Macropore Diameter Research Articles

Colloid mobilization and transport in response to freeze-thaw cycles: Insights into the heavy metal(loid)s migration at a smelting site

Smelting sites often exhibit significant heavy metal(loid)s (HMs) contamination in the soil and groundwater, which are inevitably subjected to environmental disturbances. However, there is limited information available regarding the migration behaviors of HMs in a disturbed scenario. Thus, this work explored the migration of HMs-bearing colloids in response to freeze-thaw treatments by laboratory simulation and pore-scale study. Ultrafiltration results of soil effluents revealed that 61.5 %, 47.6 %, 68.0 %, and 59.2 % of Zn, Cd, Pb, and As were present in colloidal phase, and co-transported during treatments. Nanoparticle tracking analysis (NTA) further confirmed that freeze-thaw cycles were conducive to the generation of colloidal particles and showed the heteroagglomeration among different particles. Pore-network model (PNM) was used to quantify the soil macropore characteristics (macropore diameter, macropore number, coordination number, and Euler value) after treatments. It is evident that freeze-thaw cycles induced the formation of larger macropores while simultaneously enhancing macropore connectivity, thereby establishing an optimal pathway for colloid migration. These findings underscored the importance of environmental disturbances as a trigger for the release and migration of HMs in the smelting site, offering valuable insights for controlling HMs pollution. Environmental implicationThe contaminated site has been subjected to prolonged environmental disturbances, causing the exacerbation of pollutants leaching and frequent occurrences of unstable pollution situations. This work explored the migration of HMs-bearing colloids in response to freeze-thaw treatments by laboratory simulation and pore-scale study. The distinct effects of freeze-thaw treatment on colloidal particle number concentration and macropore characteristics may explain the generation and migration of colloid-associated HMs driven by environmental disturbances. This work revealed the underlying mechanisms driving the redistribution of HMs under freeze-thaw cycles, offering valuable insights for risk assessment of soil and groundwater associated with HMs migration.

Evaporation-induced self-assembly of hierarchical zinc silicate hybrid scaffolds for bone tissue engineering: Meso and macro scale porosity design

In this study, zinc silicate hybrid scaffolds with hierarchical meso/macroporous structures were synthesized using evaporation-induced self-assembly and sacrificial foamy templates. F127 triblock copolymer and polyurethane (PU) foam served as templates for mesoporosity and macroporosity, respectively. The scaffolds were calcined at 550, 650, and 750 °C for 2 h to remove the templates and form the crystalline phase. Analytical techniques, including BET, XRD, SEM, FTIR, and STA, were used to study the impact of calcination temperature on the scaffolds' meso-texture and crystalline phase. Results showed that increasing the calcination temperature to 750 °C significantly enhanced the overall crystallinity. The crystallized ZnO content increased from 10.3 wt% to 32 wt%, and the willemite (Zn2SiO4) crystalline phase formed. Willemite content was approximately 3 wt% at 650 °C and 67 wt% at 750 °C, as determined by quantitative XRD analyses via Rietveld refinement. The emergence of the willemite phase adversely impacted the specific surface area, leading to a reduction from 123.18 m2/g to 2.18 m2/g, and compromised meso-texture-related characteristics, indicating a substantial disruption in mesoporosity. The pure willemite sample was also obtained by increasing the calcination temperature up to 1000 °C. Although the sample contained no secondary phase, the specific surface area and total mesopore volume were drastically reduced, indicating the negative effect of high calcination temperature on mesoporosity. In contrast to the mesostructure, the macrostructure of the scaffolds exhibited negligible sensitivity to calcination temperature, maintaining a mean macropore diameter of around 200 μm. Furthermore, the in vitro performance of the scaffolds was evaluated by assessing apatite formation ability, degradability, and cytocompatibility. It was demonstrated that the scaffolds calcined at 750 °C exhibited superior performance in terms of apatite formation and cytocompatibility when cultivated with MG-63 human osteosarcoma cells.

3D printing calcium phosphate ceramics with high osteoinductivity through pore architecture optimization

The osteoinductivity of 3D printed calcium phosphate (CaP) ceramics has a large gap compared with those prepared by conventional foaming methods, and improving the osteoinductivity of 3D printing CaP ceramics is crucial for successful application in bone regeneration. Pore architecture plays a critical role in osteoinductivity. In this study, CaP ceramics with a hexagonal close-packed (HCP) spherical pore structure were successfully fabricated using DLP printing technology. Additionally, octahedral (Octahedral), diamond (Diamond), and helical (Gyroid) structures were constructed with similar porosity and macropore diameter. CaP ceramics with the HCP structure exhibited higher compression strength (8.39 ± 1.82 MPa) and lower permeability (6.41 × 10−11 m2) compared to the Octahedral, Diamond, and Gyroid structures. In vitro cellular responses indicated that the macropore architecture strongly influenced the local growth rate of osteoblast-formed cell tissue; cells grew uniformly and formed circular rings in the HCP group. Furthermore, the HCP group promoted the expression of osteogenic genes and proteins more effectively than the other three groups. The outstanding osteoinductivity of the HCP group was confirmed in canine intramuscular implantation studies, where the new bone area reached up to 8.02 ± 1.94 % after a 10-week implantation. Additionally, the HCP group showed effective bone regeneration in repairing femoral condyle defects. Therefore, our findings suggest that 3D printed CaP bioceramics with an HCP structure promote osteoinductivity and can be considered as candidates for personalized precise treatment of bone defects in clinical applications. Statement of significance1. 3D printing BCP ceramics with high osteoinductivity were constructed through pore architecture optimization.2. BCP ceramics with HCP structure exhibited relatively higher mechanical strength and lower permeability than those with Octahedral, Diamond and Gyroid structures.3. BCP ceramics with HCP structure could promote the osteogenic differentiation of MC3T3-E1, and showed the superior in-vivo osteoinductivity and bone regeneration comparing with the other structures.

Freeze-thaw effects on pore structure of clay by 3D X-ray computed tomography and mercury intrusion porosimetry

Thaw settlement of soils is a comprehensive reflection of multiscale pore changes induced by freeze-thaw (F-T). In this study, three-dimensional (3D) X-ray computed tomography (CT) tests were utilized to investigate alterations in the macropore and mesopore structures, while mercury intrusion porosimetry (MIP) tests were used to examine the micropore structure in clay due to F-T influenced by different freezing temperatures without water supply. The maximum increase in CT transverse-sectional porosity after F-T can be used to identify where ice lenses formed most abundantly in the clay after thawing, and the diameter and horizontal orientation of the macropores exhibit the most significant increase after thawing. As the freezing temperature decreases, the location becomes farther from the cold end. Macropores are significantly more affected by F-T compared to mesopores, and changes in macropore porosity and diameter can be attributed to moisture migration and freezing shrinkage, with lower freezing temperatures amplifying the influence of freezing shrinkage and weakening the impact of moisture migration. Considering the small size of samples, the MIP porosity was defined to analyze the effects of F-T on the micropores. Compared to the CT volumeratic porosity, the influence of F-T on micropore porosity is less significant. As the freezing temperature decreases, the changes in micropore diameter become smaller. Overall, the lower the freezing temperature, the smaller the changes in macropores, mesopores and micropores. Lastly, a method is proposed for predicting the mass porosity based on the CT volumetric porosity and MIP porosity. This study demonstrates that changes in soil mass porosity reflect a comprehensive representation of multiscale pore variations and provides important theoretical support for thaw settlement control in artificial freezing engineering.

Three-dimensionally ordered macroporous CeZrVOx catalyst with remarkable NH3-SCR performance and SO2 tolerance: Key roles of the morphology and highly dispersed V species

Developing effective low-temperature deNOx catalysts with high activity, SO2 tolerance, and stability is crucial yet challenging. Thus, in this work, CeZrVOx catalyst with a three-dimensional ordered macroporous structure was successfully prepared using the PMMA hard template method, and the catalyst has a macropore diameter of up to 110−140 nm. The modification with highly dispersed V significantly enhances the low-temperature activity and broadens the activity temperature window of the catalyst. This is mainly attributed to the increased number of surface acid sites, as well as the higher proportion of Ce3+ and active surface oxygen species induced by V modification. The V species prepared by this method are highly dispersed on the CeZrOx solid solution and combine with Ce to form CeVO4, which is also an important factor in enhancing catalytic activity. The catalyst does not react with SO2 to produce inactive sulfate species; even the formed cerium sulfate species are beneficial for high-temperature performance. More importantly, due to its unique interconnected three-dimensional ordered structure, the catalyst can significantly inhibit the blockage and coverage of NH4HSO4 on the catalyst, thereby exhibiting remarkable resistance to physical poisoning caused by SO2. Even in high concentrations of sulfur-containing atmospheres, the catalyst still shows high catalytic activity. This work offers meaningful guidance into developing denitration catalysts that show superior performance and robust resistance to both physical and chemical poisoning induced by SO2.

Improvement of absorbability, osteoconductivity, and strength of a β-tricalcium phosphate spacer for opening wedge high tibial osteotomy: clinical evaluations with 106 patients

BackgroundAn ideal synthetic spacer for medial opening wedge high tibial osteotomy (MOWHTO) has not yet been developed. The authors have developed a new β-tricalcium phosphate (β-TCP) spacer with 60% porosity (N-CP60) by modifying the micro- and macro-pore structures of a conventional β-TCP spacer (CP60) that is widely used in clinical practice. The purpose of this study was to compare the absorbability, osteoconductivity, and in vivo strength of the N-CP60 spacer with those of the CP60 spacer, when used in MOWHTO.MethodsFirst, the porosity, diameter distribution of macro- and micropores, and compressive strength of each β-TCP block were examined using methodology of biomaterial science. Secondly, a clinical study was performed using a total of 106 patients (106 knees) with MOWHTO, who were followed up for 18 months after surgery. In these knees, the N-CP60 and CP-60 spacers were implanted into 49 tibias and 57 tibias, respectively. The absorbability and osteoconductivity were radiologically evaluated by measuring the area of the implanted spacer remaining unabsorbed and assessing with the Hemert’s score, respectively. The incidence of cracking in the implanted spacers was determined using computed radiography. Statistical comparisons were made with non-parametric tests. The significance level was set at p = 0.05.ResultsThe N-CP60 and CP60 blocks had almost the same porosity (mean, 61.0% and 58.7%, respectively). The diameter of macropores was significantly larger (p < 0.0001) in the N-CP60 block than in the CP60 block, while the diameter of micropores was significantly smaller (p = 0.019) in the N-CP60 block. The ultimate strength of the N-CP60 block (median, 36.8 MPa) was significantly greater (p < 0.01) than that of the CP60 block (31.6 MPa). As for the clinical evaluations, the absorption rate of the N-CP60 spacer at 18 months after implantation (mean, 48.0%) was significantly greater (p < 0.001) than that of the CP60 spacer (29.0%). The osteoconductivity of the N-CP60 spacer was slightly but significantly higher (p = 0.0408) than that of the CP60 spacer only in zone 1. The incidence of in vivo cracking of the posteriorly located N-CP60 spacer at one month (mean, 75.5%) was significantly lower (p = 0.0035) than that of the CP60 spacer (91.2%).ConclusionsThe absorbability, osteoconductivity, and compressive strength of the new N-CP60 spacer were significantly improved by modifying the macro- and micro-pore structures, compared with the conventional CP60 spacer. The N-CP60 spacer is more clinically useful than the CP60 spacer.Trial registration numberH29-0002.

Electrochemical Etching of Nitrogen Ion‐Implanted Gallium Nitride – A Route to 3D Nanoporous Patterning

Dopant‐selective electrochemical etching (ECE) of gallium nitride (GaN) results in well‐defined porous layers with tunable refractive index, which is extremely interesting for integrating photonic components into nitride technology. Herein, the impact of nitrogen implantation with and without subsequent rapid thermal annealing (RTA) on the porosification process of highly n‐doped GaN ([Si] 3 × 1019 cm−3) is investigated. Implantation is expected to compensate the donors of the n‐GaN layer to spatially suppress porosification during ECE. Optical transmission, electrochemical capacitance–voltage, and X‐Ray diffractometry of as‐grown and as‐implanted GaN suggest successful compensation of n‐dopants. Cross‐sectional scanning electron microscopy reveals the presence of mesopores (diameter 2–50 nm) after ECE of the as‐grown n‐GaN. In the case of implanted n‐GaN, it is found that ECE results in macropores (diameter &gt; 50 nm), which can be suppressed by an intermediate RTA step. The implanted and annealed n‐GaN layers solely exhibit mesopores at the top and bottom, while the intermediate region remains unimpaired. Chronoamperometry and gravimetry provide additional insight and confirm the presence of macro‐ and mesopores in samples without and with RTA, respectively. The results demonstrate a successful implementation of etch‐resisting subsurface layers, which are required for 3D refractive index engineering in porous GaN.

Slow photon photocatalytic enhancement of H2 production in TaON inverse opal photonic crystals

In this study, tantalum oxynitride inverse opal (TaON IO) photonic crystals with different macropore diameters (D) were synthesized in a two-step process involving colloidal crystal templating and thermal nitridation, then applied as visible light-driven photocatalysts for hydrogen production. The TaON inverse opals showed photonic band gaps (PBGs) at visible wavelengths, with the PBG position redshifting as the diameter of the macropores increased in accordance with a modified Bragg's law expression. By aligning the electronic absorption edge of TaON (Eg ∼ 2.4 eV) with the blue edge (short-wavelength side) or red edge (long-wavelength side) of the PBGs, slow photon enhancement of photocatalytic H2 generation was realized. H2 production tests conducted in 10 vol% methanol containing H₂PtCl6 under Xe lamp irradiation (150 W) showed that the hydrogen production rate was enhanced by ∼1.3–1.4 times when the TaON absorption edge (∼510 nm) aligned with blue edge of the PBG (0.3421 mmol g−1 h−1) or the red edge of the PBG (0.3254 mmol g−1 h−1) in the inverse opals. The red edge enhancement was due to increased light absorption and charge carrier generation in TaON, whereas the blue edge effect was likely due to suppression of electron-hole pair recombination. Results demonstrate that photonic crystal engineering to exploit slow photon effects is a viable approach for boosting photocatalytic hydrogen production rates.

Soil Macropore and Hydraulic Conductivity Dynamics of Different Land Uses in the Dry–Hot Valley Region of China

Soil macropores and hydraulic conductivity are important indexes used to describe soil hydrology. In the dry-hot valley region of Southwest China, with its dramatic seasonal dry–wet rhythm, soil properties and hydraulic conductivity can reflect unique dynamics as determined by the interaction between land use and the seasonal dry–wet cycle. In this study, the soil macropore characteristics and hydraulic conductivity of five land uses (traditional corn, plum orchard, pine forest, grassland, and abandoned cropland) in a dry–hot valley region were quantified using X-ray computed tomography (CT) and a mini disk infiltrometer in the rainy season (July) and dry season (November), respectively. The results showed that the soil macropore indexes (soil macroporosity, mean diameter of macropores, connectivity, hydraulic radius and compactness) in the rainy season were, on average, 1.26 times higher than those in the dry season. Correspondingly, the hydraulic conductivity of different land uses in the rainy season was significantly higher than those in the dry season (2.10 times higher, on average). Correlation analysis and principal component analysis (PCA) indicated that the hydraulic conductivity was mainly determined by soil macropore parameters rather than by general soil properties, such as organic matter (OM) and bulk density (BD). The hydraulic conductivity for the five land uses followed the order of PF &gt; GL &gt; TC &gt; PO &gt; AC in both the rainy and the dry seasons. This ranking order reflects the protective effect of vegetation in reducing raindrop splash and soil crust formation processes. The above results can help guide soil water conservation and vegetation restoration in the dry-hot valley region of Southwest China.

Stress-dependent water retention behaviour of two intact aeolian soils with multi-modal pore size distributions

The water retention curve (WRC) of unsaturated soils plays a significant role in evaluating rainfall-induced geohazards in geological and geotechnical engineering, such as ground subsidence and slope failure. Stress can affect WRC because loading/unloading alters not only density but also pore size distribution (PSD). Previous studies of stress-dependent WRC focused on soils with mono- and bi-modal PSDs only. In this study, the WRCs of intact paleosol and intact loess with quadri- and tri-modal PSDs were measured using suction- and stress-controlled pressure plate tests. The full-range PSDs of tested specimens were determined by combining X-ray computed tomography (CT) and mercury intrusion porosimetry (MIP). Experimental results show that the multi-modal PSDs and hence WRCs of both soils are strongly affected by stress in a similar approach. For instance, the relationship between degree of hysteresis and suction showed a double-humped pattern, in which the Peak-I and Peak-II were identified at the relatively low (0.1–20 kPa) and high (20–400 kPa) suctions, respectively. The application of stress resulted in a decrease of hysteresis in the Peak-I (about 30%) but an increase in the Peak-II (about 31%). The increase of hysteresis in the Peak-II differs from the behaviour of soils with mono- and bi-modal PSDs, mainly because the reduction of mega- and macro-pore diameters upon loading increases pore non-uniformity in the range corresponding to the Peak-II.

Carbon-Free, Binder-Free MnO2@Mn Catalyst for Oxygen Reduction Reaction

Reasonable design and feasible preparation of low-cost and stable oxygen reduction reaction (ORR) catalysts with excellent performance play a key role in the development of fuel cells and metal-air batteries. A 3D porous superimposed nanosheet catalyst composed of metal manganese covered with MnO2 nanofilms (P-NS-MnO2@Mn) was designed and synthesized by rotating disk electrodes (RDEs) through one-step electrodeposition. The catalyst contains no carbon material. Therefore, the oxidation and corrosion of the carbon material during use can be avoided, resulting in excellent stability. The structural and composition characterizations indicate that the nanosheets with sharp edges exist on the surface of the wall surrounding the macropore (diameter ∼ 5.07 μm) and they connect tightly. Both the nanosheets and the wall of the macropore are composed of metal manganese covered completely with MnO2 film with a thickness of less than 5 nm. The half-wave potential of the synthesized P-NS-MnO2@Mn catalyst is 0.86 V. Besides, the catalyst exhibits good stability with almost no decay after a 30 h chronoamperometric test. Finite element analysis (FEA) simulation reveals the high local electric field intensity surrounding the sharp edges of the nanosheets. Density functional theory (DFT) calculations reveal that the novel nanosheet structure composed of MnO2 nanofilms covered on the surface of the Mn matrix accelerates the electronic transfer of the MnO2 nanofilms during the ORR process. The high local electric field intensity near the sharp edge of the nanosheets effectively promotes the orbital hybridization and strengthens the adsorbing Mn-O bond between the active site Mn in the nanosheets and the intermediate OOH* during the ORR process. This study provides a new strategy for preparing transition metal oxide catalysts and a novel idea about the key factors affecting the catalytic activity of transition metal oxides for the ORR.

Quantitative characterization of pore-fracture structure of medium and high-rank coal based on micro-CT technology

ABSTRACT Coal is a natural and complex porous medium, which contains pore-fracture structures of different scales. The pore-fracture structures of coal directly affect the characteristics of gas storage and migration. In this paper, high-resolution X-ray CT scanning technology is used to quantitatively characterize the pore-fracture structure of medium and high-rank coals. First, the porosity inversion method is used to determine the optimal threshold segmentation of pores and fracture in medium and high-rank coals. Then, the pore and fracture model of representative element volume (REV) was extracted and established to characterize the area porosity, pore surface area, and shape factor of the two coals, and the relationship between pore surface area and shape factor was investigated. Finally, an equivalent pore network model (PNM) of connected pore topology was established, and pore-throat parameters are statistically analyzed, including pore volume, pore radius, throat radius, throat length, and coordination number. The results show that the average pore diameter and average surface area of macropores in medium-rank coals are larger than those of high-rank coals, and high-rank coals have fewer isolated pores. With the increase of coal rank, the length and radius of the throat gradually decrease, which indicates that the throat of the medium-rank coal has a higher degree of development, and the gas seepage ability in the throat is stronger. The outcome of this study is of great significance for comprehensively understanding the pore-fracture structure of coal in micro-scale.

Selective and efficient removal of emerging contaminants by sponge-like manganese ferrite synthesized using a solvent-free method: Crucial role of the three-dimensional porous structure

Ubiquitous macromolecular natural organic matter (NOM) in wastewater seriously influences the removal of emerging small-molecule contaminants via heterogeneous advanced oxidation processes because this material covers active sites and quenches reactive oxygen species. Here, sponge-like magnetic manganese ferrite (MnFe2O4-S) with a three-dimensional hierarchical porous structure was prepared via a facile solvent-free molten method. Compared with the particle-like structure of MnFe2O4-P, the sponge-like structure of MnFe2O4-S presents an enlarged specific surface area (112.14 m2·g−1 vs. 58.73 m2·g−1) and a smaller macropore diameter (68.2–77.2 nm vs. 946.5 nm). Enlarging the specific surface area increases the exposure of active sites, and adjusting the pore size helps sieve NOM and emerging contaminants. These changes are expected to effectively improve the degradation activity and overcome interference. To confirm the superiority of the sponge-like structure, MnFe2O4-S was used to activate peroxymonosulfate (PMS) for the degradation of multiple emerging contaminants, and its ability to degrade bisphenol A with and without humic acid (HA) was compared with that of MnFe2O4-P. The degradation activity of MnFe2O4-S was 1.6 times greater than that of MnFe2O4-P. Moreover, 20 mg·L−1 HA inhibited the degradation activity of MnFe2O4-S by only 7.1%, which was much lower than that obtained for MnFe2O4-P (53.4%). In addition, the excellent performance was maintained in multiple water matrices. Notably, under lake water matrices, the degradation activity of MnFe2O4-P was inhibited by 35.6% while that of MnFe2O4-S was hardly inhibited. More importantly, the MnFe2O4-S/PMS system was also applicable to the treatment of actual wastewater and 73.0% and 90.1% of total organic carbon and chemical oxygen demand was removed from bio-treated coking wastewater containing non-biodegradable contaminants and NOM. This study provides an alternative route for the green production of high-activity porous spinel ferrites with environmental anti-interference properties.

Quantification of Root Systems and Soil Macropore Networks Association to Soil Saturated Hydraulic Conductivity in Forested Wetland Soils

Understanding the relationship between root systems, soil macropore networks, and soil hydraulic properties is important to better assess ecosystem health. In this study, treatments were performed in forested wetland soils with different vegetation densities, i.e., large (LWa) and small communities (LWb) of reed (Phragmites australis (Cav.) Trin. ex Steud.). At each plot, three undisturbed PVC cylinders (10 cm in diameter and 50 cm in height) were obtained, and X-ray microtomography (μCT) scanning was used to determine the root and macropore architectures. Results showed that the values of total root length and total root volume at LWa were significantly larger than those at LWb (p &lt; 0.05). Imaged macroporosity, macropore volume, macropore length density, macropore node density, macropore branch density, mean macropore surface area, mean macropore diameter, and mean macropore volume at LWa were significantly larger than those at LWb (p &lt; 0.05), whereas mean macropore length, mean macropore branch length, and mean macropore tortuosity at LWb were larger than those at LWa. Total root length and total root volume were positively correlated with soil saturated hydraulic conductivity. Imaged macroporosity, macropore volume, macropore length density, macropore node density, macropore branch density, mean macropore surface area, mean macropore diameter, and mean macropore volume were positively correlated with soil saturated hydraulic conductivity, whereas mean macropore length, mean macropore branch length, and mean macropore tortuosity were negatively correlated with soil saturated hydraulic conductivity. In conclusion, root systems and soil macropore networks constitute a complex synthesis inside soil environments, and together affect soil hydrological responses.

Three-phase co-assembly of compositionally tunable WO3/TiO2 inverse opal photoelectrodes

Heterostructured WO3/TiO2 photonic crystal films in the form of three-dimensional macroporous inverse opals were developed by single-step, three-phase co-assembly of colloidal templates with water soluble precursors enabling simultaneous growth of both metal oxides into a firmly interconnected periodic pore framework whose skeletal walls consisted of uniformly distributed nanoscale type II WO3-TiO2 heterojunctions. A marked size- and composition-dependence of the binary WO3/TiO2 inverse opal properties was evidenced by controlling the W/Ti molar ratio and macropore diameter that allowed Fermi level and photonic band gap engineering according to optical and photoelectron spectroscopies supplemented by electrochemical measurements. Compositional tuning along with the reduction of WO3 nanocrystallite size and the concomitant W5+ defect growth with increasing TiO2 phase content were explored for the optimization of photocurrent generation by WO3/TiO2 inverse opal photoanodes combining reduced charge carrier recombination and optimal slow light trapping. One step co-assembly of mixed metal oxides is concluded as a promising route for the development of heterostructured inverse opal networks with tailored electronic properties and improved solar light harvesting for photo-induced applications.

Effects of freeze-thaw cycles on soil structure under different tillage and plant cover management practices

Soil structure plays a central role in many soil processes that are environmentally relevant. Intermittent freezing of the soil over winter is an important abiotic disturbance in temperate climates and its effects on soil structure depend on the soil’s preexistent structural strength and cohesion. Management choices such as tillage and plant cover after harvest strongly influence soil structure, and therefore the soil’s response to freeze-thaw. We examined the effects of 5 freeze-thaw cycles (FT) on the µCT-detectable structure of intact topsoil cores (Ø=100 mm, h=80 mm) from a long-term rotation and tillage experiment in Denmark. The cores were divided among two tillage treatments and two plant cover treatments, corresponding to a gradient of structural strength: CT-B<CT-V<NT-B<NT-V (CT=conventional tillage, NT=no-till, B=bare fallow and V=winter rye volunteers). We classified the µCT-detectable macropore volume in four size ranges (Full Range, <300 µm, 300–1020 µm and >1020 µm) and analyzed the macroporosity (Vt), mean macropore diameter (dm) and mean Euclidian distance to the nearest macropore (EDm). Additionally, we analyzed the effects of tillage and plant cover on several µCT-derived geometric parameters in Full Range. Overall, NT-B and NT-V resulted in lower macroporosity than in CT-B and CT-V. Similarly, we found fewer, less branched macropores with shorter mean branch length in NT compared to CT for both plant cover treatments. However, we propose that µCT-derived geometric parameters might be confounded by the overlapping influence of relatively few, complex and voluminous coarse macropores and the more abundant, less complex very fine macropores. Freeze-thaw, in turn, caused crumbling of soil around coarse macropores, reducing Vt and dm in Full Range and reducing Vt in the > 1020 µm range. Additionally, FT caused significant increases in Vt and reductions in dm and EDm in the < 300 µm range, indicating creation of new very fine macropores and expansion of previously indiscernible macropores. Overall, the effects of FT were reduced in NT (for equal plant cover treatments) and V (for equal tillage treatments), indicating greater resilience against FT in both cases.

Effect of the interconnecting window diameter of hydroxyapatite scaffolds on vascularization and osteoinduction

The interconnectivity of the scaffold determines oxygen and nutrients transmission, and metabolic waste discharge, which plays a crucial role in cell migration, blood vessel, and tissue regrowth. In the present study, three types of porous hydroxyapatite scaffolds (HAS) with the same pore sizes but different interconnecting window diameters were fabricated by sugar spheres-leaching and heat treatment technique and were used to investigate the effect of interconnecting window diameter on ectopic angiogenesis and osteogenesis. In vitro cell culture experiments showed that the interconnectivity did not influence the performance of cells, while in vivo animal experiments revealed that the interconnecting window diameter of HAS impacted not only angiogenesis but also osteogenesis. The mean diameter of blood vessels was increased with the increase of interconnecting window diameter after 4 weeks of implantation, and the sample of mHAS (with about 0.25 w/m ratio of interconnecting window diameter to macro-pore diameter) exhibited the best osteogenesis after 12 weeks of implantation. This study provides a new reference for designing the porous structure of HAS effectively to enhance the new bone formation of bone tissue engineering scaffolds via vascularization in clinic application.

Synthesis and characterization of macroporous tin oxide coatings

Porous coatings of tin dioxide (SnO2) with a high surface area were obtained using a modified method on glass slides. The coatings were obtained with the “Doctor Blade” method and a closed drying system at room temperature. This drying system provides favorable conditions to decrease significantly cracks on the macroporous coatings. This is an alternative way to synthesize macroporous coatings using polymethylmethacrylate (PMMA) microspheres as a template. A precursor dispersion was made from the mixture of PMMA and tin tetrachloride salt dissolution at 0.5 M. The coatings synthesis parameters were optimized to obtain a uniform porous layer. The precursor dispersion and coatings were studied by thermogravimetric analysis. The coatings material surface area was 87 m2/g determined by BET, and the crystalline structure was characterized by X−ray diffraction. The structure and morphology of the coatings were determined with optical and electron microscope techniques, and the residual contaminations were studied by IR spectroscopy. The macroporous spherical diameter is around 312 ± 35 nm, and they are built by nanocrystalline size particles of 6 ± 1 nm in diameter.

Slow Photon-Enhanced Heterojunction Accelerates Photocatalytic Hydrogen Evolution Reaction to Unprecedented Rates

Slow Photon-Enhanced Heterojunction Accelerates Photocatalytic Hydrogen Evolution Reaction to Unprecedented Rates

Land use impact on carbon mineralization in well aerated soils is mainly explained by variations of particulate organic matter rather than of soil structure

Abstract. Land use is known to exert a dominant impact on a range of essential soil functions like water retention, carbon sequestration, organic matter cycling and plant growth. At the same time, land use management is known to have a strong influence on soil structure, e.g., through bioturbation, tillage and compaction. However, it is often unclear whether the differences in soil structure are the actual cause of the differences in soil functions or if they only co-occur. This impact of land use (conventional and organic farming, intensive and extensive meadow, extensive pasture) on the relationship between soil structure and short-term carbon mineralization was investigated at the Global Change Exploratory Facility, in Bad Lauchstädt, Germany. Intact topsoil cores (upper 10 cm, n=75) were sampled from all land use types at the early growing season. Soil structure and microbial activity were measured using X-ray-computed tomography and respirometry, respectively. Differences in microstructural properties between land uses were small in comparison to the variation within land uses. The most striking difference between land uses was larger macropore diameters in grassland soils due to the presence of large biopores that are periodically destroyed in croplands. Grasslands had larger amounts of particulate organic matter (POM), including root biomass, and also greater microbial activity than croplands, both in terms of basal respiration and rate of carbon mineralization during growth. Basal respiration among soil cores varied by more than 1 order of magnitude (0.08–1.42 µg CO2-C h−1 g−1 soil) and was best explained by POM mass (R2=0.53, p&lt;0.001). Predictive power was only slightly improved by considering all bulk, microstructure and microbial properties jointly. The predictive power of image-derived microstructural properties was low, because aeration did not limit carbon mineralization and was sustained by pores smaller than the image resolution limit (&lt;30 µm). The frequently postulated dependency of basal respiration on soil moisture was not evident even though some cores were apparently water limited, as it was likely disguised by the co-limitation of POM mass. This finding was interpreted in regards to the microbial hotspots which form on decomposing plant residues and which are decoupled from water limitation in bulk soil. The rate of glucose mineralization during growth was explained well by substrate-induced respiration (R2=0.84) prior to growth, which in turn correlated with total microbial biomass, basal respiration and POM mass, and was not affected by pore metrics. These findings stress that soil structure had little relevance in predicting carbon mineralization in well-aerated soil, as mineralization appeared to by predominantly driven by the decomposition of plant residues in intact soil. Land use therefore affects carbon mineralization in well-aerated soil mainly in the amount and quality of labile carbon.