Preparation Of Metal-loaded Porous Silica-based Materials And Their Removal Perfomance For Tetracycline

Tetracycline（TC）is widely used in human medicine and veterinary medicine.Due to its incomplete metabolism in organisms,a large amount of TC was released into the water environment,which posed an increasing threat to aquatic ecosystem and human health.Nowadays,TC has become an environmental contaminant widely present in water environment.Among various treatment techniques for TC removal,sorption and photocatalytic methods based on functional materials are the two most economical and effective techniques.Firstly,to achieve the purpose of exploring the adsorption mechanism of TC removal from water environment,metal-loaded mesoporous silica with suitable pore size and ordered pore size distribution was prepared,and used as an adsorption model material to investigate the adsorption force in the process of TC removal.Secondly,based on the in-depth understanding of the adsorption mechanism,different types of metal-loaded silica-based materials were synthesized to examine their TC adsorption performance and TC removal in real water environment.Finally,based on the goal of complete elimination TC from water environment,metal single atoms loaded silica-based composites were prepared and applied for TC removal.The adsorption/photocatalytic degradation performance on TC was evaluated.Based on the above research objectives,three different types of metal-loaded porous silica-based composites were constructed to obtain high-performance adsorption/photocatalytic degradation materials for TC removing with industrial application potential.The specific contents and novelties were summarized as follows:（1）Mesoporous silica with uniform and ordered pore size and stable loading of Mn was prepared by a post-grafting method,and the underlying mechanism of TC removal from water environment was systematically elucidated.Firstly,an ethylenediamine terminated silane N-（2-aminoethyl-3-aminopropyl）trimethoxysilane was grafted on MSNs,and subsequently,the functional material with a target metal-centered stable octahedral was synthesized by the reaction of amino silane and metal cations.The synthesized Mn（Ⅱ）encapsulated MSNs（Mn-MSNs）was used for removing TC from water environment.The adsorption results showed that the adsorption capability of Mn-MSNs on TC was 235 mg g^-1,which was much higher than that of MSNs on TC（49.5 mg g-1）.It was found that TC could be effectively removed at different concentration ranges(5μg L^-1 to 450 mg L^-1).Results obtained from batch experiments,spectroscopic analysis and DFT theoretical calculations collectively indicated that TC removal was contributed by multiple adsorption forces,including Mn-TC complexation,electrostatic attraction and cation-π,where the Mn-TC complexation played an important role in improving the adsorption capacity and adsorption affinity for TC removal.（2）A one-pot rapid co-gel method was developed to prepare low-cost and high metal loading copper/chitosan/silica（Cu/CS/Si）ternary aerogel hybrids.Its adsorption property for TC removal from water environment was investigated.The Cu/CS/Si hydrogel was firstly synthesized by a one-pot method using chitosan,water glass and copper chloride as raw materials.Followed by freeze-drying,the Cu/CS/Si aerogel hybrids with high copper loading and uniform dispersion was prepared.The results of the removal performance showed that increasing the loading of copper in the Cu/CS/Si aerogel hybrids could improve its adsorption capacity for TC removal,in which the Cu₃-CS₂-Si aerogel hybrids with high copper loading(185 mg g^-1)had fast adsorption rate（>95%removal efficiency within 30 min）and wide range of pH applications（pH≈5-10）.Batch sorption experiments combined with spectroscopic and microscopic analyses collectively indicated that Cu-TC surface complexation through Cu-O bond was responsible for TC adsorption on Cu₃-CS₂-Si.In addition,the synthesized Cu₃-CS₂-Si aerogel hybrids exhibited good recyclability,which can be used for the removal of TC from real water samples.（3）A low-temperature supercritical carbonization method was developed to synthesize series of carbon-nitrogen-silicate composites with different morphologies and controllable metal loading.Ni/CS/Si composite hydrogels with different Ni contents were firstly prepared by a one-pot rapid co-gelation strategy,followed by a supercritical dry and carbonization treatment.The 40%Ni-C-Si with high TC sorption performance and 5%Ni-C-Si with high TC visible photocatalytic performance could be obtained by flexibly adjusting the contents of Ni in Ni/C/Si composites.The sorption results showed that the 40%Ni-C-Si with high Ni loading exhibit a large specific surface area and abundant active adsorption sites of Ni,which demonstrated excellent adsorption performance on TC through Ni-TC complexation.The photocatalytic degradation results showed that the 5%Ni-C-Si single-atom catalyst can decompose TC（>99%）within 20 min under visible light irradiation.High efficiency of 5%Ni-C-Si for TC degradation was attributed to the isolated Ni dispersion and formation of C/Si C heterojunction.The dominant active species that played a role in the photocatalytic degradation process were h⁺and·O₂^-.In addition,the degradation products derived from TC photocatalysis and their ecotoxicities were assessed by using high-resolution mass spectrometry and ECOSAR procedure.The results showed that photocatalytic degradation of TC by 5%Ni-C-Si can reduce the toxicity of TC in the aqueous environment to some extent.These Ni/C/Si composites exhibited multi-functional performance for adsorption and photocatalytic degradation,which can be flexibly applied to the removal of TC under different scenarios.