Study On Adsorption And Removal Of Various Pollutants In Graphite By Graphite

Graphene is a novel 2-dimensional polymeric carbon material. Graphene and its chemical precursor, graphene oxide(GO) have gained wide research concern in water treatment field due to its high surface area and surface reactivity and is considered as a fine potential raw material for adsorbents. In this study, the relationship between the surface structure of graphene and its adsorption performance was systematically studied and a number of graphene-based adsorbents were prepared.It is important to have a comprehensive understanding to the fundamental characteristics of a material prior to its modification and practical application. Thus we studied the structure-performance relationship of GO in the beginning. In the structure-performance study, a series of GOs were prepared and the effect of their surface structure to their methylene blue (MB) and aromatic organic compounds (AOC) was studied. According to the results, further oxidation greatly improves the adsorption capacity of methylene blue. This is due to the rise in oxygen containing groups and the increase in surface area. The adsorption behavior of MB was also affected by the surface structure of GO, the adsorption changed from multilayer to monolayer as the oxidation degree went up. Compared with MB, the predominant interactions in AOC adsorption are hydrophobic ones, and the adsorption is pH-independent unless there is acidic/basic groups in the AOC molecule. Based on the adsorption data of the AOCs, a semiquantitative model was proposed and the data fitted the model well. The structure-performance study indicates that GO is itself a fine adsorbent for hydrophilic pollutants. Increasing its oxidation degree would improve its uptake for these pollutants, while in turn inhibits its uptake for hydrophobic pollutants. Besides, GO is difficult to separate after adsorption, which needs to be dealt with in practical applications.Following the structure-performance study we prepared a few graphene-based adsorbents and studied their adsorption behaviors to different pollutants. Firstly, to solve the separability problem of GO, a magnetic GO composite (MGO) was prepared using co-precipitation method. It was characterized and its removal performance for iron and manganese was assessed. The characterization results showed that the GO sheets roughly retained their structure in MGO and MGO can be efficiently separated from water by external magnetic field. The adsorption results indicated that MGO can completely and rapidly remove iron and manganese from micro-polluted water samples. And the saturate uptake of MGO is fine among various adsorbents. In a binary system of iron and manganese, MGO can remove both of them in low concentrations and in high concentrations MGO can selectively remove iron. After adsorption, iron/manganese loaded MGO can be reused as an adsorbent for F", and the F" uptake is satisfactory. Overall, MGO is suitable for fast and deep treatment for micro-polluted effluents of iron and manganese.For organic pollutants, a magnetic reduced graphene oxide composite (MRGO) was prepared via co-precipitation and green reduction. The structure of the material and its adsorption performance for chlorophenols were studied. According to the results, the carbon sheets of MRGO were effectively reduced and the magnetic nanoparticles were successfully composited. The aggregation of the reduced carbon sheets was also inhibited by the magnetic nanoparticles on their surface. MRGO showed better removal efficiency to chlorophenols with more chlorine substitution and higher molecular weight. The adsorption is achieved by π-π interaction and hydrophobic effect. And the uptake falls with increasing solution pH. The isothermal adsorption behavior of chlorophenol on MRGO followed Freundlich model, which is heterogeneous and multilayer. And kinetically there may be multiple mechanisms. After adsorption MRGO can be regenerated and recycled with little uptake loss.As the aforementioned adsorbents are for specific pollutants, we then prepared a versatile amphoteric adsorbent from GO and chitosan (CS-GO). The adsorbent combines the advantages of both and covers the limitations. It has a pH-tunable surface charge. CS-GO was used for removal for multiple pollutants with different charges, namely methyl orange (MO), Cr(VI), MB and Cu(II). According to the results, CS-GO showed better affinity for MO and MB. The uptakes of anionic pollutants fell with increasing pH while those of cationic pollutants rose with pH. The isothermal adsorption experiments indicated that pollutants that are adsorbed onto either one component of CS-GO follow Langmuir model, and those are adsorbed onto both components of CS-GO follow Freundlich model. The kinetic data of the pollutants showed consistency with both pseudo-first order model and pseudo-second order model, indicating dual kinetic mechanism. In binary system of the cationic/anionic pollutants, competition mainly took place on ionic sites and the uptakes of dyes were a little higher. Overall CS-GO is a versatile adsorbent and capable for removal of various pollutants.In summary, graphene-based materials show fine removal efficiency to multiple pollutants and have great application potential. Although there are still issues to solve when putting it into practical use, such as its cost, considering that the field of graphene is just at its beginning and its cost problem mainly originates from its synthetic procedure rather than rarity. These problems can be overcome. And we are optimistic to the future of graphene-based materials. We sincerely hope that this study can do some help to the development of graphene-based materials.