Dear Charles,

Sol gel method is effective and one can try microemulsion 

Calcination temperature is one of the most important parameter in the synthesis of nanoparticles. In chemical or green synthesis technique the particles are usually in the matrix of some organic like citric acid or so, but wen we calcine it the particles get assembled and we get desired particle size. Higher the temperature more the thermal energy and more and more particles get assembled and result in bigger size. one can obtain smaller size particles at low temperature about 250-300 C of calcination temperature. as you increase the calcination temp particle size will be larger and larger.

Green synthesis can be done by organic precursor route. In the calcination stage of the stabilized nanoparticles, destruction of organic part is done which is followed by phase development. Apart from heating method, it can be done by Flame Spray Pyrolysis method. 

calcination nanomaterials is one of the ways to make nanomaterials crystalline.which crystaline materials show better properties in comparisson with their amorph phase. in the synthesis of some mono disperse inorganic nanomaterials usually uses of organic templates which in the calcination process this organic materials removed and you can take nanomaterials with good morphology. beside hydrothermal is one of the green synthesis protocols.

calcination is used to increase crystalinity of  material.In case of any impurities present on the surface is also removed and also calcination temperature utilized to  prepared material  converted one phase to other.Generally calcination temperature its favors the crystal growth.

Green synthesis approach depends on: the reactants used, the waste, the ease of the procedure (the easiest, the waste-less). And, on the other hand, the activity of a nanomaterial depends on its nature, structure, species adsorbed, functional groups, etc. Calcination is useful to get crystalline materials, but sometimes is aggressive for the material. If you want just to dry your material, you can use lyophilization. Everything depends on what you desire to get.

Calcination temperature is very important in determining the size and morphology of the crystallites  in nano materials as mentioned by Dr.Brajesh Pandey;.