Synthesis and Characterization of Halloysite/Carbon Nanocomposites for Enhanced NSAIDs Adsorption from Water

Lignin-based porous carbon/palygorskite composites doped with different metals for efficient iodine capture: Structure, performance, and mechanism

Radioactive iodine waste from the nuclear power industry will cause air and water pollution. Here, a series of metal (Bi, Zn and Fe)-doped lignin-based porous carbon/palygorskite composites (ELC-P-X) were prepared by wet impregnation and carbonization method for enhancing the iodine capture. Their morphology, porosity, and surface functional groups of ELC-P-X were characterized in detail, these metal species showed different sizes of nanoparticles with the oxide form. Zn, Fe doping enhanced its porosity of ELC-P (247.5 m2/g), and up to 359.5 m2/g, while Bi doping had slight negative influence on the porosity. Adsorption experiments showed that the iodine vapor adsorption capacity of ELC-P-X followed an order of ELC-P-Zn > ELC-P-Fe > ELC-P-Bi> ELC-P, the highest adsorption capacity can reach 650.0 mg/g. The results suggested that above metal doping can promote iodine vapor adsorption. Meanwhile, the adsorption capacity of ELC-P-X for iodine in n-hexane solution only showed an increase on ELC-P-Fe (362.2 mg/g), compared to ELC-P (332.0 mg/g). ELC-P-Fe still had good adsorption stability, acid and alkali resistance and cycling performance. We found that the adsorption of iodine vapor could mainly depend on the porosity of ELC-P-X materials, while the surface functional groups, iodine-affinity metal species, and micro-nano structure made a major contribution synergistically to the enhanced adsorption for the iodine solution. The adsorption mechanism study revealed that the Lewis acid-base interaction, electrostatic interactions, and charge transfer action accompanied by weak chemisorption were the main driving force for the iodine molecule adsorption on ELC-P-Fe. This work provided an important reference for the rational preparation of lignin based iodine adsorbents and proposed a kind of universal strategy for enhancing iodine adsorption.

Morphological, Thermal, and Mechanical Properties of Nanocomposites Based on Bio-Polyamide and Feather Keratin-Halloysite Nanohybrid

One solution to comply with the strict regulations of the European Commission and reduce the environmental footprint of composites is the use of composite materials based on bio-polymers and fillers from natural resources. The aim of our work was to obtain and analyze the properties of bio-polymer nanocomposites based on bio-PA (PA) and feather keratin-halloysite nanohybrid. Keratin (KC) was mixed with halloysite (H) as such or with the treated surface under dynamic conditions, resulting in two nanohybrids: KCHM and KCHE. The homogenization of PA with the two nanohybrids was conducted using the extrusion processing process. Two types of nanocomposites, PA-KCHM and PA-KCHE, with 5 wt.% KC and 1 wt.% H were obtained. The properties were analyzed using SEM, XRD, FTIR, RAMAN, TGA, DSC, tensile/impact tests, DMA, and nanomechanical tests. The best results were obtained for PA-KCHE due to the stronger interaction between the components and the uniform dispersion of the nanohybrid in the PA matrix. Improvements in the modulus of elasticity and of the surface hardness by approx. 75% and 30%, respectively, and the resistance to scratch were obtained. These results are promising and constitute a possible alternative to synthetic polymer composites for the automotive industry.

Simple and scalable preparation of lignin based porous carbon coated nano-clay composites and their efficient removal for the diversified iodine

Here, lignin and nano-clay were used to prepare novel composite adsorbents by one-step carbonization without adding activators for radioactive iodine capture. Specially, 1D nano-clay such as halloysite (Hal), palygorskite (Pal) and sepiolite (Sep) were selected as skeleton components, respectively, enzymatic hydrolysis lignin (EHL) as carbon source, lignin based porous carbon/nano-clay composites (ELC-X) were prepared through ultrasonic impregnation, freeze drying, and carbonization. Characterization results indicated lignin based porous carbon (ELC) well coated on the surface of nano-clay, and made its surface areas increase to 252 m2/g. These composites appeared the micro-mesoporous hierarchical structure, considerable N doping and good chemical stability. Results of adsorption experiments showed that the introduction of ELC could well promote iodine vapor uptake of nano-clay, and up to 435.0 mg/g. Meanwhile, the synergistic effect between lignin based carbon and nano-clay was very significant for the adsorption of iodine/n-hexane and iodine ions, their capacity were far exceed those of a single material, respectively. The relevant adsorption kinetic and thermodynamics, and mechanism of ELC-X composites were clarified. This work provided a class of low-cost and environmentally friendly adsorbents for radioactive iodine capture, and opened up ideas for the comprehensive utilization of waste lignin and natural clay minerals.

Occurrence, toxicity, impact and removal of selected non-steroidal anti-inflammatory drugs (NSAIDs): A review

Non-steroidal anti-inflammatory drugs (NSAIDs) are among the most frequently used pharmaceuticals for human therapy, pet therapeutics, and veterinary feeds, enabling them to enter into water sources such as wastewater, soil and sediment, and seawater. The control of NSAIDs has led to the advent of the novel materials for treatment techniques. Herein, we review the occurrence, impact and toxicity of NSAIDs against aquatic microorganisms, plants and humans. Typical NSAIDs, e.g., ibuprofen, ketoprofen, diclofenac, naproxen and aspirin were detected at high concentrations in wastewater up to 2,747,000 ng L-1. NSAIDs in water could cause genotoxicity, endocrine disruption, locomotive disorders, body deformations, organs damage, and photosynthetic corruption. Considering treatment methods, among adsorbents for removal of NSAIDs from water, metal-organic frameworks (10.7-638 mg g-1) and advanced porous carbons (7.4-400 mg g-1) were the most robust. Therefore, these carbon-based adsorbents showed promise in efficiency for the treatment of NSAIDs.

Efficient Rhodamine B Dye Removal from Water by Acid- and Organo-Modified Halloysites

The halloysite has been subjected to modification through ultrasound (HU), sulfuric acid (HU-SA), and oligocyclopentadiene resin (HU-OCPD). The modified materials were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetry (TG), and N2 adsorption-desorption isotherms, and tested as low-cost adsorbents for removal of Rhodamine B dye (RhB) from aqueous solutions. Batch experiments were conducted to study the effect of different operational parameters such as adsorbent dose, solution pH, and contact time. It was observed that the adsorption was strongly pH-dependent and that solution pH at 2.0 had the greatest removal efficiency for the dye. The experimental data were modeled using several isotherm and kinetic models such as Freundlich, Langmuir, Temkin as well as pseudo-first-order, pseudo-second-order, and intraparticle diffusion. It was found that the equilibrium adsorption data can be fitted well using the Freundlich isotherm model and the adsorption kinetics follows a pseudo-second-order model. The adsorption capacity of HU, HU-SA, and HU-OCPD was found to be 8.37, 13.1, and 17.8 mg/g, respectively. The results revealed that surface modification of halloysite via acid activation and polymer loading results in a significant increase in the removal of RhB from aqueous solution. This study has shown potential on organo-halloysite for organic dye adsorption from water.

Influence of selective acid-etching on functionality of halloysite-chitosan nanocontainers for sustained drug release

The functionality of halloysite (Hal) nanotubes as drug carriers can be improved by lumen enlargement and polymer modification. This study investigates the influence of selective acid etching on Hal functionalization with cationic biopolymer chitosan. Hal was subjected to lumen etching under mild conditions, loaded under vacuum with nonsteroidal antiinflammatory drug aceclofenac, and incubated in an acidic solution of chitosan. The functionality of pristine and etched Hal before and upon polymer functionalization was assessed by ζ-potential measurements, structural characterization (FT-IR, DSC and XRPD analysis), cell viability assay, drug loading and drug release studies. Acid etching increased specific surface area, pore volume and pore size of Hal, decreased ζ-potential and facilitated binding of the cationic polymer. XRPD and DSC analysis revealed crystalline structure of etched Hal. Successful chitosan binding and drug entrapment were further confirmed by FT-IR and DSC studies. XRPD showed surface polymer binding. DSC and FT-IR analyses confirmed the presence of the entrapped drug in its crystalline form. Drug loading was increased for ≈81% by selective lumen etching. Slight decrease of drug content occurred during chitosan functionalization due to aceclofenac diffusion in the polymer solution. The drug release was more sustained from etched Hal nanocomposites (up to ≈87% for 12 h) than from pristine Hal (up to ≈97% for 12 h) due to more intensive chitosan binding. High human fibroblast survival rates upon exposure to pristine and etched Hal before and after chitosan functionalization (>90% in the concentration of 1000 μg/mL) confirmed that both lumen etching under mild conditions and polymer functionalization had no significant effect on cytocompatibility. Based on these findings, selective lumen etching in combination with polycation modification appears to be a promising approach for improvement of Hal nanotubes functionality by increasing payload, polymer binding capacity, and sustained release properties with no significant effect on their cytocompatibility.

A flexible N-doped carbon-nanofiber film reinforced by halloysite nanotubes(HNTs) for adsorptive desulfurization

This report introduced the facile synthesis of the carbon-nanofiber films reinforced by halloysite nanotubes (HNTs) via electrospinning. The HNTs-reinforced N-doped carbon-nanofiber films (PAN/HNTs-CNFs) possessed the higher strength and toughness while keeping the prospective adsorption capability for different sulfur compounds in oil due to the higher N doping content. The PAN/HNTs-CNFs were produced by firstly electrospinning for the HNTs-filled polyacrylonitrile (PAN) nanofiber films, followed by the high-temperature carbonization for the conversion of the polymer films into the carbon-nanofiber films with the N doping. The characterizations testified that the HNTs were capable of fulfilling the uniform and disordered dispersion in the carbon-nanofibers. For overcoming the toughness of the carbon-nanofiber film, the HNTs filling the obviously improved the mechanical performance of the carbon-nanofiber films by the pulling-out and bridging effect. Due to accessing the lipophilic and acid surface, abundant hierarchical pore structure and highly N-doping content, the PAN/HNTs-CNFs exhibited the remarkable adsorption performances for thiophene, benzothiophene, and dibenzothiophene (46.73 mg S/g, 38.4 mg S/g and 35.03 mg S/g for 800 ppm sulfur model oil), especially being suitable to the adsorption of thiophene. Furthermore, the study on the adsorption kinetics, equilibrium isotherms, and thermodynamics of thiophene over the PAN/HNTs-CNFs were conducted to discuss the adsorption mechanism.

Surface Properties of Halloysite-Carbon Nanocomposites and Their Application for Adsorption of Paracetamol

Analysis of surface properties of halloysite-carbon nanocomposites and non-modified halloysite was carried out with surface sensitive X-ray photoelectron spectroscopy (XPS) and inverse gas chromatography (IGC). The XPS spectra were measured in a wide range of the electron binding energy (survey spectra) and in the region of C 1s photoelectron peak (narrow scans). The IGC results show the changes of halloysite surface from basic for pure halloysite to acidic for carbon-halloysite nanocomposites. Halloysite-carbon nanocomposites were used as adsorbents of paracetamol from an aqueous solution. The adsorption mechanism was found to follow the pseudo-second-order and intra-particle diffusion models. The Langmuir multi-center adsorption model described well the obtained experimental data. The presence of carbon increased significantly the adsorption ability of halloysite-carbon nanocomposites for paracetamol in comparison to the non-modified halloysite.