Photoinduced Charge Separation Rate Research Articles

Hybrid photovoltaic-thermoelectric structure based on multilayer combinations of Cr and Fe oxides

Cr and Fe oxide-based multilayer structures with enhanced photovoltaic properties were prepared by a reactive pulsed laser deposition on Si(100) substrate. Their charge carriers’ transport properties were studied by surface photovoltage technique. The results reveal that optimal bilayer structure grown on a cold substrate exhibits a photovoltage enhancement that corresponds to the high separation rate of photo-induced charges. Integral responsivity in the spectral region 360–1100 nm is about 500 V/W. A synergetic effect of thermoelectric and photovoltaic phenomena in multilayer combinations of oxides is discussed.

In suit constructing 2D/1D MgIn2S4/CdS heterojunction system with enhanced photocatalytic activity towards treatment of wastewater and H2 production

A novel visible-light-driven 2D/1D MgIn2S4/CdS catalyst with heterostructure was fabricated for sewage treatment and energy conversion. In this study, MIS/CdS-0.3 heterostructure catalyst displayed the remarkable photocatalytic performance, which could reduce about 100% of Cr(VI) within 30 min and decompose approximately 95.98% of oxytetracycline (OTC) after 60 min. Meanwhile, the degradation details and possible decomposition pathways for OTC solution were further verified by 3D EEM and LC-MS. Moreover, the as-obtained 2D/1D MgIn2S4/CdS hybrid composites signally promoted the hydrogen evolved in the light illumination at 420 nm. Meanwhile, some consequences based on various characterization technologies confirmed that the significant photo-induced charge separation rate is a crucial factor in the enhancement of photocatalytic capacity. The intimate contact and the formation of heterostructure between 2D MgIn2S4 nanosheets and 1D CdS nanorods with matched band gaps were beneficial for charge migration. Moreover, the band structures and the density of states (DOS) of MgIn2S4 and CdS were obtained based on density functional theory (DFT). In addition, the results of cycling experiments, XRD spectra and PL showed that the composition and performance of the composite are well-maintained, suggesting the great recyclability and stability. This work indicated that developing a 2D/1D heterostructure photocatalyst offers a cracking approach to enhance the photocatalytic property of semiconductor-based catalysts for pollutant removal and the generation of clean energy.

BiFeO3–BiOI impregnation to UiO-66(Zr/Ti) as a promising candidate visible-light-driven photocatalyst for boosting urea photodecomposition in a continuous flow-loop thin-film slurry flat-plate photoreactor

The BiOI/BiFeO3/UiO-66(Zr/Ti)-MOF composite as a new ternary separable visible light photocatalyst was synthesized and well-characterized through the XRD, FE-SEM, FTIR, PL, VSM and DRS analyses. The BiOI/BiFeO3/UiO-66 photocatalytic performance for urea photo-oxidation to N2, H2O and CO2 were evaluated in a continuous flow-loop thin-film slurry flat-plate photoreactor (TFSR) equipped to blue light-emitting diodes (LEDs) illumination. Results show that the introduction of BiFeO3 perovskite and BiOI on the UiO-66(Zr/Ti) surface improves the separation and migration rate of photo-induced charges and thereby boosting the photocatalytic efficiency. Additionally, the appropriate band alignment, photo-stability and electron-hole pairs separation improvement of BiOI/BiFeO3/UiO-66(Zr/Ti)-MOF cause to enhance the urea decomposition. Moreover, five operational parameters including solution flow rate, pH, initial urea concentration, photocatalyst mass and light irradiation time were analyzed and optimized using the central composite design (CCD) and desirability function (DF), respectively. The maximum urea photocatalytic oxidation and elimination efficiency (88.53%) with the desirability value of 0.84 was achieved at the optimum conditions: 603 ​ml/min, 0.12 ​g/L, 7, 136 ​min and 60 ​ppm for flow rate, photocatalyst mass, pH, irradiation time and initial urea concentration, respectively.

Synthesis and enhanced piezophotocatalytic activity of Ag2O/K0.5Na0.5NbO3 composites

Ag2O/K0.5Na0.5NbO3 (Ag2O/KNN) piezophotocatalysts with different weight ratios of Ag2O to KNN were synthesized by a facile two-step method involving hydrothermal and precipitation methods. Ag2O particles were attached on the surface of KNN via a precipitation method. Ag2O/KNN composites exhibit better photoactivity than pure Ag2O and KNN under visible light irradiation. Moreover, under both irradiations of visible light and ultrasound, the piezophotocatalytic activity was further enhanced in comparison with photoactivity. Based on the experimental results, the improved piezophotocatalytic activities of Ag2O/KNN composites should be attributed to the formation of p-n heterojunction between Ag2O and KNN and the generation of external electric field of KNN, which leads to high separation rate of photo-induced charges. The photostability and corresponding piezophotocatalytic mechanism were discussed.

One step to prepare CNTs modified porous g-C3N4 with excellent visible-light photocatalytic performance

A kind of carbon nanotubes (CNTs) modified porous graphitic carbon nitride (CNTs/pg-C3N4) photocatalyst was successfully synthesized via one step thermal polycondensation and completely measured by some instruments, such as XRD, FTIR, TEM, BET, DRS, PL, etc. And the relevant experimental data indicated that loaded CNTs could be beneficial to the photoinduced charges transfer, facilitating photoinduced charge separation rate. Meanwhile, surface area and visible light adsorption of CNTs/pg-C3N4 photocatalyst could be increased and improved. These synergetic effects resulted in the as-synthesized CNTs/pg-C3N4 photocatalyst exhibiting better visible-light-induced photocatalytic performance for organic pollutant degradation and the product of clean energy than bulk g-C3N4, pg-C3N4 and CNTs modified bulk g-C3N4, and excellent stable photocatalytic performance was also observed after several recycling experiments. Finally, a reasonable improved photocatalytic reaction mechanism for CNTs/pg-C3N4 photocatalyst is presented.

Remarkably enhanced photoinduced charge separation rate of Bi2WO6 by Cu2+ doping

In this paper, Cu2+ was successfully doped into Bi2WO6 to further promote the photocatalytic performance of Bi2WO6. The presence of Cu2+ in the lattice of Bi2WO6 can be confirmed by the results of X-ray diffraction (XRD), energy dispersive spectrometer (EDS), high-resolution transmission electron microscopy (HRTEM) and element mapping images. The results of surface photovoltage spectroscopy (SPS) show that doping Cu2+ into the lattice of Bi2WO6 can greatly boost the separation rate of photoinduced electron–hole pairs. The electron spin-resonance (ESR) and trapping investigation exhibit that ·O2− is the main active free radicals. The photocatalytic performance of Cu-doped Bi2WO6 photocatalysts toward decolorization of rhodamine B (RhB) was evaluated under simulated sunlight irradiation using a 500 W Xe lamp as light source. Cu-doped Bi2WO6 photocatalysts display remarkably enhanced photocatalytic performance than the bare Bi2WO6, and when the molar ratio of Cu/Bi is 0.6%, the photocatalyst prepared displays the best photocatalytic activity.

Large enhancement of sunlight-driven photocatalytic performance of CdMoO4 prepared by SDBS-assisted microwave hydrothermal method

In this paper, CdMoO4 photocatalyst with enhanced sunlight-driven photocatalytic performance was prepared by a microwave hydrothermal method with the assistance of sodium dodecylbenzenseulfonate (SDBS). The photocatalysts were characterized by powder X-ray diffraction (XRD), Brunauer-Emmett-Tellermethod method (BET), surface photovoltage spectroscopy (SPS), scanning electron microscopy (SEM), and UV-Vis diffuse reflectance spectroscopy (DRS). The photocatalytic activities of the photocatalysts were evaluated by the decay of rhodamine B (RhB) and methyleneblue (MB) aqueous solution under simulated sunlight irradiation. The results demonstrate that adding SDBS into the reaction system increases the specific surface area, enhances the photo-induced charge separation rate of CdMoO4 and the formation of ·O2–. The photocatalytic activity of SDBS-CdMoO4 is higher than that of the reference CdMoO4, originating from the efficient separation of photo-induced charge pairs and increased specific surface area.

G-C3N4/UiO-66 nanohybrids with enhanced photocatalytic activities for the oxidation of dye under visible light irradiation

In this study, g-C3N4 nanosheets coated UiO-66 nanohybrids were fabricated via a simple solvothermal method. The physicochemical parameters, structural and electrochemical properties of g-C3N4/UiO-66 nanohybrids (CNUO-x) were investigated. The nanohybrids were systematically characterized by XRD, FT-IR, TGA, TEM, SEM, EDS elemental mappings, XPS, N2 adsorption-desorption isotherms, PL and DRS. It was found that the addition of moderate g-C3N4 could enhance the separation and migration rate of photo-induced charges, consequently leading to the increase of photocatalytic efficiency. The CNUO-1 nanohybrid exhibited better photocatalytic activity for the oxidation of Rh B under visible light irradiation, and displayed about 6.0 and 3.3 times faster than that of g-C3N4 and UiO-66, respectively. Meanwhile, the nanohybrid showed excellent stability and reusability in four cyclic experiments. Finally, the increased photocatalytic reaction mechanism was also proposed. O2−, h+ and OH were further found to be the main active contributors.

SDBS-assisted hydrothermal treatment of TiO2 with improved photocatalytic activity

To meet the practical application, it is still a challenge to prepare TiO2 with excellent photocatalytic performance. Therefore, in this work, TiO2 photocatalyst with enhanced sunlight-driven photocatalytic activity was facilely obtained after hydrothermal treatment of TiO2 with the assistance of sodium dodecyl benzene sulfonate (SDBS). TiO2 and SDBS-TiO2 were characterized by Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), UV–Vis diffuse reflectance spectra (DRS), scanning electron microscopy (SEM), surface photovoltage (SPV) spectroscopy and X-ray photoelectron spectroscopy (XPS), respectively. The photocatalytic performance of the photocatalysts toward Rhodamine B (RhB) discolorization was evaluated. The results display that a much higher photo-induced charge separation rate, active free radicals and surface hydroxyl radical content were produced in the SDBS-TiO2 photocatalytic system. The results further reveal that the photocatalytic performance of SDBS-TiO2 is more than two times of that of the reference TiO2.

Metal organic framework g-C3N4/MIL-53(Fe) heterojunctions with enhanced photocatalytic activity for Cr(VI) reduction under visible light

In this study, hybrid nanocomposites based on Fe-based MOF and graphitic carbon nitride (g-C3N4) were developed by a facile solvothermal method. The as-prepared materials were characterized by XRD, FESEM, TEM, XPS and PL analysis. It was showed that the introduction of a certain amount of g-C3N4 on the surface of MIL-53(Fe) would improve the separation and migration rate of photo-induced charges, consequently resulting in the boost of photocatalytic efficiency. Compared with g-C3N4 and MIL-53(Fe), the CMFe composites displayed more excellent visible light-resposive photocatalytic activity for the reduction of Cr(VI). The optimal doping content of g-C3N4 in g-C3N4/MIL-53(Fe) composite was determined to be 3.0wt%, and it showed about 2.1 and 2.0 times as high photocatalytic efficiency for the reduction of Cr(VI) as that of pure g-C3N4 and MIL-53(Fe), respectively. Meanwhile, the composite exhibited good reusability and stability in the process of cyclic experiments. A possible photocatalytic reaction mechanism was also investigated in detail by the related electrochemical analysis.

Charge separation behaviors of novel AgI/BiOI heterostructures with enhanced solar-photocatalytic performance

The photocatalytic efficiency of the bare BiOI has been greatly restricted because of the high recombination rate of electron-hole charge pairs. To further regulate the photocatalytic performance of BiOI, in this work AgI was employed to couple with BiOI. A serial of novel AgI/BiOI heterostructures with improved sunlight-driven photocatalytic activities were prepared in-situ by a hydrothermal method. The results reveal that the presence of AgI in the composites alters band gap of the samples and greatly affects the photo-induced charge separation rate benefited from the strong interaction between AgI and BiOI. ·OH and ·O2− were observed using electron spin-resonance (ESR) spectroscopy. The photocatalytic activities of AgI/BiOI heterostructures for the decay of methyl orange (MO) and phenol solution under the simulated sunlight irradiation were investigated, the results display that the composite photocatalysts exhibit higher photocatalytic activity than the bare BiOI and excellent stability. The charge separation and transfer mechanism was proposed based on the experimental results.

Effects of the molar ratio on the photo-generated charge separation behaviors and photocatalytic activities of (BiO)2CO3-BiOBr composites

The molar ratio of two semiconductors will remarkably influence the photo-induced charge separation behaviors of the composites constructed, thus affecting the corresponding photocatalytic activity. Therefore, it is critical to reveal the relationship between the molar ratio of two semiconductors and the photo-induced charge separation; the information can shed light on the study of nature of surface catalysis. In this work, (BiO)2CO3-BiOBr composites were facilely fabricated in-situ through a pore impregnating approach using HBr aqueous solution. The samples were studied by BET, XRD, SEM, UV–Vis DRS and surface photovoltage spectroscopy (SPS). The photocatalytic activities of the samples were evaluated by the discoloration of methyl orange (MO) aqueous solution upon the simulated sunlight illumination. The results reveal that the (BiO)2CO3-BiOBr composite with 3/4 M ratio of (BiO)2CO3/BiOBr displays the highest photo-induced charge separation rate and photocatalytic activity, the results further manifest that no different electronic transfer property occurs after coupling (BiO)2CO3 with BiOBr.

Preparation of point-line Bi2WO6@TiO2 nanowires composite photocatalysts with enhanced UV/visible-light-driven photocatalytic activity

Bi2WO6@TiO2 nanowires composite photocatalysts (BWO-TNWS) with point-line structures have been successfully fabricated by hydrothermalsynthesis method, and characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible diffuse reflectance spectra (UV–vis DRS), photoluminescence (PL) and electrochemical impedance spectroscopy (EIS). The effects of coupling narrow-band-gap semiconductor Bi2WO6 (BWO) to photocatalytic activity for degrading Rhodamine B (RhB) and Phenol under UV–vis light irradiation were investigated. The results demonstrate that the photocatalytic activities of the prepared photocatalysts are associated with the content of Bi2WO6 (BWO). 20% BWO-TNWS (containing 20wt% BWO) composite exhibits the highest degradation rate for RhB and Phenol up to 78% and 33%, respectively. It can be concluded that the improved photocatalytic performance of the BWO-TNWS composite is mainly ascribed to its high photoinduced charge separation rate resulting from the effective heterojunction structure of BWO and TNWS, as well as the enlarged optical response range owing to coupling narrow-band-gap semiconductor BWO.

Improved Sun light photocatalytic activity of α-Fe2O3 prepared with the assistance of CTAB

In this paper, α-Fe2O3 photocatalyst with enhanced solar-driven photocatalytic activity was prepared by a facile hydrothermal routine with the assistance of cetyltrimethylammonium bromide (CTAB). The surface parameters, the distribution of particle size, structure, morphology, and the photo-induced charge separation rate of the photocatalyst prepared (CTAB-Fe2O3) were characterized by the Brunauer-Emmett-Teller (BET) method, particle size analyzer, X-ray diffraction (XRD), scanning electron microscopy (SEM) and surface photovoltage (SPV) spectroscopy, respectively. The results reveal that CTAB alters the surface parameter and the morphology, decreases the particle size, and enhances the photo-induced charge separation rate of α-Fe2O3. The photocatalytic activity of CTAB-Fe2O3 for decolorization of methyl orange (MO) solution was evaluated. The results show that the photocatalytic activity of CTAB-Fe2O3 is more than five times of that of the reference Fe2O3 and the possible reason was discussed.

Enhanced photo-induced charge separation and sun light-driven photocatalytic performance of g-C3N4 modified by phosphate

Phosphate-decorated g-C3N4 photocatalysts with enhanced photo-induced charge separation in visible light region and sun light-driven photocatalytic performance were prepared by a facile pore impregnation approach. The photocatalysts were characterized by Brunauer–Emmett–Teller method, X-ray diffraction, scanning electron microscopy, UV–Vis diffuse reflectance spectroscopy, and surface photovoltage spectroscopy, respectively. The results show that decorating g-C3N4 by phosphate increases the adsorption of rhodamine B on the photocatalysts and the rate of photo-induced charges separation, especially the photo-induced charge separation rate in visible light region. The photocatalytic activities of g-C3N4 decorated by phosphate for decolorization of rhodamine B aqueous solution were evaluated. The result shows that when the concentration of phosphate is 4 M, g-C3N4 modified exhibits the best photocatalytic activity under simulated solar irradiation and the possible reason is discussed.

PEG-assisted hydrothermal synthesis of BiOCl with enhanced photocatalytic performance

BiOCl photocatalyst with enhanced photocatalytic performance was prepared by a hydrothermal routine with the assistance of polyethylene glycol 6000 (PEG 6000). The specific surface parameters, the crystal structure, the morphology, the distribution of particle size, the chemical states, and the photo-induced charge separation rate of the photocatalyst prepared (PEG-BiOCl) were characterized by Brunauer–Emmett–Teller method, X-ray diffraction, scanning electron microscopy, particle size analyzer, X-ray photoelectron spectroscopy, and surface photovoltage spectroscopy, respectively. Adding PEG 6000 into the synthesis system greatly changes the specific area parameters of BiOCl, decreases the particle size, and enhances the photo-induced charge separation rate and hydroxyl content. The superoxide radical is the main active species during the photocatalytic process. The photocatalytic activity of PEG-BiOCl for decolorization of methyl orange aqueous solution under both ultraviolet light and simulated solar light irradiation was investigated. The results show that PEG-BiOCl exhibits higher photocatalytic performance than that of the reference BiOCl, and the possible mechanism was discussed.

P123-assisted hydrothermal synthesis of BiOI with enhanced photocatalytic performance

Bismuth oxyiodide (BiOI) with enhanced photocatalytic performance was prepared by a hydrothermal routine with the assistance of EO20PO70EO20 (P123). The samples were characterized by Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), scanning electron microscopy (SEM), surface photovoltage spectroscopy (SPS) studies and UV–vis diffuse reflectance spectroscopy, respectively. Adding P123 into the synthesis system greatly changes the specific area parameters of BiOI, widens the bandgap and enhances the photo-induced charge separation rate. The catalytic activities of photocatalysts for decolorization of methyl orange aqueous solution were investigated. The result shows that activity of BiOI–P123 is 2.5 times of that of the reference BiOI.

Theoretical Study of Hemicyanine Dye as a Dye-Sensitized Solar Cell Light-Absorbing Material

We used first-principles calculations to investigate the photo-induced electron transfer (PIET) process of the hemicyanine-(TiO2)(n), complex ((TiO2)(n)-dye) for n=5, 9, 15. The geometries of the (TiO2)(n)-dye in the ground state were optimized using density functional theory (DFT) and their excited states were investigated using the time-dependent OFT (TDDFT) method. The excited energies, which were calculated using the long-range-corrected functionals, CAM-B3LYP and omega B97X-D, were in good agreement with the experimentally observed values. The wave functions based on DFT were used to calculate the charge transfer integrals by the generalized Mulliken-Hush (GMH) approach. In addition, the photo-induced charge separation rate constant (k(CS)) and charge recombination rate constant (k(CR)) were calculated using Marcus theory. The calculated results showed that there were a cascade of electron transfer channels from the dye into the (TiO2) cluster, which increases the k(CS) value. In contrast, the single channel of charge recombination decreases the k(CR), value, which is negligible compared with k(CS), indicating that electron recombination is not favored.

Photocatalytic degradation of organic compounds by Au-TiO2/sepiolite composites as the highly efficient catalysts

Photocatalytic oxidation of methyl orange (MO) and Congo red (CR) as typical model organic contaminants was investigated in aqueous solution within a cooperating Au/TiO2/sepiolite heterostructure system under UV light irradiation. The Au/TiO2/sepiolite composites with a single-crystalline (anatase) framework was synthesized by a facile sol-gel method using titanium tetrachloride as a TiO2 precursor and depositing metal Au on the surface of TiO2 nanostructures via a facile chemical reduction process. The crystal structure, surface area, light adsorption and the photoinduced charge separation rate of the photocatalyst prepared were characterized in detail. As compared with the pristine TiO2, the Au/TiO2/sepiolite hybrid material exhibited good photocatalytic efficiency (90%) for the UV-light photooxidation of methyl orange, which is four-fold of that of reference TiO2. In addition, Au/TiO2/sepiolite hybrid material also shows a good photodegradation performance toward Congo red removal. The highly efficient photocatalytic activity is associated with the strong adsorption ability of sepiolite for aromatic dye molecules, fast photogenerated charge separation due to the formation of Schottky junction between TiO2 and metallic Au. This work suggests that the combination of the excellent adsorption properties of sepiolite and the efficient separation effect of noble metallic nanoparticles provides a versatile strategy for the synthesis of novel and highly efficient photocatalysts.

Enhanced Photocatalytic Activity of α-Fe<sub>2</sub>O<sub>3</sub> Prepared with the Assistance of Ionic Liquid

In this paper, α-Fe2O3 photocatalyst with high photocatalytic activity (IL-α-Fe2O3) was fabricated via hydrothermal routine using 1-ethyl-3- methylimidazolium dihydrophosphate ([EMIm]H2PO4). The specific surface area, structure, the photo-induced charge separation rate were characterized by Brunauer-Emmett-Teller (BET) measurements, X-ray diffraction (XRD), and surface photovoltage spectroscopy (SPS), respectively. The results show that adding ([EMIm]H2PO4 into the synthetic system alters the specific surface parameters and photo-induced charge separation rate. The photocatalytic activity for decolorization of methyl orange (MO) solution was investigated. The results show that the photocatalytic activity of IL-α-Fe2O3 is more than 2.5 times that of the reference α-Fe2O3 and the underlying mechanisms are discussed.