Phosphorus can react with most elements of the periodic table to form different classes of phosphides, ranging from ionic for the alkali and alkaline-earth elements to metallic or covalent for the transition elements and covalent for the main-group elements. Among them, InP and GaP (III-V semiconductors) have various applications in telecommunications, optoelectronic devices and solar cells, [1,2] while transition-metal phosphides are attractive candidates for high-performance catalytic, electronic, and magnetic applications. [3] A variety of methods for synthesizing bulk metal phosphides, including direct reaction of the appropriate elements for prolonged periods at high temperature, reaction of phosphine with metals or metal oxides, reduction of metal phosphates by hydrogen, electrolysis of molten metal phosphate salts, solid-state metathesis, thermal decomposition of single-source precursors, and self-propagation high-temperature synthesis, are known. [4][5][6] These methods typically require extremely high reaction temperatures (sometimes above 1000 8C) and/or long reaction times. Metal phosphides can be obtained under milder conditions in a solvothermal approach, but this method is not feasible for the deposition of metal phosphides on supports, and in cases where yellow phosphorus and sodium are employed, care must be taken to ensure the rigorous absence of oxygen and water. [7] Only two methods, namely the reduction of metal phosphates by H 2[4] and the phosphidation of metals or metal oxides with PH 3 /H 2 , [5] are generally feasible for the preparation of supported transition-metal phosphides for use as hydrotreating or hydrogenation catalysts. Supported metal phosphides are usually prepared by the reduction method due to the high toxicity of PH 3 . Nevertheless, the conversion of oxide precursors to phosphides is neither thermodynamically nor kinetically favorable. Since the formation of Ni 2 P from the oxides by means of the temperature-programmed reduction (TPR) method (Scheme 1) is thermodynamically unfavorable, the forward reaction has to be aided by high temperature and low water vapor pressure.[8] Thus, Ni 2 P can only be obtained at a low heating rate (e.g. 1 8C min À1 ) and a high H 2 flow velocity to purge the water (by-product) off the solid surface. The forward reaction is slow because the H 2 molecules must be split into hydrogen atoms, therefore the metal oxide must first be reduced and then spilt-over hydrogen atoms can reduce the phosphorus oxide, followed by a solid-state reaction to form the metal phosphide. As a consequence, Ni 2 P can only be prepared by means of the TPR method above 550 8C.Herein we describe a new strategy for synthesizing metal phosphides that uses nonthermal H 2 plasma as the reduction medium instead of the H 2 used in the TPR method. Highenergy electrons collide inelastically with hydrogen molecules in the plasma and transfer their energy to the latter, which leads to the production of excited hydrogen species and ions with a significantly higher reduction abilit...
Phosphorus can react with most elements of the periodic table to form different classes of phosphides, ranging from ionic for the alkali and alkaline-earth elements to metallic or covalent for the transition elements and covalent for the main-group elements. Among them, InP and GaP (III-V semiconductors) have various applications in telecommunications, optoelectronic devices and solar cells, [1,2] while transition-metal phosphides are attractive candidates for high-performance catalytic, electronic, and magnetic applications. [3] A variety of methods for synthesizing bulk metal phosphides, including direct reaction of the appropriate elements for prolonged periods at high temperature, reaction of phosphine with metals or metal oxides, reduction of metal phosphates by hydrogen, electrolysis of molten metal phosphate salts, solid-state metathesis, thermal decomposition of single-source precursors, and self-propagation high-temperature synthesis, are known. [4][5][6] These methods typically require extremely high reaction temperatures (sometimes above 1000 8C) and/or long reaction times. Metal phosphides can be obtained under milder conditions in a solvothermal approach, but this method is not feasible for the deposition of metal phosphides on supports, and in cases where yellow phosphorus and sodium are employed, care must be taken to ensure the rigorous absence of oxygen and water. [7] Only two methods, namely the reduction of metal phosphates by H 2[4] and the phosphidation of metals or metal oxides with PH 3 /H 2 , [5] are generally feasible for the preparation of supported transition-metal phosphides for use as hydrotreating or hydrogenation catalysts. Supported metal phosphides are usually prepared by the reduction method due to the high toxicity of PH 3 . Nevertheless, the conversion of oxide precursors to phosphides is neither thermodynamically nor kinetically favorable. Since the formation of Ni 2 P from the oxides by means of the temperature-programmed reduction (TPR) method (Scheme 1) is thermodynamically unfavorable, the forward reaction has to be aided by high temperature and low water vapor pressure. [8] Thus, Ni 2 P can only be obtained at a low heating rate (e.g. 1 8C min À1 ) and a high H 2 flow velocity to purge the water (by-product) off the solid surface. The forward reaction is slow because the H 2 molecules must be split into hydrogen atoms, therefore the metal oxide must first be reduced and then spilt-over hydrogen atoms can reduce the phosphorus oxide, followed by a solid-state reaction to form the metal phosphide. As a consequence, Ni 2 P can only be prepared by means of the TPR method above 550 8C.Herein we describe a new strategy for synthesizing metal phosphides that uses nonthermal H 2 plasma as the reduction medium instead of the H 2 used in the TPR method. Highenergy electrons collide inelastically with hydrogen molecules in the plasma and transfer their energy to the latter, which leads to the production of excited hydrogen species and ions with a significantly higher reduction abili...
Various hydrophobic hairy carbonaceous fibers are obtained by a low-temperature CVD process on catalyst-patterned surface patches which are selectively coated with silica to make the surface superhydrophobic and yet allow strong water adhesion for the "Salvinia effect". The versatility of the functional hairy fiber surfaces is demonstrated with a liquid barrier grid for cell microarray, a gas retaining capability under water/liquid for a membrane-free microfluidic chemical process, and functionalized papillae for cell immobilization with green algae.
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