Dual-porosity Structure Research Articles

Water retention behavior and shear strength of artificially cemented granite residual soil subjected to free drying

Artificially cemented soils have been widely used as filling materials in highway and railway construction. The shear strength evolution of filling materials upon moist variation can determine the stability of subgrade and embankments. This study conducted water retention tests, MIP tests, and multi-stage triaxial shear tests on cement-treated granite residual soil (GRS) to determine its water retention curve (WRC) upon free drying, pore structure, and peak shear strength qf, respectively. The water retention behavior and shear strength evolution upon free drying were modeled based on the dual-porosity structure of cement-treated GRS and the effective stress principle, respectively. Results show that the drying-WRC is bimodal and higher cement dosage yields a more severe decrease in the water retention capacity within a specific suction range. For a given confining pressure, the peak shear strength qf increased with increasing cement dosage or suction value s. The peak shear strength qf also solely depends on the suction value in the peak stress state. In addition, the cement-treated GRS has a bimodal pore size distribution curve, and its macro- and micro-void ratios remain almost unchanged after free drying. The bimodal drying-WRC of the cement-treated GRS can be modeled by differentiating the water retention mechanisms in macro- and micro-pores. Moreover, using the macro-pore degree of saturation as the effective stress parameter χ = SrM, the qf–pf′ relationship (where pf′ is the effective mean pressure at failure) under various suction and stress conditions can be unified, and the qf–s relationships at various net confining pressures σ3,net can be well reproduced. These findings can help design subgrade and embankments constructed by artificially cemented GRS and assess their safe operation upon climate change.

Experimental and modeling study of shear strength of unsaturated fine-grained soils with bi-modal water-retention characteristics

The mechanical behavior and strength characteristics of unsaturated fine-grained soils with dual-porosity are of crucial importance in geotechnical designs. Nanyang fine-grained soils have been selected as typical dual-porosity structure soils to perform experimental tests under a wide range of suction and different initial densities while studying its stress-strain-strength properties constitute the main scope of this study. Axial translation and vapor equilibrium techniques are jointly employed to apply a wide suction range. Our data suggest that soil behavior transits from strain-hardening with shear-induced contraction to strain-softening with shear-induced dilation as suction and density increase. By exploiting a bi-modal soil–water retention curve (SWRC) explicitly separating capillarity and adsorption mechanisms, the shear strength is allowed to be analyzed in the capillary suction stress-shear stress space. The strength envelop exhibits bi-linear characteristics. Building upon these findings, we propose a bi-linear shear strength criterion specifically for dual-porosity fine-grained soils. We utilize the obtained test data to evaluate existing strength criteria based on effective stress and dual stress variables that consider the bi-modal SWRC characteristics. The comparison indicates that the proposed bi-linear shear strength criterion can more reasonably represent the variation of shear strength under a wide range of suction for unsaturated dual-porosity fine-grained soils.

Hydrogeological assessment of a major spring discharging from a calcarenitic aquifer with implications on resilience to climate change

Groundwater is a vital source of freshwater, serving ecological, environmental, and societal needs. In regions with springs as a predominant source, such as the Northern Apennines (Italy), resilience of these springs to climate-induced recharge changes is crucial for water supply and ecosystem preservation. In this study, Nadìa Spring in the Northern Apennines is examined through an unprecedented array of multidisciplinary analyses to understand its resilience and unique characteristics. The Nadìa Spring's exceptional response, characterized by a sustained base flow even in the face of drought, is attributed to a combination of factors including a substantial groundwater reservoir, a complex network of faults/fractures, slope instabilities, and karst dissolution. The investigation reveals a dual porosity system in the aquifer, consisting of fast-flow conduits and a diffuse fracture network. While fast-flow conduits contribute to rapid responses during high-flow conditions, the diffuse system becomes predominant during low-flow periods. This dual porosity structure helps the spring maintain a consistent base flow in the face of climate-induced recharge fluctuations. The study shows that Nadìa Spring exhibits remarkable resilience to year-to-year variations in recharge, as evidenced by stable minimum discharge values. While the spring has undergone a decline in discharge over the past century due to long-term climate change, it is becoming more resilient over interdecadal timescales due to transition to a diffuse drainage system that mitigates the impact of reduced recharge. The availability of a century-long spring discharge monitoring was a crucial piece of information for understanding the spring's discharge response and drawing conclusions about its long-term resilience to recharge fluctuations. Continuing long-term monitoring and research in the future will be essential to validate and expand upon these findings in the context of changing climatic conditions. This research serves as a model for assessing strategic groundwater discharge points in geological settings similar to the Northern Apennines.

Salt distribution of earthen heritage site wall and its mechanism in northern China

Salt damage is one of the most important causes of the destruction of earthen heritage sites. The study of salt distribution is of great significance for identifying potential erosion patterns of earthen heritage sites. In previous studies, the salt distributions in only a few earthen heritage sites have been analysed. In this study, 35 typical earthen heritage sites in northern China were investigated that are more widely distributed and more universal than those in previous studies. The salt content and natural water content at different locations on the earthen wall were compared, and the differences in the soluble-salt distribution for different regions of northern China were explored. The results show that the salt content of the loose layer was higher than that of the surface crust, except in the Subash Buddhist Ruins. The difference for the Subash Buddhist Ruins may be the special dual-porosity structure with inter-aggregate pores (large pores) and intra-aggregate pores (small pores) in the coarse-grained soil. The threat of soluble salt to earthen heritage sites in northeast China was found to be far less than that in northwest China, which may have been caused by different rainfall and evaporation intensities. Finally, the reasons for the salt distribution, the prevention of salt damage, and the application of the results to earthen heritage sites in northern China were examined.

Dual-Porosity (Ta0.2Nb0.2Ti0.2Zr0.2Hf0.2)C High-Entropy Ceramics with High Compressive Strength and Low Thermal Conductivity Prepared by Pressureless Sintering

Porous (Ta0.2Nb0.2Ti0.2Zr0.2Hf0.2)C high-entropy ceramics (HEC) with a dual-porosity structure were fabricated by pressureless sintering using a mixture powder of ceramic precursor and SiO2 microspheres. The carbothermal reduction in the ceramic precursor led to the formation of pores with sizes of 0.4-3 μm, while the addition of SiO2 microspheres caused the appearance of pores with sizes of 20-50 μm. The porous HECs exhibit competitive thermal insulation (4.12-1.11 W·m-1 k-1) and extraordinary compressive strength (133.1-41.9 MPa), which can be tailored by the porosity of the ceramics. The excellent properties are ascribed to the high-entropy effects and dual-porosity structures. The severe lattice distortions in the HECs lead to low intrinsic thermal conductivity and high compressive strength. The dual-porosity structure is efficient at phonon scattering and inhabiting crack propagations, which can further improve the thermal insulation and mechanical properties of the porous HECs.

Modeling of water retention behavior of densely compacted Gaomiaozi bentonite based on pore structure evolution

Compacted bentonite has a dual-porosity structure characterized by intra- and inter-aggregate pores. The density of the water preserved in these two types of pores differs, and the interactions between these two types of pores lead to a complicated water retention behavior. In this study, this issue was addressed by establishing a dual-porosity water retention curve (WRC) based on the porewater density and pore structure evolution. The water retention behavior of densely compacted Gaomiaozi bentonite was tested. WRCs at three dry densities were obtained and unified using the water ratio ew (void ratio times the degree of saturation, eSr) as a state variable. Subsequently, mercury intrusion porosimetry (MIP) tests of samples taken from the specimens after the water retention tests were conducted. The intra- and inter-aggregate void ratios were determined based on the results of the MIP tests, and the pore structure evolution was described in terms of the intra-aggregate void ratio (em). The evolution of the microstructure state variable ξm (em/e) along the confined wetting path and its boundary state after water saturation were also determined. Moreover, water contents of the intra- and inter-aggregate pores were differentiated using the boundary water contents at which the intra-aggregate pores reached saturation, and the degrees of saturation of the intra- and inter-aggregate pores were calculated based on their porewater density. Finally, van Genuchten type WRCs were introduced for the intra- and inter-aggregate pores, and the overall WRC was derived by integrating ξm. The WRCs based on the porewater density and pore structure evolution are in better agreement with the testing data than those directly fitted from the experimental calculations, especially in the transition zone where the intra-aggregate pores approach water saturation. This dual-porosity WRC would help in modeling the hydromechanical behaviors of compacted bentonite in deep geological repositories for the disposal of high-level radioactive waste.

Bimodal SWCC and Bimodal PSD of Soils with Dual-Porosity Structure

The soil–water characteristic curve (SWCC) and pore-size distribution (PSD) are fundamental characteristics of soils that determine many physical and mechanical properties. Recent studies demonstrate that both SWCC and PSD sometimes exhibit a bimodal feature. In this paper, soils with bimodal SWCCs are mainly divided into three categories: gap-graded soils, compacted clayey soils, and natural dual-porosity structural soils, from the perspective of microporosity structure. Based on the Fredlund and Xing unimodal SWCC equation, a bimodal SWCC equation is presented. The bimodal PSD equation d v / d log r for mercury intrusion porosimetry (MIP) is derived theoretically, according to the relationship between the mercury intrusion process in MIP and the water desorption process along the drying SWCC. These two associated equations have the same set of parameters, so the corresponding relationship between the bimodal SWCC and bimodal PSD can be directly shown. Three main presenting forms of PSD in MIP tests are summarized. Regression analysis results show that the proposed PSD equation can well fit bimodal PSD experimental data of various soils in the literature, and the SWCCs are predicted at the same time.

Coal permeability prediction method based on the microscopic pore-fracture dual-porosity structure

To better understand the effect of the pore-fracture dual-porosity structure on the coal permeability, the methods for calculating the pore size distribution as well as the fracture width distribution based on the Euclidean distance map function were given first. On this basis, a permeability estimation model considering pore-fracture structure was derived. Then, the pore-fracture structure and permeability of coal samples were quantitatively analyzed by scanning electron microscopy (SEM). By considering the pore size distribution and fracture width distribution characteristics separately, the complex pore structure of the coal sample can be more clearly defined. We found that both pores and fractures have their own distribution characteristics, but due to the effect of resolution, there is some influence in quantifying the minimum size distribution, especially in quantifying the pore size distribution. In predicting the permeability, the direct calculation using the pore and fracture size distribution is significantly larger than the experimental results (1.18✕10−14 m2 vs. 6.9✕10−16 m2 (measured) for the A1 and 1.22✕10−14 m2 vs. 8.1 ✕10−16 m2 (measured) for the A2 at ✕1000 magnification). However, by further considering the effect of tortuosity, more accurate prediction results can be obtained (1.14✕10−15 m2 for the A1 and 1.22✕10−15 m2 for the A2 at ✕1000 magnification). Fractures occupy less space, but they would cause higher permeability. The method proposed in the current study can be further applied to quantify the pore-fracture structure and permeability characteristics in microgeology.

Predicting chemical influence on soil water retention curves with models established based on pore structure evolution of compacted clay

The mechanism of the effect of salt solution on the water retention capacity of compacted clay is studied from the microscopic perspective. Based on the fractal theory and the double-porosity characteristic of compacted clay, the fractal model and dual-porosity model for predicting the soil-water retention curve of compacted clay are established. And the gravimetric water content and matric suction calculated from the pore size distribution data in the relevant literature are fitted by the established models. Results show that there is a “flat section” caused by the dual-porosity structure of compacted clay in the soil-water retention curve, which tends to be lower with the increase of salt solution concentration. In this case, the dual-porosity model fits the data better than the fractal model. The soil-water retention curve shows no “flat section” for the compacted clay with inconspicuous dual-porosity structure. Due to the inhibition of the formation of the diffusion double layer, the reduction of macro-pore volume is prevented during hydration. The chemical correction equation for the fitting parameters is also established, which well reflects the change of the fitting parameters with the concentration of solution by using the two models to predict the soil-water retention curves of compacted BES (ρd = 1.5 Mg/m3) and compacted FEBEX bentonite (ρd = 1.65 Mg/m3). The modified parametric equation is substituted into two models, and subsequently the modified soil-water retention model considering the effect of pore structure and chemical solution is obtained.

Negative Unjacketed Pore Modulus in Limestones? Critical Examination of a Peculiar Laboratory Observation

AbstractThere is recent experimental evidence that the effective pressure coefficient for pore volume exceeds unity in limestones with dual porosity structure. Within the realm of linear poroelastcity, this means that the unjacketed pore modulus is negative. This would be a rather unusual rock behavior since it implies that the pore volume increases for a positive pressure increment during hydrostatic compression. Generally, any deviation of the unjacketed pore modulus from strictly positive mineral bulk modulus means that the deformation is inhomogeneous. We critically examine these observations by attempting to reconcile them with the poroelastic constitutive equations of micro‐inhomogeneous rocks that encompass inhomogeneous deformations. Consistency checks among measured poroelastic constants reveal that the measurement accuracy of pore volume changes concurring with the deformation experiments is not as high as desired. However, assigning moderate variations to the measured pore volume changes either due to random or systematic measurement errors, we show that the experimental observations are indeed reconcilable with the constitutive poroelastic equations. Hence, the negative unjacketed pore modulus observed is deemed plausible though overestimated. Within the poroelasticity framework for micro‐inhomogeneous rocks, a negative unjacketed pore modulus is the result of a partial localization of elastic strain energy in the fluid space. This in turn could be caused by dissolved calcite particles that block thin pore throats and thus generate temporary fluid pressure compartmentalization. A far‐reaching consequence of a negative unjacketed pore modulus is that description of the undrained bulk modulus in rocks with dual porosity structure is more complicated than previously thought.

Microstructure observations in compacted clays subjected to thermal loading

The response of clayey materials to thermal variation has been the subject of extensive studies, given the wide range of engineering applications which involve subjecting soils to substantial temperature fluctuations. A number of hypotheses have been proposed to explain the volumetric changes induced in the clays as a result of temperature variations. Most associate the observed volumetric changes to re-orientation as well as changes in the clay microstructure, with no microstructural experimental evidences to date. The work presented in this note is a first attempt at studying the evolution of the internal structure of two types of clays, an Illite and a Kaolin, compacted dry of optimum, submerged until saturation, reconsolidated to various vertical effective stresses and then subjected to thermal loading. A series of thermal oedometer, mercury intrusion porosimetry (MIP) and tomography tests were conducted in order to induce, detect, and quantify microstructural alterations within the clay as a consequence of temperature changes. Results of heating and cooling tests on Illite showed a thermal contraction which could be attributed to the deformation/collapse of macro-pores in its dual-porosity structure assemblage. The magnitude of the observed contraction varied with the level of pre-imposed effective vertical stresses. Higher effective vertical stresses resulted in larger shear stresses at the contacts of clay-assemblages, and thus in easier deformation of the macro-pores. The Kaolin samples which presented a unimodal pore size distribution, with a relatively small dominant pore size (0.25 μm), did not exhibit changes in the microstructure which could be captured by the MIP.

Gas seepage in underground coal seams: Application of the equivalent scale of coal matrix-fracture structures in coal permeability measurements

Coal is a complex dual-porosity porous medium that consists of both fractures and coal matrices containing pores. The gas seepage characteristics in coals are closely related to the coal matrix-fracture structures. However, the elements that compose the dual-porosity structure of coal (i.e., the coal matrix and the fracture) are often simplified to geometries with regular shapes in theoretical research investigations due to the complexity of coal structures. Therefore, the geometrical size of the simplified geometries can be regarded as the equivalent scale of the coal matrices and the fractures. The equivalent scale characteristics can optimize the properties of the complex fracture system in coal bodies. Based on this, a simplified permeability evolution model in the complete stress-strain process of coals was proposed. The new model takes into account the impacts of the equivalent scale characteristics of the coal matrix-fracture structures, the effective stress and the matrix sorption induced strain on the evolution laws of coal permeability. Then, a simple and convenient method for measuring the permeability in coal seams based on the new permeability evolution model was put forward, and the reliability of the new method was verified by comparing its results with field test data. This research enriches the theory of gas seepage in coal seams and lays a foundation for studying the evolution mechanism of coal permeability during plastic deformation occurs in coal bodies.

Workflow for Upscaling Wettability from the Nanoscale to Core Scale

Wettability is a key factor influencing multiphase flow in porous media. In addition to the average contact angle, the spatial distribution of contact angles throughout the porous medium is important, as it directly controls the connectivity of wetting and nonwetting phases. The controlling factors may not only relate to the surface chemistry of minerals but also to their texture, which implies that a length-scale range from nanometers to centimeters has to be considered. So far, an integrated workflow addressing wettability consistently through the different scales does not exist. In this study, we demonstrate that such a workflow is possible by combining microcomputed tomography (mu CT) imaging with atomic-force microscopy (AFM). We find that in a carbonate rock, consisting of 99.9% calcite with a dual-porosity structure, wettability is ultimately controlled by the surface texture of the mineral. Roughness and texture variation within the rock control the capillary pressure required for initializing proper crude oil-rock contacts that allow aging and subsequent wettability alteration. AFM enables us to characterize such surface-fluid interactions and to investigate the surface texture. In this study, we use AFM to image nanoscale fluid-configurations in 3D at connate water saturation and compare the fluid configuration with simulations on the rock surface, assuming different capillary pressures.

Model development and analysis of coal permeability based on the equivalent characteristics of dual-porosity structure

Abstract Mining is a dynamic fracture process of coal and/or rock. The structural failure of coal bodies will change the coal matrix-fracture characteristics and then affect the distribution characteristics of the coalbed methane (CBM). Because of the structural complexity of coal, the coal matrices and fractures will be assumed to the geometries with rule shapes when the gas seepage characteristics in coals are analyzed. The size of the simplified geometries is the equivalent scale of dual-porosity coal structures (i.e. the equivalent fracture width and equivalent matrix scale). In this paper, according to the reasonable assumptions with regarding to dual-porosity coal structures, a new coal permeability evolution model based on the equivalent characteristics of dual-porosity structure (ECDP model) was built and the effect of the equivalent characteristics of dual-porosity structure on the coal permeability evolution law was analyzed. It is observed that if the initial fracture porosity is constant and the equivalent matrix scale increases, the range in which the permeability of coal rises with rising gas pressure increases; if the equivalent fracture width decreases and the equivalent matrix scale is constant, the range in which the permeability of coal rises with rising gas pressure decreases. The ECDP model is more suitable for revealing the evolution law of the coal permeability when large deformations occur in the coal bodies and/or the coal structure is damaged irreversibly, especially during enhancing CBM recovery.

Transient characteristics of effective porosity and specific yield in bedrock aquifers

Studies of bedrock aquifers have often treated effective porosity and specific yield as having a similar, time-invariant value. Here, we apply a series of tests of specific yield and effective porosity at multiple temporal scales to the Chalk aquifer of east Hampshire, England. These include analysis of natural water level, discharge and water quality variations, numerical model calibrations, hydrograph recession analysis, pumping tests, and tracer tests using both injected and environmental tracers. Values of both effective porosity and specific yield are shown to be transient phenomena that are dependent upon the temporal test scale, an effect which results from the dual-porosity structure of the aquifer. Over short time periods, aquifer response is dominated by preferential flow through the low-storage, high-permeability fracture network; effective porosities on a timescale of hours to days are 0.0001–0.001. Over longer time periods, aquifer response becomes increasingly dominated by the high-storage, low-permeability matrix, with the effective porosity rising to approximate total porosity (0.39) on a timescale of decades. Specific yield also increases as a function of timescale, though there is much less variability than with effective porosity. Our findings demonstrate that it is critical to use an effective porosity value appropriate to the timescale when making transport calculations. Preferential flow through fracture networks is common in bedrock aquifers. Consequently, the transient nature of both effective porosity and specific yield that has been demonstrated in the Chalk aquifer is likely to be broadly representative of most bedrock aquifers.

Short Term Effects of Salinization on Compound Release from Drained and Restored Coastal Wetlands

Over the past two decades, great efforts have been made to restore coastal wetlands through the removal of dikes, but challenges remain because the effects of flooding with saline water on water quality are unknown. We collected soil samples from two adjacent coastal fen peatlands, one drained and diked, the other open to the sea and rewetted, aiming at assessing the mobility and export of various compounds. Microcosm experiments with constant flow-through conditions were conducted to determine the effluent concentrations of dissolved organic carbon (DOC), ammonium ( NH 4 + ), and phosphate ( PO 4 3 − ) during saline–fresh water cycles. Sodium chloride (NaCl) was used to adjust salinity (saline water, NaCl concentration of 0.12 mol L−1; fresh water, NaCl concentration of 0.008 mol L−1) and served as a tracer. A model analysis of the obtained chloride ( Cl − ) and sodium ( Na + ) breakthrough curves indicated that peat soils have a dual porosity structure. Sodium was retarded in peat soils with a retardation factor of 1.4 ± 0.2 due to adsorption. The leaching tests revealed that water salinity has a large impact on DOC, NH 4 + , and PO 4 3 − release. The concentrations of DOC in the effluent decreased with increasing water salinity because the combination of high ionic strength (NaCl concentration of 0.12 mol L−1) and low pH (3.5 to 4.5) caused a solubility reduction. On the contrary, saline water enhanced NH 4 + release through cation exchange processes. The PO 4 3 − concentrations, however, decreased in the effluent with increasing water salinity. Overall, the decommissioning of dikes at coastal wetlands and the flooding of once drained and agriculturally used sites increase the risk that especially nitrogen may be leached at higher rates to the sea.

Transport of chloride and deuterated water in peat: The role of anion exclusion, diffusion, and anion adsorption in a dual porosity organic media

The dual-porosity structure of peat and the extremely high organic matter content give rise to a complex medium that typically generates prolonged tailing and early 50% concentration breakthrough in the breakthrough curves (BTCs) of chloride (Cl−) and other anions. Untangling whether these observations are due to rate-limited (physical) diffusion into inactive pores, (chemical) adsorption or anion exclusion remains a critical question in peat hydrogeochemistry. This study aimed to elucidate whether Cl− is truly conservative in peat, as usually assumed, and whether the prolonged tailing and early 50% concentration breakthrough of Cl− observed is due to diffusion, adsorption, anion exclusion or a combination of all three. The mobile-immobile (MiM) dual-porosity model was fit to BTCs of Cl− and deuterated water measured on undisturbed cores of the same peat soils, and equilibrium Cl− adsorption batch experiments were conducted. Adsorption of Cl− to undecomposed and decomposed peat samples in batch experiments followed Freundlich isotherms but did not exhibit any trends with the degree of peat decomposition and sorption became negligible below aqueous Cl− concentrations of ~310 mg L−1. The dispersivity determined by fitting the Cl− BTCs whether assuming adsorption or no adsorption were significantly different than determined by the deuterated water (p < .0001). However, no statistical differences in dispersivity (p = .27) or immobile water content (p = .97) was observed between deuterated water and Cl− when accounting for anion exclusion. A higher degree of decomposition significantly increased anion exclusion (p < .0001) but did not influence the diffusion of either tracer into the immobile porosity. Contrary to previous assumptions, Cl− is not truly conservative in peat due to anion exclusion, and adsorption at higher aqueous concentrations, but the overall effect of anion exclusion on transport is likely minimal.

Numerical simulation study on CO2 storage in coalbed

ABSTRACTAlthough CO2 storage has been comprehensively investigated, fewer scholars have taken the effect of temperature and the dual-porosity structure of coal into account, which brought a large deviation for the study of CO2 storage. In this work, a hydraulic-mechanical-thermal coupled model of CO2 storage is established, considering the dual-porosity structure features and non-isothermal adsorption of coal. The controlled variable method was used to simulate CO2 injection into coalbed with different characteristic parameters. The results show that the CO2 storage rate follows the law of first reducing and then stabilizing. The variation of permeability is a competition result of two types of factors: one is the coal matrix shrinkage caused by pressure increase and the other is the coal matrix expansion caused by the increase of temperature and CO2 adsorption. In the process of CO2 injection into the coal seam, the matrix expansion caused by the increase of temperature and CO2 adsorption becomes the dominant role, which makes the permeability reduce with time. The higher the initial temperature of coal seam, the less the volume of CO2 adsorbed by the unit mass of coal and the smaller the CO2 storage rate; the greater the degree of coal fracture development, the greater the CO2 seepage rate, the smaller the CO2 storage rate, and the increased volume strain of coal, which can reduce the storage rate of CO2. The initial temperature of coalbed, fracture development degree, and geostress have different degrees of influence on CO2 storage. Taking CO2 storage rate as an evaluation criterion, the fracture development degree has the greatest impact on it, and the influence of geostress is the least.

L-Arginine-Catalyzed Synthesis of Nanometric Organosilica Particles through a Waterborne Sol-Gel Process and Their Porous Structure Analysis.

We report an efficient and easy-to-implement waterborne sol-gel process for the synthesis of nanometric organosilica particles. In this process, tetraethyl orthosilicate (TEOS) and 3-(methacryloxy)propyl trimethoxy silane (γ-MPS), employed as silica sources, were heterogeneously delivered in an aqueous solution of l-arginine, a basic amino acid used as a catalyst, from a top organic layer. Co-condensation of TEOS with γ-MPS led to the formation of organosilica particles with diameters between 30 and 230 nm when increasing the γ-MPS content from 0 to 10.1 mol % in the silica source. Nitrogen sorption analyses confirmed the microporous nature of the obtained particles after calcination. The Brunauer-Emmett-Teller (BET) surface areas increased from 27 (before calcination) to 684 m2 g-1 (after calcination) for the organosilica particles containing 10.1 mol % of γ-MPS. Fourier transform infrared spectroscopy and 29Si NMR were employed to analyze the chemical structure of the organosilica spheres and provide insight into the mechanism of particle formation. In the second part, hybrid organosilica particles with a core-shell morphology were synthesized through the combination of Pickering emulsion and the sol-gel process. γ-MPS emulsion droplets stabilized by tiny silica particles (formed in a separate step) were first generated and used as seeds to grow a silica shell on their surface through TEOS addition from the top organic layer. Transmission electron microscopy and pore size analyses of the resulting particles after calcination revealed a unique dual-porosity structure with a mesoporous inner core and a micro/mesoporous silica shell with ink-bottle-type pores.

Facile Synthesis and High Activity of Novel Composite C/Fe-BiVO₄ Photocatalyst for Degradation of Cipfloxacin.

A novel C/Fe-BiVO4 nanosheet composite photocatalyst combining the properties of both semiconductor and Fenton like catalyst was prepared via a two-step method involving Resin carbonization and hydrothermal process. The samples were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared spectroscopy (FT-IR) and nitrogen adsorption-desorption measurements and fluorescence spectrum technique. Structure analyses indicated that C/Fe-BiVO4 presented a nanosheet and macro-meso dual porosity structure. Photocatalytic degradation of cipfloxacin (CIP) (10 mg/L) was studied using C/Fe-BiVO4 under simulated solar light (SSL) irradiation in a cylindrical reactor. Three experimental parameters were chosen as independent variables: pH, C/Fe-BiVO4 concentration, and H2O2 concentration. The catalyst shows high catalytic activity in cipfloxacin photodegradation reaction with the cipfloxacin conversion efficiency higher than 95.61% at experimental conditions (catalyst dose, 0.75 g · L-1; H2O2 dose, 200 mg · L-1; solution pH, 5.0). The process obeyed the pseudo first-order kinetics by assuming a constant concentration of OH•. The as-prepared composite exhibited high efficiency in the photocatalytic decomposition of Cipfloxacin (CIP) by the assistance of H2O2. This method is promising due to its inexpensive starting materials and good photocatalyst for degradation of emerging micropollutants.