Catalytic degradation of chlorinated volatile organic compounds (CVOCs) over Ce-Mn-Ti composite oxide catalysts

Developing industrially moldable catalysts with harmonized redox performance and acidity is of great significance for the efficient disposal of chlorinated volatile organic compounds (CVOCs) in actual exhaust gasses. Here, commercial TiO2, typically used for molding catalysts, was chosen as the carrier to fabricate a series of Ce0.02Mn0-0.24TiOx materials with different Mn doping ratios and employed for chlorobenzene (CB) destruction. The introduction of Mn remarkedly facilitated the synergistic effect of each element via the electron transfer processes: Ce3++Mn4+/3+↔Ce4++Mn3+/2+ and Mn4+/3++Ti4+↔Mn3+/2++Ti3+. These synergistic interactions in Ce0.02Mn0.04-0.24TiOx, especially Ce0.02Mn0.16TiOx, significantly elevated the active oxygen species, oxygen vacancies and redox properties, endowing the superior catalytic oxidation of CB. When the Mn doping amount increased to 0.24, a separate Mn3O4 phase appeared, which in turn might weaken the synergistic effect. Furthermore, the acidity of Ce0.02Mn0.04-0.24TiOx was decreased with the Mn doping, regulating the balance of redox property and acidity. Notably, Ce0.02Mn0.16TiOx featured relatively abundant B-acid sites. Its coordinating redox ability and moderate acidity promoted the deep oxidation of CB and RCOOH- intermediates, as well as the rapid desorption of Cl species, thus obtaining sustainable reactivity. In comparison, CeTiOx owned the strongest acidity, however, its poor redox property was not sufficient for the timely oxidative decomposition of the easier adsorbed CB, resulting in its rapid deactivation. This finding provides a promising strategy for the construction of efficient commercial molding catalysts to decompose the industrial-scale CVOCs.

Enhanced chlorobenzene removal by internal magnetic field through initial cell adhesion and biofilm formation

Magnetic fields (MF) have been proven efficient in bioaugmentation, and the internal MFs have become competitive because they require no configuration, despite their application in waste gas treatment remaining largely unexplored. In this study, we firstly developed an intensity-regulable bioaugmentation with internal MF for gaseous chlorobenzene (CB) treatment with modified packing in batch bioreactors, and the elimination capacity increased by up to 26%, surpassing that of the external MF. Additionally, the microbial affinity to CB and the packing surface was enhanced, which was correlated with the ninefold increased secreted ratio of proteins/polysaccharides, 43% promoted cell surface hydrophobicity, and half reduced zeta potential. Furthermore, the dehydrogenase content was promoted over 3 times, and CB removal steadily increased with the rising intensity indicating enhanced biofilm activity and reduced CB bioimpedance; this was further supported by kinetic analysis, which resulted in improved cell adhesive ability and biological utilisation of CB. The results introduced a novel concept of adjustable magnetic bioaugmentation and provided technical support for industrial waste gas treatments. KEY POINTS: • Regulable magnetic bioaugmentation was developed to promote 26% chlorobenzene removal • Chlorobenzene mineralisation was enhanced under the magnetic field • Microbial adhesion was promoted through weakening repulsive forces.

Homogeneous and heterogeneous atmospheric ozonolysis of chlorobenzene:Mechanism, kinetics and ecotoxicity assessment

The reactions between chlorobenzene(CB) and ozone have been studied comprehensively in this paper. Chlorobenzene is a commonly found chlorinated aromatic volatile organic compound(VOC), and its emission into the atmosphere can cause harm to the ecosystem and human health. The frequent occurrence of mineral particles from sandstorms exerts a significant influence on the atmospheric chemistry of the troposphere. Mineral particles are abundant in SiO2 and Al2O3 content. Therefore, we investigated the homogeneous and heterogeneous reaction processes of CB and ozone in the atmosphere by using density functional theory (DFT) method at the M06-2X/6-311++g(3df,2p)//M06-2X/6-31+g(d,p) level. The atmospheric fate, reaction rate and toxicity evaluation of CB ozonation were studied in the gas-phase section. Toxicity evaluation results showed that ozonation of CB could effectively reduce its toxicity. For the heterogeneous process, we simulated three types of SiO2 clusters and nine types of (Al2O3)n clusters, and studied the configurations of CB adsorbed on the cluster surfaces. We found that adsorption of CB on the SiO2 clusters was achieved through hydrogen bonding, while adsorption of CB on the Al2O3 clusters was achieved through both hydrogen bonding and metal bonding. The energy for CB adsorption on the (Al2O3)n cluster surface was higher than that for the SixOy(OH)z cluster surface, and both types of clusters exhibited efficient adsorption of CB. As the SixOy(OH)z clusters grew larger, the rates for the reactions between O3 and CB increased. CB travelled long distances along the Al2O3 clusters, leading to an extended influence range.

Nonthermal plasma coupled with liquid-phase UV/Fe-C for chlorobenzene removal

Catalyst poisoning problems limit the application of gas-solid non-thermal plasma (NTP) catalyzed decomposition of chlorinated volatile organic compounds (Cl-VOCs). To mitigate the catalyst deactivation, catalyst iron-loaded activated carbon (Fe-C) was added to the UV-activated liquid phase downstream of the NTP reactor (NTP + UV/Fe-C(L)) for the degradation of chlorobenzene (CB) in this study. The CB removal efficiency and mineralization efficiency (MR) of NTP + UV/Fe-C(L) were up to 94% and 68%, respectively, which were increased by 39% and 30% compared with the single NTP system. Compared with the conventional gas-solid NTP + UV/Fe-C(S) system, the stability of the NTP + UV/Fe-C(L) system was significantly improved due to the dissolved organic intermediates and low residuals on the catalyst surface. Reactive oxygen species ·OH and ·O₂^- dominated the decomposition of CB in the liquid phase, and with the help of UV, much more ·OH and ·O₂^- were produced by Fe-C catalytic O₃. In addition, Fe-C improved the removal of CB by increasing its absorption mass transfer coefficient from 0.0016 to 0.0157 s^-1. The degradation pathway of CB in the NTP + UV/Fe-C(L) system was proposed based on the detected organic intermediates. Overall, this study provides a new tactic to solve the catalyst poisoning problem in the NTP catalytic oxidation of Cl-VOCs.

Synthesis of hierarchical porous carbon with high surface area by chemical activation of (NH4)2C2O4 modified hydrochar for chlorobenzene adsorption

In this work, hydrothermal technique combined with KOH activation were employed to develop a series of porous carbons (NPCK-x) using tobacco stem as a low-cost carbon source and (NH₄)₂C₂O₄ as a novel nitrogen-doping agent. Physicochemical properties of NPCK-x were characterized by Brunauer-Emmett-Teller, field emission scanning electron microscopy, X-ray diffraction, Raman microscope, elemental analysis, and X-ray photoelectron spectroscopy. Results showed that the NPCK-x samples possessed large surface areas (maximum: 2875 m²/g), hierarchical porous structures, and high degree of disorder. N-containing functional groups decomposed during activation process, which could be the dominant reason for appearance of abundant mesopores and well-developed pore structure. Dynamic chlorobenzene adsorption experiments demonstrated that carbon materials with (NH₄)₂C₂O₄ modification exhibited higher adsorption capacity (maximum: 1053 mg/g) than those without modification (maximum: 723 mg/g). The reusability studies of chlorobenzene indicated that the desorption efficiency of (NH₄)₂C₂O₄ modified porous carbon reached 90.40% after thermal desorption at 100°C under N₂ atmosphere. Thomas model fitting results exhibited that the existence of mesopores accelerated the diffusion rate of chlorobenzene in porous carbon. Moreover, Grand Canonical Monte Carlo simulation was conducted to verify that micropores with pore sizes of 1.2-2 nm of the optimized porous carbon were the best adsorption sites for chlorobenzene and mesopores with pore sizes of 2-5 nm were also highly active sites for chlorobenzene adsorption.

Total organic carbon content as an index to estimate the sorption capacity of micro- and nano-plastics for hydrophobic organic contaminants

The worldwide existing micro- and nano-plastics (MNPs) showed high sorption capacity for hydrophobic organic contaminants (HOCs), and thus leading to change of the environmental behaviors and fates of HOCs. However, there is a lack of general index for evaluating the sorption capacity of MNPs for HOCs. Herein, we investigated the sorption of chlorobenzene, naphthalene and phenanthrene to 10 MNPs of different polymer types with and without UV-aging, respectively. It was found that the sorption was well fitted by Freundlich isotherm model with coefficients R² in the range of 0.892-1.00, and aging of most MNPs resulted in decreased sorption capacity for naphthalene and phenanthrene but slightly increased sorption capacity for chlorobenzene. More importantly, for the 8 MNPs commonly present in the environment and with measured total organic carbon (TOC) covering the range of 23.0-91.9%, the logarithm sorption constant (logK_d) values of the studied HOCs positively correlated with TOC contents of MNPs, with a good determination coefficient (R²) of 0.923 for naphthalene, 0.694 for chlorobenzene, and 0.565 for phenanthrene. Our study demonstrated that the TOC content of MNPs is a good index for estimating the contribution of total MNPs to the sorption of nonpolar HOCs in the environmental media.

[Determination of chlorobenzene metabolite-p-chlorophenol in urine by solid phase extraction-gas chromatography]

Objective: A method to determine chlorobenzene metabolite-p-chlorophenol in urine by solid phase extraction-gas chromatography was established. Methods: In May 2021, the urine sample was hydrolyzed at 100 ℃ for 1.5 h with 2 ml concentrated hydrochloric acid. After cooling and filtering, the sample was enriched and purified by Oasis(®)MAX 6cc SPE column. Drip washing with 0.01 mol/L hydrochloric acid solution and elution with acetonitrile, the eluent was volumized to 5 ml with acetonitrile and determined by gas chromatography, and quantify by standard curve method. Results: Calibration curve of the method was linear within the range of 1.61-80.30 μg/ml and showed good linearity with r=0.9997, the regression equation was y=1.51602x-0.10234. The determination limit was 0.17 μg/ml, and the limit of quantitation was 0.55 μg/ml. Recovery rates were between 89.3%-104.4%, the relative standard deviation (RSD) of intra-day measurements ranged from 4.3% to 6.7%, and the RSD of inter-day measurements ranged from 4.5% to 6.7%. Conclusion: This method could optimize sample pretreatment, and eliminate the interference of impurities, which is sensitive, efficient and accurate for the determination of chlorobenzene metabolite-p-chlorophenol in urine.

Suitability of chlorobenzene-based single-electron transistor as HCN, AsH3, and COCl2 sensor

A density functional theory (DFT)-based first principle approach has been employed to investigate the suitability of chlorobenzene-based single-electron transistor (SET) for the detection of few toxic gases such as hydrogen cyanide, arsine, and phosgene. The adsorption aspect of toxic gas molecules on the chlorobenzene with different orientations has been analyzed. The attributes such as charge density, molecular energy spectrum, density of states, and Mulliken population have been computed to scrutinize the effect of gas molecules on the surface of chlorobenzene. The sensing mechanism of adsorbate (toxic gases) with the adsorbent (chlorobenzene) has been authenticated in a single-electron transistor (SET) environment through total energy vs. gate voltage plot and charge stability diagram. The recovery time of the chlorobenzene-based SET gas sensor on the adsorption of HCN, AsH₃, and COCl₂ has been computed as 1.93 ns, 0.45 ns, and 36.31 ns, respectively. Based on these findings, it is interesting to see that the COCl₂ gas molecule shows strong physical adsorption with the most significant adsorption distance (3.629 Å) with chlorobenzene, while AsH₃-adsorbed chlorobenzene SET displays a low recovery time in comparison with other considered gases. The present analysis confirms a significantly better range of detection and improved recovery time using chlorobenzene-based single-electron transistor.

Abatement of chlorobenzene by plasma catalysis: Parameters optimization through response surface methodology (RSM), degradation mechanism and PCDD/Fs formation

Dielectric barrier discharge coupled with 10 wt% Co/γ-Al₂O₃ catalyst was developed to degrade chlorobenzene in this study. The effects of experimental parameters including applied voltage, flow rate, initial chlorobenzene concentration, and their interactions on the chlorobenzene degradation performance were investigated by the response surface methodology integrated with a central composite design. Results indicated that applied voltage was the most significant parameter affecting the mineralization rate and the concentration of ozone generated, while energy yield was mainly determined by initial chlorobenzene concentration. As a key precursor of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorophenols were found during the identification of the intermediates produced during chlorobenzene degradation through GC-MS. Furthermore, HRGC-HRMS was used to detect the remaining byproducts on the catalyst surface after 3 and 10 h discharge time, and three types of PCDD/Fs (2,3,7,8-TCDF, 1,2,3,4,6,7,8-HCDF and OCDD) were detected after 10 h of discharge. The degradation mechanism of chlorobenzene was analyzed based on these detected intermediates, and the possible formation mechanisms of the three PCDD/Fs were proposed for the first time in plasma catalytic degradation of chlorobenzene.

Catalytic oxidation of chlorobenzene and PCDD/Fs over V2O5-WO3/TiO2: insights into the component effect and reaction mechanism

In this work, titania supported catalysts (V-W/Ti) with different vanadium-tungsten contents were prepared and evaluated in the catalytic oxidation of chlorobenzene, which was used as the model compound of dioxins. The results showed that V₂O₅ is the main active component for chlorobenzene oxidation, and doping of WO₃ affects the valence distributions of vanadium, contributing a bimetallic synergistic effect. The catalysts were investigated by XRD, SEM-EDS mapping, Raman, and XPS, and the changes in V element valence state and chlorine content on fresh and used catalysts were observed by XPS. Moreover, in situ FTIR studies and chlorine balance were also conducted, the addition of WO₃ is helpful to the breakage of C-Cl, and a reaction mechanism for the catalytic oxidation of chlorobenzene was proposed. 3 V-5 W/Ti catalyst with better catalytic activity was selected for catalytic oxidation of PCDD/Fs using a lab scale PCDD/Fs generating and decomposing system. The degradation efficiency was 66.5% at 200 °C and 62.2% at 300 °C, which indicated that the low reaction temperature of 200 °C was conducive to the catalytic degradation of PCDDs, while the high temperature of 300 °C was facilitated the degradation of PCDFs.

Simultaneous catalytic removal of NO, mercury and chlorobenzene over WCeMnOx/TiO2-ZrO2: Performance study of microscopic morphology and phase composition

Nitrogen oxides, mercury and chlorobenzene are important air pollutants emitted by waste incineration and other industries. Coordinated control of multiple pollutants has become an important technology for air pollution control. Through solid-phase structure control, the catalytic performance of the WCeMnO_x/TiO₂-ZrO₂ catalyst for simultaneous catalytic removal of NO, mercury and simultaneous removal of NO and chlorobenzene were improved. MnWO₄ improved the solid acidity of the catalyst and improved the catalytic activity at high temperature. The formation of Ce_0·75Zr_0·25O₂, Ce₂WO₆, Ce₂Zr₂O₇ and Ce₂Ti₂O₇ improved the catalytic activity at low temperature. The presence of TiOSO₄ would affect the valence of metal ions and the reduction of chemisorbed oxygen, thereby reducing the catalytic activity at low temperature. Within the same size range of nanoparticles, cyclic nanoparticles exposed more active sites due to their hollow structure, and their catalytic performance was better than spherical nanoparticles. The thickness of the circular nanoparticles of WCM/TZ-14 catalyst was about 14 nm, and the diameter was about 40 nm Ce_0.75Zr_0.25O₂ and MnWO₄ were also present in the phase composition. Therefore, it exhibited the best performance for simultaneous catalytic removal of NO, mercury and simultaneous removal of NO and chlorobenzene. The coincidence temperature window was 347-516 °C. Finally, WCM/TZ-14 catalyst followed both E-R and L-H mechanisms in the NH₃-SCR reaction.

Remarkable enhancement in the N2 selectivity of NH3-SCR over the CeNb3Fe0.3/TiO2 catalyst in the presence of chlorobenzene

The simultaneous removal of NO_x and dioxins is the frontier of environmental catalysis, which is still in the initial stage and poses several challenges. In this study, a series of CeNb₃Fe_x/TiO₂ (x = 0, 0.3, 0.6, and 1.0) catalysts were prepared by the sol-gel method and examined for the synergistic removal of NO_x and CB. The CeNb₃Fe_0.3/TiO₂ catalyst exhibits an optimum catalytic performance, with an NO_x conversion greater than 95% at 260-380 °C. It also exhibits an optimal CB oxidation activity, in which CB promoted both the NO_x conversion and N₂ selectivity below 250 °C. Moreover, the more favorable ratios of Ce⁴⁺ to Ce³⁺ and plentiful surface-adsorbed oxygen species are the reasons why CeNb₃Fe_0.3/TiO₂ catalyst has better catalytic activity than other catalysts at the lower temperature. Simultaneously, owing to the modulation of Fe to the redox properties of Ce and Nb, the large number of oxygen vacancies and acid sites was generated, and the CeNb₃Fe_0.3/TiO₂ catalyst is beneficial to NO_x reduction and CB oxidation. Furthermore, the results of in situ DRIFTS study reveal the NH₃-SCR reactions over CeNb₃Fe_0.3/TiO₂ catalysts are mainly conformed to by the L-H mechanism (< 350 °C) and E-R mechanism (> 350 °C), respectively, and the multi-pollutant conversion mechanism in the synergistic reaction was systematically studied.

Synthesis of new composite based on TiO2 immobilized in glass fibers for photo-catalytic degradation of chlorobenzene in aqueous solutions

In this study photo-catalytic degradation of chlorobenzene from aqueous solutions using CQD decorated Fe-doped TiO₂ immobilized in Glass Fibers (GF) was investigated. Characteristics of the synthesized photo-catalyst were determined by EF-SEM, EDX, BET, XRD, FTIR, and DRS analysis. Additionally, DRS analysis demonstrated adding CQD to the TiO₂-Fe reduced its band gap energy from 2.96 eV to 2.91eV, while that was 3.10 eV for undoped TiO₂. Among that three photo-catalysts, GF/CQD_(4.5 wt%) decorated Fe-TiO₂ composite had performance nearly 100.0%, when pH was 5 and low concentration of chlorobenzene. In addition, GF/CQD_(4.5 wt%) decorated Fe-TiO₂ composite show it could be well applied for five times and with a little reduction on the performance. Also, no detectable Fe found to be released from the composite. Minimum inhibitory concentration (MIC) for E. coli bacteria was 12.2 mg L^-1 of chlorobenzene residual. Our findings show the catalyst was successful for chlorobenzene removal in the wastewater effluent. In conclusion, present hybrid composite could successfully and safely remove chlorobenzene from synthetic aqueous solution.

Improvement of Al2O3 on the multi-pollutant control performance of NOx and chlorobenzene in vanadia-based catalysts

We compared the influences of Al₂O₃ and SiO₂ on a traditional V₂O₅-MoO₃/TiO₂ for the simultaneous removal of NO_x and chlorobenzene (CB). The Al₂O₃ doping catalyst considerably broadens the active temperature window with higher NO_x reduction and CB oxidation efficiencies than the SiO₂ doping one and the V₂O₅-MoO₃/TiO₂. Furthermore, its resistance to SO₂ was preserved and the quantities of polychlorinated byproducts also decreased. The increase in activity at low temperatures could be due to the promotion of vanadia reducibility via interactions between V₂O₅ and Al₂O₃. Moreover, the high temperature activity could be due to the additional surface acidities provided by Al₂O₃, in which the Lewis acid sites played the predominant role in both NH₃ adsorptions and CB de-chlorination compared to the Brønsted acid sites. Finally, we proposed that Al₂O₃ is an effective addition for vanadia-based catalyst in NO_x and CB simultaneous removal from stationary sources.

Distribution and risk assessment of hexachlorobutadiene, pentachloroanisole, and chlorobenzenes in sediment and wild fish from a region affected by industrial and agricultural activities in South China

Hexachlorobutadiene, pentachloroanisole, and chlorobenzenes are regulated to control their release into the environment. There is little information regarding the distribution and risks of these pollutants in Chinese rivers. Therefore, we selected a prosperous agricultural and industrial region in South China as our study area and investigated the contamination profiles and risks of these pollutants in sediment and fish tissue samples. The results showed that, when compared with their levels in sediment, these lipophilic pollutants tended to accumulate in fish tissues in the following order: liver > brain > muscle. Some trichlorobenzene was found to be the result of reductive dechlorination of higher chlorinated benzenes. Hexachlorobutadiene and hexachlorobenzene could pose medium risks at certain sampling sites, but in general, almost no risk was found to the ecosystem. When the estimated daily human intakes of analytes through fish consumption were calculated for different age groups, the results suggested the analytes were unlikely to be a serious health concern for human. Our results could be used to update the existing data on the occurrence of these pollutants in the aquatic environment and to provide information for further pollution control by the local government.

Silicotungstic acid modified CeO2 catalyst with high stability for the catalytic combustion of chlorobenzene

The catalysts' redox capacity and surface acidity was important during the catalytic combustion of chlorobenzene (CB). CeO₂ showed great attractiveness due to its high oxygen storage capacity. Furthermore, the increase of acidity on the catalyst surface could improve the resistance to the chlorine poisoning. In this work, the silicotungstic (HSiW) modified CeO₂ catalysts prepared by four cerium salts and exhibited the different morphologies and catalytic activity. The HSiW modified CeO₂ catalyst prepared by Ce(CH₃COO)₃ (Cat-A) exhibited the best catalytic activity due to its abundant surface weak acid sites, more Ce³⁺ species and surface adsorption oxygen. The HSiW mainly located on the CeO₂ (111) planes of the Cat-A, which was conducive to redox property of CeO₂, thus promoting the deep oxidation of CB. Meanwhile the redox ability together with the weak acidity influenced the catalytic efficiency at low temperature. And the redox ability played a major role at high temperature. In addition, the Cat-A still possessed high stability and water resistance and maintained high activity after continuous catalytic oxidation of CB at 235 and 295 °C for 100h, exhibiting the possibility of industrial application.

Concentrations and profiles of persistent organic pollutants unintentionally produced by secondary nonferrous metal smelters: Updated emission factors and diagnostic ratios for identifying sources

Secondary nonferrous metal smelters are important sources of unintentionally produced persistent organic pollutants (UPOPs) including polychlorinated biphenyls (PCBs), polychlorinated naphthalenes, pentachlorobenzene, and hexachlorobenzene. Quantifying UPOP emissions by the main sources is an important step when evaluating UPOP emissions and establishing an inventory. In this study, field investigations were performed to allow UPOP emissions and distributions in stack gases emitted by secondary nonferrous metal smelters to be compared. A total of 25 stack gas samples were collected from secondary copper smelters (SCus), secondary zinc smelters, and secondary lead smelters in China. The mean toxic equivalent concentrations (TEQs) and mass concentrations of most of the UPOPs were highest in the secondary zinc smelter stack gas samples, next highest in the SCu stack gas samples, and lowest in the secondary lead smelter stack gas samples. The mean dioxin-like PCB and polychlorinated naphthalene TEQs were ∼8.9 and ∼6.6 times higher in stack gases from a SCu equipped with an oxygen-enriched smelting furnace than in stack gases from a SCu with a converter furnace. The mean PCB-118 to PCB-123 ratios and CN-10 to CN-35 ratios varied strongly and could be used as diagnostic ratios for apportioning the sources of UPOPs in the environment. Emission factors for dioxin-like PCBs, polychlorinated naphthalenes, pentachlorobenzene, and hexachlorobenzene in stack gases from secondary nonferrous metal smelters were derived and updated. The results improve our understanding of UPOP emission and provide data for establishing UPOP emission inventories for secondary nonferrous metal smelters.

Performance enhancement of a biofilter with pH buffering and filter bed supporting material in removal of chlorobenzene

Acidic substances, which produced during chlorinated volatile organic compounds, will corrode the commonly used packing materials, and then affect the removal performance of biofiltration. In this study, three biofilters with different filter bed structure were established to treat gaseous chlorobenzene. CaCO₃ and 3D matrix material was added in filter bed as pH buffering material and filter bed supporting material, respectively. A comprehensive investigation of removal performance, biomass accumulation, microbial community, filter bed height, voidage, pressure drops, and specific surface area of the three biofilters was compared. The biofilter with CaCO₃ and 3D matrix material addition presented stable removal performance and microbial community, and greater biomass density (209.9 kg biomass/m³ filter bed) and growth rate (0.033 d^-1) were obtained by using logistic equation. After 200 days operation, the height, voidage, pressure drop, specific surface area of the filter bed consisted of perlite was 27.4 cm, 0.39, 32.8 Pa/m, 974,89 m²/m³, while those of the filter bed with CaCO₃ addition was 28.2 cm, 0.43, 21.3 Pa/m, and 1021.03 m²/m³, and those of the filter bed with CaCO₃ and 3D matrix material addition was 28.7 cm, 0.55, 17.4 Pa/m, and 1041.60 m²/m³. All the results verified the biofilter with CaCO₃ and 3D matrix material addition is capable of sustaining the long-term performance of biofilters. CaCO₃ could limit the changes of removal efficiency, microbial community and filter bed structure by buffering the pH variation. And 3D matrix material could maintain the filter bed structure by supporting the filter bed, regardless of the buffering effect.

Radiolytic degradation of chlorobenzene in aerated and deoxygenated aqueous solutions

Radiation-induced degradation of chlorobenzene was conducted at 0.1, 0.4, 0.5, 0.7, and 1.0 mmol/dm³ concentrations in aerated environment and at 1.0 mmol/dm³ in oxygen-free and N₂O-saturated solutions. The results demonstrated that the elimination of chloride is important when the solution is oxygen free, because the [Formula: see text] attacks at the ipso position of the chloro group produces hydrochloric acid. The degradation was affected to a large extent by the concentration and to a lesser extent by the presence or absence of oxygen in the solutions which were irradiated. Thereby, the degradation occurred faster in the solutions with air and without oxygen and more slowly in the saturated solution with N₂O. Some by-products were identified using an HPLC-UV-mass system. In addition, it was found that there is a linear correlation between the ln C/C₀ and the dose, indicating that the radiolytic degradation followed pseudo-first-order reaction kinetics. The radiolytic oxidation was followed by the chemical oxygen demand (COD) test. The COD decreases when the solute concentration increases. The COD results were for a 0.47 mmol/dm³ of 5.94 mg O₂ dm^-3 kGy^-1 and for 0.09 mmol/dm³ of 7.45 mg O₂ dm^-3 kGy^-1.

Sequential biodegradation of 1,2,4-trichlorobenzene at oxic-anoxic groundwater interfaces in model laboratory columns

Halogenated organic solvents such as chlorobenzenes (CBs) are frequent groundwater contaminants due to legacy spills. When contaminated anaerobic groundwater discharges into surface water through wetlands and other transition zones, aeration can occur from various physical and biological processes at shallow depths, resulting in oxic-anoxic interfaces (OAIs). This study investigated the potential for 1,2,4-trichlorobenzene (1,2,4-TCB) biodegradation at OAIs. A novel upflow column system was developed to create stable anaerobic and aerobic zones, simulating a natural groundwater OAI. Two columns containing (1) sand and (2) a mixture of wetland sediment and sand were operated continuously for 295 days with varied doses of 0.14-1.4 mM sodium lactate (NaLac) as a model electron donor. Both column matrices supported anaerobic reductive dechlorination and aerobic degradation of 1,2,4-TCB spatially separated between anaerobic and aerobic zones. Reductive dechlorination produced a mixture of di- and monochlorobenzene daughter products, with estimated zero-order dechlorination rates up to 31.3 μM/h. Aerobic CB degradation, limited by available dissolved oxygen, occurred for 1,2,4-TCB and all dechlorinated daughter products. Initial reductive dechlorination did not enhance the overall observed extent or rate of subsequent aerobic CB degradation. Increasing NaLac dose increased the extent of reductive dechlorination, but suppressed aerobic CB degradation at 1.4 mM NaLac due to increased oxygen demand. 16S-rRNA sequencing of biofilm microbial communities revealed strong stratification of functional anaerobic and aerobic organisms between redox zones including the sole putative reductive dechlorinator detected in the columns, Dehalobacter. The sediment mixture column supported enhanced reductive dechlorination compared to the sand column at all tested NaLac doses and growth of Dehalobacter populations up to 4.1 × 10⁸ copies/g (51% relative abundance), highlighting the potential benefit of sediments in reductive dechlorination processes. Results from these model systems suggest both substantial anaerobic and aerobic CB degradation can co-occur along the OAI at contaminated sites where bioavailable electron donors and oxygen are both present.

Sequential biodegradation of 1,2,4-trichlorobenzene at oxic-anoxic groundwater interfaces in model laboratory columns

Halogenated organic solvents such as chlorobenzenes (CBs) are frequent groundwater contaminants due to legacy spills. When contaminated anaerobic groundwater discharges into surface water through wetlands and other transition zones, aeration can occur from various physical and biological processes at shallow depths, resulting in oxic-anoxic interfaces (OAIs). This study investigated the potential for 1,2,4-trichlorobenzene (1,2,4-TCB) biodegradation at OAIs. A novel upflow column system was developed to create stable anaerobic and aerobic zones, simulating a natural groundwater OAI. Two columns containing (1) sand and (2) a mixture of wetland sediment and sand were operated continuously for 295 days with varied doses of 0.14-1.4 mM sodium lactate (NaLac) as a model electron donor. Both column matrices supported anaerobic reductive dechlorination and aerobic degradation of 1,2,4-TCB spatially separated between anaerobic and aerobic zones. Reductive dechlorination produced a mixture of di- and monochlorobenzene daughter products, with estimated zero-order dechlorination rates up to 31.3 μM/h. Aerobic CB degradation, limited by available dissolved oxygen, occurred for 1,2,4-TCB and all dechlorinated daughter products. Initial reductive dechlorination did not enhance the overall observed extent or rate of subsequent aerobic CB degradation. Increasing NaLac dose increased the extent of reductive dechlorination, but suppressed aerobic CB degradation at 1.4 mM NaLac due to increased oxygen demand. 16S-rRNA sequencing of biofilm microbial communities revealed strong stratification of functional anaerobic and aerobic organisms between redox zones including the sole putative reductive dechlorinator detected in the columns, Dehalobacter. The sediment mixture column supported enhanced reductive dechlorination compared to the sand column at all tested NaLac doses and growth of Dehalobacter populations up to 4.1 × 108 copies/g (51% relative abundance), highlighting the potential benefit of sediments in reductive dechlorination processes. Results from these model systems suggest both substantial anaerobic and aerobic CB degradation can co-occur along the OAI at contaminated sites where bioavailable electron donors and oxygen are both present.

GC-MS/MS analysis for source identification of emerging POPs in PM2.5

Emerging POPs have received increasing attention due to their potential persistence and toxicity, but thus far the report regarding the occurrence and distribution of these POPs in PM_2.5 is limited. In this study, an extremely sensitive and reliable method, using ultrasonic solvent extraction and silica gel purification followed by gas chromatography coupled with electron ionization triple quadrupole mass spectrometry, was developed and used for the trace analysis of hexachlorobutadiene (HCBD), pentachloroanisole (PCA) and its analogs chlorobenzenes (CBs) in PM_2.5 from Taiyuan within a whole year. The limits of detection and limits of quantitation of analytes were 1.14 × 10^-4‒2.74 × 10^-4 pg m^-3 and 3.80 × 10^-4‒9.14 × 10^-4 pg m^-3. HCBD and PCA were detected at the mean concentrations of 3.69 and 1.84 pg m^-3 in PM_2.5, which is reported for the first time. Based on the results of statistical analysis, HCBD may come from the unintentional emission of manufacture or incineration of chlorinate-contained products but not coal combustion, while O₃-induced photoreaction was the potential source of PCA in PM_2.5. The temporal distributions of CBs in PM_2.5 were closely related to coal-driven or agricultural activities. Accordingly, our study reveals the contamination profiles of emerging POPs in PM_2.5 from Taiyuan.

Chlorobenzene levels, component distribution, and ambient severity in wastewater from five textile dyeing wastewater treatment plants

Chlorobenzenes (CBs) present in synthetic dyes are discharged into natural waters during the treatment of textile dyeing wastewater, which may have adverse effects on human and environment. In this study, the existence and removal of 12 CBs in different units of five treatment plants were examined. The ecological risk of CBs in textile dyeing wastewater was assessed by ambient severity (AS) and risk quotients (RQs). The results showed that trichlorobenzene, tetrachlorobenzene, pentachlorobenzene and hexachlorobenzene were ubiquitous in textile dyeing wastewater, and their distribution was similar. In one of the plants, the content of hexachlorobenzene was found to be as high as 9.277 μg/L in the raw water, which was an oil-water mixture. In other plants, there was no significant difference in the content and composition of CBs among influent and effluent suggesting that the conventional wastewater treatment plants cannot improve the existence of them. Monochlorobenzene and dichlorobenzene were not detected, which may have been related to strong volatility, biochemical properties, and weak instrument sensitivity. In the treatment process and effluent, trichlorobenzene is the main pollutant and accounted for 39.51% of all CB. CB removal was found only in the anaerobic system, while the aerobic system did not have the corresponding removal effect on CB and total organic carbon. According to ecological risk assessment, CBs in effluent has not been found the significant potential harm to human health (AS < 1), but posed moderate ecological risk to aquatic ecosystem (RQs > 0.1).

Elimination of chloroaromatic congeners on a commercial V2O5-WO3/TiO2 catalyst: The effect of heavy metal Pb

Catalytic elimination of chlorinated volatile organic compounds (CVOCs) from the industrial sources of emission usually confronted with catalyst deactivation and secondary pollution. As a widely used catalyst in selective catalytic reduction (SCR) of nitric oxides, V₂O₅-WO₃/TiO₂ catalysts (denoted as VWT) have been also applied for eliminating the CVOCs, especially those from the municipal solid waste (MSW) incineration. However, the effect of heavy metals on the reaction characteristics of this catalyst is lack of exploration, which has been considered to be a main cause for catalyst deactivation. Herein, we investigated the effect of lead (Pb), a critical heavy meal in the flue gas of MSW incineration, on the catalytic elimination of chlorobenzene (CB) over the VWT catalyst. Variations of catalytic activity, CO₂/HCl selectivity and chlorine adsorption/desorption behaviors were evaluated. In particular, the reaction byproducts with and without Pb loadings were qualitatively and quantitatively analyzed. It was noted that the loading of excessive Pb could change the reaction route over the VWT catalyst, leading to low CB oxidation efficiency and CO₂ selectivity. However, these Pb spices likely acted as "a sink" to capture the dissociated Cl that hindered the electrophilic chlorination reaction, and avoided the formation of more toxic polychlorinated byproducts.

Ethylene glycol assisted synthesis of hierarchical Fe-ZSM-5 nanorods assembled microsphere for adsorption Fenton degradation of chlorobenzene

A unique zeolite catalyst, Fe doped ZSM-5 microsphere assembled by uniform nanorod-like crystals with hierarchical pore structure, was successfully synthesized and applied for the adsorption and degradation of trace chlorobenzene (CB) in the presence of H₂O₂. The organic ferric salts as the precursors, ethylene glycol as a chelating/reducing agent and the dynamic two-stage temperature-varied hydrothermal technique, together made the synthesized hierarchical Fe-ZSM-5 nanorods assembled microspheres (FZ-CA-5EG) to be characterized by abundant highly dispersed and valency-controlled framework Fe^3+/2+ species. As a result of these features, the FZ-CA-5EG showed excellent ability of adsorption and degradation efficiency of CB, and enhanced durability due to negligible leaching of framework Fe species. Moreover, the hydroxyl radicals were determined as the main the reactive oxygen species of CB oxidation degradation, and a possible adsorption-oxidation degradation pathway was proposed.

Catalytic oxidation of chlorobenzene over noble metals (Pd, Pt, Ru, Rh) and the distributions of polychlorinated by-products

Catalytic oxidation of chlorobenzene over noble metal catalysts Pd/TiO₂, Pt/TiO₂, Ru/TiO₂, and Rh/TiO₂ was evaluated, and Ru/TiO₂ contributed the highest catalytic activity and CO₂ selectivity. During the oxidation, polychlorinated benzenes PhCl_x (x ≥ 2) were observed, and Ru/TiO₂ showed apparently lower PhCl_x concentrations than other three samples. With the improvement of temperature, the maximum concentration appeared in the sequence of dichlorobenzene (PhCl₂), trichlorobenzene (PhCl₃), tetrachlorobenzene (PhCl₄), and pentchlorobenzene (PhCl₅), whereas the concentration of hexachlorobenzene (PhCl₆) was always low and showed no apparent regularity. Besides, the dioxin-like PCBs (dl-PCBs) were collected and analyzed for Pd/TiO₂ and Ru/TiO₂. The ∑dl-PCBs produced by Pd/TiO₂ (0.0055 ng WHO-TEQ/Nm³) was about 1.5 times that of Ru/TiO₂ (0.0027 ng WHO-TEQ/Nm³). XPS analyses revealed that Ru/TiO₂-used and Rh/TiO₂-used gave the lowest and the highest Cl content of 0.61% and 1.87%. Ru/TiO₂-used afforded the lowest (Cl_ad+Cl_or)/Cl value (22.1%) and the highest Cl_br/Cl value (77.9%), which might be an important reason for its strongest chlorine removal ability and the lowest yields of polychlorinated by-products, whereas other three catalysts showed similarity in the Cl distributions. Additionally, systematic in-situ FTIR studies were conducted, and a reaction mechanism for the catalytic oxidation of chlorobenzene was proposed.

Immobilized palladium-catalyzed electro-Fenton's degradation of chlorobenzene in groundwater

This study investigates the effect of palladium (Pd) form on the electrochemical degradation of chlorobenzene in groundwater by palladium-catalyzed electro-Fenton (EF) reaction. In batch and flow-through column reactors, EF was initiated via in-situ electrochemical formation of hydrogen peroxide (H2O2) supported by Pd on alumina powder or by palladized polyacrylic acid (PAA) in a polyvinylidene fluoride (PVDF) membrane (Pd-PVDF/PAA). In a mixed batch reactor containing 10 mg L-1 Fe2+, 2 g L-1 of catalyst in powder form (1% Pd, 20 mg L-1 of Pd) and an initial pH of 3, chlorobenzene was degraded under 120 mA current following a first-order decay rate showing 96% removal within 60 min. Under the same conditions, a rotating Pd-PVDF/PAA disk produced 88% of chlorobenzene degradation. In the column experiment with automatic pH adjustment, 71% of chlorobenzene was removed within 120 min with 10 mg L-1 Fe2+, and 2 g L-1 catalyst in pellet form (0.5% Pd, 10 mg L-1 of Pd) under 60 mA. The EF reaction can be achieved under flow, without external pH adjustment and H2O2 addition, and can be applied for in-situ groundwater treatment. Furthermore, the rotating PVDF-PAA membrane with immobilized Pd-catalyst showed an effective and low maintenance option for employing Pd catalyst for water treatment.

Occurrence and characteristics of PCDD/Fs formed from Chlorobenzenes production in China

China had a large production capacity of chlorobenzenes. An extensive investigation was conducted to understand the occurrence and characteristics of PCDD/Fs from four chlorobenzene production plants. The concentrations of PCDD/Fs in mono-CB production and in a new di-CB production routine were revealed. Concentrations of PCDD/Fs in residues, byproducts, products and wastewater varied between 8.4*10³-4.0*10⁶ ng TEQ/kg, 1.5-5.0*10⁴ ng TEQ/kg, ND∼0.12 ng TEQ/kg and 6.0*10⁴-9.1*10⁴ pg TEQ/L, respectively. OCDF, 2,3,4,7,8-PeCDF, 1,2,3,4,7,8-HxCDF, and 2,3,7,8-TeCDF were the most abundant congeners of the 17 2,3,7,8-substituted PCDD/Fs. In most samples, PCDFs contributed more than 99% of the total TEQs of PCDD/Fs, in which 2,3,4,7,8-PeCDF was the dominating contributor. It is inferred PCDFs were mainly formed in the chlorination reactions. The emission factors were suggested and the amount of PCDD/Fs formed in CB production was estimated to be 450 g TEQ in 2012. Residue, byproduct and wastewater were potentially the main pathways of PCDD/Fs to the environmental releases.

Evaluation of the hydrological flow paths in a gravel bed filter modeling a horizontal subsurface flow wetland by using a multi-tracer experiment

In recent years, constructed wetland systems have become into focus as means of cost-efficient organic contaminant management. Wetland systems provide a highly reactive environment in which several removal pathways of organic chemicals may be present at the same time; however, specific elimination processes and hydraulic conditions are usually separately investigated and thus not fully understood. The flow system in a three dimensional pilot-scale horizontal subsurface constructed wetland was investigated applying a multi-tracer test combined with a mathematical model to evaluate the flow and transport processes. The results indicate the existence of a multiple flow system with two distinct flow paths through the gravel bed and a preferential flow at the bottom transporting 68% of tracer mass resulting from the inflow design of the model wetland system. There the removal of main contaminant chlorobenzene was up to 52% based on different calculation approaches. Determined retention times in the range of 22d to 32.5d the wetland has a heterogeneous flow pattern. Differences between simulated and measured tracer concentrations in the upper sediment indicate diffusion dominated processes due to stagnant water zones. The tracer study combining experimental evaluation with mathematical modeling demonstrated the complexity of flow and transport processes in the constructed wetlands which need to be taken into account during interpretation of the determining attenuation processes.

Catalytic oxidation of PCDD/F on a V2O5-WO3/TiO2 catalyst: Effect of chlorinated benzenes and chlorinated phenols

Catalytic oxidation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) is a well-proven technique, applied in a rising number of Municipal Solid Waste Incineration plants, yet the simultaneous and possibly competitive co-oxidation of other compounds, such as chlorinated benzenes (CBz) or phenols (CP), is still poorly documented. In this study, a grinded commercial catalyst (vanadium-tungsten supported on titanium dioxide) was submitted to exploratory testing: the PCDD/F present in a gas test flow were catalytically oxidised (200°C, 10,000h^-1), either as such or in the presence of benzene (Bz), monochlorobenzene (MCBz), and 1,2-dichlorobenzene (DCBz) and the effect of these additions on the catalytic destruction of PCDD/F was verified experimentally. Both removal efficiency (RE) and destruction efficiency (DE) declined during the exploratory testing and, importantly, some DCBz even converted into supplemental PCDD/F. Also, the occurrence of carbon deposition negatively influenced catalytic oxidation activity. Regeneration with oxygen or air allowed to remove the deposited carbon and the original catalytic activity was largely restored after calcination. In a second part of this study, the PCDD/F-formation from DCBz, hexachlorobenzene (HCBz), o-monochlorophenol (o-MCP) and pentachlorophenol (PeCP) was demonstrated and tentatively explored. To prepare for further elucidation of the reaction mechanism, a complete isomer-specific analysis was prepared.

N-acyl-homoserine lactone dynamics during biofilm formation of a 1,2,4-trichlorobenzene mineralizing community on clay

In Gram-negative bacteria, quorum sensing systems are based on the N-acyl-homoserine lactone (AHL) molecule. The objective of this study was to investigate the role of quorum sensing systems during biofilm formation by a microbial community while degrading the pollutant. Our model system included 1,2,4-trichlorobenzene (1,2,4-TCB) and its mineralizing Gram-negative bacterial community to investigate the relationships between AHL dynamics, cell growth and pollutant degradation. Biomineralization of 1,2,4-TCB was monitored for both the planktonic bacterial community with and without sterile clay particles in liquid cultures. The bacterial growth and production of AHLs were quantified by fluorescent in situ hybridization and immunoassay analysis, respectively. A rapid production of AHLs which occurred coincided with the biofilm formation and the increase of mineralization rate of 1,2,4-TCB in liquid cultures. There is a positive correlation between the cell density of Bodertella on the clay particles and mineralization rate of 1,2,4-TCB. 3-oxo-C_12:1-HSL appears to be the dominant AHL with the highest intensity and rapidly degraded by the bacterial community via two main consecutive reactions (lactone hydrolysis and decarboxylic reaction). These findings suggest that the integrated AHLs and their degraded products play a crucial role in biofilm formation and biomineralization of 1,2,4-TCB in culture.

Pharmaceuticals, benzene, toluene and chlorobenzene removal from contaminated groundwater by combined UV/H2O2 photo-oxidation and aeration

This study was performed to test the feasibility of several decontamination methods for remediating heavily contaminated groundwater in a real contaminated locality in the Czech Republic, where a pharmaceuticals plant has been in operation for more than 80 years. The site is polluted mainly by recalcitrant psychopharmaceuticals and monoaromatic hydrocarbons, such as benzene, toluene and chlorobenzene. For this purpose, an advanced oxidation technique employing UV radiation with hydrogen peroxide dosing was employed, in combination with simple aeration pretreatment. The results showed that UV/H₂O₂ was an efficient and necessary step for degradation of the pharmaceuticals; however, the monoaromatics were already removed during the aeration step. Characterization of the removal mechanisms participating in the aeration revealed that volatilization, co-precipitation and biodegradation contributed to the process. These findings were supported by bacterial metabolite analyses, phospholipid fatty acid analysis, qPCR of representatives of the degradative genes and detailed characterization of the formed precipitate using Mössbauer spectroscopy and scanning electron microscopy. Further tests were carried out in a continuous arrangement directly connected to the wells already present in the locality. The results documented the feasibility of combination of the photo-reactor employing UV/H₂O₂ together with aeration pretreatment for 4 months, where the overall decontamination efficiency ranged from 72% to 99% of the pharmaceuticals. We recorded even better results for the monoaromatics decontamination except for one month, when we encountered some technical problems with the aeration pump. This demonstrated the necessity of using the aeration step.

Efficient degradation of chlorobenzene in a non-thermal plasma catalytic reactor supported on CeO2/HZSM-5 catalysts

Chlorobenzene removal was investigated in a non-thermal plasma reactor using CeO₂/HZSM-5 catalysts. The performance of catalysts was evaluated in terms of removal and energy efficiency. The decomposition products of chlorobenzene were analyzed. The results show that CeO₂/HZSM-5 exhibited a good catalytic activity, which resulted in enhancements of chlorobenzene removal, energy efficiency, and the formation of lower amounts of by-products. With regards to CO₂ selectivity, the presence of catalysts favors the oxidation of by-products, leading to a higher CO₂ selectivity. With respect to ozone, which is considered as an unavoidable by-product in air plasma reactors, a noticeable decrease in its concentration was observed in the presence of catalysts. Furthermore, the stability of the catalyst was investigated by analyzing the evolution of conversion in time. The experiment results indicated that CeO₂/HZSM-5 catalysts have excellent stability: chlorobenzene conversion only decreased from 78% to 60% after 75hr, which means that the CeO₂/HZSM-5 suffered a slight deactivation. Some organic compounds and chlorinated intermediates were adsorbed or deposited on the catalysts surface as shown by the results of Fourier Transform Infrared (FT-IR) spectroscopy, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses of the catalyst before and after the reaction, revealing the cause of catalyst deactivation.

Effects of tidal operation on pilot-scale horizontal subsurface flow constructed wetland treating sulfate rich wastewater contaminated by chlorinated hydrocarbons

Three different flow regimes were carried out in a pilot-scale horizontal subsurface flow constructed wetland-treating sulfate rich wastewater contaminated with monochlorobenzene (MCB) and perchloroethene (PCE). The three regimes were continuous flow, 7-day cycle discontinuous flow, and 2.5-day cycle discontinuous flow. The results show that intensifying the tidal regime (2.5-day cycle) significantly enhanced MCB removal before 2 m from the inlet and increasing PCE removal efficiency at 0.5 m. The PCE dechlorination process was promoted with tidal operation, especially under the 2.5-day cycle regime, with significant increases of cis-1,2- dichloroethenes (DCEs), vinyl chloride (VC), and ethene, but trans-1,2-DCE was significantly decreased after tidal operation. Due to the high sulfate concentration in the influent, sulfide was observed in pore water up to 20 and 23 mg L^-1 under continuous flow and 7-day cycle regime, respectively. However, sulfide concentrations decreased to less than 4 mg L^-1 under intensified tidal operation (2.5-day cycle). The increase of oxygen concentration in pore water through intensified tidal operation resulted in better MCB removal performance and the successful inhibition of sulfate reduction. In conclusion, intensifying tidal operation is an effective approach for the treatment of chlorinated hydrocarbons and inhibiting sulfide accumulation in horizontal subsurface flow constructed wetland.

Synthesis, characterization, and photocatalytic activity of porous La-N-co-doped TiO2 nanotubes for gaseous chlorobenzene oxidation

The photocatalytic oxidation of gaseous chlorobenzene (CB) by the 365nm-induced photocatalyst La/N-TiO2, synthesized via a sol-gel and hydrothermal method, was evaluated. Response surface methodology (RSM) was used to model and optimize the conditions for synthesis of the photocatalyst. The optimal photocatalyst was 1.2La/0.5N-TiO2 (0.5) and the effects of La/N on crystalline structure, particle morphology, surface element content, and other structural characteristics were investigated by XRD (X-ray diffraction), TEM (Transmission Electron Microscopy), FTIR (Fourier transform infrared spectroscopy), UV-vis (Ultraviolet-visible spectroscopy), and BET (Brunauer Emmett Teller). Greater surface area and smaller particle size were produced with the co-doped TiO2 nanotubes than with reference TiO2. The removal of CB was effective when performed using the synthesized photocatalyst, though it was less efficient at higher initial CB concentrations. Various modified Langmuir-Hinshelwood kinetic models involving the adsorption of chlorobenzene and water on different active sites were evaluated. Fitting results suggested that competitive adsorption caused by water molecules could not be neglected, especially for environments with high relative humidity. The reaction intermediates found after GC-MS (Gas chromatography-mass spectrometry) analysis indicated that most were soluble, low-toxicity, or both. The results demonstrated that the prepared photocatalyst had high activity for VOC (volatile organic compounds) conversion and may be used as a pretreatment prior to biopurification.

The effect of natural organic matter on bioaccumulation and toxicity of chlorobenzenes to green algae

The effect of natural organic matter (NOM) on toxicity and bioavailability of hydrophobic organic contaminants (HOCs) to aquatic organisms has been investigated with conflicting results and undefined mechanisms, and few studies have been conducted on volatile HOCs. In this study, six volatile chlorobenzenes (CBs) with 1-6 chlorine substitutions were investigated for their bioaccumulation in an acute toxicity to a green alga (Chlorella pyrenoidosa) in the presence/absence of Suwannee River NOM (SRNOM). The fluorescence quenching efficiency of SRNOM increased as the number of chlorine substitutions of CBs increased. SRNOM increased the cell-surface hydrophobicity of algae and decreased the release rates of algae-accumulated CBs, thus increasing the concentration factor (CF) and accumulation of the CBs in the algae. SRNOM increased the toxicity of monochlorobenzene and 1,2-dichlorobenzene, decreased the toxicity of pentachlorobenzene and hexachlorobenzene, and had no significant effect on the toxicity of 1,2,3-trichlorobenzene and 1,2,3,4-tetrachlorobenzene. Relationships between the 96 h CF/IC50 (i.e., the CB concentration leading to a 50% algal growth reduction compared with the control) and physicochemical properties of CBs with/without SRNOM were established, providing reasonable explanations for the experimental results. These findings will help with the accurate assessment of ecological risks of organic pollutants in the presence of NOM.

Releases of chlorobenzenes, chlorophenols and dioxins during fireworks

In fireworks, organic additives with high chlorine content such as hexachlorobenzene (HCB) are used for the improvement of illumination effects. In the course of a monitoring campaign for the detection of HCB in fireworks, atmospheric concentrations of chlorobenzenes (CBs), chlorophenols (CPs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), were measured during the Swiss National holiday August 1, 2011 which is celebrated with fireworks nationwide. Samples were collected in the city of Zurich using high-volume air samplers equipped with quartz fiber filters and poly-urethane foam plugs. With one sampling period of 3h, a peak HCB concentration of 297 pg m(-3) was detected. Maximum total concentrations of pentachlorophenol and PCDD/Fs were 218 pg m(-3) and 61 fg I-TEQ m(-3), respectively. These levels are in the order of ten times above background concentrations measured one week before and two weeks after the event. Atmospheric emissions of HCB and CPs were quantified using a multimedia mass balance model to interpret the field measurements resulting in total emissions of HCB and CPs during the event of 23 g and 25 g, respectively. Based on per capita amounts this corresponds to total annual emissions from fireworks of 1.5 kg for each of the two pollutants in Switzerland. Starting from an estimation of the total worldwide emissions of HCB, in Switzerland emissions from fireworks may represent about 2-14% of total HCB releases.

Atmospheric oxidation mechanism of chlorobenzene

The atmospheric oxidation mechanism of chlorobenzene (CB) initiated by the OH radicals is investigated at M06-2X/6-311++G(2df, 2p) and ROCBS-QB3 levels. The oxidation is initiated by OH addition to the ortho (∼50%), para (∼33%) and meta (∼17%) positions, forming CB-OH adducts as R2, R3, and R4; while the ipso-addition is negligible (∼0.2%). The reactions of the CB-OH adducts with the atmospheric oxygen are further investigated in detail by coupling the unimolecular reaction rate theory calculations with master-equation (RRKM-ME). The CB-OH adducts react with O2 either by irreversible H-abstraction to form chlorophenol and HO2 or by reversible additions to form CB-OH-O2 radicals, which subsequently cyclize to bicyclic radicals. RRKM-ME calculations show that the addition reactions of CB-OH and O2 at the atmospheric pressure are close to but not yet reach their high-pressure-limits. The RRKM-ME simulations predict the yields of 93%, 38%, and 74% for ortho-, meta- and para-chlorophenols from the reactions of O2 with R2, R3 and R4, being lower than their high-pressure-limit yields of 95%, 48%, an 80%, respectively. Overall, the yield of chlorophenols is determined as 72% at the atmospheric pressure.

Optimization of headspace solid phase microextraction based on nano-structured ZnO combined with gas chromatography-mass spectrometry for preconcentration and determination of ultra-traces of chlorobenzenes in environmental samples

In this study, a simple, novel and efficient preconcentration method for the determination of some chlorobenzenes (monochlorobenzene (MCB), three isomeric forms of dichlorobenzene (diCB), 1,3,5-trichlorobenzene (triCB) and hexachlorobenze (hexaCB)) has been developed using a headspace solid phase microextraction (HS-SPME) based on nano-structured ZnO combined with capillary gas chromatography-mass spectrometry (GC-MS). ZnO nanorods have been grown on fused silica fibers using a hydrothermal process. The diameter of ZnO nanorods was in the range of 50-80 nm. The effect of different variables on the extraction efficiency was studied simultaneously using an experimental design. The variables of interest in the HS-SPME were stirring rate, desorption time and temperature, ionic strength, extraction time and temperature. For this purpose, a multivariate strategy was applied based on an experimental design using a Plackett-Burman design for screening and a Box-Behnken design for optimizing of the significant factors. The detection limit and relative standard deviation (RSD) (n=5) for the target analytes were in the range of 0.01-0.1 ng L(-1) and 4.3-7.6%, respectively. The developed technique was found to be successfully applicable to preconcentration and determination of the target analytes in environmental water and soil samples.

Photochemical sample treatment: a greener approach to chlorobenzene determination in sediments

Due to worker׳s exposure, solvent and stationary phases׳ consumption, sample purification is one of the most polluting steps in analytical procedures for determination of organic pollutants in real samples. The use of photochemical sample treatment represents a valid alternative methodology for extracts clean up allowing for a reduction of the used amount of organic solvents. In this paper we report the first application on the photolytic destruction of organic substances to eliminate some of the interferences in the analysis of Chlorobenzenes in sediment samples. The method׳s efficiency and robustness were compared with classic silica column purification process currently used in clean up procedures in sediment analysis. Quality parameters such as recovery, linearity and reproducibility were studied. The entire procedure was validated by three replicate analysis of spiked real sediment sample. The quantification limits (LOQ) obtained by us ranged from 1.0 to 2.3 ng g(-1), while the detection limits (LOD) were of 1.0 ng g(-1). The RSD for each congener was below 10% and recoveries were in the range 95-130%. Results based on the analysis of real samples showed similar or improved detection thresholds and pointed out the advantages of the photochemical methodology in terms of costs, use of chemical substances and operator׳s safety according to Green Analytical Chemistry principles.

Iron oxides stimulate microbial monochlorobenzene in situ transformation in constructed wetlands and laboratory systems

Natural wetlands are transition zones between anoxic ground and oxic surface water which may enhance the (bio)transformation potential for recalcitrant chloro-organic contaminants due to the unique geochemical conditions and gradients. Monochlorobenzene (MCB) is a frequently detected groundwater contaminant which is toxic and was thought to be persistent under anoxic conditions. Furthermore, to date, no degradation pathways for anoxic MCB removal have been proven in the field. Hence, it is important to investigate MCB biodegradation in the environment, as groundwater is an important drinking water source in many European countries. Therefore, two pilot-scale horizontal subsurface-flow constructed wetlands, planted and unplanted, were used to investigate the processes in situ contributing to the biotransformation of MCB in these gradient systems. The wetlands were fed with anoxic MCB-contaminated groundwater from a nearby aquifer in Bitterfeld, Germany. An overall MCB removal was observed in both wetlands, whereas just 10% of the original MCB inflow concentration was detected in the ponds. In particular in the gravel bed of the planted wetland, MCB removal was highest in summer season with 73 ± 9% compared to the unplanted one with 40 ± 5%. Whereas the MCB concentrations rapidly decreased in the transition zone of unplanted gravel to the pond, a significant MCB removal was already determined in the anoxic gravel bed of the planted system. The investigation of hydro-geochemical parameters revealed that iron and sulphate reduction were relevant redox processes in both wetlands. In parallel, the addition of ferric iron or nitrate stimulated the mineralisation of MCB in laboratory microcosms with anoxic groundwater from the same source, indicating that the potential for anaerobic microbial degradation of MCB is present at the field site.

Gas phase catalytic hydrodechlorination of chlorobenzene over cobalt phosphide catalysts with different P contents

The gas phase catalytic hydrodechlorination (HDC) of chlorobenzene (CB) at atmospheric pressure was investigated over silica-supported cobalt and cobalt phosphide catalysts containing different P loading and a fixed amount of cobalt (5 wt.%). The effect of the initial P/Co molar ratio on the stoichiometry of the cobalt phosphide phase, the acidity and the hydrogen activation capability were discussed and these properties correlated with the catalytic activity. Catalytic results indicated that the cobalt phosphide phase is much more active than the monometallic cobalt one. The activity raised with the P content present in the sample due to the formation of the CoP phase instead of the Co₂P one, which favored the formation of hydrogen spillover species, increased the amount of weak acid sites and the number of exposed superficial cobalt atoms probably related to a better dispersion of the active phase. All the catalysts gave rise benzene as the main reaction product.