Adsorption Of Tetracycline By Biochar Prepared By Two-step Pyrolysis In Water

Tetracycline is a class of antibiotics produced by Streptomyces,which has the characteristics of low price,low toxicity and widespread use.At present,a certain concentration of tetracycline has been detected in many typical lakes and rivers in my country.Tetracycline has the characteristics of strong persistence in the environment and is difficult to degrade.At the same time,it may induce the production of resistant microorganisms and resistance genes,thereby accelerating the spread and spread of resistant microorganisms and threatening public health.Biochar has been widely used as a new adsorbent in recent years due to its excellent carbon framework,environmental friendliness and low price.Which material is used to prepare biochar and the different preparation methods selected will change the physicochemical properties of biochar.Therefore,the selected materials and the preparation method of biochar are the hotspots in the current research direction of biochar.In this paper,biomass-cow dung was pyrolyzed by one-step pyrolysis and multi-step pyrolysis.At the same time,the adsorption effect of cow dung biochar prepared by two methods on tetracycline(TC)in aqueous solution was evaluated.The application value of this biochar preparation method was explored.(1)Staged preparation between any two temperatures of 500 °C,700 °C and 900 °C(i.e.500-900 °C,500-700 °C,700-900 °C,900-500 °C,900-700 °C and 700-500 °C),the prepared cow dung biochar was then screened by the pyrolysis rate,residence time and other preparation factors,Compared with BC-500,BC-700 and BC-900 prepared by one-step pyrolysis,the adsorption effect of tetracycline was compared,and BC900-700 and BC700-900 with the best adsorption effect were selected.Then,the optimal biochar pyrolysis conditions were explored by two factors of residence time and pyrolysis rate.The results showed that the adsorption capacity was the best when the residence time was 1 h and the pyrolysis rate was 5 °C/min.(2)In this study,the biochar was studied and analyzed by scanning electron microscopy,specific surface area and pore size analysis,elemental analysis,thermogravimetric analysis,X-ray diffraction analysis and Fourier transform infrared spectroscopy analysis.The structure is better,the pore size is abundant,the specific surface area will be larger and the adsorption effect will be better.(3)The optimal adsorption environment of the best biochar prepared by one-step pyrolysis and multi-step pyrolysis was determined by single-factor experiments.The optimal adsorption time was 6 h,and the adsorption addition amount was 0.4 g/L,the adsorption performance of biochar is the best.(4)Model fitting of three kinds of biochars shows that the pseudo-first-order and pseudo-second-order kinetics show that BC900-1-5,BC700-900-1-5 and BC900-700-1-5 all conform to pseudo-second-order kinetics;And through the fitting of Langmuir and Freundlich isotherm models,the maximum adsorption capacity of the three biochars was calculated,and it was known that the maximum adsorption capacity of BC900-1-5,BC700-900-1-5 and BC900-700-1-5 The amounts were 138.89 mg/g,163.93 mg/g and 161.29 mg/g,respectively.(5)The mechanism analysis showed that the adsorption of tetracycline by one-step pyrolysis and multi-step pyrolysis of cow dung biochar may be the result of the combined effect of hydrogen bonding,electrostatic interaction,π-π interaction and ion exchange.(6)This experiment shows that the multi-step pyrolysis biochar has stronger adsorption capacity than one-step pyrolysis biochar in practical application,and the tetracycline concentration reaches 96.15% and 93.51%,respectively.BC700-900-1-5 and BC900-700-1-5,found in the comparison of three different tetracycline concentrations of 0.3 mg/L,3 mg/L,and 10 mg/L),the tetracycline removal rates of low and medium concentrations were similar in cycles,and reached equilibrium in the fourth cycle,but the removal rates of high concentrations of tetracycline reached equilibrium in the third cycle.In this study,by preparing cow dung biomass into biochar,we explored the changes in the adsorption performance of biochar by one-step pyrolysis and two-step pyrolysis preparation.It is more abundant,provides more adsorption sites for tetracycline,is a good adsorbent,and has application prospects as a new type of adsorption material.