Inner-sphere Complexes Research Articles

Continuous-flow phosphate removal using Cry-Ca-COS Monolith: Insights from dynamic adsorption modeling.

Continuous-flow phosphate removal using Cry-Ca-COS Monolith: Insights from dynamic adsorption modeling.

Mechanism of the solid-liquid interfacial reaction between dissolved Cd species and the CaCO3 surface.

Mechanism of the solid-liquid interfacial reaction between dissolved Cd species and the CaCO3 surface.

Molecular Insights into Scale Inhibition: A Molecular Dynamics Study of Phosphonate-Based Inhibitors on a Calcite Surface.

The formation and deposition of mineral scales impose significant challenges to the safety and integrity of field operations across various sectors such as water treatment, desalination, and oil and gas. To mitigate the mineral deposition issues, scale inhibitors (SIs) with phosphonate and carboxylate-based structures are widely employed. Understanding of how these inhibitors interact with minerals and ions is essential for creating more effective, environmentally friendly solutions that meet operational demands. In this study, we employed molecular dynamics (MD) simulations to explore how widely used phosphonate-based SIs adsorb onto calcite surfaces, examining their behavior under different temperatures and salinity levels, both in bulk solutions and within calcite nanopores. Results reveal that the SIs exhibit high compatibility with salty environments, showing low aggregation tendencies. Interestingly, SIs do not form large aggregates in high-salinity brine (213,000 ppm of total dissolved salts), indicating their compatibility with such conditions. MD simulations reveal that phosphonate-based SIs predominantly adsorbed as hydrated outer-sphere surface complexes (OSSC) within the Stern double layer. While the carboxylate-based SIs formed both inner-sphere surface complexes (ISSC) and OSSC with higher adsorption than phosphonate-based SIs. The observed superior performance of phosphonate-based SIs over carboxylate-based SIs can be attributed to two primary factors: reduced loss into reservoir formations due to weaker adsorption and superior thermal stability. Phosphonate-based SIs were found to be significantly more thermally stable than their carboxylate counterparts, which is crucial for high-temperature applications. Diffusion coefficient calculations further indicated that brine salinity has minimal impact on the mobility of SIs, highlighting their robust performance under varying salinity conditions. This study provides detailed atomistic insights into the adsorption mechanisms of SIs on scale-forming mineral surfaces. These findings offer valuable guidance for the development of more efficient and environmentally sustainable scale inhibitors.

Distribution and speciation of Cu and Zn near spring barley (Hordeum vulgare) roots in digested sewage sludge-amended soil

Risk management for agricultural use of digested sewage sludge requires better understanding of the behaviour and fate of contaminant metals in the plant root zone. A study employing rhizo-pot and plug-tray experiments was conducted to identify the zone near spring barley roots (Hordeum vulgare) where concentration and speciation of Cu and Zn are affected. Cu and Zn bonding environments in the root epidermis/cortex and vascular tissue were also identified. In the digested sludge-amended soil, spring barley absorbed Cu only from the immediate vicinity of the roots (<< 1 mm), but Zn was taken up from further afield (> 1 mm). In the rhizosphere Cu was predominately present as Cu(I) oxides or as Cu(II) absorbed/bonded to phosphate, whereas Zn was present as Zn(II) in inner-sphere complexes with metal oxide surfaces, as Zn(II) sulphides or Zn(II) bonded to/incorporated into carbonates. Cu taken-up by spring barley roots was largely sequestered in the root epidermis and/or cortex predominately in the coordination environments similar to those seen in the rhizosphere. Only a small proportion of the Cu was translocated into the vascular tissue (where it is in the same two bonding environments). Zn taken-up by spring barley roots was present as Zn(II) sulphides, Zn(II) absorbed to/incorporated into carbonates, or Zn(II)-organic complexes. Zn was readily translocated from roots to shoots. Better understanding of these differences in the mobility and uptake of Cu and Zn in sludge-amended agricultural soils could be used to undertake element specific risk assessments.

Enrichment Mechanisms of Cadmium in Natural Manganese-Rich Nodules from Karst Soils.

Natural manganese (Mn)-rich nodules effectively sequester cadmium (Cd) in soils and influence on the geochemical cycling of soil Cd, yet microscale understanding of their enrichment mechanisms remains limited. From a regional survey of 1448 rhizosphere soil-rice sample pairs in karst areas of Guangxi, China, we identified and characterized Mn-rich nodules from representative sites to investigate their role in Cd sequestration. Using chemical extractions combined with laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and X-ray photoelectron spectroscopy (XPS), we revealed that Mn oxides serve as primary Cd carriers in Mn-rich nodules, accounting for approximately 63.6% of total Cd, dominating Cd enrichment through binding mechanisms of Cd-O and Cd-OH bonds characteristic of inner-sphere surface complexation and structural incorporation. The stability of these chemical interactions was confirmed by pH-dependent experiments, showing <5.0% of total Cd release even at pH = 3.0. The high Mn(III) mass ratios (36.0%-40.0%) in nodules facilitated stable inner-sphere complexation, resulting in increased Cd retention. These study findings reveal the exceptional Cd sequestration capacity of natural Mn-rich nodules, and provide insights for the high concentrations and low availabilities of soil Cd in karst, which can aid in developing strategies for managing Cd-polluted karst soils.

Sustainable Phosphate Remediation via Hierarchical Mg-Fe Layered Double Hydroxides on Magnetic Biochar from Agricultural Waste

Addressing aquatic phosphate pollution requires advanced materials that combine high selectivity with recyclability. Here, we present a hierarchically structured composite integrating Mg-Fe layered double hydroxides (LDHs) with magnetic biochar derived from mulberry branches—an abundant agricultural byproduct. Through hydrothermal synthesis, the composite achieves a unique architecture combining Fe3O4-enabled magnetic recovery (2.63 emu·g−1 saturation) with LDHs’ anion exchange capacity and biochar’s porous network. Systematic characterization reveals phosphate capture mechanisms dominated by hydrogen bonding through deprotonated carboxyl groups, inner-sphere complexation with metal oxides, and interlayer anion exchange, enabling 99.22% phosphate removal at optimal conditions (pH 6, 25 °C). Crucially, the material demonstrates exceptional selectivity over competing Cl− and NO3− ions while maintaining 87.83% efficiency after three regeneration cycles via alkaline treatment. Kinetic and thermodynamic analyses confirm chemisorption-driven uptake aligned with pseudo-second-order kinetics (R2 &gt; 0.9998) and Langmuir monolayer adsorption (7.72 mg·g−1 capacity). This waste-derived magnetic composite establishes a sustainable paradigm for eutrophication control, merging selective phosphate sequestration with energy-efficient recovery for circular water treatment applications.

The interaction of phenylphosphonic acid with the surface of goethite: Isotherms, kinetics, electrophoretic mobility and ATR-FTIR spectroscopy.

The interaction of phenylphosphonic acid with the surface of goethite: Isotherms, kinetics, electrophoretic mobility and ATR-FTIR spectroscopy.

Mechanisms and Implications of Phosphate Retention in Soils: Insights from Batch Adsorption Experiments and Geochemical Modeling

Soil plays a critical role as a natural barrier in mitigating the infiltration of industrial-derived phosphate pollution into groundwater, with its phosphate retention capacity governed mainly by its mineralogical composition. In this study, three soil samples were collected from the Huangmailing phosphate mine area, and the minerals responsible for phosphate retention were identified through batch adsorption experiments, chemical extraction, and spectroscopy analyses. The distribution of phosphate retention within soil samples was further quantified using a geochemical model. The results indicate that the adsorption capacity of soils to phosphate ranges from 0.193 to 0.217 mg/g. Adsorption equilibrium was reached at 750 min, conforming to the intra-particle diffusion kinetic model. Elevated temperatures facilitate phosphate adsorption. Under acidic and neutral conditions, approximately 80–90% of the phosphate is adsorbed onto iron oxides, primarily through inner-sphere surface complexation, thus unaffected by ionic strength. Under alkaline conditions, the retention mechanism was dominated by the release of exchangeable Ca2+ from vermiculite and biotite, as well as the precipitation of hydroxyapatite. Notably, the critical pH at which the retention mechanism shifts decreased with increasing content of layered silicate minerals and the concentration of cations in the solution. Our study underscores the distinct roles of effective minerals in phosphate retention under different pH conditions and highlights the significance of exchangeable Ca2+ in layered silicate minerals under alkaline conditions. Based on these findings, it is recommended that sites with favorable mineralogical characteristics tailored to the pH of phosphate-containing wastewater be prioritized for phosphorus chemical industries. This study also assesses the cost-effectiveness of adding vermiculite to soil in industrial and agricultural applications. The findings can provide a scientific basis for preventing groundwater phosphorus pollution in critical areas.

Fe-based metal-organic frameworks: performance and advantages on removal organophosphate pesticides in water for human consumption.

The study of real-world applications of adsorbent materials for water treatment enhances the feasibility of wastewater reuse and upgrades purifying processes for water supplies, thereby decreasing risks to public health. This study examined the removal of organophosphate pesticides from agricultural runoff samples using MIL-101(Fe). Rapid microwave-assisted synthesis, stability up to 350°C, environmental safety, and potential reusability were promising features related to synthesized MIL-101(Fe). The MIL-101(Fe) performance in the simultaneous adsorptive removal of glyphosate (GLY), glufosinate (GLU), and aminomethylphosphonic acid (AMPA) was evaluated. It achieved a 99.2% removal efficiency (%RE) for GLY within 15min of contact and 85.4 and 64.2% for AMPA and GLU after 120min, respectively. Good experimental adsorption capacities (≥ 97mg/g) for the three pollutants were obtained. Characterization analysis after adsorption indicates the possible synergistic effects of hydrogen bonding, active sites of material, pore filling, and inner-sphere surface complex as likely to predominate the mechanism of adsorption. MIL-101(Fe) exhibited satisfactory recycling results for GLY and AMPA, with %RE that decreased from 99 to 83% and 87 to 59%, respectively, after 5 recycles. The high stability of the adsorbent was confirmed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). Finally, the MIL-101(Fe) potential for practical applications was demonstrated with the successful removal in real water samples above 92, 80 and 60% for GLY, AMPA, and GLU, respectively. The obtained findings provide further progress in the MIL-101(Fe) remarkable use for large-scale future applications for pesticide removal in complex aqueous environments.

Competitive adsorption of arsenate and phosphate on hematite facets: Molecular insights for enhanced arsenic retention.

Competitive adsorption of arsenate and phosphate on hematite facets: Molecular insights for enhanced arsenic retention.

Uptake, desorption, and hysteresis of heavy metals and PAHs with environmental concerns onto quick clays: effects of salinity and temperature.

This study investigated the sorption, desorption, and trapping of 9,10 dimethylated anthracene (DMA), copper (Cu), and cadmium (Cd) onto quick clay (QC), focusing on the effects of temperature, salinity, and their environmental relevance. Sorption isotherms were generated at different temperatures (4, 10, and 20°C) and salinities (1 and 25g·L-1). Thermodynamic parameters were calculated to elucidate the underlying mechanisms. Isosteric heat of adsorption (ΔHX) was determined to assess the heterogeneity of adsorption sites. Isotherms results were processed using the Freundlich model to assess sorption and hysteresis parameters of QC. Kinetic studies revealed a rapid initial uptake of DMA followed by a slower logarithmic phase, reaching equilibrium within 1440min. The presence of the methyl group in DMA compared to non-methylated PAHs from other studies likely influences its adsorption rate. Temperature and salinity significantly impacted both the adsorption and desorption processes. Notably, Cd adsorption was nearly made ineffective with increasing salinity. Interestingly, Cu hysteresis index (HI) decreased from 1.57 to - 0.08 with increasing salinity, suggesting a shift from inner-sphere complexation at low salinity to outer-sphere complexation at high salinity. Conversely, DMA adsorption increased by 1.83-fold with increasing salinity, likely due to the salting-out effect. Thermodynamic analysis indicated a spontaneous and endothermic adsorption process driven by a positive entropy change (ΔS0). The ΔHX values supported physical adsorption as the dominant mechanism. The observed homogeneity in ΔHX values for DMA and Cd suggests consistent interaction with the clay surface, while the heterogeneity observed for Cu signifies a variation in adsorption site energies.

U(VI) sorption onto rutile surface in the presence or absence of EDTA: A combined macroscopic and spectroscopic study.

U(VI) sorption onto rutile surface in the presence or absence of EDTA: A combined macroscopic and spectroscopic study.

Effective treatment of thioantimonates-bearing waters by nanocrystalline iowaite, an iron-based layered double hydroxide.

Effective treatment of thioantimonates-bearing waters by nanocrystalline iowaite, an iron-based layered double hydroxide.

Novel Ce(III) based Ce-oxide/Fe3O4 composite for high-efficiency removal of Sb(V) and Sb(III) from wastewater at wide pH range.

Novel Ce(III) based Ce-oxide/Fe3O4 composite for high-efficiency removal of Sb(V) and Sb(III) from wastewater at wide pH range.

Three-dimensional, multi-functionalized nanocellulose/alginate hydrogel for efficient and selective phosphate scavenging: Optimization, performance, and in-depth mechanisms.

Three-dimensional, multi-functionalized nanocellulose/alginate hydrogel for efficient and selective phosphate scavenging: Optimization, performance, and in-depth mechanisms.

Synergistic enhancement in ultra-trace thallium(I) removal using the titanium dioxide/biochar composite.

Synergistic enhancement in ultra-trace thallium(I) removal using the titanium dioxide/biochar composite.

PH-Dependent preferential adsorption and stability of humic substances on goethite: The dual role of aromatic and aliphatic moieties.

pH-Dependent preferential adsorption and stability of humic substances on goethite: The dual role of aromatic and aliphatic moieties.

Effects of dimethylarsenate coprecipitation with ferrihydrite on Fe(II)-induced mineral transformation and the release of dimethylarsenate.

Effects of dimethylarsenate coprecipitation with ferrihydrite on Fe(II)-induced mineral transformation and the release of dimethylarsenate.

Mechanism of removal of Sb from printing and dyeing wastewater by a novel titanium-manganese binary oxide.

Mechanism of removal of Sb from printing and dyeing wastewater by a novel titanium-manganese binary oxide.

Mechanisms of interactions and the significance of different colloidal structures in the vertical transport of glyphosate in soils with contrasting mineralogies.

Mechanisms of interactions and the significance of different colloidal structures in the vertical transport of glyphosate in soils with contrasting mineralogies.