Fabrication of Ag3PO4/N-doped TiO2 nanotubes heterojunction photocatalysts for visible-light-driven photocatalysis.

As an environmentally friendly and energy-efficient technology, photocatalysis holds considerable potential for eliminating organic pollutants. In this study, novel visible-light-driven Ag3PO4-decorated nitrogen-doped TiO2 nanotubes (Ag3PO4/N-TNTs) photocatalysts with advanced properties of heterostructures were successfully synthesized and used to degrade methylene blue (MB) dye. The fabrication of Ag3PO4/N-TNTs photocatalysts involved a two-step electrochemical anodization to obtain TiO2 nanotubes (TNTs) and the wet impregnation of the amorphous tubular structure in NH3 solution, followed by calcination in air to obtain crystallized nitrogen-doped TiO2 nanotubes (N-TNTs). Finally, the decoration of the N-TNTs with Ag3PO4 nanoparticles was conducted to enhance visible-light reactivity. Various heterojunction photocatalysts were obtained by changing the concentration of NH3 (0.5-2.5 M) and the dosage of Ag3PO4 (0.25-1.5 wt%) in the composites. Results of ultraviolet-visible (UV-Vis) absorption, photocurrent transient, and electrochemical impedance spectroscopy measurement revealed that Ag3PO4/N-TNTs possessed a significant response in the visible-light range and good photoelectronic properties. The superior photocatalytic activity of the Ag3PO4/N-TNTs catalyst was achieved under the optimal conditions of N-doping using 2-M NH3 and Ag3PO4 deposition at a dosage of 0.75 wt%. Based on the degradation efficiency (DE) of MB, the optimal Ag3PO4/N-TNTs exhibited rate constants of 4.5 and 2 times higher than those of the pristine TNTs and N-TNTs, respectively. The high stability of Ag3PO4/N-TNTs was confirmed through four cycles of reutilization, with a small decay of only 5.3% in the DE of MB dye for each run of photocatalysis. The scavenger tests of generated reactive oxygen species revealed that ·OH and ·O2- were the primary contributors to photocatalytic performance. The synthesized Ag3PO4/N-TNTs heterostructure photocatalysts were proven to possess efficient separation of photogenerated charge carriers, high reactivity, and stability in the visible-light region.

Fabrication of an Extremely Cheap Poly(3,4-ethylenedioxythiophene) Modified Pencil Lead Electrode for Effective Hydroquinone Sensing.

Hydroquinone (HQ) is one of the major deleterious metabolites of benzene in the human body, which has been implicated to cause various human diseases. In order to fabricate a feasible sensor for the accurate detection of HQ, we attempted to electrochemically modify a piece of common 2B pencil lead (PL) with the conductive poly(3,4-ethylenedioxythiophene) or PEDOT film to construct a PEDOT/PL electrode. We then examined the performance of PEDOT/PL in the detection of hydroquinone with different voltammetry methods. Our results have demonstrated that PEDOT film was able to dramatically enhance the electrochemical response of pencil lead electrode to hydroquinone and exhibited a good linear correlation between anodic peak current and the concentration of hydroquinone by either cyclic voltammetry or linear sweep voltammetry. The influences of PEDOT film thickness, sample pH, voltammetry scan rate, and possible chemical interferences on the measurement of hydroquinone have been discussed. The PEDOT film was further characterized by SEM with EDS and FTIR spectrum, as well as for stability with multiple measurements. Our results have demonstrated that the PEDOT modified PL electrode could be an attractive option to easily fabricate an economical sensor and provide an accurate and stable approach to monitoring various chemicals and biomolecules.

Enhanced electrochemical degradation of ibuprofen in aqueous solution by PtRu alloy catalyst.

Electrochemical advanced oxidation processes (EAOPs) regarded as a green technology for aqueous ibuprofen treatment was investigated in this study. Multi-walled carbon nanotubes (MWCNTs), Pt nanoparticles (Pt NPs), and PtRu alloy, of which physicochemical properties were characterized by XRD and X-ray absorption spectroscopy, were used to synthesize three types of cheap and effective anodes based on commercial conductive glass. Furthermore, the operating parameters, such as the current densities, initial concentrations, and solution pH were also investigated. The intermediates determined by a UPLC-Q-TOF/MS system were used to evaluate the possible reaction pathway of ibuprofen (IBU). The results revealed that the usage of MWCNTs and PtRu alloy can effectively reduce the grain size of electrocatalysts and increase the surface activity from the XRD and XANES analysis. The results of CV analysis, degradation and mineralization efficiencies revealed that the EAOPs with PtRu-FTO anode were very effective due to advantages of the higher capacitance, CO tolerance, catalytic ability at less positive voltage and stability. The concentration trend of intermediates indicated that the potential cytotoxic to human caused by 1-(1-hydroxyenthyl)-4-isobutylbenzene was completely eliminated as the reaction time reaches 60 min. Therefore, EAOPs combined with synthesized anodes can be feasibly applied on the electrochemical degradation of ibuprofen.

Accumulation of heavy metals and trace elements in fluvial sediments received effluents from traditional and semiconductor industries.

Metal accumulation in sediments threatens adjacent ecosystems due to the potential of metal mobilization and the subsequent uptake into food webs. Here, contents of heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn) and trace elements (Ga, In, Mo, and Se) were determined for river waters and bed sediments that received sewage discharged from traditional and semiconductor industries. We used principal component analysis (PCA) to determine the metal distribution in relation to environmental factors such as pH, EC, and organic matter (OM) contents in the river basin. While water PCA categorized discharged metals into three groups that implied potential origins of contamination, sediment PCA only indicated a correlation between metal accumulation and OM contents. Such discrepancy in metal distribution between river water and bed sediment highlighted the significance of physical-chemical properties of sediment, especially OM, in metal retention. Moreover, we used Se XANES as an example to test the species transformation during metal transportation from effluent outlets to bed sediments and found a portion of Se inventory shifted from less soluble elemental Se to the high soluble and toxic selenite and selenate. The consideration of environmental factors is required to develop pollution managements and assess environmental risks for bed sediments.

Adsorption Removal of Environmental Hormones of Dimethyl Phthalate Using Novel Magnetic Adsorbent.

Magnetic polyvinyl alcohol adsorbent M-PVAL was employed to remove and concentrate dimethyl phthalate DMP. The M-PVAL was prepared after sequential syntheses of magnetic Fe3O4 (M) and polyvinyl acetate (M-PVAC). The saturated magnetizations of M, M-PVAC, and M-PVAL are 57.2, 26.0, and 43.2 emu g(-1) with superparamagnetism, respectively. The average size of M-PVAL by number is 0.75 µm in micro size. Adsorption experiments include three cases: (1) adjustment of initial pH (pH0) of solution to 5, (2) no adjustment of pH0 with value in 6.04-6.64, and (3) adjusted pH0 = 7. The corresponding saturated amounts of adsorption of unimolecular layer of Langmuir isotherm are 4.01, 5.21, and 4.22 mg g(-1), respectively. Values of heterogeneity factor of Freundlich isotherm are 2.59, 2.19, and 2.59 which are greater than 1, revealing the favorable adsorption of DMP/M-PVAL system. Values of adsorption activation energy per mole of Dubinin-Radushkevich isotherm are, respectively, of low values of 7.04, 6.48, and 7.19 kJ mol(-1), indicating the natural occurring of the adsorption process studied. The tiny size of adsorbent makes the adsorption take place easily while its superparamagnetism is beneficial for the separation and recovery of micro adsorbent from liquid by applying magnetic field after completion of adsorption.

Decomposition and Mineralization of Dimethyl Phthalate in an Aqueous Solution by Wet Oxidation.

Dimethyl phthalate (DMP) was treated via wet oxygen oxidation process (WOP). The decomposition efficiency η DMP of DMP and mineralization efficiency η TOC of total organic carbons were measured to evaluate the effects of operation parameters on the performance of WOP. The results revealed that reaction temperature T is the most affecting factor, with a higher T offering higher η DMP and η TOC as expected. The η DMP increases as rotating speed increases from 300 to 500 rpm with stirring enhancement of gas liquid mass transfer. However, it exhibits reduction effect at 700 rpm due to purging of dissolved oxygen by overstirring. Regarding the effects of pressure P T, a higher P T provides more oxygen for the forward reaction with DMP, while overhigh P T increases the absorption of gaseous products such as CO2 and decomposes short-chain hydrocarbon fragments back into the solution thus hindering the forward reaction. For the tested P T of 2.41 to 3.45 MPa, the results indicated that 2.41 MPa is appropriate. A longer reaction time of course gives better performance. At 500 rpm, 483 K, 2.41 MPa, and 180 min, the η DMP and η TOC are 93 and 36%, respectively.

Effective anodic oxidation of naproxen by platinum nanoparticles coated FTO glass.

This study investigated applications of the electrochemical anodic oxidation process with Pt-FTO and Pt/MWCNTs-FTO glasses as anodes on the treatment of one of the most important emerging contaminants, naproxen. The anodes used in this study have been synthesized using commercial FTO, MWCNTs and Pt nanoparticles (PtNP). XRD patterns of Pt nanoparticles coated on FTO and MWCNTs revealed that MWCNTs can prevent the surface of PtNPs from sintering and thus provide a greater reaction sites density to interact with naproxen, which have also been confirmed by higher degradation and mineralization efficiencies in the Pt/MWCNTs-FTO system. Results from the CV analysis showed that the Pt-FTO and Pt/MWCNTs-FTO electrodes possessed dual functions of decreasing activation energy and interactions between hydroxyl radicals to effectively degrade naproxen. The lower the solution pH value, the better the degradation efficiency. The existence of humic acid indeed inhibited the degradation ability of naproxen due to the competitions in the multiple-component system. The electrochemical degradation processes were controlled by diffusion mechanism and two major intermediates of 2-acetyl-6-methoxynaphthalene and 2-(6-Hydroxy-2-naphthyl)propanoic acid were identified. This study has successfully demonstrated new, easy, flexible and effective anodic materials which can be feasibly applied to the electrochemical oxidation of naproxen.

Degradation of phenol by using magnetic photocatalysts of titania.

Magnetic TiO2 (MT) composites were prepared and applied to degrading phenol, which is one of the listed priority pollutants. The effects of heat treatment under preparation on the photocatalytic activity of MT composites have been investigated by varying the soaking time under a constant final temperature of 823 K. The total organic carbon and ring-remaining intermediates of o-DHB, p-DHB and 1,4-BQ in solution were detected during the photodegradation of phenol. All the resulting MT composites were the single-phase anatase and magnetite judged by X-ray diffraction patterns. The calcination of the as-prepared particles was proven to be extremely crucial to the photocatalytic activity. The best condition of heat treatment was found to be soaking time of 2 h at T = 823 K due to the good performance of photocatalytic activity, stable magnetic property, and reusability over three times. The results lead to the conclusion that recyclable MT composites prepared in this study, which belonged to the category of recyclable green materials, exhibit good photocatalytic activity to degrade phenol so as to possess applicable potential for the degradation of refractory organics in the aqueous solution. Furthermore, the environmental and health impacts were reduced as MT composites were applied in the treatment of water pollution.

Adsorption behavior of pesticide methomyl on activated carbon in a high gravity rotating packed bed reactor.

High gravity rotating packed bed (HGRPB) reactor possesses the property of high mass transfer rate, which is expected to promote the adsorption rate for the process. In this study, HGRPB has been applied on adsorption removal of methomyl from solution, adopting the adsorbent of activated carbon F400. The influence of operating parameters of HGRPB on mass transfer such as the rotating speed (N(R)), the flow rate of solution (F(L)) and initial concentration of methomyl (C(b0)) were examined. The traditionally internal mass transfer models combined with Freundlich isotherm were used to predict the surface and effective diffusion coefficients. In addition, the results have also been compared with those obtained from the traditional basket stirred batch reactor (BBR). The results showed that the larger values of N(R) and F(L) enhanced the effective intraparticle diffusion and provided more accessible adsorption sites so as to result in lower equilibrium concentration in HGRPB system when compared to SBR system. The results of adsorption kinetics demonstrated that surface and effective diffusions were both significantly greater in HGRPB system instead of BBR system. Furthermore, the values of Bi(S) also manifested less internal mass transfer resistance in HGRPB system. The contribution ratio (R(F)) of the surface to pore diffusion mass transport showed that the larger contribution resulted from the surface diffusion in HGRPB system. Therefore, the results reasonably led to the conclusion that when the HGRPB system applied on the adsorption of methomyl on F400, the lower equilibrium concentration and faster internal mass transfer can be obtained so as to highly possess great potential to match the gradually stricter environmental standard.

Kinetics and equilibrium of desorption removal of copper from magnetic polymer adsorbent.

This study examined the desorption of copper ions, which were adsorbed on the magnetic polymer adsorbent (MPA) of polyvinyl acetate-iminodiacetic acid (M-PVAC-IDA), by ethylenediaminetetraacetic acid (EDTA). Stage-wise desorptions were applied to remove the Cu(II) ions from the Cu(II) adsorbed M-PVAC-IDA (A-M-PVAC-IDA). About seven desorption runs were needed to regenerate the A-M-PVAC-IDA. The Cu(II) desorbed M-PVAC-IDA (D-M-PVAC-IDA) was then reused to adsorb the Cu(II) ions from the Cu(II) ions-containing solution. The cyclic adsorption and desorption operations (CADOs) were performed to further elucidate the kinetics and equilibria of the desorption system of EDTA/A-M-PVAC-IDA and the adsorption system of Cu(II)-containing solution/D-M-PVAC-IDA. Two simple kinetic models, the pseudo-first-order equation and pseudo-second-order equation, were employed to simulate the kinetic behaviors of adsorption and desorption. With respect to the kinetics of adsorption behavior, the simulated results by both kinetic models exhibit good agreement with the experimental data. However, the adsorption capacities (q(e)) estimated by the pseudo-first-order equation are more accurate in comparison with those simulated by the pseudo-second-order equation. As for the desorption kinetics, the examination of correlation coefficients of model fittings of data shows that the pseudo-first-order kinetic model gives the better agreement for the cases with different initial solid-phase concentrations and can accurately compute the equilibrium concentrations of solid-phase. The values of q(e) after CADOs are consistent with the predicted results via the previous work, evidencing that the adsorption behavior and the characteristics of the regenerated adsorbent of D-M-PVAC-IDA were not altered. In the experiments of desorbing copper ions and CADOs, the desorption isotherm was set up. The Freundlich and Langmuir adsorption (or desorption) isotherms were used to simulate the equilibrium of desorption. The results indicate that the Freundlich equation shows better agreement with the experimental data than the Langmuir equation. The information thus obtained is useful for the better use of M-PVAC-IDA on the removal of heavy mental ions of Cu(II) from the Cu(II) ion-containing water solution with the consideration of its regeneration.

Pt-catalyzed ozonation of aqueous phenol solution using high-gravity rotating packed bed.

In this study, a high-gravity rotating packed bed (HGRPB or HG) was used as a catalytic ozonation (Cat-OZ) reactor to decompose phenol. The operation of HGRPB system was carried out in a semi-batch apparatus which combines two major parts, namely the rotating packed bed (RPB) and photo-reactor (PR). The high rotating speed of RPB can give a high volumetric gas-liquid mass transfer coefficient with one or two orders of magnitude higher than those in the conventional packed beds. The platinum-containing catalyst (Dash 220N, Pt/gamma-Al(2)O(3)) and activated alumina (gamma-Al(2)O(3)) were packed in the RPB respectively to adsorb molecular ozone and the target pollutant of phenol on the surface to catalyze the oxidation of phenol. An ultra violet (UV) lamp (applicable wavelength lambda=200-280 nm) was installed in the PR to enhance the self-decomposition of molecular ozone in water to form high reactive radical species. Different combinations of advanced oxidation processes (AOPs) with the HGRPB for the degradation of phenol were tested. These included high-gravity OZ (HG-OZ), HG catalytic OZ (HG-Cat-OZ), HG photolysis OZ (HG-UV-OZ) and HG-Cat-OZ with UV (HG-Cat-UV-OZ). The decomposition efficiency of total organic compound (eta(TOC)) of HG-UV-OZ with power of UV (P(UV)) of 16W is 54% at applied dosage of ozone per volume sample m(A,in)=1200 mg L(-1) (reaction time t=20 min), while that of HG-OZ without the UV irradiation is 24%. After 80 min oxidation (m(A,in)=4800 mg L(-1)), the eta(TOC) of HG-UV-OZ is as high as 94% compared to 82% of HG-OZ process. The values of eta(TOC) for HG-Cat-OZ process with m(S)=42 g are 56% and 87% at m(A,in)=1200 and 4800 mg L(-1), respectively. By increasing the catalyst mass to 77 g, the eta(TOC) for the HG-Cat-OZ process reaches 71% and 90% at m(A,in)=1200 and 4800 mg L(-1), respectively. The introduction of Pt/gamma-Al(2)O(3) as well as UV irradiation in the HG-OZ process can enhance the eta(TOC) of phenol significantly, while gamma-Al(2)O(3) exhibits no significant effect on eta(TOC). For the HG-Cat-UV-OZ process with m(S)=42 g, the values of eta(TOC) are 60% and 94% at m(A,in)=1200 and 4800 mg L(-1), respectively. Note that the decomposition of TOC via HG-UV-OZ is already vigorous. Thus, the enhancing effect of catalyst on eta(TOC) is minor.

Combined photolysis and catalytic ozonation of dimethyl phthalate in a high-gravity rotating packed bed.

In this study, a high-gravity rotating packed bed (HGRPB) was used as a catalytic ozonation reactor to decompose dimethyl phthalate (DMP), an endocrine disrupting chemical commonly encountered. The HGRPB is an effective gas-liquid mixing equipment which can enhance the ozone mass transfer coefficient. Platinum-containing catalyst (Pt/-Al2O3) of Dash 220N and ultra violet (UV) lamp were combined in the high-gravity ozonation (HG-OZ) system to enhance the self-decomposition of molecular ozone in liquid to form highly reactive radical species. Different combinations of HG-OZ with Dash 220N and UV for the degradation of DMP were tested. These include HG-OZ, HG catalytic OZ (HG-Pt-OZ), HG photolysis OZ (HG-UV-OZ) and HG-UV-Pt-OZ. The result indicated that all the above four ozonation processes result in significant decomposition of DMP and mineralization of total organic carbon (TOC) at the applied ozone dosage per volume of liquid sample of 1.2gL(-1). The UV and Pt/gamma-Al2O3 combined in HG-OZ can enhance the TOC mineralization efficiency (eta(TOC)) to 56% (via HG-UV-OZ) and 57% (via HG-Pt-OZ), respectively, while only 45% with ozone only. The process of HG-UV-Pt-OZ offers the highest eta(TOC) of about 68%.

Products and bioenergy from the pyrolysis of rice straw via radio frequency plasma and its kinetics.

The radio frequency plasma pyrolysis technology, which can overcome the disadvantages of common pyrolysis methods such as less gas products while significant tar formation, was used for pyrolyzing the biomass waste of rice straw. The experiments were performed at various plateau temperatures of 740, 813, 843 and 880K with corresponding loading powers of 357, 482, 574 and 664W, respectively. The corresponding yields of gas products (excluding nitrogen) from rice straw are 30.7, 56.6, 62.5 and 66.5wt.% with respect to the original dried sample and the corresponding specific heating values gained from gas products are about 4548, 4284, 4469 and 4438kcalkg(-1), respectively, for the said cases. The corresponding combustible portions remained in the solid residues are about 64.7, 35, 28.2 and 23.5wt.% with specific heating values of 4106, 4438, 4328 and 4251kcalkg(-1) with respective to solid residues, while that in the original dried sample is 87.2wt.% with specific heating value of 4042kcalkg(-1). The results indicated that the amount of combustibles converted into gas products increases with increasing plateau temperature. The kinetic model employed to describe the pyrolytic conversion of rice straw at constant temperatures agrees well with the experimental data. The best curve fittings render the frequency factor of 5759.5s(-1), activation energy of 74.29kJ mol(-1) and reaction order of 0.5. Data and information obtained are useful for the future design and operation of pyrolysis of rice straw via radio frequency plasma.

Adsorptive removal of the pesticide methomyl using hypercrosslinked polymers.

The hypercrosslinked polymers Macronet MN-150 and MN-500 (denoted as MN-150 and MN-500) were investigated to remove the pesticide methomyl from aqueous solutions via adsorption. Furthermore, the effect of humid acid (used as background organic compound) on the adsorption capacity of methomyl for MN-150 was examined. The equilibria and kinetics of the adsorption of methomyl onto MN-150 and MN-500 can be well correlated with Langmuir and Freundlich isotherms, and conventional kinetic models (e.g., surface and pore diffusion models), respectively. The polymer MN-150 possesses a high potential to be applied as adsorbent for the removal of methomyl from aqueous solution when compared with MN-500. Furthermore, the competitive effect of humic acid on adsorption of methomyl on MN-150 can be ignored at low equilibrium concentrations. The transport of methomyl from solution into the polymer adsorbents is controlled by both, external and internal mass transfer mechanisms with film-surface diffusion model offering the better description. The surface mobility and flux of surface diffusion increase as the initial concentration increases.

Mineralization of Reactive Black 5 in aqueous solution by basic oxygen furnace slag in the presence of hydrogen peroxide.

Basic oxygen furnace slag (BOF slag) is a solid waste arisen from the steel making process. FeO is one of the major components of BOF slag. The FeO-containing property of BOF slag makes it possible to catalyze the Fenton reaction. Reactive Black 5 (RB5) dye is chosen as the target compound in this study. This study has investigated the catalytic performance of BOF slag on the Fenton reaction to decompose RB5 in aqueous solution. A first-order kinetic model with respect to TOC was adopted to explain the mineralization of RB5 by the H(2)O(2)/BOF slag process. The experimental results in this study suggested that dosage with 1.49 x 10(-4)M min(-1) H(2)O(2) and 12.5 g l(-1) BOF slag in the solution at pH 2 provided the optimal operation conditions for the mineralization of RB5 yielding a 51.2% treatment efficiency at 100 min reaction time, and complete decoloration can be achieved within 30 min reaction time. The H(2)O(2)/Fe(2+) ratio was then determined to be 6.06:1.

Adsorption of naphthalene on zeolite from aqueous solution.

Polynuclear aromatic hydrocarbons (PAHs), which are environmental hormones and carcinogens, are viewed as the priority pollutants to deal with by many countries. Most PAHs are hydrophobic with high boiling and melting points and high electrochemical stability, but with low water solubility. Compared with other PAH species, naphthalene has less toxicity and is easily found in the environment. Thus, naphthalene is usually adopted as a model compound to examine the environmental and health aspects of PAHs. This study attempted to use an adsorption process to remove naphthalene from a water environment. The adsorption equilibrium of naphthalene on zeolite from water-butanol solution, which is a surfactant-enriched scrubbing liquid, was successfully evaluated by Langmuir, Freundlich, and linear isotherms. Among the tested kinetics models in this study (e.g., pseudo-first-order, pseudo-second-order, and Elovich rate equations), the pseudo-second-order equation successfully predicted the adsorption.

Investigating the adsorption of 2-mercaptothiazoline on activated carbon from aqueous systems.

2-Mercaptothiazoline (2-MT) is widely used as an organic corrosive as well as a diffusion inhibitor due to its high ability to form metal-chelate Schiff base complexes. This study investigated the elimination of 2-MT from aqueous systems with adsorption process to reach the goal of sustainable use of water resources. The Freundlich and Langmuir adsorption isotherms were adopted to examine the adsorption behavior of two types of 2-MT (i.e., 2-MT molecule and 2-MT complex) on activated carbon (AC) Chemviron Filtrasorb 400 (F 400) in three different solutions. The results of adsorption isotherm data showed that the adsorption ability of 2-MT molecule is much higher than that of 2-MT complex, whose ability may be reduced due to the electrostatic repulsion. The good applicability of Langmuir adsorption isotherm to experimental data indicated that the adsorption of 2-MT complexes on F 400 might be limited to a monolayer. Higher ionic strength and lower pH value of the solutions promoted the uptake of 2-MT onto F 400 from the solutions. In addition, not only 2-MT molecule and complex but also Cu(II) can be adsorbed on the surface of F 400, which was demonstrated by energy dispersive analysis of X-ray (EDAX). Effects of the two major interactions, chemical and physical interactions, on the adsorption of 2-MT on F 400 were compared as well in this study.