Polyacid functionalized cellulose nanofiber membranes for removal of heavy metals from impaired waters

Nanocellulose: Recent advances and its prospects in environmental remediation

Among many other sustainable functional nanomaterials, nanocellulose is drawing increasing interest for use in environmental remediation technologies due to its numerous unique properties and functionalities. Nanocellulose is usually derived from the disintegration of naturally occurring polymers or produced by the action of bacteria. In this review, some invigorating perspectives on the challenges, future direction, and updates on the most relevant uses of nanocellulose in environmental remediation are discussed. The reported applications and properties of nanocellulose as an adsorbent, photocatalyst, flocculant, and membrane are reviewed in particular. However, additional effort will be required to implement and commercialize nanocellulose as a viable nanomaterial for remediation technologies. In this regard, the main challenges and limitations in working with nanocellulose-based materials are identified in an effort to improve the development and efficient use of nanocellulose in environmental remediation.

Novel Carbon Paper@Magnesium Silicate Composite Porous Films: Design, Fabrication, and Adsorption Behavior for Heavy Metal Ions in Aqueous Solution

It is of great and increasing interest to explore porous adsorption films to reduce heavy metal ions in aqueous solution. Here, we for the first time fabricated carbon paper@magnesium silicate (CP@MS) composite films for the high-efficiency removal of Zn²⁺ and Cu²⁺ by a solid-phase transformation from hydromagnesite-coated CP (CP@MCH) precursor film in a hydrothermal route and detailedly examined adsorption process for Zn²⁺ and Cu²⁺ as well as the adsorption mechanism. The suitable initial pH range is beyond 4.0 for the adsorption of the CP@MS to remove Zn²⁺ under the investigated conditions, and the adsorption capacity is mainly up to the pore size of the porous film. The composite film exhibits excellent adsorption capacity for both of Zn²⁺ and Cu²⁺ with the corresponding maximum adsorption quantity of 198.0 mg g^-1 for Zn²⁺ and 113.5 mg g^-1 for Cu²⁺, which are advantageous over most of those reported in the literature. Furthermore, the adsorption behavior of the CP@MS film follows the pseudo-second-order kinetic model and the Langmuir adsorption equation for Zn²⁺ with the cation-exchange mechanism. Particularly, the CP@MS film shows promising practical applications for the removal of heavy metal ions in water by an adsorption-filtration system.

Recent Advances in Nanocellulose Composites with Polymers: A Guide for Choosing Partners and How to Incorporate Them

In recent years, the research on nanocellulose composites with polymers has made significant contributions to the development of functional and sustainable materials. This review outlines the chemistry of the interaction between the nanocellulose and the polymer matrix, along with the extent of the reinforcement in their nanocomposites. In order to fabricate well-defined nanocomposites, the type of nanomaterial and the selection of the polymer matrix are always crucial from the viewpoint of polymer⁻filler compatibility for the desired reinforcement and specific application. In this review, recent articles on polymer/nanocellulose composites were taken into account to provide a clear understanding on how to use the surface functionalities of nanocellulose and to choose the polymer matrix in order to produce the nanocomposite. Here, we considered cellulose nanocrystal (CNC) and cellulose nanofiber (CNF) as the nanocellulosic materials. A brief discussion on their synthesis and properties was also incorporated. This review, overall, is a guide to help in designing polymer/nanocellulose composites through the utilization of nanocellulose properties and the selection of functional polymers, paving the way to specific polymer⁻filler interaction.

Rapid Sample Preparation for Alpha Spectroscopy with Ultrafiltration Membranes

This contribution describes a rapid, fieldable alpha spectroscopy sample preparation technique that minimizes consumables and decreases the nuclear forensics timeline. Functional ultrafiltration membranes are presented that selectively concentrate uranium directly from pH 6 groundwater and serve as the alpha spectroscopy substrate. Membranes were prepared by ultraviolet grafting of uranium-selective polymer chains from the membrane surface. Membranes were characterized by Fourier-transform infrared spectroscopy before and after modification to support functionalization. Membrane performance was evaluated using uranium-233 or depleted uranium in both deionized and simulated groundwater at pH 6. Functionalized membranes achieved peak energy resolutions of 31 ± 2 keV and recoveries of 81 ± 4% when prepared directly from pH 6 simulated groundwater. For simulated groundwater spiked with depleted uranium, baseline energy resolution was achieved for both isotopes (uranium-238 and uranium-234). The porous, uranium-selective substrate designs can process liters per hour of uranium-contaminated groundwater using low-pressure (<150 kPa) filtration and a 45 mm diameter membrane filter, leading to a high-throughput, one-step concentration, purification, and sample mounting process.

Plasma modified PLA electrospun membranes for actinorhodin production intensification in Streptomyces coelicolor immobilized-cell cultivations

Most of industrially relevant bioproducts are produced by submerged cultivations of actinomycetes. The immobilization of these Gram-positive filamentous bacteria on suitable porous supports may prevent mycelial cell-cell aggregation and pellet formation which usually negatively affect actinomycete submerged cultivations, thus, resulting in an improved biosynthetic capability. In this work, electrospun polylactic acid (PLA) membranes, subjected or not to O₂-plasma treatment (PLA-plasma), were used as support for immobilized-cell submerged cultivations of Streptomyces coelicolor M145. This strain produces different bioactive compounds, including the blue-pigmented actinorhodin (ACT) and red-pigmented undecylprodigiosin (RED), and constitutes a model for the study of antibiotic-producing actinomycetes. Wet contact angles and X-ray photoelectron spectroscopy analysis confirmed the increased wettability of PLA-plasma due to the formation of polar functional groups such as carboxyl and hydroxyl moieties. Scanning electron microscope observations, carried out at different incubation times, revealed that S. coelicolor immobilized-cells created a dense "biofilm-like" mycelial network on both kinds of PLA membranes. Cultures of S. coelicolor immobilized-cells on PLA or PLA-plasma membranes produced higher biomass (between 1.5 and 2 fold) as well as higher levels of RED and ACT than planktonic cultures. In particular, cultures of immobilized-cells on PLA and PLA-plasma produced comparable levels of RED that were approximatively 4 and 5 fold higher than those produced by planktonic cultures, respectively. In contrast, levels of ACT produced by immobilized-cell cultures on PLA and PLA-plasma were different, being 5 and 10 fold higher than those of planktonic cultures, respectively. Therefore, this is study demonstrated the positive influence of PLA membrane on growth and secondary metabolite production in S. coelicolor and also revealed that O₂-plasma treated PLA membranes specifically promoted higher ACT production than not treated membranes.

The binding of metal ions to molecularly-imprinted polymers

Imprinting polymerization is a flexible method to make resins specific for different compounds. Imprinting polymerization involves the polymerization of the resin in the presence of a template, here cadmium ions or arsenate. The template is then removed by washing, leaving specific binding sites in the resin. In water treatment, the removal of toxic metal ions is difficult due to the limited affinity of these ions to ion exchange resins. Imprinting polymerization of ion-exchange resins is used to develop resins with high capacity and some selectivity for cadmium ions or arsenate for water treatment that still function as general ion-exchange resins. A minimum binding capacity of 325 meq/g was achieved for cadmium ions. Competition experiments elucidate the type of bonds present in the imprinting complex. The capacity and bond types for the cadmium ions and arsenate were contrasted. In the case of cadmium, metal-ligand bonds provide significant specificity of binding, although significant binding also occurs to non-specific surface sites. Arsenate ions are larger than cadmium ions and can only bind via ionic and hydrogen bonds, which are weaker than metal-ligand bonds. This results in lower specificity for arsenate. Additionally, diffusion into the resin is a limiting factor due to the larger size of the arsenate ion. These data elucidate the bonds formed between metal ions and the imprinting sites as well as other parameters that increase the capacity for heavy metals and arsenate.

Extraction and modification of cellulose nanofibers derived from biomass for environmental application

Cellulose nanofibers obtained from various plants and microbial sources, their extraction methods and various environmental applications are discussed.

Nanofiber Ion-Exchange Membranes for the Rapid Uptake and Recovery of Heavy Metals from Water

An evaluation of the performance of polyelectrolyte-modified nanofiber membranes was undertaken to determine their efficacy in the rapid uptake and recovery of heavy metals from impaired waters. The membranes were prepared by grafting poly(acrylic acid) (PAA) and poly(itaconic acid) (PIA) to cellulose nanofiber mats. Performance measurements quantified the dynamic ion-exchange capacity for cadmium (Cd), productivity, and recovery of Cd(II) from the membranes by regeneration. The dynamic binding capacities of Cd(II) on both types of nanofiber membrane were independent of the linear flow velocity, with a residence time of as low as 2 s. Analysis of breakthrough curves indicated that the mass flow rate increased rapidly at constant applied pressure after membranes approached equilibrium load capacity for Cd(II), apparently due to a collapse of the polymer chains on the membrane surface, leading to an increased porosity. This mechanism is supported by hydrodynamic radius (R_h) measurements for PAA and PIA obtained from dynamic light scattering, which show that R_h values decrease upon Cd(II) binding. Volumetric productivity was high for the nanofiber membranes, and reached 0.55 mg Cd/g/min. The use of ethylenediaminetetraacetic acid as regeneration reagent was effective in fully recovering Cd(II) from the membranes. Ion-exchange capacities were constant over five cycles of binding-regeneration.