DOI: 10.14457/tu.the.2022.787
title: Preparation of Ti3C2Tx MXene by various fluoride salts etching for adsorption of enrofloxacin

description: The occurrence of the antibiotics in water and soil are now becoming a severe threat in many countries. Overuse of antibiotic drugs has promoted antibiotic-resistant bacteria in both human and animals. In response to the excessive antibiotic contamination in natural environment, removal of antibiotic residues is needed for accessing clean water and protecting water-related ecosystem. MXenes are a new family of two-dimensional transition metal carbides, nitride, and carbonitride which have demonstrated potentials in many applications due to their unique properties such as metallic conductivity, hydrophilicity, wide interlayer space, abundant surface functional groups, and ion intercalability. In this work, MXene (Ti3C2Tx) material was investigated for removal of enrofloxacin, an antibiotic drug frequently used in aquaculture, by using adsorption technique. MXene (Ti3C2Tx) was synthesized from MAX phase (Ti3AlC2) with acid/salts etchant from in-situ HF etching. The preparation of various fluoride salts in hydrochloric acid (HCl), including lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF), Zinc fluoride (ZnF2) were studied. We also investigated the influence of concentration of acid etchant and etching time to minimize the reaction. The results suggested that MXene could be produced upon 4 hours by using hydrochloric acid (9mol/L) and fluoride salt (9 mol/L). The surface morphology analysis by scanning electron microscopy (SEM) indicated that all samples etched at 4 hours and 24 hours showed accordion-like structure in multilayer (MLs). The removal of Al element of synthesized material confirmed by EDX analysis decreased after etching of 4 hours and 24 hours compared to that of the MAX phase precursor. The simultaneous cation intercalation caused the obtained MXene to have larger interlayer space as confirmed by XRD results. Lithium cation intercalation of Ti3C2 showed vast inter-layer spacing compared to other fluoride salts etching system potentially due to its large solvation radii. As-prepared MX-Li-4h was further delaminated/fully exfoliated in DI water, LiCl, and ethanol by ultrasonication for 20 minutes. Well exfoliated/delaminated MXene was produced in DI water. From dynamic light scattering, the hydrodynamic particle size of the obtained Ti3C2/DI was approximately 380.2±4.7nm with the negative zeta potential −45mV. Transmission electron microscopy (TEM) results confirmed the successful exfoliation of the obtained MXene sonicated in DI water (sMX/DI) with a few layers. Adsorption of enrofloxacin (ENR) antibiotic onto MLs ion-intercalated MXene, which include MX-Li, MX-Na, MX-K and MX-Zn, the ENR adsorption seems to be slower than that of the monolayer MXene (sMX/DI) due to the MLs being occupied by the intercalated cations, which required longer time to adsorb the drug molecules. A multilayer MX-HF, etched by direct HF also show poorly performance due to smaller interlayer space which has low chance for ENR adsorbing at the active site inside layer structure. ENR sorption onto monolayer MX (sMX/DI) has improved adsorption capacity compared to that of Li-MX multilayer which some adsorption sites occupied by Li+. A delamination MX-Li-4h in TBAOH into single layer also revealed that monolayer MX binding with TBA+ would not be likely to exchange with ENR. Thus, monolayer MX with abundant adsorption site is a better candidate than cation intercalated MLs MX or smaller interlayer space MLs MX for ENR adsorption performance. For monolayer MXene (sMX/DI), the adsorption capacity reached the value of 8.35 mg/g in 3 hours, which is higher than those of the MLs MXene MX-Li, MX-Na, MX-K, MX-Zn which took almost 10 hours to reach equilibrium with the lower adsorption capacity values of 6.80 mg/g, 3.65 mg/g, 4.76 mg/g, 2.76 mg/g, respectively. The adsorption isotherms were well fitted by the Langmuir model, which provides the maximum adsorption capacity of the monolayer MXene of 17.45 mg/g. The enrofloxacin adsorption is in the order of monolayer MXene &gt; cation intercalated multi-layer MXene &gt; multi-layer MXene.