Construction Of Highly Sensitive Nanoprobes Based On MOFs For The Detection Of Environmental Pollutants

Metal-organic frameworks(MOFs)are crystalline porous materials made by linking metal containing nods(e.g.metal ions and clusters)with organic ligands(e.g.carboxylate ligands and other negatively charged ligands).Due to high specific surface area,ultra-high porosity,large pore volume,adjustable cage structure and open metal sites,MOFs hold great potentialfor many applications,such as catalytic,sensing,energy storage and gas separation.However,the application of analytical chemistry of MOFs still remains a great challenge,because of poor chemical stability,mechanical strength,electrical conductivity and even lack of active group.To solve these problems,novel MOFs composites were constructed by MOFs and other materials,which had a wide application prospect.In this paper,different composite materials were developed based on three kinds of MOFs,which were applied to the analysis of formaldehyde(FA),nitrite(NO₂^-)and mercury ions(Hg²⁺),respectively.The main research contents are as follows:(1)Naphthalimide derivative-functionalized metal organic framework(MOF)for highly sensitive determination of formaldehyde:Formaldehyde(FA),a familiar indoor air pollutant,is usually released from furniture,wood-based flooring,coating,insulation,textiles and even cosmetic makeup,posing a significant threat to human health.Herein,facile and sensitive determination of formaldehyde(FA)is of great significance.A fluorescent probe,termed PHN@MOF,was synthesized by embedding the fluorescent molecule of N-propyl-4-hydrazine-naphthalimide(PHN)into a metal organic framework(MOF)for sensitive and visual monitoring of FA.The hydrazine group of PHN acts as the specific reaction group with FA based on the condensation reaction.The host of MOF(Ui O-66-NH₂)offers the surrounding confinement space required for the reaction.Owing to the enrichment effect and molecular sieve selection of Ui O-66-NH₂ to FA,PHN@MOF,compared with free PHN,exhibits very high sensitivity and selectivity based on space confinement-induced sensitivity enhancement(SCISE).Moreover,the fluorescence of Ui O-66-NH₂ offers a reference signal for FA detection.Using this ratiometric fluorescent PHN@MOF probe,a colorimetric gel plate and test paper were developed and used to visually monitor FA in air.(2)Novel MIL-101@PVP/PVDF composite material for nitrite specific detection:Nitrite(NO₂^-)is widely used in food factory,industrial manufacture and agricultural production as an antimicrobial or flavor agent in foodstuff as well as a raw material in manufacture plants.Unfortunately,nitrite can react with amines in stomach to form a severely carcinogenic species of N-nitrosamines.Therefore,sensitive and selective detection of nitrite has become a focus attention.Diazotization-based spectrofluorimetric methods,which based on the diazotization of a suitable aromatic amine by acidified nitrite to produce diazonium salt,showed characteristics of simpleness,practicability,selectivity,etc.Conventional organic fluorescent probes were usually suffered from tedious synthesis process,small stokes shift,difficult practice in aqueous solutions.Inspired by special characteristics of MOFs,we envisaged that the luminescent MOFs functionalized with amino groups will be good nitrite sensors based on the diazotization.In this study,the MIL-101@PVP/PVDF had been facilely prepared with the MIL-101-NH₂ and blending PVDF-PVP,and composite materials prepared display high sensitivity for the detection of NO₂^-.The amino group of MOF reacted with nitrite to form diazo salt,resulting in fluorescence quenching.Moreover,PVDF and PVP enhance the chemical stability of MIL-101-NH₂ in water.The high-ordered nanoscale cavity and the large surface area of the probe showed target gathering effect to the nitrite,which could benefit to decrease the detection limit and enhance sensitivity.Not only the sensor has good linearity in the range of 20-60?mol/L,but also the detection limit is 3.6?M.The study provides a potential strategy for the determination of nitrite in aqueous solution by fluorescence spectrometry.(3)Colorimetric detection of Hg(II)based on the gold amalgam-triggered mimetic activity in aqueous solutions by employing Au NPs@MOF nanoparticles:Mercury ion(Hg²⁺)is one of the most dangerous heavy metals that contaminate the world soil and water.Hg²⁺can cause accumulation in body cells,leading to chronic harm to brains,kidney,liver,nervous system,digestive system,and even death.It is very important to develop a highly sensitive and selective method for the detection of Hg²⁺in water.The potential of gold amalgam as a nanometer enzyme for the detection of Hg²⁺has been confirmed.But its practical application has been limited due to the high surface energy of Au NPs,which tends to aggregate during the catalytic process.Therefore,it is necessary to further design Au NPs to achieve better application detection.A hybrid material of Au nanoparticle and MOF(Au NP@MOF),which was constructed by immobilization of Au NP uniformly on the cavity surface of iron-5,10,15,20-tetrakis(4-carboxyl)-21H,23H-porphyrin-based MOF(Fe-TCPP-MOF),has been successfully synthesized.On the bases of Hg²⁺ions triggered Au catalysis of methylene blue(MB)reduction,a colorimetric method for highly sensitive and selective detection of Hg²⁺ions has been established.This detection method showed advantages of fast response time,high sensitivity and selectivity.