What is the difference between an anoxic reaction medium and anaerobic conditions provided with a continuous flow of nitrogen gas for NZVI preparation?
Dear M S Islam for a great overview on zero-valent iron nanoparticles (NZVI) please have a look at the following very useful review article (published in 2020):
Synthesis and Application of Zero-Valent Iron Nanoparticles in Water Treatment, Environmental Remediation, Catalysis, and Their Biological Eects
Fortunately this review article has been published Open Access, which means that it is freely available form the internet (please see attached pdf file).
As for your original question, you will find many potentially useful answers when you check out the following closely related question which has been asked earlier on RG:
What is the difference between anaerobic and anoxic conditions?