Separation Of Electron-hole Pairs Research Articles

Infrared optoelectronics in twisted black phosphorus

Electrons and holes, fundamental charge carriers in semiconductors, dominate optical transitions and detection processes. Twisted van der Waals (vdW) heterostructures offer an effective approach to manipulate radiation, separation, and collection processes of electron-hole pairs by creating an atomically sharp interface. Here, we demonstrate that twisted interfaces in vdW layered black phosphorus (BP), an infrared semiconductor with highly anisotropic crystalline structure and properties, can significantly alter both recombination and separation processes of electron-hole pairs. On the one hand, the twisted interface breaks the symmetry of optical transition states resulting in infrared light emission of originally symmetry-forbidden optical states along the zigzag direction. On the other hand, spontaneous electronic polarization/bulk photovoltaic effect is generated at the twisted interface enabling effective separation of electron-hole pairs without external voltage bias. This is supported by first-principles calculations and repeated experiments at various twisted angles from 0 to 90°. Importantly, these phenomena can be observed in twisted heterostructures with thickness beyond two-dimensional. Our results suggest that the engineering of vdW twisted interfaces is an effective strategy for manipulating the optoelectronic properties of materials and constructing functional devices.

Design of novel Z-scheme g-C3N4/TiO2/CuCo2O4 heterojunctions for efficient visible light-driven photocatalyic degradation of rhodamine B

One of the most important environmental challenges that needs to be resolved is the industrial discharge of synthetic dyes. Graphitic carbon nitride (g-C3N4), Titanium dioxide (TiO2) and flower-like copper oxide (CuO)/copper cobaltite (CuCo2O4) nanocomposites were synthesized in order to synthesis an effective visible light driven photocatalyst that could degrade Rhodamin B (Rh.B) dye under simulated solar light irradiation. The SEM and TEM results verifies that the flower-like CuO/CuCo2O4 (CCO) structure and g-C3N4/TiO2 (g-CN/TO) generated a smart hybrid structure with superior g-CN distribution. According to the photocatalytic studies, g- C3N4/TiO2/CuO/CuCo2O4 (g-CN/TO/CCO) shows good photodegradation of Rh.B dye (99.9%) in minmal times (1 h) in CCO: g-CN/TO (2:1) ratio by Z-Scheme mechanism. The enhanced visible light absorption and effective electron-hole pair separation provided by the synergistic dispersion of CuO/CuCo2O4 and g-C3N4 can be attributed to the improved photocatalytic performances. These novel insights into g-CN/TO/CCO based photocatalysts are useful for treating industrial effluent.

Self-powered γ-In2Se3/p-Si heterojunction for photodetection: exploring humidity and light intensity dependent photoresponse

In this study, high-quality γ-In2Se3 thin films were successfully deposited on p-Si substrates via the RF sputtering technique. Structural characterization using XRD and Raman spectroscopy confirmed the formation of the hexagonal γ-phase of In2Se3 film. FESEM analysis revealed the presence of small, homogeneous, and well-defined grains in the prepared γ-In2Se3 film. EDS analysis confirmed the stoichiometric composition (∼ 2:3) of the In2Se3 films. XPS further validated the presence of In, Se, and Si elements in the deposited films. Band gap analysis using UV-visible spectroscopy yielded a value of 1.96 eV for the γ-In2Se3 film. Integration of γ-In2Se3 with p-type Si enhanced photoresponsivity of 47.9 mA/W, photosensitivity of 282, and photo detectivity of 8.45 × 1010 Jones. The self-powered γ-In2Se3/p-Si heterojunction-based photodetector exhibited rapid rise time attributed to the type II band alignment structure, facilitating efficient electron-hole pair separation and minimizing recombination. Furthermore, humidity and light intensity-dependent photodetector properties of γ-In2Se3/p-Si heterojunction photodetector were also investigated. An increase in photocurrent from 271 to 291 µA was observed with rising humidity levels, indicating the device’s sensitivity to humidity variations. Furthermore, light intensity dependence studies revealed a linear relationship between photocurrent and incident light intensity, demonstrating the device’s reliable response across various illumination levels.

Semiconductor Nanoporous Anodic Alumina Photonic Crystals as a Model Photoelectrocatalytic Platform for Solar Light‐Driven Reactions

In this study, nanoporous anodic alumina distributed‐Bragg reflectors (NAA–DBRs) functionalized with tungsten trioxide (WO3) are used as prototype photoelectrocatalysts (PEC) for harnessing the slow photon effect to maximize photon‐to‐electron conversion efficiency under UV–visible–NIR illumination. NAA–DBR structures are structurally engineered by anodization, where their characteristic photonic stopband is precisely tuned along specific positions of the UV–visible spectrum. Subsequent atomic layer deposition is employed to coat the inner surface of these porous structures with WO3 semiconductor layers. Upon the application of overpotential bias, these platforms reveal excellent electron–hole pair separation to boost photoelectrocatalytic reactions. Photoelectrochemical degradation of methylene blue is used as a model reaction to elucidate enhancements associated with structural and optoelectronic arrangements. Notably, precise spectral alignment between the photonic stopband's red edge and the absorbance band of methylene blue enhances the degradation performance through the slow photon effect. Applying an overpotential bias further improves the photodegradation performance through efficient charge separation. These systems outperform comparable structures in this model reaction, achieving a maximum kinetic rate of 13.7 ± 2.0 h−1. The findings create new opportunities to develop high‐performing PEC technologies harnessing light–matter interactions.

Microwave-Assisted Synthesis of CdS-MOF MIL-101 (Fe) Composite: Characterization and Photocatalytic Performance.

The present study outlines the synthesis of cadmium sulfide-metal-organic framework (CdS-MOF) MIL-101 (Fe) heterojunctions achieved via fast microwave-assisted reactions. Thus, different CdS-MOF MIL-101 (Fe) ratios were prepared to study their effectiveness as photocatalysts. These compounds were employed in the photocatalytic degradation of methylene blue (MB) under UV and visible irradiation. Structural, morphological, textural, compositional, and optical properties of the synthesized compounds determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy were utilized to characterize the structural, morphological, textural, compositional, and optical properties. Electrochemical impedance spectroscopy (EIS) was also employed to determine photovoltage and photocurrent densities. The resulting valence band offset (Vfb) and band gap energy values were utilized to construct an energy band scheme. Our research revealed that the CdS-MOF MIL-101 (Fe) heterojunction enhances the efficiency of electron-hole pair separation, thereby mitigating charge carrier recombination effects. Moreover, the type I electronic band structure established an efficient reaction mechanism, effectively suppressing the recombination of photogenerated electron-hole pairs. The photocatalytic system demonstrated exceptional behavior, achieving complete MB removal within 30 min of reaction time and exhibiting outstanding stability and reusability after four reaction cycles. These findings highlight the potential of the synthesized compounds in the field of wastewater treatment for organic pollutants, offering a promising alternative to current environmental issues.

Single-atom Rh[sbnd]S bond on defective CdZnS for enhanced photocatalytic hydrogen production

It is highly necessary but challenging to modify sulfides at the atomic scale to boost the separation of electron-hole pairs for enhanced photocatalytic performance. In this regard, single Rh atoms (Rh1) are assembled on CdZnS support with S vacancy defects (def-CZS) through RhS bond, creating a highly efficient photocatalyst. The optimized Rh1/def-CZS achieves an outstanding hydrogen evolution activity (30,512 μmol h−1 g−1), 4.32 and 3.34 folds enhancement that of CZS and def-CZS, respectively. The defective CZS support provides abundant S vacancy defects for Rh atom anchoring, where Rh bonds with neighboring S atoms (RhS). Theoretical calculations suggest that Rh can not only act as new H generation-release sites, but also optimize electron distribution around S defects simultaneously through the RhS bond, facilitating the separation of electron-hole pairs. Furthermore, in line with DFT results, in situ Raman confirms Rh (RhH) and electron-rich S atoms (SH) two main sites for proton reduction during hydrogen evolution.

WO3@MOF heterostructure in-situ transformed and deposited on La-Bi2WO6-BiFeWOx composite with enhanced photocatalytic performance for degradation of harmful and toxic substances produced by tobacco

Nowadays, tobacco is widely cultivated, and there are millions of people who smoke around the world. The cultivation of tobacco, along with the handling of cigarettes and the consumption of tobacco products, can produce numerous harmful and toxic substances. Many researchers are working diligently to eliminate these harmful and toxic substances. However, the results have been minimal. In this paper, we successfully prepared a novel La-Bi2WO6-BiFeWOx-WO3@MOF using hydrothermal and in-situ transformation methods. All samples were thoroughly investigated using various characterization techniques, including XRD, SEM, TEM, XPS, UV–Vis absorption spectra, transient photocurrent responses, and electron spin resonance. Furthermore, La-Bi2WO6-BiFeWOx-WO3@MOF was utilized as a catalyst for the degradation of harmful and toxic substances produced by tobacco, including phenol, nicotine, benzopyrene, and nitrosamines. The results indicate that La-Bi2WO6-BiFeWOx-WO3@MOF exhibits efficient separation and transfer of photo-generated electron-hole pairs under visible light irradiation. La-Bi2WO6-BiFeWOx-WO3@MOF also exhibits excellent photocatalytic activity, efficiently degrading phenol (98.62%), nicotine (92.41%), benzopyrene (81.74%), and nitrosamine (98.23%). Furthermore, the effects of varying catalyst dosage, phenol concentration, and pH values, as well as the degradation of nicotine, benzopyrene, and nitrosamine by La-Bi2WO6-BiFeWOx-WO3@MOF, were also investigated. The main active radicals are ·OH and ·O2– during the degradation process. Finally, a potential degradation mechanism for phenol, nicotine, benzopyrene, and nitrosamine by La-Bi2WO6-BiFeWOx-WO3@MOF is proposed.

Piezoelectric field accelerating charge transfer in Z-scheme heterojunction 2D-KNbO3/1D-CdS for efficient piezo-photocatalytic H2 evolution and TCH degradation

The piezo-phototronic effect utilizes the piezoelectric polarization field to tune the photogenerated carrier separation and transport performance in heterojunctions, which portrays a promising strategy for addressing energy shortage and environmental pollutants. Herein, a novel Z-scheme piezoelectric semiconductor heterojunction, 2D-KNbO3/1D-CdS-x (KNCS-x), was fabricated using hydrothermal and solvothermal methods, resulting in enhanced redox capacity. Under the simultaneous light and strain, KNCS-15 exhibits the highest piezo-photocatalytic activity, with degradation rates of tetracycline hydrochloride degradation rate constant, H2O2 as well as H2 production rates being 1.806 × 10−2 s−1, 45.56 mM·h−1·g−1 and 8.87 mmol·h−1·g−1, respectively, which are 1.4, 2.4 and 1.9 times of photocatalysis alone, and 9.8, 9.2 and 9.8 times of piezocatalysis alone. DFT calculations, EPR and PALS indicate that the Z-scheme structure realizes effective separation of electron-hole pairs with strong redox ability and a higher carrier concentration. The enhanced catalytic activity is attributed to the introduction of piezoelectric potential, which facilitates improved spatial separation of electrons with high reduction and holes with high oxidation potential.

Z-scheme InVO4/ZnFe2O4 heterojunction for efficient photocatalytic nitrogen fixation

Given outstanding light absorption and utilization capabilities, narrow-bandgap semiconductors receive intensive interests in the photocatalysis field. However, the narrow bandgap is a double-edged sword, with the non-negligible charge carrier recombination and hinderance of redox reactions due to the limited redox capability. The construction of Z-scheme heterojunctions could address the aforementioned issues. In this work, we selected two band-matched narrow-bandgap semiconductor catalysts (InVO4 and ZnFe2O4) for the construction of a Z-scheme heterojunction. Compared with pure InVO4 and pure ZnFe2O4, the as-obtained InVO4/ZnFe2O4 Z-scheme heterojunction exhibited improved light harvesting capability and enhanced photogenerated electron-hole pair separation rate. The regulated energy band structure of as-formed InVO4/ZnFe2O4 Z-scheme heterojunction could accelerate the spatial separation of photogenerated electrons and holes, reduce the recombination probability, and provide sufficient electrons to participate in the nitrogen reduction, ultimately significantly promoting photocatalytic activity. Benefiting from above improvements, the NH3 yield of InVO4/ZnFe2O4 for photocatalytic nitrogen fixation was up to 453.37 μmol/gcat/h, which was about 17.7 times and 62.9 times higher than that of pure InVO4 and ZnFe2O4 samples, respectively. This study gives a promising guidance to the facile design and utilization of Z-scheme heterojunction composed of narrow-bandgap semiconductors.

Doping-Engineered Piezoelectric Ultrathin Nanosheets for Synergistically Piezo-Chemocatalytic Antitumor and Antibacterial Therapies Against Cutaneous Melanoma.

The post-surgical melanoma recurrence and wound infections have persistently troubled clinical management. Piezocatalytic therapy features high efficiency in generating reactive oxygen species (ROS) for tumor therapy, but it faces limitations in piezoelectricity and redox-active site availability. Herein, Fe-doped ultrathin Bi4Ti3O12 nanosheets (designated as Fe-UBTO NSs) with synergistically piezo-chemocatalytic activity are engineered for antitumor and antibacterial treatment against cutaneous melanoma. The doping-engineered strategy induces oxygen vacancies and lattice distortions in Fe-UBTO NSs, which narrows bandgap to enhance piezocatalytic 1O2 and H2O2 generation by improving the electron-hole pairs separation, hindering their recombination, and increasing oxygen adsorption. Moreover, Fe doping establishes a piezo-chemocatalytic system, in which the piezocatalysis enables the self-supply of H2O2 and expedites electron transfer in Fenton reactions, inducing increased ·OH production. Besides, the atomic-level thickness and expanded surface area enhance the sensitivity to ultrasound stimuli and expose more redox-active sites, augmenting the piezo-chemocatalytic efficiency, and ultimately leading to abundant ROS generation. The Fe-UBTO-mediated piezo-chemocatalytic therapy causes intracellular oxidative stress, triggering apoptosis and excessive autophagy of tumor cells. Moreover, this strategy accelerates wound healing by facilitating sterilization, angiogenesis, and collagen deposition. This work provides distinct options to develop doping-engineered ultrathin nanosheets with augmented piezo-chemocatalytic activity for postoperative management of cutaneous melanoma.

One-pot hydrothermal synthesis of g-C3N4/BiOBr/Bi2MoO6 as a Z-scheme heterojunction for efficient photocatalytic degradation of ciprofloxacin (CIP) antibiotic and Rhodamine B (RhB) dye

Photocatalytic degradation of toxic organic pollutants using natural sunlight is a rapidly advancing area of research, particularly involving binary or ternary component photocatalysts with Z-type heterojunctions. In this study, ternary g-C3N4/BiOBr/Bi2MoO6 photocatalysts were fabricated using a simple one-pot solvothermal method. The morphology and physicochemical properties of the samples were characterized using various techniques, including X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), confirming the presence of BiOBr, Bi2MoO6, and g-C3N4 components. The inclusion of g-C3N4 increased the BET surface area of the composite up to 46 m2/g, compared with BiOBr. In addition, g-C3N4 also enhanced the light absorption capability of the composite into the visible light range, while BiOBr and Bi2MoO6 significantly improved separation of electron-hole pairs, as evidenced by photoluminescence (PL) intensity. Under visible light illumination (LED lamp), the prepared photocatalyst showed high efficiency, achieving 94 % degradation of ciprofloxacin (CIP) antibiotic in 180 min and 92 % degradation of Rhodamine B (RhB) dye in 240 min. Moreover, under natural sunlight irradiation, the photocatalyst achieved degradation efficiencies of approximately 91 % for CIP and 100 % for RhB within 180 minutes. The photodegradation of the pollutants followed first-order kinetics with a Z-scheme type heterojunction. The photogenerated electrons played a crucial role as the main active species involved in detoxification of the organic contaminants. The photocatalyst exhibited excellent structural stability and good cycling ability, maintaining its original photocatalytic performance even after five cycles of use. This work demonstrates a promising strategy for developing sunlight-active ternary heterojunctions for environmental remediation.

Decorating nitrogen-deficient crystalline g-C3N4 with Ti3C2(OH)2 for photocatalytic CO2 reduction and RhB degradation enhancement

Visible light responding photocatalytic technology has shown great potential to mitigate the greenhouse effect and global pollution issues in recent years. Herein, alkalized titanium carbide Ti3C2Tx (TCOH) is combined with nitrogen-deficient g-C3N4 (CN-Nx) by simply mixing for photocatalytic CO2 reduction and RhB degradation. TCOH replaces noble metals as a co-catalyst for CN-Nx due to its full-spectrum absorption properties and excellent conductivity, which effectively enhances the overall light absorption capacity of CN-Nx. Additionally, a large Fermi energy level difference between TCOH and CN-Nx leads to a built-in electric field forming at their interface when combined. This built-in electric field can enhance the photogenerated electron-hole pair separation and reduce the recombination rate. So the visible light utilization ranges of optimized 2TCOH-30 %/CN-N0.02 expanded from 477 nm (CN-N0.02) to 481 nm, and the average lifetimes of the photogenerated carriers is 4.37 ns, which is 2.64 times longer than CN-N0.02. Moreover, the CO yield reaches 67.55 μmol/g during photocatalytic CO2 reduction of 2TCOH-30 %/CN-N0.02, which is 4.06 and 2.54 times than 2TCOH and CN-N0.02. During the RhB degradation, 2TCOH-30 %/CN-N0.02 can remove approximately 98.3 % of RhB in 15 min, which is1.6 and 1.4 times of 2TCOH and CN-N0.02. Also, 2TCOH-30 %/CN-N0.02 shows excellent stability, the photocatalytic capacity for CO2 reduction and RhB degradation has no significant degradation after six times circles.

A flower-like g-C3N4/CDs/Bi2WO6 hierarchical structure for enhanced photocatalytic degradation of tetracycline

Tetracycline (TC), as one of antibiotic emerging pollutants, has posed potential threats to ecological environment and human health because it is hardly biodegradable and prone to be accumulated in water. In this study, g-C3N4/CDs/Bi2WO6 S-scheme heterojunction with flower-like hierarchical structure was synthesized by hydrothermal method. The optimized composite demonstrates significantly enhanced photocatalytic activity with a TC degradation efficiency of 90.1% after 120 min of visible light irradiation and good reusability up to four consecutive cycles. This can be attributed to the improved light capture capability and efficient separation of photo-generated electron-hole pairs in the constructed S-scheme heterojunction. The introduced carbon dots (CDs) can be served as an efficient carrier transport highway, providing a superior photogenerated carrier separation efficiency and an expanded absorption spectrum. As a result, the strongest redox potentials of the CBCN and VBBWO can be retained for participating the photocatalytic reaction. Free radical capture and electron spin resonance experiments indicate that ·O2- and h+ are the principal active species in the g-C3N4/CDs/Bi2WO6 system. This work provides new strategy for the development of advanced materials in the field of photocatalytic treatment of wastewater.

Synthesis of MoS2@MoO3/(Cu+/g-C3N4) ternary composites with double S-scheme heterojunction for peroxymonosulfate activation exposing to visible light

The construction of semiconductor heterojunction is an effective way for charge separation in photocatalytic degradation of pollutants. In this study, a novel MoS2@MoO3/(Cu+/g-C3N4) ternary composites (MMCCN) was prepared via a simple calcination method. The as-prepared composites exhibited exceptional performance in activating peroxymonosulfate (PMS) for the degradation of rhodamine B (RhB). The activity testing results indicated that 99.41 % of RhB (10 mg·L−1, 10 mL) was effectively removed by the synergistic effect of composites photocatalyst (0.1 g·L−1) and PMS (0.1 g·L−1) under visible light irradiation for 40 min. Its reaction rate constant exceeded that of Cu+/g-C3N4, MoO3 and MoS2 by a factor of 3.56, 17.30 and 11.73 times, respectively. The crystal structure, band gap and density of states (DOS) of the semiconductors were calculated according to the density functional theory (DFT). Free radical trapping tests and electron spin resonance spectroscopy validated that 1O2, O2− and h+ are primary reactive species participating in the decomposition of RhB. The ternary composites demonstrated good stability and maintained excellent degradation efficiency even across four reaction cycles. Furthermore, the activation mechanism and the intermediates produced during the decomposition course of RhB by MMCCN/PMS/vis system were analyzed and elucidated. A double S-scheme heterojunctions was responsible for efficient separation of photo-induced electron-hole pairs. This work presents a novel method in the construction of double S-scheme heterojunctions for PMS activation which is expected to find wide applications in wastewater treatment and environmental remediation.

Effects of UV ozone treatment on the photoresponse of the Pt nanoparticles decorated WS2

Chemical vapor deposition (CVD)-grown and Pt nanoparticles (NPs) decorated multilayer WS2 is treated by ultraviolet (UV) ozone for the modification of the surface roughness to realize the enhanced hot carriers injection via the internal photoemission (IPE). The morphology, structure and photophysical properties as well as the dependence of the photoresponse on the UV ozone treatment are investigated. The UV ozone treatment demonstrates obvious effect on the WS2 surface roughness (Sa), which reaches the maximum around 14nm after 2 minutes exposure and subsequently decrease with the extension of treatment duration. UV ozone treatment also leads to obviously diminished photoluminescence (PL) and shortened excitons lifetime for bare WS2 while its influence on the electronic structure is negligible. The diminished PL, shortened PL decaying lifetime and increased Sa are all originated from the formation of WOx due to the consumption of top WS2 layer by the severe oxidation, and such effects will be greatly alleviated when the fresh and undisturbed underlying WS2 layer appears with the treatment duration extended to 4 minutes. The 2 minutes UV ozone treated WS2/Pt exhibits optimal wide spectrum photoresponse (400-900nm) with the near infrared (NIR) responsivity around 18 A/W at 750nm, about 60% higher compared to that of untreated one while the 4 minutes overtreated WS2/Pt demonstrates much deteriorated photoresponse. Such behavior can be ascribed to the enhanced hot electrons injection from Pt to WS2 due to the formation of rough Schottky contact as well as the separation of photo-excited electron-hole pairs by Schottky junction. Our study proves that the Sa is a key factor not only for the exciton dynamics but also for the hot electron injection from Pt to WS2.

Transition metal nickel nanoparticle-decorated g-C3N4 photocatalyst for improving tetracycline hydrochloride degradation

Metallic nickel nanoparticles (Ni NPs)-supported g-C3N4 have been developed using a solvothermal technique in N,N-dimethylformamide solvent. A uniformly dispersion of Ni NPs anchored on a g-C3N4 photocatalyst can improve the photocatalytic efficiency. The optimized Ni/g-C3N4 catalyst demonstrated a high photodegradation rate of TCH at 6.0 × 10−3 min−1 under LED light irradiation, which was approximately three times greater than that of the bare g-C3N4 catalyst. This superior performance originates from the capable separation of electron-hole pairs, facilitated by the strong interaction between Ni0 NPs and the host g-C3N4, as supported by optical and electrochemical property analysis. Our work provides a facile manner for the effective degradation of pollutants using heterojunction photocatalysts.

One-step conversion of FeOCl/Fe2O3 to BiOCl/Fe2O3 for boosted visible-light-driven photocatalysis

BiOCl nanosheets/Fe2O3 nanorods heterostructures were synthesized via a one-step conversion of FeOCl/Fe2O3 nanorods. The optimal 20 %BiOCl/Fe2O3 heterostructure demonstrated a catalytic rate constant 85.5 times greater than FeOCl/Fe2O3 in visible-light-driven photodegradation of RhB. This excellent performance is due to the forming of an S-scheme heterostructure between BiOCl and Fe2O3 with abundant heterointerfaces, which greatly enhances the separation of electron-hole pairs and promotes the generation of active h+ and O2− species.

Preparation of Cu-doped MIL-125(Ti)-derived carbon-based composites for the sonodynamic degradation of organic dyes

Sonocatalysis provides a green and sustainable strategy to remove industrial organic pollutants. Toward improving the sonocatalytic performance to remove the organic dyes, a new Cu-C@TiO2 catalyst was prepared via doping the Cu(II) ions into the MIL-125(Ti) and then carbonizing the resultant Cu-MIL-125(Ti) in this study. By the SEM, EDS and BET, the obtained Cu-C@TiO2 was a porous carbon-based hybrid with bimetallic centers, retaining a large amount of organic frameworks to supply adequate specific surface area for the adsorption; By the XPS and UV–vis DRS, the band gap of Cu-C@TiO2 was reduced to significantly broaden the light absorption region and facilitate the separation of electron-hole pairs; By the fluorescence spectra, the graphite-like structure and Cu particles produced on the catalyst surface served as an electron trap to inhibit the recombination of charge carriers. The Cu-C@TiO2 showed an excellent sonocatalytic performance to organic dyes, and under the ultrasound irradiation (35 KHz, 150 W), it could remove more than 95 % of rhodamine B (5.00 mg/L) and methylene blue (5.00 mg/L) within 10 min. By the kinetic analysis, it was found that the dye removal obeyed the first-order kinetic model, and the scavenging studies of free radicals (OH and O2−) verified the Cu-C@TiO2-mediated sonodynamic degradation was in the dye removal. In the end, a Cu-C@TiO2-mediated adsorption/sonodynamic degradation mechanism was proposed to thermodynamically expound the removal process of organic dyes.

Effects of MOF-MoO3-x derivatives synthesis and oxygen defect engineering on photocatalytic CO2 reduction

Photocatalytic conversion of CO2 into valuable fuels is considered a promising approach for the development of sustainable and renewable energy sources. In this study, we utilized Mo-MOF as a precursor to obtain MoO3 by pyrolytic derivatization and treated it to obtain MOF-MoO3-x containing oxygen vacancies as a catalyst for the photocatalytic reduction of CO2 to CO. MOF derivatization altered the morphology of the MoO3, which made the formation of oxygen vacancies easier and facilitated the separation of electron-hole pairs. Meanwhile, the increased specific surface area and the appearance of surface oxygen vacancies enhanced the CO2 adsorption and activation capabilities of MOF-MoO3-x. As a result, MOF-MoO3-x demonstrated a significant enhances in the photoreduction activity of CO2. Its CO yield was 29.1 μmolg−1h−1, which was 3.7 times higher than that of MOF-MoO3 and 2.4 times higher than that of H-MoO3-x. This innovative strategy may provide a new avenue for improving the comprehensive performance of photocatalysts and developing renewable energy sources.

Cathodic shift in flatband potential of hematite based photoelectrodes: Evaluating and correlating the redshift to solar driven photocatalysis

As a promising metal oxide semi-conductor, hematite (α-Fe2O3) has interesting optical properties to be regarded as photoactive material. In this study, we evaluated the cathodic shift in onset potential (Eonset) and the negative shift in flat band potential (Efb). It was observed that the Eonset value of -0.457 V for α-Fe2O3 based electrode shifted to -0.638 V for the ternary nanocomposite (PNFC) [Pani/Ni-α-Fe2O3/CNT] based electrode. The flat band potential for α-Fe2O3 in 1 M NaOH is at -0.49 V which shifts to -0.68 V for the ternary nanocomposite (PNFC). This photoelectrochemical enhancement appears due to electron-hole pair separation. Therefore, it apparently increases the photocurrent trace for PNFC at -0.60 V to 7.04 mA cm-2, compared to the photocurrent of 4.52 mA cm-2 observed for pristine α-Fe2O3. According to the Mott-Schottky plot, the donor concentration (Nd) for the α-Fe2O3 is 4.83 ×109 cm-3, whereas for the ternary nanocomposite (PNFC) is 7.68 ×109 cm-3, respectively. As evident, the Nd value increase for the ternary nanocomposite PNFC points to the proximity of the Fermi (Ef) level below the CB edge when Ni doped α-Fe2O3 comes in contact with polyaniline (Pani). Indeed, the ternary nanocomposite PNFC with lower Eg value (1.32 eV) and higher photocurrent (7.04 mA cm-2) show higher photo-activity with percent degradation of 98.42% for photocatalytic degradation of Sunset Yellow under visible light irradiation. The aforementioned correlations of the energetic levels of band edges with the shifting of Efb to more negative potentials provide insight into the high photo-activity observed.