Seawater Penetration Research Articles

Self-passivation/self-delivery/self-healing anticorrosion polymer coating for marine applications

Corrosion of steel in the marine environment greatly reduces their service life. Polymeric coatings are the most popular anticorrosion technology, but seawater penetration cannot be prohibited because of the distinct stacking structure of the macromolecular chains. In this context, a novel anticorrosive hyperbranched polyurethane-based coating with dopamine (DOPA) at the terminals is prepared herein. The built-in DOPA is able to capture the iron ions released from the corroded substrate and form DOPA-Fe3+ complexation, which further cooperates with the surrounding seawater and imparts self-passivation, self-delivery and self-healing capabilities to the coating. Under the joint action of these measures, the corrosion of tinplate (serving as the steel model) is reduced to a record-low level (corrosion current = 1 × 10−9 A cm−2, corrosion rate = 1 × 10−5 mm year−1). Conceptually, the present dynamic active anticorrosion strategy greatly outperforms the traditional static passive approach, and turns the unfavorable but unavoidable seawater into a favorable factor, which paves the way for the development of long-lasting marine coatings.

Macrozoobenthos in the estuary of the small salmon river of Sakhalin Island on example of the Gornaya River

Estuaries as a connecting link between freshwater and marine ecosystems play a special role in salmon rivers. The success of adaptation of juvenile salmonids during the transition to the marine period of life depends on the conditions in estuaries. The work continues the previously started series of publications on the rivers of Sakhalin Island. Using the example of one of the small watercourses in the southeastern part of the island, the hydrological parameters and the structural organization of benthos communities in the atypical estuary have been considered. In the absence of storm surges, penetration of sea water into the water body does not occur; at high tide, water with a salinity of more than 12 psu is observed only at the mouth at the bottom; at low tide, the estuary is completely filled with water with a salinity of 0.1 psu and lower. Studies of the hydrological regime and composition of the bottom fauna were carried out in July 2022. Zoobenthos samples were taken along the longitudinal profile of the estuary at five sections (75 samples in total). Most of the estuarine reach is inhabited by species characteristic of the lower parts of the island watercourses. High environmental variability determines the formation in the estuary of young and unstable benthos communities represented by rapidly reproducing small-sized species.

The synergistic effect of microorganisms and multiple admixtures on improving the self-healing of cracks in biogenic mortar exposed to different marine environments

Existing research has inadequately addressed the synergistic effects of microorganisms and admixtures in promoting self-healing behavior and mechanisms of cracks in marine environments, including the atmospheric zone, tidal-splash zone, and submerged zone. This study primarily involved the incorporation of multiple admixtures and microorganisms into cement to prepare two types of biogenic mortars: Bacillus pasteurii-based mortar (BPM) and Bacillus subtilis-based mortar (BSM), with ordinary mortar (OM) serving as the control group. The mechanical properties, electrical flux, and pore structure of the mortars were investigated. Additionally, the self-healing behavior and mechanisms of cracks were studied under atmospheric, tidal-splash, and submerged conditions. The results indicate that with increasing curing age, the synergistic effect of admixtures and microorganisms continuously refined the pore structure of the specimens and enhanced their flexural strength, compressive strength, and resistance to chloride ion penetration. The atmospheric environment was found to be unfavorable for the self-healing of cracks in the specimens. However, in the submerged and tidal-splash zones, the combined action of microorganisms and admixtures led to more pronounced self-healing phenomena in the biogenic mortars compared to OM. Particularly, the self-healing effect of BSM cracks was more pronounced in the tidal-splash zone, with a 100% self-healing efficiency observed after 53 days. This was attributed to the ability of microorganisms in the tidal-splash zone to induce calcium carbonate precipitation on the surface of cracks in admixture-modified cementitious materials, thereby reducing the penetration of seawater, CO2, and O2 into the cracks, lowering the carbonation reaction of Ca(OH)2 crystals, and reducing the formation of brucite crystals inside the cracks, consequently enhancing the water permeability resistance of the specimens. These research findings hold significant engineering implications for improving the durability and service life of coastal self-healing concrete structures.

Modeling coastal inundation for adaptation to climate change at local scale: the case of Marche Region (central Italy)

Climate change is raising sea level rise and storminess effects on coastal systems, affecting the morphology of coastlines and impacting coastal communities and ecosystems. It is essential to gain information at an adequate scale to identify effective adaptation measures. This is of major importance in areas combining high vulnerability to climate change with high socio-economic development, like the Northern Adriatic coastal area. To this aim, in this work two different approaches have been applied to investigate inland penetration of sea water along the Marche Region: (a) a simple “bathtub” method applied to the entire Marche coastline, to highlight areas likely prone to intense inundation; (b) a more accurate numerical model applied to two test sites, to gain detailed knowledge of inundation perimeters. Both approaches have been applied with forcing conditions provided by the Intergovernmental Panel on Climate Change and the Copernicus Climate Change Service through the RCP8.5 emission scenario projected to 2070. Results showed that a 100-year return period sea storm would cause the inundation of beaches and infrastructures located along the coast, as well as affecting harbor facilities and urban areas. Information obtained with the model has been integrated in the Regional Plan for Adaptation to climate change to define specific adaptation measures.

Two metasomatic events recorded by noble gas characteristics in the Finero mantle wedge: Extreme fractionation (He, Ar) and seawater penetration into the mantle deformation zone

Here, we report that the Finero phlogopite peridotite massif, southern Italy, a sliver of the former subcontinental lithospheric mantle (SCLM), experienced two stages of fluid/melt percolation, which had different origins and scales in the mantle wedge based on noble gas analysis and the deformation structure. In the field investigation, we found a mylonite zone several tens of meters wide in the massif, inferred to have been caused by deformation in the mantle. Systematic differences in noble gas compositions between samples from inside and outside the mylonite zone reflect two stages of fluid/melt infiltration. In the first event, the fluid/melt with a noble gas mixture of seawater, radiogenic, and mantle components penetrated the Finero SCLM. It likely occurred simultaneously with the famous metasomatism that crystallized phlogopite and amphibole throughout the massif. This first event produced a 4He/40Ar ratio much higher than those of the convecting mantle and crustal components, probably during metasomatism by hydrous melt derived from the slab in the mantle wedge. The second event was probably synchronous with the development of mylonitization and locally supplied seawater-rich components. The 40Ar/36Ar ratios tend to be atmospheric as mylonitization progresses. Our results provide two insights: (i) the first demonstration of the formation of extremely high He/Ar ratios during mantle metasomatism of natural samples and (ii) differences in the deformation structure affecting the noble gas composition and distribution in the SCLM. Regarding (i), the elemental fractionation can be attributed to two factors: one is the difference in the solubility between noble gas elements in particular minerals in the slab, and the other is the difference in the diffusion coefficients of He and Ar. Our results imply that the recycling of volatiles within subduction zones is significantly influenced by the thermal structures of slabs. This is because these thermal structures control the stability of hydrous minerals on the slabs, temperature conditions, and potentially the efficiency of diffusion in mantle wedges.

FLY ASH AND SILICA FUME SUBSTITUTION ON COMPRESSIVE STRENGTH AND PERMEABILITY OF CONCRETE IN THE MARINE ENVIRONMENT

Cement, as a concrete-forming material, is a contributor to CO2 emissions in the world. Reducing cement and substituting fly ash and silica fume as concrete substitution materials in the manufacture of concrete makes green concrete without lowering the quality of the concrete. Concrete in the marine environment is frequently destroyed by severe environmental elements, such as seawater penetration; hence, high-performance concrete materials are required. This research aims to analyze the effect of adding fly ash and silica fume on concrete compressive strength and permeability. The specimens made were then immersed in freshwater and seawater. Analysis of the compressive strength test result shows that the compressive strength values ​​for the samples treated with freshwater or seawater have exceeded the expected compressive strength of 30 MPa. The permeability test on the test object resulted in the supplementary fly ash to the concrete immersed in freshwater having a good value, i.e., the water penetration was below that required by DIN-1045, namely 5 cm. The penetration of concrete with fly ash impressed in seawater is good only in concrete with a 10% fly ash variation. The water penetration value still meets the requirements in concrete with silica fume for all variations with freshwater and seawater treatment.

INFLUENCE OF TEMPERATURE ON THE RECOVERY OF OILS SPILLED IN SEAWATER USING HYDROPHOBIZED POST-CONSUMER POLYURETHANE FOAMS

Although economically vital, whether in cold Scandinavian or warm Caribbean waters, offshore oil exploration accounts for oil spills at sea. One of the mechanisms used for recovering spilled oil consists of using porous materials with high sorption capacity in the cleanup process. Post-consumer polyurethane foams (PC-PUFs) are highly porous polymers typically disposed by consumers in Brazilian cities. In this work, PC-PUFs obtained from discarded mattresses were modified superficially to promote hydrophobization and increase their selectivity for oils over water. The characterization showed foams with well-defined macro pores. Surfaces of MoS2-modified foams (MoS2-PC) showed an increase in seawater penetration rejection and oil attraction when compared to unmodified foams (Un-PC). Sorption tests simulating oil spillage at 1 °C, 12 °C, and 23 °C were conducted to verify the influence of temperature on oil recovery by PC-PUFs. Tests on the seawater-diesel system showed that diesel, a low-viscosity oil with slight viscosity variation with temperature reduction, penetrated both Un-PC and MoS2-PC foams easily, making the modifications on MoS2-PC irrelevant. In the seawater-S46 lubricant system, which had a more viscous oil and presented a substantial variation in viscosity with temperature reduction, there was greater difficulty in penetrating the Un-PC foam when compared to MoS2-PC, showing that the modifications were responsible for the increase in the recovery of more viscous oils spilled in seawater at different temperatures.

A magnetic “Band-Aid” incorporated with Fe3O4 NPs modified epoxy binder for in-situ repair of organic coating under seawater

To repair the anti-corrosive coatings directly under seawater is an up-and-coming approach, which can effectively prolong the service life of coated steel structures once the coatings suffered from unexpected scratches. Inspired by the design of Band-Aid for the healing of wound, a magnetic “Band-Aid” (MB) combined with oleic acid modified Fe3O4 nanoparticles (OMNPs) was designed to realize the in-situ repair of anti-corrosion coatings under seawater and the experimental results indicated that this coating repair method by MB incorporated with OMNPs modified epoxy binder is satisfying and effective when the addition of OMNPs epoxy binder was more than 1.0 wt%. Furthermore, the penetration of seawater in the vertical direction of the coating can be prevented by MB during the curing process of epoxy binder, the formation of permeation channels parallel to the coating can be blocked with the aid of OMNPs, which mainly based on the magnetic force between the MB and substrate steel, as well as the competitive-wetting and target-driving functions of OMNPs. The current work may provide a feasible approach to repair the organic anti-corrosion coating directly, which coated on the steel structures under seawater.

Growth and mineralization characteristics of Bacillus subtilis isolated from marine aquaculture wastewater and its application in coastal self-healing concrete

There are many studies on the microbial remediation of cracks in cement-based materials in freshwater environments but fewer studies in marine environments, especially the use of bacterial strains with high mineralization ability obtained from marine aquaculture wastewater for coastal self-healing concrete. In this paper, the growth and mineralization characteristics of Bacillus subtilis (BS) isolated from seawater in shrimp farms were investigated, and the BS was used to repair coastal concrete cracks. Common Bacillus pasteurii (BP) was used as a control strain. The results showed that although the growth laws of the BS and the BP were similar, the mineralization ability of the BS was higher than that of the BP. In addition, in the process of crack self-healing, BS-induced calcium carbonate filled the mortar cracks (the initial crack width range was 0.20–0.25 mm), making the mortar cracks almost self-healing within 1 day, and its area self-healing rate was 2 times that of the BP mortar and 7 times that of ordinary mortar. This property of the BS can more successfully decrease the penetration of seawater into the mortars through cracks, improving the durability of its structures. These results have had a positive impact on the development of coastal self-healing concrete.

Bond performance and mechanisms of sulphoaluminate cement-based UHPC for reinforcing old concrete substrate

Many essential reinforced concrete structures exposed to marine environments have experienced severe corrosion since their construction due to their aggressive surroundings. Thus, one of the major problems facing reinforced concrete structures nowadays is their repair and reinforcement. Compared to conventional ordinary Portland cement (OPC) concrete, ultra-high performance concrete (UHPC) is commonly used for strengthening existing concrete stuctures due to its excellent mechanical properties and durability. However, UHPC made with Portland cement can not show high strength early, which may not meet the needs of some special projects that require to show early strength performance of the concrete. Since concrete with early strength performance has relatively little research in bonding porperties between new and old concrete, further research is need. Sulphoaluminate cement (SAC)-based material is an effective repair material. However, the commonly-used SAC-based repair material has a relatively high water to cement ratio and large porosity, leading to poor performance and a higher risk of seawater penetration. This paper investigates the use of SAC-based UHPC with low water to cement ratio andporosity as a repair material for OPC concrete substrate, providing a reference for the reinforcement of reinforced concrete structures that are exposed to the marine environment. Considering the shrinkage of the repair material, this paper uses cylinder specimens and prism samples to compare the bond performance. The bond performance between SAC-based UHPC and OPC substrate using common interfacial agents is studied, and bond strength testing and SEM analysis are carried out. The results indicate that SAC-based UHPC has beneficial mechanical properties, including compressive and flexural strength, at an early age, which makes it possible to use the SAC-based UHPC as repair material for concrete structure. In addition, bonded specimens with no bond agents at the interface show a better bond performance than that of samples with different interfacial agents, and SEM analysis of the interface transition zone verifies the results of the bond strength test.

A novel bathymetry signal photon extraction algorithm for photon-counting LiDAR based on adaptive elliptical neighborhood

Ice Cloud and Land Elevation Satellite-2 (ICESat-2) uses a 532-nm laser with a strong seawater penetration ability, and can provide reliable water depth information for sea areas that in situ bathymetric data are lacking. However, because of the complexity of underwater terrain, background noise, optical signal attenuation in water, and other factors, there are still some obstacles to accurately extract bathymetry photons using ICESat-2 data This paper proposes an novel bathymetry signal extraction algorithm based on an adaptive elliptical neighborhood window. The direction-adaptive elliptical neighborhood strategy ensures the directionality and continuity of signal extraction. The size-adaptive neighborhood strategy satisfies the demand for extraction of both shallow, dense signals and deep, sparse signals. The kernel density estimation (KDE) based strategy for sea surface elevation extraction and above-water signal separation makes it possible to determine the sea surface elevation accurately while correctly separating the above-water photons. Four study areas with different environmental conditions in the Xisha Islands, the Bahamas, and the Gulf of Aden were selected, and the key results are as follows. (1) For a water-land interface area with dense noise, the proposed algorithm can effectively reduce the impact of land and accurately eliminate noise photons in shallow water. (2) For an extremely sparse signal in a deep-water area, which is difficult to process using classical algorithms, the proposed algorithm can accurately extract signal photons in water approximately 50 m deep while effectively extracting the dense signal photons in shallow water. (3) In the extraction results obtained using this algorithm, the signal strip has better continuity and smoothness than the classical algorithm and therefore can portray the seafloor terrain more completely. As the in situ water depth confirms, the overall mean absolute error (MAE) and mean relative error (MRE) of the water depth information extracted by the proposed algorithm are 0.79 m and 7.54%, respectively, which indicate high reliability.

Effects of rheological stratification and elasticity of lithosphere on subduction initiation

The breaking and bending of rigid and elastic lithosphere was probably essential for the initiation of plate subduction, although how this occurred is still poorly understood. Here we test effects of rheological stratification and elasticity of lithosphere on subduction initiation, which are possibly resulting from thermal cracking and seawater penetration into the lithosphere. In addition to the strong influence of water on rheological behavior, the material rigidity is also sensitive to the development of crack and fluid saturation. Numerical modeling indicates that water-weakening and a low-rigidity lithosphere are essential for the initiation of plate subduction, and such conditions are likely to have arisen on the early Earth due to extensive thermal contraction of the planet. Our results indicate that the formation of thermal cracks and penetration of seawater play an important role on subduction initiation, and are likely to have operated on planets other than Earth. However, if the ocean is disappeared, fluid penetration is likely to cease and plate tectonics would have stopped due to increasing the strength and rigidity of the lithosphere.

Hydrodynamic modelling of a stratified estuary: the example of the Neretva River (Croatia)

In this paper, we describe a numerical model for unsteady stratified flow without mixing at the interface (halocline), which was applied for the calculation of salinization in the Neretva River (Croatia) i.e. the first line of penetration. The mathematical model is based on the principles of conservation of mass and momentum. Since, the set of equations does not have analytical solution it is solved numerically, e.g. through finite element method (FEM). Computed variables are water discharges and elevations for each layer separately in each point of finite element mesh. Calibration of the model is based on in-situ measurements. The most important factor for salt water intrusion in an estuary is the fresh water discharge. In the Neretva estuary, salt water was found in Metkovic (22 km from the sea) for freshwater flows of less than 180 m3/s, while for flows greater than 500 m3/s salt water was completely extruded from the riverbed. The plan is to build a mobile barrier (gate) in the Neretva River to protect it against sea water penetration. Additionally, upstream of the barrier, fresh water would be provided in the riverbed that could be primarily used for irrigation. The same numerical model has been also successfully applied to the estuary of the Jadro River, a small river near Split. Since the model is general, it can be applied on any river mouth with stratified conditions. The projections of sea level changes in the Adriatic Sea shows increase of a few decimeters in 21st century. Generally, rising sea levels will increase salt water pressure on the coast, estuaries, water resources, aquifers and farmland. Therefore, the management of estuaries will require even greater engagement of experts from different areas to successfully deal with future difficulties.

Multi-mode chemical exchange in seafloor alteration revealed by lithium and potassium isotopes

Elemental exchange during seafloor alteration exerts substantial control on the chemical compositions of seawater and oceanic crust, as well as the global elemental cycling. However, detailed processes and mechanisms for element transport and isotopic exchange remain unclear. Here, we report Li and K isotopic compositions across an altered MORB-like pillow basalt from Mariana Trench. We find large and systematic isotopic variations on a centimeter scale, with δ7Li decreasing from +9.07‰ to +6.21‰ and δ41K increasing from −0.12‰ to +0.33‰ from the rim to the core. The heavier-than-mantle Li and K isotopic compositions in the core likely inherit from an enriched mantle source rather than post-magmatic alteration processes. The low K and high Li isotopic compositions at the outmost rims result from adsorption during seawater-rock interactions. The basin-shaped elemental and isotopic variations were subsequently formed by chemical diffusion and spontaneous seawater penetration from the weathered rind to the interior of pillow basalt sample. This study uses a small-scale sampling approach and provides the first evidence for multi-mode chemical exchange in oceanic basalts and improves our understanding of the seafloor alteration processes.

Oxidizing fluids associated with detachment hosted hydrothermal systems: Example from the Suye hydrothermal field on the ultraslow-spreading Southwest Indian Ridge

The redox state of hydrothermal fluids on mid-ocean ridges, which is indirectly affected by the depth of hydrothermal circulation and crustal permeability, plays an important role on the diversity of hydrothermal precipitates and associated ecosystems. Primary hydrothermal fluids that circulate along detachment faults are generally reducing as a result of the serpentinization of ultramafic rocks, while significant seawater infiltration may shift the redox state from reducing to oxidizing. However, the depth of penetration of oxidizing fluids into detachment related systems remain unclear, largely because current observations are based primarily on hydrothermal products that precipitated at the seafloor. Here, we report the first observations of oxidizing mineral assemblages in stockwork samples from the Suye hydrothermal field on the ultraslow spreading Southwest Indian Ridge. This field is hosted by mafic lithologies, while the low As, high Ni and Co contents, and high Au/As, Ag/As, and Ni/As ratios in pyrite from the stockwork samples indicate that the fluids reacted with both mafic and ultramafic rocks in the subseafloor. The high δ34S values (average of 9.8‰) indicate a high proportion (up to 50%) of seawater derived reduced sulfur involved in the stockwork zone formation. The high homogenization temperatures (∼320 °C) and salinity (∼12 wt.% NaCl) of fluid inclusions indicate that the stockwork zone of Suye was formed by a fluid that underwent phase separation deeper in the system that was subsequently diluted by 4–5 times subsurface seawater. The deep penetration of seawater is facilitated by the unique tectonic setting of the Suye hydrothermal field, which occurs between the two stage detachment faults that creates high permeability. Our findings demonstrate that hydrothermal fluid associated with detachment faults could be oxidized below the subsurface stockwork zone, and that deep-rooted detachment faults at ultraslow-spreading ridges can sustain both reducing and oxidizing hydrothermal systems in the same fault system. These results call for a reevaluation of the fate of base metal in ultramafic hosted hydrothermal fields.

Long-term moisture penetration in concrete exposed to marine tidal conditions

The depth of concrete influenced by seawater penetration plays a vital role in many durability processes affecting reinforced concrete structures in the marine tidal zone. In this study, a phenomenological moisture transport model in concrete is developed and is validated with numerous experimental results reported in the literature. The boundary conditions for cyclic wetting–drying in the tidal zone are formulated based on a novel superimposed tide model that more accurately represents real-time tides. The moisture profiles over a large number of wet–dry cycles are evaluated in the tidal zone using the developed models. The long-term moisture penetration characterised by (i) the influential depth of moisture transport (IMDT) and (ii) the cyclic water absorption amount (CWAA) is compared at various locations along the entire tidal zone. Sensitivity analysis was carried out to estimate the influence of material properties and environmental conditions on the IDMTs and CWAAs. The results of the study revealed that the IDMTs and CWAAs predicted by the realistic superimposed tide model are about 3.5 times greater than those predicted by conventional diurnal tide models. This substantial difference justifies the importance of the correct choice of tide model for durability studies in the tidal zone.

Xigaze ophiolite (South Tibet) records complex melt-fluid-peridotite interaction in the crust-mantle transition zone beneath oceanic slow-ultraslow spreading centers

The formation and evolution of the crust-mantle transition zone (CMTZ) under oceanic slow-ultraslow spreading centers, compared with the well-documented examples that developed under fast spreading centers, remain largely unknown due to the lack of suitable targets. In this study, we systematically examine the CMTZ of the Xigaze ophiolite in the Yarlung Zangbo suture zone (south Tibet). This ophiolite represents a rare lithospheric fragment produced in oceanic slow-ultraslow spreading settings. We conduct detailed field mapping and petrological as well as geochemical studies on the CMTZ in the Dazhuka massif, the easternmost segment of the Xigaze ophiolite. Our aim is to characterize the lithological architecture and associated melt-fluid-peridotite interaction history of the CMTZ. The CMTZ (~1800 m thick) in the Dazhuka ophiolite consists of 4 subzones with complex lithological associations. They range successively from clinopyroxene-rich harzburgite with weak metasomatism and without amphibole in Zone 1 (the bottom) to clinopyroxene-poor harzburgite with strong melt impregnation and more amphibole in Zone 3 (the upper part, with Zone 2 transitional harzburgite in between), all cut by a wealth of dyke rocks (gabbro, dolerite and dunite). The Al2O3 contents decrease consistently in whole-rock (2.97–0.57 wt%), orthopyroxene (4.99–0.85 wt%) and clinopyroxene (5.25–1.22 wt%) for the harzburgites from Zones 1–3, contrary to the trends for the spinel Cr# (0.17–0.65) and clinopyroxene Li/Y, and bulk rare earth element (REE), Pb and Sr contents. The plagioclase-bearing peridotite (commonly enclosed in layered gabbro) in Zone 4 (the top) has remarkably elevated TiO2 contents (0.12–0.34 wt%) and Cr# values (0.45–0.53) in spinel, suggesting equilibration and strongest interaction with MORB-like melts among the CMTZ. The troctolite in Zone 4 has olivine Mg# (80.6–84.2) and NiO (0.37–0.45 wt%) and spinel Cr# (0.68–0.73). The fluid-mobile elements (U, Pb, Sr and Li) in both whole rock and clinopyroxene as well as amphibole abundances increase consistently from Zones 1–4, implying that the interaction of the mantle rocks with hydrothermal fluids became increasingly intensive from bottom to top of the CMTZ.These vertical variations collectively suggest the complex melt-fluid-peridotite interaction during the upward movement of deeply sourced melts and the downward penetration of seawater. We propose that such interactions are ultimately controlled by the relative slow spreading rates, where the less melt supply and very thin or even missing oceanic crust facilitate the downward seawater injection and enhance pervasive fluid metasomatism. This may represent a suitable explanation for the CMTZ with intriguing lithological and chemical heterogeneity under many other active or fossil oceanic slow-ultraslow spreading environments.

Pervaporation Membranes for Seawater Desalination Based on Geo-rGO-TiO2 Nanocomposites. Part 1: Microstructure Properties.

This is the first of two papers about the synthesis and microstructure properties of the Geo–rGO–TiO2 ternary nanocomposite, which was designed to suit the criteria of a pervaporation membrane for seawater desalination. The performance and capability of Geo–rGO–TiO2 as a seawater desalination pervaporation membrane are described in the second paper. A geopolymer made from alkali-activated metakaolin was utilized as a binder for the rGO-TiO2 nanocomposite. A modified Hummer’s method was used to synthesize graphene oxide (GO), and a hydrothermal procedure on GO produced reduced graphene oxide (rGO). The adopted approach yielded high-quality GO and rGO, based on Raman spectra results. The nanolayered structure of GO and rGO is revealed by Transmission Electron Microscopy (TEM) images. The Geo–rGO–TiO2 ternary nanocomposite was created by dispersing rGO nanosheets and TiO2 nanoparticles into geopolymer paste and stirring it for several minutes. The mixture was then cured in a sealed mold at 70 °C for one hour. After being demolded, the materials were kept for 28 days before being characterized. Fourier Transform Infrared (FTIR) and X-ray Diffraction (XRD) measurements revealed that the geopolymer matrix efficiently bonded the rGO and TiO2, creating nanocomposites. Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) was used to examine the morphology of the outer layer and cross-sections of nanocomposites, and the results displayed that rGO were stacked on the surface as well as in the bulk of the geopolymer and will potentially function as nanochannels with a width of around 0.36 nm, while TiO2 NPs covered the majority of the geopolymer matrix, assisting in anti-biofouling of the membranes. The pores structure of the Geo–rGO–TiO2 were classified as micro–meso pores using the Brunauer–Emmet–Teller (BET) method, indicating that they are appropriate for use as pervaporation membranes. The mechanical strength of the membranes was found to be adequate to withstand high water pressure during the pervaporation process. The addition of rGO and TiO2 NPs was found to improve the hyropobicity of the Geo–rGO–TiO2 nanocomposite, preventing excessive seawater penetration into the membrane during the pervaporation process. The results of this study elucidate that the Geo–rGO–TiO2 nanocomposite has a lot of potential for application as a pervaporation membrane for seawater desalination because all of the initial components are widely available and inexpensive.

Physical modeling of sand columns application in recharge reservoir to prevent seawater intrusion

Abstract This study aims to provide visual evidence by the physical simulation to demonstrate the sand column performance of a recharge reservoir to control seawater encroachment and confirm some previous studies. In this analysis, a two-dimensional sand tank illustrates the sand column's role in overcoming seawater intrusion. Besides using dyes, the sand tank is also fitted with sensors to observe the length of seawater penetration. Furthermore, the simulation using SEAWAT numerical modeling is used as a reference in this analysis. The criteria analyzed were the number of sand columns, the reservoir water level, and the isochlors concentration. The results revealed a reasonably close match between physical and computational modeling. It was also found that the more sand columns and the higher the reservoir water level, resulted in the decrease of seawater penetration length that occurred. Physical and computational modeling findings indicated that the optimal results are derived using three sand columns with an RMSE value of 0.76. The seawater infiltration length decreased to 84.72% relative to sand column-free conditions at a reservoir water level of 15.0 cm.

Mantle-derived helium released through the Japan trench bend-faults

Plate bending-related normal faults (i.e. bend-faults) develop at the outer trench-slope of the oceanic plate incoming into the subduction zone. Numerous geophysical studies and numerical simulations suggest that bend-faults play a key role by providing pathways for seawater to flow into the oceanic crust and the upper mantle, thereby promoting hydration of the oceanic plate. However, deep penetration of seawater along bend-faults remains controversial because fluids that have percolated down into the mantle are difficult to detect. This report presents anomalously high helium isotope (3He/4He) ratios in sediment pore water and seismic reflection data which suggest fluid infiltration into the upper mantle and subsequent outflow through bend-faults across the outer slope of the Japan trench. The 3He/4He and 4He/20Ne ratios at sites near-trench bend-faults, which are close to the isotopic ratios of bottom seawater, are almost constant with depth, supporting local seawater inflow. Our findings provide the first reported evidence for a potentially large-scale active hydrothermal circulation system through bend-faults across the Moho (crust-mantle boundary) in and out of the oceanic lithospheric mantle.