Robust Photocatalyst Research Articles

Photocatalytic degradation of tetracycline by using a regenerable (Bi)BiOBr/rGO composite

The development of advanced and robust photocatalysts is vital for efficient photocatalytic degradation of the antibiotic tetracycline. Herein, a hierarchical heterojunction (Bi)BiOBr/rGO was facilely synthesized by employing an in-situ reduction strategy. An obvious synergistic effect between adsorption and photocatalysis was observed. A >98% tetracycline degradation efficiency was obtained within 20 min, and high performance could be maintained for over 50 h in a continuous operation without any post-treatment. The experimental and DFT calculation results suggested that there existed a built-in electric field between the interfaces, leading to the fast electron migration. Furthermore, rGO could significantly enhance the tetracycline adsorption, and Bi largely suppressed the charge carrier recombination owing to the surface plasmon resonance (SPR) effect. A possible tetracycline degradation pathway was proposed based on the HPLC-MS analysis. This study provides pathways for the rational design of advanced and robust photocatalysts to effectively degrade emerging contaminants in practical continuous-flow configurations.

Mixed-Valence Bimetallic Ce/Zr MOF-Based Nanoarchitecture: A Visible-Light-Active Photocatalyst for Ciprofloxacin Degradation and Hydrogen Evolution.

A mixed-valency bimetallic Ce/Zr MOF with Ce3+/Ce4+ ions incorporated and an oxygen vacancy-rich single-component photocatalyst have been designed through the one-step solvothermal route to harness photons from the visible-light spectrum for green energy (H2) generation and ciprofloxacin (CIP) degradation. The one-pot-engineered bimetallic Ce/Zr MOF shows visible-light-active characteristics accompanied by a narrower band gap, along with enhanced exciton separation and superior ligand-to-metal charge transfer (LMCT), due to the presence of an interconvertible Ce3+/Ce4+ ions pair in comparison to its pristine MOF counterpart. The Ce ion insertion led to increase in electron density around the Zr4+ ion, along with generation of some oxygen vacancies (OV), which cumulatively led to the rise in the photo-reaction output. The synthesized UNH (Ce/Zr 1:1) MOF displayed a boosted photocatalytic H2 production rate of 468.30 μmol h-1 (ACE = 3.51%), which is around fourfolds higher than that of pristine MOFs. Moreover, for CIP photodegradation, the UNH (Ce/Zr 1:1) shows an enhanced efficiency of 90.8% and follows pseudo-first-order kinetics with a rate constant of 0.0363. Typically, the active species involved in the photo-redox reaction of the CIP photodegradation follows the order hydroxyl radical (OH•) < superoxide radical (O2•-), as confirmed by the TA and NBT tests. Consequently, the bimetallic Ce/Zr MOF can be readily employed as a robust photocatalyst with enhanced tendencies towards CIP degradation and H2 evolution.

Improved charge transfer by binary Ni3S2-NiS2 for boosting the photocatalytic hydrogen generation over g-C3N4

Developing efficient, cheap and robust photocatalysts for hydrogen evolution is promising to solve the issues of energy shortage and environmental degradation. In this work, binary Ni3S2-NiS2 was in-situ grown on g-C3N4 (CN) through a one-pot hydrothermal method. The optimal hydrogen evolution activity (1206.6 μmol g-1h−1) was achieved from Ni3S2-NiS2/CN-3 with excellent stability under visible light irradiation. Improved light absorption and superior interfacial charge transfer properties including suppressed photogenerated carrier recombination and efficient separation of photogenerated electron-hole pairs have been observed, which account for the enhanced photocatalytic performance.

Homojunction type of carbon nitride as a robust photo-catalyst for reduction conversion of CO2 in water vapor under visible light

The value-added conversion of CO2 by photocatalytic reduction is considered as a potential way to solve the current energy and environmental crisis. In this paper, we report that a mechanical mixture of the as-thermally polymerized melamine (Me)- and 3-amino-1,2,4-triazole (AT)-based nitride carbons (MCN and TCN) can turn into a homojunction material (MTCN) by a calcination under air. A series of characterizations and photo-catalytic tests, combined with DFT calculations, support that the constructed MTCN has an improved porosity and photoelectric conversion efficiency. And the nitrogen-rich structure not only broadens the visible light response range but also provides stronger Lewis basic sites for the adsorption and activation of CO2 at the surface. As a result, MTCN exhibits the most outstanding performance on tetracycline degradation under visible light illumination. In particular, its photo-catalytic efficiency for the visible-triggered CO2 reduction under normal temperature and pressure can reach 7.75 μmol·g−1·h−1, which is 13.8 or 16.1 times higher than the single MCN or TCN. This work provides a facile pathway to construct CN-based homojunction photocatalyst for the efficient conversion of CO2 into valuable products.

Green immobilization of CdS-Pt nanoparticles on recombinant Escherichia coli boosted by overexpressing cysteine desulfurase for photocatalysis application

Herein, we propose a facile synthetic strategy for biogenic photocatalyst by sequentially immobilizing CdS and Pt nanoparticles (NPs) on engineered recombinant Escherichia coli (e-E. coli) strains. In particular, we transferred the cysteine desulfurase gene to the heterologous host to overexpress cysteine desulfurase and the resulting e-E. coli strain could serve as a biofactory for the extracellular growth of CdS NPs involving catalyzing L-cysteine (Cys) to form a reactive sulfur source, followed by the precipitation of CdS via the reaction between Cd2+ ions and the locally concentrated active sulfur source around the strain. The subsequent modification of e-E. coli/CdS composites with noble metal Pt NPs further enhanced the catalytic degradation performance towards organic dyes, due to suppressing the recombination of the photogenerated electron-hole pairs. Accordingly, the ternary e-E. coli/CdS/Pt composites emerged as robust photocatalysts for pollutant degradation in waste-water treatment, which is promising for environmental remediation in ambient conditions.

Development of photocatalyst based on NaYF4: Yb, Tm@NaYF4: Yb, Ce/NH2-MIL-101 (Cr): Doping Ce3+ ions to promote the efficient energy transfer between core and shell

Utilization of the whole solar spectrum for the photocatalysis is still a challenge and interesting topic. A series of novel photocatalysts are fabricated by combination of core–shell upconversion nanoparticles NaYF4: Yb, Tm@NaYF4: Yb, Ce (Tm@Ce) with the NH2-MIL-101 (Cr) (NMC) (Tm@Ce/NMC). Tm@Ce/NMC displays the high stability, wide photoresponsive range from UV–Vis to NIR, and excellent photocatalytic activity for decomposition of RhB. With the optimal doping amount of Ce3+ ions and ratio between Tm@Ce and NMC, the degradation of RhB is improved by 1.13, 1.14, and 1.50 times as compared with NaYF4: Yb, Tm/NMC (Tm@NMC), under the simulated solar light, UV + Vis, and NIR, respectively. The enhanced photocatalytic activity of Tm@Ce/NMC is mainly attributed to the efficient energy transfer between core and shell by the doping Ce3+ ions along with the distinct charge separation and suppressed recombination. By the controlled synthesis, the NaYF4: Yb, Tm (YT) nanoparticle is developed with the similar size as the Tm@Ce to further testify the effect of doping Ce3+ ions and exclude the influence of the increased size. The photocatalytic activity of YT/NMC is the less than that of Tm@Ce/NMC, which is almost the same with that of Tm/NMC. It suggests that to merely increase the size of upconversion nanoparticles is not the judicious choice for enhancement of the photocatalytic activity. On the basis of the trapping experiments and other spectra properties, the possible photocatalytic mechanism is conjectured, which is helpful to refine the structure design with the ultimate aim to get the robust photocatalyst.

Non-stoichiometric Ag-In-S quantum dots for efficient photocatalytic CO2 reduction: Ag/In molar ratio dependent activity and selectivity

Photocatalytic reduction of CO2 to syngas is a desirable strategy for recycling CO2 into valuable products, meeting energy demands in a sustainable way. Herein, we report the use of non-stoichiometric Ag-In-S quantum dots (QDs) as highly efficient and robust photocatalysts for visible-light-driven photocatalytic reduction of CO2 to syngas at atmospheric pressure and room temperature. The introduction of Co(bpy)32+ (bpy = 2′2-bipyridine) cocatalyst can promote the conversion of CO2 to CO reaction and meanwhile improve the photo-stability of Ag-In-S QDs. The photocatalytic activity and selectivity of Ag-In-S QDs are strongly dependent on the Ag to In molar ratios, and the optimized sample exhibits the highest CO evolution rate of 9.20 μmol h−1 and H2 evolution rate of 3.13 μmol h−1, corresponding to the CO selectivity of 74.61%, outperforming most of the reported QDs based photocatalysts. This work provides a new example of Cd and Pb free QDs photocatalyst for efficient and stable CO2 photoreduction.

Pyrimidine-modified g-C3N4 nanosheets for enhanced photocatalytic H2 evolution

Designing visible-light-driven, high-efficiency, robust photocatalysts with practical potential is an important direction in the photocatalysis field. Herein, pyrimidine-modified g-C3N4 (Pym-CN) photocatalysts with curled nanosheet morphology were prepared through a facile supramolecular assembly method. Pyrimidine has only two N atoms, thus leading to the deficiency formation in the supramolecular assembly of cyanuric acid with melamine. Upon calcination, the deficiency decreases the polycondensation degree of g-C3N4, thereby further affecting its morphology and optoelectronic property. The pyrimidine modification can enhance the absorption capacity toward visible light and facilitates the separation of photo-generated carriers. By changing the adding amount of pyrimidine, the optimal Pym-CN photocatalyst exhibits a H2 evolution rate of 1046 μmol g−1 h−1 under visible light, which is almost 30 times higher than that of pristine g-C3N4. This work may afford a novel approach to modifying organic polymer semiconductor photocatalysts with small organic molecules of nonplanar structure.

Toward practical solar-driven photocatalytic water splitting on two-dimensional MoS2 based solid-state Z-scheme and S-scheme heterostructure

Solar-driven splitting of water to hydrogen production is one of the utmost auspicious and cost-effective technologies providing sustainable fuel as it necessitates only sunlight and water. This substantial technology can be achieved in a two step-photoexcitation system using an artificial Z-scheme process. The key to comprehend this reaction is to discover an effective and robust photocatalyst which preferably makes sufficient use of solar energy. Benefiting from the ultrahigh surface area, appropriate band potentials and unique physiochemical properties of 2D layered structure, MoS2 has attained intensive research attention for hydrogen evolution reaction. The comprehensive review summarizes the recent progression in solid mediator Z-scheme based MoS2 particularly in the field of water splitting. The review initiates with the important bases of Z-scheme water splitting mechanism in addition to structural and optoelectronic properties of MoS2. In addition, detailed discussion on the solid-mediator Z-schemes to further improve the photocatalytic efficacy and limit the back (water-forming) reactions. The review mainly focuses on the solid-mediator based Z-schematic systems involving new tandem structures with an efficient synergistic effect to achieve both wide-range light absorptivity and charge pairs transference. In addition, a new S-scheme heterostructing is briefly introduced to understand the charge-transport route clearly and vividly. The aim of wide-spreading water splitting devices from lab-scale to wide-range potential applications has been considered as ‘artificial photosynthetic leaf-to-tree challenge’. Finally, a summary and outlook on the challenges and future research topics on MoS2 based Z-scheme heterostructure photocatalysts are presented.

Gold anchoring to CuFe2F8(H2O)2 oxyfluoride for robust sono-photodegradation of Rhodamine-B

This work presents mixed-anion blends (e.g., oxynitrides and oxysulfides) as prospective representatives for visible-light sono-photocatalyst. While generally tolerate oxidative degradation of photogenerated holes causes to medium durability and stability. Hence, an exceptionally stable, mixed-anion oxyfluoride photocatalyst was designed and prepared based on CuFe2F8(H2O)2, decorated by gold nanoparticles (Au-NPs) as a sink for photogenerated electron and sacrificial electron mediator. Electrochemical analysis revealed Au-NPs can appearance Schottky barriers with CuFe2F8(H2O)2, injection of electrons into CuFe2F8(H2O)2, cause to electron capturing at profound surface pitfall states of CuFe2F8(H2O)2. Au-NPs sensitized CuFe2F8(H2O)2 were applied as a robust photocatalyst in pairs with ultrasound (US) waves for Rhodamine B (RhB) dye degradation. Quenching investigations indicated that •OH and •O2− were productive species for RhB degradation on Au/CuFeF8(H2O)2 which the kinetics of it was the first order and fitted to the Langmuir-Hinshelwood model. This study displays the first type of sonophotocatalytic decomposition (SPD) of an organic dye driven by visible-light excitation of a metal-doped oxyfluoride with Schottky barrier and surface plasmonic resonance (SPR).

Graphitic Carbon Nitride/CdSe Quantum Dot/Iron Carbonyl Cluster Composite for Enhanced Photocatalytic Hydrogen Evolution

A g-C3N4/CdSe quantum dot/[Fe2S2(CO)6] composite has been successfully constructed. The structure and chemical composition of the composite were investigated via, inter alia, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The ability of the assembly to act as a photocatalyst for proton reduction to form hydrogen gas was studied. With visible light irradiation for 4 h, the total H2 production catalyzed by the g-C3N4/CdSe quantum dot/[Fe2S2(CO)6] composite was found to be 9 times as high as a corresponding CdSe/[Fe2S2(CO)6] assembly and significantly higher than either the CdSe quantum dots or g-C3N4 alone. The g-C3N4 support/matrix was found to enhance the stability and efficiency of the CdSe quantum dot/iron carbonyl cluster assembly in the photocatalytic hydrogen evolution process. Results from recycling tests showed that the g-C3N4/CdSe quantum dot/[Fe2S2(CO)6] composite is a sustainable and robust photocatalyst, maintaining the same activity after three cycles. The photoinduced charge carrier transfer dynamics in the g-C3N4/CdSe quantum dot/[Fe2S2(CO)6] composite system has been investigated by transient absorption (TA) and time-resolved photoluminescence (TRPL) spectroscopies. The spectroscopic results indicate efficient hole transfer from the valence band of the excited CdSe quantum dots to the molecular iron carbonyl clusters and from the defect state of the quantum dots to g-C3N4 in the g-C3N4/CdSe quantum dot/[Fe2S2(CO)6] composite, which significantly inhibits the recombination of photogenerated charge carriers in CdSe quantum dots and boosts the photocatalytic activity and stability for hydrogen evolution. Energy transfer from g-C3N4 to the CdSe quantum dot/[Fe2S2(CO)6] assembly with a time constant of 0.7 ns also contributed to the charge transfer process.

Glucose‐assisted preparation of n‐TiO2‐P25/Ag: An efficient and robust photocatalyst for enhancing visible‐light photo‐oxidation of benzyl alcohol

This paper describes the novel method of Ag deposition on the surface of TiO2, additionally investigates the photocatalytic properties of the new photocatalyst in the oxidation of benzyl alcohol under visible‐light as well as sunlight. Silver nanoparticles were deposited on surface of titanium dioxide through the Tollens test method. Ag(0) has been prepared in situ by reduction of [Ag (NH3)2]+ by glucose as a moderate and green reducing agent for the first time. The properties of n‐TiO2‐P25/Ag were investigated through X‐ray powder diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), energy dispersive X‐Ray (EDX), inductively coupled plasma optical emission spectrometry (ICP‐OES), BET analysis, UV–visible/DRS techniques, and photoluminescence (PL) analysis.

Graphitic Carbon Nitride-based New Advanced Materials for Photocatalytic Applications

Background: The present scenario of rapid industrial and population growth has become a serious threat to environmental and energy concerns. Extremely noxious pollutants like dyes, heavy metal ions, phenols, antibiotics and pesticides in water are the reason behind deprived water quality leading to inadequate access to clean water. Photocatalysis is a prominent strategy for environmental remediation as photocatalytic materials not only convert solar energy into usable energy expedient but also shows potential application in pollutant mitigation. An effectual photocatalytic system must possess wide visible absorption range, high physio-chemical firmness, and effective space-charge separation along with strong redox ability. Polymeric graphitic carbon nitride a metal-free semiconductor photocatalyst has outshined as a robust photocatalyst for various photocatalytic applications. Methods: Hybridizing polymeric g-C3N4 with other semiconductor photocatalysts has not only conquer the limitations related to pristine g-C3N4 but also displayed improved photoactivity. Different photocatalytic systems involving g-C3N4 coupled metal-oxides, metal-free systems and complex heterojunction systems are reviewed. Moreover, an all-embracing study based on g-C3N4 based nanocatalysts is explored via heterojunction formation taking g-C3N4 as one component. Results: Photocatalytic experiments involving photodegradation of pollutants, revealed the significance of metal-free g-C3N4 in the heterojunction system which remarkably boost the photoactivity through effective separation and migration of photocarriers. Moreover, from recyclability experiments, exceptional photostability of g-C3N4 based photocatalysts was observed. Photocatalytic pollutant degradation is a complex phenomenon which requires significant experimental techniques to support the mechanism. With the help of photoelectrochemical analysis, the mechanisms behind photodegradation can be evaluated and explored. Conclusion: Metal-free polymeric g-C3N4 is a potential semiconductor photocatalyst which can be optimally utilized for wastewater treatment. Coupling g-C3N4 with another semiconductor material with an appropriate band edge can effectively enhance the photocatalytic efficacy. Herein, g-C3N4 derived metal-oxide, metal-free and complex heterojunction systems are explored and their photocatalytic efficiency is evaluated for pollutant degradation. However, more effective research efforts are needed for large-scale applications of g-C3N4 based photocatalysts.

Atomic-Level Charge Separation Strategies in Semiconductor-Based Photocatalysts.

Semiconductor-based photocatalysis as a productive technology furnishes a prospective solution to environmental and renewable energy issues, but its efficiency greatly relieson the effective bulk and surface separation of photoexcited charge carriers. Exploitation of atomic-level strategies allows in-depth understanding on the related mechanisms and enables bottom-up precise design of photocatalysts, significantly enhancing photocatalytic activity. Herein, the advances on atomic-level charge separation strategies toward developing robust photocatalysts are highlighted, elucidating the fundamentals of charge separation and transfer processes and advanced probing techniques. The atomic-level bulk charge separation strategies, embodied by regulation of charge movement pathway and migration dynamic, boildownto shortening the charge diffusion distance to the atomic-scale, establishing atomic-level charge transfer channels, and enhancing the charge separation driving force. Meanwhile, regulating the in-plane surface structure and spatial surface structure are summarized as atomic-level surface charge separation strategies. Moreover, collaborative strategies for simultaneous manipulation of bulk and surface photocharges are also introduced. Finally, the existing challenges and future prospects for fabrication of state-of-the-art photocatalysts are discussed on the basis of a thorough comprehension of atomic-level charge separation strategies.

Visible-light-driven photocatalysis of anisotropic silver nanoparticles decorated on ZnO nanorods: Synthesis and characterizations

Having junctions of noble metals and semiconductors is an appealing approach to fabricate a robust photocatalyst for the complete degradation of organic pollutants with visible light activation. Herein, we synthesize Ag/ZnO nanorods (NRs) by a two-step chemical route. ZnO NRs are first grown via a solvothermal process with a length and a diameter of about 300 ± 10 nm and 60 ± 3 nm, respectively. Anisotropic silver nanoparticles (Ag NPs) are then deposited on the surface of the ZnO NRs by a self-assembly process. Thereby, the spatial separation of electron-hole (e–−h+) pairs in the Ag/ZnO NR composites is considerably enhanced because of the localized surface plasmon resonance (LSPR) effect derived from Ag NPs and the suitable energy band alignment between ZnO and Ag. By taking this advantage, Ag/ZnO NRs outperform bare ZnO NRs in photocatalytic activity against rhodamine B (RhB). The Ag/ZnO NRs retain their excellent performance of 86% even after being used repetitively for three recycling rounds. The free radicals trapping test suggests that photogenerated electron is the key factor in the photocatalytic RhB degradation of Ag/ZnO NRs.

ZnO nanorods/Fe3O4-graphene oxide/metal-organic framework nanocomposite: recyclable and robust photocatalyst for degradation of pharmaceutical pollutants.

Nanosized semiconductors are widely utilized as solar energy based photocatalyst. However, the deficiencies such as poor adsorption toward contaminants and recyclability issues, rapid recombination of photo-introduced radicals, and deactivation by scavengers are still be the obstacle. To addressing those obstacles, zeolitic imidazolate framework-8 (ZIF-8), photosensitive ZnO, and paramagnetic Fe3O4 were anchored on conductive graphene oxide (GO) to prepare a nanocomposite photocatalyst ZnO/Fe3O4-GO/ZIF. The photocatalyst showed good robustness to scavengers of hydroxyl radicals (OH•), superoxide radicals (O2•-), and hole (h+) with hydrophobic ZIF-8 modified surface. Finally, four pharmaceuticals (sulfamethazine, metronidazole, norfloxacin, and 4-acetaminophen) were degraded rapidly under simulated solar irradiation for 1h, and the photocatalyst could be recycled at least ten times without obvious deactivation. The final results show that combination of semiconductor, graphene oxide and ZIF-8 is a good idea for construction of efficient photocatalyst. It offers new views in interface modification of nanomaterials, photocatalysis, and adsorption.

Three-in-one: achieving a robust and effective hydrogen-evolving hybrid material by integrating polyoxometalate, a photo-responsive metal–organic framework, and in situ generated Pt nanoparticles

A three-in-one hybrid material (P2W18@NU-1000-Pt) was constructed and investigated as an effective and robust photocatalyst towards hydrogen production in a water-compatible photocatalytic system.

Multifunctional Ni–Mg bimetal-activated Zn(O,S) for hydrogen generation and environmental remediation with simulated solar-light irradiation

NMZ-S10 is a powerful and robust photocatalyst that is capable of conducting the hydrogen evolution reaction, chromium (Cr6+) reduction, mixed-dye degradation, and hydrogenation reaction under solar light illumination.

Plasmonic Au nanoclusters dispersed in nitrogen-doped graphene as a robust photocatalyst for light-to-hydrogen conversion

Au nanoclusters (2.18 wt%) consisting of a few tens of atoms supported nitrogen-doped graphene deliver an impressive hydrogen evolution reaction rate of 3.16 μmol mgcat−1 h−1 under visible-light irradiation and a high maximum quantum yield of 14.3%.

Correction: Plasmonic Au nanoclusters dispersed in nitrogen-doped graphene as a robust photocatalyst for light-to-hydrogen conversion

Correction for ‘Plasmonic Au nanoclusters dispersed in nitrogen-doped graphene as a robust photocatalyst for light-to-hydrogen conversion’ by Dung Van Dao et al., J. Mater. Chem. A, 2021, DOI: 10.1039/D1TA05445G.