ABSTRACT
Diffusion of pollutants in the earth's strata threatens both the environment and human health. The clay soil microstructure that plays a crucial role in the diffusion of pollutants is significantly influenced by the pore water chemistry. However, there is still a lack of quantitative evaluation of pore water chemistry on clay fabric evolution. To bring new insights, we systematically examined the impact of water chemistry (mainly refers to salt ion concentration and pH) on the self-assembly form (fabric) of kaolin platelets and evaluated the fabric quantitatively. The results show that as the salt ion concentration increases, the "kaolin book" structure is formed, which can be captured by the (001) and (020) pole figures. Under acidic conditions, kaolin platelets turn randomly arranged; however, with the increase of pH, the edge-to-face (EF) microstructure of kaolin platelets gradually changes to a face-to-face (FF) structure. Under alkali-eq conditions, kaolin platelets form a dispersion assembly dominated by FF repulsion. However, the strong alkaline condition triggers the decomposition of kaolin, leading to a notable decrease in the maximum pole density. The conclusions were substantiated through insightful AFM tests. Moreover, we addressed the advantages and limitations of 1DXRD and 2DXRD by analyzing the trend between the OI and pole density, with 2DXRD being favored for its accuracy. Overall, this study provides insights into clay platelets and the self-assembly of kaolin under different water chemistry conditions, which have significant implications for predicting and modeling the physical properties of clay under special environmental conditions.
ABSTRACT
The microbial-induced carbonate precipitation (MICP) has acquired significant attention due to its immense potential in sustainable engineering applications, particularly in soil improvement. However, the precise control of microbial-induced calcium carbonate precipitation remains a formidable challenge in engineering practices, owing to the uncertain movement paths of bacteria and the nonuniform distribution of soil pores. Taking inspiration from targeted therapy in medicine, this paper presents novel research on the development and validation of magnetically responsive bacteria. These bacteria demonstrate the ability to target calcium carbonate precipitation in a microfluidic chip, thereby promoting an environmentally friendly and ecologically sustainable biomineralization paradigm. The study focuses on investigating the migration of magnetite nanoparticles (MNPs) in aqueous solutions and enhancing the stability of MNP culture liquids. A specially designed microfluidic chip is utilized to simulate natural sand particles and their pores, while an external magnetic field is applied to precisely control the movement path of the artificial magnetic bacteria, enabling targeted precipitation of calcium carbonate at the micron-scale. Verification of the engineered artificial magnetic bacteria and their ability to induce calcium carbonate precipitation is conducted through SEM-EDS analysis, microfluidic chip observations, and the application of the K-means algorithm and ImageJ software to analyze calcium carbonate formation. The influence of the concentration of magnetic nanoparticles on the calcium carbonate production rate was also studied. The results confirm the potential of the artificial magnetic bacteria for future engineering applications. KEY POINTS: ⢠Sporosarcina pasteurii is first time successfully engineered into artificial magnetic bacteria. ⢠The artificial magnetic bacteria show excellent performance of targeted transportation and directional deposition of CaCO3 in microfluidic chip. ⢠The emergence of artificial magnetic bacteria promotes paradigm shift of next generation environmentally friendly biomineralization.
Subject(s)
Calcium Carbonate , Soil , Algorithms , Bacteria , Magnetic FieldsABSTRACT
Coastal water pollution has a significant impact on sedimentary environments, altering the microstructure of clay-rich sediments and further destabilizing river-dominated delta strata. However, the understanding of the microstructure of clay sediment, influenced by burial depth and pore water chemistry, remains limited due to challenges in quantitatively analyzing clay texture at varying depths. The perturbable of clay microstructures, and the cost of deep sampling have hindered such efforts. To address this issue, this study aims to quantitatively analyze the clay anisotropy at different depths and pore water chemistry through laboratory-simulated sediment samples by using centrifugal modeling and 2DXRD technology. The results suggest that 1DXRD (Orientation index) is prone to generating incorrect conclusions, whereas 2DXRD (pole density) yields more precise and reliable results. Specifically, the results indicated that the introduction of salt ions promoted clay precipitation and stabilized the oriented microstructure at shallower depths. In acidic solutions, clay sediment still contained a certain proportion of edge to face (EF) microstructure at depths less than 6 m, suggesting higher soil thixotropy and lower strength than that of clay sediments in other types of solutions. Overall, our findings provide valuable insights into the relationship between water pollution, delta disappearance, and ocean acidification, highlighting the urgent need for effective environmental management strategies to prevent further damage to fragile coastal ecosystems.
Subject(s)
Rivers , Water Pollutants, Chemical , Clay , Ecosystem , Seawater , Hydrogen-Ion Concentration , Geologic Sediments/chemistry , Water , Water Pollution , Environmental Monitoring , Water Pollutants, Chemical/analysisABSTRACT
This study aimed to investigate the superhydrophobic mechanism of kaolinite particles modified with poly(dimethylsiloxane) (PDMS), which has potential as a superior hydrophobic coating. The study employed a combination of density functional theory (DFT) simulation modeling, characterization of the chemical properties and microstructure, contact angle measurements, and chemical force spectroscopy of atomic force microscopy. The results showed successful PDMS grafting onto the kaolinite surface, resulting in micro- and nanoscale roughness and a contact angle of 165°, indicating a successful superhydrophobic effect. The study also identified the mechanism of the hydrophobic interaction through two-dimensional micro- and nanoscale hydrophobicity images, highlighting the potential of this approach for developing new hydrophobic coatings.
ABSTRACT
Water chemistry alteration induced strength weakening of natural sediment, which leads to the differential settlement of infrastructures in coastal areas, has caused numerous disasters and engineering failures. To thoroughly understand the underlying mechanisms of how water chemistry influences the microfabric and mechanical properties evolution of coastal sediments, herein, the authors adopted centrifuge test, X-ray diffraction (XRD), and atomic force microscope (AFM) to quantitatively study the structure anisotropy index (i.e., orientation index (OI)), micromorphological property (i.e., root mean square height (Sq)), and micromechanics (i.e., microscale apparent modulus) of clay sediments in different water chemistry conditions and gravity gradients. The results show that the change rule of OI is: OIsaline > OIalkaline > OIwater > OIacid, along the vertical sedimentary depth. Randomly distributed clay flocs and loose flocculated soil skeleton (mainly consisted by edge-to-face (EF) and edge-to-edge (EE) contact of the kaolinite platelets) are associated with the acidic water chemical conditions. The action of supergravity and face-to-face (FF) repulsive contact mode lead to high degree of anisotropy of kaolinite sediments in alkaline environment. Clay platelets are compacted closely under the synergetic effect of centrifugal pressure and prevailing van der Waals attraction (reduction of electric double layer repulsion) in saline environment. The change of 1/Sq is highly consistent with the change of OI at different depths in different water chemical environments. Along the sedimentary depth (i.e., transition from the normal gravity (1 g) to supergravity (8000 g)), the microscale apparent modulus of kaolinite sediment was found to be the highest in alkaline environment. As the water chemistry changes from alkaline to acidic, however, the microscale apparent modulus of kaolinite aggregate decreased, and it showed the smallest in the saline environment.