Visible-light Photocatalytic Hydrogen Evolution Activity Research Articles

Sustainable one-step synthesis of nanostructured potassium poly(heptazine imide) for highly boosted photocatalytic hydrogen evolution

Regulating bulk polymeric carbon nitride (PCN) into nanostructured PCN (NPCN) has long been proved effective to improve its photocatalytic activity, which is applicable to crystalline carbon nitride: potassium poly (heptazine imide) (K-PHI). Currently, simplifying the synthesis of nanostructured K-PHI (NK-PHI) is challenging and has drawn widespread attention. This work demonstrated the one-step concise and sustainable synthesis of NK-PHI by a steam-assisted method. The NK-PHI exhibited a highly boosted visible-light photocatalytic hydrogen evolution activity, which is 38.4, 4.4 and 3.4 times to that of PCN, NPCN and K-PHI. The improvement of photocatalytic activity mainly benefitted from increased active sites and highly facilitated photoinduced charges transfer and separation. Moreover, the sustainability of this approach was proved by recycling the structure-directing agents (KCl) and steam source (Mg(OH)2) to repeatedly synthesize high-quality NK-PHI.

Construction of MoS2/ZnO heterostructures as highly efficient photocatalysts for enhanced visible-light decomposition of methylene blue and hydrogen evolution

The MoS2/ZnO heterostructures can be successfully prepared by combined facile hydrothermal and wet chemistry methods. The surface morphologies, microstructures, crystal structures, chemical compositions, optical properties of the MoS2/ZnO heterostructures study through the different kinds of characterization techniques. Compared with MoS2 nanoflakes, MoS2/ZnO heterostructures can increase electron-hole pairs separation, light-harvesting ability, and high specific surface area to improve the photocatalytic decomposition of methylene blue solution under visible light irradiation. Also, MoS2/ZnO heterostructures exhibited better visible-light photocatalytic hydrogen evolution activity. Furthermore, the MoS2/ZnO heterostructures also exhibited superior photocatalytic reusability and stability for long-term photocatalytic processes.

Doping copper ions in a metal-organic framework (UiO-66-NH2): Location effect examined by ultrafast spectroscopy

We constructed two types of copper-doped metal-organic framework (MOF), i.e., Cu@UiO- 66-NH2 and Cu-UiO-66-NH2. In the former, Cu2+ ions are impregnated in the pore space of the amine-functionalized, Zr-based UiO-66-NH2; while in the latter, Cu2+ ions are in-corporated to form a bimetal-center MOF, with Zr4+ being partially replaced by Cu2+ in the Zr−O oxo-clusters. Ultrafast spectroscopy revealed that the photoinduced relaxation kinetics associated with the ligand-to-cluster charge-transfer state is promoted for both Cu-doped MOFs relative to undoped one, but in a sequence of Cu-UiO-66-NH2>Cu@UiO-66-NH2>UiO-66-NH2. Such a sequence turned to be in line with the trend observed in the visible-light photocatalytic hydrogen evolution activity tests on the three MOFs. These findings highlighted the subtle effect of copper-doping location in this Zr-based MOF system, further suggesting that rational engineering of the specific metal-doping location in alike MOF systems to promote the photoinduced charge separation and hence suppress the detrimental charge recombination therein is beneficial for achieving improved performances in MOF-based photocatalysis.

Enhanced interfacial electron transfer and boosted visible-light photocatalytic hydrogen evolution activity of g-C3N4 by noble-metal-free MoSe2 nanoparticles

Rationally designing noble-metal-free metallic cocatalysts modified graphitic carbon nitride (g-C3N4) as heterostructured photocatalysts is an efficient strategy for enhancing photocatalytic hydrogen (H2) evolution. Herein, uniform molybdenum diselenide (MoSe2) nanoparticles were synthesized through a simple solvothermal approach, and the MoSe2 nanoparticles anchored g-C3N4 nanosheets were subsequently prepared by a solution-phase strategy. The resulting MoSe2/g-C3N4 nanocomposite displayed good performance toward visible-light photocatalytic H2 production. The optimal amount of MoSe2 nanoparticles was 7% of composite by weight, displaying the highest H2 production rate of 287.3 μmol h−1 g−1. The excellent photocatalytic performance of the MoSe2/g-C3N4 hybrids was ascribed to the introduction of MoSe2 nanoparticles, which facilitated the charge separation and dramatically promoted the photoelectron transport. The insight into the charge transfer through the interface between MoSe2 nanoparticles and g-C3N4 nanosheets was revealed by photoluminescence spectra, electrochemical and photoelectrochemical experiments. This work provides solid evidence that MoSe2 nanoparticles can be a promising cocatalyst loaded g-C3N4 for enhanced photocatalytic performance.

Self-assembled CdS@BN core-shell photocatalysts for efficient visible-light-driven photocatalytic hydrogen evolution

CdS@BN NRs core-shell photocatalysts for hydrogen evolution were synthesized by a solvothermal and chemical adsorption method. CdS NRs coated by 5 wt% boron nitride (BN) shell exhibited remarkably visible-light photocatalytic hydrogen evolution activity of up to 30.68 mmol g−1 h−1, nearly 6.79 times higher than that of pure CdS NRs, and the apparent quantum efficiency at 420 nm was 7.5%. Transmission electron microscopy showed the CdS NRs were coated with a thin (~5 nm) BN layer, which together with the hydrogen evolution results proved the photocatalytic ability of CdS NRs was significantly improved. The hydrogen evolution rate of CdS NRs coated by 5 wt% BN remained at 91.4% after four cycles, indicating the photocorrosion of CdS NRs was effectively alleviated. Moreover, the large and close coaxial interfacial contact between the CdS core and the BN shell was beneficial to the separation and transfer of photogenerated electron-hole pairs.

A Facile Method for the Preparation of Colored Bi₄Ti₃O12-x Nanosheets with Enhanced Visible-Light Photocatalytic Hydrogen Evolution Activity.

Bi4Ti3O12−x nanosheet photocatalysts with abundant oxygen vacancies are fabricated by a facile solid-state chemical reduction method for the first time. This method is simple in operation, has short reaction time, and can be conducted at mild temperatures (300~400 °C). The electron paramagnetic resonance, thermogravimetric analysis, X-ray photoelectron spectrometer, and positron annihilation lifetime spectra results indicate that oxygen vacancies are produced in Bi4Ti3O12−x, and they can be adjusted by tuning the reduction reaction conditions. Control experiments show that the reduction time and temperature have great influences on the photocatalytic activities of Bi4Ti3O12−x. The optimal Bi4Ti3O12−x is the sample undergoing the reduction treatment at 350 °C for 60 min and it affords a hydrogen evolution rate of 129 μmol·g−1·h−1 under visible-light irradiation, which is about 3.4 times that of the pristine Bi4Ti3O12. The Bi4Ti3O12−x photocatalysts have good reusability and storage stability and can be used to decompose formaldehyde and formic acid for hydrogen production. The surface oxygen vacancies states result in the broadening of the valence band and the narrowing of the band gap. Such energy level structure variation helps promote the separation of photo-generated electron-hole pairs thus leading to enhancement in the visible-light photocatalytic hydrogen evolution. Meanwhile, the narrowing of the band gap leads to a broader visible light absorption of Bi4Ti3O12−x.

Enhanced visible-light photocatalytic hydrogen evolution activity of Er3+:Y3Al5O12/PdS–ZnS by conduction band co-catalysts (MoO2, MoS2 and MoSe2)

Several conduction band co-catalysts (CBCOs), MoO2, MoS2 and MoSe2, were prepared to improve the visible-light photocatalytic hydrogen evolution activity of Er3+:Y3Al5O12/PdS–ZnS from water splitting, in which the PdS is a valence band co-catalyst (VBCO) used to facilitate the photo-generated hole transfer and the Er3+:Y3Al5O12 is an up-conversion luminescence agent from visible light to ultraviolet light used to provide the ultraviolet light satisfying the energy demands of wide band-gap ZnS photocatalyst. XRD, SEM, TEM and EDX analyses were employed to confirm the morphology, microstructure and composition of the prepared photocatalysts. UV–vis absorption and PL spectra were also determined to explore luminescence effect of the Er3+:Y3Al5O12. The visible-light photocatalytic hydrogen evolution activity of the prepared photocatalysts was evaluated by using Na2S and Na2SO3 as sacrificial reagents in aqueous solution under visible light irradiation. The influential factors such as contents of CBCOs (MoO2, MoS2 and MoSe2) and visible-light irradiation time on visible-light photocatalytic hydrogen evolution of Er3+:Y3Al5O12/PdS–ZnS–MoX2 (X = O, S and Se) were investigated in detail. Particularly, Er3+:Y3Al5O12/PdS–ZnS–MoSe2 with 0.30 wt% MoSe2 shows the highest photocatalytic hydrogen evolution activity.

The effect of different co-catalysts (CuO, MoS2 and Pt) on hydrogen production of Er3+:YAlO3/NaTaO3 by visible-light-induced methanol splitting

In this work, a high effective up-conversion luminescence agent (from infrared and visible light to ultraviolet light), Er3+:YAlO3, was synthesized by sol–gel method. And then, the CuO, MoS2 and Pt were adopted as co-catalysts and the NaTaO3 was used as bulk catalyst, and then the three corresponding visible-light photocatalysts, Er3+:YAlO3/CuO–NaTaO3, Er3+:YAlO3/MoS2–NaTaO3 and Er3+:YAlO3/Pt–NaTaO3, were successfully prepared by hydrothermal and direct mixing methods, respectively. Er3+:YAlO3, NaTaO3, Er3+:YAlO3/CuO–NaTaO3, Er3+:YAlO3/MoS2–NaTaO3 and Er3+:YAlO3/Pt–NaTaO3 were all characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The visible-light photocatalytic activities of Er3+:YAlO3/CuO–NaTaO3, Er3+:YAlO3/MoS2–NaTaO3 and Er3+:YAlO3/Pt–NaTaO3 were examined through photocatalytic hydrogen evolution from methanol aqueous solution under visible-light irradiation. The influence factors such as the contents of co-catalysts (CuO, MoS2 and Pt), heat-treated temperature and initial pH value on the visible-light photocatalytic hydrogen evolution activity of Er3+:YAlO3/CuO–NaTaO3, Er3+:YAlO3/MoS2–NaTaO3 and Er3+:YAlO3/Pt–NaTaO3 were studied. The results showed that the Er3+:YAlO3/MoS2–NaTaO3 with 0.2 wt% MoS2 in solution (pH = 6.0) with 5.0 wt% methanol displayed the highest visible light photocatalytic hydrogen production activity.

Enhancement of visible-light photocatalytic activity of Pt supported potassium niobate (Pt-KNbO3) by up-conversion luminescence agent (Er3+:Y3Al5O12) for hydrogen evolution from aqueous methanol solution

In this paper, a high effective up-conversion luminescence agent (Er3+:Y3Al5O12) is synthesized by sol–gel method, and then its corresponding visible-light photocatalysts (Er3+:Y3Al5O12/Pt-KNbO3) are successfully prepared by hydrothermal and direct mixing methods. For comparison, Er3+:Y3Al5O12, Pt-KNbO3 and Er3+:Y3Al5O12/Pt-KNbO3 are all characterized by XRD (X-ray diffractometer), SEM(scanning electron microscopy) and EDX(energy dispersive X-ray spectroscopy ). At first, the visible-light photocatalytic activity of Er3+:Y3Al5O12/Pt-KNbO3 is examined through photocatalytic hydrogen evolution from aqueous methanol solution under visible-light irradiation. Lastly, the influence factors such as Er3+:Y3Al5O12 and Pt-KNbO3 mass ratio, heat-treated temperature and initial pH value on the visible-light photocatalytic hydrogen evolution activity of Er3+:Y3Al5O12/Pt-KNbO3 are studied. Particularly, Er3+:Y3Al5O12/Pt-KNbO3 catalysts with 0.5:1.0 mass ratio heat-treated at 500 °C in aqueous methanol solution with initial pH = 6.0 show the highest photocatalytic activity in hydrogen evolution from aqueous methanol solution.

Efficient visible-light photocatalytic hydrogen evolution over platinum supported titanium dioxide nanocomposites coating up-conversion luminescence agent (Er3+:Y3Al5O12/Pt–TiO2)

In this work, a novel up-conversion luminescence agent (Er3+:Y3Al5O12) was synthesized by sol-gel method and then for visible-light photocatalytic hydrogen evolution a corresponding visible-light photocatalyst, platinum supported titanium dioxide nanocomposites coating up-conversion luminescence agent (Er3+:Y3Al5O12/Pt–TiO2 nanocomposite particles), was successfully prepared by sol-gel and calcination methods. Er3+:Y3Al5O12, Pt–TiO2 and Er3+:Y3Al5O12/Pt–TiO2 were all characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDX). The visible-light photocatalytic activity of Er3+:Y3Al5O12/Pt–TiO2 nanocomposites was examined through photocatalytic hydrogen evolution from methanol splitting under visible-light irradiation. The influence factors such as Er3+:Y3Al5O12 and Pt–TiO2 mole ratio, heat-treated temperature and heat-treated time on the visible-light photocatalytic hydrogen evolution activity of Er3+:Y3Al5O12/Pt–TiO2 nanocomposites were also studied. Particularly, Er3+:Y3Al5O12/Pt–TiO2 nanocomposites with 1.5:1.0 M ratio heat-treated at 500 °C for 60 min showed the highest visible-light photocatalytic activity in hydrogen evolution from methanol splitting.