Preparation And Application Of Novel Silsesquioxane-based High Efficiency Adsorbents

With the development of the times,the metal resources contained in the cities where people live are becoming more and more abundant with the new iteration of electronic products.It is of great scientific significance and practical value to explore and develop advanced materials and their preparation methods to recover and reuse metal ions from water.Compared with other common metal ion recovery techniques,the adsorption method has the advantages of easy operation and no consumption of electrical and thermal energy.The preparation of efficient adsorbent is the key technology of adsorption method.In this thesis,a series of novel metal ion adsorbents were prepared by using caged sesquisiloxane as the initial raw material.In recent years,hybrid network materials based on caged sesquisiloxanes have been developed rapidly,offering a completely new solution for wastewater treatment.Although research on sesquisiloxane materials is increasing,there are still some unresolved issues in the field of water treatment.For example,the dispersion of silsesquioxyl materials in aqueous solution is poor,and the adsorption capacity of heavy metal ions is not high,and the adsorption mechanism is still being explored.Therefore,we plan to construct a series of hybrid network functional materials based on caged silsesquioxanes,taking full advantage of the diversity of its substituents,inorganic core,nanometer three-dimensional structure.The main studies are as follows.1.By changing the acid scavenger from NEt3 to NaHCO3,two novel kinds of amine-functionalized silsesquioxane-based hybrid networks(PCS-N1,PCS-N2)with different molar ratios of-NH2/NH-and NH3+ were successfully prepared via nucleophilic substitution of octa(3-chloropropyl)silsesquioxane(SQ-Cl8)with triaminoethylamine,respectively.No porosity was observed for these two hybrid networks:however,they exhibited good thermal stability and hydrophilicity.The adsorption capacities for Ag(Ⅰ)and Hg(Ⅱ)are as high as 358 and 721 mg/g,respectively.More interestingly.PCS-N1 can selectively adsorb the anionic dye methyl orange with a capacity as high as 731 mg/g.Furthermore,they regenerate easily and offer potential for water purification.This work provides a new approach to prepare and tune amine-functionalized SQ-based networks for multipurpose.2.Considering that selectivity should be designed in the construction of new adsorbents,and the economic benefits of new adsorbents should be increased.Two different kinds of thioamide-bridged silsesquioxane-based adsorbents of PCS-STOH with open cage and PCS-ST with close cage.were synthesized by the crosslinking reaction of thiocarbonohydrazide with octa(3-chloropropyl)silsesquioxane(SQ-Cl8)in the presence or absence of NaHCO3,respectively.Compared to PCS-ST(633 mg/g),PCS-STOH can absorb 1721 mg/g of Au(Ⅲ).Moreover,PCS-STOH can remarkably reduce the Au(Ⅲ)concentrations from ppm level(12 mg/L)to ppb level(0.001 mg/L).Their adsorption behaviors were systematically studied at pH,ion concentration and contact time,and the adsorption mechanism may be attributed to oxidation-reduction,coordination and electrostatic interaction between adsorbents and Au(Ⅲ).Importantly,the Au(Ⅲ)loaded PCS-STOH and PCS-ST can act as heterogeneous catalysts to transform 4-nitrophenol to 4-aminophenol.This work provides a strategy for preparing open/close cage silsesquioxane-based thioamide-functionalized hybrid networks.Facile and low-cost synthetic procedure make it very promising to be industrialized and be of great use in the field of selective recovery of gold ions.3.In the study,the synergistic effect of N and O heteroatoms was found to make the hybrid network very effective in the adsorption of metal ions.An amine-functionalized silsesquioxane-based hybrid network(PCS-PAA)was successfully synthesized through the cost-effective,mild amine-ene reaction of acrylate-functionalized SQ with triaminoethylamine(TAA).Hydrophilic PCS-PAA helps to adsorb Au(Ⅲ)via the coordination with abundant heteroatoms(N and O).The Langmuir model is more suitable to describe the adsorption process,and the pseudo-second-order model well fits the adsorption kinetic.Surprisingly,most Au(Ⅲ)ions are in situ reduced to Au(0)particles,which are uniformly distributed on the surface of PCS-PAA.PCS-PAA-Au(PCS-PAA loaded with Au)can reduce 4-nitrophenol to 4-aminophenol with high catalytic activity.More interestingly,PCS-PAA can selectively adsorb Au(Ⅲ)from e-waste.This work provides a convenient and mild method to recover Au(Ⅲ)from wastewater or e-waste for multiple purposes.4.Although the adsorbent prepared by the amine alkene reaction has good effect,it is not stable enough in aqueous solutions.A double cross-linked system hybrid network material(PCS-SNO)was prepared by the reaction of amine alkene as well as thiolene,which is rich in heteroatoms N,O,and S and provides rich binding sites for subsequent adsorption of Au(Ⅲ).The reaction conditions of amidene as well as mercaptoene are mild and do not require catalysts,which is favorable for large-scale practical applications.Since the PCS-SNO hybrid network contains a large number of heteroatoms sulfur.nitrogen and oxygen with strong affinity for Au(Ⅲ),it can selectively capture Au(Ⅲ)from many coexisting ions.In addition,the adsorption capacity of PCS-SNO for Au(Ⅲ)was 2100 mg/g due to electrostatic attraction,chelation and redox reaction.More interestingly,a large amount of Au(Ⅲ)was reduced to Au(0)and Au nanoparticles were uniformly distributed on the adsorbent.Moreover,PCS-SNO can selectively remove Au(Ⅲ)from e-waste.These results suggest that PCS-SNO is very promising for the recovery of precious metals.