Large-scale mutl-step synthesis method for ultralong silver nanowire with contrallable diameter

A method of large-scale multi-step synthesis for an ultralong silver nanowire with a controllable diameter comprising the following steps:

• step 1, phase of screening of crystal seeds:
• heating ethylene glycol solution containing a surfactant at a temperature of 140 to 160° C. to obtain a solution I with strong reducibility;
• adding alkali metal halide dissolved in ethylene glycol into the solution I to yield a solution II;
• dissolving silver nitrate in ethylene glycol for preparing a precursor solution, the concentration of silver nitrate is between 0.001 to 5 mol/L;
• adding the precursor solution into the solution II that reduces silver nitrate rapidly into a large number of multiple twinned crystal seeds with different sizes and part of isotropic seeds;
• adding etching agent into the above solution with a large number of crystal seeds results in preferentially etching the isotropic seeds which are not resistant to etching and the multiple various sizes of the twinned crystals, thus screening limited amount of particular sizes of the multiple twinned crystal seeds;
• step 2, phase of breaking through the threshold of etching multiple twinned crystal seeds:
• after the addition of etching agent in Step 1, increasing the reaction temperature immediately to 160-200° C. for a continuous reaction in the temperature until turbidities appearing;
• increasing the temperature significantly boosts the reaction rate until the threshold of etching multiple twinned crystal seeds by few by-products, namely nitric acid, is broken through;
• step 3, phase of longitudinal growth:
• decreasing the reaction temperature to 60-140° C. for a completed reaction under such condition once the appearance of turbidities;
• the decrease of temperature, which effectively reduces the reaction rate and depletes the isotropic seeds generated by self-nucleation, allows more free silver ions to be reduced longitudinally along nanowires for obtaining ultralong silver nanowires.