Porous silicon

#This application is the U.S. national phase of International Application No. PCT/GB2010/052112, filed 16 Dec. 2010, which designated the U.S. and claims priority to GB Application No. 0922063.3, filed 17 Dec. 2009, the entire contents of each of which are hereby incorporated by reference.

#This invention relates to, porous silicon, methods for making porous silicon, porous silicon obtainable from said methods and uses of the porous silicon.

#Porous silicon is found in a variety of applications where its benign nature, electronic and optical properties and entrapment of other materials is desirable.

#Embodiments of the invention will now be described, by way of example only and without limitation, with reference to the accompanying drawings and the following Examples, in which:

#FIG. 1 illustrates a reaction exotherm for Example 1;

#FIG. 2 illustrates reaction exotherms for Examples 1-3;

#600 ml of 1.85M (aqueous) ferric chloride solution was added to 120 ml of 40% (aqueous) hydrofluoric acid. The resulting solution was chilled to −25° C. and poured into a 2 L polyethylene bottle containing 10 g of metallurgical-grade silicon powder (d10=0.71 μm, d50=2.10 μm, d90=8.9 μm). The bottle was returned to the chilling bath (−25° C.), covered and stirred with an acid-resistant screw-propeller stirring rod (˜400 rpm). The temperature was monitored in accordance with FIG. 1. At t=˜30 min, 500 ml of de-ionised water (room temperature) was added to the mixture and the diluted mixture immediately poured into a large-area PTFE vacuum-filtration vessel containing a 10 μm MITEX filter membrane. The mixture was filtered until a damp powder remained on the membrane (the filter time was 19 min). The membrane/powder was removed and dried on a hotplate at 45° C. for 24 hr, in air and the resulting powder was weighed. This gave a 23.7% yield of porous silicon which possessed: a surface area=479.7 m2/g, an average pore volume=0.52 ml/g; an average pore diameter=3.8 nm.

#600 ml of 1.85M (aqueous) ferric chloride solution was added to 120 ml of 40% (aqueous) hydrofluoric acid. The resulting solution was chilled to −25° C. and poured into a 2 L polyethylene bottle containing 10 g of metallurgical-grade silicon powder (d10=0.71 μm, d50=2.10 μm, d90=8.9 μm). The bottle was returned to the chilling bath (−25° C.), covered and stirred with an acid-resistant screw-propeller stirring rod (˜400 rpm). The temperature was monitored in accordance with FIG. 2. At t=˜30 min, 500 ml of de-ionised water (room temperature) was added to the mixture and the diluted mixture immediately poured into a large-area PTFE vacuum-filtration vessel containing a 10 μm MITEX filter membrane. The mixture was filtered until a damp powder remained on the membrane (the filter time was 15 min). The membrane/powder was removed and dried on a hotplate at 45° C. for 24 hr, in air and the resulting powder was weighed. This gave a 40.3% yield of porous silicon which possessed: a surface area=141.2 m2/g, an average pore volume=0.305 ml/g; an average pore diameter=6.8 nm.

#600 ml of 1.85M (aqueous) ferric chloride solution was added to 120 ml of 40% (aqueous) hydrofluoric acid. The resulting solution was chilled to −15° C. and poured into a 2 L polyethylene bottle containing 10 g of metallurgical-grade silicon powder (d10=0.71 μm, d50=2.10 μm, d90=8.9 μm). The bottle was returned to the chilling bath (−15° C.), covered and stirred with an acid-resistant screw-propeller stirring rod (˜400 rpm). The temperature was monitored in accordance with FIG. 2. At t=˜30 min, 500 ml of de-ionised water (room temperature) was added to the mixture and the diluted mixture immediately poured into a large-area PTFE vacuum-filtration vessel containing a 10 μm MITEX filter membrane. The mixture was filtered until a damp powder remained on the membrane (the filter time was 14 min). The membrane/powder was removed and dried on a hotplate at 45° C. for 24 hr, in air and the resulting powder was weighed. This gave an 18.7% yield of porous silicon which possessed: a surface area=359.6 m2/g, an average pore volume=0.463 ml/g; an average pore diameter=4.4 nm.