Diffuse Reflectance Spectroscopy Measurements Research Articles

Acrylate-based Polymerizable Sol–Gel Synthesis of Magnetically Recoverable TiO2 Supported Fe3O4 for Cr(VI) Photoreduction in Aerobic Atmosphere

TiO2 synthesized by polymerizable sol–gel approach is used to demonstrate the photoreduction of Cr(VI) in aqueous medium. Fe3O4 is chosen as the magnetically recoverable support, onto which, 10, 20, 30 and 50% of TiO2 have been dispersed following the polymerizable sol–gel approach. The synthesized materials are characterized using XRD, SEM, XPS, Raman spectroscopy, diffuse reflectance spectroscopy and BET surface area measurement. Different hole-scavengers (oxalic acid, ammonium oxalate and ethanol) and an electron scavenger (potassium periodate) have been studied to compare the efficiency of Cr(VI) photoreduction in nitrogen as well as air atmosphere. With 5 mM oxalic acid as the hole-scavenger, the TiO2/Fe3O4 materials have demonstrated superior activity to the nonsupported bulk TiO2 toward Cr(VI) photoreduction in aerobic atmosphere. Particularly, 30% TiO2/Fe3O4 has shown the highest Cr(VI) photoreduction rate among the lot. The 30% TiO2/Fe3O4 catalyst has also demonstrated good recoverability as well...

La1−xAgxFeO3/halloysites nanocomposite with enhanced visible light photocatalytic performance

La1−xAgxFeO3/halloysites nanotubes (HNTs) nanocomposite was synthesized by sol–gel method. It was characterized by X-ray diffraction, transmission electron microscope, Fourier transform infrared spectroscopy and UV–visible diffused reflectance spectroscopy measurements. The photo-activity of the La1−xAgxFeO3/HNTs nanocomposite was evaluated via degradation of methylene blue (MB) under visible-light irradiation. The results showed that the HNTs with unique pore structure favored the adsorption of organic molecules. Adequate Ag+ doping improved the absorption ability for visible light. The La0.95Ag0.05FeO3/HNTs demonstrated the best photocatalytic performance, which achieved as high as 99 % for MB degradation exposed 2 h irradiation. However,further increasing of Ag+ doping gradually reduced the photocatalytic activity. The nanocomposite catalyst showed outstanding recyclability after eight cycles which still remained up to 90 %.

Gold nanocluster sensitized TiO2 nanotube arrays for visible-light driven photoelectrocatalytic removal of antibiotic tetracycline.

It is of technical interest to develop low-cost, high-quality and scalable photosensitizers that could efficiently harvest visible light. Here we design an efficient photoelectrocatalyst by integrating a recently developed gold nanocluster (AuNC, as a photosensitizer) into two types of highly ordered TiO2 nanotube arrays (TNAs, as substrates to host the photosensitizers). The TNA electrodes used in this study are a short TNA (∼0.5 µm in length, synthesized by the anodic oxidation in an aqueous hydrofluoric (HF) acid solution) and a long TNA (∼4.5 µm in length, synthesized by the anodic oxidation in a fluorinated ethylene glycol (EG) solution). A number of characterization techniques (e.g., FESEM, XRD and XPS) were applied to study the as-synthesized nanocomposites. In particular, diffuse reflectance spectroscopy and photochemical measurements suggest that the AuNC-coated TNA electrodes have successfully extended visible light absorption and improved their photochemical performance. Compared with the blank TNAs, the as-designed nanocomposites exhibit an evidently enhanced photoelectrocatalytic performance towards tetracycline (an emerging antibiotic contaminant in aquatic environment) decomposition, where the removal efficiency increases from 65% to 81% for AuNC/long-TNA and from 46% to 73% for AuNC/short-TNA electrodes, respectively. The improved performance is largely attributed to the photo-electro-chemical synergetic effect. The photochemical performance of the as-designed nanocomposites could be further improved by fine tuning the size, composition, and surface of the AuNC-based photosensitizers.

Disclosing the electronic structure and optical properties of Ag4V2O7crystals: experimental and theoretical insights

This work combines experimental and computational techniques to exploit the best of both methodologies and thus provide a tool for understanding the geometry, cluster coordination, electronic structure, and optical properties of Ag4V2O7 crystals. This tool has been developed to create structural models and enable a much more complete and rapid refinement of 3D (three dimensional) structures from limited data, aiding the determination of structure–property relationships and providing critical input for materials simulations. Ag4V2O7 crystals were synthesized by a simple precipitation method from an aqueous solution at 30 °C for 10 min. The obtained crystals were characterized by X-ray diffraction (XRD) and Rietveld refinement, and micro-Raman spectroscopy. The crystal morphology was determined by field emission scanning electron microscopy (FESEM), and the optical properties were investigated by ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy and photoluminescence (PL) measurements. The geometric and electronic structures of Ag4V2O7 crystals were investigated by first-principles quantum-mechanical calculations based on the density functional theory. The theoretical results agree with the experimental data to confirm that Ag4V2O7 crystals have an orthorhombic structure, and that the building blocks of the lattice comprise two types of V clusters, [VO4] and [VO5], and two types of Ag clusters, [AgO5] and [AgO6]. This type of fundamental studies, which combine multiple experimental methods and first-principles calculations, have been proved valuable in obtaining a basic understanding of the local structure, bonding, band gap, and electronic and optical properties of Ag4V2O7 crystals.

Synthesis and characterization of Ni2+ ions incorporated CuO nanoparticles and its application in antibacterial activity

In this present work, Ni doped CuO nanoparticles were successfully prepared by chemical precipitation method. The structural and chemical compositions of the products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The obtained products were identified to be of monoclinic structure and these results demonstrate that the Ni ions were substituted into the CuO lattice. The optical properties of the products were studied by diffuse reflectance spectroscopy and room temperature photoluminescence measurements. The morphological analyses were obtained by using field emission scanning electron microscopy and transmission electron microscopy. The magnetic properties were investigated at room temperature using the vibrating sample magnetometer and the hysteresis loops confirmed the ferromagnetic behaviour of CuO on doping due to smaller size effect. Further, as-formed doped and undoped CuO nanoparticles exhibit significant antibacterial activity against pathogenic bacterial strains namely Gram −ve (Pseudomonas aeruginosa, and Escherichia coli), Gram +ve bacteria (Bacillus subtilis, Staphylococcus aureus).

Morphology and photoluminescence of BaMoO4 micro- and nano-crystals synthesized by coprecipitation method

Barium molybdate (BaMoO4) micro- and nano-crystals were synthesized by the coprecipitation method. Utilizing the water as the solvent provides octahedron-like nanostructures. These nano-crystals were structurally characterized by X-ray diffraction, energy dispersive X-ray micro-analysis, Fourier transform infrared spectra. The size and shape were observed by scanning electron microscopy. The optical properties were studies by ultraviolet–visible diffuse reflectance spectroscopy and photoluminescence measurements at room temperature. The effects of temperature, solvent, surfactant and barium source were considered to obtain a controlled shape. It is found that the morphology, particle size and phase of the final products are extremely affected by these parameters.

Enhancement of the Cr(VI) adsorption and photocatalytic reduction activity of g-C3N4 by hydrothermal treatment in HNO3 aqueous solution

An effective and environmental-friendly method was adopted to enhance the Cr(VI) adsorption and photocatalytic reduction activity of g-C3N4, which was prepared by thermal condensation of melamine. The enhancement was realized by hydrothermal treatment of g-C3N4 in 1.9–7.6mol/L HNO3 aqueous solutions at 80–120°C for 3–12h. The compositions, structures and physiochemical properties of the hydrothermally treated g-C3N4 were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption isotherms, Zeta potential analysis, UV–vis diffuse reflectance spectroscopy and photocurrent measurement, and their dark adsorption and visible-light (wavelength >420nm)-driven photocatalytic reduction of Cr(VI) in aqueous solution were tested. It was found that the hydrothermally treated g-C3N4 exhibited significantly enhanced Cr(VI) adsorption and photocatalytic reduction activity than g-C3N4. Moreover, larger concentration of HNO3 aqueous solution, higher hydrothermal temperature or longer treatment time resulted in higher Cr(VI) adsorption and photocatalytic reduction activity of the hydrothermally treated g-C3N4. The reasons accounting for the enhanced Cr(VI) adsorption and photocatalytic reduction activity of the hydrothermally treated g-C3N4 were discussed, and the different mechanisms for the photocatalytic reduction of Cr(VI) over g-C3N4 and the hydrothermally treated g-C3N4 were also proposed.

Black TiO2(B)/anatase bicrystalline TiO2–x nanofibers with enhanced photocatalytic performance

Black TiO2(B)/anatase bicrystalline TiO2–x nanofibers were synthesized from a porous titanate derivative by calcination in H2, and were characterized using field-emission scanning electron microscopy, Raman spectroscopy, N2 adsorption-desorption analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, ultraviolet-visible diffuse reflection spectroscopy and photoluminescence measurements. Characterization results showed that no Ti3+ was present on the surface of black bicrystalline TiO2–x and oxygen vacancies were distributed in the bulk of both TiO2(B) and anatase phases. The O/Ti atom stoichiometric ratio of black bicrystalline TiO2–x was estimated to be 1.97 from the difference of mass loss between black bicrystalline TiO2–x and white bicrystalline TiO2 without oxygen vacancies. The photocatalytic activity of black bicrystalline TiO2–x was 4.2 times higher than that of white bicrystalline TiO2 and 10.5 times higher than that of anatase TiO2. The high photocatalytic activity of black bicrystalline TiO2–x was attributed to its effective separation of electrons and holes, which may be related to the effects of both bicrystalline structure and oxygen vacancies. Black bicrystalline TiO2–x also exhibited good photocatalytic activity after recycling ten times. The black bicrystalline TiO2–x nanofibers show potential for use in environmental and energy applications.

Layering MoS2 on soft hollow g-C3N4 nanostructures for photocatalytic hydrogen evolution

Hollow MoS2/g-C3N4 hybrids were obtained through a combination route of hard-templating technique and impregnation-sulfidation method. The physicochemical, optical/electric and electrocatalytic properties of the obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy, photoluminescence (PL) spectroscopy and electrochemical measurement. Their photocatalytic activities were evaluated by H2 production from lactic acid aqueous solution with visible-light irradiation. The results showed that MoS2/HCNS nanojunctions exhibited enhanced photocatalytic H2 production, which could be attributed to the thin layered junctions formed between MoS2 and HCNS for efficient charge separation and the active sites provided by MoS2 for H2 production at lower over potentials.

Photocatalytic degradation of organic compounds by PbMoO4 synthesized by a microwave-assisted solvothermal method

The microwave-assisted solvothermal (PbMH) and conventional solvothermal (PbH) synthesis were successfully used to prepare PbMoO4 particles with different morphologies, crystallinity degree and particle size. The material was structurally characterized by X-ray diffraction (XRD), their morphologies were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The textural and optical properties were analyzed by adsorption–desorption N2 isotherms (BET), diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) measurements, respectively. The photocatalytic activity of PbMoO4 particles was evaluated by degradation of indigo carmine (IC), orange G (OG), tetracycline (TC), salicylic acid (SA) and ciprofloxacin (CIP) compounds in aqueous solution under UV–vis light irradiation. The PbMH sample showed the highest photocatalytic activity reaching half-life times (t1/2) of 6, 7, 18, 75 and 125min for TC, CIP, IC, SA and OG. Moreover, PbMoO4 samples were evaluated in the H2 production from aqueous solutions using ethanol as sacrificial agent. The results showed that the PbH sample has the highest photocatalytic activity for hydrogen generation probably attributed to its high crystallinity degree.

Zn1−xCoxWO4 (0 ≤ x ≤ 1) full range solid solution: Structure, optical properties, and magnetism

A novel full-range solid-solution Zn1−xCoxWO4 (0≤x≤1) was successfully developed via a facile one-pot hydrothermal route. The phase structure and microstructure were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectra and scanning electron microscopy (SEM). The Zn1−xCoxWO4 solid solution possesses similar wolframite crystal structure with the same space group P2/c. Diffuse reflection spectroscopy (DRS) measurements on Zn1−xCoxWO4 (0≤x≤1) demonstrated that the optical band gap can be continuously tuned from 3.56eV to 2.61eV for direct transition and 1.87eV for indirect transition, respectively, with increasing x from 0 to 1. Magnetic susceptibility measurements reveal that CoWO4 has an antiferromagnetic transition at TN=42K, whereas Zn0.5Co0.5WO4 exhibits paramagnetic behavior. Moreover, CoWO4 and Zn0.5Co0.5WO4 obey the Curie–Weiss law from 200k down to 50K, and their effective magnetic moments were determined.

Enhanced Visible Light Photocatalytic Activity of Br-Doped Bismuth Oxide Formate Nanosheets.

A facile method was developed to enhance the visible light photocatalytic activity of bismuth oxide formate (BiOCOOH) nanosheets via Br-doping. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, the Brunauer–Emmett–Teller surface area, UV-vis diffuse reflectance spectroscopy, photoluminescence spectra, and N2 adsorption-desorption isotherms measurement. The Br− ions replaced the COOH− ions in the layers of BiOCOOH, result in a decreased layer distance. The photocatalytic activity of the as-prepared materials was evaluated by removal of NO in qir at ppb level. The results showed that the Br-doped BiOCOOH nanosheets showed enhanced visible light photocatalytic activtiy with a NO removal of 37.8%. The enhanced activity can be ascribed to the increased visible light absorption and the promoted charge separation.

Diffuse reflectance spectroscopy accurately quantifies various degrees of liver steatosis in murine models of fatty liver disease

BackgroundA real-time objective evaluation for the extent of liver steatosis during liver transplantation is currently not available. Diffuse reflectance spectroscopy (DRS) rapidly and accurately assesses the extent of steatosis in human livers with mild steatosis. However, it is yet unknown whether DRS accurately quantifies moderate/severe steatosis and is able to distinguish between micro- and macrovesicular steatosis.MethodsC57BL/6JolaHsd mice were fed wit a choline-deficient l-amino acid-defined diet (CD-AA) or a choline-sufficient l-amino acid-defined control diet (CS-AA) for 3, 8, and 20 weeks. In addition B6.V-Lepob/OlaHsd (ob/ob) mice and their lean controls were studied. A total of 104 DRS measurements were performed in liver tissue ex vivo. The degree of steatosis was quantified from the DRS data and compared with histopathological analysis.ResultsWhen assessed by histology, livers of mice fed with a CD-AA and CS-AA diet displayed macrovesicular steatosis (range 0–74 %), ob/ob mice revealed only microvesicular steatosis (range 75–80 %), and their lean controls showed no steatosis. The quantification of steatosis by DRS correlated well with pathology (correlation of 0.76 in CD-AA/CS-AA fed mice and a correlation of 0.75 in ob/ob mice). DRS spectra did not distinguish between micro- and macrovesicular steatosis. In samples from CD-AA/CS-AA fed mice, the DRS was able to distinguish between mild and moderate/severe steatosis with a sensitivity and specificity of 86 and 81 %, respectively.ConclusionDRS can quantify steatosis with good agreement to histopathological analysis. DRS may be useful for real-time objective evaluation of liver steatosis during liver transplantation, especially to differentiate between mild and moderate/severe steatosis.

Catalytic performance of CoMo/Al2O3-MgO-Li(x) formulations in DBT hydrodesulfurization

In this work, it is reported the catalytic performance of low acidity catalysts in the hydrodesulfurization reaction of dibenzothiophene. Catalytic CoMo formulations supported on materials based on Al2O3-MgO modified with several amounts of lithium oxide (x=1, 5 and 10wt.% of Li2O) were used. It was correlated the effect of the atomic lithium content on the dispersion of the Mo and Co phases in their oxidized and sulfided forms, in order to explain their catalytic performance. Elemental chemical composition on the catalyst surface as well as sulfurization degree and the interaction of sulfided Co and Mo phases with the support were determined by X-ray photoelectron spectroscopy (XPS). Textural properties were measured by N2 physisorption technique; the identification of the crystalline phases was studied by X-ray powder diffraction (XRD) and Raman spectroscopy (RS). The chemical coordination state was determined from diffuse reflectance spectroscopy (DRS) measurements. Reducibility was determined by temperature programmed desorption (TPR). Dispersion of MoS2 crystallites was revealed by high resolution transmission electron microscopy (HRTEM). Catalytic activity of the formulations was evaluated using a pressurized batch reaction system through the hydrodesulfurization reaction of dibenzothiophene as a model molecule, selectivity toward direct desulfurization reaction route was studied following the biphenyl and cyclohexylbenzene reaction products identified by using gas chromatography; results show that there is an optimal amount of 3.7 at.% of Li, which maintains hydrodesulfurization function and decrease the hydrogenation function compared to the conventional CoMo catalyst.

Polymer supported graphene–CdS composite catalyst with enhanced photocatalytic hydrogen production from water splitting under visible light

A polymer supported graphene structure was synthesized using organic microspheres as the support of the graphene oxide. Graphene oxide was reduced to graphene and CdS was decorated on the surface of the graphene through a solvothermal process. The photocatalytic hydrogen production reaction was carried out using the composite catalyst under visible light irradiation (λ>400nm). A series of composite catalysts were synthesized with different reaction time. The maximal hydrogen production rate of 175μmolh−1 was obtained from the 3h prepared sample (PSGM/rGO/CdS-3), which is 19.3 times higher than the mechanical mixing sample with the same composition. The quantum efficiency of the PSGM/rGO/CdS-3 sample was 3.99% at 420nm. Graphene served as electron acceptor and hydrogen evolution sites to promote the separation of the photo-induced charge carriers. Quantum size effect was observed from ultraviolet–visible diffuse reflectance spectroscopy and PL measurements. The presence of quantum size effect widened the bandgap of the catalyst and enhanced the photocatalytic hydrogen production rate. The stability of the composite catalyst was tested and demonstrated that this graphene-based composite catalyst was a stable and potential catalyst for photocatalytic hydrogen production.

Efficient dye-sensitized solar cells based on carbon-doped TiO2 hollow spheres and nanoparticles

Different structures of TiO2 photoelectrodes are fabricated with various arrangement modes of the layers. TiO2 nanoparticles, synthesized by stabilizing agent free non-hydrolytic sol–gel method, are employed as the under layer, whereas carbon-doped TiO2 hollow spheres, prepared by hydrothermally grown carbon template, are used as the scattering layer of solar cells. The nanoparticles (22 nm) have anatase structure, while 300–700 nm hollow spheres show mixtures of anatase and rutile phases. X-ray photoelectron spectroscopy confirms that carbon is doped into TiO2 hollow spheres, resulting in a decrease in band gap energy in the range 2.96–3.13 eV compared with 3.04 eV band gap energy for the nanoparticles. The diffuse reflectance spectroscopy measurements show that the hollow spheres exhibit higher scattering property than the nanoparticles. The single layer solar cell made of nanoparticles and carbon-doped TiO2 hollow spheres shows the highest efficiency of 7.21 and 7.02 %, respectively. Further enhancement of photovoltaic performance is obtained by light scattering mechanism aided by fabrication of double layer solar cells due to higher incident photon-to-current conversion and less recombination. The double layer solar cell made of nanoparticles as the under layer and hollow spheres (containing 86 % anatase–14 % rutile) as the scattering layer shows the highest efficiency of 8.55 %.

Synthesis and characterization of a novel BiVO4/SiO2 nanocomposites

A novel hybrid BiVO4–SiO2 composites with mesoporous composite structure were synthesized by hydrothermal calcination method. The as-prepared BiVO4/SiO2 hybrid material was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, UV–vis diffuse reflectance spectroscopy and BET measurements, respectively. Its photocatalytic activity was evaluated by the performance for decomposing C.I. Reactive Blue 19 in aqueous solution under visible light irradiation, and photocatalytic efficiency was effectively improved compared to the pure semiconductor materials.

Band Gap Tuning of h-MoO3 Nanocrystals for Efficient Visible Light Photocatalytic Activity Against Methylene Blue Dye.

The photocatalytic degradation of methylene blue (MB) dye in aqueous solution was investigated using hexagonal molybdenum oxide (h-MoO3) nanocrystals under visible light irradiation. Chemical precipitation method was utilized to synthesize h-MoO3 and control over the crystal size, shape and distribution were characterized by using HNO3 and HCl as precipitating reagents. The photocatalysts were examined through X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectrum (EDX) for structural, functional, surface morphology and elemental analysis, respectively. The XRD results revealed that the samples were in single phase hexagonal crystal structure. XRD peak broadening analysis was used for crystallite size and strain estimation. The particles were anisotropic in nature and showed one dimensional (1-D) rod structure with hexagonal cross section. Further, the crystal phase stability, optical absorption and emission properties were studied by thermo gravimetric analysis (TGA), diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) measurements, respectively. The photocatalytic results demonstrated that the photocatalytic activity of h-MoO3 synthesized using HCl was improved, in comparison to that of HNO3 utilized h-MoO3 sample.

Effect of Mn doping on structural, optical and photocatalytic behaviors of hydrothermal Zn1−xMnxS nanocrystals

Undoped and Mn-doped ZnS nanocrystals (Ncs) have been synthesized by using the hydrothermal method at 200°C. X-ray diffraction (XRD) patterns revealed that the synthesized Ncs have cubic zinc blende structure. Typical SEM images show that undoped and Mn-doped ZnS Ncs are agglomerated in microspheres. Raman spectra informed that the Mn doping has improved the crystallinity of the ZnS Ncs up to the concentration 3%. The optical properties of Mn-doped ZnS Ncs were studied through UV–vis diffuse reflection spectroscopy, photoluminescence (PL), PL decay and PL excitation (PLE) measurements. The optical band gap was found to decrease from 3.59 to 3.35eV with increasing the Mn doping concentration. PL spectra demonstrate clearly that Mn2+ ions reduce the density of defect in both ZnS lattice and surface. An efficient excitation transfer from the ZnS host to Mn2+ ions is evidenced from PL decays.ZnS:Mn Ncs were found to be good photocatalyst for sunlight degradation of Rhodamine B. The optimum Mn dopant concentration was 3%, above which photocatalytic activity decreased. The degradation reaction obeyed pseudo-first-order kinetics.

One-pot hydrothermal synthesis of a novel BiPO4/BiOBr composite with enhanced visible light photocatalytic activities

The BiPO4/BiOBr composites were successfully fabricated by a facile one-step hydrothermal method. The X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (DRS), photoluminescence (PL) and photocurrent (PC) measurements were employed to characterize the crystal structures, morphologies, optical properties, recombination of photo-generated electron–hole pairs, and electron–hole separation effect of the photocatalysts. BiPO4/BiOBr composites exhibited much higher photocatalytic activity for the degradation of RhB and MO dye than single BiOBr and BiPO4 under visible light and simulated sunlight irradiation, respectively. The results of PL and PC measurements demonstrated that the large enhancement of photocatalytic activity could be mainly ascribed to the surface junction of BiPO4/BiOBr composite which can effectively improve electron–hole separation speed during photocatalytic process.