Ultrasonic Wet-Precipitation of Prussian Blue Nanocubes

Prussian Blue or iron hexacyanoferrate is a nano-structured metal organic framework (MOF), that is used in sodium‐ion battery manufacturing, biomedicine, inks and electronics. Ultrasonic wet-chemical synthesis is efficient, reliable and rapid pathway to produce Prussian Blue nanocubes and Prussian blue analogues such as copper hexacyanoferrate and nickel hexacyanoferrate. Ultrasonically precipitated Prussian Blue nanoparticles are characterised by narrow particle size distribution, mono-dispersity and high functionality.

Prussian Blue and Hexacyanoferrate Analogues

Prussian Blue or iron hexacyanoferrates are widely used as as a functional material to design electrochemical applications and to manufacture chemical sensors, electrochromic displays, inks and coatings, batteries (sodium‐ion batteries), capacitors and supercapacitors, cation storage materials such as for H+ or Cs+, catalysts, theranostics and others. Due to its good redox activity and high electrochemical stability, Prussian Blue is a metal-organic framework (MOF) structure that is used widely for electrode modification.
Besides various other applications, Prussian Blue and its analogues copper hexacyanoferrate and nickel hexacyanoferrate are used as colour inks of blue, red and yellow colour, respectively.
A huge advantage of Prussian Blue nanoparticles is their safety. Prussian Blue nanoparticles are fully biodegradable, biocompatible, and approved by FDA for medical applications.

Sonochemical Synthesis of Prussian Blue Nanocubes

The synthesis of Prussian Blue / hexacyanoferrite nanoparticles is reaction of heterogeneous wet-chemical precipitation. In order to obtain nanoparticles with a narrow particle size distribution and monodispersity, a reliable precipitation route is required. Ultrasonic precicipitation is well known for the reliable, efficient and simple synthesis of high-quality nanoparticles and pigments such as magnetite, zinc molybdate, zinc phosphomolybdate, various core-shell nanoparticles etc.

Wet-Chemical Synthesis Routes for Prussian Blue Nanoparticles

The sonochemical route of Prussian Blue nanoparticle synthesis is efficient, facile, rapid and environmental-friendly. Ultrasonic precipitation yields in high-quality Prussian Blue nanocubes, which are characterised by uniform small size (approx. 5nm), narrow size distribution, and monodispersity.
Prussian Blue nanoparticles can be synthesized via various precipitation routes with or without polymeric stabilisers.
Avoiding the use of a stabilizing polymer, Prussian Blue nanocubes can be precipitated simply by ultrasonically mixing FeCl₃ and K₃[Fe(CN)₆] in presence of H₂O₂.
The use of sonochemistry in this kind of synthesis helped obtaining smaller nanoparticles (i.e., 5 nm in size instead of a size of ≈50 nm obtained without sonication). (Dacarro et al. 2018)

Case Studies of Ultrasonic Prussian Blue Synthesis

Generally, Prussian blue Nanoparticles are synthesized by employing ultrasonication method.
In this technique, 0.05 M solution of K₄[Fe(CN)₆] is added to 100 ml of hydrochloric acid solution of (0.1 mol/L). The resulting K₄[Fe(CN)₆] aqueous solution is kept at 40ºC for 5 h whilst sonicating the solution and then allowed to cool at room temperature. The obtained blue product is filtered and washed repeatedly with distilled water and absolute ethanol and finally dried in a vacuum oven at 25ºC for 12 h.

The hexacyanoferrite analogue copper hexacyanoferrite (CuHCF) was synthesised via following route:
The CuHCF nanoparticles were synthesized as per the following equation:
Cu(NO₃)₃ + K₄[Fe(CN)₆] –> Cu₄[Fe(CN)₆] + KN0₃

CuHCF nanoparticles are synthesized by the method developed by Bioni et al., 2007. The mixture of 10 mL of 20 mmol L^-1 K₃[Fe(CN)₆] + 0.1 mol L^-1 KCl solution with 10 mL of 20 mmol L^-1 CuCl₂ + 0.1 mol L^-1 KCl, in an sonication flask. The mixture is then irradiated with high intensity ultrasound radiation for 60 min, employing a direct immersion titanium horn (20 kHz, 10Wcm^-1) that was dipped till a depth of 1 cm into the solution. During the mixture, the appearance of a light-brown deposit is observed. This dispersion is dialysed over 3 days in order to obtain a very stable, light-brown coloured dispersion.
(cf. Jassal et al. 2015)

Wu et al. (2006) synthesised Prussian Blue nanoparticles via sonochemical route from K₄[Fe(CN)₆], in which Fe2+ was produced by the decomposition of [FeII(CN)6]4− by ultrasonic irradiation in hydrochloric acid; the Fe²⁺ was oxidized to Fe³⁺ to react with remaining [FeII(CN)₆]4− ions. The research group concluded that the uniform size distribution of synthesized Prussian blue nanocubes is caused by the effects ultrasonication. The FE-SEM image on the left shows sonochemically synthesized iron hexacyanoferrate nanocubes by Wu’s research group.

Large-scale synthesis: to prepare PB nanoparticles on a large-scale, PVP (250 g) and K₃[Fe(CN)₆] (19.8 g) were added into 2,000 mL of HCl solution (1 M). The solution was sonicated until clear and then placed in an oven at 80°C to achieve an ageing reaction for 20–24 hours. The mixture was then centrifuged at 20,000 rpm for 2 hours for the collection of PB nanoparticles. (Safety note: In order to expel any HCN created, the reaction should be carried out in a fume hood).

Sono-Electrochemical Synthesis of Prussian Blue

Another highly efficient synthesis technique for Prussian Blue is the sono-electrochemical route, which synergistically combines electrochemical deposition with high-intensity ultrasound. This method enhances mass transport, accelerates nucleation kinetics, and promotes uniform nanoparticle formation through cavitation-induced micro-mixing and surface activation. This makes the sono-electrochemical Prussian Blue synthesis a reliable pathway for the industrial production of nanoscale Prussian Blue.
Read more about the sono-electrochemical setup for Prussian Blue synthesis!

Ultrasonic Probes and Sonochemical Reactors for Prussian Blue Synthesis

Hielscher Ultrasonics is long-termed experiences manufacturer of high-performance sonicators that are used worldwide in research laboratories and industrial production. The sonochemical synthesis and precipitation of nanoparticles and pigments is a demanding application that requires high-power ultrasonic probes which generate constant amplitudes. All Hielscher sonicators are designed and manufactured to be operated for 24/7 under full load. Ultrasonic processors are available from compact 50 watts ultrasonic probes to 16,000 watts powerful inline ultrasonic reactors. A wide variety of booster horns, sonotrodes and flow cells allow for the individual setup of an sonochemical system in correspondence to the precursors, pathway and final product.

Sonochemical Synthesis – Batch or Inline Tailored to Your Needs

Hielscher ultrasonic probes can be used for batch and continuous inline sonication. Depending on reaction volume and reaction speed, we will recommend you the most suitable ultrasonic setup. Lab, bench-top, pilot and fully-industrial sonicators allow the processing of any volume.

Highest Quality Standards – Designed and Manufactured in Germany

As a family-owned and family-run business, Hielscher prioritizes highest quality standards for its ultrasonic processors. All ultrasonicators are designed, manufactured and thoroughly tested in our headquarter in Teltow near Berlin, Germany. Robustness and reliability of Hielscher ultrasonic equipment make it a work horse in your production. 24/7 operation under full load and in demanding environments is a natural characteristic of Hielscher high-performance ultrasonic probes and reactors.

The table below gives you an indication of the approximate processing capacity of our ultrasonicators: