Photodegradation Of P-nitrophenol Research Articles

Fabrication of FeTCPP@CNNS for Efficient Photocatalytic Performance of p-Nitrophenol under Visible Light

A photocatalyst of iron–porphyrin tetra-carboxylate (FeTCPP)-sensitized g-C3N4 nanosheet composites (FeTCPP@CNNS) based on g-C3N4 nanosheet (CNNS) and FeTCPP have been fabricated by in situ hydrothermal self-assembly. FeTCPP is uniformly introduced to the surface of CNNS. Only a small amount of FeTCPP is introduced, and the stacked lamellar structure is displayed in the composite. As compared with pure CNNS, the FeTCPP@CNNS composites exhibit significantly improved photocatalytic performance by the photodegradation of p-nitrophenol (4-NP). At the optimum content of FeTCPP to CNNS (3 wt%), the photodegradation activity of the FeTCPP@CNNS photocatalyst can reach 92.4% within 1 h. The degradation rate constant for the 3% FeTCPP@CNNS composite is 0.037 min−1 (4-NP), which is five times that of CNNS (0.0064 min−1). The results of recycling experiments show that 3% FeTCPP@CNNS photocatalyst has excellent photocatalytic stability. A possible photocatalytic reaction mechanism of FeTCPP@CNNS composite for photocatalytic degradation of 4-NP has been proposed. It is shown that superoxide radical anions played the major part in the degradation of 4-NP. The appropriate content of FeTCPP can enhance the charge transfer efficiency. The FeTCPP@CNNS composites can provide more active sites and accelerate the transport and separation efficiency of photogenerated carriers, thus further enhancing the photocatalytic performance.

Enhanced photocatalytic activity of titanium dioxide-doped graphene aerogel towards p-nitrophenol removal from aqueous solutions

ABSTRACT Titanium dioxide-doped graphene aerogel (TiO2/GA) was synthesized via one-pot the hydrothermal method. The characterisation of the prepared nanocomposite was thoroughly investigated with various modern analysis method. The results revealed a good terms in both of photo–absorption and nanoparticle sizing. The low band-gap energy of 2.61 eV and the larger specific surface area of TiO2/GA are the main differentiators when compared to the pristine materials. The size of TiO2 nanoparticles has been observed to range from 5 to 20 nm, which is necessary to promote a high photocatalytic performance. The photocatalytic performance of TiO2/GA was examined through photodegradation of p-nitrophenol (PNP). The optimization via Box-Behnken model suggested that 99.89% of PNP could be removed at the pH 7, 20 mg photocatalyst dosage, and 1 mL H2O2 volume. With the excellent results obtained, TiO2/GA material has extensive promise in the emoval of phenolic.

Facile and Green Synthesis of Silver Quantum Dots Immobilized onto a Polymeric CTS-PEO Blend for the Photocatalytic Degradation of p-Nitrophenol.

Immobilization of inorganic metal quantum dots (especially, noble transition metals) onto organic polymers to synthesize nanometal–polymer composites (NMPCs) has attracted considerable attention because of their advanced optical, electrical, catalytic/photocatalytic, and biological properties. Herein, novel, highly efficient, stable, and visible light-active NMPC photocatalysts consisting of silver quantum dots (Ag QDs) immobilized onto polymeric chitosan–polyethylene oxide (CTS–PEO) blend sheets have been successfully prepared by an in situ self-assembly facile casting method as a facile and green approach. The CTS–PEO blend polymer acts as a reducing and a stabilizing agent for Ag QDs which does not generate any environmental chemical pollutant. The prepared x wt % Ag QDs/CTS–PEO composites were fully characterized through X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis, and UV/visible spectroscopy. The characterization results indicated the successful synthesis of the Ag QDs/CTS–PEO composites by the interactions and complexation between x wt % Ag QDs and CTS–PEO blend sheets. TEM images revealed small granules randomly distributed onto the CTS–PEO blend sheets, indicating the immobilization of Ag QDs onto CTS–PEO composites. The presence of a surface plasmon resonance (SPR) band and the shifting of the absorption edge toward higher wavelengths in the UV/vis spectra indicated the formation of x wt % Ag QDs/CTS–PEO composites. The Ag QDs in the polymeric blend matrix led to remarkable enhancement in the optical, thermal, electrical, and photocatalytic properties of x wt % Ag QDs/CTS–PEO composites. The photocatalytic efficiency of the prepared composites was evaluated by the photodegradation of p-nitrophenol (PNP) under simulated sunlight. The maximum photocatalytic degradation reached 91.1% efficiency within 3 h for the 12.0 wt % Ag QDs/CTS–PEO photocatalyst. Generally, the Ag QDs immobilized onto CTS–PEO blend composites significantly enhance the SPR effect and the synergistic effect and reduce the band gap, leading to a high photocatalytic activity.

One-Pot Synthesis of W-TiO2/SiO2 Catalysts for the Photodegradation of p-Nitrophenol

Double modifications of TiO2 by doping with WO3 and by dispersing on a SiO2 support were made by the one-pot sol-gel method. Doping with W shifts the TiO2 band gap energy from 3.2 eV to around 3.06 eV. The surface area of the supported W-TiO2/SiO2 material was significantly increased, by approximately 3 times, in comparison to the bare TiO2. The photocatalytic activities of the catalysts were evaluated in the degradation reaction of p-nitrophenol in aqueous solution and basic medium. After 240 min of photodegradation, more than approximately 99% p-nitrophenol could be mineralized with the most active W-TiO2/SiO2 catalyst. Under UV irradiation, p-nitrophenol was initially photodegraded into hydroquinone and benzosemiquinone intermediates, which were further degraded into smaller fragments such as organic carboxylic acids and finally completely mineralized. A proposed photoreaction mechanism was presented based on the key roles of the surface hydroxyl species and superoxide radicals such as O2- and ⋅OH, together with W6+/W5+ couples and e-/h+ pairs in the catalysts in the p-nitrophenol photodegradation. The one-pot sol-gel synthesis method was proven to be effective to obtain W-TiO2/SiO2 catalyst with large surface area and high photocatalytic activity, and it can be also used for the preparation of other heterogeneous catalysts.

In-Situ Growth of Au on KTaO3 Sub-Micron Cubes via Wet Chemical Approach for Enhanced Photodegradation of p-Nitrophenol.

KTaO3/Au hetero-nanostructures were synthesized by in-situ reduction of HAuCl4 on the surface of hydrothermally-grown KTaO3 sub-micron cubes. The concentration of Au source was found to be a critical factor in controlling the hetero-nucleation of Au nanoparticles on the surface of KTaO3 sub-micron cubes. Loading of Au particles on KTaO3 nanocrystals enriched KTaO3 additional UV-vis absorption in the visible light region. Both KTaO3 and KTaO3/Au nanocrystals were shown to be active in the photo-degradation of p-nitrophenol, while the loading of Au on KTaO3 clearly improved the photo-degradation efficiency of p-nitrophenol compared to that on bare KTaO3 nanocrystals, probably due to the improved light absorption and charge separation.

Tailored synthesis of Sm2O3 and Eu2O3 doped ZrO2 nanoparticles: photodegradation of p-nitrophenol in water

A series of zirconia nanoparticles with relatively high photocatalytic degradation ability toward the organic dyes were synthesized. The obtained nanomaterials were fully identified using the X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), infrared spectroscopy (FT-IR) and photoluminescence spectroscopy (PL) techniques. By XRD results, it was proved that the samples represented pure tetragonal phase even at high temperatures having the most photocatalytic activities for these processes. A water solution of p-nitrophenol with the concentration of 10 ppm, was employed to test the photocatalytic activities of the zirconia samples. The photodegradation of p-nitrophenol by zirconia samples was followed by the UV–Vis spectroscopy technique using the maximum absorbance of this organic dye at 320 nm. The rates of photodegradation were measured employing the obtained absorbance spectra and kinetic first order equation. Finally, the effects of calcination temperature and amount of dopant on the photocatalytic activity of the zirconia nanoparticles were investigated.

Microwave-assisted synthesis of ZnNiAl-layered double hydroxides with calcination treatment for enhanced PNP photo-degradation under visible-light irradiation

In this paper, ZnNiAl-layered double hydroxide (LDH) photocatalysts were successfully prepared using a facile and timesaving microwave-assisted method. ZnNiAl-layered double oxides (LDOs) were then achieved from ZnNiAl-LDHs photocatalyst with calcination treatment. As a control, the corresponding photocatalysts were synthesized using a traditional hydrothermal method. A set of characterization technologies including XRD, SEM, FT-IR, and N2 adsorption was carried out to investigate the physical and chemical properties of the prepared photocatalysts. The photocatalytic activities were evaluated by the degradation of p-nitrophenol (PNP) under visible-light irradiation. Moreover, the influences of calcination temperature, photocatalyst dosage, and initial PNP concentration were also explored in this system. The results indicated that the sample transformed from LDH to LDO after 700 ○C calcination treatment and the prepared LDO showed an outstanding photocatalytic activity. When the photocatalyst dosage was 1.0 g·L−1 and initial PNP concentration was 10 mg·L−1, PNP removal efficiency was as high as 93.0% within 180 min under visible-light irradiation. After six cycles, the newly designed photocatalyst showed a good stability and reusability. This study shares a new preparation method for ZnNiAl-LDO as a novel photocatalyst with high efficiency for wastewater treatment.

Tungsten-doped TiO2/reduced Graphene Oxide nano-composite photocatalyst for degradation of phenol: A system to reduce surface and bulk electron-hole recombination

Recombination of photogenerated charges is the main factor affecting the photocatalytic activity of TiO2. Here, we report a combined strategy of suppressing both the bulk as well as the surface recombination processes by doping TiO2 with tungsten and forming a nanocomposite with reduced graphene oxide (rGO), respectively. Sol-gel method was used to dope and optimize the concentration of W in TiO2 powder. UV-Vis, XPS, PL and time resolved PL spectra along with DFT calculations indicate that W6+ in TiO2 lattice creates an impurity level just below the conduction band of TiO2 to act as a trapping site of electrons, which causes to improve the lifetime of the photo-generated charges. Maximum reduction in the PL intensity and the improvement in charge carrier lifetime was observed for TiO2 doped with 1 at.% W (1W-TiO2), which also displayed the highest photo-activity for the degradation of p-nitro phenol pollutant in water. Tuning of rGO/TiO2 ratio (weight) disclosed that the highest activity can be achieved with the composite formed by taking equal amounts of TiO2 and rGO (1:1), in which the strong interaction between TiO2 and rGO causes an effective charge transfer via bonds formed near the interface as indicated by XPS. Both these optimized concentrations were utilized to form the composite rGO/1W-TiO2, which showed the highest activity in photo-degradation of p-nitro phenol (87%) as compared to rGO/TiO2 (42%), 1W-TiO2 (62%) and pure TiO2 (29%) in 180 min. XPS and PL results revealed that in the present nanocomposite, tungsten species traps the excited electron to reduce the interband recombination in the bulk, while the interaction between TiO2 and rGO creates a channel for fast transfer of excited electrons towards the latter before being recombined on the surface defect sites.

A comprehensive study on photocatalytic activity of supported Ni/Pb sulfide and oxide systems onto natural zeolite nanoparticles

The Ni(II)-Pb(II) exchanged clinoptilolite nanoparticles (NCP) were transformed to corresponding oxides and sulfides via calcination and sulfiding processes, respectively. The obtained catalysts were characterized by XRD, FT-IR, TEM and DRS and used in photodegradation of p-nitrophenol (4-NP) aqueous solution under Hg-lamp irradiation. Results showed considerable increase in activity of the coupled semiconductors with respect to monocomponent one. In NiO-PbO-NCP system, conduction band (CB) of NiO is enough negative for easily migration of photogenerated electrons to CB-PbO level, while such phenomena take place from more negative CB-PbS level to CB-NiS level in NiS-PbS-NCP. These phenomena significantly prevented from electron-hole recombination which increased photocatalytic activity of the coupled semiconductors. Best photodegradation activities obtained by NiO1.3%–PbO14.7%-NCP and NiS2.1%–PbS10.0%-NCP, confirming semiconductors' mass-ratio dependence of the photocatalytic process. The supported coupled semiconductors showed blue shifts in band gap energies with respect to the bulk semiconductors which confirm formation of semiconductors nanoparticles inside the zeolite framework. The highest degradation percentage of 4-NP was obtained at: 0.5gL−1 photocatalysts, 15mgL−1 4-NP at pH 7.5.

Fabrication and photoelectrochemical study of vertically oriented TiO2/Ag/SiNWs arrays

Ordered channeled and porous TiO2 and Ag modified silicon nanowires (TiO2/Ag/SiNWs) heterostructured nanocrystals arrays are synthesized by a two-step method based on an electrochemical etching procedure and a sol–gel process. The morphology and photoelectrochemical properties of the TiO2/Ag/SiNWs are studied. The TiO2/Ag/SiNWs photocatalysts possess ordered channels and a porous structure with large specific surface area. UV–visible diffuse reflectance spectroscopy and ultraviolet Raman scattering demonstrate that the incorporated Ag significantly enhances light absorption by the TiO2/SiNWs in the visible spectral range and improves the separation of photo-induced charge carriers in the TiO2/SiNWs. The photoelectrochemical properties of the TiO2/Ag/SiNWs are investigated by monitoring the degradation of pnitrophenol (PNP) and Ag enhances PNP photodegradation under UV–vis irradiation due to the Ag–TiO2 heterojunctions and surface texture. The photoelectrochemical properties of TiO2/Ag/SiNWs have promising applications in photoelectrochemical solar cells and other light-harvesting devices.

Photodegradation of p-nitrophenol using octahedral Cu2O particles immobilized on a solid support under a tungsten halogen lamp

Octahedral Cu2O particles were prepared on an indium-tin oxide glass via electrodeposition and were employed in the catalytic degradation of p-nitrophenol in the presence of H2O2. Under irradiation of a warm visible-light source, tungsten halogen lamp, Cu2O particles not only acted as a photocatalyst, but might also act as a thermal-catalyst to induce the decomposition of H2O2 and produce O2 at higher temperatures. The photogenerated electrons and holes could react with H2O2, O2, and H2O to produce abundant OH radicals, resulting in the effective oxidation of p-nitrophenol. High-performance liquid chromatography measurements of degradation intermediates showed that p-nitrophenol was first decomposed into hydroquinone and benzoquinone and then mineralized. The degradation efficiency was dependent on electrodeposition time, light intensity, H2O2 amount, and solution temperature. This catalyst could be easily recycled and used in the efficient degradation of other phenolic compounds.

Photodegradation of <i>p</i>-Nitrophenol Catalyzed by ZnO/MWCNTs Composite Catalyst in Water

Photodegradation ofp-nitrophenol catalyzed by ZnO/MWCNTs composite in water was investigated. The effects of pH, irradiation time, catalyst loading, initial substrate concentration and MWCNTs content on the degradation were investigated. Experiment results revealed that the optimal conditions were ap-nitrophenol concentration of 60.0 mg/L at pH 5.0 with catalyst loading of 10.0 g/L under solar irradiation for the illumination of 180 min. The highest efficiency on photodegradation ofp-nitrophenol can be achieved with an optimal MWCNTs/ZnO mass ratio of 0.16%. Possible decomposing mechanisms were also discussed. The repeatability of photocatalytic activity was tested. The photocatalyst was used ten cycles with degradation efficiency still higher than 95%. The results of the study showed the feasible and potential use of ZnO/MWCNTs composite in degradation of toxic organic pollutants.

Calorimetric, optical and catalytic activity studies of europium chloride–polyvinyl alcohol composite system

Polyvinyl alcohol (PVA) films doped with europium chloride (EuCl 3) have been prepared by casting from their aqueous solutions. The phase transitions and thermal decomposition behavior of the prepared samples were investigated by thermal analysis and the interactions between the host PVA and Eu 3+ were examined by FTIR spectroscopy. The optical absorption was recorded at room temperature in the range of 190–1000 nm. From the absorption edge studies, the values of the Urbach energy ( E e ) were found to be 0.56 eV in case of the pure polymer; however, its value increased to be in the range of 1.21–1.75 eV. These energy values indicate that the model based on electronic transitions between localized states is not preferable and transitions are made between band tails. Optical parameters such as refractive index and complex dielectric constant have been determined. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model. Color properties of the prepared samples are discussed in the framework of CIE L⁎ u* v* color space. The prepared samples have been used as catalysts in the photocatalytic degradation of p-nitrophenol (PNP) in aqueous solution under UV light irradiation using H 2O 2 as oxidizing agent. The catalytic activity of the Eu-polymer towards the photodegradation of PNP greatly increased after doping with Eu 3+ ions. The highest catalytic activity was noticed at the optimum pH value of 5.5.

Hydrogen bond interactions at the TiO 2 surface: Their contribution to the pH dependent photo-catalytic degradation of p-nitrophenol

We have obtained p K a values of p-nitrophenol–TiO 2 by measuring the adsorption equilibrium constants of p-nitrophenol (PNP) on the TiO 2 surface at different pH values. These values have been obtained from Langmuir isotherms and from a plot of 1/rate vs. 1/[PNP] o obtained during TiO 2 catalyzed solar light photo-degradation of PNP. Two limit equilibrium constants are readily obtained depending on the solution pH: at pH 5 at which the TiO 2 surface is mainly positively charged and at pH 8 when it is negatively charged. With these and other adsorption equilibrium constants and the PNP p K a value in solution, thermodynamic cycles are established in order to obtain the PNP p K a when it is adsorbed on positively charged, neutral and negatively charged TiO 2 surfaces. From these p K a values useful information on the PNP–TiO 2 interaction is readily obtained. For instance, the PNP nitro group interacts with the TiO 2 surface via a hydrogen bond, arising from the complex of water molecules with the Ti 4+ ions on its surface. The weaker the hydrogen bond donor, the stronger the oxygen nitro group basicity. Therefore, p K a changes on the phenolic hydroxyl group result from these interactions. Linear free energy correlations, maximum PNP adsorption capacity values ( Q L) and FTIR ATR, spectrum support this proposal. A k obs vs. pH degradation profile of p-nitrophenol is also provided.

Enhanced Photodegradation of PNP on Soil Surface under UV Irradiation with TiO2

Photodegradation of p-nitrophenol (PNP) on soil surface was investigated to explore the photochemical remediation of soil polluted by nitrophenols. Soil samples spiked with PNP were irradiated by UV light with and without the addition of TiO 2 . The addition of 0.5–2 wt% TiO 2 enhanced PNP photodegradation with approximately 1.36 times increase in apparent rate of PNP disappearance. Soil moisture, humic acid and soil pH were important factors influencing the rate of PNP photodegradation. Increase in soil moisture improved the degradation significantly, whereas humic acid reduced the degradation rate. Changes in soil pH resulted in different degradation rates, and higher degradation efficiencies were observed under alkaline condition.

Enhanced photodegradation of phenolic compounds by adding TiO 2 to soil in a rotary reactor

Photodegradation of pentachlorophenol (PCP) and p-nitrophenol (PNP) in soil was carried out in a designed rotary reactor, which can provide the soil particles with continually uniform irradiation, and on a series of thin soil layers. TiO 2, as a kind of environmental friendly photocatalyst, was introduced to the soil to enhance the processes. Compared with that on the soil layers, photodegradation of PCP at initial concentration of 60 mg/kg was improved dramatically in the rotary reactor no matter whether TiO 2 was added, with an increase of 3.0 times in the apparent first-order rate constants. The addition of 1 wt% TiO 2 furthered the improvement by 1.4 times. Without addition of TiO 2, PNP (initial concentration of 60 mg/kg) photodegradation rate in the rotary reactor was similar to that on the soil layers. When 1 wt% additional TiO 2 was added, PNP photodegradation was enhanced obviously, and the enhancement in the rotary reactor was 2 times of that on the soil layers, which may be attributed to the higher frequency of the contact between PNP on soil particles and the photocatalyst. The effect of soil pH and initial concentrations of the target compounds on the photodegradation in the rotary reactor was investigated. The order of the degradation rate at different soil pH was relative to the aggregation of soil particles during mixing in the rotary reactor. Photodegradation of PCP and PNP at different initial concentrations showed that addition of TiO 2 to enhance the photodegradation was more suitable for contaminated soil with higher concentration of PCP, while was effective for contaminated soil at each PNP concentration tested in our study.