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

Síntesis y caracterización por microondas de nanohojas de hidróxido de níquel

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.

Autor destacado: Una síntesis hidrotermal rápida asistida por microondas de nanohojas de hidróxido de níquel 

Efecto de las condiciones de síntesis de microondas en la estructura de nanoláminas de hidróxido de níquel

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  

Síntesis asistida por microondas de nanohojas de α-Ni(OH)2

Comience a preparar la solución precursora mezclando 105 mililitros de etilenglicol y 15 mililitros de agua ultrapura. Luego agregue 4.1 gramos de uria y agregue 5.0 gramos de nitrato de níquel hexahidratado, y cubra la solución. Sonicar la solución precursora durante 30 minutos en un sonicador de baño lleno de hielo y agua a una frecuencia de 40 kilohercios y a plena potencia sin pulso.Transfiera 20 mililitros de la solución precursora sónica a un vial de reacción de microondas equipado con una barra agitadora de PTFE. Selle el recipiente de reacción con una tapa de bloqueo con un revestimiento de PTFE. Coloque el vial dentro del reactor de microondas y configure el programa del reactor lo más rápido posible, que aplica la máxima potencia hasta alcanzar la temperatura deseada.A partir de entonces, aplique potencia variable para mantener la temperatura de reacción durante 13 a 30 minutos. Una vez completada la reacción, ventile la cámara de reacción con aire comprimido hasta que la temperatura de la solución alcance los 55 grados centígrados. Transfiera la solución posterior a la reacción a tubos de centrífuga de 50 mililitros.Centrifugar los tubos a temperatura ambiente durante cuatro minutos y decantar el sobrenadante. Vuelva a suspender las nanoláminas de hidróxido de níquel resultantes en 25 mililitros de agua ultrapura y centrifugue una vez más como se demostró anteriormente. Después de decantar el sobrenadante, cubra los tubos de la centrífuga con un pañuelo de papel o una toalla de papel que sirva como cubierta porosa para minimizar la posible contaminación.Finalmente, seque las nano láminas a temperatura ambiente en un horno de muestra a 70 grados centígrados durante 21 horas. A 120 grados Celsius, la presión máxima de reacción generada fue de nueve a 11.5 libras por pulgada cuadrada o PSI. Mientras que a 180 grados centígrados, aumentó a 138 PSI.El aumento de la temperatura de reacción de 120 a 180 grados Celsius también cambió el color del sobrenadante posterior a la reacción de verde a azul. En C2, las fotografías de la reacción a 180 grados Celsius mostraron un color verde turbio cuando terminó la reacción, pero cambió a azul turbio a medida que la reacción se enfrió. Después de la centrifugación, el lavado y el secado, todas las reacciones, independientemente del tiempo y la temperatura, produjeron un polvo verde.El pH del sobrenadante de la reacción de 180 grados Celsius fue mucho más alto en relación con los sobrenadantes de la reacción de 120 grados Celsius. La reacción a 180 grados Celsius también registró un rendimiento mucho mayor que las reacciones a 120 grados 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 ...