Z-scheme Heterostructure Research Articles

Construction of dual Z-scheme heterostructure TCN/In2O3/ZnO composite with oxygen vacancies for enhanced artificial nitrogen fixation

The synergistic effect between vacancy engineering and heterostructures can effectively improve the interfacial charge transfer ability and efficiency of catalytic nitrogen reduction. Herein, a ternary dual Z-scheme tubular carbon nitride composited oxygen vacancy-induced indium oxide and oxygen vacancy-induced zinc oxide catalyst (TCN/Vo-In2O3/Vo-ZnO) was constructed, and the synergistic mechanism of charge transport at the catalyst interface was explored. The excellent efficiency of nitrogen fixation could reach 171.56 μmol/L within 120 min, and the high stability of TCN/Vo-In2O3/Vo-ZnO was favorable for practical applications. All experiments indicated that the dual-Z scheme heterostructure and oxygen vacancies have a synergistic effect. Oxygen vacancies could control the valence band position. This control improved the transfer rate of photogenerated charge carriers between heterojunctions, thereby enhancing the adsorption and activation of N2. This study may offer new insights into the synthesis of highly efficient catalysts for photocatalytic nitrogen fixation.

Design of novel Z-scheme Ce2(WO4)3 heterostructure using tubular g-C3N4 for boosted photocatalytic performance via effective electron transfer pathway

Herein, we report a novel Z-scheme heterostructure catalyst based on tubular shaped graphitic carbon nitride with cerium tungstate catalysts synthesized by ultrasonic-assisted thermal impregnation route. The physicochemical, morphological and optical features of the materials were characterized by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance (UV–vis DRS), photoluminescence (PL) spectroscopy and N2-adsorption-desorption measurements. The results demonstrated that the Ce2(WO4)3/g-C3N4 hybrid catalyst achieved superior photocatalytic activity although they had poor performance individually. The kinetic rate constant of the hybrid sample was calculated as 0.0134 min-1 which was 3.4 times higher than the pristine Ce2(WO4)3 for the degradation of tetracycline antibiotic under visible light irradiation. The improved catalytic activity was assigned to higher surface area, narrower band gap energy and formation of Z-scheme heterojunction mechanism between Ce2(WO4)3 and g-C3N4 according to band structure analysis. This research demonstrated the potential utilization and modification of Ce2(WO4)3 as a new metal tungstate in the photocatalytic remediation of different types of pollutants.

Atomic catalysis meets heterostructure synergy: Unveiling the trifunctional efficacy of transition Metal@WS2/ReSe2

Integrating and advancing renewable energy storage and conversion technologies such as water splitting and rechargeable air-based batteries face significant challenges in finding appropriate catalysts that offer both high activity and low cost. This paper successfully designed efficient, cost-effective, and eco-friendly catalysts that meet the requirements for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) catalytic activity by employing two-dimensional (2D) transition metal dichalcogenides (TMDs) interface engineering combined with a single-atom doping strategy. First, the heterostructure was constructed, and its optimal layer spacing (3.13 Å) was determined by calculating the most negative binding energy. These materials were theoretically evaluated using density functional theory (DFT), demonstrating that transition metal (TM) can all be firmly attached to the S1 site of the WS2/ReSe2 Z-scheme heterostructure with favorable binding energies and excellent electronic properties. By comparing the catalysts doped with different metals (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn), the three functional catalysts with the best performance were finally selected: Mn@WS2/ReSe2, Ni@WS2/ReSe2, and Cu@WS2/ReSe2. In particular, Mn@WS2/ReSe2 exhibited exceptional promise as multifunctional catalysts, with overpotentials for the HER/OER/ORR of 0.05/0.29/0.35 V, respectively. The superior catalytic performance of this WS2/ReSe2 Z-scheme heterostructure was attributed to the introduction of TM atoms and the synergistic interaction between rhenium and the TM atoms. This interaction facilitated more efficient electron transfer between the catalyst and the reactants, enhancing the overall catalytic activity. This research is a successful attempt to combine interface engineering with single-atom catalysis (SACs). It provided valuable insights into the design of next-generation multifunctional electrocatalysts, offering a novel approach to address the growing energy demands in an environmentally benign and economically viable way.

Incorporating ReS2 Nanosheet into ZnIn2S4 Nanoflower as Synergistic Z-Scheme Photocatalyst for Highly Effective and Stable Visible-Light-Driven Photocatalytic Hydrogen Evolution and Degradation.

Inspired by natural photosynthesis, the visible-light-driven Z-scheme system is very effective and promising for boosting photocatalytic hydrogen production and pollutant degradation. Here, a synergistic Z-scheme photocatalyst is constructed by coupling ReS2 nanosheet and ZnIn2S4 nanoflower and the experimental evidence for this direct Z-scheme heterostructure is provided by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and electron paramagnetic resonance. Consequently, such a unique nanostructure makes this Z-scheme heterostructure exhibit 23.7 times higher photocatalytic hydrogen production than that of ZnIn2S4 nanoflower. Moreover, the ZnIn2S4/ReS2 photocatalyst is also very stable for photocatalytic hydrogen evolution, almost without activity decay even storing for two weeks. Besides, this Z-scheme heterostructure also exhibits superior photocatalytic degradation rates of methylene blue (1.7 × 10-2 min-1) and mitoxantrone (4.2 × 10-3 min-1) than that of ZnIn2S4 photocatalyst. The ultraviolet-visible absorption spectra, transient photocurrent spectra, open-circuit potential measurement, and electrochemical impedance spectroscopy reveal that the superior photocatalytic performance of ZnIn2S4/ReS2 heterostructure is mostly attributed to its broad and strong visible-light absorption, effective separation of charge carrier, and improved redox ability. This work provides a promising nanostructure design of a visible-light-driven Z-scheme heterostructure to simultaneously promote photocatalytic reduction and oxidation activity.

Construction of direct Z-scheme Sn3O4/WO3 heterostructure photocatalyst for enhanced Congo red degradation and Cr(Ⅵ) reduction performance

The development of well-designed architectures is crucial in accelerating the transport of photon-generated carriers in composite photocatalysts. In this study, a direct Z-scheme Sn3O4/WO3 (SW) photocatalyst was successfully fabricated utilizing a straightforward hydro/solvothermal approach, where Sn3O4 nanosheets (NSs) grew in-situ onto WO3 nanorods (NRs) uniformly. The optimal SW-2 composite exhibits a remarkable reduction rate of 93.5 % for Congo Red (CR) within 40 min, with a rate constant (k) of 0.075 min−1. This performance surpasses that of pristine Sn3O4 and WO3, which have rate constants of 0.027 min−1 and 0.018 min−1, respectively. Additionally, the SW-2 composite effectively removes 89.2 % of Cr(VI) over 100 min, achieving a k value of 0.019 min−1, which is higher than that of Sn3O4 (0.013 min−1) and WO3 (0.001 min−1). Furthermore, the photocatalytic degradation performance of the recovered samples retains their photocatalytic degradation performance after five consecutive experimental cycles, indicating excellent durability. The enhanced photocatalytic performance can be attributed to the construction of a direct Z-scheme heterostructure, which not only broadens the spectral response range, bur also ensures efficient separation of photoexcited carriers and fosters robust photo-redox capacity within the composite. This study is expected to provide some valuable insights into the design and synthesis of Z-scheme heterojunction photocatalysts, aimed at addressing pressing environmental pollution challenges.

Rational design of Z-scheme configured polymeric carbon nitride-decorated ZnWO4 nanofibers for enhanced visible-light-driven photodegradation of antibiotics

In this study, a Z-scheme heterostructure was meticulously engineered between zinc tungstate (ZnWO4) nanofibers and polymeric carbon nitride (PCN) nanosheets to augment the photocatalytic degradation of tetracycline (TC) under visible light irradiation. A cohesively integrated PCN/ZnWO4 photocatalyst structure was synthesized through an in-situ gas-solid reaction. The quantity and spatial distribution of PCN nanosheets were modulated by fine-tuning the gas precursor and reaction parameters. Relative to pristine ZnWO4 nanofibers and PCN photocatalysts, the distinct three-dimensional PCN/ZnWO4 heterostructure manifests a notable enhancement in photocatalytic performance, attributed to its plethora of active sites and a Z-scheme configuration that bolsters charge separation efficiency, achieving a tetracycline degradation rate of 95.4% upon exposure to simulated sunlight for 160 minutes. The employment of gas-solid reaction as a design paradigm pioneers a fresh paradigm in the strategic assembly of Z-scheme heterostructured photocatalysts, thereby illuminating a promising pathway for advancements in environmental remediation technologies.

Rationally designed photothermal-pyroelectric Fe0.9Ni0.1S2/ZnSnO3 Z-scheme heterojunction for promoting electrical charge polarization towards optimized photocatalytic H2 evolution and intermolecular N-N coupling reaction

Developing a photocatalytic composite system that can couple hydrogen (H2) evolution and benzylamine (BA) oxidation is a challenging task, especially while avoiding sacrificial agents and value-added chemicals. Here, a practical approach is reported to develop a photothermal-pyroelectric-Fe0.9Ni0.1S2/ZnSnO3 photocatalytic system with core–shell and Z-scheme heterostructure via hydrothermal and annealing methods. Although Fe0.9Ni0.1S2 nanoparticles (NPs) could convert most of near-infrared (NIR) light energy into heat energy to drive the pyroelectric effect of ZnSnO3, it also results in temperature fluctuations (ΔT) in the system, causing natural polarization and thermoelectric effects under the condensed water circulation. As a result, the as-designed Fe0.9Ni0.1S2/ZnSnO3-2 composites could yield up to 7.194 mmol g-1h−1 with exceptional photocatalytic H2 evolution under simulated sunlight. This result is 5.41 and 4.92-fold those of Fe0.9Ni0.1S2 and ZnSnO3, respectively, with 16.66 % apparent quantum yield (AQY) under 365 nm monochromatic light. At the same time, the composites could also oxidize BA and yield up to 6.640 mmol g-1h-1n-benzylidene benzylamine (NBBA) with a 90.2 % selectivity. Due to the synergistic effect of Z-scheme’s built-in electric field and photothermal-pyroelectric of Fe0.9Ni0.1S2/ZnSnO3, the surface charges released on them could direct the charge transfer pathways and restrain their recombination with accelerated electron transfer kinetics, thus extending the carrier lifetime. This work offers a new perspective for designing electrical charge polarized by the photothermal-pyroelectric effect, which can enhance H2 evolution and BA oxidation concurrently.

All-solid-state red phosphorus/RGO/WO3 Z-scheme heterostructure for photocatalytic overall water splitting

Red phosphorus’s (Red P) photocatalytic overall water splitting activity is limited by rapid charge recombination. In this case, Red P/RGO/WO3, an all-solid-state Z-scheme heterostructure, was created by simply dispersing, mixing, and heating Red P, WO3, and graphene oxide (GO). Among them, Reduced GO (RGO) facilitated the Z-scheme charge transmission between Red P and WO3. Achieving the space separation between electrons stored in Red P’s conduction band and holes accumulated in WO3′s valence band would prolong the lifespan of photogenerated carriers and increase their redox capacity, which will increase photocatalytic activity. When exposed to visible light, Red P/RGO/WO3 demonstrated an effective overall water splitting activity, producing 287.00 μmol h−1 g−1 of H2, which is around 2.5 times more than Red P. This study constructs Z-scheme heterostructures as a possible means of enhancing Red P’s photocatalytic overall water splitting activity.

Improving photoexcited carrier separation through Z-scheme W18O49/BiOBr heterostructure coupling carbon quantum dots for efficient photoelectric response and tetracycline photodegradation

Building Z-scheme heterostructure integrating oxygen vacancies seems to effectively encourage photoexcited charge partition and hence photoelectric response and photocatalytic performance. Here, through the inclusion of carbon quantum dots (CQDs) with W18O49/BiOBr (WB) for enhancing electron exchange and band structure control, we have developed one Z-scheme ternary CQD/W18O49/BiOBr heterostructures (CWB) with intense oxygen vacancies. The optimal CWB heterostructure shows superior photocatalytic and photoelectric response execution. The findings indicate that CWB has higher photocatalytic degradation efficiency of tetracycline hydrochloride (TC) at 97 % compared to WB or W18O49 alone. Additionally, the CWB shows a higher photocurrent density, surpassing WB and W18O49 by 2.5 times and 5.4 times. A potential self-supplied photoelectrochemical-type photodetector utilizing CWB displays relatively quick and stable photoelectric response at 0 V. The improved photo-electric performance are linked to the combined impact of separation and redistribution of charges caused by Z-scheme heterostructure and oxygen vacancies, as well as intensive light absorbance by localized surface plasmon resonance. Our research also validates significance of CQDs as cocatalyst in accelerating the splitting of photo carriers in Z-scheme ternary CWB heterostructures, which will stimulate interest in creating advanced photoactive heterojunction substance with carbon nanomaterials.

Modulating stacking mode and molecular polarization in CTF/molecule heterojunction for meliorating photocatalytic CO2 conversion with nearly 100% CO selectivity

Herein, two conjugated molecules, i.e., D-π-A TAPT and non-D-A TAPB, are finely designed to incorporate with covalent triazine framework (CTF) in A-A and A-B stacking mode via π-π interaction, respectively. The transient photocurrent response of the generated AA-CTF/TAPT Z-Scheme heterostructure is 1.14 × 10-7 A, significantly higher than that of the other two metal-free heterostructures (AA-CTF/TAPB and AB-CTF/TAPT). The promoted photocarrier transportation is attributed to strong polarization (dipole moment = 2.634 D) imposed by the D-π-A effect in TAPT that motivates the interfacial charge separation, and the coexisting charge transfer channel built by the ordered A-A stacking mode in AA-CTF that expedites the charge delivery. The photocatalytic CO2 conversion conducted by AA-CTF/TAPT gives the optimal CO conversion rate as 7.47 μmol·g−1·h−1, and with nearly 100 % product selectivity obtained, which is attributable to the lower energy barrier of CO desorption barrier (−1.07 eV) rather than that of CHO* formation (1.52 eV) for generating CH4.

Z-scheme heterostructure of ZnO@NPC/Au/ZnIn2S4 for chemical replacement reaction-mediated signal-on photoelectrochemical assay of mercury ion

Herein, an advanced Zn-based metal organic framework (Zn-MOF) derived ZnO embedded in a nitrogen-doped porous carbon (ZnO@NPC) polyhedron/Au/ three-dimensional (3D) chrysanthemum-like ZnIn2S Z-scheme heterojunction was employed for the chemical replacement reaction-mediated signal-on photoelectrochemical (PEC) sensing detection of mercury ions (Hg2+). The p-type ZnO@NPC polyhedron was initially prepared by carbonising the zeolitic imidazolate framework (ZIF)-8 polyhedron, followed by modification with Au nanoparticles (NPs) via an in situ photocatalytic reduction method. Subsequently, the ZnO@NPC/Au polyhedron was combined with n-type 3D chrysanthemum-like ZnIn2S4 through physical adsorption, forming the ZnO@NPC polyhedron/Au/3D chrysanthemum-like ZnIn2S4 Z-scheme heterostructure. The newly constructed heterostructure exhibited strong visible light–harvesting capacity, and considerably improved photoelectric conversion efficiency. The 3D chrysanthemum-like ZnIn2S4 functioned not only as a photosensitiser but also as an Hg2+ recognition probe. Importantly, the PEC sensor exhibited a considerably increased photocurrent response to Hg2+. This is presumably because the introduction of Hg2+ triggered a selective Zn-to-Hg chemical replacement reaction, leading to the in-situ formation of a ZnO@NPC/Au/ZnIn2S4/HgS heterojunction, which further improved charge separation. Consequently, Hg2+ was sensitively detected with a wide linear range from 0.5 pM to 2 μM and a low detection limit of 0.07 pM. Furthermore, the proposed sensor was validated by detecting Hg2+ in food and aqueous environments, indicating its potential application in food safety and environmental monitoring.

Fabrication and photocatalysis of novel Z-scheme Cu2O/Cu-Ag/AgCl heterojunction possessed broad-spectrum antibacterial performance and degradation capabilities

The construction of nanostructured Z-heterostructures is a potent strategy for achieving efficient photocatalyst synthesis. Herein, a novel Cu2O/Cu-Ag/AgCl (CCAA) Z-scheme heterostructure was created via photoreduction precipitation and utilized for pollutant decomposition and microorganism inactivation. Subject to visible light (λ > 420 nm) illumination, specimen CCAA-2 demonstrated superior photodegradation competence for Congo Red (CR), achieving a degradation rate of 92.6 % within 60 min. The superior removal performance is attributed to the Z-scheme heterostructure, featuring precise interfacial contact, and the combined effect of adsorption and photocatalytic activity. Meanwhile, the optimal sample, CCAA-2, was able to achieve 100 % inactivation of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) within 15 min under visible light. The photocatalytic performance of CCAA nanocomposites is primarily attributed to the surface plasmon resonance (SPR) effect of the noble metal Ag and the fabrication of Z-Scheme heterostructures to improve the utilization efficiency of electrons (e-) and holes (h+). Particularly, the photocatalytic mechanism was scrutinized via active substance capture experiments and electron spin resonance (ESR) analysis, uncovering that •O2ˉ and h+ served as key active constituents. Hence, this research presents a feasible approach for designing and constructing Z-Scheme heterojunctions for efficacious removal of contaminants from water.

A novel 0D/3D Z-Scheme heterojunction ZnS/MIL-88(A) with significantly boosted photocatalytic activity toward tetracycline

Coupling two different photocatalytic materials to construct a heterojunction is a preferable strategy for obtaining the composite photocatalyst with high activity. Herein, a novel 0D/3D Z-scheme heterostructure ZnS/MIL-88(A) was constructed by anchoring 0D ZnS nanoparticles on the surface of the 3D MIL-88(A). The prepared ZnS/MIL-88(A) was characterized by using FT-IR, XRD, SEM, UV–vis and XPS. The photodegradation of tetracycline (TC) was conducted under the irradiation of visible light to evaluate the photocatalytic performance of ZnS/MIL-88(A). The creation of the Z-scheme heterostructure between ZnS and MIL-88(A) enables ZnS/MIL-88(A) to exhibit excellent visible-light absorption ability and dramatically boost separation and transfer of the photo-induced charge carriers. Compared with MIL-88(A), ZnS/MIL-88(A) shows prominently enhanced photocatalytic activity toward tetracycline, achieving a TC degradation rate of 94 %. The highest photodegradation rate constant (0.02083 min−1) of TC by ZnS/MIL-88(A) is 7.77 and 12.33 folds as large as those by MIL-88(A) and ZnS, respectively. After five cycles of reuse, ZnS/MIL-88(A) shows only a slightly decreased TC removal rate, presenting excellent photo-stability. Furthermore, the Z-scheme interfacial charge migration mode and the photocatalytic mechanism of ZnS/MIL-88(A) were discussed according to the band position as well as the identification result of the active species. The radicals ·O2− and ·OH generated in photocatalysis serve as major reactive species to decompose TC. This work provides a new way for designing efficient composite photocatalysts.

Synthesis of a novel bismuth molybdite/iron oxide thin film for oxytetracycline degradation in a photoelectrocatalytic system

In this study, heterostructures based on Bismuth molybdite/iron oxide (Bi2MoO6/Fe2O3) thin films were fabricated by a dip-coating technique using precursor solutions. The heterostructures were deposited on fluorine-doped tin oxide glass substrates. From a detailed characterization using X-ray diffraction and X-ray photoelectron spectroscopy, the formation of the orthorhombic phase for Bi2MoO6 and the co-existence of hematite and maghemite in Fe2O3 was demonstrated. Meanwhile, the field emission scanning electron microscopy cross-section images confirm the formation of well-defined Bi2MoO6 film under the Fe2O3 deposition. The optical band gap energies for the heterostructure obtained were estimated from the diffuse reflectance spectra and ranged from 2.3 to 3.5 eV. Photoluminescence analysis revealed an improved separation and faster transfer of photogenerated electrons and holes for the Bi2MoO6/Fe2O3 (Het) film. The best oxytetracycline (OTC) removal percentage through photoelectrocatalytic treatment was 96.85% using the Het. Besides, were carried out the variation of parameters which affect the OTC photoelectrocatalytic degradation as pH, potential applied, and scavenger assay. The 1O2 was the oxidant predominate, which attack the OTC ring to initiate and accelerate the degradation process. Based on the analysis of degradation intermediates and characteristics of Bi2MoO6/Fe2O3, possible degradation pathways and mechanisms of OTC were displayed. An enhancement of oxytetracycline degradation efficiency of Het fabricated compared to pristine oxides was achieved mainly due to avoid the charge recombination of photogenerated electron-hole pairs provided by Direct Z-scheme heterostructure. Finally, the Het fabricated represents a promising material for efficient and sustainable pharmaceutical removal applications.

First-principles study of GeC/Ga2SO heterostructure as a potential direct Z-scheme photocatalyst for water splitting

The rational design of van der Waals heterostructure offers an effective avenue for improving the photocatalytic efficiency of individual two-dimensional materials, garnering extensive interest in recent years. Herein, the feasibility of GeC/Ga2SO heterostructure as a photocatalyst for overall water splitting has been explored based on the first-principles calculations. Our findings reveal that the electronic bandstructure of GeC/Ga2SO heterostructure can be engineered in staggered or straddling band alignment depending on stacking patterns. Particularly, in the GeC/Ga2SO heterostructure with staggered band alignment, an intrinsic built-in electric field is established at the interface with the direction from GeC to Ga2SO, facilitating the formation of a direct Z-scheme heterostructure. Also importantly, the band-edge positions of Z-scheme GeC/Ga2SO heterostructure cross the water redox potentials, providing adequate driving force for both the reduction and oxidation reactions of water. Gibbs free energy calculations demonstrated that the photocatalytic overall water splitting can proceed spontaneously in the neutral environment (pH = 7) under light irradiation. Moreover, GeC/Ga2SO heterostructure exhibits good thermal stability and a strong (magnitude in 105 cm−1) and broad (from visible to ultraviolet light) optical absorption. Finally, through applying the tensile strain, further enhancements in the optical absorption and carrier redox ability are achieved due to the favorable modulation in the bandgap. Therefore, all these features make GeC/Ga2SO heterostructure show great potential in the application of photocatalytic water splitting.

Dual boosting of the built-in polarization field in the BiFeO3/ZnS heterostructure for water purification: Effects of Z-scheme heterostructure and corona poling

In this study, we have designed a novel 1D-0D lead-free Z-scheme heterostructure of BiFeO3–ZnS (BFO/ZnS) using an isoelectric point-assistant annealing method for piezocatalytic reactions. The open circuit voltage measurements exhibited a greater internal electric field for BFO/ZnS (90/10) than for individual components, causing its excellent piezocatalytic performance for MTZ antibiotics, organic dyes oxidation, and Cr(VI) reduction. BFO/ZnS (90/10) was treated by corona poling to boost its polarization, resulting in the highest remanent polarization and dielectric constant. Piezocatalytic experiments demonstrated that BFO/ZnS (90/10; poled) can degrade 99% of RhB by 9 min ultrasonic vibration with kapp = 0.44 min−1, which is 2.5, 5.5, and 16.3 times greater than those of BFO/ZnS (90/10), BFO, and ZnS, respectively. Also, the efficiency of piezodegradation for MTZ, Cr(VI), MO, and MB over BFO/ZnS (90/10; poled) was found to be 74.5% (90 min), 84.6% (60 min), 95.3% (40 min), and 97.2% (30 min), respectively. This outstanding piezocatalytic performance of BFO/ZnS (90/10; poled) is ascribed to the enhanced built-in polarization field due to the Z-scheme heterostructure and corona poling treatment. As supported by PL and EIS analysis, the stronger built-in electric field can effectively separate and transmit the charge carriers, causing excellent piezocatalytic activity.

Enabling highly efficient navy-blue dye degradation over the LaFeO3/B-g-C3N4/WO3 double z-scheme heterostructure

Chemical reactivity, optical and electronic features of conventional photocatalysts can be improved by chemical modification and nanocomposites fabrication techniques. Herein, a double Z-scheme LaFeO3/B-g-C3N4/WO3 (LFO/B-CN/WO) heterostructure nanocomposite has been successfully fabricated via a hydrothermal approach. XRD, FT-IR, SEM/EDS, TEM, TGA/DSC, and UV–visible spectroscopy confirmed crystallographic planes, phase purity, and heterojunction between LFO, WO and B-CN. From UV visible absorption spectroscopy, it was confirmed that optical band gap energy of CN is remarkably reduced after boron doping. The LFO/B-CN/WO photocatalyst revealed 96 % degradation performance for Navy Blue (NB) dye after visible light irradiation for 130 min under neutral pH conditions. The data were analyzed using pseudo-first and pseudo-second order kinetics models to evaluate the dye degradation kinetics. Compared to the CN, B-CN, LFO-CN and WO-CN photocatalysts, the performance of LFO/B-CN/WO was much significant. Improved light absorption capability, effective spatial separation and prolonged charge-carrying capacity of the double Z-scheme system resulted in enhanced photocatalytic performance. This study offers new insights into the design and synthesis of highly efficient Z-scheme heterojunction photocatalysts for environmental decontamination and clean energy purposes.

Simple synthesis of 2D/3D mpg-C3N4/ZnO nanocages with built-in driven Z-scheme heterostructures: Photocatalytic degradation of tetracycline antibiotics and lifting the limitation of the complex water environment

Tetracycline antibiotics have attracted attention due to their difficulty in being degraded by the natural environment. In this work, 2D/3D mesoporous graphitic carbon nitride (mpg-C3N4)/ zinc oxide (ZnO) hollow nanocage (MCNZH) complexes with Z-scheme heterostructure were prepared for the photocatalytic degradation of tetracycline antibiotics. The catalysts were characterized by SEM, TEM, BET, XRD, FT-IR, EIS, etc. The degradation of tetracycline hydrochloride (40 mg L–1) by MCNZH (1.2 g L–1) can reach 92.08 %. Further, the energy band structure of the catalysts were calculated and the possible degradation mechanism was proposed. The results showed that ·OH– and ·O2– were the main active species, and the internal electric field suppressed the compounding of photogenerated carriers. The catalysts exhibited broad-spectrum degradation of tetracycline antibiotics. Practical sample spiking experiments on soil and river water confirmed its practicability, which provide great significance for the application of the photocatalytic technology in the practical environmental purification.

Surface plasmon resonance effect cooperated with Z-scheme heterostructure for enhancing photocatalytic nitrogen reduction to ammonia

The photocatalytic efficiency can be improved by constructing a Z-scheme heterojunction, but hindered by the only half utilization efficiency of photogenerated carriers. Thus, a novel material, UiO-66-NH2@TAPB-BTCA-COP-Ag (U6N@COP-Ag), with surface plasmon resonance (SPR) effect synergistic Z-scheme heterostructure has been prepared by depositing Ag nanoparticles (Ag NPs) on TAPB-BTCA-COP (COP)-coated UiO-66-NH2. The deposited Ag NPs expand the range of light absorption and introduce more photogenerated electrons in the composite. The SPR effect of noble metal compensates for the limited utilization of the Z-scheme heterojunction photogenerated carriers and the increased density of semiconductor carriers at the reducing end, which is more conducive to the redox reaction of the catalyst. Without sacrificial agents, U6N@COP-Ag shows great photocatalytic nitrogen reduction conversion efficiency with the rate of NH4+ in ammonia water at 167.63μmol g-1h−1, which is 6.6 and 2.8 times that of the original UiO-66-NH2 and COP, respectively. In-situ XPS and Kelvin probe technology verify that UiO-66-NH2 and Ag nanoparticles provide more photogenerated electrons to COP. The cleavage and conversion of N2 to NH4+ on U6N@COP-Ag was confirmed by the enhancement of NH bonds and NH4+ characteristic absorption peaks in the in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS). This work presents a great method to improve the Z-scheme heterojunction photogenerated carrier utilization and the density of semiconductor carriers at the reducing end by the noble metal SPR effect, which is more conducive to enhance the redox reaction of the catalyst.

Synergetic enhancement effect of MOF-derived porous ZnO/ Co3O4 cage Z-scheme heterostructure for high-performance photodegradation

Using solar energy for photocatalytic degradation of pollutants is a clean and effective method for treating the increasingly severe problem of environmental pollution. Herein, porous ZnO/Co3O4 cages with improved charge separation ability was designed via a facile ZIF-8@ZIF-67-derived approach for tetracycline (TC) photodegradation. Great photodegradation performance and good stability were achieved. The degradation rate was as high as 97 % within 60 min. The enhancement mechanism of TC photodegradation was investigated. The porous structure of ZnO/Co3O4 produced a number of active sites. The effective utilized spectrum was extended from the ultraviolet to the red region. The presence of two mixed valence states of Cobalt, Co2+ and Co3+, increased the density of defect states and was conducive to the adsorption of TC. The composite had a Z-scheme heterojunction, in which strong oxidative capacity can be maintained, combination of electrons and holes was greatly reduced and efficient charge transfer occurred. This study would give new insights into the design of new photocatalysts with synergetic enhancement effect for TC photodegradation.