Wide Light Absorption Range Research Articles

Nickel phosphate improved silicon nanowires arrays hybrid nanostructures for solar-driven photoelectrochemical hydrogen production

Solar-driven photoelectrochemical (PEC) hydrogen production is a promising and environmentally friendly approach to relieve energy crisis and serve the carbon neutrality goal. Silicon nanowires (SiNWs), as one of p-type semiconductors, have more negative conduction band position than the water-resolved hydrogen potential, and wide range of light absorption due to their narrow band gap. Their PEC performance can be further improved by co-catalysts, and they can be used as photocathodes for hydrogen production. In this work, nickel phosphate (Ni3(PO4)2) was in situ decorated onto the SiNWs via a chemical vapor deposition (CVD). The Ni3(PO4)2 nanoparticles with diameters of about 20 to 50 nm were uniformly distributed on SiNWs arrays to construct heterostructures (Ni3(PO4)2-SiNWs). The Ni3(PO4)2-SiNWs composite showed a low onset potential to trigger water reduction. Compared with SiNWs, the Ni3(PO4)2-SiNWs composite had a much higher photocurrent and better PEC hydrogen production performance, which exhibited a stable photocurrent density of 16 mA cm−2 at 0 V (vs. reversible hydrogen electrode (RHE)) under simulated amplitude modulation (AM) 1.5G solar irradiation. This work provided a new solution to obtain nickel phosphate and fabricate the SiNWs-based photocathode.

Effect of SrTiO3 amount and ultrasonic disperse on the thickness of Bi2O3 nanosheets and the photocatalytic performance of the composite α-Bi2O3/SrTiO3

Due to the correlation between structure and activity, even the photoelectric performance of simple materials can be improved by designing component structures reasonably. Taking α-Bi2O3/SrTiO3 as an example, this article reports a novel ultrasound assisted synthesis method for adjusting the thickness of α-Bi2O3 nanosheets (NSs) in heterojunctions. The continuous variation from ∼200 to ∼10 nm confirms that the thickness of NSs is limited by the amount of SrTiO3 added, and ultrasonic dispersion before calcination is a key initiative. Systematic tests indicate that the opto-electronic properties of the heterojunctions are highly thickness-dependent. The heterojunction with a thickness of ∼20 nm α-Bi2O3 NSs has a wider light absorption range (>550 nm), higher photocurrent response (52.8 μA cm−2), lower charge transfer resistance, and efficient catalytic ability for organic degradation (0.071 min−1 for 0.1 g·L−1 RhB). Various spectroscopic evidences display that Bi-O-Ti oxygen bridge bonds provides an efficient transport channel for photogenerated carriers. Furthermore, large specific surface area, and the built-in electric field of heterojunctions jointly accelerate the oxidation degree of pollutants. As high as 98.9% (0.1 g·L−1) and 55.9% (0.5 g·L−1) degradation efficiencies in 1 h, importantly, documented that the α-Bi2O3/SrTiO3 heterojunctions was competitive for the dispose of high-concentration [RhB] outlet water.

Surface Modification of TiO2 by Hyper-Cross-Linked Polymers for Efficient Visible-Light-Driven Photocatalytic NO Oxidation.

Solar-driven photocatalysis offers an environmentally friendly and sustainable approach for the removal of air pollutants such as nitric oxides without chemical addition. However, the low specific surface area and adsorption capacity of common photocatalysts restrict the surface reactions with NO at the ppb-level. In this study, imidazolium-based hyper-cross-linked polymer (IHP) was introduced to modify the surface of TiO2 to construct a porous TiO2/IHP composite photocatalyst. The as-prepared composite with hierarchical porous structure achieves a larger specific surface area as 309 m2/g than that of TiO2 (119 m2/g). Meanwhile, the wide light absorption range of the polymer has brought about the strong visible-light absorption of the TiO2/IHP composite. In consequence, the composite photocatalyst exhibits excellent performance toward NO oxidation at a low concentration of 600 ppb under visible-light irradiation, reaching a removal efficiency of 51.7%, while the generation of the toxic NO2 intermediate was suppressed to less than 1 ppb. The enhanced NO adsorption and the suppressed NO2 generation on the TiO2/IHP surface were confirmed by in situ monitoring technology. This work demonstrates that the construction of a porous structure is an effective approach for efficient NO adsorption and photocatalytic oxidation.

2D/2D Janus BiTeCl/GeSe vdW heterostructure as a robust high-performance S-scheme photocatalyst for water splitting

Two-dimensional (2D) S-scheme van der Waals (vdW) heterostructures (HSs) have aroused much interest as advanced photocatalysts due to their strong redox ability and light utilization. In this work, we have proposed a 2D/2D vdW HS composed of Janus BiTeCl monolayer (ML) and GeSe ML, and systematically investigated its photocatalytic performance using first-principles calculations. Our results show that the HS exhibits an appropriate electronic band in which the existence of intrinsic built-in electric field from GeSe ML to BiTeCl ML enhances the separation of photo-induced electron-hole pairs and certifies a S-scheme mechanism in the HS. Furthermore, the optical and electronic properties of the HS are nearly independent of either biaxial or uniaxial strain, showing robustness of the HS applied in an ever-changing environment. Notably, the HS can achieve spontaneously solar-driven water splitting and exhibits an enhanced solar-to-hydrogen (STH) efficiency up to 19.27 % owing to its S-scheme mechanism and wide range of light absorption with high absorption coefficient. Our results give insights to the structure, electronic and photocatalytic properties of 2D/2D Janus BiTeCl/GeSe vdW HS and may provide a promising S-scheme photocatalyst for overall water splitting.

2D indium-VA semiconductors: Promising photocatalysts with intrinsic electric fields for water splitting

Exploration of two-dimensional (2D) semiconductors with intrinsic electric fields for photocatalytic applications has recently attracted great attention due to their prospective ability to inhibit the recombination of photo-generated carriers. Herein, employing first-principles calculations, we report a new group of 2D semiconductors, monolayer indium-VA (ML-InXs; X = P, As, and Sb), with intrinsic dipole as potential photocatalysts for water splitting. We systematically investigated the geometry, electronics and optics of ML-InXs, and identified their excellent structural stability, suitable band gaps, appropriate band edge positions, outstanding carrier transport and wide range of light absorption, which make them excellent photocatalysts for water splitting. More importantly, the electric field induced by the intrinsic dipole in ML-InXs would suppress the recombination of photogenerated electron-hole pairs, greatly enhancing the energy conversion efficiency during the photocatalytic reaction. In addition, we find that strain engineering can effectively tune the band gap and light absorption of ML-InXs and significantly enhance their solar-to-hydrogen efficiency for water splitting. Our results provide fundamental insight into the 2D photocatalysts with an intrinsic electric field and shed light on future design and modification of superior photo-catalysts for water splitting and other important chemical reactions.

One-pot synthesis of 2D Ag/BiOCl/Bi2O2CO3 S-scheme heterojunction with oxygen vacancy for photocatalytic disinfection of Fusarium graminearum in vitro and in vivo

2D Ag/BiOCl/Bi2O2CO3 S-scheme heterojunction was prepared with oxygen vacancy (OVs) via one-pot hydrothermal method. The XRD and XPS analysis indicated the synthesized sample contained Ag nanoparticles (AgNPs) instead of Ag ions. The SEM and HRTEM pictures showed that BiOCl/Bi2O2CO3 nanosheets were modified with AgNPs. Compared with AgNPs, BiOCl, and Bi2O2CO3, Ag/BiOCl/Bi2O2CO3 exhibited highly photocatalytic inactivation of pathogenic fungi (Fusarium graminearum) due to the wide light absorption range and S-scheme heterojunction structure, which improved the production and transfer of photogenerated carrier, and enhanced the separation of photogenerated e−/h+ pairs. In addition, the improved photocatalytic disinfection against Fusarium graminearum of Ag/BiOCl/Bi2O2CO3 was verified in Sedeveria Letizia plant. Furthermore, active species capture assay and ESR experiments disclosed the involvement of OVs, h+, ∙O2−, ∙OH, and –for Fusarium graminearum destruction during photocatalysis process. The S-scheme heterojunction was proved via oxygen vacancy, which was extensively beneficial to increase charge transmission and separation efficiency. Our work proposed Ag/BiOCl/Bi2O2CO3 was an efficient and ecological fungicide to inactive Fusarium graminearum in vitro and vivo for crop disease.

MIL-53(Fe)@BiOBr/TCN/Ti photoanode assembled visible light responsive photocatalytic fuel cell to enhance rhodamine B degradation and electricity generation

In this research, MIL-53(Fe)@BiOBr/TCN/Ti photoanode was created using the secondary silica sol drop coating method, and assembled with Cu cathode to form photocatalytic fuel cell (PFC) to degrade rhodamine B and generate electricity. The resulting PFC has high visible light response and photocatalytic activity. It has a rhodamine B degradation efficiency of 92.19%, a maximum power density of 6.2 μW cm−2, and a maximum photocurrent density of 0.11 mA cm−2. Its strong photocatalysis capabilities benefits from the wider light absorption range and lower charge carrier recombination rate of the photoanode. The double Z-scheme heterojunction formed among BiOBr, MIL-53(Fe) and TCN in the composite catalyst of the photoanode provide more transfer channels for photogenerated e− and encourage the separation of e−-h+ pairs. ∙OH and ∙O-2 are the main active substances for rhodamine B degradation. This study offers a novel approach to the development of high-efficiency photoanodes for PFC.

Band shifting triggered ·OH evolution and charge separation enhanced H2O2 generation in piezo-photocatalysis of Silleń-Aurivillius-structured Bi4W0.5Ti0.5O8Cl

Photocatalytic oxygen activation shares a broad prospect as it reveals a giant potential in advanced oxidation and H2O2 production. This work demonstrated the efficient oxygen activation via ultrasonic/visible-light triggered piezo-photocatalysis of Bi4W0.5Ti0.5O8Cl, a novel Silleń-Aurivillius-structured piezoelectric material with a wide light-absorption range. The material possessed a superior oxygen activation performance in piezo-photocatalysis that far exceeded that in the individual photocatalysis or piezocatalysis. In situ electrochemical and fluorescence measurements were introduced to analyze the mechanism of the enhanced catalytic activity systematically. Due to the downward band shifting and anisotropic migration caused by ultrasonic induced piezo-potential, not only the oxygen reduction reaction (ORR) process in oxygen activation was kinetically facilitated, but also the VB potential of Bi4W0.5Ti0.5O8Cl was positive enough so that the water oxidation and ·OH generation reaction were thermodynamically favorable. With the boosted effect from multiple aspects, the maximum yield of H2O2 reached 530.4 μmol·h−1·g−1 by Bi4W0.5Ti0.5O8Cl catalyst without metal-deposition in non-sacrificial system. Our work illustrated the effect of charge modulation on oxygen activation in Silleń-Aurivillius-structured Bi4W0.5Ti0.5O8Cl, and delivered insight into the mechanism of piezo-enhanced photocatalytic H2O2 generation.

A photoelectrochemical aptasensor based on CoN/g-C3N4 donor-acceptor configuration for sensitive detection of atrazine

Atrazine (ATZ), as a widely used herbicide, is easy to cause water pollution and serious harm to human health because of its high mobility and long residue period. Herein, a photoelectrochemical (PEC) aptasensor based on graphitic carbon nitride (g-C3N4) loaded by CoN nanoparticles as the electron acceptor (CoN/g-C3N4) was proposed for sensitive detection of ATZ. CoN/g-C3N4 composites were synthesized by using a straightforward hydrothermal and ammonia calcination process. CoN can act as the electron acceptor to promote the transfer of photogenerated charge on the electron donor (g-C3N4). The strong electron-absorbing capacity and wide visible light absorption range of CoN nanoparticles are conducive to the extraction of photogenerated charge. The photocurrent response of g-C3N4 under visible light irradiation was remarkably improved when CoN nanoparticles were introduced. Based on the excellent PEC performance of CoN/g-C3N4, a PEC aptasensor for detecting ATZ was successfully constructed. The linear response range of the sensor to ATZ was to be from 1.0 × 10−4 to 10 fM, and the detection limit was up to 3.3 × 10−5 fM. This aptasensor had excellent stability, selectivity, and excellent anti-jamming capability against real water samples. In view of specific recognition and excellent sensing performance, this aptasenor can be used as a practical technology for selective and sensitive detection of ATZ in the aquatic environment.

CeO2 Nanoparticles Modified on Graphite Sheet Electrodes for Photoelectrochemical Tobacco Wastewater Detection, Degradation, and Toxicity Measurement

Monitoring and implementation of gutka wastewater treatment using a fast and feasible fabrication method, owing to the clean water environment, have a great socioeconomic impact. A facile approach is promoted for detecting and degrading nicotine and gutka wastewater by the means of a wide range of ultraviolet light absorption and is applied in our current research. In this report, we successfully synthesized cerium oxide nanoparticles (CeO2 NPs) by a co-precipitation method for photoelectrochemical (PEC) detection and degradation of smokeless tobacco from wastewater. X-ray diffraction study confirmed the face-centered cubic structure of CeO2 NPs. Raman analysis and ultraviolet–visible spectroscopy endorsed the formation of CeO2 NPs. The as-fabricated CeO2 NP-modified graphite sheet electrode showed high sensitivity (98.1 μA/μM) and good linear range (10–150 nM) for the detection of tobacco from wastewater. The limit of detection was calculated as 0.15 nM. The catalyst photoelectrochemically degraded 93% of nicotine and 94.21% of gutka wastewater at 120 min. Toxicity studies of gutka with an in vivo nematode model, Caenorhabditis elegans, and Vigna radiata proved that PECO-degraded gutka waste had no deleterious effects on the survival (95.43%) (p < 0.01) of C. elegans when compared to nondegraded gutka waste (11.93%) and did not affect the physiological functions and reactive oxygen species production.

Ferroelectric polarization and interface engineering coupling of Z-scheme ZnIn2S4/α-In2Se3 heterostructure for efficient photocatalytic water splitting

It is of great significance to design an efficient heterostructure for photocatalytic hydrogen production to solve the energy shortage and environmental crisis. In this letter, we investigate the structure, electron of interface, optical, charge transfer, and photocatalytic mechanism of three different ZnIn2S4/α-In2Se3 heterostructures by hybrid density functional calculation. It is interesting that the presence of an external electric field not only can change the bandgap but also can modulate the band alignment type. Among them, heterostructure A belongs to type II heterostructure, and heterostructure B and C belong to a Z-scheme heterostructure. Especially in heterostructure C, the electrons deposited on CBM of a ZnIn2S4 monolayer will play an important role in the hydrogen production process. Meanwhile, the small bandgap of ZnIn2S4/α-In2Se3 Z-scheme heterostructures enables it to obtain a wide light absorption range. Therefore, this study contributes to the design of a novel and potential Z-scheme heterostructure photocatalyst with broad application prospects in both electronic and optoelectronic fields.

SnS2-covalent organic framework Z-scheme van der Waals heterojunction for enhanced photocatalytic reduction of uranium (VI) in rare earth tailings wastewater

Uranium removal by photocatalytic reduction is one of the most promising methods to reduce radioactive contamination in wastewater. Herein, a Z-scheme van der Waals heterojunction photocatalyst (SnS2COF) was synthesized in situ by combining covalent organic frameworks (COF) with semiconductor (SnS2) for U (VI) reduction in rare earth tailings wastewater. The synthesis method of van der Waals heterojunction is simple and solves the problem of no hanging bond in composite components. In this heterojunction, large areas of van der Waals interaction form high-speed electron transport channels. In addition, it is deduced that SnS2COF fits the Z-scheme heterojunction electron transport mode through the theoretical calculation of the ground state and excited state electron density difference and the related band structure. Under the photoexcitation, the direction of electron flow is reversed, which further promotes the separation of the photogenerated electron (e−)-hole (h+) under the action of the built-in electric field, maintains the high reducibility of the conduction band, and avoids the photocorrosion of SnS2. Compared with inorganic-inorganic heterojunction, SnS2COF has a wider light absorption range, more active sites, and higher e−-h+ separation and transfer efficiency. Therefore, it had a higher U (VI) reduction removal capacity, up to 1123.3 mg g−1, far surpassing the SnS2 and COF counterparts under ultraviolet/visible light. And the U (VI) removal rate reached 98.5 % in rare earth tailings wastewater. The design concept of organic–inorganic heterojunction materials provides an alternative strategy for improving the photocatalytic performance.

Engineering of efficient visible light photocatalysts: Ti1–x+yCuxLayO2 (x = 0.03; y = 0, 0.005, 0.01) compositions

In dye-photocatalysis, widening the wavelengths absorption range of catalysts as well as aborting the recombination of the photoexcited charge carriers (electrons–holes pairs) are of paramount significance. In the current study, we report the photocatalytic characteristics of four compositions composed of TiO2, Ti0.97Cu0.03O2, Ti0.965Cu0.03La0.005O2 and Ti0.96Cu0.03La0.01O2 powders for two harmful dyes (Congo red and methylene blue). The X-ray diffraction technique verified the configuration of mixed anatase and rutile phases in pure TiO2 and Ti0.97Cu0.03O2 powders while Ti0.965Cu0.03La0.005O2 and Ti0.96Cu0.03La0.01O2 powders possess anatase phase only. The changes of the band gap structure and dimensions of the unit cell volume of TiO2 confirm the substitution of Ti4+ sites by Cu2+ and La3+ ions. Remarkable widening of wavelengths absorption with formation of long absorption tails were found in TiO2 (3.13 eV) through insertion of La3+ plus Cu2+ ions. Ti0.965Cu0.03La0.005O2 and Ti0.96Cu0.03La0.01O2 samples exhibit a visible light band gap of 2.3 and 2.7 eV, respectively. Based on SEM images, incorporation of Cu2+ and La3+ ions influences the surface morphology of TiO2. The resulting Ti0.97Cu0.03O2, Ti0.965Cu0.03La0.005O2 and Ti0.96Cu0.03La0.01O2 powders present enhanced photocatalytic activity towards Congo red dye degradation compared to pure one under natural solar spectrum. The best Ti0.96Cu0.03La0.01O2 catalyst exhibits superior photocatalytic activity of 96% for 10 ppm CR dye in 20 min as well as above average photocatalytic efficiency of 63% for 30 ppm CR dye in 120 min. As well, it showed acceptable photodegradation activity of 52% for 30 ppm MB solution in 140 min of sunlight irradiation. The heightened photodegradation efficiency of Ti0.96Cu0.03La0.01O2 catalyst can be clarified in terms of higher charge carriers’ separation (Cu2+ + e– → Cu+, La3+ + e– → La2+), oxygen vacancies, full anatase phase structure as well as the wide range of visible light absorption.

PDINH bridged NH2-UiO-66(Zr) Z-scheme heterojunction for promoted photocatalytic Cr(VI) reduction and antibacterial activity

Z-scheme mechanism was a promising approach to considerably enhance photocatalytic activity. In this work, the PDINH/NH2-UiO-66(Zr) (PNU) heterojunctions were made using a facile ball-milling method. As expect, the optimum PNU-1 composite acted as highly active photocatalyst with 97% Cr(VI) to be reduced within 60 min of LED light illumination. Moreover, the antibacterial rate almost reached 100% for E. coli and S. aureus in 4 h, which was more conspicuous than the others. The wider light absorption range, promoted charge separation because of Z-scheme mechanism and efficient generation of reactive 1O2, •O2-, and •OH contributed greatly to the enhanced photocatalytic activity. Meanwhile, the superior stability and repeatability of the composites were also demonstrated by five cyclic experiments and related physicochemical characterizations. Therefore, this work provides a novel insight for designing high-efficiency Z-scheme heterostructures between MOFs and organic PDINH for wastewater remediation.

Clustered tubular S-scheme ZnO/CdS heterojunctions for enhanced photocatalytic hydrogen production

Herein, a cluster-like ZnO/CdS nanotube heterojunction photocatalyst was prepared on an FTO conductive glass substrate by a two-step hydrothermal method. The photocatalytic performance and electron transfer mechanism of ZnO and ZnO/CdS composite structures were analyzed through comparing the hydrogen production efficiency of ZnO and ZnO/CdS. The photocatalytic hydrogen production activity of ZnO/CdS (molar ratio 1:1) achieved 7669 μmol/g/h with the AQE of 55.25 %. Unique clustered tubular structure, wider light absorption range and higher carrier transfer rate endowed the composite with marvellous photocatalytic hydrogen production activity. In addition, the measurement of hydroxyl radicals and ESR verified that the electron transfer mechanism followed the S-scheme, which improved the separation efficiency of electron-hole pairs. The residual ratio of catalysts on the FTO substrate remained above 99 % after two cycles, which was remarkably higher than that of the powder catalyst (63 %). This work provides terrific potential for high-efficient, low-cost and recyclable photocatalysts of hydrogen production in the future.

VIS-active TiO2 films decorated by expanded graphite: impact of the exfoliation time on the photocatalytic behaviour

ABSTRACT TiO2/C nanocomposite films were applied on water treatment. Expanded graphite nanosheets (EG) were obtained by UVC-assisted liquid-phase exfoliation technique, without the addition of acids, surfactants, or aggressive oxidizing agents, which characterizes the process as an eco-friendly method. The carbon nanosheets were synthesized directly from graphite bulk at different times and deposited on TiO2 films surface by airbrush spray coating method, forming a TiO2/C heterojunction. The increase in the exfoliation time promoted a more efficient photocatalytic dye removal under visible light. Morphological modifications, changes in the electronic structure, and wide range of light absorption were observed from the TiO2/C heterojunction formation. The results showed that hybrid TiO2/C supported photocatalyst is a promise alternative for practical photocatalytic applications under sunlight.

Rational Construction of Metal Organic Framework Hybrid Assemblies for Visible Light-Driven CO2 Conversion

Photocatalytic reduction of CO2 to value-added chemicals is known to be a promising approach for CO2 conversion. The design and preparation of ideal photocatalysts for CO2 conversion are of pivotal significance for the sustainable development of the whole society. In this work, we integrated two functional organic linkers to prepare a novel metal organic framework (MOF) photocatalyst {[Co(9,10-bis(4-pyridyl)anthracene)0.5(bpda)]·4DMF} (Co-MOF). The existence of anthryl and amino groups leads to a wide range of visible light absorption and efficient separation of photogenerated electrons. To extend the lifetime of photogenerated electrons in the photocatalytic system, we modified Co-MOF particles onto g-C3N4. As expected, Co-MOF/g-C3N4 composites exhibited an ultrahigh selectivity (more than 97%) in the photocatalytic process, and the highest CO production rate (1824 μmol/g/h) was 7.1 and 27.2 times of Co-MOFs and g-C3N4, respectively. What's more, we also discussed the reaction mechanism of the Co-MOF/g-C3N4 photocatalytic CO2 reduction, and this work paves the pathway for designing photocatalysts with ideal CO2 reduction performance.

High-performance γ-MnO 2 Dual-Core, Pair-Hole Fiber for Ultrafast Photonics

Manganese dioxide (MnO 2 ) is a widely used and well-studied 3-dimensional (3D) transition metal oxide, which has advantages in ultrafast optics due to large specific surface area, narrow bandgap, multiple pores, superior electron transfer capability, and a wide range of light absorption. However, few studies have considered its excellent performance in ultrafast photonics. γ-MnO 2 photonics devices were fabricated based on a special dual-core, pair-hole fiber (DCPHF) carrier and applied in ultrafast optics fields for the first time. The results show that the soliton molecule with tunable temporal separation (1.84 to 2.7 ps) and 600-MHz harmonic solitons are achieved in the experiment. The result proves that this kind of photonics device has good applications in ultrafast lasers, high-performance sensors, fiber optical communications, etc., which can help expand the prospect of combining 3D materials with novel fiber for ultrafast optics device technology.

Construction of full solar-light driven NaYF4:Yb,Tm,Er@NaYF4:Eu/NH2-MIL-101(Fe) composite photocatalyst toward degradation of antibiotics: introducing the energy trapping centers

Photocatalysis is a promising pathway to degrade the pollution in the water with the distinct advantages. However, to remove the antibiotics in the aqueous solution is still a perplexing issue due to the stability. Development of full solar-driven heterogeneous photocatalyst is a feasible strategy to decompose the antibiotics into the nontoxic small molecules. A novel heterogeneous photocatalyst, NaYF4:Yb,Tm,Er@NaYF4:20% Eu/NH2-MIL-101(Fe) (TmEr@YEu(20%)/NMF) is synthesized, in which the energy trapping center is introduced in the shell to reduce the energy loss and improve the upconversion efficiency. Under the simulated solar light, the degradation extent of TmEr@YEu(20%)/NMF toward amoxicillin (AMX) is 90%, which is 40% larger than that of NMF. It is attributed to the wide light absorption range and heterogeneous structure of TmEr@YEu(20%)/NMF. As compared with the TmEr/NMF, the photocatalytic activity of TmEr@Y/NMF is increased by 14 %. And it is further enhanced by 16% for TmEr@YEu(20%)/NMF indicating that the core-shell structure and involvement of energy trapping center play the same important role. The mechanism is proposed according to upconversion emission spectra, active species trapping experiments and pump power dependence of upconversion emission intensities. Involvement of shell and energy trapping center is a robust approach to achieve the enhanced upconversion efficiency and achieve the expected photocatalytic activity. This work suggests a new strategy to synthesize the upconversion nanoparticles with the improved upconversion efficiency.

Fabrication of Fe3O4@Ti-PDA nanoparticles with enhanced photocatalytic activities for degradation of organic dye

In this paper, we synthesized a core-shell structured Fe3O4@Ti-PDA nanoparticles as photocatalyst by a facile method in environmental friend mild reaction conditions without organic solvent. Firstly, Fe3O4 was synthesized by solvothermal method, and Fe3O4@PDA was formed by dopamine (DA) self-polymerization to encapsulate Fe3O4 to form polydopamine (PDA) lager. Then, the surface of Fe3O4@PDA was wrapped by coordinating bis(2-hydroxypropionic acid) diammonium dihydroxide(Ti-BALDH) with DA combined DA self-polymerizing to obtain Fe3O4@Ti-PDA. As control, we synthesized another photocatalyst Fe3O4@PDA@TiO2. Compared with Fe3O4@PDA@TiO2 (band gap 3.0 eV), Fe3O4@Ti-PDA had a narrower band gap (2.5 eV) and a wider light absorption range (from ultraviolet to visible light to near-infrared light), as a photocatalyst, which can make full use of sunlight to improve photocatalytic efficiency. Meanwhile, magnetic core of Fe3O4@Ti-PDA made it was easy to separate from aqueous solution for convenient recovery. Using methylene blue (MB) as model pollutant, the degradation efficiency of Fe3O4@Ti-PDA on MB reached to 92.4% under visible light irradiation for 120 min without cocatalyst, while for Fe3O4@PDA@TiO2 only to 32.5%. The result indicated Fe3O4@Ti-PDA enabled photocatalytic oxidation and rapid separation when photogenerated electron-hole pairs were generated. After three recycles, the degradation efficiency of Fe3O4@Ti-PDA on MB still remained at 86.47%, showing good recycle stability.