TITLE OF THE INVENTION

A METHOD TO TRANSFORM CRYSTALLINE MINERALS TO NANOPARTICLES BY MICRODROPLETS

FIELD OF THE INVENTION

The present invention relates to a method to transform crystalline minerals to nanoparticles by microdroplets.

BACKGROUND OF THE INVENTION

Soil is formed by the weathering of rocks. While physical, chemical, and biological weathering occurs, the process of soil formation is slow, taking millions of years.

Microdroplets are known to cause chemical synthesis at an accelerated rate or convert large protected nanoparticles of 10-50 nanometer in diameter to smaller ones of 3-5 nanometer in diameter.

The present invention demonstrates that the charged microdroplets breaks the common minerals such as quartz and ruby to nanoparticles in microdroplets.

SUMMARY OF THE INVENTION

The present invention relates to a method to transform crystalline minerals to nanoparticles by microdroplets.

In one embodiment, the present invention illustrates the fragmentation of natural minerals or synthetic minerals by charged microdroplets. The charged microdroplets break common minerals such as quartz and ruby to nanoparticles, where pieces of natural minerals, of a few micrometers in size were broken to particles of 5-10 nanometer in diameter, in aqueous droplets, formed in an electrospray. These microdroplets were deposited on substrates, and the nanoparticles formed were characterized. This formation of nanoparticles of minerals in aqueous droplets is expected to be important in the chemical and biological evolution of Earth.

Other aspects of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learnt by the practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 a. Schematic representation of disintegration of mineral particles in microdroplets, i) Syringe filled with particle suspension, ii) spray emitter, iii) Taylor cone emerging from the electrospray, iv) Conducting surface at a distance of L=1.5 cm from the tip of the emitter. Preliminary characterization of natural quartz, b. Optical image of the natural quartz, c FESEM image of a natural quartz showing the size range of particles between 1-5 um.

Figure 2 HRTEM images (at different magnifications) of natural quartz NPs after electrospray at a voltage of 4 kV, at a distance of 1.5 cm from the tip to the conducting surface, flow rate of 0.5 ml/h. a Large-area TEM image of a single mesh, showing the absence of initial bigger particles. Expanded images: b, c, d TEM images showing particle size <10 nm. The (110) lattice plane of quartz NPs; the HRTEM image of a particle is expanded in the inset of d.

Figure 3 XRD analysis showing the characteristic planes of natural quartz, a Before electrospray deposition, b After electrospray deposition.

Figure 4 HRTEM images (at different magnifications) of natural ruby, after electrospray at optimized conditions. Lattice planes are marked in the inset of b showing the (110) phase of alumina.

Figure 5 HRTEM images (at different magnifications) of fused alumina, after electrospray at optimized conditions. Lattice planes are marked in the inset of b, showing the (012) phase of alumina.

Figure 6 Raman analysis showing the characteristic peaks of natural quartz, a Before electrospray deposition, b After electrospray deposition.

Figure 7 Mass spectra of silica, a Full mass spectrum of the deposited silica showing the peaks for the formation of silicates, b Mass spectrum of the standard sodium silicate. Tandem mass spectra of m/z 95 c and m/z 173 d showing the water loss during the fragmentation.

Referring to the drawings, the embodiments of the present invention are further described. The figures are not necessarily drawn to scale, and in some instances the drawings have been exaggerated or simplified for illustrative purposes only. One of ordinary skill in the art may appreciate the many possible applications and variations of the present invention based on the following examples of possible embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the present invention. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

The present invention relates to a method to transform crystalline minerals to nanoparticles by microdroplets. The present invention shows that charged microdroplets can break common minerals such as quartz and ruby to nanoparticles. In this process, pieces of natural minerals, of a few micrometers in size were broken to particles of 5-10 nanometer in diameter, in aqueous droplets, formed in an electrospray. These microdroplets were deposited on substrates in a time scale of microseconds from the point of formation to point of deposition, and the nanoparticles formed were characterized. This formation of nanoparticles of minerals in aqueous droplets is expected to be important in the chemical and biological evolution of Earth. Experimental details

Micrometer scale particles of natural quartz and ruby are prepared by grinding it in a mortar and pestle. The powder containing particles ~l-5 pm in size were separated, suspended in distilled water, and subjected to electrospray, at a spray potential in the range of 4 kV. Care was taken to ensure that lower size particles were not taken, which was accomplished by centrifugation. The experimental set-up and images of the rock particles are shown in Figure 1. The particles are mostly in the size range of 1-5 pm (Figure lb), larger and smaller particles are not seen in the high-resolution scanning electron microscopy (HRSEM) image (Figure 1c). A 0.1 mg/ml suspension of the particles was electrosprayed through a 50 pm inner diameter capillary, with or without nebulisation by gases such as air and nitrogen, at a flow rate of 0.5 ml/h. The plume appears similar to the shape shown in Figure la. The products were collected at 1.5 cm away from the spray tip. Surprisingly, the product collected on a transmission electron microscopy grid showed only 5-10 nm diameter particles (Figure 2). The particles under higher magnification showed (110) planes of quartz (Figure 2d). For collecting larger quantities of product, a multi-nozzle electrospray unit composed of 6 nozzles was prepared. Collecting the sample with this set-up for 15 days by electrospraying of 1 L of the suspension discontinuously, at the optimized conditions of 6 ml/h flow rate, results in a deposit of 50 mg, composed of nanoparticles. Thin film X-ray diffraction of the deposit using Cu Ka radiation confirmed this material to be made of quartz (Figure 3), in the form of nanoparticles of 16 nm average diameter. Particle size was calculated using the Scherrer formula. Similar results were obtained with ruby (Figure 4). Experiments were also conducted with fused alumina (Figure 5) giving similar results. These experiments suggest that both natural and synthetic minerals can be fragmented in charged microdroplets.

Electrospray produces nearly uniform nanoparticles upon optimizing the conditions. Parameters such as electrospray voltage, tip to collector distance, nebulization pressure and particle loading were optimized to result in an image shown in Figure 2. Optimized parameters are mentioned in the figure caption. The sample was characterized by other techniques such as Raman spectroscopy (Figure 6), which showed features due to quartz. The prolonged electrospray deposition of silica gives silicates (Figure 7) and shows the formation of silicates in microdroplet.

Although the precise reason is uncertain, we believe that various processes that can happen in the microdroplet environment can drive such a rapid process. Chemical reaction rates can be accelerated by a factor of 10 ⁹ in such environments. Although several factors such as pH, reactive species such as radicals, their surface segregation, strong electric field at the interface etc., are thought to contribute to these effects, a precise understanding of such rate acceleration is yet to emerge. In the present case, where there are no reagents, we believe that physical effects are likely to play a greater role. Aspects such as microdroplet convection and shock waves producing pressures in the range of Mbar are likely in droplets, which could drive such effects. Further research is needed to understand the cause of this effect and to expand it to other areas. Implications of this observation to natural processes and weathering of rocks need to be explored.

The fragmentation process may be enhanced by the presence of other chemical species or physical stimuli such as light. Larger quantities of nanomaterials could be produced using multiple sprays or by spray using other methods. Uses of the product materials are to be investigated. It may be appreciated by those skilled in the art that the foregoing drawings, examples and experimental evidences are merely illustrative and are not to be taken as limitations upon the scope of the invention.