The aim of this study was to investigate the mechanism of Cr(VI) reduction and Cr(III) immobilization by resting cells of Pseudomonas aeruginosa using batch experiments and analysis techniques. Data showed that resting cells of this strain (3.2 g/L dry weight) reduced 10 mg/L of Cr(VI) by 86% in Tris-HCl buffer solution under optimized conditions of 5 g/L of sodium acetate as an electron donor, pH of 7.0 and temperature of 37 °C within 24 h. Cr(VI) was largely converted to nontoxic Cr(III), and both soluble crude cell-free extracts and membrane-associated fractions were responsible for Cr(VI) reduction. While remnant Cr(VI) existed only in the supernatant, the content of resultant Cr(III) in supernatant, on cell surface and inside cells was 2.62, 1.06, and 5.07 mg/L, respectively, which was an indicative of extracellular and intracellular reduction of chromate. Scanning electron microscopy analysis combined with energy dispersive X-ray spectroscopy revealed the adsorption of chromium on the bacterial surface. Interaction between Cr(III) and cell surface functional groups immobilized Cr(III) as indicated by Fourier transform infrared analyses and X-ray photoelectron spectroscopy. Transmission electron microscopy revealed Cr(III) precipitates in bacterial interior suggesting that Cr(II) could also be intracellularly accumulated. Thus, it can be concluded that interior and exterior surfaces of resting P. aeruginosa cells were sites for reduction and immobilization of Cr(VI) and Cr(III), respectively. This is further insight into the underlying mechanisms of microbial chromate reduction.

•The composites show a strong absorption in visible light region.•Chemical bond of Ti-N-Ox is formed on the surface of the composite.•Co-doped TiO2 immobilized on rectorite displayed higher degradation rate of p-CP.•The photocatalytic activity of prepared composites remained stable after recycle.To further enhance the photocatalytic properties of doped-TiO2, a series of (N, Cu) co-doped TiO2/rectorite composites with different amount of N doping were prepared for adsorption and catalytic oxidation of p-chlorophenol (p-CP) under visible light. The physicochemical properties of the obtained composites were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), etc. The results showed that the (N, Cu) co-doped TiO2 catalyst was immobilized well onto rectorite, and the doping of N and Cu could affect the crystal structure of TiO2. The optimal N doping amount was determined by the photocatalytic degradation of p-CP in a stirred quartz reactor under visible light (> 420 nm) irradiation. It was found that the doping of N can improve significantly the degradation of p-CP and the optimum N doping amount is 1.0%. The adsorption of p-CP by the composites could accelerate the degradation rate of p-CP in situ. The photocatalytic activity of the (N, Cu) co-doped TiO2/rectorite composites remained stable after five cycles of photoreaction. A possible mechanism for the photocatalytic degradation of p-CP is proposed. Our work implied that rectorite has great potential to be applied in the field of photocatalysis.Download high-res image (192KB)Download full-size image

•C60 modified ZnAlTi-LDO enhance the photocatalytic reduction of BPA.•C60 modified ZnAlTi-LDO was an efficient photocatalytic in the degradation of BPA under visible light.•Superoxide radical species played a predominant role in the photocatalytic reaction system.•C60 expanded the absorption of ZnAlTi-LDO to visible-light region with the increasing content of C60.In this study, ZnAlTi layered double hydroxide (ZnAlTi-LDH) combined with fullerene (C60) was fabricated by the urea method, and calcined under vacuum atmosphere to obtain nanocomposites of C60-modified ZnAlTi layered double oxide (ZnAlTi-LDO). The morphology, structure and composition of the nanocomposites were analyzed by Scanning Electron Microscopy, High-resolution transmission electron microscopy, X-ray diffraction patterns, Fourier transform infrared and specific surface area. The UV-vis diffuse reflectance spectra indicated that the incorporation of C60 expanded the absorption of ZnAlTi-LDO to visible-light region. The photo-degradation experiment was conducted by using a series of C60 modified ZnAlTi-LDO with different C60 weight percentage to degrade Bisphenol A (BPA) under simulated visible light irradiation. In this experiment, the degradation rate of C60 modified ZnAlTi-LDO in photo-degradation of BPA under simulated visible light irradiation was over 80%. The intermediates formed in the degradation of BPA process by using LDO/C60-5% were 4-hydroxyphenyl-2-propanol, 4-isopropenylphenol and Phenol. Photogenerated holes, superoxide radical species, ·OH and singlet oxygen were considered to be responsible for the photodegradation process, among which superoxide radical species and ·OH played a predominant role in the photocatalytic reaction system. C60 modified ZnAlTi-LDO catalysts for photocatalytic reduction shows great potential in degradation of organic pollutants and environmental remediation.Download high-res image (322KB)Download full-size image

•Different structures of organic vermiculites were prepared from different types of amphoteric surfactant.•The removal of bisphenol A (BPA) and tetrabromobisphenol A (TBBPA) were very fast and ascribed to hydrophobic interactions.•The maximum adsorption capacity was 92.67 mg g−1 for BPA and 88.87 mg g−1 for TBBPA and adsorbents were easy to regeneration.•The amphoteric modification endows the potential for vermiculite to remove ionic and hydrophobic pollutants simultaneously.Three novel organic vermiculites (VER) modified by amphoteric surfactants (BS, SB and PBS) with different negatively charged groups (carboxylate, sulfonate and phosphate) were demonstrated and used for removal of bisphenol A (BPA) and tetrabromobisphenol A (TBBPA). The difference in the structure and surface properties of modified vermiculites were investigated using a series of characterization methods. BS and SB surfactant mainly adsorbed on the surface and hard to intercalate into the interlayer of VER, while both adsorption and intercalation occurred in PBS modification. This difference resulted in different packing density of surfactant and hydrophobicity according to the results of contact angle, and affect the adsorption capacities ultimately. The adsorption of two pollutants onto these modified vermiculites were very fast and well fitted with pseudo-second-order kinetic model and Langmuir isotherm. PBS-VER exhibited the highest adsorption capacity (92.67 and 88.87 mg g−1 for BPA and TBBPA, respectively) than other two modified vermiculites in this order PBS-VER > BS-VER > SB-VER. The ionic strength (Na+, Ca2+) and coexisting compounds (Pb2+, humic acid) have different effects on the adsorption. PBS-VER had a good reusability and could remove ionic (methylene blue and orange G) and molecular (BPA) pollutants simultaneously and effectively due to the function of amphoteric hydrophilic groups and alkyl chains. The results might provide novel information for developing low-cost and effective adsorbents for removal of neutral and charged organic pollutants.Download high-res image (538KB)Download full-size image

•Regeneration of spent iron-montmorillonite was achieved by high-temperature strategy.•Fe-Mt-TC-C showed excellent performance for degradation of BPA.•Degradation pathway of BPA in the Fenton-like system was proposed.Download high-res image (95KB)Download full-size image

In the present study, the mixed metal oxides (rGO-ZnTi-MMO-x, x presents weight percentage of GO) were obtained by thermal treatment of a Zn–Ti layered double hydroxides-graphene oxide (GO-ZnTi-LDHs) composite. rGO-ZnTi-MMOs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectra techniques. The photocatalytic activity of the obtained photocatalysts showed significantly enhanced activities in the degradation of bisphenol A (BPA). Compared with pristine ZnTi-MMOs, 88.12% of BPA at 10 mg L−1 was degraded using 0.5 g L−1 of rGO-ZnTi-MMO-2% as a catalyst under 3 h of simulated solar light irradiation. Photo-generated holes, ˙OH and singlet oxygen radicals were demonstrated to be the predominant active species responsible for the photo-degradation of BPA. UV-vis diffuse reflectance spectra, photoluminescence spectra electrochemical impedance spectroscopy and transient photocurrent response of the photocatalyst confirmed that the enhanced photocatalytic activity of rGO-ZnTi-MMOs composites was attributed to the extended visible light absorption region and efficient transportation and separation of photo-induced electron–hole pairs of rGO-ZnTi-MMOs with unique hetero-nanostructure. Therefore, this work presents a facile method for the fabrication of a kind of graphene-based photocatalyst for water treatment.

In this work, ZnCr–mixed metal oxides (MMO) hybridized with functionalized carbon nanotubes (A-CNTs) have been successfully fabricated via vacuum calcination of the layered double hydroxide precursors. The structural and morphological characterization of the samples was investigated by multiple techniques such as XRD, SEM, TEM, XPS, BET, Raman and UV-vis DRS. The results showed that A-CNTs were well incorporated into the MMO nanoparticles to form a nanohybrid structure dependent upon intimate interfacial contact. As compared to pristine MMO, the obtained MMO–CNTs nanohybrids exhibited significantly enhanced photocatalytic performance for bisphenol A (BPA) degradation under simulative solar light irradiation, providing powerful evidence for the superiority of the hybridization with A-CNTs. The key role of A-CNTs played in enhancing the photocatalytic activity of the nanohybrids was probably ascribed to the larger surface area, higher visible light absorption and the more efficient restriction of charge carriers recombination.

ZnTiO3–TiO2/organic pillared montmorillonite (pMt) composite catalyst was successfully prepared in this paper by immobilizing ZnTiO3–TiO2 onto pMt. The composition and texture of the prepared composite catalyst were characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, energy dispersive spectrometry, ultraviolet–visible light (UV–Vis) diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity was tested via photocatalytic degradation of methyl blue (MB) under both visible irradiation and UV light. The results indicated that the ZnTiO3–TiO2/pMt composite catalyst had an apparent absorption at the area of visible irradiation, and exhibited a higher efficiency of photocatalytic degredation of MB under visible irradiation. This was due to the heterostructure of ZnTiO3–TiO2, and the mesoporous structure and specific surface area of the ZnTiO3–TiO2/pMt composite. In addition, the results of the radical scavenging experiments showed that the holes and superoxide radicals are responsible for the degradation of MB under visible irradiation.

Vermiculites modified with Mercaptoethylamine (MEA) and 3-Mercaptopropyltrimethoxysilane (MPTMS) were used as effective adsorbents for the removal of Hg(II) from aqueous solution. The physicochemical characteristics of the pristine and functionalized vermiculites were analyzed by XRD, BET, FTIR, SEM, TEM and Zeta potentials, confirming that the vermiculite was successfully functionalized by the organic ligands containing the thiol (SH) metal-chelating groups. Batch adsorption experiments demonstrated that the factors such as initial pH, contact time, temperature, coexisting cations and initial Hg(II) concentration could significantly influence the adsorption behaviors typically for VER and MEA-VER, whereas the adsorption capacity of MPTMS-VER showed negligible dependence on such factors. The maximum adsorption capacity of Hg(II) ions was greatly improved after functionalization, which was in the order of MPTMS-VER > MEA-VER > VER (286.29 μg g−1, 176.33 μg g−1, 99.95 μg g−1, respectively). The adsorption isotherm could be well described with Langmuir model and the kinetic studies indicated that the adsorption process fitted well with the pseudo-second-order model. The calculated thermodynamic parameters suggested that the adsorption process was feasible and spontaneous. The adsorption mechanism of Hg(II) on thiol groups was studied through XPS analysis. Considering the favorable adsorption capacities, thiol-functionalized vermiculites show a promising application in the removal of Hg(II) from wastewater.

3D hierarchical honeycomb nano-structured o-MWCNTs coupled with CoMnAl-layer double oxides have been successfully fabricated and characterized as a heterogeneous catalyst for bisphenol A (BPA) degradation using potassium monopersulfate (PMS) as oxidant. The role of MWCNTs was investigated and discussed in terms of surface morphology, structure, composition and catalytic activity of the as-prepared nanohybrid by investigation of SEM, TEM, XRD, XPS, and Raman measurements, etc. The results showed that catalytic performance of the CNTs–LDO can be significantly enhanced with the increase of o-MWCNTs content in the hybrids, and MWCNTs provided orientation/confinement for nanohybrid formation and the defects generated by calcination might increase PMS activation for the production of sulfate radicals.

Laboratory batch experiments were conducted to investigate the role of clay minerals, e.g., kaolinite and vermiculite, in microbial Cr(VI) reduction by Pseudomonas aeruginosa under growth condition in glucose-amended mediums as a method for treating Cr(VI)-contaminated subsurface environment such as soil. Our results indicated that glucose could acted as an essential electron donor, and clay minerals significantly enhanced microbial Cr(VI) reduction rates by improving the consumption rate of glucose and stimulating the growth and propagation of P. aeruginosa. Cr(VI) bioreduction by both free cells and clay minerals-amended cells followed the pseudo-first-order kinetic model, with the latter one fitting better. The mass balance analyses and X-ray photoelectron spectroscopy analysis found that Cr(VI) was reduced to Cr(III) and the adsorption of total chromium on clay minerals-bacteria complex was small, implying that Cr(VI) bioremoval was not mainly due to the adsorption of Cr(VI) onto cells or clay minerals or clay minerals-cells complex but mainly due to the Cr(VI) reduction capacity of P. aeruginosa under the experimental conditions studied (e.g., pH 7). Atomic force microscopy revealed that the addition of clay minerals (e.g. vermiculite) decreased the surface roughness of Cr(VI)-laden cells and changed the cell morphology and dimension. Fourier transform infrared spectroscopy revealed that organic matters such as aliphatic species and/or proteins played an important role in the combination of cells and clay minerals. Scanning electron microscopy confirmed the attachment of cells on the surface of clay minerals, indicating that clay minerals could provide a microenvironment to protect cells from Cr(VI) toxicity and serve as growth-supporting materials. These findings manifested the underlying influence of clay minerals on microbial reduction of Cr(VI) and gave an understanding of the interaction between pollutants, the environment and the biota.

The synthesis of a layer-by-layer ordered nanohybrid with a sandwich structure was based on electrostatically driven self-assembly between the negatively charged carboxyl graphene monolayer and the positively charged ZnAl-layered double hydroxide nanosheets. The characteristics of the layer-by-layer ordered nanohybrid were investigated by SEM, TEM, AFM and XRD. The enhanced photocatalytic activity of the calcined product was determined by the photocatalytic degradation of the cationic dye methylene blue (MB) and anionic dye orange G (OG) under visible light. The enhanced photocatalytic efficiency was mainly attributed to the effective electronic coupling between graphene and calcined ZnAl-LDH. Additionally, the chemical stability of the calcined ZnAl-LDH is significantly improved by hybridization of graphene and this is attributed to the protection provided by the close contacted graphene with highly stability. This work also establishes a simple method for fabricating graphene-based nanohybrids with a sandwich structure.

•A novel material is prepared to remove cesium from water effectively.•The surface properties of vermiculite are improved by the corrosion of ethylamine.•The effect of coexisting organic acid in solution on Cs+ adsorption is discussed.•Cesium is largely removed by modified vermiculite with high specific surface area.Ethylamine modified vermiculite (Ethyl-VER) with high specific surface area and excellent pore structure was prepared to remove cesium from aqueous solution. The physic-chemical properties of the pristine and modified vermiculite were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), specific surface area (BET) and scanning electron microscopy/energy disperse spectroscopy (SEM/EDS). The corroding effect of ethylamine increased the specific surface area of vermiculite from 4.35 to 15.59 m2 g−1, and the average pore diameter decreased from 6.8 to 5.34 nm. Batch adsorption experiments were conducted as a function of pH, initial Cs+ concentration, contact time, coexisting cations (K+, Na+, Ca2+) and low-molecular-weight organic acids (acetic acid, oxalic acid, citric acid) to illustrate the adsorption behavior. The study found that the adsorption capacity of cesium in aqueous solution was improved from 56.92 to 78.17 mg g−1 after modification. The formation of micropores and mesopores and the increased surface area played a critical role in the enhancement of cesium adsorption. Kinetic experiments indicated that the adsorption process can be simulated well with a pseudo-second-order model. The presence of cations or low-molecular-weight organic acids inhibited cesium adsorption in different degrees. On the basis of our results, Ethyl-VER with good surface characteristics and high adsorption capacity is a suitable adsorbent for cesium removal from aqueous solution.Graphical abstract

•CNiZnAl-LDHs materials were successfully prepared for photocatalytic application.•Solar light was used as the energy source for the photocatalytic experiments.•The important experimental parameters were studied in detail.In this paper, well-crystallized NiZnAl layered double hydroxides (NiZnAl-LDHs) at different Zn2+/Ni2+ molar ratio (from 2 to 4) were prepared using dynamic urea hydrolysis method and further calcined at 873 K to obtain the layered NiZnAl mixed metal oxides with high photocatalytic activity. The as-synthesized catalysts were characterized by multiple techniques including XRD, FT-IR, TG-DSC, XPS, XRF, N2 adsorption–desorption isotherms, UV–vis DRS, and SEM. Additionally, their photocatalytic properties were evaluated by degrading orange G (OG) under solar radiation, with the investigation of isothermal adsorption behavior of OG on NiZnAl-LDHs before. Several factors influencing the photocatalytic activity like Zn2+/Ni2+ molar ratio of the catalyst, catalyst dosage, initial dye concentration, and initial pH, have been studied and optimized as 3, 0.5 g L−1, 50 mg L−1 and neutral, respectively, with a maximum of 99% degradation of OG achieved within 100 min reaction. Furthermore, the kinetic study suggested that the photodecomposition process was well fitted to the Langmuir–Hinshelwood model and the mineralization of OG was confirmed by the FT-IR analysis of the catalyst after the degradation. Finally, a probable mechanism was proposed to explain the process of photocatalytic reaction.

A series of La and Ce doped hydroxyl FeAl intercalated montmorillonite (FeAl-Mt) were prepared by a co-intercalation method for catalytic oxidation of Reactive Blue 19 (RB19) by a heterogeneous photo Fenton process under natural sunlight irradiation. The physicochemical properties of the obtained catalysts were deciphered by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS) and UV-vis diffuse reflectance spectroscopy (DRS). The results showed that Ce or La doped FeAl Keggin polyoxocations were intercalated into the gallery of montmorillonite and the physicochemical properties of intercalated FeAl Keggin polyoxocations were mildly changed after Ce or La doping, resulting in defects and lattice vacancies. The doping of Ce or La could effectively improve the catalytic performance of FeAl-Mt measured by heterogeneous photo Fenton degradation of RB19 catalyzed by the obtained products. The synergistic effect between the doped element and FeAl intercalated montmorillonite played a crucial role in the enhancement of heterogeneous catalytic activity under natural sunlight irradiation.

In this study, environment-friendly vermiculite (VMT) was used to support nanoscale zero-valent iron (nZVI) and nZVI doped with palladium (abbreviated as Fe-VMT and Pd/Fe-VMT, respectively). The physicochemical properties of the products obtained were analyzed by X-ray diffraction (XRD), specific surface area (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the BET surface areas of Fe-VMT and Pd/Fe-VMT were 39.5 m2 g−1 and 59.1 m2 g−1, and 18.9 m2 g−1 for unsupported nZVI nanoparticles. The presence of vermiculite led to a decrease in the aggregation of nZVI and Pd/Fe as observed by SEM and TEM. Batch experiments were conducted to investigate the catalytic performance of nZVI, Pd/Fe, VMT, Fe-VMT and Pd/Fe-VMT via the dechlorination reaction of 2,4-dichlorophenol (2,4-DCP). The dechlorination rates of 2,4-DCP by Pd/Fe-VMT (by adding Pd) were greater than that achieved by Fe-VMT. Additionally, the dechlorination of 2,4-DCP by Pd/Fe-VMT would be influenced by temperature, initial pH values, Pd loading, initial concentration of 2,4-DCP and the dosage of materials. It was confirmed that the ultimate reduction product of 2,4-DCP was phenol. Overall, Pd/Fe-VMT is a promising material for the dechlorination of 2,4-DCP.

The potential role of parameters in the reduction of hexavalent chromium [Cr(VI)] by Pseudomonas aeruginosa is not well documented. In this study, laboratory batch studies were conducted to assess the effect of a variety of factors, e.g., carbon sources, salinity, initial Cr(VI) concentrations, co-existing ions and a metabolic inhibitor, on microbial Cr(VI) reduction to Cr(III) by P. aeruginosa AB93066. Strain AB93066 tolerated up to 400 mg/L of Cr(VI) in nutrient broth medium compared to only 150 mg/L of Cr(VI) in nutrient agar. This bacteria exhibited different levels of resistance against Pb(II) (200 mg/L), Cd(II) (100 mg/L), Ni(II) (100 mg/L), Cu(II) (100 mg/L), Co(II) (50 mg/L) and Hg(II) (5 mg/L). Cr(VI) reduction was significantly promoted by the addition of glucose and glycerine but was strongly inhibited by the presence of methanol and phenol. The rate of Cr(VI) reduction increased with increasing concentrations of Cr(VI) and then decreased at higher concentrations. The presence of Ni(II) stimulated Cr(VI) reduction, while Pb(II), Co(II) and Cd(II) had adverse impact on reduction ability of this strain. Cr(VI) reduction was also inhibited by high levels of NaCl, various concentrations of sodium azide and 20 mM of SO42−, MoO42−, NO3−, PO43−. No significant relationship was observed between Cr(VI) reduction and redox potential of the culture medium. Scanning electron microscopy showed visible morphological changes in the cells due to chromate stress. Fourier transform infrared spectroscopy analysis revealed chromium species was likely to form complexes with certain functional groups such as carboxyl and amino groups on the surface of P. aeruginosa AB93066. Overall, above results are beneficial to the bioremediation of chromate-polluted industrial wastewaters.

•Four kinds of layered double hydroxides (LDHs) were synthesized to adsorb the DNA.•We compared the adsorption between different LDHs and discovered the difference.•Discussed the influence of various factors variables on adsorption process.•Some models were used to discuss the adsorption mechanism between LDHs and DNA.Four kinds of layered double hydroxides (LDHs) were prepared by chemical coprecipitation method and used as DNA adsorbents. Multiple characterization tools such as power X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Standard electronic modules (SEM) were employed to characterize the LDHs. By examining the effect of initial concentration, solution pH, adsorption experiments were carried out to investigate the adsorption capacities of LDHs for DNA. The results revealed that the LDHs with Mg/Al = 3 had higher ability on adsorbing the DNA and were not affected by pH values. The LDHs exhibited excellent adsorption properties and completely adsorbed DNA within 2 h. The adsorption equilibrium data were fitted to the Langmuir and Freundlich models, showing that the Langmuir model which represented monolayer adsorption had better correlation with the adsorption linear equation. In addition, Circular dichroism (CD) spectrum, UV–vis spectorscopy and agarose gel electrophoresis revealed the integrity of DNA structure, suggesting that there had no damage on the DNA structure during the adsorption process.Graphical abstract

A tripeptide (Glutathione, GSH) is chosen as a model drug to intercalate into layered double hydroxides (LDHs) by ion exchange, and a systematic study combining experimental and theoretical investigation is carried on X-ray diffraction (XRD) demonstrates that GSH had been intercalated into LDHs. IR and Raman spectroscopies, and the 13C NMR chemical shifts, are applied to clarify the characteristic changes in functional groups after intercalation. These results are interpreted with the density functional theory (DFT) calculations in order to verify the experimental data. For the first time, by using XPS for N 1s detecting, the related content of the native guest NO3- and the GSH in the LDHs’ interlayer are investigated, and the research results show that the reaction temperature affects the intercalation of GSH based on the XRD patterns. Furthermore, the reaction mechanism of intercalating GSH into LDHs was explained by the intrinsic reaction coordinate (IRC). The present study reveals that GSH as zwitterions (NH3+COO− formation) in water solvent first suffers hydrogen transfer and proton migration and then could be intercalated into LDH through ion exchange to occupy an interlayer site of NO3-.Graphical abstract.Highlights► Experimental measurements and theoretical computation were used. ► First time used XPS techniques to analyze the relative content in the LDHs’ interlayer. ► Reacting temperature affects the intercalation of GSH into LDH interlayer. ► The reaction mechanism of intercalating GSH into LDHs was explained by the IRC.

In this paper, an unstable chiral drug l-alanyl-glutamine (l-(Ala-Gln)) was intercalated into layered double hydroxides (LDHs) and a systematic study combining experimental and theoretical investigation was carried out. Structural characterization reveals the microstructure of LDHs and properties of the intercalated l-(Ala-Gln). Solid-state UV–vis spectroscopy is adopted to observe the energy absorption. This result shows that LDHs can block the UV light, and inhibition of configuration conversion works in the LDH host. Circular dichroism (CD) spectra suggest that the intercalated l-(Ala-Gln) can maintain its configuration in the interlayer even when irradiated under UV light. Density functional theory (DFT) computations at the B3PW91/6-31G(d, p) level have been carried out to understand the mechanism of l-(Ala-Gln) racemization. The computed result demonstrates that the thermal energy based on the reaction temperature cannot support l-(Ala-Gln) to give an excited state, but it can be excited under the irradiation of UV light with a wavelength less than 240 nm and undergoes conformational transition. When intercalated in the interlayer of LDHs, l-(Ala-Gln) is involved in strong guest–host interaction with the layers and thus inhibition of configuration conversion is effective in the LDH interlayer.

To investigate the effect of dissolved organic matter (DOM) on the adsorption of phenanthrene (PHE) by montmorillonite (MMT), organic clay complex was prepared by associating montmorillonite with DOM extracted from landfill leachate. Both the raw MMT, DOM, and MMT complex (DOM–MMT) were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray photo-emission spectroscopy (XPS), and scanning electron microscope (SEM). Batch adsorption studies were carried out on the adsorption of PHE as a function of contact time, temperature, and adsorbent dose. The sorption of PHE on complex was rapid, and the kinetics could be described well by the Pseudo-first-order model (R2 > 0.99), with an equilibrium time of 120 min. The adsorption isotherm was in good agreement with the Henry equation and Freundlich equation. Also, thermodynamic studies showed that the adsorption process was exothermic and spontaneous in nature. Compared with MMT, the adsorption capacity of DOM–MMT complex for PHE was greatly enhanced. The effects of DOM on PHE sorption by MMT may be attributed to the changes in the surface structure, the specific surface area, the hydrophobic property, and the average pore size of MMT. A series of atomistic simulations were performed to capture the structural and functional qualities observed experimentally.Graphical abstractThe objective of this work was to compare the difference between DOM–MMT complexes and the raw MMT on sorption behavior to phenanthrene using a combination of spectroscopic, microscopic adsorption techniques and molecular modeling.Highlights► MMT combined with DOM in leachate enhance the sorption of PHE. ► DOM was bound on the surfaces of MMT via H-bondings and cation bridges. ► DOM-MMT complex possessed higher Si/O atomic ratio on silica layers. ► The characteristic of PHE sorption isotherm is linear.

In the present study, a novel heterogeneous photo-Fenton catalyst was prepared by iron pillared vermiculite (Fe-VT). The catalyst Fe-VT was characterized by laser particle size analyzer, X-ray diffraction (XRD), X-ray fluorescence (XRF), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. It was found that hydroxy-Fe of low polymerization degree intercalated into the silicate layers of vermiculite successfully. Under the following experimental conditions: 100 mg/L reactive brilliant orange X-GN (named as X-GN) solution, pH 3, 30 °C, 3.92 mM H2O2 and 0.5 g/L Fe-VT dosage, 98.7% decoloration and 54.4% TOC removal could be achieved with 75 min UV irradiation. The kinetics results showed that decoloration kinetics of X-GN was well fitted by a pseudo-first order equation. In addition, the maximum dissolved iron, determined by atomic absorption spectrophotometer (AAS), was less than 1 ppm, while decoloration efficiency was till higher than 90% after the catalyst Fe-VT being used for 3 cycles. Hence, taking into account the favorable photocatalytic properties and low leaching of iron ions, iron pillared vermiculite is a promising catalyst for dye wastewater treatment.

The nanopaticles of TiO2 doped with nitrogen and cadmium are synthesized by sol–gel method followed by 2 h calcination at 400 °C in air atmosphere. Its chemical composition and optical absorption are investigated by XRD, UV–vis absorption spectra, TEM, XPS and Raman spectra. The results show that nitrogen and cadmium co-doping cause the absorption edge of TiO2 to shift to the visible-light region. The Cd2+ doping hinders the recombination rate of excited electrons/holes and prevents the aggregation of powder during the calcination. Superior catalytic activity of the co-doped TiO2 was observed for the decomposition of rhodamine B under visible light irradiation. The interstitial nitrogen atoms in co-doped TiO2 nanoparticles powder are responsible for the visible light photocatalytic activity.

The montmorillonite samples from Heping, China had been studied by chemical analysis, DAT, TG, XRD and MAS NMR. The results showed that the hydroxyl in octahedra sheets begins dehydrating, when the thermal treatment temperature reaches 650 °C, but the layer structure remains, the corresponding Al(VI) was turned into Al(IV) in octahedra sheets. When the temperature reaches 900 °C, the layer structure of montmorillonite is destroyed, and the new mineral phase μ-cordierite is found. When the temperature reaches 1200 °C, the μ-cordierite phase loses stability, and decomposes into cristobalite phase and mullite phase, meanwhile, the recrystallization phenomena in thermal treatment products is obvious. There is a small quantity of Al(VI) signal in MAS NMR spectrum, this Al(VI) corresponds to the Al of mullite. When the temperature reaches 1350 °C, the cristobalite and mullite phases reduce slightly, and more Fe-cordierite phase appear. There is corresponding Fe-cordierite spectrum in XRD and MAS NMR.

•A facile and low cost pyrolysis strategy was used to dispose the spent Mt.•The obtained N-doped graphene-like carbon can be used as efficient electrocatalyst.•The link between treatments of pollution and development of energy was built.Montmorillonite (Mt), as an efficient adsorbent, has been widely applied in the treatment of wastewater. However, it is important to develop appropriate disposal methods, which are currently lacking for spent Mt after adsorption. We utilized Mt after adsorption of tetracyclines (TC) as carbon source to obtain a by-product, N-doped graphene-like carbon-based electrocatalysts (TC-C), by a facile and low cost pyrolysis strategy. Physicochemical and electrochemical characterization of TC-C indicated that the resultant TC-C was made up of many ultrathin nanosheets, which resembled the morphology of graphene, and it had a large Brunauer-Emmett-Teller surface area with narrow slit-like pores. Nitrogen doping was evaluated through X-ray photoelectro-spectra measurements and four nitrogen-bonding configurations were identified and quantified, including pyridinic N, pyrrolic N, graphitic N and pyridinic N+–O−. Electrochemical studies showed that TC-C exhibited high catalytic activity for the oxygen reduction reaction (ORR) in alkaline medium with outstanding methanol tolerance compared to the commercial Pt/C catalysts. Furthermore, the effect of the adsorbed amount of TC on the ORR activity of TC-C was slight and the pyrolysis temperature of 700 °C was demonstrated to be the optimal temperature for the pyrolysis process in the recycling of spent Mt.

•The FeOOH-loaded MnO2 with flower-like structure was developed.•The FeOOH-loaded MnO2 showed a fast removal rate for Tl(I).•The material had higher adsorption capacity (450 mg g−1) for Tl(I) than MnO2.•The removal mechanism existed adsorption and oxidation at the same time.•The material has potential to be used for thallium pollution incident.A FeOOH-loaded MnO2 nano-composite was developed as an emergency material for Tl(I) pollution incident. Structural characterizations showed that FeOOH successfully loaded onto MnO2, the nanosheet-flower structure and high surface area (191 m2 g−1) of material contributed to the excellent performance for Tl(I) removal. FeOOH-loaded MnO2 with a Fe/Mn molar ratio of 1:2 exhibited a noticeable enhanced capacity for Tl(I) removal compared to that of pure MnO2. The outstanding performance for Tl(I) removal involves in extremely high efficiency (achieved equilibrium and drinking water standard within 4 min) and the large maximum adsorption capacity (450 mg g−1). Both the control-experiment and XPS characterization proved that the removal mechanism of Tl(I) on FeOOH-loaded MnO2 included adsorption and oxidation: the oxidation of MnO2 played an important role for Tl(I) removal, and the adsorption of FeOOH loaded on MnO2 enhanced Tl(I) purification at the same time. In-depth purification of Tl(I) had reach drinking water standards (0.1 μg L−1) at pH above 7, and there wasn't security risk produced from the dissolution of Mn2+ and Fe2+. Moreover, the as-prepared material could be utilized as a recyclable adsorbent regenerated by using NaOH-NaClO binary solution. Therefore, the synthesized FeOOH-loaded MnO2 in this study has the potential to be applied as an emergency material for thallium pollution incident.Download high-res image (199KB)Download full-size image

The synthesis of a layer-by-layer ordered nanohybrid with a sandwich structure was based on electrostatically driven self-assembly between the negatively charged carboxyl graphene monolayer and the positively charged ZnAl-layered double hydroxide nanosheets. The characteristics of the layer-by-layer ordered nanohybrid were investigated by SEM, TEM, AFM and XRD. The enhanced photocatalytic activity of the calcined product was determined by the photocatalytic degradation of the cationic dye methylene blue (MB) and anionic dye orange G (OG) under visible light. The enhanced photocatalytic efficiency was mainly attributed to the effective electronic coupling between graphene and calcined ZnAl-LDH. Additionally, the chemical stability of the calcined ZnAl-LDH is significantly improved by hybridization of graphene and this is attributed to the protection provided by the close contacted graphene with highly stability. This work also establishes a simple method for fabricating graphene-based nanohybrids with a sandwich structure.