Synthesis And Application Of Novel Gallium-Based Metal-Organic Gels And Their Sodium Alginate Composites

With the acceleration of modernization,antibiotics are exploited to protect humans and animals from infections by bacteria or fungi,and even promote animal growth.However,most antibiotics enter the water environment through the feces from humans and animals due to incomplete metabolism,which are frequently detected in various water environment such as river water,groundwater and even drinking water,posing a serious threat to ecosystems and human health.Chlortetracycline hydrochloride（CTC）and ciprofloxacin hydrochloride（CIP）are widely used because of the low cost and the ability to treat and prevent diseases.They usually coexist in aqueous solution on account of the low biodegradability,which are urgent to remove by an effective water treatment technology.Adsorption is more economical and suitable owing to simple operation,wide applicability,low cost and easy recovery.However,the current adsorbents cannot achieve the ideal removal effect with the limited adsorption capacity and poor recovery stability,thus their performance needs to be further improved before practical application.Compared with traditional nanomaterials,the great potential of metal-organic gels（MOGs）in adsorption removal of antibiotics from aqueous solution is attributed to their possibility of large-scale preparation,high specific surface area,excellent chemical stability and adjustable porosity.Considering the general unavoidable problems of MOGs of the direct application in powder forms,such as poor water stability,easy agglomeration and difficulty in separation and recovery,it is of great practical significance to prepare new adsorbents with high adsorption capacity,convenient separation and good reusability.Using the eggshell structure formed via the cross-linking of divalent cations(like Ca²⁺)and sodium alginate（SA）,MOGs are encapsulated and converted into composites,which could not only enhance the adsorption performance but also effectively avoid difficult recycling and material loss in separation and regeneration process,as well as secondary pollution,greatly expanding the application range of MOGs in different fields.Based on the above discussion,a novel gallium-based metal-organic gel GMOG was prepared,then encapsulated in SA and converted into GMOG/SA beads.Both of them were applied to remove CTC and CIP from the aqueous solution.Furthermore,the influence of different factors on the adsorption process was investigated,and the main adsorption mechanism and competition mechanism were explored.The main findings were shown as follows:（1）In this study,a novel GMOG was synthesized by the solvothermal method,and the adsorption capacities of CTC and CIP in single system could reach 406.50 mg g^-1 and 158.23 mg g^-1,and 207.90 mg g^-1 and126.90 mg g^-1 in binary system,respectively;in order to further improve adsorption capacity and recyclability of GMOGs,they were encapsulated in SA and converted into composites to obtain GMOG/SA beads,and the adsorption capacities of CTC and CIP reached 1085.19 mg g^-1 and 862.07mg g^-1 in single system,and 588.24 mg g^-1 and 571.42 mg g^-1 in binary system,respectively.（2）In single system,the effects such as solution pH,adsorbent dosage,antibiotic concentration,co-existing inorganic ions,ionic strength and humic acid on the adsorption process were systematically studied,and the response surface methodology（RSM）were used to investigate the optimal operating conditions of powdery GMOGs.Combined with BET,XPS and FT-IR characterization results,it is shown that pore filling,electrostatic interaction,π-πelectron donor-acceptor interaction,hydrophilic-lipophilic balance and chemical coordination jointly promoted the adsorption of CTC and CIP.（3）In binary system,the competition effect between CTC and CIP was studied by adsorption kinetics and isotherms.On account of the competitive effect,both the adsorption of CTC and CIP by GMOGs was strongly inhibited.Specifically,the adsorption rate was reduced,the equilibrium time was prolonged,and the adsorption capacity decreased significantly.Moreover,the selectivity coefficientsβ_CIP^CTCof GMOGs and GMOG/SA beads were both larger than 1.0,indicating the better selectivity for CTC by both adsorbents,probably due to the fact that CTC possesses more functional groups for bonding and more aromatic rings forπ-πinteraction.（4）The superior recycling rate of GMOG/SA beads over GMOGs was demonstrated through a regeneration experiment.Then their ability to continuously remove CTC and CIP was tested by microunit and adsorption column,where CTC showed the higher removal efficiency than CIP.In addition,the removal efficiencies of CTC and CIP by GMOG/SA beads were more than 90%in real water.At the same time,the average cost of GMOG/SA beads was estimated to be about 0.0283 RMB/g from the economic view,which proved that GMOG/SA beads were expected as adsorbents to remove CTC and CIP in practical applications.