Pt Deposites on TiO2 for Photocatalytic H2 Evolution: Pt Is Not Only the Cocatalyst, but Also the Defect Repair Agent

Elucidation of a Core-Shell Structure in Phenyl-Grafted Carbon Nitride/TiO2 Nanohybrids for Visible-Light-Mediated H2 Production with Simultaneous Rhodamine B Degradation

Dual-functional photocatalysts help to maximize resource utilization in water remediation, but often they are visible-light-inactive, toxic, and cost-intensive. Herein, a type-II heterojunction visible-light-active photocatalyst is reported for tandem degradation of Rhodamine B and generation of H2. A Rhodamine B degradation rate of 2.3 × 10-2 min-1 and H2 production activity of 5789 μmol h-1 g-1 are shown. The hybrid shows a gradient core-shell morphology with a visible - light-absorbing phenyl-modified carbon nitride (PhCN) core and a porous PhCN/TiO2 outer shell, resulting in an enhanced interaction between the catalyst and the surroundings. The nanoscale crystallization of TiO2 on PhCN's surface, shifts the triazine network structure, while autoclave treatments further increase the band gap and suppress charge carrier recombination. The influence of nanoscale morphological changes on photocatalytic activity was examined by varying the component ratios and thermal treatments, highlighting the strong correlation between the nanoscale architecture and the enhanced catalytic activity. This work provides a detailed guide to the exploration of environmentally friendly dual-functional photocatalysts.

Enhanced visible-light photocatalytic oxidative desulfurization of model fuel over Pt-decorated carbon-doped TiO2 nanoparticles

Modification of photocatalysts to improve their adsorption and photocatalytic activity in the oxidative desulfurization of liquid fuels has been reported by many investigators. In this study, Pt-decorated carbon-doped TiO2 nanoparticles were synthesized by hydrothermal and photo-deposition techniques and were subsequently used in photocatalytic oxidative desulfurization of dibenzothiophene (DBT) in n-heptane as a simulated liquid fuel with methanol as the extracting solvent. Carbon-doped TiO2 was first synthesized by a simple self-doping method. Pt was then loaded by a photo-deposition technique. The synthesized photocatalysts (labeled as YPt-CT where Y is percent Pt loading) were characterized by of X-ray diffraction (XRD), photoluminescence (PL), field emission scanning electron microscopy (FESEM), N2-physisorption, UV-Vis diffusive reflectance spectra (UV-Vis DRS), transmission electron microscopy (TEM), Fourier transform infrared spectra (FTIR), and nitrogen sorption measurements. The removal efficiency of DBT was 98% in the presence of 2 g/l of 0.5Pt-CT catalyst under visible-light irradiation (λ > 400 nm), ambient pressure, and reaction temperature of 40°C.

Recovery of platinum group metals from spent automotive converters and their conversion into efficient recyclable nanocatalysts

The study reported in this article has shown for the first time that strongly acidic solutions (pH < 0.5) obtained after hydrometallurgical treatment of spent automotive converters (SAC) may be valuable secondary sources of platinum group metal (PGM) nanoparticles (NPs). The PGM precipitation strongly depended on the solution pH; the yield of the precipitated PGM NPs increased considerably from 40% to almost 100% when the pH was adjusted to 7-8. To improve the NPs stability, commercial TiO2 was used as support to obtain efficient recyclable PGM@TiO2 catalysts. The size of the PGM NPs was smaller than 5 nm, while the diameter of the supported particles varied from 10 to 50 nm. The size and dispersion of PGM NPs on the support strongly depended on the pH of the medium: at pH < 0.5, the Pt and Pd NPs were significantly smaller than the NPs obtained at pH 7-8. Also, in the case of Pt@TiO2 and Rh@TiO2, the NPs were well dispersed on the support in contrast to the large agglomerates of Pd@TiO2. The PGM@TiO2 showed catalytic properties in the reduction of 4-nitrophenol to 4-aminophenol, particularly, at pH above 11. The highest conversion of 98% was obtained with 1% Pd@TiO2 at pH 14 after only 15 min. The catalyst was easily separated from the reaction mixture and reused in 7 consecutive cycles without significant loss of activity. The PGM@TiO2 synthesized from the real solution showed a similar catalytic activity (70% conversion at pH 14) as that obtained from model solution.

Electrospun composite nanofibers as novel high-performance and visible-light photocatalysts for removal of environmental pollutants: A review

Environmental pollution caused by industries and human manipulations is coming a serious global challenge. On the other hand, the world is facing an energy crisis caused by population growth. Designing solar-driven photocatalysts which are inspired by the photosynthesis of plant leaves is a fantastic solution to use solar energy as green, available, and unlimited energy containing ∼50% visible light for the removal of environmental pollutants. The polymeric and non-polymeric-based electrospun composite nanofibers (NFs) are as innovative photocatalytic candidates which increase photocatalytic activity and transition from UV light to visible light and overcome the aggregation, photocorrosion, toxicity, and hard recycling and separation of the nanosized powder form of photocatalysts. The composite NFs are fabricated easily by either embedding the photocatalytic agents into the NFs during electrospinning or via their decorating on the surface of NFs post-electrospinning. Polyacrylonitrile-based, tungsten trioxide-based, zinc oxide-based, and titanium dioxide-based composite NFs were revealed as the most reported composite NFs. All the lately investigated electrospun composite NFs indicated long-term stability, high photocatalytic efficiency (∼> 80%) within a short time of light radiation (10-430 min), and high stability after several cycles of use. They were applied in various applications including degradation of dyes/antibiotics, water splitting, wastewater treatment, antibacterial usage, etc. The photogenerated species especially holes, O₂^∙-, and ^.OH were mostly responsible for the photocatalytic mechanism and pathway. The electrospun composite NFs have the potential to use in large-scale productions in condition that their thickness and recycling conditions are optimized, and their toxicity and detaching are resolved.

Evaluation of Antifungal Properties of Titania P25

Commercial titania photocatalyst—P25 was chosen for an antifungal property examination due to it exhibiting one of the highest photocatalytic activities among titania photocatalysts. Titania P25 was homogenized first (HomoP25) and then annealed at different temperatures. Additionally, HomoP25 was modified with 0.5 wt% or 2.0 wt% of platinum by a photodeposition method. The obtained samples were characterized by diffuse-reflectance spectroscopy (DRS), X-ray photoabsorption spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectroscopy. Moreover, photocatalytic activity was tested for methanol dehydrogenation under UV/vis irradiation. The spore-destroying effect of photocatalysts was investigated against two mold fungal species, i.e., Aspergillus fumigatus and Aspergillus niger. Both the mycelium growth and API ZYM (estimation of enzymatic activity) tests were applied for the assessment of antifungal effect. It was found that annealing caused a change of surface properties of the titania samples, i.e., an increase in the noncrystalline part, a growth of particles and enhanced oxygen adsorption on its surface, which resulted in an increase in both the hydrogen evolution rate and the antifungal effect. Titania samples annealed at 300−500 °C were highly active during 60-min UV/vis irradiation, inhibiting the germination of both fungal spores, whereas titania modification with platinum (0.5 and 2.0 wt%) had negligible effect, despite being highly active for hydrogen evolution. The control experiments revealed the lack of titania activity in the dark, as well as high resistance of fungi for applied UV/vis irradiation in the absence of photocatalysts. Moreover, the complete inhibition of 19 hydrolases, secreted by both tested fungi, was noted under UV/vis irradiation on the annealed P25 sample. It is proposed that titania photocatalysts of large particle sizes (>150 nm) and enriched surface with oxygen might efficiently destroy fungal structures under mild irradiation conditions and, thus, be highly promising as covering materials for daily products.

Efficient electron extraction by CoS2loaded onto anatase TiO2for improved photocatalytic hydrogen evolution

Titanium dioxide (TiO₂) as a benchmark photocatalyst has been attracting attention due to its photocatalytic activity combined with photochemical stability. In particular, TiO₂with anatase polymorph holds promise for driving reduction reactions, such as proton reduction to evolve H₂via photocatalysis. In this study, anatase TiO₂is loaded with CoS₂through the hydrothermal route to form a CoS₂@TiO₂photocatalyst system. X-ray absorption near edge structure confirms the +2-oxidation state of the Co cation, while extended x-ray absorption fine structure shows that each Co²⁺cation is primarily coordinated to six S^-anions forming a CoS₂-like species. A small fraction of the Co²⁺species is also coordinated to O^2-anions forming Co_xO_yspecies and substitutionally resides at the Ti⁴⁺-sites. Further investigations with steady-state IR absorption induced by UV-light and time-resolved microwave conductivity suggest an efficient electron transfer from the conduction band of TiO₂to the surface-loaded CoS₂which acts as a metallic material with no bandgap. The CoS₂shallowly traps electrons at the host surface and facilitates proton reduction. An appreciably enhanced H₂evolution rate (8 times) is recognised upon the CoS₂loading. The CoS₂is here proposed to function as a proton reduction cocatalyst, which can potentially be an alternative to noble metals.

Recent advances in Co-based co-catalysts for efficient photocatalytic hydrogen generation

Recent progress in photocatalytic hydrogen generation reaction highlights the critical role of co-catalysts in enhancing the solar-to-fuel conversion efficiency of diverse band-matched semiconductors. Because of the compositional flexibility, adjustable microstructure, tunable crystal phase and facet, cobalt-based co-catalysts have stimulated tremendous attention as they have high potential to promote hydrogen evolution reaction. However, a comprehensive review that specifically focuses on these promising materials has not been reported so far. Therefore, this present review emphasizes the recent progress in the pursuing of highly efficient Co-based co-catalysts for water splitting, and the advances in such materials are summarized through the analysis of structure-activity relationships. The fundamental principles of photocatalytic hydrogen production are profoundly outlined, followed by an elaborate discussion on the crucial parameters influencingthe reaction kinetics. Then, the co-catalytic reactivities of various Co-based materials involving Co, Co oxides, Co hydroxides, Co sulfides, Co phosphides and Co molecular complexes, etc, are thoroughly discussed when they are coupled with host semiconductors, with an insight towards the ultimateobjective of achieving a rationally designed photocatalyst for enhancing water splitting reaction dynamics. Finally, the current challenge and future perspective of Co-based co-catalysts as the promising noble-metal alternative materials for solar hydrogen generation are proposed and discussed.

Visible-Light Photocatalysts and Their Perspectives for Building Photocatalytic Membrane Reactors for Various Liquid Phase Chemical Conversions

Photocatalytic organic synthesis/conversions and water treatment under visible light are a challenging task to use renewable energy in chemical transformations. In this review a brief overview on the mainly employed visible light photocatalysts and a discussion on the problems and advantages of Vis-light versus UV-light irradiation is reported. Visible light photocatalysts in the photocatalytic conversion of CO2, conversion of acetophenone to phenylethanol, hydrogenation of nitro compounds, oxidation of cyclohexane, synthesis of vanillin and phenol, as well as hydrogen production and water treatment are discussed. Some applications of these photocatalysts in photocatalytic membrane reactors (PMRs) for carrying out organic synthesis, conversion and/or degradation of organic pollutants are reported. The described cases show that PMRs represent a promising green technology that could shift on applications of industrial interest using visible light (from Sun) active photocatalysts.

Synthesis of Ni- and N-Doped Titania Nanotube Arrays for Photocatalytic Hydrogen Production from Glycerol–Water Solutions

Synthesis of Ni- and N-doped Titania Nanotube Arrays (Ni-N-TiNTAs) was conducted to produce photocatalysts for hydrogen production from a glycerol–water mixture. Ni-N-TiNTAs were synthesized in two steps, namely anodization and chemical reduction. Ti foil was anodized at 50 V for two h in an electrolyte solution containing 0.2% urea as a source of N atoms. Ni doping (at various content of 5%, 10%, 15%, and 20% wt) was performed by one-hour chemical reduction with sodium borohydride as a reducing agent. The photocatalyst was annealed at different temperatures, i.e., 500 °C, 550 °C, and 600 °C under 60 mL/min N2 gas for two h. On the basis of X-ray Diffraction (XRD) patterns, Ni-N-TiNTAs are mostly of anatase crystallite phase when annealed at 500 °C and 550 °C, while that of rutile was observable when calcination was done at 600 °C. The morphology of the photocatalysts was scrutinized by means of Field Emission Scanning Electron Microscopy (FESEM) imaging, which reveals nanotubular structures, with elemental composition measured by Energy Dispersive X-ray (EDX). The bandgap of the photocatalysts was analyzed using Ultraviolet Diffuse Reflectance Spectroscopy (UV DRS), which showed a lower value for the case of Ni-N-TiNTAs as compared to those of TiNTAs and N-TiNTAs. Photocatalytic tests showed that the highest amount of hydrogen produced (ca. 30973 μmol/m2) was obtained in the case of Ni-N-TiNTAs with a Ni content of 10wt%.