Rapid and facile synthesis of Ti-MCM-48 mesoporous material and the photocatalytic performance for hydrogen evolution

A rapid and facile method was used to synthesize high quality titanium containing cubic MCM-48 mesoporous materials at room temperature. Four kinds of titanium containing MCM-48 mesoporous materials were prepared by addition of the titanium precursor at different stages during the formation of MCM-48 gel. The mesoporous structure and the light absorption characteristics of Ti-MCM-48 were studied by X-ray diffraction (XRD), diffuse reflectance spectra (DRS), and nitrogen isotherm studies. The photocatalytic activities of these heterogeneous Ti-MCM-48 catalysts were tested for photocatalytic hydrogen evolution from methanol–water mixture under UV irradiation. High activity was achieved in the absence of platinum cocatalyst, which is usually indispensable to TiO₂ photocatalyst for hydrogen evolution.     

Co3O4/CeO2 p-n heterojunction construction and application for efficient photocatalytic hydrogen evolution

The construction of p-n type heterojunction is an effective way to enhance the efficiency of photocatalytic hydrogen evolution. In this work, Co₃O₄/CeO₂ p-n heterojunction was construct by a simple hydrothermal method. This heterojunction mainly uses the internal electric field formed and accelerate the separation of electrons and holes in the opposite direction. In addition, according to SEM and TEM characterization, it was found that the granular cobalt oxide nanoparticles prepared by in-situ hydrothermal method were firmly and uniformly dispersed in cerium oxide, which effectively increased the active sites of hydrogen evolution. And combined with the BET results, it shows that the growth of cobalt oxide effectively increases the specific surface area and increases the active sites for hydrogen evolution. By exploring the hydrogen evolution capacity of different ratios of the complex, the test results showed that in all different ratios of the catalyst, CC-0.16 showed the best performance, and the hydrogen production efficiency reached 2298.52 μmol g⁻¹h⁻¹, which was 71 times that of nanobelt CeO₂ and 2.72 times that of Co₃O₄. According to the characterization results, the photocatalytic water splitting mechanism of the p-n heterojunction was proposed, and the charge transfer mechanism in the process was discussed in depth.     

Review on hydrogen production photocatalytically using carbon quantum dots: Future fuel

They are sometimes identified as zero-dimensional (0D) nanoparticles. These particles have gained much attention in water splitting into hydrogen and oxygen through photocatalytic conversion. CQDs act as semiconductor few nm sizes, due to very small size; their optical and electronic properties differ from larger particles. CQDs particle has high stability, mild toxicity besides conductivity. These particles are environmentally friendly due to low toxicity and also have excellent luminescence. Therefore they can be utilized as a potential source for the splitting of water photocatalytically. The parting of water into H₂ and O₂ will enable us to produce or collect hydrogen to be used as a future fuel. The review summarizes the efforts made by various researchers in the field of utilizing carbon quantum dabs for water splitting which may be further followed by future researchers for commercial-scale hydrogen production. Thus, the study concludes the methods for the production of CQDs and their utilization under sunlight by catalytically hydrogen gas production from water.     

Electron transfer via a carbon channel for efficient Z-scheme solar hydrogen production

Z-scheme photocatalysis provides a promising solution to photocatalytic solar water splitting, yet restricted by inferior interfacial charge transfer. Here, we demonstrate a Z-scheme composite photocatalyst made of Fe₂O₃, a carbon layer, and g-C₃N₄ that can achieve efficient hydrogen generation from solar water decomposition. The success relies on in-situ preparation of core-shell Fe₂O₃@C structure at the surface of g-C₃N₄. Carbon as an intermediate layer thus acts as a bridge that significantly accelerates the migration of photogenerated electrons from Fe₂O₃ conduction band to g-C₃N₄ valence band. As a result, the highest rate of H₂ generation reaches 5.26 mmol h⁻¹g⁻¹. This activity is approximately 33-time greater than that achieved over pristine g-C₃N₄ and about 4-time larger than that obtained over a Fe₂O₃/g-C₃N₄ heterojunction without internal carbon layer. This work explicates the potential insight of the composite and paves a promising way to engineer the charge transfer behavior.     

Origin of the overall water splitting activity over Rh/Cr2O3@ anatase TiO2 following UV-pretreatment

Anatase TiO₂ has long been known to be one of the best photocatalysts. Its conduction band potential is thermodynamically allowed to drive a diverse range of photooxidation reactions. However, anatase TiO₂ cannot oxidize water into oxygen in photocatalytic overall water splitting that involves multi-hole transfers. In the present study, a simple pretreatment of anatase TiO₂ with highly-intense UV irradiation is demonstrated to enable overall water splitting upon loading with a Rh/Cr₂O₃ cocatalyst. Based on light-induced infrared absorption spectroscopy and time-resolved microwave conductivity, it is suggested that the efficient removal of deep hole traps permits free holes to possess a sufficiently strong oxidizing potential for water oxidation over Rh/Cr₂O₃@TiO₂.     

Bandgap engineering of KTaO3 for water-splitting by different doping strategies

In this work, different doping strategies are adopted to improve the photocatalytic activity of KTaO₃ (KT) by hybrid functional theory. The La and W monodoped KTs are n-type semiconductors and the photocatalytic performance of Ti, Mo, Cr, N, La–Bi, La–Cr, W–N, Cr–N, Cr–Ti doped KTs are limited by either wide bandgaps or the appeared local unoccupied impurity states. The Bi, C monodoped and La–C, Mo–N, Mo–Ti, W–Ti codoped KTs possess suitable bandgaps of 2.12, 2.06, 1.39, 2.66, 2.66, and 2.61 eV for absorbing visible light without the introduction of localized unoccupied states. The band edge alignments suggest that Mo–N and W–Ti codoped KTs possess the ability for spontaneous overall water-splitting, Bi and Mo–Ti doped KTs can only spontaneously produce oxygen, and C doped KTs only spontaneously generate hydrogen. While La–C doped KT is thermodynamically unfeasible to generating both hydrogen and oxygen. Thus, Mo–N and W–Ti codoped KTs are promising photocatalysts for overall water-splitting, and Bi, C, and Mo–Ti doped KTs are considered for Z-scheme photocatalysis.     

New insights in the performance and reuse of rGO/TiO2 composites for the photocatalytic hydrogen production

The viability of the photocatalytic hydrogen production is closely related to the performance and long term stability of the photocatalyst. In this work rGO/TiO₂ composites have been synthetized with graphene oxide (GO) ratios from 1% to 10% and experimentally assessed towards hydrogen generation from methanol solutions. The performance of the composite with 2% of rGO (2 GT) has been compared to bare TiO₂ working with 20% volume methanol solution. The hydrogen production initial rate showed similar values with both photocatalysts decreasing after about 24 h. Further analysis of the photocatalytic process at longer times showed the negative influence of hydrogen accumulation in the reaction system. Thus, an experimental procedure with argon purge was developed and the behavior of TiO₂ and 2 GT photocatalysts was compared. It is concluded that TiO₂ keeps its activity after 8 operation cycles while 2 GT performance reduces progressively. This can be attributed to the further reduction of GO and the increase of defects in its structure.     

A facile method for fabrication of highly ordered hollow Ag/TiO2 nanostructure and its photocatalytic activity

This letter reports a facile and efficient strategy for the designed preparation of highly ordered hollow Ag/TiO₂ nanostructure. Different from previous reports, the presently proposed method conveniently combines the long-range ordering porosity and the property of Ag nanoparticles by a general colloidal crystal-templating technique. The sample was characterized by SEM and XRD. The results show that such hollow nanostructured material is composed of anatase TiO₂ and metal Ag. The as-prepared sample shows a good photocatalytic activity for photodegradation of methyl orange compared with the reference samples, which was attributed to its long-range ordering porosity and the addition of Ag nanoparticles.     

Batch slurry photocatalytic reactors for the generation of hydrogen from sulfide and sulfite waste streams under solar irradiation

In this study, two solar slurry photocatalytic reactors i.e., batch reactor (BR) and batch recycle reactor with continuous supply of inert gas (BRRwCG) were developed for comparing their performance. The performance of the photocatalytic reactors were evaluated based on the generation of hydrogen (H₂) from water containing sodium sulfide (Na₂S) and sodium sulfite (Na₂SO₃) ions. The photoreactor of capacity 300 mL was developed with UV-vis transparent walls. The catalytic powders ((CdS/ZnS)/Ag₂S + (RuO₂/TiO₂)) were kept suspended by means of magnetic stirrer in the BR and gas bubbling and recycling of the suspension in the BRRwCG. The rate constant was found to be 120.86 (einstein⁻¹) for the BRRwCG whereas, for the BR it was found to be only 10.92 (einstein⁻¹). The higher rate constant was due to the fast desorption of products and suppression of e⁻/h⁺ recombination.     

Modification of the photocatalytic properties of self doped TiO2 nanoparticles for hydrogen generation using sunlight type radiation

Synthetic approaches/methodologies can change the properties of nanoparticles significantly. In this study, the photocatalytic property of self (Ti³⁺) doped TiO₂ nanoparticles was modified by synthesizing through different routes. Solvothermal (T-Sol), sonochemical (T-Son) and polyol (T-Pol) methods were employed to prepare TiO₂ nanoparticles and the photocatalytic activities of these samples were compared with that of the sample prepared by precipitation using ammonia solution (T-Ppt). All samples had particle size below 30 nm except T-Son, where small nanoparticles existed as large spherical agglomerates with size around 500 nm. Surface area and porosity measurements of these different TiO₂ samples showed a significant dependency on the synthesis method. UV–Visible absorption spectra showed the onset of absorption at ∼440 nm for all samples due to the presence of defect levels originating from anion vacancies. Photocatalytic activity for hydrogen generation decreased in the order T-Sol > T-Son > T-Pol > T-Ppt and the observed activity is correlated with their physical properties such as surface area and crystallinity. The hydrogen yield was highly enhanced by the addition of Pd metal as co-catalyst on the surface of TiO₂ photocatalysts. Present experiments clearly demonstrate the importance of synthesis route to improve the photocatalytic activity of TiO₂.