Chlorobenzene Removal Research Articles

Mechanism of chlorobenzene removal in biotrickling filter enhanced by non-thermal plasma: Insights from biodiversity and functional gene perspectives

Biotrickling filter (BTF) technology is inefficient in the treatment of Cl-containing volatile organic compounds (VOCs) such as chlorobenzene (CB). This study adopted non-thermal plasma (NTP) as a pretreatment and conducted in-depth analyses, especially in microorganisms, to investigate strengthening mechanism of a NTP to a BTF in the process. The introduction of NTP enhance efficiency of CB removal from 65 % to 90 %, and CO2 generation from 60 % to 85 %. It is found that the protein content of the extracellular polymeric substances increases from 212 × 10-3 mg·g−1 filler to 299 × 10-3 mg·g−1 filler, thus CB capturing and utilization enhanced. Metagenomic analysis showed that bacteria with CB-degrading properties were enriched in BTF, and CB was involved in cellular metabolism as a carbon source. The presence of active substances from NTP is found to stimulate the ability of BTF treatment. The findings of this study will provide theoretical support for the application of NTP–BTF technology.

Remarkable chlorobenzene absorption by carboxylic acid based deep eutectic solvents

A novel purification technology for the absorption of chlorobenzene (CB) using carboxylic acid based deep eutectic solvents (DESs) as absorbents was proposed and systematically investigated, combining experiments with microscopic molecular simulations. A series of newly designed DESs synthesized and evaluated for their CB absorption performance, revealing that DESs with quaternary phosphonate as hydrogen bond acceptors (HBAs) and long-chain fatty acid-based hydrogen bond donors (HBDs) exhibit remarkable CB absorption performance. Additionally, it illustrated that both the structure and acidity of HBD significantly impact the absorption capacity. Consequently, the DES comprising tetrabutylphosphonium chloride ([P4444][Cl]) and decanoic acid (DecA) with molar ratio of 1:2 was identified as the possessing optimal absorbent. Notably, after undergoing five cycles of absorption–desorption processes, the CB absorption capacity in [P4444][Cl]-DceA (1:2) was almost maintained at approximately 467 mg/g (Henry’s law constant of 4.90Pa m3/mol) at 30 °C. NMR characterization revealed no chemical bonding between [P4444][Cl]-DceA and CB, indicating that it’s a physical absorption process. Finally, the interaction mechanism was elucidated by COSMO-RS model, quantum chemical calculations and wave function analysis. This work fills the gap of CB removal by DES absorption and proves that DES is a promising green solvent for the removal of chlorinated volatile organic compounds.

Sulfur-resistant mechanism of MnOx@CeO2@MgO core-shell catalyst in simultaneous removal of NOx and chlorobenzene

Herein, Mn-Ce based catalysts with different structures were rationally designed to explore their sulfur-resistant mechanism for simultaneous removal of NOx and chlorobenzene (CB) from waste incineration at low temperature. In the presence of SO2, MnOx@CeO2@MgO exhibits the highest sulfur resistance among prepared catalysts. Both NOx and CB conversion over MnOx@CeO2@MgO can reach up to 80 % at 300 °C. However, the significant deactivation is observed for MnCeMgOx within all temperature ranges. For the selectivity of products, MnOx@CeO2@MgO displays the excellent N2 selectivity (93 %) and good CO2 selectivity (80 %) at 300 °C. Compared with NO reduction, SO2 has a greater impact on CB destruction due to the consumption of reactive oxygen species during SO2 oxidation. The reduction of active oxygen is proposed to be the reason for the significant inhibition of CB oxidation. The addition of MgO shell increases the proportion of lattice oxygen, which is beneficial to improving the sulfur resistance of MnOx@CeO2@MgO catalyst. In addition, SO2 can react with MgO preferentially to protect the active sites and improve the sulfur resistance. This work indicates that MnOx@CeO2@MgO core-shell catalyst with good sulfur tolerance and stability is expected to be applied in the potential application.

A superior Mn5CeTi5Ox catalysts for synergistic catalytic removal of chlorobenzene and NOx: Performance enhancement and mechanism studies

The transition metal titanium-doped Mn-Ce-Ox catalysts catalyst were employed to achieve synergetic removal of NO and CB at 180–220 °C. The Mn5CeTi5Ox catalyst with a molar ratio of Mn/Ce/Ti = 5:1:5 exhibits excellent activity, and the NOx and CB removal efficiencies reach 96 % and 89 % at 160–220 °C, respectively. The selectivity for N2 and CO2 are 93 % and 78 %, respectively. The N2-physisorption, NH3-TPD, H2-TPR and XPS results show that Ti doping makes the catalyst possess a mesoporous structure, suitable particle sizes, and excellent redox and Lewis site properties. All of these features contribute to the observed high NO and CB removal efficiency. The synergetic removal of CB and NO over Mn5CeTi5Ox results from the synergistic catalysis between the redox and the solid acid. On the one hand, in the synergistic removal process, CB and NH3 are competitively adsorbed on the catalyst surface, resulting in a decrease in the NH3-SCR activity. On the other hand, the removal of NO and CB has a synergetic effect. The byproduct NO2 produced by the NH3-SCR reaction promotes the oxidation of CB, which is beneficial for CB removal. Moreover, the consumption of NO2 indirectly promotes the NH3-SCR reaction, which partially compensates for the decrease in the NO removal efficiency caused by competitive adsorption between NH3 and CB. Ti doping promotes the participation of the SCR byproduct NO2 in the CBCO reaction and promotes the formation of maleic acid, an intermediate product of CB oxidation. In summary, the Mn5CeTi5Ox catalyst exhibits good activity for the synergistic removal of NOx and CB and is a promising candidate for the effective and economical removal of NO and CB during waste incineration.

Simultaneous removal of chlorobenzene and Cr(VI) from groundwater using microbial fuel cell with low-cost Si modified ferrihydrite electrodes

Aromatic chlorinated compounds and Cr(VI) in groundwater pose significant challenges due to their resistance. This study explores microbial fuel cells using low-cost Si-modified ferrihydrite (SiFh) electrodes for simultaneous chlorobenzene and Cr(VI) removal. The voltage output of MFC assembled with SiFh modified electrode was approximately 1.63 times higher than the bare electrode, achieving 1.23 times higher in chlorobenzene degradation efficiency. CF-SiFh loaded MFC had the highest power generation and best EET efficiency, which was positive to greatest and fastest chlorobenzene removal. Microbial community analysis identified the dominance of Cupriavidus and Pandoraea in chlorobenzene oxidation, while Lentimicrobiaceae and Rhodobacteraceae were key genera that may facilitate direct and indirect electron transfer within the biofilms. Cr species analysis in solution and solids confirmed it was reduced to Cr(OH)3 or CrxFe1-x(OH)3 coprecipitates at cathode. MFCs with SiFh-modified electrodes thus offer a promising technology for simultaneous chlorinated compound and Cr(VI) removal, promising in contaminated groundwater remediation.

Dielectric barrier discharge plasma for chlorobenzene removal: Performance optimization, process modeling, and toxicity evaluation

Bio-purification has been recognized as an effective method of removal of volatile organic pollutants (VOCs), yet exist a technical bottleneck of low removal efficiency in the treatment of high toxicity and low water-soluble VOCs, especially chlorobenzene (CB). Herein, dielectric barrier discharge (DBD) technology was used as a pre-treatment technology, and the effect of process parameters (specific input of energy (SIE), inlet concentration of CB, humidity, and discharge length) of DBD on the removal performance of CB was analyzed, in order to investigate the feasibility of DBD as a pre-treatment approach for bio-purification. Taking energy yield, by-product analysis and exhaust evaluation as considerations, an SIE of 1,131.57 J·L-1, an inlet CB concentration of 300 ppm, a humidity of 50 %, and a discharge length of 10 cm were selected as the most suitable experimental conditions for the air DBD reactor. The temperature of gas flow was analyzed. Results suggested that DBD have no adverse thermal effect on the subsequent biotechnology (decreased by about 8 K during the discharge process). The temperature change caused by the degradation of CB (e.g., phenyl ring-opening and other processes) accounts for about 90 % of the total temperature change, where remaining part of temperature decreased caused by the large number of active substances produced by electron excitation, collision and cracking during discharge. The regulation of short-life active substances (e.g., ·NO, ·NO2,·OH, and O2–·) further reduced the toxicity of the outlet gas generated by DBD through affect the contents the long-life active substances (e.g., H2O2, and O3). This study provides a better understanding of the feasibility of DBD as a treatment for bio-purification and a new coupling technology for the effective removal of CB.

Catalytic Oxidation of Chlorobenzene over HSiW/CeO2 as a Co-Benefit of NOx Reduction: Remarkable Inhibition of Chlorobenzene Oxidation by NH3.

There is an urgent need to develop novel and high-performance catalysts for chlorinated volatile organic compound oxidation as a co-benefit of NOx. In this work, HSiW/CeO2 was used for chlorobenzene (CB) oxidation as a co-benefit of NOx reduction and the inhibition mechanism of NH3 was explored. CB oxidation over HSiW/CeO2 primarily followed the Mars-van-Krevelen mechanism and the Eley-Rideal mechanism, and the CB oxidation rate was influenced by the concentrations of surface adsorbed CB, Ce4+ ions, lattice oxygen species, gaseous CB, and surface adsorbed oxygen species. NH3 not only strongly inhibited CB adsorption onto HSiW/CeO2, but also noticeably decreased the amount of lattice oxygen species; hence, NH3 had a detrimental effect on the Mars-van-Krevelen mechanism. Meanwhile, NH3 caused a decrease in the amount of oxygen species adsorbed on HSiW/CeO2, which hindered the Eley-Rideal mechanism of CB oxidation. Hence, NH3 significantly hindered CB oxidation over HSiW/CeO2. This suggests that the removal of NOx and CB over this catalyst operated more like a two-stage process rather than a synergistic one. Therefore, to achieve simultaneous NOx and CB removal, it would be more meaningful to focus on improving the performances of HSiW/CeO2 for NOx reduction and CB oxidation separately.

Synergistic catalytic removal of NOx and chlorinated organics through the cooperation of different active sites

The synergistic removal of NOx and chlorinated volatile organic compounds (CVOCs) has become the hot topic in the field of environmental catalysis. However, due to the trade-off effects between catalytic reduction of NOx and catalytic oxidation of CVOCs, it is indispensable to achieve well-matched redox property and acidity. Herein, synergistic catalytic removal of NOx and chlorobenzene (CB, as the model of CVOCs) has been originally demonstrated over a Co-doped SmMn2O5 mullite catalyst. Two kinds of Mn-Mn sites existed in Mn-O-Mn-Mn and Co-O-Mn-Mn sites were constructed, which owned gradient redox ability. It has been demonstrated that the cooperation of different active sites can achieve the balanced redox and acidic property of the SmMn2O5 catalyst. It is interesting that the d band center of Mn-Mn sites in two different sites was decreased by the introduction of Co, which inhibited the nitrate species deposition and significantly improved the N2 selectivity. The Co-O-Mn-Mn sites were beneficial to the oxidation of CB and it cooperates with Mn-O-Mn-Mn to promote the synergistic catalytic performance. This work paves the way for synergistic removal of NOx and CVOCs over cooperative active sites in catalysts.

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.

Deep Oxidation of Chlorinated VOCs by Efficient Catalytic Peroxide Activation over Nanoconfined Co@NCNT Catalysts.

The catalytic removal of chlorinated VOCs (CVOCs) in gas-solid reactions usually suffers from chlorine-containing byproduct formation and catalyst deactivation. AOP wet scrubber has recently attracted ever-increasing interest in VOC treatment due to its advantages of high efficiency and no gaseous byproduct emission. Herein, the low-valence Co nanoparticles (NPs) confined in a N-doped carbon nanotube (Co@NCNT) were studied to activate peroxymonosulfate (PMS) for efficient CVOC removal in a wet scrubber. Co@NCNT exhibited unprecedented catalytic activity, recyclability, and low Co ion leakage (0.19 mg L-1) for chlorobenzene degradation in a very wide pH range (3-11). The chlorobenzene removal efficiency was kept stable above 90% over Co@NCNT, much higher than that of nonconfined Co@NCNS (45%). The low-valence Co NPs achieved a continuous electron redox cycling (Co0/Co2+ → Co3+ → Co0/Co2+) and greatly promoted the O-O bond dissociation of PMS with the least energy (0.83 eV) inside the channel of Co@NCNT to form abundant HO• and SO4•-. Thus, the deep oxidation of chlorobenzene was achieved without any biphenyl byproducts from the coupling reaction. This study provided a new avenue for designing novel nanoconfined catalysts with outstanding activity, paving the way for the deep oxidation of CVOC waste gas via AOP wet scrubber.

Defects materials of Institut Lavoisier-125(Ti) materials enhanced photocatalytic activity for toluene and chlorobenzene mixtures degradation: Mechanism study

In this paper, the effect of three monocarboxylic acids on MIL-125 synthesis was systematically investigated and the results were discussed in detail. X-ray diffractometry (XRD) and nitrogen adsorption–desorption curves indicated that small molecule acids (acetic acid, propionic acid and butyric acid) affected the morphology of MIL-125 and induced lamellar pores and structural defects in the crystals. Thermogravimetric measurements confirmed the presence of acid-regulated defective metal–organic frameworks (MOFs). Electrochemical tests and density function theory calculations indicated that acid modulation could change the forbidden bandwidth of the material. The acid modification strategy effectively promoted the transfer of photogenerated electrons and enhanced the adsorption and activation of O2 and H2O molecules, generating reactive radicals. The modified MOFs also showed excellent performance in the removal of mixed toluene and chlorobenzene. The degradation pathways of the mixture were analyzed by in situ infrared (IR) and gas chromatography-mass spectrometry (GC–MS). The mixture was converted to chlorophenolic intermediates in the presence of reactive oxygen species, further decomposed to form ethers and ethanol, and finally formed small molecules such as carbon dioxide and water. A feasible method was provided for the preparation of photocatalysts for the treatment of mixed VOCs.

Enhancement of gaseous chlorobenzene biodegradation and power generation in a microbial fuel cell by bifunctional Acinetobacter sp. HY-99C

The efficient biodegradation of volatile chlorinated hydrocarbons using microbial fuel cells (MFCs) offers a feasible approach for purifying waste gas and alleviating energy crises. However, power generation is limited by poor pollutant biodegradation and slow electron transfer. The bifunctional bacterium Acinetobacter sp. HY-99C was screened and used to improve the performance of a conventional MFC. The inoculation of strain HY-99C into the conventional MFC promoted the formation of a compact biofilm with high metabolic activity and an enriched bifunctional genus (Acinetobacter), which resulted in the accelerated decomposition of chlorinated aromatic compounds into biodegradable organic acids. This led to efficient chlorobenzene removal and power generation from the MFC, with a chlorobenzene elimination capacity of 70.8 g m−3 h−1 and power density of 89.6 mW m−2, which are improved over those of previously reported MFCs. This study provides novel insights into enhancing pollutant removal and power generation in MFCs.

Simultaneous catalytic removal of NO and chlorobenzene over Mn–Ce-Sm-Sn-Ox/P84 composite catalytic filter

The integration of surface filtration and catalytic decomposition functions in catalytic bags enables the synergistic removal of multiple pollutants (such as dust, nitrogen oxide, acid gases, and dioxins) in a single reactor, thus effectively reducing the cost and operational difficulties associated with flue gas treatment. In this study, Mn–Ce-Sm-Sn (MCSS) catalysts were prepared and loaded onto high-temperature resistant polyimide (P84) filter through ultrasonic impregnation to create composite catalytic filter. The results demonstrate that the NO conversion rates of the composite catalytic filter consistently achieve above 95 % within the temperature range of 160–260 °C, with a chlorobenzene T90 value of 230 °C. The ultrasonic impregnation method effectively loaded the catalyst onto the filter, ensuring high dispersion both on the surface and inside the filter. This increased exposure of catalyst active sites enhances the catalytic activity of the composite catalytic filter. Additionally, increasing the catalyst loading leads to a gradual decrease in permeability, an increase in pressure drops and the long residence time of the flue gas, thereby improving catalytic activity. Compared to ordinary impregnation methods, ultrasonic impregnation improves the bonding strength between the catalyst and filter, as well as the permeability of the composite catalytic filter under the same loading conditions. Overall, this study presents a novel approach to prepare composite catalytic filter for the simultaneous removal of NO and chlorobenzene at low temperatures.

Metal–organic framework derived bio-anode enhances chlorobenzene removal and electricity generation: Special Ru4+/Ru3+-bridged intracellular electron transfer

Efficient removal of chlorinated organic contaminants using the microbial fuel cell (MFC) provides a promising strategy to alleviate water pollution and energy crisis. However, bio-degradation is challenged by poor biofilm formation and sluggish intracellular electron transfer, causing unsatisfactory electricity generation. To address those problems, a metal–organic framework derivative, Ru-porous TiO2 (Ru-PT) bio-anode has been artfully designed herein for chlorobenzene removal. The Ru-PT bio-anode not only formed a compact anodic biofilm due to the large specific surface area of PT, but more importantly, it introduced special pseudocapacitance-enhanced intracellular electron transfer by slowly implanting Ru4+/Ru3+ redox pair into bacteria. Such a Ru4+/Ru3+ implantation was then found to directionally induce the enrichment of a dual-functional genus (degrader & exoelectrogen), Pseudomonas, thereby enhancing the conversion of bio-refractory chlorophenols towards biodegradable carboxylic acids. These features allowed our MFC to have a resilient chlorobenzene removal and accompanied satisfactory electricity generation, with power density, coulombic efficiency, and turnover frequency reaching 662 mW m−2, 8.7%, and 386,622 s−1, which outcompeted those of other MFCs reported. Further, benefiting from the reversible pseudocapacitance, the Ru-PT bio-anode intriguingly functioned as an internal capacitor for electricity storage. This work provided important insights into cost-effective bio-anode development and offered an avenue for engineering MFC.

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.

Simultaneous catalytic removal of NO and chlorobenzene over MnCeSmSnOx: Catalytic performance and removal mechanism

Mn-based catalysts have great potential in the synergistic removal of NO and chlorobenzene but exhibit serious chlorine poisoning and low catalytic activity at low temperatures. In this study, the performance of MnCeOx for simultaneous catalytic removal of NO and chlorobenzene at low temperatures was optimized by the modification of Sm and Sn. Results showed that the modification of Sm and Sn afforded a loose overall structure of the catalyst with a large specific surface area. The addition of Sm and Sn effectively increased the concentration of Mn4+, Ce3+, chemisorbed oxygen, and the amount of acid on the catalyst surface. This considerably improved the activity of the catalyst for simultaneous removal of NO and chlorobenzene at low temperatures. The intermediates formed by the MCSS-0.086 catalyst during the low-temperature simultaneous catalytic removal of NO and chlorobenzene were CHCl3, CCl4, C2HCl3, and C2Cl4. The presence of SnO2 promoted the deep oxidation of chlorobenzene and inhibited the chlorine poisoning of the catalyst. Thus, the low-temperature stability of the catalyst was improved. The chlorobenzene-oxidation efficiency and the NO-removal efficiency of MCSS-0.086 were more than 90% and 95%, respectively, within the range of 178 °C-300 °C. The NH3-selective catalytic reduction curve of NO removal over the MnCeSmSnOx catalyst followed the Langmuir–Hinshelwood mechanism at low temperatures. The catalytic degradation of chlorobenzene finally yielded small molecules: CO2, H2O, and HCl.

Enhancing bioelectrocatalytic oxidation of gaseous chlorobenzene by introducing transmembrane Ru4+/Ru3+-mediated reversible intracellular electron transfer

Microbial electrolysis cell (MEC) is a cost-effective process to eliminate chlorinated volatile organic compounds. Poor mass transfer and sluggish intracellular electron transfer remain obstacles. To overcome these, a Ru-mesoporous TiO2/macroporous carbon (Ru-MeT/MaC) bio-anode was tailored here. The hierarchically meso-macroporous structure separated biofilm formation and chlorobenzene adsorption, improving chlorobenzene mass transfer. Further, modifying Ru created a reversible intracellular electron transfer pathway by introducing transmembrane Ru4+/Ru3+ redox couple within bacteria. Such a unique transmembrane introduction induced a compelling bacteria-electricity synergism accompanied by the acclimation of dual-functional genera (degrader & exoelectrogen), promoting the decomposition of aromatic compounds toward organic acids. Those features enabled the resulting MEC to exhibit a super-prominent chlorobenzene elimination capacity (136.7 g m−3 h−1) with a short empty bed residence time (60 s), superior to those of state-of-the-art bioelectrocatalytic processes reported. Leveraging the reversible electron transfer, the Ru-MeT/MaC bio-anode was operated in the charging-discharging mode to further enhance chlorobenzene removal. SynopsisThe concept of introducing bioavailable conductive redox couple into bacteria via reasonably designing the functional structure of the bio-anode is expected to enhance the bioelectrocatalytic oxidation of hydrophobic Cl-VOCs and therefore alleviate air pollution.

Synergistic degradation of chlorobenzene using intimate coupling of visible-light responsive TiO2/oxygenous groups decorated g-C3N4 composites and Ralstonia sp. XZW-1

The effective and economic treatment of chlorobenzenes has become one of the most intractable issues in the field of air pollution control. Herein, a visible-light photocatalysis coupled with biodegradation (VPCB) system was developed by integrating an innovative visible-light responsive TiO2/oxygenous groups decorated g-C3N4 (TiO2/OCN) with polyurethane carriers immobilized with Ralstonia sp. XZW-1 for chlorobenzene removal. Performance tests showed that light intensity, preparation of the MICs, catalyst dosage and composition of the TiO2/OCN cast significant influence on chlorobenzene removal efficiency, with the degradation efficiency, mineralization and dechlorination ratios of VPCB achieving 100%, 35.5%, and 99.4% under the optimal conditions, respectively, outcompeting the sum of visible-light photocatalytic system and biodegradation protocols. Cycling tests further demonstrated the excellent stability of VPCB. Mechanism analysis found that increased reactive sites, improved visible-light harvesting, accelerated charge transfer and separation, and the resulting abundant active species jointly contributed to the enhanced photocatalytic activity of TiO2/OCN. Photogenerated holes were most significant active species for chlorobenzene removal, followed by OH and O2− radicals. The carriers could effectively protect microorganisms from light illumination and strong oxidizing species, allowing the further microbial metabolism of chlorobenzene photocatalytic oxidation intermediates with good biodegradability, not only greatly promoting the microbial growth and activity, but further enhancing chlorobenzene photocatalytic degradation. Plausible synergistic mechanism for chlorobenzene degradation between photocatalysis and biodegradation was also revealed. Furthermore, the VPCB system constructed presented wide applicability towards various pollutants, and its performance was found closely related with the hydrophobicity of pollutants. This work provided insight into the design and application of the VPCB system for the efficient and economic treatment of refractory pollutants.

Enhancing photothermal VOCs removal in ZnO-based catalysts via transition metal-based band edge tuning and oxygen vacancy engineering

In this study, the band edge tuning and oxygen vacancy optimization of ZnO-based catalysts were explored via transition metal doping for application to photothermal aromatic and halogenated VOCs degradation. Initial minute doping (0.5 wt %) experiments were conducted to determine the dopant with the highest potential, and it was revealed that Zr4+ doping was able to improve chlorobenzene removal to 74.14 % after 4 h of simulated solar light irradiation at 320 K. Further optimization of Zr (Zr0.05ZnOx; 5 % Zr doping) resulted to even greater reduction of toluene and chlorobenzene, from 300 ppmv to 0.4 ppmv (99.9 %) and 52.9 ppmv (82.4 %), respectively. Additional comparative removal experiments also showed the superior performance of Zr0.05ZnOx in contrast to ZnO. The extent of removal highly depended on the functional group attached, with the removal efficiency following the trend: o-xylene ≥ toluene > benzene > bromobenzene > chlorobenzene. Based from the comprehensive analysis of the EPR, XPS, and UV-DRS results, the observed boost in the photocatalytic activity from pristine ZnO can be attributed to 1) the increase in the concentration of oxygen vacancies, resulting in improving the hole-carrier separation, and 2) the valence band shifts associated to the doping of Zr4+ into the ZnO lattice for an enhanced potential difference towards ·OH generation. Comparison with commercially available photocatalysts (TiO2 and ZnO) also revealed that the VOC removal over sol-gel derived Zr0.05ZnOx was much higher, suggesting immense potential for industrial application.

Structural Characteristics and Functional Genes of Biofilms in Microbial Electrolysis Cells for Chlorobenzene Abatement

Chlorobenzene (CB) is typically emitted during industry and waste incineration, posing hazards to the safety of humans and the ecosystem. Successful CB elimination has been achieved in microbial electrolysis cells (MECs), whereas little is known about elimination effectiveness in response to the structural and functional characteristics of biofilms. Herein, the bacterial viability and functional gene abundance of biofilms in MECs with carbon cloth (CC), reticulated vitreous carbon (RVC), and nickel foam (NF) as cathodes are emphasized. Experimental results reveal that bacterial viability on RVC is 62 and 92% higher than that of CC and NF, respectively, achieving 30 and 65% superior CB removal efficiency. Notably, the MEC with RVC outperforms that with the highly conductive NF due to low electron loss, causing a twice as much increase in coulombic efficiency. Metagenomic analysis indicates that the CB degrader (i.e., Pandoraea), electrochemically active bacteria (i.e., Chryseobacterium), and genes responsible for CB metabolism (i.e., todD and clcB) in RVC biofilms increase by over 30%, fourfold, and 10%, respectively, compared to CC and NF. Moreover, CB degradation is found to occur via two possible pathways: (1) thorough elimination by dechlorination, hydrolysis, and oxidation after conversion to 3-chlorocatechol, and (2) conversion into phenol and benzoate for complete degradation.