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

Síntese de Microondas e Caracterização de Nanofolhas 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 em destaque: uma síntese hidrotermal rápida e assistida por microondas de nanofolhas de hidróxido de níquel 

Efeito das Condições de Síntese por Micro-ondas na Estrutura de Nanofolhas 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  

Síntese assistida por micro-ondas de nanofolhas de α-Ni(OH)2

Comece a preparar a solução precursora misturando 105 mililitros de etilenoglicol e 15 mililitros de água ultrapura. Em seguida, adicione 4,1 gramas de uria e adicione 5,0 gramas de hexahidrato de nitrato de níquel e cubra a solução. Sonicar a solução precursora por 30 minutos em um sonicador de banho cheio de gelo e água na frequência de 40 kilohertz e potência total sem pulso.Transfira 20 mililitros da solução precursora sónica para um frasco para injetáveis de reacção de micro-ondas equipado com uma barra de agitação de PTFE. Sele o recipiente de reação usando uma tampa de travamento com um forro de PTFE. Coloque o frasco para injetáveis dentro do reator de micro-ondas e ajuste o programa do reator para o mais rápido possível, que aplica a potência máxima até que a temperatura desejada seja atingida.Em seguida, aplicar potência variável para manter a temperatura de reação por 13 a 30 minutos. Após a conclusão da reação, ventile a câmara de reação com ar comprimido até que a temperatura da solução atinja 55 graus Celsius. Transfira a solução pós-reação para tubos de centrífuga de 50 mililitros.Centrifugar os tubos à temperatura ambiente durante quatro minutos e decantar o sobrenadante. Ressuspenda as nanofolhas de hidróxido de níquel resultantes em 25 mililitros de água ultrapura e centrífuga mais uma vez, como demonstrado anteriormente. Depois de decantar o sobrenadante, cubra os tubos da centrífuga com um lenço de papel ou papel toalha que sirva como uma cobertura porosa para minimizar a contaminação potencial.Finalmente, seque as nanofolhas sob uma atmosfera ambiente em um forno de amostra a 70 graus Celsius por 21 horas. A 120 graus Celsius, a pressão máxima de reação gerada foi de nove a 11,5 libras por polegada quadrada ou PSI. Enquanto a 180 graus Celsius, aumentou para 138 PSI.O aumento da temperatura de reação de 120 para 180 graus Celsius também mudou a cor sobrenadante pós-reação de verde para azul. Em fotografias C2 da reação a 180 graus Celsius mostraram uma cor verde turva quando a reação terminou, mas mudou para azul turvo à medida que a reação esfriou. Após centrifugação, lavagem e secagem, todas as reações, independentemente do tempo e da temperatura, produziram um pó verde.O pH do sobrenadante da reação de 180 graus Celsius foi muito maior em relação aos sobrenadantes da reação de 120 graus Celsius. A reação de 180 graus Celsius também registrou um rendimento muito maior do que as reações a 120 graus 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 ...

Química

Characterization and Analysis of &#945;-Ni(OH)2 Nanosheets

Characterization and Analysis of &#945;-Ni(OH)2 Nanosheets  

Caracterização e Análise de Nanofolhas de α-Ni(OH)2