Honeycomb-like Nanosheet Array Ailver Catalysts For Highly Efficient Reduction Of 4-Nitrophenol

Green chemistry has aroused more and more concern because of the increasingly serious.environmental pollution.4-nitrophenol(4-NP)is a notorious industrial pollutant exhibiting high solubility and stability in water.The reduction of nitro group to amino group over noble metal NPs in the presence of NaBH4 is the most efficient,green and economical route to dispose nitro-compounds.Compared with other precious metals such as gold(Au),palladium(Pd)and platinum(Pt),silver(Ag)is relatively cheap,non-toxic and environmentally friendly.Therefore,Ag-based catalysts have attracted more and more attention.Herein,a series of honeycomb-like nanosheet array Ag catalysts were prepared via a simple and green self-redox process and by using glutathione-protected Ag nanocluster precursor method,the catalytic performance for the reduction of 4-NP and structure-activity relationship are studied.A series of honeycomb-like nanosheet array catalysts Agx/CoAl-LDH/rGO(x=0.045,0.12,0.43,0.86,2.56 wt%,Ag loading in wt%(ICP),LDH:layered double hydroxide,rGO:reduced graphene oxide),as well as Ag0.11/NiAl-LDH/rGO and Ag0.14/MgAl-LDH/rGO were prepared by a simple self-redox process,in which Ag+is combined with-OH groups in pre-prepared MAl-LDH/rGO(M=Co,Ni,Mg)hybrid supports,thus can be easily in-situ reduced to Ag nanoparticles(NPs)uniformly bonded to the surface of LDH nanosheets.The series of laminates containing Co catalysts Agx/CoAl-LDH/rGO show high activity for selective reduction of 4-nitrophenol,and the Ag0.12/CoAl-LDH/rGO shows the highest TOF value(5393 h-1).Then,the laminates containing Ni catalyst Ag0.11/NiAl-LDH/rGO exhibits even higher activity(6122 h-1)than Ag0.12/CoAl-LDH/rG0 and Ag0.14/MgAl-LDH/rGO.The excellent activity of Ag0.11/NiAl-LDH/rGO can be ascribed to its highly dispersed Ag NPs with the smallest size of-3.7 nm with high dispersion characteristics,obvious ?-? stacking effect between substrate and catalyst,unique nanosheet array-like morphology and the strongest Ag—NiAl-LDH-rGO three-phase synergistic effect.The catalyst Ag0.12/CoAl-LDH/rGO also shows excellent reduction activity for 2-NP 3-NP,2,4-dinitrotoluene and organic dyes(methyl orange,rhodamine B,acid orange).Moreover,Ag0.12/CoAl-LDH/rGO can cycle 15 times and activity will not be significantly reduced,giving the present catalysts long-term stability.Therefore,the preparation of the above mentioned Agx/MAl-LDH/rGO(M=Co,Ni,Mg)catalysts provide a useful platform for obtaining simple and environmentally friendly noble metal nanocatalysts,which will greatly improve the efficiency of various catalytic reduction process.Water-soluble silver clusters Ag:SG protected by glutathione(GSH)ligand were synthesized by one-pot method and then separated by polyacrylamide gel electrophoresis to obtain the Ag nanoclusters with the size of 1.54 ± 0.4 nm approximately composed of 110-120 Ag atoms,and then a series of Ag NCs/NiAl-LDH/rGO-x(x=0.085,0.15,0.82 wt%(ICP))catalysts were prepared by electrostatic adsorption on NiAl-LDH/rGO hybrid support.Three Ag NCs/NiAl-LDH/rGO-x catalysts show excellent higher activity for the reduction of 4-NP and the Ag NCs/NiAl-LDH/rGO-0.15 shows the highest TOF value(6916 h-1),can be attributed to its ultrasmall Ag NCs(-1.6 nm)and unique honeycomb-like nanoarray morphology.