Construction Of Two-dimensional Nano-enzyme-like Active Materials With Noble Metal Functionalities And Their Optical/electrical Sensing Applications

Environmental pollution has become a serious obstacle to the sustainable development of world economy and human society.In our country,a large number of organic and inorganic pollutants were poured unscrupulously,which have been seriously threatened the safety of soil soil,water,food and the human physical and mental health as well.In order to efficiently monitor organic and inorganic pollutants,various analytical methods have been developed.Among all the detection methods developed,colorimetric and electrochemical analyses are more practical due to their naked-eye monitoring or remarkable sensitivity.However,most of the traditional colorimetric methods possessed poor accuracy and the electrochemical analyses could not visually detect the analytes.In this work,some two-dimensional nanozymes will be proposed,in which 2D Ni/Co oxide or graphene substrates were modified by noble metals nano particles.It was expected the target 2D nanozymes with high catalytic activities could be applied as dual colorimetric and electrochemical sensing platforms for the detection of environmental pollutions with ultra-high sensitivity and low detection limits.In this dissertation,the main studies are illustrated as follows:1.2D Co₃O₄ stabilizing Rh nano composites with synergetic-reinforcing oxidase-like activity for visual detection of urea and p-aminophenol:In order to expand the application prospect of nanoenzyme,2D Co₃O₄ supporting Rh nanoparticles(2D Co₃O₄@Rh NC)were designed through one-step surfactant-aided coreduction.Due to synergetic-reinforcing effect between 2D Co₃O₄ NS and Rh NPs,2D Co₃O₄@Rh NC exhibited excellent oxidase mimic activity in a wide temperature range from 20 to 60 ?.It could oxidize3,3',5,5'-tetramethylbanzidine(TMB)to a blue oxide with Michaelis-Menten constant(K_m)and V_max value of 0.018 m M and 6.45×10^–8 M·s^–1,respectively.Importantly,2D Co₃O₄@Rh NC could be applied to detect urea and p-aminophenol in environmental water,soil and urine samples,accompanying with differentiable color changes.Under the optimized conditions,it exhibited a low detection limits(0.68?M for p-Ap and 1.1?M for urea)and reliable recoveries(96.0?105.8%).Moreover,oxidase-like behavior and the different reaction mechanisms of 2D Co₃O₄@Rh NC sense urea and p-Ap were investigated in detail.2.2D NiCo₂O₄ supported Pd nano composites with controllable morphorgies and adjustable enzymatic properties for Hg²⁺detection with different chromogenic effects:To adjust enzyme-like properties,three 2D NiCo₂O₄ nanosheets supported Pd nano composites(Pd@NiCo₂O₄)with controllable morphologies were constructed with the aide of surfactants(CTAB,PVP and SDS),i.e.2D NiCo₂O₄ supported Pd NPs(CTAB-Pd@NiCo₂O₄ NS),2D NiCo₂O₄ stabilizing Pd Ths(PVP-Pd@NiCo₂O₄ NS)and 3D porous fingerprint-shaped NiCo₂O₄supported Pd NPs(SDS-Pd@NiCo₂O₄ NS).After their structure and enzymic activities were investigated,it was noted to find that CTAB-Pd@NiCo₂O₄ and PVP-Pd@NiCo₂O₄ both possessed dual-enzyme mimetic activity,i.e.,oxidase-like and peroxidase-like activities.However,SDS-Pd@NiCo₂O₄ NS only possessed excellent oxidase mimic activity with an obvious bathochromic shift for oxTMB from 652 nm to 682 nm.Importantly,PVP-Pd@NiCo₂O₄NS and SDS-Pd@NiCo₂O₄ NS could sense Hg²⁺with different color changes,which enlarged greatly the visuality.Under the optimized conditions,the present PVP-Pd@NiCo₂O₄ NS and SDS-Pd@NiCo₂O₄ NS systems were successfully applied for colorimetric assay of Hg²⁺in some environmental water and biomedical samples,with low LOD(9.5×10^-10 M and 1.2×10^-8 M)and satisfactory R.S.D.(3.7%and 3.4%).3 2D graphene oxide stabilized nano Ag₂S composite as Hg²⁺-stimulated oxidase for dual colorimetric and electrochemical detection of Hg²⁺:In order to enhance sensitivity and selectivity of visual detection of Hg²⁺,2D graphene oxide stabilized nano Ag₂S(Ag₂S@GO)was synthesized by one-pot homogeneous precipitation.The properties of Ag₂S@GO were investigated in detail,such as electrochemical performance,enzymatic catalytic activity,reaction mechanisms and naked-eye responses to Hg²⁺.The results showed that Ag₂S@GO possessed excellent Hg²⁺-stimulated oxidase-like activity to oxidize TMB to blue oxTMB accompanying with an obvious chromogenic effect.Under the optimal conditions,Ag₂S@GO was successfully applied to visually sense Hg²⁺in some real environmental samples with a nM level detection limit of 9.8×10^–9 M and an excellent standard deviation less than 3.1%.Importantly,Ag₂S@GO also expressed synergistic-enhanced electrochemical properties for the specific detection of Hg²⁺with a pM-level detection limit of 8.63×10^-12 M and a wide linear range among 0.0 to 290.0×10^-10 M.Once applied for sensing Hg²⁺in really environmental water samples and fruit juice samples,the recoveries were between 95.5%and 105.7%.This work will provide a potential perspective in constructing and applying multifunctional photoelectric sensors in future.