Two different types of clay nanoparticle hybrid, iron oxide nanoparticle clay hybrid (ICH) and Al(2)O(3)-SiO(2) nanoparticle clay hybrid (ASCH), were synthesized and their effects on the rheological properties of aqueous bentonite fluids in steady state and dynamic state were explored. When ICH particles were added, bentonite particles in the fluid cross-link to form relatively well-oriented porous structure. This is attributed to the development of positively charged edge surfaces in ICH that leads to strengthening of the gel structure of the bentonite susensions. The role of ASCH particles on the interparticle association of the bentonite fluids is different from that of ICH and sensitive to pH. As pH of ASCH-added bentonite suspensions increased, the viscosity, yield stress, storage modulus, and flow stress decreased. In contrast, at low pH, the clay suspensions containing ASCH additives were coagulated and their rheological properties become close to those of ICH added bentonite fluids. A correlation between the net surface charge of the hybrid additives and the rheological properties of the fluids indicates that the embedded nanoparticles within the interlayer space control the variable charge of the edge surfaces of the platelets and determine the particles association behavior of the clay fluids.

The effects of electronic band structure, electron-hole recombination, and photocatalytic property of Nand/or Fe-doped TiO 2 were systematically explored. Hydrothermal reaction was used to incorporate N and/or Fe into TiO 2 nanoparticles. Structural analysis using Raman spectra, X-ray diffraction, and transmission electron microscope (TEM) indicates that hydrothermally grown TiO 2 particles have anatase phase, and their average size is ∼10 nm. In addition, hydrothermal doping of N and/or Fe was found to significantly modify the electronic band structure. The photocatalytic performance of undoped and doped nanomaterials was examined under UV or visible light. N doping increased the photocatalytic efficacy of TiO 2 under visible light by more than 2 times. In contrast, Fe-doped and N/Fe-codoped TiO 2 show worse photocatalytic performance than pure TiO 2 under both UV and visible light, in spite of their smaller band gaps. Fluorescence of terephthalic acid indicates that a change in the photocatalytic performance of doped TiO 2 is closely related to the amount of photoinduced radical ions. X-ray photoelectron spectroscopy and low-temperature photoluminescence were employed to study the doping mechanism. While both N and Fe facilitate the absorption of the visible light, it is found that only Fe increases the electron-hole recombination rate, leading to the opposite effects of N and Fe doping on the photocatalytic performance of TiO 2 .

Heterostructures between montmorillonite and embedded α-Fe2O3 nanoparticles are explored to create new hybrid particles with high magnetic response and magnetic-field induced tunability. α-Fe2O3 nanoparticles are hybridized to montmorillonite clays by using an intercalation technique. Also, stable aqueous fluids consisting of the heterostructured particles are prepared and the rheology of the fluids under external magnetic field is examined. When α-Fe2O3 nanoparticles are embedded in the interlayer space of montmorillonite clays, the magnetization per Fe atom increases at most 60 times. This unique combination of the magnetization and the coercivity is traced to the suppressed growth of embedded α-Fe2O3 nanoparticles by the aluminosilicate layers, leading to the size control, anisotropic magnetic interaction, and uniaxial stress of two-dimensionally distributed α-Fe2O3 nanoparticles. Furthermore, high magnetization of heterostructured particles leads to strong dependence of fluids’ viscosity on the external magnetic field. The present study indicates that the new heterostructured particles have unique magnetic field-dependent properties that are not attainable in individual clay or iron oxide particles.

Three-dimensional (3-D) flower-like shape (FLS) Fe 3 O 4 and Fe particles were successfully synthesized using FLS precursor particles that are prepared through a facile microwave-assisted reaction. The mechanism underlying the self-assembly process and shape evolution of FLS particles was systematically investigated by changing reaction parameters such as reaction temperature, reaction time and reaction pressure. During the reaction, iron alkoxide, a-Fe 2 O 3 and FeOOH nanoparticles are formed first and are subsequently transformed to 3-D hierarchical FLS particles by the self-assembly of the primary nanoparticles. Reaction temperature and pressure play critical roles in the formation of the hierarchical flower-like superstructure. There is an optimum window of the reaction temperature (y180 uC) for the formation of 3-D FLS particles, which is attributed to the competition between the self-assembly process and growth process of the nanoparticles. Also, since FeCl 3 , ethylene glycol, and urea are used together as raw materials, the appearance of FLS particles is strongly dependent on the reaction pressure. As the reaction pressure becomes larger than 1 MPa, the flake type particles become more thermodynamically favorable than the FLS particles, due to the limited decomposition of urea. Brunauer-Emmett-Teller (BET) analysis shows that FLS particles have a large surface area (.40 m 2 g 21). Because of their high specific surface area and intrinsic reactivity, FLS particles efficiently remove sulfur ions in aqueous solution. This suggests that these flower-like particles can be promising materials to treat toxic gas such as H 2 S in an environmentfriendly way.