Xiaoyu Guan

A magnetically-separable Fe3O4 nanoparticle surface grafted with polyacrylic acid for chromium(III) removal from tannery effluents

Chromium(III) contamination in tannery effluents continues to represent a significant challenge towards sustainable development of the global leather industry. Despite various magnetite-supported adsorbents for chromium removal previously reported, few of them were specifically designed to address trivalent chromium and the complexity of pollutants in tannery effluents. In the present study, polyacrylic acid, capable of adsorbing chromium(III) by coordination, was grafted from the surface of Fe3O4 nanoparticles via the bridging function of a silane coupling agent to produce a magnetically-separable nanoadsorbent (PAA@VTES@Fe3O4) for chromium(III) remediation from tannery effluents. The structure and morphologies of the nanoadsorbent were systematically characterized by scanning electron microscopy, low-temperature nitrogen adsorption/desorption experiments, energy dispersive X-ray spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, total organic carbon content and X-ray diffraction analysis. With a saturated magnetization of 46.8 emu g−1, PAA@VTES@Fe3O4 could be separated from water within 5 min by using a magnet. Adsorption experiments showed that chromium(III) adsorption on PAA@VTES@Fe3O4 was pH- and adsorbent dose-dependent; adsorption equilibrium could be reached in 2.5 h, resulting in a chromium(III) removal percentage of more than 90% under optimized conditions. The adsorption kinetics were best described by pseudo-first order and pseudo-second order models, while the isotherm data were found to agree well with both Langmuir and Freundlich models. Based on the fitting results, it was found that PAA@VTES@Fe3O4 exhibited high adsorption capability relative to many other adsorbents previously suggested as efficient for chromium(III) removal from effluents. In addition, a thermodynamic study revealed that the adsorption process was endothermic and spontaneous in nature. By chemical desorption, PAA@VTES@Fe3O4 could be regenerated and repeatedly used for five cycles without significantly compromising the adsorption capacity. Even in the presence of large amounts of decomposing organic matter, hair, lime, sulphide and organic nitrogen, PAA@VTES@Fe3O4 was still capable of removing more than 90% of chromium(III) from tannery effluents, exhibiting a high potential for practical application.

Polyacrylic acid-grafted magnetite nanoparticles for remediation of Pb(II)-contained water

Toxic Pb(II) contaminants in water pose a significant threat to the environment and public health, and thus technologies for Pb(II) remediation are attracting increasing industrial interests. In the present work, polyacrylic acid, offering abundant carboxyl groups capable of coordination with Pb(II) cations, was grafted from the magnetite nanoparticle surface via the bridging function of silane coupling agent for remediation of Pb(II)-contained water. Multiple techniques were employed to characterize the structure of the nanocomposite, and the effects of nanoadsorbent dose, pH value, and temperature on Pb(II) removal capability of the nanocomposite were investigated, respectively. Furthermore, adsorption kinetics and isotherms studies were performed for better understanding the mechanism by which Pb(II) cations were adsorbed. Finally, the feasibility of regenerating the exhausted nanoadsorbent by simply changing pH value was explored. According to these results, we intend to offer an efficient, separable, and reusable magnetic nanoadsorbent that may be a potential candidate for remediating Pb(II) contamination in water.

Poly(N-acryloyl ciprofloxacin-co-acrylic acid) grafted magnetite nanoparticles for microbial decontamination of collagen solution: have we conquered the problem of antimicrobial residues?

Widespread concern over antimicrobial toxicity and resistance development necessitates the thorough recovery of antimicrobial compounds from decontaminated collagen. Herein, ciprofloxacin molecules were acryloylated by reaction of the secondary amine in 7-piperazinyl substituent with acryloyl chloride, and then covalently immobilized, for the first time, on the vinyl-functionalized Fe3O4 nanoparticle surface via graft copolymerization with acrylic acid, in an effort to design a magnetically-recoverable nanocomposite potentially applicable for microbial decontamination of collagen solution. Unlike previous magnetite-supported antimicrobials invariably involving the release of antimicrobially-active component, these immobilized ciprofloxacin moieties proved non-leachable, in whole or in part, from the magnetite core, exerting antimicrobial activity as free ciprofloxacin, and thus could be thoroughly recovered from decontaminated collagen solution under magnetic fields. Also, it was found that the unique triple-helical conformation and, hence, bioactive properties of tropocollagens remained intact after decontamination using such recoverable antimicrobials. This proof-of-principle study aims to shed light on a long-standing dilemma in the collagen community: how to decontaminate collagen using antimicrobial compounds without being subject to antimicrobial residues?

Remediation of chromium(III)-contaminated tannery effluents by using gallic acid-conjugated magnetite nanoparticles

Potential ecological risks of chromium(III) contaminates in tannery effluents have evoked considerable discussion and re-examination over the future role of chrome tannage, which has been long considered as the foundation of the modern leather industry. Despite previous magnetite-supported adsorbents for chromium removal, few of them were specifically engineered to address trivalent chromium, as well as the composition complexity in tannery effluents. Herein, gallic acid, a natural triphenolic compound capable of coordination to chromium(III), was covalently conjugated onto engineered magnetite nanoparticles via 1-ethyl-3-(3-dimethylaminepropyl) carbodiimide hydrochloride/N-hydroxysuccinimide (EDC/NHS) chemistry, in an effort to design a magnetically separable nanoadsorbent applicable for remediating chromium(III)-contaminated tannery effluents. The structure of the nanoadsorbent was systematically characterized by multiple techniques, and the influence of pH value, adsorbent dose, temperature, and leather-related co-existing substances on its chromium(III) removal potency was investigated, respectively. Also, kinetics, equilibrium, and thermodynamics studies were conducted to decipher the mechanism by which chromium(III) cations were adsorbed. Finally, the feasibility of treating real tannery effluents that also contained high concentrations of sulfides, chlorides, ammonium nitrogen, total suspended solids, chemical oxygen demand (CODCr), and biochemical oxygen demand (BOD) by using the nanoadsorbent designed herein was explored. It was found that the chromium(III) removal percentage was approximately 95.2 ± 1.6%, and the exhausted nanoadsorbent could be conveniently separated from the effluents via a simple magnetic process. By chemical desorption, the nanoadsorbent was regenerable, and reusable for multiple cycles without a significantly compromised adsorption potency. According to these results, we aim at providing an efficient solution that may be a great addition to the ongoing fight against chromium(III) contamination in tannery effluents.

Stepwise Deprotonation of Magnetite-Supported Gallic Acid Modulates Oxidation State and Adsorption-Assisted Translocation of Hexavalent Chromium

Recently, a synergistic strategy involving reduction of carcinogenic Cr(VI) into less toxic Cr(III) followed by Cr(III) adsorption and subsequent separation by surface-engineered magnetite nanoparticles has emerged as a promising alternative to address the environmental hazards associated with Cr(VI)-contaminated water. Despite several previous attempts exploiting this synergy, modulating the oxidation state and translocation of Cr(VI) with high spatiotemporal precision remains a major challenge. Here, we report how Cr(VI) responds accordingly in a well-defined manner to deprotonation of gallic acid covalently immobilized on magnetite nanoparticles, which proceeds through a fixed spatial sequence of distinct stages. To the best of our knowledge, this proof-of-principle study, for the first time, demonstrates that accurate spatiotemporal control over the cascading reduction-adsorption process of Cr(VI) by magnetic adsorbents is feasible, which provides guidance for rational design of more exquisite, magnetite-supported surfaces, where a predictable, and hence controllable, synergy can manifest for Cr(VI) detoxification.

Interfacial regions in spherical nanoparticle-doped glassy polymers: interfaces or interphases?

Whether an extra, subtle high-free-volume interphase in glassy polymers containing spherical nanoparticles really exists remains an open question, posing fundamental challenges for accurately predicting and intentionally tailoring the macroscopic transport behavior of these nanocomposites, which is crucial for a broad spectrum of industrial applications. Herein, we report new evidence supporting this controversial interphase by computational simulation and offer a generic framework for understanding how the interphase is shaped, based on a comparative strategy. This framework, validated by our previous experimental data, may provide guidance for rationally designing interfacial architectures in these nanocomposites that enable bottom-up tuning of their transport properties for specific applications.

Sulfonated poly(styrene-divinylbenzene-glycidyl methacrylate)-capsulated magnetite nanoparticles as a recyclable catalyst for one-step biodiesel production from high free fatty acid-containing feedstocks

The decrease in fossil fuel resources and the negative environmental impact of greenhouse gas emissions from their combustion have stimulated interest in finding alternative energy resources. Of various alternatives, biodiesel is surging in popularity given its renewability and lower environmental impact. Herein, magnetite nanoparticles were prepared by a chemical co-precipitation technique, and then capsulated with a sulfonated poly(styrene-divinylbenzene-glycidyl methacrylate) copolymer, yielding a recyclable catalyst suitable for biodiesel production from high free fatty acid-containing feedstocks, such as waste or recycled oil. The morphology and structure of the resultant catalyst were characterized by multiple techniques, and the influence of catalyst dose, temperature, molar ratio of methanol to feedstock oil, and free fatty acid content on the biodiesel yield was evaluated, respectively. The results indicated that this catalyst was capable of catalyzing the transesterification of triglycerides and the esterification of free fatty acids simultaneously, enabling a simple, one-step procedure for biodiesel production from feedstocks containing a high content of free fatty acids. Under the optimal conditions, the biodiesel yield was found to reach 91.1%. In addition, such a catalyst was proved to be easily recyclable under an external magnetic field, and reusable, which promised its potential application in the environmentally-benign production of biodiesel from cheap waste or recycled oil.