Synthesis And Applications Of PNIPAm Based Microgel Composite With Photo- And Temperature-responsive Property

Pesticides have made important contributions to improving grain yield and quality.However,the excessive use of agrochemical products?such as imidacloprid?and their intermediates?such as p-nitrophenol and p-nitroaniline?has serious adverse effects on surface water,groundwater and soil.Controlling pesticide release and catalytic degradation of pesticide intermediates is an effective way to improve pesticide efficiency and environmental pollution.Poly?N-isopropylacrylamide??PNIPAm?has both hydrophilic acylamides and hydrophobic isopropyl groups on its macromolecular chain,which makes the water solution of linear PNIPAm and the crosslinked PNIPAm hydrogel show temperature-sensitive properties.The phase transition of chemically crosslinked PNIPAm polymer shrinks abruptly from swelling state to shrinking state when the temperature rises to about 32 ^oC.In recent years,these thermosensitive polymers have been widely used in controlled drug release,biochemical separation and catalysis.In this paper,the composite microgel materials were prepared by combining the thermo sensitive properties of PNIPAm with the degradable polydopamine microspheres,and applied in the controlled release of pesticides and the rapid degradation of p-nitrophenol and p-nitroaniline.The main research contents are listed as follows:?1?A NIR-and temperature-responsive pesticide release platform through core-shell polydopamine@PNIPAm nanocompositesControlled stimuli-responsive release systems are a feasible and effective way to increase the efficiency of pesticides and help improve environmental pollution issues.However,NIR-responsive systems for encapsulation of pesticides for controlling release have not been reported because of high cost and load ability of conventional NIR absorbers as well as complicated preparation process.Herein,we proposed polydopamine?PDA?microspheres as a photothermal agent owing to their abundant active sites,satisfactory photothermal efficiency,low cost and easy fabrication,followed by capping with a PNIPAm thermosensitive polymer shell.In this core-shell PDA@PNIPAm hybrid system,the PDA core provided excellent temperature and NIR-light sensitivity as well as high loading capacity,while the PNIPAm applied as both a thermosensitive gatekeeper and a pesticide reservoir.The structure of the PDA@PNIPAm nanocomposites was characterized by TEM and SEM,FT-IR,UV-vis,DLS and TGA;the results showed that the nanocomposites had a well-defined core-shell configuration for efficient loading of small pesticide molecules.Moreover,the core-shell PDA@PNIPAm nanocomposites exhibited high loading capacity and temperature or NIR-controlled release performance.Overall,this system has significant potential in controlled drug release and agriculture-related fields as a delivery system for pesticides with photothermal responsive behavior.?2?Mussel-Inspiredsmartnanoreactorbasedonpolydopamineand poly?N-isopropylacrylamide?with NIR light-and Temperature-responsive catalytic activityThe development of metal nanoparticles loaded temperature-responsive microgels that exhibit switchable volume and tunable catalytic properties with temporal and spatial resolution is of great importance in many fields.However,it remains challenging to develop smart nanoreactors that dramatically change their properties in response to both temperature and near-infrared?NIR?lights.Herein,photo,thermal and catalytic properties are integrated into a single platform to realize remote control of catalytic activity.To this end,manodisperse PDA microspheres is used as a photoconversion agent and the core,thermosensitive PNIPAm is grafted on the surface of PDA by introducing of SiO₂ as interlayer,and subsequently Ag NPs are evenly distributed within the microgel.Combination of the PDA and PNIPAm provides the microgels with an excellent NIR-responsive property and photothermal stability.Most importantly,the catalytic activity of immobilized Ag NPs can be modulated by temperature and power density of the NIR light,demonstrating that the core-shell microgels can serve as“smart nanoreactors”.Therefore,the metal NPs-incorporated functional nanoreactors with temperature-and NIR light-responsive propertied are highly promising for fabricating remote light-controlled devices,sensors and so on.?3?Controllable assembly of Au nanoparticles onto photo-and thermo-sensitive microgels for tunable catalysis4-nitroaniline?4-NA?is one of the main pollutants produced in industrial production and pesticide transformation.In this chapter,PDA-SiO2-PNIPAm core-shell nanocomposites were prepared by a simple method and used as carriers of gold nanoparticles.The effects of near infrared light on the catalytic kinetics of 4-NA were investigated and compared with the traditional temperature response catalytic kinetics.More importantly,we found that by adjusting the amount of reductant,the spatial distribution and size of metal particles can be effectively controlled.In the presence of NaBH₄,B-Au NPs?<5 nm?is uniformly loaded in the network structure of PDA-SiO₂-PNIPAm microgels.Because polydopamine has the characteristics of in situ reduction of metal nanoparticles,Au NPs?3 nm¹5 nm?is only located on the surface of PDA-SiO₂-PNIPAm PDA microspheres without adding NaBH₄,but does not appear in the gel network structure.In order to compare the catalytic properties of two kinds of composite microgels,the SiO₂ interlayer of microgels was specifically removed to form yolk shell structured Au@PDA-PNIPAm and B-Au@PDA-PNIPAm microgels.In the B-Au@PDA-PNIPAm microgel system,the PNIPAm shell can regulate the dispersion or aggregation of nanoparticles by volume expansion or shrinkage,which leads to an increase or decrease in catalytic activity.For Au@PDA-PNIPAm yolk-shell microgels,the PNIPAm shell acts as a temperature responsive valve to control the diffusion rate of reactants to the gel through volume changes,thereby affecting the catalytic process.Therefore,the catalytic activity of microgel metal particle composites can adjust the volume change of PNIPAm shell through traditional direct heating or near infrared light irradiation,and ultimately achieve the purpose of controlling the catalytic activity of gold microgel nanocomposites.In contrast to the traditional direct heating mode,PDA microspheres in microgels provide a new strategy for regulating and controlling catalytic activity,which not only regulates the distribution and particle size of gold nanoparticles in microgels,but also enables microgel metal particle composites to be used in intelligent nano reactors with light and heat adjustable catalysis.