Core-shell Photocatalyst Research Articles

Visible-light-driven overall water splitting with a largely-enhanced efficiency over a Cu2O@ZnCr-layered double hydroxide photocatalyst

Overall water splitting through solar radiation is highly attractive for alternative energy utilization. Herein, we designed and fabricated a Cu2O@ZnCr-layered double hydroxide (LDH) core-shell photocatalyst to achieve a high-performance, visible-light overall water splitting. The Cu2O@ZnCr-LDH nanostructure exhibits a high activity (with H2 and O2 production rate of 0.90 and 0.44 μmol h−1, respectively) under visible-light without any sacrificial agent and co-catalyst, which is among the highest level of reported photocatalysts under the same conditions. Both experimental and computational investigations demonstrate that the Cu2O@ZnCr-LDH heterostructure fully exploits the synergistic effect of Cu2O and ZnCr-LDH, in terms of band structure matching. Most significantly, the S2O32− group in the gallery of ZnCr-LDH acts as an effective mediator between these two individual components, which not only inhibits the photocorrosion of Cu2O but also accelerates the immigration of photo-induced electron-hole pairs. Therefore, this work provides a deep insight for the design and preparation of visible-light-responsive photocatalysts, which show promising applications in photochemical reactions and energy conversion.

Magnetic recyclable photocatalysts of Ni-Cu-Zn ferrite@SiO2@TiO2@Ag and their photocatalytic activities

Abstract Ag nanoparticles with different weight percentage loaded on Ni-Cu-Zn ferrite@SiO 2 @TiO 2 composite were successfully prepared via sol-gel method. The effect of deposited amount of Ag nanoparticles on structural, magnetic and photocatalytic properties of the composite was investigated. XPS characterization confirmed that Ag nanoparticles deposited on the surface of Ni-Cu-Zn ferrite@SiO 2 @TiO 2 composite. Particle size and shape of magnetic recyclable photocatalysts were observed using TEM, showing a core-shell structure with an average particle size of 20 nm of Ag. Based on room temperature magnetic hysteresis curves, as 0.4 wt% Ag immobilized on Ni-Cu-Zn ferrite@SiO 2 @TiO 2 composite revealed the maximum saturation magnetization of 39.9 emu/g. Photocatalytic degradation of Ni-Cu-Zn ferrite@SiO 2 @TiO 2 @Ag was carried out in methylene blue (MB) solutions illuminated under a 35-W Xe arc lamp and color temperature of 6000 K. The results revealed that 83.9% of MB was photodegraded for 0.4 wt% of Ag-loaded Ni-Cu-Zn ferrite@SiO 2 @TiO 2 . Moreover, it can be easily separated and recycled without significant loss of photocatalytic activity after being used five times. Compared to the conventional photocatalysts, the magnetic core–shell photocatalyst is suitable for large scale applications in industrial wastewater system.

Precisely controlled fabrication of magnetic 3D γ-Fe 2 O 3 @ZnO core-shell photocatalyst with enhanced activity: Ciprofloxacin degradation and mechanism insight

Abstract A novel magnetically separable three-dimensional (3D) γ-Fe2O3@ZnO core-shell photocatalyst was successfully fabricated by hydrothermal-sintering and a subsequent atomic layer deposition (ALD) method. The uniform and conformal ZnO shell layer was precisely deposited on γ-Fe2O3, improving the specific surface area and surface potential. The photocatalytic capacity of γ-Fe2O3@ZnO composite was investigated by ciprofloxacin degradation. Results showed that the γ-Fe2O3@ZnO exhibited excellent degradation efficiency under simulated sunlight irradiation. The first-order kinetic rate constant of γ-Fe2O3@ZnO was demonstrated to be almost 4 and 20 times higher that of pure ZnO and γ-Fe2O3. Moreover, the recycling degradation experiments revealed that the γ-Fe2O3@ZnO core-shell photocatalyst was stable and reusable, which could be easily separated under an additional magnetic field. The mechanism of the remarkably enhanced photocatalysis was further explored by analyzing its heterostructure and determining the role of active radicals. The newly-designed type II heterostructure facilitated the separation of photo-induced carriers. Radical-trapping tests indicated that the holes and hydroxyl radicals played major roles in ciprofloxacin degradation. In prospect, the magnetic 3D γ-Fe2O3@ZnO core-shell photocatalyst has great potential for degradation of other refractory contaminants in water with solar light irradiation.

Nanocuboid TiO2 based organic-inorganic hybrids for fast RhB trapping and photodegradation

Joints provide a smart and efficient route to capture and move objects. Inspired by this, we designed and synthesized an anatase TiO2 based organic-inorganic hybrid photocatalyst using a facile one-pot solvothermal method, which has hard cores (single-crystal TiO2 nanocuboids) and soft shells (organic composites). The smart-joint organic layer (DMEA and LA) plays a crucial role in trapping Rhodamine B molecules and delivering them on the TiO2 interfaces. The novel core-shell photocatalyst shows superior RhB photodegradation performance, 10 times higher than Degussa P25, which enables the RhB degradation in several minutes. TiO2-DMEA-LA-120 system, which plays the similar synergy as the arm with joints, provides a novel method to improve catalytic performance learning from nature.

TiO<sub>2</sub> Surface Coating of Mn-Zn Dopped Ferrites Study

This study deals with TiO2 coating of powder Mn-Zn ferrite in order to recieve photocatalytic layer on the top of these particles, forming core-shell catalyst. Powder catalysts are of great advance over the world due to the high surface area, considering the kinetics proceeds through heterogenous phase boundary catalysis. However their withdrawal from cleaning systems often requires energetically and economically demanding processes such as filtration and ultrafiltration. Since the ferrite is magnetic, the advantage of such formed core-shell photocatalyst is easibility of removing from photocatalytic decomposition system using external magnetic field. In this study the surface coating is performed, using Ti alkoxides mixtures with nanosized TiO2 particles and C and Au coating to form film layer of TiO2 on the surface of ferrite. XRD, SEM – EDS analyses are employed to study surface coating.

A cocatalyst-free CdS nanorod/ZnS nanoparticle composite for high-performance visible-light-driven hydrogen production from water

Highly efficient, visible-light-induced hydrogen (H2) production via water splitting can be achieved without the help of a cocatalyst by using a noble-metal-free core–shell photocatalyst, in which zinc sulfide (ZnS) nanoparticles are anchored on cadmium sulfide nanorods (CdS NRs).

Prepare an effective nano size core shell photocatalyst for degradation of methyl orange

In the present work, PbS@CdS core shell nanoparticles have been synthesized via a facile chemical reaction with the aid of Pb(CH3COO)2·3H2O, Cd(CH3COO)2·2H2O, and thioacetamide (TAA). The effect of preparation parameters such as reaction temperature, speed of the reaction stirrer, and the rate of adding sulfide source to the morphology of PbS@CdS core–shell nanoparticles were studied by SEM images. Furthermore, photocatalyst activity of products were investigated by photodegradation of methyl orange (MO) dye test. The as-synthesized products were characterized by XRD, TEM, HRTEM, PL, SEM, EDS, and UV–Vis techniques. Extended to larger scales of an aqueous synthesis of QDs.

Photoactivity of TiO2/CdS and SiO2/CdS hybrid nanostructured systems in the partial oxidation of ethanol under irradiation with visible light

The activity of hybrid nanostructured core-shell photocatalysts based on cadmium sulfide, titanium dioxide, and silicon dioxide has been investigated in the partial oxidation of ethanol under irradiation with visible light. The SiO2/CdS and TiO2/CdS photocatalysts have been synthesized by the sol-gel method and have been characterized by a variety of physicochemical methods, including X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and diffuse reflectance infrared Fourier-transform spectroscopy. The synthesized TiO2/CdS samples exhibit a high activity in the partial photocatalytic oxidation of ethanol to acetaldehyde under irradiation with visible light (λ > 420 nm) in a batch reactor. Their high activity can be due to heterojunctions occurring between cadmium sulfide and titanium dioxide nanoparticles and causing the separation of photogenerated charges.

Facile synthesis of Ag@CeO2 core–shell plasmonic photocatalysts with enhanced visible-light photocatalytic performance

Novel Ag@CeO2 core–shell nanostructures with well-controlled shape and shell thickness were successfully synthesized via a green and facile template-free approach in aqueous solution. As-prepared samples were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflection spectroscopy (DRS), electron spin resonance (ESR) and photoluminescence spectroscopy (PL). The structures with different core shapes and controllable shell thickness exhibited unique optical properties. It is found that the nanoscale Ag@CeO2 core–shell photocatalysts exhibit significantly enhanced photocatalytic activities in the O2 evolution and MB dye degradation compared to pure CeO2 nanoparticals. The enhancement in photocatalytic activities can be ascribed to the localized surface plasmon resonance (SPR) of Ag cores. Moreover, larger active interfacial areas and contact between metal/semiconductor in the core–shell structure facilitate transfer of charge carriers and prolong lifetime of photogenerated electron-hole pairs. It is expected that the Ag@CeO2 core–shell structure may have great potential in a wider range of light-harvesting applications.

Synthesis of Fe3O4@SiO2@ZnO–Ag core–shell microspheres for the repeated photocatalytic degradation of rhodamine B under UV irradiation

Herein, novel Fe3O4@SiO2@ZnO–Ag core–shell microstructures were synthesized through template synthesis and layer-by-layer deposition. The obtained samples were characterized in terms of morphology, composition, optical and magnetic property by various analytical techniques and subsequently tested for the photocatalytic activities. In comparison with Fe3O4@SiO2@ZnO, the as-obtained multi-shelled Fe3O4@SiO2@ZnO–Ag hierarchical microspheres exhibit a significant enhanced photocatalytic activity toward the photodegradation of Rhodamine B (RhB) aqueous solution under UV light. The enhanced photocatalytic activities of the core–shell photocatalyst are primarily ascribed to the reduced recombination probability of photogenerated electrons/holes in the surface of hierarchical microspheres. Moreover, the hierarchical microstructured Fe3O4@SiO2@ZnO–Ag photocatalysts could be easily collected and separated by using a magnetic field and reused without any appreciable decrease on photocatalytic efficiency after running six times. The enhanced photocatalytic performance and magnetic recyclability, in combination with the superior chemical stability, make these multifunctional microstructures promising candidates to eliminate aquatic contaminants and meet the demands of future environmental issues.

Improving the photocatalytic performance of polyimide by constructing an inorganic-organic hybrid ZnO-polyimide core–shell structure

Inorganic–organic hybrid ZnO-polyimide core–shell photocatalysts were facilely fabricated through a one-step calcination process. The resultant hybrids showed remarkablly enhanced photocatalytic activity for methylene blue (MB) decolorization under visible light irradiation. The decolorization rate of the optimum ZnO-polyimide photocatalyst (∼31wt% of ZnO) is 1.2 times of the pristine polyimide under the same experimental conditions. The photocatalytic mechanism reveals that the direct oxidation by photogenerated holes is the main reaction pathway for MB degradation. The enhanced photoactivity for MB decolorization over ZnO-polyimide hybrids is attributed to the effective interfacial charge transfer between ZnO and polyimide, thereby, suppresses the recombination of the photoexcited electron-hole pairs and improves the photocatalytic efficiency.

Magnetic core–shell CuFe2O4@C3N4 hybrids for visible light photocatalysis of Orange II

Novel CuFe2O4@C3N4 core–shell photocatalysts were fabricated through a self-assembly method and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, transmission electron microscopy and Uv–vis diffuse reflection spectroscopy. The photocatalytic performances of the CuFe2O4@C3N4 catalysts were evaluated in photo Fenton-like discoloration of Orange II dye using H2O2 as an oxidant under visible-light irradiation (λ>420nm). It was found the CuFe2O4@C3N4 hybrid (mass ratio of CuFe2O4/g-C3N4 at 2:1) exhibits a superior activity as compared with single component of CuFe2O4 or g-C3N4 and the mixture of g-C3N4 and CuFe2O4, due to the elevation of the separation efficiency of photoinduced electron–hole pairs, resulted from the heterojunction between the interfaces of g-C3N4 and CuFe2O4. The quenching tests of different scavengers displayed that O2•−, OH and h+ are responsible for the Orange II decolorization. In addition, the effects of initial concentration of the dye contaminant (0.014–0.140mM), different anions (Cl−, SO42−, NO3−, CH3COO− and HCO3−) and temperature (15–65°C) in photoreaction were also investigated. The CuFe2O4@C3N4 sample exhibited stable performance without obvious loss of catalytic activity after five successive runs, showing a promising application for the photo-oxidative degradation of environmental contaminants.

Photocatalytic hydrogen production by magnetically separable Fe3O4@ZnS and NiCo2O4@ZnS core–shell nanoparticles

Photocatalytic active material ZnS was grown on the surfaces of magnetic cores, Fe3O4 and NiCo2O4, by the solvothermal method to produce magnetically separable Fe3O4@ZnS and NiCo2O4@ZnS core–shell photocatalysts. These hydrogen production photocatalysts can be recycled by magnetic force for repeated hydrogen generation. The morphology, crystalline property, magnetic property, photocatalytic activity, and magnetic separation capability of the core–shell photocatalysts were studied. Fe3O4@ZnS based core–shell photocatalysts had better magnetic separation capability than the NiCo2O4@ZnS analog. The optimized photocatalytic hydrogen production rates of NiCo2O4@ZnS and Fe3O4@ZnS core–shell nanoparticles reached 880 μmol h−1 g−1 and 3900 μmol h−1 g−1, respectively. Both photocatalysts can be recycled by magnetic force. Recycled photocatalysts exhibited good hydrogen generation performance after being recycled for three times.

Chemical protection of ZnO nanorods at ultralow pH To form a hierarchical BiFeO3/ZnO core-shell structure.

ZnO is an interesting material for photoactive and optoelectronic devices because of the wide range of available nanostructures and advantageous semiconducting properties. However, a significant drawback of ZnO is the low stability in high or low pH solutions. This has limited the development of ZnO core-shell materials for use in Z-scheme systems or photovoltaics, where any secondary phase is produced using chemical solution processing at low or high pH. Here, we show a simple process to produce an organic capping layer of 3-aminopropyltriethoxysilane that can successfully stabilize nanostructured ZnO for processing below pH 1. We demonstrate that this process can be used to produce a ZnO-BiFeO3 (BFO) core-shell structure by a sol-gel process. Using a range of physical and analytical techniques, we show that BFO is highly crystalline and produces a conformal coating with a thickness of 2.5 nm. X-ray photoelectron spectroscopy and X-ray diffraction confirm the phase and expected chemical composition of BFO. Finally we are able to demonstrate that diodes produced using the ZnO-BFO core-shell structure have improved performance with a rectification ratio at ±3 V of 2800 because of the reduction in reverse current typically associated with surface recombination on ZnO. Our process opens a route to producing a range of hitherto prohibited ZnO core-shell structures that may have applications ranging from photovoltaic devices to core-shell photocatalysts.

Nanostructuring of a GNS-V2O5–TiO2 core–shell photocatalyst for water remediation applications under sun-light irradiation

The GNS-V2O5–TiO2 composite, as a new class of nanoarchitecture, has been successfully fabricated by a facile hydrothermal process followed by a sol–gel technique.

Crystalline ZnO/ZnSxSe1−xcore–shell nanowire arrays for efficient visible-light photoelectrocatalysis

ZnO/ZnSxSe1−x core–shell nanowire arrays on a silicon substrate were successfully prepared via a hydrothermal method followed by chemical vapor deposition (CVD) of the ZnSxSe1−x shell. By optimizing the CVD growth conditions, a crystalline ZnSxSe1−x shell and well-aligned ZnO/ZnSxSe1−x interface were achieved, which plays an important role towards the enhanced performance of photocatalytic activity. The introduction of the crystalline, lattice-matched ZnSxSe1−x shell to ZnO nanowires significantly enhances the photocatalytic and photoelectrocatalytic activity under UV light irradiation. More attractively, after being combined with the ZnSxSe1−x shell, the visible light photoelectrocatalytic activity of the ZnO/ZnSxSe1−x core–shell nanowires is observed. The performance enhancement of ZnO/ZnSxSe1−x core–shell nanowires under irradiation is mainly due to matching lattice and band energy level alignment between the crystalline ZnSxSe1−x shell and ZnO nanowire core. The high crystal quality of the ZnSxSe1−x shell and the band alignment of the ZnO/ZnSxSe1−x core–shell greatly enhance the charge separation efficiency and prolong the life-time of photogenerated charge carriers. Our finding is expected to provide a new insight into the fabrication of novel and high performance nanowire based core–shell photocatalysts.

Increasing the Photoactivity of N-doped Tio2 Photocatalysts Using Phosphors as Light Carriers

The aim of the work was to increase the photoactivity of N-doped TiO2 photocatalyst, active in visible light region, through the improving of the illumination efficiency. Microradiators like phosphors (namely, ZPS) which absorb an electromagnetic radiation by the external light source (UV) and, with no time delay, emit visible light, opportunely selected to be able to excite N-doped TiO2 photocatalyst. Preliminary investigations were performed on physical mixtures of phosphors and N-doped TiO2, evaluating the decolourization of methylene blue (MB). The simultaneous presence of N-doped TiO2 and light carriers showed an increased decolourization activity, reaching about 100 % with a total TOC removal after 3 h of irradiation. To get core-shell photocatalysts, N-doped TiO2 was supported on ZPS (NTiO2-ZPS) by a modified sol–gel method. The content of N-doped TiO2 was varied in the range 5-50 wt % to find an optimum loading. The photocatalytic activity of NTiO2-ZPS was evaluated for the removal of MB under UV illumination. The performances of NTiO2-ZPS showed an improved efficiency in decolourization process of MB, equal to 100 % after 90 min of irradiation, with a total TOC removal. The influence of several parameters, such as dye type and concentration has been studied.

Photocatalytic hydrogen production by stainless steel@ZnS core–shell wire mesh photocatalyst from saltwater

Ni-doped stainless steel@ZnS core–shell wire mesh photocatalyst for photocatalytic hydrogen production was prepared by a solvothermal method. Effects of wire mesh density, doping, and surface texture on the photocatalytic activity were studied. The photocatalytic activity of the catalyst was evaluated by splitting Na2S/Na2SO3 solution into H2. The effects of surface texture and doping on the surface wettability and photocatalytic activity were investigated. Energy-dispersive X-ray spectroscopy (EDX) analysis and Ni mapping images indicated that a small amount of Ni is loaded on the ZnS. The highest hydrogen evolution is obtained for the Ni-doped core–shell photocatalyst when ZnS is grown on wire mesh substrate (distance between adjacent wires = 60 μm) with precursor solution (Ni(CH3COO)2/Zn(CH3COO)2 = 1%) by a solvothermal reaction for 0.5 h. The enhanced performance results from enhanced separation of the photoinduced carriers by Ni-doping, and effective contact among sacrificial aqueous solution and the ZnS shell. Photocatalytic activity and photocurrent of three repeated tests of recycled photocatalysts were also investigated.

Photocatalytic Syntheis of L-Pipecolinic Acid from L-Lysine by Hollow Core-Shell Titania Particles

A possible approach for photocatalytic selective organic synthesis is utilization of photocatalysts of or in defined microstructures. We have reported [1,2] fabrication of a novel core-shell photocatalyst which consisted of commercially available titania (TiO2) particles incorporated in a hollow silica shell (SiO2/void/TiO2) showing size-selective properties in the photodecomposition of organic compounds. Recently, we have attempted to use the SiO2/void/TiO2 photocatalyst for the synthesis of L-pipecolinic acid (PCA), a useful intermediate material for various fine chemicals, and found another function of silica shell to improve stereoselectivity, instead of molecular-size selectivity and report here.Hollow core-shell silica (SiO2)-TiO2, "SiO2/void/TiO2", was prepared and platinized as reported (Fig. 1) [3,4]. For the photocatalytic reaction of redox-combined stereoselective synthesis of PCA from L-lysine (L-Lys), a platinum-loaded photocatalyst (0.05 g as TiO2) was suspended in an aqueous solution (5.0 cm3) containing L-Lys (100 µmol) and photoirradiated by a mercury arc (400 W) under argon (Ar) at 298 K under vigorous magnetic stirring. The yield of enantiomers of PCA, as well as the amount of unreacted L-Lys, was measured by HPLC.Photoirradiation of the photocatalysts suspended in an aqueous L-Lys solution led to the formation of PCA. Complete consumption of L-Lys was achieved using TiO2 and also mec-SiO2+TiO2 (a mechanical mixture of silica and TiO2). These photocatalysts showed very similar results in terms of selectivity (SPCA), optical purity (OPPCA) and the rate of PCA formation (RPCA), suggesting that the mechanical mixing of silica with TiO2 does not give any effect on this reaction as only the TiO2 part was responsible for PCA production. As expected, dir-SiO2/TiO2, without void space between SiO2 and TiO2, showed poor photocatalytic activity to convert only 14% of L-Lys, thus proving that direct coverage of the TiO2 surface with SiO2 hinders the activity of the TiO2 by prohibiting platinum deposition as well as L-Lys adsorption onto the bare TiO2 surface. The SiO2(0.5)/void/TiO2 particles prepared with 0.5-h silylation period showed the performance almost the same as that of bare TiO2. Although the selectivity (43%) was slightly lower than that of bare TiO2, SiO2/void/TiO2 exhibited the highest OPPCA (70%), 13% more than that of platinized bare TiO2, among all the samples.In order to further prove the effectiveness of the structure, SiO2/void/TiO2 with thicker layer of silica shell were also prepared, by extending the silylation period (1.5 h and 3.0 h). The thickness of the silica layer was increased to 14–32 nm and 28–45 nm, respectively, from 9–10 nm for 0.5-h silylated sample. While SiO2(1.5)/void/TiO2 exhibited the best performance among the tested samples, it seemed that the photocatalytic performance (conversion, SPCA, OPPCA and RPCA) was almost independent of the silica shell thickness. This suggests that the silica shell behaves as highly porous optically transparent penetration-free layer which surrounds the TiO2 core and that this swollen sponge-like silica layer controls the stereoselectivity of the reaction through redox-combined process.

Ultrathin TiO2 Layer Coated-CdS Spheres Core–Shell Nanocomposite with Enhanced Visible-Light Photoactivity

Development of various strategies for controllable fabrication of core-shell nanocomposites (CSNs) with highly active photocatalytic performance has been attracting ever-increasing research attention. In particular, control of the ultrathin layer TiO2 shell in constructing CSNs in an aqueous phase is a significant but technologically challenging issue. Here, this paper demonstrates the interface assembly synthesis of CdS nanospheres@TiO2 core-shell photocatalyst via the electrostatic interaction of negatively charged water-stable titania precursor with positively charged CdS nanospheres (CdS NSPs), followed by the formation of the ultrathin-layer TiO2 shell through a facile refluxing process in aqueous phase. The as-formed CdS NSPs@TiO2 core-shell nanohybrid exhibits a high visible-light-driven photoactivity for selective transformation and reduction of heavy metal ions. The ultrathin TiO2 layer coated on CdS NSPs results in excellent light transmission property, enhanced adsorption capacity, and improved transfer of charge carriers and lifespan of photoinduced electron-hole pairs, which would prominently contribute to the significant photoactivity enhancement. It is anticipated that this facile aqueous-phase synthesis strategy could be extended to design a variety of more efficient CSN photocatalysts with controllable morphology toward target applications in diverse photoredox processes.