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•Cyano group-enriched crystalline g-C3N4 is prepared by ethyl acetate-mediated method.•The resultant g-C3N4 shows further improved ordered structure and more cyano groups.•The ...improved ordered structure and more cyano groups cause high H2-evolution rate.
The molten salt-assisted route is one of the most important methods to improve the crystallinity of conventionally disordered bulk graphitic carbon nitride (g-C3N4). However, the residual potassium ions from potassium chloride/lithium chloride molten salt can greatly impact the ordered structure of g-C3N4 and serve as the recombination centers of photoinduced carriers, causing limited photocatalytic hydrogen-evolution performance. In this article, the ethyl acetate-mediated method is first developed to not only further improve the ordered structure of traditional crystalline g-C3N4, but also produce more cyano groups for preparing highly efficient g-C3N4 photocatalysts. Herein, the ethyl acetate can gradually hydrolyze to produce hydrogen ions, which can promote the more ordered sheet-like structure and more cyano groups by effective removal of residual potassium ions in the traditional crystalline g-C3N4, leading to the formation of cyano group-enriched crystalline g-C3N4 photocatalysts (CC-CN). As a result, the resultant CC-CN displays the remarkably enhanced photocatalytic hydrogen-evolution performance (295.30 µmol h−1 with an apparent quantum efficiency about 12.61%), in comparison to the bulk g-C3N4 (14.97 µmol h−1) and traditional crystalline g-C3N4 (24.60 µmol h−1). The great improvement of photocatalytic performance can mainly be ascribed to the synergism of improved ordered structure and abundant cyano groups, namely, the efficient transfer and separation of photoinduced charges as well as excellent interfacial hydrogen-generation reaction, respectively. The present work may deliver new strategies to prepare other high-crystalline photocatalysts with great efficiency.
CuO/Cu2O composite hollow microspheres with controlled diameter and composition were prepared without the addition of templates and additives by hydrothermal synthesis using Cu(CH3COO)2·H2O as a ...precursor. Increasing the precursor concentration from 0.02 to 0.2 M increased the diameter of the composite hollow microspheres from 500 nm to 5 μm. Moreover, the content of Cu2O in the composite hollow microspheres increased with increasing the reaction time or/and precursor concentration to produce a range of composite hollow microspheres with Cu2O contents from 20 to 80 wt %. A localized Ostwald ripening mechanism was proposed to account for the formation of CuO/Cu2O composite hollow microspheres. The photocatalytic activity experiment indicated that the prepared CuO/Cu2O composite hollow microspheres exhibited a higher photocatalytic activity for the photocatalytic decolorization of methyl orange aqueous solution under the visible-light illumination than the single phase CuO or Cu2O samples.
The Z-scheme has been proven to be an effective strategy to develop a high-efficiency visible-light photocatalyst. However, the visible-light-responding active component in the Z-scheme system is ...usually restricted to semiconductor materials sensitive to visible light. On the other hand, noble-metal nanoparticles (such as Ag) can act as an active component for the design of high-efficiency plasmonic photocatalysts due to their strong absorption in the visible light region. In this study, H2WO4·H2O/Ag/AgCl composite nanoplates were prepared by a one-step ionic reaction between Ag8W4O16/Ag nanorods and HCl aqueous solution. The photocatalytic activity experiments indicated that the H2WO4·H2O/Ag/AgCl composite nanoplates exhibited a much higher photocatalytic activity than the one-component (H2WO4·H2O) or two-component (such as Ag/AgCl and H2WO4·H2O/Ag) photocatalysts. On the basis of photocatalytic activity and band structure analysis, a plasmonic Z-scheme photocatalytic mechanism is proposed; namely, two-step visible-light absorption is caused by the localized surface plasmon resonance of metallic Ag nanoparticles and the band gap photoexcitation of H2WO4·H2O. The present results suggest that metallic Ag nanoparticles can act as an effective active component for the construction of a Z-scheme visible-light photocatalyst. Considering the versatility and flexibility of noble-metal nanoparticles and semiconductors, this work may provide some insight into the design of novel and highly efficient Z-scheme visible-light photocatalysts.
Compared with stable-phase hexagonal CdS, the metastable cubic CdS photocatalyst usually shows a lower H2-evolution performance under visible-light irradiation. Thus, the widely reported ...high-performance CdS photocatalysts are mainly focused on the hexagonal phase, while the cubic-phase CdS with a high H2-evolution activity has seldom been concerned. In this study, a direct precipitation method in a sulfur-rich Na2S–Na2SO3 system has been developed to prepare the suspensible cubic-phase CdS nanocrystal (c-CdS-NC) photocatalyst with a high H2-evolution activity. In this case, the resultant c-CdS-NC with a small crystal size (ca. 5 nm) and high specific surface area (>75.23 m2/g) exhibits a stable and suspensible photocatalysts due to the massive and preferential adsorption of S2–/SO3 2– ions on the nanocrystal surface. Photocatalytic results indicated that the suspensible c-CdS-NC photocatalysts clearly exhibited an obviously higher H2-evolution performance (0.36 mmol h–1) than the traditional hexagonal CdS (0.14 mmol h–1) by a factor of 2.6 times. Based on the present results, a S2–/SO3 2–-mediated mechanism was proposed for the enhanced H2-evolution performance of the suspensible c-CdS-NC, namely the massive adsorbed S2– ions on the suspensible c-CdS-NC surface not only promote the rapid capture of photogenerated holes but also can work as the effective active sites for H2-evolution reaction. The present work may provide important insights for developing high-performance photocatalytic materials.
Ag modification has been demonstrated to be an efficient strategy to improve the photocatalytic performance of TiO2 photocatalysts. However, the previous studies about the Ag modification are only ...restricted to the surface loading of metallic Ag or Ag(I) doping, investigations have seldom been focused on the simultaneously deposited and doped Ag/Ag(I)-TiO2 photocatalyst. In this study, Ag/Ag(I)-TiO2 photocatalyst was prepared by a facile impregnated method in combination with a calcination process (450 °C) and the photocatalytic activity was evaluated by the photocatalytic decomposition of methyl orange and phenol solutions under both UV- and visible-light irradiation, respectively. It was found that Ag(I) doping resulted in the formation of an isolated energy level of Ag 4d in the band gap of TiO2. On the basis of band-structure analysis of Ag/Ag(I)-TiO2 photocatalyst, a possible photocatalytic mechanism was proposed to account for the different UV- and visible-light photocatalytic activities. Under visible-light irradiation, the isolated energy level of Ag 4d contributes to the visible-light absorption while the surface metallic Ag promotes the effective separation of the following photogenerated electrons and holes in the Ag/Ag(I)-TiO2 nanoparticles, resulting in a higher visible-light photocatalytic activity than the one-component Ag-modified TiO2 (such as Ag(I)-TiO2 and Ag/TiO2). Under UV-light irradiation, the doping energy level of Ag(I) ions in the band gap of TiO2 acts as the recombination center of photogenerated electrons and holes, leading to a lower photocatalytic performance of Ag-doped TiO2 (such as Ag/Ag(I)-TiO2 and Ag(I)-TiO2) than the corresponding undoped photocatalysts (such as Ag/TiO2 and TiO2). Considering the well controllable preparation of various Ag-modified TiO2 (such as TiO2, Ag/TiO2, Ag(I)-TiO2, and Ag/Ag(I)-TiO2), this work may provide some insight into the smart design of novel and high-efficiency photocatalytic materials.
Modification of nickel sulfide cocatalysts is considered to be a promising approach for efficient enhancement of the photocatalytic hydrogen production performance of g-C3N4. Providing more NiS ...cocatalyst to function as active sites of g-C3N4 is still highly desirable. To realize this goal, in this work, a facile sulfur-mediated photodeposition approach was developed. Specifically, photogenerated electrons excited by visible light reduce the S molecules absorbed on g-C3N4 surface to S2−, and subsequently NiS cocatalyst is formed in situ on the g-C3N4 surface by a combination of Ni2+ and S2− due to their small solubility product constant (Ksp = 3.2 × 10−19). This approach has several advantages. The NiS cocatalyst is clearly in situ deposited on the photogenerated electron transfer sites of g-C3N4, and thus provides more active sites for H2 production. In addition, this method utilizes solar energy with mild reaction conditions at room temperature. Consequently, the synthesized NiS/g-C3N4 photocatalyst achieves excellent hydrogen generation performance with the performance of the optimal sample (244 μmol h−1 g−1) close to that of 1 wt% Pt/g-C3N4 (316 μmol h−1 g−1, a well-known excellent photocatalyst). More importantly, the present sulfur-mediated photodeposition route is versatile and facile and can be used to deposit various metal sulfides such as CoSx, CuSx and AgSx on the g-C3N4 surface, and all the resulting metal sulfide-modified g-C3N4 photocatalysts exhibit improved H2-production performance. Our study offers a novel insight for the synthesis of high-efficiency photocatalysts.
NiS is deposited on the electron transfer sites of g-C3N4 by a sulfur-mediated photodeposition approach and provides active sites to improve the photocatalytic H2-production of g-C3N4.
Photocatalytic degradation of organic compounds requires photoexcited holes with strong oxidative power in the valence band (VB) of semiconductors. Although numerous types of doped semiconductors, ...such as nitrogen-doped TiO2, have been studied as visible-light-sensitive photocatalysts, the quantum yields of these materials were very low because of the limited oxidation power of holes in the nitrogen level above the VB. Recently, we developed visible-light-sensitive Cu(II) and Fe(III) nanocluster-grafted TiO2 using a facile impregnation method and demonstrated that visible-light absorption occurs at the interface between the nanoclusters and TiO2, as electrons in the VB of TiO2 are excited to the nanoclusters under visible-light irradiation. In addition, photogenerated holes in the VB of TiO2 efficiently oxidize organic contaminants, and the excited electrons that accumulate in nanoclusters facilitate the multielectron reduction of oxygen. Notably, Cu(II) and Fe(III) nanocluster-grafted TiO2 photocatalyst has the highest quantum yield among reported photocatalysts and has antiviral, self-cleaning, and air purification properties under illumination by indoor light fixtures equipped with white fluorescent bulbs or white light-emitting diodes.
We have prepared a TiO2-based novel visible-light-sensitive photocatalyst, in which Fe(III) species were grafted on a rutile TiO2 surface (denoted as Fe(III)/TiO2). With use of X-ray absorption fine ...structure analysis, the grafted iron species were determined to be in the 3+ state and adopt an amorphous FeO(OH)-like structure. Fe(III)/TiO2 displayed optical absorption in the visible light range over 400 nm, which was assigned to the interfacial charge transfer from the valence band of TiO2 to the surface Fe(III) species. Its photocatalytic activity was evaluated by the decomposition of gaseous 2-propanol under visible light (400−530 nm), which revealed a high quantum efficiency (QE) of 22%. Monochromatic light experiments indicated that the effective wavelength region was extended as far as 580 nm while maintaining a QE of greater than 10%. On the basis of the analogy to Cu(II)-grafted TiO2 photocatalyst (Irie, H.; et al. Chem. Phys. Lett. 2008, 457, 202), we speculate that the high performance of the present photocatalyst is derived from the photoproduced holes that are generated in the valence band of TiO2 and contribute to the oxidative decomposition of 2-propanol, and the catalytic reduction of oxygen (presumably multielectron reduction) by photoproduced Fe(II) species on TiO2.
Abstract
Gold-based co-catalysts are a promising class of materials with potential applications in photocatalytic H
2
O
2
production. However, current approaches with Au co-catalysts show limited H
2
...O
2
production due to intrinsically weak O
2
adsorption at the Au site. We report an approach to strengthen O
2
adsorption at Au sites, and to improve H
2
O
2
production, through the formation of electron-deficient Au
δ+
sites by modifying the electronic structure. In this case, we report the synthesis of TiO
2
/MoS
x
-Au, following selective deposition of Au onto a MoS
x
surface which is then further anchored onto TiO
2
. We further show that the catalyst achieves a significantly increased H
2
O
2
production rate of 30.44 mmol g
−1
h
−1
in O
2
-saturated solution containing ethanol. Density functional theory calculations and X-ray photoelectron spectroscopy analysis reveal that the MoS
x
mediator induces the formation of electron-deficient Au
δ+
sites thereby decreasing the antibonding-orbital occupancy of Au-O
ads
and subsequently enhancing O
2
adsorption. This strategy may be useful for rationally designing the electronic structure of catalyst surfaces to facilitate artificial photosynthesis.
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•A photoinduced reduction approach of mass-transfer control was developed.•Well-dispersed AuPd alloy nanococatalysts were obtained for H2O2 production.•The synergy of electronic and ...geometric effects exists in AuPd nanococatalysts.•The BiVO4 (010)-AuPd photocatalyst presented 11.38% AQE value under 420 nm light.
Owing to excellent activity and selectivity for two-electron O2 reduction to H2O2, well-dispersed AuPd nanoalloy cocatalyst is high desired for photocatalytic H2O2 production. In practice, however, it is hardly realized due to technical difficulty. Utilizing the directed transfer of photocarriers in BiVO4 single crystal with crystal-facet exposure, in this work, a mass-transfer control approach is developed for selective photodeposition of well-dispersed AuPd cocatalysts to boost photocatalytic H2O2 production. The as-obtained BiVO4 (010)-AuPd photocatalysts exhibit improved photocatalytic activity for H2O2 production compared with BiVO4 (010)-Au (1.15 mmol L−1) and BiVO4 (010)-Pd (1.37 mmol L−1). Therein, the optimum BiVO4 (010)-AuPd photocatalyst (the mass ratio of Au to Pd for 19:1) presents the highest H2O2 production (2.29 mmol L−1 in 2 h under 420 nm light irradiation) and the corresponding AQE value is 11.38 %. In the case, the synergistic effect of electronic effects and geometric effects for the well-dispersed AuPd nanoalloy cocatalysts contribute to excellent activity and selectivity for two-electron O2 reduction to H2O2 and thus boost the photocatalytic H2O2 production of BiVO4. The present work also provides an insight into the modification of well-dispersed nanoalloy cocatalysts for photocatalytic H2O2 production.
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