Ti₃C₂ Mxene Co-catalyst Assisted Bi₂Wo₆ For Enhanced Photocatalytic Tetracycline Degradation

Tetracycline（TC）is a kind of broad-spectrum antibiotic,which has been widely detected in natural water and wastewater treatment plants.Residual antibiotics not only had caused environmental pollutions,but also resulted in the production of antibiotic resistant bacterias（ARBs）and antibiotic resistant genes（ARGs）,which represented a potential hazard to ecosystem security and health of human.Tetracycline has strong antibacterial and chemical stability,therefore it is difficult to be completely removed by traditional water treatment technologies,photocatalytic is an environmental friendly and efficient advanced oxidation technology,which can effectively degrade and mineralize organic contaminants.Among the photocatalysts,Bi₂WO₆ has attracted intense attention due to its narrow band gap and visible light response.However,the low absorption of visible light and rapid recombination of photogenerated carriers of pristine Bi₂WO₆,which restrict its application.We hybridize Bi₂WO₆ with co-catalyst Ti₃C₂（MXene）,the enhanced photocatalytic performance mechanisms of Bi₂WO₆ with Ti₃C₂ as a co-catalyst were discussed,and the feasibility of Bi₂WO₆/Ti₃C₂ in practical application was further analyzed.The main conclusions of this study are as follows:（1）The Ti₃C₂ was synthesized by HF etching method,then Ti₃C₂ was loaded on Bi₂WO₆ surface by evaporation-induced self-assembly method and Bi₂WO₆/Ti₃C₂hybrid photocatalysts with different ratios were synthesized.（2）By TEM,XRD and XPS characterization methods,it was proved that Ti₃C₂was successfully compounded with Bi₂WO₆,and formed a strong interfacial interaction.The characterization results of SEM showed that Bi₂WO₆and Bi₂WO₆/Ti₃C₂ both were nanosheet structures,the latter had a rougher surface which is consistent with the characterization of BET,the specific surface area of Bi₂WO₆/Ti₃C₂（58.25 m²/g）was about 2.3 times than that of pristine Bi₂WO₆（25.39 m²/g）,it indicated that Bi₂WO₆/Ti₃C₂ could provide more actives for adsorb pollutants and promote the photocatalytic process.The photocurrent test confirmed that Ti₃C₂ loaded on the Bi₂WO₆ could effectively separate photogenerated carriers and prolong the lifetime of electrons.Through the analysis of UV-Vis DRS,it was revealed that the enhanced visible light adsorption capability of Bi₂WO₆/Ti₃C₂.（3）TC was selected as the target organic pollutants for photodegradation experiments.The photocatalytic recations of TC were in accordance with pseudo-second-order kinetic model,Bi₂WO₆/Ti₃C₂ composites shows higher photocatalytic degradation to TC.When the mole ratio of Ti₃C₂ was 2%,Bi₂WO₆/Ti₃C₂ composites（BWT-2%）had the best photocatalytic activity,the reaction rate constant(0.0152 L·mg^-1·min^-1)of BWT-2%,which was 19 times than that of pristine Bi₂WO₆(0.0008 L·mg^-1·min^-1),and the TOC removal efficiency reached 69.14%within 100 min.The effects of different influencing factors on TC degradation in BWT-2%were also discussed.The removal rate of TC decreased with the increasing of initial TC concentration（5～20mg/L）,therefore BWT-2%is more suitable for the treatment of tetracycline wastewater with concentration less than 10 mg/L.The removal rate of TC increased first and then decreased with the increasing of p H（3～11）,BWT-2%showed the highest degradation rate（92.68%）at the p H of 6.92.It was worth noting that the effects of different anions on removal efficiency were not alike,Cl^-and NO₃^-just slightly inhibited TC degaradation,then followed HCO₃^-,CO₃²,SO₄^2-had obvious inhibition on the degaradation of TC,the removal rate of TC decreased to 61.05%.Generally,BWT-2%showed good anti-interference ability to water quality changes.（4）Via the radical quenching experiments and EPR tests,it was proved that the active species in the TC degradation by Bi₂WO₆/Ti₃C₂ were mainly h⁺and some·O₂^-,while the active species was only h⁺in Bi₂WO₆ system.The characterizations of UV-Vis DRS and VB-XPS revealed that the interfacial interaction formed between Ti₃C₂and Bi₂WO₆ changed the valence band and conduction band potential of Bi₂WO₆.The valence band potential of Bi₂WO₆/Ti₃C₂ was more positive,which enhanced the oxidation ability of the photogenerated h⁺for improving the photocatalytic performance.In addition,the degradation products of TC in Bi₂WO₆/Ti₃C₂co-catalysis system was detected by LC-MS,and the possible TC degradation pathways were analyzed.（5）After four cycles,Bi₂WO₆/Ti₃C₂ still maintained a high TC removal rate（71.25%）,and via XRD characterization,it is revealed that there was no obvious change in crystal structure after four times of recycling.Through the daphinia magna toxicity experiments,it was inferred that the EC₅₀ of TC was about 55 mg/L,and the acute toxicity increased first and then decreased along with the photodegradation process of TC in Bi₂WO₆/Ti₃C₂ system,and the acute toxicity of the solution after the reaction was lower than that of the initial solution.Moreover,Bi₂WO₆/Ti₃C₂ could effectively remove a variety of contaminants,the removal rates of reactive red（RR）,oxytetracycline（CTC）,methyl orange（MO）,norfloxacin（NOR）,ofloxacin（OFL）were respectively 94.42%,95.44%,84.38%,71.78%,50.71%.Consequently,Bi₂WO₆/Ti₃C₂has certain prospects in applications for its simple synthesis method,high photocatalytic acticity and good recycling performance.