Synthesis Of Graphene Nanocomposites And Their Adsorption And Photocatalytic Behaviors Study

Graphene is a two-dimensional carbon material with single layer of hexagonal carbon atoms and it owns the ideal lattice structure and unique optical,electrical,thermal and mechanical properties,which can be applied widely in the field of optoelectronic,energy storage devices,biomedical and environmental treatment.The graphene based materials mainly include graphene oxide?GO?,reduced graphene oxide?rGO?,functionalization of graphene and graphene based composites,which are primarily used in the adsorption and catalysis process of the environmental field.Graphene based materials as the noval adsorbents can effectively remove organic compounds and metal ions from wastewater,but they are very easy to agglomerate,leading to the sharp decline of specific surface area,and thus resulting to the decrease of the adsorption performance.As a zero band gap semiconductor material,graphene has the excellent electron transmission ability,and it can separate the charge effectively.Furthermore,graphene has the good adsorption ability to organic pollutants because of its large specific surface area.Therefore,graphene is widely considered to be a high efficiency carrier in photocatalytic reaction.Based on the structure and properties of graphene,and its application characteristics in the field of adsorption and photocatalysis,graphene was tried to be used as an adsorbent in the treatment of simulated industrial wastewater,and these studies can provide theoretical research foundation for the graphene materials in the practical water treatment application.Considering the industrialized applications need huge amount of graphene materials,we only can use the chemical synthesis methods to prepare.So GO,rGO and GN prepared by chemical methods were used as the effective adsorbents in this research.In order to avoid the agglomeration of graphene materials in engineering application,the surfactant cetyltrimethyl ammonium bromide?CTAB?modified GO,hydroxo aluminum pillared rGO,nanoscale zero-valent iron?NZVI?loaded GO,GO combine with Bi₂₅FeO₄₀ or metal-organic framework were synthesized and used as adsorbents or photocatalysts,and to obtain possible industrial applications of graphene-based wastewater treatment materials.Firstly,considering to improve the water soluble ability of rGO and avoiding the agglomeration phenomenon,water-soluble CTAB was used to modify GO,and modified GO was use towards hexavalent chromium adsorption.Secondly,NZVI was used to load with graphene to increase the active sites,and then used CTAB to modify NZVI-GN to improve its dispersion in an aqueous solution,and studied the composites on the adsorption of para-nitrochlorobenzene.Thirdly,starting from the idea of preventing the reunion of rGO,hydroxo aluminum was used to pillar rGO to enhance the adsorption capacity,and then used different surfactants to modify NZVI-GN to obtain the rGO-based adsorbent material with stable structure,and it possesses high removal performance toward Congo Red.Fourthly,while many researchers have concentrated on the clean-up of heavy metals through adsorption,relatively little attention has been paid to the further utilization of the saturated adsorbent once it has done its clean-up job.To reduce the cost of raw materials,we used the low cost of sawdust and graphene to prepare graphene composites,and used as an adsorbent for nickel ions and then transform them into metal oxide particles by reduction that can catalyze degradation of phenol.So the polluters,metal ions,are not only removed from the polluted water but also turn to the useful catalyst.Finally,starting from the idea of eliminating the toxicity of pollutants after adsorption enrichment and recyclable recycling,Bi₂₅FeO₄₀,MIL-88?Fe?or MIL-101 and Pd was loaded on porous GO,respectively.Results indicate the three different composites had the excellent photocatalytic properties toward specific contaminants removal,and most importantly,the composite can be recycled.The detailed contents are described as follows:?1?The introduction of CTAB groups to the GN surface can improve its colloidal stability and significantly increase the adsorption capacity of GN for heavy metal removal.The adsorption capacity varies with different pH values of the solution.The optimal pH for the removal of Cr?VI?is about 2.The highest adsorption capacity of CTAB-GN for Cr?VI?is found to be 21.57 mg/g at 293 K.It is found in this study that the Cr?VI?adsorption processes have reached their equilibrium state in about 40 min,which is faster than most of carbon-based adsorbents can do.?2?We use NZVI to load with the grapheme to increase the active sites,and in order to improve the stability of graphene in an aqueous solution,we then use CTAB to modified graphene after loaded of NZVI.We investigated its adsorption capacity for p-NCB from aqueous solution.We have shown that C-N-GN can act as the good adsorbent for p-NCB from aqueous solutions.The highest adsorption capacity of C-N-GN for p-NCB is found to be105.15 mg/g at 293 K.It is found in this study that the p-NCB adsorption process reaches its equilibrium state in about 2 h.Competitive adsorption experiments show that HA has a strong suppression effect on p-NCB uptake.?3?The surfactant modified hydroxo aluminum/graphene composites with highly efficient adsorption performance for CR have been successfully produced.The resulting composites combined both the features of hydroxo aluminum and graphene,and thus exhibited extraordinary removal capacity and fast adsorption rates for CR dye removal inwater,which are due to the electrostatic attraction between the surface oxygen containing groups and CR and the ?-? interactions between the CR molecules and the aromatic rings of graphene.The adsorption capacity varies with different pH values of the solution.The optimal pH for the removal of CR is about 3.The optimal dosage of adsorbent is 1 g/L.The as-prepared adsorbents all have good reusability,and the optimal eluent buffer is ethanol,NaOH,and HCl,respectively.?4?We use the low cost cinnamomum camphora sawdust?CCS?to load with the graphene,and in order to improve the stability of graphene in an aqueous solution,we then use carboxymethylcellulose?CMC?as a stabilizer to modified graphene after loaded of CCS.We investigated its adsorption capacity for nickel ions from aqueous solution.The graphene oxide/sawdust composite showed excellent adsorption capacity for nickel ions.The composite was used as an adsorbent for nickel ions and then transform them into metal oxide particles by reduction that can catalyze degradation of phenol.So the polluters,metal ions,are not only removed from the polluted water but also turn to the useful catalyst.The catalyst was prepared using sodium borohydride as the reducing agent,after a saturated adsorption of nickel ions from water was achieved.The catalyst significantly improved the removal efficiency of phenol at pH 10 with a dosage of 2 g/L.The experimental results demonstrate that the degradation of phenol is an endothermic reaction.The maximum adsorption capacity of phenol was 158.98 mg/g.The degradation process is very fast in the beginning 10 minutes and reached equilibrium within 30 minutes.?5?The composite based on the Bi₂₅FeO₄₀ and rGO was synthesized by the one-step reduction method and can further improve the photocatalytic acitivity for phenol and p-chlorophenol under visible light.The performance of photocatalytic degradation of phenol and p-chlorophenol under visible light of Bi₂₅FeO₄₀/rGO composites was investigated.The results showed that the photocatalytic degradation rate of phenol and p-chlorophenol by Bi₂₅FeO₄₀/rGO composites was higher than Bi₂₅FeO₄₀ and rGO.The photocatalytic efficiency of rGO,Bi₂₅FeO₄₀,Bi₂₅FeO₄₀/rGO for phenol was 83.79%,95.23% and 100% at 40 min of exposure,respectively.The photocatalytic efficiency of rGO,Bi₂₅FeO₄₀,Bi₂₅FeO₄₀/rGO for p-chlorophenol was 69.06%,83.97% and 100% at 60 min of exposure,respectively.On the one hand,Bi₂₅FeO₄₀ can prevent the reunion of rGO and improve the adsorption capacity of phenol and p-chlorophenol.On the other hand,it can photocatalytic degradate of phenol and p-chlorophenol.Furthermore,the Bi₂₅FeO₄₀/rGO composite can be directly recycled by magnetic separation.?6?The porous graphene oxide is as the carrier,loaded with metal organic frameworkMIL-88?Fe?,and to build a stable performance,enhanced catalytic activity of MIL-88?Fe?loaded with graphene oxide composites.We studied the structure morphology of MIL-88?Fe?@GO composite,and assessed the photocatalytic properties of methylene blue and rhodamine B.The MIL-88?Fe?@GO composites demonstrate the fast MB and RB degradation performance with an almost complete degradation of MB and RB within 20 and 30 min,respectively.Furthermore,the as-prepared MIL-88?Fe?@GO composites could improve the catalytic efficiency greatly for the degradation of MB and RB than MIL-88?Fe?and GO.GO does not directly involved in the process of photocatalytic degradation,while the photocatalytic activity enhancement of MIL-88?Fe?@GO composites can be attributed to the combination of the chemical bonds between GO and MIL-88?Fe?,thus improving the separation efficiency of electrons and holes.On the one hand,MIL-88?Fe?can prevent the reunion of GO and improve the adsorption capacity of MB and RB.On the other hand,it can photocatalytic degradate of MB and RB.?7?The metals?chromium?organic framework MIL-101 and palladium nanoparticle?Pd?simultaneously loaded with graphene composite?Pd/MIL-101/rGO?was prepared by hydrothermal or solvent thermal synthesis method.The composite owns a stable structure and enhanced photocatalytic activity.And we evaluated the photocatalytic performance to triphenylmethane dyes,such as brilliant green?BG?and acid fuchsin?AF?.The Pd/MIL-101/rGO photocatalyst demonstrated the fast BG and AF degradation performance with an almost complete degradation of BG and AF within 15 and 20 min,respectively.Furthermore,the as prepared Pd/MIL-101/rGO photocatalyst showed improved photocatalytic efficiency greatly for degradation of BG and AF than MIL-101 and MIL-101/rGO.Cyclic experiments demonstrated that the photocatalyst showed good reusability and stability for the dye degradation.This study showed the as-prepared Pd/ MIL-101/rGO photocatalyst could be utilized as the efficient photocatalyst for the environmental cleanup.