Synergistic augmentation and fundamental mechanistic exploration of β-Ga2O3-rGO photocatalyst for efficient CO2 reduction

We explore the novel photodecomposition capabilities of β-Ga2O3 when augmented with reduced graphene oxide (rGO). Employing real-time spectroscopy, this study unveils the sophisticated mechanisms of photodecomposition, identifying an optimal 1 wt% β-Ga2O3-rGO ratio that substantially elevates the degradation efficiency of Methylene Blue (MB). Our findings illuminate a direct relationship between the photocatalyst's composition and its performance, with the quantity of rGO synthesis notably influencing the catalyst's morphology and consequently, its photodegradation potency. The 1 wt% β-Ga2O3-rGO composition stands out in its class, showing a notable 4.7-fold increase in CO production over pristine β-Ga2O3 and achieving CO selectivity above 98%. This remarkable performance is a testament to the significant improvements rendered by our novel rGO integration technique. Such promising results highlight the potential of our custom-designed β-Ga2O3-rGO photocatalyst for critical environmental applications, representing a substantial leap forward in photocatalytic technology.

The mechanism behind the formation of microstructures originates from the sample fabrication process.During synthesis, the capillary action leads rGO sheets to adhere differently from β-Ga 2 O 3 1 .As the quantity of rGO increases, the sheets also expand, eventually enveloped the β-Ga 2 O 3 .However, energy accumulates at the unbound edges of the rGO sheets in this state 2,3 , prompting additional rGO sheets to stack at these edges to reduce the energy.This series of actions results in an increased surface area of rGO enveloping the β-Ga 2 O 3, leading to a phenomenon where, with rising rGO content, instead of encapsulating the surface area, it conglomerates.Another study proposed that, in thin sheets, an increase in thickness leads to a stable form where conglomerating at the edges or within specific regions, rather than enveloping the surface, is more stable 4,5 .As shown in Fig. S1, as the rGO content increases and the thickness escalates, energy concentrates at the edges of the rGO sheets, creating a folded appearance due to stacking at those regions.Subsequently, more rGO is layered onto these areas, forming the shape of an rGO flake.
We examined the sample's morphology using FE-SEM and investigated the sample's interfaces via TEM, as presented in Fig. S2, offering cross-sectional images into the nanoscale architecture of the β-Ga 2 O 3 -rGO 2 wt.% sample.Fig. S1b represents an enlargement of the red region shown in Fig. S1a.TEM images clearly reveal the interfaces between β-Ga 2 O 3 and rGO.When compared to Fig. 3a (β-Ga 2 O 3 -rGO 1 wt.%), it is evident that the rGO layer encapsulates β-Ga 2 O 3 more extensively, with a significantly greater thickness (around 55 nm).

Raman studies of -Ga 2 O 3 -rGO samples 𝛽
As seen in Fig. S3, the Raman spectrum of rGO predominantly exhibits the D-band peak(1353cm -1 ) attributed to sp3 defects and the G-band peak(1597cm -1 ) originating from in-plane vibrations of sp2 carbon atoms.No other peaks are observed, indicating the absence of impurities in the rGO sample 6 .
In the Raman spectra of β-Ga 2 O 3 -rGO 0.5wt.%,both the characteristic peaks of β-Ga 2 O 3 and rGO are observed concurrently.As the rGO content increases, the D and G bands become more prominent, while the peaks associated with β-Ga 2 O 3 notably diminish.This phenomenon arises from the inherent differences in scattering intensity between rGO and β-Ga 2 O 3 .Notably, at the transition point of β-Ga 2 O 3 -rGO 1wt.%, the I D /I G ratio experiences a slight increase from 0.92 to 1.00.The increase in the I D /I G ratio is attributed to structural disorder 7,8 .As confirmed by FESEM and TEM, at 1 wt.%, the catalyst encapsulation differs from previous concentrations, leading to a significant increase in photodegradation efficiency.Therefore, this indicates that the rGO layers initially undergo simple stacking but then encapsulate the catalyst upon reaching a critical concentration.Structural defects occur in the rGO layers to facilitate the encapsulation of the catalyst.The rGO layers are then continuously stacked with the catalyst encapsulated, resulting in a fixed I D /I G ratio of 1.00 as only the thickness increases.
These findings reaffirm that β-Ga 2 O 3 -rGO 1wt.% represents the critical concentration.Except for the slight increase in the I D /I G ratio from 0.92 to 1.00, no significant changes in peak width or peak shift are observed, suggesting that β-Ga 2 O 3 was synthesized with rGO without significant defects.on the y-axis.This conversion is facilitated through wavelength calibration 9 .Fig. S4a presents the light spectrum transmitted through the reference solution, as discussed in the experimental stage.On the other hand, Fig. S4b represents the light spectrum that has passed through the MB-containing sample.The spectrum of MB is then derived by subtracting the signal values of these two images, as shown in Fig. S4c 9 .Fig. S4d illustrates the absorption spectra for the MB specimen, taken from three distinct dash-lined paths within the absorption contour map (as shown in Fig. S4c).Crucially, the spatial characteristics of the samples are represented along the y-axis (camera pixel), allowing any spatial variations in the illuminated zones of the samples to be monitored.

Comparison of the photodegradation efficiency of methylene blue on various photocatalysts
Compared to photocatalysts currently under investigation, our engineered photocatalyst exhibits superior dye degradation performance.Various photocatalysts, including TiO 2 , are being explored for dye removal applications [10][11][12][13][14][15][16][17][18][19] .While xenon lamps with a broad spectrum of wavelengths, akin to natural light, are commonly utilized, ultraviolet light sources are also employed to enhance efficiency in Ga 2 O 3 and other photocatalysts due to their large bandgap.In this study, we achieved an outstanding photocatalytic efficiency of 94.8% using a broad-spectrum light source.This exceptional performance can be primarily attributed to the reduced recombination of EHPs facilitated by the separation and transport of these pairs.What further distinguishes our results apart is the rapid degradation achieved through rGO synthesis.In contrast, other photocatalysts have demonstrated over 90% degradation efficiency, with an average time requirement of 120 minutes, and the shortest reported time for dye degradation being 15 minutes.Conversely, our photocatalyst achieved a remarkable 94.8% degradation efficiency in a mere 1.3-minute timeframe.This underscores the substantial impact of preventing EHP recombination in photocatalysts on achieving high photocatalytic efficiency.

Fig. S1
Fig. S1 Illustration of β-Ga 2 O 3 -rGO composite formation with varying rGO concentrations.At 0.5 wt.%, rGO sheets begin adhering to the porous β-Ga 2 O 3 nanorods.With an increase to 1 wt.%, the rGO sheets cover more surface area, creating a more uniform encapsulation.At 2 wt.% and beyond, the rGO sheets exhibit increased stacking and wrinkling at the edges, leading to the formation of rGO clusters at 5 wt.%, which indicates a transition from encapsulation to agglomeration.This microstructural evolution reflects the balance between capillary action during synthesis and energy minimization at the rGO edges, influencing the photocatalytic efficiency and stability of the composite.

Figure
Figure S5a indicates a slight delay of approximately 50 seconds in ethylene (C 2 H 4 )

Figure
Figure S5b outlines the correlation between C 2 H 4 product yield and methylene blue

Fig. S4
Fig. S4 Representative contour images obtained by pixel-wavelength conversion of the spectrum taken by a camera when the light passes through (a) the reference solution, (b) the MB solutions.(c) A representative absorbance contour map of the MB sample obtained by subtracting the spectra

Fig. S6
Fig. S6 Assessing various photocatalysts investigated for the degradation of methylene blue dyes.