Carbon dioxide-switched removal of nitrate ions from water by cellulose nanocrystal-grafted and free multi-responsive block copolymers

Cellulose nanocrystal-based polymer hydrogel embedded with iron oxide nanorods for efficient arsenic removal

A cellulose nanocrystal (CNC) polymer hydrogel containing magnetic iron oxide nanorods (Fe3O4NRs) was prepared for As(III) removal in water. Systematic studies on the performance of these prepared CNC-based composite hydrogels for the removal of As(III) have been undertaken. The maximum adsorption capacity of the CNC-g-PAA/qP4VP (CPqP) hydrogel was 241.3 mg/g. After introduction of Fe3O4NRs in the hydrogel, the maximum adsorption capacity of the resulting Fe3O4NRs@CNC-g-PAA/qP4VP (FN@CPqP) hydrogel was further improved to 263.0 mg/g. The high adsorption performance can be attributed to the facts that the 3D interconnected porous network of the hydrogel allows As species to easily enter into the hydrogel, the quaternized P4VP chains provides more adsorption sites, Fe3O4NRs uniformly distributed in the internal cavity of the hydrogel significantly reduces the nanoparticle aggregation. The adsorption kinetics indicated that the adsorption of arsenic by the hydrogel was mainly chemisorption. The isotherm analysis revealed that the adsorption of arsenic by the hydrogel was principally monolayer adsorption on a homogeneous surface. Moreover, the as-prepared CNC-based polymer hydrogels exhibited good stability and reusability with negligible performance loss after five adsorption-desorption cycles. The novel FN@CPqP hydrogel demonstrates great potential as a cost-effective adsorbent for the removal of arsenic contaminants from wastewater.

One-Component Nanocomposites Made from Diblock Copolymer Grafted Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) are bio-based, rod-like, high-aspect-ratio nanoparticles with high stiffness and strength and are widely used as a reinforcing nanofiller in polymer nanocomposites. However, due to hydrogen-bond formation between the large number of hydroxyl groups on their surface, CNCs are prone to aggregate, especially in nonpolar polymer matrices. One possibility to overcome this problem is to graft polymers from the CNCs' surfaces and to process the resulting "hairy nanoparticles" (HNPs) into one-component nanocomposites (OCNs) in which the polymer matrix and CNC filler are covalently connected. Here, we report OCNs based on HNPs that were synthesized by grafting gradient diblock copolymers onto CNCs via surface-initiated atom transfer radical polymerization. The inner block (toward the CNCs) is composed of poly(methyl acrylate) (PMA), and the outer block comprises a gradient copolymer rich in poly(methyl methacrylate) (PMMA). The OCNs based on such HNPs microphase separate into a rubbery poly(methyl acrylate) phase that dissipates mechanical energy and imparts toughness, a glassy PMMA phase that provides strength and stiffness, and well-dispersed CNCs that further reinforce the materials. This design afforded OCNs that display a considerably higher stiffness and strength than reference diblock copolymers without the CNCs. At the same time, the extensibility remains high and the toughness is increased up to 5-fold relative to the reference materials.

Water treatment using stimuli-responsive polymers

Stimuli-responsive polymers are a new category of smart materials used in water treatment via a stimuli-induced purification process and subsequent regeneration processes.

Fabrication of a CO2-responsive chitosan aerogel as an effective adsorbent for the adsorption and desorption of heavy metal ions

In the traditional desorption method, strong acid is commonly used as an eluent for the regeneration of adsorbents. It is of critical economic and environmental significance to develop a chemical-free desorption method. In this study, a new CO₂-responsive chitosan aerogel adsorbent was synthesized from CO₂-responsive poly(acrylic acid-2-(dimethylamino)ethyl methacrylate) and chitosan by physicochemical double crosslinking for the adsorption of Cu²⁺. Compared with the chitosan aerogel, the adsorption capacity of Cu²⁺ and mechanical properties of CO₂-responsive chitosan aerogel increased by 162% and 660%, respectively. Most importantly, after the adsorption of Cu²⁺ by CO₂-responsive chitosan aerogel, the Cu²⁺ could be desorbed by CO₂ bubbling, and the desorption rate of metal ions was more than 80%. The adsorption of Cu²⁺ by aerogel was attributed to chelation and complexation. The desorption of porous chitosan/P(AA-co-DMAEMA) aerogels (CPA) by CO₂ mainly occurred through charge repulsion of protonated ‒NH₂ and ‒N‒ groups. After 6 cycles, the adsorption capacity of CPA for metal ions still reached 70% of the initial adsorption capacity, and the desorption rate reached 75%. This novel CO₂-responsive chitosan aerogel is a highly efficient and environmentally friendly adsorbent for the adsorption and recovery of metal ions.

Polymer-functionalization of carbon nanotube by in situ conventional and controlled radical polymerizations

Functionalization of carbon nanotube (CNT) with polymers has drawn much attention due to its wide range of applications. Polymer-functionalized CNT could exhibit variety of properties, such as responsivity to environmental stimuli, ability of complexation with metal ions, increased dispersibility in different solvents, higher compatibility with polymer matrix, etc. Chemical and physical methods have been developed for the preparation of polymer-functionalized CNT. Polymer chains are chemically bonded to the CNT edge or surface in the chemical methods, which results in highly stable CNT/polymer composites. "Grafting to", "grafting from", and "grafting through" methods are the most common chemical methods for polymer-functionalization of CNT. In "grafting to" method, pre-fabricated polymer chains are coupled with the either functionalized or non-functionalized CNT. In "grafting from" and "grafting through" methods, CNT is functionalized by polymers simultaneously synthesized by in situ polymerization methods. Conventional free radical polymerization (FRP) and also controlled radical polymerization (CRP) are the most promising methods for in situ tethering of polymer brushes onto the surface of CNT due to their control over the grafting density, thickness, and functionality of the polymer brushes. The main focus of this review is on the synthesis of polymer-functionalized CNT via both the "grafting from" and "grafting through" methods on the basis of FRP and CRP routs, which is commonly known as in situ polymerizations. Finally, the most important challenges and applications of the in situ polymer grafting methods are discussed, which could be interesting for the future works.