Enhanced photocatalytic activities of three-dimensional graphene-based aerogel embedding TiO2 nanoparticles and loading MoS2 nanosheets as Co-catalyst
Graphical abstract
A three-dimensional interconnected network MoS2/P25/graphene-aerogel was prepared by a facile one-pot hydrothermal process, which shows superior durability photoelectrochemical properties and outstanding photodegradation activities.
Introduction
As one of the most investigated functional material in semiconductor photocatalysis, titanium dioxide (TiO2) has been widely used in the fields of environmental pollutant degradation and energy conversion for its non-toxicity, effectiveness, low cost, and chemical stability [1], [2], [3], [4], [5], [6]. However, the photocatalytic activities of titanium dioxide are seriously limited by the photocatalytic sensitivity in the UV region and the fast recombination of photogenerated electron–hole pairs [5], [7], [8]. Therefore, many positive and effective approaches have been employed to improve the photocatalytic activity of TiO2, such as modifying the surface [9], optimizing the structure [10], doping of metal or nonmetal elements [11], [12], [13], [14], [15], [16], and coupling of other photosensitive materials [17], [18] to modulate the optical absorption and facilitate the charge transfer.
Graphene, a flat monolayer of carbon atoms, was first reported by Andre Geim and Kostya Novoselov a decade ago [19], leading to a revolution in the graphene related research field. Owing to its fast two-dimensional (2D) electron-transfer kinetics, large surface areas, and superior mechanical, thermal and chemical stability [20], [21], [22], [23], graphene was found to be an attractive supporting material to load functional materials. Many attempts have been paid to composite the TiO2 with graphene, these TiO2/graphene composites have been reported to exhibit enhanced photocatalytic activity, but they still suffer from the low usage of natural sunlight, recombination of the electron–hole pairs and the limited amount of active reaction centers [24], [25], [26], [27], [28], [29], [30]. Recently, molybdenum disulfide (MoS2), a quasi-two-dimensional transition metal dichalcogenide with layered structure, has been highlighted as a promising hydrogen evolution catalyst. For instance, Chhowalla's [31] group reported the chemically exfoliated MoS2 nanosheets possessed excellent activity for hydrogen evolution reaction. Lu's [32] group reported the limited-layered MoS2, as a high active co-catalyst, loaded on reduced graphene oxide (RGO) sheets as an alternative of Pt for hydrogen evolution. In particular, the synergetic effect of MoS2 and graphene as co-catalysts for TiO2 nanoparticles which exhibited superior photocatalytic H2 production activity, was first reported by Yu's [33] group. Those findings explicitly indicate the significant potential of ultrathin MoS2 nanosheets in photocatalysis. However, it has been reported that large accessible surface areas in the above 2D graphene-based macrostructures are inevitably sacrificed given that graphene nanosheets are particularly prone to form irreversible agglomerates, limiting the accessible surface areas for electrolyte ion infiltration and leading to a huge loss of electro-active sites [34], [35], [36]. To overcome these obstacles, 3D graphene macrostructures (hydrogels and aerogels) have been developed recently, which are composed of a unique 3D porous graphene skeleton [37], [38], [39], [40], [41]. It is noted that this graphene aerogels or hydrogels can not only preserve the large accessible surface areas of the graphene sheets but also possesses highly porous structures with pore sizes of several micrometers, making the most possible for embedding nanoparticles in the 3D graphene nanocomposites during a reduction and self-assembly process owning to its porous structure, good electrical conductivity and the maximization of accessible sites. Till now, most of these composites are consisted of graphene and a single type of nanostructure, and very few studies are concentrated in the assembly of 3D graphene-based aerogel with deposited multifarious types of nanomaterials. Dramatically, a series of unique ternary graphene-based nanomaterials has been reported with significantly enhanced performance, benefitting from the advantages of each component and synergistic interaction among the three components [33], [42], [43], [44], [45].
In this work, aim at solving the fast recombination of photogenerated electron–hole pairs and the limited photocatalytic reaction sites of TiO2 under UV irradiation. To improve the photocatalytic activity of TiO2 (P25, 20% rutile and 80% anatase), we embedded it in 3D graphene structure and decorated with MoS2 nanosheets to enhance light absorption, accelerate charge separation and increase reaction sites, we firstly synthesize a ternary 3D graphene-based MoS2/P25/graphene nanocomposite aerogel via a facile one-step hydrothermal reaction. Such 3D MoS2/P25/graphene aerogel shows an interconnected macroporous framework of graphene sheets with uniform deposition of TiO2 nanoparticles and MoS2 nanosheets. Taking photoelectrochemical measurement and photodegradation methyl orange (MO) (0.02 g/L) test of the as-prepared samples under UV irradiation, the ternary MoS2/P25/graphene-aerogel shows the best photocatalytic properties, which may benefit from the porous structure, good electrical conductivity and the increasing accessible sites of 3D graphene aerogel, as well as the novel optoelectronic and catalytic properties of MoS2 nanosheets, and the positive synergetic effect of this hybrid. The durability was also investigated via a more than 80 cycles photoresponse measurement and four cycling runs in the photodegradation of MO. These excellent properties demonstrate that this 3D ternary graphene-based structure is an efficient method to improve the photocatalytic activity of TiO2.
Section snippets
Sample preparation
As a precursor, graphene oxide (GO) was synthesized from graphite powder (>99.8%, Sinopharm Chemical Reagent Co. Ltd) by the modified Hummer's method [46]. As another precursor, ultrathin MoS2 nanosheets were synthesized from the MoS2 bulk (99.999%, Aladdin Chemistry Co, Led) crystals by intercalation of lithium ions (Li+) via hydrothermal treatment [47], a large quantity of MoS2 nanosheets were obtained after the resulting lithiated materials were exfoliated in water. The details about the
Morphology and microstructure characterizations
The powder X-ray diffraction pattern of the as-prepared ternary MoS2/P25/graphene aerogel was shown in Fig. 1(a), which was compared with pure P25 nanoparticles and sole MoS2 nanosheets. The XRD pattern of the MoS2/P25/graphene aerogel indicates that the ternary sample is well crystallized. Meanwhile, it is easy to find that all the diffraction peaks for the pristine MoS2 nanosheets sample could be well indexed to molybdenite-2H phase MoS2 (JCPDS file no. 37-1492), and that pristine P25 is well
Optical characterization
As is well known, the charge recombination rate is a key factor to the photocatalysis activity. Since PL emission is the result of the recombination of free carriers [54], it has been widely used to investigate the efficiency of charge carrier trapping, migration, and transfer and to understand the fate of electron hole pairs in semiconductor particles. Fig. 3 shows the PL emission spectra of P25, MoS2/P25, P25/graphene, and MoS2/P25/graphene aerogel, respectively. For the pure P25, the main
Photoelectrochemical measurements
To access the photoelectrochemical activities, the MoS2/P25/graphene electrode is used as a photoanode in the PEC cell in sulfide-sulfite (S2−/SO32−) electrolyte under UV irradiation. Moreover, to further emphasize the good electrical conductivity and the maximization of accessible sites of both 3D interconnected network graphene-based aerogel and the introduction of MoS2 nanosheets, control experiments were also carried out. The linear sweep voltammograms (J–V curve) are illustrated in Fig. 5.
Photocatalytic performance
The photocatalytic activities of MoS2/P25/graphene-aerogel, P25/graphene, graphene/P25/MoS2-composite, MoS2/P25, MoS2/graphene and P25 were measured by the photo-degradation of methyl orange (MO) as a model reaction under UV irradiation. Before irradiation, a dark adsorption test was carried out to estimate the adsorptivity of the as-prepared samples. Fig. 8(a) shows the time dependent absorption to MO solutions of these photocatalysts during the dark adsorption. It is easy to find that the MoS2
Photocatalytic mechanism
Based on the above discussions and analysis, the superior photocatalytic activity of the ternary MoS2/P25/graphene aerogel is summarized for the following factors: (i) 3D graphene porous architecture with a highly porous ultrafine nano-assembly network structure, excellent electric conductivity, and the maximization of accessible sites, (ii) increasing active adsorption sites and photocatalytic reaction centers for the introduction of MoS2 nanosheets, (iii) positive synergic effects among
Conclusion
In conclusion, we have demonstrated a new strategy by integrating the good electrical conductivity and the maximization of accessible sites of unique 3D graphene porous aerogel and the MoS2 nanosheets with increasing reaction sits to enhance the photocatalytic efficiency of TiO2. Following such ideas, a new type of multifunctional 3D MoS2/P25/graphene ternary aerogel has been fabricated by a facile one-step hydrothermal self-assembled approach. The obtained hybrid aerogel exhibit well defined
Acknowledgments
This work was supported by the Grants from National Natural Science Foundation of China (Nos. 51002129), Project supported by Provincial Natural Science Foundation of Hunan (No. 14JJ3079), Open Fund based on innovation platform of Hunan Colleges and Universities (No. 13K045), the China Postdoctoral Science Foundation funded project (No. 20100480068), and the Supported by Hunan Provincial Innovation Foundation For Postgraduate (No. CX2014B263 and No. CX2014A011). And also supported by the
References (67)
- et al.
Titanium dioxide photocatalysis
J Photochem Photobiol C Photochem Rev
(2000) - et al.
A review and recent developments in photocatalytic water-splitting using for hydrogen production
Renew Sustain Energy Rev
(2007) - et al.
Structural properties of CuO/TiO2 nanorod in relation to their catalytic activity for simultaneous hydrogen production under solar light
Int J Hydrogen Energy
(2013) - et al.
Effective water splitting using N-doped TiO2 films: role of preferred orientation on hydrogen production
Int J Hydrogen Energy
(2014) - et al.
Effective improvement of photocatalytic hydrogen evolution via a facile in-situ solvothermal N-doping strategy in N-TiO2/N-graphene nanocomposite
Int J Hydrogen Energy
(2014) - et al.
Enhanced photocatalytic hydrogen production by improving the Pt dispersion over mesostructured TiO2
Int J Hydrogen Energy
(2014) - et al.
Carbon-incorporated TiO2 microspheres: facile flame assisted hydrolysis of tetrabutyl orthotitanate and photocatalytic hydrogen production
Int J Hydrogen Energy
(2012) - et al.
Highly stable CdS-modified short TiO2 nanotube array electrode for efficient visible-light hydrogen generation
Int J Hydrogen Energy
(2011) - et al.
Nanocomposite of graphene oxide with nitrogen-doped TiO2 exhibiting enhanced photocatalytic efficiency for hydrogen evolution
Int J Hydrogen Energy
(2013) - et al.
TiO2-graphene nanocomposites for photocatalytic hydrogen production from splitting water
Int J Hydrogen Energy
(2012)
Design of graphene sheets-supported Pt catalyst layer in PEM fuel cells
Electrochem Commun
Photocatalytic activity of Ag-TiO2-graphene ternary nanocomposites and application in hydrogen evolution by water splitting
Int J Hydrogen Energy
The enhancement of photodegradation efficiency using Pt-TiO2 catalyst
Chemosphere
Review of photoluminescence performance of nano-sized semiconductor materials and its relationships with photocatalytic activity
Sol Energy Mater Sol Cells
A green and facile synthesis of TiO2/graphene nanocomposites and their photocatalytic activity for hydrogen evolution
Int J Hydrogen Energy
How and to what extent do carbon materials catalyze solar hydrogen production from water?
Appl Catal B Environ
Electrochemical impedance spectroscopy study of the passive oxide film on titanium for implant application
Electrochimica Acta
Electrochemical photolysis of water at a semiconductor electrode
Nature
A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films
Nature
Environmental applications of semiconductor photocatalysis
Chem Rev
Photocatalysis on TiO2 surfaces: principles, mechanisms, and selected results
Chem Rev
Photocatalytic comparison of TiO2 nanoparticles and electrospun TiO2 nanofibers: effects of mesoporosity and interparticle charge transfer
J Phys Chem C
Apatite-coated Ag/AgBr/TiO2 visible-light photocatalyst for destruction of bacteria
J Am Chem Soc
A two-dimensional phase of TiO2 with a reduced bandgap
Nat Chem
Highly enhanced photoreductive degradation of perchlorinated compounds on dye-sensitized metal/TiO2 under visible light
Environ Sci Technol
The electronic origin of the visible-light absorption properties of C-, N- and S-doped TiO2 nanomaterials
J Am Chem Soc
Highly efficient quantum-dot-sensitized solar cell based on Co-sensitization of CdS/CdSe
Adv Funct Mater
Electric field effect in atomically thin carbon films
Science
Graphene-based nanoassemblies for energy conversion
J Phys Chem Lett
Graphene-based composite materials
Nature
Electronic transport in single-walled carbon nanotube/graphene junction
Appl Phys Lett
Graphene based new energy materials
Energy & Environ Sci
P25-graphene composite as a high performance photocatalyst
ACS Nano
Cited by (163)
One-step hydrothermal formation of porous N-graphyne decorated TiO<inf>2</inf>/Ti<inf>3</inf>C<inf>2</inf> composites with enhanced photocatalytic activity
2024, International Journal of Hydrogen EnergyStructure optimization of graphene aerogel-based composites and applications in batteries and supercapacitors
2023, Chemical Engineering JournalPhysicochemical and optical studies of novel heterogeneous oxysulfide catalyst based on Mo for potential application in reduction reactions
2023, Materials Chemistry and PhysicsAerogels-Inspired based Photo and Electrocatalyst for Water Splitting to Produce Hydrogen
2022, Applied Materials TodayIn-situ hydrothermal synthesis of NiCo(X)Se compound on nickel foam for efficient performance of water splitting reaction in alkaline media
2022, Journal of Electroanalytical Chemistry