Microwave-assisted regeneration of spent activated carbon containing zinc acetate and its application for removal of congo red

The spent activated carbon (AC) loaded with zinc acetate from the vinyl acetate synthesis industry has been used as a raw material to prepare AC-ZnO porous adsorbents using microwave irradiation technique with three different activating agents. The morphology and surface chemical compositions of the prepared samples were characterized by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, and N-2 adsorption-desorption isotherm. The regenerated AC-ZnO composites exhibited a well-developed porous structure with Brunauer-Emmett-Teller surface area in excess of 1,100 m(2)/g, and the ZnO nanoparticles decomposed from zinc acetate loaded on the surface of the regenerated AC without aggregation. The adsorption performance of the AC-ZnO composites was further evaluated by adsorbing Congo Red (CR) from aqueous solutions. The experimental isotherms data were analyzed using Langmuir, Freundlich, and Temkin models. Langmuir and Temkin models were found to satisfactorily match the experimental data with the maximum CR adsorption capacity of 16.72 mg/g for the sample activated by CO2 at 308 K. Similarly, the kinetics of adsorption were tested with pseudo-first-order, pseudo-second-order, and intraparticle diffusion models, and the data were found to conform to the pseudo-second-order kinetics with high correlation coefficient. The intraparticle diffusion model indicated external film diffusion, and intraparticle diffusion has taken place during the adsorption process.