Direct Z-scheme Charge Transfer Research Articles

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.

Theoretical design of Sc2CF2/Ti2CO2 heterostructure as a promising direct Z-scheme photocatalyst towards efficient water splitting

Van der Waals (vdW) heterostructure catalysts with the direct Z-scheme charge transfer path are highly expected for photocatalytic water splitting to address the energy crisis. In this work, the novel Sc2CF2/Ti2CO2 heterostructure has been developed and its photocatalytic utility was evaluated based on the first-principles method. Results indicate the heterostructure is an indirect semiconductor with improved carrier mobilities and absorption. The transfer of photogenerated carriers in this heterostructure follows the Z-scheme path, and the band edge positions confirm its suitability for water splitting. More importantly, the change in Gibbs free energy indicates that solar energy can drive water splitting in Sc2CF2/Ti2CO2 heterostructure with an attractive solar-to-hydrogen efficiency of 41.7%. Besides, biaxial tensile strain can turn Sc2CF2/Ti2CO2 heterostructure into a direct semiconductor, while its photocatalytic performance can be improved. In brief, all findings prove the potential of Sc2CF2/Ti2CO2 heterostructure as a promising direct Z-scheme photocatalyst for efficient water splitting.

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).

Janus PtSSe-based van der Waals heterostructures for direct Z-scheme photocatalytic water splitting

The semiconductor photocatalysts based on van der Waals heterostructures (vdWHs) and direct Z-scheme mechanism are viable candidates for water splitting using sunlight. In this study, we exploit the combined effects of the inherent dipole in a Janus PtSSe monolayer and the intrinsic electric field present at the interface of Janus PtSSe-based vdWHs for water splitting. These vdWHs exhibit type-II band edge position, narrow band gap and intrinsic electric fields, establishing them as prototypical direct Z-scheme systems. Remarkably, the density functional theory-based results find the potential drop of ∼0.2–3.2 eV across the interface of vdWHs, promoting the interlayer photogenerated carrier's recombination while suppressing the intralayer charge transfer, which leads to a direct Z-scheme charge transfer pathway with robust redox capabilities. In conjunction with redox reactions, the built-in electric field at the interface generates sufficient driving force for the photogenerated carrier's separation. Also, these Janus PtSSe-based vdWHs possess exceptional abilities in capturing visible light with high solar-to-hydrogen (STH) conversion efficiency. The results obtained from this study are important to designing efficient direct Z-scheme photocatalysts for splitting water under sunlight and offer valuable insights for potential commercial implementations.

Interfacial electric field competition in strain-modulated MoSTe/Hf2CO2: Inducing a direct-Z scheme charge transfer pathway for overall water splitting

The key to high-performance photocatalysts is efficient charge separation and easy regulation. A two-dimensional (2D) MoSTe/Hf2CO2 heterojunction has been proposed using density-functional theory (DFT), and the charge transfer path of the direct-Z scheme has been realized in the presence of strain. Importantly, the MoSTe/Hf2CO2, with its abundant tunability, is able to effectuate the transition from Type–II–A → Type-I → Type–II–B → direct Z-scheme → Type-III. In particular, under +2% and +3% biaxial strains, the band gaps of MoSTe/Hf2CO2 heterojunction are 0.335 and 0.024 eV, respectively, smaller than those of conduction band offset (CBO) and valence band offset (VBO), which favors the recombination of interlayer carriers and thus the formation of direct Z-scheme heterojunctions. While the charge transfer at the interface is subjected to two interfacial electric fields (IEF), IEFMoSTe and IEFInterface, which have obvious competition, the tensile strain leads to the enhancement of the interlayer coupling, which in turn strengthens the competitive advantage of the IEFInterface of the heterojunction. Moreover, the Gibbs free energy in hydrogen evolution reaction (HER) of the MoSTe/Hf2CO2 at a strain of +3% is very near to 0, meeting the requirements for an ideal photocatalyst. In this study, not only is a high-performance direct-Z scheme photocatalyst that can undergo overall water splitting proposed but also the abundant tunability of this heterojunction will have great application prospects in optoelectronic devices.

Boosted photocatalytic accomplishment of 3D/2D hierarchical structured Bi4O5I2/g-C3N4 p-n type direct Z-scheme heterojunction towards synchronous elimination of Cr(VI) and tetracycline

The threats posed by heavy metal ions and antibiotics present in natural aqueous environments have been a serious cause of concern across the globe. The synchronous elimination of these contaminants through visible light responsive semiconductor mediated photocatalysis is a suitable strategy to solve this problem. However, designing proficient photocatalysts for the said purpose is a crucial task. Herein, hierarchical 3D/2D architectures of Bi4O5I2/g-C3N4 p-n type direct Z-scheme heterojunction photocatalysts (BOCNs) were fabricated by a two-step solvothermal-calcination approach. The characterisation of BOCNs by XRD, FTIR, XPS, SEM, TEM, HRTEM, LSV and MS techniques corroborated the robust heterojunction formation between Bi4O5I2 and g-C3N4. The presence of g-C3N4 and application of high treatment temperature (400 °C) assisted the formation of BiOC bond which is responsible for the development of an intimate interfacial interaction in BOCN. The heterostructured photocatalyst (BOCN3) demonstrated higher rate constant (kCr(VI)/synchronous) of 0.068 min−1 for Cr(VI) detoxification and that (kTCH/synchronous) of 0.075 min−1 for TCH degradation synchronously with respect to the reported values. The determined rate constants are about 1.8 folds greater than those were observed in isolated systems. The expedited photocatalytic activity can be ascribed to its wide visible light response, minimum charge recombination rate and increased redox ability. These are resulted from the synergistic effect of hierarchical 3D/2D architecture construction, existence of strong BiOC interfacial bond, p-n heterojunction formation and prevalence of direct Z-scheme charge transfer principle. The synchronous elimination of Cr(VI) and TCH over BOCN3 up to the fifth consecutive cycle without any appreciable change in photoactivity signified its enhanced stability and reusability. The plausible mechanism for the spectacular photocatalytic performance of BOCN3 was proposed.

Ferroelectric polarization promotes a CdS/In2Se3 heterostructure for photocatalytic water splitting.

The rapid recombination of photogenerated electrons and holes greatly limits the efficiency of photocatalyst based on semiconductor. In order to address this issue, we predicted a novel ferroelectric polarized heterojunction photocatalyst, CdS/In2Se3, which enables the spontaneous overall water splitting reaction. The CdS/In2Se3 heterojunction exhibits a band-edge staggered alignment and it is easy to form a direct Z-scheme charge transfer pathway. Besides, the built-in electric field (Eint) in the CdS/In2Se3 heterojunction promoted the charge transfer of CdS/In2Se3, leading to an improved separating efficiency of photo-generated carriers. Moreover, the vertical intrinsic polarized electric field (Ep) not only alters the position of the band edge but also reduces the bandgap limitations commonly associated with photocatalytic materials. Furthermore, the CdS/In2Se3 heterojunctions demonstrate separate catalytic activity for the hydrogen evolution reaction (HER) on the surface of the CdS monolayer and oxygen evolution reaction (OER) on the surface of In2Se3, respectively. Notably, the CdS/In2Se3-down configuration enables spontaneous photocatalytic water splitting in pH = 7, while the CdS/In2Se3-up configuration efficiently facilitates the HER process. This study highlights the significant advantages of CdS/In2Se3 heterojunctions as photocatalytic materials, offering unique insights into the development and research of this promising heterojunction architecture.

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.

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.

Rational construction of g-C3N4/SnO2/CoFe2O4 dual Z-scheme system as a potential scaffold for fluorescence sensing and visible light driven photocatalytic degradation of lethal pollutants

Mimicking the natural photosynthesis process, novel direct dual Z-scheme CN/SnO2/CoFe2O4 heterostructures with different weight ratios (CN/SnO2:CoFe2O4 be 1:1, 2:1 and 1:2; namely CSnCo-1, CSnCo-0.5 and CSnCo-2, respectively) were successfully fabricated and employed for photocatalytic degradation of anthracycline drug, doxorubicin (DXR) and aromatic compound, p-nitrophenol (PNP) and fluorescence detection of heavy metal ion, Hg2+; DXR and PNP. CSnCo-0.5 displayed exceptional photocatalytic capability having pseudo first order rate constant values 5.60, 3.02, 1.23 and 1.38 times higher for DXR; and 4.2, 3.0, 1.18 and 1.12 times higher for PNP in comparison to CN, CSn-20, CSnCo-1 and CSnCo-2, respectively. UV–vis DRS study, photoluminescence spectra and electrochemical impedance results inveterate the formation of direct dual Z-scheme charge transfer, which is beneficial for boosting photocatalytic performance of the system. Additionally, CSnCo-0.5 proved to be highly selective and sensitive for the FL sensing of Hg2+, DXR and PNP with detection limits as low as 0.57 µM, 0.05 µM and 0.63 µM, respectively. Further, sensor provided good analytical performance in real water samples.

Simultaneous photocatalytic tetracycline oxidation and Cr(VI) reduction by a 0D/3D hierarchical Bi2WO6@CoO Z-scheme heterostructure: In situ interfacial engineering and charge regulation mechanism

Constructing visible-light driven semiconductor heterojunction with high redox bifunctional characteristics is a promising approach to deal with the increasingly serious environmental pollution problems, especially the coexistence of organic/heavy metal pollutants. Herein, a simple in-situ interfacial engineering strategy for the fabrication of 0D/3D hierarchical Bi2WO6@CoO (BWO) heterojunction with an intimate contact interface was successfully developed. The superior photocatalytic property was reflected not only in individual tetracycline hydrochloride (TCH) oxidation or Cr(VI) reduction, but also in their simultaneous redox reaction, which could be predominantly attributed to the outstanding light-harvesting, high carrier separation efficiency and enough redox potentials. In the simultaneous redox system, TCH acted as a hole-scavenger for Cr(VI) reduction, replacing the additional reagent. Interestingly, superoxide radical (·O2−) played the role as oxidants in TCH oxidation but as electron transfer media in Cr(VI) reduction. On account of the interlaced energy band and tight interfacial contact, a direct Z-scheme charge transfer model was established, which was verified by the active species trapping experiments, spectroscopy, and electrochemical tests. This work provided a promising strategy for the design/fabrication of highly efficient direct Z-scheme photocatalysts in environmental remediation.

An Unprecedented Strategy to Fabricate Inside/Surface Homojunction in Bismuth Oxychloride for Efficient Photocatalysis

The design of an efficient homojunction in bismuth oxychloride via simple means is still challenging. Herein, an inside/surface homojunction of bismuth oxychloride via fabricating surface-layer oxygen vacancies from a sulfur dopant and surface-layer hydroxyl from an alkali modification (BOCSO) in a one-pot hydrothermal process is successfully prepared. BOCSO exhibits enlarged specific surface area, improved adsorption of substrate, and enhanced photogenerated charge separation and transfer efficiencies. Extensive characterizations and density functional theory (DFT) calculations demonstrate BOCSO can form a defect level via surface oxygen vacancies and S doping to narrow the energy gap and capture the photogenerated electrons and holes. Meanwhile, both oxygen vacancies and hydroxyls on the BOCSO surface can also form an inside/surface homojunction containing an interfacial electric field (IEF) to induce a direct Z-scheme charge transfer mechanism. Taking advantage of the above, the photocatalytic degradation activity is remarkably elevated compared to that of pristine BiOCl (BOC). This work provides a new strategy for the fabrication of an inside/surface homojunction in bismuth oxychloride via novel surface modification engineering.

Ultrasound-Activatable g-C3 N4 -Anchored Titania Heterojunction as an Intracellular Redox Homeostasis Perturbator for Augmented Oncotherapy.

Energyband structure of inorganic nano-sonosensitizers is usually optimized by surface decoration with noble metals or metal oxide semiconductors, aiming to enhance interfacial charge transfer, augment spin-flip and promote radical generation. To avoid potential biohazards of metallic elements, herein, metal-free graphitic carbon nitride quantum dots (g-C3 N4 QDs) are anchored onto hollow mesoporous TiO2 nanostructure to formulate TiO2 @g-C3 N4 heterojunction. The direct Z-scheme charge transfer significantly improves the separation/recombination dynamics of electron/hole (e- /h+ ) pairs upon ultrasound (US) stimulation, which promotes the yield of singlet oxygen (1 O2 ) and hydroxyl radicals (·OH). The conjugated g-C3 N4 QDs with peroxidase-mimic activity further react with the elevated endogenous H2 O2 and aggravate oxidative stress. After loading prodrug romidepsin (RMD) in TiO2 @g-C3 N4 , stimulus-responsive drug delivery can be realized by US irradiation. The disulfide bridge of the released RMD tends to be reduced by glutathione (GSH) into a monocyclic dithiol, which arrests cell cycle in G2/M phase and evokes apoptosis through enhanced histone acetylation. Importantly, reactive oxygen species accumulation accompanied by GSH depletion is devoted to deleterious redox dyshomeostasis, leading to augmented systemic oncotherapy by eliciting antitumor immunity. Collectively, this paradigm provides useful insights inoptimizing the performance of TiO2 -based nano-sonosensitizers for tackling critical diseases.

Heterojunction nanoarchitectonics of WOx/Au-g-C3N4 with efficient photogenerated carrier separation and transfer toward improved NO and benzene conversion

Topics on effectively improving the photochemical CO2/benzene/NO oxidation conversion performances of g-C3N4 based materials via charge transfer and separation enhancement are still considered challenging, despite the growing popularity of applying these materials in a variety of energy conversion related applications. Based on the idea of nanoarchitectonics, a post-nanotechnology concept, WOx/Au-g-C3N4 heterostructures are synthesized using two-step thermal polymerization and solvothermal treatment methods in this paper. Small Au nanoparticles are incorporated in superior thin g-C3N4 via mechano-chemical pre-reaction and two-step thermal polymerization (treated at 500 and 700 °C). Enhanced photocurrent density is observed after incorporation of Au, which is also in good agreement with the photocatalytic activity (H2 generation and CO2 reduction) data. Layered WOx with abundant oxygen vacancies are further incorporated into Au-modified g-C3N4 nanosheets to form heterojunctions possessing excellent photocatalytic CO2 photo-reduction performances with CO and CH4 generation rate of 5.64 and 2.58 μmolg−1h−1, respectively, under full solar spectrum. The heterojunctions constructed via in-situ formation show direct Z-scheme charge transfer pathway with improved charge separation and transport efficiencies. These highly stable and recyclable hierarchical g-C3N4 hybrid nanostructures (WOx/Au-g-C3N4 heterojunctions) show outstanding conversion rate (88.1%) and selectivity (99.3%) for benzene to phenol conversion under full solar spectrum condition, as well as excellent NO removal rate (61%).

Photo-Fenton assisted AgCl and P-doped g-C3N4 Z-scheme photocatalyst coupled with Fe3O4/H2O2 system for 2, 4-dimethylphenol degradation

In this study graphitic carbon nitride (g-C3N4 or GCN) and phosphorus doped graphitic carbon nitride (p-g-C3N4 or PCN) were prepared using facile thermal polycondensation method. Phosphorus doping was employed to preserve the non-metallic nature of GCN. The AgCl/PCN/Fe3O4 heterojunction was synthesized using a simple in-situ route. The photocatalytic performance of the GCN, PCN, Fe3O4 and AgCl/PCN/Fe3O4 was tested towards 2, 4-dimethylphenol (DMP) pollutant. The work explored improvement in physiochemical properties and reduction of band gap of GCN after P doping (through Tauc's plot method). Coupling with AgCl (silver halide) also enhanced photoinduced charge carriers' separation and migration ability due to apt band alignment among both AgCl and PCN photocatalysts which resulted in formation of direct Z-scheme charge transfer mechanism. Similarly, the incorporation of ferrimagnetic material i.e. Fe3O4 enhanced the generation of hydroxyl (•OH) radicals via photo-Fenton process and facilitated photocatalysts easy separation from the aqueous medium. Through PL and EIS analysis the enhanced charge separation and migration ability in AgCl/PCN/Fe3O4 nanocomposite was validated. The attained DMP degradation efficiency of photo-Fenton assisted AgCl/PCN/Fe3O4/H2O2 Z-scheme nanocomposite was much higher i.e. 99% compared to other photocatalysts within 60 min of visible light irradiation following pseudo-first-order kinetics. Electron paramagnetic resonance (EPR) and scavenging tests confirmed the substantial role of •OH and •O2− radicals in the photo-Fenton reaction. Furthermore, liquid chromatography-mass spectrometry (LC-MS) analysis detected the generated oxidative products and mineralization pathways associated with DMP degradation. The proposed direct Z-scheme charge transfer route presented efficient charge separation and migration ability in AgCl/PCN/Fe3O4 nanocomposite. Recycle ability of the fabricated AgCl/PCN/Fe3O4 photocatalyst was tested up to 5 cycles with 90% removal efficacy, confirming the excellent reusability and stability of AgCl/PCN/Fe3O4 photocatalyst.

Direct Z-scheme heterojunction Bi/Bi2S3/α-MoO3 photoelectrocatalytic degradation of tetracycline under visible light

A hot research topic in visible-light-driven photoelectrocatalytic (PEC) oxidation technology is the development of superior photoanode materials. The design of the photoanode system with a direct Z-scheme charge transfer mechanism is crucial to achieving effective charge separation for sustainable photoelectrocatalysis. Here, a novel Bi/Bi2S3/α-MoO3 heterostructure was successfully assembled by a simple and feasible strategy. The direct Z-scheme heterogeneous formed between Bi2S3 and α-MoO3 has the advantages of low resistance, high optical response current and the surface plasmon resonance (SPR) effect of Bi nanoparticles (Bi NPs). Thus, the efficiency of photogenerated carrier separation and transfer is further enhanced, and the catalytic activity is significantly improved. It is impressive that the unique photoanode has achieved a maximum removal efficiency of 85.8% of tetracycline (TC) pollutants under visible light irradiation within 60 min and has excellent stability, which is expected to degrade antibiotics efficiently and environmentally in harsh environments. These characteristics give Bi/Bi2S3/α-MoO3 promising candidates for practical applications in antibiotic degradation.

Construction of Direct Z-Scheme SnS2 Quantum Dots/Conjugated Polyimide with Superior Photocarrier Separation for Enhanced Photocatalytic Performances.

In this study, a novel direct Z-scheme SnS2 quantum dots/sulfur-doped polyimide (SQDs/SPI) photocatalyst was firstly fabricated by an in situ crystallization growth of SnS2 quantum dots on sulfur-doped polyimide through a facile hydrothermal method. The photocatalytic hydrogen production activity of 5SQDs/SPI samples reached 3526 μmoL g-1 in the coexistence of triethanolamine and methanol used as hole sacrificial agents, which is about 13 times higher than that of SPI under the same conditions and 42 times higher than that of SPI only as a hole sacrificial agent. The improvement can be related to the direct Z-scheme charge transfer in the tight interface between SQDs and SPI, which promoted rapid separation and significantly prolonged the lifetime of photoexcited carriers. The Z-scheme charge transfer mechanism was proposed. This discovery comes up with a new strategy for the development of an efficient, environmentally friendly, and sustainable sulfide quantum dots/polymer non-noble metal photocatalyst.

A novel direct Z-scheme heterojunction of CoTiO3/ZnIn2S4 for enhanced photocatalytic H2 evolution activity

The shortage of fossil energy has become a growing global concern. It is particularly important to make full use of the infinite solar energy resources, and transform them into sustainable and clean energy. The development of hydrogen energy has become a feasible solution to solve the energy shortage problem. The preparation of photocatalysts featuring efficient charge transfer channels and high hydrogen production activity provides a pathway for the development of hydrogen energy. In this paper, we report for the first time the direct assembly of 2D ZnIn2S4 (ZIS) nanosheets on the surface of CoTiO3 (CTO). The synthesized CoTiO3/ZnIn2S4 (CTO/ZIS) photocatalyst features a direct Z-scheme charge transfer channel, which enhances the separation rate of photogenerated carriers, and accelerates the photocatalytic H2 evolution (PHE) rate. Without the assistance of any co-catalyst, the PHE rate of prepared CoTiO3/ZnIn2S4 was as high as 5.21 mmol g−1 h−1. Moreover, the H2 evolution rate of CoTiO3/ZnIn2S4 almost did not decrease significantly after four consecutive 4 h cycles. This investigation provides a valuable approach for the exploitation of novel and efficient Z-scheme photocatalysts in the application of solar energy to hydrogen energy conversion.

Direct Z-Scheme Heterojunction α-MnO2/BiOI with Oxygen-Rich Vacancies Enhanced Photoelectrocatalytic Degradation of Organic Pollutants under Visible Light

The degradation efficiency of photoelectrocatalytic (PEC) processes for the removal of organic pollutants is highly dependent on the performance of the photoelectroanode catalyst. The design of PEC systems with a direct Z-scheme charge transfer mechanism and visible light excitation is essential to enhance the degradation efficiency of organic compounds. Here, a α-MnO2/BiOI direct Z-scheme heterojunction photocatalyst was successfully synthesized through a convenient and feasible method. It is remarkable that the photoanode exhibited excellent PEC performance under visible light irradiation; a 95% removal rate of tetracycline (TC) pollutants was achieved within 2 h, and it had excellent stability and reusability, which was expected to degrade antibiotics efficiently and environmentally in harsh environments. The presence of oxygen vacancies (OVs) in the α-MnO2/BiOI heterojunction was confirmed by electron spin resonance technique, and the OVs acted as electron traps that contributed substantially to the separation efficiency of photogenerated carriers. ESR characterization showed that the main reactive radicals during TC degradation were •OH and •O2−. By analyzing the intermediates, the possible degradation pathways of TC were further analyzed and a suitable degradation mechanism was proposed. The toxicity changes in the degradation process were explored by evaluating the toxicity of the intermediates. This study provides a new way to enhance the performance of Bi-based semiconductor photocatalysts for the effective degradation of TC in water.

Defects level and internal electric field co-induced direct Z-scheme charge transfer for efficient photocatalytic H2 evolution over ZnIn2S4/In2Se3

Developing rational strategy on inducing efficient direct Z-scheme charge transfer for boosting photocatalytic H2 evolution is stilling a challenging work. In this work, sulfur-deficient ZnIn2S4/In2Se3 (Vs-ZIS/In2Se3) was fabricated, in which, photogenerated electrons in the defect level of Vs-ZIS migrated to the valence band of In2Se3, meanwhile, the interfacial internal electric field provided charge transfer driving force. Under the synergistic effect of defect level and internal electric field, Z-scheme charge transfer was realized in Vs-ZIS/In2Se3, not only accelerated the separation of photocarriers, but also reserved a great deal of photogenerated electrons with intense reducing ability. As a result, the optimized Vs-ZIS/In2Se3 photocatalyst exhibited a visible light-driven H2 evolution rate of 36.53 mmol·g−1·h−1 and an AQE of 17.14 % at 420 nm, about 9.72 and 104.4-folds of that of Vs-ZIS and In2Se3 respectively. This work donates an advanced pattern for inducing direct Z-scheme charge transfer through creating defect level and internal electric field.