Core-shell Structure Photocatalysts Research Articles

Nano core-shell Mn0.5Cd0.5S@ copper phthalocyanine heterojunction structured with high hydrogen production efficiency

The core-shell structure photocatalysts have attracted extensive attention in photocatalysis due to large contact area, multiple reaction sites and high photocatalytic performance. Herein, a series of Mn0.5Cd0.5S@CuPc nano core-shell composites photocatalyst were successfully synthesized by facile solution method. The results showed that the as-prepared Mn0.5Cd0.5S photocatalyst hydrogen evolution was only 0.40 mmol/g·h, while Mn0.5Cd0.5S@CuPc composites show strong light absorption from 600 nm to 800 nm and high catalytic performance compared with pure Mn0.5Cd0.5S. Notably, the hydrogen evolution of Mn0.5Cd0.5S @CuPc-5% reached up to 2.14 mmol/(g·h), representing a remarkable 5.35 times improvement compared to the pure Mn0.5Cd0.5S when the optimal loading capacity of CuPc was set at 5%. The Mn0.5Cd0.5S@CuPc-5% exhibits excellent photocatalytic performance can be attributed to the CuPc forms a uniform molecular film on the surface of Mn0.5Cd0.5S, and the close contact between Mn0.5Cd0.5S and CuPc which can effectively promote the transfer and separation of photo-generated carriers. Moreover, the 5% Mn0.5Cd0.5S@CuPc nano core-shell composites have excellent stability, photocatalyst hydrogen activity reduce was approximately 20.1% after four runs for 12 h. This nano core-shell structure photocatalyst research offers a new strategy for constructing organic-inorganic nanocomposite photocatalysts.

Synergy mechanism of confined effect and Z-scheme electron transfer in core–shell structure photocatalyst for boosting photoreduction CO2 activity

Core-shell structure photocatalysts are favored due to their confinement effect that enhances photoreaction efficiency, but their synergistic effect with heterojunctions is frequently overlooked. Herein, we synthesized a porous core–shell photocatalyst TiO2 nanoparticles@graphitic carbon nitride (labeled as TNPs@CN) from self-assembled supramolecular precursors for high-efficient photocatalytic CO2 reduction. The porosity facilitates CO2 transport and adsorption, while Z-scheme on the core–shell interface enhances electron transfer. Both in situ experimental and theoretical calculations have proved the Z-scheme heterojunction of TNPs@CN with a high photoreduction CO2 rate of 26.89 and 8.91 μmol g−1h−1 for CO and CH4, respectively, which are far higher than those of amorphous TNPs-CN. A 13CO2 labeled isotopic experiment and in situ FT-IR results laid the foundation for the mechanism of CO2 photoreduction, which was then investigated in-depth by calculating free energy profile. This work provides valuable insights for designing high-performance photocatalysts that leverage the synergistic effect of core–shell structure and Z-scheme electron transfer for artificial photosynthesis.

Elucidation of mechanisms, pathways, and toxicity of fabricated Z-scheme KNbO3/ZnIn2S4 hollow core–shell composites for enhanced ciprofloxacin photodegradation

Semiconductor photocatalysis technology for environmental remediation faces primary challenges, such as charge-carrier recombination and interfacial charge transfer inhibition, which affect its degradation efficiency in removing organic contaminants. In this work, we successfully synthesized a unique Z-scheme KNbO3/ZnIn2S4 hollow core–shell microsphere via a combined hard template, thermal treatment, and hydrothermal processes as the photocatalyst for ciprofloxacin (CIP), oxytetracycline hydrochloride (OTCH), and rhodamine B (RhB) remediation under sunlight irradiation. Compared to the pure KNbO3 and ZnIn2S4, our optimized 15-KNbO3/ZnIn2S4 composite exhibited enhanced photodegradation performance with up to 99.8 %, 96.8 % and 97.5 % for CIP, OTCH, and RhB removal within 110 min, respectively. At the KNbO3/ZnIn2S4 heterojunction interface, the composite developed its internal electric field and enhanced its photoabsorption under visible light region, thus boosting its charge separation. Subsequently, we evaluate the removal of total organic carbon (TOC) concentration and the influence of different ions on CIP degradation. In addition, we systematically investigated the Z-scheme charge migration process within the heterojunction with a series of experiments. Our results indicated that the hydroxyl and superoxide radicals were the dominant active species during photocatalysis. The composite also could achieve excellent stability and adaptability. We also managed to identify the CIP-degraded intermediates and deduce their possible degradation pathways. Lastly, our toxicity analysis revealed that CIP toxicity could decrease gradually during photocatalysis. In this work, we presented a unique method for preparing inexpensive and highly efficient Z-scheme hollow core–shell structure photocatalysts with excellent antibiotic remediation in water under simulated sunlight illumination.

Evaluation of visible photocatalytic performance of microwave hydrothermal synthesis of MnO2/TiO2 core-shell structures and gaseous mercury removal

MnO 2 /TiO 2 core-shell structure photocatalyst was prepared by a two-step microwave method. Under visible light irradiation, this core-shell photocatalyst exhibited enhanced catalytic activity for the degradation of organic dye Rhodamine B and the oxidative removal of gaseous heavy metal Hg 0 . The MnO 2 shell not only enhanced the visible light absorption of TiO 2 , but also increased its specific surface area to 227.94 m 2 g −1 . In addition, the formation of core-shell heterojunction promotes the migration of carriers and the separation of photo-generated electron-hole pairs, and improves the stability of the composite, thus enabling it to exhibit enhanced photocatalytic performance. • MnO 2 /TiO 2 core-shell structure photocatalysts were prepared by a two-step microwave method. • MnO 2 /TiO 2 core-shell structure improves visible light absorption capacity, specific surface area and carrier separation. • MnO 2 /TiO 2 core-shell structure catalysts show photocatalytic activity to Hg 0 and RhB under visible light. This study provides an effective idea for the rapid preparation of high-efficiency core-shell photocatalysts, and is expected to contribute to the treatment of organic pollution in water and purification of metallurgical flue gas.

Hierarchical polypyrrole encapsulating Bi2O4 to enhance charge separation and light absorption with boosted visible light photocatalytic activity

Bi2O4, as a typical visible-light responsive photocatalyst (band gap～ 2.0 eV), has aroused enormous attention in recent years. However, single Bi2O4 has the problem of high recombination probability of photogenerated electron-hole pairs, which inevitably hampers its photocatalytic performance. Herein, hierarchical polypyrrole encapsulated Bi2O4(Bi2O4@PPy) has been constructed via an in-situ vapor-phase polymerization method, producing PPy tightly coated Bi2O4 core-shell structure photocatalyst. Thanks to this full coating and hierarchical structure, the charges separation efficiency, and the light absorption capacity of Bi2O4@PPy hybrid are promoted, leading to obviously enhanced visible light photocatalytic activity. The optimal Bi2O4@PPy composite could be obtained through controlling the polymerization time for 9 h, whose catalytic activity is as 2.43 times as that of Bi2O4 alone. The active species trapping experiments suggest that holes play a vital role in the photocatalytic degradation process. A plausible reaction mechanism over the Bi2O4@PPy hybrid photocatalyst is also proposed based on the characterization and experimental results.

Metal-free plasmonic boron phosphide/graphitic carbon nitride with core-shell structure photocatalysts for overall water splitting

In this work, we report a novel metal-free plasmonic boron phosphide/graphitic carbon nitride (BP@g-C3N4) catalyst for photocatalytic overall water splitting. The BP@C3N4 catalyst exhibits broadened spectral adsorption in UV–vis to NIR region and shows the activity for hydrogen evolution even under 730 nm illumination, which is close to NIR region of solar irradiation. The highest H2 production rate reaches 31.5 μmol g−1 h−1 under visible light irradiation, which is 34.3 and 112.6 times higher than corresponding data of Pt/g-C3N4 and g-C3N4 catalysts respectively without noble metal loading. The finite element frequency-domain simulations indicate that the significantly improved photocatalytic water splitting performance is due to the BP plasmon resonance leading to effectively photo-induced carrier separation and transfer, which is crucially for solar energy harvesting and utilization. The metal-free earth-abundant plasmonic BP@g-C3N4 can catalyze photocatalytic overall water splitting by the plasmonic effect under visible light and near infrared irradiation efficiently.

Synthesis and Visible-Light Photocatalytic N2/H2O to Ammonia of Au@CDs Core-Shell Nanocatalyst

Synthesis and visible-light photocatalytic N2/H2O to ammonia at atmospheric pressure and room temperature is considered to be the most ideal ammonia synthesis technology. In this study, coal-based carbon dots (CDs) were prepared by H2O2 oxidation method using cheap and ubiquitous coal as the carbon source. Then the gold sol was connected to CDs to obtain a core-shell structure photocatalyst Au@CDs by sodium borohydride (NaBH4) reduction method. While characterizing the material structure, the photocatalytic N2/H2O to ammonia performance of Au@CDs was investigated. The results show that the introduction of CDs in Au @CDs photocatalysts can not only improve the performance of the catalyst to excite carriers in visible light, but also inhibit the recombination of photogenerated electron-hole pairs, promote the charge transport ability and make photogenerated electrons and holes move smoothly to the catalyst surface. Meanwhile, the adsorption and dissociation capacity of N2 on the catalyst surface can be improved, thereby the photocatalytic N2/H2O ammonia synthesis reaction of Au@CDs can proceed smoothly.

Pt nanoparticles-modified WO3@TiO2 core–shell ternary nanocomposites as stable and efficient photocatalysts in tetracycline degradation

Core–shell structure photocatalysts have attracted extensive attention in the field of wastewater treatment because of their desirable capacity of efficient charge separation. In this study, a novel Pt nanoparticles-modified WO3@TiO2 core–shell ternary structure was synthesized and its photocatalytic property was evaluated by degrading 30 ppm of tetracycline (TC) under simulated solar light. It was found that the optimal Pt-WO3@TiO2 ternary structures exhibit extremely superior performance in photocurrent response (30 times higher) and photocatalysis (10 times higher) compared to the pristine WO3 nanorods. The enhanced photocatalytic performance is attributed to the long lifetime of charge carriers and the increment of oxygen vacancies generated by introducing Pt nanoparticles. The radicals trapping experiments verified a two-step TC photodegradation process which can be ascribed to the existence of superoxide radicals ( $$\cdot {\text{O}}_{2}^{ - }$$ ) and holes (h+). This work may shed light on the design of novel ternary core–shell structure for efficient degradation of TC under solar light.

Novel stable enhanced visible light photocatalytic system based on a Ag3PO4@polypyrrole core-shell Z-scheme with in-situ generated metallic Ag ohmic contacts

Maintaining the high photocatalytic activity and stability of Ag3PO4 in practical applications is a still a major challenge. In this study, a series of Ag3PO4@polypyrrole (PPy) core-shell structure photocatalysts were prepared successfully by facile in-situ oxidative polymerization. A transmission electron microscopy image of the composite showed that the PPy shell with a thickness of 5–10 nm was coated tightly on the surface of the Ag3PO4 particle core. X-ray diffractometer and X-ray photoelectron spectroscopy analyses demonstrated that the silver ions were reduced to metallic Ag during polymerization. Ultraviolet–visible diffuse reflectance spectra indicated that the light response range of PA-5 broadened from 300 to 630 nm. Compared with pure Ag3PO4, the composites exhibited higher photocatalytic activities and better photostability, especially Ag3PO4@PPy with a PPy content of 5 wt% (PA-5). The degradation rate of PA-5 with organic dyes exceeded 98% within 15 min under visible light irradiation. Even after five repeated reactions, PA-5 still maintained a high degradation rate of 94.98%. The degradation rate of the pure Ag3PO4 decreased significantly from 94.53% to 60.33% after five cycles. Based on the experimental results, a reasonable mechanism is proposed for the Z-scheme electron-transfer photocatalytic system with metallic Ag as an ohmic contact.

Surface-defect-rich mesoporous NH2-MIL-125 (Ti)@Bi2MoO6 core-shell heterojunction with improved charge separation and enhanced visible-light-driven photocatalytic performance

Mesoporous NH2-MIL-125(Ti)@Bi2MoO6 core-shell heterojunctions with surface defects were fabricated through a facile solvothermal method. The mesoporous core-shell structure with a large relative surface area of 87.7 m2 g−1 and narrow pore size of 8.2 nm extends the photoresponse to the range of visible light due to the narrow band gap of ∼1.89 eV. The visible-light-driven photocatalytic degradation efficiency of highly toxic dichlorophen and trichlorophenol were 93.28 and 92.19%, respectively, and the corresponding rate constants were approximately 8 and 17 times higher than the rates achieved by pristine NH2-MIL-125(Ti). The photocatalytic oxygen production rate was increased to 171.3 µmol g−1. Recycling for several cycles indicates high stability, which is favorable for practical applications. The excellent photocatalytic performance can be ascribed to the formation of the core-shell heterojunctions and to the surface defects that favor charge separation and visible light absorption; the mesoporous structure offers an adequate number of surface active sites and mass transfer. This novel mesoporous core-shell photocatalyst will have potential applications in the environment, and this strategy offers a new insight into fabrication of other high-performance core-shell structure photocatalysts.

Efficient photocatalytic overall water splitting over a core-shell GaInZnON@GaInON homojunction

Direct overall water splitting via photocatalysis provides a potential pathway for solar energy conversion. The essential section is to develop efficient and stable photocatalysts, yet with limited success to date. Here a novel p-type gallium indium zinc oxynitride homojunction photocatalyst with core-shell structure is reported, which exhibits H2 and O2 evolution rates of 603 and 274 μmol h−1 g−1 with an apparent quantum efficiency of 3.5% at 430 nm from overall pure water splitting. Precise characterizations and DFT calculations reveal that the excellent photocatalytic performance is ascribed to the facilitated charge transfer contributed by the ideal type-I band alignment between GaInZnON core and GaInON shell, combined with the intermediate level formed nearby the Fermi level of GaInON shell. Our work offers insight into the development of facile synthesis of core-shell structure photocatalysts towards efficient solar-driven overall water splitting.

Controlled synthesis of g-C3N4@BiPO4 core–shell nanorods via low temperature reassembled strategy

The g-C3N4@BiPO4 nanorod core–shell structure photocatalysts were prepared by a new neutral hydrothermal reaction system combined with low temperature reassembled strategy. The CN precursors were successfully reassembled on the surface of BiPO4 nanorod to form ultrathin g-C3N4 layer (about 1 nm) under low temperature. Due to the formation of the core–shell structure, it can effectively promote the separation of photogenerated charge, thereby greatly improving the photocatalytic activity under UV light irradiation. The photodegradation activity of the phenol by the g-C3N4@BiPO4 nanorod core–shell structure photocatalyst annealing at the optimized conditions exhibits 1.6 times that of pure BiPO4 nanorod. The relationship between core–shell structure and photocatalytic activity under UV light irradiation was profoundly revealed through a comprehensive contrast experiment, and the mechanism of the enhancement activity of core–shell structure photocatalyst was also explored. It was found and detailedly demonstrated that the CN precursors prepared by neutral hydrothermal reaction can be polymerized into graphite-like phase C3N4 on the surface of Bi-based photocatalytic materials via low temperature thermal catalytic reassembled method. The novel method was proved to be a universal method for construction of core–shell structures. The establishment of g-C3N4@BiPO4 core–shell structure can provide blueprints for the construction of other organic–inorganic interface electric field catalytic system and can greatly improve the attractive prospect in practical applications owing to the perfect photocatalytic performance.

Photocatalytic activity enhancement of core-shell structure g-C3N4@TiO2via controlled ultrathin g-C3N4 layer

The g-C3N4@TiO2 core-shell structure photocatalysts with controlled ultrathin g-C3N4 layer (0nm, 1.0nm, 1.5nm, 3.0nm) were prepared by a new method of the sol-gel approaches in situ coating re-assembled. The g-C3N4@TiO2 sample with 1.0nm thickness of shell layers has the highest visible light photocatalytic degradation phenol activity which is almost 7.2 times as high as that of bulk g-C3N4. The highest photocurrent response intensity is increased by ten times higher than that of g-C3N4 and five orders of magnitude compare to TiO2. The removal rate of phenol using g-C3N4@TiO2 core-shell catalyst is 30% and the degree of mineralization by the same catalyst is 19.8%, which dramatically increase compared with that of g-C3N4 and TiO2. The enhanced performance of the degradation phenol and the mineralization is owing to effective charge separation revealed by the photoluminescence (PL), electrochemical impedance spectroscopy (EIS) and density functional theory calculations (DFT), superoxide radicals as the main oxidative species proved by electron spin resonance spectroscopy (ESR). And the core-shell structure could effectively promote the electron transfer from g-C3N4 to TiO2 during the catalytic process. The results of repetitive experiment and cycle experiment show that the g-C3N4@TiO2 has a strong binding force between the core and shell, which is stable, without secondary pollution and convenient for recovery. What's more, the results revealed the law between the different g-C3N4 shell layers (0nm, 1.0nm, 1.5nm, 3.0nm) over the g-C3N4@TiO2 samples and the corresponding catalytic activity, which successfully established the structure-activity relationship. A new catalytic concept namely layer-dependent effect was found, that is number of layers over g-C3N4 of the core-shell structure determines photocatalytic activity.

In situ growth of Ag3PO4 on N-BiPO4 nanorod: A core–shell heterostructure for high performance photocatalyst

Enhanced light absorption and effective separation of photogenerated charges are the main strategies to improve the performance of photocatalytic materials. In this study, Ag3PO4/N-doped BiPO4 (N-BiPO4) core–shell structure photocatalyst was synthesized by a simple in-situ growth strategy in an organic solvent. The separation of photogenerated electron–hole was enhanced by the doping of nitrogen, because of the emergence of N–O impurity energy levels. The increased photocatalytic activity of Ag3PO4/N-BiPO4 could be attributed to the in-situ formation of chemical bonds between Ag3PO4 and N-BiPO4, which accelerate the separation of electron–hole pairs. The photocatalytic performance of the as-synthesized Ag3PO4/N-BiPO4 was evaluated by monitoring the decolorization of methyl orange under sunlight irradiation. Ag3PO4/N-BiPO4 was capable of bleaching 95% MO within 40min.

Facile one-step synthesis and photoluminescence properties of Ag–ZnO core–shell structure

Ag–ZnO core–shell structures were gained via one-step solvothermal process. The products were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, photoluminescence (PL) and UV–vis spectroscopy, respectively. It was shown that the properties were greatly changed compared to pure ZnO from the PL and Raman spectra, which indicated the strong interfacial interaction between ZnO and Ag. The work provides a feasible method to synthesize Ag–ZnO core–shell structure photocatalyst, which is promising in the further practical application of ZnO-based photocatalytic materials.