UV-visible Light Absorption Research Articles

Interactions between bromophenol blue and cetyl- trimethylammonium bromide in aqueous solutions and microemulsions

ABSTRACTThe UV-Vis light absorption spectroscopy of bromophenol blue (BPB) in a series of cetyltrimethylammonium bromide (CTAB) aqueous solutions and microemulsions has been determined. There exist association interactions between the BPB and cationic surfactant CTAB. By establishing the appropriate association models and measuring the absorbance in different concentrations of BPB aqueous solutions and microemulsions that have different R values, the association constants K were obtained and the values of thermodynamics functions of association ΔrGm were calculated. It shows that the formation of microemulsion has inhibitory effects on the association reaction.

Enhanced photocatalytic properties of reusable TiO2-loaded natural porous minerals in dye wastewater purification

Diatomite-based recyclable photocatalysts containing single lanthanide doped TiO2 nanoparticles (NPs) were synthesized by using simple sol–gel method. Photocatalytic activities of the prepared Ce- or La- single doped TiO2/diatomite catalysts were estimated by the degradation of Rhodamine B (RhB) under simulated sunlight irradiation. The XRD and Raman spectra shown only anatase phase of TiO2 for the un-doped and Ce-doped samples. The TEM images revealed uniform distribution of TiO2 NPs on the matrix, indicating that diatomite played an important role to prevent the agglomeration of TiO2 NPs. Ce-TiO2/diatomite showed a red shift in UV–visible light absorption edge with enhanced absorption intensity than un-doped sample, whereas La-TiO2/diatomite showed a blue shift. The bandgap energy of 1.5%-Ce doped sample is as low as 2.75eV. The XPS spectra showed the presence of both Ce3+ and Ce4+ oxidation states for Ce dopant. The photoluminescence spectra of the Ce-doped samples showed first decrease in the recombination centers with the maximum decrease for 1.5%-Ce doped sample and then started increase with the increasing Ce in the samples. As compared to the La-doped samples, a desired behavior was observed for the Ce-doped hybrid due to the redox Ce4+/Ce3+ pairs acting as electron scavengers and localized unoccupied Ce 4f level narrowing the band gap. The incorporation with diatomite as support of TiO2 nanoparticles is contributed for the improved reusability and also gives a promising strategy to enable the application of nano-photocatalysts in a real wastewater remediation treatment.

Construction of graphite/TiO2/nickel foam photoelectrode and its enhanced photocatalytic activity

Graphite/TiO2/nickel foam photoelectrode was constructed through a modified sol-gel method, followed by coating procedure. Morphology, structure and optical property of the as-prepared photoelectrode was characterized via transmission electron microscopy (TEM), scanning electrons microscopy (SEM), X-ray photoelectron microscopy (XPS), X-ray diffraction (XRD) and UV–vis diffuse reflection spectroscopy (DRS). Results indicated that nickel foam framework was partly covered by graphite/TiO2 and the crystallite sizes of anatase TiO2 were found to be about 10nm.C elements were incorporated into the lattice of TiO2 nanoparticles through replacing titanium atom. Graphite/TiO2/nickel foam photoelectrode showed the enhancement of light absorption in entire UV–vis regions. Besides, the photoelectrochemical performances of the graphite/TiO2/nickel foam electrode were studied by transient photocurrent response (TPR), open circuit voltage (OCV) and electrochemical impedance spectroscopy (EIS). Moreover, photodecomposition properties of the electrode were evaluated by the generation of hydroxyl (OH) radicals, photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of methyl orange (MO). The graphite/TiO2/nickel foam electrode revealed high transient photogenerated current of 0.054mAcm−2, open circuit photovoltage of −0.32mVcm−2, yield of OH radicals, PC activity of 85.1% and PEC activity of 99.8% for removal of MO. The improved PEC efficiency could be mainly ascribed to the coupled graphite, nickel foam support and applied bias voltage, which could not only enhance the UV–vis light absorption, but also accelerate the charges separation and transfer.

Cadmium Sulphide-Reduced Graphene Oxide-Modified Photoelectrode-Based Photoelectrochemical Sensing Platform for Copper(II) Ions.

A photoelectrochemical (PEC) sensor with excellent sensitivity and detection toward copper (II) ions (Cu2+) was developed using a cadmium sulphide-reduced graphene oxide (CdS-rGO) nanocomposite on an indium tin oxide (ITO) surface, with triethanolamine (TEA) used as the sacrificial electron donor. The CdS nanoparticles were initially synthesized via the aerosol-assisted chemical vapor deposition (AACVD) method using cadmium acetate and thiourea as the precursors to Cd2+ and S2-, respectively. Graphene oxide (GO) was then dip-coated onto the CdS electrode and sintered under an argon gas flow (50 mL/min) for the reduction process. The nanostructured CdS was adhered securely to the ITO by a continuous network of rGO that also acted as an avenue to intensify the transfer of electrons from the conduction band of CdS. The photoelectrochemical results indicated that the ITO/CdS-rGO photoelectrode could facilitate broad UV-visible light absorption, which would lead to a higher and steady-state photocurrent response in the presence of TEA in 0.1 M KCl. The photocurrent decreased with an increase in the concentration of Cu2+ ions. The photoelectrode response for Cu2+ ion detection had a linear range of 0.5–120 μM, with a limit of detection (LoD) of 16 nM. The proposed PEC sensor displayed ultra-sensitivity and good selectivity toward Cu2+ ion detection.

Facile assembly of TiO2 nanospheres/SnO2 quantum dots composites with excellent photocatalyst activity for the degradation of methyl orange

In this report, SnO2 quantum dots anchored on TiO2 nanospheres (TiO2/SnO2 composites) have been synthesized by a simple one-step hydrothermal process, and then employed as photocatalyst in photodegradation system. The microstructure of TiO2/SnO2 composites reveals that the SnO2 quantum dots are dispersed on the surface of TiO2 nanospheres uniformly. The photocatalytic behavior of the as-prepared samples revealed that the composites exhibited highly efficient performance by degrading 100mL of 10mg/L methylene orange in 15min completely under ultraviolet-visible light. Owning to the special structure of the composites, TiO2/SnO2 shows a more UV–vis light absorption than either pure TiO2 nanospheres or pure SnO2 quantum dots. This study offers a facile method to prepare TiO2/SnO2 composites, which will be a choice for greatly extending potential applications in water pollution treatment, degradation of pollutants and other related fields.

Effects of process conditions on the structure and optical properties of Zn/Fe/Sn/Sb-TiO2 three dimensional particle-electrodes

In this work, a novel magnetic photocatalysic mesoporous material with excellent photoluminesce properties such as superior light absorption was synthesized using the sol-gel method. With tetrabutyl titanate, zinc acetate, stannic chloride, antimonic chloride and ferric nitrate as precursors, and tri-blocked copolymer F127 as the template, it was demonstrated that if the annealing temperature was at 550°C, and the annealing time was 120min, the doping amount of Zn of this material could reach 4.0 at%, leading to a superior luminescence and UV–vis light absorbance. In particular, if the weight of template was set to 1.5g, the porous structures for the obtained photocatalysic materials were mainly distributed within 1.2nm to 4.7nm with a specific surface area larger than 110m2/g, leading to the most excellent absorption.

Microstructural and Optical Performances of Sol-Gel- Synthesized Nd-Doped ZnO Nanoparticles with Various Nd Contents

This work presents the manufacture and potential application of the ZnO materials with various cation dopings in recent literature and patent and then focus on the deposition and Nd doping effect of ZnO nanoparticles. The influence of Nd-doping in the range of 0-0.79 at % on microstructural and optical properties of ZnO nanoparticles were studied. X-ray diffraction measurement revealed the formation of single-phase ZnO nanocrystallite with a nanoscale particle size in the range of ~36.8-39.5nm. With increasing Nd content, UV-visible light absorbance first decreased and then increased, whereas band gap first widened and then narrowed. The absorbance and band gap show optimal values as Nd content is 0.39 at %. The nanoparticles showed strong visible emission varied with Nd doping due to variation of average particle size. The Nd doping also introduced a new emission center and weakened the visible defect emissions. Keywords: Nanostructure materials, Nd doping; optical properties, semiconductors, sol-gel preparation, spectroscopy, ZnO.

Effects of calcining temperature on photocatalysis of g-C3N4/TiO2 composites for hydrogen evolution from water

A composite of graphitic carbon nitride and TiO2 (g-C3N4/TiO2) with enhanced photocatalytic hydrogen evolution capacity was achieved by calcining melamine and TiO2 sol-gel precursor. Characterization results reveal that heating temperature had a great influence on the structure, surface area and properties of the composites. Compared with the polycondensation of pure melamine, the presence of TiO2 precursor can promote the formation of melon at a low temperature. The highest photocatalytic activity of g-C3N4/TiO2(400) was achieved when the calcination was performed at 400°C, exhibiting H2 production rate of 76.25μmol/h under UV–vis light irradiation (λ>320nm) and 35.44μmol/h under visible light irradiation (λ>420nm). The highest photocatalytic performance of g-C3N4/TiO2(400) can be attributed to: (1) the strong UV–vis light absorption due to the narrow bandgap caused by synergic effect of TiO2 and g-C3N4, (2) high surface area and porosity, (3) the effective separation of photo-generated electron-holes owing to the favorable heterojunction between TiO2 and g-C3N4.

Application of UV–Visible Light Absorption and Scattering technique to low absorption fuels under diesel-like conditions

Light Absorption and Scattering technique (LAS) has been applied for the measurement of fuel vapor distribution in diesel-type sprays. This technique is usually limited to fuels with relatively high absorptivity, which are sometimes not commonly used as surrogate fuels. In the present paper, a comparison of fuels with very different absorptive properties has been made to determine the range of application of the methodology. A calibration procedure has been applied to n-decane (DEC), a binary blend of n-decane and n-hexadecane (50DEC) and three blends of n-heptane with a highly-absorpting fuel (HEPB1, HEPB2 and HEPB3). This methodology enables the in-situ quantification of absorption coefficients at high pressure and temperature by creating a uniform mixture inside the cylinder. Results have been later applied for the quantification of fuel vapor distribution in sprays for DEC, 50DEC and HEPB3. Results obtained with these range of fuels have enabled to establish the limit in terms of absorption coefficient needed to get consistent results with the technique.

The Effect of Process Condition on the Structure and Optical Properties of Zn/Fe/Sn/Sb-TiO2Three Dimensional Particle-Electrode

In this experiment, photocatalysic material ,which is magnetic, photoluminesce and has superior light absorbing mesoporous, was synthesized by sol-gel method with tetrabutyl titanate, zinc acetate, stannic chloride , antimonic chloride and ferric nitrate as precursors, and tri-blocked copolymer F 127 as the template.Based on the experiment results, when the annealing temperature is at 550°C, the annealing time is 120min , the doping amount of Zn is 4.0at%. These produced samples were shown to have superior luminescence and UV-vis light absorbance. When the weight of template was set to 1.5g, the obtained photocatalysic materials, indicated that their porous mainly distributed within 1.2nm to 4.7nm and their specific surface areas were larger than 110m 2 /g, and had excellent absorption properties.

Fabrication and Characterization of High Stability (EDA)(FA)$lt;inf$gt;2$lt;/inf$gt;[Pb$lt;inf$gt;3$lt;/inf$gt;I$lt;inf$gt;10$lt;/inf$gt;] Layered Perovskite Film

A new two-dimensional layered hybrid perovskite solar-cell absorber was synthesized by one-step method, using (EDA)I-2, (FA)I, and PbI2 with a 1 : 2 : 3 stoichiometric ratio in a solvent mixture of N, N-dimethylformamide(DMF). Ethylenediamine(EDA) cation was introduced into the perovskite lattice to synthesize a layered structure with improved resistance to the degradation by humidity in air. The effects of humidity and time on crystal structure, composition, morphology, and absorption spectra of (EDA)(FA)(2)[Pb3I10] and CH3NH3PbI3 were analyzed by in situ grazing incidence X-ray diffraction(GIXRD), X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope(AFM), and UV-Vis spectroscope. The results reveal that the prepared (EDA)(FA)(2)[Pb3I10] film is more moisture resistant than the CH3NH3PbI3 film which is widely used in the perovskite solar cell. SEM analysis reveals that the (EDA)(FA)(2)[Pb3I10] film has a layered structure, which can reduce the degradation caused by moisture. What's more, UV-Vis light absorption spectroscopy and atomic force microscopy(AFM) results show that the layered structure film is also a suitable absorber for perovskite solar cells. Photoluminescence spectrum(PL) reveals that bandgap of the (EDA)(FA)(2)[Pb3I10] film is 1.67 eV, which is close to the optimum value for solar photoelectric conversion. As compared to CH3NH3PbI3 film, the low-cost perovskite structure offers greater tunability on a molecular level for further material optimization and possibility for widely used in the future.

Two star-shaped tetranuclear Ru(II) complexes containing uncoordinated imidazole groups: synthesis, characterization, photophysical and pH sensing properties.

Tetrapodal ligands H4L(1) and H4L(2) containing imidazole groups have been synthesized by the reaction of 1,10-phenanthroline-5,6-dione with 1,2,4,5-tetrakis[(4-formylphenoxy)methyl]benzene and 1,2,4,5-tetrakis[(3-formylphenoxy)methyl]benzene, respectively, in presence of NH4OAc. Two star-shaped complexes [{Ru(bpy)2}4(μ4-H4L(1))](PF6)8 and [{Ru(bpy)2}4(μ4-H4L(2))](PF6)8 (bpy = 2,2'-bipyridine) have been prepared by refluxing Ru(bpy)2Cl2 ·2H2O and each ligand in ethylene glycol. The deprotonated complexes [{Ru(bpy)2}4(μ4-L(1))](PF6)4 and [{Ru(bpy)2}4(μ4-L(2))](PF6)4 have been obtained by the reaction of sodium methoxide with [{Ru(bpy)2}4(μ4-H4L(1))](PF6)8 and [{Ru(bpy)2}4(μ4-H4L(2))](PF6)8, respectively, in methanol. The pH effects on the UV-vis light absorption and emission spectra of both complexes have been studied, and ground- and excited-state ionization constants of both complexes have been derived. The photophysical properties of both complexes are strongly dependent on the solution pH. They act as proton-induced off-on-off luminescent sensors through two successive deprotonation processes of imidazole groups, with a maximum on-off ratio of 8 in buffer solution at room temperature. Theoretical calculations for the highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LOMO) orbitals of bridging ligand are also presented for plausible explanations of the fluorescence changes.

Characteristics of Dye-Sensitized Solar Cells Using Dye from Pitaya Fruit

Dye-sensitized solar cell (DSSC) consists of TiO2nanoporous coating which acts as a photo electrode, a sensitizer of dye molecules soaked in the TiO2film, liquid electrolyte and a counter electrode. This paper focuses on the usage of a sensitizer from the Pitaya fruit. Pitaya or commonly known as dragon fruit (Hylocereus polyrhizus) was extracted and used as a sensitizer to fabricate the dye sensitized solar cell (DSSC). The photoelectrochemical performance of Pitaya based solar cell shows an open circuit voltage (VOC) of 237 mV, short circuit current (ISC) of 4.98 mA, fill factor (FF) of 0.51, solar cell efficiency (η) of 0.70 % and has a peak absorbance rate of 2.7 at 550 nm. The photoelectrochemical and UV-Visible light absorbance performance of Pitaya-DSSC shows good potential in future solar cell fabrication.

Application of Time-Dependent Density Functional and Natural Bond Orbital Theories to the UV-vis Absorption Spectra of Some Phenolic Compounds.

The UV-vis properties of 22 natural phenolic compounds, comprising anthraquinones, neoflavonoids, and flavonoids were systematically examined. The time-dependent density functional theory (TDDFT) approach in combination with the B3LYP, B3LYP-D2, B3P86, and M06-2X functionals was used to simulate the UV-vis spectra of the investigated compounds. It was shown that all methods exhibit very good (B3LYP slightly better) performance in reproducing the examined UV-vis spectra. However, the shapes of the Kohn-Sham molecular orbitals (MOs) involved in electronic transitions were misleading in constructing the MO correlation diagrams. To provide better understanding of redistribution of electron density upon excitation, the natural bond orbital (NBO) analysis was applied. Bearing in mind the spatial and energetic separations, as well as the character of the π bonding, lone pair, and π* antibonding natural localized molecular orbitals (NLMOs), the "NLMO clusters" were constructed. NLMO cluster should be understood as a part of a molecule characterized with distinguished electron density. It was shown that all absorption bands including all electronic transitions need to be inspected to fully understand the UV-vis spectrum of a certain compound, and, thus, to learn more about its UV-vis light absorption. Our investigation showed that the TDDFT and NBO theories are complementary, as the results from the two approaches can be combined to interpret the UV-vis spectra. Agreement between the predictions of the TDDFT approach and those based on the NLMO clusters is excellent in the case of major electronic transitions and long wavelengths. It should be emphasized that the approach for investigation of UV-vis light absorption based on the NLMO clusters is applied for the first time.

Physicochemical evolution of nascent soot particles in a laminar premixed flame: from nucleation to early growth

In this work, particle inception and early growth stages were investigated in an ethylene/air premixed flame by the evolution of the particle size and structure with flame residence time. Particle size distribution was measured by a scanning mobility particle seizer and chemical–physical investigation was carried out by Raman microspectroscopy, UV–visible light absorption and cyclic voltammetry.From early inception of particles, just downstream the flame front, to the formation of primary soot particles, in the post-oxidation flame zone, particles participate in a series of chemical and physical reactions that strongly modify their nanostructure and physicochemical properties, resulting in different optical and electronic characteristics. The results presented in this study show that the evolution from a mono-modal to a bi-modal size distribution is associated to a particle graphitization process consisting of a slight increase of the in plane average size of the polyaromatic units within the particles, La, and on the formation of stacks of polyaromatic planes. These outcomes suggest that in our flame conditions particle coagulation/coalescence has a major role in the initial soot formation, affecting both physical and chemical particle properties.

An Inexpensive Co-Intercalated Layered Double Hydroxide Composite with Electron Donor-Acceptor Character for Photoelectrochemical Water Splitting.

In this paper, the inexpensive 4,4-diaminostilbene-2,2-disulfonate (DAS) and 4,4-dinitro-stilbene-2,2- disulfonate (DNS) anions with arbitrary molar ratios were successfully co-intercalated into Zn2Al-layered double hydroxides (LDHs). The DAS(50%)-DNS/LDHs composite exhibited the broad UV-visible light absorption and fluorescence quenching, which was a direct indication of photo-induced electron transfer (PET) process between the intercalated DAS (donor) and DNS (acceptor) anions. This was confirmed by the matched HOMO/LUMO energy levels alignment of the intercalated DAS and DNS anions, which was also compatible for water splitting. The DAS(50%)-DNS/LDHs composite was fabricated as the photoanode and Pt as the cathode. Under the UV-visible light illumination, the enhanced photo-generated current (4.67 mA/cm2 at 0.8 V vs. SCE) was generated in the external circuit, and the photoelectrochemical water split was realized. Furthermore, this photoelectrochemical water splitting performance had excellent crystalline, electrochemical and optical stability. Therefore, this novel inorganic/organic hybrid photoanode exhibited potential application prospect in photoelectrochemical water splitting.

Facile, Nonhydrothermal, Mass-Producible Synthesis of Mesoporous TiO2 Spheres for Dye-Sensitized Solar Cells

We report a facile, non-hydrothermal (or non-solvothermal) and mass-producible synthesis of mesoporous TiO2 spheres (MTSs) suitable for use in dye-sensitized solar cells (DSSCs). The synthesis is a facile bulk calcination in which the inexpensive polymer ethyl cellulose (EC) is used as a structure-directing agent; the EC concentration is controlled to induce spherical morphology. The size of MTSs can be adjusted by tuning the solute–solvent interactions; for example, the addition of the poor solvent toluene to the solute resulted in the formation of smaller MTSs. A DSSC fabricated using a polymer electrolyte containing ionic liquid and iodine (I2) and using a layer of MTSs on a nanocrystalline (NC) TiO2 layer exhibited an efficiency of up to 6.3%, which is much higher than those of DSSCs with an NC layer only (5.0%) or with a commercial scattering layer (CSL) on an NC layer (5.7%). A solid-state DSSC (ssDSSC) using a single component solid polymer, namely poly((1-(4-ethenylphenyl) methyl)-3-butyl-imidazolium iodide) (PEBII), also exhibited an excellent efficiency of up to 6.4%. The improved efficiency was due to the role of the MTSs in improving surface area and light harvesting properties, as demonstrated by N2 adsorption/desorption isotherm, UV-visible light absorption, reflectance spectroscopy, incident photon-to-current efficiency (IPCE), and electrochemical impedance spectroscopy (EIS) analyses.

Structural analysis and visible light-activated photocatalytic activity of iron-containing soda lime aluminosilicate glass

A relationship between structure and visible light-activated photocatalytic activity of iron-containing soda lime aluminosilicate (15Na2O⋅15CaO⋅40Fe2O3⋅xAl2O3⋅(30−x)SiO2) glass (xNCFAS) was investigated by means of 57Fe-Mössbauer spectroscopy, X-ray diffractometry (XRD) and UV–visible light absorption spectroscopy (UV–VIS). The 57Fe-Mössbauer spectrum of 11NCFAS glass measured after heat-treatment at 1000°C for 100min was composed of a paramagnetic doublet due to FeIII(Td) and two magnetic sextets due to regular hematite (α-Fe2O3) and hematite with larger internal magnetic field. X-ray diffraction patterns of heat-treated xNCFAS samples resulted in decrease of α-Fe2O3 and increase of Ca2Fe22O33 or CaFe2O4 with alumina content. A quick decrease in methylene blue (MB) concentration from 15.6 to 4.7μmolL−1 was observed in the photocatalytic reaction test with 40mg of heat-treated 11NCFAS glass under visible light-exposure. The largest first-order rate constant of MB decomposition (k) was estimated to be 9.26×10−3min−1. Tauc’s plot yielded a band gap energy (Eg) of 1.88eV for heat-treated 11NCFAS glass, which is smaller than previously reported Eg of 2.2eV for α-Fe2O3. These results prove that addition of Al2O3 into iron-containing soda lime silicate glass is favorable for the preparation of improved visible light-photocatalyst with ‘ubiquitous’ elements.

Fe-doped cryptomelane synthesized by refluxing at atmosphere: Structure, properties and photocatalytic degradation of phenol

Fe-doped cryptomelanes were synthesized by refluxing at ambient pressure, followed by characterization with multiple techniques and test in photocatalytic degradation of phenol. The introduction of Fe(III) into the structure of cryptomelane results in a decrease in particle size and the contents of Mn and K+, and an increase in the Mn average oxidation state (AOS), specific surface area and UV–vis light absorption ability. Mn and Fe K-edge extended X-ray absorption fine structure spectroscopy analysis indicates that some Fe(III) is incorporated into the framework of cryptomelane by replacing Mn(III) while the remaining Fe3+ is adsorbed in the tunnel cavity. These Fe-doped cryptomelanes have significantly improved the photocatalytic degradation rate of phenol, with the sample of ∼3.04wt.% Fe doping being the most reactive and achieving a degradation rate of 36% higher than that of the un-doped one. The enhanced reactivity can be ascribed to the increase in the coherent scattering domain size of the crystals, Mn AOS and light absorption, as well as the presence of sufficient K+ in the tunnel. The results imply that metal doping is an effective way to improve the performance of cryptomelane in pollutants removal and has the potential for modification of Mn oxide materials.

Visible light absorption and photo-sensitizing properties of spinach leaves and beetroot extracted natural dyes

Herein, chlorophyll and betalain dyes are extracted from fresh spinach leaves and beetroots. Fourier transform infrared spectra are used to identify the characteristic peaks of the extracted dyes. UV–vis light absorption characteristics of the dyes and their mixed counterpart are investigated by varying their pH and temperature. These dyes are used as photo sensitizer for fabrication of zinc oxide photo-anode based dye sensitized solar cells (DSSCs). The photo-voltaic characteristics of the developed DSSCs are measured under simulated solar light (power of incident light 100mWcm−2 from Air Mass 1.5G). The solar to electric conversion efficiencies for the chlorophyll, betalain and mixed dye based solar cells are estimated as 0.148%, 0.197% and 0.294% respectively. The highest conversion efficiency for mixed dye based solar cell is attributed due to the absorption of wider range of solar spectrum.