"Breathing" CO2 -, O2 -, and Light-Responsive Vesicles from a Triblock Copolymer for Rate-Tunable Controlled Release.

A well-defined amphiphilic triblock copolymer, poly[(ethylene glycol)methyl ether]-block-poly(N,N-dimethylamino ethyl methacrylate-co-2,2,2-trifluoroethyl methacrylate)-block-poly(4-(4-methoxy-phenylazo)phenoxy methacrylate) (PEG-b-P(DMAEMA-co-TFEMA)-b-PMEPPMA), is successfully synthesized by stepwise atom transfer radical polymerization. Owing to its amphiphilic nature, PEG-b-P(DMAEMA-co-TFEMA)-b-PMEPPMA can self-assemble into vesicles in aqueous solution and exhibits a reversible triple-responsive behavior toward CO2 , O2 , and light stimuli. More importantly, such vesicles can exhibit a controlled "breathing" behavior via external stimuli due to their suitable chemical structure and stimuli responsiveness. Consequently, these vesicles can be employed as nanocarriers for rate-tunable controlled release via adjustment of their membrane permeability by a single stimulus or various stimuli combinations.

CO2 Responsive Imidazolium-Type Poly(Ionic Liquid) Gels.

Poly(ionic liquid) (PIL) gels with CO2 stimulus responsiveness have been synthesized through the copolymerization of an imidazolium-type ionic liquid monomer with 2-(dimethyl amino) ethyl methacrylate. Upon bubbling with CO2 gas, the prepared PIL solution is converted to a transparent and stable gel, which can be turned back to the initial solution state after N2 bubbling. The reversible sol-gel phase transition behavior is proved by the reversible values of viscosity and ionic conductivity. The possible mechanism for such a reversible sol-gel phase transition is demonstrated by NMR, conductivity, and rheological measurements.

Urchin-like CO2-responsive magnetic microspheres for highly efficient organic dye removal.

CO2-responsive materials have emerged as promising adsorbents for the remediation of refractory organic dyes-contaminated wastewater without the formation of byproducts or causing secondary pollution. However, realizing the simultaneous adsorption-separation or complete removal of both anionic and cationic dyes, as well as achieving deeper insights into their adsorption mechanism, still remains a challenge for most reported CO2-responsive materials. Herein, a novel type of urchin-like CO2-responsive Fe3O4 microspheres (U-Fe3O4 @P) has been successfully fabricated to enable ultrafast, selective, and reversible adsorption of anionic dyes by utilizing CO2 as a triggering gas. Meanwhile, the CO2-responsive U-Fe3O4 @P microspheres exhibit the capability to initiate Fenton degradation of non-adsorbable cationic dyes. Our findings reveal exceptionally rapid adsorption equilibrium, achieved within a mere 5 min, and an outstanding maximum adsorption capacity of 561.2 mg g-1 for anionic dye methyl orange upon CO2 stimulation. Moreover, 99.8% of cationic dye methylene blue can be effectively degraded through the Fenton reaction. Furthermore, the long-term unresolved interaction mechanism of organic dyes with CO2-responsive materials is deciphered through a comprehensive experimental and theoretical study by density functional theory. This work provides a novel paradigm and guidance for designing next-generation eco-friendly CO2-responsive materials for highly efficient purification of complex dye-contaminated wastewater in environmental engineering.

Versatile CO2-responsive Sponges Decorated with ZIF-8 for Bidirectional Separation of Oil/Water and Controllable Removal of Dyes.

The complex wastewater containing water-soluble dyes and water-insoluble oils has given rise to significant environmental concerns that demand urgent remediation. Herein, a novel "smart" multifunctional sponge (ZIF-8@PMS) stepwise decorated with ZIF-8 nanoparticles and CO2-responsive copolymer (poly(2-(diethylamino) ethyl methacrylate-co-3-(trimethoxysilyl)propyl acrylate-co-stearyl methacrylate) was successfully prepared for CO2 controllable oil/water separation and dyes removal. The results revealed that the sponge coated with CO2-responsive copolymer for three cycles (ZIF-8@PMS-3) exhibited optimal comprehensive properties. The ZIF-8@PMS-3 had excellent compressive-resilient characteristics and chemical stability. As expected, it displayed tunable wettability and charged state under the regulation of CO2. Based on these features, ZIF-8@PMS-3 presented highly efficient removal of oil and dyes, even for the dye-containing oil/water emulsions, via a synergistic combination of adsorption and separation methods. The adsorption capacity for oil and various organic solvents ranged from 21.3 to 50 g g-1. The maximum adsorption capacities toward anionic dyes: methyl orange with 1205.89 mg g-1 and methyl blue with 880.00 mg g-1 in the presence of CO2 through electrostatic interaction. In the absence of CO2, it achieved maximum adsorption capacities for cationic dyes, including malachite green with 1246.15 mg g-1 and rhodamine B with 203 mg g-1, primarily driven by π-π interactions. According to distinct adsorption mechanisms, ZIF-8@PMS-3 could selectively adsorb either anionic or cationic dyes by exploiting CO2 as a trigger. Furthermore, the separation efficiencies for both types of oil/water emulsions surpassed 99.9%, with respective fluxes of 1566.99 L m-2 h-1 (water-in-oil emulsion) and 310.37 L m-2 h-1 (oil-in-water emulsion). Additionally, the as-prepared sponges exhibited remarkable antibacterial properties and exceptional recyclability. Therefore, the ZIF-8@PMS-3 holds substantial promise for potential applications in practical industrial wastewater treatment.

A CO2-Responsive Imidazole-Functionalized Fluorescent Material Mediates Cancer Chemotherapy.

We present a breakthrough in the synthesis and development of functional gas-responsive materials as highly potent anticancer agents suitable for applications in cancer treatment. Herein, we successfully synthesised a stimuli-responsive multifunctional material (I-R6G) consisting of a carbon dioxide (CO2)-sensitive imidazole moiety and spirolactam-containing conjugated rhodamine 6G (R6G) molecule. The resulting I-R6G is highly hydrophobic and non- or weakly fluorescent. Simple CO2 bubbling treatment induces hydrophobic I-R6G to completely dissolve in water and subsequently form self-assembled nanoparticles, which exhibit unique optical absorption and fluorescence behaviours in water and extremely low haemolytic ability against sheep red blood cells. Reversibility testing indicated that I-R6G undergoes reversible CO2/nitrogen (N2)-dependent stimulation in water, as its structural and physical properties can be reversibly and stably switched by alternating cycles of CO2 and N2 bubbling. Importantly, in vitro cellular assays clearly demonstrated that the CO2-protonated imidazole moiety promotes rapid internalisation of CO2-treated I-R6G into cancer cells, which subsequently induces massive levels of necrotic cell death. In contrast, CO2-treated I-R6G was not internalised and did not affect the viability of normal cells. Therefore, this newly created system may provide an innovative and efficient route to remarkably improve the selectivity, safety and efficacy of cancer treatment.

CO2-responsive functional cotton fibers decorated with Ag nanoparticles for "smart" selective and enhanced dye adsorption.

Novel Ag nanoparticles (NPs) decorated CO2-responsive cotton fiber (PCCF@Ag) as eco-friendly adsorbent was prepared via in-situ growth of Ag NPs on the poly(2-(dimethylamino) ethyl methacrylate-co-4-acryloyloxybenzophenone) coated cotton fiber. The as-prepared PCCF@Ag displayed excellent adsorption performance toward both anionic and cationic dyes with or without CO2 stimulation, even under a wide range of pH from 3 to 11. The maximum adsorption capacities of the as-prepared PCCF@Ag toward anionic dye (1538.5 mg g-1 for MO) and cationic dyes (944.0 mg g-1 for MEB and 415.6 mg g-1 for NR) were satisfactory. The adsorption processes were described better by the Langmuir isotherm and pseudo-second-order kinetic models, respectively. Notably, upon CO2 stimulation, the PCCF@Ag exhibited significantly enhanced adsorption capacity toward anionic dyes, following ultrafast adsorption rate, which made the PCCF@Ag could selectively adsorb anionic dyes from mixture because of greatly different adsorption rates between anionic dyes (adsorption equilibrium within 2 min) and cationic dyes (adsorption equilibrium over 12 h). Additionally, the PCCF@Ag could maintain over 91.0% of adsorption capacity even after ten cycles, indicating its outstanding reusability. Meanwhile, the as-obtained PCCF@Ag exhibited excellent antibacterial activity. Overall, the as-obtained PCCF@Ag could be considered as a promising dye scavenger for wastewater remediation.

Facile and Scalable Fabrication of Antibacterial CO2-Responsive Cotton for Ultrafast and Controllable Removal of Anionic Dyes.

A novel CO2-responsive cotton as an eco-friendly adsorbent derived from poly(4-acryloyloxybenzophenone-co-2-(dimethylamino) ethyl methacrylate) and cotton was fabricated via a facile and fast dip-coating method. As expected, upon CO2 stimulation, the protonated cotton presented CO2-induced "on-off" selective adsorption behaviors toward anionic dyes owing to electrostatic interactions. The adsorption isotherms and kinetics of the CO2-responsive cotton toward anionic dyes obeyed the Langmuir isotherm and pseudo-second-order kinetics models, respectively. It is noteworthy that the CO2-responsive cotton exhibited high adsorption capacity and ultrafast adsorption rate toward anionic dyes with the maximum adsorption capacities of 1785.71 mg g-1 for methyl orange (MO), 1108.65 mg g-1 for methyl blue (MB), and 1315.79 mg g-1 for naphthol green B (NGB), following the adsorption equilibrium times of 5 min for MO, 3 min for MB, and 4 min for NGB. Moreover, the CO2-responsive cotton also exhibited high removal efficiency toward anionic dyes in synthetic dye effluent. Additionally, the CO2-responsive cotton could be facilely regenerated via heat treatment under mild conditions and presented stable adsorption properties even after 15 cycles. Finally, the as-prepared CO2-responsive cotton exhibited outstanding antibacterial activity against E. coli and S. aureus. In summary, this novel CO2-responsive cotton can be viewed as a promising eco-friendly adsorbent material for potential scalable application in dye-contaminated wastewater remediation.

Development of eco-friendly CO2-responsive cellulose nanofibril aerogels as "green" adsorbents for anionic dyes removal.

A novel CO2-responsive cellulose nanofibril aerogel as a "green" adsorbent derived from poly(methacrylic acid-co-2-(dimethylamino) ethyl methacrylate) and carboxylated cellulose nanofibrils was successfully prepared via stepwise cation-induced gelation and freeze drying method. This aerogel exhibited CO2-triggered adsorption behavior towards anionic dyes with a rapid adsorption rate and a high adsorption capacity, as well as satisfactory mechanical properties. Upon CO2 stimulation, the charged aerogel can selectively adsorb anionic dyes from aqueous solutions based on an electrostatic interaction. The maximum adsorption capacities of this aerogel towards methyl blue (MB), naphthol green B (NGB), and methyl orange (MO) were 598.8, 621.1 and 892.9 mg g-1, respectively, accompanied by fast adsorption equilibriums towards MB and NGB within 7 min, and MO within 12 min. Meanwhile, the adsorption isotherms and the kinetics of the CO2-responsive adsorbents followed the Freundlich isotherm and the pseudo-second-order model, respectively. Furthermore, the resulting CO2-responsive adsorbent exhibited outstanding recyclability, as its adsorption performance can still be maintained even after twenty cycles. Accordingly, the resultant CO2-responsive cellulose nanofibril aerogel could be a promising adsorbent material for the removal of anionic dyes in wastewater remediation.

Carboxymethyl chitosan has sensitive two-way CO2-responsive hydrophilic/hydrophobic feature.

Carboxymethyl chitosans (CMC) with various degrees of carboxymethyl substitution were prepared and investigated on their changes in water solubility in response to bubbling of CO2 or N2 as a function of the relative concentrations of COOH and NH2 side groups. When having similar concentrations of COOH and NH2, the produced CMC was water soluble at pH 10 and consecutively experienced peculiar dissolution-to-precipitation-to-dissolution during bubbling of CO2, and experienced reverse dissolution-to-precipitation-to-dissolution process during subsequently bubbling of N2. With the concentration of COOH much higher than that of NH2, the water soluble CMC at pH 10 exhibited no phase changes in response to bubbling of CO2 and N2. This newly developed CMC solution system with novel CO2 responsive amphiphilic feature has a potential use as a CO2 switchable surfactant to control interface of mixtures of hydrophilic and hydrophobic species in emulsification/demulsification applications.

CO2-Responsive Nano-Objects with Assembly-Related Aggregation-Induced Emission and Tunable Morphologies.

CO2-responsive polymeric nano-objects with assembly-related aggregation-induced emission (AIE) are obtained via polymerization-induced self-assembly (PISA) of 2-(dimethylamino)ethyl methacrylate (DMAEMA), 2-(4-formylphenoxy)ethyl methacrylate (MAEBA), and 4-(1,2,2-triphenylvinyl)phenyl methacrylate (TPEMA). These nano-objects exhibit, depending on the feed of MAEBA, a morphology evolution process from spherical micelles to vesicles. Due to the presence of DMAEMA units, CO2 promotes morphology transformation of the nano-objects from spheres to a mixture of "jellyfish" and vesicles and vesicles to complex vesicles. Moreover, TPEMA endows the AIE feature to these nano-objects, offering a strategy to monitor the morphology evolution process in real time. Thus, this approach is significant for exploring the assembly mechanism of copolymer in polymerization-induced self-assembly and designing multistimuli-responsive polymeric nanomaterials with tunable morphologies and sizes.

CO(2)-responsive polyacrylamide microspheres with interpenetrating networks.

HYPOTHESIS: CO2-responsive microspheres fabricated via co-polymerization protocol are attractive due to their promising applications. However, the inevitable particles-agglomeration restrained their further utilizations. Towards this challenge, interpenetrating network (IPN) protocol would be a potential choice to construct the "intelligent" microspheres, which presents superiority in comparison with co-polymerization mode. EXPERIMENTS: A series of CO2-responsive microspheres with polyacrylamide (PAM)/poly(dimethyl aminopropyl methacrylamide) (PDMAPMA) IPN-structure were fabricated via inverse seed suspension polymerization by adjusting DMAPMA loading and crosslinking-degree of seeds. The resultant particles and responsiveness were examined using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), optical microscopy (OM) and laser particle size analyzer (LS), respectively. FINDINGS: The interior-structure and fracture-morphology of IPN-particles could be intuitively observed by SEM, showing homogeneous and compact structure without phase separation, offering the direct proof for the formation of IPN-microstructures; the particle morphology altered from IPN to IPN-membrane when gradually increasing DMAPMA concentration. Upon alternating treatment with CO2 and N2, these particles experience reversible volume expansion and collapse. Besides, the non-agglomerated responsive particles with varying composition can be prepared by changing the crosslinking-degree of seeds, from which maximum responsiveness, relative swelling volume (RSV), could reach 11.6 when PDMAPMA loading is at 87%.