Next Article in Journal
A Novel ZnO/Co3O4 Nanoparticle for Enhanced Photocatalytic Hydrogen Evolution under Visible Light Irradiation
Next Article in Special Issue
A Brief Review on the Latest Developments on Pharmaceutical Compound Degradation Using g-C3N4-Based Composite Catalysts
Previous Article in Journal
Recent Progress in Conjugated Polymers-Based Donor–Acceptor Semiconductor Materials for Photocatalytic Hydrogen Evolution from Water Splitting
Previous Article in Special Issue
Fabrication of FeTCPP@CNNS for Efficient Photocatalytic Performance of p-Nitrophenol under Visible Light
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Catalysts
Volume 13
Issue 5
10.3390/catal13050851
catalysts-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Visible-Light-Driven GO/Rh-SrTiO3 Photocatalyst for Efficient Overall Water Splitting

by
Shuai Zhang
1,
Enhui Jiang
2,
Ji Wu
1,
Zhonghuan Liu
1,
Yan Yan
1,
Pengwei Huo
1,* and
Yongsheng Yan
1,*
1
School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China
2
School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, China
*
Authors to whom correspondence should be addressed.
Catalysts 2023, 13(5), 851; https://doi.org/10.3390/catal13050851
Submission received: 28 March 2023 / Revised: 2 May 2023 / Accepted: 3 May 2023 / Published: 8 May 2023
(This article belongs to the Special Issue Development of g-C3N4-Based Photocatalysts: Environmental Purification and Energy Conversion)
Browse Figures
Review Reports Versions Notes

Abstract

:
The combining of the heterostructure construction and active sites modification to remodel the traditional wide-band-gap semiconductor SrTiO3 for improving visible light absorption capacity and enhancing photocatalytic performance is greatly desired. Herein, we research a novel GO/Rh-SrTiO3 nanocomposite via a facile hydrothermal method. The champion GO/Rh-SrTiO3 nanocomposite exhibits the superior photocatalytic overall water splitting performance with an H2 evolution rate of 55.83 μmol∙g−1∙h−1 and O2 production rate of 23.26 μmol∙g−1∙h−1, realizing a breakthrough from zero with respect to the single-phased STO under visible light (λ ≥ 420 nm). More importantly, a series of characterizations results showed that significantly improving photocatalytic performance originated mainly from the construction of heterostructure and more active sites rooted in Rh metal. In addition, the possible photocatalytic reaction mechanisms and the transport behavior of photogenerated carriers have been revealed in deeper detail. This work provides an effective strategy for heterostructure construction to improve solar utilization through vastly expanding visible light response ranges from traditional UV photocatalysts.

Graphical Abstract

1. Introduction

The excessive consumption of fossil energy has led to serious energy and environmental problems [1] while promoting the research of green alternative energy sources [2]. Hydrogen is considered to be an optimal clean energy source because of its low density, high calorific value, easy storage, and non-toxicity [3]. At the same time, its combustion product is only water, which effectively avoids greenhouse gas emissions, so achieving efficient, clean, and low-energy hydrogen production is significant in the current development. Unlike fossil fuels, hydrogen is not readily available directly in nature. Fortunately, hydrogen can be produced from primary energy sources such as coal, crude oil, natural gas, biomass, and solar energy. Many process technologies for hydrogen production have been developed, such as pyrolysis, fermentation, electrocatalysis, and photocatalysis [4]. Currently, the largest hydrogen production comes from coal gasification, methane steam reforming, and methane partial oxidation technologies [5]. However, the excessive depletion of fossil fuels and significant environmental issues have promoted the development of viable alternatives. Among them, photocatalytic water splitting, which uses solar energy and water, is a promising option [6]. In recent years, photocatalytic technology has received widespread attention because of its clean, safe, sustainable, and longevous advantages. In the photocatalytic system, a decisive role in the overall water splitting efficiency is played by the photocatalyst, which is the core of the whole system [7,8]. It is well known that suitable band structure, abundant reactive sites, and efficient photogenerated carrier separation are the criteria for excellent photocatalysts [9,10]. However, there are very few photocatalysts that can meet these criteria. Therefore, it is essential to study an efficient photocatalyst.
In recent years, SrTiO3 (abbreviated as STO) has been widely used in photocatalysis [11], sensors [12], dye-sensitized solar cells (DSCC) [13], and supercapacitors [14] because of its excellent properties, including high dielectric constant, resistance to photochemical corrosion, relatively stable properties, and non-toxicity [15,16]. Nevertheless, the excessively wide energy band (~3.2 eV) of STO semiconductors leads to poor photogenerated electron–hole pair separation and low utilization of visible light, which results in poor photocatalytic performance [17]. Therefore, improving the visible light utilization of STO is a major challenge. Currently, the modification of photocatalysts involves heterostructure construction [18,19], defect generation [20,21], elemental doping [22,23], and active sites modification [24,25]. Ha’s group synthesized SrTiO3/TiO2 heterostructures with different morphologies by a simple hydrothermal method. The SrTiO3/TiO2 heterostructures not only facilitate the rapid separation of photogenerated electron–hole pairs but also allow more light absorption, which has a synergistic effect that enhances the photocatalytic activity of SrTiO3/TiO2 heterostructures [26]. Deng’s group synthesized SrTiO3-SrCO3 heterostructures by a simple hydrothermal method. The SrTiO3-SrCO3 heterostructures facilitate the rapid separation and transmission of photogenerated carriers. Under simulated sunlight irradiation, the champion SrTiO3-SrCO3 showed a great photocatalytic H2 production rate of 4.73 mmol∙h−1∙g−1, which was 21 times higher than that of pure SrTiO3 [27]. The strategy of constructing heterostructures was applied to STO and other semiconductors, significantly improving the utilization of visible light and the separation and migration of charge carriers [28].
Graphene oxide (GO) is widely used for the synthesis of efficient photocatalysts because of its big specific surface area, outstanding electrical conductivity, and powerful light absorption ability [29,30]. For example, Jung’s group combined GO with TiO2 and ZnO to increase light utilization and reduce electron–hole pairs recombination in the composite [31]. Gao’s group synthesized GO/CdS composites by a novel two-phase hybrid method. The efficient electron transfer from CdS to GO decreased the recombination of photogenerated carriers which improved the catalytic activity [32]. Hunge’s group has synthesized GO/TiO2 composite using a hydrothermal process. A series of characterizations showed that the occurrence of GO not only accelerates electron transfer and thus inhibits the recombination of photogenerated electron–hole pairs but also increased light absorption and utilization, which improved the photocatalytic activity [33]. Herein, GO was applied to improve STO light utilization and conductivity. Meanwhile, the active sites are also important for overall water splitting, and metal elements are usually chosen as the electron acceptor and as the active sites for the reaction. For example, Cai’s group successfully constructed metal/phosphide heterostructures by photo-deposition which drove a dual active site mechanism thereby overcoming the low efficiency of precious metal water splitting and providing an effective strategy for the preparation of high performance water splitting catalysts [34]. The use of the Rh metal as the electron acceptors greatly increases the exposed active sites and promotes the electron–hole separation.
In this work, heterostructure construction and active site modification strategies have been applied to fabricate GO/Rh-STO composites by a hydrothermal process. Notably, the prepared GO/Rh-STO composites show excellent photocatalytic overall water splitting performance under visible light. In addition, the influencing factors to enhance the photocatalytic activity and the rational photocatalytic reaction mechanism were also investigated in depth. This study combines heterostructure construction techniques (GO improved light absorption) and active sites modification (Rh metal increased active sites) to improve photocatalytic overall water splitting performance, which provides a new strategy to transform traditional UV catalysts into visible-light-responsive catalysts with abundant active sites applied to energy conversion.

2. Results and Discussions

2.1. Characterization of GO/Rh-STO Photocatalysts

The microstructure and morphological characteristics of the prepared catalysts were analyzed by SEM, TEM, HRTEM, and EDS mapping. Figure 1a,d show the SEM and TEM images of STO which show a smooth surface of hexagonal nanosheets without any other impurities, thereby confirming the formation of STO nanosheets. Figure 1b shows the SEM image of GO with a large specific surface area, clearly illustrating the disorderly stacked, and folded sheet-like accumulation. Figure 1c,e show SEM and TEM images of GO/Rh-STO heterostructures, showing that STO nanoparticles grown on the GO flakes. In Figure 1f, the HRTEM image of the GO/Rh-STO heterostructure shows the heterostructure interface between GO and STO, thereby confirming the formation of the GO/Rh-STO heterostructure. Moreover, the clean lattice spacing of 0.224 nm matches well with the (111) plane of STO, while GO is amorphous with no clear lattice. In addition, Figure 1g shows the HAADF and EDS mapping images which show all elements of Sr, Ti, O, Rh, and C in the GO/Rh-STO composite catalysts, which further confirms the formation of GO/Rh-STO composite catalysts. The above results confirm the formation of GO/Rh-STO heterostructures.

2.2. The Crystal Structure and Chemical States Analysis

To better understand the structure and chemical state of pure STO and GO/Rh-STO, XRD patterns and XPS analysis were investigated. As shown in Figure 2a, the STO nanosheets show good crystallinity with diffraction peaks at 22.75°, 32.40°, 39.96°, 46.47°, 52.35°, 57.76°, and 67.83°, which corresponds to (100), (110), (111), (200), (012), (211), and (220) crystal planes of the STO structure, respectively. These peaks are characteristic peaks of STO, indexing to JCPDS card number 35-0734 [35]. The STO crystalline structure is well-developed based on the well-defined and very sharp peaks in the XRD patterns of the STO nanosheets. As shown in Figure 2b, the XRD pattern of GO shows an intense and sharp peak at 2θ = 10.40° that correspond to the (001) plane of GO, which is usually determined by the synthesis process and the number of water layers in the interplanar space of GO [36,37]. The XRD patterns of GO/Rh-STO nanocomposites clearly show GO and STO characteristic diffraction peaks, which proves the presence of GO and STO in the nanocomposites, while the decrease of GO characteristic peak intensity indicates that the aggregation of GO sheets has been greatly decreased. Therefore, the XRD patterns confirmed the successful synthesis of GO, STO, and GO/Rh-STO nanocomposites. Figure 3a shows that there are Ti, Sr, Rh, C, and O elements in GO/Rh-STO. As shown in Figure 3b, two symmetric diffraction peaks (309.4 eV and 314.4 eV) appeared in the Rh 3d XPS spectrum which corresponded to Rh 3d 5/2 and 3d 3/2, representing Rh4+ rather than Rh3+ or the oxide form of Rh [38,39]. This suggests that Rh is successfully modified into the STO lattice by substitution at the Ti position. Figure 3c shows the XPS patterns of O elements in GO and GO/Rh-STO samples. The diffraction peak of lattice oxygen in GO/Rh-STO sample shifts from 529.8 eV to lower binding energy, which is due to the interference generated by Rh atoms entering the STO crystal structure, and further confirms the successful modification of Rh in STO. The XPS spectra of Ti 2p and Sr 3d of STO and GO/Rh-STO are shown in Figure 3d,e, respectively, which show that the integration of Rh metal active sites modification and GO heterostructure construction in the STO nanosheets does not change the XPS of Ti 2p and Sr 3d too much. This result suggests that the incorporation of GO and the Rh metal does not change the core structure of STO.
The XPS atomic percentage analysis of xGO/Rh-STO as shown in Table 1. The percentages of C atomic were 3.8%, 7.2%, 12.2%, and 16.9%, respectively, and named 3.8% GO/Rh-STO, 7.2% GO/Rh-STO, 12.2% GO/Rh-STO, and 16.9% GO/Rh-STO, according to the atomic percentage analysis of XPS.

2.3. Photocatalytic Performance Evaluation

The photocatalytic performance of the prepared photocatalysts was investigated by overall water splitting for H2 and O2 production. As shown in Figure 4a, pure STO cannot overall water splitting under visible light (λ ≥ 420 nm) due to the fact that it can only absorb and utilize UV light. However, the overall water splitting of GO/STO heterostructure can work under visible light. The champion GO/Rh-SrTiO3 nanocomposite exhibits the superior photocatalytic overall water splitting performance with an H2 evolution rate of 55.83 μmol∙g−1∙h−1 and O2 production rate of 23.26 μmol∙g−1∙h−1 under visible light (λ ≥ 420 nm), illustrating that the heterostructure construction and Rh metal active sites modification enhanced the utilization of visible light and photocatalytic performance of STO. As shown in Figure 4b, the H2 and O2 production rates over the xGO/Rh-STO samples are increased and then decreased with the increasing amount of GO, the possible reason for which can be ascribed to the fact that the excess GO reduces the exposed active sites of STO, resulting in a reduction in the overall water splitting rate. Notably, the 7.2% GO/Rh-STO photocatalyst displays the highest H2 production rate (55.83 μmol∙g−1∙h−1) and O2 production rate (23.26 μmol∙g−1∙h−1) under visible light (λ ≥ 420 nm).
In recent years, there have been many works aimed at enhancing the performance of STO overall water splitting as shown in Table 2. Modulating the morphology of STO is also an effective strategy to improve photocatalytic activity, in addition to the forming of composite materials. Many different morphological STO samples have been reported, such as nanoparticles, nanosheets, nanospheres, nanorods, coral-like and flower-like microspheres, etc. [40,41,42,43] The study of STO with different morphologies revealed that highly interconnected porous structures are more favorable for reactant adsorption, light utilization, and carrier migration. For example, flower-like STO with a large number of cavities facilitates a reduction in photogenerated carrier recombination while facilitating the reflection of light to improve light utilization [42,43]. These are the keys to improving the photocatalytic activity of STO. Morphological modulation provides a strategy to further improve the photocatalytic activity of GO/Rh-STO. The modified STO catalysts showed relatively high overall water splitting performance under UV light and low performance under visible light. This work synthesized GO/Rh-STO photocatalyst and exhibited excellent overall water splitting performance compared to other works under visible light. The GO/Rh-STO composites have great potential for large-scale photocatalytic overall water splitting applications, but their performance at present is still insufficient and much work needs to be carried out to improve the overall water splitting performance of GO/Rh-STO under visible light.

2.4. The Influence Factors of Enhancing Photocatalytic Performance

The valence and conduction band structures are essential for the analysis of the underlying causes of the enhanced photocatalytic activity. As shown in Figure 5a, the UV-vis DRS of pure STO shows an absorption edge at 385 nm, consistent with the published literature [52]. Surprisingly, the GO/STO photocatalyst has a much higher absorption capacity for visible light compared to pure STO. Meanwhile, according to the equation (αhυ) = A (hυ − Eg)n/2, the plotting of (αhυ)1/2 with respect to the energy (hυ) is performed to calculate the band gap energy due to the indirect band gap (n = 1) property of STO [53], while the plotting of (αhυ)2 with respect to the energy (hυ) is performed due to the direct band gap (n = 4) property of GO/Rh-STO [33]. In Figure 5b, the band gap energies of STO and GO/Rh-STO are calculated to be 3.20 eV and 2.09 eV, respectively, which indicates that the combination of GO and STO greatly reduces the band gap energy and enhances the absorption and utilization of visible radiation. In addition, Mott–Schottky measurements were performed to investigate the conduction bands of STO and GO/Rh-STO. As shown in Figure 5c,d, the Mott–Schottky slopes of STO and GO/Rh-STO indicate a positive correlation, which indicates that they are all n-type semiconductors. The conduction band potentials of STO and GO/Rh-STO are −0.41 eV and −0.65 eV (vs. NHE), respectively, as calculated by the equation ENHE = EAg/AgCl + 0.059 × PH + 0.197. The VB potentials of STO and GO/Rh-STO were determined to be 2.79 eV and 1.44 eV from the empirical equation of EVB = ECB + Eg [54,55].
The photoelectric properties are closely related to the transfer and separation ability of the charge carriers of the photocatalyst. As shown in Figure 6a, the surface charge transfer efficiency of the samples was studied by EIS and the GO/Rh-STO samples show a much smaller semicircular diameter and much lower charge transfer resistance than pure STO. By calculating the diameter of the semicircle obtained by EIS, the charge transfer resistance (Rct) of GO/STO, GO, and pure STO were 103.2, 41.3, and 279.5 Ω, respectively, and the conductivity (Rct−1) was from the largest to the smallest sample as GO>GO/STO>STO. This is also demonstrated by the linear sweep voltage plot (LSV) shown in Figure 6c, where the overpotential of GO/Rh-STO (1.19V) is smaller than that of pure STO (1.93 V) at −10 mA·cm−2, indicating that the conductivity of GO/Rh-STO samples is better than that of STO. The improved electrical conductivity of GO/Rh-STO composites is due to the introduction of GO with excellent electrical conductivity. Furthermore, Figure 6b shows the photocurrent responses of the prepared STO, GO, and GO/Rh-STO heterostructures, which all exhibit stable photocurrent signals over six cycles. Notably, the photocurrent intensity of the GO/Rh-STO samples is stronger than that of pure STO and GO, indicating that the GO/Rh-STO composites have better separation of charge–hole pairs.
In this study of the behavior of charge separation of samples by photoluminescence (PL) and transient photoluminescence spectroscopy (TRPL), the PL spectra of photocatalysts at the excitation wavelength of 385 nm are depicted in Figure 7a, in which PL emission at 480 nm on as-prepared photocatalysts is shown. As shown in Figure 7b, under the condition of λex = 385 nm and λem = 480 nm, we tracked the transient photoluminescence (TRPL) emission profile. From Figure 7b, the average decay lifetimes of GO/STO (1.6 ns) and GO/Rh-STO (1.9 ns) composite catalysts are longer compared to pure STO (1.1 ns), which further demonstrates the effective facilitative effect of the separation and transfer of photoinduced charges.
Furthermore, the specific surface area was investigated in order to investigate the factors affecting the activity of photocatalytic water splitting. As is shown in Figure 8a–c, the N2 adsorption–desorption isotherms show that the samples GO, STO, and GO/Rh-STO all exhibit typical type IV isotherms with H3-type hysteresis loops. This indicates the existence of multi-porous structures in GO, STO, and GO/Rh-STO. The BET surface area of the GO/Rh-STO (22.537 m2/g, Figure 8a) composites was significantly larger compared to that of STO (4.15 m2/g, Figure 8c), which was mainly attributed to the large specific surface area of GO. In addition, the composition of GO/Rh-STO nanocomposites was analyzed by Raman spectroscopy. As shown in Figure 8d, STO has secondary Raman scattering from 160 cm−1 to 451 cm−1, which leads to a continuous broadband. STO shows its characteristic peaks at 171, 245, 307, 609, 674, and 1044 cm−1 [56,57] and GO shows its characteristic peaks at 1393 cm−1 (D-band) and 1596 cm−1 (G-band). Two additional bands of GO/Rh-STO were obtained at 1392 (D-band) and 1595 cm−1 (G-band) [58], which confirmed the presence of GO. Therefore, the Raman spectra illustrate the successful preparation of GO/Rh-STO nanocomposites.

2.5. Photocatalytic Mechanism Research

Based on the above experimental results, the mechanism of the photocatalytic reaction on GO/Rh-STO heterostructure is shown in Figure 9. According to the above study, the VB and CB energy levels of STO were confirmed to be 2.79 eV and −0.41 eV, respectively. The Fermi energy level of GO is −0.008 V with respect to NHE [59]. The CB energy level of STO is −0.41 eV, which is positive for the Fermi energy level of GO. As a result, the photoexcited electrons are rapidly transferred from the CB of STO to GO, thereby suppressing the photoexcited e−/h+ pairs’ recombination and improving their separation efficiency. During the photocatalytic experiments, when the light starts being exposed on the photocatalyst, STO absorbs the light and the e− production of STO transfers from VB to CB and the h+ were left at VB of STO. Due to the solid-solid tight contact interface, GO facilitates the rapid transfer of e− to the Rh active sites. The e− transfers quickly to the Rh active sites and produces H2 with H+. Meanwhile, h+ on the VB of STO produces O2 with water, because the valence band maximum for the STO is located at a more positive position than the O2/H2O energy level [60].

3. Experiment

3.1. Materials

Titanium butoxide (C16H36O4Ti), sodium hydroxide (NaOH), strontium chloride (SrCl2), rhodium(III) chloride trihydrate (RhCl3·3H2O), and graphite powder were obtained from Shanghai Aladdin Technology Co., Ltd. (Shanghai, China). Ethanol (C2H5OH), hydrochloric acid (HCl), sulphuric acid (H2SO4), hydrogen peroxide solution (H2O2), sodium nitrate (NaNO3), and potassium permanganate (KMnO4) were obtained from Shanghai Sinopharm Co., Ltd. (Shanghai, China). All reagents involved in the experiments were of analytical grade (purity ≥ 99.0%) and the water used throughout the study was deionized water (DI).

3.2. Synthesis and Preparation

3.2.1. Synthesis of Graphene Oxide (GO)

GO was synthesized using a modified Hummer method which is reported in the other literature [61]. In short, 100 mL H2SO4 (98%) was added to a round-bottom flask (500 mL) in an ice bath with stirring at 450 rpm. Graphite powder (5 g), NaNO3 (1.6 g), and KMnO4 (10 g) were added to concentrated sulfuric acid. An amount of 100 mL H2O was added to the mixture when the color of the reaction mixture turned light gray. After increasing the temperature of the reaction vessel to 102 °C for 2 h, H2O2 (40 mL) was added. The reaction mixture was washed with 5% HCl until the filtrate became colorless after stirring the reaction mixture for 1 h. Then, we obtained graphite oxide after washing 3 times with H2O and dried it in a desiccator at 60 °C. Finally, we obtained GO by ultrasonication of the dispersed graphite oxide in water.

3.2.2. Synthesis of Strontium Titanate (STO)

The STO nanoparticle was synthesized via a hydrothermal route [62]. Firstly, SrCl2 (0.01 mol) was added to an autoclave (50 mL) followed by 30 mL of water. After stirring for 20 min, 3.4 mL titanium butoxide was added, then 0.8 g NaOH. After stirring for 2 h, the autoclave was heated to 195 °C and held for 23 h. After the completion of the reaction, the reaction was washed by centrifugation several times and dried at 60 °C. Finally, we obtained STO white powder.

3.2.3. Synthesis of GO/Rh-STO Composite Catalysts

GO/Rh-STO composites were synthesized by the hydrothermal method [63]. Firstly, SrCl2 (0.01 mol) and RhCl3·3H2O (50 mg) were added to an autoclave (50 mL) followed by 30 mL of water. After stirring for 20 min, 3.4 mL titanium butoxide was added, then 0.8 g NaOH. After stirring for 30 min, 20 mg GO was added. After stirring for 2 h, the autoclave was heated to 195 °C and held for 23 h. After the completion of the reaction, the reaction was washed by centrifugation several times and dried at 60 °C to obtain GO/Rh-STO precursor powder. Finally, we obtained the GO/Rh-STO composite catalysts by annealing at 200 °C in ambient for 2 h. The xGO/Rh-STO composites were synthesized by changing the amount of GO (10 mg, 20 mg, 40 mg, 60 mg). The percentages of C atomic were 3.8%, 7.2%, 12.2%, and 16.9%, which named 3.8% GO/Rh-STO, 7.2% GO/Rh-STO, 12.2% GO/Rh-STO, and 16.9% GO/Rh-STO, respectively, according to the C atomic percentage analysis of XPS in Table 1.

3.3. Evaluation on Efficiency of Photocatalysts

The evaluation of the overall water splitting performance was performed on a CEL-PAEM-D8 photocatalytic activity evaluation system (CEL-PF300-T9) equipped with a 300W xenon lamp (Beijing Zhongjiao Jinyuan Technology Co., Ltd., Beijing, China) and a cutoff filter allowing λ > 420 nm. Briefly, 0.1 g of catalyst was dispersed in an light reactor containing 100 mL of water, connected to the photoreaction system, and then evacuated. The reactor was irradiated with a 300w xenon lamp as the light source for performance testing. The produced H2 and O2 were evaluated hourly on a gas chromatograph (GC 7920) using high-purity Ar as the carrier gas, and the amounts of H2 and O2 were calculated from their standard curves.

3.4. Characterization

The structure and crystalline phase of the samples were analyzed by XPS (Thermo Fisher Scientific K-Alpha, Waltham, MA, USA) and XRD (Rigaku Ultima IV, Tokyo, Japan). X-ray photoelectron spectroscopy (XPS) analysis was conducted on a Thermo Fisher Scientific K-Alpha photoelectron spectroscopy at 5.0 × 10−10 mbar. X-ray diffraction (XRD) patterns of the samples were collected with a scan rate of 0.02°. The morphology was observed on a field emission scanning electron microscope (Hitachi Regulus 8100, Tokyo, Japan) and a field emission transmission electron microscope (FEI Talos F200X G2, Waltham, MA, USA). Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images were obtained by an FEI Talos F200X G2 instrument at an accelerating voltage of 200 kV. The diffuse reflectance UV-visible (DRS) was recorded with a PE Lambda 750. The specific surface area was analyzed on an N2 adsorption–desorption device (TriStar II 20, Waltham, MA, USA) at 77 K, and the samples were degassed at 120 °C for 6 h in a vacuum before the measurements were taken. The photoluminescence (PL) spectra and transient photoluminescence spectra (TRPL) were measured using an Edinburgh FLS-1000 spectrofluorometer.

3.5. Electrochemical Tests

The electrochemical properties of the samples were tested on a CHI600E electrochemical workstation. The platinum electrode, ITO glass (1 cm × 2 cm) coated by sample, and Ag+/AgCl electrode served as counter electrode, working electrode, and reference electrode to build the three-electrode system in 0.5 M H2SO4 electrolyte.

4. Conclusions

In conclusion, we reported a GO/Rh-SrTiO3 composite that was prepared by a simple hydrothermal process for overall water splitting. The champion catalyst realized H2 production rate of 55.83 μmol∙g−1∙h−1 and O2 production rate of 23.26 μmol∙g−1∙h−1 under visible light (λ ≥ 420 nm). The studies of microstructure, physicochemical properties, and photoelectric behavior demonstrated that the GO/Rh-SrTiO3 heterojunction can work under visible light, which greatly improves the utilization of sunlight. Moreover, the Rh metal as the electron acceptor, which greatly increases the active sites and promotes the electron–hole separation and transfer. This work provides a new strategy to transform traditional UV catalysts into visible-light-responsive catalysts with abundant active sites.

Author Contributions

Conceptualization, P.H. and Y.Y. (Yongsheng Yan); methodology, Y.Y. (Yan Yan); software, E.J.; validation, S.Z., J.W. and Z.L.; formal analysis, Y.Y. (Yan Yan); investigation, S.Z.; resources, Y.Y. (Yongsheng Yan); data curation, S.Z.; writing—original draft preparation, S.Z.; writing—review and editing, E.J.; visualization, S.Z.; supervision, J.W.; project administration, Y.Y. (Yan Yan); funding acquisition, Y.Y. (Yongsheng Yan). All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (Grant No. 21776117 and 21806060).

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no competing financial interest.

References

  1. Wang, W.; Xu, M.; Xu, X.; Zhou, W.; Shao, Z. Perovskite oxide based electrodes for high-performance photoelectrochemical water splitting. Angew. Chem. Int. Ed. 2020, 59, 136–152. [Google Scholar] [CrossRef] [PubMed]
  2. Niu, W.; Yang, Y. Graphitic carbon nitride for electrochemical energy conversion and storage. ACS Energy Lett. 2018, 3, 2796–2815. [Google Scholar] [CrossRef]
  3. Zhou, Z.; Pei, Z.; Wei, L.; Zhao, S.; Jian, X.; Chen, Y. Electrocatalytic hydrogen evolution under neutral pH conditions: Current understandings, recent advances, and future prospects. Energy Environ. Sci. 2020, 13, 3185–3206. [Google Scholar] [CrossRef]
  4. Holladay, J.D.; Hu, J.; King, D.L.; Wang, Y. An overview of hydrogen production technologies. Catal. Today 2009, 139, 244–260. [Google Scholar] [CrossRef]
  5. LeValley, T.L.; Richard, A.R.; Fan, M. The progress in water gas shift and steam reforming hydrogen production technologies—A review. Int. J. Hydrogen Energy 2014, 39, 16983–17000. [Google Scholar] [CrossRef]
  6. Hisatomi, T.; Kubota, J.; Domen, K. Recent advances in semiconductors for photocatalytic and photoelectrochemical water splitting. Chem. Soc. Rev. 2014, 43, 7520–7535. [Google Scholar] [CrossRef] [PubMed]
  7. Jiang, R.; Lu, G.; Yan, Z.; Wu, D.; Zhou, R.; Bao, X. Insights into a CQD-SnNb2O6/BiOCl Z-scheme system for the degradation of benzocaine: Influence factors, intermediate toxicity and photocatalytic mechanism. Chem. Eng. J. 2019, 374, 79–90. [Google Scholar] [CrossRef]
  8. Che, H.; Che, G.; Zhou, P.; Liu, C.; Dong, H.; Li, C.; Li, C. Nitrogen doped carbon ribbons modified g-C3N4 for markedly enhanced photocatalytic H2-production in visible to near-infrared region. Chem. Eng. J. 2020, 382, 122870. [Google Scholar] [CrossRef]
  9. Tang, M.; Ao, Y.; Wang, C.; Wang, P. Rationally constructing of a novel dual Z-scheme composite photocatalyst with significantly enhanced performance for neonicotinoid degradation under visible light irradiation. Appl. Catal. B Environ. 2020, 270, 118918. [Google Scholar] [CrossRef]
  10. Li, C.; Yu, S.; Zhang, X.; Wang, Y.; Liu, C.; Chen, G.; Dong, H. Insight into photocatalytic activity, universality and mechanism of copper/chlorine surface dual-doped graphitic carbon nitride for degrading various organic pollutants in water. J. Colloid Interface Sci. 2019, 538, 462–473. [Google Scholar] [CrossRef]
  11. Patial, S.; Hasija, V.; Raizada, P.; Singh, P.; Singh, A.A.P.K.; Asiri, A.M. Tunable photocatalytic activity of SrTiO3 for water splitting: Strategies and future scenario. J. Environ. Chem. Eng. 2020, 8, 103791. [Google Scholar] [CrossRef]
  12. Szafraniak, B.; Fusnik, Ł.; Xu, J.; Gao, F.; Brudnik, A.; Ry-dosz, A. Semiconducting metal oxides: SrTiO3, BaTiO3 and BaSrTiO3 in gas-sensing applications: A review. Coatings 2021, 11, 185. [Google Scholar] [CrossRef]
  13. Jayabal, P.; Sasirekha, V.; Mayandi, J.; Jeganathan, K.; Ramakrishnan, V. A facile hydrothermal synthesis of SrTiO3 for dye sensitized solar cell application. J. Alloys Compd. 2014, 586, 456–461. [Google Scholar] [CrossRef]
  14. Ghosh, D.; Giri, S.; Sahoo, S.; Das, C.K. In situ synthesis of graphene/amine-modified graphene, polypyrrole composites in presence of SrTiO3 for supercapacitor applications. Polym. Plast. Technol. Eng. 2013, 52, 213–220. [Google Scholar] [CrossRef]
  15. Muhamad, N.F.; Osman, R.A.M.; Idris, M.S.; Yasin, M.N.M. Physical and electrical properties of SrTiO3 and SrZrO3//EPJ Web of Conferences. EDP Sci. 2017, 162, 01052. [Google Scholar]
  16. Hu, X.J.; Yang, Y.; Hou, C.; Liang, T.X. Thermodynamic and Electronic Properties of Two-Dimensional SrTiO3. J. Phys. Chem. C 2021, 126, 517–524. [Google Scholar] [CrossRef]
  17. Liu, G.; Zhao, Y.; Sun, C.; Li, F.; Lu, G.Q.; Cheng, H.M. Synergistic effects of B/N doping on the visible-light photocatalytic activity of mesoporous TiO2. Angew. Chem. Int. Ed. 2008, 47, 4516–4520. [Google Scholar] [CrossRef]
  18. Zhang, X.; Wang, Y.; Liu, B.; Sang, Y.; Liu, H. Heterostructures construction on TiO2 nanobelts: A powerful tool for building high-performance photocatalysts. Appl. Catal. B Environ. 2017, 202, 620–641. [Google Scholar] [CrossRef]
  19. Zhang, Z.; Huang, L.; Zhang, J.; Wang, F.; Xie, Y.; Shang, X.; Wang, X. In situ constructing interfacial contact MoS2/ZnIn2S4 heterostructure for enhancing solar photocatalytic hydrogen evolution. Appl. Catal. B Environ. 2018, 233, 112–119. [Google Scholar] [CrossRef]
  20. Maarisetty, D.; Baral, S.S. Defect engineering in photocatalysis: Formation, chemistry, optoelectronics, and interface studies. J. Mater. Chem. A 2020, 8, 18560–18604. [Google Scholar] [CrossRef]
  21. Bai, S.; Zhang, N.; Gao, C.; Xiong, Y. Defect engineering in photocatalytic materials. Nano Energy 2018, 53, 296–336. [Google Scholar] [CrossRef]
  22. Putri, L.K.; Ong, W.J.; Chang, W.S.; Chai, S.P. Heteroatom doped graphene in photocatalysis: A review. Appl. Surf. Sci. 2015, 358, 2–14. [Google Scholar] [CrossRef]
  23. Cui, D.; Hao, W.; Chen, J. The synergistic effect of heteroatom doping and vacancy on the reduction of CO2 by photocatalysts. ChemNanoMat 2021, 7, 894–901. [Google Scholar] [CrossRef]
  24. Zhang, L.H.; Shi, Y.; Wang, Y.; Shiju, N.R. Nanocarbon catalysts: Recent understanding regarding the active sites. Adv. Sci. 2020, 7, 1902126. [Google Scholar] [CrossRef] [PubMed]
  25. Li, Y.; Li, X.; Zhang, H.; Fan, J.; Xiang, Q. Design and application of active sites in g-C3N4-based photocatalysts. J. Mater. Sci. Technol. 2020, 56, 69–88. [Google Scholar] [CrossRef]
  26. Ha, M.N.; Zhu, F.; Liu, Z.; Wang, L.; Liu, L.; Lu, G.; Zhao, Z. Morphology-controlled synthesis of SrTiO3/TiO2 heterostructures and their photocatalytic performance for water splitting. RSC Adv. 2016, 6, 21111–21118. [Google Scholar] [CrossRef]
  27. Deng, Y.; Shu, S.; Fang, N.; Wang, R.; Chu, Y.; Liu, Z.; Cen, W. One-pot synthesis of SrTiO3-SrCO3 heterojunction with strong interfacial electronic interaction as a novel photocatalyst for water splitting to generate H2. Chin. Chem. Lett. 2023, 34, 107323. [Google Scholar] [CrossRef]
  28. Pan, J.H.; Shen, C.; Ivanova, I.; Zhou, N.; Wang, X.; Tan, W.C.; Wang, Q. Self-template synthesis of porous perovskite titanate solid and hollow submicrospheres for photocatalytic oxygen evolution and mesoscopic solar cells. ACS Appl. Mater. Interfaces 2015, 7, 14859–14869. [Google Scholar] [CrossRef]
  29. Xiang, Q.; Yu, J.; Jaroniec, M. Graphene-based semiconductor photocatalysts. Chem. Soc. Rev. 2012, 41, 782–796. [Google Scholar] [CrossRef]
  30. Zhang, N.; Zhang, Y.; Xu, Y.J. Recent progress on graphene-based photocatalysts: Current status and future perspectives. Nanoscale 2012, 4, 5792–5813. [Google Scholar] [CrossRef]
  31. Johra, F.T.; Jung, W.G. RGO–TiO2–ZnO composites: Synthesis, characterization, and application to photocatalysis. Appl. Catal. A Gen. 2015, 491, 52–57. [Google Scholar] [CrossRef]
  32. Gao, P.; Liu, J.; Sun, D.D.; Ng, W. Graphene oxide–CdS composite with high photocatalytic degradation and disinfection activities under visible light irradiation. J. Hazard. Mater. 2013, 250, 412–420. [Google Scholar] [CrossRef] [PubMed]
  33. Hunge, Y.M.; Yadav, A.A.; Dhodamani, A.G.; Suzuki, N.; Terashima, C.; Fujishima, A.; Mathe, V.L. Enhanced photocatalytic performance of ultrasound treated GO/TiO2 composite for photocatalytic degradation of salicylic acid under sunlight illumination. Ultrason. Sonochem. 2020, 61, 104849. [Google Scholar] [CrossRef] [PubMed]
  34. Wang, Y.; Du, Y.; Fu, Z.; Ren, J.; Fu, Y.; Wang, L. Construction of Ru/FeCoP heterointerface to drive dual active site mechanism for efficient overall water splitting. J. Mater. Chem. A 2022, 10, 16071–16079. [Google Scholar] [CrossRef]
  35. Shahabuddin, S.; Muhamad Sarih, N.; Mohamad, S.; Joon Ching, J. SrTiO3 nanocube-doped polyaniline nanocomposites with enhanced photocatalytic degradation of methylene blue under visible light. Polymers 2016, 8, 27. [Google Scholar] [CrossRef]
  36. Zhang, K.; Zhang, L.L.; Zhao, X.S.; Wu, J. Graphene/polyaniline nanofiber composites as supercapacitor electrodes. Chem. Mater. 2010, 22, 1392–1401. [Google Scholar] [CrossRef]
  37. Kumar, N.A.; Choi, H.J.; Shin, Y.R.; Chang, D.W.; Dai, L.; Baek, J.B. Polyaniline-grafted reduced graphene oxide for efficient electrochemical supercapacitors. ACS Nano 2012, 6, 1715–1723. [Google Scholar] [CrossRef]
  38. Kiss, B.; Manning, T.D.; Hesp, D.; Didier, C.; Taylor, A.; Pickup, D.M.; Rosseinsky, M.J. Nano-structured rhodium doped SrTiO3–Visible light activated photocatalyst for water decontamination. Appl. Catal. B Environ. 2017, 206, 547–555. [Google Scholar] [CrossRef]
  39. Kawasaki, S.; Nakatsuji, K.; Yoshinobu, J.; Komori, F.; Takahashi, R.; Lippmaa, M.; Kudo, A. Epitaxial Rh-doped SrTiO3 thin film photocathode for water splitting under visible light irradiation. Appl. Phys. Lett. 2012, 101, 033910. [Google Scholar] [CrossRef]
  40. Kiran, K.S.; Ashwath Narayana, B.S.; Lokesh, S.V. Enhanced photocatalytic activity of perovskite SrTiO3 nanorods. Solid State Technol. 2020, 63, 1913–1920. [Google Scholar]
  41. Zhao, W.; Wang, H.; Liu, N.; Rong, J.; Zhang, Q.; Li, M.; Yang, X. Hydrothermal synthesis of Litchi-like SrTiO3 with the help of ethylene glycol. J. Am. Ceram. Soc. 2019, 102, 981–987. [Google Scholar] [CrossRef]
  42. Yang, D.; Sun, Y.; Tong, Z.; Nan, Y.; Jiang, Z. Fabrication of bimodal-pore SrTiO3 microspheres with excellent photocatalytic performance for Cr (VI) reduction under simulated sunlight. J. Hazard. Mater. 2016, 312, 45–54. [Google Scholar] [CrossRef] [PubMed]
  43. Kong, C.; Su, X.; Qing, D.; Zhao, Y.; Wang, J.; Zeng, X. Controlled synthesis of various SrTiO3 morphologies and their effects on photoelectrochemical cathodic protection performance. Ceram. Int. 2022, 48, 20228–20236. [Google Scholar] [CrossRef]
  44. Fan, Y.; Liu, Y.; Cui, H.; Wang, W.; Shang, Q.; Shi, X.; Tang, B. Photocatalytic overall water splitting by SrTiO3 with surface oxygen vacancies. Nanomaterials 2020, 10, 2572. [Google Scholar] [CrossRef] [PubMed]
  45. Wei, Y.; Wang, J.; Yu, R.; Wan, J.; Wang, D. Constructing SrTiO3–TiO2 heterogeneous hollow multi-shelled structures for enhanced solar water splitting. Angew. Chem. Int. Ed. 2019, 58, 1422–1426. [Google Scholar] [CrossRef]
  46. Iwase, A.; Udagawa, Y.; Yoshino, S.; Ng, Y.H.; Amal, R.; Kudo, A. Solar Water Splitting under Neutral Conditions Using Z-Scheme Systems with Mo-Doped BiVO4 as an O2-Evolving Photocatalyst. Energy Technol. 2019, 7, 1900358. [Google Scholar] [CrossRef]
  47. Han, K.; Lin, Y.C.; Yang, C.M.; Jong, R.; Mul, G.; Mei, B. Promoting photocatalytic overall water splitting by controlled magnesium incorporation in SrTiO3 photocatalysts. ChemSusChem 2017, 10, 4510–4516. [Google Scholar] [CrossRef]
  48. Kanazawa, T.; Nozawa, S.; Lu, D.; Maeda, K. Structure and photocatalytic activity of PdCrOx cocatalyst on SrTiO3 for overall water splitting. Catalysts 2019, 9, 59. [Google Scholar] [CrossRef]
  49. Qureshi, M.; Garcia-Esparza, A.T.; Jeantelot, G.; Ould-Chikh, S.; Aguilar-Tapia, A.; Hazemann, J.L.; Takanabe, K. Catalytic consequences of ultrafine Pt clusters supported on SrTiO3 for photocatalytic overall water splitting. J. Catal. 2019, 376, 180–190. [Google Scholar] [CrossRef]
  50. Zhang, X.; Li, Z.; Liu, T.; Li, M.; Zeng, C.; Matsumoto, H.; Han, H. Water oxidation sites located at the interface of Pt/SrTiO3 for photocatalytic overall water splitting. Chin. J. Catal. 2022, 43, 2223–2230. [Google Scholar] [CrossRef]
  51. Zhuo, Z.; Wang, X.; Shen, C.; Cai, M.; Jiang, Y.; Xue, Z.; Sun, S. Construction of TiO2/SrTiO3 Heterojunction Derived from Monolayer Ti3C2 MXene for Efficient Photocatalytic Overall Water Splitting. Chem. A Eur. J. 2023, 29, e202203450. [Google Scholar] [CrossRef] [PubMed]
  52. Liu, J.W.; Chen, G.; Li, Z.H.; Zhang, Z.G. Electronic structure and visible light photocatalysis water splitting property of chromium-doped SrTiO3. J. Solid State Chem. 2006, 179, 3704–3708. [Google Scholar] [CrossRef]
  53. Ouyang, S.; Tong, H.; Umezawa, N.; Cao, J.; Li, P.; Bi, Y.; Ye, J. Surface-alkalinization-induced enhancement of photocatalytic H2 evolution over SrTiO3-based photocatalysts. J. Am. Chem. Soc. 2012, 134, 1974–1977. [Google Scholar] [CrossRef] [PubMed]
  54. Zhao, Y.; Wang, Y.; Liang, X.; Shi, H.; Wang, C.; Fan, J.; Liu, E. Enhanced photocatalytic activity of Ag-CsPbBr3/CN composite for broad spectrum photocatalytic degradation of cephalosporin antibiotics 7-ACA. Appl. Catal. B Environ. 2019, 247, 57–69. [Google Scholar] [CrossRef]
  55. Xu, B.; Li, Y.; Gao, Y.; Liu, S.; Lv, D.; Zhao, S.; Ge, L. Ag-AgI/Bi3O4Cl for efficient visible light photocatalytic degradation of methyl orange: The surface plasmon resonance effect of Ag and mechanism insight. Appl. Catal. B Environ. 2019, 246, 140–148. [Google Scholar] [CrossRef]
  56. Yu-Lei, D.; Guang, C.; Ming-Sheng, Z.; Sen-Zu, Y. Phonon characteristics of polycrystalline cubic SrTiO3 thin films. Chin. Phys. Lett. 2003, 20, 1561. [Google Scholar] [CrossRef]
  57. Rahman, J.U.; Du, N.V.; Nam, W.H.; Shin, W.H.; Lee, K.H.; Seo, W.S.; Lee, S. Grain boundary interfaces controlled by reduced graphene oxide in nonstoichiometric SrTiO3-δ thermoelectrics. Sci. Rep. 2019, 9, 8624. [Google Scholar] [CrossRef]
  58. Kogularasu, S.; Govindasamy, M.; Chen, S.M.; Akilarasan, M.; Mani, V. 3D graphene oxide-cobalt oxide polyhedrons for highly sensitive non-enzymatic electrochemical determination of hydrogen peroxide. Sens. Actuators B Chem. 2017, 253, 773–783. [Google Scholar] [CrossRef]
  59. Huang, C.; Li, C.; Shi, G. Graphene based catalysts. Energy Environ. Sci. 2012, 5, 8848–8868. [Google Scholar] [CrossRef]
  60. Chen, S.; Takata, T.; Domen, K. Particulate photocatalysts for overall water splitting. Nat. Rev. Mater. 2017, 2, 17050. [Google Scholar] [CrossRef]
  61. Wang, X.; Dou, W. Preparation of graphite oxide (GO) and the thermal stability of silicone rubber/GO nanocomposites. Thermochim. Acta 2012, 529, 25–28. [Google Scholar] [CrossRef]
  62. Wei, X.; Xu, G.; Ren, Z.; Xu, C.; Weng, W.; Shen, G.; Han, G. Single-Crystal-like Mesoporous SrTiO3 Spheres with Enhanced Photocatalytic Performance. J. Am. Ceram. Soc. 2010, 93, 1297–1305. [Google Scholar]
  63. Wei, X.; Xu, G.; Ren, Z.; Xu, C.; Shen, G.; Han, G. PVA-Assisted Hydrothermal Synthesis of SrTiO3 Nanoparticles with Enhanced Photocatalytic Activity for Degradation of RhB. J. Am. Ceram. Soc. 2008, 91, 3795–3799. [Google Scholar] [CrossRef]
Catalysts 13 00851 g001 550
Figure 1. SEM images of (a) STO, (b) GO and (c) GO/Rh-STO; (d) TEM image of STO, (e) TEM, (f) HRTEM, (g) HADDF and EDS mapping images of GO/Rh-STO.
Figure 1. SEM images of (a) STO, (b) GO and (c) GO/Rh-STO; (d) TEM image of STO, (e) TEM, (f) HRTEM, (g) HADDF and EDS mapping images of GO/Rh-STO.
Catalysts 13 00851 g001
Catalysts 13 00851 g002 550
Figure 2. (a,b) XRD patterns of the GO, STO, and GO/Rh-STO.
Figure 2. (a,b) XRD patterns of the GO, STO, and GO/Rh-STO.
Catalysts 13 00851 g002
Catalysts 13 00851 g003 550
Figure 3. XPS spectra of STO and GO/Rh-STO: (a) the total survey spectra, (b) Rh 3d, (c) O 1s, (d) Ti 2p, (e) Sr 3d.
Figure 3. XPS spectra of STO and GO/Rh-STO: (a) the total survey spectra, (b) Rh 3d, (c) O 1s, (d) Ti 2p, (e) Sr 3d.
Catalysts 13 00851 g003
Catalysts 13 00851 g004 550
Figure 4. (a) Time course of H2 and O2 evolution over STO, GO/STO, GO/Rh−STO, and (b) photocatalytic activity of xGO/Rh−STO (x = 3.8%, 7.2%, 12.2%, or 16.9%) under visible light (λ ≥ 420 nm) irradiation.
Figure 4. (a) Time course of H2 and O2 evolution over STO, GO/STO, GO/Rh−STO, and (b) photocatalytic activity of xGO/Rh−STO (x = 3.8%, 7.2%, 12.2%, or 16.9%) under visible light (λ ≥ 420 nm) irradiation.
Catalysts 13 00851 g004
Catalysts 13 00851 g005 550
Figure 5. (a) UV−vis diffuse reflectance spectra and (b) curves of (αhυ)1/2 and (αhυ)2 versus energy (hυ) of STO and GO/Rh−STO; Mott−Schottky curves of (c) GO/Rh−STO and (d) STO.
Figure 5. (a) UV−vis diffuse reflectance spectra and (b) curves of (αhυ)1/2 and (αhυ)2 versus energy (hυ) of STO and GO/Rh−STO; Mott−Schottky curves of (c) GO/Rh−STO and (d) STO.
Catalysts 13 00851 g005
Catalysts 13 00851 g006 550
Figure 6. (a) EIS Nyquist plots, the electrical equivalent circuit model of as-prepared samples is shown in the inset of (a) including charge transfer resistance (Rct), resistance of solution (Rs), double layer capacitance (Cdl) and Warburg resistance (RW); (b) the transient photocurrent responses and; (c) LSV curves of STO, GO and GO/Rh−STO.
Figure 6. (a) EIS Nyquist plots, the electrical equivalent circuit model of as-prepared samples is shown in the inset of (a) including charge transfer resistance (Rct), resistance of solution (Rs), double layer capacitance (Cdl) and Warburg resistance (RW); (b) the transient photocurrent responses and; (c) LSV curves of STO, GO and GO/Rh−STO.
Catalysts 13 00851 g006
Catalysts 13 00851 g007 550
Figure 7. (a) PL spectra and (b) TRPL spectra of STO, GO/STO, and GO/Rh-STO (λex = 385 nm and λem = 480 nm).
Figure 7. (a) PL spectra and (b) TRPL spectra of STO, GO/STO, and GO/Rh-STO (λex = 385 nm and λem = 480 nm).
Catalysts 13 00851 g007
Catalysts 13 00851 g008 550
Figure 8. Nitrogen adsorption–desorption curves of (a) GO/Rh−STO, (b) GO, (c) STO, and (d) Raman spectra of GO, STO, and GO/Rh−STO.
Figure 8. Nitrogen adsorption–desorption curves of (a) GO/Rh−STO, (b) GO, (c) STO, and (d) Raman spectra of GO, STO, and GO/Rh−STO.
Catalysts 13 00851 g008
Catalysts 13 00851 g009 550
Figure 9. Schematic representation of possible photocatalytic degradation mechanism.
Figure 9. Schematic representation of possible photocatalytic degradation mechanism.
Catalysts 13 00851 g009
Table
Table 1. The XPS atomic percentage analysis of xGO/Rh-STO.
Table 1. The XPS atomic percentage analysis of xGO/Rh-STO.
GO Addition Amount (mg)Atomic %CAtomic %OAtomic %RhAtomic %SrAtomic %Ti
103.853.90.725.116.5
207.253.70.623.115.4
4012.251.40.521.714.2
6016.948.10.418.412.5
Table
Table 2. The comparison of overall water splitting performance of STO-based photocatalysts in other works.
Table 2. The comparison of overall water splitting performance of STO-based photocatalysts in other works.
MaterialsCatalyst Dosage (mg)CocatalystsReactant Solution Water (mL)Light SourceH2 Rate (μmol
h−1·g−1)		O2 Rate (μmol
h−1·g−1)		Ref.
GO/Rh-STO100/100300W Xe Lamp
(λ > 420 nm)		55.8323.26This work
SrTiO3-C950400/10300W Xe Lamp
(λ > 420 nm)		2.31.0[44]
SrTiO3/TiO250Pt (0.3 wt%)150300W Xe Lamp
(λ > 420 nm)		10.65.1[45]
SrTiO3:Rh-RGO-BiVO4:Mo200Ru (0.7 wt%)
Co (0.1 wt%)		120300W Xe Lamp
(λ > 420 nm)		146.1[46]
Mg-doped SrTiO325Ni (1 wt%)25300W Xe Lamp
(λ > 300 nm)		8.84.2[47]
PdCrOx/SrTiO3100/140300W Xe Lamp
(λ > 300 nm)		155[48]
Ultrafine Pt clusters on SrTiO350/100300W Xe Lamp
(λ > 300 nm)		2312[49]
SrTiO3
(impregnation methods)		300Pt (0.3 wt%)150300W Xe Lamp
(λ > 300 nm)		3820[50]
TiO2/SrTiO3100Rh (0.1 wt%)
Cr (0.05 wt%)
Co (0.05 wt%)		50300W Xe Lamp
(λ < 380 nm)		38.619.2[51]
oxygen
vacancies
SrTiO3		100Pt (0.3 wt%)60300W Xe Lamp
(λ < 380 nm)		8140[43]
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Zhang, S.; Jiang, E.; Wu, J.; Liu, Z.; Yan, Y.; Huo, P.; Yan, Y. Visible-Light-Driven GO/Rh-SrTiO3 Photocatalyst for Efficient Overall Water Splitting. Catalysts 2023, 13, 851. https://doi.org/10.3390/catal13050851

AMA Style

Zhang S, Jiang E, Wu J, Liu Z, Yan Y, Huo P, Yan Y. Visible-Light-Driven GO/Rh-SrTiO3 Photocatalyst for Efficient Overall Water Splitting. Catalysts. 2023; 13(5):851. https://doi.org/10.3390/catal13050851

Chicago/Turabian Style

Zhang, Shuai, Enhui Jiang, Ji Wu, Zhonghuan Liu, Yan Yan, Pengwei Huo, and Yongsheng Yan. 2023. "Visible-Light-Driven GO/Rh-SrTiO3 Photocatalyst for Efficient Overall Water Splitting" Catalysts 13, no. 5: 851. https://doi.org/10.3390/catal13050851

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop