AN APPARATUS AND METHOD FOR PREPARATION OF METAL NANOPARTICLES

Field of the invention

[0001] The present application relates to an apparatus and a method for the manufacture of nanoparticles. In more detail, the present application relates to an apparatus and a method that employs a spinning disk-spinning bowl (SD-SB) reactor for the rapid synthesis of nanoparticles.

Background of the invention

[0002] Nanoparticles possess huge surface areas and high chemical activities, which make them suitable for many applications such as non-volatile memory devices, transducers in chemo-resistive sensors, among others. Gold nanoparticles have many medical applications, where these particles are used to detect toxins, pathogens and cancers, and life sciences applications such as labeling, delivery, heating, and sensing.

[0003] Presently, there exist barriers to high throughput production by chemical means of uniformly-sized nanoparticles.

[0004] Several types of reactors are known and are in use for mixing and reacting reagents to form soluble and/or precipitated products such as nanoparticles. Stirred tank reactors, tubular reactors, and micro-channel reactors with radially inter-digitated, Y, and T mixers are employed for facilitating precipitation for production of nanoparticles. In stirred tank reactors, the energy input is provided using an impeller. Such arrangement may suffer from high energy losses due to friction, macro-agitation, among other factors. In addition, stirred tank reactors produce particles with large polydispersity due to back-mixing. Micro-channel reactors typically require high-pressure drops to maintain flow through the narrow channels and/or suffer on account of choking of channels due to the deposition of nanoparticles on channel walls. Another known reactor is a spinning disk reactor (SDR) employed for process intensification in precipitation reactions. Typically, such reactors include a rotating or spinning surface like a rotating disk, onto which one or more liquid reactants are supplied. Centrifugal forces cause the reactants to pass outwardly across the surface in the form of a film. They are more energy efficient as compared to micro-channel reactors at a given throughput and are easier to fabricate and operate.

Spinning dis1: reactors have been used for synthesis of nanoparticles of barium sulphate, barium carbonate, magnesium hydroxide and zinc oxide. Unfortunately, contacting of highly reactive streams using such reactors may result in formation of substantially large sized particles owing to low rate of mixing. Synthesis of gold nanoparticles using this reactor, with two precursor streams introduced on the spinning disk, leads to formation of quite large size aggregated particles.

[0005] It is therefore desirable to provide a high-yield reactor for contacting reactive streams, with low back-mixing and no clogging related problems, so as to use it in applications such as continuous production of nanoparticles.

[0006] It is also desirable to design a high-yield reactor, free from wall deposition related problems, for synthesis of uniformly-sized nanoparticles.

Objects of the present invention

[0007] The object of the present invention is to provide an apparatus, which is a high-yield reactor, for synthesis of uniformly-sized nanoparticles, in continuous mode of production at low energy input.

[0008] An aspect of the present invention is to provide an apparatus that employs a spinning disk-spinning bowl (SD-SB) reactor to rapidly synthesize nanoparticles.

[0009] It is an aspect of the present invention is to provide an apparatus, which is a high-yield spinning disk-spinning bowl (SD-SB) reactor that is free from choking problems, for the rapid synthesis of nanoparticles in continuous mode of production and at low energy input.

[0010] Another aspect of the present invention is to provide an apparatus, which is a high-yield spinning disk-spinning bowl (SD-SB) reactor that combines a centrifugal acceleration with a sweeping flow to carry nuclei away from the point of contact of precursor streams, to generate small size mono-disperse nanoparticles.

[0011] Still another aspect of the present invention is to provide an apparatus, which is a high-yield spinning disk-spinning bowl (SD-SB) reactor, to synthesize nanoparticles from at least two precursor streams.

[0012] Further aspect of the present invention is to provide an apparatus, which is a high-yield spinning disk-spinning bowl (SD-SB) reactor that enhances mixing between the reacting precursors, leading to synthesis of nanoparticles with controlled size and shape.

[0013] It is also an aspect of the present invention to provide an apparatus that provides a rapid synthesis of nanoparticles, in a continuous fashion, using the spinning disk-spinning bowl (SD-SB) reactor that results in smaller and more uniform particles as compared to the continuous-stirred tank reactor and spinning disk reactors.

[0014] Another aspect of the present invention is to provide a spinning disk- spinning bowl (SD-SB) reactor that facilitates synthesis of substantially uniform sub-10 nm nanoparticles, while enabling a high processing rate (about ten times) as compared to known reactors that are commonly employed for such purposes.

Summary of the present invention

[0015] A spinning disk-spinning bowl (SD-SB) reactor is disclosed for the rapid synthesis of nanoparticles. The spinning disk-spinning bowl (SD-SB) reactor provides for rapid synthesis of nanoparticles in a continuous fashion that results in smaller and more uniform nanoparticles. The reactor includes platforms to which prime movers with rotatable shafts, which are connected to a rotatable reaction chamber, having reaction zones. A spinning disk connected to one of the rotatable shafts and disposed in the rotatable reaction chamber. Conduits are disposed to inject precursors into the rotatable reaction chamber from different entry points. A collector with an outlet is connected to the rotatable reaction chamber to collect the nanoparticles.

Brief Description of the drawings

FIG 1 is an isometric view of spinning disk-spinning bowl (SD-SB) reactor of the present invention in vertical orientation.

FIG 2 is an isometric view of spinning disk-spinning bowl (SD-SB) reactor of the present invention depicting a rotatable reaction chamber in non-uniform configuration.

FIG 3 is a cross-sectional view of the spinning disk-spinning bowl (SD-SB) reactor of the present invention illustrating the flow of precursor feeds and reaction zones.

FIG 4 is a cross-sectional view of the spinning disk-spinning bowl (SD-SB) reactor of the present invention depicting an inner reaction chamber with perforations.

FIG 5 is a cross-sectional view of the spinning disk-spinning bowl (SD-SB) reactor of the present invention with two spinning disks.

FIG 6 is a cross-sectional view of the spinning dis.k-spinning bowl (SD-SB) reactor of the present invention with a single spinning disk.

FIG 7 is a cross-sectional view of the spinning disk-spinning bowl (SD-SB) reactor in a horizontal orientation.

Detailed description of the invention

[0016] An apparatus according to one embodiment of the present invention, depicted in FIGl, which is an isometric view of spinning disk-spinning bowl (SD-SB) reactor of the present invention, includes a rotatable reaction chamber 101, which is arranged in between a first platform 102 and a second platform 103, as hereinafter described. In an aspect of the present invention, the rotatable reaction chamber 101 is positioned vertically to ground axis GA. The rotatable reaction chamber 101 acts a spinning bowl (SB), where the precursors feeds, as hereinafter described, enter and react in the synthesis of the desired nanoparticles. The rotatable reaction chamber 101 is a hollow cylindrical chamber with first and second portions. The first portion acts a bottom surface for the rotatable reaction chamber 101, in case of the vertical orientation of the reactor to a ground axis GA as shown in FIG. 1. The second portion of the rotatable reaction chamber 101 is with an open end and the open end may be covered with a suitable lid or cover (not shown in the Figure), in case of any such need. The cross-section of the reaction chamber 101 is uniformly cylindrical, with a desired internal storage and reaction space. The internal storage and reaction space can be suitably varied or increased, subject to manufacturers' or users' requirements. The rotatable chamber 101 is disposed to rotate on its axis, both in clockwise and counter clockwise directions 'd'.

[0017] The rotatable reaction chamber 101 is equipped with other conventional elements to facilitate reaction process, such as heating and pressure systems, with temperature and pressure monitoring devices, for maintaining a desired level of temperature and pressure inside the rotatable reaction chamber 101.

[0018] In an aspect of the present invention, the rotatable reaction chamber 101 is made of metallic or non-metallic materials such as steel, alloys of metal, polymer, ceramic or any material having anti-corrosion properties and do not degrade at high temperatures. The rotatable reaction chamber 101 can also be made from a combination of polymeric and metallic materials that can withstand the chemical and physical parameters of the reactors of this nature.

[0019] In the case of corrosive streams, the inner surface of the rotatable reaction chamber 101 is preferably provided with a suitable anti-corrosion treatment without altering wetting character of the inner surface.

[0020] In one aspect of the present invention, the rotatable reaction chamber 101 is covered with a jacket made of suitable material, on its body to maintain and regulate the temperature conditions inside the reaction chamber 101, during the course of reaction.

[0021] A collector 105 is circumferentially arranged on the periphery of the distal portion of the rotatable reaction chamber 101 to collect the reacted products from the reaction chamber 101. The collector 105 provides a circumferential room or a temporary collecting space on the top surface of the rotatable chamber 101 for the collection of the end products (nanoparticles) that reach the upper region of the reaction chamber 101 due to centrifugal motion of the precursor reactants. The collector 105 is arranged in manner that it is stationary and does not rotate along with rotatable reaction chamber 101, during the course of reaction process. It is also within the purview of this invention to use a rotatable collector 105, without hampering the reaction dynamics of the reacted products as collected in the collector 105.

[0022] At least an exit port 106 is connected to the collector 105 that acts as an outlet, to facilitate the egress of reacted products (nanoparticles) from the collector 105.

[0023] A first prime mover 107 is connected to the first platform 102, as shown in FIGl. The first prime mover 107 is an electro-mechanical device, such as a motor having a rotor. The first prime mover 107 is equipped with rotary capacities to rotate the rotatable reaction chamber 101, to generate a desired centrifugal acceleration to reactants (precursor feeds) present in the rotatable reaction chamber 101. The first prime mover 107 can be a variable speed motor having speed capacities in the range of 800-5000 rpm, preferably in the range of 1000-4000 rpm.

[0024] A central pass-through hole 104 is arranged on the first platform 102 and a pass-through hole 104a is provided at the central region of the bottom portion of the rotatable reaction chamber 101. The pass-through hole 104a is co-axial to the central passage hole 104 of the first platform 102.

[0025] A first rotatable shaft 108 is connected to the first prime mover 107 and arranged vertically to the ground axis GA, to extend towards the bottom portion of the rotatable reaction chamber 101. The rotatable first shaft 108 extending from the first prime mover 107 through the pass-through holes 104 and 104a, is rotatably abutted to the rotatable reaction chamber 101. The rotation of the rotatable first shaft 108 actuates the rotary motion of the rotatable reaction chamber 101.

[0026] The rotatable first shaft 108 is hollow and provided with a tubular cross- secfion and having a first conduit 109, rotates about an axis and in a direcfion 'd'. The rotation of the first shaft 108 can be a clock-wise or a counter-clockwise. The rotatable first shaft 108 extends further and opens into the bottom portion of the rotatable reaction chamber 101 through the opening 104a, after traversing through the first platform 102, as shown in FIG.1. The first conduit 109 of the first shaft 108, axially extends through the tubular cross-secfion of the rotatable first shaft 108, with its one end opening into the rotatable chamber 101 and the other end connected to a first precursor feed source (not shown in the Figure). The first conduit 109 transports the first precursor feed, into the rotatable reaction chamber 101 at a desired flow rate. It is also understood that the first conduit 109 can extend along the outer region of the rotatable first shaft 108, while extending into the rotatable reaction chamber 101.

[0027] A second prime mover 110 is connected to the second platform 103 as shown in FIGl and is co-axial to the first prime mover 107. The constructional features and functions of the second prime mover 110 are same as that of the first prime mover 107 as described above. The position of the second prime mover 110 is variable along the vertical axis of the reactor. The second prime mover 110 is also provided with a second rotatable shaft 111, which extends through the central passage hole 104 of the second platform 103 and suspended into the rotatable reaction chamber 101, through the distal portion or upper region of the reaction chamber 101.

[0028] A spinning disk (SD) 112, which is defined by a circular shape and having a planar surface, is arranged at the terminal portion of the second rotatable shaft HI and positioned perpendicular to axis of the second rotatable shaft 111. The spinning disk 112 rotates along with the rotation of the second rotatable shaft 111, inside the rotatable reaction chamber 101 in the direction 'd'. In one aspect of the present invention the outer surface of the spinning disk 112 is provided with an anti-corrosion treatment without altering its wetting properties.

[0029] The spinning disk 112 and the rotatable reaction chamber 101 are arranged to rotate in clockwise and counter clockwise directions.

[0030] An intervening space 113 is arranged between the bottom portion of the rotatable reaction chamber 101 and the outer surface of the spinning disk 112.

[0031] A second conduit 114 is permitted to enter through the rotatable reaction chamber 101, in proximity to the second platform 103 through an opening 104c. The second conduit 114 is permitted to extend along the second rotatable shaft 111 and open into the rotatable reaction chamber 101, in proximity to the outer surface of the spinning disk 112. The second conduit 114 transports the second precursor feed, into the rotatable reaction chamber 101 at a desired flow rate. The flow rate of the precursor feed is maintained less than the maximum at which the thin film on the spinning disc 112 starts breaking into ligaments instead of small drops. The opening of the second conduit 114 is positioned in a manner that the second precursor feed is initially allowed to hit the surface of the spinning disk 112 before it is dispersed in the rotatable reaction chamber 101 due to the centrifugal action generated by the rotation of the spinning disk 112. The spinning disk 112 is made of stainless steel material and any other type of material such as metallic alloys and polymers can also be used. The spinning disk 112 is also coated with a coating material such as Teflon to prevent corrosion of its surface.

[0032] An approximate flow path of first and second precursor feeds entering the rotatable reaction chamber 101, through the first and second conduits 109 and 114, is indicated with arrows as shown in FIGl. A reaction zone (RZ) is a localized area of the rotatable reaction chamber 101, where the first and second precursor feeds collide and react together.

[0033] In an aspect of the present invention, as shown in FIG 3 the configuration of the rotatable reaction chamber 101 is having a non-uniform cross-section. In this exemplary embodiment the internal diameter of the rotatable reaction chamber 101 is gradually increased from the area of entry of the first conduit 109 (vertical arrangement) to the area of second conduit 114, thereby imparting a conical shape to the rotatable reaction chamber 101. It is also within the purview of the invention to use various other cross-sections such as circular, oval for the rotatable reaction chamber 101, without actually compromising on the centrifugal action of the precursor feeds.

[0034] In further aspect of the present invention as shown in FIG 4, an inner rotatable reaction chamber 112 is arranged inside the rotatable reaction chamber 101 and the inner chamber is perforated 119. In other words, the perforated rotatable reaction chamber 101 performs the role of the spinning disk (SD). The second precursor feed entering into the rotatable reaction chamber 101, exits through the perforations 119 while the rotatable reaction chamber 101 rotates. The second precursor feed exiting from the rotatable reaction chamber 101 reacts with the first precursor feed at the reaction zone (RZ) due to centrifugal action generated.

[0035] In another aspect of the present invention as shown in FIG 5, at least two spinning disks 112a and 112b are connected to the second rotatable shaft 111, with intervening gaps between them. Precursor feed conduits 117 and 118 are provided to each of the spinning disks 112a and 112b, preferably, on either side of the spinning disks 112a and 112b, to facilitate the transport of feeds inside the rotatable reaction chamber 101. The provisioning of multiple spinning disks enhances the capacity of the reactor by increasing the number of reaction zones (RZ) and the rapid synthesis of nanoparticles. The number of spinning disks can also be suitably increased in order to scale up the capacity and the rapid synthesis of nanoparticles.

[0036] In yet another aspect of the present invention, the reactor for the rapid synthesis of nanoparticles with a single spinning disk (SD) 112, driven by a single prime mover 107 is shown in FIG 6. In this arrangement the first precursor feed is fed through the first conduit 109 that is connected to the first shaft 108 and the second precursor feed is fed through the second conduit 114.

[0037] In another aspect of the present invention, as shown in FIG 7 the reactor is arranged horizontally to the ground axis (GA). In this arrangement, the first and second feed precursors enter into the rotatable reaction chamber 101 laterally and the reacted products (nanoparticles) are collected in the collector 105. In this horizontal orientation of the reactor, the rotatable reaction chamber 101 and the spinning disk 112, function in the manner as described above. An exit port 106 is suitably positioned at the bottom surface of the collector 105 to collect the reacted products. The use of horizontal arrangement of the reactor permits large throughputs to be realized without any loss of performance.

[0038] The spinning disk-spinning bowl (SD-SB) reactor of the present invention employs a combination of disk and bowl arrangement, functioning in vertical and horizontal positions, where the precursor feeds for the desired nanoparticles are pumped in the reactor. The precursor feeds inside the reactor, form thin films using centrifugal acceleration generated inside the reactor, which is combined with a sweeping flow, to carry nuclei away from the point of contact of two reagent streams, to synthesize uniform-size nanoparticles.

[0039] The following is a description of a preferred embodiment of the process for the synthesis of gold nanoparticles according to a preferred embodiment of the present invention.

[0040] In this exemplary process a precursor feed of HAuCU is dispersed as fine micron-sized non-interacting droplets into a film of another precursor feed, which is tannic acid (C76H52O46), for the synthesis of gold nanoparticles. Accordingly, two different precursor feed streams are permitted to enter into the rotatable reaction chamber of the reactor from two different entry points, before they meet at a reaction zone. The first precursor feed of tannic acid solution of 0.5 mM concentration is transported into the bottom portion of the rotatable reaction chamber, through the first conduit, at room temperature, using a syringe pump arrangement, a desired flow rate. A second precursor feed of HAuCU solution of 2.5 mM concentration, is transported into the rotatable reaction chamber, at a desired flow rate and room temperature, through the second conduit and directed to fall on the spinning disk. The flow rate of the streams is determined based on the factors such as their stoichiometry and the stability of the particles. The spinning disk is rotated at the speed 3000 rpm and the rotatable reaction chamber is rotated at the speed 1500 rpm. The solution of HAuCU is dispersed (spun off the spinning disk) as fine micron-sized non-interacting droplets into the uniform film of tannic acid. The thin film of tannic acid solution rising up along the wall of the rotatable reaction chamber, with streamlined flow, carries with it the drops containing HAuCU impinging on it and the particles formed upon contact in the reaction zone. The fluid moves along wall of the rotatable reaction chamber, due to the centrifugal acceleration, caused by rotation of the rotatable reaction chamber. Each of the non-interacting HAuCU droplets impinging on tannic acid acts as an isolated well-mixed micro-reactor to form gold nanoparticles of uniform size. The gold nanoparticles are collected in the collector at a processing rate of 3g/hr flow rate of 2 litres/hour and having a particle size of 5.7 nm ± 2.1 nm. The gold nanoparticles may be further processed to transfer them to organic phase. The particle size of the nano particles in the order of 4.7 nm ±1.2 is observed when concentration levels of HAuCU and TA are 0.25 mM and 0.5 mM, respectively.

[0041] A demonstration of a comparative account of flow rate, processing rate and particle size of gold nanoparticles that are produced using known micro channel reactors and SD-SB reactor of the present invention, is illustrated in the following Table.

David Shalom, Robert C.R. Wootton, Richard F. Winkle, Ben F. Cottam, Ramon Vilar, Andrew J. deMello, C. Paul Wilde, 2007. Synthesis of thiol functionalized gold nanoparticles using a continuous flow microfluidic reactor. Materials Letters 61. 1146-1150.

4. Wagner, J., Kohler, J.M., 2005. Continuous synthesis of gold nanoparticles in a microreactor Nano Letters 5(4), 685-91.

[0042] Accordingly, the reactor of the present invention provides a high-yielding rapid synthesis (measured in mass of product generated per unit time) of uniform-sized nanoparticles, with throughput at the order of 10 times that of conventional reactors for nanoparticle generation. The high processing rate is facilitated by the use of centrifugal acceleration in the reactor to pump both the precursor streams. The mixing introduced by the impact of a drop containing one of the precursors onto a flowing thin film containing another precursor and sweeping away of the products formed by the reaction eliminates back mixing hence resulting in continued nucleation and formation of small-sized nanoparticles.

[0043] The SD-SB reactors, in comparison with micro-channel reactors, have the additional advantage that they require substantially reduced power input at steady state operation. Energy is spent to provide only angular momentum to the incoming precursor streams. This is achieved by making the precursor streams flow over the rotating solid surfaces.

[0044] The spinning disk-spinning bowl (SD-SB) reactor of the present invention can be suitable adapted to synthesize other types of metallic and non-metallic nanoparticles including ceramic, semiconductor, metal alloys, metal nitrides and metal oxides etc.,

[0045] While the subject matter of the present invention has been described in terms of what is presently considered to be most practical and preferred embodiments, it is to be understood that the features of the invention need not be limited to the disclosed embodiments. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.

We Claim:

1. A spinning disk-spinning bowl (SD-SB) reactor for rapid synthesis of nanoparticles, comprising:

a first and a second prime mover with rotatable first and second shafts, connected to first and second platforms;

a rotatable reaction chamber, operably connected to the first and second rotatable shafts;

at least a spinning disk, connected to the second rotatable shaft and disposed in the rotatable reaction chamber;

a first conduit disposed to inject a first precursor feed through one end of the rotatable reaction chamber;

a second conduit disposed to inject a second precursor feed through the other end of the rotatable reaction chamber onto the spinning disk;

at least a pre-determined reaction zone for the first and second feeds, arranged in the rotatable reaction chamber; and

a collector with an outlet connected to the rotatable reaction chamber, to collect nanoparticles.

2. The reactor according to claim 1, wherein the shafts are tubular.

3. The reactor according to claim 1, wherein the rotatable reaction chamber is disposed vertically or horizontally to the ground axis.

4. The reactor according to claim 1, wherein the rotatable reaction chamber is uniformly cylindrical or non-uniform.

5. The reactor according to claim 1, wherein the rotatable reaction chamber is metallic or non-metallic.

6. The reactor according to claim 1. wherein the inner surface of the rotatable reaction chamber is coated with a corrosion-resistant material.

7. The reactor according to claim 1, wherein the direction of rotation of the spinning disk and the rotatable reaction chamber is clockwise or counterclockwise.

8. The reactor according to claim 1, wherein at least two spinning disks are connected to the second rotatable shaft.

9. The reactor according to claim 1, wherein a single prime mover is operably connected to a single rotatable shaft and a single spinning disk.

10. The reactor according to claim 1, wherein a perforated inner rotatable chamber is disposed in the rotatable reaction chamber.