The Preparation Of Anti-fouling Polyacrylamide-based Hydrogels And Their Adsorption Properties Of Uranium

In view of the actual problem of insufficient uranium supply for the nuclear industry caused by the current shortage of terrestrial uranium resources,the development of high-efficiency seawater uranium extraction adsorbents will provide technical support for the sufficient and stable uranium supply for our country’s nuclear industry.Polyacrylamide（PAM）based hydrogel materials are widely used in the preparation of adsorbent materials and water treatment,because of their large amount of hydrophilic groups and excellent ions adsorption properties.However,PAM hydrogel is far from satisfying the needs of practical applications,due to its single function,few adsorption sites and poor mechanical properties.Therefore,this article starts from the construction of PAM hydrogel absorbents with high adsorption capacity,anti-biofouling property and high mechanical strength.By using dopamine（DA）intercalated montmorillonite（MMT）,arginine（Arg）grafted oxidized carboxycellulose nanofibers（OCNFs）,polypyrrole（PPy）loaded copolymer network and metal-organic frameworks（MOFs）loaded copolymer network to obtain a unique microstructure,fast ion transmission path,and excellent antifouling properties,thereby improving the extraction capacity,extraction speed and cycle stability of PAM-based hydrogels.Specifically includes four aspects:Polydopamine（PDA）intercalation of MMT nanosheets and radical polymerization of acrylamide（AM）monomers were utilized to construct a MMT-PDA/PAM nanocomposite hydrogel with a three-dimensional network structure of microfiber.Mechanical studies have shown that theεvalue of the prepared hydrogel reaches 90%after 30 compression cycle fatigue hysteresis tests,and the hydrogel still exhibits a large strain capacity after being immersed in seawater for 30 days.Compared with the initial value（1678%）,it only dropped by 27%.The adsorption performance test shows that the prepared MMT₁₀-PDA_0.6/PAM has the maximum adsorption capacity for uranyl ions when the added amounts of DA and MMT are 0.6 wt.%and10 wt.%,respectively.Combined with the kinetic model,adsorption isotherm model and thermodynamic fitting results,the adsorption of uranyl ions on MMT₁₀-PDA_0.6/PAM is a spontaneous endothermic monolayer chemical adsorption,the theoretical maximum adsorption capacity reaches 617.28 mg·g^-1 at 298.15 K and p H=6.5 in a uranium solution with the adsorbent dosage of 0.4 g·L^-1 and initial concentration of 500 mg·L^-1.The anti-seaweed test confirmed that MMT₁₀-PDA_0.6/PAM did not affect the growth of Nitzschia closterium and showed good anti-adhesion properties within eight days,which is in sharp contrast with MMT₁₀-PDA_0.6 and MMT₁₀/PAM.The adsorption performance of the MMT₁₀-PDA_0.6/PAM for uranium reaches2130μg·g^-1 in 1 mg·L^-1 uranium-spiked simulated seawater containing algae.An OCNFs-g-Arg/PAM nanocolloid hydrogel with a highly arranged three-dimensional network structure is obtained by grafting the natural zwitterionic Arg onto the surface of OCNFs,derived from hemp fibers through covalent cross-linking,followed by filling the AM precursor solution into the residual channel of the OCNFs-g-Arg composite material through a hydrogen bond cross-linking reaction.Mechanical tests show that OCNFs-g-Arg/PAM shows significantly improved mechanical properties after introducing OCNFs-g-Arg composites into PAM hydrogels,and the tensile strength at break increases by 12 times compared with PAM.The adsorption experiment shows that the maximum theoretical adsorption capacity of this material is 465.12 mg·L^-1 in uranium-spiked seawater with the adsorbent dosage of 0.2 g·L^-1 at 298.15K,p H=8.0,and an initial concentration of 200 mg·L^-1.The adhesion density after contacting Nitzschia closterium for seven days is 51.66±6.12 mm^-2 with the mass ratio of OCNFs-g-Arg to AM as 3:20,which is 7.76%of the surface adhesion amount of OCNFs/PAM.After six uranium adsorption-desorption experiments,the uranium adsorption capacity and tensile stress of OCNFs-g-Arg/PAM only decreased by 6.80%and 26.40%of the initial value.Under simulated seawater and real seawater conditions,OCNFs-g-Arg/PAM shows excellent affinity for uranyl ions.DFT calculations show that the guanidine groups and carboxyl end groups in OCNFs-g-Arg/PAM can replace one CO₃^2-from UO₂（CO₃）₃^4-to form a more stable structure.A hydrogel film is obtained by one-pot synthesis based on AM,polyvinylpyrrolidone（PVP）and 1-vinyl-3-butylimidazolium（VBIMBr）through a radical polymerization reaction triggered by ultraviolet light,and then the galvanostatic polymerization method is used to uniformly load polypyrrole（PPy）nano-level additives into the hydrogel film,and finally prepare the anti-fouling P（VP-AM-VBIMBr）/PPy hydrogel film with hierarchical pore structure.The mechanical properties show that the hydrogel film has good mechanical properties under the ratio of PVP,AM and VBIMBr as 1:4:1,the tensile strength and the elongation at break are109.85 k Pa and 311.84%,respectively.The adsorption experiment shows that the maximum theoretical adsorption capacity is 558.66 mg·g^-1 in uranium spiked seawater with the adsorbent dosage of 0.3 g·L^-1 at 298.15 K,p H=8.0 and an initial concentration of 200 mg·L^-1.The adsorption of uranyl ions on P（VP-AM-VBIMBr）/PPy is a spontaneous endothermic monolayer chemical adsorption process.The anti-bacterial and anti-seaweed tests show that P（VP-AM-VBIMBr）/PPy obviously inhibits the growth of S.aureus,E.coli,marine bacteria and Nitzschia closterium,because the polar group from the material combines with the hydrophobic side chains on the cell membrane of bacteria or alga.In addition,in the presence of interfering ions,P（VP-AM-VBIMBr）/PPy still extracts 19.93±0.63 mg·g^-1 uranyl ions from seawater spiked with100 times the coexisting ions within 24 h.The balanced charged double-network polyelectrolyte hydrogel is prepared by the combination of the first network formed by the electrostatic interaction between the oppositely charged sodium alginate（SA）and polyethyleneimine（PEI）and the second network formed by the cross-link between N,N-methylenebis（acrylamide）（MBA）and PAM chain.Furthermore,the final ZIF-67/SAP double network hydrogels with water stability,hierarchical porosity and biofouling resistance were constructed by the templated growth of ZIF-67 crystals in the above hydrogels.The mechanical properties show that the compression modulus of the material reaches 102.88±5.94 k Pa with the ratio of SA to PEI as 1:0.45,and the water content of ZIF-67/SAP_0.45 is 91.10±2.90%.The adsorption experiment shows that the maximum theoretical adsorption capacity is 621.12 mg·g^-1 in uranium spiked seawater with the adsorbent dosage is0.4 g·L^-1 at p H=8.0,298.15 K and an initial concentration of 200 mg·L^-1.After five adsorption-desorption cycles,the ZIF-67/SAP_0.45 double network hydrogel still enhibitis sufficient stability.Antibacterial and anti-algae tests show that the balanced charged double network hydrogel effectively inhibits the growth of bacteria and prevents the adhesion from macroalgae,leading to improved uranium adsorption performance in seawater.The adsorption capacity of the adsorbent reaches 6.99±0.26mg·g^-1 in real sea environment.Additionally,this general balanced charged strategy is able to convert different kinds of MOFs crystals（such as HKUST-1,MIL-100 and ZIF-8）into formable hydrogels,which is expected to be used as an ideal adsorbent for uranium extraction from seawater.