Showing papers by "Jianxi Zhu published in 2014"

The constraints of transition metal substitutions (Ti, Cr, Mn, Co and Ni) in magnetite on its catalytic activity in heterogeneous Fenton and UV/Fenton reaction: From the perspective of hydroxyl radical generation

Abstract: In this paper, the heterogeneous Fenton and UV/Fenton catalytic activities of transition metal substituted magnetites, Fe3−xMxO4 (M = Ti, Cr, Mn, Co and Ni), were compared in the perspective of •OH radicals generation. In heterogeneous Fenton reaction, the substitutions of Cr(III), Mn(II) and Co(II) enhanced the rate of •OH formation, while Ni(II) and Ti(VI) showed the negative effect. In heterogeneous UV/Fenton reaction, the Ni(II) and Co(II) introduction did not show notable changes on •OH generation efficiency, whetreas the Cr(III), Ti(VI) and Mn(II) incorporation improved this reaction and accordingly enhanced the UV/Fenton catalytic activity of magnetite. Redundancy and Pearson correlation analyses were carried out to interpret the influence factors in Fenton and UV/Fenton reactions.

Surface Heterogeneity of SiO2 Polymorphs: An XPS Investigation of α-Quartz and α-Cristobalite

Abstract: 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...

Co-sorption of Cd and phosphate on the surface of a synthetic hydroxyiron-montmorillonite complex

Abstract: Hydroxymetal-clay complexes, which contain reactive surface hydroxyl groups, have a strong affinity for both heavy-metal cations and oxyanions and hence can serve as efficient sorbents for ionic contaminants. The co-sorptive behavior of heavy-metal cations and oxyanions on the surface of hydroxymetal-clay complexes is not well understood, however. The objective of the present investigation was to help bridge that gap by determining the feasibility of co-sorbing Cd cations and phosphate from aqueous solution to a hydroxyiron-montmorillonite complex (HyFe-mont). A montmorillonite-rich clay from Inner Mongolia, China, was the starting material. The results showed that Cd and phosphate could be sorbed, simultaneously and synergistically, to HyFe-mont without a change in solution pH. Similarly, when phosphate was sorbed before Cd, the sorption capacities were comparable to those obtained in the simultaneous sorption experiment, and the solution pH did not change.When Cd was pre-sorbed, however, the subsequent sorption of both Cd and phosphate decreased as did solution pH. X-ray photoelectron spectroscopy (XPS) indicated that the binding energies of P2p, Cd3/2, and Cd5/2 were of similar magnitude for both the simultaneous sorption system and the phosphate pre-sorbed system. In addition, the single Cd and Cd pre-sorbed systems had similar Cd3/2 and Cd5/2 binding energies. The combined sorption and XPS results suggested that sorbed phosphate and Cd formed P-bridged ternary complexes on the HyFe-mont surface, contributing to the synergistic uptake of the contaminants in the simultaneous sorption system.

Aluminum ion occupancy in the structure of synthetic saponites: Effect on crystallinity

Abstract: Two series of saponites with fixed (Si+Al)/Mg and Si/Mg ratios, respectively, were synthesized by using hydrothermal methods. The obtained products were characterized by XRD, XRF, 27Al, and 29Si MAS NMR, SEM, and TEM. XRD patterns showed that well-ordered saponites were obtained in the initial Si/Al ratio range of 5.43–7.89. Beyond this Si/Al ratio range, poorly crystallized saponites were obtained with small crystallized particles, which can be seen from TEM images. When intercalating saponite with surfactant, the intercalated products displayed strong and well-ordered (00 l ) reflections, indicating that layered saponite has been successfully synthesized in the present study. 27Al MAS NMR spectra demonstrated that well-crystallized synthetic saponites had a higher Al(IV)/Al(VI) ratio than the poorly crystallized samples, which is an important factor affecting the crystallinity of synthetic saponite. A one-to-one substitution (i.e., 1 Al3+ → 1 Mg2+) actually occurred in the octahedral sheet and this substitution had a negative effect on the crystallinity of the synthetic saponites. After grafting the synthetic saponites with silane, the decreased intensity of the 29Si NMR signal at −86 ppm and the increased intensity of Q3 Si(0Al) and Q3 Si(1Al) signals strongly suggested that the signal at ca. −86 ppm corresponded to Q2 Si at the layer edges of saponite.

Investigation of structure and thermal stability of surfactant-modified Al-pillared montmorillonite

Abstract: For combining the properties of organoclays and pillared clays, inorganic–organic clays have attracted much attention in recent years. In this study, Al Keggin cation pillared montmorillonites (Al-Mts) were first prepared and parts of Al-Mts were calcined at different temperatures (C-Al-Mts). The inorganic–organic montmorillonites were synthesized by intercalating Al-Mts and C-Al-Mts with the cationic surfactant, hexadecyltrimethyl ammonium bromide (HDTMAB). The products were characterized by X-ray diffraction, X-ray fluorescence, and simultaneous thermogravimetric analysis. For HDTMAB-modified uncalcined Al Keggin cation pillared montmorillonites (H-Al-Mts), the basal spacing increased with the increment of surfactant loading level, but the Al content of H-Al-Mts decreased simultaneously, indicating that the intercalated surfactant replaced some Al Keggin cations in the interlayer space. However, in the case of C-Al-Mts, the interlayer spaces could not be further expanded after surfactant modification, implying that the neighboring montmorillonite layers were “locked” by the aluminum pillars which were formed by dehydroxylation of Al Keggin cation pillars during thermal treatment. The thermal stability of HDTMAB-modified C-Al-Mts (H-C-Al-Mts) was much better than that of H-Al-Mts. The major mass loss of H-C-Al-Mts occurred at ca. 410 °C, corresponding to decomposition of intercalated surfactant cations. In contrast, H-Al-Mts displayed two mass loss temperatures at ca. 270 and 410 °C, corresponding to the evaporation of surfactant molecules and the decomposition of surfactant cations in the interlayer space, respectively.

Preparation method for doped graphene-like structural nanometer carbon material

Abstract: A disclosed preparation method for a doped graphene-like structural nanometer carbon material comprises the steps: 1) putting montmorillonite into a dye-containing solution to perform sufficient adsorption processing; and 2) successively performing drying, crushing, carbonization, acidification washing and drying on the montmorillonite adsorbing a dye, so as to obtain a product. By taking montmorillonite as a template and taking the dye as a carbon source as well as a doping source, the doped graphene-like structural nanometer carbon material is obtained by employing a simple one-step method. A new method for synthesizing a series of heteroatom-doped graphene-like materials is provided, and therefore application of the doped graphene-like carbon material to fields such as nanometer electrical appliances, sensors, energy-storage equipment and the like is facilitated to be promoted.

The UV/Fenton degradation of tetrabromobisphenol A catalyzed by nanocrystalline chromium substituted magnetite.

Abstract: The heterogeneous UV/Fenton degradation of tetrabromobisphenol A (TBBPA) catalyzed by nanocrystalline Fe3O4 and Fe2.04Cr0.96O4 was investigated, with focus on the influence of UV light and initial pH, degradation pathways and effect of Cr substation. The catalysts were prepared by a precipitation-oxidation method and characterized by chemical analysis, XRD, XAFS, TG-DSC, BET surface area and magnetometer. At pH 6.7 and under UV irradiation, almost complete degradation of TBBPA by Fe2.04Cr0.96O4 was accomplished within 240 min, and the leaching Fe ions were negligible. The substitution of chromium greatly increased the BET specific surface area and surface hydroxyl amount, which improved the heterogeneous UV/Fenton catalytic activity of magnetite. Moreover, Cr3+ on the octahedral sites enhanced the electron transfer process in the magnetite structure to accelerate the *OH generation. The produced *OH radicals preferentially attacked the C-Br bonds of TBBPA and then β-cleavaged the C-C bonds between benzene rings and isopropyl groups. The above results are of great significance for well understanding the effect of transition metal substitution on the UV/Fenton catalytic activity of magnetite and prospecting the application of magnetite minerals in environmental purification.

Preparation method for high-adsorptivity organic bentonite

Abstract: The invention discloses a new method for enhancing the adsorption performance of organic bentonite. The method comprises: performing original soil grinding and crushing on bentonite, performing lithium ion exchange, then utilizing a certain amount of organic cations to exchange part of lithium ions, finally performing heating processing, so as to migrating interlayer lithium ions into bentonite lamella and further to obtain the organic bentonite adsorption material with good adsorption performance. The method provided by the invention is characterized by pre-exchanging organic cations to bentonite interlayer, utilizing the pillared effect of the organic cations to prevent bentonite layer structure from collapsing, then performing heating charge-reducing treatment, so as to furthest retaining the interlayer adsorption space and improve the specific surface area and adsorption sites of organic bentonite, and further enhance the adsorption performance of organic bentonite to toxic organic pollutants. The preparation method provided by the invention helps to reduce the sewage processing cost of organic bentonite and thus has wide application prospect in pollution control.

Method for regenerating porous template carbon material by utilizing LDH

Abstract: A disclosed method for regenerating a porous template carbon material by utilizing LDH comprises the following steps: successively performing drying, crushing, carbonization, acidifying washing for removing metal oxides and drying on waste LDH adsorbing dye to obtain the porous template carbon material. By taking waste LDH as the raw material, the simple method is used to prepare the porous template carbon material with relatively large specific surface area, also the method helps to provides a new approach for solving recovery and utilization of the waste LDH adsorbing the dye and realize the recycling of waste LDH after wastewater is processed, and consequently the application of LDH to dye-printing and dyeing wastewater is facilitated.