Light Diffuse Reflectance Research Articles

Enhanced electrochromic properties of TiO2 nanoporous film prepared based on an assistance of polyethylene glycol

Polyethylene glycol (PEG) was employed as pore-forming agent to prepare TiO2 nanoporous film based on spin-coating a TiO2 nanoparticle mixed paste on fluorine doped tin oxide (FTO) glass. The electrochromic and optical properties of the obtained TiO2 film were investigated by cyclic voltammetry (CV), chronoamperometry (CA) and UV–Vis spectrophotometer. The results show that the PEG in the mixed paste endows the TiO2 film with well-developed porous structure and improves the uniformity of the TiO2 film, which are helpful for the rapid intercalation and extraction of lithium ions within the TiO2 film and the strengthening of the diffuse reflection of visible light in the TiO2 film. As a result, the TiO2 film derived from the mixed paste with PEG displays higher electrochemical activity and more excellent electrochromic performances compared with the TiO2 film derived from the mixed paste without PEG. The switching times of coloration/bleaching are respectively 10.16/5.65 and 12.77/6.13 s for the TiO2 films with PEG and without PEG. The maximum value of the optical contrast of the TiO2 film with PEG is 21.2% while that of the optical contrast of the TiO2 film without PEG is 14.9%. Furthermore, the TiO2 film with PEG has better stability of the colored state than the TiO2 film without PEG.

Research on an uplink carrier sense multiple access algorithm of large indoor visible light communication networks based on an optical hard core point process.

The IEEE 802.15.7 protocol suggests that it could coordinate the channel access process based on the competitive method of carrier sensing. However, the directionality of light and randomness of diffuse reflection would give rise to a serious imperfect carrier sense (ICS) problem [e.g., hidden node (HN) problem and exposed node (EN) problem], which brings great challenges in realizing the optical carrier sense multiple access (CSMA) mechanism. In this paper, the carrier sense process implemented by diffuse reflection light is modeled as the choice of independent sets. We establish an ICS model with the presence of ENs and HNs for the multi-point to multi-point visible light communication (VLC) uplink communications system. Considering the severe optical ICS problem, an optical hard core point process (OHCPP) is developed, which characterizes the optical CSMA for the indoor VLC uplink communications system. Due to the limited coverage of the transmitted optical signal, in our OHCPP, the ENs within the transmitters' carrier sense region could be retained provided that they could not corrupt the ongoing communications. Moreover, because of the directionality of both light emitting diode (LED) transmitters and receivers, theoretical analysis of the HN problem becomes difficult. In this paper, we derive the closed-form expression for approximating the outage probability and transmission capacity of VLC networks with the presence of HNs and ENs. Simulation results validate the analysis and also show the existence of an optimal physical carrier-sensing threshold that maximizes the transmission capacity for a given emission angle of LED.

Electrospinning fabrication of mesoporous nano Fe2O3-TiO2@activated carbon fiber membrane for hybrid removal of phenol from waste water

A mesoporous iron–titanium mixed-oxides@activated carbon(AC) fiber membrane was fabricated by an electrospinning method and applied to the treatment of phenol waste water. The physical and chemical properties of the composite fiber membrane were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption/desorption, UV–Vis light diffuse reflectance spectroscopy (DRS), Raman spectroscopy, respectively. The results indicate that the composite nanofiber membrane is composed of α-Fe2O3, anatase TiO2 and activated carbon phases with a specific surface area of 231 m2 g–1 and narrow pore size distribution of 3–6 nm. DRS reveals that the composite membrane has high photons absorption from both ultraviolet light and visible light irradiation owing to the combination of Fe2O3, TiO2 and carbon. The prepared nano Fe2O3–TiO2@AC fiber membrane can act as an efficient reusable photocatalyst and adsorbent for 100% remo val of phenol pollutant. This hybrid technique is hopeful to be widely used in the treatment of various organic waste waters.

Synthesis of novel potassium peroxodisulfate-modified titanium dioxide for photocatalytic oxidation of acetaminophen under visible light irradiation

In recent years, traces of acetaminophen, a widely used analgesic and anti-inflammatory and known to be an over-the-counter drug, have been detected unaltered in effluents of conventional wastewater treatment facilities. About 58–68% released through excretion during patient’s therapeutic treatment, and only about 80–86% were removed by the wastewater treatment facility. This study investigated the improved performance of photocatalysis in degrading or removing acetaminophen. The visible light active potassium peroxodisulfate-doped titanium dioxide photocatalysts synthesized via sol–gel method was used to eliminate acetaminophen from aqueous solutions through photocatalytic oxidation. The effects of the amount of dopant, calcination temperature and calcination time on the properties and visible light photocatalytic activity of potassium peroxodisulfate-doped titanium dioxide were also investigated. Increasing the amount of the dopant and calcination temperature up to a certain extent increases removal efficiency while further decreased the removal rate. Potassium peroxodisulfate-doped titanium dioxide photocatalysts were characterized by X-ray diffraction, ultraviolet–visible light diffuse reflectance spectroscopy, Brunauer–Emmett–Teller method and X-ray photoelectron spectroscopy. Potassium peroxodisulfate-doped titanium dioxide with 0.5%w dopant and calcined at 300 °C for 3 h degrades about 100% acetaminophen in aqueous solution within 540 min. The reaction of acetaminophen with the photocatalyst has an apparent rate constant of 8.39 × 10−3 min−1.

Iridium, carbon and nitrogen multiple-doped TiO2 Nanoparticles with enhanced photocatalytic activity

The aim of this research is to enhance the photocatalytic activity of TiO2 nanoparticles for the UV–visible light by multiple-doping with Iridium, carbon and nitrogen. The tridoped TiO2 photocatalyst were prepared by wet chemical method, and characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible light diffuse reflection spectroscopy and room temperature photoluminescence spectroscopy. Besides, the photocatalytic H2 evolution performance of Ir-C-N tridoped TiO2 under UV–visible light irradiation was evaluated. It was found that Ir existed as Ir4+ by substituting Ti in the lattice of TiO2; meanwhile, C and N were also incorporated into the surface of TiO2 nanoparticles in interstitial mode. Meanwhile, Ir-C-N tridoping extended the absorption of TiO2 into the visible light region and narrowed its band gap to ~3.0eV, resulting in enhanced photocatalytic H2 evolution under UV–visible light irradiation. This could be attributed to narrow band gap and proper electronic structure of TiO2 after Ir-C-N tridoping.

Carbon nitride nanodots decorated brookite TiO2 quasi nanocubes for enhanced activity and selectivity of visible-light-driven CO2 reduction

A new kind of brookite TiO2/g-C3N4 nanocomposite, in which g-C3N4 nanodots (CNDs) with a mean size of ∼2.8nm are decorated on brookite TiO2 quasi nanocube (BTN) surfaces (hereafter referred as BTN-CNDs heterojunction), is prepared via a facile calcination process of the mixture of urea and the home-made BTN powders, and then used as visible-light-responsive photocatalyst for CO2 reduction. Electron microscopy, X-ray powder diffraction (XRD), ultraviolet-visible light (UV-vis) diffuse reflectance absorption spectra (DRS), X-ray photoelectron spectra (XPS) and its valance band (VB) spectra are adopted to investigate the microstructure, composition, energy band structure, and the possible photogenerated electron transfer processes between BTN and CNDs. After optimizing the photocatalytic condition, enhanced visible-light-driven CO2-reduction activity and selectivity for CH4 generation as compared to g-C3N4 and BTN alone are observed, and a photosensitization mechanism is proposed to explain the differences in the photocatalytic performance among g-C3N4, BTN, and BTN-CNDs. The pronounced CH4 generation activity and selectivity over BTN-CNDs heterojunction demonstrate a new strategy for improving the interfacial charge transfer and the photocatalytic CO2 reduction performance though tailoring the microstructures of the semiconductor-based nanocomposites.

Effects of vanadium doping on microstructures and optical properties of TiO2

To improve the photocatalytic activity of titanium dioxide (TiO2), the vanadium (V) was selected to modify TiO2. Pure and V-doped TiO2 samples were first synthesized, then effects of the V doping on microstructures and optical properties of TiO2 were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible light diffuse reflectance spectra (UV–vis DRS). Results indicated that the prepared TiO2 samples only contained anatase phase. The V dopant was uniformly dispersed in TiO2 lattices, not affecting the crystal phase structures of TiO2. The crystallite sizes of TiO2 were decreased first and then increased with the increase in V dopant content within the diameter range from 12 to 16nm. The V dopant inhibited the increase in TiO2 crystallite size. Also, the dispersity of TiO2 nanoparticles was improved with the increase in V dopant content. The V doping brought more defects in TiO2 lattices to capture charge carriers, and to decrease the recombination of electron–hole pairs. Additionally, the prepared TiO2 included such elements as Ti, V and oxygen (O). V consisted of two chemical states of V4+ and V5+, which were served as trapping centers of photo-generated electrons to promote the photocatalytic oxidation process. Ti existed in the form of Ti4+, and O presented in the form of such chemical bonds as Ti-O, Ti-OH and Ti-O-V in V-doped TiO2. Finally, the optical absorption edges of V-doped TiO2 show obvious red shift. The optimal V dopant content is 1.0% for pure TiO2 sample. The V dopant could introduce the doping energy level and narrow the band gap of TiO2, extending the absorption spectral range of TiO2. The V doping was an effective method to improve optical absorption properties of TiO2 in visible light region.

Synthesis and characterization of plasmonic and magnetically separable Ag/AgCl-Bi2WO6@ Fe3O4@SiO2 core-shell composites for visible light-induced water detoxification

A magnetic photocatalyst composite (Ag/AgCl-Bi2WO6) was proposed and investigated. Magnetic Bi2WO6 was hydrothermally loaded onto silica-coated Fe3O4 which was synthesized by coprecipitation in addition to a modified Stöber process. Ag nanoparticles were then photoreduced on the surface of Bi2WO6. The prepared samples were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet–visible light diffuse reflectance spectroscopy. Magnetic properties were investigated using a superconducting quantum interface magnetometer, with samples exhibiting quasi-superparamagnetic behaviour. The visible light-induced photocatalytic activities were evaluated by degrading a model dye, RhB, as well as a colourless aromatic organic compound, phenol. Samples found to possess an excellent performance in terms of detoxification. Pathways and mechanisms for the photocatalytic degradation of organic compounds in the presence of Ag/AgCl-(M) Bi2WO6 were also investigated and proposed.

Preparation of ZnFe2O4 nanoparticles by mechanical alloying and annealing for sensitizing C-modified TiO2 and acquirement of efficient photocatalyst

ZnFe2O4 nanoparticles sensitized by C-modified TiO2 hybrids (ZnFe2O4–TiO2/C) were successfully prepared by a feasible method. The ZnFe2O4 nanoparticles were prepared by mechanical alloying and annealing. The residual organic compounds in the synthetic process of TiO2 were selected as the carbon source. The as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, X-ray fluorescence, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible light diffuse reflectance spectroscopy (UV–Vis) and N2 adsorption–desorption analysis. The photocatalytic activity of the photocatalysts was measured by degradation of methyl orange under ultraviolet (UV) light and simulated solar irradiation, respectively. The results show that the carbon did not enter the TiO2 lattice but adhered to the surface of TiO2. The photocatalytic activity of the as-prepared C-modified TiO2 (TiO2/C) improved both under UV and simulated solar light irradiation, but the improvement was not dramatic. Introduction of ZnFe2O4 into the TiO2/C could enhance the absorption spectrum range. The ZnFe2O4–TiO2/C hybrids exhibited a higher photocatalytic activity both than that of the pure TiO2 and TiO2/C under either UV or simulated solar light irradiation. The complex synergistic effect plays an important role in improving the photocatalytic performance of ZnFe2O4–TiO2/C composites. The optimum photocatalytic performance was obtained from the ZnFe2O4(0.8 wt%)–TiO2/C sample.

Determination of fat content in goat milk using annular photoelectric sensor system

In this paper, a new method for quantitative determination of fat content in goat milk at room temperature (25°C), based on the annular photoelectric sensor system, has been developed. The measurement system consists of an annular photoelectric sensor, thermoelectric cooler (TEC), amplifier, A/D converter, microprocessor and other components. Based on Mie theory, the diffuse reflection light intensity is adopted as the optical parameter representing the fat content in goat milk. In this way, the standard model of the system can be established and loaded into the processor to realize data acquisition, processing and output. The proposed method has been tested on goat milk samples with variable fat content in the prediction experiment. The results show that the fitting equation is y=−0.366 x+0.295 ( R2=0.987) and measurement errors are within ±3%, which indicates that the presented method has high prediction performance and can measure the fat content in goat milk accurately and in real time.

A General Synthesis Strategy for Highly Dispersed Amorphous MoO3 over Supported Catalysts

AbstractAmorphous MoO3 was evenly deposited on a Bi2SiO5/SiO2 support by a strategy of heterogenous coprecipitation using Ti as structural promoter. The structure and properties of MoO3‐Bi2SiO5/SiO2 have been characterized by a series of techniques, including N2 adsorption/desorption analysis, X‐ray diffraction (XRD), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and ultraviolet‐visible light (UV‐vis) diffuse reflectance spectra (DRS).The addition of n‐butyl alcohol into synthesis medium resulted in the most dispersive amorphous MoO3, with an average particle size of 4 nm. Selective oxidation of propylene was chosen as a probe reaction to test the performance of catalysts. Kinetic study revealed that the method of heterogeneous coprecipitation enhanced catalytic performance via increasing the number of active sites, rather than changing the nature of it. This is well compatible with characterization results.

On the limitation of dual-view triangulation in reducing the measurement error induced by the speckle noise in scanning operations

A triangulation-based laser displacement sensor using the diffuse reflection light has a strong practical advantage in its robustness against the tilting of the object surface to the sensor’s sensitive direction. On the other hand, it is often subject to higher-frequency noise-like measurement error in scanning operations. This error is caused by the movement of the speckle in the reflected laser beam spot with the scanning operation. This paper first discusses how the dual-view triangulation, using two image sensors aligned symmetrically about the laser beam axis, can reduce the scanning noise in principle. Then, its inherent limitation is discussed. Since different points on the target surface cast the specular reflection to each image sensor, the influence of the sensor’s lateral movement cannot be canceled by comparing the reflected spot’s displacement on each image sensor. This issue can be observed clearer when measuring a surface of a less random surface profile. It is experimentally validated.

Enhanced sunlight photocatalytic activity and recycled Ag–N co-doped TiO2 supported by expanded graphite C/C composites for degradation of organic pollutants

Removing organic pollutants from wastewater is urgent for developing a sustainable ecological environment. A highly efficient visible light photocatalyst was synthesized through a sol–gel method using C/C composites (expanded graphite dipping in the phenol formaldehyde resin, EGC) coated with Ag, N co-doped TiO2. The as-prepared composites were characterized through scanning electron microscopy (SEM), X-ray diffraction (XRD), N2 adsorption–desorption (BET), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible light diffuse reflectance spectroscopy (UV–Vis-DRS). The XRD and N2 adsorption–desorption (BET) results revealed that the photocatalysts were composed of mesoporous structures mainly with anatase TiO2. The effects of Ag content and calcination temperature on the photocatalytic activity of Ag–N-TiO2/EGC photocatalysts were studied. The results showed that under visible light, the photocatalytic efficiencies of Ag1.0-N-TiO2/EGC (550 °C) obtained for the degradation of Rhodamine B (RB) and diesel are 7.4 times and 3.9 times higher, respectively, than those of N-TiO2/EGC with high mineralization. The enhanced photocatalytic activity of the Ag–N-TiO2/EGC composites was attributed to the porosity and flexible electron transport paths for formation of superoxide radicals. These characteristics assured Ag–N-TiO2/EGC photocatalyst as a high-efficiency photocatalytic material for organic pollutant degradation under visible light.

Reflection of diffuse light from dielectric one-dimensional rough surfaces.

We study the reflection of diffuse light from 1D randomly rough dielectric interfaces. Results for the reflectance under diffuse illumination are obtained by rigorous numerical simulations and then contrasted with those obtained for flat surfaces. We also explore the possibility of using perturbation theories and conclude that they are limited for this type of study. Numerical techniques based on Kirchhoff approximation and reduced Rayleigh equations yield better results. We find that, depending on the refractive index contrast and nature of the irregularities, the roughness can increase or decrease the diffuse reflectance of the surface.

Synthesis and characterization of Ag/AgBr–activated carbon composites for visible light induced photocatalytic detoxification and disinfection

Abstract A novel Ag/AgBr–activated carbon (AC) composite photocatalyst was proposed and investigated. The composite was prepared by impregnation–precipitation–photoreduction, and characterized by X-ray diffraction, scanning electron microscopy, N2 sorption, and ultraviolet–visible light diffuse reflectance spectroscopy. The prepared material possessed an “egg-shell” structure, where the photocatalyst formed heterogeneous agglomerates on the outside surface of the adsorbent host material. Ag/AgBr–AC exhibited enhanced absorption in the visible light region, and photocatalysis was studied for the degradation of model organic pollutants (methyl orange dye (MO), phenol) and a model microorganism (Escherichia coli K-12). Photocatalytic degradation of organic pollutants under visible light occurred with pseudo-first order rate constants of 0.0491 min−1 and 0.007 min−1 for MO and phenol, respectively using a catalyst loading of 0.5 g L−1. Photocatalytic inactivation of 50 mL of a 106 CFU mL−1 bacterial suspension induced a 3-log loss of culturability in 60 min with a catalyst loading of 5 g L−1. The mechanism of photocatalytic action for Ag/AgBr–AC composites was discussed with respect to the adsorption, localized surface plasmon resonance, and conventional semiconductor photocatalysis processes that took place under visible light.

266 nm陶瓷激光器反射照相在指纹显现中的应用

本文研究潜在指纹显现的新技术，用自主研发的266 nm短波紫外陶瓷激光器作为光源照射检材，通过反射照相方法显现各种非渗透性客体表面的潜在指纹。紫外陶瓷激光器能有效显现出光滑客体表面的潜在指纹，并且油脂指纹检出率高于汗液指纹检出率。陶瓷材料由于其良好的化学稳定性、耐高温性、尺寸稳定性、光漫反射特性等优点，利用该266 nm短波紫外陶瓷激光器可以显现非渗透性客体表面的潜在指纹，在刑侦领域上有较好的应用前景。 This paper describes visualization of latent fingerprints by 266 nm ultraviolet ceramic laser. Self-made 266 nm ultraviolet laser with a ceramic gain medium was used to illuminate the latent fingerprints on the non-porous substrates. The images were recorded by ultraviolet camera through reflection photography. The results showed that the marriage of ultraviolet ceramic laser and reflection photography was an effective method on visualization of latent fingerprint on non-porous substrates. The visualization rate of oil fingerprints is higher than the sweat fingerprints. Ceramic materials have the advantages of good chemical stability, high-tem- perature resistance, size stability and light diffuse reflection. The 266 nm ultraviolet ceramic laser could be adopted to the visualized latent fingerprints on the non-porous substrates. The ultraviolet ceramic laser operating at 266 nm has potential application in the field of criminal investigation.

Band gap manipulation of cerium doping TiO2 nanopowders by hydrothermal method

Cerium doped TiO2 nanopowders were prepared by hydrothermal method with cerium nitrate. The samples were characterized by high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), ultraviolet–visible light diffuse reflectance spectra. Results show that the crystal of cerium dioxide can be observed in the grains of TiO2. The morphology of TiO2 prepared by hydrothermal methods changed from nanosheets to nanopowders by cerium doping. Meanwhile cerium doping can significantly reinforce the absorption of visible light, and adjust the absorption cut-off wavelength, from 373 nm to 499 nm for the undoped and the 25% doped 499 nm samples respectively. With the increase in doping ratio of cerium, the band gaps also decreased from 3.32 to 2.48 eV. Based on our observations, it can be concluded that cerium oxide can improve the absorptivity of TiO2 and may have potential applications in the areas of solar cells and photocatalysis.

Comparative Study of Photocatalytic Performance on Different TiO<SUB>2</SUB>/EG Composite Nanocatalyst

In the present study, two kinds of TiO2/EG composite nanocatalysts were fabricated through different procedures. Subsequently, the resulting samples were characterized through scanning electron microscope (SEM), X-ray diffraction (XRD), UV-visible light diffuse reflection spectrum (UV-vis DRS) and exfoliated volume (EV) measurements. Results showed that both TiO2/EG nanocatalysts displayed an obviously enhanced visible light absorbance. Besides, the S-TiO2/EG nanocatalyst exhibited higher adsorptive and photocatalytic (PC) performance than those of M-TiO2/EG sample, which was mainly attributed to the more intense visible light absorbance and well-developed porosity. Furthermore, the effects of massive ratio between TiO2 and EG and calcination temperature on the PC performances were investigated in detail. Under the optimized conditions, 89.6% of phenol solution could be degraded within 120 min visible light irradiation by S-TiO2/EG nanocatalyst.

In English

The CuO and NiO doped silica/titania nanocomposites were investigated using ultraviolet-visible light diffuse reflectance spectroscopy (UV-Vis DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the samples was studied in photooxidation of caffeine (CAF). The band gaps were calculated using the Tauc plot for non-direct allowed optical transitions except a system at C NiO = 30 wt. % analyzed using a direct allowed optical transition. Copper oxide concentration increase leads to almost exponential diminution of the band gap. The band gap of NiO doped composites demonstrates almost linear change with C NiO . According to the XPS data, the doping oxides are completely absent at a composite surface. All the composites are shown to be more effective photocatalysts than titania Degussa P25.

Preparation and characterization of ZnTiO3–TiO2/pillared montmorillonite composite catalyst for enhanced photocatalytic activity

ZnTiO3–TiO2/organic pillared montmorillonite (pMt) composite catalyst was successfully prepared in this paper by immobilizing ZnTiO3–TiO2 onto pMt. The composition and texture of the prepared composite catalyst were characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, energy dispersive spectrometry, ultraviolet–visible light (UV–Vis) diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic activity was tested via photocatalytic degradation of methyl blue (MB) under both visible irradiation and UV light. The results indicated that the ZnTiO3–TiO2/pMt composite catalyst had an apparent absorption at the area of visible irradiation, and exhibited a higher efficiency of photocatalytic degredation of MB under visible irradiation. This was due to the heterostructure of ZnTiO3–TiO2, and the mesoporous structure and specific surface area of the ZnTiO3–TiO2/pMt composite. In addition, the results of the radical scavenging experiments showed that the holes and superoxide radicals are responsible for the degradation of MB under visible irradiation.