Thermoresponsive PNIPAM Research Articles

Block copolymer brushes modified cotton fabric for antifouling oil-water separation materials with thermal responsiveness

Polymer brushes have proven to have great potential in oil-water separation but it remains a long-standing challenge to improve their operational stability and service endurance. In this work, we sequentially grafted polydimethylsiloxane (PDMS) and poly (N-isopropylacrylamide) (PNIPAM) brushes on the cotton fabric to prepare a durable and self-reparing oil-water separation film (Co@PDMS/PNIPAM). The grafting of liquid PDMS brushes significantly improved the antifouling performance through its lubricating effect thereby improving the durability. The hydrophilic and thermoresponsive PNIPAM was synthesized through a surface-initiated atom transfer radical polymerization (SI-ARGET ATRP). Co@PDMS/PNIPAM shows high flux in various oily water and bio-solution. More remarkably, Co@PDMS/PNIPAM exhibited intelligent self-repairing characteristics, and this further enhances its stability and service endurance in the application of oil-water separation. The results provide pathways to the preparation of antifouling and durable membranes in the application of water treatment, and resource recovery.

Smart wireless flexible bandage containing drug loaded polycaprolactone microparticles for real-time monitoring and treatment of chronic wounds.

The quality of life is negatively impacted by chronic wounds for more than 25 million people in the US. They are quite prone to infection, which may lead to the eventual loss of a limb. By exposing the ulcers to treatment agents at the appropriate time, the healing rate is increased. On-demand drug release in a closed-loop system will aid us in reaching our goal. In this study, we have developed a platform capable of real-time diagnosis of bacterial infection by wirelessly reading wound pH, as well as slow and on-demand local administration of antibiotics. The drug carrier microparticles, an electrical patch, a thermoresponsive hydrogel with an integrated microheater, and a flexible pH sensor comprised the closed-loop patch. Here it is reported that slow and smart release of cefazolin can be addressed by incorporation of drug encapsulated hydrophobic microparticles embedded into a thermo-responsive hydrogel. The utilization of a programmable bandage to provide antibiotic medication highlights the need of not only choosing appropriate therapeutic substances but also the controlled release of the medicine and its rate of release within the wound area. The results of our study indicate that the use of cefazolin encapsulated polycaprolactone (PCL) microparticles can effectively regulate the application of antibiotic treatment for chronic skin wounds. The results also showed a substantial gradual release of cefazolin from the thermo-responsive Pnipam hydrogel when the wound dressing was subjected to a temperature of 37°C. We believe that the developed flexible smart bandage can have a significant impact on chronic wound healing.

Cation-induced morphological transitions and aggregation of thermoresponsive PNIPAM nanogels

Poly(N-isopropylacrylamide) (PNIPAM) nanogels are promising responsive colloidal particles that can be used in pharmaceutical applications as drug carriers. This work investigates the temperature-dependent morphological changes and agglomeration of PNIPAM nanogels in the presence of mono- and multi-valent cationic electrolytes. We described the deswelling, flocculation, thermal reversibility behaviour and aggregated morphology of PNIPAM nanogels over a range of electrolyte concentrations and temperatures revealing the critical transition points from stable suspension to spontaneous agglomeration. We demonstrated that the flocculating ability and the rate of aggregate formation follow the order of deswelling behaviour. Transmission electron microscopy and atomic force microscopy analysis revealed the presence of a shell-like layer with varying density in the multivalent electrolyte solutions when compared to those in aqueous medium. We identified a concentration threshold of the thermally induced reversible aggregation/dispersion for the PNIPAM nanogels in the presence of Na+ and K+ ions at 10 mM, for Mg2+ and Ca2+ ions at 1 mM and for Al3+ ions at 0.1 mM concentrations. Such concentration thresholds indicated the effective destabilization of the electrolyte system with multivalency following the Schulze–Hardy rule. Our findings were supported by applying a Debye screening model that accounts for the shielding effect of multivalent cationic electrolytes on these nanogel systems. Our experiments and the models confirmed the compression of the electric double layer as the valency and ionic strength increased, except for Al3+ at higher concentrations which seemed to disrupt the electrical double layer and cause reversal of zeta potential. Our work highlights the significant impact the presence of multivalent cations can impose on the stability and morphology of nanogels, and this understanding will help in designing responsive nanogel systems based on PNIPAM nanogels.

Synthesis of Thermoresponsive Chitosan-graft-Poly(N-isopropylacrylamide) Hybrid Copolymer and Its Complexation with DNA.

A hybrid synthetic-natural, thermoresponsive graft copolymer composed of poly(N-isopropyl acrylamide) (PNIPAM) side chains, prepared via RAFT polymerization, and a chitosan (Chit) polysaccharide backbone, was synthesized via radical addition-fragmentation reactions using the "grafting to" technique, in aqueous solution. ATR-FTIR, TGA, polyelectrolyte titrations and 1H NMR spectroscopy were employed in order to validate the Chit-g-PNIPAM copolymer chemical structure. Additionally, 1H NMR spectra and back conductometric titration were utilized to quantify the content of grafted PNIPAM side chains. The resulting graft copolymer contains dual functionality, namely both pH responsive free amino groups, with electrostatic complexation/coordination properties, and thermoresponsive PNIPAM side chains. Particle size measurements via dynamic light scattering (DLS) were used to study the thermoresponsive behavior of the Chit-g-PNIPAM copolymer. Thermal properties examined by TGA showed that, by the grafting modification with PNIPAM, the Chit structure became more thermally stable. The lower critical solution temperature (LCST) of the copolymer solution was determined by DLS measurements at 25-45 °C. Furthermore, dynamic and electrophoretic light scattering measurements demonstrated that the Chit-g-PNIPAM thermoresponsive copolymer is suitable of binding DNA molecules and forms nanosized polyplexes at different amino to phosphate groups ratios, with potential application as gene delivery systems.

Thermoresponsive Lamellar Hydrogels with Tunable Turbidity, Structural Color, and Anisotropic Swelling.

We report a thermoresponsive anisotropic photonic hydrogel: poly(dodecyl glyceryl itaconate)/polyacrylamide-poly(N-isopropylacrylamide) hydrogel (PDGI/PAAm-PNIPAM hydrogel). Hydrogels with uniaxially aligned lamellar bilayers possess bright structural color and swelling anisotropy, while PNIPAM-based hydrogels exhibit distinct thermoresponsive properties around a lower critical solution temperature (LCST). Hybridization of thermoresponsive PNIPAM with the lamellar hydrogel can give the anisotropic photonic hydrogel various fascinating thermoresponsive properties, such as structural color/turbid transition, thermoresponsive structural color, and anisotropic deswelling/reswelling behavior by temperature stimuli. The temperature-induced changes in turbidity, structural color, and anisotropic swelling of the gel around the LCST can be tuned by controlling the incorporated PNIPAM density. PNIPAM can be regioselectively incorporated into the specific region of the lamellar hydrogels by photomasking during UV polymerization. The PDGI/PAAm-PNIPAM hydrogel can find diverse promising applications such as smart windows and smart displays.

Chitosan hydrogels with MK2 inhibitor peptide-loaded nanoparticles to treat atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disorder that lacks ideal long-term treatment options due to a series of side effects, such as skin atrophy, related to the most common treatment prescribed to manage moderate-to-severe AD. In this study, a cell-penetrating MK2 inhibitor peptide YARA (YARAAARQARAKALNRQGLVAA) was loaded into hollow thermo-responsive pNIPAM nanoparticles (NP), which were further incorporated into chitosan hydrogels (H-NP-YARA) to promote local drug delivery, improve moisture and the anti-inflammatory activity. The NPs exhibited high loading efficiency (>50%) and the hydrogel remained porous following NP incorporation as observed by scanning electron microscopy (SEM). Both nanoparticles and hydrogels were able to improve the release of YARA and sustained release to up to 120 h. The hydrogels and NPs delivered 2 and 4-fold more YARA into viable skin layers of porcine skin in vitro at 12 h post-application than the non-encapsulated compound in intact and impaired barrier conditions. Furthermore, the YARA-loaded NPs (NP-YARA) and H-NP-YARA treatment decreased the levels of inflammatory cytokines up to 20 time-fold compared with the non-treated group of human keratinocytes under inflammatory conditions. Consistent with the results in cell culture, the loading of YARA in NP reduced the levels of IL-1β, IL-6, and TNF-α up to 3.3 times in an ex vivo skin culture model after induction of inflammation. A further decrease of up to 17 times-fold was observed with H-NP-YARA treatment compared to the drug in solution. Our data collectively suggest that chitosan hydrogel containing YARA-loaded nanoparticles is a promising new formulation for the topical treatment of AD.

Synthesis of thermoresponsive PNIPAm nanogel adsorbent by microwave-assisted polymerization for wastewater treatment application

This research demonstrated the fast synthesis technique using microwave-assisted polymerization for the preparation of thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) nanogel which was to be used for paraquat pesticide adsorption. PNIPAm nanogel was synthesized by free-radical polymerization in an aqueous solution using water-soluble ammonium peroxodisulfate (APS) and N,Ń-methylenebisacrylamide (BIS) as initiators and cross-linker, respectively. Microwave irradiation was used as an alternative heating technique and its efficiency was compared to that of the conventional heating method. The results showed that reaction time could be greatly shortened from several hours to only 20 min with the yield of PNIPAm nanogel of approximately 65 % using microwave heating method. The FTIR analysis confirmed that microwave irradiation did not alter the chemical structure of PNIPAm nanogel. The cross-linker concentrations and the sequence of cross-linker addition affected the hydrodynamic diameter of PNIPAm nanogel. The hydrodynamic diameter of swollen PNIPAm nanogels at 25 °C decreased as increasing the cross-linker concentrations and then further decreased when the cross-linker was added after 10 min of the irradiation time. Besides, all PNIPAm nanogel showed well thermoresponsive reversibility over 5 cycles, across the volume phase transition temperature (VPTT) at around 32 °C. The adsorption and release mechanisms of the paraquat took advantage of the phase transition change (swelling-collapse) in response to temperature stimuli, respectively. The PNIPAm nanogel synthesized from the microwave heating method had a profound effect on paraquat adsorption, having 60 – 70 % adsorption with a paraquat release of around 35 – 45 %. These results demonstrated that PNIPAm nanogels could be used as an alternative adsorbent material for industrial wastewater treatment.

Synthesis of thermoresponsive PNIPAm-b-PVP-b-PNIPAm hydrogels via aqueous RAFT polymerization

A stimuli-responsive BAB triblock copolymer of PNIPAm-b-PVP-b-PNIPAm, which displayed a thermoreversible sol–gel transition, was readily synthesized via redox-initiated aqueous RAFT mediated polymerization, under mild conditions.

Thermal Conductivity of PNIPAm Hydrogels and Heat Management as Smart Windows

AbstractThough thermoresponsive lower critical solution temperature (LCST) hydrogels have attracted intense attention to be applied in smart windows, less efforts are paid on the LCST effect on the heat transfer process. Herein, the research mainly focuses on heat transfer process of thermoresponsive PNIPAm hydrogels. It is the first time reported that LCST behaviors can decrease thermal conductivity upon heating process. To be utilized as a smart window, thermal conduction flux is investigated yet the thermal conduction energy occupies little to manage the thermal transfer process in a model house. It is found that radiation thermal transfer predominates the heat transfer process for PNIPAm‐based smart windows. These results are meaningful to provide basic data for energy transfer in using thermoresponsive hydrogels.

Increasing the Efficiency of Thermoresponsive Actuation at the Microscale by Direct Laser Writing of pNIPAM

AbstractThermoresponsive hydrogels such as poly(N‐isopropylacrylamide) (pNIPAM) are highly interesting materials for generating soft actuator systems. Whereas the material has so far mostly been used in macroscopic systems, here it is demonstrated that pNIPAM is an excellent material for generating actuator systems at the micrometer scale. Two‐photon direct laser writing is used to precisely structure thermoresponsive pNIPAM hydrogels at the micrometer scale based on a photosensitive resist. This study systematically shows that the surface‐to‐volume ratio of the microactuators is decisive to their actuation efficiency. The phase transition of the pNIPAM is also demonstrated by nanoindentation experiments. It is observed that the mechanical properties of the material can easily be adjusted by the writing process. Finally, it is found that not only the total size and surface structure of the microactuator play an important role, but also the crosslinking of the polymer itself. The results demonstrate for the first time a systematic study of pNIPAM‐based microactuators, which can easily be extended to systems of microactuators that act cooperatively, e.g., in microvalves.

Thermoresponsive PNIPAm on anti-corrosion antibacterial coating for controlled Ag ions release

The accumulation of dead bacterial cells on the surface of general antibacterial and anti-corrosion coating will provide nutrition for subsequent cells, resulting in the rapid decomposition of the coating, which is the main factor restricting the service life of the coating. In this study, PDA was combined with PNIPAm to attain core-shell microspheres with thermoresponsive. Afterward, the modified scales were obtained by combining the pretreated basalt scales with core-shell microspheres and then depositing AgNPs. The thermoresponsive anti-corrosion and antibacterial composite coating were prepared by spraying. The results of cyclic immersion experiments at different temperatures showed that the coating prevented bacterial adhesion at 37 °C and removed adhesion bacteria at 4 °C. Concurrently, the coating realized the controlling release of the antibacterial agent through the temperature change. The EIS and SEM results indicated that the coating provided long-term protection for the matrix.

Tunnelling the structural insights between poly(N-isopropylacrylamide) and imidazolium sulfate ionic liquids

The integration of polymers and ionic liquids (ILs) leads to the substantial development and establishment of sustainable technologies to fabricate novel polymeric composites and polymeric materials. In this regard, poly(N-isopropylacrylamide) (PNIPAM), a classic biomedical thermoresponsive polymer (TRP), has attracted wide attention in the scientific, technological, and industrial fields owing to its characteristic tuning ability with the surrounding environment. ILs have been regarded as potential candidates as green solvents that can function as reaction and solvent media. Owing to the wide-ranging importance of these materials in diverse fields, it is imperative to study the interactions between TRPs and ILs to fabricate polymeric-IL-based materials. In this paper, we study the comparative effect of imidazolium-based ILs such as 1-ethyl-3-methylimidazolium methyl sulfate [Emim][MtSO4] and 1-butyl-3-methylimidazolium ethyl sulfate [Bmim][EtSO4] on the phase transition behavior of biomedically renowned thermoresponsive PNIPAM. To probe into these changes, we conduct various experimental studies such as temperature-dependent dynamic light scattering, thermal fluorescence spectroscopy, steady-state fluorescence spectroscopy, and UV–visible absorption spectroscopy. Our experimental results explicitly elucidate the phenomenological changes in the molecular interactions, variations in absorbance, and agglomeration behavior of PNIPAM and ILs aqueous mixtures. The temperature-dependent dynamic light scattering studies demonstrate the alterations in the phase transition behavior of PNIPAM with the addition of ILs. Both the added ILs decreased the lower critical solution temperature of PNIPAM towards different extents. The current work will contribute to the design of polymeric ionic liquid-based materials.

Engineering of Stable Cross-Linked Multilayers Based on Thermo-Responsive PNIPAM-Grafted-Chitosan/Heparin to Tailor Their Physiochemical Properties and Biocompatibility.

The thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) is ubiquitously applied in controlled drug release and tissue engineering. However, the lack of bioactivity of PNIPAM restricts its use in cell-containing systems being a thermo-responsive adhesive substratum with no regulating effect on cell growth and differentiation. In this study, integrating PNIPAM with chitosan into PNIPAM-grafted-chitosan (PNIPAM-Chi) allows a layer-by-layer assembly with bioactive heparin to fabricate PNIPAM-modified polyelectrolyte multilayers (PNIPAM-PEMs). Grafting PNIPAM chains of either 2 (LMW) or 10 kDa (HMW) on the chitosan backbone influences the cloud point (CP) temperature in the range from 31 to 33 °C. PNIPAM-Chi with either a higher molecular weight or a higher degree of substitution of PNIPAM chains exhibiting a significant increase in diameter above CP as ensured by dynamic light scattering is selected to fabricate PEM with heparin as a polyanion at pH 4. Little difference of layer growth is detected between the chosen PNIPAM-Chi used as polycations by surface plasmon resonance, while multilayers formed with HMW-0.02 are more hydrated and show striking swelling-and-shrinking abilities when studied with quartz crystal microbalance with dissipation monitoring. Subsequently, the multilayers are covalently cross-linked using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide to strengthen the stability of the systems under physiological conditions. Ellipsometry results confirm the layer integrity after exposure to the physiological buffer at pH 7.4 compared to those without cross-linking. Moreover, significantly higher adhesion and more spreading of C3H10T1/2 multipotent embryonic mouse fibroblasts on cross-linked PEMs, particularly with heparin terminal layers, are observed owing to the bioactivity of heparin. The slightly more hydrophobic surfaces of cross-linked PNIPAM-PEMs at 37 °C also increase cell attachment and growth. Thus, layer-by-layer constructed PNIPAM-PEM with cross-linking represents an interesting cell culture system that can be potentially employed for thermally uploading and controlled release of growth factors that further promotes tissue regeneration.

Front Cover: In‐situ ATR‐IR Spectroscopy Reveals Complex Absorption‐Diffusion Dynamics in Model Polymer‐Membrane‐Catalyst Assemblies (PCMA) (ChemCatChem 10/2022)

The Front Cover shows the interplay between chemisorption of carbon monoxide probe molecules and diffusion through a porous catalyst with stimulus responsive polymeric brushes that can switch the transfer process ON- and OFF with temperature. In their Research Article, M. J. Enes da Silva et al. showed that on a Polymer-Membrane-Catalyst Assembly (PCMA) system consisting of PET membranes with a well-defined pore structure coated with thermo-responsive polymer (poly(n-isopropylacrylamide) or p-NIPAM) coupled to an in-situ ATR-IR cell the molecular diffusion is only diminished at temperatures above the LCST when the polymer is located on the surface of the pores. This was attributed to sluggish molecular diffusion at high temperatures in which the polymer forms a dense polymer layer on top of the pore entrance. Surprisingly, the opposite trend is observed when the polymer is primarily located on the walls of the pores. In this scenario, the polymer acts as a sink for molecules depending on the polymer-reactant affinity and the additional barrier for transport induced by the polymer. More information can be found in the Research Article by M. J. Enes da Silva et al.

Highly conductive thermoresponsive silver nanowire PNIPAM nanocomposite for reversible electrical switch.

Highly conductive nanocomposite hydrogels have been challenging to produce due to their high water volumes inhibiting the incorporation of an essential amount of conductive nanofillers. Furthermore, the most common fillers used, typically for easy integration, display small aspect ratios. Thus, the formation of interparticle pathways for electronic travel is limited, resulting in low conductivities. Here, we introduce ultralong silver nanowires (ULAgNWs) into a thermoresponsive, volume changing PNIPAM gel to form a nanocomposite that shows switchable electronic performance. The produced nanocomposite surpasses other PNIPAM nanocomposites by expressing the largest electrical switch ratio and the highest peak conductivity. The PNIPAM matrix possesses an interconnected microporous structure that offers a spacious network for the dispersion of nanowires while still maintaining a high volume switch ratio and excellent elastic behavior under extreme compression cycles (98% compression). The ULAgNWs significantly enhance the probability of more numerous connections forming during shrinking cycles. The high swellability displayed by the PNIPAM gel provides the ability to separate the embedded nanowires by many lengths. Together, they form a nanocomposite that can thermo-modulate its electrical properties. Moreover, the conductive PNIPAM maintains the electrical switch of 4.3-4.4 orders of magnitude with thermo-responsive cycles. Because of their high electrical conductivity and outstanding elastic behavior, these stimuli-responsive nanocomposite hydrogels may expand the prospects for conductive hydrogel applications and provide greater performance in their applications.

Stimuli-responsive hydrogel sponge for ultrafast responsive actuator

With the ability to deform in response to specific stimuli, polymeric hydrogel actuators are important bionic materials. However, because shape deformation is derived from the diffusion of water molecules, the response rate of hydrogel actuators is usually slow, which severely limits their potential applications. In this work, a thermo-responsive PNIPAm hydrogel sponge is developed, and the hydrogel sponge shows ultrafast de-swelling/swelling capacity (equilibrium time 7 s) and large deformation degree (40%) due to the assistance of capillary force. Hydrogel sponge actuator with rapid response performance is further constructed, and the hydrogel sponge actuator could be used to capture moving objects and living creatures. Moreover, light-controlled directional movement can be achieved by incorporating photothermal functional components into the hydrogel sponge actuator. This work would promote the application of hydrogel actuators in soft robots.

In-situ polymerization for mechanical strong composite actuators based on anisotropic wood and thermoresponsive polymer

Stimuli-responsive hydrogels hold an irreplaceable statue in intelligent actuation materials because of their reversible stretchability and excellent biocompatibility. However, the poor mechanical performance and complicated fabrication process of anisotropic structures severely limit their further applications. Herein, we report a high-strength thermoresponsive wood-PNIPAM composite hydrogel actuator with complex deformations, through a simple in-situ polymerization. In this composite hydrogel actuator, the anisotropic wood and the thermoresponsive PNIPAM hydrogel hydroel can work together to provide bending and even other complex deformations. Owing to strong interfacial interaction, this actuator perfectly realized the combination of good mechanical properties (∼1.1 MPa) and fast actuation speed (∼0.9 s). In addition, by adjusting the orientation direction of wood, this actuator can achieve various complex deformations. Such composite hydrogel actuator could be a good candidate for intelligent applications, such as intelligent actuators, smart valves, manipulators and even soft robots.

Temperature-responsive polymer-tethered Zr-porphyrin MOFs encapsulated carbon dot nanohybrids with boosted visible-light photodegradation for organic contaminants in water

Zirconium-based porphyrin metal–organic frameworks (MOFs) have attracted extensive attention in the photocatalysis because of their considerable specific surface area, powerful visible light efficiency and semiconductor properties. However, the rapid charge recombination and self-aggregation limit their applications. Here, porphyrin-based Zr-MOF (PCN-222) nanohybrids (CDs@PCN-222@PNIPAM) as an efficient hydrophilic photocatalyst were fabricated by encapsulating various carbon dots (CDs) into PCN-222 nanopores with surface wettability modification by catechol-terminated thermo-responsive PNIPAM having various chain lengths. Due to the electron collecting effect of the nitrogen-doped CDs (N-CDs) and their synergistic effect with PCN-222, the photocatalytic performance of the prepared nano-hybrid photocatalyst were significantly improved. Furthermore, the introduction of hydrophilic polymer with moderate molecular weight effectively enhanced the transfer efficiency of photo-generated charges and the surface wettability of photocatalyst, and improved the water dispersibility of catalyst so that effectively promotes the enrichment and catalytic conversion of water-soluble target pollutants around the active site of the photocatalyst. The removal efficiency of RhB and tetracycline (TC) under visible light irradiation reached almost 100 % and 90.93 % in just 20 min, respectively. In addition, polymer-functionalized Zr-MOF-based nanohybrids revealed an interesting temperature-response switching behavior for the photocatalysis. The study on the catalytic mechanism and degradation pathways of TC showed that the h+ plays a major role in the degradation process, and other reactive species are also involved in the further mineralization of pollutants. This work provides a new insight for the functional modification of MOFs and the design of high efficiency photocatalyst.

Thermoresponsive PNIPAM-b-PAA block copolymers as “smart” adsorbents of Cu(II) for water restore treatments

Copper(II) as a heavy metal ion is posing risk to aquatic ecosystems including algae, fish, mollusks, and bacteria, negatively affecting human life because of bioaccumulation and non-biodegradability. In this study, two thermoresponsive PNIPAM-b-PAA block copolymers with different characteristics in terms of molecular weight and PAA composition were investigated to remove copper ions from simulated water. We chose to utilize those block copolymers in CuSO4 adsorption experiments in order to comprehend how the combination of the thermoresponsive PNIPAM block and the binding ability that PAA block offers, affects the adsorption of Cu2+ and SO42− and provides eventually their removal from aqueous solutions. The adsorption protocol includes simple mixing of the copolymer and CuSO4 aqueous solutions under stirring. Dynamic and electrophoretic light scattering, pH, UV–vis, turbidity and ICP-OES measurements were conducted to verify the PNIPAM-b-PAA ability as smart adsorbents. The results showed that the PNIPAM-b-PAA_50−50 sample offers the possibility of Cu2+ and SO42- adsorption of greater percentage especially when temperature increases to 60 °C. Therefore, PNIPAM-b-PAA block copolymers comprise efficient and smart Cu2+ and SO42- adsorbents.

Mussel-inspired preparation of temperature-responsive polymer brushes modified layered double hydroxides@Pd/carbon dots hybrid for catalytic applications

A novel type of multicomponent nanocomposite of LDH@PDA@PNIPAM@Pd/carbon dots (CDs) was successfully constructed for highly efficient heterogeneous catalytic reduction from two-dimensional layer double hydroxide (LDH) nanosheet functionalized with thermo-responsive PNIPAM polymer brushes based on the mussel-inspired chemistry. CDs were used as a reductant and stabilizer by in situ loading metal Pd onto LDH@PDA@PNIPAM. Compared with LDH@PDA@PNIPAM@Pd catalyst without CDs modification, the designed LDH@PDA@PNIPAM@Pd/CDs nanohybrid catalyst had better catalytic reduction ability for various dyes and nitrophenol thanks to the synergistic catalytic effect between metal active center and CDs, LDH and their high dispersion stability. Especially, a good catalytic reduction activity was demonstrated for methylene blue (MB) with a high TOF (545.2 min−1). Furthermore, the nanohybrid presented interesting thermo-responsive catalytic property due to the existence of PNIPAM polymer chains. In addition, the prepared catalyst also exhibited outstanding catalytic property for the Knoevenagel condensation reaction. Our study provides a new way for the composite preparation of organic-inorganic hybrid materials by polymer and inorganic materials, and shows great potential in the field of catalytic applications.