Optical investigations of the (dis)continuous metal-insulator transitions in strongly-coupled electron-lattice systems.

Optical properties of four model systems (Na-, K-, Rb- or Cs-doped quasi-two-dimensional X 1.95Al1.95Si2.05O8.00; X = Na, K, Rb, or Cs) used to study the metal-insulator transition (MIT) in a deformable lattice are investigated. The doping evolution of the optical absorption band(s) originating from small bipolarons show strong variations depending on the electron-lattice coupling strength [Formula: see text]. Despite the increasing number density of small (bi)polarons, the Na-system remains a stubborn (bi)polaronic insulator due to strong [Formula: see text], while the other three systems show closing of the respective mobility gaps giving way to conducting phases with differing properties. These interesting evolutions and dynamical properties are compared and discussed. We conjecture that the manifestation of anomalous electronic transport properties and Mooij correlations near the MIT or superconductor-insulator transition in systems with non-negligible electron-lattice coupling effects may be linked to the coexistence of competing polaronic phases and the dynamical intertwining of the deformable lattice and the random electronic potential.

Conversion of rice husk ash to zeolite beta.

White rice husk ash (RHA), an agriculture waste containing crystalline tridymite and alpha-cristobalite, was used as a silica source for zeolite Beta synthesis. The crystallization of zeolite Beta from RHA at 150 degrees C in the presence of tetraethylammonium hydroxide was monitored by XRD, FTIR and (29)Si MAS NMR techniques. It was found that zeolite Beta started to form after 12h and the complete crystallization of zeolite Beta phase was achieved after 2d. XRD, (29)Si MAS NMR and solid yield studies indicate that the transformation mechanism of silica present in RHA to zeolite Beta involves dissolution of the ash, formation of an amorphous aluminosilicate after 6h of crystallization, followed by dissolution in the mother liquor and final transformation to pure zeolite Beta crystals.

Simultaneous adsorption of a mixture of paraquat and dye by NaY zeolite covered with alkylsilane.

The surfaces of NaY zeolite particles were modified by the alkylsilylation of n-octadecyltrichlorosilane (OTS). Two kinds of modified NaY zeolites were prepared; one with its external surface partially and the other fully covered with alkylsilyl groups. Since the size of OTS is bigger than the pore diameter of NaY, it is attached on the external surface, leaving the internal pore accessible to adsorbate molecules. As a result of alkylsilylation, the adsorption properties of these sorbents were improved. The adsorption properties of these materials were tested by their reaction in a mixture of paraquat and blue dye. The results demonstrate that the alkysilylated NaY materials are capable of simultaneous adsorption of paraquat and blue dye. Paraquat was selectively adsorbed into the internal pore of the zeolite whereas the dye on the externally attached alkylsilyl groups of the sorbent; displaying the unique bimodal amphiphilic character of the alkylsilylated NaY zeolites.