The Characterization And The Study Of Properties Of The Cryptomelane Doped With Iron Nickel And Vanadium

Cryptomelane is a kind of manganese oxide. It is a2x2tunnel structured manganese oxide octahedral molecular sieve (OMS-2) material. It has large surface area, excellent reaction activities and stability, and also owns a varitey of environment effects (adsorption, tunnel effect and redox effect). So It has many important applications as catalysts, adsorbents and so on. Transition metal ions doping has important influence on the structure, crystal chemistry properties, adsorption, oxidation and photocatalysis properties of cryptomelane. However, owing to the different physical and chemical properties and the different crystal field behaviors of various transition metal(TM) elements their incorporation into the structure of cryptomelane will cause different changes in the structures and physicochemical properties.In this work, the reflux methods at atmospheric pressure were used to synthesize Fe-, Ni-and V-doped cryptomelanes with different TM concentrations. The structures and physicochemical properties of doped cryptomelane were investigated by powder XRD, thermal gravimetric analysis (TGA), specific surface area analyzer (BET), scanning electron microscope (SEM), infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). The performances of these doped cryptomelanes on adsorption of heavy metals (Pb2+/Zn2+) and degradation of phenol were also investigated. The main results are showed as follows:1. The levels of Fe, Ni and V entering into cryptomelane is different under the reflux methods at atmospheric pressure. The upper limit of Fe and V were15%and7%, but Ni was less than1%. The basic tunnel structure of cryptomelane did not change after doping. The crystallinity of crypromelane firstly increases and then decreases with the increase of Fe content, leading to firstly increase and then decrease in particle size, accompanied by aggregation. The morphology of Ni-doped cryptomelane is similar to that of undoped cryptomelane, The crystallinity of Ni-doped cryptomelane almost did not change. The crystallinity gradually decreases with the increase of V content of the V-doped cryptomelane, leading to decrease in particle size and increase in the specific surface areas. The Fe, Ni, V mainly exists as the valence of+3,+2,+5in the doped samples, the manganese average oxidation states (AOSs) of these doped cryptomealnes increased slightly by substitution of Mn3+in the structure, and/or Mn3+/2+in the surface. The morphology of Fe-and V-doped cryptomelane changed from needle-like to particle, but the change of Ni-doped cryptomelane is small, as the needle.2. Fe-doping can cause certain changes in the unit cell parameters and volumes of cryptomelanes. The unit cell parameters a, c and cell volumes of these Fe-doped cryptomelane are firstly increased and then decreased. However those of Ni-and V-doped cryptomelanes almost do not change. The contents of hydroxyl groups on the mineral surfaces are also gradually increased after doping.3. These Fe-and V-doped cryptomelanes have enhanced adsorption capacities for Pb2+, but the change for the adsorption capacities of Zn2+is not obvious. This is associated with the lattice defect induced by doping, special surface area, the content of surface hydroxyl groups and the changes of high and/or low energy sites.4. The Fe and V-doped cryptomelanes have improved catalytic ability towards phenol degradation, but the change of Ni-doped cryptomelane was not obvious. The reason is that the former increases the specific surface area, Mn AOSs and surface active groups, and also enhanced broad and strong light absorption band.