Ambient Processed rGO/Ti3CNTx MXene Thin Film with High Oxidation Stability, Photosensitivity, and Self-Cleaning Potential

Solution-based processing offers advantages for producing thin films due to scalability, low cost, simplicity, and benignity to the environment. Here, we develop conductive and photoactivated self-cleaning reduced graphene oxide (rGO)/Ti3CNTx MXene thin films via spin coating under ambient conditions. The addition of a thin rGO layer on top of Ti3CNTx resulted in up to 45-fold improvement in the environmental stability of the film compared to the bare Ti3CNTx film. The optimized rGO/Ti3CNTx thin film exhibits an optical transmittance of 74% in the visible region of the spectrum and a sheet resistance of 19 kΩ/sq. The rGO/Ti3CNTx films show high rhodamine B discoloration activity upon light irradiation. Under UV irradiation, the electrically conductive MXene in combination with in situ formed semiconducting titanium oxide induces photogenerated charge carriers, which could potentially be used in photocatalysis. On the other hand, due to film transparency, white light irradiation can bleach the adsorbed dye via photolysis. This study opens the door for using MXene thin films as multifunctional coatings with conductive and potentially self-cleaning properties.


Preparation of reduced graphene oxide (rGO) referential samples
To study the optoelectronic properties of rGO alone, we fabricated rGO thin film by using a mixture of graphene oxide (4 mg/mL) and L-ascorbic acid (50 mM) with a volume ratio of 1:1.
The mixture was further drop-casted on the activated glass substrate with the volume of 30 μL and heated at 150°C for 20 minutes in ambient condition.Here, we used the drop-casting technique, as layer-by-layer spin coating is unsuitable for depositing rGO due to its hydrophobic nature.

Studied on the electrochemical properties
To study the flat band potential, we performed Mott-Schottky (MS) measurements using an electrochemical workstation (VSP-300, Biologic, France).The prepared samples were coated on glassy carbon as a working electrode, while Ag/AgCl (saturated in KCl) and a platinum wire were used as reference and counter electrodes, respectively.Here, 0.1 M KCl was used as a supporting electrolyte.To prepare the working electrode, the samples were sonicated for 30 minutes.Then 10 μL of the solution is drop-casted on the GC and dried overnight at the ambient temperature.MS measurement analysis was done under the frequency of 1 kHz.All the measurements were done in the dark at room temperature.

Figure S1 .
Figure S1.SEM image of GO flakes obtained by a modified Hummer's method.

Figure S7 .
Figure S7.The Zeta potential distribution graph of SL Ti3CNTx

Figure S9 .
Figure S9.The calculation of the mass extinction coefficient of SL Ti3CNTx.Here, the calibration curves of the solution were obtained by taking the peak absorption maxima of Ti3CNTx at the visible region (667 nm).

Figure S10 .
Figure S10.The calculation of Ti3CNTx thin films figure of merit obtained by taking the slope of (τ550) -0.5 -1 and vs Z0/2Rs plot.

Figure S11 .
Figure S11.The oxidation stability test of Ti3CNTx thin films spin-coated with an increasing number of cycles.The test was conducted by exposing the films for seven days.

Figure S12 .
Figure S12.(a) Surface morphology image, (b) cross-sectional image, and (c) the corresponding magnified image of rGO/Ti3CNTx thin films on Si substrate.(d) backscattered electron image of rGO/Ti3CNTx thin film.Yellow arrows indicated Ti3CNTx flakes covered by rGO flakes.

Figure S13 .
Figure S13.(a) SEM and (b) scanning tunneling electron microscopy images showing the interfacial connection between rGO and Ti3CNTx.

Figure S14 .
Figure S14.Sheet resistance changes of Ti3CNTx and GO/Ti3CNTx thin films measured up to 21 days of storage.

Figure S15 .
Figure S15.I-V curve of rGO/Ti3CNTx and Ti3CNTx thin films after 7 months of storage.The inset shows the magnified curve of Ti3CNTx.

Figure S16 .
Figure S16.Sheet resistance value of Ti3CNTx and GO/Ti3CNTx thin films.

Figure S17 .
Figure S17.Photocurrent density of Ti3CNTx thin film upon irradiation by different wavelengths.The bias voltage of 1.5V was used.

Figure S18 .
Figure S18.Photocurrent density of rGO/Ti3CNTx thin film upon irradiation by different wavelengths.The bias voltage of 1.5V was used.

Figure S19 .
Figure S19.Photocurrent density of rGO thin film upon UV and white light irradiation.The inset shows the digital photograph of rGO thin film deposited on the glass substrate for the photocurrent test.The bias voltage of 1.5V was used.

Figure S20 .
Figure S20.Photocurrent density of rGO thin film upon irradiation by different wavelengths.The bias voltage of 1.5V was used.

Figure S22 .
Figure S22.Digital photograph of RhB photolytic discoloration under visible and UV light.

Figure S23 . 1 Figure
Figure S23.RhB discoloration kinetics under (a) UV light and (b) white light irradiation performed up to 120 minutes.Here, the pseudo-first-order kinetic model is used. 1

Figure S25 .
Figure S25.The Mott-Schottky plot of Ti3CNTx at the frequency of 1 kHz.

Table S1 .
Atomic and weight percentage of chemical elements identified by EDS for SL Ti3CNTx samples.: Observable Cu and excessive C contributions come from carbon coated copper TEM grid.Potassium contribution in EDS comes from the impurity. *

Table S2 .
The comparison of electrical and optical properties of photocatalytic thin films reported in the literature.