Synthesis Of Nanocrystalline Cellulose/hydroxyapatite Nanocomposite And Study On Adsorption Performance Of Chlortetracycline Hydrochloride

The large-scale production and excessive use of antibiotics have seriously threatened the ecological environment and human health.Tetracyclic antibiotics are among the most widely used antibiotics among many antibiotics.Chlortetracycline Hydrochloride(CTC·HCl)is a kind of broad-spectrum antibacterial drug,which has antibacterial and bactericidal effects.And it is a tetracycline antibiotic.The presence of CTC·HCl in the environment will not only interfere with the respiration,nitrification and phosphatase activity of soil microorganisms,but also cause the resistance of pathogenic microorganisms,thus causing more serious environmental problems.The adsorption method is effective in the treatment of antibiotic wastewater and there are many adsorbents,so it has become a research hotspot.The most commonly reported adsorbents are:carbon nanotubes,granular activated carbon,graphene,biochar,montmorillonite,and kaolin.However,these adsorbents have the disadvantages of high cost,difficult regeneration,and secondary pollution to the environment.There are many preparation methods of hydroxyapatite(HAP),and the raw materials are simple and cheap.It is an environmentally friendly adsorbent.The surface is rich in OH^-,Ca²⁺,PO₄^3-ions,and it has good ion exchange performance.Therefore,HAP was used to adsorb CTC·HCl in this study.It was found that although the adsorption efficiency was very fast,it did not reach the ideal adsorption capacity.In order to further develop the adsorption potential of HAP for CTC·HCl,we use the cellulose nanocrystals(NCC)as the enhancer to improve the adsorption performance of HAP.The adsorption effect of HAP added with NCC to CTC·HCl is better than that of pure HAP.In this paper,the in-situ precipitation method was used to synthesize NCC/HAPs powder materials,and the effects of the mass ratio of NCC to HAP,the pH value of the reaction and the reaction temperature on the NCC/HAPs were investigated.It was found that the better preparation conditions were that the mass ratio of NCC to HAP was 1:1,the pH value was 7,and the temperature was 20?.X-ray powder diffraction,Fourier infrared spectroscopy analysis,thermal performance analysis,scanning electron microscope,transmission electron microscope,N ₂ desorption-adsorption isotherm analysis,ultraviolet spectrophotometry and other means wer e used to characterize and analyze the synthesized samples.The characterization results are consistent with the literature reports,indicating that the NCC/HAPs were successfully synthesized in this study,and it is also speculated that there may be SO₃-Ca²⁺binding between NCC and HAP precursors,and non-covalent interaction between C-OH and Ca²⁺.It is found that the crystal crystallinity is slightly worse after adding NCC,but the specific surface area of NCC/HAPs increases with the increase of NCC cont ent(from 38.791 m²/g to 85.605 m²/g).The effects of adsorption time,initial concentration of CTC·HCl,and solution pH on the adsorption performance of CTC·HCl by NCC/HAPs were also investigated.It was found through experiments that the optimal adsorption condition was that the initial concentration of CTC·HCl was 200 mg/g,and the pH of the solution was 7.Under this condition,the adsorption capacity of CTC·HCl to NCC/HAPs could reach139.44 mg/g.In order to test the adsorption effect of CTC·HCl,we carried out a kinetic study.The results shows that the adsorption process of CTC·HCl on NCC/HAPs follows pseudo second-order kinetic model,indicating that there is chemical adsorption.In order to further explore the adsorption mechanism of NCC/HAPs for CTC·HCl,we conducted an isotherm and thermodynamic study on the adsorption behavior of NCC/HAPs.The results showed that the adsorption of CTC·HCl by NCC/HAPs was in accordance with Freundlich adsorption model,which shows that the adsorption process is dominated by multi-molecular layer heterogeneous adsorption,and the thermodynamic experiment shows that the adsorption is a s pontaneous endothermic reaction.The results of pH experiment show that with the increase o f pH,the surface charge of NCC/HAPs changes from positive to negative,and the adsorption of CTC·HCl is better when the pH of the solution is neutral.From the above results,it can be concluded that the adsorption mechanism of CTC·HCl on NCC/HAPs is complex,and it is speculated that there are van der Waals interaction,Molecular diffusion,electrostatic interaction,cation exchange mechanism,cation bridging,complexation and hydrogen bonding.However,desorption experiments proved that calcium ion interaction(including cation exchange mechanism,cation bridging interaction and complexation)may be the main driving force for NCC/HAPs to adsorb CTC·HCl.The research results show that the NCC/HAPs has good adsorption performance for CTC·HCl,which can provide certain guidance for its process development,and it is conducive to the removal of CTC·HCl in water environment.