Improving activity of commercial P25 titanium dioxide photocatalyst

Titanium dioxide (TiO2) is recognized as one of the most active photocatalysts for degradation of organic pollutants. Among the available commercial TiO2, particular attention is focused on the P25 TiO2 having a mixture of anatase-rutile phases and act as the benchmark for the TiO2 photocatalysts. While numerous studies have been reported on the high activity of the P25 TiO2 for degradation of organic pollutants, improving the activity of the P25 TiO2 remained as a great challenge. On the other hand, impregnation method has been used conventionally to introduce metal oxide on the photocatalyst. This method is usually followed by calcination at high temperature to convert the metal precursor to metal oxide. Controversial results have been reported on the activity of P25 TiO2 after calcination process. It was reported that the calcined P25 TiO2 at 773 K showed two times higher activity than the untreated one for decolorization of methyl orange [1]. In contrast, the activity of P25 TiO2 was found to decrease with the increase of the calcination temperatures for decomposition and reduction reactions of NO [2], photodegradation of light hydrocarbons mixture [3] and butanol [4]. In the present study, the effect of calcination temperatures on the activity of P25 TiO2 was examined for photocatalytic removal of 2,4-dichlorophenoxyacetic acid (2,4-D) as the model of organic pollutants. The activity of the P25 TiO2 was slightly improved when the photocatalyst was calcined at 573 K, but decreased when calcined at 773 K. The P25 TiO2 were further modified by different metal oxides, i.e., copper oxide, cobalt oxide, and lanthanum oxide by impregnation method, followed by calcination at 773 K. All the series gave similar results; 1) addition of the metal oxides did not affect much the crystallinity, phase composition, and morphology of the P25 TiO2, 2) only small amount of added metal oxide (ca. 0.1-0.5 mol%) led to the improved photocatalytic activity, while addition of high loading amount decreased the activity of P25 TiO2, 3) the increased photocatalytic activity might be due to the ability of added metal oxide to suppress the charge recombination without blocking the active sites of the P25 TiO2. Among the investigated series and under the same reaction conditions, the La(0.1 mol%)/P25 TiO2 gave the highest photocatalytic activity for the removal of 2,4-D. After 1 hour reaction, the La(0.1 mol%)/P25 TiO2 gave ca. 1.25 times higher photocatalytic activity than the unmodified P25 TiO2 [5]

A urea precursor to synthesize carbon nitride with mesoporosity for enhanced activity in the photocatalytic removal of phenol

A urea precursor was used for the first time to prepare mesoporous carbon nitride (MCN) by a thermal polymerization process with silica nanospheres as a hard template. Although the prepared MCN samples have similar structures and optical properties, it was revealed that the specific surface area, pore-size distribution, and morphology of the MCN samples depend on the initial mass ratio of urea to silica. Compared to the bulk carbon nitride (BCN) that only gave 20?% phenol removal (6 h of irradiation), the activities can be enhanced up to 74?% on MCN samples for photocatalytic removal of phenol under visible-light irradiation. The highest conversion was obtained on MCN with an initial mass ratio of urea to silica of 5, which has high surface area of 191 m2?g-1 and a nanoporous structure with uniform pore-size distribution of 7 nm. In addition to the high activity, the MCN sample also showed high photocatalytic stability

Metal-free carbon nitride as a fluorescence sensor for nitrate ions

In this study, a metal-free carbon nitride (CN) was investigated for the first time as a potential fluorescence sensor for detection of nitrate ions (NO3 -). The CN was prepared through thermal polymerization of urea precursor at 823 K and characterized by diffuse reflectance ultraviolet-visible (DR UV-vis), Fourier transform infrared (FTIR), and fluorescence spectroscopies. The DR UVVis spectrumconfirmedthat CN could absorb light up to 430 nm. On the other hand, the FTIR spectrum revealed the presence of graphitic CN single and double bond characters in the 800- 1700 cm-1 region. From the fluorescence spectroscopy, two excitation peaks at 278 and 369 nm were observed due to the presence of N=C and N-C groups, respectively. The fluorescence sensor capability of the CN was then investigated usingdifferent concentrations of NO3 - (300-1800 µM).It was confirmed that the intensity of the emission site excited at either 278 or 369 nm was quenched linearly with the concentrations of the NO3 -. The Stern-Volmer plots showed that the quenching rate for N=C and N-C was 210-4 and 110-4µM-1, respectively. These results suggested that CN might act as a fluorescence sensor for NO3 -

Novel visible light-driven photocatalyst of mesoporous tud-1 supported chromium oxide doped titania for phenol photodegradation

Novel visible light driven mesoporous photocatalysts of Technische Universiteit Delft-1 (TUD-1) supported 1 mol% Cr oxide doped TiO2 (Cr-TiO2) were synthesized. Low angle XRD and FTIR results confirmed the amorphous and mesoporous silicate framework of TUD-1 in the materials. The mesostructure was further confirmed via N2 adsorption-desorption analysis showing type IV isotherm with narrow average pore size distribution (2.5 nm) and high surface area (864 m2/g). TEM analysis results indicated the attainment of nanoparticles and the porous channels in the synthesized materials. An increase in band-gap energy was observed after loading of Cr-TiO2 into TUD-1. As compared to the unsupported Cr-doped TiO2, all the TUD-1 supported Cr-doped TiO2 photocatalysts showed higher photocatalytic activity for phenol degradation under visible light irradiation. Amongst, sample Cr oxide doped TiO2 supported on TUD-1 with molar ratio Si/Ti = 30 exhibited the highest photodegradation of phenol (82%). The phenol photodegradation followed the Langmuir adsorption isotherm with first order kinetics

Synthesis and characterization of amphiphilic triazole ligand and its complex for potential application in phosphorescent temperature sensor materials

Phosphorescent materials have attracted much attention due to their promising applications in sensors, display, and optical imaging. Extensive studies have reported on trinuclear gold (I) complexes such as imidazolate, pyrazolate and carbeniete ; however, triazolate is rarely reported. Although hydrophobic trinuclear gold (I) triazolate complex has been reported in a solid state with luminescence center at near infrared area (750 nm) at room temperature, but no example of phosphorescent amphiphilic trinuclear gold (I) triazolate complex with liquid crystalline properties has been reported for potential application in near infrared phosphorescent temperature sensor materials. Here we report the synthesis of triazole ligand bearing amphiphilic side chain and then use it for complexation with gold salt to form amphiphilic trinuclear gold (I) triazolate complex. Triazole ligand was prepared in six stepwise reactions from triethylene glycol (EG3) to tosilate ethylene glycol (TsEG3,step 1; 180g, 90%), mono substitution triethylene glycol with decanediol (C10EG3OH, step 2; 17g, 43%), bromination (C10EG3Br, step 3; 9g, 45%), Williamson ether substitution reaction (C10EG3BnCOOMe,step 4; 3.5g, 67%), carboxylation (C10EG3COOH,step 5; 2g, 80%) and amidation (C10EG3TzH,step 6; 240mg, 23%). The resulting triazole ligand will be reacted with dimethylsulfide gold (I) chloride ([Au(SMe2]Cl) in methanol in the presence of excess freshly distilled triethylamine (Et3N) to form the gold complex. The phosphorescent properties will be discussed later

Effect of calcination temperatures on the photocatalytic activities of commercial titania nanoparticles under solar simulator irradiation

In this study, the effect of calcination temperatures on the photocatalytic activity of commercial TiO2 photocatalysts (Evonik P25, Evonik P90, Hombikat UV100, Hombikat N100) was evaluated for degradation and removal of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide under solar simulator irradiation. The calcined samples were prepared by heating commercial TiO2 photocatalysts at 573 or 773 K for 4 hours. It was confirmed that before calcination treatment, the P25 TiO2 showed similar activity to the P90 TiO2, which activity was higher than those of Hombikat UV100 and N100 TiO2. The activity of P25 and P90 was reduced when the photocatalysts were calcined at 573 K and 773 K. On the other hand, the Hombikat catalysts showed an improved activity with the increase of calcination temperatures

Synthesis and characterization of amphiphilic triazole ligand and its complex for liquid crystals of phosphorescent temperature sensor materials

Phosphorescent materials have attracted much attention due to their promising applications in sensors, display, optical imaging and drug delivery. Extensive studies have been only reported on the syntheses of trinuclear gold(I) azolate complexes such as imidazolate, pyrazolate and carbeniete. On the other hand, liquid crystal materials with anisotropic properties have been developed based on supramolecular self-assembly of weak non-covalent interactions due to it precise control and easily tunable characteristic for high performance applications. Although single crystal of trinuclear gold(I) triazolate complex has been reported in a solid state with luminescence center at near infrared area (750 nm) at room temperature, no example of phosphorescent amphiphilic trinuclear gold(I) triazolate complex with liquid crystalline properties has been reported for potential applications in near infrared phosphorescent temperature sensor materials. Here we report the successful synthesis of a triazole ligand bearing amphiphilic side chains by reacting methyl gallate with amphiphilic alkyl bromide via Williamson ether substitution reaction (45% yield), followed by hydrolysis (81% yield), and reaction with 4-amino-1,2,4-triazole (23% yield). Complexation with gold salt in Schlenk tube gave an amphiphilic trinuclear gold(I) triazolate complex. The phosphorescent characteristics including the liquid crystalline properties of this metal complex will be discussed later

Highly efficient zinc oxide-carbon nitride composite photocatalysts for degradation of phenol under UV and visible light irradiation

In order to utilize solar light in an efficient way, a good photocatalyst shall absorb both UV and visible light. In this study, a series of composite photocatalyst consisting of zinc oxide (ZnO) and carbon nitride (CN) was successfully prepared through a physical mixing method. The ZnO is an ultraviolet (UV)-based photocatalyst, while the CN is known as a visible light-driven photocatalyst. The effect of zinc to carbon mol ratio (Zn/C) towards the properties and photocatalytic activities was investigated. X-ray diffraction (XRD) patterns revealed that the prepared ZnO-CN composite photocatalysts composed of wurtzite ZnO and graphitic CN. The presence of ZnO and CN made the composites have absorption at both UV and visible region, suggesting the potential application as photocatalysts under both UV and visible light. Fluorescence studies revealed that all ZnO-CN composites showed emission peaks at 445 and 460 nm when excited at 273 nm, but with lower intensity as compared to those of the CN. The lower emission intensity suggested the role of ZnO to reduce the charge recombination and improve the charge separation on the CN. The ZnO-CN composites were further evaluated for photocatalytic degradation of phenol. The amount of degraded phenol was determined by a gas chromatography, in which a flame ionization detector was used in this study (GC-FID). The composite photocatalyst with an optimum content of 1% Zn/C gave almost 1.15 times higher activity than the CN under visible light irradiation. On the other hand, the composite photocatalyst with an optimum content of 50% Zn/C showed 2.6 times higher activity than the CN under UV light. The improved photocatalytic efficiency on the ZnO-CN composite photocatalysts was caused by the synergic effect between ZnO and CN. The ZnO would boost the separation efficiency of photogenerated electrons on the CN, while the CN would enable ZnO to absorb visible light region as the ZnO-CN composites

Photocatalytic oxidation of nitrite ion over carbon nitride

Nitrite ion (NO2-) is a toxic inorganic contaminant, which is widely used in industry and agriculture as a food preservative and a fertilizing agent. One of the methods to reduce the toxicity of the NO2- is by oxidizing it into less hazardous compounds, such as nitrate ion (NO3-). In this study, we demonstrated that a simple and green photocatalytic process can be employed to oxidize the NO2- to NO3- over a metal free-carbon nitride photocatalyst under ultraviolet (UV) light irradiation. The carbon nitride was synthesized via pyrolysis of urea precursor by a thermal polymerization process at 823 K for 4 hours. The prepared carbon nitride was then characterized by using X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), diffuse reflectance UV-visible (DR UV-vis), fluorescence, and Fourier transform infrared (FTIR) spectrophotometers, as well as nitrogen adsorption-desorption isotherm analyzer. All the characterization results supported the successful synthesis of the carbon nitride. The carbon nitride was then used as the photocatalyst for oxidation of NO2- to NO3- under UV light irradiation for 3 h. The decrease of the NO2- and the formation of the NO3- were analyzed by using a high performance liquid chromatography (HPLC) equipped with Hypersil GoldTM PFP column. The mobile phase used was a mixture of methanol (MeOH) and water (H2O) with the ratio of MeOH:H2O was 30:70. The addition of orthophosphoric acid was required to set the pH at 2.5. The flow rate was fixed at 0.8 ml min-1 and the monitored wavelength was 220 nm. It was revealed that carbon nitride could oxidize NO2- to NO3- with a moderate conversion of 15%. Fluorescence quenching showed that there were good interactions between the emission sites of carbon nitride and the NO2- molecules. The good interactions would be one driving force for the carbon nitride to act as a good photocatalyst to oxidize the NO2- to NO3-. The oxidation pathway by the photogenerated species was also proposed

Size-exclusion liquid chromatography for effective purification of amphiphilic trinuclear gold(I) pyrazolate complex

Column gravity chromatography suffered from several drawbacks such as time-consuming and need a large amount of eluents. Herein we reported an efficient technique for effective separation of amphiphilic trinuclear gold(I) pyrazolate complex ([Au 3 Pz 3 ] C10TEG ) with high polarity based on size-exclusion principle of chromatographic technique. Based on the size-exclusion limit, [Au 3 Pz 3 ] C10TEG having a larger size with molecular weight of 4011.39 Da (4030.40 Da when added Na + ) was successfully eluted and collected firstly from its impurities after being recycled for 2 times. In the chromatogram for first cycle, an intense peak upon excitation at 220 nm for [Au 3 Pz 3 ] C10TEG was observed at retention time of 58 mins, while small peaks due to the presence of impurities was observed in the range between 73 to 85 mins. In the second cycle, the impurities were flushed away before [Au 3 Pz 3 ] C10TEG was successfully collected at retention time of 170 mins in the third cycle. The columns were a set of polystyrene/divinylbenzene (PS/DVB) JAIGEL-1H and -2.5H connected in series having exclusion limit of 1 X 10 3 and 2 X 10 4 in which chloroform was used as the eluent at flow rate of 3.5 mL min -1. As a result, the visual appearance of dark-yellowish [Au 3 Pz 3 ] C10TEG was successfully purified to give pale-yellowish product. Moreover, differential scanning calorimetry thermogram showed that extra shoulder from impurities at 6.13 °C in the first endothermic peak of [Au 3 Pz 3 ] C10TEG at 0.76 °C was completely removed. Hence, it can be concluded that size-exclusion chromatography can be used as an effective purification method with much more convenience and small consumption of solvents