Diffuse Reflectance Spectroscopy Techniques Research Articles

Investigation of photocatalytic removal and photonic efficiency of maxilon blue dye GRL in the presence of TiO2 nanoparticles

ABSTRACTTiO2 nanoparticles have been synthesized by solvent-free hydrothermal process. TiO2 nanoparticles were annealed at 500°C for enhancing the characterization and the photocatalytic activity. The synthesized TiO2 was characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), BET, and diffuse reflectance spectroscopy (UV-DR) techniques to study the morphology and structural configuration. The effects of different parameters such as the initial dye concentration, catalyst concentration, pH of the solution, light intensity, and reactive oxygen species (ROS) on relative photonic efficiencies and photocatalytic degradation kinetics of GRL were investigated, and the degradation of GRL follows pseudo-first order kinetics according to the Langmuir–Hinshelwood model. The ROS studies indicate that hydroxyl radicals and holes are the predominant reactive species within the same step, contributing up to 92.64%, hydroxyl radicals participate for about 55%, and holes share for about 37.64% in the photocatalytic degradation of GRL.

Solid state synthesis of erbium doped ZnO with excellent photocatalytic activity and enhanced visible light emission

The doped ZnO crystals with different erbium content were prepared by solid state reaction technique. The method is simple, relatively less expense and enables the production in large scale. The samples were characterised by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV/vis diffuse reflectance spectroscopy and photoluminescence techniques. Photocatalytic activity of samples was investigated by the degradation of methylene blue under UV light irradiation and was observed that, small fractions of erbium incorporation have a significant role in the enhancement of photocatalytic activity of ZnO. And the good stability of prepared catalysts makes them suitable for practical applications. Fluorescent property studies of erbium doped ZnO at room temperature show enhanced visible light emission due to the production of induced defects like antisite oxygen OZn and interstitial oxygen Oi. This work reports the co-existence of two mutually exclusive properties such as fluorescence and photocatalytic activity at their best in 0.6wt% erbium doped ZnO.

Synthesis and characterization of Bi1.56Sb1.48Co0.96O7 pyrochlore sun-light-responsive photocatalyst

Novel nanostructure pyrochlore Bi1.56Sb1.48Co0.96O7 was successfully synthesized via solid state reaction method in air. The as-synthesized photocatalyst was characterized by X-ray diffraction, Scanning electron microscopy and UV–vis diffuse reflectance spectroscopy techniques. The results showed that the BSCO was crystallized with the pyrochlore-type structure, cubic crystal system and space group Fd3m. The average particle size and band gap for BSCO were D=76.29nm and Eg=1.50eV respectively. Under the optimum conditions for discoloration of the dye: initial concentration of 20mgL−1 RhB, pH 7, 25°C, 0.5mL H2O2 and BSCO/dye mass ration of 1gL−1, 97.77 and 90.16% of RhB were removed with BSCO/H2O2 photocatalytic system within 60min of irradiation time under UVA- and SL irradiations respectively. Pseudo-second-order kinetic model gave the best fit, with highest correlation coefficients (R2≥0.99). On the base of these results, the mechanism of the enhancement of the discoloration efficiency was discussed. .

Utilization of polypyrrole coated iron-doped titania based hydrogel for the removal of tetracycline hydrochloride from aqueous solutions: Adsorption and photocatalytic degradation studies

The removal of tetracycline hydrochloride (TCH) from aqueous solutions with a novel photocatalyst, polypyrrole coated iron-doped titania polymerised with itaconic acid [poly(IA)-(Fe–TiO2–PPy)] was investigated in a batch system. All the prepared samples were characterized using scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Diffuse reflectance spectroscopy (DRS) techniques. The effects of pH, contact time, adsorbent dose and ionic strength on the adsorption of TCH onto poly(IA)-(Fe–TiO2–PPy) were investigated. The kinetic data were found to follow pseudo-second-order kinetic model. The equilibrium adsorption data were fitted to Langmuir isotherm model, with maximum adsorption capacity 149.25mg/g. Swelling capacity of the adsorbent relative to pH and time were also investigated. The photodegradation kinetics of TCH by the photocatalyst was found to follow Langmuir–Hinshelwood mechanism of first-order kinetics. Regeneration experiments and repeated use of adsorbent were tried for four cycles. From the results, it can be concluded that the prepared poly(IA)-(Fe–TiO2–PPy) could be an efficient adsorbent-cum-photocatalyst for the degradation of TCH form aqueous solutions under solar light.

Copper, copper oxide nanoparticles and copper complexes supported on mesoporous SBA-15 as catalysts in the selective oxidation of benzyl alcohol in aqueous phase

Copper(II) complexes, copper and copper oxide nanoparticles supported on SBA-15 have been prepared and their catalytic performance in benzyl alcohol oxidation in aqueous phase studied. Hybrid mesoporous SBA-15 functionalized with imidazole ionic liquid and functionalized with an amino alcohol chelate ligand have been used as solid supports in order to tether copper(II) complexes. From these materials, copper nanoparticles and copper oxide nanoparticles supported on SBA-15 have also been synthesized. Copper based materials have been characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 adsorption-desorption, transmission electron microscopy (TEM) with microanalysis by energy-dispersive X-ray (EDX), solid-state nuclear magnetic resonance spectroscopy (CP-MAS-NMR), Fourier-transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (DRUV-vis), thermogravimetric analysis (TG-DTG) and electrochemical techniques. The catalyst synthesized by immobilization of ionic liquid containing copper and followed by chemical reduction method showed the highest activity in the oxidation of benzyl alcohol with a 73% conversion and 54% selectivity of benzaldehyde (30 min reaction time). The stability of the catalysts has been also examined by voltammetry measurements.

Synthesis and characterization of reduced-graphene oxide/TiO2/Zeolite-4A: A bifunctional nanocomposite for abatement of methylene blue

Abstract A bifunctional nanocomposite photocatalyst that possesses high photocatalytic activity as well as enhanced adsorption capability was developed. The adsorption component, graphene oxide was synthesized following an improved oxidation method from graphite flakes; while the photoactive component, TiO2 was synthesized by the polymerizable sol–gel route. The as-synthesized graphene oxide was partially photo-reduced, and got anchored as reduced graphene oxide onto TiO2. The materials have been thoroughly characterized with XRD, FT-IR, Raman spectroscopy, TGA, SEM and diffuse reflectance spectroscopy techniques. This reduced-graphene oxide/TiO2 was dispersed over the Zeolite-4A and this nanocomposite hybrid system exhibited remarkable adsorption capability as well as high photocatalytic degradation efficiency for methylene blue.

Synergetic effects of Sr-doped CuBi2O4 catalyst with enhanced photoactivity under UVA- light irradiation.

Sr-doped CuBi2O4 micro-particles were successively synthesized via a solid-state technique and were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and UV-vis diffuse reflectance spectroscopy (UV-vis-DRS) techniques. Results show that Sr-doped CuBi2O4 was crystallized with a spinel-type structure and tetragonal crystal system, and the band gap energy was about 1.35eV. The as-prepared Sr-doped CuBi2O4 treated at 573°C for 12h exhibited the highest efficiency, as a result of 97.22% of CR degradation within 220min, which is approximately 31 times greater than CR photodegradation when catalyzed by CuBi2O4 (3.13%) and about 2.3 times superior than that catalyzed by the untreated Sr-doped CuBi2O4 sample (42.08%). Pseudo-first-order kinetic model gave the best fit, with highest correlation coefficients (R (2) = 0.94-0.97). The Sr-doping and extending reaction time up to 12h could be effective in producing Sr-doped CuBi2O4 materials that delay electron-hole recombination, thereby increasing the lifetime of the electron electron-hole separation and support the charge carrier transfer to the catalyst surface. On the basis of the calculated energy band positions, superoxide radical anions (O2 (•-)) were the main oxidative species responsible for the photocatalytic degradation of CR dye solution.

Fabrication of AgBr/Ag2CrO4 composites for enhanced visible-light photocatalytic activity

Ag2CrO4 and AgBr/Ag2CrO4 photocatalysts were synthesized by a simple precipitation reaction and were compared for their photocatlytic activity. These photocatalysts were characterized by X-ray diffraction, Scanning electron microscopy, Fourier transform infrared spectroscopy and UV–vis diffuse reflection spectroscopy techniques. The photocatalytic performance of the samples was evaluated by photocatalytic oxidation of rhodamine B (RhB) dye under visible-light irradiation. The results indicated that the AgBr/Ag2CrO4 exhibited a higher photocatalytic activity than the pure Ag2CrO4. The enhancement of photocatalytic activity was related to the stronger light absorption ability and also due to the fact that the insoluble AgBr effectively protected the Ag2CrO4 photocatalyst from dissolution in aqueous solutions to enhance its structural stability.

Synthesis and characterization of Ce, Cu co-doped ZnS nanoparticles

Ce, Cu co-doped ZnS nanoparticles were prepared at room temperature using a chemical co-precipitation method. The prepared nanoparticles were characterized by X- ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive analysis of X-rays (EDAX), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) and high resolution Raman spectroscopic techniques. Transmission electron microscopy (TEM) and X-ray diffraction studies showed that the diameter of the particles was around 2–3nm. Broadened XRD peaks revealed the formation of nanoparticles with a face centered cubic (fcc) structure. DRS studies confirmed that the band gap increased with an increase in the dopant concentration. The Raman spectra of undoped and Ce, Cu ions co-doped ZnS nanoparticles showed longitudinal optical mode and transverse optical mode. Compared with the Raman modes (276 and 351cm−1) of undoped ZnS nanoparticles, the Raman modes of Ce, Cu co- doped ZnS nanoparticles were slightly shifted towards lower frequency. PL spectra of the samples showed remarkable enhancement in the intensity upon doping.

Silver nanoparticles decorated anatase TiO2 nanotubes for removal of pentachlorophenol from water

One-dimensional nanotubes are promising materials for environmental applications. In this study, anatase TiO2 nanotubes (TNTs) were fabricated using an alkaline hydrothermal method at 130°C and then calcinated at 400°C for 2h. Ag nanoparticles were photo-deposited onto the TNTs for enhanced photodegradation of pentachlorophenol (PCP) under simulated solar light. The samples were characterized using transmission electron microscopy, physical adsorption of nitrogen, X-ray diffraction, X-ray photoelectron spectroscopy and UV–Visible diffuse reflectance spectroscopic techniques. The as-synthesized TNTs showed tubular structures with the outer and inner diameter of 9–10 and 5–6nm, respectively. The results showed that metallic Ag nanoparticles were uniformly dispersed on the TNTs surface, and Ag/TNTs exhibited significant visible-light absorption. After 180min irradiation, about 99% PCP was removed by Ag/TNTs (5.4at.%), compared to 54.3% by P25 and 59.4% by pure TNTs. This is attributed to the synergistic effects between Ag nanoparticles acting as traps to effectively capture the photo-generated electrons, and the localized surface plasmon resonance (LSPR) of Ag nanoparticles promoting the absorption of visible light. The intermediates during the PCP photodegradation were systematically analyzed, ruling out the existence of high toxic polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans. Ag/TNTs showed excellent stability even after five cycles.

Highly efficient photocatalytic degradation of methyl orange and Rhodamine B by hierarchical BiOBr microspheres

Hierarchical BiOBr microspheres were successfully synthesized via a solvothermal method by using the diethylene glycol(DEG) as the solvent and soft‐template. The as‐obtained products were characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM), N2 adsorption–desorption and UV–Vis diffuse reflectance spectroscopy(DRS) techniques. The formation mechanism for the growth of hierarchical BiOBr microspheres has been studied. The possible mechanism of photocatalysis has been discussed. Remarkably, the as‐prepared BiOBr microspheres has a large specific surface area, which can reach a maximum surface area of 55.9307 m2/g. In addition, the superior enhanced photocatalytic activities of BiOBr microspheres were evaluated by the photodegradation of methyl orange (MO) and Rhodamine B (RhB) under visible‐light illumination, which presented the efficiency up to 98.10% just within 50 min and 98.64% within 30 min, respectively. BiOBr microspheres can be a promising candidate as highly efficient photocatalyst for decompositing of organic contaminants for environmental remediation.

Enhanced photocatalytic removal of phenazopyridine by using silver-impregnated SiO2–TiO2 nanoparticles: optimization of synthesis variables

Silver-impregnated silicon oxide/titanium oxide nanoparticles (Ag/SiO2–TiO2) were prepared via impregnation method. X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and UV–Vis diffuse reflectance spectroscopy techniques were used for the characterization of prepared nanoparticles. The effects of synthesis variables such as nanoporous SiO2 content, Ag content, impregnation pH, and calcination temperature were studied in the photocatalytic activity of prepared nanoparticles in the removal of phenazopyridine as a model drug contaminant. Response surface methodology as a statistical technique was employed for modeling and optimizing synthesis variables. Results showed that the maximum removal efficiency (97.14 %) was achieved for Ag/SiO2–TiO2 nanoparticles at the optimized preparation conditions: SiO2 content of 34.68 wt%, Ag content of 2.36 wt%, impregnation pH of 5.1, and calcination temperature of 439 °C, whereas at the same conditions, using TiO2, SiO2–TiO2, and Ag–TiO2 samples lead to 50.14, 60.37, and 71.45 % removal efficiency, respectively. Coupling SiO2 with large surface area significantly enhanced adsorption of drug molecules, and also impregnation of Ag onto the hybrid system by its ability to trap electrons, provided a synergistic effect in the enhancement of the TiO2 nanoparticles photocatalytic activity.

In situ ion exchange preparation of AgBr/Ag3PO4/HAP nanocomposite photocatalyst with enhanced visible light photocatalytic performance

A novel AgBr/Ag3PO4/HAP (Ca10(PO4)6(OH)2) nanocomposite photocatalyst was prepared by a facile in situ ion exchange route. X-Ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy techniques were used to investigate the phase structure, composition, morphology and optical property of the AgBr/Ag3PO4/HAP product. Under visible light irradiation, as-synthesized AgBr/Ag3PO4/HAP catalyst exhibited the higher visible light photocatalytic activity than Ag3PO4/HAP and AgBr/Ag3PO4, and displayed a better stability compared with Ag3PO4/HAP. The AgBr/Ag3PO4/HAP photocatalyst had a higher photodegradation rate for rhodamine B (RhB, a cationic dye) than methyl orange (MO, an anionic dye) and showed the excellent photoactivity in the acid solution or in the basic solution. The superoxide radicals (O2−•) and holes (h+) were considered to be the main active species for dye degradation in the AgBr/Ag3PO4/HAP suspension.

Effect of polar and movable (OH or NH2 groups) on the photocatalytic H2 production of alkyl-alkanolamine: a comparative study

The photocatalytic production of molecular hydrogen (H2) from aqueous solutions of alkyl-alkanolamines (triethanolamine (tri-EOA), diethanolamine (di-EOA), ethanolamine (EOA), ethylamine (EA) and ethanol over Pt-loaded commercial (Sachtleben Hombikat UV100) nanoparticle titanium dioxide photocatalysts was studied. These photocatalysts were characterized using X-ray diffraction, Brunauer−Emmett−Teller, field-emission scanning electron microscopy, atomic force microscopy and UV–vis diffuse reflectance spectroscopy techniques. Effect of pH and temperature on photocatalytic hydrogen production of alkyl-alkanolamines was investigated. It was found for all molecules under study that the amount of hydrogen produced at a constant illumination time is a function of pH and temperature. At all temperatures investigated the rate of hydrogen production at pH 9 followed the order tri-EOAethanolamine >> di-EOA ≈ EOA > ethanol > EA. From the values of the photocatalytic rate constants at various temperatures, the apparent activation energies were determined for the hydrogen production. The observed dependence of the reaction rate on solution temperature cannot be related to light-driven reaction steps, because the band-gap energy of the semiconductor is too high for thermal excitation to become significant in the temperature range investigated.

Detoxification of hexavalent chromium in wastewater containing organic substances using simonkolleite-TiO2 photocatalyst

Innovative simple method for the preparation of simonkolleite-TiO2 photocatalyst with different Zn contents was achieved. The prepared photocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), FT-IR, Raman and diffuse reflectance spectroscopy techniques. The photocatalytic activities of the materials were evaluated for the simultaneous detoxification of hexavalent chromium (Cr(VI)) and oxidation of organic compounds commonly present in wastewater under simulated solar light. The best photoreduction efficiency of Cr(VI) has been achieved at 1000ppm simonkolleite-TiO2 photocatalyst of 5% Zn/TiO2 weight ratio, and pH value of 2.5 to enhance the adsorption onto catalyst surface. Photoreduction was significantly improved by using formic acid as holes scavenger owing to its chemical adsorption on the catalyst surface. Finally, 100% photoreduction of Cr(VI) could be achieved using formic/simonkolleite-TiO2 systems under sunlight.

Zinc oxide nanoparticles synthesis by electrochemical method: Optimization of parameters for maximization of productivity and characterization

In this study, zinc oxide nanoparticles were synthesized using electrochemical method. Zinc was used as electrode whereas oxalic acid in aqueous solution was used as an electrolyte. A L9 (34) Taguchi optimization methodology was used to find out the individual and interactive effect of all four independent experimental parameters namely pH (pHo): 5–8, oxalic acid concentration (m): 0.05–0.15M, conductivity (k): 20–30 (mS/cm) and operating voltage (Vo): 5–8V. These experimental parameters were optimized so as to maximize the productivity (g) and correspondingly find out specific energy consumption (kWh/kg) and specific electrode consumption (kg/kg). At the optimum condition of pHo=5, m=0.05M, k=30 (mS/cm) and Vo=8V, values of productivity, SENC and SELC were found to be 1.03g, 3.79kWh/kg and 1.76kg/kg, respectively. Nanoparticles synthesized at optimum conditions have been further characterized by scanning electron microscopy, X-ray diffraction and UV–Visible diffuse reflectance spectroscopy techniques so as to confirm its ZnO nature.

Synthesis of simple and novel biocomposite doped nanocrystalline tin oxide and its humidity sensing properties

The Hygrophila Spinosa T. Anders (HST) plant seed that contains mineral constituents were doped in SnO2 prepared by the conventional method. The structural parameters, functional groups, surface morphology, elemental analysis and optical behavior of the prepared samples was made using X-ray diffraction, Fourier transform-infra red, scanning electron microscope, energy dispersive X-ray analysis, diffuse reflectance spectroscopy techniques respectively have been studied. XRD-surface area for all the samples was obtained from the Williamson–Hall plot. Photoconductivity studies were carried out for all the samples prepared with different HST composition in SnO2. The negative photoconductivity was observed for the HST doped SnO2 and HS samples, except pristine SnO2. The SH2 sample with high specific surface area shows good response and recovery characteristics toward humidity.

Synthesis and Characterization of High Efficiency and Stable Spherical Ag3PO4 Visible Light Photocatalyst for the Degradation of Methylene Blue Solutions

A facile method for the synthesis of Ag3PO4 visible light photocatalyst has been developed to improve the photocatalytic activity and stability. The as‐prepared samples are investigated by X‐ray powder diffraction, scanning electron microscopy, infrared spectroscopy, photoluminescence (PL) spectroscopy, and UV‐Vis diffuse reflectance spectroscopy techniques. The results reveal that the prepared Ag3PO4 has cube structure with a band gap of 2.26 eV. The as‐prepared samples show higher photocatalytic activity for methylene blue (MB) degradation than that of N‐TiO2 under visible light irradiation.

ß‐Ga2O3 Nanorod Synthesis with a One‐step Microwave Irradiation Hydrothermal Method and its Efficient Photocatalytic Degradation for Perfluorooctanoic Acid

ß-Ga2O3 nanorod was first directly prepared by the microwave irradiation hydrothermal way without any subsequent heat treatments, and its characterizations were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), UV-Vis diffuse reflection spectroscopy techniques, and also its photocatalytic degradation for perfluorooctanoic acid (PFOA) was investigated. XRD patterns revealed that ß-Ga2O3 crystallization increased with the enhancement of microwave power and the adding of active carbon (AC). PFOA, as an environmental and persistent pollutant, is hard decomposed by hydroxyl radicals (HO·); however, it is facilely destroyed by ß-Ga2O3 photocatalytic reaction in an anaerobic atmosphere. The important factors such as pH, ß-Ga2O3 dosage and bubbling atmosphere were researched, and the degradation and defluorination was 98.8% and 56.2%, respectively. Reductive atmosphere reveals that photoinduced electron may be the major reactant for PFOA. Furthermore, the degradation kinetics for PFOA was simulated and constant and half-life was calculated, respectively.

AgI/Ag3PO4 hybrids with highly efficient visible-light driven photocatalytic activity

Highly efficient visible-light-driven AgI/Ag3PO4 hybrid photocatalysts with different mole ratios of AgI were prepared via an in situ anion-exchange method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) technique. Under visible light irradiation (>420nm), the AgI/Ag3PO4 photocatalysts displayed the higher photocatalytic activity than pure Ag3PO4 and AgI for the decolorization of acid orange 7 (AO 7). Among the hybrid photocatalysts, AgI/Ag3PO4 with 80% of AgI exhibited the highest photocatalytic activity for the decolorization of AO 7. X-ray photoelectron spectroscopy (XPS) results revealed that AgI/Ag3PO4 readily transformed to be Ag@AgI/Ag3PO4 system while the photocatalytic activity of AgI/Ag3PO4 remained after 5 recycling runs. In addition, the quenching effects of different scavengers displayed that the reactive h+ and O2− play the major role in the AO 7 decolorization. The photocatalytic activity enhancement of AgI/Ag3PO4 hybrids can be ascribed to the efficient separation of electron–hole pairs through a Z-scheme system composed of Ag3PO4, Ag and AgI, in which Ag nanoparticles act as the charge separation center.