In the context of global warming, energy conservation and emission reduction have become the inherent needs of all walks of life. In recent years, "green synthesis" technology based on mild reaction conditions and non-toxic green materials has attracted more and more attention. Compared with traditional physical and chemical synthesis, "green synthesis" technology has the advantages of low energy consumption, low risk of synthesis process, and strong stability of synthetic materials. Especially the "green synthesis" technology with plant waste as the main raw material, the raw materials are pure natural, non-toxic, and low-cost, which fits the current sustainable development theme very well. The application of these synthetic green materials to wastewater treatment is also in line with the concept of "using waste to treat waste" and promotes a circular economy.

Dye wastewater mainly comes from the production industry of dyes and dye intermediates. It has the characteristics of complex composition, high chroma, large discharge, high toxicity, and poor biodegradability. It has always been a problem in wastewater treatment. As a wastewater adsorbent, biochar is regarded as a substitute for activated carbon, which has the advantages of low cost, high cost performance, and low energy consumption in the production process. Biochar can be used to remove various pollutants, including inorganic anions (NO3?, PO43-), metal cations (Pb(II), As(III) and Cd(II)), organic dyes (crystal violet, cationic red X- GRL) and so on. However, the ability of biochar to adsorb pollutants depends on its physical and chemical properties, and the properties of biochar prepared under different raw materials and pyrolysis conditions are very different.

Studies have shown that using physical and chemical methods to combine biochar with other materials to prepare materials with new properties and new structures, its comprehensive performance is better than the original constituent materials and can meet various requirements. However, the large-scale production and practical application of biochar composites still face greater challenges, which are mainly related to the complex synthesis methods and the use of hazardous reagents. In the previous research, a green synthesis method of a bimetallic iron copper oxide adsorbent with a controllable size was proposed, and the adsorbent showed good removal performance for malachite green dye. The study showed that the biological Active molecules can act as reducing agents during the synthesis process. Therefore, "green synthetic" materials based on plant extracts have greater application potential, and may be better than a single plant biochar in the treatment of dye wastewater.