Direct Charge Transfer Research Articles

Interfacial Charge Transfer Bridge Prolongs Carrier Recombination Lifetimes of CoFe Metal‐Thiolate Framework/Hematite Photoanode for Water Oxidation

AbstractConstructing heterostructural photoanodes is attractive for elevating the photoelectrochemical (PEC) performance, however, it is a long‐standing challenge to achieve highly efficient interfacial charge transfer. Herein, a CoFe metal‐thiolate framework (CoFe MTF)/Fe2O3 photoanode connected by an interfacial Fe─O─N/S bond is designed to modulate the behavior of charge carriers and improve water oxidation performance. It is disclosed that this interfacial bond functions as a direct charge transfer bridge between shallow trap states of Fe2O3 and CoFe MTF, leading to prolonged carrier recombination lifetimes (85 ns for CoFe MTF/Fe2O3 compared to 37 ns for Fe2O3) and enhanced charge transfer efficiency. Alternatively, a robust interfacial electric field is established in the CoFe MTF/Fe2O3 p–n heterojunction, facilitating efficient charge transfer. As expected, the CoFe MTF/Fe2O3 photoanode exhibits significant enhancement in water oxidation, resulting in a three‐fold increase in photocurrent density compared to pristine Fe2O3. This study highlights the significance of designing interfacially bonded heterostructural photoelectrodes to regulate the transfer characters of charge carriers.

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

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

Internal electric field modulation by copper vacancy concentration of cuprous sulfide nanosheets for enhanced selective CO2 photoreduction

Although the internal electric field (IEF) of photocatalysts is acknowledged as a potent driving force for photocharge separation, modulating the IEF intensity to achieve enhanced photocatalytic performances remains a challenge. Herein, cuprous sulfide nanosheets with different Cu vacancy concentration were employed to study IEF modulation and corresponding direct charge transfer. Among the samples, Cu1.8S nanosheets possessed intensified IEF intensity compared with those of Cu2S and Cu1.95S nanosheets, suggesting that an enhanced IEF intensity could be achieved by introducing more Cu vacancies. This intensified IEF of Cu1.8S nanosheets induced numerous photogenerated electrons to migrate to its surface, and the dissociative electrons were then captured by Cu vacancies, resulting in efficient charge separation spatially. In addition, the Cu vacancies on Cu1.8S nanosheets accumulated electrons as active sites to lower the energy barrier of rate-determining step of CO2 photoreduction, leading to the selective conversion of CO2 to CO. Herein, the manipulation of IEF intensity through Cu vacancy concentration regulation of cuprous sulfide photocatalysts for efficient charge separation has been discussed, providing a scientific strategy to rationally improve photocatalytic performances for solar energy conversion.

Gas Sensing Properties of PLD Grown 2D SnS Film: Effect of Film Thickness, Metal Nanoparticle Decoration, and In Situ KPFM Investigation.

This study employs novel growth methodologies and surface sensitization with metal nanoparticles to enhance and manipulate gas sensing behavior of two-dimensional (2D)SnS film. Growth of SnS films is optimized by varying substrate temperature and laser pulses during pulsed laser deposition (PLD). Thereafter, palladium (Pd), gold (Au), and silver (Ag) nanoparticles are decorated on as-grown film using gas-phase synthesis techniques. X-ray diffraction (XRD), Raman spectroscopy, and Field-emission scanning electron microscopy (FESEM) elucidate the growth evolution of SnS and the effect of nanoparticle decoration. X-ray photoelectron spectroscopy (XPS) analyses the chemical state and composition. Pristine SnS, Ag, and Au decorated SnS films are sensitive and selective toward NO2 at room temperature (RT). Ag nanoparticle increases the response of pristine SnS from 48 to 138% toward 2ppm NO2, which indicates electronic and chemical sensitization effect of Ag. Pd decoration on SnS tunes its selectivity toward H2 gas with a response of 55% toward 70ppm H2 and limit of detection (LOD) < 1ppm. In situ Kelvin probe force microscopy (KPFM) maps the work function changes, revealing catalytic effect of Ag toward NO2 in Ag-decorated SnS and direct charge transfer between Pd and SnS during H2 exposure in Pd-decorated SnS.

A Solvent Free Neutral Cobalt Complex Exhibiting Macroscopic Polarization Switching Induced by Directional Charge Transfer

Materials with polarization switching induced by directional charge transfer under the external stimuli are of great interest due to their fast swicthing rate and potential applications. Nonetheless, most of these...

External electric field driven conformation transition between lithium salts and electride-like molecules: intriguing NLO switches in Li@corannulene.

The external electric field has emerged as a powerful tool for building molecular switches with excellent properties. In this work, we investigate the impact of an external electric field on the transition between lithium salt and electride-like molecule conformations in Li@corannulene. Remarkably, the distance between the Li atom and the corannulene bottom displays a sharp increase under the influence of an external electric field strength of F-z = 110 × 10-4 a.u. As the external electric field strength increases, the Li atom brings about different directions of charge transfer (CT). The natural population analysis (NPA) charge and the molecular electrostatic potential (ESP) results show that the intermolecular CT occurs from the Li atom to the corannulene with the F-z ranging from 0 to 100 × 10-4 a.u. Interestingly, when the external electric field reaches F-z = 110 × 10-4 a.u., the CT is oriented from the corannulene to the Li atom. Moreover, electron localization function (ELF) basins are presented under an F-z of 110 × 10-4 a.u., which indicates that Li@corannulene exhibits electride-like (e-⋯[Li@corannulene]+) molecules and lithiation salt (Li+[corannulene]-) under an F-z of 0 to 100 × 10-4 a.u. Significantly, the differences in charge transfer also contribute to a significant improvement in hyperpolarizabilities (βtot) during the conformation transition from lithiation salt (Li+[corannulene]-) to electride-like (e-⋯[Li@corannulene]+) molecules. This study explores the potential of Li@corannulene as a promising second-order NLO material, and the external electric field provides an efficient strategy for designing and developing NLO switching devices.

Tuning optical properties of π-conjugated double nanohoops under external electric field stimuli-responsiveness.

Carbon nanorings have attracted substantial interest from synthetic chemists due to their unique topological structures and distinct physical properties. An intriguing π-conjugated double-nanoring structure, denoted as [8]CPP-[10]cyclacene, was constructed via the integration of [8]cycloparaphenylene ([8]CPP) into [10]cyclacene. Using the external electric field stimuli-responsiveness of [8]CPP-[10]cyclacene, directional charge transfer can be induced, resulting in the emergence of intriguing properties. The effects of the external electric field in three specific directions were explored, vertically in the [8]CPP unit (Fy), vertically in the [10]cyclacene unit (Fz), and horizontally along the double nanorings diameter (Fx). Interestingly, the external electric field vertically to the [10]cyclacene unit significantly enhanced the first hyperpolarizability (βtot) compared to that vertically to the [8]CPP unit. Notably, [8]CPP-[10]cyclacene under Fx exhibited significantly larger the βtot values (1.48 × 105 a.u.) than those of vertical Fy and Fz. This work opens up a wide range of nonlinear optics, making it a compelling area to explore in the field of carbon nanomaterials.

Direct electron transfer in a covalent triazine framework for enhanced photocatalytic hydrogen evolution.

Inspired by the direct charge transfer in the natural photosystems, herein, we design covalent triazine frameworks (CTFs) with direct electron transfer by constructing the minimal amount of -donor-acceptor 1-acceptor 2- type moieties in the CTF backbone for photocatalytic hydrogen evolution. By introducing only 0.75% of the acceptor 2, the as-prepared CTF exhibited an enhanced hydrogen evolution rate of 3215 μmol g-1 h-1.

Photosensitizer-free singlet oxygen generation via a charge transfer transition involving molecular O2 toward highly efficient oxidative coupling of arylamines to azoaromatics.

Photosensitizer (PS)-mediated generation of singlet oxygen, O2 (a1Δg) is a well-explored phenomenon in chemistry and biology. However, the requirement of appropriate PSs with optimum excited state properties is a prerequisite for this approach which limits its widespread application. Herein, we report the generation of O2 (a1Δg) via direct charge-transfer (CT) excitation of the solvent-O2 (X3Σg -) collision complex without any PS and utilize it for the catalyst-free oxidative coupling of arylamines to azoaromatics under ambient conditions in aqueous medium. Electron paramagnetic resonance (EPR) spectroscopy revealed the formation of O2 (a1Δg) upon direct excitation with 370 nm light. The present approach shows broad substrate scope, remarkably fast reaction kinetics (90 and 40 min under an open and O2 atm, respectively), high selectivity (100%), and excellent yields (up to 100%), and works well for both homo- and hetero-coupling of arylamines. The oxidative coupling of arylamines was found to proceed through the generation of amine radicals via electron transfer (ET) from amines to O2 (a1Δg). Notably, electron-rich amines show higher yields of azo products compared to electron-deficient amines. Detailed mechanistic investigations using various spectroscopic tools revealed the formation of hydrazobenzene as an intermediate along with superoxide radicals which subsequently transform to hydrogen peroxide. The present study is unique in the way that molecular O2 simultaneously acts as a light-absorbing chromophore (solvent-O2 complex) as well as an efficient oxidant (O2 (a1Δg)) in the same reaction. This is the first report on the efficient, selective, and sustainable synthesis of azo compounds in aqueous medium under an ambient atmosphere without any PCs/PSs and paves the way for further in-depth understanding of the chemical reactivity of O2 (a1Δg) generated directly via CT excitation of the solvent-O2 complex toward various photochemical and photobiological transformations.

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

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

Synthesis, single crystal X-ray, Hirshfeld surface analysis and DFT calculation based NBO, HOMO-LUMO, MEP, ECT and molecular docking analysis of N'-[(2,6-dichlorophenyl)methylidene]-2-{[3-(trifluoromethyl)phenyl]amino}benzohydrazide

A new Schiff base compound of N'-[(2,6-dichlorophenyl)methylidene]-2-{[3-(trifluoromethyl)phenyl]amino}benzohydrazide was synthesized and characterized through various spectroscopic techniques, including infrared, 1H NMR, 13C NMR spectroscopy and X–ray diffraction. Experimental results collected by XRD were compared with theoretical results obtained from Density functional theory method. Hirshfeld surface analysis was used to obtain three dimension molecular surface and two dimension fingerprint plots to illustrate the intermolecular bonding. Theoretical calculations provide valuable insights into both global and local chemical activity, as well as the properties of molecules and chemicals, including their nucleophilic and electrophilic nature. The DFT method at B3LYP/6–311++G (d,p) basis set was employed to study the optimized structure and geometric parameters, as well as to explore the frontier molecular orbitals, global reactive parameters, Mullikan population analaysis, Natural bond orbital and molecular electrostatic potential characteristics which cannot be obtained by experimental methods. Additionally, electrophilicity based charge transfer study was carried out with DNA bases to determine the direction of charge transfer. Finally, an investigation was carried out using molecular docking analysis to examine the binding energies of the title compound with PDB ID: 2QDJ protein target. The analysis yielded significant insights into the possible interactions, offering valuable findings in the process.

Bi3O2.5Se2: a two-dimensional high-mobility polar semiconductor with large interlayer and interfacial charge transfer.

Two-dimensional semiconductors with large intrinsic polarity are highly attractive for applications in high-speed electronics, ultrafast and highly sensitive photodetectors and photocatalysis. However, previous studies mainly focus on neutral layered polar 2D materials with limited vertical dipoles and electrostatic potential difference (typically <1.5 eV). Here, using the first-principles calculations, we systematically investigated the polarity of few-layer Bi3O2.5Se2 semiconductors with ultrahigh predicted room-temperature carrier mobility (1790 cm2 V-1 s-1 for the monolayer). Thanks to its unique non-neutral layered structure, few-layer Bi3O2.5Se2 contributes to a substantial interlayer charge transfer (>0.5 e-) and almost the highest electrostatic potential difference (ΔΦ) of ∼4 eV among the experimentally attainable 2D layered materials. More importantly, positioning graphene on different charged layers ([Bi2O2.5]+ or [BiSe2]-) switches the charge transfer direction, inducing selective n-doping or p-doping. Furthermore, we can use polar Bi3O2.5Se2 as an exemplary assisted gate to gain additional holes or electrons except for the external electric field, thus breaking the traditional limitations of gate tunability (∼1014 cm-2) observed in experimental settings. Our work not only expands the family of polar 2D semiconductors, but also makes a conceptual advance on using them as an assisted gate in transistors.

Engineering MOF/carbon nitride heterojunctions for effective dual photocatalytic CO2 conversion and oxygen evolution reactions.

Photocatalysis appears as one of the most promising avenues to shift towards sustainable sources of energy, owing to its ability to transform solar light into chemical energy, e.g. production of chemical fuels via oxygen evolution (OER) and CO2 reduction (CO2RR) reactions. Ti metal-organic frameworks (MOFs) and graphitic carbon nitride derivatives, i.e. poly-heptazine imides (PHI) are appealing CO2RR and OER photo-catalysts respectively. Engineering of an innovative Z-scheme heterojunction by assembling a Ti-MOF and PHI offers an unparalleled opportunity to mimick an artificial photosynthesis device for dual CO2RR/OER catalysis. Along this path, understanding of the photophysical processes controlling the MOF/PHI interfacial charge recombination is vital to fine tune the electronic and chemical features of the two components and devise the optimum heterojunction. To address this challenge, we developed a modelling approach integrating force field Molecular Dynamics (MD), Time-Dependent Density Functional Theory (TD-DFT) and Non-Equilibrium Green Function DFT (NEGF-DFT) tools with the aim of systematically exploring the structuring, the opto-electronic and transport properties of MOF/PHI heterojunctions. We revealed that the nature of the MOF/PHI interactions, the interfacial charge transfer directionality and the absorption energy windows of the resulting heterojunctions can be fine tuned by incorporating Cu species in the MOF and/or doping PHI with mono- or divalent cations. Interestingly, we demonstrated that the interfacial charge transfer can be further boosted by engineering MOF/PHI device junctions and application of negative bias. Overall, our generalizable computational methodology unravelled that the performance of CO2RR/OER photoreactors can be optimized by chemical and electronic tuning of the components but also by device design based on reliable structure-property rules, paving the way towards practical exploitation.

The photocatalyst with a strong internal electric field grown in situ on the surface of copper foam collaborates with peroxymonosulfate to enhance directional charge transfer and achieve ultra-fast Mn+/M(n+1)+ cycling

To address three pressing problems that limit the application of photocatalytic synergic peroxymonosulfate (PMS) technology, namely difficult reuse, low photogenerated carrier separation efficiency, and sluggish metallic ions redox cycle, we utilized an in-situ growth method to construct a vertical nanosheet heterojunction on the surface of copper foam (CF). This heterojunction is characterized by a strong internal electric field (IEF) that serves as both a “pump” for the rapid and efficient migration of electrons and a driving force for the activation of PMS by these electrons. In the CF@CCS@CO-3/7/Vis/PMS system, the photoelectrons generated by photocatalysis quickly replenish the high valence metals activated by PMS, allowing for highly efficient cycling of differently valenced metal ions and reducing the dissolution of high valence metal ions produced by PMS. As a result, close to 100 % of ciprofloxacin (CIP) was degraded within 60 min in the CF@CCS@CO-3/7/Vis/PMS system with a reaction rate constant k of 0.0621 min−1, which is about 3.22 times higher than that of the CF@CCS@CO-3/7/Vis system and 2.65 times higher than that of the CF@CCS@CO-3/7/PMS system. Moreover, the in-situ growth of active ingredients with vertical nanosheet structure on the CF surface can well maintain structure and reactivity in complex environments, allowing more than 10 cycles to be realized. The results of the free radical burst assay and EPR analysis indicated that SO4∙−, ∙O2− and h+ were the main reactive species involved in the catalytic process. Building upon CF@CCS@CO-3/7, we assembled a fixed-bed continuous treatment device that enables high mineralization flow treatment of pharmaceutical wastewater (after Secondary biological treatment).

Direct Z-scheme In2S3@BiYWO6 heterojunction photocatalysts for highly efficient environmental remediation

Novel In2S3@BiYWO6 heterojunction photocatalysts were designed and synthesized by a simple two-step hydrothermal method, which exhibit extremely excellent photocatalytic activity for degrading the residual antibiotics in wastewater. Especially, In2S3@BiYWO6 composite with mass ratio of 10:1 shows the highest photo-degradation efficiency towards Tetracycline Hydrochloride, which is about 2.46 and 7.55 times than that of pristine In2S3 and BiYWO6, respectively. A direct Z-scheme charge transfer mechanism was demonstrated in these heterojunctions through the XPS analysis, radical species trapping experiments and fluorescence detection. Within the framework of this mechanism, the critical built-in electric field (Ei) formed at the contact interface between In2S3 and BiYWO6 spatially separates reduction or oxidation sites and thus preserves the photogenerated carriers with stronger redox ability on reaction sites, which ultimately enhances the photocatalytic activity of the heterojunction catalysts. It is commendable that such Z-scheme heterostructures between In2S3 and BiYWO6 exist in a wide span of component ratios (from 5:1 to 30:1), which is beneficial for the environmental remediation applications. It is believed that this work provides new ideas for design and synthesis of novel Z-scheme heterojunction photocatalysts.

In situ reversible assembly of atomic interfacial structure in BiOI/Bi5O7I p-n heterojunctions to promote visible-light photocatalysis

Constructing efficient p-n heterojunctions holds great potential in the realm of photocatalysis for promoting the sustainable development of the environment and energy industries. However, traditional p-n heterojunctions suffer from limited interfacial interaction which severely restricts the effectiveness of the built-in electric field in boosting charge separation. Herein, we present an in situ reversible assembly approach to fabricate functional p-n junction in BiOI/Bi5O7I composites at room temperature. By controlling the reaction time or the amount of KI precursor added, we attain the as-designed BiOI@Bi5O7I and Bi5O7I@BiOI heterojunctions with large specific surface area and ample interfacial electric field. Subsequent application of the optimized heterojunction material as visible-light photocatalyst achieves efficient photoreduction of CO2 reactant into CO product (0.46 μmol g−1h−1), even without using any sacrificial agent in the gas–solid reaction system. This catalytic performance is notably ∼ 6.6 times and 15.3 times higher than that of standalone BiOI and Bi5O7I materials, respectively. In situ XPS, in situ Kelvin probe force microscopy, and theoretical calculations reveal that the built-in electric field induces directional charge transfer to greatly boosts the efficiency of separating photogenerated electron-hole pairs at the interface of BiOI and Bi5O7I. This study provides valuable insights for the rational design and straightforward fabrication of next-generation, integrated heterostructured photoelectronic materials for efficient energy, environmental, and chemical applications.

Potential window alignment regulating ion transfer in faradaic junctions for efficient photoelectrocatalysis

In the past decades, a band alignment theory has become a basis for designing different high-performance semiconductor devices, such as photocatalysis, photoelectrocatalysis, photoelectrostorage and third-generation photovoltaics. Recently, a faradaic junction model (coupled electron and ion transfer) has been proposed to explain charge transfer phenomena in these semiconductor heterojunctions. However, the classic band alignment theory cannot explain coupled electron and ion transfer processes because it only regulates electron transfer. Therefore, it is very significant to explore a suitable design concept for regulating coupled electron and ion transfer in order to improve the performance of semiconductor heterojunctions. Herein, we propose a potential window alignment theory for regulating ion transfer and remarkably improving the photoelectrocatalytic performance of a MoS2/Cd-Cu2ZnSnS4 heterojunction photocathode. Moreover, we find that a faradaic potential window, rather than the band position of the intermediate layer, is a criterion for identifying interface charge transfer direction. This finding can offer different perspectives for designing high-performance semiconductor heterojunctions with suitable potential windows for solar energy conversion and storage.

Oxygen vacancy induced robust interfacial electric field for efficient photocatalytic hydrogen peroxide production

Photocatalytic production of hydrogen peroxide (H2O2) can convert low-density solar energy into storable chemical energy by only utilizing water and oxygen as feedstock, and sunlight as stimulator. However, it is encountered a great deal of hurdles for further improving the photocatalytic H2O2 production, such as the narrow light absorption range of a single semiconductor, low separation efficiency of photogenerated electron-hole pairs and limited surface active sites. Although construction of heterojunction is an effective tactic to modulate the charge transfer path and improve the utilization of visible light, realizing close interfacial contact with a strong interfacial electric field (IEF) remains challenging. Herein, we construct a chemically bonded heterojunction, abbreviated as BON-Ov/CN, which consists of g-C3N4 and Bi2O2(NO3)(OH) decorated with oxygen vacancies (Ovs) to solve all the above problems in one fell swoop. The optimal BON-Ov/CN exhibits a photocatalytic H2O2 production performance of 706.2 µmol L-1, which is 19.1, 14.9 and 4.9 times higher than that of BON, BON-Ov and CN, respectively. It was demonstrated that the largely enhanced catalytic activity is attributed to the type-II heterojunction between BON-Ov and CN. In particular, the introduction of Ovs on BON can induce a strengthened IEF to boost the interfacial directional charge transfer and enhance its surface active sites to some extent. This study offers a fresh perspective on improving interfacial charge migration of heterojunctions by vacancy-induced IEF regulation strategy.

Highly efficient Bi2O2CO3 coupled with interlayer expanded MoS2 photocatalyst with oxygen vacancy mediated direct Z-scheme charge transfer for photocatalytic degradation of organic pollutant

The development of photocatalysts to degrade organic pollutants from wastewater under visible light has attracted a lot of interest. Herein, a series of Bi2O2CO3 (BOC) coupled with interlayer expanded MoS2 (IEM) photocatalysts were synthesized via a facile two-pot hydrothermal technique. Among all the samples, 5 % of BOC with IEM (5 % BOC-IEM) nanocomposite exhibited the highest photodegradation with 94 % (4.97 × 10−2 min−1) for Methylene Blue (MB) dye removal under 1 W LED visible light. The performance by 5 % BOC-IEM is 1.5 times and 13.4 times higher than the parent IEM and BOC, respectively. Increased photocurrent density, lowest PL intensity, and smallest EIS arc further evidenced the lowered charge carrier’s recombination rate in the optimized 5 % BOC-IEM heterostructure. Moreover, the outstanding photocatalytic performance of 5% BOC-IEM was due to the presence of oxygen vacancies, enhanced light absorption, and improved migration and separation of charge carriers. An Ohmic contact formed on the interfaces of BOC and IEM boosts the Z-scheme charge transfer mechanism, which greatly improves the photocatalytic activity of 5% BOC-IEM.

Visible-light-driven photodegradation of methylene blue and doxycycline hydrochloride by waste-based S-scheme heterojunction photocatalyst Bi5O7I/PCN/tea waste biochar

Herein, we have reported a photocatalytic Bi5O7I, protonated g-C3N4 heterojunction with directional charge transfer channels provided by tea waste biochar to achieve effective e−/h+ pair isolation for the improved degradation of Methylene blue (MB) and Doxycycline hydrochloride (DCHCl). An S-scheme heterojunction was fabricated via the novel method that combined hydrothermal and ultrasonic dispersion, followed by an electrostatic self-assembly route. The as-fabricated Bi5O7I/protonated g-C3N4/Tea waste biochar heterojunction formed a strong contact at the interface, as supported by the electron microscopic results. As per the adsorption and photocatalytic degradation kinetics study, Bi5O7I/Tea waste biochar/protonated g-C3N4 (40 wt%) heterojunction showed a higher adsorption rate of 41.56% and 32% for MB and DCHCl within 30 min in the dark. Also, 92.02% MB and 90.21% DCHCl degradation rates in 60 and 90 min, respectively, are approximately 43 and 32 times higher than bare Bi5O7I and protonated g-C3N4 photocatalysts. The highest adsorption and degradation rate was achieved owing to the addition of Tea waste biochar and protonated g-C3N4 in a controlled ratio, and the sufficient interfacial contact between Bi5O7I and protonated g-C3N4 is for the improved isolation rate of e−/h+ pairs as evidenced by zeta potential values photoluminescence spectra as well as from scanning and transmission electron microscopy. Moreover, Bi5O7I/Tea waste biochar/protonated g-C3N4 (40 wt%) possessed high stability and recyclability after four consecutive cycles without much altering the degradation ability. Therefore, we believe that the as-fabricated Bi5O7I/Tea waste biochar/protonated g-C3N4 (40 wt%) provides new insight into the highly efficient S-scheme mechanisms significant for accelerating multicomponent photocatalytic redox reactions; while forming an effective visible light responsive candidate for treating wastewater.