Photocatalysis Water Splitting Research Articles

Insight of indium single atom loading on TiO2 for remarkable photocatalytic hydrogen evolution

Hydrogen production by photocatalysis water splitting is an attractive and promising development method, but the current efficiency is too low for application. Loading single atoms can significantly enhance the photocatalytic efficiency, however, the insightful understanding of the impact of single atom loading on catalytic performance is still ambiguous. In this work, InSA/TiO2 photocatalysts modified with indium single atom (InSA) were synthesized by photo-deposition process. Under 300W Xe lamp illumination, the hydrogen production rate of the optimized InSA/TiO2 photocatalyst achieves 6.11 mmol g−1 h−1, which is 7.6 times that of TiO2 prepared under the same conditions. The results of characterization analysis and density functional theory (DFT) calculations indicate that some of the Ti atoms on the TiO2 surface are replaced by the doped In, and the local electronic structures of the photocatalyst are regulated, which results in effectively separating of the photo-generated carriers, and significant increasing the activity of the surrounding unsaturated oxygen, thus, the photocatalytic hydrogen production performance is effectively improved. This work provides a strategy to improve photocatalytic activity, and also deepens the understanding of metal single atom modification mechanism.

Metal halide HgI2 monolayer with auxetic property and photocatalysis application

Recently, two-dimensional (2D) metal halides have shown extraordinary performances as photocatalysts, triggering our enormous interest to explore new 2D metal halides for photocatalysis water splitting. Here, based on an unbiased first-principles swarm intelligence structure search, we identified a thermally and dynamically stable HgI2 monolayer. Interestingly, its atomic configuration forms an unusual in-plane negative Poisson's ratio, resulting in an auxetic property. More importantly, the HgI2 monolayer exhibits excellent optoelectronic properties, including suitable direct bandgap (∼2.45 eV), good carrier mobility (×102 cm2 V−1 s−1), excellent light absorption coefficient (×105 cm−1), and suitable band edges for photocatalytic water splitting. These excellent characteristics make the HgI2 monolayer fulfill the basic criteria of efficient photocatalysts for water splitting, supporting it as a promising candidate for photocatalytic materials. Our findings bloom the 2D metal halides family and offer a new candidate material for photocatalysis water splitting.

Broadened photocatalytic capability to near-infrared for CdS hybrids and positioning hydrogen evolution sites

Wide-spectrum light harvesting is critical in determining practical photocatalysis water splitting. Hybridization presents a viable strategy to broaden photocatalytic capability, yet the direct conversion of near-infrared (NIR) light remains a matter of great concern. Herein, a state-of-art ternary Au nanorods@MoS2-CdS (AMC) hybrid is designed to address this challenge. AMC achieves a leap-forward apparent quantum yield (AQY) of 1.06% at 700 nm and an AQY of 35.7% at 450 nm, extending the hydrogen evolution reaction (HER) capability of CdS hybrids to the NIR region firstly. It is revealed that the energetic hot electrons supplied by Au nanorods (NRs) are responsible for this extension. Indispensable, MoS2 performs a platform to collect the hot electrons from Au NRs and the photoinduced electrons from CdS. The HER active sites are positioned as MoS2-CdS interfaces both from experimental and theoretical viewpoints. This work opens up a new horizon for the forward of the wide-spectrum photocatalysis design.

Flame spray pyrolysis made Pt/TiO2 photocatalysts with ultralow platinum loading and high hydrogen production activity

In this paper, flame spray pyrolysis (FSP) is used to synthesize Pt/TiO2 catalysts with surface-supported isolated Pt atoms through elaborate precursor/solvent formulation and flame temperature history control. It is a pivotal factor to this FSP process that there is a major distinction on saturated vapor pressure between two components (Pt species and Ti species), and thereby they exist as gas phase and particle phase at a certain temperature range, respectively. When the flame is quenched to ambient temperature with cold sheath gas, Pt species of gaseous PtO2 (being in the vapor phase above 723 K) condense into deposition state on the surface of TiO2 nanoparticles. Combined with X-ray photoelectron spectroscopy (XPS) analysis and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) detection, we identify that Pt atoms are dispersed and anchored on the catalyst surface. Single-atom Pt dispersed Pt/TiO2 catalysts can be well achieved by controlling the loading at a very low level, which offers an effective way to maximize the atom economy for surface catalysis of scarce noble metals. In this work, considering that Pt as the best co-catalyst of hydrogen evolution, the FSP-made Pt/TiO2 catalysts are tested in a photocatalysis water splitting system aiming to a simple and attractive means of renewable hydrogen production. The highest activity presents in 0.1Pt/TiO2 with 0.1% molar ratio of Pt to Ti, reaching 108.5 times of the benchmark sample from commercial flame-made TiO2 (P25). The high activity is attributed to the fact that the isolated Pt atom serves as the main active site for photocatalysis hydrogen evolution. Therefore, the performance and cost efficiency of catalysts are greatly improved by the FSP, mainly ascribed to engineering atomically dispersing Pt on the support surface.

Two-dimensional O-phase group III monochalcogenides for photocatalytic water splitting

The atomically thin group III monochalcogenides have emerged as potential candidates for nanoscale optoelectronic applications due to their tunable bandgaps and high carrier mobility. In this work, by means of ab initio calculations, we have systematically investigated the geometrical structures, electronic structures, and optical properties of the orthogonal phase (O-phase) group III monochalcogenides MX (M = Ga and In, X = S, Se and Te) monolayers, nanoribbons, heterostructures and their potential applications as photocatalysts for water splitting. It is highlighted that the two-dimensional (2D) O-phase MX monolayers not only are dynamically and thermally stable, but also exhibit distinguished optical properties (~105 cm−1) with broad absorption spectrum in the visible and ultraviolet light regions. Furthermore, it is noted that nano-structure designing can further modulate their electronic structures in desirable ways. For instance, the bandgap of O-phase GaTe is relevant to the width of 1D nanoribbon. On the other hand, the type-II InSe/GaTe and InTe/GaTe heterostructures confine the photo-generated electrons and holes at the opposite parts, which is beneficial for the separation of hydrogen and oxygen during the photocatalysis water splitting process.

Photo-catalysis water splitting by platinum-loaded zeolite A

Under the λ≥420 nm visible light illumination, the Pt4+ ions exchanged LTA zeolite powders without further heat-treatment presented H2 evolution at a rate of 5 μl/(15 mg·h) via photocatalysis water splitting. It was shown that the efficiency of H2 generation by the Pt4+ exchanged LTA zeolite powders without further heat-treatment was higher than the counterpart of the samples with heat treatment. In addition, the samples with lower Pt loading concentration showed higher H2 evolution rate than those of higher Pt loading did. The higher H2 evolution efficiency can be attributed to the effective isolation of water molecules and Pt at the atomic or the few atom ‘cluster’ scale by LTA zeolite’s periodical porous structure, which ensures a more efficient electron transfer efficiency for H2 evolution. However, after extra heat treatment, the Pt atoms reduced from Pt4+ in LTA zeolite’s cavities may tend to migrate to the surface and then form nano-particles, which led to the lower H2 evolution efficiency.

Removal of reactive blue 19 dye by sono, photo and sonophotocatalytic oxidation using visible light

An efficient sonophotocatalytic degradation of reactive blue 19 (RB 19) dye was successfully carried out using sulfur-doped TiO2 (S-TiO2) nanoparticles. The effect of various treatment processes that is sonolysis, photolysis, catalysis, sonocatalysis, photocatalysis, and sonophotocatalysis were investigated for RB 19 removal. S-TiO2 were synthesized in 1, 3 and 5wt.% of sulfur by sol–gel process and characterized by X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX), UV–Visible diffuse reflectance spectra (DRS). The results confirm anatase phase of TiO2, porous agglomerate structure, and a red shift in the absorbance spectra of S-TiO2. The dye degradation was studied by using UV–Vis spectrophotometer at λmax=594nm. The reaction parameters such as pH, catalyst dosage, initial dye concentration, ultrasonic power and effect of sulfur doping in different weight percent were studied to find out the optimum degradation conditions. Optimum conditions were found as: S-TiO2=5wt.%, catalyst (S-TiO2 5wt.%)=50mg, RB 19 solution concentration=20mgL−1, pH=3, ultrasound power=100 and operating temperature=25°C. The response of 5wt.% S-TiO2 was found better than 1 and 3wt.% S-TiO2 and other forms TiO2. The sonophotocatalysis process was superior to other methods. During this process the ultrasound cavitation and photocatalysis water splitting takes place which leads to the generation of OH. As reveled by the GCMS results the reactive blue 19 (20mgL−1) was degraded to 90% within 120min. The S-TiO2 sonophotocatalysis system was studied for the first time for dye degradation and was found practicable, efficient and cost effective for the degradation of complex and resistant dyes such as RB19.