Design And Properties Of Asymmetric Nanomaterials Based On Interface-Oriented Etching Of Silver And Tellurium Nanomaterials

Asymmetric inorganic nanomaterials,which possess asymmetric shape and/or compositions on their opposite sides,have attracted intensitive attention in the field of catalysis,energy,sensing,optoelectronic devices,and biological imaging because of their unique physical and chemical properties.The properties of asymmetric inorganic nanomaterials are closely linked to their morphologies and ingredients.Thus,developing morphology-and ingredient-controlled strategy for preparing asymmetric inorganic nanomaterials has become one of the central topics.To date,there are various methods for preparation of asymmetric nanoparticles,which,however,lack universality and controllability,only suitable for some kinds of specific matters,and the product yields are extremely low.In terms of this concept,this dissertation employs interface-confinement effects to develop a universal method for designing asymmetric nanoparticles-by using the feature of interfacial nanoparticles existing in two different phases,we successfully achieved asymmetrical etching of interfacial nanoparticles or deposition of another material on one side of interfacial nanoparticles with the help of galvanic replacement reaction,obtained a series of metal–metal,metal–semiconductor asymmetric nanomaterials with unique morphologies,and studied the properties(e.g.,photoelectric response and electrocatalysis)of the resulting asymmetric nanostructures.The contents of the dissertation are summarized as follows:(1)By employing oil/water interfacial Ag nanoparticles(nanowires and nanocubes)with different morphologies and sizes as etching objects and Au Cl₄^-as the etchant,the etching behavior of nanoparticles at the oil/water interface is systematically studied,fabricating a series of asymmetric Ag Au alloy inorganic nanoparticles with unique morphology and structure,and clarifying the similarities and differences of etching reaction processes between oil/water and air/water interfacial nanoparticles.Various techniques are employed to characterize t he morphology and structure of the products.The results show that the formation of the“nanoring”and“cowboy hat”-like Ag Au alloy nanoparticles at the oil/water interface can be explained with“bi-interfacial layers mass transfer mechanism”that we previously proposed when studied the etching of air/water interfacial nanoparticles.This study not only improves“bi-interfacial layers mass transfer mechanism”by combining oil/water and air/water interfacial etching,also provides new insights for constructing other asymmetric inorganic nanomaterials on the oil/water interface.(2)By employing Ag nanowires and Au Cl₄^-as the scarified matter and the etchant,respectively,ultra-thin Ag Au alloy nanotroughs are fabricated by the water/air interface-confined asymmetric etching,and successfully transformed into Au–Ag₂S metal-semiconductor asymmetric nanomaterials by one-step vulcanization treatment.As-prepared one-dimensional(1D)Au/Ag₂S shows a core/shell heterostructure and still remains a trough-like morphology as original Ag Au nanotrough.Also,Au/Ag₂S asymmetrical heterostructure shows enhanced absorption in the visible-near-infrared region owing to the local surface plasmon resonance(LSPR)effect of Au and the 1D morphological feature,exhibiting outstanding photoelectrical sensitivity.Au/Ag₂S asymmetrical heterostructure as a photoelectrically active material,compared with pure Ag₂S,generates much larger photocurrent signal and has a lower charge transfer resistance.The photoelectrochemical biosensor based on Au–Ag₂S asymmetrical heterostructure shows excellent analytical performance for?-thrombin(TB):a broad linear response ranging from 1.00 to 10.00 pmol L^-1 and a low detection limit of 0.67 pmol L^-1.This study provides a new preparation method for designing metal-semiconductor photoelectric active materials.(3)By employing Ag nanowires as a scarified template and combining the water/air interface-confined effect with galvanic replacement reaction,we develop a novel strategy for in-situ construction of two-dimensional(2D)metal-semiconductor(Ag-Ag₂S)asymmetric nanostructure at the water/air interface for the study of photoelectric properties.The results show that the formation of 2D asymmetric Ag-Ag₂S nanowire film may be attributed to the interface-confined vulcanization of Ag nanowires exposed in the water phase,and in contrast,the side of Ag nanowire open to the air is well preserved.As-formed asymmetric Ag-Ag₂S nanostructure can be directly transferred to the electrode surface for the measurement of photoelectrical property,avoiding the aggregation of nanoparticles caused by the drip-coating method,which greatly improves the photoelectric conversion efficiency.Because of the asymmetric property of ingredients on the oppisite sides,the top and bottom sides of Ag-Ag₂S film show different magnitude of photocurrent response:the bottom side shows much larger photocurrent than the top side.The photoelectrochemica biosensor based on Ag–Ag₂S asymmetric nanostructure shows practical analytical performance for micro RNA-375 with a broad linear response ranging from 0.05-100 pmol L^-1 and a low detection limit of 7.6 fmol L^-1.This study opens up a new avernue and provides new insights for the in-situ construction of other metal-semiconductor photoelectric active materials.(4)To extend the interface-confined galvanic replacement reaction to design other asymmetric nanomaterials other than Ag,we successfully fabricate a three-dimensional(3D)highly ordered“self-supporting”Pt₁₆Te hierarchical nanostructure by employing Te nanowires as sacrificed templates and H₂Pt Cl₆ as the etchant and investigate its electrooxidation capability towards methanol.Pt₁₆Te hierarchical nanostructure has an asymmetrical architecture composed of side-by-side nanotroughs and nanopillars,and nanopillars are perpendicular to nanotroughs.Pt ₁₆Te hierarchical nanostructure has a“self-supported”feature and,when directly used as the catalyst for methanol electrooxidation,exhibits superior catalytic activity(>4times larger in mass activity than commercial Pt/C in either acidic or basic medium)and long-term durability(after 7 h cycling oxidation,more than 50%specific activity remains whereas Pt/C only remains 25%specific activity in acidic medium and loses all activity in basic medium).The Pt₁₆Te nanostructure integrates a variety of merits helpful for methanol electrooxidation,such as 3D,highly-ordered,“self-supporting”and active-site-abundant.This study demonstrates that interface-confined design of asymmetrical nanostructures can be achieved for other possible material besides Ag.(5)To further improve the electrocatalytic activity of Pt Te towards ethanol,a step-by-step strategy is proposed by etching Te nanowires at oil/water interface with Pt Cl₆^2-and subsequently,after evaporation of the oil,continuously etching the interfacial product at air/water interface with Au Cl ₄^-.By employing this strategy,a series of morphology-and ingredient-controlled Au Pt Te asymmetric nanowires are designed:the Pt and Au components are enriched on the top and bottom sides,respectively;additionally,by optimizing preparation conditions,a Au Pt Te asymmetric“self-supporting”nanofilm is also fabricated.The formation of these unique asymmetric structures can be attributed to the asymmetric etching reaction between Au Cl₄^-and as-formed Pt or Te.By taking Au Pt Te nanowires with different Au content as an example,the electrocatalytic performance of Au Pt Te nanowires is well studied.Because of its asymmetric geometric effect and the electronic synergy effect,Au Pt Te nanowires show much better electrocatalytic activity and stability towards ethanol electrooxidation than commercial Pt/C catalyst.The catalytic performance of Au Pt Te nanowires is closely linked with its morphology and compositions:Au₅₅Pt₃₄Te₁₁nanowire shows the largest specific activity(108 m A cm^-2),?49 times that of commercial Pt/C(2.2 m A cm^-2);Au₇₅Pt₂₀Te₅ nanowire shows the largest mass activity of?11.9 A mg _Pt^-1,?17 times that of commercial Pt/C(0.7 A mg _Pt^-1).After continuous electrocatalytic oxidation of ethanol for 4000 s,the mass activity of Au₇₅Pt₂₀Te₅nanowire is still maintained 170 m A mg _Pt^-1 while commercial Pt/C almost loses all activity.In addition,constructing a“self-supporting”asymmetric nanoarray with high mechanical strength can further improve its catalytic durability.This study provides a new avernue for constructing other novel multi-metal asymmetric nanostructures at phase interfaces.