Application Of Nanoporous Materials For Detection And Removal Of Typical Pollutants In Aqueous Solution

With the rapid development of modern industry,water pollution threatens the survival and development of mankind.Typical water pollutants,e.g.endocrine disruptors and antibiotics,cause a huge threat to ecological environment and human health.It is an imminent task to find efficient,simple and low-cost detection and removal methods.Nanoporous materials have the characteristics of large specific surface area and controlled nanometer pore size,which are widely concerned in sensing,catalysis,energy storage,adsorption and separation.In this paper,two kinds of metal endocrine disruptors Pb2+ and Hg2+ were selected,and nanoporous gold(NPG)was used to construct electrochemical aptamer sensors for the detection of Pb2+ and Hg2+.Carbonaceous nanoporous materials were selected to study the removal behavior of Pbru and Hgri.For the organic water pollutants,which have complex structures and/or similar chemical structures,the current detection methods are mainly gas chromatography and liquid chromatography.Thus this paper focuses on the removal mechanisms of organic endocrine disruptors and antibiotics.Carbonaceous nanocomposites were synthesized for the removal of sulfamethazine(SMT)and cutinase immobilized NPG composites were synthesized for the removal of di(2-ethylhexyl)phthalate(DEHP).The first section described an amplified detection strategy employing NPG and gold nanoparticles(AuNPs)to detect metal endocrine disruptors Pb2+ in aqueous solution.The thiol modified Pb2+-specific DNAzyme was self-assembled onto the surface of the NPG modified electrode for hybridizing with the AuNPs labeled oligonucleotide and for forming the DNA double helix structure.Electrochemical signal,redox charge of hexaammineruthenium(III)chloride(RuHex),was measured by chronocoulometry.Taking advantage of amplification effects of the NPG electrode for increasing the reaction sites of capture probe and DNA-AuNPs complexes for bringing about the adsorption of large numbers of RuHex molecules,this electrochemical sensor could detect Pb2+ quantitatively,in the range of 0.05 to 100 nM,with a limit of detection as low as 0.012 nM.Selectivity measurements revealed that the sensor was specific for Pbro even with interference by high concentrations of other metal ions.This sensor was also used to detect Pb2+ ions from samples of tap water,river water,and landfill leachate samples spiked with Pb2+ ions,and the results showed good agreement with the found values determined by an atomic fluorescence spectrometer.NPG used in this experiment has theoretical and practical significance in the field of electrochemical aptamer sensor construction.The second section is optimized and simplified on the basis of the first section,avoiding the blockage of NPG nanopores caused by the introduced AuNPs.A simple,practical and reusable electrochemical aptasensor,based on thymine-Hg2+-thymine(T-Hg2+-T)coordination chemistry and NPG for signal amplification,was designed for sensitive and selective detection of metal endocrine disruptors Hg2+.The thiol modified T-rich hairpin capture probe was self-assembled onto the surface of the NPG modified electrode for hybridizing with ferrocene-labeled T-rich probe in the presence of Hg2+ via T-Hg2+-T coordination chemistry.As a result,the hairpin capture probe was opened,and the ferrocene tags were close to the NPG modified electrode.Taking advantage of the amplification effect of NPG electrode for increasing the reaction sites of thiol modified capture probe,the proposed electrochemical aptasensor could detect Hg2+ quantitatively in the range of 0.01 to 5000 nM,with a detection limit as low as 0.0036 nM.Moreover,the proposed electrochemical aptasensor can be regenerated by adding cysteine and Mg2g.The aptasensor was also used to detect Hgig from real water samples,and the results showed excellent agreement with the values determined by atomic fluorescence spectrometer.This aptasensor showed a promising potential for on-site detecting Hg2+ in drinking water.The third section compared the removal behaviours of Pb2+ and Hg2+ by carbon nanotube(CNT),graphene oxide(GO),activated carbon(AC),300 ℃ biochar(BC300),and 600 ℃ biochar(BC600).The adsorption capacity of the five carbonaceous nanomaterials for 100 mg L-1 Pb2+ was in the order:GO>BC300>AC>CNT>BC600.The adsorption capacity for 2 mg L-1 Hg2+ was in the order:AC>BC300>CNT>GO>BC600.The adsorption of BC300,BC600,AC,CNT and GO was fitted well with Langmuir isotherm.The adsorption capacity were 70.6 mgg g-1、114.9 mg g-1、54.7 mg g-1、63.5 mg g-1、357.7 mg g-1 for Pb2+ and 6.2 mg g-1、2.1 mg g-1、6.0 mg g-1、4.4 mg g-1、1.7 mg g’1 for Hg2+,respectively.The primary mechanisms for Pb2+ and Hg2+ adsorption included complexation,electrostatic adsorption and ion exchange caused by surface oxygenic functional groups,and the five carbonaceous nanoporous materials have good adsorption capacity in real water samples and good reusability.This work has a guiding effect on the control of typical water pollutants.The fourth section,a novel carbonaceous nanocomposite was synthesized for the removal of SMT.The carbonaceous nanocomposites were synthesized by dip-coating straw biomass in carboxyl functionalized multi-walled carbon nanotubes solution and then pyrolyzed at 300 ℃ and 600 ℃ in the absence of air.The sorption performance of high temperature carbonaceous nanocomposite on SMT was excellent,as measured sorption distribution coefficient in the order of 103-105.5 L kg-1.Carbonaceous nanocomposites were aged either alone or mixed with soil via exposure to nutrients and soil extract(biological aging)or 80 ℃for 100 d(chemical aging).No obvious effects of harsh aging on SMT sorption were observed in the presence of soil and/or biological and chemical aging.The primary mechanisms for SMT sorption included partition caused by Van der Waals forces and adsorption caused by hydrogen bonding and π-π electron-donor-acceptor interaction.Comprehensively considering the cost,renewability,and the application to real water samples,the carbonaceous nanocomposites have potential in removal of SMT and possibly other typical water pollutants from wastewater.In section five,on the basis of section three and section four,a DEHP hydrolytic enzyme was introduced to study the effective way to radically remove typical contaminants in water.A cutinase loaded NPG-polyethyleneimine(NPG-PEI)was fabricated.The overall DEHP removal efficiency was about 92.8%,in which enzymatic hydrolysis contributed about 85.6%,and the enzymatic degradation products of DEHP were mainly non-toxic 1,3-isobenzofurandione(IBF).And the cutinase loaded NPG-PEI could hydrolyze DEHP in the presence of low concentration of Pb2+.Due to its high removal capacity,easy separation and effective reusability,cutinase loaded NPG-PEI presented excellent potential in the treatment of DEHP and other phthalate endocrine disruptors.