Preparation And Properties Of Hybrids Of Black Phosphorus Nanosheets And Fullerene C₆₀

Black phosphorus(BP)as an emerging two-dimensional(2D)material has been attracting increasing interest owing to its anisotropic 2D layered structure with tunable bandgap in the range of 0.3-2.0 eV and high carrier mobility,rendering potential applications of BP in many fields,including energy storage,catalysis,solar cells,and biosensing.The experimental study of the activity of BP for photocatalytic hydrogen evolution has not been reported although it has been theoretically predicted in 2014.The key issue hindering the application of BP is that BP,especially the few-layered black phosphorus,can be easily oxidized under ambient condition.While,fullerene represented by C60 has high stability in water,oxygen,and air environments,and has a unique molecular structure,electronic structure,and physicochemical properties.That If C60 is hybridized with the black phosphor nanosheets,not only the stability of the black phosphor nanosheets can be improved,but also the black phosphor-fullerene hybrids will may shows more excellent properties.This dissertation is aimed at synthesizing novel BP nanosheet-fullerene hybrid materials,focused on developing new methods to prepare BP nanosheet-fullerene hybrid materials in which fullerene C60 attaches onto BP nanosheets via covalent bonding.We further studied the properties including photocatalytic hydrogen evolution activity of BP nanosheet-fullerene hybrid materials.We have carried out the following works:(1)We developed a new method to prepare few-layer BP nanosheets via mechanochemical route,and demonstrated the visible light photocatalytic H2 evolution activity of BP nanosheets for the frst time.Using bulk BP as the starting material,we employed a facile and environmentally friendly solid-state ball-milling method in the existence of a LiOH additive,and succeeded in preparing few-layer BP nanosheets(abbreviated as BP-BM).We proposed that the chemical structure of BP-BM as few-layer BP nanosheets with edges functionalized by hydroxyl groups based on a series of spectroscopic characterizations.Furthermore,we studied the photocatalytic hydrogen evolution activity of the as-prepared BP-BM,and obtained a H2 evolution rate of 512μmol h-1 g-1 without using any cocatalyst,which is～18 times higher than that of the bulk BP.On the basis of a series of spectroscopic and morphological characterizations,such a significantly enhanced photocatalytic H2 evolution activity is primarily attributed to the formation of few-layer BP nanosheets,which shifts the conduction band(CB)negatively along with a positive shift of the valence band(VB)with respect to bulk BP.The consequent increased bandgap and the positive shift of VB of BP-BM render the enhanced electron reduction ability and inhibition of the electron-hole recombination.(2)Using bulk BP and pure C60 as the starting materials,we employed a solid-state ball-milling method without using any additive,and succeeded in preparing a novel BP nanosheet-C60 hybrid(abbreviated as BP-C60)in which C60 molecules covalently attach onto the edges of BP nanosheets.Based on a series of morphological and spectral characterizations,we proposed that C60 molecules selectively attach onto the edges of BP nanosheets via P-C covalent bonds.In order to verify whether the edge-selective functionalization by C60 can stabilize BP nanosheets,we investigated the ambient stability of BP-C60 hybrid in water and compared it with that of BP-BM,and found that the ambient stability of BP-C60 hybrid in water was dramatically improved by a factor of 4.6 relative to that of BP-BM.We further applied the BP-C60 hybrid inphotoelectrochemical cell and photocatalytic dye degradation,and found that the BP-C60 hybrid exhibited significantly enhanced photoelectrochemical response and photocatalytic activity relative to those of BP-BM and a physical mixture of BP-BM and C60.The reason is that,owning to the strong electron-accepting ability of C60,involvement of C60 leads to the photoinduced electron transfer from BP to C60 within the BP-C60 hybrid,which can inhibit the recombination of charge carriers and consequently enhance not only the photoelectric conversion property but also the photocatalytic activity of BP.(3)We designed and synthesized another novel BP nanosheet-C60 hybrid in which C60 molecules attach onto the surface of BP nanosheets via an aryl bridge(abbreviated as BP-Azide-C60).First,we synthesized an aryl-functionalized BP nanosheet(abbreviated as BP-Azide)by reacting BP nanosheets with 4-azidobenzoic acid,in which carboxyl groups were grafted onto BP nanosheets.We then employed an esterification reaction between BP-Azide and C60 fullerols(C60(OH)x)to synthesizing BP-Azide-C60.We confirmed the chemical structure of BP-Azide-C60 by Raman,FT-IR and XPS spectroscopic characterizations.