Ultraviolet-visible Diffuse Reflectance Spectra Research Articles

In situ loading of Ni2P on Cd0.5Zn0.5S with red phosphorus for enhanced visible light photocatalytic H2 evolution

Using non-toxic red phosphorus as the phosphorus source, Ni2P was synthesized and in situ loaded on Cd0.5Zn0.5S photocatalyst by a simple solvothermal method for photocatalytic H2 evolution under visible light (λ ≥ 420 nm) irradiation. The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), ultraviolet–visible diffuse reflectance spectra (UV–Vis DRS), Brunauer–Emmett–Teller (BET) surface area measurements and electrochemistry techniques. The photocatalytic hydrogen evolution activity over Cd0.5Zn0.5S is significantly increased by in situ-loaded Ni2P due to the intimate interface contact and efficient charge transfer from Cd0.5Zn0.5S to Ni2P. The 4 wt%Ni2P-loaded Cd0.5Zn0.5S photocatalyst shows five times higher H2 evolution rate than that of the pristine Cd0.5Zn0.5S. The highest H2 evolution rate of 65.6 μmol/h and the apparent quantum yield (AQY) of 29% at 420 nm is achieved under the optimized conditions. The noble metal free Ni2P is stable during 20 h photocatalytic reaction.

Template-free synthesis of three-dimensional porous CdS/TiO2 with high stability and excellent visible photocatalytic activity

A novel stereo porous and highly stable photocatalyst CdS/TiO2-400 (composite CdS/TiO2 calcined at 400 °C) was synthesized by hydrolysis-hydrothermal-calcined method without the assistance of template. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet–visible diffuse reflectance spectra (UV–vis DRS), transient photocurrents, photoluminescence emission spectra (PL) and Brunauer-Emmett-Teller (BET) to study their crystallinity, morphologies, structure, optical properties and specific surface area. The experimental results validated that as-prepared CdS/TiO2-400 could effectively improve the separation efficiency of photogenerated electron-hole pairs and displayed superior photocatalytic activity in the degradation process of methyl orange (MO), oxytetracycline (OTC) and tetracycline (TC). The promoted photocatalytic activity was attributed to the calcination procedure and high specific surface area. A possible photocatalytic mechanism of CdS/TiO2-400 was proposed on the basis of trapping experiments.

Hydrothermal preparation of 3D flower-like BiPO4/Bi2WO6 microsphere with enhanced visible-light photocatalytic activity

A novel 3D flower-like BiPO4/Bi2WO6 photocatalyst was prepared using hydrothermal method. The crystal structure, surface morphologies and optical properties of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) and Ultraviolet–visible diffuse reflectance spectrum (UV–vis DRS). The photocatalytic activity of the BiPO4/Bi2WO6 composites was evaluated by using rhodamine B (RhB) as a target organic pollutant under visible light irradiation. The composite with the content of 15% BiPO4 exhibited the highest photocatalytic property with the 92% removal rate of RhB within 100 min under visible light irradiation, which ascribed to the fast separation efficiency of photo-induced charge carriers, according with the results of photoluminescence (PL), photocurrent (PC) and electrochemical impedance spectroscopy (EIS). Also, it showed superior stability after three times of recycling. Eventually, the possible photocatalytic mechanism of BiPO4/Bi2WO6 composite was proposed according to the energy band structure and the radical-trapping experiment.

Preparation of graphene/WO3/TiO2 composite and its photocathodic protection performance for 304 stainless steel

Graphene/WO3/TiO2 composite (RGO/WO3/TiO2) was successfully fabricated via a two-step hydrothermal method. The structure, morphology and optical property of the as-prepared composite were characterized by X-ray powder diffraction, fourier transform infrared spectra, Raman spectra, transmission electron microscope, scanning electron microscope and ultraviolet-visible diffuse reflectance spectra, respectively. Results showed that the composite was incorporated by graphene nanosheets, WO3 nanorods and TiO2 nanoparticles. It exhibited favorable absorption ability in both UV and visible light region. The photocathodic protection performance for 304 stainless steel (304SS) was proven by photocurrent density, open circuit potential, Tafel polarization curves and electrochemical impedance spectroscopy. It was found that the composite could provide an efficient protection for 304SS under visible light irradiation and even in the dark compared to the pure TiO2. The electrode potentials negatively shifted to −760 mV under visible light. The possible photocathodic protection mechanism of the composite was also proposed.

The synergistic effect of nitrogen-doped titanium dioxide/mercaptobenzoic acid/silver nanocomplexes for surface-enhanced Raman scattering

We synthesized titanium dioxide (TiO2) and nitrogen-doped TiO2 nanoparticles (N-TiO2 NPs) via a sol-hydrothermal method using ammonium chloride (NH4Cl) as the nitrogen (N) source. Furthermore, an N-TiO2/4-mercaptobenzoic acid (4-MBA)/silver (Ag) nanocomplex served as an active substrate for surface-enhanced Raman scattering (SERS) and was prepared by self-assembly. During SERS, the Raman signals of 4-MBA of the N-TiO2/MBA/Ag nanocomplexes exhibited higher intensity and sensitivity than pure TiO2/MBA/Ag, with 1% N doping in N-TiO2, producing the strongest Raman signals. We characterized the N-TiO2 hybrid materials by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and ultraviolet-visible diffuse reflectance spectra. N doping did not influence the phase of the TiO2 crystal. The doped N entered into the crystal lattice of the TiO2, replacing some oxygen (O) to form Ti-O-N or Ti-N-O linkage. The results indicated that an appropriate amount of N doping could enhance the SERS performance of the TiO2 SERS substrate via N substitution doping. These doping forms were beneficial to the molecular charge transfer (CT), and this resulted in improved SERS performance for N-doped TiO2 NPs. We attributed this improvement to the formation of N-doping energy levels that were beneficial to the process of TiO2 to MBA molecule CT. This work not only enriched the nonmetal-doped CT mechanism in SERS but also provided several reference values for practical applications.

Sugarcane juice derived carbon dot-graphitic carbon nitride composites for bisphenol A degradation under sunlight irradiation.

Carbon dots (CDs) and graphitic carbon nitride (g-C3N4) composites (CD/g-C3N4) were successfully synthesized by a hydrothermal method using urea and sugarcane juice as starting materials. The chemical composition, morphological structure and optical properties of the composites and CDs were characterized using various spectroscopic techniques as well as transmission electron microscopy. X-ray photoelectron spectroscopy (XPS) results revealed new signals for carbonyl and carboxyl groups originating from the CDs in CD/g-C3N4 composites while X-ray diffraction (XRD) results showed distortion of the host matrix after incorporating CDs into g-C3N4. Both analyses signified the interaction between g-C3N4 and CDs. The photoluminescence (PL) analysis indicated that the presence of too many CDs will create trap states at the CD/g-C3N4 interface, decelerating the electron (e−) transport. However, the CD/g-C3N4(0.5) composite with the highest coverage of CDs still achieved the best bisphenol A (BPA) degradation rate at 3.87 times higher than that of g-C3N4. Hence, the charge separation efficiency should not be one of the main factors responsible for the enhancement of the photocatalytic activity of CD/g-C3N4. Instead, the light absorption capability was the dominant factor since the photoreactivity correlated well with the ultraviolet–visible diffuse reflectance spectra (UV–vis DRS) results. Although the CDs did not display upconversion photoluminescence (UCPL) properties, the π-conjugated CDs served as a photosensitizer (like organic dyes) to sensitize g-C3N4 and injected electrons to the conduction band (CB) of g-C3N4, resulting in the extended absorption spectrum from the visible to the near-infrared (NIR) region. This extended spectral absorption allows for the generation of more electrons for the enhancement of BPA degradation. It was determined that the reactive radical species responsible for the photocatalytic activity were the superoxide anion radical (O2•−) and holes (h+) after performing multiple scavenging tests.

Preparation of attapulgite/TiO2/graphene composite and its application for the photocatalytic degradation of chlorotetracycline

An attapulgite/TiO2/graphene composite (ATP/TiO2/RGO) was prepared and characterized by X-ray powder diffraction, Fourier transform infrared spectra, Raman spectra, transmission electron microscope, scanning electron microscope, ultraviolet–visible diffuse reflectance spectra, photoluminescence spectra and X-ray photoelectron spectroscopy. Results showed that TiO2 nanoparticles were loaded on the surface of ATP uniformly and the introduction of RGO successfully expanded the light response range of TiO2. The photocatalytic performance of the composite toward the degradation of chlorotetracycline was then evaluated, and a plausible mechanism was proposed. It was found that the ternary composites exhibited excellent photoactivity when compared with the ATP/TiO2 binary material and pure TiO2, indicating that the synergistic effect of TiO2, ATP and RGO greatly enhanced the photocatalytic activity of the present ternary composite.

Enhanced selective photocatalytic reduction of CO2 to CH4 over plasmonic Au modified g-C3N4 photocatalyst under UV–vis light irradiation

A series of Au-g-C3N4 (Au-CN) catalysts were prepared through a NaBH4-reduction method using g-C3N4 (CN) from pyrolysis of urea as precursor. The catalysts’ surface area, crystal structure, surface morphology, chemical state, functional group composition and optical properties were characterized by X-ray diffraction, transmission electron microscope, X-ray photoelectron spectroscopy, ultraviolet visible (UV–vis) diffuse reflectance spectra, fourier transform infrared, photoluminescence and transient photocurrent analysis. The carbon dioxide (CO2) photoreduction activities under ultraviolet visible (UV–vis) light irradiation were significantly enhanced when gold (Au) was loaded on the surface of CN. 2Au-CN catalyst with Au to CN mole ratio of 2% showed the best catalytic activity. After 2 h UV–vis light irradiation, the methane (CH4) yield over the 2Au-CN catalyst was 9.1 times higher than that over the pure CN. The CH4 selectivity also greatly improved for the 2Au-CN compared to the CN. The deposited Au nanoparticles facilitated the separation of electron-hole pairs on the CN surface. Moreover, the surface plasmon resonance effect of Au further promoted the generation of hot electrons and visible light absorption. Therefore, Au loading significantly improved CO2 photoreduction performance of CN under UV–vis light irradiation.

Bioinspired Synthesis of Carbon Dots/g-C3N4 Nanocomposites for Photocatalytic Application

This study reports a fast and green preparative strategy to synthesize water soluble and fluorescent carbon quantum dots (CQDs) through hydrothermal method by using low cost organic waste of human fingernails as the carbon precursor for the first time. The coupling of CQD with pure carbon nitride (g-C3N4) was further explored to enhance the latter’s performance in photocatalysis of 2,4-dicholorophenol (2,4-DCP), a toxic and recalcitrant compound mostly released from industrial effluent. Such coupling overcame the weakness of pure g-C3N4 in photocatalysis process by broadening its visible light absorption and promoting the charge separation. As a result, the removal rate of CQD/ g-C3N4(10) was up to 71.53%, which was approximately 1.5 times higher than that of pure g-C3N4 under sunlight irradiation. The morphological structure, optical properties and chemical compositions of CQDs/g-C3N4 composites were characterized using various spectroscopic techniques including field emission scanning electron microscopy (FESEM), Energy Dispersive X-Ray (EDX) and Ultraviolet-visible diffuse reflectance spectra (UV-DRS).

Hydrogen production by aqueous phase reforming of phenol derived from lignin pyrolysis over NiCe/ZSM-5 catalysts

Incipient wetness impregnation was used to synthesized the NiCe/ZSM-5 catalysts with different ratio of Ni:Ce, and CeO2 was added as an assistant in the synthesis process. The physicochemical properties of the prepared catalysts were characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), N2-Sorption, H2 temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared Spectroscopy (FTIR) and ultraviolet–visible diffuse reflectance spectra (UV–Vis DR). The catalytic activities of the obtained catalysts were tested by using the reaction of aqueous phase reforming of phenol to produce hydrogen. Adding appropriate doze of Ce to the catalysts can increase the dispersion of nickel on the ZSM-5 support. The results showed that hydrogen selectivity was higher over 8Ni8Ce/ZSM-5 than using 8Ni/ZSM-5 as aqueous phase reforming catalysts. The content of carbon monoxide in the products after reaction over different catalysts was very low. However, the dispersion of carbon dioxide and hydrocarbons was significantly different over the two catalysts.

A Facile Fabrication of Graphene Oxide (GO)/Ag3PO4 Composite to Enhance Its Photocataltytic Activity under Visible Light

Graphene oxide (GO) modified Ag3PO4 nanoparticles with highly visible light photocatalytic activities were prepared by a facile chemisorption method. The resulting GO/Ag3PO4 composite photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet–visible diffuse reflectance spectra (DRS). The enhanced photocatalytic activities were mainly ascribed to the strong conductivity of graphene, which led to an improved separation efficiency of electron-hole pairs. The highefficient hybrid photocatalysts are expected to show considerable potential applications in wastewater treatment and water splitting.

Enhanced photoactivity of BiPO4/(001) facet-dominated square BiOBr flakes by combining heterojunctions with facet engineering effects

In this study, BiPO4/highly (001) facet exposed square BiOBr flake heterojunction photocatalysts with different molar ratios were fabricated via a two-step method. The synergetic effect of the heterojunction and facet engineering was systematically investigated. The physicochemical properties of the BiPO4/square BiOBr flake composites were characterized based on X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller method, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectra, photoluminescence, electrochemical impedance spectroscopy, and the photocurrent response. The BiPO4/square BiOBr flake heterojunction photocatalyst exhibited much higher photocatalytic performance compared with the individual BiPO4 and BiOBr. In particular, the BiPO4/BiOBr composite where P/Br = 1/3 exhibited the highest photocatalytic activity. The intensified separation of photoinduced charges at the p-n heterojunction between the BiPO4 nanoparticle and (001) facet of BiOBr was mainly responsible for the enhanced photoactivity.

A strawsheave-like metal organic framework Ce-BTC derivative containing high specific surface area for improving the catalytic activity of CO oxidation reaction

A metal organic framework Ce-BTC derivative with a special morphology and a large surface area was prepared by a simple method. Several analytical tools such as scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), fourier transform infrared (FT-IR), N2 adsorption-desorption (BET), H2 temperature programmed reduction (H2-TPR), ultraviolet visible diffuse reflectance spectrum (UV-Vis DRS), photoluminescence (PL), X-ray photoelectron spectroscopic (XPS) and elemental analysis (EA) have been used to characterize the samples. It is found that Ce-BTC calcined with O2 at 250 °C (Ce-BTC250) maintains the special strawsheave-like structure, and the surface area rapidly increases from 42 m2 g-1 to 648 m2 g-1. Moreover, the prepared strawsheave-like Ce-BTC250 exhibited excellent catalytic activity, long-term stability and water resistance. Further studies have shown that the MOF structure of Ce-BTC250 was gradually converted to carbon-free CeO2 during the catalytic reaction. Interestingly, the catalyst after the reaction still has a large surface area (124 m2 g-1) and the strawsheave-like morphology. The improved catalytic activities may be due to the formation of porous and large surface area of strawsheave-like Ce-BTC derivative, which provided more active sites and oxygen vacancy for CO oxidation. This work provides a novel sight for preparing high efficient carbon-free derivative with large surface area by controlling synthesis and reaction conditions of Ce based MOF.

Structure and electrical behavior of unpoled and poled 0.97(Bi0.5Na0.5)0.94Ba0.06TiO3-0.03BiAlO3 ceramics

The ceramics (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT) and 0.97BNBT-0.03BiAlO3 (BNBTA/0.03) were synthesized via a solid-state reaction method. Effects of electric poling and Al3+-doping on structure and electrical behavior of BNBT and BNBTA/0.03 were studied. The results of Raman spectroscopy and X-ray diffraction confirm lattice distortion due to the doping of Al3+. BNBT and BNBTA/0.03 exhibit pure phase and dense microstructures. The tetragonal-rhombohedral morphotropic phase boundary exists in both samples. Electric poling causes an increase in the amount of the tetragonal phase. Dielectric behavior is sensitive to the electric poling and Al3+-doping. Compared to BNBT, BNBTA/0.03 exhibits pinched polarization loops, current-electric field curves with four peaks, and higher normalized piezoelectric constant. Based on the results of ultraviolet–visible diffuse reflectance spectra, electric conductivity, and Rayleigh analysis, it is suggested that the differences in electrical behavior between BNBT and BNBTA/0.03 are related to oxygen vacancies.

Pd-MnO2 nanoparticles/TiO2 nanotube arrays (NTAs) photo-electrodes photo-catalytic properties and their ability of degrading Rhodamine B under visible light

Pd-MnO2/TiO2 nanotube arrays (NTAs) photo-electrodes were successfully fabricated via anodization and electro deposition subsequently; the obtained Pd-MnO2/TiO2 NTAs photo electrodes were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and characterized accordingly. Moreover, the light harvesting and absorption properties were investigated via ultraviolet–visible diffuse reflectance spectrum (DRS); photo degradation efficiency was investigated via analyzing the photo catalytic degradation of Rhodamine B under visible illumination (xenon light). The performed analyses illustrated that Pd-MnO2 codoped particles were successfully deposited onto the surface of the TiO2 nanotube arrays; DRS results showed significant improvement in visible light absorption which was between 400 and 700nm. Finally, the photo catalytic degradation efficiency results of the designated organic pollutant (Rhodamine B) illustrated a superior photocatalytic (PC) efficiency of approximately 95% compared to the bare TiO2 NTAs, which only exhibited a photo catalytic degradation efficiency of approximately 61%, thus it indicated the significant enhancement of the light absorption properties of fabricated photo electrodes and their yield of OH radicals.

Preparation of TiO2/ZnO composite catalysts and their photocatalytic activity for degradation of pentachlorophenol

PurposeThis paper aims to report a novel preparation method of titanium dioxide (TiO2)/zinc oxide (ZnO) composites with different mole ratios of TiO2:ZnO and their photocatalytic activity.Design/methodology/approachTiO2/ZnO composites are prepared by a facile route. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and ultra-violet–visible diffuse reflectance spectra (UV-vis DRS) are used to characterize the products. Photocatalytic activity of the samples is evaluated by degradation of persistent organic pollutant pentachlorophenol under ultra-violet (UV) irradiation.FindingsIt is found that all the as-prepared TiO2/ZnO composites not only have good catalytic activity under UV light irradiation, but also have excellent circulation stability. The optimal mole ratio of TiO2:ZnO is 0.75:1.Originality/valueThis report presents a simple and rapid method for the preparation of TiO2/ZnO composites with excellent photocatalytic activity. Experimental results could provide useful reference for the treatment of chlorophenols in the future.

Nanosized amorphous tantalum oxide: a highly efficient photocatalyst for hydrogen evolution

A facile synthetic route for the preparation of highly active tantalum oxide photocatalysts was developed without using any surfactants. The prepared products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectra, thermogravimetric analysis, and Raman, and their activity was evaluated by photocatalytic H2 evolution under UV–Vis light irradiation (320 < λ < 780 nm). To elucidate the photocatalytic activity, the nitrogen adsorption–desorption isotherms experiment, ultraviolet–visible diffuse reflectance spectra, photoluminescence and steady-state surface photo-voltage measurements were performed. The recyclable photocatalytic properties were also conducted to demonstrate its high stability. Notably, the obtained samples prepared by direct evaporation are amorphous and own a large specific surface area, and furthermore exhibit a far greater photocatalytic performance than commercial Ta2O5. On the basis of the above experiment results, the enhanced photocatalytic activity of a-Ta x O y could be ascribed to the efficient separation and migration of photo-generated carriers as well as the higher energy of the conduction band minimum. Therefore, the direct evaporation synthesis opens a door to the facile preparation of highly active amorphous photocatalysts.

Photocatalytic hydrogen production by flower-like graphene supported ZnS composite photocatalysts

Flower-like graphene (FG) prepared by a transformer coupled plasma enhanced chemical vapor deposition method was used as support for the preparation of composite photocatalysts. Small ZnS particles were formed on the surface of FG by a hydrothermal process with ZnCl2 and Na2S precursors. The surface morphology, surface area, surface chemistry, crystalline property, optical properties, photogenerated current and photocatalytic hydrogen production activity of the FG-ZnS photocatalysts were investigated by using the X-ray diffraction, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectra, photocurrent response, photoluminescence spectra, electrochemical impedance spectra and photocatalytic hydrogen production tests. The maximum hydrogen production rate of FG-ZnS composite photocatalyst ZS-G0.02 was 11600 μmol g−1h−1 under UV light irradiation at a graphene/ZnCl2 precursor weight ratio of 0.02. The flower-like structure of FG may help the light absorption, adsorption of sacrificing agents in the solution, and separation of photogenerated carriers. In comparison with pristine ZnS photocatalyst, the FG-ZnS nanocomposites exhibits enhanced photocatalytic hydrogen production activity.

Structural investigation and photoluminescent properties of ZnWO4:Dy3+ nanocrystals

In this study, ZnWO4:Dy3+ nanocrystals containing 0.5, 1, and 2 mol% of Dy3+ were synthesized by a coprecipitation method and grown in a microwave-assisted hydrothermal system at 140 °C for 1 h. X-ray diffraction, Rietveld refinement, and Fourier transform Raman and infrared spectroscopy analyses indicated that each of the crystals had a wolframite-type monoclinic structure, with no other phases present. Structural refinement was carried out to model the distorted octahedral [ZnO6], [DyO6], and [WO6] clusters. Furthermore, transmission scanning electron microscopy images revealed interesting crystal morphologies and a decrease of the average crystal size, which were dependent on the Dy3+ doping concentration. Ultraviolet–Visible diffuse reflectance spectra indicated that the optical band gap increases with increasing replacement of Zn2+ by Dy3+ ions. The photoluminescent properties, chromaticity coordinates, and lifetimes of the ZnWO4:Dy3+ nanocrystals were studied.

A facile microwave-hydrothermal method to fabricate B doped ZnWO4 nanorods with high crystalline and highly efficient photocatalytic activity

A series length of 50∼200nm B doped ZnWO4 nanorods with high crystallinity were fabricated via a fast microwave-hydrothermal method. The effects of B doping on the physical properties of ZnWO4 nanorods were intensively characterized by N2 physical adsorption, XRD, TEM, FT-IR, XPS, ultraviolet-visible diffuse reflection spectrum (UV–vis DRS), photolunminescence spectrum (PL), transient photocurrent response (TPR). The results indicated that the doped B could replace the lattice tungsten ion in ZnWO4 crystals, which caused the lattice spacing contraction, particle size decrease, specific surface area increase. More importantly, the separation of the photogenerated electrons and holes in ZnWO4 was significantly enhanced by B doping. With doped optimum B concentration (2.42wt%), B/ZnWO4 displayed super photocatalytic performance in dyes decomposition. The degradation rate constant (0.065h−1) of Rhodamine B over B (2.42wt%)/ZnWO4 is 4 times of that over ZnWO4 (0.016h−1).