Z-scheme Charge Transfer Mechanism Research Articles

A hybrid MOFs/Ti-Fe2O3 Z-scheme photoanode with enhanced charge separation and transfer for efficient photoelectrochemical water oxidation

The construction of Z-scheme charge transfer pathways simulating natural photosynthesis is considered a promising method for improving reaction driving forces. Here, we modified the surface of titanium doped Fe2O3 (Ti-Fe2O3) nanorods with NH2-MIL-125(Ti) (Ti-MOFs) and a promising organic-inorganic hybrid Z-scheme NH2-MIL-125(Ti)/Ti-Fe2O3 was successfully prepared. At 1.23 V vs. RHE, the photocurrent density of the composite photoanode reaches 2.67 mA/cm2, which is 5 times higher than that of Ti-Fe2O3. The results of surface photovoltage, ESR and fs-TAS indicate that this improvement is mainly due to the effective Z-scheme charge transfer mechanism providing a strong driving force for charge separation and transport, greatly suppressing carrier recombination and allowing carriers with strong oxidation ability to participate in water oxidation. Meanwhile, NH2-MIL-125(Ti) can enhance light absorption and reduce the surface defect state of Ti-Fe2O3. This study not only provides a feasible approach for the photoanode water splitting of traditional inorganic semiconductor/MOF based heterostructures, but also provides rich and effective means for revealing Z-scheme charge transfer mechanism in depth.

Piezo-enhanced photocatalysis of MoS2/Bi4O5Br2/PVDF-HFP film for wastewater purification

To date, the piezoelectric field has been demonstrated as a promising approach to inhibit the recombination of photogenerated carrier in photocatalyst applications. Herein we propose a MoS2/Bi4O5Br2/PVDF-HFP piezo-photocatalytic film in the organic pollutants remediation. MoS2/Bi4O5Br2 as the photocatalytic material is incorporated to poly (vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP) as the supporting layer via a simple phase transition method. The polarised electric field generated on PVDF-HFP and MoS2/Bi4O5Br2 under aeration synergised with the built-in electric field formed between MoS2/Bi4O5Br2 Z-scheme heterojunction to promote the interfacial charge transfer. The degradation rates of rhodamine B (RhB) and tetracycline hydrochloride (TC) under aeration and visible light irradiation in 60 min reached 98.9% and 92.2%, respectively. Meanwhile, density functional theory calculations (DFT) further demonstrated the effective charge separation and transfer induced by the Z-scheme charge transfer mechanism constructed by MoS2 composite with Bi4O5Br2, as well as the synergistic effect of the double electric field in favour of suppressing carrier recombination. This work provides an interesting solution for effectively combining piezoelectric catalysis with photocatalysis.

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 photocatalytic CO2 reduction achieved by constructing Bi4O5Br2/Bi-MOF Z-scheme heterojunction

Building efficient catalysts is an urgent issue in the field of photocatalytic CO2 reduction, and Z-scheme heterojunction structures can availably suppress the recombination of photo generated carriers and improve photocatalytic performance. This study successfully prepared a new type of Bi4O5Br2/Bi-MOF composite photocatalyst through self-assembly method. After 5 h of simulated sunlight exposure, the optimized sample 50-Bi4O5Br2/Bi-MOF photocatalytic reduction of CO2 to CO efficiency (23.78 μmol·g−1·h−1) was 5.09 times higher than pure Bi4O5Br2, and the CH4 yield (5.39 μmol·g−1·h−1) was 2.52 times that of pure Bi-MOF. In addition, in the cyclic experiment, the catalyst had high stability and reusability. The Z-scheme charge transfer mechanism was confirmed through band structure analysis, Electron spin resonance (ESR), Ultraviolet photoelectron spectroscopy (UPS) and other related characterizations. This work provided an important strategy for designing efficient Z-scheme heterojunction photocatalysts.

BaTi0.85Zr0.15O3/MOF-5 nanocomposite: Synthesis, characterization and photocatalytic activity toward tetracycline

It has been proposed that oriented anchoring strategies can be used to organize BaTi0.85Zr0.15O3 (BTZ) quantum dots (QD) with MOF-5 to provide highly efficient catalytic degradation of tetracycline (TC). This study presents the preparation of [Zn4O (BDC)3] (BDC = benzene-1,4dicarboxylate) metal–organic framework-5 (MOF-5)/BTZ nanocomposites by a facile one-pot solvent-thermal precipitation method. The as-synthesized samples were identified by XRD, TG-DTG, UV–VIS DRS, FESEM, FTIR, BET, TEM, PL, and EDX characterization techniques. The photocatalytic ability of nanocomposite BTZ (30 %wt)/MOF-5 was particularly impressive among the binary photocatalysts. In a 10 ppm solution of TC, BTZ (30 wt%)/MOF-5 demonstrated superior photodegradation activity, with 95 % degradation efficiency of TC determined by HPLC. The best response was achieved at pH 11 with catalyst dosages of 0.2 g/L, irradiation time of 150 min, and CTC of 10 ppm. An internal electric field was suggested to mediate the direct Z-scheme charge transfer mechanism between BTZ and MOF-5. The improvement was achieved by fabricating BTZ and MOF-5 in an indirect Z-scheme heterojunction system. Photogenerated electron-hole separation can be accelerated by BTZ/MOF-5 with improved redox capabilities. Overall, taking advantage of an enhanced redox capacity under ultraviolet (UV) light irradiation, this study demonstrates how to promote efficient antibiotic degradation using MOF-based nanocomposites. Moreover, photodegradation kinetics were studied using the Hinshelwood formula, giving 0.0113 min−1 (slope) and 61.32 min as t1/2. In the COD experiment, mineralized TC molecules had y = -0.0144 + 0.0444x, r2 = 0.9942, and k = 0.0144 min−1 (t1/2 = 48.12 min).

Efficient hierarchical ZIF-based electro/photocatalyst toward hydrogen generation and evolution

In this study, a well-designed hierarchical BiFeO3/ZIF-67 (BFO-ZIF) composite was successfully synthesized to improve the performance of photocatalytic hydrogen generation in comparison to bare BiFeO3 and ZIF-67. Moreover, the behavior of the resultant electrocatalysts was also investigated in the hydrogen evolution reaction (HER). The synthesized electro-photocatalysts were characterized by various physical and photo/electrochemical analyses. The remarkable outcomes of the composite with 50 wt% of ZIF-67 in hydrogen generation correspond to the high specific surface area of the photocatalyst concurrently with the formation of active sites and new charge channels, leading to a modified charge transfer pathway and lower electron-hole recombination. The maximum H2 generation rate over the optimal BFO-ZIF composite (BFO-ZIF(50)) attained 1617 μmol g−1 h−1 during visible light exposure, surpassing the rates observed for pure BFO and ZIF-67. Furthermore, the BFO-ZIF(50) electrocatalyst, with the onset potential of −0.089 V, resulted in an overpotential of −0.19 V at a current density of 10 mA cm−2, while a Tafel slope of 81.6 mV dec−1 in 1.0 M KOH showed the highest activity. The elevated photocatalytic hydrogen generation and improved HER performance of the developed catalysts signify a synergistic effect resulting from the junction and the Z-scheme charge transfer mechanism between the ZIF-67 and BFO nanomaterials. This introduces the BFO-ZIF composite as an efficient photocatalyst and electrocatalyst for hydrogen generation and evolution reaction.

Carbon based cobalt titanate perovskite nanocomposite: Synthesis, characterization, and excellent visible light driven photocatalytic performance

Titanium-based perovskite oxides are the promising photocatalysts for an efficient degradation of organic pollutants. However, charge carriers recombination and wide band gap energy are still the main challenges in their visible-light-driven photocatalytic applications of Titanate perovskites, ATiO3. The immobilization of Titanium-based perovskites on a carbonaceous substrate such as nitrogen-rich carbon nitride, can be considered as an excellent option for enhancing photocatalytic performance. Here, the CoTiO3/C3N5 nanocomposite was synthesized by simple reflux method and used for photocatalytic degradation of three organic pollutants including methylene blue (MB), tetracycline hydrochloride (TC), and bisphenol A (BPA). The results indicated that the photocatalytic activity of the CoTiO3 perovskite was considerably improved by introducing C3N5 nanosheets and fabricating CoTP/C3N5 nanocomposite. The crystalline structure of CoTiO3/C3N5 (CoTP/C3N5) nanocomposites was confirmed successfully by XRD analysis. The specific surface area of the synthesized CoTP/C3N5 nanocomposite was 8.15 m2/g calculated by N2 adsorption–desorption technology. In the 60th minute of the photocatalytic process, the degradation efficiency of MB, TC, and BPA by CoTP/C3N5 were obtained as 98.70, 60.33, and 92.90 %, respectively, which were higher than pristine CoTiO3 nanorods and C3N5 nanosheets. Electrochemical impedance analysis shows that the CoTP/C3N5 nanocomposite has good electrochemical performance. The improvement photocatalytic activity CoTP/C3N5 can be attributed to the suppressing the recombination of photogenerated electrons and holes and good electrochemical performance with high electron transfer capability. The results achieved from UV–Visible Diffused Reflectance Spectroscopy (DRS), mott-schottky measurements and the photocatalytic degradation experiments in the presence of scavengers confirmed the significantly accelerating the Z-scheme charge transfer mechanism where photoexcited carriers can migrate between CoTiO3 perovskite and C3N5 nanosheets.

A novel Z-scheme heterojunction photocatalyst CeO2@WO3 nanocomposite with enhanced visible-light photocatalytic performance for wastewater treatment by cephalexin antibiotic degradation: Process optimization

Considering growing global environmental concerns, there is a heightened focus on expediting the synthesis of highly efficient catalytic materials to address these challenges effectively. Herein, a novel CeO2@WO3 heterojunction photocatalyst was synthesized using an ultrasonic-assisted method for the environmentally friendly degradation of cephalexin (CPX) under visible light. The optimized photocatalyst synthesis condition was achieved by assessing the influence of effective parameters, including the CeO2 content (5–25 wt%) and calcination temperature (300–600 °C), employing the RSM method. The synthesized photocatalysts were comprehensively characterized through XRD, SEM, TEM, EDS-mapping, BET, FTIR, and UV–Vis band gap analysis. Using optimal photocatalyst (CeO2 content: 15.78 %, calcination temperature: 440.59 °C, and ultrasonic power: 80 W), the influence of four critical variables on CPX degradation was thoroughly investigated via RSM-CCD. The maximum CPX degradation efficiency of 98.8 % was attained under the following optimal conditions: CPX concentration: 20.00 mg/L, solution pH: 6.79, photocatalyst dosage: 0.019 g/L, and visible light time: 94.82 min. Statistical analysis confirmed the accuracy of the regression model based on empirical data. The CeO2@WO3 heterojunction demonstrated substantial Chemical Oxygen Demand (COD) removal, reaching 73.26 % during the mineralization of CPX, surpassing the outcomes of previous studies. Trapping experiments and EPR analysis indicated the crucial involvement of hydroxyl radicals and superoxide radicals as highly active species due to their non-selective oxidation capabilities. Furthermore, a Z-scheme charge transfer mechanism was proposed to elucidate the enhanced photocatalytic activity. Identifying degradation intermediates was accomplished through HPLC-MS analysis, leading to a plausible pathway for CPX degradation. Overall, CeO2@WO3 exhibited excellent stability and could endure five cycles with minimal cerium leaching, highlighting its effectiveness in decomposing organic contaminants.

Photocatalytic degradation of rhodamine B over Z-scheme photocatalyst BiFeO3/3DOM-TiO2-x in a fixed-bed reactor

In this work, a Z-scheme BiFeO3/3DOM-TiO2-x photocatalyst was synthesized using a hydrothermal method and extensively evaluated for its photocatalytic capabilities in the rhodamine B (RhB) degradation within a fixed-bed reactor. The results demonstrated the synergistic effects of enhanced visible light absorption, a Z-scheme charge transfer mechanism, oxygen vacancies, and unique three-dimensional ordered macropore structure, which collectively enhance the photocatalytic activity of BiFeO3/3DOM-TiO2-x. The active groups responsible for RhB degradation included hydroxyl radicals (•OH), hole (h+), and reactive superoxide radical (•O2−), of which •O2− played a predominant role in RhB photodegradation. A kinetic model of dye degradation in a fixed-bed reactor was proposed, providing a realistic description of RhB degradation.

Rational construction of carbon-rich g-C3N4 wrapped over CePO4 nanorods: Oxygen vacancy mediated 1D/2D Z-scheme photocatalyst towards removal of congo red dye

The rational construction of Z-scheme photocatalysts is an effective way for separating charge carriers and has gained great interest due to the potential to alleviate energy as well as environmental challenges. Here, oxygen vacancy mediated CePO4/g-C3N4 Z-scheme nanocomposite photocatalyst was developed with different mass concentration of carbon rich g-C3N4 by grinding-calcination method. The study reveals the improved crystal quality, large surface area and intimate line-to-face contact of nanocomposite essential for electronic transition between CePO4 and g-C3N4. The presence of vacancy was studied by X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. The total removal percentages of CR dye over CePO4/g-C3N4 (38 wt%) nanocomposite were 85% and 99% with reaction rates 3.7 and 2.8 times greater than that of pure g-C3N4 under visible and solar irradiation, respectively, and nanocomposite demonstrated good recycle stability. The superoxide radicals were found to be the main reactive species that participated dominantly in the reaction. From band structure, PL and radical trapping experiments, a Z-scheme charge transfer mechanism was proposed. The causes of improved degradation could be the result of enhanced crystal quality, improved surface area and a delay in charge carrier recombination via the Z-scheme process. This study gives a good foundation for building Z-scheme heterojunctions and sheds light to create highly active photocatalysts.

Construction of Z-scheme AgCl/BiOCl heterojunction with oxygen vacancies for improved pollutant degradation and bacterial inactivation.

A facile Z-scheme AgCl/BiOCl heterojunction photocatalyst with oxygen vacancies was fabricated by a water-bath method. The structural, morphological, optical and electronic properties of as-synthesized samples were systematically characterized. The oxygen vacancies were confirmed by EPR, which could optimize the band-gap of the AgCl/BiOCl heterojunction and improve the photo-induced electron transfer. The optimized AgCl/BiOCl heterojunction showed excellent photocatalytic degradation efficiency (82%) for tetracycline (TC). Simultaneously, E. coli was completely inactivated within 60 min due to the AgCl/BiOCl heterojunction. The elevated catalytic activity of the optimal AgCl/BiOCl heterojunction was ascribed to the synergistic effect of the enhanced light absorption and effective photoinduced charge carrier separation and transfer. Moreover, the degradation efficiency of the AgCl/BiOCl heterojunction towards ofloxacin, norfloxacin and Lanasol Red 5B was 73%, 74% and 96%, respectively. The experimental factors for the degradation efficiency of TC were also studied. Furthermore, active species trapping experiments indicated that superoxide radicals (˙O2-) were the main reactive species, and the Z-scheme charge transfer mechanism helped to improve the photocatalytic activity.

Augmented photocatalysis induced by 1T-MoS2 bridged 2D/2D MgIn2S4@1T/2H-MoS2 Z-scheme heterojunction: mechanistic insights into H2O2 and H2 evolution.

In the realm of composite photocatalysts, the fusion of the co-catalyst effect with interfacial engineering is recognized as a potent strategy for facilitating the segregation and migration of photo-induced charge carriers. Herein, an innovative mediator-based Z-scheme hybrid, i.e. MIS@1T/2H-MoS2, has been well designed by pairing MIS with 1T/2H-MoS2via a facile hydrothermal strategy as a competent photocatalyst for H2O2 and H2 generation. The co-catalyst, i.e. metallic 1T-phase bridging between semiconducting 2H-MoS2 and MIS, serves as a solid state electron mediator in the heterostructure. Morphological findings revealed the growth of 1T/2H-MoS2 nanoflowers over MIS microflowers, verifying the close interaction between MIS and 1T/2H-MoS2. By virtue of accelerated e-/h+ pair separation and migration efficiency along with a proliferated density of active sites, the MMoS2-30 photocatalyst yields an optimum H2O2 of 35 μmol h-1 and H2 of 370 μmol h-1 (ACE of 5.9%), which is 3 and 2.7 fold higher than pristine MIS. This obvious enhancement can be attributed to photoluminescence and electrochemical aspects that substantiate the diminished charge transfer resistance along with improved charge carrier separation, representing a good example of a noble metal-free photocatalyst. The proposed Z-scheme charge transfer mechanism is aided by time-resolved photoluminescence (TRPL), XPS, radical trapping experiments, and EPR analysis. Overall, this endeavour provides advanced insights into the architecture of noble metal-free Z-scheme heterostructures, offering promising prospects in photocatalytic applications.

Direct Z-scheme In2S3@BiYWO6 heterojunction photocatalysts for highly efficient environmental remediation

Novel In2S3@BiYWO6 heterojunction photocatalysts were designed and synthesized by a simple two-step hydrothermal method, which exhibit extremely excellent photocatalytic activity for degrading the residual antibiotics in wastewater. Especially, In2S3@BiYWO6 composite with mass ratio of 10:1 shows the highest photo-degradation efficiency towards Tetracycline Hydrochloride, which is about 2.46 and 7.55 times than that of pristine In2S3 and BiYWO6, respectively. A direct Z-scheme charge transfer mechanism was demonstrated in these heterojunctions through the XPS analysis, radical species trapping experiments and fluorescence detection. Within the framework of this mechanism, the critical built-in electric field (Ei) formed at the contact interface between In2S3 and BiYWO6 spatially separates reduction or oxidation sites and thus preserves the photogenerated carriers with stronger redox ability on reaction sites, which ultimately enhances the photocatalytic activity of the heterojunction catalysts. It is commendable that such Z-scheme heterostructures between In2S3 and BiYWO6 exist in a wide span of component ratios (from 5:1 to 30:1), which is beneficial for the environmental remediation applications. It is believed that this work provides new ideas for design and synthesis of novel Z-scheme heterojunction photocatalysts.

Photocatalytic water splitting properties of GeC/InS van der Waals heterostructure: first-principles calculations

Based on first-principles, we conducted an in-depth study of the GeC/InS van der Waals heterostructure formed by GeC and InS and discussed its structure, electronic properties and optical properties. First, we observe that this heterostructure has negative binding energy, indicating that the interlayer interactions are mainly affected by van der Waals forces. Through band structure and density of state analysis, we confirmed its type-II band alignment characteristics, which means that photogenerated carriers have the ability to automatically separate in space. Moreover, the average charge density difference and Bader charge analysis show that there is a built-in electric field in the heterostructure, and further proves that GeC/InS forms a Z-scheme charge transfer mechanism. Interestingly, the band edge position spans the water redox potential and can fully induce the redox reaction of water splitting, indicating that it is a potential photocatalyst. The high light absorption coefficient shown in the absorption spectrum also further confirms its excellent photocatalytic activity. The most striking thing is that the solar hydrogen production efficiency of GeC/InS heterostructure is as high as 44.39%. Our research demonstrates the theoretical basis for GeC/InS heterostructure as a photocatalyst.

Enhanced Photocatalytic Activity of π-Conjugated Pyridine Rings-Modified C3N4/Bi@BiOCl Z-Scheme Heterogeneous Material.

The enhanced photocatalytic properties of Z-Scheme Bi@BiOCl/C3N4-DPY heterojunction materials were successfully prepared by the ultrasonic-assisted coprecipitation method. The Bi@BiOCl/C3N4-DPY heterojunction exhibited remarkable photocatalytic activity under visible light irradiation, and the degradation rate of methyl orange (MO) was about 90.6% in 180 min. This impressive efficiency is mainly due to the Z-Scheme charge transfer mechanism in Bi@BiOCl/C3N4-DPY, resulting in the efficient separation of charge carriers and an increase in the REDOX potential of photogenerated electrons and holes. C3N4 was modified with a π-deficient conjugated pyridine ring, which caused the light absorption redshift, promoted the formation of oxidizing •O2-, and improved the photocatalytic activity. At the same time, a well-aligned heterojunction is formed at the interface between C3N4-DPY and BiOCl, facilitating the seamless transfer of light-induced electrons from the LUMO of C3N4-DPY to the CB of BiOCl. In addition, the addition of Bi introduces a unique band gap reduction effect, resulting in a change in the density of the band states, which further promotes charge transfer and separation. It is worth noting that the introduction of metallic bismuth (Bi) brings about a unique band gap reduction effect, resulting in a change in the density of states within the band, which ultimately promotes charge transfer and separation. The Z-scheme charge migration inside Bi@BiOCl/C3N4-DPY further promotes the efficient separation of photogenerated electron-hole pairs, greatly improving the overall efficiency of the material. The Z-structured photocatalyst developed in this study has great application potential in various fields of photocatalysis.

Highly efficient Bi2O2CO3 coupled with interlayer expanded MoS2 photocatalyst with oxygen vacancy mediated direct Z-scheme charge transfer for photocatalytic degradation of organic pollutant

The development of photocatalysts to degrade organic pollutants from wastewater under visible light has attracted a lot of interest. Herein, a series of Bi2O2CO3 (BOC) coupled with interlayer expanded MoS2 (IEM) photocatalysts were synthesized via a facile two-pot hydrothermal technique. Among all the samples, 5 % of BOC with IEM (5 % BOC-IEM) nanocomposite exhibited the highest photodegradation with 94 % (4.97 × 10−2 min−1) for Methylene Blue (MB) dye removal under 1 W LED visible light. The performance by 5 % BOC-IEM is 1.5 times and 13.4 times higher than the parent IEM and BOC, respectively. Increased photocurrent density, lowest PL intensity, and smallest EIS arc further evidenced the lowered charge carrier’s recombination rate in the optimized 5 % BOC-IEM heterostructure. Moreover, the outstanding photocatalytic performance of 5% BOC-IEM was due to the presence of oxygen vacancies, enhanced light absorption, and improved migration and separation of charge carriers. An Ohmic contact formed on the interfaces of BOC and IEM boosts the Z-scheme charge transfer mechanism, which greatly improves the photocatalytic activity of 5% BOC-IEM.

Novel Z-scheme Nb2O5/C3N5 photocatalyst for boosted degradation of tetracycline antibiotics by visible light-assisted activation of persulfate system

Photocatalytic-assisted activation of persulfate (PDS) is regarded as a promising method for the rapid and efficient degradation of refractory pollutants in the water environment. In this study, a novel Nb2O5/C3N5 (NOCN) p-n heterojunctions composite was created by loading n-type Nb2O5 onto p-type C3N5 via an in-situ facile one-step calcination method. The NOCN/PDS system exhibited excellent performance in degrading tetracycline (TC) antibiotics under visible light and had great cyclic stability. The degradation efficiency of the coupled system reached 95 %, surpassing the pure C3N5 and PDS systems by 3.5 times and 2.4 times, respectively. The degradation rate of target pollutants was improved by the coupled system with the photocatalytic activation of PDS. The photogenerated electrons (e-) in NOCN were able to activate PDS effectively, which facilitated the creation of more reactive species. The Photoluminescence (PL) and other photoelectrochemical data demonstrated that the interfacial charge separation and photoresponsivity were remarkably enhanced in the coupled system. According to Mott-Schooky and electron spin resonance (ESR) characterization, it was confirmed that the reaction mechanism was the Z-scheme charge transfer mechanism based on p-n heterojunctions in the NOCN/PDS system. In addition, LC-MS analyses, TOC monitoring and biotoxicity analyses detected that the target pollutants were degraded to weakly bio-toxic micromolecules. In conclusion, this work provides valuable insights into the application of visible light-activated PDS technology in the degradation of organic pollutants, highlighting its potential for practical implementation.

Surface diffusion induced degradation enhancement and zero-order kinetics in edge-connected MoS2/Au/TiO2 Z-scheme photocatalytic system

Heterostructured photocatalysts have demonstrated great potential in the photodegradation of organic pollutants, while the surfaces & interfaces of their multiple structural components play critical roles in determining their photocatalytic mechanisms and kinetics. Here, we fabricate an edge-connected MoS2/Au/TiO2 photocatalytic system via a selective photodeposition method and utilize a surface-diffusion mechanism to maximize the synergistic effects among the components. The resultant photocatalytic system behaves as a Z-scheme with well spatially separated redox reaction sites. The optimal catalyst 10 % MS/Au/T exhibited a pseudo 1st-order rate constant of 0.0145 min−1 within 120 min, which is seven times more than that of pristine TiO2. The edge-deposited MoS2 in the nanocomposite serves as a reservoir to adsorb and then transport the pollutant molecules rapidly to TiO2 surface for oxidation. Such a pre-concentration effect, as well as the Z-scheme charge transfer mechanism, has enhanced the overall degradation efficiency, and induced the occurrence of zero-order degradation kinetics. The charge transfer behaviors, the diffusion-enhancement mechanism, zero-order kinetics, and the order transition are then thoroughly studied against the MoS2 mass loading. 10 % MS/Au/T showed the highest values of zero and first-order constants, which were 0.073 ppm/min and 0.011 min−1, respectively. A diffusion-enhanced model is developed and validated to explain the experimental observations. This work provides meaningful insights into degradation enhancement and kinetic analysis for heterostructured photocatalytic systems.

Construction of novel g-C3N4/β-FeOOH Z-Scheme heterostructure photocatalyst modified with carbon quantum dots for efficient degradation of RhB

The degradation of organic pollutants using semiconductor photocatalysts is a new ecological approach, but the currently available photocatalysts are not very efficient. Herein, in order to obtain efficient visible-light photocatalysts, g-C3N4/β-FeOOH-modified carbon quantum dots (CDs) composite photocatalysts with Z-Scheme charge transfer mechanism were successfully synthesized. The phase composition and morphology of the composite were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectrophotometry (FT-IR), and X-ray photoelectron spectroscopy (XPS) techniques. Due to the upconversion effect of the CDs, the optical response range of the composite was effectively widened, and the optical utilization rate was improved. The Z-Scheme heterostructure not only improves the light trapping ability, significantly inhibits charge-carrier complexation, and realizes the spatial separation of redox sites, but also ensures that the photocatalyst maintains a suitable valence-conductivity band position and maintains the strong redox reactivity. In addition, CDs have the unique characteristics of electronic storage and transfer, which effectively enhance the quantum separation efficiency of the composite. The photocatalytic efficiency was measured by degrading rhodamine B (RhB) under visible light. The degradation performance was the best when the weight ratio of CDs was 6%, and the RhB solution degradation rate reached 100 % in 60 min. The unique structure and reliable mechanism provide a way for the development of advanced photocatalyst.

MOF-Derived Spindle-Shaped Z-Scheme ZnO/ZnFe2O4 Heterojunction: A Magnetic Recovery Catalyst for Efficient Photothermal Degradation of Tetracycline Hydrochloride.

The development of photocatalysts with a wide spectral response and effective carrier separation capability is essential for the green degradation of tetracycline hydrochloride. In this study, a magnetic recyclable Z-scheme ZnO/ZnFe2O4 heterojunction (ZZF) was successfully constructed via the solid phase method, using MIL-88A(Fe)@Zn as the precursor. An appropriate band gap width and Z-scheme charge transfer mechanism provide ZZF with excellent visible light absorption performance, efficient charge separation, and a strong redox ability. Under visible light irradiation, the degradation efficiency of tetracycline hydrochloride for the optimal sample can reach 86.3% within 75 min in deionized water and 92.9% within 60 min in tap water, exhibiting superior stability and reusability after five cycles. Moreover, the catalyst in the water can be conveniently recovered by magnetic force. After visible light irradiation for 70 min, the temperature of the reaction system increased by 21.9 °C. Its degradation constant (35.53 × 10-3 min-1) increased to 5.1 times that at room temperature (6.95 × 10-3 min-1). Using thermal energy enhances the kinetic driving force of the reactants and facilitates carrier migration, meaning that more charge is available for the production of •O2- and •OH. This study provides a potential candidate for the efficient degradation of tetracycline hydrochloride by combining thermal catalysis with a photocatalytic heterojunction.