In Situ Preparation Of Nanometals By Spherical Polyelectrolyte Brush Nanoreactor And Their Application

Nanometals are highly favored in the fields of detection,industrial catalysis,and enzyme-like catalysis due to their unique size effects,electronic properties,and high-density active sites.However,due to their high surface energy,nanometal particles tend to aggregate in practical applications,which reduces their stability and performance.Therefore,preventing metal nanoparticles aggregation,controlling particle size,and improving stability are crucial issues in the preparation and application of nanometals.By using materials with nanoscale spaces as nanoreactors to prepare nanometals,nucleation and growth of metal nanoparticles can be restricted within the nanospace,and control of the shape,size,and material of the nanoreactor can be used to regulate the resulting metal nanoparticles.Spherical polyelectrolyte brushes（SPB）a re a type of nanoparticle with a core-shell structure.The shell of SPB can efficiently enrich metal ions through electrostatic interactions and Dnonnan effects.Nanoconfinement of SPB provides a specific microenvironment for the nucleation,growth and stability of metal nanoparticles;while the isolation effect of polyelectrolyte chains not only control the growth of metal nanoparticles,but also maintain the stability of them.Therefore,the spherical polyelectrolyte brush is an ideal nanoreactor for preparing metal nanoparticles.This paper first prepared different types of spherical polyelectrolyte brushes using photoemulsion polymerization,and successfully prepared nanoscale platinum,gold,and gold-platinum alloy using them as nanoreactors.The generation of metal nanoparticles in the nanoreactor was systematically studied using characterization methods such as small-angle X-ray scattering.Finally,the applications of these metal nanoparticles were explored in fields such as biomolecule detection,catalysis,and pesticide residue detection.The specific work is as follows:（1）Nanoplatinum were prepared in situ in a spherical poly(2-（methacryloxy）ethyl]trimethylammonium chloride brush（PMAETA-SPB）nanoreactor,and its application in the colorimetric detection of cysteine was studied.Firstly,the spherical polyelectrolyte brush nanoreactors were prepared by photoredox emulsion polymerization,and the nanoplatinum（Pt NPs）were synthesized in situ by the reduction of chloroplatinic acid with sodium borohydride inside the nanoreactors.The synthesized Pt NPs were systematically characterized by small-angle X-ray scattering（SAXS）,transmission electron microscopy（TEM）,dynamic light scattering（DLS）,X-ray diffraction（XRD）,and X-ray photoelectron spectroscopy（XPS）.The results showed that the Pt NPs had a small size of about 1.9 nm,a narrow size distribution,and were uniformly distributed in the poly-electrolyte brush layer.Using SPB@Pt NPs as a peroxidase mimetic catalyst and 3,3’,5,5’-tetramethylbenzidine（TMB）as an oxidant substrate in the presence of hydrogen peroxide,the peroxidase-like activity of SPB@Pt NPs was investigated.Based on the effect of cysteine on the peroxidase-like activity of SPB@Pt NPs,a method for detecting cysteine was designed and developed,with a detection limit of 0.11μM and a detection range of 0.4-3.5μM.The method is simple to operate,highly sensitive,and has good selectivity for samples with complex components.（2）Cationic spherical poly（2-aminoethyl methacrylate hydrochloride）brushes（PAEMH-SPB）were prepared by photoemulsion polymerization for in situ fabrication of nanogold（Au NPs）.The formation and distribution of Au NPs in the brush layer and the interaction between Au NPs and PAEMH-SPB were systematically studied by means of SAXS and Cryo-TEM.The results show that Au NPs are uniformly distributed in the shell of PAEMH-SPB,and the stable immobilization of the Au NPs in SPB was the result of multiple interactions including complexation and electrostatic interaction.In order to further study the interaction between Au NPs and spherical polyelectrolyte brushes,PAEMH-SPB,electrically neutral spherical poly（N-isopropylacrylamide）brushes（PNIPAM-SPB）,anionic spherical polyacrylic acid brushes（PAA-SPB）and spherical copolymer brushes（P（NIPAM-co-AA）-SPB）are used as a carrier to immobilize pre-prepared Au NPs.It is found that PAEMH-SPB can immobilize Au NPs inside the brush layer through weak electrostatic interaction;PNIPAM-SPB can immobilize Au NPs outside the brush layer through non-specific interaction.However,both PAA-SPB and P（NIPAM-co-AA）-SPB can not immobilize Au NPs due to the influence of electrostatic repulsion.（3）In order to further improve the stability of the prepared gold nanoparticles,silica shell（Si O₂）was prepared using spherical poly[2-（methacryloxy）ethyl]trimethylammonium chloride brush as the nanoreactor and catalytic template.Firstly,the PMAETA-SPB nanoreactor was prepared by photoemulsion polymerization,and Au NPs were in situ synthesized using the PMAETA-SPB nanoreactor,followed by using the SPB@Au NPs as a nanoreactor and catalytic template to directly catalyze the synthesis of the Si O₂ shell without the need for additional catalysts.Finally,the polystyrene core was removed by chemical etching with tetrahydrofuran to obtain hollow silica-supported gold nanoparticles（HSNPs@Au NPs）.The synthesized HSNPs@Au NPs were characterized systematically using various techniques including TEM,DLS,SAXS,UV-vis,TG,BET,and XPS,which confirmed their stable spherical morphology and high Au NPs loading.The Au NPs were found to be uniformly distributed in the Si O₂ shell with an average size of 4.3 nm.The catalytic performance of HSNPs@Au NPs was explored using p-nitrophenol（p-NP）degradation as a model reaction.Due to its structural advantages,HSNPs@Au NPs exhibited excellent catalytic activity in reducing p-NP with sodium borohydride in aqueous solution.Moreover,HSNPs@Au NPs were easily recovered and maintained good catalytic activity and structural stability even after six cycles.（4）In order to further improve the catalytic performance of metal nanoparticles,nano gold-platinum alloy was prepared in situ using spherical poly[2-（methacryloxy）ethyl]trimethylammonium chloride brush nanoreactor,and its application in the detection of pesticide was explored.The PMAETA-SPB brush layer uniformly adsorbed Au Cl₄^-and Pt C1₆^2-through electrostatic attraction and the Donnan effect.The simultaneous growth of Au Pt bimetals was achieved by the reduction of sodium borohydride.Finally,the nano Au Pt alloys with narrow size distribution,adjustable metal proportion and uniform distribution are obtained in the PMAETA brush layer(SPB@Au₃₃Pt₆₇,SPB@Au₆₇Pt₃₃ and SPB@Au₉₂Pt₈).The oxidase-like activities of prepared nano Au Pt alloy were systematically investigated by choosing SPB@Au Pt with different ratios of gold and platinum as enzyme-like catalysts and TMB as oxide substrates.It was found that the catalytic activity of SPB@Au₃₃Pt₆₇ is the highest and it presents unique multi-channel signals（370 nm,450 nm and 652 nm）in the UV spectrogram.Based on this,a SPB@Au₃₃Pt₆₇-TMB multichannel colorimetric sensor array was constructed for pesticide detection.By identifying the suppression or enhancement effect of pesticides on the catalytic activity of SPB@Au₃₃Pt₆₇,five pesticides,including thiamethoxam,fluroxypyr,butocarboxim,methomyl,and glyphosate,were successfully detected.Moreover,the constructed SPB@Au₃₃Pt₆₇-TMB multichannel colorimetric sensor array showed great potential in detecting pesticide mixtures.Finally,the multichannel colorimetric sensor array was applied to the colorimetric detection of different concentrations of thiamethoxam,and the limit of detection（LOD）was 0.09μg/m L.The detection range was 1.0-9.0μg/m L,further demonstrating the excellent detection performance of the multichannel sensor array.