Reducing CO2 into high value fuels and chemicals is considered a great challenge in the 21st century. Efficiently activating CO2 will lead to an important way to utilize it as a resource. This article reviews the latest progress of g-C3N4 based catalysts for CO2 reduction. The different synthetic methods of g-C3N4 are briefly discussed. Article mainly introduces methods of g-C3N4 shape control, element doping, and use of oxide compounds to modify g-C3N4. Modified g-C3N4 has more reactive sites, which can significantly reduce the probability of photogenerated electron hole recombination and improve the performance of photocatalytic CO2 reduction. Considering the literature, the hydrothermal method is widely used because of its simple equipment and process and easy control of reaction conditions. It is foreseeable that hydrothermal technology will continue to innovate and usher in a new period of development. Finally, the prospect of a future reduction of CO2 by g-C3N4-based catalysts is predicted.

The amount of carbon dioxide emission is continuously increasing and many researchers are concerned about climate change caused by its emission. Hence, some technologies which can reduce its emission have been developed and commercialized in many industries. These technologies are commonly called Carbon Capture and Storage (CCS) technology. In conventional CCS technology, carbon dioxide gas produced from industrial processes was usually captured by basic liquid absorbent such as monoethanolamine(MEA) and so on. After it is captured by those absorbents, they was flown to desorption step and was compressed at high pressure and transported to suitable places such as deep ocean or deep underground. However, there exist some problems when carbon dioxide is stored in such places. For instance, leak into the atmosphere can occur. Also, some nations including Korea may have difficulty finding suitable places for its storage since area of the nations is not that large and the ground is not stable. So, the method that can utilize captured carbon dioxide has been developed. When carbon dioxide is combined with metal cation such as calcium ion, it becomes calcium carbonate (CaCO3) which can be used for various purposes like construction materials, pharmaceutical manufacture, additives and so on. This is called Carbon Capture and Utilization (CCU) technology. In this research, seawater was used to supply calcium ions. There contained much amount of calcium component in seawater and amount of seawater is virtually limitless. MEA was used as absorbents and saturated by simulated flue gas. Pretreated seawater was then added to saturated absorbent. When carbon dioxide gas is dissolved to MEA, it exist in forms of ions and they can easily produce precipitated calcium carbonate (PCC) salts by reacting with calcium ions contained in seawater.