Two-Dimensional Layer Materials For Dye Separation And Toxic Heavy Metal Treatment

In the past century,as the rapid growth of global population,explosive development of industrialization and greater demand of energy,water scarcity has already been the serious global emerging challenge that is predicted to be worse in the future.Nanomaterial and nanotechnology have emerged as the most possible way to develop new way for high-efficiency and low-cost water treatment,and help solve the expected global water crisis.The emergence of nanomaterial also endows adsorption separation and membrane separation,as two typical techniques in water treatment,a new future.Graphene oxide(GO),as a typital derivate of graphene,has attracced more and more attention by people in adsorption and membrane separation fields.Besides,more and more new two-dimensional materials are still on the way.In this thesis,we have developed some new kinds of graphene oxide-based materials employed in dye separation field,via diging in-plane nanopore by re-oxidation and GQDs modification.2D Ti3C2Tx was also empolyed to remove toxic Cr(VI)from water.The primary contents of this thesis are summarized as follows:(1)GO nanosheets with in-plane nanopores were prepared by a re-oxidation process.Then a porous GO membrane was assembled through vacuum filtarion method,which exhibited a nice separation performance,with Evans Blue(EB)rejection of 89%and water permeance of 191 liter per hour per square meter per bar(LHM bar-1).Compored with that of pristine GO membrane,the water flux has 3-fold enhancement with a same rejection.We also have characterized the size of nanochannels within porous GO membrane by various species,as well as studied the separation mechanism.Finally,we have explored the pressure-induced separation performance and nanochannel structure change with different loading pressure.(2)Graphene quantum dots(GQDs)was employed as a stabilizer to prepare thermally reduced graphene oxide(TRG)aqueous dispersions with good stability,which was benefited to enlarge the real effective surface area and further enhanced its adsorption ability.An excellent removal capacity(497 mg g-1)and record-breaking adsorption rate(475 mg g-1 min-1 at 20 ?)were demonstrated for Rhodamine B(RhB).We have detailed studied the adsorption dynamics and adsorption thermodynamics processes.This unique absorption behavior of the modified graphene was expanded to other typical toxic aqueous aromatic dyes such as EB,Methyl Orange(MO),Malachite Green(MG)and Rose Bengal(RB),to investigate the adsorption mechanism.What is more,a unique desorption behavior of dyes was first observed when employing different solvents,which enabled the GQDs modified TRG(GQDs-TRG)to be exploited for selective extraction of dyes and recycling of the adsorbents.(3)GQDs-1-TRG membrane,with extremely high stability,was assembled by vacuum filtration method,and employed on cross-flow and dead-end modules for membrane separation.The GQDs-1-TRG membrane demonstrates an excellent long-term continuous separation performance(120 h)in cross-flow module,with a water permeance of 2000±70 LHM·bar-1 and EB rejection of 96.1 ±0.2%.The water permeance is 27 times higher than that of GO membrane and about 2 orders of magnitude higher than those of commercial filtration membranes with similar rejection.Based on dead-end setup,we also studied the impacts of surface water flow,loading pressure and membrane thickness on separation performance.In addition,we conducted molecular dynamic simulations to confirm the significant effect of pressure on membrane selectivity.On gravity-driven separation system,under 10-cm liquid column,the GQDs-1-TRG membrane(2.34 ?m thickness and 12.56 cm2 effective area)exhibits a water permeance of 800±30 LHM·bar-1,EB rejection above 95.2±0.4%,and durability more than 7-month operation.(4)2D Ti3C2Tx nanosheets are fabricated by etching bulk Ti3AlC2 powders in HF solution and delaminating ultrasonically,which exhibit excellent removal capacity for toxic Cr(?)from water(250 mg g-1),due to their high surface area,well dispersibility,and reductivity.The residual concentration of Cr(?)within treated water is less than 5 ppb,far below the concentration(0.05 ppm)of Cr(?)in the drinking water standard recommended by the World Health Organization(WHOs).We discuss the effect of HF concentration on Cr(?)removal ability of 2D Ti3C2Tx nanosheets.Then,we analyst the Cr(?)removal mechanism of 2D Ti3C2Tx nanosheets.In addition,we exploit a new method to fabricate nano-sized noble particles on the furface of 2D Ti3C2Tx nanosheets,which holds the potential to be used in catalysis field.