Study On The Characteristics And Mechanism Of Adsorption And Catalytic Degradation Of Tetracycline In Water By Modified Coconut Shell Charcoal

The efficient and low-cost removal of tetracycline（TC）in water is a hot spot in water pollution research.In recent years,modified biochar with large specific surface area,high adsorption and catalytic efficiency has been widely studied in the removal of tetracycline in water.However,the existing modified biochar materials with good performance have problems such as complex preparation process,high cost,unclear active site and mechanism of action.In this paper,two new high-performance modified biochar materials were successfully prepared by synchronizing heteroatom doping and active material loading during the preparation of biochar,and the performance improvement mechanism was analyzed by combining the characterization data and pollutant removal efficiency,in order to provide new ideas for the development of modified biochar technology.Specifically,it mainly includes the following two parts:（1）Using agricultural waste coconut shell and boric acid as raw materials,the carbon-based skeleton formation and heteroatom doping were synchronously realized through one-step pyrolysis,and a new boron-doped coconut shell biochar material（B-CSC）was prepared.Field emission scanning electron microscopy（SEM）,specific surface area and pore size analyzer（BET）,X-ray photon spectrometer（XPS）,etc.were used to characterize and analyze its microstructure and physical and chemical properties,and the results showed that one-step pyrolysis doping could successfully incorporate B into the matrix surface and crystal lattice of coconut shell charcoal,resulting in a larger specific surface area,pore volume and pore size,and the morphology introduced into B was mainly H₃BO₃,B₂O₃,B and B₄C.The effects of key preparation conditions（pyrolysis temperature,boron-carbon mass ratio）on the adsorption performance of B-CSC were systematically studied.Based on the system optimization of the preparation process,the adsorption performance of B-CSC with the best performance was 8.9 times,2.0 times,960.2 times and 18.8 times that of pure coconut shell carbon（CSC）and other conventional adsorbents such as commercial powder activated carbon,granular activated carbon and graphene Go.At the same time,B-CSC has good adsorption capacity for common pollutants rhodamine B（Rh B）,tetracycline（TC）,bisphenol A（BPA）,and methylene blue（MB）,which are common pollutants in the water environment.The effects of initial p H,different metal cations,different organic pollutants and different actual wastewater on the adsorption effect were investigated,and the results showed that B-CSC could maintain a high adsorption capacity under all influencing factors.（2）Combined with the characterization results and experimental data,the adsorption mechanism and active site of B-CSC were analyzed in depth.The results show that the adsorption process of B-CSC to TC is more in line with the Freundlich adsorption isotherm model,and the adsorption kinetic data are more in line with the quasi-secondary kinetic model and the intraparticle diffusion model,and the adsorption process is dominated by physicochemical interaction.The adsorption process mainly involves liquid film diffusion,surface adsorption,mesoporous and microporous diffusion and active site adsorption,and the adsorption strengthening mechanism is mainly B doping to reduce the chemical inertness of its carbon network,enhance itsπ-πinteraction and hydrogen bonding with TC molecules,among which H₃BO₃ is the main active substance with enhanced adsorption performance.（3）On the basis of B-CSC related research,in order to further improve the catalytic performance of biochar,boron doping and loading zero-valent iron were carried out simultaneously in the one-step pyrolysis process with ferrous sulfate as the iron source and sodium borohydride as the reducing agent,and a new type of iron-boron co-doped coconut shell biochar（Fe-B-CSC）was successfully prepared.The successful loading of elemental iron was confirmed by field emission transmission electron microscopy（TEM）,field emission scanning electron microscopy（SEM）,X-ray crystal diffractometer（XRD）,the main occurrence forms of elements B and Fe were detected,and the effects of key preparation conditions（sodium borohydride addition,ferrous sulfate addition）on the structure and catalytic properties of Fe-B-CSC were systematically analyzed.The Fe-B-CSC obtained after system optimization has excellent catalytic activity,and the degradation effect of activated permonosulfate（PMS）on TC is 4.56 times that of pure biochar,and it is far better than that of commercial granular activated carbon,powdered activated carbon,manganese dioxide,nano-ferric oxide and other catalysts.At the same time,it has good activation effect on persulfate（PS）and hydrogen peroxide（H₂O₂）,and can maintain high catalytic performance at a wide range of p H.（4）The catalytic mechanism of Fe-B-CSC-activated PMS process was analyzed from the aspects of composition of active substances,proportion of relative contribution rate of each active substance and catalytic active site.The active substances of its activated PMS are mainly SO₄^-·and·OH,where·OH is the active substance that plays a major role,accounting for 61.7%-62.4%of the contribution rate.In addition,the main active sites and strengthening mechanism of Fe-B-CSC were systematically analyzed and discussed by combining the catalyst structure,microstructure changes before and after the reaction and chemical quenching,and the main reason for the improvement of catalytic capacity was that the loaded elemental B and Fe⁰ greatly improved the activation efficiency and utilization rate of PMS.