Metal-loaded carbonaceous adsorbents templated from porous clay heterostructures

Abstract

Carbonaceous adsorbents with small amounts of highly dispersed metals were synthesized within various porous clay heterostructures (PCHs) serving as templates. To increase chemical heterogeneity, PCHs that contained iron, zinc, or copper were used and sucrose served as a carbon precursor. The samples were carbonized at 900 °C. The inorganic templates were removed using HF and HCl treatment. The carbons obtained were highly porous, with surface areas of 500–800 m 2/g and pore volumes of 0.500–0.800 cm 3/g. The pore size distributions indicated the heterogeneity of the structure with micropore sizes similar in size to those in the PCH material. Thermal analysis showed that even though the final materials consist mainly of carbon, minor amounts of PCH still remained. The content of metals decreased gradually after HF and HCl washing. Elemental analysis indicated that of all the metal-loaded carbons, only the one with iron contains a significant amount of metal, above 1%. This is due to hydrolysis of iron and formation of insoluble hydr(oxides) which are difficult to remove using HCl or HF treatment. XRD measurements indicated that some short-range order exists in the carbons obtained, suggesting the memory effect of the layered PCHs structure. The high volume of mesopores is due to metals migration and metal reduction during pyrolysis, which resulted in the consumption of carbon and formation of channels/imperfections connecting the stacked-together layers of carbons. Moreover, TEM analysis indicated the presence of tubular entities that could be inherited from the PCH templates. Long-range order in these materials was not detected. The carbons can find applications in catalysis where the presence of mesopores is required along with high dispersion of metals. The results indicate that the content of metals/inorganic phase can be tailored by extent of acid washing.