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

Nickel Hydroxide Nanosheets의 마이크로파 합성 및 특성화

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.

저자 스포트라이트: 수산화니켈 나노시트의 신속한 마이크로파 보조 열수 합성 

마이크로파 합성 조건이 수산화니켈 나노시트의 구조에 미치는 영향

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  

α-Ni(OH)2 나노시트의 마이크로파 보조 합성

105ml의 에틸렌 글리콜과 15ml의 초순수를 혼합하여 전구체 용액 준비를 시작합니다. 그런 다음 4.1g의 요를 넣고 5.0g의 질산 니켈 육수화물을 넣고 용액을 덮습니다. 얼음과 물로 채워진 수조 초음파 발생기에서 30 분 동안 전구체 용액을 40 킬로헤르츠 주파수와 맥박이없는 최대 전력으로 초음파 처리합니다.20mL의 음파 전구체 용액을 PTFE 교반 막대가 장착된 마이크로파 반응 바이알에 옮깁니다. PTFE 라이너가 있는 잠금 뚜껑을 사용하여 반응 용기를 밀봉합니다. 마이크로파 반응기 내부에 바이알을 놓고 원하는 온도에 도달할 때까지 최대 전력을 적용하는 반응기 프로그램을 가능한 한 빨리 설정합니다.그 후, 13 내지 30분 동안 반응 온도를 유지하기 위해 가변 전력을 인가한다. 반응이 완료되면 용액 온도가 섭씨 55도에 도달할 때까지 압축 공기로 반응 챔버를 환기시킵니다. 반응 후 용액을 50밀리리터 원심분리기 튜브로 옮깁니다.튜브를 실온에서 4분 동안 원심분리하고 상층액을 디캔팅합니다. 생성 된 수산화 니켈 나노 시트를 25 밀리리터의 초순수에 재현탁시키고 이전에 설명한 대로 원심 분리기를 한 번 더 재현탁시킵니다. 상층액을 디캔팅한 후 잠재적인 오염을 최소화하기 위해 다공성 덮개 역할을 하는 티슈나 종이 타월로 원심분리기 튜브를 덮습니다.마지막으로 나노 시트를 섭씨 70도의 샘플 오븐에서 주변 분위기 하에서 21시간 동안 건조시킵니다. 섭씨 120도에서 생성된 최대 반응 압력은 제곱인치당 9 내지 11.5파운드 또는 PSI였습니다. 섭씨 180도에서는 138PSI로 증가했습니다.반응 온도를 섭씨 120도에서 180도로 높이면 반응 후 상층액 색상도 녹색에서 파란색으로 변경되었습니다. 섭씨 180도에서의 반응에 대한 C2 사진에서 반응이 종료될 때 탁한 녹색을 보였지만 반응이 냉각됨에 따라 탁한 파란색으로 바뀌었습니다. 원심분리, 세척 및 건조 후 시간과 온도에 관계없이 모든 반응에서 녹색 분말이 생성되었습니다.섭씨 180도 반응의 상층액의 pH는 섭씨 120도 반응 상층액에 비해 훨씬 높았다. 섭씨 180도의 반응은 섭씨 120도의 반응보다 훨씬 높은 수율을 기록했습니다.

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 ...