Abstract
A reliable glass capillary microfluidic method was developed for a continuous production of well-controlled gold nanoparticles (AuNPs) capped with polyvinylpyrrolidone (PVP) of different molecular weights (PVP K15, PVP K30 and PVP K90). A two-phase co-flow glass capillary microfluidic device with an injection orifice diameter ranging between 100 and 240µm was used to synthesise 100–240µm was used to synthesise AuNPs via the chemical reduction between tetrachloroaurate trihydrate (HAuCl4·3H2O) and ascorbic acid. AuNPs with an average diameter between 48 and 135nm were synthesised, as determined by DLS measurements. Decreasing the injection orifice diameter, increasing the flow rate of ascorbic acid stream and its pH resulted in smaller AuNPs. The polydispersity index (PDI) was found to be independent on the injection orifice diameter or the molecular weight of PVP, but increased with the increase of flow rate and the pH of ascorbic acid stream. The stability study over 6-week period confirmed that PVP K30 with an average Mw of 40000g/mol was the best capping agent to synthesize and stabilise smaller AuNPs. The reactor fouling due to deposition of AuNPs on reactor walls and orifices was mitigated by hydrophobization of reactor/capillary walls with octadecyltrimethoxisilane and the use of ascorbic acid solution of higher pH.
Highlights
NaBH4 reacts with water and generates hydrogen, which forms bubbles in the microfluidic channels that interfere with the flow pattern and interrupt or affect the continuous production of AuNPs and inherently their properties
Compared to bulk and batch methods, continuous microfluidic devices offer an enhanced control over mixing, which in-turn enables a better control of both nucleation and growth and in agreement with the classical nucleation theory, the size distribution of the synthesized NPs can be precisely tuned
Polyvinylpyrrolidone (PVP) capped AuNPs were synthesized in a continuous co-flow microfluidic device made out of coaxially aligned borosilicate glass capillaries, using ascorbic acid as the reducing agent and tetrachloroaurate(III) ions as the gold precursor
Summary
Polyvinylpyrrolidone (PVP) capped AuNPs were synthesized in a continuous co-flow microfluidic device made out of coaxially aligned borosilicate glass capillaries, using ascorbic acid as the reducing agent and tetrachloroaurate(III) ions as the gold precursor. To the best of our knowledge, this is the first application of glass capillary microfluidic devices for the synthesis of size-tailored AuNPs. The effect of operating and geometrical parameters on the size and polydispersity of the produced AuNPs has been investigated, such as orifice diameter of the injection capillary, pH of the ascorbic acid stream, flow rates of the reactant streams, and the type of capping agent
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