Site-Selected Doping of Upconversion Luminescent Er3+into SrTiO3for Visible-Light-Driven Photocatalytic H2or O2Evolution

Construction of SrTiO3–LaCrO3 Solid Solutions with Consecutive Band Structures for Photocatalytic H2 Evolution under Visible Light Irradiation

SrTiO3–LaCrO3 continuous solid solutions with LaCrO3 content ranging from 0.00 to 1.00 were prepared via a polymerized complex method. The light absorption ability of SrTiO3 was improved by the consecutive tuning of the bandgap upon the introduction of LaCrO3 (up to 570 nm). The solid solutions exhibited significantly enhanced photocatalytic activities for H2 evolution under visible light irradiation, with an optimized H2 evolution rate of 1368 μmol h−1 g−1 obtained when LaCrO3 content was 0.10 (with 1 wt% Pt as cocatalyst), corresponding to an apparent quantum yield of 3.68% at 400 nm. Supported by comprehensive characterization, the improved photocatalytic performance was attributed to the simultaneously adjusted conduction band and valance band originating from the hybridization of Cr 3d, Ti 3d and O 2p orbitals, as well as the accelerated separation and migration of photogenerated charge carriers derived from the distortion of TiO6 octahedra.

Visible light-driven photocatalytic activity of wide band gap ATiO3 (A = Sr, Zn and Cd) perovskites by lanthanide doping and the formation of a mesoporous heterostructure with ZnS QDs

Charge carrier recombination and wide band gap energy are still the main challenges in the visible-light-driven photocatalytic applications of titanate perovskites, ATiO₃. Herein, three strategies are rationally used to achieve a titanate-based photocatalyst with high photocatalytic performance under visible light. In the first step, SrTiO₃, ZnTiO₃, and CdTiO₃ perovskites were synthesized and their photocatalytic activity was evaluated in the degradation of methylene blue (MB) and bisphenol A (BPA). Then, a dysprosium cation (Dy³⁺) was doped into an ATiO₃ crystalline lattice. Systematic investigations indicate that Dy doping in SrTiO₃ and CdTiO₃ extends the ligand to metal charge transfer absorption edge to visible wavelengths leading to the activation of doped perovskites under visible light. Higher visible-light-driven photocatalytic performance (73.29% for MB and 52.57% for BPA) and higher total organic carbon (TOC) removal (59.20% for MB and 39.53% for BPA) have been achieved by Dy doped CdTiO₃ compared to other photocatalysts. Finally, we prepared a Dy-CdTP/ZnS QD mesoporous type-II heterostructure by the in situ growth of ZnS QDs on a flower-like Dy-CdTP. This design accelerates the separation and transfer of photogenerated electron-hole pairs. The surface area of the Dy-CdTP/ZnS QD heterostructure was ∼11.6 times greater than that of Dy-CdTP, offering a large surface area for the adsorption of organics, and abundant active sites for photocatalytic degradation. Taking advantage of the large surface area and considerable suppressing of the charge carrier recombination, the optimized Dy-CdTP(0.6)/ZnS QD photocatalyst exhibits excellent and stable performance for the degradation of MB (98.25%) and BPA (89.12%) with their considerable mineralization under visible light.

Insight into the effect of OH modification on the piezo-photocatalytic hydrogen production activity of SrTiO3

Surface modification by hydrophilic functional group have a tremendous influence on the catalytic activity of photocatalyst, however, there are few reports on improving piezoelectric catalytic performance through surface functionalization. Herein, OH-modified SrTiO₃ was successfully obtained via a novel low-temperature solid-state precursor method and employed as a catalyst for photocatalytic, piezocatalytic and piezo-photocatalytic hydrogen production. Thanks to the super hydrophilic that is facilitating the contact of catalyst and water molecular and the more oxygen vacancies that can promote electron-hole separation, the photocatalytic, piezocatalytic and piezo-photocatalytic hydrogen generation of OH-modified SrTiO₃ (OH-STO) is about two times higher than pristine SrTiO₃ (STO). It is worth mentioning that the optimal piezo-photocatalytic hydrogen evolution rate of OH-STO (701.2 µmol h^-1 g^-1) is 5.3 times higher than the photocatalytic hydrogen evolution process of STO. This study presents a low-energy approach to the rational design of functional group modification nanomaterials that possess excellent piezo-photocatalytic performance.

Erbium Single Atom Composite Photocatalysts for Reduction of CO2 under Visible Light: CO2 Molecular Activation and 4f Levels as an Electron Transport Bridge

It is still challenging to design a stable and efficient catalyst for visible-light CO₂ reduction. Here, Er³⁺ single atom composite photocatalysts are successfully constructed based on both the special role of Er³⁺ and the special advantages of Zn₂ GeO₄ /g-C₃ N₄ heterojunction in the photocatalysis reduction of CO₂ . Especially, Zn₂ GeO₄ :Er³⁺ /g-C₃ N₄ obtained by in situ synthesis is not only more conducive to the tight junction of Zn₂ GeO₄ and g-C₃ N₄ , but also more favorable for g-C₃ N₄ to anchor rare-earth atoms. Under visible-light irradiation, Zn₂ GeO₄ :Er³⁺ /g-C₃ N₄ shows more than five times enhancement in the catalytic efficiency compared to that of pure g-C₃ N₄ without any sacrificial agent in the photocatalytic reaction system. A series of theoretical and experimental results show that the charge density around Er, Ge, Zn, and O increases compared with Zn₂ GeO₄ :Er³⁺ , while the charge density around C decreases compared with g-C₃ N₄ . These results show that an efficient way of electron transfer is provided to promote charge separation, and the dual functions of CO₂ molecular activation of Er³⁺ single atom and 4f levels as electron transport bridge are fully exploited. The pattern of combining single-atom catalysis and heterojunction opens up new methods for enhancing photocatalytic activity.

Designed Construction of SrTiO3 /SrSO4 /Pt Heterojunctions with Boosted Photocatalytic H2 Evolution Activity

Efficient separation of photogenerated electron-hole pairs is a crucial factor for high-performance photocatalysts. Effective electron-hole separation and migration could be achieved by heterojunctions with suitable band structures. Herein, a porous SrTiO₃ /SrSO₄ heterojunction is prepared by a sol-gel method at room temperature followed by an annealing process. XRD characterization suggests high crystallinity of the heterostructure. A well-defined interface between the two phases is confirmed by high-resolution (HR)TEM. The photocatalytic H₂ evolution productivity of the SrTiO₃ /SrSO₄ heterojunction with Pt as co-catalyst reaches 396.82 μmol g^-1  h^-1 , which is 16 times higher than that of SrTiO₃ /Pt. The boosted photocatalytic activity of SrTiO₃ /SrSO₄ /Pt can be ascribed to the presence of SrSO₄ , which promotes the transfer and migration of photogenerated carriers by forming the heterojunction and porous structure, which provides a large amount of active sites. This novel porous heterostructure brings new ideas for the development of high-efficiency photocatalysts for H₂ release.

UiO-66-NH2 Metal-Organic Frameworks with Embedded MoS2 Nanoflakes for Visible-Light-Mediated H2 and O2 Evolution

Hydrogen evolution from water splitting by means of a photocatalytic approach is an ideal future energy source and free of fossil reserves, in contrary photocatalytic O₂ evolution remains a bottleneck due to high over potential and low efficiency. For reasonable use of solar light, photocatalysts must be sufficiently stable and efficient toward harvesting of sunlight from both theoretical and practical viewpoints. In this regard, here we have prepared MoS₂-modified UiO-66-NH₂ MOF through a facile hydrothermal technique and evaluated its efficiency toward photocatalytic H₂ and O₂ evolution by water splitting in the presence of sacrificial agents. A couple of similar type of analyses have been studied previously; however, this analysis represents a diverse scientific approach on the basis of interfacial contact toward reveal the actual potential of nanoflakes MoS₂ as well as UiO-66-NH₂. In this regard the as-synthesized photocatalyst was well-characterized by XRD, FTIR, UV-vis diffuse reflectance spectra, FESEM, HRTEM, XPS, and BET analysis techniques, which provide sufficient evidence toward successful synthesis of the pristine materials and efficacious anchorage of MoS₂ on the active surface of UiO-66-NH₂ by the ionic interaction between Zr-O and S/Mo. Among the synthesized photocatalysts (3 wt %) MoS₂/UiO-66-NH₂ shows the optimum outcome toward H₂ and O₂ evolution, i.e., 512.9 μmol/h (4.37 times greater than bare UiO-66-NH₂) and 263.6 μmol/h (4.25 and 11.32 times greater than bare UiO-66-NH₂ and MoS₂, respectively). The superior performance obtained by the composite is due to the synergistic effect of pristine UiO-66-NH₂ and MoS₂ which proceeds through a type-II interband alignment for the facile channelization of excitons. This investigation will bestow a beneficial blue-print to construct challenging photocatalysts and to find out the paramount performance toward photocatalytic water redox reaction.

Crystal phase induced upconversion enhancement in Er3+/Yb3+ doped SrTiO3 ceramic and its temperature sensing studies

Through doping of Er³⁺/Yb³⁺ ions the SrTiO₃ perovskite ceramic is turned into an optically active material keeping its ferroelectric property intact. A huge enhancement of around 20 times in upconversion (UC) emission intensity is observed due to the transformation of cubic crystal structure to tetragonal phase. The intensity ratio of green to red band is found too high to neglect the contribution from the red emission band, which is not observed normally in such type of relatively moderate phonon frequency materials containing Yb³⁺/Er³⁺ ions. The change in emission intensity is reflected in the decay time measurement. Optical temperature sensing behavior based on FIR technique also has been discussed for Er³⁺/Yb³⁺ doped SrTiO₃ ceramic.

Lanthanide Doped Near Infrared Active Upconversion Nanophosphors: Fundamental Concepts, Synthesis Strategies, and Technological Applications

Near infrared (NIR) light utilization in a range of current technologies has gained huge significance due to its abundance in nature and nondestructive properties. NIR active lanthanide (Ln) doped upconversion nanomaterials synthesized in controlled shape, size, and surface functionality can be combined with various pertinent materials for extensive applications in diverse fields. Upconversion nanophosphors (UCNP) possess unique abilities, such as deep tissue penetration, enhanced photostability, low toxicity, sharp emission peaks, long anti-Stokes shift, etc., which have bestowed them with prodigious advantages over other conventional luminescent materials. As new generation fluorophores, UCNP have found a wide range of applications in various fields. In this Review, a comprehensive overview of lanthanide doped NIR active UCNP is provided by discussing the fundamental concepts including the different mechanisms proposed for explaining the upconversion processes, followed by the different strategies employed for the synthesis of these materials, and finally the technological applications of UCNP, mainly in the fields of bioimaging, drug delivery, sensing, and photocatalysis by highlighting the recent works in these areas. In addition, a brief note on the applications of UCNP in other fields is also provided along with the summary and future perspectives of these materials.

Large enhanced photocatalytic activity of g-C3N4 by fabrication of a nanocomposite with introducing upconversion nanocrystal and Ag nanoparticles

A novel heterostructured nanocomposite UCNPs@SiO₂@Ag/g-C₃N₄ was developed for the first time to substantially boost the solar-light driven photocatalytic activity of g-C₃N₄. Its photocatalytic properties and photocatalytic mechanism were investigated. The as-synthesized photocatalyst with excellent improvement in the solar absorption and separation efficiency of photoinduced electron–hole pairs exhibited optimum solar-induced photocatalytic activity in dye degradation and hydrogen production. The experimental results showed that the rates of degradation of Rhodamine B (RhB) and hydrogen evolution were about 10 and 12 times higher than that of pristine g-C₃N₄, respectively. The excellent photocatalytic activity was attributed to the synergetic effect of upconversion nanoparticles (UCNPs) and Ag nanoparticles (NPs) on the modification of the photocatalytic properties of g-C₃N₄, resulting in a broad light response range for g-C₃N₄ as well as the fast separation and slow recombination of photoinduced electron–hole pairs. This study provides new insight into the fabrication of g-C₃N₄-based nanocomposite photocatalysts with high catalytic efficiency through the artful assembly of UCNPs, Ag NPs and g-C₃N₄ into a hetero-composite nanostructure. The prominent improvement in photocatalytic activity enables the potential application of g-C₃N₄ in the photocatalytic degradation of organic pollutants and hydrogen production utilizing solar energy.

A novel heterostructured nanocomposite UCNPs@SiO₂@Ag/g-C₃N₄ was developed for the first time to substantially boost the solar-light driven photocatalytic activity of g-C₃N₄.

Molten Ag2 SO4 -based Ion-Exchange Preparation of Ag0.5 La0.5 TiO3 for Photocatalytic O2 Evolution

Ag_0.5 La_0.5 TiO₃ with an ABO₃ perovskite structure was synthesized by a newly developed ion-exchange method. Molten Ag₂ SO₄ instead of traditional molten AgNO₃ was used as Ag⁺ source in view of its high decomposition temperature (1052 °C), thereby guaranteeing the complete substitution of Ag⁺ for Na⁺ in Na_0.5 La_0.5 TiO₃ with a stable ABO₃ perovskite structure at a high ion-exchange temperature (700 °C). Under full-arc irradiation, the O₂ -evolution activity of Ag_0.5 La_0.5 TiO₃ was about 1.6 times that of Na_0.5 La_0.5 TiO₃ due to the optimized electronic band structures and local lattice structures. On the one hand, the substitution of Ag⁺ for Na⁺ elevated the VBM and thus narrowed the band gap from 3.19 to 2.83 eV, thereby extending the light-response range and, accordingly, enhancing the photoexcitation to generate more charge carriers. On the other hand, the substitution of Ag⁺ for Na⁺ induced a lattice distortion of the ABO₃ perovskite structure, thereby promoting the separation and migration of charge carriers. Moreover, under visible-light irradiation, Ag_0.5 La_0.5 TiO₃ displayed notable O₂ evolution whereas Na_0.5 La_0.5 TiO₃ showed little O₂ evolution, thus demonstrating that the substitution of Ag⁺ for Na⁺ enabled the use of visible light to evolve O₂ photocatalytically. This work presents an effective route to explore novel Ag-based photocatalysts.

Site selective substitution and its influence on photoluminescence properties of Sr0.8Li0.2Ti0.8Nb0.2O3:Eu3+ phosphors

Effects of substitution of Eu³⁺ ions at Sr²⁺ sites and simultaneously at Sr²⁺ and Ti⁴⁺ sites on the luminescence properties of lithium niobate incorporated strontium titanate.

Growth and Post-Deposition Treatments of SrTiO3 Films for Dye-Sensitized Photoelectrosynthesis Cell Applications

Sensitized SrTiO3 films were evaluated as potential photoanodes for dye-sensitized photoelectrosynthesis cells (DSPECs). The SrTiO3 films were grown via pulsed laser deposition (PLD) on a transparent conducting oxide (fluorine-doped tin oxide, FTO) substrate, annealed, and then loaded with zinc(II) 5,10,15-tris(mesityl)-20-[(dihydroxyphosphoryl)phenyl] porphyrin (MPZnP). When paired with a platinum wire counter electrode and an Ag/AgCl reference electrode these sensitized films exhibited photocurrent densities on the order of 350 nA/cm(2) under 0 V applied bias conditions versus a normal hydrogen electrode (NHE) and 75 mW/cm(2) illumination at a wavelength of 445 nm. The conditions of the post-deposition annealing step-namely, a high-temperature reducing atmosphere-proved to be the most important growth parameters for increasing photocurrent in these electrodes.

Co3(OH)2(HPO4)2 as a novel photocatalyst for O2 evolution under visible-light irradiation

Co₃(OH)₂(HPO₄)₂ was proved to be a novel visible-light-driven photocatalyst for O₂ evolution due to the unique characteristics of Co²⁺ octahedra.

Synthesis of Er3+-doped perovskite nanorods with outstanding UC PL behavior

The Er-doped perovskite single-crystal NaNbO₃ nanorods with outstanding UC PL behavior were successfully synthesized by hydrothermal method.

Inorganic perovskite photocatalysts for solar energy utilization

This review specifically summarizes the recent development of perovskite photocatalysts and their applications in water splitting and environmental remediation.

Decoration of upconversion nanoparticles@mSiO2 core–shell nanostructures with CdS nanocrystals for excellent infrared light triggered photocatalysis

Upconversion nanoparticles@mesoporous silica (mSiO₂)/CdS nanostructures have been designed and fabricated for infrared light triggered photocatalytic degradation towards RhB dye.

Continuous solid solutions of Na0.5La0.5TiO3–LaCrO3 for photocatalytic H2 evolution under visible-light irradiation

(Na_0.5La_0.5TiO₃)_1−x(LaCrO₃)_x solid solutions showed enhanced visible-light-driven photocatalytic activities for H₂ evolution due to the narrowed bandgaps and increased lattice distortion.

Core–shell SrTiO3:Yb3+,Er3+@mSiO2 nanoparticles for controlled and monitored doxorubicin delivery

The investigation of nano-carriers with controllable and trackable drug release kinetics has attracted worldwide attention for theranostic protocols with catabatic side effects.

Synthesis of Ordered Mesoporous CuO/CeO₂ Composite Frameworks as Anode Catalysts for Water Oxidation

Cerium-rich metal oxide materials have recently emerged as promising candidates for the photocatalytic oxygen evolution reaction (OER). In this article, we report the synthesis of ordered mesoporous CuO/CeO₂ composite frameworks with different contents of copper(II) oxide and demonstrate their activity for photocatalytic O₂ production via UV-Vis light-driven oxidation of water. Mesoporous CuO/CeO₂ materials have been successfully prepared by a nanocasting route, using mesoporous silica as a rigid template. X-ray diffraction, electron transmission microscopy and N₂ porosimetry characterization of the as-prepared products reveal a mesoporous structure composed of parallel arranged nanorods, with a large surface area and a narrow pore size distribution. The molecular structure and optical properties of the composite materials were investigated with Raman and UV-Vis/NIR diffuse reflectance spectroscopy. Catalytic results indicated that incorporation of CuO clusters in the CeO₂ lattice improved the photochemical properties. As a result, the CuO/CeO₂ composite catalyst containing ~38 wt % CuO reaches a high O₂ evolution rate of ~19.6 µmol·h-1 (or 392 µmol·h-1·g-1) with an apparent quantum efficiency of 17.6% at λ = 365 ± 10 nm. This OER activity compares favorably with that obtained from the non-porous CuO/CeO₂ counterpart (~1.3 µmol·h-1) and pure mesoporous CeO₂ (~1 µmol·h-1).

NIR light induced H2evolution by a metal-free photocatalyst

A novel metal-free photocatalyst composed of g-C₃N₄and carbon quantum dots drives near-infrared induced H₂generation from water.

Lanthanide-doped upconversion materials: emerging applications for photovoltaics and photocatalysis

Photovoltaics and photocatalysis are two significant applications of clean and sustainable solar energy, albeit constrained by their inability to harvest the infrared spectrum of solar radiation. Lanthanide-doped materials are particularly promising in this regard, with tunable absorption in the infrared region and the ability to convert the long-wavelength excitation into shorter-wavelength light output through an upconversion process. In this review, we highlight the emerging applications of lanthanide-doped upconversion materials in the areas of photovoltaics and photocatalysis. We attempt to elucidate the fundamental physical principles that govern the energy conversion by the upconversion materials. In addition, we intend to draw attention to recent technologies in upconversion nanomaterials integrated with photovoltaic and photocatalytic devices. This review also provides a useful guide to materials synthesis and optoelectronic device fabrication based on lanthanide-doped upconversion materials.

Functionalized nanostructures for enhanced photocatalytic performance under solar light

Photocatalytic hydrogen production from water has been considered to be one of the most promising solar-to-hydrogen conversion technologies. In the last decade, various functionalized nanostructures were designed to address the primary requirements for an efficient photocatalytic generation of hydrogen by using solar energy: visible-light activity, chemical stability, appropriate band-edge characteristics, and potential for low-cost fabrication. Our aim is to present a short review of our recent attempts that center on the above requirements. We begin with a brief introduction of photocatalysts coupling two or more semiconductors, followed by a further discussion of the heterostructures with improved matching of both band structures and crystal lattices. We then elaborate on the heterostructure design of the targeted materials from macroscopic regulation of compositions and phases, to the more precise control at the nanoscale, i.e., materials with the same compositions but different phases with certain band alignment. We conclude this review with perspectives on nanostructure design that might direct future research of this technology.

Nanoporous Sr-rich strontium titanate: a stable and superior photocatalyst for H2 evolution

A synthetic route to prepare nanoporous Sr-rich strontium titanate (Sr : Ti ≈ 1.03) with a high surface area is reported. The as-obtained porous nanomaterial serves as a stable and superior photocatalyst for H2 evolution.

Photon upconversion in hetero-nanostructured photoanodes for enhanced near-infrared light harvesting

A hetero-nanostructured photoanode with enhanced near-infrared light harvesting is developed for photo-electrochemical cells. By spatially coating upconversion nanoparticles and quantum dot photosensitizers onto TiO2 inverse opal, this architecture allows direct irradiation of upconversion nanoparticles to emit visible light that excites quantum dots for charge separation. Electrons are injected into TiO2 with minimal carrier losses due to continuous electron conducting interface.

Engineering light: advances in wavelength conversion materials for energy and environmental technologies

Upconversion photoluminescence (UC) occurs in optical materials that are capable of absorbing low energy photons and emitting photons of higher energy and shorter wavelength, while downconversion (DC) materials may absorb one high energy photon and emit two of lower energy for quantum yields exceeding unity. These wavelength conversion processes allow us to transform electromagnetic radiation so it may be more effectively utilized by light-capturing devices and materials. Progress in designing more efficient organic and inorganic photochemical conversion systems has initiated a recent surge in attempts to apply these processes for practical uses, including enhancement of many energy and environmental technologies. In this review, we introduce important concepts in UC and DC materials and discuss the current status and challenges toward the application of wavelength conversion to solar cells, photocatalysis, and antimicrobial surfaces.