Study On The Membrane Preparation,Seawater Desalination And Supported Silver Catalysis Of Graphene Oxide

As a derivative of graphene,graphene oxide?GO?has attracted great interest in membrane separation field,including gas and liquid separation,due to their high chemical stability,high tensile strength and multi-functional surface chemistry.GO has a two-dimensional planar structure which similar to graphene,and sheets of GO possess numerous oxygen-containing functional groups:hydroxyl and carboxyl groups are located around the edges,whereas carbonyl and epoxide groups are in the center.Due to the plenty of oxygen-containing functional groups were introduced on the GO surface,the hydrophilicity and chemically active sites for chemical modification as well as provided.So it is quite possible that the GO membrane or modified-GO membrane is a promising membrane material for seawater desalination.Firstly,this paper makes an in-depth study of GO in the field of seawater desalination using cross-linking modification method with amine molecules,and graphene oxide composite membranes?GOCMs?were prepared on the?-Al₂O₃ tubes through vacuum filtration.Due to the introduction of the built-in molecules,three-dimensional membrane structure can be obtained,which might lead to the increasing permeation of the GOCMs owning to the reduction of the mass transferring resistance.Secondly,a series of aliphatic terminal diamines with different kinetic diameter length were selected as built-in molecules of GO to fabricate diamine modified graphene oxide nanosheets?Ax-GO?,the type of the aliphatic diamines in the GO layer was discussed,and investigated the relationship between alkyl chain length and the interlayer spacing of Ax-GO.Finally,a novel catalyst of rGO/PDA/Ag was synthesized that supported on the rGO surface using dopamine?DPA?,the prepared catalyst of rGO/PDA/Ag exhibits a fascinating catalytic activity for the hydrogenation of 4-nitrophenol and degradation performance of methylene blue?MB?at normal temperature and pressure without ultraviolet radiation.1)Two kinds of diamine molecules,including 1,4-cyclohyxanediamine?CDA?and p-phenylenediamine?pPDA?,were used as cross-linking for modification of graphene oxide?GO?nanosheets to prepare GOCMs with different interlayer spacing and hydrophilicity.From the X-ray diffraction?XRD?and water contact angles?WCA?results,the CDA-GOCM possesses the most outstanding hydrophilicity,while the pPDA-GOCM has a largest interlayer spacing and lowest WCA.Attributing to the enhancement of interlayer spacing and surface hydrophilicity after CDA modification,the CDA-GOCM shows a higher water flux(20.1 kg·m^-2·h^-11 with ion rejection of 99.9%)for desalination of 3.5 wt%seawater at 90°C,which is higher than that of GO membrane(11.4 kg·m^-2·h^-11 with ion rejection of 99.9%).However,since the hydrophilicity of the GO markedly decreases after pPDA modification,the pPDA-GOCM exhibits a lower water flux(10.7 kg·m^-2·h^-1 with ion rejection of 99.8%)at 90°C,indicating that the cross-linking molecules has great effect on the separation performance of the developed GOCMs,and hydrophilicity plays an essential role in the water flux than interlayer spacing for seawater desalination.2)A series of aliphatic terminal diamines with different kinetic diameter length were selected as built-in molecules of GO to fabricate diamine modified Ax-GO,and the relationship between alkyl chain length and the interlayer spacing of Ax-GO was investigated.Meanwhile,the type of the chains in the GO layers and the theoretical calculate method of the Ax-GO interlayer spacing were also proposed,and compared to the actual values?From XDR results?.3)Silver-nanoparticles?Ag-NPs?catalyst prepared on the surface of rGO recur to the reducibility and adhesivity of DPA.The average particle size of Ag-NPs is 50⁶0 nm,and the rGO/PDA/Ag catalyst exhibits a fascinating catalytic performance for the hydrogenation of 4-nitrophenol by NaBH₄ to 4-aminophenol.It is confirmed that the conversion efficiency reaches up to 99.1%for the hydrogenation of 4-nitrophenol by NaBH₄ with rGO/PDA/Ag catalyst in 2min at normal temperature and pressure,while the degradation efficiency of the 10 ppm MB aqueous is approximately 98.7%under a continue stirring condition for 60 min at normal temperature and pressure without ultraviolet radiation.