Preparation And Properties Of Nano-Carbon/MOFs Composite Membrane Assisted By Graphene Dispersant

This article designs and synthesizes a highly reactive graphene dispersant（NSi DEA）based on adenine molecules.It can not only disperse various nano carbon materials at high concentrations in water at low dosage,but also contains multiple highly reactive silicon hydroxyl groups,which can undergo crosslinking reactions with other substances.With the help of the dispersant,graphene（GR）and metal organic frameworks（MOFs）nanoparticles were successfully uniformly compounded,and cross-linked GR/MOFs composite films were obtained.The film not only has good mechanical strength,but also retains the structural characteristics of MOFs with high porosity and high active site,which overcomes the shortcomings of powder MOFs such as poor convenience in practical applications,separation and recovery difficulties.The application of this thin film in ion adsorption separation showed good selectivity and large adsorption capacity for Mo（Ⅵ）ions.At the same time,the composite thin film also showed good cycling stability performance,which has good practical application prospects.The main research content and results of the paper are as follows:1.A highly reactive graphene dispersant with adenine molecules as the conjugated center and multiple silicon hydroxyl groups was synthesized.First,adenine is taken as the parent,and the reactive nitrogen species atom in its molecule is used to carry out substitution reaction with epichlorohydrin（ECH）,then it reacts with excess ethylene diamine（EDA）,9 times molar weight of 3 glycidyl ether oxypropyl trimethoxysilane（GPTMS）in turn,and finally hydrolyzes under acidic conditions to obtain the dispersant NSi DEA with a large number of highly reactive active silanol groups（-Si-OH）at the molecular end.The molecular synthesis method is simple.It was applied to the dispersion of nano carbon materials in water and ethanol.Through SEM,Zeta potential,dynamic light scattering（DLS）and other characterization results,it was found that the dispersant had good dispersion and stability effects on GR,industrial graphite oxide（TNIRGO）,carbon nanotubes（MWCNTs）,etc.Under the condition of a 1:1 mass ratio of dispersant and carbon material,the concentrations of the three in water can reach5 mg mL^-1,12 mg mL^-1,and 10 mg mL^-1,respectively.Further analysis by Raman scattering revealed electron transfer behavior between NSi DEA and carbon materials.The delocalizedπelectrons on the pyrimidine ring and imidazole ring of the dispersant can achieveπ-πconjugation with electron rich carbon materials.The dispersed solution can self crosslink to form a carbon-based film through simple vacuum filtration or drop coating drying operations.The silicon hydroxyl groups on the molecules can also be crosslinked with other materials through dehydration and condensation,further achieving their versatility.2.A type of MOFs with cross-linking activity was synthesized and compounded with graphene under the assistance of dispersants to prepare GR/MOFs composite films with high mechanical strength and high MOFs content.Firstly,using UiO-66-NH₂ as the matrix,a series of chemical modifications such as ECH,EDA,and GPTMS were carried out to obtain an active MOFs aqueous dispersion containing-Si-OH groups on the surface.The self crosslinking film-forming ability of such MOFs,the composite film-forming ability with graphene at different ratios,and the film-forming ability assisted by hydrophilic polymer crosslinking agents were studied.Through XRD,it was proven that the composite film can maintain the crystal structure of MOFs,and the uniform distribution of MOFs in SEM and Mapping proves that the surface of the cross-linked composite film is uniform and dense.In tensile testing,MOFs:PEG=1:0.4 can bear a weight of 200 g,and MOFs:PEG:GR=1:0.4:5wt%has a breaking force of 8.7 N.The composite film structure has high strength and good flexibility,and can be bent and folded freely.The membrane flux of MOFs:PEG=1:0.4 is as high as 5305.2 L m^-2 h^-1.3.The composite film mentioned above was used for ion separation and its adsorption and separation effect on molybdate was studied.Molybdenum mainly exists in the form of polymolybdenum oxygen cluster anions in solution.This article utilizes the electron deficient quaternary ammonium salt structure formed by N in MOFs to achieve efficient adsorption of molybdenum through electrostatic attraction.The isotherm of molybdate adsorption on the film conforms to the Langmuir model.On the basis of ensuring structural stability,the maximum saturated adsorption capacity of molybdate on the composite film MOFs:PEG=1:0.4 can reach 130 mg·g^-1.Its adsorption kinetics conform to the Pseudo-second-order model.In the coexisting solution of molybdate,Zn²⁺,Mn²⁺,Cu²⁺and Fe³⁺,the composite film exhibits high selectivity for molybdate and can resist the interference of various metal ions.But when coexisting with Re O^4-,the film also exhibits a certain adsorption effect on Re O^4-,making it difficult to achieve complete separation of the two.After 7 cycles of experiments,the adsorption performance of MOFs:PEG:GR=1:0.4:3wt%material for molybdate can still be maintained at over 70%.