Name: Microwave-Assisted Synthesis of &#945;-Ni(OH)2 Nanosheets
Uploaded: 2023-08-18T14:20:00
Description: Watch this Scientific Journal Video about Microwave-Assisted Synthesis of α-NiOH2 Nanosheets at JoVE.com

microwave-assisted synthesis of &#945;-ni(oh)2 nanosheets

Mikrobølgesyntese og karakterisering af nikkelhydroxid-nanoplader

Nickel hydroxide, Ni(OH)2, is used for numerous applications including nickel-zinc and nickel-metal hydride batteries1,2,3,4, fuel cells4, water electrolyzers4,5,6,7,8,9, supercapacitors4, photocatalysts4, anion exchangers10, and many other analytical, electrochemical, and sensor applications4,5. Ni(OH)2 has two predominant crystal structures: &#946;-Ni(OH)2 and &#945;-Ni(OH)211. &#946;-Ni(OH)2 adopts a brucite-type Mg(OH)2 crystal structure, while &#945;-Ni(OH)2 is a turbostratically layered form of &#946;-Ni(OH)2 intercalated with residual anions and water molecules from the chemical synthesis4. Within &#945;-Ni(OH)2, the intercalated molecules are not within fixed crystallographic positions but have a degree of orientational freedom, and also function as an interlayer glue stabilizing the Ni(OH)2 layers4,12. The interlayer anions of &#945;-Ni(OH)2 affect the average Ni oxidation state13 and influence the electrochemical performance of &#945;-Ni(OH)2 (relative to &#946;-Ni(OH)2) toward battery2,13,14,15, capacitor16, and water-electrolysis applications17,18.
Ni(OH)2 can be synthesized by chemical precipitation, electrochemical precipitation, sol-gel synthesis, or hydrothermal/solvothermal synthesis4. Chemical precipitation and hydrothermal synthesis routes are widely utilized in the production of Ni(OH)2, and different synthetic conditions alter the morphology, crystal structure, and electrochemical performance. The chemical precipitation of Ni(OH)2 involves adding a highly basic solution to an aqueous nickel (II) salt solution. The phase and crystallinity of the precipitate are determined by the temperature and&#160;identities&#160;and concentrations of the nickel (II) salt and&#160;basic solution used4.
Hydrothermal synthesis of Ni(OH)2 involves heating an aqueous solution of precursor nickel (II) salt in a pressurized reaction vial, allowing the reaction to proceed at higher temperatures than ordinarily allowed under ambient pressure4. Hydrothermal reaction conditions typically favor &#946;-Ni(OH)2, but &#945;-Ni(OH)2 can be synthesized by (i) using an intercalation agent, (ii) using a non-aqueous solution (solvothermal synthesis), (iii) lowering the reaction temperature, or (iv) including urea in the reaction, resulting in ammonia-intercalated &#945;-Ni(OH)24. The hydrothermal synthesis of Ni(OH)2 from nickel salts occurs via a two-step process that involves a hydrolysis reaction (equation 1) followed by an olation condensation reaction (equation 2).19
[Ni(H2O)N]2+ + hH2O &#8596; [Ni(OH)h(H2O) N-h](2-h)++ hH3O+ (1)
Ni-OH + Ni-OH2 Ni-OH-Ni + H2O (2)
Microwave chemistry has been used for the one-pot synthesis of a wide variety of nanostructured materials and is based on the ability of a specific molecule or material to convert microwave energy into heat20. In conventional hydrothermal reactions, the reaction is initiated by the direct absorption of heat through the reactor. In contrast, within microwave-assisted hydrothermal reactions, the heating mechanisms are dipolar polarization of the solvent oscillating in a microwave field and ionic conduction generating localized molecular friction20. Microwave chemistry can increase the reaction kinetics, selectivity, and yield of chemical reactions20, making it of significant interest for a scalable, industrially viable method to synthesize Ni(OH)2.
For alkaline battery cathodes, the &#945;-Ni(OH)2 phase provides improved electrochemical capacity compared with the &#946;-Ni(OH)2 phase13, and synthetic methods to synthesize &#945;-Ni(OH)2 are of particular interest. &#945;-Ni(OH)2 has been synthesized by a variety of microwave-assisted methods, which include microwave-assisted reflux21,22, microwave-assisted hydrothermal techniques23,24, and microwave-assisted base-catalyzed precipitation25. The inclusion of urea within the reaction solution significantly influences the reaction yield26, mechanism26,27, morphology, and crystal structure27. The microwave-assisted decomposition of urea was determined to be a critical component for obtaining &#945;-Ni(OH)227. Water content in an ethylene glycol-water solution has been shown to impact the morphology of microwave-assisted synthesis of &#945;-Ni(OH)2 nanosheets24. The reaction yield of &#945;-Ni(OH)2, when synthesized by a microwave-assisted hydrothermal route using an aqueous nickel nitrate and urea solution, was found to depend on the solution pH26. A prior study of microwave synthesized &#945;-Ni(OH)2 nanoflowers using a precursor solution of EtOH/H2O, nickel nitrate, and urea found that temperature (in the range of 80-120 &#176;C) was not a critical factor, provided the reaction is conducted above the urea hydrolysis temperature (60 &#176;C)27. A recent paper that studied the microwave synthesis of Ni(OH)2 using a precursor solution of nickel acetate tetrahydrate, urea, and water found that at a temperature of 150 &#176;C, the material contained both &#945;-Ni(OH)2 and &#946;-Ni(OH)2 phases, which indicates that temperature can be a critical parameter in the synthesis of Ni(OH)228.
Microwave-assisted hydrothermal synthesis can be used to produce high-surface area &#945;-Ni(OH)2 and &#945;-Co(OH)2 by using a precursor solution composed of metal nitrates and urea dissolved in an ethylene glycol/H2O solution12,29,30,31. Metal-substituted &#945;-Ni(OH)2 cathode materials for alkaline Ni-Zn batteries were synthesized using a scaled-up synthesis designed for a large-format microwave reactor12. Microwave-synthesized &#945;-Ni(OH)2 was also used as a precursor for obtaining &#946;-Ni(OH)2 nanosheets12, nickel-iridium nanoframes for oxygen evolution reaction (OER) electrocatalysts29, and bifunctional oxygen electrocatalysts for fuel cells and water electrolyzers30. This microwave reaction route has also been modified to synthesize Co(OH)2 as a precursor for cobalt-iridium nanoframes for acidic OER electrocatalysts31 and bifunctional electrocatalysts30. Microwave-assisted synthesis was also used to produce Fe-substituted &#945;-Ni(OH)2 nanosheets, and the Fe substitution ratio alters the structure and magnetization32. However, a step-by-step procedure for microwave synthesis of &#945;-Ni(OH)2 and the evaluation of how varying reaction time and temperature within a water-ethylene glycol solution affects the crystalline structure, surface area, and porosity, and local environment of interlayer anions within the material&#160;has not been previously reported.
This protocol establishes procedures for high-throughput microwave synthesis of &#945;-Ni(OH)2 nanosheets using a rapid and scalable technique. The effect of reaction temperature and time were varied and evaluated using in situ reaction monitoring, scanning electron microscopy, energy dispersive X-ray spectroscopy, nitrogen porosimetry, powder X-ray diffraction (XRD), and Fourier transform infrared spectroscopy to understand the effects of synthetic variables on reaction yield, morphology, crystal structure, pore size, and local coordination environment of &#945;-Ni(OH)2 nanosheets.

Forfatter Spotlight: En hurtig, mikrobølgeassisteret hydrotermisk syntese af nikkelhydroxid-nanoark 

Effekt af mikrobølgesyntesebetingelser på strukturen af nikkelhydroxidnanoark

Watch this Scientific Journal Video about Microwave-Assisted Synthesis of α-NiOH2 Nanosheets at JoVE.com

Microwave-Assisted Synthesis of &#945;-Ni(OH)2 Nanosheets  

Mikrobølgeassisteret syntese af α-Ni (OH) 2 nanoark

Begynd at forberede forløberopløsningen ved at blande 105 ml ethylenglycol og 15 ml ultrarent vand. Derefter tilsættes 4,1 gram uria og tilsættes 5,0 gram nikkelnitrathexahydrat, og dæk opløsningen. Sonikere forløberopløsningen i 30 minutter i et bad sonikator fyldt med is og vand ved 40 kilohertz frekvens og fuld effekt uden puls.Overfør 20 ml af den soniske prækursoropløsning til et hætteglas med mikrobølgereaktion udstyret med en PTFE-omrøringsstang. Reaktionsbeholderen forsegles ved hjælp af et låselåg med en PTFE-foring. Placer hætteglasset inde i mikrobølgereaktoren, og indstil reaktorprogrammet til så hurtigt som muligt, hvilket anvender maksimal effekt, indtil den ønskede temperatur er opnået.Anvend derefter variabel effekt for at opretholde reaktionstemperaturen i 13 til 30 minutter. Efter afslutningen af reaktionen udluftes reaktionskammeret med trykluft, indtil opløsningstemperaturen når 55 grader Celsius. Efterreaktionsopløsningen overføres til 50 ml centrifugerør.Glassene centrifugeres ved stuetemperatur i fire minutter, og supernatanten dekanteres. Resuspender de resulterende nikkelhydroxid nanoplader i 25 ml ultrarent vand og centrifuger igen som tidligere vist. Efter dekantering af supernatanten dækkes centrifugeglassene med et serviet- eller papirhåndklæde, der fungerer som porøst dæksel, for at minimere potentiel kontaminering.Til sidst tørres nanopladerne under en omgivende atmosfære i en prøveovn ved 70 grader Celsius i 21 timer. Ved 120 grader Celsius var det maksimale genererede reaktionstryk ni til 11,5 pund pr. Kvadrattomme eller PSI. Mens det ved 180 grader Celsius steg til 138 PSI.Forøgelse af reaktionstemperaturen fra 120 til 180 grader Celsius ændrede også supernatantfarven efter reaktionen fra grøn til blå. I C2 viste fotografier af reaktionen ved 180 grader Celsius en grumset grøn farve, da reaktionen sluttede, men den ændrede sig til grumset blå, da reaktionen afkøledes. Efter centrifugering, vask og tørring frembragte alle reaktionerne, uanset tid og temperatur, et grønt pulver.PH-værdien i supernatanten ved 180 grader Celsius-reaktionen var meget højere i forhold til 120 grader Celsius-reaktionssupernatanterne. 180 graders Celsius-reaktionen registrerede også et meget højere udbytte end reaktionerne ved 120 grader Celsius.

Research

JoVE Journal

Chemistry

Microwave-Assisted Synthesis of &#945;-Ni(OH)2 Nanosheets

Effect of Microwave Synthesis Conditions on the Structure of Nickel Hydroxide Nanosheets

A protocol for rapid, microwave-assisted hydrothermal synthesis of nickel hydroxide nanosheets under mildly acidic conditions is presented, and the effect ...