Haizhen Li

Enhanced adsorption removal of methyl orange from aqueous solution by nanostructured proton-containing δ-MnO2

Two nanostructured proton-containing δ-MnO2 (H-δ-MnO2) materials were synthesized through proton exchange for K-containing δ-MnO2 (K-δ-MnO2) nanosheets and nanoparticles prepared by the hydrothermal homogeneous precipitation method and solid-state reaction. Energy-dispersive spectroscopy (EDS) measurements showed that the K+ cations were successfully leached away and replaced with H+ ions. The role of K+ cations in the adsorption process was first explored by replacing the K+ ions in the δ-MnO2 with H+ ions and the adsorption capacities for organic pollutants were investigated using methyl orange (MO) as a model. Experimental results indicated that the H-δ-MnO2 materials with a similar morphology and crystal structure showed excellent adsorption capacities of 375 and 427 mg g−1 for MO, because both of the nanostructured H-δ-MnO2 materials have much larger Brunauer–Emmett–Teller (BET) surface areas than that of K-δ-MnO2. The remarkable adsorption capacities of dye onto H-δ-MnO2 materials indicate that K+ cations in the layered δ-MnO2 structure have an unfavorable influence on the adsorption process. Moreover, physical adsorption mechanisms including electrostatic interaction play a dominant role in the adsorption mechanism between MO and adsorbents. This finding suggests that the proton-exchange process may be a useful method to improve the adsorption affinity of dye contaminants on δ-MnO2 and nanostructured proton-containing δ-MnO2 samples are good candidates for efficient MO removal from wastewater.

Adsorption-photocatalytic degradation of methyl orange over a facile one-step hydrothermally synthesized TiO2/ZnO–NH2–RGO nanocomposite

A novel TiO2/ZnO–NH2–reduced graphene oxide (TZ-a-RGO) nanocomposite was successfully prepared using a facile one-step hydrothermal method. The TZ-a-RGO was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) surface area analysis and UV-vis absorption spectrophotometry to investigate its structural features. The TZ-a-RGO was used as a catalyst to remove methyl orange (MO) from wastewater, and the results indicated that this catalytic system has a good performance in terms of removal of MO. The adsorption experiments of the TZ-a-RGO followed the pseudo-second-order kinetic model, and the adsorption isotherms were accurately represented by the Langmuir model. The degradation of methyl orange (MO) by TZ-a-RGO fitted well with the Langmuir–Hinshelwood model, and MO removal was obtained through a synergistic effect of adsorption and photocatalysis. The photocatalytic rate of MO over the composites was as high as 8.2 and 3.2 times that over commercial P25 (Degussa) and TiO2/ZnO, respectively. The potential photocatalytic mechanism for the TZ-a-RGO nanocomposite under UV was discussed.

Facile synthesis of Fe3O4/hierarchical-Mn3O4/graphene oxide as a synergistic catalyst for activation of peroxymonosulfate for degradation of organic pollutants

Highly effective Fe3O4/Mn3O4/reduced graphene oxide (rGO) hybrids were synthesized as a heterogeneous catalyst for the degradation of organic dyes in aqueous solution using sulfate radical-based advanced oxidation processes. The physicochemical properties of the composite were characterized by several techniques, such as X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectra (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) theory. The effects of different parameters on the catalytic activity of Fe3O4/Mn3O4/rGO, including initial Methylene Blue (MB) concentration, peroxymonosulfate (PMS) concentration, catalyst dosage, pH value, and temperature were assessed. Typically, 98.8% removal of 50 mg L−1 of MB and 68.3% reduction of TOC could be achieved in 30 min under the following conditions: temperature 25 °C, 100 mg L−1 of catalyst, and PMS dosage of 0.3 g L−1, showing a significant enhancement of the catalytic activity of the catalyst in the degradation of organic pollutants in aqueous solution compared with Fe3O4/rGO and Mn3O4/rGO. The catalyst exhibited high stability and good reusability according to three successive repeated reactions. Based on the radical experiments, the catalytic activity of Fe3O4/Mn3O4/rGO hybrids for degradation of MB is closely related with the amount of the sulfate and hydroxyl radicals generated from PMS. The excellent catalytic performance of the Fe3O4/Mn3O4/rGO is mainly attributed to the synergistic effects of Fe3O4, Mn3O4, rGO, and Oxone.

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-step synthesis of magnetic 1,6-hexanediamine-functionalized reduced graphene oxide–zinc ferrite for fast adsorption of Cr(VI)

A one-step solvothermal method was developed to prepare nearly cubic ZnFe2O4 nanoparticles loaded on 1,6-hexanediamine-functionalized reduced graphene oxide (HDA–RGO–ZnFe2O4) for fast removal of Cr(VI). The materials were characterized by transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, Raman, and vibrating sample magnetometry. Experimental results indicated that Cr(VI) adsorption by HDA–RGO–ZnFe2O4 is strongly pH dependent and the adsorption equilibrium could be reached within 12 min. The kinetic adsorption of different initial concentrations can be accurately described by the pseudo-second-order model. The overall rate process was apparently influenced by external mass transfer and intraparticle diffusion. The Langmuir isotherm model is consistent with the experimental data at different temperatures and the maximum adsorption capacity was determined to be 172.4 mg g−1. Moreover, the thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic. The adsorption mechanism and desorption experiments were also studied. After adsorption, the HDA–RGO–ZnFe2O4 could be quickly separated from the media by an external magnetic field and the adsorption capacity can remain up to 82% after five times of usage. The results implied that HDA–RGO–ZnFe2O4 is a promising adsorbent for the removal of Cr(VI).

Introduction of α-MnO2 nanosheets to NH2 graphene to remove Cr6+ from aqueous solutions

The planar structure of the designed α-MnO2–NH2–RGO hybrid was prepared and characterized and used to remove hexavalent chromium ions (Cr6+) from aqueous solutions. The characterization of the novel adsorbent was carried out using the Fourier transform infrared spectrum (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and the Brunauer–Emmett–Teller (BET) theory. Cr6+ adsorption efficiency was investigated as a function of the pH of Cr6+ solution, contact time and temperature. The results showed that the adsorption capacity strongly depended on the pH and that the adsorption equilibrium data were best described by the Freundlich isothermal model. The maximum sorption capacity towards Cr6+ was 371 mg g−1. The kinetic adsorption was fitted to the pseudo-second-order kinetics model and it indicated that the adsorption mechanism is physical or chemical sorption on heterogeneous materials. The thermodynamic parameters were obtained, and the results showed that the adsorption process is spontaneous and exothermic. The adsorption capacity of α-MnO2–NH2–RGO can remain as high as 81% after five usage cycles. As a result, these findings propose that α-MnO2–NH2–RGO could be used as an outstanding adsorbent for Cr6+.

Multifunctional Fe3O4@SiO2 nanoparticles for selective detection and removal of Hg2+ ion in aqueous solution

In the present work, a multifunctional magnetic core–shell Fe3O4@SiO2 nanoparticle decorated with a rhodamine-based receptor, which exhibits high selectivity and sensitivity toward Hg2+ over other metal ions in aqueous solution, has been synthesized by the graft method and characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometry, and UV-vis absorption and fluorescence spectra. The multifunctional nanoparticles show superparamagnetic behavior, clear core–shell architecture, and also exhibit high optical sensing performance for the detection of Hg2+. The fluorogenical responses of RB-Fe3O4@SiO2 are stable under a broad pH range. Additionally, these nanoparticles show high performance in the magnetic separability and effective removal of excess Hg2+ in water via an external magnetic field. These results indicate that these multifunctional magnetic nanoparticles may find potential and practical applications for selective detection and simple removal of Hg2+ in environmental, toxicological, and biological fields.

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.