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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.

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.

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.

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.

A functional palygorskite-supported Fe/Ni (Pal-Fe/Ni) nanocomposite material is synthesised to remove 2,4-dichlorophenol (2,4-DCP) in an aqueous solution. The hypothesis is that Pal-Fe/Ni has superior efficacy than other Fe materials, such as Pal-Fe and Fe/Ni with regard to 2,4-DCP removal even though it requires less loading amount of metallic influencing the reaction. The surface morphology and surface chemical environments of Pal-Fe/Ni are studied using SEM, TEM, XRD and XPS characterisation methods. As revealed from batch experiments, initial pH, sample amount and reaction time are the key parameters influencing the 2,4-DCP removal efficiency. A further experiment reveals that iron leaching plays a main role for 2,4-DCP removal. Kinetic study reveals that removal of 2,4-DCP can be described by pseudo first-order model. A synergistic adsorption and catalytic reduction mechanism for the removal of 2,4-DCP by Pal-Fe/Ni is studied using UV–Vis, total organic carbon and HPLC-MS analyses. The results reveal complete dechlorination and 2,4-DCP degradation together with high total organic carbon removal. This study on immobilising Fe/Ni bimetallic nanoparticles onto palygorskite creates a new prospect for the practical application of Pal-Fe/Ni nanocomposite in remediation of contaminated aqueous solutions.

The enrichment of mercury in sphalerite plays an important role in the migration and accumulation of Hg in the earth system. Despite Fe being the most common foreign ion in natural sphalerite, the ...

Methyl orange (MO) is a common anionic azo dye that is harmful to the environment and biology, so it must be treated innocuously before it can be discharged. Adsorption is an effective method to remove anionic dyes. Nanotube mineral is a natural one-dimensional adsorption material, and its unique morphology and structure endow it with good adsorption capacity. Although there are many related studies, there is a lack of in-depth discussions on the influence of nanotube’s composition and structure on the adsorption of dyes and other pollutants. In this paper, two kinds of natural one-dimensional silicate minerals [halloysite nanotubes (HNTs) and chrysotile nanotubes (ChNTs)] with similar morphology but slightly different compositions and crystal structures were used as adsorbents, and MO solution was used as simulate pollutants. It is the first time to discuss in depth the influence of the composition and structure of nanotube minerals on their charge properties and the adsorption performance of methyl orange dyes. It is found that HNTs and ChNTs have different adsorption capacity due to the difference of electronegativity between Al3+ and Mg2+ in the crystal, so they possess negative and positive charges respectively in near-neutral solution, which leads to the adsorption capacity of MO by ChNTs with positive charges which is greater than that of HNTs.

The cobalt oxides and manganese oxides have high-activity potential for catalytic oxidation of volatile organic compounds (VOCs), while the mesoporous hollow morphology is crucial to the mass transfer of reactant and product. Therefore, it is worth investigating the effect of manganese substitution in mesoporous hollow cobalt oxides on catalytic oxidation. Herein, a partially disordered spinel structure is formed by the Mn substitution in Co3O4 and the mesoporous hollow microsphere is improved in morphology homogeneity with the decrease of Co/Mn ratio in the range of 1.8–28.8. The 5Co1Mn (Mn-substituted Co3O4 with Co/Mn at 5.4) exhibits outstanding catalytic activity for toluene oxidation with 50% CO2 generation at 237 °C, which is 21 °C lower than Co3O4. Moreover, the 5Co1Mn displays satisfactory stability in reusability, lifetime, and water resistance. The small defective crystallite, mesoporous hollow morphology, and high specific surface area endow Mn-substituted Co3O4 with more surface chemical adsorbed oxygen, enhancing the catalytic oxidation of toluene. Theoretical calculation on (3 1 1) plane of Co3O4 reveals that Mn2+ or Mn3+ substitution increases the formation energy of oxygen vacancy and makes it difficult to adsorb gaseous oxygen on the defective surface. The interaction between Co and Mn impedes the improvement of toluene oxidation because the mobility of lattice oxygen, the surface distribution of Co3+, and the ratio of surface adsorbed oxygen to surface lattice oxygen are hindered by Mn substitution. The chemical adsorbed oxygen is more active than lattice oxygen in the oxidation of adsorbed intermediates (phenolate, benzoate species, etc.). The Langmuir-Hinshelwood mechanism dominates in the catalytic oxidation at 200–250 °C, while the catalytic oxidation follows both the Langmuir-Hinshelwood mechanism and Mars-van Krevelen mechanism above 250 °C. This work provides some enlightenment for exploring the role of surface oxygen species in VOCs oxidation and uncovering the interaction in binary spinel oxides.

Distinctive Cr-MOF@Da composites have been constructed using chromium-based metal-organic frameworks (MOFs) and diatomite (Da). The new materials have hierarchical pore structures containing micropores, mesopores and macropores. We have synthesized various morphologies of the MOF compound Cr-MIL-101 to combine with Da in a one-pot reaction step. These distinctive hierarchical pore networks within Cr-MIL-101@Da enable exceptional adsorptive performance for a range of molecules, including hydrogen (H2), carbon dioxide (CO2) and water (H2O) vapor. Selectivity for H2 or CO2 can be moderated by the morphology and composition of the Cr-MIL-101 included in the Cr-MOF@Da composite. The encapsulation and growth of Cr-MIL-101 within and on Da have resulted in excellent water retention as well as high thermal and hydrolytic stability. In some cases, Cr-MIL-101@Da composite materials have demonstrated increased thermal stability compared with that of Cr-MIL-101, for example, decomposition temperatures &gt, 340 ℃ can be achieved. Furthermore, these Cr-MIL-101@Da composites retain structural and morphological integrity after 60 cycles of repeated hydration/dehydration, and after storage for more than one year. These characteristics are difficult to achieve with many MOF materials, and thus suggest that MOF&ndash, mineral composites show high potential for practical gas storage and water vapor capture.

Acid-base reactivity is a key factor for understanding the interfacial geochemistry of clay minerals. Numerous studies showed the significant role of surface acidity of clay minerals in the geological processes and environmentally related applications. In this work, montmorillonite (Mt) was pillared by polycations of Keggin-Al13 and Keggin-Al30. Arrangement models of Keggin-Al13 and Keggin-Al30 in the interlayer region of Mt were put forward based on the chemical composition analysis, the structural formula calculation of Mt, and the results of powder X-ray diffraction. Ammonia temperature-programmed desorption and diffuse reflectance Fourier transform infrared methods were applied to explore the impacts of pillaring by polycations (Keggin-Al13 and Keggin-Al30) on the surface acidic characteristics of Mt. Results demonstrated that one Keggin-Al30 polycation can affect an area of 9.5 unit cells (from two layers, with 4.7-4.8 unit cells in each layer) in Mt, whereas a Keggin-Al13 polycation controls an area of 7.1 unit cells (from two layers, with 3.5-3.6 unit cells in each layer). Pillaring by polycations could lead to a lot of surface acid sites (1.33 mmol NH3/g) on Mt with the main type of Bronsted acid sites. The increase of surface acid sites on both Keggin-Al13-pillared Mt (Al13-PILM) and Keggin-Al30-pillared Mt (Al30-PILM) is attributed to the high positive charge and high content of aluminum per unit of polycation, which affects the formation of Bronsted acid sites and structural changes of Mt layers. Catalytic oxidation of toluene provided evidence for the high catalytic activity of Al30-PILM under much lower temperature at 78 °C compared with that of Al13-PILM and Mt at 207 and 285 °C, respectively. The basic finding in this study not only reveals the possible sources of abundant micropores and mesopores in the micro/mesoporous materials of Al13-PILM and Al30-PILM but also provides a reasonable mechanism for the formation of abundant Bronsted surface acid sites on these two types of pillared materials. The novel Al30-PILM with an excellent micro/mesoporous structure and extremely high thermal stability also exhibits a potential ability in the application of heterogeneous acid catalysis.

Herein, we have reported an effective strategy to solve the rate-limiting step in a heterogeneous Fenton reaction, i.e., the generation of Fe(II) from Fe(III), which also inevitably consumes a large amount of H2O2. For the first time, a novel heterogeneous photo-Fenton catalyst - Ag/AgBr/ferrihydrite (Ag/AgBr/Fh) was successfully developed by combing AgBr with ferrihydrite (Fh) and then in-situ generating Ag nanoparticles on the surface of AgBr/Fh. This strategy can introduce photo-generated electrons from semiconductor-based plasmonic photocatalysts to heterogeneous Fenton catalysts and significantly increase the efficiency to degrade contaminants. The presence of both AgBr and Ag nanoparticles was proved by a combination of structural characterization studies (i.e., XRD, SEM, TEM, and XPS). Under visible light irradiation, the generated Fe(II) on the samples and the degradation rate constants of bisphenol A (BPA) followed the same order: Ag/AgBr/Fh > AgBr/Fh > Fh, which could be attributed to the accelerated reduction of Fe(III) to Fe(II) by the photo-generated electrons from AgBr and Ag nanoparticles, and also profit from the strong electron trapping ability of Ag nanoparticles in separating the electron-hole pairs of AgBr. The Ag/AgBr/Fh system could produce more hydroxyl radicals (•OH), and its catalytic performance was less affected by decreasing H2O2 concentration, which suggested a more efficient utilization of H2O2. The Ag/AgBr/Fh system exhibits relatively high photo-Fenton reactivity even at neutral pH. In addition, a much lower Fe3+ dissolution indicates that a large portion of the contribution is from the direct heterogeneous Fenton reaction in this system.

Cadmium sulfide (CdS) is an excellent visible light responsive material for the appropriate band gap, but the high electron-hole recombination and particle aggregation of CdS seriously limited its practical application in photocatalysis. In this work, the CdS/ZnAlO heterostructures photocatalyst was synthesized via a facile hydrothermal method. The structural characterizations showed that the particles aggregation of CdS and the separation of photogenerated electron-hole pairs were obviously improvement. The CdS/ZnAlO composite showed the highest photocatalytic activity for Cr(VI) reduction under visible light within 120 min. The enhanced photocatalytic activity might be attributed to the synergistic effect of the effective separation of photogenerated electron-hole and the adsorption of Cr(VI) on the interface of the catalyst. In addition, the possible mechanism of Cr(VI) reduction over CdS/ZnAlO was also proposed. The present work is devoted to synthesise a high efficient and stable photocatalyst for Cr(VI) contaminated wastewater treatment.

Nanostructuring is an effective strategy to enhance the structural and cycling stability of silicon anodes in lithium-ion batteries. However, a controllable and cost-effective method for synthesizing nanostructured silicon with various morphology is still a challenge. Herein, we synthesize zero-dimensional, two-dimensional, and three-dimensional silicon nanostructures directly using low-cost and abundant clay minerals as precursors without any pretreatment and templates. Our results show that the morphology and microstructure of the resulting nanostructured silicon strongly depend on the architectural features of clay minerals, i.e., zero-dimensional silicon from palygorskite, two-dimensional silicon from montmorillonite, and three-dimensional silicon from halloysite. The silicon nanostructures show large specific surface area (over 80 m2 g−1) and hierarchical pore structure. As anodes in lithium-ion batteries, two-dimensional nanostructured silicon from montmorillonite exhibits the best electrochemical performance (i.e., 1369 mAh g−1 at 1.0 A g−1 with a capacity retention of 78% over 200 cycles). This work provides a universal guideline from clay minerals to various silicon nanostructures via an economical and scalable strategy, and reveals the fundamental structure-property relationship of different silicon nanostructures synthesized under the same condition, which would contribute to the large-scale production of high-performance and low-cost silicon-based anodes in lithium-ion batteries.

Two-dimensional carbon nanomaterials have been widely applied in the field of catalysis due to their unique structure and properties. In this work, the cobalt and nitrogen co-doped two-dimensional carbon nanomaterials with graphene-like and porous structure were synthesized via template method. Here, rhodamine B acted as the carbon source was intercalated into the CTAB-pillared montmorillonite. And the cobalt porphyrin was used as the cobalt and nitrogen precursors that made a great contribution to generate highly dispersed active sites due to their unique Co N4 structure. The characterization techniques such as HAADF-STEM, XPS, XRD, and Nitrogen adsorption-desorption were used to investigate the surface composites and structures of the Co N C catalysts. In addition, the as-prepared catalysts with relatively high specific surface area, large pore volume, and well-dispersed active sites were further evaluated for the selective oxidation of ethylbenzene using tert-butyl hydroperoxide as oxidant. The Co N/C s H catalyst synthesized via impregnation method presented an ethylbenzene conversion of 96% and selectivity of 99% to acetophenone, which was the highest catalytic activity among the investigated catalysts. The superior catalytic performance could be ascribed to the unique two-dimensional porous graphene-like structure, highly dispersed active sites, and the synergistic effect between the Co Ox and Co Nx.

The Honghai VMS Cu-Zn deposit is located in the Dananhu-Tousuquan arc, Eastern Tianshan, northwestern China. Orebodies of the Honghai deposit are buried 300 m underground and hosted by the Middle Ordovician-Upper Silurian Daliugou Formation felsic to intermediate volcanic-sedimentary rocks. At the footwall and hanging wall of the massive sulfide lens, intensive and pervasive phyllic alterations were found. Detailed drill core logging, petrographic study and electron microprobe analyses had delineated six alteration/mineralization zones, namely (from top to bottom) Zone I (chlorite-albite-white mica-carbonate), II (epidote-chlorite-albite-white mica-carbonate), III (quartz-white mica-pyrite), IV (massive sulfide), V (chlorite-pyrite ± white mica) and VI (chlorite-quartz-white mica). Our new data supported the sub-seafloor replacement influence for the Honghai VMS deposit, as evidenced by the presence of (1) sulfide breccias in the immediate host rocks; (2) rapid emplacement of host rocks; (3) strong phyllic alteration in the immediate hanging wall; (4) replacement textures of the massive sulfides; (5) barite as gangue minerals. Moreover, intensive chlorite and epidote alterations and vein mineralization are present in the hanging wall, which are comparable with porphyry-related propylitic alteration. Besides, different mineralogy and mineral chemistry are present between chlorites from the hanging wall and footwall at Honghai, which probably suggested porphyry-style alteration and mineralization overprinting at Honghai. Short wavelength infrared (SWIR) spectral analysis had identified mainly white mica, chlorite and epidote, and minor montmorillonite, calcite, gypsum, kaolinite and prehnite. The wavelengths of the AlOH absorption feature for white mica range from 2194 to 2221 nm, suggesting compositions from paragonite, through muscovite to phengite. The wavelengths of FeOH absorption feature for chlorite range from 2249 to 2261 nm, indicating compositions from Mg-rich to Fe-rich chlorite. According to SWIR measurements and electron microprobe analyses (EMPA), areas proximal to the massive sulfides are characterized by short wavelength of the AlOH absorption feature and high Alvi content of white mica. Petrography and EMPA showed that chlorite in the ore proximal zones are more Mg-rich than that in ore distal zones. These findings indicated high temperature for the white mica formation and more seawater influx during the chlorite formation in areas near the massive sulfides. This study suggested that SWIR analysis, supported by petrographic study and EMPA, can serve as an effective tool in alteration mapping, and mineral geochemical variations are potential deposit-scale exploration vectoring tools.

Biomineralization is an interesting naturally occurring process of forming minerals by microorganisms, which offers an efficient way to sequester heavy metal ions within relatively stable solid phases. In this study, Bacillus cereus Cd01 was selected to investigate effects of self-mediated pH on biosorption and biomineralization of Cd2+ in whole 72h cultivation period. Results revealed that strain Cd01-mediated pH decrease of the cultivation medium from 7.0 to 6.1 inhibited biosorption of Cd2+ on Cd01 cells at the initial cultivation period, while an increased pH from 6.1 to 7.4 facilitated biosorption of Cd2+ on Cd01 cells at the middle and late cultivation period. The reasons were mainly that self-mediated pH altered cell surface hydrophobicity and cell membrane fluidity of strain Cd01. Moreover, biosorption and bioaccumulation of Cd2+ on Cd01 cells in the period of increased pH promoted biomineralization of Cd2+ observed by the transmission and scanning electron microscopes. The analyses of energy dispersive spectroscopy, X-ray photoelectron spectroscopy and select area electron diffraction demonstrated that Cd2+ loaded on Cd01 cells was biomineralized into polycrystalline and/ or amorphous cadmium sulfide and cadmium phosphate. These results suggest that strain Cd01 may play a potential role in biomineralization remediation of heavy metal contaminated soils.

The conventional heterogeneous Fenton reaction is often confined by the lower regeneration of Fe2+, which then inhibits the decomposition of H2O2 and the generation of OH. Here we propose a novel idea to significantly accelerate the redox cycling of Fe2+/Fe3+ in heterogeneous Fenton reaction by introducing photo-generated electrons from plasmonic particles. Towards this aim, novel plasmonic Ag/AgCl nanoparticles coated ferrihydrite (Ag/AgCl/Fh) have been synthesized. Compared with pure Fh, a remarkable enhancement in the photo-Fenton degradation towards bisphenol (BPA) can be observed for all Ag/AgCl/Fh samples under visible light. Noticeably, the rate constant of 6%Ag/AgCl/Fh is 0.0506 min−1, which is about 5.1 times as high as that of pure Fh (0.0099 min−1). Moreover, the catalytic activity of 6%Ag/AgCl/Fh on the degradation of BPA remains quite efficient with a low Fe leaching after 4 recycles. The results of the effect of initial pH indicates that Ag/AgCl/Fh samples exhibit relatively high photo-Fenton catalytic activity even at pH 6. The electron spin resonance (ESR) analysis reveals that OH plays a significant role in the photo-Fenton reaction. The concentration of OH can even reach 267.6 μmol/L after 60 min, which is much higher than that of pure Fh (69.2 μmol/L). The measurement of Fe2+ concentration and the XPS Fe2p spectra of Ag/AgCl/Fh before and after the degradation of BPA indicate the loading of Ag/AgCl can accelerate the conversion of Fe3+/Fe2+ by the photo generated electrons from Ag nanoparticles due to the surface plasmon resonance (SPR) effect under the visible light irradiation.

In this work, at different temperatures, thermal characteristics, structure transformation process and calcination products of Mt, Al13-PILM and Al30-PILM have been investigated and compared in detail. The thermal stability of Mt after intercalating and pillaring by Keggin-Al13 and Keggin-Al30 cations could be enhanced significantly. For Al13-PILM and Al30-PILM, layers of Mt don't collapse until 800 °C, which is due to the protection of aluminum oxides pillars formed in the interlayer space. Results of thermogravimetric (TG) analysis, high temperature X-ray diffraction (HTXRD) characteristics and N2 adsorption-desorption investagation have proved that Al30-PILM is more stable than Al13-PILM. Abundance of micropores and mesopores were still retained in Al30-PILM even under 800 °C. When heated to high temperature at 1100 °C, layered structures of Mt are destroyed and new phases could form. This work is a continuation of our previous innovative work on Keggin-Al30 pillared montmorillonite (Al30-PILM) and the fundamental finding will offer exciting opportunities to the preparation of excellent porous materials with superior thermal stability properties.

Layered double hydroxides (LDHs) are a significant sink of anions (CO32–, SO42–, NO3–, Cl–, etc.) and divalent transition-metal cations in soil. The anion exchange capacity gives rise to functional...

In this paper, acid-activated palygorskite (APal x ) samples were prepared by a facile acid treatment method with different concentrations of HCl (0.5, 1, 3, 5 and 7 mol/L). The dynamic toluene adsorption performances of APal x were evaluated and the relevant adsorption mechanism was discussed. The prepared adsorbents were characterized using X-ray diffraction (XRD), elemental analysis, transmission electron microcopy (TEM), nitrogen adsorption-desorption isotherms and Fourier-transform infrared spectroscopy (FTIR). The results show that the palygorskite has a good resistant ability to acid attack, the structure still remains when the acid concentration is as high as 7 mol/L. Acid activation could significantly enhance the surface area (228, 250, 271, 273, 329 and 308 for Pal, APal0.5, APal1, APal3, APal5 and APal7, respectively) and porosity of palygorskite. APal5 has the best toluene adsorption capacity (90.4 mg/g) due to its highest S BET (329 m 2 /g) and V micro (0.055 cm 3 /g). The adsorption performance in terms of dynamic toluene adsorption capacities follows the order of Pal (44.6 mg/g) x to become a promising candidate for the adsorption of volatile organic compounds in practical applications.

This research presented six natural clay minerals (NCM) evaluated for the effectiveness of NH4+ adsorption from aqueous solution. For the first time, the NH4+ adsorption capacities of kaolinite, halloysite, montmorillonite, vermiculite, palygorskite, and sepiolite were examined and compared in the same study. All the NCM were fully characterized by XRD, SEM/EDS, XRF,FTIR, CEC, zeta potential and nitrogen adsorption-desorption isotherms to better understand the adsorption mechanism-property relationship. Adsorption kinetics showed that the adsorption behavior followed the pseudo-second-order kinetic model. The adsorption isotherms fitted by the Langmuir model illustrated that among all the NCM studied, vermiculite (50.06 mg/g) and montmorillonite (40.84 mg/g) showed the highest ammonium adsorption capacities. Our results revealed that the cation exchange is the main mechanism for the NH4+ adsorption. Additionally, negatively charged surface, water absorption process and surface morphology of NCM might also contribute to the high adsorption capacity for the NH4+. The maximum adsorption capacities for all NCM were rapidly obtained within 30 min with a dosage of 0.3 g/25 mL at pH of 7. The results illustrated that the NCM have significant potential as economic, safe and effective adsorbent materials for the NH4+ adsorption from the aqueous solution.

Pyrite oxidation not only is environmentally significant in the formation of acid mine (or acid rock) drainage and oxidative acidification of lacustrine sediment but also is a critical stage in geochemical sulfur evolution. The oxidation process is always controlled by the reactivity of pyrite, which in turn is controlled by its surface structure. In this study, the oxidation behavior of naturally existing {1 0 0}, {1 1 1}, and {2 1 0} facets of pyrite was investigated using a comprehensive approach combining X-ray photoelectron spectroscopy, diffuse reflectance Fourier transform infrared spectroscopy, and time-of-flight secondary-ion mass spectrometry with periodic density functional theoretical (DFT) calculations. The experimental results show that (i) the initial oxidation rates of both pyrite {1 1 1} and {2 1 0} are much greater than that of pyrite {1 0 0}; (ii) the initial oxidation rate of pyrite {2 1 0} is greater than that of pyrite {1 1 1} in low relative humidity, which is reversed in high relative humidity; and (iii) inner sphere oxygen-bearing sulfur species are originally generated from surface reactions and then converted to outer sphere species. The facet dependent rate law can be expressed as: r { hkl } = k { hkl } h a P 0.5 ( t + 1 ) - 0.5 , where r{hkl} is the orientation dependent reaction rate, k{hkl} is the orientation dependent rate constant, h is the relative humidity, P is the oxygen partial pressure, and t is the oxidation time in seconds. {1 1 1} is the most sensitive facet for pyrite oxidation. Combined with DFT theoretical investigations, water catalyzed electron transfer is speculated as the rate-limiting step. These findings disclose the structure–reactivity dependence of pyrite, which not only presents new insight into the mechanism of pyrite oxidation but also provides fundamental data to evaluate sulfur speciation evolution, suggesting that the surface structure sensitivity should be considered to estimate the reactivity at the mineral–water interface.

Nanostructured silicon has gained increasing interests due to its unique properties and wide applications. A facile, low-cost, and scalable strategy for producing nanostructured silicon remains a challenge. In this work, three natural clay minerals with different nanostructures, i.e., tabular halloysite, layered montmorillonite, and chain-layered palygorskite, were directly employed as precursors to synthesize porous nanostructured silicon via a combination of molten salt and magnesiothermic reduction. Results indicated that molten salt could efficiently absorb the massive heat generated from the exothermic reaction, which consequently inhibited the formation of high temperature phases (i.e., spinel and mullite) and the fusion of the generated silicon nanoparticles. Apart from acting as a reductant, metal Mg also consumed a part of the released heat through its vaporization to further lower the local reaction temperature. As a result, the as-synthesized nanostructured silicon showed large specific surface areas and enhanced porous architectures, e.g., 115.5 m2/g of specific surface area and 0.547 cm3/g of porosity for the sample obtained from palygorskite. Moreover, the microstructure and morphology of the resulting nanostructured silicon could be readily adjusted by properly choosing the clay mineral precursors and the added amounts of NaCl and Mg. Our strategy does not need to specially eliminate Al in clay minerals before reduction reaction, and greatly broadened the selection of clay minerals that can be directly used as silicon precursors, which would be beneficial to the practical production and wide applications of nanostructured silicon.

Bismuth oxyhalides are important visible-light-responsive photocatalysts due to their unique electronic and layered crystal structure. In this study, Pd nanoparticles with the size of about 3–6 nm were loaded on the Bi4O5Br2 nanosheets by applying solvothermal-reduction method. The photoelectrochemical performance and photocatalytic activity for the degradation of Bisphenol A in aqueous solution of Bi4O5Br2 and Pd/Bi4O5Br2 were evaluated. Compared with pure Bi4O5Br2, Pd/Bi4O5Br2 exhibited an excellent photocatalytic activity for the degradation of Bisphenol A in aqueous solution under LED visible light irradiation. 1.0 wt% loading of Pd was found to be most effective for improving the photocatalytic activity of Bi4O5Br2 for the degradation of Bisphenol A and near to 95.8% of degradation was achieved after 70 min LED visible light irradiation. Under 535 and 630 nm monochromatic LED visible light irradiation for 70 min, only 7.9% and 4.8% Bisphenol A were degraded over 1.0% Pd/Bi4O5Br2 photocatalysts, respectively. Therefore, the improved photocatalytic activity of Pd/Bi4O5Br2 is mainly attributed to the formation of a Schottky barrier between the Pd nanoparticle and the Bi4O5Br2 nanosheet, promoting efficient separation of photogenerated electrons and holes.

Highlights Nowadays, two-dimensional (2D) nanosheets, such as layered double hydroxides (LDH), have received considerable attention for their potential to meeting clean energy demand and solving environmental problems. In this work, novel and efficient photocatalysts of plasmonic Ag nanoparticles coated Zn/Ti-LDH nanosheets have been synthesized through low-temperature reduction method. The structural characteristics of the as-prepared products were investigated by a series of characteristic methods The scanning electron microscopy (SEM) and transmission electron microscope (TEM) images showed that Ag nanoparticles were distributed on the surface of Zn/Ti-LDH uniformly. The UV–vis diffuse reflectance spectra (DRS) showed that the absorbance of Ag/LDH in visible-light region enhanced markedly and presented a broad band at 500–600 nm, which was resulted from the surface plasmon resonance (SPR) effect of Ag nanoparticles. The photocatalytic activities of Ag/LDH were evaluated by degradation of Rhodamine-B (RhB) and NO. The photocatalytic experiments showed that Ag/LDH had higher photocatalytic activity than that of pure LDH, and 2%Ag/LDH exhibited the highest photocatalytic activity. In addition, the 2%Ag/LDH exhibited high photochemical stability after multiple reaction runs. The obtained results from photoluminescence (PL) spectroscopic measurement and transient photocurrent (I–V) analysis both revealed the existence of Schottky barriers between LDH and Ag nanoparticles. The electron spin resonance (ESR) showed that radical dotOH were the dominant active species in the photo-degradation process. The enhanced photocatalytic performance of the composite should be ascribed to both the SPR effect of Ag nanoparticles in visible light and the Schottky barriers between LDH and Ag nanoparticles.

Acid drainage (AD) poses a significant concern for water pollution due to its strong acidity and the toxicity of its various contaminants (e.g., heavy metal ions). In order to minimize the harmful effects of AD, the acidity must be neutralized and the contaminants be removed. The capacity of calcined Mg/Al layered double hydroxide (Mg/Al-CLDH) for simultaneously neutralizing the pH of AD and removing various heavy metal cations and oxyanions (Cr(VI) and phosphate) was studied herein. The interactions throughout co-removal between metal cations (in short M) and oxyanions were particularly investigated. In the solution with only M, Mg/Al-CLDH was capable of neutralizing solution pH and removing M. The reconstruction of LDH from Mg/Al-CLDH produced OH– to neutralize pH and partially remove M through precipitation. FT-IR results suggested that forming H-bonds with the reconstructed LDH (R-LDH) might also contribute to M removal. In the solution containing both M and oxyanions, M and oxyanions could mutually affect their removal efficiency by Mg/Al-CLDH. M weakened the removal capacities of Cr(VI) and phosphate, because it could compete for adsorption sites on R-LDH. Cr(VI) and phosphate showed complex effects on the removal of M: Low concentrations of Cr(VI) promoted the removal of M by providing extra adsorption sites; high concentrations of Cr(VI), however, had the opposite effect, as a high concentration of Cr(VI) might largely occupy the adsorption sites on R-LDH. By contrast, phosphate inhibited the removal of M considerably, which might be ascribed to its strong buffering ability that maintained a relatively strong acidic nature of the solution. Our results, for the first time, showed that Mg/Al-CLDH is particularly suitable for the treatment of AD containing various contaminants.

Ag2O nanoparticles-loaded Bi5O7I microspheres forming a three dimensional Ag2O/Bi5O7I p–n heterojunction photocatalyst with wide-spectrum response were synthesized in this study. The results of transmission electron microscopy observations revealed that the Ag2O nanoparticles with the diameter of ca. 10–20 nm were distributed on the surfaces of Bi5O7I nanosheets. The as-synthesized Ag2O/Bi5O7I exhibited an excellent wide-spectrum response to wavelengths ranging from ultraviolet (UV) to near-infrared (NIR), indicating its potential for effective utilization of solar energy. Compared with pure Bi5O7I, the Ag2O/Bi5O7I composite also demonstrated excellent photocatalytic activity for the degradation of Bisphenol A and phenol in aqueous solution under visible LED light irradiation. Among samples, the 20% Ag2O/Bi5O7I composite photocatalyst showed the highest photocatalytic activity for the degradation of Bisphenol A and phenol in aqueous solution. In addition, the 20% Ag2O/Bi5O7I composite also exhibited a photocatalytic activity for the degradation of Bisphenol A under NIR light irradiation. The improved photocatalytic activity is attributed to the formation of a p-n heterojunction between Ag2O and Bi5O7I, allowing the efficient utilization of solar energy (from UV to NIR) and high separation efficiency of photogenerated electron-hole pairs. The present work is desirable to explore a possible avenue for the full utilization of solar energy.

Nanostructured silicon is an attractive anode material for next-generation lithium-ion batteries, but its commercialization remains a challenge owing to the energy-intensive, costly, and complex preparation of nanostructured silicon. Herein, one-dimensional (1D) silicon nanorods (SNRs) have been synthesized from natural sepiolite by a simple self-templating synthesis method. The intrinsic crystal structure and chemical composition of sepiolite allow for the maintenance of 1D structures during magnesiothermic reduction without any additional templates and heat scavengers. The as-prepared SNRs showed a large specific surface area (∼122 m2 g−1) and hierarchical porous structure (i.e., macro- and meso-pores). As anodes for lithium-ion batteries, SNRs exhibited a high reversible capacity of 1350 mA h g−1 at 1.0 A g−1 after 100 cycles, and 816 mA h g−1 at 5.0 A g−1 after 500 cycles (with a capacity retention of 98%). With a low-cost precursor and facile approach, this strategy for synthesizing 1D nanostructured Si would be promising in practical production of high-performance anode materials for lithium-ion batteries.

ZnAl-layered double hydroxide/H3PMo12O40 (ZnAl-LDH/PMo12) nano-hybrids were prepared by self-assembly between positively charged LDH nano-sheets and negatively charged PMo12 nano-clusters. The catalytic performance of ZnAl-LDH/PMo12 (ZAM) nano-hybrids on methyl orange (MO) degradation under room temperature and ambient pressure was investigated. The self-assembly process was evidenced by various characterization results, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption measurements, and X-ray photoelectron spectroscopy, which also suggested that the structure and morphology of the ZnAl-LDH/PMo12 hybrids played a critical role in their catalytic performance. The ZAM nano-hybrid with a 1:1.59 M ratio of ZnAl-LDH to PMo12 exhibited an excellent catalytic activity for MO degradation, with a 74.2% discoloration rate and a 66.2% total organic carbon (TOC) removal efficiency. After five cycles of reactions, the discoloration rate remained at 62.5%. This high catalytic activity might be attributed to the formation of O2•−, which was generated from the reduction of the dissolved oxygen by PMo12. Overall, the results show that the formation of novel nano-hybrid catalysts through self-assembly of LDH nano-sheets with PMo12 nano-clusters leads to a significant improvement in the catalytic activity and stability of Mo based catalysts under room temperature and ambient pressure.

The environmental behaviors and pollution control of engineered nanomaterials are drawing increasing interests nowadays. This work showed that the calcined layered double hydroxides (LDH), i.e., layered double oxides (LDO), could effectively adsorb polyhydroxy fullerenes (PHF) from aqueous solution. The maximum adsorption capacity of LDO reached ~ 476 mg/g, much higher than that on LDH (~ 47 mg/g) and activated carbon (~ 28 mg/g). All of the three equilibrium adsorption isotherms could be well fitted with the Langmuir equation. The high adsorption capacity of PHF on LDO can be attributed to the enhanced accessibility to the adsorption sites for PHF during structural reconstruction of LDO. In addition, the rehydrated LDH, with a net positive surface charge, has high affinity for negatively charged PHF through an electrostatic interaction. Cl−, CO32 −, and SO42 − could slightly enhance the adsorption of the PHF on LDO, while HPO42 − showed an evident inhibiting effect in the whole concentration range of PHF. The adsorbents before and after the adsorption of PHF were characterized by XRD, FT-IR, and TG. The obtained results indicated that the adsorbed PHF could not intercalate into the interlayer spaces of the reconstructed LDH, but could effectively compete with CO32– during the adsorption process.

Buckminsterfullerene (C60) is one of the most important carbon-based nanoparticles (CNPs). Industrial-scale production of C60 has reached the level of tons; release to the environment has been confirmed (Tremblay, 2002; Qiao et al., 2007). The present study was devoted to study of the effect of clay minerals on the migration process of C60. Molecular dynamics (MD) simulations were used to study the interaction of CNPS with clay minerals through study of the adsorption of C60 on various surfaces of kaolinite and pyrophyllite in vacuum and aqueous environments. Two kinds of surfaces, hydrophobic siloxane surfaces and hydrophilic hydroxyl surfaces, were investigated. C60 is mainly adsorbed onto the vacancy of the six-membered ring, composed of SiO4 tetrahedra or AlO6 octahedra, on clay-mineral surfaces. A single adsorption layer consisting of C60 molecules with an ordered hexagonal arrangement is presented for all surfaces in vacuum. In aqueous environments, however, the monolayer appears on the siloxane surfaces only, while a cluster of C60 molecules is formed on the hydroxyl surfaces. Free energies prove that the attachment of two C60 molecules is stronger than the adsorption of C60 onto the hydroxyl surface in water, which is the reason for unfavorable formation of C60 monolayer. On the other hand, the adsorption free energy is more negative on the hydrophobic siloxane surface, explaining the monolayer formation. The existence of water, which forms hydration layers on the surfaces of clay minerals, produces energy barriers, and reduces the adsorption affinity to some extent. Because clay minerals act as geosorbents in the environment, the present study is significant in terms of understanding the migration and fate of CNPS in nature.

Properties of water confined in layered double hydroxides (LDH) are relevant with hydration, dehydration, and protonic conduction in interlayer galleries. Evolutions of structure and dynamics of water in LDHs (Mg2Al(OH)6Cl·mH2O) with temperature are disclosed through molecular dynamics simulations performed in the range from 300 to 430 K. LDHs with m = 0.78 and 1.44 which characterize two different hydration states are investigated. Water in the lower hydration state is characterized with higher ordered structure. Irrespective of water content, water becomes less hydrogen bonded and more disordered as temperature increases. This leads to a large decrement in dehydration enthalpy, which facilitates dehydration energetically. Irrespective of temperature or water content, water exhibits the preference for being fixed in hydroxyl sites and it diffuses through jumping between neighbor sites. Jump diffusion approximately exhibits an Arrhenius dependence on temperature. A jump is a collective process consisting ...

Iron oxides are abundant in natural waters and soils and have high capacities for scavenging Pb(II) by adsorption, which affects the transport and fate of Pb on the earth's surface. We investigated the adsorption of Pb(II) on magnetites substituted with commonly incorporated transition metals such as Cr, Mn, Co, and Ni. The adsorption capacity, mechanism, and local coordination of Pb(II) were investigated by traditional macroscopic studies, i.e., acid-base titration and batch adsorption experiment, complemented with X-ray absorption fine structure (XAFS) spectrum analysis and surface complexation model (SCM). The substitution increased the surface site density, while pHpzc did not vary. Pb(II) adsorption was not suppressed by the presence of background electrolyte and improved as pH increased. The isotherms were well fit to the Langmuir adsorption model. The XAFS analysis demonstrated that Pb(II) ions were adsorbed on magnetite surface predominantly via inner-sphere complexation, where the adsorbed Pb(II) species was in bidentate binuclear corner-sharing geometry, independent of the adsorption capacity. This adsorption geometry can be applied to fit the experimental adsorption data well with the diffuse layer model (DLM). The substitutions improved the adsorption capacity in the following order: Cr > Ni > Mn > Co, and were discussed regarding the measured values of active site density and local coordination of adsorbed Pb(II). This study is the first documentation of Pb(II) adsorption on magnetite with different substitutions. The obtained results are of great significance for the understanding of Pb(II) surface complexation reactions on magnetite surface.

Ordered mesoporous carbon supported Co-N-C catalysts (Co-N-C/OMC) were prepared through a combined method of impregnation and pyrolysis, in which the fabricated cobalt porphyrin and ordered mesoporous carbon (OMC) served as precursor and support, respectively. The catalysts displayed high activity toward the oxidation of arylalkanes. And the catalysts showed interconnected porous structure with tailorable pore sizes that could influence the catalytic performance. Furthermore, the catalysts showed an excellent catalytic activity and reusability, which was attributed to the synergistic effect between Co-N-C and OMC.

Heterogeneous photo-Fenton catalysts generally show very weak photo-Fenton activity at near-neutral pH because of the relatively low rate of Fe 2+ regeneration. The aim of this work is to develop novel heterogeneous photo-Fenton catalysts, which can accelerate the regeneration of Fe 2+ and thus have superior photo-Fenton activity at near-neutral pH. In this study, ferrihydrite (Fh) was modified with BiVO 4 to synthesize BiVO 4 /Fh composites, and we expected that the photogenerated electrons from BiVO 4 would accelerate the regeneration of Fe 2+ on Fh. Mechanistic investigation of H 2 O 2 consumption showed that the introduction of BiVO 4 promoted the decomposition of H 2 O 2 into reactive oxygen species (ROS). In addition, the presence of BiVO 4 deterred O 2 − production and accelerated the formation of OH, according to the results of ROS formation, as shown with EPR spectroscopy and fluorescent probes tools. Furthermore, the Fe 2+ concentration on the surface of BiVO 4 /Fh was higher than that on Fh based on the results of XPS characterization and quantitative measurement with a 1,10-phenanthroline spectrophotometric method. These results demonstrated that the introduction of BiVO 4 can accelerate the reduction of Fe 3+ to Fe 2+ by transferring photogenerated electrons from BiVO 4 to Fe 3+ on the surface of Fh. Meanwhile, a higher decolorization efficiency of acid red 18 by BiVO 4 /Fh than by Fh and pure BiVO 4 verified that the introduction of BiVO 4 can significantly enhance the photo-Fenton catalytic activity of Fh even at near-neutral pH. Overall, our work has important implications for understanding the photo-Fenton mechanisms on semiconductor modified heterogeneous photo-Fenton catalysts and confirms that the introduction of a semiconductor can enhance the photo-Fenton catalytic activity of heterogeneous photo-Fenton catalysts in acidic and neutral pH.

Recycling solid waste as functional materials is important for both environmental remediation and resource recycling. This study attempts to recycle spent Cu/Fe layered double hydroxide (Cu/Fe-LDH) which is generated from the adsorption of dyes by converting to Cr(VI) reductant and porous carbon material. Results showed that the obtained reductant was mainly composed of Fe0 and Cu0, and exhibited good reductive activity toward Cr(VI). The species of Fe0, Fe2+, Cu0, and Cu+ all favored the reduction of Cr(VI) according to X-ray photoelectron spectroscopy analysis. During Cr(VI) removal, solution pH could increase to neutral which caused the metal ions to precipitate near completion. On the other hand, the spent Cu/Fe-LDH could be employed to produce porous carbon materials, and the generated waste metals solution herein could be reused for LDH synthesis. Specific surface areas of the obtained carbon materials varied from 141.3–744.2 m2/g with changes in adsorbed amount of dyes on the LDH. This study illustrates that all the components of wastes can be useful resources, offering a simple recycling approach for similar organic-inorganic solid wastes. This work also enlightens us that designing a proper initial product is crucial to make waste recycling simpler.

Metal oxide hollow sphere have emerged as a kind of promising nanostructured materials for catalysis, energy conversion, and storage capacity. Herein, a “silica-protective-layer-assisted” approach is adopted to synthesize Co-N-C supported MnOx-CeO2 hollow mesoporous spheres, which can effectively suppress the sintering of metal oxide. The metal oxide hollow mesoporous spheres are prepared through silica template, MnOx-CeO2 shell, cobalt porphyrin precursor, and silica protective layer via a layer-by-layer strategy. The Co-N-C/MnOx-CeO2 catalysts show a remarkable catalytic performance for the oxidation of ethylbenzene (ethylbenzene conversion to 44.5%). Moreover, the catalysts have well-defined morphology, homogeneously dispersed, high specific surface area and porous structure. The enhanced catalytic performance is attributed to the hollow hierarchically mesoporous structure and the synergistic effect between oxygen vacancy and Co-Nx active sites derived from the pyrolysis of cobalt-N4 macrocycles of cobalt porphyrin.

In order to enhance the dispersion of active centers and decrease the size of metal particles, cobalt-coordinated N-doped carbon (Co-N−C)with small particle size (3∼8 nm) were synthesized via pyrolyzing a special homogenous solution, namely the mixture of casein and cobalt porphyrin dissolved in 1-butyl-3-methyllimidazolium chloride ionic liquid. And the catalysts have been characterized by N2 adsorption-desorption isotherm, XRD, TEM, XPS and so on. The asprepared Co-N−C exhibiteda remarkable catalytic performance (conversion of ethylbenzene reached 35.3 %) with molecular oxygen as oxidant under solvent-free conditions.Moreover, the best Co-N−C showed superior cycling stability over 5 cycles. Those may be attributed to the well-dispersed acitve sites with small particle size and powerful Co−N bond which effectively prevents metal particles from aggregation.

Uniform porous Bi 5 O 7 I (BOI) microspheres photocatalysts co-doped with Fe 3+ and Er 3+ were synthesized by a solvothermal-thermal decomposition method, in which Er 3+ with upconversion properties could transform infrared light beyond the absorption edge of Bi 5 O 7 I into visible light, and also activate the Fe 3+ -doped Bi 5 O 7 I (Fe-BOI). The photocatalytic activities of the photocatalysts were evaluated by the degradation of three typical colorless model pollutants, i.e., phenol, bisphenol A (BPA), and chloramphenicol (CAP), under visible light irradiation (800 nm > λ > 400 nm). The results showed that the photocatalytic activity of Fe 3+ /Er 3+ co-doped Bi 5 O 7 I (Er/Fe-BOI) was much higher than that of the undoped, Fe 3+ -doped and Er 3+ -doped Bi 5 O 7 I photocatalysts. In addition, Fe 3+ /Er 3+ co-doped Bi 5 O 7 I exhibited photocatalytic activity under a 3W LED lamp (red light, λ = 630 nm) with the wavelength beyond the absorption edge of Bi 5 O 7 I, which further testified that the upconversion effect of Er 3+ generates the enhanced photocatalytic activity of Bi 5 O 7 I. Photodegradation mechanism was systematically studied by using various radical quenchers and it was revealed that photogenerated holes ( h + ) and superoxide radicals (O 2 − ) actively participated, whereas hydroxyl ( OH) radicals had negligible contribution in photodegradation of phenol.

Novel porous Eu-doped Bi5O7I spherical-like powders were successfully synthesized by thermal decomposition of Eu-doped BiOI microspheres in atmosphere under 450 °C for 2 h. The Eu-doped Bi5O7I powders were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), the Brunauer–Emmett–Teller surface area and UV–Vis diffuse reflection spectroscopy. In this work, Rhodamine B (RhB) was used as the typical simulative pollutant to examine the photodegradation efficiency of these as-prepared Eu-doped Bi5O7I samples. The results shown that 99.3% of RhB can be degraded by 3% Eu-doped Bi5O7I sample after 18 min visible light irradiation. The scavenger test results indicated that the photo-generated h+ played an important role in the degradation of RhB. The photodegradation mechanisms for RhB over the Eu-doped Bi5O7I photocatalysts was also studied. The enhancement of photocatalytic activity could be attributed to the Eu3+ ions. From our perspective, Eu3+ ions can improve the separation rate of photoinduced electron–hole pairs. Furthermore, the 3% Eu-doped Bi5O7I sample was also exhibited superior photocatalytic activity for methyl orange and phenol under visible light irradiation.

Highlights - Keggin-Al30 pillared montmorillonites were successfully prepared for the first time. - Both liquid and solid-state 27Al NMR were employed to give proofs on Al30 cations. - Al30-PILM has larger specific surface area and total pore volume than Al13-PILM. Abstract Pillared interlayered clays (PILCs) draw intensive attention in the fields of chemistry and material sciences, owing to their strong surface acidity and large microporosity. These materials are superior selective heterogeneous catalysts and adsorbents. However, conventional hydroxy-aluminum pillared clays are based on Al13, which cannot provide desirable properties due to its inherent limitation of size. Herein, a convenient method has been developed to prepare Al30 PILCs from montmorillonite (Mt) and a base-hydrolyzed solution of Al (III) chloride. To the best of our knowledge, this is the first time that porous pillared interlayered Mt with large Al30 pillars (2 × 1x1 nm) has been successfully prepared. This fundamental work may open up entirely new avenues for developing novel PILCs as heterogeneous catalysts and porous adsorbents.

A novel and efficient photocatalyst was synthesized by surface hybridizing Zn/Ti-LDH (LDH) with C60 molecules. The structural characteristics of the resulting products (C60/LDH) were studied using a variety of characterization methods, and the photocatalytic activities of C60/LDH were tested using Orange II (OII) as a model contaminant under simulated solar irradiation. The FT-IR spectra showed that the characteristic mode of C60 at 1182 cm-1 split into two peaks at approximately 1240 and 1156 cm-1; in addition, the Raman spectra showed the band at 1422 cm-1 for C60 was upshifted to 1431 cm-1 with the increased doping amount of C60. In addition, the XPS spectra revealed that the peaks of O1s, Zn 2p, and Ti 2p were downshifted slightly. These results demonstrated that chemical interaction existed between C60 and LDH on C60/LDH. The UV-vis diffuse reflectance spectra confirmed that the absorbance of C60/LDH in visible-light region enhanced markedly, as compared with that of pristine LDH. The photoluminescence (PL) spectroscopic measurement revealed that the C60/LDH composites exhibited much weaker PL intensity than that of LDH sample, and the transient photocurrent (I-V) analysis showed that C60/LDH had higher photocurrent density than pristine LDH. The results of PL spectra and I-V analysis suggested that C60 molecule could effectively transfer the photoelectrons from the conduction band of LDH, leading to a lower recombination rate of the photo-induced electrons and holes. The photocatalytic experiments showed that C60/LDH had much higher photocatalytic activity in the decolorization of OII than that of pristine LDH, and 2%C60/LDH composite exhibited the highest photocatalytic activity. Furthermore, the stability test indicated that the decolorization efficiency of OII by 2%C60/LDH was still quite efficient after being used for 5 cycles.

The thermal characteristics of montmorillonite (Mt) play significant roles in the application of Mt In this work, a systematic and comparative study regarding the influence of interlayer species on thermal characteristics of Mt was conducted. The raw Mt (Ca-Mt) was first saturated with small inorganic cation (Li + ), polyhydroxy-metal cation (polyhydroxy-aluminum, Al 13 ), and organic cation (methylene blue, MB), respectively. The obtained Mt samples (i.e., Li-Mt, Al 13 -Mt, and MB-Mt) and Ca-Mt were heated from room temperature to 1100 °C under Ar atmosphere. X-ray diffraction results indicated that the layers of Ca-Mt and Li-Mt collapsed at 500 and 300 °C, respectively; while those of Al 13 -Mt and MB-Mt would not collapse in this temperature range, owing to the protection of the aluminum oxide pillars and graphene-like carbon sheets within the interlayer spaces, respectively. As the temperature further increased, the layers of Al 13 -Mt was directly destroyed at 900 °C, while those of MB-Mt could be somewhat preserved even at 1100 °C. Thermogravimetry analysis showed the DSC exothermic peaks related to the breakdown of the layered structures and the formation of new phases increased in the order Li-Mt 13 -Mt; while no evident DSC exothermic peak was observed for MB-Mt in this high temperature range. Fourier transform infrared spectroscopy further confirmed that the formation of high-temperature mineral phases greatly depended on the interlayer species of Mt. This work would contribute to better understanding the physico-chemical properties of Mt, and developing novel Mt-based materials.

Pure Bi 4 Ti 3 O 12 (BTO) and Fe-doped Bi 4 Ti 3 O 12 (Fe/BTO) nanosheets with exposed {001} facets were synthesized by a one-step molten salt method. Au nanoparticles with a diameter range of 20–50 nm were loaded on 2%Fe-doped Bi 4 Ti 3 O 12 (Au-2%Fe/BTO) nanosheets via a room-temperature hydrogen peroxide reduction method. The UV–vis diffuse reflectance spectra showed that the Fe/BTO and Au-2%Fe/BTO samples exhibit an obvious red shift in visible light absorption band in comparison with the pure BTO. Phenol and bisphenol A solutions were chosen as model organic pollutants to verify the influence of Fe 3+ -doping and plasmonic effect of Au nanoparticles on the photocatalytic activity of the catalyst. The Au-2%Fe/BTO sample exhibited the highest photocatalytic activity compared with other samples. The high photocatalytic activity of Au-2%Fe/BTO rises from two contributions: i) the Fe 3+ ion acts as an efficient scavenger to trap electrons, and hence promotes the separation of photo-induced electron-hole pairs; ii) the visible light response of the catalyst is enhanced by the surface plasmon resonance effect from the Au nanoparticles.