Interactive Fe2O3/porous SiO2 nanospheres for photocatalytic degradation of organic pollutants: Kinetic and mechanistic approach.

A uniformly distributed mesoporous silica nanospheres has been successfully synthesized. Silica nanospheres have been loaded with different content of Fe2O3 nanoparticles synthesized by the sol-gel process followed by calcination to form the Fe2O3 supported on silica nanospheres composite. The as-synthesized photocatalyst has been characterized for crystal structure, morphology, stability, surface area and also surface composition was determined. The photocatalytic oxidation ability of the composite photocatalyst was evaluated by degrading aqueous solutions of Methylene Blue and Congo red dyes under visible light having intense absorption in the wavelength range between 550 and 560 nm. The prime significance of silica is to act as catalyst support for uniform distribution of hematite particles for enhanced catalytic reactivity. Highest degradation has been achieved with 20 wt % loading of hematite nanoparticles indicating the less agglomeration and availability of more catalytic sites. Furthermore, colorless organic pollutants 2-chlorophenol and 2, 4-dichlorophenol have been degraded with high efficiency in the presence of H2O2 oxidizer. The scavenger experiments confirmed that hydroxyl radicals are the majorly participating species in this catalytic system. The composite system also shows good recyclability of the materials and advocates the promising nature of the designed system for multiple hazardous environmental contaminants.

Radiolytic oxidation and degradation of 2,4-dichlorophenol in aqueous solutions.

Radiolytic oxidation of 2,4-dichlorophenol (2,4-DClP) in aqueous solutions demonstrated that ·OH predominantly adds to the unsubstituted positions of the aromatic ring and that elimination of chloride at the 4 position is important because the -OH group enhances the electron density at this position, which is favorable for the electrophilic reactions. The total yield obtained was 0.540 µmol/J. Radiation-induced degradation of 2,4-DClP was conducted in oxygen-free aqueous solutions (0.1, 0.25, 0.50, and 0.7 mmol/dm3), saturated with N2O, and aerated and under irradiation at low and high doses. The results demonstrate that the largest degradation occurred in oxygen-free solutions due to oxidation (·OH) and reduction reactions (H· and [Formula: see text]) and attack of the [Formula: see text] at the ipso position of -Cl, producing HCl. The degradation was affected to a large extent by the concentration and to a lesser extent by the presence or absence of oxygen in which the 2,4-DClP solution was irradiated. At concentrations less than 1 mmol/dm3, 2,4-DClP was degraded in the solution at an absorbed dose level of 1 kGy. At higher doses, the product concentrations increased to up to 30% of the dose required for the total degradation of 2,4-DClP; then, they decreased. A graph plotting the logarithm of the relative concentration as a function of the dose shows a linear correlation, which indicates that the radiolytic degradation followed pseudo-first-order reaction kinetics. The oxidation was followed by the chemical oxygen demand (COD). COD decreases when the solute concentration increases. This fact has a dependence on the presence or absence of oxygen too.

Synthesis of graphene/black phosphorus hybrid with highly stable P-C bond towards the enhancement of photocatalytic activity.

Black phosphorus (BP), a superior two-dimensional (2D) semiconductor, has attracted much attention due to its unique properties. The graphene (GR)-BP hybrid was synthesized through one pot chemical vapor transport (CVT) approach. The characterization results indicated that P atom was successfully incorporated into GR by the formation of P-C bond. Remarkably, the newly-synthesized GR-BP represented high photocatalytic activity towards 2-chlorophenol (2-CP) degradation, due to the high efficiency of charge separation and transformation caused by the direct band gap of BP and carrier mobility of GR. The removal efficiency for 2-CP reached up to 87.08% within visible light irradiation for 180 min (λ > 420 nm). The degradation rate of GR-BP hybrid for 2-CP was approximately 7.29-fold than that of BP within 30 min. In addition, the little increasing of the peak for P-O bond in GR-BP hybrid was observed after being exposed in air for 15 days, meant that the stability of BP was significantly enhanced. It was caused by the decreasing of the oxidation sites in BP due to the formation of P-C bond in hybrid. In brief, our synthetic method for GR-BP not only provides a novel route for the improvement of the stability of BP, but also constitutes an insight into the promising practical application of BP in the photocatalysis field.

Photodegradation of 2,4-dichlorophenol by supported Pd(X2) catalyst (X = Cl, Br, N3): a HOMO manipulating point of view.

Three different palladium(II) complexes with ligands containing nitrogenized aromatic rings were investigated theoretically as model to obtain the computational band gap energies. The results demonstrated promising possibility for designing palladium(II) complexes with photocatalytic properties at visible light irradiation. Deliberated products were synthesized via grafting on the silica-coated Fe3O4 magnetic nanoparticles (Fe3O4@SiO2). Formation of complexes on the surface of Fe3O4@SiO2, as insoluble and reusable photocatalysts, was proved by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric (TGA), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), transmission electron microscope (TEM), and scanning electron microscopy (SEM) analyses. The trend of the band gap energies of prepared structures was calculated via experimental and theoretical methods. The photocatalytic capability of these nanoparticles was investigated in degradation of 2,4-dichlorophenol by means of HPLC analysis. A tentative reaction mechanism for the formation of intermediates was proposed. Graphical abstract ᅟ.

A novel Z-scheme BiPO4-Bi2O2(OH)(NO3) heterojunction structured hybrid for synergistic photocatalysis.

Photocatalysis has been gaining a growing popularity in water treatment, and their engineered applications inspire the development of effective photocatalyst materials. To develop photocatalyst that is effective for degradation of organic pollutants, we fabricate a novel direct solid Z-scheme BiPO4-Bi2O2(OH)(NO3) (BPO-BHN) heterojunction structured hybrid. The results demonstrate an enhanced photocatalytic activity of BPO-BHN to produce OH radicals, according to diffuse reflectance spectroscopy (DRS), electron spin-resonance resonance (ESR), photoelectrochemical measurements, and theoretical calculation results. The BPO-BHN is shown to greatly promote the degradation of 2,4-dichlorophenol (2,4-DCP) under ultraviolet light. On the basis of pseudo-first-order kinetics, the apparent degradation rate constant (kapp) of 0.050 min-1 obtained for BPO-BHN is approximately 3.33 and 12.5 times of that for individual BPO (kapp = 0.015 min-1) and BHN (kapp = 0.004 min-1), respectively. This suggests a virtually synergistic photocatalysis of BPO and BHN when they form a direct solid Z-scheme heterojunction structure, which is favorable for improving UV-light harvesting, hole/electron separation and oxidizing capability. In particular, as a novel non-linear optical (NLO) material, the BHN plays a significant role in the formation of Z-scheme structure for its unique ability of capturing photo-electrons from BPO by high-potential C+ face in valence band. This study provides a proof-of-concept strategy to develop more effective photocatalysts for degradation of organic pollutants in water.

Quantitative assessment on the contribution of direct photolysis and radical oxidation in photochemical degradation of 4-chlorophenol and oxytetracycline.

In UV-254 nm/H2O2 advanced oxidation process (AOP), the potential degradation pathways for organic pollutants include (1) hydrolysis, (2) direct H2O2 oxidation, (3) UV direct photolysis, and (4) hydroxyl radical (HO(•)) reaction. In this study, the contribution of these pathways was quantitatively assessed in the photochemical destruction of 4-chlorophenol (4-CP), demonstrating pathways (3) and (4) to be predominantly responsible for the removal of 4-CP by UV/H2O2 in 50 mM phosphate buffer solution. Increasing reaction pH could significantly enhance the contribution of direct photolysis in UV/H2O2 process. The contribution of HO(•) oxidation was improved with increasing initial H2O2 concentration probably due to the increased formation of HO(•). Presence of sodium carbonate (Na2CO3) as in UV/H2O2/Na2CO3 system promoted the degradation of 4-CP, with carbonate radical (CO3 (•-)) reaction and direct photolysis identified to be the main contributing pathways. The trends in the contribution of each factor were further evaluated and validated on the degradation of the antibiotic compound oxytetracycline (OTC). This study provides valuable information on the relative importance of different reaction pathways on the photochemical degradation of organic contaminants such as 4-CP and OTC in the presence and absence of a CO3 (•-) precursor.

Characterization and evaluation of the efficiency of SiO2/tetra-α-(2,4-di-tert-butylphenoxy)-phthalocyaninato zinc nanocomposite as photosensitizers for oxidation of 2,4,6-trichlorophenol.

A photosensitizer tetra-α-(2,4-di-tert-butylphenoxy)-phthalocyaninato zinc [ZnPc(OAr)4] was successfully encapsulated in SiO2 nanoparticle by the microemulsion method. The photosensitized composite nanoparticle was able to degrade 2,4,6-trichlorophenol (TCP) in aqueous solution. Under visible light irradiation, the nanoparticles efficiently generated reactive oxygen species; 95.4% of TCP was degraded after 270 min of reaction. Some aromatic compounds and aliphatic carboxylic acids were detected by mass spectrometry as the reaction intermediates. The results were different from those of previously reported photocatalytic reactions, in which valence band holes or hydroxyl radicals functioned as the main oxidants. The photosensitizing composite nanoparticle is potentially applicable to the oxidation of phenol.

Photocatalytic degradation of p-chlorophenol by hybrid H2O2 and TiO2 in aqueous suspensions under UV irradiation.

In this study, TiO2 particles were used as photocatalysts for the degradation of aqueous p-chlorophenol (p-CP) under UV irradiation. The effect of TiO2 dose (0-3 g/L), initial p-CP concentration, H2O2 concentration (2-45 mM), solution pH (4.6-9.5), and UV light intensity on the degradation of p-CP were examined. Four oxidative degradation processes, which utilized UV alone (direct photolysis), H2O2/UV, TiO2/UV, and H2O2/TiO2/UV, were compared in a batch photoreactor with a 100-W high-pressure mercury lamp. The photodegradation of p-CP could be described by the pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. Moreover, the apparent degradation rate constants increased considerably from 3.5 × 10(-)(3) min(-)(1) (direct photolysis) to 19.9 × 10(-)(3) min(-)(1) (H2O2/TiO2/UV system).

Arsenite oxidation-enhanced photocatalytic degradation of phenolic pollutants on platinized TiO2.

The effect of As(III) on the photocatalytic degradation of phenolic pollutants such as 4-chlorophenol (4-CP) and bisphenol A (BPA) in a suspension of platinized TiO2 (Pt/TiO2) was investigated. In the presence of As(III), the photocatalytic degradation of 4-CP and BPA was significantly enhanced, and the simultaneous oxidation of As(III) to As(V) was also achieved. This positive effect of As(III) on the degradation of phenolic pollutants is attributed to the adsorption of As(V) (generated from As(III) oxidation) on the surface of Pt/TiO2, which facilitates the production of free OH radicals ((•)OHf) that are more reactive than surface-bound OH radicals ((•)OHs) toward phenolic pollutants. The generation of (•)OHf was indirectly verified by using coumarin as an OH radical trapper and comparing the yields of coumarin--OH adduct (i.e., 7-hydroxycoumarin) formed in the absence and presence of As(V). In repeated cycles of 4-CP degradation, the degradation efficiency of 4-CP gradually decreased in the absence of As(III), whereas it was mostly maintained in the presence of As(III), which was either initially present or repeatedly injected at the beginning of each cycle. The positive effect of As(III) on 4-CP degradation was observed over a wide range of As(III) concentrations (up to mM levels) with Pt/TiO2. However, a high concentration of As(III) (hundreds of µM) inhibited the degradation of 4-CP with bare TiO2. Therefore, Pt/TiO2 can be proposed as a practical photocatalyst for the simultaneous oxidation of phenolic pollutants and As(III) in industrial wastewaters.

Photolytic degradation of chlorophenols from industrial wastewaters by organic oxidants peroxy acetic acid, para nitro benzoic acid and methyl ethyl ketone peroxide: identification of reaction products.

In this investigation, chlorophenol (CP) containing industrial wastewater was remediated by ultraviolet irradiation in conjunction with organic oxidants, peroxy acetic acid (PAA); para nitro benzoic acid (PNBA); and methyl ethyl ketone peroxide (MEKP). CP mineralization was studied with regard to chemical oxygen demand (COD) and chloride ion release under identical test conditions. COD depletion to the extent of 81% by PAA, 66% by PNBA, and 67% by MEKP was noted along with an upwardly mobile trend of chloride ion release upon irradiation of samples at 254 nm. A 90-99% decrease in CP concentration (as per high pressure liquid chromatography (HPLC) analysis) was achieved with an additional 15.0 ml of organic oxidant in all cases. Gas chromatography high resolution mass spectroscopy (GC-HRMS) results also indicated the formation of such reaction products as are free from chlorine substitutions. This treatment also leads to total decolorization of the collected samples.

A role for calcium hydroxide and dolomite in water: acceleration of the reaction under ultraviolet light.

Organic environmental pollutants are now being detected with remarkably high frequency in the aquatic environment. Photodegradation by ultraviolet light is sometimes used as a method for removing organic chemicals from water; however, this method is relatively inefficient because of the low degradation rates involved, and more efficient methods are under development. Here we show that the removal of various organic pollutants can be assisted by calcined dolomite in aqueous solution under irradiation with ultraviolet light. It was possible to achieve substantial removal of bisphenol A, chlorophenols, alkylphenols, 1-naphthol and 17ß-estradiol. The major component of dolomite responsible for the removal was calcium hydroxide. Our results demonstrate that the use of calcium hydroxide with ultraviolet light irradiation can be a very effective method of rapidly removing organic environmental pollutants from water. This is a new role for calcium hydroxide and dolomite in water treatment.

Photo-Fenton effect of 4-chlorophenol in ice.

The photoconversion of 4-chlorophenol (4-CP) in a simulated sunlight-Fenton system was investigated in ice and aqueous solution. It was found that the hydroxyl radical (OH) had an important effect on the photoconversion of 4-CP in both phases, but the effects of Cl(-), SO4(2-), NO3(-), and HCO3(-) were different. In aqueous solution, the photoconversion efficiency of 4-CP was proportional to the OH concentration, and hence, Cl(-) and HCO3(-) as OH scavengers prohibited the photoconversion; SO4(2-) had little effect; NO3(-) promoted the process under certain conditions owing to OH being generated by the photolysis of NO3(-). In ice, however, the photoconversion efficiency of 4-CP was not proportional to the concentration of OH. The photoconversion efficiency of 4-CP increased with increasing concentrations of all ions, although the OH remained almost constant, only increasing or decreasing slightly. This provides new evidence for the presence of a quasi-liquid layer (QLL). Hydroxylation products were detected in both phases. All photoproducts in aqueous solution contained only a single benzene ring, whereas in ice, dimers were also detected.

[Reductive degradation of chlorophenols in aqueous solution by gamma irradiation].

Because chlorine is an electron withdrawing group, the highly chlorinated phenols may react quickly with hydrated electrons rather than with hydroxyl radicals. The process of reactions of four chlorophenols (4-CP, 2-CP, 2,4-DCP, 2,4,6-TCP) with e(aq)(-) was investigated in aqueous solutions by detecting the concentration of CPs, Cl- and intermediates. In the e(aq)(-) reductive system, the experimental results showed that the order of four kinds of chlorophenol degradation and dechlorination was 2,4,6-TCP > 2,4-DCP > 2-CP > 4-CP. The greater the chlorine content was the higher reactivity of hydrated electrons towards chlorophenols was. Furthermore, hydrated electrons may preferentially attack the ortho-position of chlorine atom rather than the para-position of chlorine atom. Phenol and Cl- were detected as the final product of the reductive reaction. Additionally, processes of degradation and dechlorination of CPs were observed as the pseudo-first-order kinetics. The reaction constant of degradation of 4-CP, 2-CP, 2,4-DCP and 2,4,6-TCP were 0.154, 0.253, 0.750 and 1.188 kGy(-1), respectively. Meanwhile, the dechlorination of 4-CP, 2-CP, 2,4-DCP and 2,4,6-TCP were 0.137, 0.219, 0.251 and 0.306 kGy(-1), respectively.

Investigation of UV-assisted chlorophenol congeners' degradation by organic oxidant p-nitrobenzoic acid in basic media.

This research specifically addressed the photodegradation of selected model chlorophenol (CP) congeners, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP), by an organic oxidant, p-nitrobenzoic acid (PNBA), in basic media. The reactions were followed by high-pressure liquid chromatography and gas chromatography-mass spectroscopy analysis for residual concentration and the identification of photodegraded products respectively. Initial degradation was confirmed by the formation of ring cleavage compounds, and subsequent mineralization was evidently marked by an increase in release of chloride ions in the time course profile. The presence of fewer/no chlorine atoms in the degraded compounds corroborated the mineralization by UV/PNBA action. The chemical oxygen demand (COD) was also observed to fall appreciably to the extent of 73% during all CP congeners' degradation. The maximum COD decrease was observed in PNBA-assisted 4-CP degradation. The overall degradation kinetics conforming to second-order reaction is observed to follow the order 4-CP > 2,4,6-TCP ∼ PCP ∼ 2,4-DCP. The findings of this investigation elucidated the fact that PNBA was capable of successfully degrading/mineralizing the selected CP congeners.

Environmental implications and applications of carbon nanomaterials in water treatment.

Carbon nanomaterials have been proposed as a basis for developing new technologies for photocatalytic oxidation and disinfection, improved membrane processes, adsorbents, and biofilm-resistant surfaces. This study details recent progress towards the development of these proposed applications. We explored the use of carbon nanomaterials such as fullerene C60, single-wall carbon nanotubes (SWCNTs), and multi-wall carbon nanotubes (MWCNTs) for a range of new technologies including, degradation of a probe organic compound by in situ generation of reactive oxygen species (ROS), new strategies for microbial disinfection, and the inhibition of biofilm development on membrane surfaces. The results show that the degradation of 2-chlorophenol by ROS produced microbial inactivation, and the mobility of the nanoparticle aggregates of the carbon nanomaterials all increased as suspensions were fractionated to enrich with smaller aggregates with sonication followed by successive membrane filtration.

N-TiO2/gamma-Al2O3 granules: preparation, characterization and photocatalytic activity for the degradation of 2,4-dichlorophenol.

Nitrogen doping TiO2 and gamma-Al2O3 composite oxide granules (N-TiO2/gamma-Al2O3) were prepared by co-precipitation/oil-drop/calcination in gaseous NH3 process using titanium sulphate and aluminum nitrate as raw materials. After calcination at 550 degrees C in NH3 atmosphere, the composite granules showed anatase TiO2 and gamma-Al2O3 phases with the granularity of 0.5-1.0 mm. The anatase crystallite size of composite granules was range from 3.5-25 nm calculated from XRD result. The UV-Vis spectra and N 1s XPS spectra indicated that N atoms were incorporated into the TiO2 crystal lattice. The product granules could be used as a photocatalyst in moving bed reactor, and was demonstrated a higher visible-light photocatalytic activity for 2,4-dichlorophenol degradation compared with commercial P25 TiO2. When the mole ratio of TiO2 to Al2O3 equal to 1.0 showed the highest catalytic activity, the degradation percentage of 2,4-chlorophenol could be up to 92.5%, under 60 W fluorescent light irradiation for 9 hours. The high visible-light photocatalytic activity might be a synergetic effect of nitrogen doping and the form of binary metal oxide of TiO2 and gamma-Al2O3.

Visible light photocatalytic activity of Fe(3+)-doped ZnO nanoparticle prepared via sol-gel technique.

The optical properties of a ZnO photocatalyst were enhanced with various dopant concentrations of Fe(3+). Doped ZnO nanoparticles were synthesized via a sol-gel method without the use of capping agents or surfactants and was then characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet-visible (UV-Vis) spectroscopy. The results showed that ZnO has a wurtzite, hexagonal structure and that the Fe(3+) ions were well incorporated into the ZnO crystal lattice. As the Fe(3+) concentration increased from 0.25 wt.% to 1 wt.%, the crystal size decreased in comparison with the undoped ZnO. The spectral absorption shifts of the visible light region (red shift) and the band gap decreases for each Fe-ZnO sample were investigated. The photocatalytic activities of the ZnO and Fe-ZnO samples were evaluated based on the degradation of 2-chlorophenol in aqueous solution under solar radiation. The samples with a small concentration of Fe(3+) ions showed enhanced photocatalytic activity with an optimal maximum performance at 0.5 wt.%. The results indicated that toxicity removal of 2-chlorophenol at same line of degradation efficiency. Small crystallite size and low band gap were attributed to high activities of Fe-ZnO samples under various concentrations of Fe(3+) ions compared to undoped ZnO.

Photochemical degradation of 4-chlorophenol in the aqueous phase using peroxyacetic acid (PAA).

The photochemical degradation of 4-chlorophenol (4-CP) using ultraviolet irradiation (UV) of 6, 12 and 18 W with peroxyacetic acid (PAA) was studied in a batch reactor. The objective of this work was to investigate degradation and mineralization of 4-CP by PAA. The degradation efficiency increased with increasing UV input. The degradation process was also pH and initial PAA concentration dependent. The optimum conditions for the photochemical degradation of 4-CP as UV input, pH and PAA concentration was found to be 18 W, 9.5 and 3,040 ppm. The reaction efficiency decreased with increasing initial 4-CP concentrations. More than 95% mineralization of 4-CP was achieved with the UV/PAA process. The chloride ion concentration and chemical oxygen demand (COD) was evaluated. The chloride ion concentration and COD were decreased gradually with increasing UV input. Samples were analyzed by high pressure liquid chromatography (HPLC), UV spectrophotometry and gas chromatography-mass spectrometry (GC-MS) for residual concentration and identification of final degraded products.

Mineralization of p-chlorophenol in water solution by AOPs based on UV irradiation.

Protection of clean aquifers requires radical minimization of water consumption, overall reduction of wastewater and, furthermore, minimization of wastewater loading. Many organic pollutants in wastewater present a specific problem because of their toxicity, bioaccumulation and poor biodegradability. The scope of this paper is to investigate and identify the benefits offered by advanced oxidation processes (AOPs) as destructive methods for treatment of wastewater loaded with recalcitrant organic pollutants. The study was performed on model wastewater containing p-chlorophenol as a representative of organic chemical industry intermediates. Several UV based AOPs were studied: UV, UV/H2O2, UV/O3, UV/H2O2/O3 and UV/Fenton. Optimal process conditions for the highest mineralization efficiency in the investigated range (pH, [H2O2] and [Fe2+]) have been determined on the basis of HPLC measurements and the following ecological parameters: total organic carbon (TOC), adsorbable organic halides (AOX), chemical oxygen demand (COD) and biochemical oxygen demand (BOD5). Toxicity is one of the most important ecological parameters in determining the level of water pollution. In this study, toxicity tests were performed on the zooplankton Daphnia magna in order to evaluate efficiency of the applied treatments. The UV/ Fenton and UV/H2O2/O3 processes were found to be the most appropriate processes for degradation and mineralization of p-chlorophenol. Complete degradation was achieved after 15 minutes ofUV/Fenton process treatment, while 92.1% TOC and 98.3% AOX removals were obtained after treatment of 60 minutes.

Synthesis of indium borate and its application in photodegradation of 4-chlorophenol.

Indium borate has been prepared by a sol-gel method. The structure, morphology, and photophysics of the resultant photocatalysts have been studied via the techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM), and diffuse reflectance UV-visible light spectroscopy. These photocatalysts have been used to photodegrade 4-chlorophenol. The photocatalytic activity depends on the annealing temperature during preparation. It is found that borates can exhibit a high photodegradation activity under UV-light irradiation, for which the efficiency can be higher than that of as-prepared TiO(2). This is explained according to the results of fluorescence spectra and valence band X-ray photoelectron spectroscopy (XPS). It is confirmed by the results of time-resolved photoluminescence decay spectra; i.e., the lifetime of electrons and holes involved in the radiative process can be longer for the borates than that for TiO(2). This implies that indium borate can be a promising photocatalyst for future applications in treatment of environment contaminants.