Z-scheme Heterojunction Research Articles

Sulfamerazine degradation employing a novel Z-scheme TiO2/KNbO3/g-C3N4 photocatalyst under artificial sunlight: Insights on degradation mechanism and toxicity

The development of a novel TiO2/KNbO3/g-C3N4 photocatalyst for the degradation of sulfamerazine under artificial sunlight was investigated in this study, aiming to obtain a highly effective material through the formation of Z-scheme heterojunctions between the proposed semiconductors. The characterizations confirmed the formation of the intended heterojunctions in the ternary composite photocatalyst, as the presence of TiO2, KNbO3, and g-C3N4 was successfully verified. Furthermore, the coupling between the semiconductors in the form of the ternary photocatalyst led to structural, morphological, and optical modifications of the TiO2 base matrix, such as a higher specific surface area and larger visible light absorption. The optimized ternary material (TiO2-5% KNbO3-0.25% g-C3N4) exhibited the highest reaction degradation capacity for the sulfamerazine (SFMZ) in both solar (86.5% degradation) and visible light (60% degradation) tests, confirming a significant enhancement over the pure TiO2, which achieved 48% degradation under solar light and 10% degradation under visible light. This result was mainly attributed to the formation of Z-scheme heterojunctions between the semiconductors, which enhanced the charge-transport efficiency during photonic excitation. Lastly, the degradation pathway proposed using mass spectroscopy analysis indicated the formation of mainly less toxic intermediates, as estimated through quantitative structure-activity relationship (QSAR) predictions.

Low dose, high function: Visible light photocatalytic performance of in-situ sensitized Ti3+/Ov self-doped rutile TiO2-x nanorods with a small amount of ultrathin g-C3N4 nanosheets

Harnessing solar energy for photocatalytic sewage purification represents a significant strategy for addressing water pollution. This study focused on synthesizing ultrathin g-C3N4 nanosheets through ultrasonic refluxing g-C3N4 aggregates in a mixture of water and triethylamine. Subsequently, Ti3+/oxygen vacancy (Ov) self-doped rutile TiO2 (TiO2-x) nanorods were synthesized via an in-situ mixed solvothermal reaction. By sensitizing a minimal quantity of these ultrathin g-C3N4 nanosheets, a Z-scheme heterojunction with reduced rutile TiO2-x nanorods was achieved. Various analytical techniques were employed, including X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), and transient photocurrent analysis. These methods determined the phase, structure, morphology, and photoelectrochemical properties of the fabricated materials. The visible light photocatalytic performance was tested using rhodamine B, methyl orange, and Cr2O72- solutions as simulated pollutants and three distinct types of actual wastewater from a pharmaceutical factory as photocatalytic degradation object. The findings revealed that Ti3+/Ov self-doping significantly enhances the visible light responsiveness of rutile TiO2. The integration of minimal amounts of ultrathin g-C3N4 nanosheets with rutile TiO2-x nanorods, formed via an in-situ mixed solvothermal reaction, effectively promoted the separation of photogenerated electrons and holes, thereby increasing the photocatalytic efficiency. Interestingly, increasing the g-C3N4 content in the mixture led to an increase in the number of defects within TiO2-x and a reduction in crystallinity. Wastewater treatments yielded varied results: wastewater containing solely phenols underwent effective photocatalytic degradation, while samples with high salt content or complex compositions proved more challenging. This study demonstrated that the heterojunction formed by sensitizing rutile TiO2-x nanorods with a small amount of ultrathin g-C3N4 nanosheets retained remarkable photocatalytic activity. These findings offer valuable insights for the design of effective photocatalysts and their application in sewage treatment.

Constructing a CeFeO3/LaFeO3/ZnIn2S4 double Z-scheme heterojunction for photocatalytic atrazine degradation under visible light irradiation

The limited light absorption range and rapid recombination of interfacial charges were deemed to be the main restriction of the photocatalysts for atrazine (ATZ) degradation, and the construction of Z-scheme heterojunction was an effective strategy. Herein, a CeFeO3/LaFeO3/ZnIn2S4 (CFO/LFO/ZIS) double Z-scheme ternary heterojunction photocatalyst was fabricated by the in-situ precipitation and hydrothermal method. The photocatalytic ATZ degradation efficiency of optimized heterojunction reached 52% within 175 min under visible light irradiation, which was 3.1, 3.7 and 1.7 times higher than that of CFO, LFO and ZIS, respectively. The enhanced photocatalytic activity was due to the excellent light capture capacity and improved photogenerated charge separation in CFO/LFO/ZIS double Z-scheme heterojunction photocatalyst. Meanwhile, some environmental factors on the influence of photocatalytic ATZ degradation performance were systematically investigated. Quenching experiments confirmed that ·OH, h+ and 1O2 were the main active species during the photocatalytic ATZ degradation process. The possible photogenerated charge separation route was proposed via the analysis of the IEF effects between CFO, LFO and ZIS. Finaly, the possible ATZ degradation pathway was deduced by LC-MS measurement and toxicity assessment of the intermediates were also evaluated by the Toxicity Estimation Software Tool (TEST). This work not only provided a potential magnetic recyclable ferrate based double Z-scheme heterojunction photocatalyst for enhancing photogenerated charge separation and light absorption, but also evaluated the intermediate toxicity and related environmental factors on the activity of photocatalyst, which was facilitating the practical application for the degradation of ATZ.

Designed construction of boosted visible-light Z-scheme TiO2/PANI/Cu2O heterojunction with elaborated photocatalytic degradation of organic dyes

A novel TiO2/polyaniline/Cu2O (T/PANI/Cu) ternary nanocomposite was synthesized via a facile in-situ polymerization of aniline and a one-step solvothermal method. The ternary nanocomposite Ti/PANI/Cu with Z-scheme heterojunction exhibited excellent photocatalytic performance as well as improved stability. The photocatalytic performance of the prepared photocatalysts (T, T/PANI, and T/PANI/Cu) was investigated by the photocatalytic decomposition of Methyl Orange dye (MO) as an organic contaminant using visible light illumination. The T/PANI/Cu ternary nanocomposite revealed the highest degradation efficiency up to 99.5% after 25 min, which is much higher than that of T (47%) and T/PANI (73%). The development of Z-scheme heterojunction is credited with the increased activity and generation of an electric field that led to an improved structure, a wider visible light response range, and a lower rate of electron-hole pair recombination. Based on trapping tests, ·O2−·OH, and h+ species were the main active species involved in the photocatalytic degradation of MO dye. Even after the fifth cycle, the T/PANI/Cu composite remained effective in the successive photocatalytic decomposition of MO, maintaining over 90% of the original degradation efficiency.

Fabrication of NiFe-LDH/MoS2 2D/2D material to construct direct Z-scheme heterojunction for enhanced CO2 photocatalytic reduction under visible light irradiation

In recent years, the utilization of solar energy for conversion of CO2 into fuels has emerged as a promising strategy for mitigating the Greenhouse effect. However, transport efficiency of photogenerated carriers plays a crucial role in determining the efficacy of CO2 photocatalytic reaction. In this paper, a 2D/2D composite material consisting of NiFe-LDH/MoS2, presenting high efficiency in separating photogenerated electron-hole pairs, has been successfully synthesized using a straightforward hydrothermal method. XRD, XPS, FTIR and other characterization results proved that the composite was successfully prepared, and its unique direct Z-scheme heterostructure improved the efficiency of CO2 photocatalytic reduction effectively. The composite material NiFe-LDH/MoS2 demonstrated enhanced rate of photo-induced electron-hole pair separation comparing with pure NiFe-LDH. Apart from this, the charge transfer resistance was reduced simultaneously, the composite material exhibited perfect photocatalytic activity. In photocatalytic reduction reaction experiment, CO yield of NiFe-LDH/MoS2 can reach 10.72 μmol/g, which is 3.93-fold and 4.17-fold that of bare NiFe-LDH and MoS2. The cyclic test also shows that the catalyst has good stability under visible light irradiation.

Solar-driven Bi6O5(OH)3(NO3)5(H2O)3/Bi2WO6 heterojunction for efficient degradation of organic pollutants: Insights into adsorption mechanism, charge transfer and degradation pathway

Actualizing controllable construction of efficient heterojunction nanocomposites remains a challenge in the field of photocatalytic water remediation, which can be got over through exploiting in-situ attachment approaches between different semiconductors. Based on this, we successfully fabricated a unique separable Z-scheme Bi6O5(OH)3(NO3)5(H2O)3/Bi2WO6 (BON/BW) nanoflowers by an in-situ growth strategy. The profitable photogenerated carriers transfer mediated by Z-scheme heterojunction greatly accelerated the generation of •O2– and •OH. The strong adsorption of 4-nitrophenols (4-NP) with parallel configuration on side Bi2WO6 in BON/BW nanocomposites also provides great convenience for subsequent degradation steps. By optimizing multiple steps in the photocatalytic reaction process, BON/BW showed far superior photodegradation performance compared to single components. The causes and consequences of 4-NP photodegradation were explored through LC-MS tests, theoretical calculations, and toxicity analysis, and a green and safe degradation pathway was proposed. More experiments have confirmed that the synthesized BON/BW composites also have excellent degradation ability against other pollutants under sunlight, demonstrating excellent universality. With any luck, the logical design of heterojunction photocatalysts for effective photocatalytic water remediation should be aided by this study.

Bi-ZFO/BMO-Vo Z-scheme heterojunction photocatalysis-PMS bidirectionally enhanced coupling system for environmental remediation

Given the urgency of organic pollutant removal and the low efficiency of advanced oxidation processes (AOPs), a novel Bi-ZFO/BMO-Vo photocatalyst was fabricated via the solvothermal method. A coupling system was constructed to combine photocatalysis with peroxymonosulfate (PMS) oxidation processes, which synergistically degrade organic pollutants. Bi-ZFO/BMO-Vo exhibited excellent photocatalytic performance, which could remove 100 % RhB in 110 min and degrade 100 % MG in 70 min, and 88 % H-TC in 50 min. The excellent catalytic performance of Bi-ZFO/BMO-Vo was not only attributed to the synergistic effect of PMS activation and photocatalysis, but also attributed to the SPR effect of Bi nanoparticles, electron capture of oxygen vacancies, and intense contact of Bi-ZFO/BMO-Vo heterojunctions. The active species capture experiments and EPR tests indicated that 1O2, SO4–·, ·OH, and O2–· worked together for the RhB removal. The degradation intermediates of RhB were identified by LC-MS. Based on the experimental results, the band structure and Z-scheme charge transfer mechanism were proposed. Toxicity evaluation indicated that Bi-ZFO/BMO-Vo-Vis/PMS could significantly reduce RhB toxicity. This efficient and stable catalyst is expected to be used in organic wastewater degradation and practical applications.

Efficient photodegradation of antibiotics by g-C3N4 and 3D flower-like Bi2WO6 perovskite structure: Insights into the preparation, evaluation, and potential mechanism

Antibiotics are emerging organic pollutants that have attracted huge attention owing to their abundant use and associated ecological threats. The aim of this study is to develop and use photocatalysts to degrade antibiotics, including tetracycline (TC), ciprofloxacin (CIP), and amoxicillin (AMOX). Therefore, a novel Z-scheme heterojunction composite of g-C3N4 (gCN) and 3D flower-like Bi2WO6 (BW) perovskite structure was designed and developed, namely Bi2WO6/g-C3N4 (BW/gCN), which can degrade low-concentration of antibiotics in aquatic environments under visible light. According to the Density Functional Theory (DFT) calculation and the characterization results of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FITR), Scanning electron microscopy - energy spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS), this heterojunction was formed in the recombination process. Furthermore, the results of 15 wt%-BW/gCN photocatalytic experiments showed that the photodegradation rates (Rp) of TC, CIP, and AMOX were 92.4%, 90.1% and 82.3%, respectively, with good stability in three-cycle photocatalytic experiments. Finally, the quenching experiment of free radicals showed that the holes (h+) and superoxide radicals (·O2−) play a more important role than the hydroxyl radicals (·OH) in photocatalysis. In addition, a possible antibiotic degradation pathway was hypothesized on the basis of High performance liquid chromatography (HPLC) analysis. In general, we have developed an effective catalyst for photocatalytic degradation of antibiotic pollutants and analyzed its photocatalytic degradation mechanism, which provides new ideas for follow-up research and expands its application in the field of antibiotic composite pollution prevention and control.

CdS@NiCr-LDH Z-scheme heterojunction with high adsorption–photocatalysis for uranium(VI) removal without any sacrificial agent

The use of photocatalysis for the removal of U(VI) has the advantages of being green, eco-friendly and sustainable. It is common practice to enhance the photocatalytic activity of photocatalysts by adding sacrificial agents, however, this is uneconomical and contrary to the vision of carbon neutrality and carbon peak in the world. Herein, we fabricate a Z-scheme heterojunction for the photocatalytic removal of uranium (VI) based on CdS nanorods@NiCr layered double hydroxide (CdS@NiCr-LDH). Excellent photocatalytic efficiencies and removals were achieved under visible light irradiation without any sacrificial agent. The optimum uranium(VI) removal rate of CdS@NiCr-LDH was 0.057 min‐1, which was 6.3 and 5.0 times higher than that of CdS and NiCr-LDH, respectively. In particular, the U(VI) removal amount over CdS@NiCr-LDH reached 2246.14 mg g−1. The CdS@NiCr-LDH heterojunction creates a narrower energy band gap (Eg = 2.06 eV), which is more favorable for visible light absorption, according to UV–vis DRS results. According to ESR and DFT calculations, possesses an intrinsic electric field between NiCr-LDH and CdS composite that efficiently prevents electron-hole complexation, resulting in highly efficient removal of U(VI) under visible light irradiation without the need of sacrificial agents. This work lays the foundation for research on photocatalytic U(VI) treatment by CdS@NiCr-LDH in wastewater.

Construction of functionalized In-based metal organic framework/BiOCl1−xIx Z-scheme heterojunction for efficient photocatalytic degradation of tetracycline: Performance and mechanism

The environmental implications of antibiotics have drawn widespread attention. Numerous monomer-based bismuth oxide halide catalysts have been extensively studied to remove tetracycline (TC) from aquatic environments. Integrating bismuth oxide halide composites with In-based metal organic framework (NH2-MIL-68(In)) might potentially serve as a novel strategy. By meticulously adjusting Cl and I within the composite bismuth halide oxide (B-x), a suite of purpose built heterojunctions (NMB-x) were synthesized, which were engineered to facilitate the efficient photodegradation of TC in simulated and actual aquatic environments. The incorporation of Z-scheme heterojunctions yielded a significant enhancement in photocatalytic responsiveness and charge carrier separation. Notably, NMB-0.3 demonstrated remarkable TC removal efficiency of 88.52 ± 3.05%, which is 3.74 times of B-0.3 within 90 min. The apparent quantum yield was also increased from 8.97% (B-0.3) to 19.68% (NMB-0.3). The removal of TC from natural water bodies was also assessed. Moreover, the photocatalyst concentration, assessed using response surface method, was found to show influential factors on TC removal. In addition, density functional theory (DFT) simulations were employed to identify vulnerable sites within TC. Intermediates and pathways in the photodegradation of TC have also been inferred. Furthermore, a comprehensive environmental toxicity assessment of representative intermediates demonstrated that these intermediates exhibited significantly reduced environmental toxicity compared to TC. This study provides a new approach to the design strategy of efficient and environmentally friendly MOF-based photocatalysts.

Engineering MOF-derived 2D NPC-TiO2 nanotablet/3D marigold-like ZnIn2S4/CdS nanoparticles dual Z-scheme heterojunction with excellent photoelectric performance: A novel material for sensitive and facile photoelectrochemical sensing detection of mercury ions in aqueous environments by ion-exchange sensing strategy

Herein, a new NH2-MIL-125-derived 2D nitrogen-doped porous carbon-titanium dioxide (NPC-TiO2) nanotablet/3D marigold-like ZnIn2S4/CdS nanoparticles (NPs) dual Z-scheme heterojunction was first exploited for photoelectrochemical (PEC) measurement of mercury ions (Hg2+). Taking NH2-MIL-125 as precursor, the 2D NPC-TiO2 nanotablet was prepared by calcination. The 3D marigold-like ZnIn2S4 and CdS NPs were synthesized by hydrothermal method and aqueous synthesis way, respectively. The acquired NPC-TiO2, ZnIn2S4 and CdS were sequentially modified on the indium tin oxide (ITO) electrode to form the PEC sensing interface by layer-by-layer assembly. Due to the matched band-edge levels, and strong light-harvesting ability, the given heterostructure on ITO electrode generated a large photocurrent. Importantly, it was found that 2D NPC-TiO2 nanotablet/3D marigold-like ZnIn2S4/CdS NPs dual Z-scheme heterojunction could show specifically increased photocurrent signal towards to Hg2+ by employing CdS NPs as Hg2+-recognition probe with selective Cd-to-Hg ion-exchange, resulting from the in-situ formation of the new quaternary NPC-TiO2/ZnIn2S4/CdS/HgS heterostructure to further facilitate the spatial transmission and separation of charges. As a result, Hg2+ was highly sensitively detected with a low detection limit of 20 fM. This PEC sensor was also verified by evaluating Hg2+ in tap water, river water and lake water, demonstrating great application prospect for environment pollutant measurement.

Efficient photocatalytic molecular oxygen activation by TTF-based heterojunction for water purification

Tetrathiafulvalene (TTF), one of the well-known organic photoelectric materials, was served as active sites to accelerate the activation of molecular oxygen to degrade organic pollutants. Herein, a kind of Z-scheme heterojunction photocatalysis was constructed based on g-C3N4 and TTF. According to the experimental results, the mechanism of Z-scheme heterojunction was supported, in which photogenerated electrons transferred from g-C3N4 to TTF. More importantly, TTF on the catalyst surface could serve not only as electron donor, but also as the terminal active site to transfer photoexcited electrons to adsorbed oxygen molecules, producing mass of ⋅O2–. Meanwhile, the activation rate constant of TCN-5 for RhB was 0.0624 min−1, which was 10 and 5 times of g-C3N4 and TTF, respectively. In addition, the results of EPR spectra, rotating disk electrode measurement and molecular oxygen activation measurement also demonstrated that this catalyst was energetically favorable to generate ⋅O2– through the single-electron reduction pathway of molecular oxygen. Finally, four possible photodegradation routes for RhB were proposed based on the results of HPLC-MS. This work provides a new insight on the application of organic photoelectric materials in the purification of wastewater by the molecular oxygen activation.

Efficient Homojunction/Heterojunction Photocatalyst via Integrating CsPbBr3 Quantum Dot Homojunction with TiO2 for Degradation of Organic Dyes.

A novel TiO2-CsPbBr3(Q) photocatalyst is proposed and rationally constructed, where CsPbBr3 perovskite quantum dots (QDs) of various sizes inside mesopore TiO2 (M-TiO2) are integrated. These perovskite QDs, generated in situ within M-TiO2, establish a type-II homojunction. Interestingly, a Z-scheme heterojunction is simultaneously formed at the interface between CsPbBr3 and TiO2. Due to the coexistence of the type-II homojunction and the Z-scheme heterojunction, photogenerated electrons are effectively transferred from TiO2 to CsPbBr3, thereby suppressing carrier recombination and thus enhancing the degradation of rhodamine B (RhB). Compared with pure CsPbBr3 and TiO2, TiO2-CsPbBr3(Q) shows significantly enhanced photocatalytic performance for RhB degradation. The degradation efficiency of RhB in the presence of the TiO2-CsPbBr3(Q) attains 97.7% in 5 min under light illumination, representing the highest efficiency observed among photocatalysts based on TiO2. This study will facilitate the development of superior semiconductor catalysts for photocatalytic applications.

ZnCdS nanoparticles decorated three-dimensional MoO3 polygonal structure: A novel photocatalyst for enhanced solar light-driven degradation of methyl orange dye

Over the last few decades, organic dyes have been identified in trace levels in surface water, effluent, and drinking water. Photocatalysis has received enormous attention for its ability to degrade organic dyes in water. The present study includes the synthesis and characterization of a novel ZnCdS/MoO3 composite which was synthesized using a facile precipitation method. Its structural, morphological, and optical characteristics were examined through various spectroscopic and analytical techniques. Sphere-like nanoparticles of ZnCdS were well decorated on the surface of the three-dimensional polygonal structure of MoO3 which consists of stacked nanosheets. The energy band gaps of ZnCdS and MoO3 were found to be 2.52 eV and 2.19 eV, respectively which were favorable to form a Z-scheme heterojunction between both the components. As an effective photocatalyst, the synthesized ZnCdS/MoO3 composite exhibited optimum degradation (90.3%) of methyl orange dye which was found to be 3.22 and 13.48 times higher than pure ZnCdS and MoO3, respectively. The enhanced photocatalytic activity of ZnCdS/MoO3 was attributed mainly to the efficient separation and migration of electrons and holes across the Z-scheme heterojunction. A scavenger study was also conducted to assess the role of major radical species in the decomposition of methyl orange dye in which superoxide radicals (•O2-) demonstrated a major role. Therefore, the present study provides an effective strategy to develop polygonal structured MoO3 anchored photocatalytic materials for the enhanced removal of harmful pollutants in an aqueous phase.

Synergistic CdS@CeO2 nanocomposites: Harnessing Z-scheme electron transfer for enhanced photocatalytic CO2 conversion and aqueous Cr(VI) reduction

The present work describes the fabrication of CdS-D@CeO2 Z-scheme heterojunctions as highly stable, efficient and recyclable photocatalysts for the visible light assisted reduction of CO2 to methanol as well as Cr(VI) to Cr(III). The bare CeO2 produced methanol with the rate of 111 μmolh−1g−1 that is much lower in comparison to CdS-D@CeO2 (501 μmolh−1g−1). In addition, the photocatalytic efficiency remained nearly same for three successive runs, indicating the higher stability and recycling ability of the heterojunctions CdS-D@CeO2. It was also observed that under direct sunlight irradiation, CdS-D@CeO2 efficiently reduced 100% Cr(VI) to Cr(III) in an aqueous medium in just 40 minutes. Moreover, >95% removal was maintained even after 5 catalytic cycles. Additionally, for mimicking real contaminated water samples, the influence of the foreign ions on Cr(VI) reduction was evaluated by using lake water sample and no adverse effects on the result were observed. Thus, this work showed a way to develop cost-effective, easily synthesized, durable and recyclable composite photocatalysts for CO2 utilization and proficient removal of waste water pollutants by employing the clean, green, and renewable solar energy.

Direct Z-scheme charge transfer Bi2O3/UiO-66-NH2 heterojunctions for boosted photocatalytic degradation of tetracycline hydrochloride in different water systems

The development of hybrid heterostructure photocatalysts with enhanced visible light absorption capacity holds significant importance in environmental remediation. However, the challenge persists in exploiting strong visible-light responsive photocatalysts with both high efficiency and stability. Herein, we successfully synthesized a hybrid Z-scheme heterojunction of Bi2O3 and UiO-66-NH2 (Bi2O3/UiO-66-NH2) through a simple hydrothermal route. The visible light photocatalytic performance of Z-scheme Bi2O3/UiO-66-NH2 heterojunction is systematically evaluated for persistent antibiotic tetracycline hydrochloride (TC-HCl) both in the clean and real water matrix. All heterojunction catalysts exhibit superior photodegradation capabilities compared to pristine Bi2O3 and UiO-66-NH2. The optimal ratio of the two components heterojunction (BUN-150), in particular, demonstrates the highest removal efficiencies for TC-HCl (95 %) within a 90-min timeframe. This remarkable photocatalytic performance is credited to the Z-scheme charge transfer occurring at the interface of Bi2O3 and UiO-66-NH2 in Bi2O3/UiO-66-NH2 heterojunction. The active species experiments and electron paramagnetic resonance analyses are conducted to identify the active reactive species during the TC-HCl degradation (·OH, h+, and ·O2−), and a precise photocatalytic degradation mechanism is explained. Additionally, the photodegradation intermediates of TC-HCl are detected using the HPLC-MS analysis to explain the degradation pathways of TC-HCl. This research paves the way for the development of novel Z-scheme Bi2O3-based heterojunction catalysts for outstanding photocatalytic applications.

Sub-Band Assisted Z-Scheme for Effective Non-Sacrificial H2O2 Photosynthesis.

Photosynthesis of H2O2 from earth-abundant O2 and H2O molecules offers an eco-friendly route for solar-to-chemical conversion. The persistent challenge is to tune the photo-/thermo- dynamics of a photocatalyst toward efficient electron-hole separation while maintaining an effective driving force for charge transfer. Such a case is achieved here by way of a synergetic strategy of sub-band-assisted Z-Scheme for effective H2O2 photosynthesis via direct O2 reduction and H2O oxidation without a sacrificial agent. The optimized SnS2/g-C3N4 heterojunction shows a high reactivity of 623.0µmolg-1h-1 for H2O2 production under visible-light irradiation (λ>400nm) in pure water, ≈6 times higher than pristine g-C3N4 (100.5µmolg-1h-1). Photodynamic characterizations and theoretical calculations reveal that the enhanced photoactivity is due to a markedly promoted lifetime of trapped active electrons (204.9ps in the sub-band and >2.0ns in a shallow band) and highly improved O2 activation, as a result of the formation of a suitable sub-band and catalytic sites along with a low Gibbs-free energy for charge transfer. Moreover, the Z-Scheme heterojunction creates and sustains a large driving force for O2 and H2O conversion to high value-added H2O2.

Photoelectrochemically converting CO2 over Z-scheme heterojunction CoPc/K7HNb6O19 with high Faraday efficiency

Photoelectrochemically converting CO2 into the high value-added chemicals and fuels is a hopeful sustainable energy conversion and storage road to alleviate the energy crisis and global warming. In this study, CoN-x Z-scheme heterojunctions were prepared by coupling CoPc with K7HNb6O19 rich in oxygen vacancy with a low-temperature calcination, and used for photoelectrocatalytic (PEC) reduction of CO2 to CO. The prepared heterojunctions demonstrate Faraday efficiency of >90 % and TOF values over a wide voltage range (−0.65 ∼ −1 V vs. RHE). The superior PEC CO2 reduction performance is mainly attributed to the designed Z-scheme heterojunction, which endows a built-in electric field to the interface of the two semiconductors, benefiting the separation of electrons and holes greatly. Additionally, the oxygen vacancy from K7HNb6O19 provides an alternative pathway for CO2 adsorption and activation, and simultaneously the incorporated K7HNb6O19 inhibits the aggregation of cobalt phthalocyanine molecules, which is beneficial for the stability of PEC catalysts. Density-functional-theory (DFT) calculation also elucidates a favorable CO2 activation energy over CoPc coupling oxygen-vacancy-rich K7HNb6O19 heterojunctions. This work may provide a viable pathway for the rational designing of efficient PEC systems to reduce CO2 to valuable fuels.

In situ synthesis of three-dimensional flower-like TiO2/WO3 heterojunction: Enhanced visible photocatalytic properties and theoretical calculations

The construction of heterojunction photocatalysts is an excellent strategy for treating wastewater. Herein, a three-dimensional nanoflower-like TiO2/WO3 heterojunction photocatalyst was synthesized in situ on the surface of pure Ti substrate by plasma electrolyte oxidation (PEO) combined with a subsequent process, and the abundant network topology and lattice defects improved the adsorption performance of the photocatalyst. The construction of Z-scheme heterojunction not only promotes the separation of photogenerated carriers, but also enhances the light absorption ability and greatly improves the photocatalytic performance of photocatalysts. Under the synergistic effect of adsorption and photocatalysis, the degradation rate of MB reached 86.2 % in 2 h, which was significantly higher than that of the single-component photocatalyst. Finally, the synthesis of TiO2/WO3 heterojunction photocatalysts by this process and the reaction mechanism of heterojunction photocatalysts for the degradation of organic dyes were illustrated by combining experiments and DFT calculations. In conclusion, this study opens up a new process for synthesizing Z-scheme heterojunction photocatalysts, which brings new insights for photocatalytic treatment of water pollution.

Heterogeneous CuS QDs/BiVO4@Y2O2S Nanoreactor for Monitorable Photocatalysis.

Exploration of multifunctional integrated catalysts is of great significance for photocatalysis toward practical application. Herein, a 1D confined nanoreactor with a heterogeneous core-shell structure is designed for synergies of efficient catalysis and temperature monitoring by custom encapsulation of Z-scheme heterojunction CuS quantum dots/BiVO4 (CuS QDs/BiVO4) and Y2O2S-Er, Yb. The dispersed active sites created by the QDs with high surface energy improve the mass transfer efficiency, and the efficient electron transport channels at the heterogeneous interface extend the carrier lifetime, which endows the nanoreactor with excellent catalytic performance. Meanwhile, real-time temperature monitoring is realized based on the thermally coupled levels 2H11/2/4S3/2→4I15/2 of Er3+ using fluorescence intensity ratio, which enables the monitorable photocatalysis. Furthermore, the nanoreactor with a multidimensional structure increases effective intermolecular collisions to facilitate the catalytic process by restricting the reaction within distinct enclosed spaces and circumvents potential unknown interaction effects. The design of multi-space nanoconfined reactors opens up a new avenue to modulate catalyst function, providing a unique perspective for photocatalytic applications in the mineralization of organic pollutants, hydrogen production, and nitrogen fixation.