Guijia Cui

Synthesis, characterization and application of amino-functionalized multi-walled carbon nanotubes for effective fast removal of methyl orange from aqueous solution

Amino-functionalized multi-walled carbon nanotubes (NH2-MWCNTs) for the removal of methyl orange (MO) from aqueous solution were prepared for the first time using 1,6-hexanediamine by a simple one-pot process at 198 °C for 8 h. The resulting materials were characterized by different techniques, such as TEM, FTIR, XPS, Raman, elemental analysis and BET surface area measurement. Experimental results indicated that the amount of 1,6-hexanediamine bound on MWCNTs was estimated to be around 5 wt% and the materials showed an excellent adsorption capacity (qmax = 185.53 mg g−1). The adsorption equilibrium could be reached within 10 min. Both Langmuir and Freundlich models showed a better fit with experimental data than the Temkin model and the adsorption kinetics could be accurately described by the pseudo-second-order model. The overall rate process was jointly controlled by intra-particle diffusion and external mass transfer. Moreover, the thermodynamic parameters indicated that the adsorption was spontaneous and exothermic. Results of this work are of great importance for environmental applications of amino-functionalized multi-walled carbon nanotubes as promising dye adsorbents in wastewater treatment.

A multifunctional magnetic core–shell fibrous silica sensing probe for highly sensitive detection and removal of Zn2+ from aqueous solution

In the present work, a multifunctional core–shell magnetic fibrous silica sensing probe AQ-Fe3O4@SiO2@KCC-1 was prepared for the detection, adsorption and removal of Zn2+. The core was composed of superparamagnetic Fe3O4 nanodots, while the shell consisted of fibrous silica molecular sieve KCC-1 and was decorated by a quinoline derived probe. The multifunctional inorganic–organic hybrid material was characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption–desorption, thermogravimetric analysis, and vibrating sample magnetometry. Its sensing performance towards Zn2+ was then discussed in detail. The experimental results suggested that this functional material exhibited enhanced fluorescence in the presence of Zn2+ ions and a high selectivity for Zn2+ over the competing metal ions in aqueous solution. The binding ratio of the AQ-Fe3O4@SiO2@KCC-1–Zn2+ complexes was determined from the Job plot to be 1:1. The association constant was calculated to be 1.85 × 105 M−1, with a detection limit of 1.08 × 10−7 M. Furthermore, the adsorption process of Zn2+ on the magnetic fibrous silica composite AQ-Fe3O4@SiO2@KCC-1 was well described by the Langmuir isotherm equation and the equilibrium adsorption capacity is 157.2327 mg g−1. These results indicate that these multifunctional magnetic fibrous silica sensing materials may find potential and favorable applications for simple detection and efficient removal of Zn2+ in toxicological and environmental fields.

One-pot preparation of a MnO2–graphene–carbon nanotube hybrid material for the removal of methyl orange from aqueous solutions

This study presents a MnO2–graphene–carbon nanotube (MnO2–G–CNT) hybrid material synthesized in a simple one-pot reaction process by a chemical method. The resulting materials were characterized by different techniques, such as TEM, XRD, FTIR, XPS, and BET surface area measurement. The adsorption behaviors of methyl orange (MO) onto the MnO2–G–CNT were firstly systematically investigated and experimental results indicated that the material with the highest loading amount of MnO2 showed an excellent adsorption capacity toward MO. The adsorption kinetics could be well described by the pseudo-second-order model and the Freundlich isotherm model showed a better fit with experimental data than the Langmuir model and the maximum adsorption capacity was determined to be qmax = 476.19 mg g−1. The overall rate process was apparently influenced by intra-particle diffusion and external mass transfer. Moreover, the thermodynamic parameters indicated that the adsorption was spontaneous and exothermic and that the physical adsorption mechanisms included electrostatic interaction, which played a dominant role in the adsorption mechanism between MO and the hybrid material.

Synthesis of poly(m-phenylenediamine)/iron oxide/acid oxidized multi-wall carbon nanotubes for removal of hexavalent chromium

Poly(m-phenylenediamine)-coated Fe3O4/o-MWCNTs nanoparticles (PmPD/Fe3O4/o-MWCNTs) were synthesized by one-step chemical oxidation polymerization. The materials were characterized by transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometry, and Brunauer–Emmett–Teller surface area measurement. Hexavalent chromium adsorption by PmPD/Fe3O4/o-MWCNTs was found to be strongly dependent on the solution pH. The adsorption isotherm of Cr(VI) onto PmPD/Fe3O4/o-MWCNTs fitted the Langmuir isotherm model at different temperatures and the maximum adsorption capacity was determined to be 346 mg g−1. The adsorption process of different initial concentrations can be described by the pseudo-second-order kinetic model. The intraparticle diffusion study revealed that external mass transfer and intraparticle diffusion apparently influenced the overall rate process. The values of thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic. In addition, the adsorption mechanism included both the physical and the chemical adsorption mechanisms. After adsorption, PmPD/Fe3O4/o-MWCNTs could be conveniently separated from the media by an external magnetic, and the adsorption capacity can remain at up to 52% after five times of usage. These results demonstrate that PmPD/Fe3O4/o-MWCNTs are a good candidate for the removal of Cr(VI) from aqueous solution.

Synthesis of manganese dioxide/iron oxide/graphene oxide magnetic nanocomposites for hexavalent chromium removal

Effective removal of heavy metal ions from wastewater is one of the important environment issues. Here, manganese dioxide/iron oxide/graphene-based magnetic nanocomposites (MnO2/Fe3O4/graphene oxide and MnO2/Fe3O4/graphene) were prepared by an easy and effective two-step reaction and investigated for the removal of hexavalent chromium ion from water. The materials were characterized by transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometry, and Brunauer–Emmett–Teller surface area measurement. MnO2/Fe3O4/graphene oxide (MnO2/Fe3O4/GO) synthesized at pH 5.0 was the most effective adsorption material among other samples synthesized under different conditions. The Langmuir isotherm model was consistent with the experimental data at different pH values. MnO2/Fe3O4/GO showed excellent adsorption capacities both at pH 5.0 (qmax = 175.4 mg g−1) and pH 2.0 (qmax = 193.1 mg g−1). Hexavalent chromium adsorption by MnO2/Fe3O4/GO was pH dependent. The adsorption kinetic data were best described by a pseudo-second-order model. MnO2/Fe3O4/GO was stable and easily recovered. These experimental results suggested that MnO2/Fe3O4/GO had great potential as an economic and efficient adsorbent of heavy metals from wastewater.

Morphology-dependent enhancement of template-guided tunable polyaniline nanostructures for the removal of Cr(VI)

Three nanostructured polyanilines (PANIs) with different morphologies, including nanofibers, nanotubes and nanosheets, have been successfully synthesized using MnO2 with tunable morphologies as the reactive templates. A growth mechanism is proposed to explain the evolution of the polyaniline morphology based on the reactive templates. The obtained PANIs were characterized by SEM, FT-IR, Raman, XRD, elemental analysis, BET and XPS. The adsorption capacities of three nanostructured PANIs with different morphologies were investigated towards the rapid removal of hexavalent chromium Cr(VI). Compared with PANI nanofibers without any templates, the template-guided PANIs showed better adsorption capacities. It was found that the adsorption capacities followed an order of PANI nanosheets > PANI nanotubes > PANI nanofibers. PANI nanosheets were the most effective adsorbent and the adsorption removal efficiency was 97.2% to remove 40 mg L−1 Cr(VI) from aqueous solution. The maximum adsorption capacity determined from the Langmuir isotherm model was 263.2 mg g−1. This finding suggests that the template-guided tunable polyaniline nanostructures method may be useful to enhance the adsorption capacity for the removal of Cr(VI).

Multifunctional optical sensing probes based on organic–inorganic hybrid composites

Several hybrid sensing materials, which are prepared by the covalent grafting of organic fluorescent molecules onto inorganic supports, have emerged as a novel and promising class of hybrid sensing probes and have attracted tremendous interest. In comparison to the organic fluorescent sensors, the hybrid sensing probes incorporate the beneficial chemical/physical properties of the organic molecules and inorganic materials, which accelerate the development of hybrid materials for ion recognition and removal. Hence, the novel hybrid sensing materials can selectively monitor and efficiently remove specific analytes, which can provide a novel opportunity to synthesize multifunctional hybrid materials. Considerable efforts have been devoted to developing effective and innovative approaches for the design and synthesis of hybrid sensing materials that can display highly desirable performance for ion detection and removal. This tutorial review firstly presents a brief description of the hybrid materials and mesoporous silica materials and then classifies the hybrid sensing materials into several categories, including mesoporous silica based hybrid sensors, magnetic core-shell particle based hybrid sensors, magnetic nanoparticle based hybrid sensors, polymer based hybrid sensors, surface-grafted composite based hybrid sensors, and host-guest interaction based hybrid sensors, followed by a detailed summary of the design and synthesis of hybrid sensing materials and their applications in environmental and biological fields. Hopefully, this review will provide perspectives and guidelines for the development and further research of hybrid sensing materials.

Synthesis and characterization of magnetic elongated hollow mesoporous silica nanocapsules with silver nanoparticles

In this study, magnetic elongated hollow mesoporous silica nanocapsules (MSNCs) with center-radial pore channels were successfully fabricated for the first time by using the surfactant-template synthesis approach. And, these novel nanomaterials were characterized by TEM, FTIR, XRD, XPS, VSM and N2 adsorption–desorption. These well-designed mesoporous silica nanocapsules have a very high specific surface area (860 m2 g−1), high pore volume (1.60 cm3 g−1) and highly opened biggish pore size (8 nm). To evaluate their supporting capability in catalytic reactions, the MSNCs were then functionalized with amino groups to robustly anchor silver nanoparticles (Ag NPs) to catalyze the reduction reaction of 4-nitrophenol and 2-nitroaniline. Significantly, Ag NPs were successfully supported in the abundant pore channels of the nanocapsules without any aggregation. The well synthesized multicomponent nanocatalyst exhibited excellent catalytic activity for the reduction of 4-NP and 2-NA in water at room temperature due to the abundant and high-efficiency accessible active sites. Interestingly, the novel catalysts have γ-Fe2O3 in the inner chamber so that they could be effortlessly recovered by magnetic separation from the reaction mixture and reused 10 times without any significant reduction in their catalytic activity. Therefore, the unique nanostructure based on the novel capsule-like mesoporous silica nanomaterial provided a useful platform for the fabrication of catalysts with superior activity, accessibility and easy recovery. And also, it is expected to be a significant template for the synthesis of other novel nanostructures.

Fibrous porous silica microspheres decorated with Mn3O4 for effective removal of methyl orange from aqueous solution

In this work, trimanganese tetraoxide (Mn3O4) functionalized fibrous porous silica microspheres (KCC-1) with well-dispersed and excellent adsorption capacities were successfully synthesized by a simple and mild method for the first time. Various conditions such as initial dye concentration, contact time, solution pH and temperature were investigated. Experimental results indicated that the content of Mn coated on KCC-1 was estimated to be around 14% (wt%) showing excellent adsorption capacity. The maximum adsorption capacity was determined to be qmax = 746 mg g−1 and the adsorption equilibrium could be reached within 120 min. The results showed that both Langmuir and Freundlich models fitted the experimental data very well. The overall rate process was influenced by intra-particle diffusion and external mass transfer. Moreover, the thermodynamic parameters indicated that the adsorption was spontaneous and exothermic.

Facile and cost-effective synthesis of CNT@MCo2O4 (M = Ni, Mn, Cu, Zn) core–shell hybrid nanostructures for organic dye removal

This study presents four hybrid materials of CNT@MCo2O4 (M = Ni, Mn, Cu, Zn) which were prepared via a simple chemical bath deposition method at room temperature followed by a post-annealing treatment. The resulting materials were characterized by different techniques including SEM, EDS, XRD, FTIR, and BET surface area measurement and were first used as adsorbents for removal of methyl orange (MO). Experimental data suggested that the CNT@MCo2O4 samples especially CNTs@NiCo2O4 showed excellent adsorption properties (1188.3 mg g−1). The kinetic adsorption of different materials could be accurately described by the pseudo-second-order model and the overall rate process was apparently influenced by external mass transfer and intraparticle diffusion. Furthermore, Langmuir and Freundlich isotherms are employed and both of them fitted the experimental data with good correlation coefficients. Moreover, the thermodynamic parameters indicated that the adsorption process was spontaneous and physical adsorption mechanisms including electrostatic interaction might play a dominant role in the adsorption mechanism between MO and adsorbents. The results of this work are of great significance for environmental applications of CNT@MCo2O4 as promising adsorbents for organic pollutants from wastewater.