Efficient Photoinduced Charge Separation Research Articles

Bi4O7 modified AgBiO3 to construct Z-scheme heterojunction for photocatalytic removing phenol

The Z-scheme heterojunction Bi4O7/AgBiO3 photocatalysts were synthesized by hydrothermal method. It exhibited excellent photocatalytic degradation efficiency (74.87%) for phenol, which is 2.6 and 4.5 times more efficient than pure AgBiO3 and Bi4O7, respectively. The improvement of photocatalytic performance can be ascribed the enhanced photo-induced charge separation efficiency of the Z-scheme heterostructure through various characterization analysis and experiment tests. In addition, the effective degradation of other organic pollutants like bisphenol A, tetracycline and ciprofloxacin of Bi4O7/AgBiO3 was also confirmed. This study provides a reference for designing photocatalysts that can degrade organic pollutants efficiently.

Ligand and band engineering-induced covalent organic framework-embedded Ti32 Oxo-cluster gels-based Z-scheme heterojunction for boosting the photocatalytic degradation performance of tetracycline

Designing and synthesizing highly efficient photocatalysts with proper energy band structures, which can accelerate the degradation of antibiotics, is crucial and challenging. Herein, by introducing a simple ligand engineering strategy, we ingeniously developed a novel approach for facile synthesis of covalent organic framework (COF) embedded and oxygen vacancies (OV) in-situ doped Ti32 oxo-cluster gels-based Z-scheme heterojunction, COF@OV-Ti32-gels (CT-X). This strategy has led to a remarkable improvement in the photodegradation efficiency of tetracycline hydrochloride (TC), increasing from 15% (pure Ti32 crystals) to an impressive 93.7%. The heterojunctions, which possess modified bandgap structures due to the presence of oxygen defects, exhibit superior photo-induced charge separation efficiency compared to Ti32 without such defects. This enhanced utilization of sunlight results in highly efficient photocatalytic degradation of TC via a built-in electric field. Intriguingly, the CT-X photocatalysts, synthesized with a unique heterojunction structure, exhibit the ability to achieve full-time domain degradation of TC. Notably, CT-X can effectively degrade TC in the absence of light, and its degradation capability is significantly enhanced upon exposure to visible light. Furthermore, the superoxide radical (•O2¯) was evidenced to play a crucial role in the photocatalytic process, and the corresponding degradation mechanism was also depicted.

Cobalt-doped iron-based metal–organic gels as efficient visible-light-driven peroxymonosulfate activators for the efficient degradation of norfloxacin with simultaneous antibacterial activity

A strategically fabricated cobalt-doped iron-based metal–organic gel (CFM) synergistically promotes peroxymonosulfate (PMS) activation and visible light-induced photocatalysis to remove norfloxacin (NOR). Cobalt incorporation into the metal–organic gel significantly optimizes its electronic structure, leading to the exceptional performance of CFM in synergistically activating PMS, amplifying visible light absorption, and enhancing photoinduced charge separation efficiency. The Vis/50 %-CFM/PMS system enables a NOR removal rate of up to 96.8 % within 60 min and a total organic carbon (TOC) removal rate of 78.3 %, signifying excellent decontamination performance. Exhibiting robust mineralization potential, the Vis/CFM/PMS system has undergone comprehensive analysis of the intermediary degradation process using Density Functional Theory (DFT) calculations. The toxicity of degradation intermediates was assessed employing the quantitative structure–activity relationship (QSAR) model. In addition, the Vis/CFM/PMS system showed antibacterial effects against E. coli and S. aureus. This investigation furnishes a novel perspective toward developing innovative PMS activation photocatalyst coupling systems for environmental remediation.

Structural Conjugation Tuning in Covalent Organic Frameworks Boosts Charge Transfer and Photocatalysis Performances.

Structural conjugation greatly affects the optical and electronic properties of the COF photocatalyst. Herein, we show that 2D hydrazone COFs with either π-extended biphenyl (BPh-COF) or acetylene (AC-COF) frameworks demonstrated distinct charge transfer and photocatalytic performances. The two COFs show good crystallinity and decent porosity as their frameworks are enforced by intra/interlayers hydrogen bonding. However, computational and experimental data reveal that AC-COF managed broader visible-light absorption and narrower optical bandgaps and performed efficient photoinduced charge separation and transfer in comparison with BPh-COF, meaning that the ethynyl skeleton with enhanced planarity better improves the π-conjugation of the whole structure. As a result, AC-COF exhibited an ideal bandgap for rapid oxidative coupling of amines under visible-light irradiation. Furthermore, taking advantage of its better charge transfer properties, AC-COF demonstrated considerable enhanced product conversion and notable functional tolerance for metallaphotocatalytic C-O cross-coupling of a wide range of both aryl bromides and chlorides with alcohols. More importantly, besides being recoverable, AC-COF showcased the previously inaccessible etherification of dihaloarene. This report shows a facile approach for manipulating the structure-activity relationship and paves the way for the development of a COF photocatalyst for solar-to-chemical energy conversion.

Host–guest complexes of perylene bisimide-based metallacage and fullerenes for efficient photoinduced charge separation

Fast photoinduced charge separation was predicted in non-covalent complexes of Pt6PBI3 metallacage and endohedral metallofullenes.

Exploring the Local Optoelectronic Properties of ALD Grown TiO2 Photoelectrode-Coatings with Atomic Force Microscopy Methods

Photoelectrochemical cells (PECs) hold great promise as an environmentally friendly method of converting sunlight into valuable fuels. However, the semiconductor components of PEC photoelectrodes are susceptible to corrosion under photoelectrochemical conditions.In order to protect the surface of these semiconductors from degradation, a thin overlayer of Titanium dioxide (TiO2) is often applied by atomic layer deposition (ALD). In addition to their protecting function, the physicochemical properties of these thin films significantly affect the overall performance of the device. The local nano-scale optoelectronic characteristics, which considerably influence their macroscopic properties, have rarely been reported in the literature.AFM methods constitute a powerful tool to investigate photo-induced charge separation, charge transport and recombination on photoelectrode surfaces with nanometer resolution.In this context, we have employed Tunneling Conductive AFM (TUNA) and Kelvin Probe Force Microscopy (KPFM) in the dark and under illumination to investigate the surface of ALD-grown TiO2. The synthesis conditions determine the morphology, which has a strong impact on the local optoelectronic properties. TUNA measurements reveal higher photogenerated currents on the grain and facet boundaries, showing that these regions can be favorable conduction pathways. Based on KPFM experiments we can quantify the more efficient photo-induced charge separation on the crystalline TiO2 inclusions, which generate a significant surface photopotential (~450 mV) upon UV-illumination. Categorization of different regions of surface topography based on morphology allows us to analyze the evolution of surface potential over time and extract localized time constants for carrier dynamic processes on the films. This spatially resolved information provides valuable insight to guide the development of macroscopically stable and efficient photoelectrodes through the engineering of microstructure at the nano scale.

Multi-electron collaborative photo-Fenton-like system for indoor air purification: A case study of Cu(II) grafted BaTiO3 with oxygen vacancies

Indoor air purification belongs to one of the most important and traditional applications of photocatalysis, which brings forward an impending need for more efficient photocatalytic systems. Herein, we initiated a multi-electron collaborative photo Fenton-like system for mineralization of indoor volatile organic compounds by jointly modified with oxygen vacancies and Cu(II) clusters on barium titanate. Oxygen vacancies effectively increase the visible light absorption and photoinduced charge separation efficiency. Benefiting from the energy level match with oxygen vacancies and Cu(II) species, the trapped electrons in the oxygen vacancies can effectively migrate towards Cu(II) clusters. More importantly, the Cu species that have received electrons can trigger the multi-electron reduction of oxygen to in-situ form H2O2 through the redox of Cu(II)/Cu(I). In parallel, the reactive •OH radicals can be effectively produced by the photo-like Fenton reaction. Thus, the newly developed barium titanate based photocatalysts exhibit over 38-fold improvement in the removal efficiency of volatile organic compounds (in terms of CO2 evolution rate) by virtue of the strong oxidizing power of holes in the valance band and multi-electron photoFenton-like reaction to generate •OH radicals. Notably, the absorbed H2O molecules play an indispensable role in the formation process of in-situ H2O2. Thus, even under high-humidity condition, our photocatalysts present stable and high photocatalytic activity, which provides great potential for practical applications in indoor air purification.

Unraveling the Synergistic Mechanism of Boosted Photocatalytic H2 O2 Production over Cyano-g-C3 N4 /In2 S3 /Ppy Heterostructure and Enhanced Photocatalysis-Self-Fenton Degradation Performance.

In this work, cyano contained g-C3 N4 comodified by In2 S3 and polypyrrole (C≡N─CN/IS/Ppy) materials are synthesized for the photocatalytic production of H2 O2 and photocatalysis-self-Fenton reaction for highly efficient degradation of metronidazole. The results from UV-vis spectrophotometry, surface photovoltage, and Kelvin probe measurements reveal the promoted transport and separation efficiency of photoinduced charges after the introduction of In2 S3 and Ppy in the heterojunction. The existence of a built-in electric field accelerates the photoinduced charge separation and preserves the stronger oxidation ability of holes at the valence band of C≡N─CN. Linear sweep voltammetry measurements, zeta potential analyzations, nitroblue tetrazolium determination, and other measurements show that Ppy improves the conversion ratio of • O2 - to H2 O2 and the utilization ratio of • O2 - , as well as suppresses decomposition of H2 O2 . Accordingly, the H2 O2 evolution rate produced via a two-step single-electron reduction reaction reaches almost 895µmol L-1 h-1 , a value 80% and 7.2-fold higher than those obtained with C≡N─CN/IS and C≡N─CN, respectively. The metronidazole removal rate obtained via photocatalysis-self-Fenton reaction attains 83.7% within 120 minutes, a value much higher than that recorded by the traditional Fenton method. Overall, the proposed synthesis materials and route look promising for the H2 O2 production and organic pollutants degradation.

Hydrothermal synthesis of Bi2WO6/Bi2O4 heterojunction with WO3 and NaBiO3·2 H2O powders as precursors to improve visible light photocatalytic degradation performance

The limited visible light response range and fast recombination rate of photoinduced carriers restrict the photocatalytic performance of Bi2WO6. Herein, a novel low temperature hydrothermal approach was developed to construct the Bi2WO6/Bi2O4 heterojunction with WO3 and NaBiO3•2 H2O powders as precursors and the latter as the only bismuth source. During the hydrothermal reaction, WO3 first reacts with NaBiO3·2 H2O to generate Bi2WO6 and then the residual NaBiO3·2 H2O converts into Bi2O4, in-situ forming the Bi2WO6/Bi2O4 heterojunction with the co-shared Bi atoms. The content of Bi2WO6 in the heterostructure can be facilely modulated by changing the amount of WO3 added. The construction of Bi2WO6/Bi2O4 heterojunction could not only extend the spectral response range but also improve the separation efficiency of photoinduced charges. Consequently, the photocatalytic degradation performance to tetracycline (phenol) for the optimal Bi2WO6/Bi2O4 heterostructure is 5.19 and 1.77 times (4.75 and 1.66 times) higher than that of single Bi2WO6 and Bi2O4 under visible light, respectively. The capture experiments of active species and electron spin resonance spectra demonstrate that radicals (·O2-) and holes (h+) are the first and second important active species, respectively, during the catalytic degradation. Our work provides a new idea for the fabrication of high-performance Bi2WO6-based junction photocatalysts.

Relative Local Electron Density Tuning in Metal-Covalent Organic Frameworks for Boosting CO2 Photoreduction.

The high electron density and efficient charge carrier separation are two important factors to affect photocatalytic activity, especially for the CO2 photoreduction reaction. However, the systematic studies on the structure-functional relationship regarding the above two factors based on precisely structure model are rarely reported. Herein, as a proof-of-concept, we developed a new strategy on the evaluation of local electron density by controlling the relative electron-deficient (ED) and electron-rich (ER) intensity of monomer at a molecular level based on three rational-designed vinylene-linked sp2 carbon-covalent organic frameworks (COFs). As expected, the as-prepared vinylene-linked sp2 carbon-conjugated metal-covalent organic framework (MCOFs) (VL-MCOF-1) with molecular junction exhibited excellent activities for CO2-to-HCOOH conversion (283.41 μmol g-1 h-1) and high selectivity of 97.1%, much higher than the VL-MCOF-2 and g-C34N6-COF, which is due to the synergistic effect of the multi-electronic metal clusters (Cu3(PyCA)3) (PyCA = pyrazolate-4-carboxaldehyde) as strong ER roles and cyanopyridine units as ED roles and active sites, as well as the boosted photo-induced charge separation efficiency of vinyl connection and increased light utilization ability. These results not only provide a strategy for regulating the electron-density distribution of photocatalysts at the molecular level but also offers profound insights for metal clusters-based COFs to effective CO2 conversion.

Copper oxide-anchored ZnO nanoflakes for the enhanced photocatalytic degradation performance and mechanistic investigations

An efficient CuO anchored ZnO nanoflakes were synthesized through facile wet chemistry method and the catalysts were well characterized using various sophisticated instruments. CuO nanoparticle incorporation was found to have a direct linear relationship with light absorbance. The degradation ability of the ZnO/CuO p-n junction was studied on the degradation of methyl orange. Under UV–Vis light illumination, the photocatalytic removal efficacy of methyl orange over CuO/ZnO p-n junction is up to 89%, which is greater than that of barecatalysts. The maximized photocatalytic degradation performance might be ascribed to the augmented visible light harvesting capacity and reduced the rate of photogenerated electron-hole pair recombination. The efficient photoinduced electron and hole pair charge separation upon excitation is aided by the effective formation of p-n junctions between ZnO and CuO. Based on the findings, a plausible photocatalytic mechanism for the as-synthesized CuO anchored ZnO nanoflake was proposed.

Promoted Charge Separation and Long-Lived Charge-Separated State in Porphyrin-Viologen Dyad Nanoparticles.

Developing light-harvesting systems with efficient photoinduced charge separation and long-lived charge-separated (CS) state is desirable but still challenging. In this study, we designed a zinc porphyrin photosensitizer covalently linked with viologen (ZnP-V) that can be prepared into nanoparticles in aqueous solution. In DMF solution, the monomeric ZnP-V dyads show no electron transfer between the ZnP and viologen units. In contrast, the ZnP-V nanoparticles in aqueous solution show fast charge separation with a CS state lifetime of up to 4.3 ms. This can be attributed to charge hopping induced by aggregation or distance modification between the donor and acceptor induced by electronic interaction. Nevertheless, the lifetime of the CS state is orders of magnitude longer than for molecular aggregates reported previously. The ZnP-V nanoparticles show enhanced photocatalytic hydrogen production as compared to the ZnP nanoparticles and still hold promise for other applications such as photovoltaic devices and photoredox catalysis.

Tailoring Morphology in Hydrothermally Synthesized CdS/ZnS Nanocomposites for Extraordinary Photocatalytic H2 Generation via Type-II Heterojunction

CdS@ZnS core shell nanocomposites were prepared by a one-pot hydrothermal route. The morphology of the composite was tuned by simply changing the Zn2+ precursor concentration. To characterize the samples prepared, various techniques were employed, including XRD, FESEM, TEM, XPS and UV-vis DRS. The band gaps of CdS and ZnS were measured to be 2.26 and 3.32 eV, respectively. Compared with pure CdS, the CdS@ZnS samples exhibited a slight blue shift, which indicated an increased band gap of 2.29 eV. The CdS@ZnS core shell composites exhibited efficient photocatalytic performance for H2 generation under simulated sunlight illumination in contrast to pure CdS and ZnS. Additionally, an optimized H2 generation rate (14.44 mmol·h−1·g−1cat) was acquired at CdS@ZnS-2, which was approximately 4.6 times greater than that of pure CdS (3.12 mmol·h−1·g−1cat). Moreover, CdS@ZnS heterojunction also showed good photocatalytic stability. The process of charge separation over the photocatalysts was investigated using photoelectrochemical analysis. The findings indicate that the CdS@ZnS nanocomposite has efficient charge separation efficiency. The higher H2 generation activity and stability for CdS@ZnS photocatalysts can be attributed to the intimate interface in the CdS@ZnS core–shell structure, which promoted the light absorption intensity and photoinduced charge separation efficiency. It is expected that this study will offer valuable insights into the development of efficient core shell composite photocatalysts.

Novel Bi2WO6/MWCNT nanohybrids synthesis for high-performance photocatalytic activity of ciprofloxacin degradation under simulated sunlight irradiation

In this research, novel Bi2WO6/MWCNT nanohybrids were synthesized via a cost-effective hydrothermal route. The photocatalytic performance of these specimens was tested through the photodegradation of Ciprofloxacin (CIP) under simulated sunlight. Various physicochemical techniques systematically characterized the prepared pure, Bi2WO6/MWCNT nanohybrid photocatalysts. The XRD and Raman spectra revealed the structural/phase properties of Bi2WO6/MWCNT nanohybrids. FESEM and TEM pictures revealed the attachment and distribution of plate-like Bi2WO6 nanoparticles along the nanotubes. The optical absorption and bandgap energy of Bi2WO6 was affected by the addition of MWCNT, which was analyzed by UV-DRS spectroscopy. The introduction of MWCNT reduces the bandgap value of Bi2WO6 from 2.76 to 2.46 eV. The BWM-10 nanohybrid showed superior photocatalytic activity for CIP photodegradation; 91.3% of CIP was degraded under sunlight irradiation. The PL and transient photocurrent test confirm that photoinduced charge separation efficiency is better in BWM-10 nanohybrids. The scavenger test indicates that h+ & •O2 have mainly contributed to the CIP degradation process. Furthermore, the BWM-10 catalyst demonstrated outstanding reusability and firmness in four successive cycles. It is anticipated that the Bi2WO6/MWCNT nanohybrids will be employed as photocatalysts for environmental remediation and energy conversion. This research presents a novel technique for developing an effective photocatalyst for pollutant degradation.

One-step hydrothermal synthesis of S-scheme heterojunction Bi2O3/Bi2Sn2O7 composites with enhanced photocatalytic CO2 reduction performance

In this study, a kind of S-scheme heterojunction Bi2O3/Bi2Sn2O7 composite material is firstly prepared by one-step hydrothermal method through adjusting the molar amount of Bi source, which further improves the photocatalytic CO2 reduction performance compared with pure Bi2Sn2O7. Combined with work-enthalpy data using density functional theory calculations, the photoexcited electrons are directionally transferred from Bi2O3 to Bi2Sn2O7 for the formation of S-scheme mechanism, achieving the significant improvement in the photoinduced charge separation efficiency and CO2 photoreduction activity to CO for as-prepared Bi2O3/Bi2Sn2O7 composite. A feasible photocatalytic CO2 reduction mechanism of S-scheme heterojunction Bi2O3/Bi2Sn2O7 composite is proposed and investigated. Our findings should provide the significant theoretical guidance and experimental data for achieving the S-scheme heterojunction construction and CO2 green conversion into low-carbon chemical fuels.

A Photosensitizing Metal–Organic Framework as a Tandem Reaction Catalyst for Primary Alcohols from Terminal Alkenes and Alkynes

AbstractOwing to the wide and growing demand for primary alcohols, the development of efficient catalysts with high regioselectivity remains a worthwhile pursuit. However, according to Markovnikov's rule, it is a challenge to obtain primary alcohols with high yields and regioselectivity from terminal alkenes or alkynes. Herein, we report the synthesis of a photosensitizing two‐dimensional (2D) metal–organic framework (MOF) from cyclic trinuclear copper(I) units (Cu‐CTUs) and a boron dipyrro‐methene (Bodipy) ligand. The MOF features broadband light absorption, excellent photoinduced charge separation efficiency, and photochemical properties. By integrating the copper‐catalyzed hydroboration and photocatalyzed aerobic oxidation, it can catalyze terminal alkenes and alkynes to produce primary alcohols via a one‐pot tandem reaction with excellent regioselectivity, good overall yields in two‐step reactions (up to 85 %), broad substrate compatibility (32 examples) and good reusability under mild conditions.

A Photosensitizing Metal-Organic Framework as a Tandem Reaction Catalyst for Primary Alcohols from Terminal Alkene and Alkyne.

Due to the wide and growing demand for primary alcohols, the development of efficient catalysts with high regioselectivity remains a worthwhile pursuit. However, according to the Markovnikov's rule, it is challenge to obtain primary alcohols with high yields and regioselectivity from terminal alkenes or alkynes. Herein, we reported the synthesis of a photosensitizing two-dimensional (2D) metal-organic framework (MOF) from cyclic trinuclear copper(I) units (Cu-CTUs) and boron dipyrro-methene (Bodipy) ligand. The MOF features broadband light absorption, excellent photoinduced charge separation efficiency, and photochemical properties. By integrating the copper-catalyzed hydroboration and photocatalyzed aerobic oxidation, it can catalyze terminal alkenes and alkynes to produce primary alcohols via one-pot tandem reaction with excellent regioselectivity, good overall yields in two-step reactions (up to 85%), broad substrate compatibility (32 examples) and good reusability under mild conditions.

Construction of CuBi2O4/CdO p-n buried junction for boosted photoelectrochemical water splitting

The rational design and construction of interface heterostructures, which can simultaneously accelerate the photoinduced carrier separation and enhance the surface hydrogen evolution kinetics, is of great necessity for photoelectrochemical (PEC) water splitting. Here we construct a CuBi2O4/CdO p-n buried junction for boosting the PEC hydrogen evolution. Compared to the bare CuBi2O4 photocathode, the CuBi2O4/CdO heterojunction reveals an anodic shift of 170 mV for the onset potential and achieves a cathodic photocurrent density of 0.32 mA cm−2 at 0.4 V vs. RHE, as well as improved long-term stability under AM 1.5 G illumination without sacrificial reagent. The experimental characterizations and theoretical calculations confirm the significance of the CuBi2O4/CdO p-n junction in increasing the photoinduced charge separation efficiency and reducing the activation energy of hydrogen evolution reaction (HER), which accounts for enhanced PEC performance. Meanwhile, the change of photoexcited charge-transition route evidenced by DFT calculation in CuBi2O4/CdO provides the fundamental explanation for spatial charge separation, which is responsible for the improved PEC hydrogen evolution stability. The present work highlights the importance of constructing heterojunctions to boost the PEC performance and elucidates the probable intrinsic mechanism involved in the interface.

Design of AIEgen‐based porphyrin for efficient heterogeneous photocatalytic hydrogen evolution

AbstractTetraphenylethylene (TPE)‐conjugated porphyrin TPE‐ZnPF is synthesized in high yield and characterized by single‐crystal X‐ray diffraction. The propeller‐shaped TPE groups not only enable exceptional aggregation‐induced emission (AIE) in the solid state but also abolish the strong π‐π stacking of porphyrin moieties and thus prohibit aggregation‐caused quenching (ACQ). TPE‐ZnPF aggregates feature long‐lived photoexcited states, which subsequently suppress non‐radiative decay channels and enhance emission intensity. Moreover, its aggregates show more efficient light‐harvesting ability due to the Förster resonance energy transfer from the TPE energy donor to the porphyrin core energy acceptor, well‐defined nanosphere morphology, and more efficient photoinduced charge separation than the porphyrin Ph‐ZnPF, which possesses ACQ and agglomerated morphology. As a result, an excellent photocatalytic hydrogen evolution rate (ηH2) of 56.20 mmol g‒1 h‒1 is recorded for TPE‐ZnPF aggregates, which is 94‐fold higher than that of the aggregates of Ph‐ZnPF (0.60 mmol g‒1 h‒1) without the TPE groups.

Facile synthesis of Z-scheme CeO2@AgBr heterojunction for improved dye degradation

CeO2 nanorods were synthesized by the hydrothermal method and coupled with AgBr via deposition approach. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmet-Teller (BET) and diffuse reflection spectroscopy (DRS) were used to characterize the structure, morphology and optical properties of the samples. The photoinduced charge separation efficiency was determined by transient photocurrent response and photoluminescence (PL) spectra. The effect of CeO2 loading on the Rhodamine B (RhB) degradation in CeO2@AgBr composites was also investigated. The results indicated that 40 wt%-CeO2@AgBr photocatalyst demonstrated the highest photocatalytic activity than pure CeO2 and AgBr. The trapping experiment showed that holes (h+) and superoxide radicals (•O2−) were the main active species for the degradation of RhB. The improved photocatalytic activity of CeO2@AgBr catalysts were attributed to the formation of Z-scheme heterojunction, which effectively inhibited the recombination of photoinduced electron-hole pairs.