PKNANONAUTS

Seawater-driven magnesium based Janus micromotors for environmental remediation

http://pubs.rsc.org/en/content/articlelanding/2013/nr/c3nr01458d#!divAbstract

• 논문 point

  • describe the use of seawater as fuel to propel Janus micromotors

  • magnesium microparticles and a nickel-gold bilayer patch : biodegradable and enviromentally friendly

  • macrogalvanic corrosion, chloride pitting corrosion process 사용

    • galvanic corrosion : refers to corrosion damage induced when two dissimilar materials are coupled in a corrosive electrolyte. 
      When a galvanic couple forms, one of the metals in the couple becomes the anode and corrodes faster than it would all by itself, while the other becomes the cathode and corrodes slower than it would alone.[2]

    • chloride pitting corrosion : is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading to very localized galvanic corrosion. The corrosion penetrates the mass of the metal, with limited diffusion of ions.[3]
      cf.passivation : 표면 부동상태 , 표면이 잘 부식되지 않게 되는 상태

• 원리

 

-Ni 등의 자기층을 가지면 마이크로파티클을 수집하거나, 운반 및 풀어놓을 수 있는 장소로 인도할 수 있게됨.

Mg(s) + 2H2O(aq) / Mg(OH)2(s) + H2(g)

2Mg+(aq)+2H2O(aq)/2Mg2+(aq)+2OH�(aq)+H2(g) 

• Mg particles have an average size of ~30μm, asymmetrically coated by e-beam evaporation with Ti, Ni and Au layers => Janus micromotors

• immersion into seawater -> 자발적인 산화 환원 반응이 일어남 : 산화=Mg 표면, 환원=H2O->H2기체

• gold layer과 chloride ions에 의해 반응이 진행 : H2 bubble이 계속적으로 만들어져서 microparticles을 나아가게함 

 

• self-propelled , speed = 90μm/s

• magnetic guidance가 micromotor 조종 => sharp and rapid turns , travels in a square pattern

 

-Ni 등의 자기층을 가지면 마이크로파티클을 수집하거나, 운반 및 풀어놓을 수 있는 장소로 인도할 수 있게됨.