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The formation of heteroaggregates is critical to controlling the stabilization and transformation of nanominerals and mineral nanoparticles (NMMNs) in nature, but the underlying mechanisms remain to be deciphered. In this work, we study the effect of surface interactions between ferrihydrite (Fh) and montmorillonite (Mnt) within their heteroaggregates on the transformation behaviors of Fh. A series of heteroaggregates composed of Fh and Mnt were synthesized by modulating their mass ratios and synthesis methods, i.e., directly complexing Fh with Mnt (Fh-Mnt) or in situ growing Fh on Mnt (Fh/Mnt). Structural characterization using XRD, TG-DSC, TEM, and FTIR indicated that Fh particles coated more evenly on the Mnt surface within the heteroaggregates synthesized by in situ growing Fh on Mnt and with lower Fh to Mnt ratio, and accordingly these heteroaggregates showed stronger surface interactions between Fh and Mnt. The phase transformation of Fh to hematite (Hem) on the heteroaggregates can be significantly affected during the heating treatment. Compared with that of pure Fh, the transformation of Fh on all of the heteroaggregates was retarded (e.g., slower transformation rate and smaller produced Hem particles), particularly for the samples with stronger surface interactions (e.g., Fh/Mnt with lower Fh to Mnt ratio). Noticeably, the heated heteroaggregates may simultaneously contain pristine Fh, intermediate maghemite, and transformed Hem, showing a heterogeneous transformation behavior of Fh. The strong interactions between Fh and Mnt will enhance the dispersion of Fh and restrict the structural rearrangement of Fh (particularly those at the interface) during the phase transformation process, resulting in retarded and heterogenous transformation of Fh on these heteroaggregates. These findings not only enrich our knowledge of the phase transformation characteristics of Fh but also advance our understanding of the important role of mineral surface interactions in stabilizing NMMNs in nature.

Aseismic slip is a stable fault slip, which allows strain to be relieved smoothly. Aseismic slip prevents the earthquake propagation, but it could nucleate an earthquake elsewhere. Understanding the mechanism of aseismic slip is promising in revealing the seismic cycle. Experimental evidence showed clay-rich fault gouge bears a low-friction strength, and the friction is strengthened with slip velocity (velocity-strengthening), which was thought to support aseismic slip. Clay minerals are comprised of platy crystalline layers with water intercalated between them, which may act as a lubricant. Sliding between clay layers was suspected to support aseismic slip but lacked a clarified mechanistic insight. We use non-equilibrium molecular dynamics simulations to show that shear-induced interlayer sliding is frictionally weak and velocity-strengthening, which evidences the role of clay minerals in aseismic slip. We find that interlayer water is a viscous fluid at most times, which explains the shear response of interlayer sliding. Depending on temperature and pressure conditions, intercalated water can be monolayer or bilayer, fluidic or ice like. Shear induces ice-like water to transform into fluidic water, which happens as a stick-slip phenomenon reflecting a first-order transition. Increased pore fluid pressure leads to the transformation from monolayer to bilayer intercalated water, resulting in a lower friction strength and enhanced velocity-strengthening behavior. Our work suggests that disclosing the hydration state of a clay mineral is preliminary when studying fault mechanics.

While noble metals often occur as minor components in host minerals in various ore deposits, little theoretical assessment exists to predict the occurrence of these metals. Here, we probe the fundamental controls responsible for the occurrence of trace elements in host minerals through first-principles calculations. We apply the theoretical model to understanding the debated issues concerning the occurrence of gold (Au) in pyrite, in which the valence of Au is ascribed to either positive or negative values. Our results indicate that (1) both positive and negative valent Au may occur in pyrite and (2) higher sulfur fugacity and lower temperature lead to more Au+ occupying Fe sites in pyrite. These findings suggest that chemical states and speciation of the Au in host pyrite are ultimately controlled by temperature and sulfur fugacity, providing insight into the formation conditions of ore deposits and facilitating strategy design for beneficiation.

Aragonite, one of the most common biological calcium carbonate minerals, is widespread in marine plankton and neritic sediments (e.g., accounting for 89% of pelagic calcification of CaCO3 in the surface ocean). Its dissolution directly affects the export fluxes of CaCO3 in seawater. The aragonite dissolution in the ocean correlates with the increase of partial pressure of carbon dioxide and is pertinent to acidic biomolecules. However, aragonite dissolution in seawater with acidic biomolecules has been overlooked, and the interaction mechanism is unclear. In-situ atomic force microscopy (AFM) was employed to observe the dissolution features of aragonite (110) growth surfaces in succinic acid (SUC, HOOC-CH2-CH2-COOH) solutions. The results demonstrate that (1) both the morphologies and spreading rates of the etch pits formed on aragonite (110) surfaces are altered by the interactions between SUC molecules and the surfaces; (2) the [1-11] and [-111] steps of the etch pits on aragonite (110) surfaces in SUC solutions are kinetically controlled; (3) dissolution rates of aragonite (110) surfaces are proportional to SUC concentrations, which is attributed to the strong complexation between SUC molecules and surface-bounded Ca atoms (≡Ca+); (4) etch pits morphologies of aragonite (110) and calcite (10.4) surfaces are different in SUC solutions, and the spreading rates of the etch pits of the former are one to two orders of magnitude lower than those of the latter. Furthermore, aragonite is found to be more sensitive to SUC molecules than calcite, suggesting that dissolving aragonitic materials could be more easily affected by circumambient biomolecules than dissolving calcitic materials. In seawater that contains organic molecules, the dissolution fluxes of aragonite could be much slower than those of calcite. These findings not only reveal the site-specific interactions between SUC molecules and the ≡Ca+ on aragonite (110) surfaces but also emphasize its implication for the oceanic aragonite dissolution fluxes.

It is recognized that different facets of minerals vary distinctively in their chemical reactivity with aqueous solutions. However, detailed molecular and atomistic understandings of these phenomena are relatively limited. This study investigated the interaction of aqueous Mn2+ and dissolved oxygen on various facets of two morphology-types of iron oxide (hematite) nanocrystals. These interactions result in the oxidation of Mn(II) and heterogeneous growth of Mn(II)/Mn(III) and Mn(III) oxides. The nanoscale morphology and atomic structure of the manganese oxide products were characterized in detail. Our results, for the first time, directly demonstrate the facet-specific oxidation of Mn(II) and nucleation of Mn(II/III) oxides, followed by their epitaxial growth on hematite. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron diffraction measurements reveal the growth of MnOx nanowires on {1 1 3} of hematite nanoplates (HNP) and {0 1 2} facets of hematite nanocubes (HNC), while the basal {0 0 1} facets on the HNP particles do not produce precipitates. The average oxidation states of the MnOx on HNP and HNC determined using electron energy-loss spectroscopy (EELS) show that both Mn(II) and Mn(III) are present. The mineral composition and growth mechanisms of MnOx catalyzed by HNP and HNC are similar. High-resolution TEM analysis reveals the presence of both hausmannite and manganite on HNP and HNC. The crystallographic relationship between the heterogeneously formed manganite with hematite, which has not been reported before, proves that hematite provides reaction sites and can function as an atomic template for the formation of MnOx nanowires. These findings advance our understanding of the redox chemistry and heterogeneous growth of minerals as controlled by the surficial structure of the substrate mineral. This has important geochemical implications as the catalytic growth of less common, highly reactive phases like MnOx are known to be consequential in complex natural and anthropogenic environments.

Carbonate-bound speciation is a critical sink of potentially toxic elements (PTEs) like cadmium (Cd) in soil and sediment. In a phosphate-rich environment, carbonate minerals could be replaced by phosphate minerals such as dicalcium phosphate dihydrate (DCPD, also known as brushite), octacalcium phosphate (OCP), and hydroxylapatite (HAP). Currently, it is unclear the migration and fate of PTEs during the replacement of PTEs-bearing carbonates by HAP and related intermediate minerals. Therefore, we synthesized Cd-bearing calcite by the coprecipitation method and converted it to DCPD, OCP, and HAP to investigate the redistribution and fate of Cd. The results showed that Cd incorporation in calcite significantly inhibited their replacement by DCPD and OCP, respectively. 1.26% of Cd in calcite was released into the solution when DCPD replaced calcite, and subsequently, most of the released Cd was recaptured by OCP. Significantly, the released Cd was below 0.05‰ when all the solid converted to HAP. These results suggested that with the application of phosphate fertilizer in alkaline soil, the secondary calcium phosphate minerals could control the environmental behavior of Cd.

Improving the separation efficiency and transfer ability of photoinduced electrons/holes in pyrite (FeS

The n–n heterojunction is formed at the interfaces of FeVO4 and ZnO under hydrothermal conditions to increase the mobility of electrons and to decrease the barrier of oxygen activation. The results from X-ray powder diffraction and X-ray photoelectron spectroscopy analyses confirm the co-existence of the FeVO4 and ZnO phases in the composite. The formation of n–n heterojunction and electron transfer behavior are explored by applying electrochemical techniques and corresponding simulation calculation. The FeVO4/ZnO (Fe:Zn = 1:0.5) sensor shows a high response value of Sg = 42 at 300 °C, excellent selectivity, fast response, stable, and superior sensitivity for ethanol detection. The effect of the formed n–n heterojunction on enhancing the gas sensitivity for detecting ethanol is discussed by electron depletion theory. When the gas atmosphere is changed from air to ethanol gas, the depletion layer on the sensor surface is also changed significantly, altering the macroscopic resistance of the material. This work offers a new mechanistic understanding of the role of n–n heterojunction in detecting target gases and paves the way for designing excellent selectivity, fast response, and stable sensors based on n–n heterojunctions.

In the present study, the competitive adsorption geometries for arsenate and phosphate on magnetite surfaces over a pH range of 4–9 were investigated using in situ attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) and two-dimensional correlation analysis (2D-COS). The adsorption energies and infrared vibrational frequencies of these surface complexes were also calculated by first-principles simulations. Arsenate and phosphate have different preferences for the magnetite surface in the presence of aqueous solvent at both acid and alkaline pH. For the adsorption of phosphate, mono-protonated monodentate mononuclear (MMM) complexes dominated at acid pH, while non-protonated bidentate binuclear (NBB) complexes were dominant at alkaline pH. Arsenate mainly formed bidentate binuclear (BB) complexes with some outer-sphere species, both of which were more prevalent at acid pH. The pre-absorbed inner-sphere arsenate species were scarcely affected by the introduction of phosphate. However, the pre-absorbed phosphate oxyanions, especially the MMM complexes, were significantly substituted by BB arsenate at the magnetite surfaces. The adsorption affinity of phosphate and arsenate species for magnetite surface was found to increase in the following order: MMM phosphate complex < NBB phosphate complex < BB arsenate complex, which was consistent with the calculated adsorption energies. The simulated infrared vibrational frequencies for the most favorable adsorption modes of each oxyanion display distinctive patterns, and their trends are in excellent agreement with experimental data. The effects of pH, adsorption sequence, and mineral species on the competitive adsorption between arsenate and phosphate oxyanions are also discussed, and their different competing ability and stability on the magnetite surfaces can be ascribed to the variations in adsorption geometry and strength of binding. To the best of our knowledge, this is the first study aiming to distinguish the stability of the different phosphate and arsenate complexes on magnetite by employing a combined approach of in situ spectroscopy and DFT simulations. Our results provide molecular-level insight into the geometries and relative stabilities of the adsorption of phosphate and arsenate on magnetite surfaces, which is useful for interpretation of the mobility and bioavailability of these anions.

Oxygen vacancies play a vital role in the catalytic activity of layered double hydroxide (LDH) catalysts in wastewater treatment. However, the mechanism of oxygen vacancy-mediated LDH-activated oxygen to produce reactive oxygen species (ROS) still lacks a reasonable explanation. In this work, a tartrate-modified CuCoFe-LDH (CuCoFe/Tar-LDH) with abundant oxygen vacancies was designed, which can efficiently degrade nitrobenzene (NB) under room conditions. The technical energy consumption is 0.011 kW h L

This review discusses a fresh pool of research findings reported on the multiple roles played by metal-based, magnetic, graphene-type, chitosan-derived, and sonicated nanoparticles in the treatment of pharmaceutical- and agrochemical-contaminated waters. Some main points from this review are as follows: (i) there is an extensive number of nanoparticles with diverse physicochemical and morphological properties which have been synthesized and then assessed in their respective roles in the degradation and mineralization of many pharmaceuticals and agrochemicals, (ii) the exceptional removal efficiencies of graphene-based nanomaterials for different pharmaceuticals and agrochemicals molecules support arguably well a high potential of these nanomaterials for futuristic applications in remediating water pollution issues, (iii) the need for specific surface modifications and functionalization of parent nanostructures and the design of economically feasible production methods of such tunable nanomaterials tend to hinder their widespread applicability at this stage, (iv) supplementary research is also required to comprehensively elucidate the life cycle ecotoxicity characteristics and behaviors of each type of engineered nanostructures seeded for remediation of pharmaceuticals and agrochemicals in real contaminated media, and last but not the least, (v) real wastewaters are extremely complex in composition due to the mix of inorganic and organic species in different concentrations, and the presence of such mixed species have different radical scavenging effects on the sonocatalytic degradation and mineralization of pharmaceuticals and agrochemicals. Moreover, the formulation of viable full-scale implementation strategies and reactor configurations which can use multifunctional nanostructures for the effective remediation of pharmaceuticals and agrochemicals remains a major area of further research.

Phosphorus removal from wastewater has become urgent because of eutrophication control. Phosphate concentration in control for phosphate removal and recovery by Mg–Fe oxide has been investigated. The results show that the adsorption capacity of phosphate by Mg–Fe oxide calcined at 450 °C was 28.3 mg/g, and it was kept at wide optimal adsorption pH ranges (4–10). The coexisting ions had influenced phosphate adsorption process and the order is CO32− > SO42− > NO3− > Cl−, with the inhibition rate of CO32− being 43%. Interestingly, phosphate concentration plays an important role in phosphate removal by Mg–Fe oxide. Under higher initial phosphate concentrations (200–800 mg/L), Sips model was well fitted. In addition, the adsorption kinetics was well described by the pseudo-second-order kinetic model before 25 min and the pseudo-first-order kinetic model after 25 min. In contrast, Langmuir model and pseudo-second-order kinetic model were fitted under lower initial phosphate concentrations (20–200 mg/L). The results of XRD, XPS, SEM, and TEM characterization show that Mg3(PO4)2 was formed by surface precipitation under 800 mg/L phosphate solution, and Mg–Fe layered structure was present via the unique memory effect under 20 mg/L phosphate solution. Mg–Fe oxide can be recovered through CO32− ion exchange, and the removal efficiency of phosphate was 56% after seven cycles.

Two-line ferrihydrite (Fh) is an omnipresent iron oxyhydroxide nanomineral with high surface reactivity and weak crystallinity, and its phase transformation in nature has drawn significant concerns...

A lamellar SiC/C composite was synthesized from organoclay via pyrolysis followed by salt-assisted magnesiothermic reduction. The in situ-formed carbon sheet within the restricted interlayer space of clay served as the carbon source and nanotemplate for forming SiC/C. With a large specific surface area, hierarchical porosity, available anchoring sites, good hydrophobicity, and thermal stability, SiC/C proved to be a promising support for Pt. The resulting Pt loaded SiC/C exhibited an excellent toluene oxidation performance.

Two-dimensional layered double hydroxides (LDHs) are currently a topic of significant interest due to their extraordinary physiochemical properties. LDHs are potentially useful in a wide range of applications, particularly in environmental, energy, catalysis, and biomaterials related fields. Despite the unique intrinsic properties of LDHs, various functionalization strategies have been applied to LDHs that yield even more exciting performance opportunities, offering guides to design novel functional nanomaterials. In this review, we address how these strategies can improve the various properties of LDHs. We provide an overview of the functionalizing strategies of intercalation, surface modification, hybridization, layered compositions regulation, size and morphology control, and defect creation. These strategies contribute significantly to the enhancement of the performance of LDHs, across a diverse range of areas such as adsorptive, catalytic, electronic, electrochemical, and optical. As a result, functionalized LDHs exhibit great potential in a wide range of applications in the environmental and energy domains. We have comprehensively highlighted their emerging potential in the environmental, energy, catalysis, and biomaterials related fields, including heavy metal removal, radionuclide capture, organic contaminants purification, oil pollution elimination, hydrogen generation, supercapacitors, batteries, solar cells, catalysis, and biomaterial fabrication.

Biogenic isoprene is an important pollutant for regional air quality. Being ubiquitously distributed on the earth surface, manganese (hydr)oxides should play a vital role in the transformation of isoprene. Cryptomelane is a typical manganese oxide with isomorphous substitution of Fe for Mn, but less attention has been paid to its heterogeneous reaction with isoprene. When Fe

Microbial-induced carbonate precipitation (MICP) is a promising technology to immobilize/remediate heavy metals (HMs) like cadmium (Cd). However, the long-term stability of MICP-immobilized HMs is unclear, especially in farmland where chemical fertilization is necessary. Therefore, we performed MICP treatment on soils contaminated with various Cd compounds (CdCO

The ammonia removal performance of tidal flow constructed wetlands (TFCWs) requires to be improved under high hydraulic loading rates (HLRs). The pH decrease caused by nitrification may adversely affect the NH

A multi-channel tunable periodic narrowband filter chip composed of cascaded silicon nitride (Si 3 N 4 ) microring resonators (MRR) is proposed and implemented in this paper. We have assembled eight MRRs with the same structure on a silicon based chip with a size of 9mm*1.8mm. The waveguide material is silicon nitride with low transmission loss, and its transmission loss is about 0.2dB/cm. The central wavelength of the MRR can be tuned by thermal-optical effect. The experimental results show that the FSR is about 260GHz, the channel's 3dB bandwidth range is 0.7B-1.33GHz, the thermal modulation coefficient is about 0.33GHz/mW, and the central frequency tuning range is about 60GHz. The chip has the following features, including multi-channel, narrow bandwidth and wide tuning range, which can be used in microwave photonic system instead of traditional optical filters.

The directional hydrogen-bond (HB) network and nondirectional van der Waals (vdW) interactions make up the specificity of water. Directional HBs could construct an ice-like monolayer in hydrophobic confinement even in the ambient regime. Here, we report a water monolayer dominated by vdW interactions confined in a phyllosilicate interlayer under high pressure. Surprisingly, it was in a thermodynamically stable state coupled with bulk water at the same pressure (P) and temperature (T), as revealed by the thermodynamic integration approach on the basis of molecular dynamics (MD) simulations. Both classical and ab initio MD simulations showed water O atoms were stably trapped and exhibited an ordered hexagonal closest-packing arrangement, but OH bonds of water reoriented frequently and exhibited a specific two-stage reorientation relaxation. Strikingly, hydration in the interlayer under high pressure had no relevance with surface hydrophilicity rationalized by the HB forming ability, which, however, determines wetting in the ambient regime. Intercalated water molecules were trapped by vdW interactions, which shaped the closest-packing arrangement and made hydration energetically available. The high pressure-volume term largely drives hydration, as it compensates the entropy penalty which is restricted by a relatively lower temperature. This vdW water monolayer should be ubiquitous in the high pressure but low-temperature regime.

The occurrence of the {2 1 0} shape of pyrite crystals has been used as an empirical indicator for gold enrichment in ore deposits. Such indicating, also called ‘typomorphism’ in ore mineralogy, was conventionally attributed to environmental factors such as sulfur fugacity and temperature and pressure conditions in the ore-forming hydrothermal fluid. Here we show that the crystal-face specific redox reactivity of pyrite is also an important governing potency that drives gold enrichment in the pyrite crystals with particular shapes. This conclusion was drawn from data compiled from chemical analysis of field samples, laboratory testing of gold deposition on natural pyrite crystals, as well as theoretical calculations. Kinetic measurements of gold reductive deposition first revealed the highest precipitation rate on the {2 1 0} faces, particularly when pyrite crystals are enclosed by complex forms containing {2 1 0}. Corroborating with the experimental observations, density functional theory (DFT) calculations further indicated that the {2 1 0} possesses a high adsorption energy for gold, a high energy state of the highest occupied molecular orbital and consequently a low Eh. These results afford evidence supporting the view that the face specific reactivity, an intrinsic property of crystal, plays an important role in the gold concentration in pyrite and the occurrence of specific pyrite shapes. Our findings not only provide a surface chemical view for understanding the empirical prospecting method but also exemplified the significance of crystal face specific-reactivity in understanding crystallographic orientation related geochemical processes. The crystal face specific reactivity may be a critical factor controlling geochemical reactions at mineral-water interface, such as prebiotic synthesis on pyrite surfaces and mineral-water interface controlled kinetic isotope fractionation.

Naturally occurring semiconducting metal (oxyhydr)oxides (MeOx) are ubiquitous geosorbents and geocatalysts, regulating the geochemical behaviors of the chemicals in the environment. The interactions between these MeOx and redox-sensitive elements may involve both the photo-catalytic redox reactions and surface adsorption, and the interplay of the two processes, therefore, makes the interactions rather complex and may have unique environmental effects. The complex interactions between Cr (Cr(III) or Cr(VI)) and hematite under simulated sunlight irradiation were systematically studied under different geochemical conditions (pH, light irradiation, beginning Cr species, etc.). The batch experimentals, X-ray photoelectron spectroscopy (XPS), transmitted electron microscopy (TEM), and energy-dispersive spectroscopy (EDS) were used to determine the concentration and distribution of Cr species (Cr(III), Cr(VI), or the sum of the two) in the aqueous and solid phases. Here we found that both the oxidation of Cr(III) and the reduction of Cr(VI) were accelerated by hematite under sunlight irradiation, resulting in the enhanced immobilization of Cr on hematite. The reduction and oxidation efficiencies were pH-dependent and more evident under acidic condition. In the Cr (III) reaction systems, the reactions can be characterized by (1) the adsorption of aqueous Cr(III) (Cr(III)aq) to hematite surfaces, (2) the oxidation of adsorbed Cr(III) (Cr(III)ad) to Cr(VI)ad by the photogenerated holes on hematite, i.e., heterogeneous oxidation, (Bargar et al., 1997) the accumulation of Cr(III)ad on hematite enhanced by Cr(VI)ad, and even the formation of Cr-riched precipitation, which was observed by TEM, and (3) the homogeneous oxidation of Cr(III)aq to Cr(VI)aq by the hydroxyl radicals, generating through interaction between O2 and the photogenerated electrons (more evident under acidic environment, e.g., pH 3). In the Cr(VI) reaction systems, the reduction of Cr(VI)ad by photogenerated electrons from hematite was also noticeable, with the yielded Cr(III) being fixed on the surfaces. Although the reactions in reduction systems were less extensive than those in the oxidation systems, the reduction reactions would reduce the environmental toxicity of Cr species; while in the oxidation systems, inspite of the higher removal efficiency, the oxidation processes actually increased the environmental risk of Cr. Our results clearly show that hematite could either oxidize Cr(III) or reduce Cr(VI), influencing the speciation and immobilization of Cr under sunlight irradiation. In this term, the natural semiconducting MeOx (e.g., hematite) on Earth's surfaces should play a significant role in affecting the environmental behaviors and toxicities of the redox-sensitive elements (e.g., Cr) through adsorption and photo-catalytic redox processes.

Heterogeneous photochemical reactions associated with natural iron (hydr)oxides and oxalic acid have attracted a great deal of scientific attention in the application of organic pollutants degradation. However, the reaction mechanism is still unclear due to the complicated iron cycles and reactive oxygen species (ROS) generation. In this study, the in situ attenuated total reflectance-Fourier transform infrared spectroscopy was implemented to investigate the adsorption process and photochemical behavior of oxalic acid on the surface of ferrihydrite. A comprehensive reaction mechanism from the perspective of charge transfer process, including homogeneous-heterogeneous iron cycling and ROS generation, was illustrated in detail. We found that oxalic acid was first adsorbed on the surface of ferrihydrite with a mononuclear bidentate binding geometry. Interestingly, this mononuclear bidentate complex on the surface of ferrihydrite was stable under visible light irradiation. Subsequently, the whole complex departed from ferrihydrite surface through non-reduction dissolution with the form of Fe(C2O4)+. In the solution, the Fe(C2O4)+ complexes would quickly convert to Fe(C2O4)2- complexes. Under visible light irradiation, the electrons generated from the photolysis of Fe(C2O4)2- complex reacted with O2 to form O2•-/•OOH. Meanwhile, Fe(III) was reduced to Fe(II). Finally, the produced O2•-/•OOH could react with Fe(II) through a one-step way to generate •OH, which possessed higher •OH formation efficiency than that through the two-step way of H2O2 as the intermediates. This study helps us with understanding of in-situ photochemical reaction mechanism of ferrihydrite-oxalic acid system, and also provides guidance to effectively utilize widespread iron (hydr)oxides and organic acids in natural environment to develop engineered systems for water treatment.

Calcite dissolution, occurring in rocks, soils and sediments, is essential to indicate element cycles and local environments in the lithosphere, biosphere, hydrosphere and atmosphere. Calcite dissolution strongly depends on metal ions in aqueous solutions. Previous studies showed that aquatic Cu2+, a typical bio-toxic metal ion, can alter the calcite dissolution behavior. However, wide concentration ranges of Cu2+ coexisting with ubiquitous anions in local environments, such as waterways in the oxidation zones of copper deposits and soils near metal processing industry, was overlooked. When a considerable amount of aquatic Cu2+ ions are released into the environment, they migrate, diffuse, and hence become an environmental pollutant. Therefore, we focused on the interaction between calcite dissolution and wide concentration ranges of Cu2+-bearing solutions with different types of anions (SO42−, Cl− and NO3−). Comprehensive approaches including in situ atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), and density functional theory (DFT) calculations were employed to investigate kinetics and mechanisms of the interaction between the calcite (10.4) surface and Cu2+-bearing solutions. Results demonstrated that both anion types and Cu2+ concentrations dramatically affect calcite dissolution. The morphology of etch pits generated in CuSO4 solutions can be fan-shaped but changed to tear-shaped in Cu(NO3)2 or CuCl2 solutions. Calcite dissolution kinetics is inhibited at cCu2+ ≤ 0.1 mM, caused by the coverage of active sites on calcite surfaces. As the Cu2+ concentration increases (1 mM ≤ cCu2+ ≤ 10 mM), calcite dissolution kinetics is enhanced due to the coupling effect of Cu2+-incorporated surface structure and solution chemistry. These results revealed the interactive mechanism between calcite dissolution and the migration of toxic Cu2+ in waterways, provided a practical consideration in dealing with the local environment.

The heterogeneous photo-Fenton reaction is an effective technique in combating organic contaminants for both soil and water remediation, and extensive studies have focused on enhancing its efficiency and reducing its costs. In this work, we developed novel photo-Fenton catalysts by simply milling commercially available TiO2 (P25) with Schwertmannite (Sh), a natural iron-oxyhydroxysulfate nanomineral. We expect that the photo-generated electrons from TiO2 could continuously migrate to Sh, which then could enhance the separation of electron-hole pairs on TiO2 and accelerate the reduction of Fe(III) to Fe(II) on Sh, leading to high degradation efficiency of the target organic contaminants. SEM and TEM results showed the distribution of TiO2 on Sh surface for the nanocomposites (TiO2/Sh). Under simulated sunlight irradiation, the much higher content of Fe(II) was determined on TiO2/Sh than on Sh via a common method in the iron ore, and the consumption of H2O2 and the production of •OH were more significant in the TiO2/Sh system than those in the TiO2 and Sh systems. These results well support our hypothesis that the photo-generated electrons could migrate from TiO2 to Sh on the composites, and can also explain the much higher degradation efficiency of Rhodamine B (RhB) in the TiO2/Sh system. Besides, TiO2/Sh had lower Fe dissolution as compared with Sh, and retained high catalytic stability after four repeated cycles. Above merits of the TiO2/Sh composites, in combining with their simple synthesis method and low-cost property, indicated that they should have promising applications as heterogeneous photo-Fenton catalysts.

BACKGROUND: Developing effective removal processes for antibiotics has attracted increasing interest recently. In this work, a novel strategy involving the combination of photocatalysis with Fenton reaction using ferrihydrite/TiO₂ (Fh/TiO₂) nanohybrids was developed to efficiently degrade the antibiotic cefotaxime. Fh/TiO₂ nanohybrids were synthesized by simply growing Fh on the surface of commercially available TiO₂. We expected that Fh of Fh/TiO₂ could capture photo‐generated electrons from TiO₂, inhibiting the recombination of electron–hole pairs; also, by virtue of Fe(III)/Fe(II) cycle on Fh/TiO₂, photo‐generated electrons could be continually transferred to H₂O₂ to produce ·OH. Accordingly, high degradation efficiency of cefotaxime could be achieved. RESULTS: With UV light and H₂O₂, Fh/TiO₂ with a Fe/Ti molar radio of 7% showed high catalytic activity indeed, and its degradation rate for cefotaxime was nearly three times higher than that of TiO₂. The decomposition of H₂O₂ and production of ·OH in the UV+7%Fh/TiO₂+H₂O₂ system were also increased markedly. The large amount of Fe(II) on 7%Fh/TiO₂ determined in this system supported our hypothesis that Fh of 7%Fh/TiO₂ could capture photo‐generated electrons from TiO₂. Although dissolved iron was observed, the contribution of Fenton reaction by dissolved iron was rather limited. After four consecutive cycles, 7%Fh/TiO₂ still retained good stability. CONCLUSIONS: The UV+7%Fh/TiO₂+H₂O₂ system provides a potential alternative in degradation of cefotaxime for further practical application, and it has the following advantages: high catalytic activity, simple preparation method, good stability and low cost, as well as continued catalytic activity after total consumption of H₂O₂. © 2019 Society of Chemical Industry

To better understand the influence of structure and surface properties of NCMs towards REE, requires individual research for each NCM. The adsorption/extraction for light (La3+) and heavy (Yb3+) REE of kaolinite (Kao), montmorillonite (Mt), muscovite (Ms), illite (Ilt), were systematically investigated and compared. Additionally, all the NCMs were fully characterized by XRD, XRF, XPS, Zeta potential and nitrogen adsorption-desorption isotherms to build the relationship between adsorption/extraction mechanism and minerals' property. Our experiments show that the Mt. exhibits highest adsorption and regeneration efficiencies for both La3+ and Yb3+ and decrease in the order of Mt > Ms > Ilt > Kao, while Kao has highest extractions efficiencies for both REE in the order of Kao > Ilt > Mt > Ms 89% for La3+ and 85% for Yb3+ were achieved from Kao and the lowest extractions were obtained from Ms. (63% for La3+ and 57% for Yb3+). The lack of Ms. on both reuse and extraction characteristics is believed to be related to presence of iron oxide associated with Ms. In addition, the important role of the pH in extraction of REE from NCMs was evidenced, when REE-NCMs come into contact with the NH4+ solution, the pH is rapidly increased over initial pH solution for both Mt. and Ms., thus leading to the decrease of the availability of ion-exchangeable REE with NH4+ions. The results illustrated that the structure and surface properties of NCMs are also the key factors that affect the rare earth leaching, thus identifying the types of NCMs and associated impurities in clay materials are important, either for getting the best leaching system or in developing a new one.

The photocatalytic performance of layered double hydroxides (LDH) is usually confined to the slow interface mobility and high recombination rate of photogenerated electron-hole pairs in material. To overcome the low photocatalytic efficiency, novel Ag2O/Ag decorated LDH (LDH-Ag2O/Ag) was successfully synthesized by depositing Ag2O on the surface of LDH and then converted to Ag° nanoparticles in the right position after heat treatment. The as-synthesized LDH-Ag2O/Ag composites were characterized by Powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–visible diffuse reflectance spectra (UV–vis DRS), photoluminescence spectra (PL) and transient photocurrent (TPC) analysis. Compared with virgin LDH, the photocatalytic activities of LDH-Ag2O/Ag composites were enhanced significantly. The optimum photocatalytic efficiency of LDH-Ag10 (0.0184 min−1) was nearly 46 times higher than that of virgin LDH (0.0004 min−1). The result of active species trapping experiments indicated that •OH, h+, and •O2− have an effect on the TC degradation, where •OH played the predominant role during the photocatalytic process. The possible photocatalytic mechanisms involving the charge transfer pathway and reactive species generation during the process of TC degradation were also discussed. The improved photocatalytic activity of LDH-Ag2O/Ag could be attributed to the synergetic effect between LDH and Ag2O/Ag that extended visible light range and reduced photogenerated charge carriers recombination.

Pd0 cluster-modified porous FeVO4 nanorods were synthesized by a hydrothermal–chemical reduction route. The Pd0-modified porous FeVO4 nanorods exhibit an enhanced selective gas sensing property for benzyl alcohol detection at 160 °C in comparison with the pure FeVO4. Moreover, Pd0-modified porous FeVO4 nanorods show a lower detection limit and higher reliability than the pure FeVO4. The significant enhancement in gas sensing property of Pd0-modified porous FeVO4 nanorods is attributed to the formed porous structure and efficient electron-hole separation resulted from the deposition of Pd0 nanoclusters.