Jiugao Guo

Arrangement models of alkylammonium cations in the interlayer of HDTMA~+ pillared montmorillonites

The orientation of HDTMA+ in the interlayer of organic pillared montmorillonites prepared at different concentrations of HDTMA+ have been studied using X-ray powder diffraction (XRD) and theoretical calculation. A series of arrangement models of HDTMA+ in the interlayer of montmorillonite have been proposed as lateral-monolayer (LM), lateral-bilayer (LB), pseudotrilayer (PT), paraffin-type-monolayer (PM), paraffin-type-bilayer (PB). With the increase of the concentration of HDTMA+, the arrangement model of HDTMA+ in the interlayer of montmorillonites changes as lateral-monolayer→lateral-bilayer→paraffin-type monolayer→pseudotrilayer→paraffin-type-bilayer and the packing density of HDTMA+ in the interlayer increases gradually. In the intermediate stages, different models may coexist.

Adsorption of phenol on inorganic-organic pillared montmorillonite in polluted water.

Both inorganic- and organic-pillared montmorillonites (PMts) were used to adsorb phenol to study suitable conditions for adsorption and adsorption isotherms. The adsorbing capacity of modified clays depends not only surface area, but mainly on micropore structure and surface components. After incandescing at 500 degrees C, the pillar structure and the basal interlayer spacing (1.83 nm) remained stable. Using modified PMt with surfactant can improve adsorbing capacity greatly. The PMt can be recycled, and it is a potential substance for adsorption of environmental pollutants.

Location and migration of cations in Cu2+-adsorbed montmorillonite

Locations of Cu2+ ion in Cu(2+)-adsorbed montmorillonite have been studied by electron paramagnetic resonance (EPR), supplemented by X-ray diffraction (XRD) and differential thermal analysis (DTA). In the EPR spectra of Cu(2+)-adsorbed montmorillonite, three signals, corresponding to Cu2+ ion, have been simultaneously recorded. Some Cu2+ ions seemed to replace the original interlayer metal cations and some entered into the hexagonal cavities. A small fraction of Cu2+ ions penetrated into the octahedral vacancies. There were two ways for the adsorption of Cu2+ ion by montmorillonite--exchangeable and specific. On heating, the hydrated Cu2+ ion in the interlayer loses the coordinating water and then enters into the hexagonal cavities. When the heating temperature further increased, dehydroxylation occurs, which facilitates Cu2+ ion in the hexagonal cavities to penetrate into the octahedral vacancies.

29Si and 27Al MAS NMR spectra of mullites from different kaolinites

Mullites synthesized from four kaolinites with different random defect densities have been studied by 27Al and 29Si magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) and X-ray diffraction (XRD). All these mullites show the same XRD pattern. However, 29Si and 27Al MAS NMR spectra reveal that the mullites derived from kaolinites with high defect densities, have a sillimanite-type Al/Si ordering scheme and are low in silica, whereas those mullites derived from kaolinites with low defect densities, consist of both sillimanite- and mullite-type Al/Si ordering schemes and are rich in silica.

29Si and 27Al MAS NMR study of the thermal transformations of kaolinite from North China

Abstract The thermal transformations of kaolinite have been studied using 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR), X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetric analysis (TG). The experimental results show that this sample is a pure kaolinite which contains ~3% carbonaceous material as impurity. 27Al and 29Si MAS NMR spectra show that the microstructural evolution of the thermal transformation of kaolinite at 450−1050°C is similar to that of the kaolinite- mullite reaction series previously published by many authors. 29Si MAS NMR spectra of mullite at 1190 and 1250°C display two resonances at ~−87 and−92 ppm, corresponding to sillimanite-type geometry around Si and the typical Si environment of mullite, respectively. At 1350°C, the splitting of (hk0) and (kh0) of mullite occurs, indicating that the primary mullite transforms into orthorhombic mullite. Simultaneously, the resonance at ~−92 ppm splits into two signals at ~ -90 and −94 ppm. 27Al MAS NMR spectra of the mullite consist of three signals centred at ~ −4, 45 and 60 ppm, corresponding to octahedral, distorted tetrahedral and tetrahedral Al sites, respectively.

Experimental Study of the Selective Adsorption of Heavy Metals onto Clay Minerals

The interaction between minerals and heavy metals has been a hot object of study in environmental science, mineralogy and soil science. Through the selective adsorption experiment of Ca-montmorillonite, illite and kaolinite to Cu2+, Pb2+, Zn2+, Cd2+ and Cr3+ ions at certain conditions, it could be concluded that Cr3+ is most effectively sorbed by all the three minerals. Also, it can be found that Pb2+ shows a strong affinity for illite and kaolinite while Cu2+ for montmorillonite. Based on the adsorption experiment at varying pH of solution, it can be found that the amount of heavy metals sorbed by minerals increases with increasing pH of the solution.

A microstructural study of acid-activated montmorillonite from Choushan, China

Abstract Bentonite samples from Choushan treated at various acid concentrations were studied using chemical analysis, XRD, 29Si and 27Al MAS NMR to investigate the microstructure of the activated montmorillonites. Two types of structural units were formed during the activation: (1) (SiO)3SiOH, in which up to 15% of Si is bound; (2) Q4(0Al), a major building unit when the acid concentration is >10%. A significant 27Al signal at 55.0 ppm was recorded for both untreated montmorillonite and (to a much greater extent) in acid-treated montmorillonites. This was interpreted as arising from four-fold coordinated Al located in the ‘bulk’ octahedral sheet of montmorillonite. In the course of activation, the removal of one of a pair of octahedral Al ions from montmorillonite removes two hydroxyl groups and leaves the other Al of the pair in four-fold coordination.

Structural state of adularia from Hishikari, Japan

Adularia sample was collected from epithermal Au-, Ag-bearing quartz-adularia veins from Hishikari, Japan. This adularia is rich in K, Or=94.63, clear, transparent, fine-grained and closely associated with quartz. In this study, it was determined by XRD, IR and29Si,27Al MAS NMR methods. The adularia studied is of high sanidine with triclinic domains in it. The occupancy of Al 2t1=0.60, IR ordering θ=0.15.29Si NMR spectrum of this adularia shows a broad triplet peak, i.e. 3 poorly separated peaks at −94.9, −96.7, −99.9. This kind29Si NMR spectrum for natural high sanidine has never been reported before. And the27Al NMR spectrum gives an asymmetry peak with chemical shift at 58.7 extending slightly to the low frequency. Under a violent boiling environment, Hishikari adularia rapidly crystallized from a supersaturated solution.