
			<td>70160</td>
			<td>used as ionomer in catalyst ink preparation&#160;</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">forming gas</td>
			<td>Airgas</td>
			<td>UHP</td>
			<td>5% H2 balanced with Ar</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">carbon dioxide</td>
			<td>Airgas</td>
			<td>LaserPlus</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">sandard gas</td>
			<td>Airgas</td>
			<td>customized</td>
			<td>500 ppm CO, 500 ppm CH4, 1000 ppm H2 balanced with Ar</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">sandard gas</td>
			<td>Air Liquide</td>
			<td>customized</td>
			<td>100 ppm H2, 100 ppm CO and other alkanes balanced with Ar</td>
		</tr>
	</tbody>
</table>

synthesis and performance characterizations of transition metal single atom catalyst for electrochemical co2 reduction

Questo protocollo presenta sia il metodo di sintesi del catalizzatore singolo atomo Ni e il test elettrochimico delle sue attività catalitica e selettività in acquoso riduzione di CO2 . Diverso dal tradizionale metallo nanocristalli, la sintesi di singoli atomi metallici comporta un materiale di matrice che può confinare i singoli atomi e impedire loro di aggregazione. Segnaliamo un elettrofilatura e termico ricottura metodo per preparare Ni singoli atomi dispersero e coordinato in un guscio di grafene, come centri attivi per la riduzione di CO2 di CO. Durante la sintesi, droganti N svolgono un ruolo critico nella generazione di posti vacanti di grafene per intrappolare atomi di Ni. Aberrazione-corretta scansione microscopia elettronica di trasmissione e tomografia sonda atomo tridimensionale sono stati impiegati per identificare singoli siti atomici Ni in grafene posti vacanti. Installazione dettagliata dell'elettrochimica CO2 riduzione apparato accoppiato con una cromatografia gas on-line è anche dimostrato. Rispetto al Ni metallico, Ni singolo atomo catalizzatore notevolmente migliorata riduzione di CO2 per mostre e soppressa reazione collaterale H2 evoluzione.

Microscopia elettronica (SEM), scansione microscopia elettronica della trasmissione (STEM) e spettroscopia a raggi x energia-dispersiva (EDX) mappatura di immagini è mostrati nella Figura 1 per la caratterizzazione della morfologia di NiN-GS. Atomo tridimensionale sonda tomografia (3D-APT) risultati sono mostrati nella Figura 2 per l'identificazione diretta dell'unico Ni siti distribuzione così come loro vicini ambiente chimico...

Watch this Scientific Journal Video about Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction at JoVE.com

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Sintesi e caratterizzazione di prestazioni di catalizzatore singolo atomo del metallo di transizione per elettrochimica CO2 riduzione

Qui, presentiamo un protocollo per la sintesi e test elettrochimico di singoli atomi di metallo di transizione coordinati in posti vacanti grafene come centri attivi per la riduzione di anidride carbonica selettiva al monossido di carbonio nelle soluzioni acquose.

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity ...

synthesis-performance-characterizations-transition-metal-single-atom

Research

JoVE Journal

Chemistry

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

18.0K Views.  Harvard University. Qui, presentiamo un protocollo per la sintesi e test elettrochimico di singoli atomi di metallo di transizione coordinati in posti vacanti grafene come centri attivi per la riduzione di anidride carbonica selettiva al monossido di carbonio nelle soluzioni acquose.

Video: Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Anticancer Metal Complexes: Synthesis and Cytotoxicity Evaluation by the MTT Assay

Titanium (IV) and vanadium (V) complexes are highly potent anticancer agents. A challenge in their synthesis refers to their hydrolytic instability; therefore their preparation should be conducted under an inert atmosphere. Evaluation of the anticancer activity of these complexes can be achieved by the MTT assay.
The MTT assay is a colorimetric viability assay based on enzymatic reduction of the MTT molecule to formazan when it is exposed to viable cells. The outcome of the reduction is a color change of the MTT molecule. Absorbance measurements relative to a control determine the percentage of remaining viable cancer cells following their treatment with varying concentrations of a tested compound, which is translated to the compound anticancer activity and its IC50 values. The MTT assay is widely common in cytotoxicity studies due to its accuracy, rapidity, and relative simplicity.
Herein we present a detailed protocol for the synthesis of air sensitive metal based drugs and cell viability measurements, including preparation of the cell plates, incubation of the compounds with the cells, viability measurements using the MTT assay, and determination of IC50 values.

A method for synthesis of air-sensitive titanium and vanadium anticancer agents is described, along with the evaluation of their cytotoxic activity towards human cancer cell line by the MTT Assay.

Antitumorali metallo Complessi: Sintesi e citotossicità valutazione da parte del saggio MTT

Titanium (IV) and vanadium (V) complexes are highly potent anticancer agents. A challenge in their synthesis refers to their hydrolytic instability; ...

Ricerca

Chimica

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and technological applications. Their signature property is their ultrahigh porosity, which however imparts a series of challenges when it comes to both constructing them and working with them. Securing desired MOF chemical and physical functionality by linker/node assembly into a highly porous framework of choice can pose difficulties, as less porous and more thermodynamically stable congeners (e.g., other crystalline polymorphs, catenated analogues) are often preferentially obtained by conventional synthesis methods. Once the desired product is obtained, its characterization often requires specialized techniques that address complications potentially arising from, for example, guest-molecule loss or preferential orientation of microcrystallites. Finally, accessing the large voids inside the MOFs for use in applications that involve gases can be problematic, as frameworks may be subject to collapse during removal of solvent molecules (remnants of solvothermal synthesis). In this paper, we describe synthesis and characterization methods routinely utilized in our lab either to solve or circumvent these issues. The methods include solvent-assisted linker exchange, powder X-ray diffraction in capillaries, and materials activation (cavity evacuation) by supercritical CO2 drying. Finally, we provide a protocol for determining a suitable pressure region for applying the Brunauer-Emmett-Teller analysis to nitrogen isotherms, so as to estimate surface area of MOFs with good accuracy.

Synthesis, activation, and characterization of intentionally designed metal-organic framework materials is challenging, especially when building blocks are incompatible or unwanted polymorphs are thermodynamically favored over desired forms. We describe how applications of solvent-assisted linker exchange, powder X-ray diffraction in capillaries and activation via supercritical CO2 drying, can address some of these challenges.

Sintesi e caratterizzazione di funzionalizzato metallo-organici quadri

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and ...

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 &#176;C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

A &#8220;removable ceramic coating method&#8221; is presented in visual format for the synthesis of non-sintered and metal-terminated monometallic and bimetallic early transition metal carbide and nitride nanoparticles with tunable sizes and crystal structures.

Reverse Sintesi Microemulsione mediata di Monometallic e bimetallico precoce transizione metallo carburo e nitruro di nanoparticelle

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The ...

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension.
Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries.
Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( &#820;500 mN/m to near zero). Furthermore, this method requires only a very modest potential (&#60; 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests.

We present a method to control the interfacial energy of a liquid metal in an electrolyte via electrochemical deposition (or removal) of a surface oxide layer. This simple method can control the capillary behavior of gallium-based liquid metals by tuning the interfacial energy rapidly, significantly, and reversibly using modest voltages.

Un metodo per manipolare Tensione superficiale di un metallo liquido tramite ossidazione superficiale e riduzione

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where ...

HKUST-1 as a Heterogeneous Catalyst for the Synthesis of Vanillin

Vanillin (4-hydoxy-3-methoxybenzaldehyde) is the main component of the extract of vanilla bean. The natural vanilla scent is a mixture of approximately 200 different odorant compounds in addition to vanillin. The natural extraction of vanillin (from the orchid Vanilla planifolia, Vanilla tahitiensis and Vanilla pompon) represents only 1% of the worldwide production and since this process is expensive and very long, the rest of the production of vanillin is synthesized. Many biotechnological approaches can be used for the synthesis of vanillin from lignin, phenolic stilbenes, isoeugenol, eugenol, guaicol, etc., with the disadvantage of harming the environment since these processes use strong oxidizing agents and toxic solvents. Thus, eco-friendly alternatives on the production of vanillin are very desirable and thus, under current investigation. Porous coordination polymers (PCPs) are a new class of highly crystalline materials that recently have been used for catalysis. HKUST-1 (Cu3(BTC)2(H2O)3, BTC = 1,3,5-benzene-tricarboxylate) is a very well known PCP which has been extensively studied as a heterogeneous catalyst. Here, we report a synthetic strategy for the production of vanillin by the oxidation of trans-ferulic acid using HKUST-1 as a catalyst.

The conversion of trans-ferulic acid to vanillin was achieved by heterogeneous catalysis. HKUST-1 was employed in this synthesis and the essential step in the catalytic process was the generation of unsaturated metal sites. Thus, when the catalyst was activated under vacuum, full vanillin conversion (yield of 95%) was obtained.

HKUST-1 come catalizzatore eterogeneo per la sintesi di vanillina

Vanillin (4-hydoxy-3-methoxybenzaldehyde) is the main component of the extract of vanilla bean. The natural vanilla scent is a mixture of approximately ...

Facile Synthesis of Worm-like Micelles by Visible Light Mediated Dispersion Polymerization Using Photoredox Catalyst

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins with the synthesis of a hydrophilic poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) homopolymer using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Under mild visible light irradiation (&#955; = 460 nm, 0.7 mW/cm2), this macro-chain transfer agent (macro-CTA) in the presence of a ruthenium based photoredox catalyst, Ru(bpy)3Cl2 can be chain extended with a second monomer to form a well-defined block copolymer in a process known as Photoinduced Electron Transfer RAFT (PET-RAFT). When PET-RAFT is used to chain extend POEGMA with benzyl methacrylate (BzMA) in ethanol (EtOH), polymeric nanoparticles with different morphologies are formed in situ according to a polymerization-induced self-assembly (PISA) mechanism. Self-assembly into nanoparticles presenting POEGMA chains at the corona and poly(benzyl methacrylate) (PBzMA) chains in the core occurs in situ due to the growing insolubility of the PBzMA block in ethanol. Interestingly, the formation of highly pure worm-like micelles can be readily monitored by observing the onset of a highly viscous gel in situ due to nanoparticle entanglements occurring during the polymerization. This process thereby allows for a more reproducible synthesis of worm-like micelles simply by monitoring the solution viscosity during the course of the polymerization. In addition, the light stimulus can be intermittently applied in an ON/OFF manner demonstrating temporal control over the nanoparticle morphology.

This article describes a process for producing polymeric self-assembled nanoparticles using visible light mediated dispersion polymerization. Using low energy visible light to control the polymerization allows for the reproducible formation of self-assembled worm-like micelles at high solids content.

Sintesi facile di micelle vermiforme dalla luce visibile mediata polimerizzazione in dispersione Utilizzando Photoredox Catalyst

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins ...

Synthesis of a Water-soluble Metal&#8211;Organic Complex Array

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

Sintesi di una serie complessa Metal-Organic solubile in acqua

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as ...

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing to 250 &#176;C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 &#176;C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. These techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.

&#160; The protocol describes the synthesis and electrochemical testing of platinum-nickel nanowires. Nanowires were synthesized by the galvanic displacement of a nickel nanowire template. Post-synthesis processing, including hydrogen annealing, acid leaching, and oxygen annealing were used to optimize nanowire performance and durability in the oxygen reduction reaction.

Sintesi di nanofili di platino-nichel e ottimizzazione per le prestazioni di riduzione di ossigeno

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen ...

Synthesis of a Thiol Building Block for the Crystallization of a Semiconducting Gyroidal Metal-sulfur Framework

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and porous metal-dithiolene network in the highly ordered single crystalline state. Unlike the highly reactive free-standing thiols, which tend to decompose and complicate the crystallization of metal-thiolate open frameworks, the thioester reacts in situ to provide the thiol species, serving to mitigate the reaction between the mercaptan units and the metal centers, and to improve crystallization consequently. Specifically, the thioester was synthesized in a one-pot procedure: an aromatic bromide (hexabromotriphenylene) reacted with excess sodium thiomethoxide under vigorous conditions to first form the thioether intermediate product. The thioether was then demethylated by the excess thiomethoxide to provide the thiolate anion that was acylated to form the thioester product. The thioester was conveniently purified by standard column chromatography, and then used directly in the framework synthesis, wherein NaOH and ethylenediamine serve to revert in situ the thioester to the thiol linker for assembling the single-crystalline Pb(II)-dithiolene network. Compared with other methods for thiol synthesis (e.g., by cleaving alkyl thioether using sodium metal and liquid ammonia), the thioester synthesis here uses simple conditions and economical reagents. Moreover, the thioester product is stable and can be conveniently handled and stored. More importantly, in contrast to the generic difficulty in accessing crystalline metal-thiolate open frameworks, we demonstrate that using the thioester for in situ formation of the thiol linker greatly improves the crystallinity of the solid-state product. We intend to encourage broader research efforts on the technologically important metal-sulfur frameworks by disclosing the synthetic protocol for the thioester as well as the crystalline framework solid.

Here, we present a one-pot, transition-metal-free synthesis of thiols and thioesters from aromatic halides and sodium thiomethoxide, followed by the preparation of single crystals of a metal-dithiolene network using thiol species generated in situ from the more stable and tractable thioester.

Sintesi di un tiolo Building Block per la cristallizzazione di un quadro di Gyroidal metallo-zolfo ossidi semiconduttori

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and ...

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

A rapid, direct solution-based reduction synthesis method to obtain Au, Pd, and Pt aerogels is presented.

Un metodo di sintesi rapida per Au, Pd e Pt Aerogels tramite riduzione diretta basata su soluzione

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various ...