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► Templated carbon obtained by using surface solid acidity and morphology of diatomite. ► The carbon with macroporous structure composed of carbon tubes and pillars. ► The carbon with ...good adsorption capacity of methylene blue and regenerability.
Hierarchically porous carbons were prepared using a facile preparation method in which diatomite was utilized as both template and catalyst. The porous structures of the carbon products and their formation mechanisms were investigated. The macroporosity and microporosity of the diatomite-templated carbons were derived from replication of diatom shell and structure-reconfiguration of the carbon film, respectively. The macroporosity of carbons was strongly dependent on the original morphology of the diatomite template. The macroporous structure composed of carbon plates connected by the pillar- and tube-like macropores resulted from the replication of the central and edge pores of the diatom shells with disk-shaped morphology, respectively. And another macroporous carbon tubes were also replicated from canoe-shaped diatom shells. The acidity of diatomite dramatically affected the porosity of the carbons, more acid sites of diatomite template resulted in higher surface area and pore volume of the carbon products. The diatomite-templated carbons exhibited higher adsorption capacity for methylene blue than the commercial activated carbon (CAC), although the specific surface area was much smaller than that of CAC, due to the hierarchical porosity of diatomite-templated carbons. And the carbons were readily reclaimed and regenerated.
The understanding of crystal nucleation and growth has evolved over the past two decades from the conventional atom-by-atom model to a non-classical approach, involving particle aggregation and ...amorphous transformation pathways. Whereas aggregation of particles instead of individual atoms/ions/ molecules has been recognized as a common crystallization pathway at the Earth’s surface conditions, few cases are known for high-temperature (e.g., melt) mineralization, which is of great importance for understanding geological processes.
Here, we present texture data for natural (e.g., igneous and metamorphic biotite and muscovite) and synthetic (e.g., fluorophlogopite) phyllosilicates suggesting that a particle attachment formation should be considered, although other crystal growth models cannot be excluded. A nonclassical crystallization model is proposed for phyllosilicates forming at elevated temperatures in magmatic and metamorphic environments whereby oriented attachment of building blocks occurs along the (001) plane or the 001 direction, or both simultaneously. In this model, the crystallization of phyllosilicates occurs in steps, with multi-ion complexes forming nanoparticles, and nanoparticles coalescing (self-assembly) to form nano-flakes that become domains in larger crystallites by oriented attachment. Adjacent domains can share a common crystallographic orientation or may be rotated at various angles relative to each other. Nanoparticles may be associated with distorted bonds or may be space separated. Thus, the phyllosilicate grows into a mosaic crystal.
Mosaic crystals can also form following classical crystallization models, but the process differs in that the mosaic character involves the intergrowths of nucleation sites (classical crystal-growth process) instead of the coalescence of nanoparticles building blocks (crystallization by particle attachment). These processes may be discerned by the textural differences that result. Oriented particle attachment of building blocks in phyllosilicates is recognized by a loss of closest packing by bond distortion or by space separation at domain boundaries. Crystallization by atom attachment occurs with closest packing within layers, and particles grow independently. The two processes may occur within a single environment and are not mutually exclusive. However, defects generated, for example, by chemical inhomogeneity, mechanical deformation, or sample preparation, cannot be completely excluded, although the use of synthetic, end-member material (e.g., fluorophlogopite) generated from a melt reduces these possibilities. Nonetheless, a particle attachment model is a viable alternative to classical crystal growth processes for high-temperature phyllosilicates with the presented supporting data, although still not yet proven.
Iron oxides are abundant in natural waters and soils and have high capacities for scavenging Pb(II) by adsorption, which affects the transport and fate of Pb on the earth's surface. We investigated ...the adsorption of Pb(II) on magnetites substituted with commonly incorporated transition metals such as Cr, Mn, Co, and Ni. The adsorption capacity, mechanism, and local coordination of Pb(II) were investigated by traditional macroscopic studies, i.e., acid-base titration and batch adsorption experiment, complemented with X-ray absorption fine structure (XAFS) spectrum analysis and surface complexation model (SCM). The substitution increased the surface site density, while pHpzc did not vary. Pb(II) adsorption was not suppressed by the presence of background electrolyte and improved as pH increased. The isotherms were well fit to the Langmuir adsorption model. The XAFS analysis demonstrated that Pb(II) ions were adsorbed on magnetite surface predominantly via inner-sphere complexation, where the adsorbed Pb(II) species was in bidentate binuclear corner-sharing geometry, independent of the adsorption capacity. This adsorption geometry can be applied to fit the experimental adsorption data well with the diffuse layer model (DLM). The substitutions improved the adsorption capacity in the following order: Cr>Ni>Mn>Co, and were discussed regarding the measured values of active site density and local coordination of adsorbed Pb(II). This study is the first documentation of Pb(II) adsorption on magnetite with different substitutions. The obtained results are of great significance for the understanding of Pb(II) surface complexation reactions on magnetite surface.
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•Substitutions improve the adsorption capacities in the following order: Cr>Ni>Mn>Co.•Adsorption isotherms is well fitted by Langmuir model and not suppressed by the presence of background electrolyte.•Inner-sphere complexation in monolayer is the dominated adsorption mode.•The adsorbed Pb(II) are in the geometry of bidentate binuclear corner-sharing, independent of the adsorption capacity.•Relationship between surface and adsorption properties was discussed by adsorption mechanism and active site density.
Smectite growth is of great importance for the geochemistry of clay minerals on the Earth’s surface and their applications in industries. However, the growth process and mechanism controlling the ...physicochemical properties of smectite are still poorly understood. Through an effective integration of particle size distributions (PSDs) and morphology of particles, this study has enhanced the understanding of smectite growth by investigating the growth processes of a synthetic tri-octahedral smectite (saponite). The starting materials were equimolar Mg-saponite and Ni-saponite that had been hydrothermally synthesised at 220 °C. Two Mg-Ni-saponite samples were obtained through further hydrothermal treatment of the starting materials at 400 and 500 °C. A systematic measurement of the size in the ab-plane of numerous saponite particles was performed to obtain their PSDs. The parameters α and β2, derived from PSDs and the morphology of saponite, indicate that saponites grow mainly via surface-controlled growth and likely via supply-controlled growth in open systems. Particle attachment via the edge surfaces of saponite is an accompanying growth mechanism, and talc-like layers favour the “three-dimensional growth”. In addition, the heterogeneous tetrahedral Al distribution of saponite could lead to the formation of elongated laths.
•The particle size distribution was used to predict saponite growth processes.•Saponite growth (ripening) proceeded via mainly surface-controlled growth.•Particle attachment occurred along with the ripening processes.•Talc-like layers favored the “three-dimensional growth” of saponite.•Heterogeneous tetrahedral Al distribution of saponite may lead to elongated laths.
The physicochemical properties of clay minerals strongly depend on their hydration characteristics which therefore have drawn great concerns from different research communities. In the present work, ...the effects of charge density of montmorillonite (Mt) on the hydration characteristics of its interlayer spaces, particularly the siloxane surface, were studied using classical molecular dynamics (MD) simulations. Four Mt. models with various octahedral charges are established, and these charges are compensated with tetramethylammonium cation (TMA). The simulation results showed that water molecules within the hydration layer of siloxane surface will donate hydrogen atoms to form H-bond with the surface oxygen atoms, while those surrounding TMA only slightly have their oxygen atoms point towards TMA. In addition, water molecules prefer to first hydrate the siloxane surface and then the TMA as the water content increases. These findings indicate that water molecules have stronger hydration interaction with siloxane surface than with TMA, and TMA can be ideal counterbalance cation in terms of studying the hydration characteristics of siloxane surface. Charge density can significantly influence the hydration of TMA-Mt. Although increasing charge density will not lead to the formation of stronger H-bond (i.e., no obvious reduction of H-bond length) between water molecules and siloxane surface, water molecules are more likely to be drawn to the siloxane surface and form more H-bonds between them. Subsequently, the hydration energy increases and the mobility of water molecules decreases as the charge density rises. These findings show that charge density can evidently influence the hydrophobicity of siloxane surface, which may further influence its interaction with organic species, e.g., the adsorption of organic contaminants.
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•The hydration of montmorillonite was studied using molecular dynamics simulations.•Charge density can evidently affect the hydration behaviors of montmorillonite.•The hydrophilicity of siloxane surface increased with charge density.•Charge density can affect both the pore structure of organoclays and their affinity toward HOC.
Aragonite, one of the most common biological calcium carbonate minerals, is widespread in marine plankton and neritic sediments (e.g., accounting for 89% of pelagic calcification of CaCO3 in the ...surface ocean). Its dissolution directly affects the export fluxes of CaCO3 in seawater. The aragonite dissolution in the ocean correlates with the increase of partial pressure of carbon dioxide and is pertinent to acidic biomolecules. However, aragonite dissolution in seawater with acidic biomolecules has been overlooked, and the interaction mechanism is unclear. In-situ atomic force microscopy (AFM) was employed to observe the dissolution features of aragonite (110) growth surfaces in succinic acid (SUC, HOOC-CH2-CH2-COOH) solutions. The results demonstrate that (1) both the morphologies and spreading rates of the etch pits formed on aragonite (110) surfaces are altered by the interactions between SUC molecules and the surfaces; (2) the 11‾1 and 1‾11 steps of the etch pits on aragonite (110) surfaces in SUC solutions are kinetically controlled; (3) dissolution rates of aragonite (110) surfaces are proportional to SUC concentrations, which is attributed to the strong complexation between SUC molecules and surface-bounded Ca atoms (≡Ca+); (4) etch pits morphologies of aragonite (110) and calcite (10.4) surfaces are different in SUC solutions, and the spreading rates of the etch pits of the former are one to two orders of magnitude lower than those of the latter. Furthermore, aragonite is found to be more sensitive to SUC molecules than calcite, suggesting that dissolving aragonitic materials could be more easily affected by circumambient biomolecules than dissolving calcitic materials. In seawater that contains organic molecules, the dissolution fluxes of aragonite could be much slower than those of calcite. These findings not only reveal the site-specific interactions between SUC molecules and the ≡Ca+ on aragonite (110) surfaces but also emphasize its implication for the oceanic aragonite dissolution fluxes.
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► Studied substitution improved the UV/Fenton degradation of TBBPA on magnetite. ► Some substituting cations can directly produce OH by Fenton-like reaction. ► Cr substituted ...magnetite is the most promising catalyst for TBBPA degradation. ► Increase in specific surface area and M-OH amount enhanced TBBPA degradation.
Magnetite catalysts doped by five common transition metals (Ti, Cr, Mn, Co and Ni) on a similar level were prepared by a precipitation–oxidation method and characterized by chemical analysis, XRD, TG-DSC, BET surface area and XANES. The effects of substituting metal species on the photocatalytic performance of magnetite were investigated and compared through the UV/Fenton degradation of tetrabromobisphenol A (TBBPA). The substitution of above metals improved the heterogeneous UV/Fenton degradation of TBBPA, and the improvement extent increased in the following order: Co<Mn<Ti≈Ni<Cr. Fewer intermediate product species were detected in the systems with higher degradation efficiency. The distinct effects of these substituting metals on the UV/Fenton catalytic activity of magnetite were discussed in terms of reaction mechanism and surface property varieties. The substituting cations participated in the H2O2 decomposition through Haber–Weiss mechanism and enhanced separation and transfer efficiency of the photo-generated electrons and holes, both of which improved the generation of OH free radicals. Furthermore, with larger specific surface area and higher surface hydroxyl amount, substituted magnetite exhibited stronger catalytic activity for TBBPA degradation.
Element incorporation and partitioning during the evolution of clay minerals have significant implications for element cycling in geochemical processes. The main aim of this experimental study is to ...further our understanding of element redistribution and crystal growth during smectite evolution under different physicochemical conditions. The precursors (i.e., pure Mg- and Ni-saponite) were separately prepared by hydrothermal syntheses at the same set of temperatures (i.e., RT, 50, 150, 180, 200, and 220 °C) for one day. Then the starting materials were obtained from the mechanical mixtures of the identical molar weight of Mg- and Ni-smectite precursors prepared at the same temperature. Subsequently, Series I samples were obtained by hydrothermally treating different starting materials at 220 °C for two weeks while Series II samples were hydrothermally synthesized under various temperatures (220, 300, 400, and 500 °C) for one week using the starting materials prepared at 220 °C. Both the precursors and resultant saponites were characterized by XRD, FTIR, TEM, and STEM. The FTIR spectra of the precursors only exhibit the
Mg3OH and
Ni3OH bands, corresponding to Mg-saponite and Ni-saponite, respectively. However, the occurrence of
Mg2NiOH and
Ni2MgOH bands in the resultant saponite indicates the dissolution of the corresponding Mg- and Ni-saponite precursors and recrystallization of Mg-Ni mixed saponite. The dissolution extents of Mg- and Ni-saponite precursors, which affect the degrees of random distribution of octahedral Ni and Mg in resultant Mg,Ni-saponite, are significantly controlled by the temperature gap (Δ
) between the precursors prepared and the resultant Mg,Ni-saponite obtained. In general, a larger Δ
leads to a higher dissolution extent of saponite precursors and a higher degree of random distribution of octahedral Ni and Mg cations in the resultant Mg,Ni-saponite structures. Thus, the distribution mode of octahedral cations in saponite, which is not only relevant to a given hydrothermal temperature but also dependent on Δ
for final products, cannot be used as a geothermometer. TEM and STEM observations provide visual evidence that the particles of saponite coarsen when Δ
is higher than zero. Both the crystal-chemical and morphological features during saponite evolution suggest that saponite particles coarsen mainly via partial/complete dissolution of precursors followed by recrystallization and growth of Mg,Ni-saponite in which crystal growth by layer attachment cannot be excluded. This study presents an experimental approach to evaluate the evolution of clay minerals in terms of crystal chemistry and crystal growth and offers a better understanding of the contributions of clay mineral evolution to element cycling.
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► Silane grafted montmorillonites have been prepared in various solvents. ► The solvent polarity has important influence on the extent of silane grafting. ► Nonpolar solvents result ...in a larger amount of loaded silane in silylated Mt. ► Nonpolar solvents lead to a higher degree of condensation among silane molecules. ► Silane grafted in nonpolar solvents lock the layers of silylated Mt.
Silylation of clay mineral surfaces has attracted much attention due to their extensive applications in materials science and environmental engineering. Silylation of montmorillonite surfaces with 3-aminopropyltriethoxysilane was carried out in polar-protic and nonpolar solvents. The swelling property of the silylated montmorillonites was investigated by intercalating with cetyltrimethylammonium bromide. Silylated montmorillonites prepared in nonpolar solvents showed a larger amount of loaded silane and a higher extent of condensation among different silane molecules, comparing with those prepared in polar-protic solvents with high dielectric constant. Meanwhile, the silylated montmorillonites prepared in nonpolar solvents displayed poor swelling property due to the linkage between silane oligomers and clay layers, that is, the neighboring clay layers were locked by the silane oligomers. The present study demonstrated that the polarity of the solvents used had an important influence on the extent of grafting, interlayer structure, and swelling property of the silylated products. This is of high importance for synthesis and application of silylated clay minerals.
In this study, TiO2-pillared montmorillonite (Ti-PILC) supported Fe catalysts were synthesized and used for the catalytic oxidation of toluene. The prepared catalysts were characterized by a ...combination of XRD, N2 adsorption-desorption isotherms, XPS, H2-TPR and NH3-TPD. The Fe introduction preserves the mesoporous structure and porosity of Ti-PILC. In the steady-state catalytic test and kinetic analysis, the toluene oxidation over studied catalysts follows the Mars-Van Krevelen mechanism. By the generation of strong acid sites and abundant surface oxygen species, Fe introduction obviously improves the catalytic activity of Ti-PILC for toluene oxidation. But with the increase of Fe content, the activity initially enhances, and then decreases. The effect of Fe species on the promoted toluene oxidation over Ti-PILC was discussed in view of reaction mechanism and above-mentioned variations of physicochemical properties. Furthermore, the Ti-PILC supported Fe catalysts display high stability and superior activity in the presence of water vapor, which present an applied interest.
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•Fe introduction does not change the pillared structure and porosity of Ti-PILC.•Strong acid sites were generated on the surface of Ti-PILC after Fe introduction.•The activity of Fe based Ti-PILC was positively related to surface oxygen species.•The catalyst displays high stability and activity in the presence of water vapor.
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