Study On Preparation Of Manganese Dioxide Modified Biochar Derived From Chinese Herbal Medicine Residues And Its Removal Of Tetracycline In Aqueous Solution

Antibiotics are widely used in a variety of fields,including agriculture,medicine,and veterinary medicine,because they are mainly used in the treatment of bacterial infections.However,most tetracyclines are not metabolized in humans and animals,causing the problem of antibiotic pollution to become more and more serious,which has an adverse impact on human health and ecology.Biochar adsorption has always been regarded as a low-cost,convenient and potential antibiotic wastewater treatment method.However,the removal effect of conventional biochar on antibiotics is general.The selection of biomass materials and how to effectively improve the removal of antibiotics from biochar are a current research hotspot.In this study,Chinese herbal medicine residue was used as raw material to prepare biochar adsorbent,loaded with nano-manganese dioxide for modification by chemical co-precipitation.A variety of characterization methods were used to compare the physical and chemical properties of biochar materials before and after modification.At the same time,tetracycline was used as the target pollutant to explore the adsorption behavior of tetracycline antibiotics under different influencing factors,and through the adsorption models,structural changes and intermediate product changes to study the removal mechanism.The main contents and corresponding results are as follows:?1?Manganese dioxide modified biochars with different modification ratios were prepared by chemical co-precipitation method.The results of SEM characterization showed that many agglomerate particles of manganese dioxide appeared on the surface of Mn-BC,and the aggregation degree and distribution of particles were related to the modification ratio.XPS results confirmed that the aggregate particles were manganese dioxide.Analysis of the XRD curve showed that the main components of the two types of biochar included silica and calcium carbonate.The specific surface area,pore volume and average pore size all showed the law of Mn-BC?1:10?>Mn-BC?1:20?>Mn-BC?1:30?>BC.?2?The results of the influencing factors of adsorption show that Mn-BC?1:10?had a better removal effect on tetracycline,which was closely related to Mn-BC's excellent structural performance.As the amount of adsorbent added increases,Mn-BC always had a higher removal rate and adsorption amount than BC.At different temperatures,the amount of TC adsorbed by Mn-BC gradually increased with time,reaching adsorption equilibrium around 1440 min.Under different p H environments,the adsorption of biochar to tetracycline was mainly affected by electrostatic interaction.?3?The results of the adsorption model showed that the pseudo-second-order kinetic model can better describe the kinetic process of TC adsorption on Mn-BC at different ambient temperatures.At temperatures of 288 K and 298 K,the effect of Freundlich model fitting is better than that of Langmuir model,and the opposite is true at 398 K.According to the Langmuir model,the maximum adsorption capacities of Mn-BC at 308 K was 131.49 mg/g,which showed great potential as a good adsorbent for TC removal.Thermodynamic results showed that this study was a spontaneous adsorption process and was related to physical adsorption.Higher ambient temperature was beneficial to the adsorption process in this system.?4?FTIR analysis showed that the strong aromatic structure,Mn-O bond and O-H group in Mn-BC played a key role in the removal of tetracycline.Mn O₂ played the role of oxidant in the degradation process of TC,but not all manganese dioxide participated in this process.HPLC-MS/MS determined the eight main conversion products?P1-P8?during the degradation process and deduced four possible degradation pathways,mainly involved structural changes such as dimethylamino,phenol of D-ring and some double bonds.