Direct Z-scheme Heterojunction Research Articles

Designing Direct Z-Scheme Heterojunctions Enabled by Edge-Modified Phosphorene Nanoribbons for Photocatalytic Overall Water Splitting.

Direct Z-scheme photocatalyst possess promising potential to utilize solar radiation for photocatalytic overall water splitting; however, the design and characterization remain challenging. Here, we construct and verify a direct Z-scheme heterojunction using edge-modified phosphorene-nanoribbons (X-PNRs, where X = OH and OCN) with first-principles ground-state and excited-state density functional theory (DFT) calculations. The ground-state calculations provide fundamental properties such as geometric structure and band alignment. The linear-response time-dependent DFT (LR-TDDFT) calculations exhibit the photogenerated charge distribution and demonstrate the generation of interlayer excitons in heterojunctions, which are advantageous to the electron-hole recombination in Z-scheme heterojunctions. The ultrafast charge transfer at the interface studied by time-dependent ab initio nonadiabatic molecular dynamics (NAMD) simulations indicates that interlayer electron-hole recombination is prior to intralayer recombination for the OH/OCN-PNRs heterojunction, showing the characteristics of a Z-scheme heterojunction. Therefore, our computational work provides a universal strategy to design direct Z-scheme heterojunction photocatalysts for overall water splitting.

Ultrasensitive Photoelectrochemical Biosensor Based on Novel Z-Scheme Heterojunctions of Zn-Defective CdS/ZnS for MicroRNA Assay.

The sensitive and accurate detection of microRNA (miRNA) has meaningful values for clinical diagnosis application as an early stage of tumor markers. Herein, a novel photoelectrochemical (PEC) biosensor was developed for the ultrasensitive and highly selective detection of microRNA-122 (miRNA-122) based on a direct Z-scheme heterojunction of Zn vacancy-mediated CdS/ZnS (CSZS-VZn). Impressively, the prepared Z-scheme heterojunction nanocomposite with defect level properties could make the photogenerated charges stay at the Zn vacancy defect levels and combine photogenerated holes in the valence bands of CdS, thus significantly achieving a better charge carrier separation efficiency and broadening the absorption of visible light and demonstrating 5-8 times enhancement of PEC response compared to single-component materials. Simultaneously, an exonuclease III (Exo-III)-assisted signal amplification strategy and a strand displacement reaction were combined to improve the conversion efficiency of the target and further increase the detection sensitivity. More importantly, the elaborated biosensor showed ultrasensitive and highly specific detection of the target miRNA-122 over a wide linear range from 10 aM to 100 pM with a low detection limit of 3.3 aM and exhibited enormous potential in the fields of bioanalysis and clinical diagnosis.

Facile construction of 3D hierarchical flower-like Ag2WO4/Bi2WO6 Z-scheme heterojunction photocatalyst with enhanced visible light photocatalytic activity

A novel Z-scheme flower-like Ag2WO4/Bi2WO6 (AWO/BWO) photocatalyst with excellent photocatalytic activity for the contaminant degradation was successfully fabricated through a facile hydrothermal-precipitation method. Various characterization techniques and electrochemical measurements were exploited to study the morphology, structure, photoelectrical property of the photocatalyst. The photocatalytic efficiency for rhodamine B (RhB) degradation over the 3 wt% AWO/BWO composite was nearly 100% within 150 min under visible light, which was 11.5 and 1.5 times higher than pure AWO and BWO. The enhanced photocatalytic performance was attributed to the direct Z-scheme heterojunction, which not only achieved high separation efficiency of photogenerated electrons and holes but also retained strong redox capability of the composite. In addition, excellent stability and recyclability of AWO/BWO composites verified the photocatalyst was suitable for practical wastewater purification. Radical trapping experiment revealed that the dominant reactive species participating in the RhB degradation were superoxide radical(O2–) and holes (h+). Furthermore, a possible mechanism for RhB degradation and charge carriers transfer path was proposed on the basis of experiment results. This work offers new insights into the construction of efficient Bi-based photocatalyst with Z-scheme heterojunction, and exhibits its potential application in the field of environmental remediation.

Preparation of magnetically retrievable flower-like AgBr/BiOBr/NiFe2O4 direct Z-scheme heterojunction photocatalyst with enhanced visible-light photoactivity

The rapid recombination of electrons and holes is the main reason affecting the performance of photocatalyst, and the difficulty in recovery of photocatalyst also impedes its practical application. Herein, the magnetically recoverable flower-like AgBr/BiOBr/NiFe2O4 (AB/BOB/NFO) ternary heterojunction photocatalyst was successfully constructed. The phase composition, morphology, the absorption of visible light of the samples, and the surface chemical environment of samples were tested by XRD, SEM, UV–vis, and XPS, respectively. Compared with pure BiOBr and BiOBr/NFO, AB/BOB/NFO showed improved photocatalytic degradation effect for RhB. 25% AB/BOB/NFO showed the best degradation performance of 100% in 90 min, which was about 3.6 times that of pure BOB. The enhanced photoactivity of AB/BOB/NFO heterojunction photocatalyst can be ascribed to the wider absorption range of visible light and the inhibited recombination of photogenerated electros and holes. Additionally, the flower-like morphology assembled by nanosheets provides more active sites and improve light absorption through reflecting multiple times and plays roles in improving the photocatalytic performance. It was also found that the AB/BOB/NFO heterojunction photocatalyst has excellent magnetic recovery ability under the action of external magnetic field. The photostability of AB/BOB/NFO heterojunction photocatalyst was also investigated, and a direct Z - type electron hole transfer mechanism was proposed according to the energy band structure. These advances provide a new way to improve the photoactivity of magnetic recyclable photocatalysts, and the as-synthesized flower-like AB/BOB/NFO has broad promising application in water environment remediation.

Rational design of direct Z-scheme heterostructure NiCoP/ZIS for highly efficient photocatalytic hydrogen evolution under visible light irradiation

• Direct Z-scheme catalyst of NiCoP/ZIS was prepared through hydrothermal method. • The 37.5% Ni 0.7 Co 0.3 P/ZnIn 2 S 4 showed the best H 2 evolution rate of 3.84 mmol g −1 h −1 . • The charge transfer pathway of NiCoP/ZIS followed the Z-scheme mechanism. Construction of Z-scheme heterojunctions has been recognized as one of the most efficient strategies to significantly improve the charge-separation efficiency and achieve highly efficient solar energy conversion in photochemical reactions. Herein, a novel direct Z-scheme catalyst of NiCoP/ZIS was rational designed and prepared by dispersing ternary metal phosphide NiCoP in ZnIn 2 S 4 (ZIS) nanoflowers under solvothermal method. The compact heterojunction structural characteristic of NiCoP/ZIS afford the composite prominent enhanced photocatalytic hydrogen (H 2 ) production performance. The relative quantities of Ni and Co in NiCoP/ZIS composite can significantly influence the photocatalytic activities of the material, and the 37.5% Ni 0.7 Co 0.3 P/ZIS composite with a Ni/Co mole ratio of 0.7: 0.3 had the best hydrogen production efficiency with a hydrogen evolution rate of 3.84 mmol g −1 h −1 , which is approximately 8 times higher than that of single ZIS. The apparent quantum efficiency (AQE) for 37.5% Ni 0.7 Co 0.3 P/ZIS is about 5.14% under the incident monochromatic light of 405 nm. The subsequent electrochemical analyses proved the significant roles of the direct Z-scheme heterojunction in accumulating the electrons at the conduction bands of ZIS with more negative potential, which contributed to the stronger reduction activity in the promoted hydrogen generation for Ni 0.7 Co 0.3 P/ZIS. This work not only reported a a novel direct Z-scheme catalyst of NiCoP/ZIS heterostructure with enhanced photocatalytic hydrogen generation performance, but also provided a promising approach to rational design and construct efficient visible-light-driven photocatalysts for solar energy utilization.

Direct Z-scheme construction of g-C3N4 quantum dots / TiO2 nanoflakes for efficient photocatalysis

The rapid recombination rate of photogenerated carriers in TiO2 has been limiting the photocatalytic performance. Herein, TiO2 thin flakes modified by g-C3N4 quantum dots (g-C3N4 QDs) were fabricated successfully through a facile thermal treatment of restacked single-layer nanosheets of Ti1.73O41.07- in the presence of urea as a source of g-C3N4 QDs. Characterizations showed that g-C3N4 QDs with a size of ~10 nm were homogeneously deposited on the surface of TiO2 thin flakes. Quenching experiments of •OH radicals and the detection of radicals by EPR certified the direct Z-scheme heterojunctions between g-C3N4 QDs and TiO2 flakes. The TiO2 nanoflakes/g-C3N4 QDs hybrid exhibited excellent activity for the photocatalytic hydrogen evolution from a methanol solution and the degradation of RhB due to the enhanced charge separation efficiency and improved light absorption in the direct Z-scheme heterojunctions. This study demonstrates that the rational design of heterojunction is effective for attaining the superior photocatalytic performance.

Charge transfer in photocatalysis of direct Z-scheme g-C3N4-based ferroelectric heterojunction

Great efforts have been made to enhance the photocatalytic efficiency of g-C3N4. The construction of Z-scheme g-C3N4-based ferroelectric heterostructures was considered to be an effective strategy to promote rapid carrier separation. However, the mechanism of charge transfer in the synergistic effect between Z-scheme g-C3N4-based heterojunction and ferroelectric polarization has not been thoroughly studied. Herein, g-C3N4-based ferroelectric catalysts with various bismuth ferrite (BiFeO3) contents have been prepared with a simple approach, and the direct Z-scheme heterojunction between BFO and g-C3N4 has been proved by experiments. Meanwhile, our study verified that the direct Z-scheme g-C3N4-based ferroelectric heterostructure plays a positive role in photocatalytic activity, and the charge transfer mechanism of this structure was discussed in detail, which provides a new strategy for improving the performance of g-C3N4-based ferroelectric catalysts.

A highly sensitive and visible-light-driven photoelectrochemical sensor for chlorpyrifos detection using hollow Co9S8@CdS heterostructures

A highly sensitive and visible-light-driven photoelectrochemical (PEC) sensor has been constructed for the quantitative assay of organophosphorus pesticides like chlorpyrifos (Chlo) using hollow Co9S8@CdS heterostructures. The Co9S8@CdS heterostructures were created by growing CdS onto Co9S8 surface via one-step oil-bath route, of which Co9S8 was fabricated with hollow tubular structures through the Co(CO3)0.35Cl0.2(OH)1.1-templated solvothermal method. It was discovered that the so-obtained Co9S8@CdS with direct Z-scheme heterojunctions could exhibit larger photocurrents than the Co9S8 or CdS because of the greatly enhanced separation efficiency of photo-generated carriers. What’s more, the photocurrent signal of Co9S8@CdS-based PEC sensor could be selectively inhibited with the addition of Chlo through the specific chelation between the N and S atoms of Chlo with CN and PS groups and Co sites of Co9S8@CdS so as to suppress the carriers transferring. The developed PEC sensor could exhibit a linear response for Chlo ranging from 0.050 to 1000 ppb, with the detection limit value down to 0.015 ppb, which was far below than those of currently reported PEC sensors. Besides, the proposed routes may provide guidelines for designing various direct Z-scheme heterojunction-based PEC analysis platforms for determining environmental pollutants like Chlo.

Z-scheme junction Bi2O2(NO3)(OH)/g-C3N4 for promoting CO2 photoreduction

Photocatalytic CO2 reduction is believed to be an emerging strategy to address fossil fuels consumption and global warming problems. However, the rapid recombination of photogenerated carriers restricts the application of photocatalytic technology severely. Constructing heterojunction structure is one of the most effective pathways to facilitate the charge separation and photocatalytic performance. In this work, a series of direct Z-scheme heterojunction Bi2O2(NO3)(OH)/g-C3N4 (BON/CN) was developed by an electrostatic self-assembly method. The optimal BON/CN-2 photocatalyst exhibits a conspicuous photocatalytic CO2 reduction activity with a high CO evolution rate of 14.84 µmol g-1h−1 under the stimulated solar light irradiation, which is about 15 and 3.5 times higher than that of pure BON and g-C3N4, respectively. The significantly promoted photocatalytic performance is attributed to the tightly-contact interface and formation of Z-scheme between BON and g-C3N4, which favor for the separation and transfer of photogenerated electrons and holes, as confirmed by high resolution transmission electron microscope (HRTEM), electron spin resonance (ESR), photoelectrochemical measurement and photoluminescence (PL) results. This work may provide a new reference for developing rational tactics to fabricate efficient Z-scheme heterojunction photocatalysts for CO2 conversion.

Enhanced degradation of organic water pollutants by photocatalytic in-situ activation of sulfate based on Z-scheme g-C3N4/BiPO4

In recent years, the excellent performance of sulfate radical (SO4·−) in advanced oxidation process has attracted more and more attention. However, it requires the consumption of expensive persulphate (PMS/PDS), and the resulting sulfate ion (SO42−) requires subsequent processing procedures, which limits its practical application value. In this work, a Z-scheme heterojunction g-C3N4/BiPO4 (CNBx) photocatalyst was constructed to in-situ activate the residual SO42− , H2O and dissolved O2 in organic wastewater simultaneously and produce SO4·−, ·OH and O2·− efficiently, so as to realize enhanced organic pollutant treatment by using clean and renewable solar energy resources. Under the condition of 10 mM SO42− addition and 100 mW·cm−1 illumination, the degradation rate of BPA (C0 = 20 mg·L−1) by optimized CNB150 catalyst was 0.30 min−1, which was 50% higher than that without SO42− (0.20 min−1). Detailed characterizations shown that a direct Z-scheme heterojunction was formed between g-C3N4 and BiPO4, which could be simultaneously stimulated by light, and then effective charge separation and migration could be achieved through the internal electric field caused by the Fermi-level difference between the g-C3N4 (-0.12 eV) and BiPO4 (0.01 eV). In general, this study makes full use of renewable solar energy and provides a feasible path for promoting the simultaneous in-situ utilization of small molecules (SO42−, H2O and O2) that originally exist in water, which makes organic wastewater treatment more economic, eco-friendly and sustainable.

Investigation of the Kinetics and Reaction Mechanism for Photodegradation Tetracycline Antibiotics over Sulfur-Doped Bi2WO6-x/ZnIn2S4 Direct Z-Scheme Heterojunction.

The rational design of direct Z-scheme heterostructural photocatalysts using solar energy is promising for energy conversion and environmental remediation, which depends on the precise regulation of redox active sites, rapid spatial separation and transport of photoexcited charge and a broad visible light response. The Bi2WO6 materials have been paid more and more attention because of their unique photochemical properties. In this study, S2− doped Bi2WO6-x coupled with twin crystal ZnIn2S4 nanosheets (Sov−BWO/T−ZIS) were prepared as an efficient photocatalyst by a simple hydrothermal method for the removal of tetracycline hydrochloride (TCH). Multiple methods (XRD, TEM, XPS, EPR, UV vis DRS, PL etc.) were employed to systematically investigate the morphology, structure, composition and photochemical properties of the as-prepared samples. The XRD spectrum indicated that the S2− ions were successfully doped into the Sov−BWO component. XPS spectra and photoelectrochemical analysis proved that S2− served as electronic bridge and promoted captured electrons of surface oxygen vacancies transfer to the valence band of T−ZIS. Through both experimental and in situ electron paramagnetic resonance (in situ EPR) characterizations, a defined direct Z-scheme heterojunction in S-BWO/T−ZIS was confirmed. The improved photocatalytic capability of S-BWO/T−ZIS results ascribed that broadened wavelength range of light absorption, rapid separation and interfacial transport of photoexcited charge, precisely regulated redox centers by optimizing the interfacial transport mode. Particularly, the Sov−50BWO/T−ZIS Z-scheme heterojunction exhibited the highest photodegradation rate was 95% under visible light irradiation. Moreover, this heterojunction exhibited a robust adsorption and degradation capacity, providing a promising photocatalyst for an organic pollutant synergistic removal strategy.

Defects regulation of Sb2S3 by construction of Sb2S3/In2S3 direct Z-scheme heterojunction with enhanced photoelectrochemical performance

Antimony sulfide (Sb2S3), as a narrow band-gap semiconductor with strong visible light absorption ability, nevertheless due to the existence of a large number of defective energy levels, the application in the field of PEC water splitting was limited. This paper aimed to construct Sb2S3/In2S3 direct Z-scheme heterojunction to effectively eliminate the adverse effect of defective energy level on the photoelectrochemical performance of Sb2S3. Cell-like Sb2S3 thin films were prepared on ITO substrates by simple hydrothermal method, followed by using solvothermal method, the Sb2S3/In2S3 direct Z-scheme heterojunction was successfully constructed. The IPCE values of Sb2S3/In2S3 could reach 10.19 % (735 nm) compared with pure Sb2S3 (4.22 %). Both the separation and injection efficiency could be improved from 3.35 % and 31.69 % to 5.19 % and 61.48 %, respectively. The maximum photocurrent density was 1.24 mA/cm2 at 1.23 V vs. RHE, which was 5.6 times higher than pristine Sb2S3 (0.22 mA/cm2). Moreover, an earlier onset potential was observed (~0.7 V vs. RHE), showing an improvement of 0.3 V when compared to the pristine Sb2S3. This work provided a new idea for the application of antimony chalcogenides in the field of PEC water splitting and the construction of efficient photoelectric devices.

Highly efficient photoelectrocatalytic degradation of cefotaxime sodium on the MoSe2/TiO2 nanotubes photoanode with abundant oxygen vacancies

Novel multifunctional photoanode on basis of MoSe2 nanoparticles modified TiO2 nanotubes(denoted as MoSe2/TiO2 NTs) were successfully prepared by facile electrochemical methods namely anodization followed by cyclic voltammetry method using titanium foil as substrate. Compared to TiO2 NTs, the MoSe2/TiO2 NTs display excellent photoeletric properties, including more abundant surface oxygen vacancies, enhanced visible-light absorption, improved photocurrent response, reduced fluorescence intensity and decreased charge transfer resistance. These enhancements should be attributed to efficient spatial separation and rapid transfer of photo-induced electrons and holes on the intimate contact interface between MoSe2 nanoparticles and TiO2 NTs. In the photo-electric synergistic catalytic system, the as-prepared MoSe2/TiO2 NTs play double roles as both photoanode and catalyst. Under simulated solar light illumination, the MoSe2/TiO2 NTs photoanode shows superior photoelectrocatalytic activity in the degradation of cefotaxime sodium at low applied bias voltage. Moreover, a possible mechanism of the transfer pathway of photo-induced charge carriers on the MoSe2/TiO2 NTs photoanode is proposed based on the synergistic effect of surface oxygen vacancies and direct Z-scheme heterojunction.

Perylenetetracarboxylic diimide covalently bonded with mesoporous g-C3N4 to construct direct Z-scheme heterojunctions for efficient photocatalytic oxidative coupling of amines

Photocatalytic oxidative coupling of amines is a promising method for imine synthesis. In this paper, a robust covalently-bonded direct Z-scheme heterostructure (PDI/mpgCN) for photocatalytic oxidative coupling of amine was reported for the first time. Perylenetetracarboxylic diimide (PDI) molecules were covalently connected to the surface of mesoporous carbon nitride (mpgCN) via an in-situ condensation strategy. Compared with the poor conversion efficiency upon pristine g-C3N4, PDI/mpgCN heterostructure exhibits a remarkable enhancement on amine oxidation rate (AOR), with the optimal AOR reaches to as high as 20.63 mmol g−1 h−1 upon 20 % PDI/mpgCN. As far as we know, it is the highest AOR achieved so far for amine photooxidation coupling with heterojunction materials. Transient absorption studies proved the formation of Z-scheme junction, and efficient interfacial charge transfer. Our study not only makes an insight into the heterojunction design with chemical bond precision, but highlights the great prospects of Z-scheme photocatalyst in photo-chemical synthesis.

Construction of three-dimensional MgIn2S4 nanoflowers/two-dimensional oxygen-doped g-C3N4 nanosheets direct Z-scheme heterojunctions for efficient Cr(VI) reduction: Insight into the role of superoxide radicals

Environmental crisis aroused from carcinogenic and mutagenic heavy metal Cr(VI)-containing wastewater has attracted great attention. Herein, a direct Z-scheme three-dimensional MgIn2S4 nanoflowers/two-dimensional oxygen-doped g-C3N4 nanosheets heterostructured composite photocatalysts were fabricated for Cr(VI) photoreduction. The crystalline structure, morphology, specific surface areas, chemical components, optical properties, as well as photoelectrochemical performance of the fabricated photocatalyst were systematically studied. All the hybrids photocatalysts exhibited superior Cr(VI) photoreduction performance than a single component. The optimal sample showed 2.0 and 343.7 times increasing than three-dimensional MgIn2S4 nanoflowers and two-dimensional oxygen-doped g-C3N4 nanosheets, respectively. The enhancement of the Cr(VI) photoreduction performance could be ascribed to the enhanced specific surface areas, the improved light absorption, and the Z-scheme charge carriers’ separation and migration pathway. Moreover, the role of superoxide radicals was investigated. It is speculated that this research would present a new sight toward photocatalytic Cr(VI) reduction.

Photocatalytic degradation of tetracycline by metal-organic frameworks modified with Bi2WO6 nanosheet under direct sunlight

Porous metal-organic frameworks (MOFs) with visible-light response have attracted much attention in the field of environmental purification and solar energy conversion. In this study, MIL-100(Fe) was modified with Bi2WO6 nanosheets by a facile hydrothermal method to fabricate a photocatalyst with direct Z-scheme heterojunction. When treating the tetracycline (TC) solution under natural sunlight, 12 wt%MIL-100(Fe)/Bi2WO6 obtained the highest apparent rate constant of (6.59 ± 0.52)✕10−3 L mg−1 min−1, which was 16.1 and 3.9 times than that of pristine MIL-100(Fe) and Bi2WO6, respectively. In addition to explore the feasibility of sunlight-activated MIL-100(Fe)/Bi2WO6 to remove TC under various conditions, the degradation intermediates and their possible transformation pathway were provided with the aid of three-dimensional excitation−emission matrix spectra and liquid chromatography-mass spectrometry system. The results of Escherichia coli culture demonstrated that the biotoxicity variation of TC solution would first increase and then decrease with the photodegradation time. Ultimately, based on the results of bandgap calculation, radicals trapping and charge flow tracking experiments, the direct Z-scheme heterojunction between MIL-100(Fe) and Bi2WO6 nanosheets was confirmed and the photocatalytic mechanism for TC degradation was rationally proposed. This work enriched MOFs-based heterojunction photocatalysts and provided a promising method to eliminate hazardous TC from aqueous solution.

Rational design of novel three-dimensional reticulated Ag2O/ZnO Z-scheme heterojunction on Ni foam for promising practical photocatalysis

Direct Z-scheme heterojunctions composed of Ag2O nanoparticles and ZnO nanorods were immobilized on Ni foam (AZN) via combined hydrothermal and precipitation methods to successfully construct 3D reticulated composites, and their photocatalytic performance were evaluated under simulated sunlight. Just as expected, the AZN samples exhibited excellent photocatalytic effects of 99.26% for the model pollutant (rhodamine B) in water after loading with Ag2O, which was 2.77 times higher than that of regular ZnO NAs/Ni foam composites. Meanwhile, the surface wettability of composite was remarkably enhanced. Besides, a series of photoelectrochemical measurements showed a significant improvement in the charge separation efficiency of AZN, which was attributed to the synergistic effect of direct Z-scheme heterojunction, matched energy band structure as well as 3D porous structure. Moreover, the AZN sample presented satisfactory stability after four cycles, meanwhile it displayed good removal performance against different types of antibiotics (Tetracycline, Sulfadiazine and Ciprofloxacin). The applicability and durability of AZN for rhodamine B degradation were evaluated by sequential batch experiments in a homemade simulated flowing water device. More importantly, the lower value of electrical energy per order indicated the photocatalyst/simulated sunlight system was more energy efficient and effective. Accordingly, this work provided a new strategy for designing 3D reticulated composites with low-dimensional nanomaterials to decompose organic pollutants in impaired waters.

1D/2D constructed Bi2S3/Bi2O2CO3 direct Z-Scheme heterojunction: A versatile photocatalytic material for boosted photodegradation, photoreduction and photoelectrochemical detection of water-based contaminants

In this work, two-dimensional Bi2O2CO3 disk is synthesized, followed by the growth of Bi2S3 over Bi2O2CO3 via topotactic transformation by controlling the amount of thiourea under hydrothermal conditions. The synthesized composite catalyst is investigated for photocatalytic oxidation and reduction of tetracycline hydrochloride and hexavalent chromium under visible light irradiation. High interfacial contact between the Bi2O2CO3 disk0 and Bi2S3 fiber is confirmed via high-resolution microscopic imaging. Enhanced light absorption and increased charge carrier separation is observed after the formation of the Bi2S3/Bi2O2CO3 composite. The Bi2S3/Bi2O2CO3 composite grown using 1 mmol of thiourea shows approximately 98% degradation of tetracycline hydrochloride after 120 min and 99% Cr(VI) reduction after 90 min of photochemical reaction under visible light irradiation. The charge separation is due to the formed internal electric field at the interface, which upon light irradiation follows a z-scheme charge transfer hindering the recombination at the Bi2S3 and Bi2O2CO3 interface, thereby contributing efficiently to the photochemical process. In addition, the mechanism of the photochemical reaction for the degradation of pollutants is supported using quencher and probe experiments. Furthermore, photoelectrochemical detection of antibiotic in aqueous solution is conducted to understand the sensing feasibility of the synthesized system.

In situ synthesis of an advanced Z-scheme Bi/BiOI/black TiO2 heterojunction photocatalysts for efficient visible-light-driven NO purification

Limited light absorption and severe charge recombination have been widely acknowledged as the two main obstacles restricting the application of P25 in NO photocatalytic conversion. In this work, an advanced heterojunction photocatalyst of Bi/BiOI/black TiO2 was synthesized via an in-situ solid-state chemical reduction method. The black TiO2 extended the light absorption to the full spectral region. It constructed a direct Z-scheme heterojunction with BiOI nanosheets, not only promoting the charge separation, but also preserving the strong oxidation ability of photogenerated holes in black TiO2 and strong reducing ability of photogenerated electrons in BiOI. Thus, more •O2− and •OH radical could form when Bi/BiOI/black TiO2 was subjected to visible light irradiation. Besides, the introduced Bi metal nanoparticles could also enhance the light utilization and served as a cocatalyst to accept the electrons. Therefore, enhanced NO photocatalytic oxidation activity was obtained, with the optimal sample Bi/BiOI/black TiO2 exhibiting a high NO conversion efficiency of ~70% and NOx removal of ~45%. This work may provide a refreshing perspective for the design of heterojunction photocatalysts for efficient NO photocatalytic purification and other photocatalytic applications.

Fabrication of novel polyaniline/ZnO heterojunction for exceptional photocatalytic hydrogen production and degradation of fluorescein dye through direct Z-scheme mechanism

In the recent years, direct Z-scheme heterojunctions exhibit an exceptional reactivity in various photocatalytic processes. Hybrid visible light driven photocatalyst consisting of semiconducting metal oxide and conducting polymer have immense capability of destruction of various organic pollutants and production of hydrogen gas as alternative renewable energy source. Herein, a novel hybrid polyaniline/ZnO heterojunction were synthesized by coupling sol-gel and oxidative polymerization of aniline in ultrasonic bath of various intensities for removal of fluorescein dye and producing large amount of hydrogen gas under visible light source. Particularly, the amount of polyaniline plays a pivotal role in optimizing the amount of hydrogen gas produced. The change in the diffraction pattern of Wurtzite ZnO nanoparticles and the remarkable reduction of PL signal intensity suggest the construction of direct Z-scheme heterojunction. The photocatalytic hydrogen production rate estimated on the optimized sample using methanol as scavenger is 9.4 mmolh −1 g −1 which is higher than that of bare ZnO nanoparticles. The sample containing 5 wt% polyaniline exhibits photocatalytic degradation rate of fluorescein dye 0.021 min −1 which is ten folds higher than that of bare ZnO. The results of our research work indicate that polyaniline is efficiently enhances the light absorption and providing an additional electrons that combine with H + to produce H 2 -gas. • Novel polyaniline/ZnO were synthesized by sonochemical route. • Positive shift of the photocatalytic response to visible region. • Exceptional photocatalytic hydrogen evolution. • High stability for five consecutive cycles.