Ultraviolet-visible Diffuse Reflectance Spectra Research Articles

Fabrication of Hybrid Fe2V4O13/ZnO Heterostructure for Effective Mineralization of Aqueous Methyl Orange Solution

A new nanocomposite composed of Fe2V4O13 and ZnO was synthesized using sol–gel technique. The properties of this compound were analyzed by performing X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray (EDX) spectrometry and elemental color mapping, high-resolution transmission electron microscopy (HR-TEM), ultraviolet–visible diffuse reflectance spectra (UV–Vis-DRS), and photoluminescence (PL) spectra measurements. A coupled semiconductor system was developed to enhance the photocatalytic efficiency of ZnO. The photocatalytic efficiency of 11 wt% Fe2V4O13/ZnO under UV-A light irradiation was ~ 1.25 times higher than that exhibited by bare ZnO. The enhanced photodegradation was ascribed to the high efficiency of charge separation of the e−/h+ pairs.

B–N co-doped black TiO2 synthesized via magnesiothermic reduction for enhanced photocatalytic hydrogen production

In this work, B–N co-doped TiO2 has been synthesized by a facile fast sol-gel method, and then, a controlled magnesiothermic reduction has been developed to synthesize B–N co-doped black TiO2 under a N2 atmosphere and at 580 °C followed by acid treatment. The prepared black TiO2 samples were characterized by X-ray diffraction, high resolution transmission electron microscopy, Raman spectrameter, photoluminescence emission spectra, X-ray photoelectron spectroscopy, and ultraviolet–visible diffuse reflectance spectra. It shows that the prepared samples possess a unique crystalline core-amorphous shell structure composed of disordered surface and oxygen vacancies, and exhibit enhanced photocatalytic activity in hydrogen production in the methanol-water system in the presence of Pt as a co-catalyst. Under the full solar wavelength range of light, the maximum hydrogen production rate of the B–N co-doped black TiO2 is 18.8 mmol h−1 g−1, which is almost 4 times higher than that of pure TiO2.

Simple Preparation of Hierarchically Porous Ce/TiO2/Graphitic Carbon Microspheres for the Reduction of CO2 with H2O under Simulated Solar Irradiation.

Hierarchically porous Ce/TiO2/graphitic carbon microsphere composites (xCe/TiO2/GCM, where x = 0.2, 1.0, 2.0, 5.0 mmol·L–1) were prepared for the first time by using a simple colloidal crystal template and characterized by X-ray diffraction, nitrogen adsorption and desorption, scanning electron microscopy, and ultraviolet–visible diffuse reflectance spectra. In addition, the photocatalytic activity of CO2 reduction by H2O under simulated solar irradiation was studied. The results showed that the Ce/TiO2/GCM composite material was characterized by large porosity, high concentration of metal compounds and graphitized carbon matrix, and the content of acetone solvent having a great impact on its form. In terms of the photocatalytic CO2 reaction, the CH4 and CO productions were 4.587 and 357.851 μmol·g–1, respectively. The 2Ce/TiO2/GCM photocatalyst gave the highest production rate for three products. Under simulated solar irradiation, the Ce/TiO2/GCM has excellent photocatalytic activity in the photoreduction of CO2 from H2O, which was related to the special composition and the Ce/TiO2/GCM structure.

Surfactant-assisted synthesis of direct Z-scheme AgBr/β-Ag2WO4 heterostructures with enhanced visible-light-driven photocatalytic activities

Compared with the conventional two-step ion exchange method used for the fabrication of AgBr/β-Ag2WO4 heterostructures, herein, a series of AgBr/β-Ag2WO4 direct Z-scheme heterostructures were efficiently fabricated via a simple surfactant-assisted one-step precipitation strategy. The phase structure, morphology, chemical composition as well as photocatalytic mechanism of the as-obtained AgBr/β-Ag2WO4 heterostructures were systematically characterized by using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Ultraviolet–Visible diffuse reflectance spectra (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), Photoluminescence spectrum (PL), photoelectrochemical tests. Photocatalytic degradation of Rhodamine (RhB) under visible light was carried out as a probe to assess its photocatalytic activity. The result indicates that AgBr/β-Ag2WO4-30% exhibits the highest photocatalytic activity, which is approximately 1.7 and 135.9 times as high as that of pure AgBr and pure β-Ag2WO4, respectively. The pathway of charge carriers separation and transfer in the AgBr/β-Ag2WO4 heterostructures and the direct Z-scheme mechanism were depicted in details based on the systematic characterizations and measurements. The enhancement of the photocatalytic performances of the as-prepared AgBr/β-Ag2WO4 heterostructures are mainly attributed to the larger specific surface area and Z-scheme system formed between these two semiconductors, leading to the spatial separation of the photoinduced electron and hole. This work may provide a new sight to understand the mechanism of AgBr/β-Ag2WO4 heterostructures, which is direct Z-scheme heterojunctions rather than type-II heterojunctions.

PVP-assisted hydrothermal synthesis and photocatalytic activity of single-crystalline BiFeO3 nanorods

One-dimensional, single-crystalline bismuth ferrite (BiFeO3) nanorods were successfully prepared by polyvinylpyrrolidone-assisted hydrothermal process. The crystal structure and morphology of the as-prepared BiFeO3 sample were characterized by X-ray diffraction (XRD), field emission scanning electron microscope and transmission electron microscopy. The XRD analysis reveals that single-phase BiFeO3 sample was obtained. Morphology observation shows that the as-formed BiFeO3 nanoparticles are the shape of nanorods. The band gap of the as-prepared BiFeO3 nanorods was identified by ultraviolet–visible diffuse reflectance spectrum. Meanwhile, the photocatalytic properties of the as-prepared BiFeO3 nanorods were evaluated by degrading Rhodamine B. The result revealed that the as-prepared BiFeO3 nanorods exhibit photocatalytic activity under visible light irradiation (λ ≥ 400 nm).

Synthesis and photoluminescence properties of a novel Ca2LaNbO6:Mn4+ double perovskite phosphor for plant growth LEDs

In this paper, a series of Ca2LaNbO6 (CLN):Mn4+ far-red phosphors with different doping concentration were successfully prepared by traditional high temperature solid state method at 1250 °C. The samples were characterized and analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence excitation (PLE) spectra, photoluminescence (PL) spectra, ultraviolet–visible diffuse reflectance spectra (UV–Vis DRS), temperature-dependent emission spectra and internal quantum efficiency (IQE). The particle size of CLN is < 3 μm. The strongest excitation peak of CLN:Mn4+ phosphors lies at 352 nm, which is attributed to the 4A2g → 2T2g transition of Mn4+ ions. The sample has a strong emission peak at 684 nm, which corresponds to the 2Eg → 4A2g energy level transition of Mn4+ ions. The optimum doping concentration of the sample is 0.03 mol%, and the quenching mechanism is dipole–quadrupole interaction. In addition, the thermal activation energy of the sample was calculated to be 0.368 eV. Importantly, under the excitation of near-ultraviolet light at 365 nm and driven by 25 mA current, the LED with CLN:0.0003Mn4+ emits bright far-red light. All the results indicated that CLN:Mn4+ phosphors have potential application value in indoor plant cultivation.

Immobilizing CuO/BiVO4 nanocomposite on PDA-templated cotton fabric for visible light photocatalysis, antimicrobial activity and UV protection

CuO/BiVO4 (BVO) nanocomposite photocatalyst was immobilized on cotton fabrics through polydopamine (PDA) templating for multiple application including highly efficient visible-light-driven photocatalysis, antimicrobial activity and UV protection. The morphology and structure of CuO/BVO nanocomposites and the coated fabrics were characterized by transmission electron microscopy (TEM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), Ultraviolet-visible diffuse reflectance spectra (UV–vis DRS), photoluminescence (PL) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and UV–Vis spectroscopy. The functionalized cotton fabrics were found to be highly effective in degradation of methylene blue (MB) under visible light irradiation with stability and recyclability, and about 97.7% of MB aqueous solution was degraded after 200 min exposure with 92.1% of the photocatalytic activity preserved even after five recycles. The mechanism of enhanced photocatalytic activity was proposed. The coated fabrics also demonstrated to be UV protective and antimicrobial. This work will benefit the development of durable and recyclable textile based photocatalysts with multiple function.

A composite of platelet-like orientated BiVO4 fused with MIL-125(Ti): Synthesis and characterization

The development of heterojunctions is the current focus of the scientific community as these materials are visible light active and the staggered positioning of their band edges combats electron-hole recombination which is the downside of most photocatalysts. In this work, a two- step hydrothermal synthesis protocol was utilized to fabricate a novel observable-light active material, composed of platelet-like BiVO4 and a titanium-based metal organic framework (MOF) called MIL-125(Ti). The tuning of specific morphologies, such as platelet-like in BiVO4, provides the exposure of most reactive facets which are more reactive towards photooxidation of organics in water, thus increasing their efficiency. The as-synthesized heterojunction was characterized by Transmission electron microscopy (TEM), scanning transmission microscopy (SEM), X-Ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS), X-Ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectra. The formation of the heterojunction lead to a positive shift of the 3-2 Bi:Ti valence band (VB) (1.78 eV) when compared to 1.27 eV VB position of BiVO4. The PL and photoelectrochemical measurements revealed that the heterojunction photocatalyst designated 3-2 Bi-Ti demonstrated inhibited recombination rate (platelet-like BiVO4 > 3-2 Bi:Ti (PM) > MIL-125 > 1–1 Bi:Ti > 2–3 Bi:Ti > 3-2 Bi:Ti) and highly efficient interfacial charge shuttle between platelet-like BiVO4 and MIL-125(Ti) through the formed n-n junction.

Graphene oxide based highly sensitive electrochemical sensor for detection of environmental pollutants and biomolecules

A simple and highly sensitive electrochemical sensor based on graphene oxide modified glassy carbon electrode (GO/GCE) is reported for the detection of hydrazine (HDZ), ascorbic acid (AA) and hydrogen peroxide (H2O2). GO nanosheets were synthesized by the oxidation of natural graphite powder via a modified Hummer’s method. The structural and surface characteristics of GO were investigated by x-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, Ultraviolet-visible diffuse reflectance spectra (UV–vis DRS) spectroscopy, Raman spectroscopy and thermogravimetric analysis (TGA). The electrochemical behaviour of the GO/GCE was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronoamperometry. Under optimized GO concentration, GO/GCE showed stable and admirable electrocatalytic response towards the oxidation of HDZ and AA, and the reduction of H2O2 at low over potentials. GO/GCE showed promising detection ability for HDZ, AA, and H2O2 with high sensitivity, wider linear detection range and lower LOD. The obtained LOD values were 1.04, 0.5 and 4 μM for HDZ, AA, and H2O2 respectively. Furthermore, GO/GCE exhibited good stability, reusability, reproducibility and anti-interference capability. The superior electrical conductivity, strong adsorptive ability and large surface area of GO nanosheets are responsible for the excellent electrocatalytic activity of the present GO-based sensor. This study reveals that GO is a promising candidate as the electrochemical sensor.

In situ preparation of g-C3N4/Bi4O5I2 complex and its elevated photoactivity in Methyl Orange degradation under visible light

A graphite carbon nitride (g-C3N4) modified Bi4O5I2 composite was successfully prepared in-situ via the thermal treatment of a g-C3N4/BiOI precursor at 400°C for 3 hr. The as-prepared g-C3N4/Bi4O5I2 showed high photocatalytic performance in Methyl Orange (MO) degradation under visible light. The best sample presented a degradation rate of 0.164 min-1, which is 3.2 and 82 times as high as that of Bi4O5I2 and g-C3N4, respectively. The g-C3N4/Bi4O5I2 was characterized by X-ray powder diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectra (DRS), electrochemical impedance spectroscopy (EIS) and transient photocurrent response in order to explain the enhanced photoactivity. Results indicated that the decoration with a small amount of g-C3N4 influenced the specific surface area only slightly. Nevertheless, the capability for absorbing visible light was improved measurably, which was beneficial to the MO degradation. On top of that, a strong interaction between g-C3N4 and Bi4O5I2 was detected. This interplay promoted the formation of a favorable heterojunction structure and thereby enhanced the charge separation. Thus, the g-C3N4/Bi4O5I2 composite presented greater charge separation efficiency and much better photocatalytic performance than Bi4O5I2. Additionally, g-C3N4/Bi4O5I2 also presented high stability. •O2- and holes were verified to be the main reactive species.

Synthesis and photocatalytic activity of YVO 4 nanocrystals through ethylenediaminetetraacetate‐assisted hydrothermal process

Tetragonal YVO4 nanoparticles of different sizes were successfully prepared through an ethylenediaminetetraacetate -mediated hydrothermal method. The crystalline structure and optical property were characterised by transmission electron microscopy (TEM), high resolution TEM, X-ray diffraction, photoluminescence spectra, and ultraviolet–visible diffuse reflection spectra, respectively. The as-prepared YVO4 displayed excellent photocatalytic performance. Among them, sample S2 has the highest photocatalytic activity with a photodegradation efficiency of 85% within 180 min illumination, which is due to its smaller size and larger specific surface area. The investigation on the photocatalytic mechanism reveals that hydroxyl radical (•OH) is the main active species in the photocatalytic oxidation process.

Synthesis of Ni12P5 on Co3S4 material for effectively improved photocatalytic hydrogen production from water splitting under visible light

Building a good catalyst with high efficiency and low cost is a key step in photocatalytic hydrogen production. In this study, catalyst Ni12P5 is successfully modified on Co3S4 by two step hydrothermal methods. The catalyst Ni12P5 has a good promoting effect on the photocatalytic hydrogen production of Co3S4. Composite samples 8% Ni12P5/Co3S4 had the highest photocatalytic hydrogen production activity, and the hydrogen yield reach 4922.4 μmol g−1 h−1, which is 4.8 times higher than that of the original Co3S4 under visible light. The composite sample Ni12P5/Co3S4 maintains good stability of photocatalytic hydrogen production in three cycles. Ni12P5/Co3S4 samples are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Ultraviolet–visible diffuse reflectance spectra (UV–Vis DRS), X-ray photoelectron spectroscopy (XPS), electrochemistry and fluorescence (PL), and their physical and chemical properties was analyzed. Electrochemical measurements show that the enhancement of photocatalytic activity is attributed to the high separation and migration of photoinduced electrons and holes, which is consistent with the photocatalytic hydrogen production activity. The results provide a novel idea for the synthesis of other non-noble metal composite photocatalyst, and have important inspiration significance.

Novel method of constructing CdS/ZnS heterojunction for high performance and stable photocatalytic activity

A series of CdS/ZnS heterojunction nanocomposites with different contents of CdS were successfully synthesized through liquid-phase thermal decomposition of a single precursor and ion adsorption method. The structures and properties of these nanocomposites were characterized by XRD, SEM, TEM, ultraviolet visible diffuse reflectance spectrum, electrochemical workstation and photodegradation test. Therefore, the influences of different contents of CdS on the photocatalytic performance of as-prepared samples were demonstrated explicitly. The CdS/ZnS (7:1) nanocomposite exhibited the highest photocatalytic efficiency when exposed to ultraviolet light for 35 min, the degradation efficiencies of rhodamine B (RhB) and methylene blue reached 96.1% and 99.6%, respectively, which is higher than other reported CdS/ZnS based photocatalysts. Moreover, with a 10-cycle test of the degradation of RhB under natural light, the degradation efficiency remained around 96%, showing the desirable photocatalytic stability of CdS/ZnS (7:1) nanocomposite. The approach provides new possibility to produce other metal sulfide nanocomposites.

The Enhancement of H2 Evolution over Sr1-1.5xTbxWO4 Solid Solution under Ultraviolet Light Irradiation.

In this work, Sr1−1.5xTbxWO4 (0 ≤ x ≤ 0.2) solid solutions were synthesized via a traditional high-temperature solid state method. Le Bail fitting on the powder X-ray diffraction (XRD) pattern showed that these solid solutions are pure phase. Scanning electron microscopy showed that the SrWO4 and Sr0.82Tb0.12WO4 samples are composed of micrometer particles and submicron crystallites, respectively. Ultraviolet–visible diffuse reflectance spectra suggested that the bandgaps of Sr1−1.5xTbxWO4 are narrower than the undoped sample. The Sr0.82Tb0.12WO4 sample, with the assistance of 1.5 wt % Ru-cocatalyst, exhibits the best performance for H2 evolution in 5 vol % aqueous triethanolamine (TEOA), which results in about 6.1 and 2.8 times efficiency improvement compared with the intrinsic SrWO4 in methanol and aqueous TEOA, respectively. All the photocatalysts recycled after the photocatalytic reactions showed no degradation when checked by powder XRD.

Synthesis, Characterization and Optical Activity of RE-doped ZnWO4 Nanorods and Nanospheres by Hydrothermal Method

This work has investigated the effect of different dopants on structure, morphology and optical property of ZnWO 4. Rare-earth doped ZnWO 4 (ZnWO 4 :RE, with 0.5, 1, and 2 mol% of Eu 3+ and Pr 3+ ) were successfully synthesized by coprecipitation method followed by microwave-assisted hydrothermal system at 140 °C for 1 h. XRD indicated that the crystals have a wolframite- type monoclinic structure and with the addition of dopants the crystallite size decreased. HR-TEM images revealed interesting homogenous nanorods for pure ZnWO 4 crystals with grow along (021) direction. For ZnWO 4 : RE we have found nanospheres morphologies, in which the decreasing crystal size were dependent on the RE doping concentration. IR spectra confirm the crystals structure. Ultraviolet–Visible diffuse reflectance spectra indicated that the optical band gap varies with increasing replacement of Zn 2+ by RE ions. E gap was characteristic of semiconductor materials. DOI: http://dx.doi.org/10.17807/orbital.v11i2.1350

Photocatalytic activity of mesoporous WO3/TiO2 nanocomposites for the photodegradation of methylene blue

The mesoporous WO3/TiO2 photocatalysts with different loadings of WO3 (5, 10 and 15) wt% were used to remove methylene blue (MB) from aqueous solution. The prepared photocatalysts were characterized by XRD, FTIR, BET, SEM and EDX analysis. The XRD showed that the samples 10 and 15 wt% WO3/TiO2 have signals of anatase and rutile phases of TiO2. FTIR results showed that more hydroxyl groups bind onto the surface of the sample 10 wt% WO3/TiO2 which enhances the photodegradation as they yield OH. The ultraviolet visible diffuse reflection spectra (DRS) indicated that the addition of WO3 to TiO2 decrease the band gap energy from 3.11 to 2.92 eV. The photocatalytic measurements showed that the addition of WO3 to the surface of TiO2 increased the photodegradation of MB to 99% after 3 h on the sample 10 wt% WO3/TiO2. Further addition of WO3 particles agglomerate on TiO2 surface and decrease the photodegradation. The kinetic studies confirmed that the photocatalytic degradation of MB follows the kinetics of the pseudo-first-order model.

Band gap tuning of g-C3N4 via decoration with AgCl to expedite the photocatalytic degradation and mineralization of oxalic acid

A series of functional organic–metal AgCl-decorated graphitic carbon nitride (AgCl-CNx) composites were synthesized and applied for the degradation of oxalic acid (OA) under visible light. The highest photocatalytic activity was achieved with AgCl decoration ratio of 1.0 (denoted as AgCl-CN1.0). The pseudo-first-order constant for OA degradation was 0.0722 min−1 with the mineralization efficiency of 90.80% after 60 min reaction in the photocatalytic process with AgCl-CN1.0. A variety of characterization techniques including Brunauer–Emmett–Teller, X-ray diffraction, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectra, ultraviolet–visible diffuse reflectance spectra, photoluminescence, and Mott–Schottky were utilized to elucidate the physicochemical, microstructure, and optical properties contributing to the improvement of the photocatalytic performance. The results showed that AgCl-CN1.0 had an oblate flaky erythrocyte-like structure with a moderate band gap energy of ~3.00 eV. In addition, the effects of the key parameters (i.e., AgCl-CN1.0 dosage, initial OA concentration, solution pH, and presence of natural organic matter) on OA degradation were systematically investigated. Radical scavenger experiments indicated that photogenerated holes, electrons, superoxide anion radicals, and hydroxyl radicals were the dominant reactive species. Moreover, AgCl-CN1.0 exhibited excellent stability and reusability for OA degradation without detectable Ag+ release in the solution over multiple reaction cycles. The efficient OA mineralization could be mainly ascribed to the moderate specific surface area, increased numbers of active sites, and effective interfacial charge transfer of AgCl-CN1.0. Overall, the AgCl-CN1.0 composite was demonstrated to be a highly efficient, stable, and recoverable photocatalyst.

Synergetic effect of BiOCl/Bi12O17Cl2 and MoS2: in situ DRIFTS investigation on photocatalytic NO oxidation pathway

The BiOCl/Bi12O17Cl2@MoS2 (BOC-MS) composites were successfully synthesized by a facile method at room temperature. The physicochemical properties of the as-obtained samples were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible diffuse reflection spectra (UV–Vis DRS), photoluminescence (PL), Brunauer–Emmett–Teller–Barrett–Joyner–Halenda (BET–BJH), and electron spin resonance (ESR) in detail. Moreover, the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was applied to elucidate the adsorption and photocatalytic reaction mechanism. The optimized BOC-MS-1.0 composites exhibited excellent visible light photocatalytic capability (51.1%) and photochemical stability for removal of NO. Based on the DMPO-ESR spin trapping, the ·O2− radicals and ·OH radicals were identified as the main active species generated from BOC-MS-1.0 under visible light irradiation. The enhanced photocatalytic performance can be ascribed to the positive synergetic effect of the MoS2 and the effective carrier separation ability.

Photodegradation of Microcystin-LR Using Visible Light-Activated C/N-co-Modified Mesoporous TiO2 Photocatalyst

Microcystin-LR (MC-LR), a potent hepatotoxin produced by the cyanobacteria, is of increasing concern worldwide because of severe and persistent impacts on humans and animals by inhalation and consumption of contaminated waters and food. In this work, MC-LR was removed completely from aqueous solution using visible-light-active C/N-co-modified mesoporous anatase/brookite TiO2 photocatalyst. The co-modified TiO2 nanoparticles were synthesized by a one-pot hydrothermal process, and then calcined at different temperatures (300, 400, and 500 °C). All the obtained TiO2 powders were analyzed by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscope (TEM), specific surface area (SSA) measurements, ultraviolet-visible diffuse reflectance spectra (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and photoluminescence (PL) analysis. It was found that all samples contained mixed-phase TiO2 (anatase and brookite), and the content of brookite decreased with an increase in calcination temperature, as well as the specific surface area and the content of non-metal elements. The effects of initial pH value, the TiO2 content, and MC-LR concentration on the photocatalytic activity were also studied. It was found that the photocatalytic activity of the obtained TiO2 photocatalysts declined with increasing temperature. The complete degradation (100%) of MC-LR (10 mg L−1) was observed within 3 h, using as-synthesized co-modified TiO2 (0.4 g L−1) at pH 4 under visible light. Based on the obtained results, the mechanism of MC-LR degradation has been proposed.

Room Temperature Synthesis of V-Doped TiO₂ and Its Photocatalytic Activity in the Removal of Caffeine under UV Irradiation.

In this work, the influence of simple acids in the room temperature sol-gel synthesis of TiO2 was investigated and the efficiency of prepared photocatalysts was evaluated in the removal of caffeine. To improve the photoactivity of TiO2, vanadium-doped TiO2 (VTiO2) samples were obtained starting from different amount of vanadyl sulphate as a dopant source. The samples were centrifuged, washed and finally dried at room temperature, and no calcination step was carried out. The prepared photocatalysts were characterized by different techniques (X-ray powder diffraction (XRD), specific surface area (SSA), ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) and Raman). VTiO2 photocatalysts were tested in the photocatalytic removal of aqueous solutions containing caffeine. The photocatalytic tests were carried out in a recirculating batch cylindrical photoreactor irradiated by a UV LEDs strip (nominal power of 12 W and wavelength emission peak at about 365 nm) surrounding the external surface of the reactor. The optimized VTiO2 photocatalyst was able to reach a caffeine degradation of about 96% after 360 min of UV light irradiation with a total organic carbon (TOC) removal of 72%.