The roles of gold and silver nanoparticles on ZnIn2S4/silver (gold)/tetra(4-carboxyphenyl)porphyrin iron(III) chloride hybrids in carbon dioxide photoreduction

The construction of hybrid catalysts composed of inorganic semiconductors and molecular catalysts shows great potential for achieving high photocatalytic carbon dioxide (CO₂) conversion efficiency. In this study, ZnIn₂S₄ was first synthesized via a solvothermal route. Gold (Au) and silver (Ag) nanoparticles were then deposited on ZnIn₂S₄ via the reduction of noble metal precursor by sulfur vacancy defects. The obtained composite was further combined with tetra(4-carboxyphenyl)porphyrin iron(III) chloride (FeTCPP) molecular catalyst for efficient photocatalytic CO₂ conversion. The roles of different noble metal nanoparticles in charge separation and interfacial electron transfer have been comprehensively studied. The photocatalytic performance and photoelectrochemical characterizations demonstrate that the introduction of Ag or Au nanoparticles is beneficial for charge separation. More importantly, the presence of Ag nanoparticles plays a crucial role in promoting the interfacial charge transfer between ZnIn₂S₄ and FeTCPP, whereas, Au nanoparticles function as active sites for the water reduction reaction.

Influences of the precursor molar ratio in synthesis on the structures and visible-light driven CO2 reduction into solar fuel of CdS catalyst

Synthesizing highly efficient photocatalysts for photoreduction of CO2 into solar fuel is of great significance for solving the energy shortage and environmental pollution. Here a series of CdS photocatalysts are...

Facile Multistep Synthesis of ZnO-Coated β-NaYF4:Yb/Tm Upconversion Nanoparticles as an Antimicrobial Photodynamic Therapy for Persistent Staphylococcus aureus Small Colony Variants

Antibacterial treatment strategies using functional nanomaterials, such as photodynamic therapy, are urgently required to combat persistent Staphylococcus aureus small colony variant (SCV) bacteria. Using a stepwise approach involving thermolysis to form β-NaYF₄:Yb/Tm upconversion nanoparticles (UCNPs) and surface ligand exchange with cetyltrimethylammonium bromide (CTAB), followed by zeolite imidazolate framework-8 (ZIF-8) coating and conversion to zinc oxide (ZnO), β-NaYF₄:Yb/Tm@ZnO nanoparticles were synthesized. The direct synthesis of β-NaYF₄:Yb/Tm@ZIF-8 UCNPs proved problematic due to the hydrophobic nature of the as-synthesized material, which was shown by zeta potential measurements using dynamic light scattering (DLS). To facilitate deposition of a ZnO coating, the zeta potentials of (i) as-synthesized UCNPs, (ii) calcined UCNPs, (iii) polyvinylpyrrolidone (PVP), and (iv) CTAB-coated UCNPs were measured, which revealed the CTAB-coated UCNPs to be the most hydrophilic and the better-dispersed form in water. β-NaYF₄:Yb/Tm@ZIF-8 composites formed using the CTAB-coated UCNPs were then converted into β-NaYF₄:Yb/Tm@ZnO nanoparticles by calcination under carefully controlled conditions. Photoluminescence analysis confirmed the upconversion process for the UCNP core, which allows the β-NaYF₄:Yb/Tm@ZnO nanoparticles to photogenerate reactive oxygen species (ROS) when activated by near-infrared (NIR) radiation. The NIR-activated UCNPs@ZnO nanoparticles demonstrated potent efficacy against both Staphylococcus aureus (WCH-SK2) and its associated SCV form (0.67 and 0.76 log colony forming unit (CFU) reduction, respectively), which was attributed to ROS generated from the NIR activated β-NaYF₄:Yb/Tm@ZnO nanoparticles.

Crystal Facet-Dependent CO2 Photoreduction over Porous ZnO Nanocatalysts

Crystal facet engineering provides a promising approach to tailor the performance of catalysts because of the close relationship between the photocatalytic activity and the surface atomic and electronic structures. An in-depth understanding mechanism of crystal facet-dependent CO₂ photoreduction is still an open question. Herein, two different types of porous ZnO nanocatalysts are used as model photocatalysts for the investigation, which are, respectively, with exposed {110} and {001} facets. The porous ZnO with an exposed {110} facet exhibits superior photocatalytic activity to the one with the {001} facet. Various influencing factors have been thoroughly studied both theoretically and/or experimentally, including light harvesting (i.e., band gap), reduction capability (potential of conduction band), crystallinity, CO₂ adsorption ability, CO₂ activation, and charge separation. The major influencing factors are eventually figured out based on the experimental and calculation results. The product selectivity and the influence of the hole scavenger can be explained too. Our work may pave a way for directing the future rational design of efficient photocatalysts for CO₂ reduction.

In-situ formation of carboxylate species on TiO2 nanosheets for enhanced visible-light photocatalytic performance

It still remains challenge for expanding the photo-response range of TiO₂ with dominant {0 0 1} facets due to the hardly achieving modification of the electronic structure without destroying the formation of TiO₂ high energy facets. Herein, we report the construction of carboxylate species modified TiO₂ nanosheets with dominant {0 0 1} facets by employing ethanol as a carbon source through a low-temperature (300 °C) carbonization method. The as-obtained samples were investigated in detail by using various characterization techniques. The results indicate that the carboxylate species derived from the oxidation and carbonization of ethanol are coordinated to the {0 0 1} facets in a bidentate bridging mode. The electron-withdrawing carboxylate species induce TiO₂ to form a lower valence band edge and a narrower bandgap, which enhances the oxidation ability of photogenerated holes and expands the photo-response range. The partially carbonized carboxylate species can also act as a photosensitizer to induce visible-light photocatalytic activity of TiO₂ nanosheets. In addition, the carboxylate species can further promote the separation of photogenerated charge carriers. The findings of this work may provide a new perspective for tuning the band structure of TiO₂ with dominant {0 0 1} facets and improving its photocatalytic performance.

Efficient upconverting carbon nitride nanotubes for near-infrared-driven photocatalytic hydrogen production

We report a facile chemical technique for synthesizing nanotube-based hybrid materials for near-infrared-driven photocatalytic hydrogen (H₂) production. Upconversion nanoparticles (UCNPs), NaYF₄:Yb,Tm,Gd (NYFG) and NaYF₄:Yb,Tm (NYF), were engineered on C₃N₄ nanotubes (C₃N₄ NTs) separately to construct heterojunction structures. With a UCNP loading content of 15 wt%, the NYFG/C₃N₄ NT heterojunction exhibits the highest H₂ generation rate of 311.6 μmol g^-1 with an apparent quantum efficiency of 0.80 ‰, about 1.4 times higher than that of the NYF/C₃N₄ NT nanocomposite under 980 nm laser irradiation. Comprehensive characterization reveals that the enhanced photocatalytic performance of the Gd doped nanostructure is attributed to the synergistic effect, stronger interaction, higher emission intensities, and faster charge transfer between the UCNPs and C₃N₄ NTs. Moreover, the steady-state and dynamic fluorescence spectra indicate that the energy from NYFG NPs was transferred to C₃N₄ NTs via a fluorescence-resonance energy-transfer process. Our work demonstrates the potential of developing near-infrared-responsive photocatalysts for energy and environmental applications.

Design of Lanthanide-Doped Colloidal Nanocrystals: Applications as Phosphors, Sensors, and Photocatalysts

The unique optical characteristics of lanthanides (Ln³⁺) such as high color purity, long excited-state lifetimes, less perturbation of excited states by the crystal field environment, and the easy spectral conversion of wavelengths through upconversion and downconversion processes have caught the attention of many scientists in the recent past. To broaden the scope of using these properties, it is important to make suitable Ln³⁺-doped materials, particularly in colloidal forms. In this feature article, we discuss the different synthesis strategies for making Ln³⁺-doped nanoparticles in colloidal forms, particularly ways of functionalizing hydrophobic surfaces to hydrophilic surfaces to enhance their dispersibility and luminescence in aqueous media. We have enumerated the various strategies and sensitizers utilized to increase the luminescence of the nanoparticles. Furthermore, the use of these colloidal nanoparticle systems in sensing application by the appropriate selection of capping ligands has been discussed. In addition, we have shown how the energy transfer efficiency from Ce³⁺ to Ln³⁺ ions can be utilized for the detection of toxic metal ions and small molecules. Finally, we discuss examples where the spectral conversion ability of these materials has been used in photocatalysis and solar cell applications.

Near-infrared light-driven photocatalytic NaYF4:Yb,Tm@ZnO core/shell nanomaterials and their performance

Herein, the infrared-responsive photocatalyst NaYF₄:Yb,Tm@ZnO has been successfully synthesized by combining semiconductor ZnO with an upconversion material, NaYF₄:Yb,Tm. In this composite, NaYF₄:Yb,Tm emits intense ultraviolet and blue upconversion luminescence upon excitation by a 980 nm laser and provides the necessary energy of ultraviolet light to ZnO. The photocatalytic activity of NaYF₄:Yb,Tm@ZnO composites has been studied using methylene blue by irradiation with a 980 nm laser, and the results indicate that the NaYF₄:Yb,Tm@ZnO composite is an advanced near-infrared-driven photocatalyst; this study presents a promising strategy to utilize the near-infrared-responsive upconversion materials for photocatalytic applications.

Herein, the infrared-responsive photocatalyst NaYF₄:Yb,Tm@ZnO has been successfully synthesized by combining semiconductor ZnO with an upconversion material, NaYF₄:Yb,Tm.

Decorating Ag3PO4 nanodots on mesoporous silica-functionalized NaYF4:Yb,Tm@NaLuF4 for efficient sunlight-driven photocatalysis: synergy of broad spectrum absorption and pollutant adsorption-enrichment

A broad-spectrum photocatalyst with pollutant-adsorption capability was synthesized by decorating silver orthophosphate nanodots on mesoporous silica-functionalized upconversion nanoparticles for efficient natural sunlight-driven photocatalysis.

NIR light-activated upconversion semiconductor photocatalysts

Harvesting of near infrared (NIR) light in the abundant and environmentally friendly solar spectrum is particularly significant to enhance the utilization rate of the cleanest energy on earth. Appreciating the unique nonlinear optical properties of upconversion materials for converting low-energy incident light into high-energy radiation, they become the most promising candidates for fabricating NIR light-active photocatalytic systems by integrating with semiconductors. The present review summarizes recent NIR light-active photocatalytic systems based on a sequence of NaYF₄-based, fluoride-based, oxide-based and Ln³⁺ ion-doped semiconductor-based photocatalysts for degradation of organic molecules. In addition, we provide an in-depth analysis of various photocatalytic mechanisms and enhancement effects for efficient photo-redox performance of different upconversion semiconductor photocatalysts. We envision that this review can inspire multidisciplinary research interest in rational design and fabrication of efficient full-spectrum active (UV-visible-NIR) photocatalytic systems and their wider applications in solar energy conversion.

Core–shell structured NaYF4:Yb,Tm@CdS composite for enhanced photocatalytic properties

NaYF₄:Yb,Tm upconversion nanocrystals with hexagonal structure possess excellent photoluminescence emission characteristics. Under near infrared (NIR) light irradiation, the Yb³⁺ ions act as sensitizers to absorb the NIR light and transform NIR light into ultraviolet (UV) and visible (Vis) light continuously. Hybrid NIR-activated photocatalysts can be fabricated by combining upconversion nanocrystals with various semiconductor nanocrystals. In this paper, NaYF₄:Yb,Tm micro-rods were hydrothermally synthesized with oleic acid as capping ligand. The NaYF₄:Yb,Tm@CdS composite was fabricated by in situ generation of CdS nanoclusters on the surface of NaYF₄:Yb,Tm micro-rods. The morphologies and structures of NaY₄:Yb,Tm and NaYF₄:Yb,Tm@CdS were characterized by XRD, SEM, TEM, XPS, UV-Vis and PL spectroscopy. The results of photocatalytic experiments indicated that the NaYF₄:Yb,Tm@CdS composite displayed photocatalytic activity under NIR irradiation. In comparison with pure CdS, the photocatalytic ability of NaYF₄:Yb,Tm@CdS composite under Vis-NIR irradiation was obviously enhanced. 82% of RhB was degraded by NaYF₄:Yb,Tm@CdS catalyst within 75 min under Vis-NIR irradiation, which was more effective than pure CdS (65% degradation of RhB).

NaYF₄:Yb,Tm upconversion nanocrystals with hexagonal structure possess excellent photoluminescence emission characteristics.

Ultrafast dynamics in co-sensitized photocatalysts under visible and NIR light irradiation

Activity modulation of co-sensitized light harvesting nanohybrids by tuning the ultrafast carrier dynamics under visible and NIR light irradiation.

Visible-light-driven CO2 photoreduction over ZnxCd1−xS solid solution coupling with tetra(4-carboxyphenyl)porphyrin iron(iii) chloride

Photocatalytic reduction of CO₂ into solar fuels is a promising approach to supply sustainable energy and efficiently use CO₂ as a resource.

Enhanced energy transfer in heterogeneous nanocrystals for near infrared upconversion photocurrent generation

The key to produce inorganic heterogeneous nanostructures, and to integrate multiple functionalities, is to enhance or at least retain the functionalities of different components of materials. However, this ideal scenario is often deteriorated at the interface of the heterogeneous nanostructures due to lattice mismatches, resulting in downgraded performance in most hybrid nanomaterials. Here, we report that there is a narrow window in controlling temperature in a Lewis acid-base reaction process to facilitate epitaxial alignment during the synthesis of hybrid nanomaterials. We demonstrate a perfectly fused NaYF₄:Yb,Tm@ZnO heterogeneous nanostructure, in which the semiconductor ZnO shell can be epitaxially grown onto lanthanide-doped upconversion nanoparticles. By achieving a matched crystal lattice, the interface defects and crystalline grain boundaries are minimized to enable more efficient energy transfer from the upconversion nanoparticles to the semiconductor, resulting in both enhanced upconversion luminescence intensity and superior photoelectrochemical properties. This strategy provides an outstanding approach to endow lanthanide-doped upconversion nanoparticles with versatile properties.

Photocatalytic degradation of microcystin-LR with a nanostructured photocatalyst based on upconversion nanoparticles@TiO2 composite under simulated solar lights

In this work, we prepared advanced upconversion nanoparticle coated with TiO₂ photocatalysts (NaYF₄:Yb,Tm@TiO₂) to utilize not only UV energy but also the large portion of NIR energy in order to improve the utilization efficiency of solar lights. The MC-LR (10 μg/mL) degradation rate can be approached 100% within 30 min at the concentration of NaYF₄:Yb,Tm@TiO₂ 0.4 mg/mL and initial pH value 4, while 61%, using pure TiO₂ (P25) under simulated solar lights. The reaction processes were studied and fitted with the pseudo-first-order kinetic model. Highly reactive hydroxyl radicals (•OH) were found to be the major reactive species. Meanwhile, seven degradation intermediates of MC-LR were examined by liquid chromatography/mass spectrometry and the degradation mechanism was analyzed. The main degradation pathways were proposed based on the molecular weight of the intermediates and the reaction mechanism are hydroxylation on the diene bonds and the aromatic ring of Adda. The products were evaluated to be nontoxic based on the construction of the intermediates. This study demonstrated that the NIR energy can be used as the driving source for photocatalysis besides the UV and the NIR-responsed photocatalysis had a high-efficiency and potential for MC-LR degradation.

Self-assembled photoadditives in polyester films allow stop and go chemical release

Near-infrared (NIR) triggered chemical delivery allows on-demand release with the advantage of external tissue stimulation. Bioresorbable polyester poly-l-lactic acid (PLLA) was compounded with photoadditives of neat zinc oxide (ZnO) nanoparticles and 980→365nm LiYF₄:Tm³⁺, Yb³⁺ upconverting nanoparticles (UCNP). Subsequently, neat ZnO and UCNP blended PLLA films of sub-50μm thickness were knife casted with a hydrophobic small molecule drug mimic, fluorescein diacetate. The PLLA films displayed a 500 times increase in fluorescein diacetate release from the 50mW NIR irradiated PLLA/photoadditive film compared to non-irradiated PLLA control films. Larger ratios of UCNP/neat ZnO increased photocatalysis efficiency at low NIR duty cycles. The synergistic increase results from the self-assembled photoadditives of neat zinc oxide and upconverting nanoparticles (UCNPs), as seen in transmission electron microscopy. Colloidal ZnO, which does not self-assemble with UCNPs, had less than half the release kinetics of the self-assembled PLLA films under similar conditions, advocating Förster resonance energy transfer as the mechanism responsible for the synergistic increase. Alternative to intensity modulation, pulse width modulation (duty cycles from 0.1 to 1) of the low intensity 50mW NIR laser diode allowed tailorable release rates from 0.01 to 1.4% per day. With the low intensity NIR activation, tailorable release rates, and favorable biocompatibility of the constituents, implanted PLLA photoadditive thin films could allow feedback mediated chemical delivery.

STATEMENT OF SIGNIFICANCE

Upconverting nanoparticles and zinc oxide nanorods were found to spontaneously self-assemble into submicron particles in organic solvents. Exposure of the submicron particles to near-infrared light allows stop and go chemical release from biocompatible polymers. Sample preparation of thin films is done with ease through physical mixing of the photoadditives followed by air-dried knife casting. A colloidal ZnO variant that does not self-assemble with upconverting nanoparticles had slower chemical release, suggesting that synergistic chemical release is brought upon by highly efficient energy transfer mechanisms when the nanoparticles are less than 10nm apart. Never before seen composite particles of UCNP/ZnO are displayed, which shows the close interaction of the photoadditives within the polymer matrix.

Facet engineered interface design of NaYF4:Yb,Tm upconversion nanocrystals on BiOCl nanoplates for enhanced near-infrared photocatalysis

The combination of upconversion nanocrystals with a wide-bandgap semiconductor is an efficient strategy to develop near-infrared (NIR)-responsive photocatalysts. The photocatalytic activity of the hybrid structures is greatly determined by the efficiency of the energy transfer on the interface between upconversion nanocrystals and the semiconductor. In this work, we demonstrate the interface design of a NaYF₄:Yb,Tm-BiOCl hybrid structure based on the choice of suitable BiOCl facets in depositing NaYF₄:Yb,Tm upconversion nanocrystals. It was found that the selective deposition of NaYF₄:Yb,Tm nanocrystals on the BiOCl(110) facet can greatly enhance the photocatalytic performance in dye degradation compared with the sample with NaYF₄:Yb,Tm nanocrystals loaded on the BiOCl(001) facet. Two effects were believed to contribute to this enhancement: (1) a stronger UV emission absorption ability of the BiOCl(110) facet from NaYF₄:Yb,Tm in generating more photo-induced charge carriers resulted from the narrower bandgap; (2) a shorter diffusion distance of photogenerated charge carriers to the BiOCl(110) reactive facet for surface catalytic reactions owing to the spatial charge separation between different facets. This work highlights the rational interfacial design of an upconversion nanocrystal-semiconductor hybrid structure for enhanced energy transfer in photocatalysis.

Photocatalysis of NaYF4:Yb,Er/CdSe composites under 1560 nm laser excitation

Upon 1560 nm excitation, higher energy levels of Er³⁺ ions are populated. FRET and photons reabsorption to occur from NaYF₄:Yb,Er to CdSe. Then activated CdSe produces electrons and holes in the conduction band and the valence band, respectively.

Near-infrared light triggered superior photocatalytic activity from MoS2–NaYF4:Yb3+/Er3+ nanocomposites

A near infrared (NIR) responsive photocatalyst, composed of a narrow band gap semiconductor (i.e. MoS₂) and an optical material possessing upconverting ability (i.e. NaYF₄:Yb³⁺/Er³⁺) has been successfully prepared via a simple hydrothermal method.

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.

Mechanisms of the blue emission of NaYF4:Tm3+ nanoparticles excited by an 800 nm continuous wave laser

Simultaneous multiwavelength excitation and the quantum transition principle are utilized to study the blue emission mechanisms of NaYF₄:Tm³⁺ UCNPs under 800 nm CW laser excitation.

Facile fabrication of highly efficient modified ZnO photocatalyst with enhanced photocatalytic, antibacterial and anticancer activity

Photocatalytic degradation of organic pollutants using hexagonal Er and Nd doped ZnO photocatalyst.

Understanding the effect of Mn2+ on Yb3+/Er3+ upconversion and obtaining a maximum upconversion fluorescence enhancement in inert-core/active-shell/inert-shell structures

NaYF₄@NaYF₄:Er³⁺/Yb³⁺/Mn²⁺@NaYF₄ (C/S_d/S) nanoparticles were synthesized which show an obvious efficiency enhancement of red upconversion emission.

A broad spectrum photon responsive, paramagnetic β-NaGdF4:Yb3+,Er3+ – mesoporous anatase titania nanocomposite

Herein, we report a novel single multifunctional platform based on broad-spectrum photoactive β-NaGdF₄:18% Yb³⁺, 2% Er³⁺ and mesoporous anatase TiO₂ for enhanced energy and simultaneous biomedical applications.

UV-visible and near-infrared active NaGdF4:Yb:Er/Ag/TiO2 nanocomposite for enhanced photocatalytic applications

A near infra-red (NIR) active NaGdF₄:Yb:Er/Ag/TiO₂ nanocomposite photocatalyst was successfully synthesized by a one-pot thermal decomposition method.

Energy gap engineering of polymeric carbon nitride nanosheets for matching with NaYF4:Yb,Tm: enhanced visible-near infrared photocatalytic activity

A highly efficient visible-NIR photocatalyst: the electronic structure of CN nanosheets is engineered to match well with the emission energy of UCPs.

CaF2-Based Near-Infrared Photocatalyst Using the Multifunctional CaTiO3 Precursors as the Calcium Source

Multistage formation of fluoride upconversion agents from the related-semiconductor precursors provides a promising route for the fabrication of near-infrared (NIR) photocatalysts with high photocatalytic activities. Herein, the cotton templated CaTiO3 "semiconduction" precursors (C-CaTiO3) were used to synthesize the NIR photocatalyst of Er3+/Tm3+/Yb3+-(CaTiO3/CaF2/TiO2) (C-ETYCCT), and the functions of the Ca2+ source for CaF2 and the heterostructure formations were displayed by C-CaTiO3. The generated CaF2 acted as the host material for the lanthanide ions, and the heterostructures were constructed among anatase, rutile, and the remaining CaTiO3. The induced oxygen vacancies and Ti3+ ions enabled the samples to utilize most of the upconversion luminescence for photocatalysis. The NIR driven degradation rate of methyl orange (MO) over C-ETYCCT reached 52.34%, which was 1.6 and 2.5 times higher than those of Er3+/Tm3+/Yb3+-(CaTiO3/TiO2) (C-ETYCT) and Er3+/Tm3+/Yb3+-(CaTiO3/CaF2) (C-ETYCC), respectively. The degradation rates of MO and salicylic acid over C-ETYCCT with UV-vis-NIR light irradiation were also much higher than those of other samples, which were mainly results of the contributions of its high upconversion luminescence and the efficient electron-hole pair separation.

Enhanced photocatalytic activities of the heterostructured upconversion photocatalysts with cotton mediated on TiO2/ZnWO4:Yb3+,Tm3+

A novel TZYT-C heterostructure material with enhanced upconversion properties was prepared.

Recent advances in energy transfer in bulk and nanoscale luminescent materials: from spectroscopy to applications

We discuss optical energy transfer involving ions, QDs, molecules etc., together with the relevant applications in different areas.

Synthesis and characterization of UV upconversion material Y2SiO5:Pr3+, Li+/TiO2 with enhanced the photocatalytic properties under a xenon lamp

The upconversion luminescence agents Y₂SiO₅:Pr³⁺, Li⁺, that can be effectively excited by the blue light from a xenon lamp 150 W, are fabricated by a hydrothermal method with mesoporous molecular sieves of MCM-48 as the suitable silica source.

Preparation of 2D hydroxyl-rich carbon nitride nanosheets for photocatalytic reduction of CO2

The nanosheet exhibits better visible-light photocatalytic activity than bulk g-C₃N₄ due to nanosheet nature and presence of more hydroxyl groups.

Preparation of thickness-tunable BiOCl nanosheets with high photocatalytic activity for photoreduction of CO2

BiOCl nanosheets with different percentages of exposed {001} facets were prepared via mild hydrolysis by a controlled facile hot injection technique, which exhibited relatively high activity for photocatalytic reduction of CO₂ to CH₄.