Copper loaded activated carbon (Cu-AC) was prepared by impregnating it with cupric nitrate followed by microwave heating and then used for removing dyes in wastewater. The Cu-AC was thoroughly characterized by N₂ adsorption and desorption isotherms, SEM, EDS, XRD, XPS, FT-IR, and Raman. It was proven that cupric nitrate was successfully loaded onto activated carbon with the resulting formation of copper, copper oxide, and cuprous oxide. The Cu-AC was used to treat five kinds of dyes in wastewaters (Rhodamine B, MB, Amaranth, Congo red, and Eosin-Y). Comparing the adsorption capacity of these five dye wastewaters, it was proven that copper and copper oxides have photocatalytic degradation ability that can improve dye removal efficiency. Experimental adsorption data of MB were fit using several kinetic and isotherm models. Kinetic studies indicated that a pseudo-second order is the most suitable model for the adsorption process with a correlation coefficient of R² > 0.999. The equilibrium adsorption data of MB showed that it followed the Langmuir isotherm; the Langmuir maximum adsorption capacity was 373 mg g⁻¹. Compared with ordinary activated carbon, the maximum adsorption capacity of Cu-AC increased by 37.8%. Additionally, through thermodynamic calculations the negative value of ΔG and positive value of ΔH showed that the adsorption was a spontaneous and endothermic process. All the above results reveal that Cu-AC can be an effective absorbent for removing dyes from wastewater.

A waste-derived adsorbent was prepared from waste carbon, which was obtained from the production process of monosodium glutamate, by microwave heating under ultrasonic spray conditions for removing methylene blue (MB) from wastewater. The preparation process was performed at 840 °C for 17 min with an ultrasonic spray rate of 2 mL min⁻¹ produced by ultrasonic spray equipment. Ultrasonic spray was successfully used for the preparation of an adsorbent from waste carbon for the first time. An adsorbent was also prepared under a steam atmosphere. The MB adsorption number of the adsorbent prepared under ultrasonic spray conditions increased by 15.27% in comparison to that prepared under a steam atmosphere under similar experimental conditions. The exhaust gases that were obtained during the preparation process of the adsorbent had a certain heating value, as the major components were carbon monoxide and hydrogen. The exhaust gases have promising utility as a heat source, which would significantly alter the commercial manufacturing process. The physicochemical properties of the adsorbent were investigated via N₂ adsorption, TG/DTG, SEM, FTIR, XPS and zeta potential measurements. Analyses of the adsorption mechanism prove that CO bonds in the adsorbent play an important role in the adsorption process of MB, as proved by zeta potential measurements and XPS analysis. The above-mentioned analyses show that an adsorbent with good MB adsorption performance can be prepared from waste carbon under ultrasonic spray preparation conditions and fuel gas can be obtained at the same time, which achieves the comprehensive utilization of waste resources.

A composite adsorbent (Fe-activated carbon) was synthesized by impregnating Fe(NO₃)₃ onto activated carbon, and heated via microwave heating to remove methylene blue (MB), utilizing ultrasound-microwave combined preparation methods. The optimal MB removal capacity and yield of Fe-activated carbon is 257 mg g⁻¹ and 83.31%, respectively, under optimal conditions such as 700 W of microwave power, 700 °C of temperature and 25 min of heating time. The ultrasound was used for assisted-impregnation of Fe(NO₃)₃ onto the activated carbon via its acoustic cavitation. The removal capacity on MB of Fe-activated carbon increases by 17.12%, as compared to that of it without ultrasound assisted-impregnation. The physico-chemical properties of Fe-activated carbon were examined by XRD, XPS, SEM, EDX, FTIR, Raman and N₂ adsorption. Moreover, the existence of Fe₃O₄ leads to Fe-activated carbon having magnetic properties, which makes it easily separable from dyes wastewater in an external magnetic field. The equilibrium adsorption data showed that the adsorption behavior followed the Langmuir isotherm, and a pseudo-second order model matched well the kinetic data. Compared with raw activated carbon, the maximum monolayer adsorption capacity of Fe-activated carbon increases by 25.96%. According to these results, Fe-activated carbon is a promising adsorbent for the removal of dye from wastewater.