Mussel-inspired Fabrication Of Functional Silica Nanocomposites And Their Environmental Applications

SiO₂ nanomaterial is one of the most common and important inorganic materials,which plays an indispensable role in our daily lives.Thanks to its good mechanical properties,excellent chemical and thermal stability,the SiO₂ nanomaterial has been widely applied in various fields,such as architecture,medicine,electronics and optics,etc.Moreover,the SiO₂ nanomaterial also offers the benefits of small size,high specific surface area,strong surface adsorption force,and huge surface energy as well as favorable dispersibility.These characteristics allow it to be potential materials in environmental applications.Nevertheless,it is still limited to further applications because of its few functional groups.Recently,the organic-inorganic silica composite has been a research focus in various fields.The organic-inorganic silica composite combines the characteristics of SiO₂ nanomaterial and the functionalities of organic compounds,which endows the silica composite wider applications.This study proposed a novel strategy,combining with the mussel inspired chemistry and several surface grafting reactions,such as Michael addition reaction,Kabachnik-Fields reaction,and surface-initiated atom transfer radical polymerization as well as surface-initiated redox polymerization,for the constructions of organic-inorganic silica composites.Besides,the applications in environment adsorption were also investigated by using the prepared silica composites as adsorbents to remove the pollutants in solution.The details of this paper were described as follows:1.Surface functionalization of monodispersed SiO₂ nanoparticles:?a?Firstly,the monodispersed SiO₂ nanoparticles were synthesized via St?ber method.Subsequently,inspired by the composition of adhesive protein in mussel,we used levodopa?DOPA?self-polymerization to form a multifunctional coating onto these SiO₂ nanoparticles.Rich functional groups,such as amine,imine,carboxyl and catechol groups,on the PDOPA coating provide much more adsorption active sites for the improvement of adsorption capacity.?b?Based on the mussel inspired chemistry,the as-prepared SiO₂ nanoparticles were firstly modified using polydopamine?PDA?coating.The residual functional groups,such as amine and catechol groups,on the PDA coating allowed it to be an excellent platform for Michael addition reaction with amine-capped polyacrylic acid?PAA?.The PAA,containing abundant carboxyl groups,endowed the SiO₂ much more active sites for the higher adsorption capacity.?c?Based on the mussel inspired chemistry,the as-prepared SiO₂ nanoparticles were firstly modified using polydopamine?PDA?coating.Then,using the amine functionalized SiO₂,glutaraldehyde and diethyl phosphite as well as mercaptoacetic acid as main materials,the phosphate immobilized SiO₂ nanocomposites?denoted as SiO₂-PDA-CSH?were prepared via Kabachnik-Fields reactions.The introduced phosphate groups played an important role for the for the higher adsorption capacity.?d?Thanks to the residual functional groups from PDA,the PDA coated SiO₂?SiO₂-PDA?nanoparticles could offer plenty of active sites for the secondary reaction.We used the itaconic acid?denoted as IA?as the functional monomer,the ammonium ceric nitrate?ACN?as initiator to synthesize poly?itaconic acid??PIA?grated SiO₂nanocomposites?denoted as SiO₂-PDA-PIA?through surface-initiated redox polymerization with Ce?IV?ions.The PIA contained plenty of carboxyl groups,which could be used as adsorption active sites for the pollutants removal.?e?On account of the residual functional groups,such as amine and catechol groups,on the PDA coating,the SiO₂-PDA nanoparticles were firstly immobilized withinitiator?bromoisobutyrylbromide?.Subsequently,the poly?3-acrylamidopropyl?trimethylammonium chloride?denoted as PAPTCl?grafted SiO₂ nanocomposites were prepared through the surface-initiated atom transfer radical polymerization?SI-ATRP?using?3-acrylamidopropyl?trimethylammonium chloride?APTCl?as the functional monomer,cuprous bromide?CuBr?as the catalyst,and the N,N,N',N'',N''-Pentamethyldiethylenetriamine?PMDETA?as the ligand.The cationic groups?quaternary ammonium groups?from PAPTCl endowed the SiO₂nanocomposites higher adsorption capacity toward anionic pollutants.After the harvest of these organic-inorganic hybrid SiO₂ composites,a series of instrumental techniques,such as transmission electron microscope?TEM?,Fourier transform infrared spectroscopy?FT-IR?,thermogravimetric analysis?TGA?,and X-ray photoelectron spectroscopy?XPS?were carried out for the clear knowledge and investigation about the products.The characterization results provided sufficient supports for the successful functionalization of SiO₂ nanoparticles.2.The investigation of adsorption performances of prepared SiO₂ composites:For the investigation of adsorption performances of prepared SiO₂ composites,the as-prepared organic-inorganic hybrid SiO₂ composites,including SiO₂-PDOPA,SiO₂-PDA-PAA,SiO₂-PDA-CSH,SiO₂-PDA-PIA and SiO₂-PDA-PAPTCl,were used as adsorbents to remove the pollutants in solution.The copper(Cu²⁺)ions,methylene blue?MB?and Congo red?CR?were selected as the models of heavy metal pollutants,cationic dyes pollutants and anionic dyes pollutants,respectively.In the study,the effects of contact time,solution pH,and initial concentration as well as temperature were investigated emphatically.Meanwhile,the adsorption kinetics,isotherms and thermodynamics were also studied.Results showed that prepared hybrid SiO₂ composites exhibited much higher adsorption capacities than the raw SiO₂ nanoparticles.The adsorption capacities of SiO₂-PDOPA,Si O₂-PDA-PAA,SiO₂-PDA-CSH,SiO₂-PDA-PIA and SiO₂-PDA-PAPTCl were up to 34.72,150.02,61.07,98.34,and 106.65 mg/g,respectively,which were 2.15,3.42,2.87,2.91 and3.72 times of the adsorption capacities of raw SiO₂ nanoparticles,respectively.