Separation Efficiency Of Photogenerated Electron-hole Pairs Research Articles

Carbon-doped Bi2MoO6 nanosheet self-assembled microspheres for photocatalytic degradation of organic dyes

Abstract In this paper, carbon-doped Bi2MoO6 (C-Bi2MoO6) nanosheet self-assembled microspheres were prepared by using the solvothermal-calcination route to improve the photocatalytic activity of Bi2MoO6. The characterization results of x-ray diffractometry, Fourier transform infrared spectrometry, Raman scattering, scanning electron microscopy, transmission electron microscopy, BET specific surface area test, and x-ray photoelectron spectrometry indicated that C replaced the O2− anion in the Bi2MoO6 lattice, thinning the nanosheets, decreasing the size of the microspheres, and increasing the specific surface area of the Bi2MoO6. Ultraviolet–visible diffuse reflectance spectroscopy, photoluminescence, electrochemical impedance spectroscopy, transient photocurrent, and linear sweep voltammetry (LSV) spectroscopy demonstrated that the carbon doping reduced the band gap energy, raised the conduction band, and enhanced the photogenerated electron–hole pairs separation efficiency of Bi2MoO6. Benefiting from these favorable changes, the C-Bi2MoO6 microspheres prepared at a molar ratio of C to Bi of 4 (4C-Bi2MoO6) exhibited the highest photocatalytic activity, and the photocatalytic degradation rate constant of rhodamine B by 4C-Bi2MoO6 microspheres was almost 2.26 times that by pristine Bi2MoO6 under simulated solar light. 4C-Bi2MoO6 microspheres (0.2 g/L) presented excellent photocatalytic performance toward RhB (20 mg/L) at pH value 1 and could remove 98.31% of the RhB within 120 min. In addition, 4C-Bi2MoO6 microspheres also possessed a high photocatalytic activity toward methylene blue and tetracycline. 4C-Bi2MoO6 microspheres assembled from thin nanosheets can be used as effective photocatalysts to degrade toxic organic molecules from wastewater.

Cooperative reinforcement of photocatalysis-coupled capacitive deionization in fructose intercalated MoS2 for removal of tetracycline

CDI technology have attracted attention as a promising next generation water remediation technology, while the sustainability and the removal capacity inhibit the application of CDI for organic pollutant removal. Herein, we introduced photocatalysis coupled with CDI technology for removal of tetracycline (TC) by using MoS2/C electrode as a bifunctional catalyst, which could achieve the self-cleaning of the working electrode through in-situ degrading the adsorbed TC. On account of the introduction of fructose, the restrained ultrathin MoS2/C nanosheets composite with enhanced ion storage capacity and promoted photo-generated electron-hole pairs separation efficiency was constructed. By using TC as a model molecule for mimicking organic contaminants, MoS2/C electrode in the photocatalysis-coupled CDI system exhibited a superior TC removal capacity of 1302.5 mg g−1, TC removal efficiency of 84.8 %, and fast removal kinetics. Moreover, it achieved six cycles through “self-cleaning” based on the cooperative effect of photocatalytic degradation and electrosorption. Finally, FT-IR and radical scavenger experiments were utilized to demonstrate the mechanism of TC degradation. This study paves a way of photoelectronic degradation of antibiotics through a synergetic effect of electrosorption and photocatalysis.

Preparation of 3D BiOI microspheres for highly efficient visible light-induced photocatalytic degradation of tetracycline

Semiconductor photocatalysts for pharmaceutical antibiotic wastewater treatment are subject to increasing attention. Herein, BiOI photocatalysts were prepared by a one-step solvothermal method using ethylene glycol (EG) as solvent and their tetracycline (TC) degradation activities under visible light irradiation were compared. Catalyst preparation temperature, time, and pH conditions were optimized, and the catalyst physicochemical properties were characterized. Solution pH was found to have a significant effect on the morphology, electronic structure, and surface exposed facet of BiOI. Catalysts synthesized in the absence of NaOH presented more regular 3D flower-like microspheres, possessed larger surface area, were composed of many small nanosheets predominantly exposing the (001) facet, and showed better photogenerated electron-hole pairs separation efficiency. The optimized BiOI presents superior TC degradation efficiency (73.6%) under visible light irradiation, and recycling experiments indicated that the catalysts have good stability and reusability. The active species were investigated by free radical trapping experiments, revealing that •O2− plays a major role in the photodegradation process. Possible TC degradation pathways are proposed according to mass spectrometry analysis.

Morphology engineering ultrathin nitrogen-doped carbon Co-FeP derived from Co-Fe Prussian Blue Analogs for wide spectrum photocatalytic H2 evolution

The design and development of economical, efficient and stable photocatalyst for photocatalytic hydrogen evolution is a frontier subject of sustainable energy research. In this work, a morphology engineered ultrathin nitrogen-doped carbon Co-FeP (Co-FeP@NC) derived from Co-Fe Prussian Blue Analogs (Co-Fe PBA) for wide spectrum photocatalytic hydrogen evolution. We demonstrate the versatility of a self-templated epitaxial growth strategy for construction of single-crystalline hollow nanostructured PBA (Co-Fe PBA cages, frames and boxes) with different geometries by adjusting the growth kinetics. Co-FeP@NC photocatalysts have tunable band structures by adjusted phosphating degree and all have a narrow band gap. In addition, the catalysts with different morphologies have different electronic structures, and surface nitrogen-doped carbon layer increases electron transfer rate, which makes the photocatalytic hydrogen evolution activity increase significantly. The Co-FeP@NC-4 cages exhibit the highest photocatalytic hydrogen evolution rate of 13309.4 μmol h−1 g−1 under visible light irradiation with EY as a photosensitizer and TEOA as an electron donor. Additionally, a high apparent quantum efficiency (8.38 % at 520 nm) and an excellent cycle stability was also achieved over Co-FeP@NC-4 cages. The larger specific surface area, strong light absorption ability and fast photogenerated electron-hole pairs separation efficiency of Co-FeP@NC cages may be responsible for the significantly improved photocatalytic hydrogen evolution activity. This work has provided an effective strategy for synthesis of nanostructures with different geometric topologies derived from PBA and recognizing their morphology-dependent photocatalytic activity.

A dual optimization approach for photoreduction of CO2 to alcohol in g-C3N4/BaTiO3 system: Heterojunction construction and ferroelectric polarization

The improved separation efficiency of photogenerated electrons and holes is an effective way to improve photocatalytic performance. Herein, the high efficiency sheet/fiber g-C3N4/BaTiO3 photocatalysts with built-in electric field are successfully synthesized by electrospinning and simple calcination method. Compared with pure g-C3N4 and BaTiO3, g-C3N4/BaTiO3 heterojunction possesses higher photogenerated electron-hole pairs separation efficiency and larger specific surface area, thus improving the photocatalytic activity of g-C3N4/BaTiO3 catalysts. Besides, the ferroelectric polarization produced by external electric field significantly promotes the CO2 reduction performance of CNBT20 [the component with mass fractions BT / (CN/BT) = 20 %], whose reduction rates of CH3OH and CH3CH2OH are 1.44 and 1.50 times that of unpolarized CNBT20, accompanied with remarkable cyclic stability. The coupling effect of heterojunction and ferroelectric polarization improves the separation efficiency of photoexcited carriers in g-C3N4/BaTiO3 significantly, hence providing broad prospects for the combination of traditional semiconductors and ferroelectric materials to improve photocatalytic performance.

Construction of a Bi2MoO6/CoOx/Au system with a dual-channel charge transfer path for enhanced tetracycline degradation

The introduction of two cocatalysts CoOx and Au constructs dual carrier transfer channels, which improves the photogenerated electron–hole pairs separation efficiency and photocatalytic performance.

Green and controllable synthesis of one-dimensional Bi2O3/BiOI heterojunction for highly efficient visible-light-driven photocatalytic reduction of Cr(VI)

BiOI nanosheets have been successfully deposited on the porous Bi2O3 nanorobs via a one-pot precipitation method. The physicochemical features of the as-prepared materials were characterized in detail by a series of techniques, and the results revealed that BiOI nanosheets were evenly distributed on the porous Bi2O3 nanorobs. Because of higher photogenerated electron-hole pairs separation efficiency and the larger specific surface area compared to the pristine Bi2O3 and BiOI, the 50%Bi2O3/BiOI composite exhibited significantly enhanced photocatalytic activity for Cr(VI) reduction under visible light irradiation, and the reduction rate constant was 0.02002 min−1, which was about 27.4 and 2.6 times higher than that of pure Bi2O3 (0.00073 min−1) and BiOI (0.00769 min−1), respectively. Moreover, the 50%Bi2O3/BiOI composite also possessed the excellent photochemical stability and recyclability, thereby facilitating its wastewater treatment application.

Enhanced visible-light-driven photocatalytic removal of refractory pollutants by Zn/Fe mixed metal oxide derived from layered double hydroxide

In this study, two typical refractory organic pollutants, methylene blue (MB) and tetracycline (TC) was effectively degraded under visible-light irradiation catalyzed by Zn/Fe mixed metal oxide (Zn/Fe-MMO) nanocomposite, which derived from the high-temperature calcination of Zn/Fe layered double hydroxide (Zn/Fe-LDH). The Zn/Fe-MMO was composed of wurzite ZnO phases and spinel-structured ZnFe2O4. The Zn/Fe-MMO exhibited superior photocatalytic activity than Zn/Fe-LDH precursor owing to the better crystallinity, broader visible light adsorption, and higher photo-generated electron-hole pairs separation efficiency. Simple assembling method, high photocatalytic activity to the degradation of organic pollutants and good reusability make Zn/Fe-MMO has great potential in practical wastewater treatment.

A modified Z-scheme Er3+:YAlO3@(PdS/BiPO4)/(Au/rGO)/CdS photocatalyst for enhanced solar-light photocatalytic conversion of nitrite

Z-scheme structure is an effectively construction to improve the photocatalytic activity due to the excellent photo-generated electron-hole pairs separation efficiency. In this paper, the Er3+:YAlO3@(PdS/BiPO4)/(Au/rGO), (Au/rGO)/CdS and modified Z-scheme Er3+:YAlO3@(PdS/BiPO4)/(Au/rGO)/CdS photocatalysts were prepared by hydrothermal, ultrasonic dispersion, deposition-precipitation and ultrasonic-assisted methods. The prepared samples were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (DRS), fourier transform infrared spectra (FT-IR), raman spectra and photoluminescence (PL) spectra. The photocatalytic activity of prepared samples were evaluated via photocatalytic conversion rate of nitrite under ultraviolet-light and simulated solar-light irradiations. Due to the enhanced separation efficiency of electron-hole pairs, the Er3+:YAlO3@(PdS/BiPO4)/(Au/rGO)/CdS exhibited excellent performance under both ultraviolet-light and simulated solar-light irradiation, reaching 94.59% and 91.25% conversion rates, respectively. Meanwhile, the effects of simulated solar-light irradiation time and corresponding reaction kinetics on photocatalytic conversion of nitrite were studied. Subsequently, the effects of electron and hole scavengers were investigated to further elaborate the possible mechanism. In addition, the study of used times showed that the prepared modified Z-scheme Er3+:YAlO3@(PdS/BiPO4)/(Au/rGO)/CdS nanocomposites can be effectively recycled without an apparent inactivation on photocatalytic activity. This research may provide a potential way by utilizing solar energy efficiently for converting nitrite and other contaminants released into the environment.

One-step hydrothermal synthesis of mesoporous Ce-doped anatase TiO2 nanoparticles with enhanced photocatalytic activity

Mesoporous Ce-doped TiO2 nanoparticles with different content of Ce are prepared by one-step hydrothermal method. The samples are characterized by XRD, TEM, Raman, XPS, BET, PL and UV–vis measurements. The results show that TiO2 doped with Ce can reduce the crystallite size. Under UV irradiation, the Ce-doped TiO2 samples exhibit much higher photocatalytic activity than pure TiO2 and commercial P25 for the degradation of Rhodamine (RhB). The maximum photocatalytic reaction rate constant for Ce-doped TiO2 sample is obtained as 0.021 min−1. The unique photocatalytic properties of Ce-doped TiO2 are attributed to the improvement of photogenerated electron–hole pairs separation efficiency and formation of more reactive oxygen species owing to the presence of Ce3+/Ce4+. A degradation mechanism is proposed for the degradation of RhB for Ce-doped TiO2 photocatalyst under UV light.

Photocatalytic degradation of gaseous benzene with CdS-sensitized TiO2 film coated on fiberglass cloth

In this paper, TiO2 film coated on fiberglass cloth was synthesized by sol–gel method and further sensitized by CdS nanoparticles using a sequential chemical bath deposition technique. Gaseous benzene was adopted as a model pollutant to evaluate the photocatalytic performances of the supported TiO2 films sensitized with variable content of CdS nanoparticles, which obtained by adjusting the concentration of Cd2+ or S2− precursor solution. Along with the increase of the CdS amount, the photocatalytic activity of these samples initially increases and then shows a downward trend. When the concentration of Cd2+ or S2− precursor solution achieved 0.005M, the sample performs the best photocatalytic property and the degradation efficiency reaches 92.8% and 32.7% under UV–vis and visible light irradiation, respectively. The enhancement of the photocatalytic activity could be attributed to the formation of micro-heterojunction. However, a thick CdS sheath covered catalyst surface will form when high concentration of Cd2+ or S2− solution is used. The low photogenerated electron–hole pairs separation efficiency and the photocorrosion process of CdS decrease the photocatalytic activity gradually.