Volume 20, Issue 1 -

The basic and applied aspects of Fenton and Fenton-like processes for removal of pollutants using zerovalent iron materials, including nanoparticles, are reviewed in this article. Only those examples including the use of the iron materials together with hydrogen peroxide addition are included. The mechanistic aspects of homogeneous and heterogeneous Fenton processes, still under discussion, are displayed. The use of biogenic generated iron nanoparticles for removal of pollutants is discussed due to their novelty and economy of synthesis.

The conventional water treatment technologies, mostly relying on physical and biological processes, seem to be inadequate for effective removal of priority substances such as pesticides, while advanced oxidation processes showed a good performance for the same purpose. The aim of the study was to evaluate UV-C/H 2 O 2 and UV-C/S 2 O 8 2– processes for treating seven pesticides listed as priority substances (PS-Ps) within the EU Water Framework directive; alachlor, atrazine, chlorfenvinphos, cybutryne, diuron, isoproturon and simazine. The influence of pH and pollutant/oxidant ratio ([PS-P]:[OX]) on the degradation kinetics was evaluated using full factorial plan and response surface modeling. The degradation of PS-Ps by both photooxidation processes obeyed first-order kinetics. Degradation kinetics of PS-Ps is highly depended on [PS-P]: [OX], while pH has minor significance, particularly in UV-C /S 2 O 8 2– process. In most cases degradation kinetics by UV-C /S 2 O 8 2– was several times faster in comparison to UV-C /H 2 O 2 process. In addition, the inhibitory influence of NOM on the degradation of PSs in the mixture was determined.

A laboratory investigation of the radiation-induced degradation of aniline by gamma irradiation is the subject of this paper. During the inquiry, several aqueous samples with aniline concentrations of 25, 50, 75, 100 and 200 mg/L were irradiated for 5, 10, 15, 20, 25 and 30 h, respectively, by a 60 Co source with an absorbed dose rate of 0.78 kGy/h at the core channel. After the testing, the project authors scrutinized the aqueous samples to determine the effects of their irradiation by analyzing the pH, the hydroxyl radical and the H 2 O 2 of the individual initial concentrations. The findings showed that gamma irradiation is effective in removing aniline from aqueous solutions and, in the process, tends to remove the chemical oxygen demand (COD). Among other findings, the tests revealed that at a 25 mg/L aniline concentration, up to 100 % removal is possible after only 5 h of exposure. The authors explained that kinetic studies have shown that the degradation of aniline follows a pseudo first-order reaction. They have also shown that pH plays a significant role in aniline-removal efficiency. The tests in this study revealed that with a dose of 7.8 kGy, the removal efficiency of COD in an alkaline environment is higher than that of an acidic environment. With the absorbed dose increases, the authors learned that an acidic environment is helpful for the removal efficiency of COD. They also found that by adding 50 g/L of sodium bicarbonate as the hydroxyl radical scavenger, there was an 8 % decrease in the removal efficiency of COD at the absorbed dose of 23.4 kGy. This indicates the importance of using a hydroxyl radical in the gamma irradiation process. Also, a 1 g/L H 2 O 2 addition increases the COD removal rate from 31 % to 55 %. This percentage-point jump shows a synergistic effect in the use of gamma irradiation. The authors also identified several major decomposition products by GC/MS which are useful in the radiation-induced degradation of aniline by gamma irradiation process. Finally, they present proposals of possible pathways for successful aniline decomposition.

Spent biological activated carbon (SAC) in a drinking water treatment plant has been regenerated with microwaves, and the regeneration effects were evaluated through iodine values, surface chemistry, surface structure energy and surface morphology by comparison with unused activated carbon (UAC). On this basis, the performance of regenerated activated carbon (RAC) was investigated by methylene blue adsorption and raw water clarification. The results showed that the iodine value of RAC recovered to 98.1 % of that of UAC, and that the BET surface area of RAC (778 m 2 /g) was larger than that of SAC (749 m 2 /g). The pore structure of RAC was more regular than that of UAC, and the removal efficiency of RAC could achieve 90.7 % due to the formation of new micropores. Organic adsorption parameters of RAC fitted the Freundich isotherm better than those of UAC, and the R 2 values for COD Mn (chemical oxygen demand determined by KMnO 4 ), DOC (dissolved organic carbon) and UV 254 (absorbance value of the wastewater containing organic matter at ultraviolet light of 254 nm) were 0.902, 0.921 and 0.940, respectively.

A green and convenient approach for synthesis of nitriles from amines has been accomplished by using the environmentally friendly and inexpensive reagent molecular iodine/aqueous NH 4 OAc. The aqueous NH 4 OAc as a green reagent is more eco-friend than ammonia water, because of gaseous ammonia could be evaporated easily from ammonia water while aqueous NH 4 OAc is not. The possible mechanism of the present reaction was also proposed.

Eleven TiO 2 powders as catalysts have been studied in process of safranin T degradation in aqueous medium using mechanochemical, microwave and ultrasonic techniques. The degree of degradation has been controlled by means of spectrophotometric analysis of safranin T solutions before and after treatment and total organic carbon measurements. XRD, DTA-TG and BET analysis, FTIR spectroscopy and mass spectrometry of initial and spent catalysts have been carried out for explanation of obtained results. It has been established that the catalytic activity of TiO 2 under mechanochemical treatment depends on phase composition and dispersity (specific surface area). Particularly, catalytic activity of mono-phase titanias inversely depends on specific surface area of initial catalyst. Sono- and microwave catalytic degradation were less effective.

Abstract: The effect of various parameters on the catalytic oxidation of 1,2-dichlorobenzene (1,2-DCBz) present in simulated flue gas was investigated. A commercial V 2 O 5 -WO 3 /nano-TiO 2 catalyst was used and characterized by X-ray diffraction (XRD), N 2 -physisorption and energy dispersive spectrometer (EDS). The 1,2-DCBz conversion efficiency was increased significantly with higher temperature and lower gas hourly space velocity (GHSV). Different influence levels of HCl on catalytic oxidation were found at lower and higher GHSV. The influence of HCl is irreversible due to the formation of volatile metal oxidochlorides, resulting in a decrease of the number of active sites.

Current conduction mechanisms of SiC metal-oxide-semiconductor (MOS) capacitors on n-type 4H-SiC with or without NO annealing have been investigated in this work. It has been revealed that Fowler-Nordheim (FN) tunneling is the dominating current conduction mechanism in high electrical fields, with barrier height of 2.67 and 2.54 eV respectively for samples with NO and without NO annealing. A higher barrier height for NO-annealed sample indicates the effect of N element on the SiC/SiO 2 interface quality. In the intermediate oxide field, instead of trap-assisted tunneling (TAT), Poole-Frenkel (PF) emission play the key role in this region. A combination of C-V characteristics also show us the advantages of NO annealing on the SiC/SiO 2 characteristics.

This study reports new findings on the sputtered Cu-polyester (Cu-PES) bacterial inactivation under low intensity visible light (λ >400 nm). Cu-PES samples sputtered for 160 s led to the complete inactivation of E. coli in anaerobic and aerobic media within 45 min. The (Cu-PES) oxidative radicals generated in aerobic media were not the only intermediates leading to bacterial inactivation. Bacterial inactivation also proceeds in the dark under anaerobic conditions. For this reason, the oxidative radicals were leading to bacterial reduction were unambiguously identified by appropriate scavengers. X-ray photoelectron spectroscopy (XPS) provided evidence for redox catalysis going within the time required by Cu-PES to induce bacterial reduction. Furthermore, the Cu-ions in the ppb range leached from the Cu-PES during bacterial reduction were monitored by inductively coupled plasma mass spectrometry (ICP-MS) and the Cu found were below the limit allowed for mammalian cells. By infrared spectroscopy (ATR-FTIR) the bacteria stretching shifts of the predominant lipo-polysaccharide (LPS) associated-(CH 2 ) groups were monitored. The overstretching of these groups determined the time necessary for bond scission/bacterial inactivation.

Wet oxidation of an industrial pharmaceutical wastewater with high concentration organic pollutants using hydrogen peroxide as an oxidant was investigated. Experiments were performed in a batch reactor to discuss the effects of reaction temperature, time, the hydrogen peroxide amount and catalyst with COD removal rate as an evaluation index. Results show that the highest COD removal rate, 81.6 %, was achieved at 240 ºC for 60 min with the addition of H 2 O 2 solution 2 mL. The increased B/C value illustrated that the biodegradability of the wastewater improved significantly after the wet oxidation process. Activated carbon acts as a catalyst in this process which can increased the efficiency significantly. Wet hydrogen peroxide oxidation (WHPO) displayed an effective pre-treatment for the high-concentration organic wastewater.

Abstract: The ignition process has a significant influence on the success of in-situ combustion at heavy oil reservoirs. During this process, oxidation reactions between crude oil and injected air mainly occurred. In this paper, a series of oxidation experiments were performed at different reaction temperatures and air-oil ratios to investigate the heavy oil oxidation characteristics at different stages of the ignition process. The results revealed that heat release and production of CO and CO 2 were observed during the entire oxidation process, while transformation of heavy components (resins and asphaltenes) in crude oil to light components (saturates and aromatics) and production of H 2 S occurred at higher temperatures. The heavy oil oxidation in ignition process can be divided into three stages based on physical and chemical characteristics of the reaction, they are low-temperature oxidation, pseudo-high temperature oxidation, and high temperature oxidation, respectively.

Abstract: Three novel, modified PbO 2 electrodes with porous titanium as the substrate were successfully prepared by the anodic deposition method. The modified electrodes contained CNT, Bi, or a combination of the two. Their microstructure and electrochemical properties were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction, linear sweep voltammetry and cyclic voltammetry. Further, their electrochemical active surface area was determined, and their capacity to generate hydroxyl radicals and induce electrochemical degradation of methyl orange was studied. Compared with pure PbO 2 , electrodes with CNT-PbO 2 , Bi-PbO 2 , and the Bi-CNT combination had PbO 2 films with educed crystal sizes, which increased their specific surface area and active sites for electrochemical reactions. The Bi-CNT-PbO 2 electrode had the highest oxygen evolution over potential, while the generation of hydroxyl radical (·OH) and the electro-catalytic degradation of methyl orange were significantly increased with the Bi-CNT electrode. It was demonstrated that this modification can significantly enhance performance in electro-oxidation processes, including degradation compounds. Such improvements can be of importance for the removal of organic pollutants from effluents.

Latex (LX) paint was tested for photocatalytic decomposition of benzo[a]pyrene (BaP) under different conditions of relative humidity (RH), temperature and irradiation. Porcelain trays coated with LX paint were loaded with BaP solution, which was dissolved in acetonitrile. Trays were placed inside the photoreactor and irradiated with UV or a fluorescent lamp. Different conditions of RH and temperature inside the photoreactor were used. BaP preliminarily adsorbed on LX paint surface was decomposed faster at higher temperature and lower RH. For example, at 42 °C and RH 20 % BaP decomposition rate reached 64 %. At same temperature and with RH of 80 % this rate decreased to only 42 %. It was also demonstrated that at high RH (80 %) and under UV irradiation water contact angle on the paint surface was decreasing at a lower rate than under RH of 20 %. It was also proven that BaP could be sufficiently decomposed under irradiation by fluorescent lamp (59 % in comparison to 64 % under same environmental conditions with use of UV light). However, its decomposition rate was approximately 5 times slower than under UV light

Spherical and nanostructured Li 4 Ti 5 O 12 powders were successfully prepared through spray-drying method. Li 4 Ti 5 O 12 began to be formed after calcining the spray-dried amorphous precursor at approximately 350 °C, and a single phase was obtained at 750 °C. Spherical and porous Li 4 Ti 5 O 12 particles consisting of polyhedral particles assembled from 21–45 nm grains and 4–24 nm pores. An about 1 nm-thick amorphous layer can also be observed on the surface of the nano-sized grains. The Li 4 Ti 5 O 12 prepared at 750 °C exhibits the initial discharge capacities of 218 and 211 mAh g −1 and a high retention of 99.90 % and 99.67 % for 50 times at a rate of 1 C or 2 C in the voltage range of 1.0–2.5 V, respectively.

To improve the efficiency of decomposition of dye wastewater, the experiments of sonocatalytic degradation of Acid Orange 7 by TiO 2 -based films with doping Co, N and Er 3+ : Y 3 Al 5 O 12 were performed in this paper. Based on analysis of the change of concentrations of the samples over time, the result showed that sonocatalytic degradation of Acid Orange 7 by TiO 2 -based films agreed with the pseudo-first-order kinetics. The effect of doping mass fraction of Er 3+ :Y 3 Al 5 O 12 , Co and N inTiO 2 -based films and reaction temperature on degradation rates were studied. The optimal doping mass fraction of Er 3+ : Y 3 Al 5 O 12 , Co and N were 1.81 %, 2.01 %, and 12.03 % respectively at 20 °C. The model of the reaction rate constants of sonocatalytic degradation of Acid Orange 7 by Co/N/Er 3+ : Y 3 Al 5 O 12 /TiO 2 films were fitted. The errors between the model values and the experimental results were all less than 15 %. So the models could be used to estimate the degradation rate and concentration of Acid Orange 7 and provide theoretical basis for the design of catalytic reaction.

Abstract: Plate-like potassium superoxide (PLPS) can be used for atmosphere control and life support as chemical oxygen in coal mine refuge chambers. To simulate oxygen generation of single PLPS piece in a confined space, five groups of experimental studies under different temperatures and humidities were performed in a simulator. Under these experimental conditions, temperature and humidity were proportional to the increase rate of oxygen concentration and inversely proportional to the effective time of oxygen generation. A kinetic model of single potassium superoxide was established based on the experimental data and their description by reaction kinetics. The evolution of oxygen was divided into fast and slow reaction stages. The explanation of the behavior of the fast reaction stage is controlled by interfacial reaction and the slow reaction stage by internal diffusion. The suitable ranges of the kinetic model and three application parameters were determined from the oxygen concentration build-up using PLPS pieces.

Abstract: Reduction of CO 2 into useful fuels is regarded as a new way to deal with increasing CO 2 emissions and its bad effects on climate. In this report, simple electrochemical oxidation-reduction method has been utilized to prepare Cu 2 O/polyaniline (PANI)/stainless steel composite electrode, which was identified as a contributor for CO 2 reduction in an aqueous solution. X-ray diffraction (XRD), transmission electron microscope (TEM) and cyclic voltammetry technique were carried out to characterize the as-obtained electrode. As-synthesized composite electrode exhibited excellent electrocatalytic activity. The production of formaldehyde that comes from the reduction of CO 2 using Cu 2 O/PANI/stainless steel based electrode (Cu 2 O/PANI/stainless steel) in 0.1 mol/L sodium sulfate solution is 0.505 μmol·L –1 ·h –1 approximately.

The influence of the variation of chemical surface properties of activated carbons on the sorption capacity of activated carbons used in hybrid heterogeneous ozonation systems is still under discussion. In this study, the effect of long exposure of activated carbon to ozone and its implication on the removal of emerging organic pollutants from waters is evaluated. A commercial activated carbon (Filtrasorb-400) is used here as a raw material. It is chemically modified by continuous ozone exposure. 2-hydroxybenzothiazole (OHBT) is chosen as a target organic contaminant, representative of emerging micro-pollutants. Results obtained here reveal that extensive exposition of activated carbon surface to ozone weakens adsorbate–adsorbent interactions. Highly exposed activated carbon to ozone increases the concentration of oxygen-containing acidic functional groups, leading to a higher concentration of surface electron-withdrawing groups such as carboxylic acid anhydrides and carboxylic acids and reducing the sorption capacity toward OHBT in the hybrid heterogeneous ozonation system. At pH conditions around the point of zero charge (pH PZC ), such sorption reduction could be due to a decrease on dispersive interactions among π-electrons of aromatic ring of OHBT molecules and the π-electron system of carbon graphene layers, coming after extensive exposition of activated carbon surface to ozone. However, at pH >pH PZC low removal of OHBT is obtained because of the appearing of repulsive electrostatic interactions among the ionised form of OHBT molecules and the de-protonated form of oxygen-containing functional groups that appears after long contact with ozone. In addition, a new concept to predict activated carbon performances in a hybrid heterogeneous ozonation process is proposed.

Abstract: The photodegradation of meclofenamic acid (MCFA) was investigated using UV irradiation process. Parameters affecting the photodegradation process such as dissolved oxygen, reaction temperature, solution pH, initial MCFA concentration, humic acid, cations and anions were carried out. The intermediate products were identified by HPLC-MS analysis, and a tentative photodegradation pathway of MCFA was proposed. Results show that the photodegradation of MCFA can be modeled by the first-order kinetics. The photodegradation efficiency increases with the decreased concentration of humic acid or the decreased initial MCFA concentration, while the reaction temperature and the inorganic ions have no significant effect on the MCFA removal. It has found that the optimal initial solution pH for MCFA degradation is about 7.0. Finally, the HPLC-MS results reveal that the Cl atom in the MCFA molecule would form Cl – , followed by dechlorination, hydroxylation and cyclization of pentacyclic compounds.

This study investigated the characteristics of liquid phase plasma-electrode catalysis system formed by micro-arc oxidation with titanium-aluminum (Ti-Al) alloy as the anode. Under different power supplies, the wastewater from printing and textile dyeing industries simulated with Rhodamine B (RhB) dye was decolored. We evaluated the impact of oxide film formed on the electrodes on the plasma effects. Our findings showed that repeated applications of opposite voltages could damage the insulating oxide film formed on the electrode surface, contributing to its breakdown and enhancing micro-arc oxidation. Intermittent power supply also modulated the coverage of oxide film by enhancing the cooling of electrolyte. Morphological study of oxide film revealed the presences of rutile and anatase titanium dioxide (TiO 2 ) in the oxide film, which is conducive to various catalytic functions in the plasma environment.

The undoped and Nd-doped TiO 2 thin films were prepared on indium-tin oxide (ITO) conductive glass by sol-gel method using dip-coating technique. The crystal structure, surface morphology, composition and surface chemical state of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) , respectively. The results show that the undoped and Nd-doped TiO 2 form anatase structure after calcining at 450 °C for 2 h and the crystalline size of TiO 2 decreases by Nd doping. The photocurrent response of the thin films was tested by electrochemical workstation. The results show that all the Nd-doped TiO 2 thin film electrodes demonstrate higher photocurrent response. The photocurrent density of Nd-doped TiO 2 thin film electrodes increases at first and then decreases with the dopant concentration increasing from 0.5 at.% to 4 at.%. The maximum photocurrent density is obtained on 1 at.% Nd-doped TiO 2 thin film electrode, which is 3.2 times higher than that obtained on undoped TiO 2 thin film electrode. The photocatalytic activity of films was investigated by the degradation of methylene blue (MB). The results reveal that higher photocurrent causes higher photocatalytic activity. The degradation rate of 1 at.% Nd-doped TiO 2 thin film increases about 60 % than that of undoped TiO 2 thin film.

This research investigated the establishment of a mathematical model for the ozonation of dimethyl phthalate (DMP) through the analysis of the mass transfer and reactions in a semi-batch bubble column reactor. Negative step tracer experiments were conducted with ozone as a tracer, which indicated that the gas phase is perfectly well mixed at the gas flow rate of 400 mL/min. Based on the results from ozone absorption experiments the mass transfer coefficient of ozone was determined to be 0.0054 s −1 . The measured stoichiometry ratio of the direct reaction between ozone and DMP was about 5. The calculated rate constant was 0.87 L/(mol·s) for the direct reaction between ozone and DMP. A mathematical model was established based on the component mass balance in the reaction system involving the direct and indirect reactions and mass transfer between gas and liquid phase s enhanced by the chemical reactions. The model can predict the removal of DMP for the early stage of the ozonation process well. At the latter stage, the predicated removals deviated from the measured results mainly due to the consumption of ozone by side reactions.

Municipal wastewater treatment plants (MWTPs) have become one of the main sources of water for potential reuse. However, some pharmaceuticals, pesticides, hormones and others organics escape conventional wastewater treatments, and therefore, new technologies must be applied to overcome the problem. This article presents an efficient alternative that combines an aerobic immobilized biomass reactor (IBR) with a solar photo-Fenton process as a tertiary treatment. Real municipal wastewater was treated in the IBR system in batch and continuous modes. Micro-pollutants were monitored by using an advanced analytical procedure consisting of pre-concentration of samples by solid phase extraction (SPE) followed by liquid chromatography coupled to mass spectrometry. Results were compared with those observed in the MWTP secondary conventional activated sludge treatment. Effluents from the IBR, operating at the maximum treatment capacity, were treated in a previously optimized solar photo-Fenton pilot plant as a tertiary treatment to entirely eliminate remnant micro-pollutants.

Abstract: BiOCl photocatalysts were successfully synthesized using Bi(NO 3 ) 3 ·5H 2 O and KCl as raw materials. The physical properties and optical absorption performances of as-prepared samples were characterized through XRD, SEM, TEM, XPS and DRS. Contrary to common expectations, catechol could be degraded with visible light on as-synthesized BiOCl. The observed visible-light induced activity could be due to the formation of charge transfer complex, confirmed by DRS, FTIR, Raman, and XPS. About 65.0 % of catechol was degraded after 120 min light irradiation, and the rate constant, k, is 9.04×10 –3  min –1 . The addition of L-ascorbic acid inhibited the degradation of catechol, indicating •O 2 – being the main active species in catechol redox reaction. Finally, the degradation mechanism of catechol under visible light irradiation with BiOCl was proposed.

SrTiO 3 was supported on HZSM-5 zeolite by sol-gel method. XRD, FT-IR, UV-Vis diffuse reflectance spectra, and N 2 adsorption-desorption were measured to the synthesized materials. The effects of SrTiO 3 loading content on phenol degradation were studied. Perovskite SrTiO 3 is coated on the surface of HZSM-5 particles. After coating SrTiO 3 on HZSM-5, the BET surface area of χSrTiO 3 /HZSM-5 increases constantly with rising HZSM-5 content. The photocatalytic activity of SrTiO 3 is greatly enhanced after loading on HZSM-5, while the maximum degradation efficiency is obtained on 30 %SrTiO 3 /HZSM-5. Intermediates and residues in phenol solution during degradation were determined using FT-IR and TOC analyses. Hydroxyl radicals produced at the beginning of illumination are combined to benzene ring. Subsequently, oxidation of benzene ring takes significant effect with further irradiation, leading to total removal of organic carbon in the solution using 30 %SrTiO 3 /HZSM-5.

In order to realize the selective oxidation of Fenton-like reaction, an inorganic molecularly imprinted Fe/Al/SiO 2 composite (IMIPF) was synthesized by sol-gel method using acid orange II as template. As a comparison, the Fe/Al/SiO 2 composite without molecular imprinting was referred to as INIPF. The adsorption performance and Fenton-like catalytic selectivity were also studied with sodium dodecyl benzene sulfonate as the coexistence interference. Adsorption results in single systems and binary systems proved that IMIPF owned special molecular recognition and priority adsorption ability of the target pollutant. In addition, both IMIPF and INIPF exhibited high catalytic activity toward the degradation of acid orange II in single systems. Benefited from the preferential adsorption and Fenton-like activity, IMIPF could achieve the goal of selective removal of target pollutants at low concentration in the presence of other pollutants at high concentration in binary systems. Moreover, IMIPF possessed a wide applicable pH range and good reusability.

A novel internal circulation batch reactor (ICBR) was utilized to treat an azo dye pollutant methyl orange (MO) solution by the Electro-Fenton process, with graphite rods as the anodes and metal processing waste iron shavings as the cathodes. The MO decoloration efficiency reached 98.6 % for 0.08 g L –1 MO after an 18-min reaction under the optimal conditions of a pH=3.00, current density=0.90 mA/cm 2 and Na 2 SO 4 concentration=7.00 g L –1 . A kinetic fitting analysis shows that the MO decoloration rule complies with the first-order kinetics model, and the rate constant reaches 0.329 min –1 under optimal conditions. The durability of the iron-shavings cathode was tested by decoloration of 5 batches of MO using the same cathode without allowing the regeneration process to proceed. MO decoloration efficiencies also reached as high as 95 % in the fifth batch 34 min into the reaction, even though the first-order rate constants decreased to 0.064 min –1 . The iron-shavings cathode could also be reused by washing with 5 % (w/w) dilute sulfuric acid. Compared to the conventional square-shaped electrolytic batch reactor (SEBR), ICBR has the remarkable advantages of MO decoloration efficiency and energy conservation.