Carbon nitride has been considered as promising metal-free polymers for low-cost photocatalysis. Most prevailing concern about this fantastic material focuses on g-C3N4, while the potential of other derivatives have been overlooked. Herein, in order to determine the desired derivatives for environmental pollutant treatment, the impact of degree of thermal polymerization on the microstructure of carbon nitride was investigated. Interestingly, melem-based derivatives exhibit 4- and 6-fold enhanced activities than g-C3N4, when used as synergetic photocatalysts for the simultaneous treatment of heavy metal ions and organic contaminants. According to the fundamental study of reactive species formation, a microstructure-dependent photocatalytic mechanism was established. Hydrogen bond-facilitated trapping of photogenerated holes and superior ability for oxygen molecular activation contributed to the high-performance of melem-based derivatives. In contrast, g-C3N4 shows inferior performance during superoxide radical-dominated photodegradation reactions, as its microstructure is favorable for the generation of circle OH. Our research not only sheds new insights into the microstructure design of metal-free carbon nitride photocatalysts, but also has immense scientific and technological values for high efficiency and synergetic environmental applications. (C) 2017 Elsevier Inc. All rights reserved.