Visible Light Sensitive Photocatalyst Research Articles

Synthesis of visible light-sensitive photocatalysts for hydrogen production

Photocatalysis is a promising way to produce green hydrogen from water under sunlight. However, it is still challenging to develop an efficient photocatalyst for hydrogen production that works under sunlight with high efficiency. In this study, sincere efforts have been made to develop a photocatalyst with enhanced light absorption within the visible spectrum and improved separation of photogenerated electron-hole (e-/h+) pairs. Phosphorus and Nickel codoped TiO2 (PNT) photocatalysts were synthesized through the sol–gel method by varying the amount of phosphoric acid, nickel nitrate, and calcination temperature. Photoluminescence and UV–Vis spectroscopy confirm that codoping enhances the separation of photogenerated e-/h+ pairs as well as improves visible light absorption. Codoped TiO2 had a higher specific surface area and higher pore volume than doped and pure TiO2. 1.5 wt% P and 3.0 wt% of Ni codoped TiO2 calcined at 400 °C (3.0 PNT 400 °C) shows the highest H2 production from water (266.471 μmolg-1h−1) and simulated seawater (148.536 μmolg-1h−1) under solar simulator bulbs in the presence of Ethylene Glycol (10 vol%). This photocatalyst exhibits good stability, with a slight reduction in hydrogen production of 9.15 % in water and 14.8 % in simulated seawater after four cycles.

Ce-doped TiO2-zeolite fibers: visible light-driven photocatalysts for indigo dye degradation.

Indigo dye is a poisonous dye that threatens human health by polluting the environment. Therefore, we prepared a visible light-sensitive photocatalyst to eliminate indigo dye especially from water sources. In this study, sol-gel and electrospinning methods have been performed to synthesize Ce-doped TiO2-zeolite fibers for indigo degradation. The structural and optical properties of the synthesized fibers were investigated by XRD, SEM, EDX, and UV-Vis spectrophotometer techniques. It has been shown that 3% Ce-doped TiO2/zeolite fibers have the highest photocatalytic activity with 100% degradation after 150h, showing that the light absorption of TiO2 expands into the visible light area by Ce doping and absorption into the zeolite. The recyclability analyses of the spent photocatalyst exhibited 87.0% degradation of indigo after four cycles, demonstrating the stability of the fiber. An effective photocatalyst has been obtained by improving the photocatalytic and electrochemical properties thanks to the fibers' high surface area and the zeolite's porous structure. Based on these findings, the study reveals the significant potential of Ce-doped TiO2/zeolite fibers for the purification of wastewater under visible light.

Book Review Advanced Materials for Wastewater Treatment and Desalination: Fundamentals to Applications

Book Review Advanced Materials for Wastewater Treatment and Desalination: Fundamentals to Applications

Zeolite Y-supported carbon-doped TiO2 nanocomposites: Efficient solar photocatalysts for the purification of medicinal wastewater

The existence of antibiotics in aquatic streams destroys water quality and thereby poses serious ecological hitches. Photocatalysis involving nanosemiconductors is an environmentally benign technique for the mineralization of antibiotics. Herein, we prepared a new visible light-sensitive photocatalyst, zeolite Y-supported carbon-doped TiO2 nanocomposite (zeolite Y-c-TiO2), for the elimination of cefazolin antibiotic in wastewater systems. The structural and optical properties of the synthesized nanocomposites were investigated by Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller surface area analysis (BET) as well as diffuse reflectance spectroscopy (UV-DRS) and photoluminescence spectroscopy (PL). The UV-Vis absorbance spectrum of zeolite Y-c-TiO2 exhibited a red shift towards longer wavelength with an increase in visible light absorption as compared to pure TiO2 nanoparticles and zeolite Y-supported TiO2 nanocomposites (zeolite Y-TiO2). Accordingly, the photocatalytic action of the zeolite Y-c-TiO2 for the degradation of methylene blue was evaluated under solar simulator, and it turned out to be highly efficient (100%) mineralization as compared to TiO2-nanoparticles (42%) and zeolite Y-TiO2 (62%) after 70 min irradiation for a 50mg L-1 methylene blue solution. Radical scavenging experiments revealed the involvement of hydroxyl radicals, superoxide radicals, and photogenerated holes in the degradation process. Consequently, zeolite Y-c-TiO2 was applied for the photocatalytic degradation of the cefazolin antibiotic in water, and complete degradation of cefazolin (50 mg L-1) was observed within 6 h of solar light irradiation on zeolite Y-c-TiO2. The degradation pathway of cefazolin was proposed by considering various intermediates detected via LC-MS analysis. The study points to the significant potential of zeolite Y-c-TiO2 photocatalyst for the purification of medicinal wastewater under sunlight.

Hydrogen production by cracking of ammonium hydroxide using liquid-phase plasma on the modified TiO2 photocatalysts

Ammonia is a promising material as a direct source of green hydrogen production. This paper reports a method for mass production of hydrogen from liquid NH3(NH4OH) through a photocatalytic decomposition reaction using liquid plasma. In this reaction, the highest hydrogen production rate was observed in the TiO2 photocatalyst doped with N and metal ions as a photocatalyst sensitive to visible light with a low bandgap. At this time, the hydrogen production rate was obtained as about 142 L/g∙h. This is due to the high photoactivity of the visible light-sensitive photocatalyst in liquid plasma emitting strong visible light and ultraviolet light. The H2 production rate obtained from the decomposition of liquid NH3 by plasma discharge to the catalyst was higher than the H2 production rate obtained from the NH3 electrolysis process.

The utilization of ball-mill in the fabrication of metallic titanium incorporated carbon nitride as an active visible light sensitive photocatalyst

• Metallic Ti incorporated into g-carbon nitride by using ball-mill followed by calcination. • The characterization data confirmed the presence of Ti nanoparticles encapsulated by the g-CN layers. • The incorporation of metallic Ti did not influence the bandgap energy of g-C 3 N 4 (2.75 eV). • The fabricated materials exhibited high photocatalytic performance in the decolourization of arsenazo III dye solution. Titanium metal (Ti) nanoparticles were incorporated into graphitic carbon nitride (CN) though one-pot synthesis solvent-free procedure. Three samples with different metallic Ti content (2, 5 and 10 wt%) were fabricated based on a thermal treatment for a mixture prepared by ball-mill. The prepared materials were characterized by several techniques such as inductively coupled plasma (ICP) for elemental analysis, X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HR-TEM), and diffuse reflectance UV–vis spectroscopy. The obtained data showed that Ti nanoparticles were incorporated into CN layers without significant change in the optical properties of CN. From application point of view the photocatalytic performance of the prepared Ti-CN samples was studied in the decolourization reaction of an Arsenazo III (ArIII) dye solution under the illumination of visible light (wavelength > 420 nm). The obtained results showed that Ti-CN samples are highly photocatalytic active in which all the prepared samples were able to photocatalyze 100% decolourization of the dye solution. An obvious trend was observed, in which the rate of the decolourization reaction is proportional to the Ti content up to 10 wt%. The sample with 10 wt% Ti exhibited the highest activity, moreover, recycling of the same sample was also examined and the sample showed promising stability.

Immobilization of bismuth oxychloride on cellulose nanocrystal for sunlight-driven superior photosensitized degradation

Semiconductor photocatalysis is considered to be an important green technology for sewage treatment. However, most of the pollutant degradation studies used simulated sunlight in a laboratory, which has great energy cost with limited applications in industry. Herein, cellulose nanocrystal (CNC) with rich hydroxyl groups and high specific surface area are used as the matrix to construct composites with BiOCl, which improves the dispersibility with an increased number of oxygen vacancies on BiOCl. The obtained composite photocatalyst, i.e., BiOCl/CNC, showed an excellent performance with good recyclability. Within 30 min, 99% of RhB (20 mg/L) was degraded under simulated visible light and 94% under natural sunlight. The reaction system maintains excellent catalytic performance after being scaled up by 10×. Compared with reported BiOCl-based composites in literature, BiOCl/CNC had excellent photocatalytic activity for the RhB degradation with good recyclability. Subsequently, by identifying the active species, a reasonable photocatalytic mechanism was proposed for RhB degradation. This work developed an economical and effective visible light sensitive photocatalyst for the treatment of organic dyes in water.

Photocatalytic hydrogen production using liquid phase plasma from ammonia water over metal ion-doped TiO2 photocatalysts

Ammonia can be applied as a hydrogen carrier and used directly as a hydrogen production supply. In this paper, a technique for mass-producing hydrogen from ammonia water is proposed by applying a liquid phase plasma (LPP) discharge technique and a photocatalyst. In this reaction, N- and Fe ion codoped TiO2 (N/Fe/TiO2) photocatalysts were prepared and applied as a visible light-sensitive photocatalyst. N/Fe/TiO2 (NFT) had a similar crystal shape and size to anatase TiO2, but the surface was doped with metal ions. The bandgap of the NFT photocatalyst obtained from the spectrum measured by photoluminescence spectroscopy was approximately 2.4 eV. Nitrogen and Fe ions played a role in narrowing the gap between the conduction band (CB) and valence band (VB) of TiO2, effectively reducing the bandgap. In the decomposition reaction of ammonia water by LPP irradiation, the NFT photocatalyst showed the highest hydrogen evolution rate. The amount of hydrogen produced from ammonia water by LPP irradiation on the NFT photocatalyst was approximately 133 L/h. The hydrogen production rate obtained from ammonia water by the photocatalyst and LPP irradiation was significantly higher than that obtained by the ammonia electrolysis process.

3D-printed photoreactor with robust g-C3N4 homojunction based thermoset coating as a new and sustainable approach for photocatalytic wastewater treatment

Recently, the rapid technological advancement in photocatalysis has gained popularity as a means of addressing climate change and environmental degradation issues. The rapid surge in interest for 3D-printing process has delivered solutions for a broad spectrum of needs primarily due to its flexibility, cost effectiveness and environmental friendliness. In addition, the development in synergizing photocatalysis and 3D-printing technology has provided an optimistic outlook for sustainable wastewater treatment. In present study, a 3D-printed photocatalytic reactor was successfully designed and constructed via digital light processing technique. Besides that, a visible-light sensitive photocatalyst, graphitic carbon nitride homojunction was synthesized via a facile hydrothermal approach. The as-developed photocatalyst was then prepared in a form of thermoset coating and subsequently applied onto the base of 3D-printed photoreactor. A series of characterization tests were conducted to gain an in-depth understanding of the surface morphology and topology, chemical structure, thermal stability, elemental compositions, and surface wettability of the photocatalyst system. The photocatalytic performance of the graphitic carbon nitride homojunction-based thermoset coating was evaluated via Rhodamine B (RhB) dye degradation under the irradiation of a 50 W LED light. A removal efficiency of 95.62% was achieved within 24 h with a corresponding kinetic rate constant of 2.1 × 10−3 min−1. The recyclability of the photocatalytic system was verified by assessing its photoactivity for five consecutive cycles and retained 98.5% of its initial photoactivity. Overall, this research work may intrigue more exploration between interdisciplinary researchers in the field of photocatalysis and additive manufacturing, especially for sustainable environmental remediation.

Development of Visible Light Sensitive Photocatalyst Composed of Vitamin B12 and Metal Ions Modified TiO2

TiO2 is one of the most promising photocatalyst with excellent efficiency and stability in photocatalytic reaction. However, TiO2 can only be activated under UV light irradiation because of the wide band gap. Recently, several metal ions surface modified TiO2 (M–TiO2) has been developed as a visible light sensitive photocatalysis1. Visible light irradiation initiates effective charge transfer between metal ions and TiO2.Here, we report novel visible light driven photocatalyst (B12−M−TiO2) composed of the vitamin B12 derivatives which is unique cobalt complex and several M–TiO2 and introduce visible light-induced green molecular transformations mediated by B12-M-TiO2 2.Reference[1] M. Okazaki, Y. Wang, T. Yokoi, K. Maeda, J. Phys. Chem. C, 2019, 123, 10429.[2] K. Shichijo, M. Fujitsuka, Y. Hisaeda, H. Shimakoshi, J. Organomet. Chem., 2020, 907, 121058. Figure 1

Antiviral Effect of Visible Light-Sensitive CuxO/TiO2 Photocatalyst

Photocatalysis is an effective technology for preventing the spread of pandemic-scale viruses. This review paper presents an overview of the recent progress in the development of an efficient visible light-sensitive photocatalyst, i.e., a copper oxide nanoclusters grafted titanium dioxide (CuxO/TiO2). The antiviral CuxO/TiO2 photocatalyst is functionalised by a different mechanism in addition to the photocatalytic oxidation process. The CuxO nanocluster consists of the valence states of Cu(I) and Cu(II); herein, the Cu(I) species denaturalizes the protein of the virus, thereby resulting in significant antiviral properties even under dark conditions. Moreover, the Cu(II) species in the CuxO nanocluster serves as an electron acceptor through photo-induced interfacial charge transfer, which leads to the formation of an anti-virus Cu(I) species and holes with strong oxidation power in the valence band of TiO2 under visible-light irradiation. The antiviral function of the CuxO/TiO2 photocatalyst is maintained under indoor conditions, where light illumination is enabled during the day but not during the night; this is because the remaining active Cu(I) species works under dark conditions. The CuxO/TiO2 photocatalyst can thus be used to reduce the risk of virus infection by acting as an antiviral coating material.

Preparation of Y3+-doped BiOCl photocatalyst and its enhancing effect on degradation of tetracycline hydrochloride wastewater

Abstract Novel, visible light-sensitive photocatalysts of yttrium-doped bismuth oxychloride (Y–BiOCl) were successfully fabricated through consecutive solvent-based and thermal processes. Several characterization strategies were employed to analyze the morphologies, chemical properties, and photocatalytic performances of the catalysts. Compared to pure BiOCl, Y–BiOCl catalysts displayed superior photocatalytic capability for visible light-induced tetracycline hydrochloride (TC) removal. Photocatalytic activity was maximized at 15-wt% Y-doping, with the resulting Y–BiOCl catalyst achieving 90.3% TC removal efficiency within only 60 min, as well as high stability and reusability. Y3+ was discovered to displace Bi3+ in the BiOCl lattices, inducing lattice distortion and thereby raising the concentration of oxygen holes and defects. Y3+-doping also narrowed the bandgap of BiOCl and significantly decreased the bandgap energy, thereby decreasing the photocarrier recombination rate and enhancing photocatalytic activity. The main accomplishment of this study was the development of a promising photocatalytic material for removing organic compounds from wastewater.

A novel ternary Pd-GO/N-doped TiO2 hierarchical visible-light sensitive photocatalyst for nanocomposite membrane

We investigated the visible-light sensitive photocatalytic ability of a designed ternary Pd-GO/TiON nano-composite for use as an effective photocatalyst in membranes. We succeeded in synthesizing the TiO2-based photocata-lyst for Suzuki coupling reaction and application of this photocatalyst for fabricating high performance photocatalytic membrane. In this regard, palladium metal as a complementary metal in combination with N-doped TiO2 (TiON) and graphene oxide (GO) nanosheets was utilized to synthesize the upgraded version of the visible light sensitive nanocom-posite photocatalyst. The synthesis of Pd-GO/TiON hierarchical nanostructure was confirmed by detecting Ti, Pd, C, O and N elements by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) and EDX mapping analysis. Then, a series of PVDF-based photocatalytic nanocomposite membranes (PhNMs) filled with Pd-GO/TiON was fabricated. Evaluating the yield of Pd-GO/TiON photocatalyst was around 99% and 70% for heterogeneous system and the prepared PhNM containing 3% Pd-GO/TiON, respectively. Although, yield of Pd-GO/TiON photocatalyst in membrane is not comparable with the high yield reported by other researchers in heterogeneous system; however, it can be considered as a valuable result because of the importance of photocatalytic reactions and the environmental advantages of membrane technology. Furthermore, various analyses were also performed to study the synthesized photocata-lysts and the prepared photocatalytic membranes, including thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and diffuse reflectance spectrophotometry (DRS).

Synthesis of zinc germanium oxynitride nanotube as a visible-light driven photocatalyst for NOx decomposition through ordered morphological transformation from Zn2GeO4 nanorod obtained by hydrothermal reaction

Oxynitrides with narrow band gap are promising materials as visible-light sensitive photocatalysts, because introduction of nitrogen ions can negatively shift the position of valence band maximum of the corresponding oxides to negative side. (Zn1+xGe)(N2Ox) with wurtzite structure is one of the oxynitride materials. (Zn1+xGe)(N2Ox) with nanotube morphology was synthesized by nitridation of Zn2GeO4 nanorods at 800 °C for 6 h. During the nitridation process, the nanorod with smooth surface was transformed into nanotube with rough surface in spite of no template for formation of tube structure. The nanotube formation can be caused by ordered morphological transformation from Zn2GeO4 nanorod during the nitridation. (Zn1+xGe)(N2Ox) nanotube exhibited a large specific surface area due to its nanotube morphology and the ability to be responsive to visible light because of the narrow band gap of 2.76 eV. Compared to (Zn1+xGe)(N2Ox) synthesized by conventional solid state reaction, the optimized (Zn1+xGe)(N2Ox) nanotube possessed enhanced photocatalytic NOx decomposition activity under both ultraviolet and visible light irradiation.

Design of Advanced Functional Materials Using Nanoporous Single-Site Photocatalysts.

Nanoporous silica solids can offer opportunities for hosting photocatalytic components such as various tetra-coordinated transition metal ions to form systems referred to as "single-site photocatalysts". Under UV/visible-light irradiation, they form charge transfer excited states, which exhibit a localized charge separation and thus behave differently from those of bulk semiconductor photocatalysts exemplified by TiO2 . This account presents an overview of the design of advanced functional materials based on the unique photo-excited mechanisms of single-site photocatalysts. Firstly, the incorporation of single-site photocatalysts within transparent porous silica films will be introduced, which exhibit not only unique photocatalytic properties, but also high surface hydrophilicity with self-cleaning and antifogging applications. Secondary, photo-assisted deposition (PAD) of metal precursors on single-site photocatalysts opens up a new route to prepare nanoparticles. Thirdly, visible light sensitive photocatalysts with single and/or binary oxides moieties can be prepared so as to use solar light, the ideal energy source.

Fabrication of Ag/AgBr/Bi2WO6 hierarchical composites with high visible light photocatalytic activity

Visible-light sensitive photocatalyst Ag/AgBr/Bi2WO6 was successfully synthesized by oil/water self-assembly method. The crystalline structure, morphologies and optical properties of the as-prepared samples were investigated. The results revealed that the Ag/AgBr successfully introduced into the surface of Bi2WO6. The modified of Ag/AgBr enhanced the absorption in the visible-light region, due to surface plasmonic resonance of the metallic Ag. The activities of as-prepared samples were investigated by the degradation of RhB and phenol under the visible-light. Experimental results revealed that the Ag/AgBr/Bi2WO6 composites exhibit high visible-light photocatalytic activity compared with that of pure Ag/AgBr and Bi2WO6.

Innovative visible light photocatalytic activity for V-doped ZrO2 structure: optical, morphological, and magnetic properties

A new visible light sensitive photocatalysts based on Zr1−xVXO2 (x = 1, 3, 5, and 7) compositions for treatment of organic dyes in wastewater were investigated. Pure and V-doped ZrO2 samples were prepared by sol–gel techniques. The XRD results of the pure ZrO2 confirmed the formation of single phase tetragonal structure. Dopant-induced structure transition from the tetragonal to monoclinic phase. Based on SEM micrographs, mixture of spherical-nanorods architectures was formed in all samples with a volume ratio related to V concentration. Enhanced visible light absorption and an amazing red shift in the absorption edge were noticed in V doped ZrO2 samples. The magnetic properties of V doped ZrO2 exhibited room temperature ferromagnetism with varied hysteresis loops shape. Zr0.97V0.03O2 structure revealed a notable ferromagnetism with complete saturation magnetization of 0.038 emu/g and coercivity of 1200 Oe. Except Zr0.93V0.07O2 structure, all V doped ZrO2 samples showed significant photocatalytic activity when irradiated with visible light. The highest photocatalytic efficiency, ~100%, for methylene blue (MB) dye degradation was achieved through Zr0.95V0.05O2 catalyst under visible light irradiation time of 150 minutes. Vanadium played a major role in oxygen vacancies formation and separation of photo-induced electron–hole pairs which enriched the visible light photocatalytic activity.

Enhancement effect on antibacterial property of gray titania coating by plasma-sprayed hydroxyapatite-amino acid complexes during irradiation with visible light

The aim of this study was to reveal the mechanism of enhancement of antibacterial properties of gray titania by plasma-sprayed hydroxyapatite (HAp)–amino acid fluorescent complexes under irradiation with visible light. Although visible-light–sensitive photocatalysts are applied safely to oral cavities, their efficacy is not high because of the low energy of irradiating light. This study proposed a composite coating containing HAp and gray titania. HAp itself functioned as bacteria catchers and gray titania released antibacterial radicals by visible-light irradiation. HAp-amino acid fluorescent complexes were formed on the surface of the composite coating in order to increase light intensity to gray titania by fluorescence, based on an idea bioinspired by deep-sea fluorescent coral reefs. A cytotoxicity assay on murine osteoblastlike cells revealed that biocompatibility of the HAp–amino acid fluorescent complexes was identical with the that of HAp. Antibacterial assays involving Escherichia coli showed that the three types of HAp–amino acid fluorescent complexes and irradiation with three types of light-emitting diodes (blue, green, and red) significantly decreased colony-forming units. Furthermore, kelvin probe force microscopy revealed that the HAp–amino acid fluorescent complexes preserved the surface potentials even after irradiation with visible light, whereas those of HAp were significantly decreased by the irradiation. Such a preservative effect of the HAp–amino acid fluorescent complexes maintained the bacterial-adhesion performance of HAp and consequently enhanced the antibacterial action of gray titania.

Facile Synthesis of Nb2O5 as a Visible Light-Sensitive Photocatalyst

Niobium pentoxide (Nb2O5) is a promising semiconductor in catalysis due to its chemical and physical properties, availability, and non-toxicity. However, because of its large bandgap energy (Eg= 3.1 – 4.0 eV), Nb2O5 does not work as a photocatalyst under visible light, which makes its use of solar light limited. Even though Nb2O5 presents this drawback, its photocatalytic activity under visible light radiation can be enhanced due to the presence of surface groups, known as niobium peroxo complexes, formed by the treatment with hydrogen peroxide. In general, the modified niobia is synthetized in multi-step processes which allow the generation of strongly reactive oxygen species (ROS) (i.e. peroxo and superoxo) on its surface. In contrast, in this study, the peroxo-niobium oxide was prepared by a facile combination of the oxidant peroxide method (OPM) and hydrothermal treatment. The ability of Nb2O5 to form the ROS using this method was investigated in respect to the different Nb:H2O2 molar ratio (1:2 or 1:10) added in the metal oxide synthesis. For this purpose, ammonium niobium oxalate was dissolved in distilled water and hydrogen peroxide was then added to the reaction medium. The niobium precursor in contact with H2O2 forms instantaneously the niobium peroxo complex that was crystallized at 120 ⁰C with a heating ramp of 1 oC/min, for 12h in a home-made teflon lined autoclave. When the desired temperature was reached, the internal pressure of the reactor varied from ca. 10 to 27 atm, depending upon the amount of hydrogen peroxide used to prepare each material. The oxidative properties of the reactive oxygen species formed on the surface of metal oxides were tested in photodegradation of caffeic acid (CA) under visible light. In addition, reuse tests were performed in order to investigate the loss of photoactivity of the best photocatalyst in the CA degradation. XRD patterns revealed that the crystallographic structures of the samples Nb2H and Nb10H contain the Nb2O5 pseudohexagonal-type phase (JCPDS 28-317) and hydrated niobium oxide. Although no changes in the crystalline structure of both materials were observed, the presence of peroxo and superoxo species in the photocatalysts was confirmed by XPS and FTIR. The composites Nb2H and Nb10H presented band gap energies of 3.20 and 3.16 eV, respectively. However, Nb10H sample absorbs visible light at more than 400 nm, suggesting that the synthesis of the Nb2O5 with excess of H2O2 shifts the absorption edge of this material to the visible range, as well as reduces the energy required to the photoactivation of the catalyst. It was found that the photocatalytic activity increased with increasing oxidant concentration in the synthesis medium due to formation of a higher amount of oxygen reactive species on the surface of niobia. The peroxo-niobium groups on the Nb2O5 surface allowed the photocatalysts to be activated by visible light, and the superoxo groups formed can be also be responsible to improve its photocatalytic efficiency. The reuse tests of the Nb10H oxide indicated that the CA removal capacity remained practically constant even after four consecutive cycles. Therefore, the possibility of using solar irradiation to supply energy to active the photocatalyst make this material promising for use in low-cost photocatalytic systems for treatment of wastewater.

Uranyl-modified TiO2 for complete photocatalytic oxidation of volatile organic compounds under UV and visible light

Three commercially available TiO2 powder photocatalysts and additional one synthesized in laboratory via the modification of anatase TiO2 with uranyl nitrate (5 wt%) have been studied in the complete oxidation of several VOCs under UV (367 nm) and visible (450 nm) light. The kinetic curves for VOC removal, intermediate formation, and final product accumulation are presented in the paper and discussed in detail. The TiO2 modification with uranyl ions (UO22+) provides the ability for photocatalyst to absorb visible light with wavelength up to 500 nm. The photocatalytic activity of the uranyl-modified TiO2 under visible light was up to 56 times higher than the activity of one of the best visible light sensitive commercial photocatalysts, KRONOClean® 7000 from Kronos Worldwide Inc. The complete oxidation of all the tested pollutants occurred over UO22+/TiO2 both under UV and visible light. The formation of gaseous intermediates was observed for certain types of VOC, but the intermediates were further completely oxidized to carbon oxides and water under long-term irradiation. The kinetic regularities of PCO process under visible light were similar to the process under UV except somewhat prolonged kinetics due to lower photonic efficiency of light utilization in the visible spectral range.