A new nano zero-valent iron (nZVI) material that generates acidic conditions in situ was prepared by grafting an acid precursor onto diatomite. This new material was used in the evaluation of Bisphenol A (BPA) degradation by a Fenton-like process. The prepared material (M-nZVI-Da) exhibited a high removal efficiency (100%) of BPA under natural pH conditions of the solution (pH ∼5.75). The degradation of BPA using this new catalyst material follows a reaction pathway modelled on Fermi's equation with predictable kinetic outcomes for increased temperature of the reaction. Experiments demonstrate that the optimum starting concentration ratio of the H2O2/sample is 200 mM g−1 for efficient catalyst use. This study shows that nZVI materials with acid precursors are efficient catalysts for removal of BPA in solution.

•A variety of characterizations was made to investigate the composition and structure of PCHs in detail.•The clay/TEOS ratio had effect on the composition and structure of PCHs.•TEOS was both the silicon source for generating the Si framework and reaction medium.•The possibility of compositional and structural control of PCHs was discussed.Understanding the composition and structure of porous clay heterostructures (PCHs) is of great importance in clarifying the topological design and performance of PCHs in applications. In this paper, we investigated the chemical composition and structural characteristics of PCHs in detail by thermal analysis, major elements analysis, XPS, FTIR, 29Si MAS NMR, XRD, HRTEM, and nitrogen adsorption/desorption at −196 °C. Based on the characterization results, the possibility of controlling the composition and structure of PCHs was discussed. With a reduced ratio of organo-montmorillonite to tetraethylorthosilicate (i.e., clay/TEOS), the carbon content of the PCH precursors was relatively decreased due to the increase in polymerized TEOS in PCH precursors. After calcination, the progressive increase in the surface silicon contents (fSiO2-s) reflected a more intensive distribution of extra-lattice silica (i.e., the amorphous silica outside the interlayer space) in PCH. In the comparable amount of bulk silicon contents (fSiO2-b), the amorphous silica from the condensation of TEOS gradually increased, which was confirmed by FTIR and 29Si MAS NMR. HRTEM images showed a partially delaminated morphology in the PCHs synthesized with the largest clay/TEOS ratio. As the clay/TEOS ratio decreased, the interlayer distances of PCH expanded and the specific delamination was not appreciable. The mesoporosity of the PCHs gradually decreased, whereas the microporosity increased in both amount and distribution. Despite the invariant dominant pore size, the pore size distributions (PSD) of PCHs can be qualitatively controlled by altering the layer charge of the base clay, the length of the hydrophobic chains of surfactants, and the clay/TEOS ratio.Download high-res image (303KB)Download full-size image

Synthesis of iron pyrite with defined morphology has long been actively pursued, due to the strong size and shape dependence of their chemical and physical properties. This review provides comprehensive information outlining current knowledge regarding the morphology controllable syntheses of micro- and nano-iron pyrite mono- and poly-crystals. The wet-chemical methods are summarized as the controllable syntheses, including the hydrothermal, solvothermal, hot-injection and heating-up methods, sulphidation and methods with other relatively high efficiencies. The present study reveals the discussion of relationship between the morphologies and major controlling factors, the temperature, precursor chemicals, solvents and surfactants. The existing challenges for future fine tuning of iron pyrite facets are also proposed for improving the performance of iron pyrite based materials.

Our molecular dynamics simulation study shows water in the nanoconfined monolayer in Cl–-Mg2Al-layered double hydroxides (Mg2Al(OH)6Cl·mH2O) diffuses in a similar way as atoms in solid lattice. A water molecule is mostly fixed in a hydroxyl group site, as an acceptor of hydrogen bonds donated by the upper and lower hydroxyl groups simultaneously. Because of exchange of acceptors, it loses hydrogen bonds from the two hydroxyl groups and accepts hydrogen bonds from another two groups in an adjacent site. Thus, a water molecule jumps from one site to another, which is rapid but rare. On average it takes ∼104 ps for a jump to happen on a water molecule. The diffusion coefficient derived by the jump model is of the same order (∼10–9 cm2/s) as that obtained by fitting the mean-square displacement, revealing water diffusion in the confined monolayer is largely contributed by a series of jump events.

The swelling behavior of clay minerals is an important issue in industrial processes and environmental applications. Mixed-layer clay minerals containing a smectite fraction, such as rectorite, are neglected even though they could swell and exist in nature widely. The hydration of rectorite has not been well comprehended even though they are meaningful to mineralogy and industry. This study combines molecular dynamics (MD) and Monte Carlo (MC) simulations to disclose the swelling behavior of rectorite and compare with montmorillonite. From grand canonical Monte Carlo (GCMC) and MD simulations, we obtain swelling curves and swelling free-energy curves of rectorite with a relative humidity of 100%. With the comparisons of swelling free-energy minima, we find that the bilayer hydrate of Na-rectorite is more thermodynamically stable than the monolayer hydrate, which is similar to Na-montmorillonite. However, the interlayer sodium ions in rectorite show an asymmetrical distribution quite different from the symmetrical distribution in montmorillonite. Because of unequal layer charges between the smectite part and illite part of retorite, sodium ions prefer to distribute close to the illite part surface.

•The valences and occupancy for Fe and Mn in magnetite were studied by XAFS.•The Fenton activity was tested in acid orange II degradation and OH production.•The Mn enhanced activity of magnetite in Fenton reaction and Pb(II) adsorption.•The above effects were discussed with changes in structure and surface properties.In this study, a series of Mn substituted magnetites were synthesized and used in catalyzing the heterogeneous Fenton degradation of acid orange II and Pb(II) adsorption, in order to investigate the effect of Mn substitution on the reactivity of magnetite. The valence and local environment of both Fe and Mn in the spinel structure of magnetite were investigated by X-ray absorption fine structure (XAFS) spectroscopy. The incorporation of Mn did not change the valence and local structure of Fe in the synthetic magnetite, while Mn was in the valences of +2 and +3. The Mn distribution on the octahedral sites of magnetite surface increased with the increase in Mn content. The Mn introduction led to an improvement of catalytic activity of magnetite. The sample with the minimum Mn content displayed the best efficiency in OH production and the degradation of acid orange II, while the other substituted samples did not show obvious difference in their catalytic performance. The adsorption capacity of magnetite samples toward Pb(II) gradually increased with the increase in Mn content. The above influences of Mn substitution on the reactivity of magnetite were discussed in views of the variations in microstructural environment and physicochemical properties.

Silica minerals, one of the most abundant mineral species on the earth, play important roles in geochemistry and environment processes. The diversity of the SiO4 tetrahedron polymerization style might result in the heterogeneity of the surface microstructures and properties of SiO2 polymorphs. The surface properties of two common crystalline SiO2 polymorphs, i.e., α-quartz and α-cristobalite, have been investigated by the surface site density measurement, batch methylene blue (MB) adsorption, and X-ray photoelectron spectroscopy (XPS). The Langmuir adsorption isotherms suggest the formation of monolayer MB on both α-quartz and α-cristobalite surfaces. The adsorption capacity of α-quartz toward MB is larger than that of α-cristobalite, which positively correlates with the density of surface site. XPS spectra reveal that the adsorption takes place between the nitrogen atom of the dimethylamino groups in MB and silanols on α-quartz and α-cristobalite surfaces. The O/Si atom ratio related with adsorption of α-quartz is found to be about 1.8:1, which is higher than that of α-cristobalite (about 1.3:1). This suggests that there are two different silanol species (single and germinal) related to adsorption on the surface of α-quartz and α-cristobalite, and the higher O/Si ratio implies a larger proportion of germinal silanols in α-quartz. The Nlow/Nhigh ratio (Nlow stands for the N atoms with lower binding energy (399.2 eV), and Nhigh for the N atoms with higher binding energy (399.7 eV)) changes to about 2:1 with the adsorption saturation, implying that the space arrangement of MB adsorbed on the surface was adjusted with the increase of adsorption amount by lifting the average tilt angle between the long axis of the MB molecule and the sample surface. The higher surface site density of α-quartz leads to a larger average tilt angle, while α-cristobalite does conversely.

Rectorite is a special kind of clay mineral, consisting of illite layer and smectite layer in a regular order. In this study, we employ classical molecular dynamics simulations to study the microscopic interlayer properties of HDTMA+ (hexadecyl trimethyl ammonium)-intercalated rectorites with and without water at different HDTMA+ loading levels. The simulation results show that as the loading level increases, monolayer, bilayer, transition, and trilayer configurations of HDTMA+ occur in succession. The different layer charge characteristics between illite sheet and smectite sheet lead to special interlayer distributions of HDTMA+. In the systems without water, the headgroups of HDTMA+ and Na+ are controlled by six-membered rings of clay surface. With water addition, water molecules show the highest mobility among the interlayer species. However, HDTMA headgroups are still controlled by clay surfaces mainly with low mobility. At the same time, most of Na+ cations escape from surfaces because of the attractions from water. But water has little influence on the mobility of Na+. Water can decrease the mobility of alkyl chains because water fills up the empty region in the organic phases. In the sample with loading level exceeding 1 CEC, anions (Cl– in this study) present very poor mobility due to the electrostatic attractions with headgroups.

Understanding microstructure of organo montmorillonites (OMts) under wet condition is of high importance in clarifying their adsorption characteristics towards hydrophobic organic compounds in water. In this work, we investigated the basal spacing evolution of a series of OMt with various cetyltrimethylammonium (CTMA) loading during the intercalation, aging, drying and rehydration processes. The aim of this work is to provide novel information for exploring microstructure of wet OMt. X-ray diffraction results show that basal spacing value of the OMt does not change evidently after 30 min during the CTMA intercalation process, and then it decreases slightly in the following aging process. Drying causes dehydration and further decrease of basal spacing value. Rehydration of the dried OMt will cause the swelling of basal spacing again, but only the samples with relatively low CTMA loading amounts can recover the large values as those before drying. At relatively high CTMA loading level, OMt always show two (0 0 1) diffraction reflections, which indicates a heterogeneous interlayer structure for these samples. Moreover, this heterogeneous interlayer structure seems to be more evident in water. Our results also show that with increasing CTMA loading amounts, the rehydrated OMt show stepwise increase of basal spacing values, i.e., from 1.90 nm to 2.70 nm, and then to 2.76 nm. Finally, the possible interlayer structures of the rehydrated OMt are proposed.Graphical abstractThe possible structure models of the wet organo montmorillonites corresponding to basal spacing values of ∼1.90 nm (a) and ∼2.70 nm (b) are proposed.Highlights► Structure changes during intercalation, dehydration and rehydration processes. ► Drying causes organo montmorillonites dehydration and decrease of basal spacing. ► Rehydration of organo montmorillonites will cause the swelling of basal spacing.

•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.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 (2×1×1 nm) has been successfully prepared. This fundamental work may open up entirely new avenues for developing novel PILCs as heterogeneous catalysts and porous adsorbents.

In this work cetyltrimethylammonium bromide (CTMA) and cationic polyacrylamide (CPAM) were used to simultaneously modify bentonite, with the aim to synthesize novel organobentonites possessing high sorption capacity towards phenol, nitrobenzene and aniline. The XRD characterization results showed that the resulting organobentonites (C/P-Bt) had larger basal spacing than the corresponding CTMA modified bentonite (C-Bt) and CPAM modified bentonite (P-Bt). This indicated that the two modifying agents were simultaneously intercalated into the interlayers of C/P-Bt. FTIR characterization results showed that the νas(CH2) and νs(CH2) modes of CTMA on C/P-Bt shifted to low wavenumbers comparing with those on the corresponding C-Bt, which indicated CTMA had higher trans/gauche conformation ratio and packing density within the interlayers of C/P-Bt. C/P-Bt showed a synergistic sorption effect towards the tested sorbates, with a sorption efficiency better than that of C-Bt + P-Bt. In addition, the sorption capacity of C/P-Bt was shown to increase with the saturated CEC until the maximum, and then began to decrease as the saturated CEC further rose. The optimal saturated CEC was in the range 114–127%. Results of this work provided additional evidence that the packing density of organic cations could significantly influence the sorption capacity of organobentonites, and also showed a method for synthesizing novel organobentonites with high sorption efficiency towards organic pollutants.

A new nano zero-valent iron (nZVI) material that generates acidic conditions in situ was prepared by grafting an acid precursor onto diatomite. This new material was used in the evaluation of Bisphenol A (BPA) degradation by a Fenton-like process. The prepared material (M-nZVI-Da) exhibited a high removal efficiency (100%) of BPA under natural pH conditions of the solution (pH ∼5.75). The degradation of BPA using this new catalyst material follows a reaction pathway modelled on Fermi's equation with predictable kinetic outcomes for increased temperature of the reaction. Experiments demonstrate that the optimum starting concentration ratio of the H2O2/sample is 200 mM g−1 for efficient catalyst use. This study shows that nZVI materials with acid precursors are efficient catalysts for removal of BPA in solution.