Ternary Z-scheme Photocatalyst Research Articles

Scatalysis: Exploring the mechanism of photocatalytic algal removal

Photocatalytic algal removal is an environmentally friendly and low-cost algal bloom control technology. In this work, carbon nitride nanosheets based on morphology control were synthesized, and a ternary Z-scheme photocatalyst was designed through heterojunction engineering for photocatalytic removal of harmful algae and their organic matter, and the removal rate of chlorophyll a was close to 100 % in 300 min. Three-dimensional fluorescence spectrograms and cellular SEM maps revealed the removal of algae and their organic matter, and the mechanism of Ag/AgCl/ZIF-8/SCN photocatalytic algal removal was explored in conjunction with the changes in membrane permeability and various physiological functions. Mechanistic studies showed that excess O2·− played a crucial role in cell inactivation and organic matter degradation. Oxidative stress caused by O2·− promoted the accumulation of H2O2 in cells and accelerates cell death. This study provides new ideas and support for the application of harmful algal bloom control and the mechanism of algal cell inactivation in real water bodies.

A superior ternary Z-scheme photocatalyst of Bi/Black Phosphorus nanosheets/P-doped BiOCl containing interfacial P–P bond and metallic mediator for H2O2 production and RhB degradation

Photocatalytic performance is significantly influenced by the efficiency of photogenerated electron-hole pairs separation and transfer. In this paper, rational designed Z-scheme Bi/Black Phosphorus Nanosheets/P-doped BiOCl (Bi/BPNs/P–BiOCl) nanoflower photocatalyst was synthesized by a facile in-situ reduction process. The interfacial P–P bond between Black phosphorus nanosheets (BPNs) and P-doped BiOCl (P–BiOCl) was investigated by the XPS spectrum. The Bi/BPNs/P–BiOCl photocatalysts exhibited enhanced photocatalytic performance for H2O2 production and RhB degradation. The optimally modified photocatalyst (Bi/BPNs/P–BiOCl-20) showed an excellent photocatalytic H2O2 generation rate of 4.92 mM/h and RhB degradation rate of 0.1169 min−1 under simulated sunlight irradiation, which was 1.79 times and 1.25 times greater than the P–P bond free Bi/BPNs/BiOCl-20. The mechanism was investigated through charge transfer route, radical capture experiments, and band gap structure analysis, indicating that the formation of Z-scheme heterojunctions and interfacial P–P bond not only enhances the redox potential of the photocatalyst but also facilitates the separation and migration of photogenerated electrons-holes. This work might provide a promising strategy for constructing Z-scheme 2D composite photocatalysts combining interfacial heterojunction and elemental doping engineering for efficient photocatalytic H2O2 production and organic dye pollutant degradation.

Development of TiO2 decorated Fe2O3QDs/g-C3N4 Ternary Z-scheme photocatalyst involving the investigation of phase analysis via strain mapping and its photocatalytic performance under visible light illumination

Development of TiO2 decorated Fe2O3QDs/g-C3N4 Ternary Z-scheme photocatalyst involving the investigation of phase analysis via strain mapping and its photocatalytic performance under visible light illumination

Fabrication of TiO2/Fe2O3/g-C3N4 ternary photocatalyst via a low-temperature calcination and solvothermal route and its visible light assisted photocatalytic properties

This study reported the fabrication of TiO2/Fe2O3/g-C3N4 ternary Z-scheme photocatalyst via low-temperature calcination followed by a nonaqueous route with tunable particle size and strong interfacial contact. The subsequent Fe2O3/g-C3N4 and TiO2/Fe2O3/g-C3N4 were investigated in terms of structure, morphology, optical properties, and surface chemical composition analysis via transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive x-ray spectroscopy (EDX), UV–visible spectroscopy, and photoluminescence spectroscopy (PL). The crystalline nature of the samples was investigated by X-ray diffraction (XRD) and HRTEM. Under visible light, the photocatalytic capabilities of as-fabricated TiO2/Fe2O3/g-C3N4 were examined by degrading Rhodamine B (RhB), and an enhancement in photocatalytic efficacy was found. TiO2 works as a primary photosensitizer, providing extra photoinduced electrons, while Fe2O3 acts as a “bridge” for electron transport from the TiO2 moiety to the g-C3N4 thereby establishing an indirect charge transport pathway based on the Z-scheme. Radical scavenging tests were conducted to further explore the cause of increased activity and degradation mechanisms. The proposed technique might be a viable option for the removal of rhodamine b compounds and remedying freshwater reservoirs.

The room temperature synthesis of a CuO-Bi-BiOBr ternary Z-scheme photocatalyst for enhanced sunlight driven alcohol oxidation

The room temperature synthesis of an all-solid-state Z-scheme CuO-doped BiOBr (CuO-Bi-BiOBr) photocatalyst has been described. These CuO-Bi-BiOBr ternary heterojunctions exhibit efficient photocatalytic activities for selective alcohol oxidation. The structures, morphologies, and compositions of the nanostructures were well characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and atomic absorption spectroscopy (AAS). The X-ray diffraction (XRD) pattern of the as-synthesized nanostructures confirms the formation of phase-segregated CuO and BiOBr nanocrystals, whereas X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) analyses clearly indicate the formation of metallic bismuth nanoparticles (NPs). Next, the developed CuO-Bi-BiOBr ternary heterojunctions were applied as an efficient photocatalyst for the oxidation of alcohols into their corresponding aldehydes/ketones with high selectivity (>99%) and high conversion ratios (>99%). Herein, Bi metal NPs act as an electron mediator and bridge the connectivity between the two semiconductors, BiOBr and CuO, and, thus, a Z-scheme heterojunction is established. As expected, CuO-Bi-BiOBr has shown significantly superior activities compared to those of pure BiOBr. A possible mechanism for the photocatalytic oxidation process has been proposed. Radical scavenging experiments suggest that the active species, h+, ˙OH, e-, and ˙O2-, are dominant in the alcohol oxidation process. The as-synthesized CuO-Bi-BiOBr was reused several times without any significant deterioration in the original activities and it thus possesses relatively high stability for practical applications.

A ternary photocatalyst of all-solid-state Z-scheme TiO2–Au–BiOBr for efficiently degrading various dyes

Abstract To construct Z-scheme not only can effectively separate the excited electron-hole pairs, but also utilize the ample redox capability of each semiconductor component in this system for the surface photocatalytic reaction. In this work, a TiO2–Au–BiOBr ternary Z-scheme photocatalyst was constructed, in which Au NPs were used as the electron mediator to join BiOBr nanosheets and TiO2 nanofibers. The results showed that, under full spectrum irradiation, TiO2–Au–BiOBr nanofibers exhibited outstanding photocatalytic performance toward the degradation of Rhodamine B (RhB) with an excellent photodegradation efficiency of 99.91% within 30 min as well as good stability. The reaction mechanism of the TiO2–Au–BiOBr Z-scheme system was systemically studied by XPS, photoelectrochemical tests and free radical trapping experiments, etc. Moreover, the photocatalyst also exhibited excellent photocatalytic activity for degrading methyl orange and methylene blue.

Bi2WO6/C-Dots/TiO2: A Novel Z-Scheme Photocatalyst for the Degradation of Fluoroquinolone Levofloxacin from Aqueous Medium.

Photocatalytic materials and semiconductors of appropriate structural and morphological architectures as well as energy band gaps are materials needed for mitigating current environmental problems, as these materials have the ability to exploit the full spectrum of solar light in several applications. Thus, constructing a Z-scheme heterojunction is an ideal approach to overcoming the limitations of a single component or traditional heterogeneous catalysts for the competent removal of organic chemicals present in wastewater, to mention just one of the areas of application. A Z-scheme catalyst possesses many attributes, including enhanced light-harvesting capacity, strong redox ability and different oxidation and reduction positions. In the present work, a novel ternary Z-scheme photocatalyst, i.e., Bi2WO6/C-dots/TiO2, has been prepared by a facile chemical wet technique. The prepared solar light-driven Z-scheme composite was characterized by many analytical and spectroscopic practices, including powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N2 adsorption–desorption isotherm, Fourier-transform infrared spectroscopy (FT-IR), photoluminescence (PL) and UV-vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the Bi2WO6/C-dots/TiO2 composite was evaluated by studying the degradation of fluoroquinolone drug, levofloxacin under solar light irradiation. Almost complete (99%) decomposition of the levofloxacin drug was observed in 90 min of sunlight irradiation. The effect of catalyst loading, initial substrate concentration and pH of the reaction was also optimized. The photocatalytic activity of the prepared catalyst was also compared with that of bare Bi2WO6, TiO2 and TiO2/C-dots under optimized conditions. Scavenger radical trap studies and terephthalic acid (TPA) fluorescence technique were done to understand the role of the photo-induced active radical ions that witnessed the decomposition of levofloxacin. Based on these studies, the plausible degradation trail of levofloxacin was proposed and was further supported by LC-MS analysis.

Palladium modified ZnFe2O4/g-C3N4 nanocomposite as an efficiently magnetic recycling photocatalyst

A palladium modified ZnFe2O4/g-C3N4 nanocomposite was synthesized via an ultrasonic-assisted self-assemble and photoreduction route. As a ternary Z-scheme photocatalyst, the as-obtained Pd/ZnFe2O4/g-C3N4 nanocomposite was methodically characterized by diverse analysis techniques. For rhodamine B (RhB) and Cr(Ⅵ) removal, the ternary Pd/ZnFe2O4/g-C3N4 photocatalyst achieved an enhanced feature in photocatalytic capability. The reason is that the excellent electron transfer efficiency through Pd nanoparticles on the interfaces between ZnFe2O4 nanospheres and g-C3N4 nanosheets. Especially, Pd nanoparticles can also provide a preferred Z-scheme transfer pathway for electrons, which can generate higher redox active species. It identified that the Pd/ZnFe2O4/g-C3N4 photocatalyst had an obvious ability of magnetical separation and good recycling stability. Additionally, the reactive mechanism of the Pd/ZnFe2O4/g-C3N4 ternary nanocomposite was also investigated during photocatalysis reaction.

Al cluster oxide modified a hematite/P3HT ternary Z-scheme photocatalyst with excellent photocatalytic performance: A discussion of the mechanism

The Z-scheme photocatalyst is valuable for use in polluted water purification, and there is a need to develop a cheap and efficient photocatalyst. This study presents a new type of Z-scheme photocatalytic material composed of hematite and P3HT, also, the Al cluster oxides were first used as a charge transfer mediator to construct Z-scheme photocatalysis system. In addition, by analyzing the electron rearrangement phenomenon exhibited by the XPS spectrum and the experimental results of the in-situ illumination XPS, it is found that Al cluster is beneficial to the electron multi-step charge transfer process and Al cluster favors the construction of Z-scheme structure between hematite and P3HT. This Poly-3-hexylthiophene (P3HT)/Al cluster oxide/hematite ternary photocatalyst exhibited an excellent degradation effect on bisphenol A and tetracycline. This study demonstrates the feasibility of using the Al cluster as a charge mediator in the Z-scheme, providing new Z-scheme catalyst construction idea which is beneficial to the popularization and use of Z-scheme system in practical applications, and providing a new material for water pollution purification.

Ternary Z-scheme photocatalyst of Ag3PO4 with nitrogen-doped graphene and g-C3N4 for efficient removal of tetracycline

Photocatalytic technologies capable of using solar energy for environmental restoration have much progressed with the increasing environmental concern. In this study, the ternary photocatalyst Ag3PO4/NG/g-C3N4 conforming to the Z-scheme mechanism was prepared by a facile in-situ deposition method. Its morphology, chemical composition and optical property were determined by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscope, Fourier transform infrared, X-ray photoelectron spectroscopy and UV–vis diffuse reflectance spectroscopy. Such photocatalyst (0.50 g/L loading) achieved the highest 93.6% degradation rate of tetracycline (TC), and 72% mineralization rate of TC comparing with single Ag3PO4 (25% mineralization rate of TC). The detection of reactive oxidative species indicates that the photodegradation of TC is mainly caused by holes, O2− and OH. The synergistic effect of Ag3PO4, nitrogen-doped graphene (NG) and g-C3N4 in the composite accelerates the separation and migration of photogenerated carrier via a solid electron mediator NG, and simultaneously inhibits the photo-corrosion of Ag3PO4, thereby improving the photo-stability of the ternary photocatalyst.

Optimal construction of WO3·H2O/Pd/CdS ternary Z-scheme photocatalyst with remarkably enhanced performance for oxidative coupling of benzylamines

In this work, an all-solid-state Z-scheme photocatalyst of WO3·H2O/Pd/CdS ternary heterostructures was constructed by introducing a small amount of Pd into the optimized WO3·H2O/CdS binary system, where Pd nanoparticles (NPs) were sandwiched between WO3·H2O nanosheets and CdS NPs. The WO3·H2O/Pd/CdS ternary heterostructures exhibited remarkably enhanced photocatalysis towards the oxidative coupling of benzylamines to imines, compared with the other photocatalysts of WO3·H2O, CdS, WO3·H2O/CdS, WO3·H2O/Pd, and WO3·H2O/CdS/Pd. The wavelength-dependent photocatalysis of WO3·H2O/Pd/CdS is in good agreement with its light-harvesting intensity at the corresponding wavelengths. The photoelectrochemical results reflected the enhanced charge carrier separation in WO3·H2O/Pd/CdS, and the photocatalytic H2 evolution confirmed the highly efficient Z-scheme charge transfer in this ternary photocatalyst. Therefore, the WO3·H2O/Pd/CdS ternary heterostructures possess distinct advantages of extended light harvesting region, spatial separation of electron and holes, and elevated redox power, which synergistically contribute to the superior photocatalysis. The Pd NPs sandwiched between WO3·H2O and CdS acted as not only an electron mediator to facilitate the interfacial charge separation but also a cocatalyst to accelerate the selective oxidation of benzylamine. This work demonstrates a rational design of highly efficient Z-scheme photocatalysts and presents some revelations about the photocatalytic mechanism for selective organic transformations.

Synthesis of α-Fe2O3 decorated g-C3N4/ZnO ternary Z-scheme photocatalyst for degradation of tartrazine dye in aqueous media

Abstract In this study, we report the synthesis of a novel α-Fe2O3 decorated g-C3N4/ZnO (g-C3N4/ZnO@α-Fe2O3) ternary Z-scheme photocatalyst for degradation of organic dye. The g-C3N4/ZnO@α-Fe2O3 ternary nanocomposite was synthesized by using the direct pyrolysis and sol-gel methods. Different physicochemical methods were used to confirm the as-synthesized nanomaterials including Transmission electron microscopy, high-resolution field-emission scanning electron microscopy, Fourier Transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The as-synthesized different nanocomposite materials were used to investigate the photodegradation of tartrazine (Acid Yellow 23). Photoluminescence spectra revealed that the g-C3N4/ZnO@α-Fe2O3 ternary nanocomposite has lower recombination rate than pristine g-C3N4. The as-synthesized nanocomposite showed high photocatalytic activity towards degradation of tartrazine than that of g-C3N4, ZnO, ZnO@α-Fe2O3. Also, g-C3N4/ZnO@α-Fe2O3 nanocomposite can able to degrade 99.34% of tartrazine within 35 min under visible light irradiation. The g-C3N4/ZnO@α-Fe2O3 nanocomposite has a higher rate constant and excellent cyclic stability towards the photodegradation of tartrazine. The electrochemical impedance spectra results confirmed that the g-C3N4/ZnO@α-Fe2O3 nanocomposite has faster electron-transfer ability towards the electrode surface than that of g-C3N4, ZnO, and ZnO@α-Fe2O3 composite.

NiS2 as trapezoid conductive channel modified ternary Z-scheme photocatalyst system, NiGa2O4/NiS2/WO3, for highly photocatalytic simultaneous conversions of NO2− and SO32−

In this work, a novel ternary Z-scheme photocatalyst, NiGa2O4/NiS2/WO3, is prepared by sol-hydrotherma and calcination methods. The photocatalytic performance of prepared photocatalyst is evaluated through the simultaneous conversions of NO2− and SO32− under simulated solar-light irradiation. At the same time, the effects of solution acidity, simulated solar-light irradiation time, e− and h+ scavengers, used times and photocatalyst species on photocatalytic conversions of NO2− and SO32− are also studied. Due to the presence of NiS2 as conducting pathway, which can quickly transfer photo-generated electron (e−) and efficiently promote separation of electrons (e−) and holse (h+), the prepared ternary Z-scheme photocatalyst, NiGa2O4/NiS2/WO3, exhibits excellent performance in the simultaneous conversions of NO2− and SO32− under simulated solar-light irradiation. The conversion ratios of NO2− and SO32− can reach 87.03% and 97.47% under optimal experimental conductions, respectively.

Novel indirect Z-scheme photocatalyst of Ag nanoparticles and polymer polypyrrole co-modified BiOBr for photocatalytic decomposition of organic pollutants

Mimicking the natural photosynthesis, artificial Z-scheme photocatalysis enables more efficient utilization of solar energy for degradation of organic pollutants. Herein, an indirect Z-scheme photocatalyst of Ag nanoparticles and polymer polypyrrole (PPy) co-modified BiOBr was rationally designed and successfully synthesized via a combination of hydrothermal technique, in-situ photo-reduction and oxidative polymerization method. Dramatically, BiOBr-Ag-PPy system showed superior photocatalytic performance and excellent stability in degradation of both the typical triphenylmethane dye (malachite green) and colorless organic compound (phenol). Especially for BAP-0.4, its degradation conversion of malachite green was 6.4, 2.4 and 1.6 times of those of pure BiOBr, BiOBr-Ag and BiOBr-PPy, respectively, and can still maintain more than 91% even after fifth cycle experiment. The trapping experiments of reactive species and electron spin resonance (ESR) tests confirmed that the O2− and h+ were main active species in photocatalytic degradation. Through experimental investigations and theoretical analyses, the possible charge carriers transfer process over BiOBr-Ag-PPy ternary Z-scheme photocatalyst was proposed. In the indirect all-solid-state Z-scheme BiOBr-Ag-PPy heterojunction structure, by quenching the photo-generated electrons and holes with weaker redox ability in metal Ag nanoparticles, the electrons in the lowest unoccupied molecular orbital (LUMO) of PPy and holes in the valence band (VB) of BiOBr can survive and then have the opportunity to participate in the surface reaction, thus showing an increased photocatalytic activity.

One-pot, facile fabrication of a Ag3PO4-based ternary Z-scheme photocatalyst with excellent visible-light photoactivity and anti-photocorrosion performance

Ag3PO4 can-not be widely used as an efficient photocatalyst in practical applications because of its susceptibility to photocorrosion. In this study, a novel, ternary Z-scheme photocatalytic system containing graphene oxide (GO), Ag3PO4 and SnS2 was fabricated by a one-pot, mild, in-situ precipitation method successfully. Using Rhodamine B (RhB) as the target of elimination, GO/Ag3PO4/SnS2 exhibited outstanding photocatalytic and anti-photocorrosion properties compared with those of Ag3PO4, Ag3PO4/SnS2 and GO/Ag3PO4. RhB was thoroughly degraded over the optimized GO/Ag3PO4/SnS2 nanocomposite after only 15 min under visible-light irradiation; this result is approximately 2.14, 3.33 and 5.83 times faster than that of GO/Ag3PO4, Ag3PO4/SnS2 and Ag3PO4, respectively. After three reuses, the photocatalytic activity of the ternary composite slightly decreased but remained 2.36, 4.08 and 12.70 times higher than those of the reused GO/Ag3PO4, Ag3PO4/SnS2 and Ag3PO4, respectively. In this system, the efficient separation and migration of the photoinduced current carriers in Ag3PO4 was realized through a double Z-scheme electron-transfer mechanism in which the GO nanosheets acted as the photocatalyst and electron mediator, thereby enhancing the photoactivity and stability of Ag3PO4. The present study provides a new perspective for enhancing photocatalytic and anti-photocorrosion performances in perishable photocatalysts for organic sewage and other environmental contamination treatments.