Separation Of Photoinduced Charge Carriers Research Articles

BiOI Particles Confined into Metal-Organic Framework NU-1000 for Valid Photocatalytic Hydrogen Evolution under Visible-Light Irradiation.

Herein, a surface site engineering strategy is used to construct a porous Z-scheme heterojunction photocatalyst for photocatalytic hydrogen evolution (PHE) by integration of BiOI in a mesoporous Zr-based metal-organic framework (MOF) NU-1000. Three high-quality and highly dispersed BiOI@NU-1000 heterojunction materials are synthesized, and a set of methods is used to characterize these materials, indicating that the BiOI@NU-1000 heterojunction can retain high porosity and crystallinity of the parent NU-1000. Furthermore, the built-in electric field of the BiOI@NU-1000 composite can effectively tune the band gap, promote the separation of photoinduced charge carriers, improve photocurrent intensity, and reduce photoelectric impedance. Under visible-light irradiation, BiOI@NU-1000-2 showed the best photocatalytic performance in the field of MOF-based photocatalysts for PHE, with a hydrogen production rate of up to 610 μmol h-1 g-1. This study will open up opportunities for the construction of Z-scheme photocatalysts based on the highly porous MOF materials to inspire the development of innovative photocatalysts.

Isotypic heterojunction based on Fe-doped and terephthalaldehyde-modified carbon nitride for improving photocatalytic degradation with simultaneous hydrogen production

To achieve an efficient photocatalytic for clean energy production and environmental remediation, the highly active Fe-doped and terephthalaldehyde-modified carbon nitride (Fe-CN/NTE) isotypic heterojunction photocatalyst is constructed via a simple annealing method for degradation of organic pollutants with simultaneous resource recovery. The Fe-CN/NTE catalyst exhibits a 93% removal rate of p-nitrophenol (4-NP) and a 1.72 mmol/g H2 evolution rate in 2 h simultaneously under visible light irradiation, which are higher than those of pristine CN, Fe-CN, and NTE, respectively. Photoelectrochemical tests show that the excellent photocatalytic performance of Fe-CN/NTE comes from the improved migration, transportation, and separation of photoinduced charge carriers and expanded light-harvesting range. Moreover, hydroxyl radical (OH), electron (e−), and hole (h+) are the main active species and the rational mechanism of 4-NP photodegradation was proposed based on scavenger measurements and liquid chromatography-mass spectrometry (LC–MS), respectively. Isotypic heterojunction Fe-CN/NTE photocatalyst possesses excellent stability in the H2 evolution and 4-NP degradation during five-run cycle tests, posing as a promising candidate in practical works for organic pollution and energy challenges.

High-efficiency separation and transfer of photo-induced charge carrier in graphene/TiO2 via heterostructure in magnetic field

Providing a driving force is an effective approach to boost the separation of photo-induced charge carriers. Photoelectrode application is the most accepted route. However, it is difficult to realize the high-efficiency photocatalytic activity of granular photocatalysts in suspension by applying the electric field. In this work, on the basis of the Lorentz force-driven improved separation of photo-induced charge carriers in TiO2 nanobelts, further enhancement of the charge transfer was achieved through constructing a heterostructure of reduced graphene oxide (rGO)/TiO2 nanobelts (NBs) in a magnetic field. The photocatalytic efficiency of the rGO/TiO2 NB heterostructure improved by 34% compared with pure TiO2 NBs under the same magnetic field conditions. This new strategy combined the Lorentz force generated in a magnetic field and the built-in electric field of rGO-TiO2 NBs to improve photo-induced charge carrier separation and transfer. Furthermore, a wireless microelectric potential was generated in rGO based on the electromagnetic induction effect, which additionally improved the charge transfer in rGO. This work provides a new idea to improve the photocatalytic activity of granular photocatalysts.

High-impressive separation of photoinduced charge carriers on step-scheme ZnO/ZnSnO3/Carbon dots heterojunction with efficient activity in photocatalytic NH3 production

Photocatalytic N2 fixation has been overgrowing since the 20th century because the Haber–Bosch process is more energy-intensive. Therefore other sustainable alternatives are highly needed. A simple procedure for constructing novel ZnO/ZnSnO3/Carbon Dots hybrid nanocomposites was exhibited through the hydrothermal approach. The surface morphology, crystal structure, and phase of the designed nanomaterials were assayed with various analyses. In this research paper, photocatalytic N2 fixation induced by ternary ZnO/ZnSnO3/Carbon Dots system. The results displayed that the ZnO/ZnSnO3/Carbon Dots (0.5 mL) system has remarkable activity in the N2 fixation process compared with the sole ZnO and ZnO/ZnSnO3 (30%), which is 11.5 and 2.1 times, respectively. The durability of the optimum system, as an essential character of the nanocomposite, was assayed in four recycles. Moreover, the effect of solvent, electron scavenger and media pH in the NH4+ generation rate was investigated. At last, a suitable mechanism was offered for the notable N2 photofixation improvement. This novel information could clarify the construction of impressive systems for nitrogen photofixation.

Construction of a hierarchical NiFe2O4/ CuInSe2 (p-n) heterojunction: Highly efficient visible-light-driven photocatalyst in the degradation of endocrine disruptors in an aqueous medium

The present study reports the effective solid-state preparation of CuInSe2/NiFe2O4 nanocomposites by simple MOF-assisted synthesis at moderate temperatures. The as-synthesized CuInSe2/NiFe2O4 nanocomposites were systematically analysed to evaluate their structural and morphological features using XRD, SEM, and HRTEM. The photocatalytic performances of the CuInSe2/NiFe2O4 nanocomposites were evaluated for the degradation of two endocrine disruptors namely, bisphenol-A and resorcinol. The photocatalytic performances revealed that the CuInSe2/NiFe2O4 nanocomposite enabled a higher removal rate of bisphenol-A and resorcinol under visible light. The generated (°OH) and holes (h+) played a major role in CuInSe2/NiFe2O4 nanocomposites by the removing of aqueous bisphenol-A and resorcinol. In addition, CuInSe2/NiFe2O4 photocatalysts could be easily separated from treated wastewater by using an external magnetic field and they were easily recycled, making them an ideal candidate for environmental remediation. Here, CuInSe2/NiFe2O4 nanocomposites were prepared for the first time by coupling MOF-derived NiFe2O4 with CuInSe2 in the solid-state, route was reported for the first time. From the experimental results and degradation studies, we proposed photocatalytic mechanisms for improving CuInSe2/NiFe2O4 nanocomposite photocatalytic performance. The well-organized heterostructure effect and effective separation of photoinduced charge carriers between NiFe2O4 and CuInSe2 enabled faster degradation. The synthesized recyclable CuInSe2/NiFe2O4 nanocomposite has been applied as an alternative photocatalyst material in the treatment of both households and various industrial pollutants.

Synergistic effect of a noble metal free MoS2 co-catalyst and a ternary Bi2S3/MoS2/P25 heterojunction for enhanced photocatalytic H2 production

Semiconductor heterojunction has been regarded as one of the most promising strategies to produce efficient photocatalysts, which construction can be beneficial to accelerate the separation of photo-induced charge carriers for boosting photocatalytic H2 production. Herein, noble-metal-free MoS2 was adopted as a co-catalyst to construct a ternary Bi2S3/MoS2/P25 heterojunction for boosting electrons transfer and further evaluating for H2 production from water under solar irradiation. Due to the synergistic effects of the co-catalyst and heterojunction in the Bi2S3/MoS2/P25 system, the optimal MoS2/P25/Bi2S3 sample provides the excellent photocatalytic activity of H2 evolution rate (13.0 mmol g−1 h−1), which can be ascribed to the positive synergetic effects of improved charge transfer and efficient separation of the light-induced charge carriers of MoS2/P25/Bi2S3 arose from the dual-channel charges transfer path. By taking full advantage of ternary heterojunction and co-catalyst for promoting H2 production, this work guarantees insights into the low-cost, large-scale production of commercial TiO2-based ternary composite materials applied in solar photocatalytic hydrogen production.

Fabrication of g-C3N4/PW12/TiO2 composite with significantly enhanced photocatalytic performance under visible light

The exploration and development of supernally effective and persistent visible-light-responsive catalysts for environment remediation is regarded as one of the most challenging topics at present. Herein, a new g-C3N4/PW12/TiO2 (CN/PT-X; X = 3.2, 6 and 9) composite photocatalyst was fabricated through a convenient electrospinning/calcination technique, followed with thermal polymerization method. In the composite, the g-C3N4 was grown on PW12/TiO2 nanofibers forming 3D nanofibrous networks, in which the g-C3N4 quality was simply operated by regulating quality ratios of urea to PW12/TiO2 during preparation process. The X-ray photoelectron spectra (XPS) results confirmed the interfacial interaction between g-C3N4 and PW12/TiO2, implying the heterojunction formation between the two components. The photocatalytic tests showed that the CN/PT composites exhibited remarkable and stable photocatalytic performance for removing tetracycline (TC), bisphenol A (BPA) and reduction of Cr(VI) with visible-light (λ > 420 nm) irradiation. Furthermore, the CN/PT-6 sample displayed the optimal catalytic activity with the rate constants of 0.03443 min−1 (TC), 0.00712 min−1 (BPA) and 0.025 min−1 (Cr(VI)), respectively. The enhanced performance could be ascribed to the enhanced adsorption in visible-light region, high specific surface area, effective separation and transfer of photoinduced charge carriers. The active species capturing tests and ESR measurements verified that h+ and ·O2− were answerable for TC degradation. The mechanism accounting for the observed photocatalytic behaviour was proposed and discussed based on the band gap structure and free radicals capture tests.

CQDs decorated oxygen vacancy-rich CeO2/BiOCl heterojunctions for promoted visible light photoactivity towards chromium (Ⅵ) reduction and rhodamine B degradation

Engineering a heterojunction with high photoactivity and better exciton separation in photocatalyst is a promising target for environmental purification. In this context, we fabricated CQDs decorated double-shell CeO2 hollow spheres(D-CeO2)/BiOCl heterojunction (D-CeO2: CQDs/BiOCl) composite by a simple method and scrutinized it photocatalytic performance toward chromium (Ⅵ) reduction and rhodamine B degradation. The resultant D-CeO2: CQDs/BiOCl composite is validated much more active under visible light irradiation with the high rhodamine B degradation rate of 0.12min−1 which is about 3 and 255 times, meanwhile, chromium (Ⅵ) reduction rate of 0.015 min−1 which is about 6 and 32 times higher than the neat BiOCl and D-CeO2, respectively. The interfacial domain of D-CeO2/BiOCl decorated with CQDs for efficient photoinduced charge carriers transfer and separation are the point to attractive photocatalytic performance which combines the double-shell hollow sphere morphology with highly efficient light harvesting, rich OVs for the charge carriers fast separation and accelerated charge transfer after the CQDs participating.

Constructing ultralong hollow chain-ball-like carbon nitride implanted with oxygen for superior visible-light photocatalytic hydrogen production

Regulating morphology has recently become an effective approach to improve the photocatalytic activity of graphite carbon nitride, but its morphology types are still limited. Herein, ultralong hollow chain-ball-like carbon nitride implanted with oxygen (OCNT) was prepared through a facile supramolecular self-assembly route. The ultralong hollow chain-ball-like structure results in enhanced photoinduced charge carrier separation. In particular, the implantation of oxygen into the chemical backbone leads to the formation of a midgap state, which can more effectively capture visible light. The H2 production rate (HPR) of OCNT is 5.47 mmol h−1 g−1, which is much higher than that of BCN by a factor of 14.0 under visible light irradiation. Moreover, BCN displays the very low HPR with values close to zero, while OCNT exhibits much superior efficiency (1.62 mmol h−1 g−1) under long visible light illumination (λ > 510 nm). The current research results may furnish fresh insights into the exploration of carbon nitride with different morphologies for high solar energy utilization.

Self-assembly synthesis of petal-like Cl-doped g-C3N4 nanosheets with tunable band structure for enhanced photocatalytic activity

Efficient separation of photo-induced charge carriers is highly desired for improving photocatalytic activity. Herein, morphology control and element doping are adopted to overcome the shortcomings of insufficient contact with pollutants and limited light-harvesting capability of the pristine g-C3N4. Petal-like Cl-doped g-C3N4 nanosheets are fabricated by a flexible self-assembly route using melamine and cyanuric as precursors, with different amounts of NH4Cl added to adjust the chlorine doping ratio. Benefiting from the enlarged specific surface area (98.330 m2 g−1), tunable band structure and the effective charge separation, the prepared chlorine doping g-C3N4 nanosheets show obviously higher efficiency in the removal of rhodamine B (90 min, 94.3 %) and tetracycline hydrochloride (120 min, 65.7 %), with degradation kinetic rates about 15.8 and 2.3 times than that of pristine g-C3N4. The supramolecular self-assembly and chlorine doping display a noticeable synergy on enhancing the photocatalytic performance, enabled g-C3N4-based nano-sized photocatalysts to be highly competitive candidates for pollutant elimination.

Fabrication of hierarchical flower-like BiOI/MoS2 heterostructures with highly enhanced visible-light photocatalytic activities

In the paper, a novel BiOI/MoS2 (BMS) heterojunction was prepared by a facile hydrothermal method. BiOI nanoplates grew in-situ on the surface of exfoliated MoS2 nanosheets, followed by anisotropic growth and self-assembly, forming a hierarchical flower-like heterostructure finally. Experimental results illustrated that MoS2 as well as the BiOI amounts play a vital role in influencing the morphology and photocatalytic activity of BMS heterojunctions. Among the obtained photocatalysts, BMS-8 displayed the strongest photocatalytic performance under visible light irradiation towards the degradation of rhodamine B (RhB) and disinfection of Pseudomonas aeruginosa (P. aeruginosa). The highly enhanced photocatalytic activity can be attributed to the synergistic effect and formation of a type II heterostructure between BiOI and MoS2, boosting the catalytic active sites, enhancing visible light harvesting, and promoting the efficient separation of photoinduced charge carriers. Moreover, BMS-8 composite showed a good stability in photocatalytic reaction, which favored a long-term use. The active species trapping experiments validated the dominating role of photogenerated holes (h+) and ⋅O2− radicals in the photocatalytic process for BMS-8 heterojunction. It is anticipated that this work can promote further interest in constructing novel heterostructures with controllable morphology and highly efficient photocatalytic activity for potential environmental purification and energy conversion.

Enhancement of Titania Photoanode Performance by Sandwiching Copper between Two Titania Layers.

Vacancies in semiconductors can play a versatile role in boosting their photocatalytic activity. In this work, a novel TiO2/Cu/TiO2 sandwich structure is designed and constructed. Abundant vacancies were introduced in TiO2 lattice by Cu reduction under heat treatment. Meanwhile, Cu atom could diffuse into TiO2 to form Cu-doped TiO2. The synergistic effect between oxygen vacancies and Cu atoms achieved about 2.4 times improved photocurrent of TiO2/Cu/TiO2 sandwich structure compared to bare TiO2 thin film. The enhanced photoactivity may be attributed to regulated electron structure of TiO2 by oxygen vacancies and Cu dopant from experimental results and density functional theory calculations. Oxygen vacancies and Cu dopant in TiO2 formed through copper metal reduction can introduce impurity levels and narrow the band gap of TiO2, thus improve the visible light response. More importantly, the Cu2+ and oxygen vacancies in TiO2 lattice can dramatically increase the charge density around conduction band and promote separation of photo-induced charge carriers. Furthermore, the oxygen vacancies on the surface may serve as active site for sufficient chemical reaction. This work presents a novel method to prepare doped metal oxides catalysts with abundant vacancies for improving photocatalytic activity.

A novel S-scheme 1D/2D Bi2S3/g-C3N4 heterojunctions with enhanced H2 evolution activity

The development of eco-friendly photocatalyst system made of earth-abundant elements is of great importance to meet the needs of both environmental and energy application. In this work, we have successfully synthesized the binary S-scheme Bi2S3/g-C3N4 heterostructure by a simple one-step solvothermal method, in which 1D Bi2S3 nanorods uniformly growing on the 2D g-C3N4 nanosheets. Under visible light illumination, the optimized Bi2S3/g-C3N4 hybrid exhibits the highest photocatalytic activity for H2 evolution. In detail, the H2 evolution rate of 0.6 % Bi2S3/g-C3N4 reach up to unexceptionable 3394.1 μmol∙g−1∙h−1, which are approximately 2.6 times higher than that of pure g-C3N4. In cycling experiment, the photocatalytic activity of 0.6 % Bi2S3/g-C3N4 almost no change that revealing its excellent stability and recyclability. Based on the radical-trapping experiment and band structure results, we can draw a conclusion that the transfer and separation of photoinduced charge carriers obeyed by the direct S-scheme mechanism, which can tremendously facilitate the separation and utilization of charge carries and thus leading to distinctly enhanced photocatalytic performance. More importantly, this work sheds light on new routes to designing eco-friendly photocatalyst system based on the earth-abundant elements for both environmental and energy application.

Preparation of meso-tetraphenyl porphyrin modified defect-rich BiOCl with enhanced visible-light photocatalytic activity for antibiotic degradation and mechanism insight

The exploration of effective photocatalysts used in wastewater treatment containing antibiotics is of significant importance for addressing the universal environment problems. In this work, the meso-tetraphenyl porphyrin (TPP) with conjugated macrocyclic π-electrons structure was successfully combined with defect-rich BiOCl to form ultrathin sheet-like TPP/defect-rich BiOCl composite as visible-light-responsive photocatalyst. The morphologies, crystal structures, chemical constitutions, optical and photo-electrochemical properties of the as-obtained photocatalyst were determined. The TPP/defect-rich BiOCl composite showed enhanced photocatalytic ability for the degradation of colorless antibiotic TC, CIP and ENR under visible light irradiation compared to defect-rich BiOCl. The effect of different TPP contents on the photodegradation activity was also investigated, and 2 wt% TPP/defect-rich BiOCl exhibited the optimal photocatalytic ability. According to the radicals trapping experiments and electron spin resonance (ESR), the hole (h+), superoxide radical (O2•−) and hydroxyl radical (•OH) contributed to the process of organic pollutant photo-degradation. The good recyclability of the photocatalyst was verified through cyclic measurements. Furthermore, a possible photodegradation mechanism was raised to clarify the effective separation and migration process of photo-induced charge carriers.

Intimately Contacted Ni2P on CdS Nanorods for Highly Efficient Photocatalytic H2 Evolution: New Phosphidation Route and the Interfacial Separation Mechanism of Charge Carriers

A new phosphidation route based on a solvothermal method is demonstrated for the deposition of Ni2P on CdS nanorods photocatalyst with NaBH4 as a crucial reactant and (H2PO2)- as dissolvable P precursor, which leads to a highly crystallized and well contacted Ni2P on CdS in an Ohmic-contact model. On the optimized sample (2%Ni2P/CdS), as high as 1.18 mmol·h-1 H2 evolution rate can be obtained over 50 mg sample, corresponding to an apparent quantum efficiency of 56% (under λ = 435 nm irradiation). The activity is significantly higher than the samples prepared by conventional phosphidation processes and the classical Pt (2%) modified CdS. The remarkable HER performance can be ascribed to the loading of intimately contacted Ni2P, which can promote the separation of photoinduced charge carriers and simultaneously decreases the overpotential for H2 evolution. Furthermore, a reservoir role for photoinduced e- was observed on the deposited Ni2P beyond as a cocatalyst.

Construction of a visible-light-driven magnetic dual Z-scheme BiVO4/g-C3N4/NiFe2O4 photocatalyst for effective removal of ofloxacin: Mechanisms and degradation pathway

Inefficient utilization of photo-induced charge carriers and low recyclability are limitations for photocatalyst to get access to the practical application. A novel ternary BiVO4/g-C3N4/NiFe2O4 composite with dual Z-scheme heterojunction was successfully developed and constructed to enhance the separation of photo-induced charge carriers and the absorption range of visible light. The structure, composition, morphology, magnetic, and optical properties of this photocatalyst were investigated comprehensively. The photocatalytic performance, mechanism, and pathway of ofloxacin degradation under visible light were studied. Results indicated that the internal interaction between different semiconductors presented the successful fabrication of ternary composite, and its red shift of adsorption range of visible light contributed to an enhancement of photocatalytic ability. The as-prepared ternary composite exhibited highest photocatalytic removal rate constant for ofloxacin, which was 3.8, 16.3 and 71.2 times as much as that of the pure BiVO4, pure g-C3N4 and pure NiFe2O4, respectively. The five successive recycling experiments exhibited the high photocatalytic stability of the as-prepared catalyst, with simple recovery operation due to its magnetic property. The holes and superoxide radicals dominated the photocatalytic degradation process of pollutants. A dual Z-scheme heterojunction other than conventional heterojunction was responsible for the enhancement on redox capacity and the separation of charge carriers. Different transformation products during ofloxacin photocatalytic degradation were identified and transformation pathway was put forward. This study provides a promising strategy on the application of visible-light-driven photocatalysts in water treatment.

γ-ray induced formation of oxygen vacancies and Ti3+ defects in anatase TiO2 for efficient photocatalytic organic pollutant degradation

Oxygen vacancies and Ti3+ defects in anatase TiO2 have attracted great attention to address the insufficient optical absorption and photoinduced charge-carrier separation in photocatalysis. In this study, we demonstrate a superficial and innovative approach for synthesizing anatase TiO2 nanoparticles with abundant oxygen vacancies via γ-ray irradiation reduction at room temperature. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) confirm that oxygen vacancies and Ti3+ defects can be quantitatively and extensively obtained by merely regulating the irradiation dosage. Photoelectrochemical measurements suggest that oxygen vacancies and Ti3+ defects promoted the separation of electron-hole pairs and then enhanced the photocatalytic degradation performance for organic pollutant. In comparison with TiO2 (no irradiation), the sample (49.5 kGy irradiation) exhibited a 20.0-fold enhancement in visible-light decomposition of phenol. In addition, the results of scavenge experiments and mechanism analysis revealed that O2− are the dominant active species. The excited electrons generated at the conduction band and oxygen vacancy level of TiO2−x-49.5 conspicuously contributes to generate much more ·O2− species. This novel study shows at room temperature, the γ-ray approach of irradiation leads to faster formation and quantification of oxygen vacancies in the semiconductor materials.

Emerging Nanomaterials for Light‐Driven Reactions: Past, Present, and Future

Emerging Nanomaterials for Light‐Driven Reactions: Past, Present, and Future

Designed synthesis of a porous ultrathin 2D CN@graphene@CN sandwich structure for superior photocatalytic hydrogen evolution under visible light

Graphite carbon nitride (CN) has recently become a promising photocatalyst while challenges still remain due to insufficient visible-light capture and poor electronic property. Herein, a porous ultrathin 2D CN@graphene@CN sandwich structure (5GO-CN) was prepared through in-situ local thermal oxygen erosion strategy. The inner graphene substantially accelerates the migration and separation of photogenerated charge carriers. Moreover, a small amount of oxygen-containing groups in inner graphene layer can effectively fix the thin layer of carbon nitride in the two outer surface layers. With the help of porous structure, spatially separated redox site, excellent visible light capture and fast separation of photoinduced charge carriers, this optimal 5GO-CN composite exhibited 14.3 times higher photocatalytic H2 production rate (5.58 mmol g−1 h−1) than bulk CN. The composition, microstructure and optical property of 5GO-CN sample were thoroughly investigated. This new strategy furnishes an effective way to modify other functional catalysts via using nanostructure design.

Enhancing visible-light driven photocatalytic performance of BiOBr by self-doping and in-situ deposition strategy: A synergistic effect between Bi5+ and metallic Bi

A novel composite photocatalyst of Bi/BiOBr-Bi5+ was successfully developed via a facile two-step procedure. The co-existence of self-doped Bi5+ and in-situ deposited Bi(M) was evidenced by X-ray diffraction, field-emission transmission electron microscope and X-ray photoelectron spectra. Its photocatalytic performance on the Rhodamine B (RhB) degradation under visible light irradiation displayed a significant improvement compared with that of Bi/BiOBr or BiOBr-Bi5+, which was mainly attributed to the synergistic effect between Bi(M) and Bi5+. For Bi(M), enhancement of visible-light absorption capacity was beneficial from surface plasmon resonance (SPR) effect while the promoted separation of photoinduced charge carriers was attributed to the formation of oxygen vacancies (OVs) and Schottky-barrier. Besides, Bi(M) induced a predominant exposure of (010) facet, further enhancing photocatalytic performance. Differently, Bi5+ brought a narrowed bandgap of BiOBr in increasing the carrier density. A plausible mechanism towards RhB degradation was proposed based on analysis of electron transfer pathway and determination of dominant active species. The work offers new routes to enhance the photocatalytic performance of Bi-based materials without introducing any impurities.