The concentration of toxic metal ions in wastewater continues to increase as a result of the increasing number of industries, and the discharge of their heavy metal-containing wastes directly into water bodies without proper treatment. These heavy metals are highly toxic and difficult to degrade, which makes the treatment and re-use of the wastewater to be very challenging. Several methods have been explored for their removal from water in order to improve on water availability. However, these conventional methods cannot transform the heavy metal ions to a less toxic species, instead they are transferred from one phase to another, which may lead to secondary pollution. In this review, the conventional techniques that have been explored for the removal of heavy metal ions were examined and their merits and demerits were highlighted. Recent advancement involving the use of composites containing graphitic carbon nitride photocatalysts were discussed as viable alternative for the conventional methods. The mechanism of photocatalytic removal of heavy metal ions and methods of synthesizing the g-C₃N₄ composites were discussed. Furthermore, the chemistry of heavy metal ion transformation, their toxicity and routes of exposure were studied. Finally, the problems associated with the fabrication of the composites were critically examined.

由于行业数量的增加，废水中有毒金属离子的浓度持续增加，并且未经适当处理就将其重金属废物直接排放到水体中。这些重金属具有剧毒且难以降解，这使得废水的处理和再利用变得非常困难。为了改善水的可利用性，已经探索了几种从水中去除的方法。然而，这些常规方法不能将重金属离子转化为毒性较小的物质，而是将它们从一相转移到另一相，这可能导致二次污染。在这篇综述中，研究了用于去除重金属离子的常规技术，并重点介绍了它们的优缺点。讨论了涉及使用包含石墨氮化碳光催化剂的复合材料的最新进展，作为常规方法的可行替代方案。光催化去除重金属离子的机理及gC的合成方法讨论了₃ N ₄复合材料。此外，研究了重金属离子转化的化学，其毒性和暴露途径。最后，严格审查了与复合材料制造相关的问题。