Solid Solution Photocatalysts Research Articles

Customized Ultrathin Oxygen Vacancy-Rich Bi2W0.2Mo0.8O6 Nanosheets Enabling a Stepwise Charge Separation Relay and Exposure of Lewis Acid Sites toward Broad-Spectrum Photothermal Catalysis.

Designing robust photocatalysts with broad light absorption, effective charge separation, and sufficient reactive sites is critical for achieving efficient solar energy conversion. However, realizing these aims simultaneously through a single material modulation approach poses a challenge. Here, a 2D ultrathin oxygen vacancy (Ov)-rich Bi2W0.2Mo0.8O6 solid solution photocatalyst is designed and fabricated to tackle the dilemma through component and structure optimization. Specifically, the construction of a solid solution with ultrathin structure initially facilitates the separation of photoinduced electron-hole pairs, while the introduction of Ov strengthens such separation. In the meantime, the presence of Ov extends light absorption to the NIR region, triggering a photothermal effect that further enhances the charge separation and accelerates the redox reaction. As such, photoinduced charge carriers in the Ov-Bi2W0.2Mo0.8O6 are separated step by step via the synergistic action of 2D solid solution, OV, and solar heating. Furthermore, the introduction of OV exposes surface metal sites that serve as reactive Lewis acid sites, promoting the adsorption and activation of toluene. Consequently, the designed Ov-Bi2W0.2Mo0.8O6 reveals an enhanced photothermal catalytic toluene oxidation rate of 2445µmolg-1h-1 under a wide spectrum without extra heat input. The performance is 9.0 and 3.9 times that of Bi2WO6 and Bi2MoO6 nanosheets, respectively.

Influence mechanism of ZnCdS solid solution composition regulation on its energy band and photocatalytic hydrogen performance

The regulation of the band structure is crucial for the improvement of the photocatalytic performance, but the relationship between the composition of solid solution catalyst and their band structure is still unclear. Herein, the solid solution catalysts ZnxCd1-xS (1 > x > 0) were designed and synthesized using a handy solid-phase thermal decomposition strategy. It is interesting that the band structure and photocatalytic hydrogen production (PHP) performance of the obtained solid solution catalyst can be cleverly regulated by controlling the atomic ratio of the solid solution. Among the obtained series of ZnxCd1-xS solid solution catalysts, the optimal solid solution catalysts Zn0.5Cd0.5S exhibits the best PHP activity and favorable cycle stability: the corresponding PHP rate is 41211.2 μmol·h−1·g−1 and the QE value is 7.7 % at 400 nm. The outstanding photocatalytic hydrogen production performance is the result of significantly narrowing the band gap of sulfide solid solution. Additionally, the effective separation and transfer rate of photogenerated carrier has also been improved effectively. The construction of bimetallic sulfide solid solution photocatalyst via an ingenious solid-state thermal decomposition strategy in this work provided a new idea for improving the photocatalytic performance of bimetallic catalysts.

The presence of Mo and O double vacancies in Bi2W0.25Mo0.75O6 solid solution promotes photogenerated charge separation and molecular oxygen activation for efficient removal of gaseous toluene under visible light

Enhancing indoor air quality and devising efficient technologies for the degradation of low-concentration volatile organic compounds (VOCs) represent pertinent topics in current research endeavors. In this study, a one-step hydrothermal method was employed to successfully synthesize a Bi2W0.25Mo0.75O6 solid solution photocatalyst featuring Mo and O double vacancies. The catalyst has excellent degradation effect on low concentration (30 ppm) gaseous toluene within 60 min of visible light irradiation, which can achieve 95.36 % in air atmosphere and 99.79 % in pure oxygen atmosphere. The incorporation of Mo vacancies in the solid solution photocatalyst proved instrumental in inhibiting carrier complexation, while O vacancies facilitated the activation of molecular oxygen. Concurrent Mo and O double vacancies extended the photo response range, expedited the transport of photogenerated charges, and diversified the reactive oxygen species pool, collectively enhancing toluene degradation. Hence, this study presents a compelling method for the fabrication of photocatalysts exhibiting visible light catalytic activity, with potential applications in the treatment and mitigation of real-world environmental pollution challenges under mild conditions.

High-performance photocatalytic hydrogen evolution in a Zn0.5Cd0.5S/MoS2 p–n heterojunction

With respect to solid-solution photocatalysts for water splitting, researchers have focused on improving the loading and stability of catalysts, which have been major concerns and research interests. Herein, the fabrication of Zn0.5Cd0.5S/MoS2 nanocomposites involved a two-step method that encompassed hydrothermal synthesis and physical mixing. Experimental results confirmed that the Zn0.5Cd0.5S/MoS2 nanocomposites exhibited outstanding photocatalytic performance. In particular, they exhibited a notable hydrogen precipitation rate of 19.41 mmol/(g*h). The hydrogen production performance of Zn0.5Cd0.5S/MoS2 was approximately nine times greater than that of pure Zn0.5Cd0.5S, indicating a considerable increase. The observed enhancement in photocatalytic efficiency can be attributed to the formation of a p–n heterojunction between Zn0.5Cd0.5S and MoS2. This particular junction helped in separating and migrating photoinduced charge carriers, ultimately improving the photocatalytic performance. Furthermore, the addition of excess thiourea in MoS2 preparation produced Mo–O defects and increased the layer spacing of the involved material, improving the electron transfer and visible-light utilization of the material. The inhibition of carrier recombination was beneficial for synthesizing efficient and long-lasting photocatalysts.

Visible-light-driven calcium alginate hydrogel encapsulating BiOBr0.75I0.25 for efficient removal of oxytetracycline from wastewater

Oxytetracycline (OTC), a widely used antibiotic, poses significant environmental risks due to its persistence in ecosystems. This study introduces a visible-light-driven photocatalytic hydrogel system for effectively removing OTC from wastewater. The system employs calcium alginate (CA) hydrogel beads encapsulating a BiOBr0.75I0.25 solid solution, which utilizes the synergistic effects of adsorption and visible-light-driven photocatalysis. The BiOBr0.75I0.25 solid solution photocatalyst was synthesized via a solvothermal method, while CA hydrogel beads encapsulating BiOBr0.75I0.25 were prepared through ionic gelation of sodium alginate with calcium chloride. The novel hydrogel, CA-BiOBr0.75I0.25, demonstrated rapid adsorption, capturing over 50 % of OTC within 30 min and achieving a 90.92 % degradation rate within 60 min under visible light. This performance is associated with the unique petal-like structure of BiOBr0.75I0.25 and the high surface area of the hydrogel, facilitating efficient charge separation and radical generation critical for photocatalytic activity. Additionally, the system showed excellent stability and reusability, maintaining an 83 % removal efficiency after five cycles. These findings highlight the potential of this novel hydrogel as a sustainable solution for advanced wastewater treatment technologies.

Preparation of BiOBrxCl1‐x solid solution photocatalyst with oxygen vacancies for degradation of methyl orange under simulated sunlight

AbstractBiOBrxCl1‐x solid solution with oxygen vacancies was synthesized using a simple one‐step hydrothermal method. The sample was characterized using comprehensive characterization techniques, and the results showed that the solid solution material was successfully prepared. Adjusting the relative proportion of halogens in BiOBrxCl1‐x solid solution has a significant impact on the morphology, optical properties, and photocatalytic activity of the sample, and oxygen vacancies are introduced into the material. The presence of oxygen vacancies improves the separation efficiency of charge carriers and facilitates the activation of oxygen molecules into superoxide radicals. Among them, BiOBr0.2Cl0.8 showed flower‐like microspheres morphology and exhibited the best photocatalytic activity. After 30 min of dark adsorption and 1 h of simulated sunlight exposure, the removal rate of methyl orange (MO) was 92.5%, which was 2.38 times higher than that of pure BiOBr (38.9%) and 2.09 times higher than that of pure BiOCl (44.3%), respectively.

Unraveling the generation mechanism of singlet oxygen in Bi2WxMo1-xO6 solid solution and roles in photocatalytic degradation of gaseous toluene under visible-light irradiation

Photocatalytic degradation volatile organic compounds (VOCs) represent an appealing strategy since the inexhaustible solar energy and facile reaction condition. In this work, a flower-like microsphere Bi2WxMo1-xO6 solid solution photocatalysts with abundant oxygen vacancies (OVs) were prepared via HTAB-assisted hydrothermal method. The mole ratio of W and Mo atoms were regulated by adjusting the stoichiometric ratio of their precursor. The optimized Bi2W0.25Mo0.75O6 presented outstanding photocatalytic performance with 96.8% of toluene degradation rate after 180 min of irradiation under visible light (>420 nm), which was 13.76 times higher than that of pure Bi2MoO6 and 10.32 times higher than that of pure Bi2WO6, respectively. The enhanced photocatalytic activity of Bi2W0.25Mo0.75O6 was attributed to the optimized band structure and efficient separation efficiency of carriers as well as the participation of singlet oxygen (1O2) radicals. Free radical trap experiments and electron spin resonance investigations revealed that 1O2, hydroxyl radical, and holes were the predominated reactive oxygen species (ROSs) in toluene degradation. Meanwhile, the generation of 1O2 was related to abundant OVs of Bi2W0.25Mo0.75O6 solid solution. This work suggested that solid solution with abundant OVs was an effective photocatalyst to improve the VOCs degradation activity under visible-light irradiation.

Modification of an oxyhalide solid-solution photocatalyst with an efficient O2-evolving cocatalyst and electron mediator for two-step photoexcitation overall water splitting.

Two-step photoexcitation overall water splitting based on particulate photocatalysts represents a promising approach for low-cost solar hydrogen production. The performance of an O2-evolution photocatalyst and electron mediator between two photocatalysts crucially influences the construction of an efficient two-step excitation water-splitting system. Bismuth-tantalum oxyhalides are emerging photocatalysts for O2 evolution reactions and can be applied in two-step water-splitting systems. In this study, a highly crystalline Bi4TaO8Cl0.9Br0.1 solid solution with microplatelet morphology was synthesized by the dual flux method. The light absorption intensity and charge transfer efficiency of the Bi4TaO8Cl0.9Br0.1 solid solution were higher than those of Bi4TaO8Cl and Bi4TaO8Br; thus, the sacrificial O2 evolution activity of Bi4TaO8Cl0.9Br0.1 photocatalyst was obviously enhanced. The two-step excitation water splitting with a solid-state electron mediator was successfully constructed using Bi4TaO8Cl0.9Br0.1 as the O2-evolution photocatalyst and Ru/SrTiO3:Rh as the H2-evolution photocatalyst. The CoOx cocatalyst and reduced graphene oxide decorations on the surface of Bi4TaO8Cl0.9Br0.1 promoted the catalytic O2 generation process on Bi4TaO8Cl0.9Br0.1 and electron transfer between CoOx/Bi4TaO8Cl0.9Br0.1 and Ru/SrTiO3:Rh photocatalysts, respectively. As a result, the apparent quantum yield for this overall water-splitting system was 1.26% at 420 nm, which surpassed the present performance of the two-step excitation water-splitting systems consisting of metal oxyhalide photocatalysts. This study demonstrates the validity of high-quality solid-solution photocatalysts with suitable surface modification for efficient solar hydrogen production from water splitting.

Interfacial electric field construction of hollow PdS QDs/Zn1-xCdxS solid solution with enhanced photocatalytic hydrogen evolution.

The regulation of hollow morphology, band structure modulation of solid solution, and introduction of cocatalysts greatly promote the separation of electron-hole pairs in photocatalytic processes, which is of great significance for the process of photocatalytic hydrogen evolution (PHE). In this study, we constructed Zn1-xCdxS hollow solid solution photocatalysts using template and ion exchange methods, and successfully loaded PdS quantum dots (PdS QDs) onto the solid solution through in situ sulfidation. Significantly, the 0.5 wt% PdS QDs/Zn0.6Cd0.4S composite material achieved a H2 production rate of 27.63 mmol g-1 h-1 in the PHE process. The hollow structure of the composite material enhances processes such as light reflection and scattering, the band structure modulation of the solid solution enables the electron-hole pairs to reach an optimal exciton recombination balance, and the modification of PdS QDs provides abundant sites for oxidation, thereby promoting the proton reduction and hydrogen evolution rate. This work provides valuable guidance for the rational design of efficient composite PHE catalysts with strong internal electric field.

Facile synthesis of oxygen-deficient BiOBrxCl1−x solid solutions for efficient photocatalytic degradation of organic pollutants

In this study, a series of oxygen-deficient BiOBrxCl1−x (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) solid solution photocatalysts by the microwave hydrothermal method. By changing the Br/Cl molar ratio, the light absorption edge of BiOBrxCl1−x was effectively red-shifted from 345 to 430 nm. The performance of BiOBr0.3Cl0.7 solid solution catalyst showed the best photocatalytic duty for the degradation of norfloxacin (NOR) and methyl orange (MO). The degradation rate of NOR reached 90.2% within 50 min (catalyst dosage: 20 mg), whereas that of MO reached 82.7% within 30 min (catalyst dosage: 5 mg). Environmental factors affecting the degradation of NOR by BiOBr0.3Cl0.7 (such as pH, type of inorganic anions, amount of catalyst, and concentration of NOR) were discussed in detail. The presence of oxygen vacancies (OVs) was confirmed by electron spin resonance (ESR) experiments. Furthermore, free radical capture and ESR experiments identified the main active free radicals involved in the degradation of NOR over BiOBr0.3Cl0.7. Finally, a possible photocatalytic degradation mechanism was proposed.

The construction of CdxZn1-xS-based photocatalysts for enhanced hydrogen generation

CdxZn1-xS (x=0~1) solid solution photocatalyst with different morphologies was synthesized by solvothermal method using ethylenediamine as solvent. The light absorption of the photocatalyst was varied by changing the morphology and electronic band structure to allow strong visible light response for hydrogen generation. The results showed that the optimum sample Cd0.5Zn0.5S showed a high hydrogen production rate of 2531.3 μmol·g-1 ·h-1 with lactic acid as sacrificial agent. Loading with NiS by solvothermal method further improves the hydrogen production performance. The photocatalytic hydrogen evolution rate of NiS/Cd0.5Zn0.5S is 4547.5 μmol·g-1 ·h-1 , which is 1.80 times that of pure Cd0.5Zn0.5S. The mechanism of hydrogen production by NiS/Cd0.5Zn0.5S is also discussed.

Adjacent Mn site boosts photocatalytic hydrogen evolution of MnXCd1-XS solid solution through a dual-metal-site design

CdS has emerged as a possible candidate for photocatalytic hydrogen generation. However, further improvement in the performance of the Cd metal site is challenging due to limited optimization space. To solve this limitation, in this work, the Mn-Cd dual-metal photocatalyst was synthesized by a one-step solvothermal method, and the effects of different proportions of bimetals on hydrogen production activity were systematically studied. The ingenious design of the bimetallic sites enhances the carrier separation efficiency and the built-in electric field intensity, which leads to significant improvement in the photocatalytic hydrogen production performance of MCS0.19. Density functional theory (DFT) calculations confirm that the introduction of the Mn element can drive electrons through the Fermi level, resulting in enhanced conductivity of the catalyst. Meanwhile, electron channels are built between Mn and S, which speeds up the rate of electron transfer and is conducive to improving hydrogen production activity. This work provides a technical-methodological entrance to improve the photocatalytic hydrogen production performance of dual-metal S solid solutions and also promises to open a novel approach to creating high-efficiency solid solution photocatalysts.

Novel B-site substituted KCuTa3-xNbxO9 solid solution photocatalysts with modulated band structure for visible-light-driven hydrogen evolution

Perovskite-like metal oxides (PLMOs), featuring unique structural and optical properties, exhibit great potential in photocatalytic water splitting field. However, the wide bandgap and strong carrier recombination severely suppress their photocatalytic hydrogen production activity. Thus, design and development of novel PLMO photocatalyst with extended photo-response range and enhanced photo-generated charge separation/transport efficiency remains an ongoing challenge. Herein, a series of novel B-site substituted KCuTa3-xNbxO9 solid solution photocatalysts were synthesized via a simple solid-state reaction method. With an increased content of Nb, a distinct red-shifted of the optical absorption edge of KCuTa3-xNbxO9 solid solution was observed, leading to a decreased bandgap (from 2.69 to 1.91 eV), and a positive shift of the conduction band bottom (from −0.54 to −0.49 eV vs RHE). All of the Nb-substituted KCuTa3O9 solid solutions exhibit enhanced separation efficiency of photoinduced charge carriers, which leads to increased hydrogen evolution activity, among which KCuTa0.75Nb2.25O9 exhibits the highest hydrogen evolution rate of 2.16 μmol h−1 under the visible light irradiation (λ > 420 nm), which is approximately 7-fold higher than that of the pure KCuTa3O9. This study demonstrates the potential of modulating band structure through constructing solid solutions for efficient perovskite-like metal oxides photocatalysis.

Bismuth-rich oxyhalide (Bi7O9I3–Bi4O5Br2) solid-solution photocatalysts for the degradation of phenolic compounds under visible light

HypothesisThe development of solid-solution photocatalysts with tunable bandgaps and band structures, which are significant factors that influence their photocatalytic properties, is crucial. ExperimentsWe fabricated a series of novel bismuth-rich Bi7O9I3–Bi4O5Br2 solid-solution photocatalysts with controlled I:Br molar ratios (denoted as B-IxBr1-x, x = 0.2, 0.3, 0.4, or 0.6) via a rapid, facile, and energy-efficient microwave-heating route. The photodegradations under visible-light irradiation of the phenolic compounds (4-nitrophenol (4NP), 3-nitrophenol (3NP), and bisphenol A (BPA)), and the simultaneous photodegradation of BPA and rhodamine B (RhB) in a coexisting BPA − RhB system were investigated. FindingsThe B-I0.3Br0.7 solid solution provided the highest photocatalytic activity toward 4NP degradation, with degradation rates 32 and 4 times higher than those of Bi7O9I3 and Bi4O5Br2, respectively. The photodegradation efficiency of the studied phenolic compounds followed the order BPA (97.5%) > 4NP (72.8%) > 3NP (27.5%). The RhB-sensitization mechanism significantly enhanced the photodegradation efficiency of BPA. Electrochemical measurements demonstrated the efficient separation and migration of charge carriers in the B-I0.3Br0.7 solid solution, which enhanced the photocatalytic activity. The B-I0.3Br0.7 solid solution effectively activated molecular oxygen to produce •O2−, which subsequently produced other reactive species, including H2O2 and •OH, as revealed by reactive-species trapping, nitroblue tetrazolium transformation, and o-tolidine oxidation experiments.

Unraveling reactive oxygen species-dependent toluene mineralization routes via construction of TixSn1−xO2 infinite solid solution photocatalysts

Intermediates seriously affect the reaction process and rate in terms of kinetics. However, there are few studies on the effect of reactive oxygen species on intermediates of toluene mineralization. Herein, SnO2 and TixSn1−xO2 infinite solid solution photocatalysts are prepared and the mineralization ability of Ti0.1Sn0.9O2 is 2.7 times that of SnO2. Introduction of Ti shifts the conduction band position upward, providing thermodynamic possibility for superoxide radicals formation. The sole hydroxyl radicals over SnO2 lead to the generation of benzyl alcohol; while synergetic hydroxyl radicals and superoxide radicals result in benzoic acid existed in solid solution catalysts. Theoretical calculation confirms that benzoic acid has lower ring opening barrier, thereby improving toluene mineralization ability over TixSn1−xO2. The synergetic roles of Ti and Sn in adsorption and activation of water and toluene moleculars are also proposed. This work provides new insights into reactive oxygen radicals regulation to alter intermediates and ease toluene removal.

In situ fabrication of BiOBrxCl1−x photocatalysts with a regulated electronic structure and enhanced visible light photocatalytic performance

BiOBr1−xClx solid solution photocatalysts were constructed with a modulated band gap structure and visible light response, achieving outstanding photocatalytic RhB degradation performance.

Tuning electronic structure for enhanced photocatalytic performance: theoretical and experimental investigation of CuM1-xM'xO2 (M, M' = B, Al, Ga, In) solid solutions.

This study introduces robust screening methodology for the efficient design of delafossite CuM1-xM'xO2 solid-solution photocatalysts using band-structure engineering. The investigation not only reveals the formation rules for various CuM1-xM'xO2 solid solutions but also highlights the dependence on both lattice compatibility and thermodynamic stability. Moreover, the study uncovers the nonlinear relationship between composition and band gaps in these solid solutions, with the bowing coefficient determined by the substitution constituents. By optimizing the constituent elements of the conduction band edge and adjusting solubility, the band structure of CuM1-xM'xO2 samples can be fine-tuned to the visible light region. Among the examined photocatalysts, CuAl0.5Ga0.5O2 exhibits the highest H2 evolution rate by striking a balance between visible-light absorption and sufficient reduction potential, showing improvements of 28.8 and 6.9 times those of CuAlO2 and CuGaO2, respectively. Additionally, CuGa0.9In0.1O2 demonstrates enhanced electron migration and surpasses CuGaO2 in H2 evolution due to a reduction in the effective mass of photogenerated electrons. These findings emphasize the pivotal role of theoretical predictions in synthesizing CuM1-xM'xO2 solid solutions and underscore the importance of rational substitution constituents in optimizing light absorption, reduction potentials, and effective mass for efficient hydrogen production.

Guest Editorial: Solar Energy Utilization

Guest Editorial: Solar Energy Utilization

Dispersible CdS1−xSex solid-solution nanocrystal photocatalysts: Photoinduced self-transformation synthesis and enhanced hydrogen-evolution activity

Modulating the electronic structure of Cadmium sulfide (CdS) by non-metallic elements to produce solid-solution photocatalysts serves as a potential route to improve its performance of photocatalytic hydrogen (H2) evolution. However, exploring an effective synthetic route of CdS-based solid solution is still a great challenge. Herein, the CdS1−xSex solid-solution nanocrystals were successfully synthesized by an accessible photoinduced self-transformation route, including the direct formation of dispersible CdS1−x(SeS)x and the in situ self-transformation of selenosulfide ((SeS)2−) to Se2− by photoexcited electrons. The prepared CdS1−xSex solid-solution photocatalysts possess a small crystallite size of ca. 5 nm and their bandgaps can be easily tuned in a wide range of 1.84–2.28 eV by tailoring the mole ratio of Se/S. The resultant CdS0.90Se0.10 solid-solution photocatalyst realizes the highest H2-production tempo of 94.6 μmol·h−1, which is 1.6 folds higher than that of CdS. The experimental and theoretical studies supported that the incorporation of Se atoms could not only narrow the bandgap value to reinforce visible-light absorption, but also tune its electronic structure to optimize interfacial H2-evolution dynamics, thus achieving an efficient photocatalytic H2-production rate of the dispersible CdS1−xSex solid solution. This study may deliver advanced inspirations for optimizing the electronic structure of photocatalysts towards sustainable H2 production.

Oxygen vacancy triggering the broad-spectrum photocatalysis of bismuth oxyhalide solid solution for ciprofloxacin removal

The construction of a broad-spectrum photocatalytic system is of great significance for maximizing the utilization of solar energy. Herein, a surface oxygen vacancy triggering high-efficient broad-spectrum BiOCl0.5I0.5 solid solution photocatalyst was successfully fabricated via a one-pot solvothermal process. The UV–vis diffuse reflectance spectra revealed that the introduced oxygen vacancy appears to extend the absorption region of BiOCl0.5I0.5 to a wider wavelength range. Under λ > 580 nm light irradiation for 5 h, nearly 85.6% ciprofloxacin was degraded by BiOCl0.5I0.5 with rich oxygen vacancy, the ciprofloxacin removal efficiency was 3.4 times higher than that with less oxygen vacancy. Moreover, the density functional theory calculations and photoelectrochemical characterizations indicated the excited electrons would preferentially transfer to the new defect level induced by oxygen vacancy, thus greatly reducing the recombination of photogenerated carriers. This work tends to deepen the understanding of defect engineering in steering the construction of broad-spectrum Bi-based solid solution photocatalysts as well as its application in environmental remediation.