Fatang Tan

Investigation on the efficiency and mechanism of Cd(II) and Pb(II) removal from aqueous solutions using MgO nanoparticles.

In this study, the removal of Cd(II) and Pb(II) from aqueous solutions using MgO nanoparticles prepared by a simple sol-gel method was investigated. The efficiency of Cd(II) and Pb(II) removal was examined through batch adsorption experiments. For the single adsorption of Cd(II) and Pb(II), The adsorption kinetics and isotherm data obeyed well Pseudo-second-order and Langmuir models, indicating the monolayer chemisorption of heavy metal ions. The maximum adsorption capacities calculated by Langmuir equation were 2294 mg/g for Cd(II) and 2614 mg/g for Pb(II), respectively. The adsorption process was controlled simultaneously by external mass transfer and intraparticle diffusion. In the binary system, a competitive adsorption was observed, showing preference of adsorption followed Pb(II) >Cd(II). Significantly, the elution experiments confirmed that neither Cd(II) nor Pb(II) could be greatly desorbed after water washing even for five times. XRD and XPS measurements revealed the mechanism of Cd(II) and Pb(II) removal by MgO nanoparticles was mainly involved in precipitation and adsorption on the surface of MgO, resulting from the interaction between active sites of MgO and heavy metal ions. Easy preparation, remarkable removal efficiency and firmly adsorptive ability make the MgO nanoparticles to be an efficient material in the treatment of heavy metal-contaminated water.

Facile modification of nanoscale zero-valent iron with high stability for Cr(VI) remediation

In this study, a highly stable nanoscale zero-valent iron composite (HS-NZVI) was obtained via modifying nanoscale zero-valent iron (NZVI) with tetraethyl orthosilicate (TEOS) and hexadecyltrimethoxysilane (HDTMOS), and used for Cr(VI) remediation in aqueous solution. The obtained HS-NZVI remained stable in water without being oxidized for over 12h. After four consecutive runs, the Cr(VI) removal efficiency of HS-NZVI maintained a value of more than 82%. Moreover, the Cr(VI) removal capacity per unit weight of NZVI in HS-NZVI reached 292.8mg/g within 60min at the initial Cr(VI) concentration of 120mg/L at pH5. The Cr(VI) removal efficiency of HS-NZVI increased with decreasing solution pH, and the experimental data for Cr(VI) removal by HS-NZVI were well-described by the pseudo-first-order reaction model. Additionally, scanning electron microscope (SEM) images, X-ray diffraction (XRD) patterns and X-ray photoelectron spectroscopy (XPS) measurements of the product after reaction revealed that the mechanism of Cr(VI) remediation by HS-NZVI mainly involved adsorption, reduction and co-precipitation. Considering the advantages of easy preparation, excellent stability and reusability, and high Cr(VI) removal capacity as well as the magnetic recovery property, HS-NZVI is expected to have notably promising applications for the remediation of Cr(VI) contaminated sites.

Room-temperature synthesis of silica supported silver nanoparticles in basic ethanol solution and their antibacterial activity

A facile and environmentally friendly route was developed to synthesize silica supported silver nanoparticles (Ag NPs) through the reduction of silver ions in basic ethanol solution without adding any other reducing agents or surfactants at room temperature. The structure, morphology and composition of as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It was found that the molar ratio of sodium hydroxide to silver nitrate was a decisive factor for the composition of the final products. If the molar ratio was larger than 1.1, the final product was pure silver particles; otherwise, part of the product was silver oxide. Moreover, it was also found that water had a negative influence on the formation of silver particles. For a simple experimental process, this is an efficient and facile method to synthesize silica supported Ag NPs in ethanol at room temperature. Additionally, since the as-prepared Ag NPs were not encapsulated with surface modifier, the Ag NPs with more active atoms exposed consequently exhibited excellent antibacterial activity against Escherichia coli.

Fabrication of pit-structured ZnO nanorods and their enhanced photocatalytic performance

ZnO nanorods have been successfully prepared at low temperature (60 °C) in the presence of ammonia via a simple aqueous solution-based chemical approach. After calcination at 300 °C, many unique pitted structures are found on the surface of ZnO nanorods, although the shape and size of ZnO nanorods have almost no changes. Furthermore, the pit-structured ZnO nanorods exhibit higher photocatalytic activity for methylene blue photodegradation with a rate constant (k) of 0.01402 min−1, which is about 3 times more than that of uncalcined sample. The formation of the pitted structures is presumably attributed to the decomposition of a trace amount of ZnO(NH3)n complex implanted into ZnO crystals. In addition, a photocatalytic mechanism is proposed to explain the enhanced photocatalytic activity of the pit-structured ZnO nanorods.

Facile preparation of Ag/Ni(OH)2 composites with enhanced catalytic activity for reduction of 4-nitrophenol

In this work, a facile and environmentally friendly process was developed for synthesis of Ag/Ni(OH)2 composites by only mixing an ethanol solution of AgNO3 with Ni(OH)2 at room temperature. The morphology and structure of the as-prepared Ag/Ni(OH)2 composites were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM) and X-ray photoelectron spectroscopy (XPS). It was found that the composites consist of ultrathin nickel hydroxide and silver nanoparticles (Ag NPs), the Ag NPs with an average diameter of around 4.7 nm evenly dispersed on the surface of Ni(OH)2 nanosheets. The catalytic properties of the obtained Ag/Ni(OH)2 composites were evaluated by the reduction of 4-nitrophenol (4-NP) using NaBH4 as a reducing agent. The results revealed that the obtained Ag/Ni(OH)2 composites exhibited an outstanding catalytic activity. In addition, the formation mechanism of Ag NPs was probed by ultraviolet-visible spectroscopy (UV-Vis). It was found that Ni(OH)2 as a substrate played an important role in the formation of silver particles, which not only acted as a superior adsorbent of silver ion but also a source of OH− that was able to accelerate the reaction. Electrochemical impedance spectroscopy (EIS) and fluorescence (FL) spectra were employed to indirectly elucidate the mechanism for reduction of 4-NP. The Ag/Ni(OH)2 composites are very promising catalytic candidates for the reduction of 4-nitrophenol because of their easy and simple preparation route and high catalytic activity.

Facile preparation of mesoporous silica/nano zero-valent iron composite for Pb(II) removal from aqueous solution

AbstractNano zero-valent iron (NZVI) particles were prone to forming aggregates owing to their intrinsic magnetism and van der Waals force. In this work, a composite material containing mesoporous silica MCM-41 and NZVI was prepared to avoid the problem of NZVI aggregation. The structures and morphologies of the as-prepared composite were confirmed using X-ray diffraction, Fourier transform infrared spectrometry, transmission electron microscopy, N2 adsorption–desorption, and X-ray photoelectron spectroscopy techniques. It was found that NZVI particles were well dispersed in the composite, although the size of NZVI particle was larger than that of bare NZVI. Moreover, the composite was used as adsorbent for removing Pb(II) from aqueous solution at room temperature. The effects of contact time, initial solution pH, and adsorbent dosage on the removal efficiency of Pb(II) were studied using batch adsorption experiments. The results indicated the composite exhibited enhanced adsorption properties, with the m...

Preparation of polyimide-graphite composite and evaluation of its friction behavior at elevated temperatures

Abstract In this paper, polyimide-graphite (PG) composite was prepared and used as a solid lubricant at elevated temperatures. PG composite was characterized by X-ray diffraction, and its thermal stability was evaluated based on thermogravimetric/differential thermal analysis and Fourier transform infrared spectrometry analysis. The results show that in PG composite, there was some interaction between the graphite (GR) and the polyimide (PI) matrix. Consequently, the PG composite exhibited better thermal stability than PI. The friction behavior of the PG composite sliding against steel at elevated temperatures (300–600°C at an interval of 100°C) was evaluated with a ring-on-ring tribometer. It was found that the PG composite exhibited excellent friction-reducing ability and good load-carrying capacity in the temperature range of 300–600°C and applied loads of 300–700 N. Moreover, this excellent lubricating performance of the PG composite might be attributed to its good thermal stability as a result of the interaction between the GR and the PI matrix. Therefore, PG composite could be used as an excellent solid lubricant under the high-temperature conditions.

Effective removal of cadmium ions from aqueous solution using chitosan-stabilized nano zero-valent iron

AbstractIn this study, a series of chitosan-stabilized nano zero-valent iron (CNZVI) composites with different amounts of chitosan were prepared and characterized by Fourier transform infrared spectra, X-ray diffraction, and transmission electron microscopy. The adsorption capacity of these composites was evaluated by the removal experiment of cadmium ion (Cd2+) from aqueous solution. These results showed that the as-prepared CNZVI8 composite with loose aggregate structure has the maximum adsorption capacity for Cd2+. Furthermore, batch adsorption experiments of Cd2+ on CNZVI8 composite were performed under various conditions, such as contact time, adsorbent dosage, initial Cd2+ concentration, and the initial pH of solution. The data revealed that the maximum adsorption capacity of CNZVI8 is 124.74 mg/g. The removal efficiency of Cd2+ increased with the increase in solution pH value, and reaches 99.9% at pH 6. In addition, the adsorption isotherm and the adsorption kinetics of Cd2+ on CNZVI8 were also inv...

g-C3N4/MgO nanosheets: light-independent, metal-poisoning-free catalysts for the activation of hydrogen peroxide to degrade organics

The huge amount of organic wastewater produced by dye manufacturing/consuming industries causes serious environmental pollution, which urges researchers to explore highly efficient and cost-effective Fenton-like catalysts. Herein, we report the synthesis of g-C3N4/MgO nanosheets through a simple two-step calcination method, exhibiting the excellent catalytic ability of activating hydrogen peroxide to degrade organic dyes in the dark. The results of this study indicate that the g-C3N4/MgO nanosheets are light-independent and metal-poisoning-free Fenton-like catalysts for enhanced degradation of organics. The efficient degradation performance is attributed to hydroxyl radical generation in the g-C3N4/MgO–H2O2 catalytic system. The bonding between the MgO and g-C3N4 parts of the g-C3N4/MgO nanosheets is considered to be a key role in activating H2O2 to produce a hydroxyl radical. This catalytic degradation process can be conducted in a wide pH range and at room temperature without external energy input. Additionally, the g-C3N4/MgO nanosheets are non-toxic, low-cost and easy to prepare. Therefore, it is reasonable to believe that g-C3N4/MgO nanosheets have a great potential in the catalytic degradation of organic contaminants and could be used in a wide range of environmental cleanup applications. Furthermore, this work provides an insight into exploiting novel Fenton-like catalysts without transition metal components or external energy excitation.