Pulsed Electrolysis Promotes CO2 Reduction to Ethanol on Heterostructured Cu2O/Ag Catalysts.

The electrochemical conversion of carbon dioxide (CO2) into ethanol with high added value has attracted increasing attention. Here, an efficient catalyst with abundant Cu2O/Ag interfaces for ethanol production under pulsed CO2 electrolysis is reported, which is composed of Cu2O hollow nanospheres loaded with Ag nanoparticles (named as se-Cu2O/Ag). The CO2-to-ethanol Faradaic efficiency is prominently improved to 46.3% at a partial current density up to 417 mA cm-2 under pulsed electrolysis conditions in a neutral flow cell, notably outperforming conventional Cu catalysts during static electrolysis. In situ spectroscopy reveals the stabilized Cu+ species of se-Cu2O/Ag during pulsed electrolysis and the enhanced adsorbed CO intermediate (*CO)coverage on the heterostructured catalyst. Density functional theory (DFT) calculations further confirm that the Cu2O/Ag heterostructure stabilizes the *CO intermediate and promotes the coupling of *CO and adsorbed CH intermediate (*CH). Meanwhile, the stable Cu+ species under pulsed electrolysis favor the hydrogenation of adsorbed HCCOH intermediate (*HCCOH) to adsorbed HCCHOH intermediate (*HCCHOH) on the pathway to ethanol. The synergistic effect between the enhanced generation of *CO on Cu2O/Ag and regenerated Cu+ species under pulsed electrolysis steers the reaction pathway toward ethanol. This work provides some insights into selective ethanol production from CO2 electroreduction via combined catalyst design and non-steady state electrolysis.

Effect of ammonium sulfate and urea on PCDD/F formation from active carbon and possible mechanism of inhibition.

The effect of ammonium sulfate ((NH4)2SO4) and urea (CO(NH2)2) on polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) formation from active carbon was investigated in this study. Both additives could significantly inhibit PCDD/F formation, and PCDD/F (TEQ) generation was reduced to 98.5% (98%) or 64.5% (77.2%) after 5% (NH4)2SO4 or CO(NH2)2 was added into model ash, respectively. The inhibition efficiency of PCDDs was higher than the value of PCDFs, however, the reduction of PCDD/F yield was mainly from PCDFs decreasing. In addition, the solid-phase products were reduced more than the gas-phase compounds by inhibitors. By the measurement of chlorine emission in the phase of ion (Cl[Cl(-)]) and molecule gas (Cl[Cl2]), it was observed that both Cl[Cl(-)] and Cl[Cl2] were reduced after inhibitors were added into ash. Cl[Cl2] was reduced to 51.0% by urea addition, which was supposed as one possible mechanism of PCDD/F inhibition.

Tackling CO2 Loss in Electrocatalytic Carbon Dioxide Reduction by Advanced Material and Electrolyzer Design.

Electrocatalytic CO2 reduction (ECO2R) has been considered as a promising approach to convert CO2 into valuable chemicals and fuels. CO2 loss in conventional alkaline electrolyzers has been recognized as a major obstacle that compromising the efficiency of the ECO2R system. This review firstly conducts an in-depth assessment of the origin and influence of CO2 loss. On this basis, this work summarizes electrolyzer configurations based on novel material and structure design that are capable of tackling CO2 loss, including acidic electrolyzer, bipolar membrane (BPM) derived electrolyzer, cascade electrolyzer, liquid-phase-anode electrolyzer, and liquid-fed electrolyzer. The design strategies and challenges of these carbon efficient electrolyzers have been deliberated in detail. By comparing and analyzing the advantages and limitations of various electrolyzer designs, this work aims to provide some guidelines for the development of efficient ECO2R technology toward large-scale industrial application.

Optimizing magnetic functionalization conditions for efficient preparation of magnetic biochar and adsorption of Pb(II) from aqueous solution.

Recoverable magnetic biochar has great potential for treating wastewater contaminants such as Pb(II). However, whether magnetic modification could enhance metal adsorption efficiency is currently contradictory in the literature mainly due to the differences in selecting various magnetic functionalization conditions. Considering this gap in knowledge, the effects of magnetic functionalization method (impregnation and precipitation), concentration of precursor iron solution (0.01-1 M), and pyrolysis temperature (300-700 °C) on the characteristics and Pb(II) adsorption capacity of biochar were systematically investigated in this paper. Results indicated that Fe3O4 was the main product for magnetic biochars synthesized using the impregnation (denoted as FWFe(3)) and precipitation methods (denoted as FWFe(2)). Magnetic functionalization resulted in remarkably increased pH and more negative zeta potential for FWFe(2) samples, whereas FWFe(3) samples showed the opposite trends. The adsorption of Pb(II) on different biochars fitted the pseudo-second order model and the Langmuir model. The maximum adsorption capacity was 817.64 mg/g for FWFe(2)1M700C (precipitation by 1 M of Fe(II)/Fe(III), pyrolysis at 700 °C), outperforming FWFe(3) and pristine biochar samples by around 5-13 times. Mechanism study indicated that the adsorption mainly involved electrostatic attraction, ion exchange, co-precipitation, and complexation. Pb(II) adsorption capacity was strongly dependent on the alkali pH of biochar. However, this efficiency was less affected by biochar surface area and its morphology. The higher pH of FWFe(2) samples not only led to an increased surface charge for stronger electrostatic attraction and ion exchange but also favored the formation of co-precipitates. By contrast, FWFe(3) samples showed a decreased adsorption capacity for Pb(II) with increased concentration of embedded iron. Overall, magnetic biochar, prepared using precipitation followed by high-temperature pyrolysis (such as, FWFe(2)1M700C), can be a promising adsorbent for Pb(II) adsorption from wastewater.

Removal effect of the low-low temperature electrostatic precipitator on polycyclic aromatic hydrocarbons.

The low-low temperature electrostatic precipitator (LLT-ESP) is one of the most used devices for pollutant control in ultra-low emission coal-fired power plants. This study investigated the influence of the LLT-ESP on polycyclic aromatic hydrocarbons (PAHs) distributions in flue gas from an ultra-low emission coal-fired power plant. The total gas-phase PAH concentration was reduced from 27.52 µg/m3 to 3.38 µg/m3. The total particulate-phase PAH concentration decreased from 14.36 µg/m3 to 0.34 µg/m3. The removal efficiency of the LLT-ESP for gas-phase and particulate phase carcinogenic higher molecular weight (HMW) PAHs was 85% and 99%, respectively. The total concentration of 16 selected PAHs in feed coal was 98.16 µg/g. The fly ash particle size successively decreased from Electric Field 1 (F1) to Electric Field 4 (F4). The total PAH concentration decreased from F1 to F2 but increased again from F3 to F4. The flue gas cooling process significantly contributed to the elimination of both gas- and particulate-phase PAHs in the flue gas. Presumably, most of the condensed PAHs were adhered to or absorbed in the fly ash and were scavenged in Field 1. Both gas- and particulate-phase 5- and 6-ring PAHs in the flue gas were completely removed in Field 1. The discharge process in the electric fields may promote the formation of several 4- or 5-ring PAHs. In this study, benzo[k]fluoranthene (BKF) and benzo[a]pyrene (BaP) were regenerated in the particles rather than in the flue gas during the discharge process in the electric fields.

Effect of oxygen content on the thermal desorption of polychlorinated biphenyl-contaminated soil.

Oxygen plays an important role during the thermal treatment of soil, contaminated with polychlorinated biphenyls (PCBs), due to the potential oxidation of PCBs to form polychlorinated dibenzofurans (PCDFs). The effect of oxygen content (0, 5, 21 and 100%) in carrier gases on PCBs and PCDD/Fs was studied both in soil and gas after thermal desorption of PCBs contaminated soil at 500 °C. All 209 congeners of PCBs and 136 congeners of PCDD/Fs (P = 4 to 8) were analysed. Oxygen content showed little effect on PCB removal and destruction. Under different carrier gases, the removal efficiency and the destruction efficiency for PCBs attained 93.8-95.5 and 83.0-85.0 %, respectively. The levels of PCDD/Fs in soil and gas were correlated positively with oxygen content. Compared with PCDDs, PCDFs in soil were not effectively removed under oxidative conditions because there was chemistry going on and PCBs were being converted to PCDFs. The total concentration of PCDFs in soil and gas was 2.6, 11.3, 15.6 and 17.5 times of the initial PCDFs concentration (21.9 ng/g) in raw soil with increasing oxygen content. Thus, substantial amounts of PCDFs were generated in the presence of oxygen during the treatment of contaminated soil.

Thermal desorption of PCB-contaminated soil with sodium hydroxide.

The thermal desorption was combined with sodium hydroxide to remediate polychlorinated biphenyl (PCB)-contaminated soil. The experiments were conducted at different temperatures ranging from 300 to 600 °C with three NaOH contents of 0.1, 0.5, and 1 %. The results showed that thermal desorption was effective for PCB removal, destruction, and detoxication, and the presence of NaOH enhanced the process by significant dechlorination. After treatment with 0.1 % NaOH, the removal efficiency (RE) increased from 84.8 % at 300 °C to 98.0 % at 600 °C, corresponding to 72.7 and 91.7 % of destruction efficiency (DE). With 1 % NaOH content treated at 600 °C, the RE and DE were 99.0 and 93.6 %, respectively. The effect of NaOH content on PCB removal was significant, especially at lower temperature, yet it weakened under higher temperature. The interaction between NaOH content and temperature influenced the PCB composition. The higher temperature with the help of NaOH effectively increased the RE and DE of 12 dioxin-like PCBs (based on WHO-TEQ).

Thermal desorption of PCBs from contaminated soil with copper dichloride.

Copper dichloride is an important catalyst both in the dechlorination of chlorinated aromatic compounds and the formation of PCDD/Fs. The effect of copper dichloride on polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) was studied in treated soil and off gas after thermal desorption of PCB-contaminated soil at 300, 400, 500, 600 °C. The presence of copper dichloride clearly enhances thermal desorption by promoting PCBs removal, destruction, and dechlorination. After thermal treatment at 600 °C for 1 h, the removal efficiency and destruction efficiency for PCBs reached 98.1 and 93.9%, respectively. Compared with the positive influence on PCBs, copper dichloride catalyzed large amount of PCDFs formation at 300 °C, with the concentration ratio of 2.35. The effect of CuCl2 on PCDFs formation weakened with the rising temperature since PCDFs destruction became dominant under higher temperature. Different from PCDFs, PCDDs concentration in treated soil and off gas decreased continuously with the increasing temperature.

Polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and dibenzofurans, and polycyclic aromatic hydrocarbons around a thermal desorption plant in China.

This study was launched to establish comprehensive environmental monitoring on the levels and patterns of polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polycyclic aromatic hydrocarbons (PAHs) both in soil and ambient air around a thermal desorption plant in China. All 209 congeners of PCBs, 136 congeners of PCDD/Fs (P = 4 to 8) and 16 EPA priority PAHs were analyzed. The concentration of PCBs ranged from 20.0 to 536 ng g(-1) (or 0.077-5.27 pg WHO-TEQ g(-1)) in soil and from 972 to 991 ng Nm(-3) (or 0.245-0.374 pg WHO-TEQ Nm(-3)) in air samples, much higher than the levels in cities. A single soil sampling point could have been affected by some transfer of PCBs from the untreated soil by the fingerprint characteristics and the statistical analysis. Establishing blank values prior to the start-up of new plant is a safe and sure method to establish subsequent impacts on the environment. During the treatment of hazardous waste, strict control of all waste materials and all emissions is required.

[Homologues Levels and Distribution Pattern of Polychlorinated Biphenyls in Typical Capacitor Contaminated Soil].

The homologues levels, distribution characteristics and TEQ of 209 PCBs in soil collected around 3 storage sites of PCB-containing wastes were investigated. The PCBs contents and environmental risk were evaluated to provide a scientific basis for site remediation of PCBs contaminated soil. Totally 12 soil samples were collected from 3 PCB-contaminated sites. The analysis results showed that the PCB-concentration in Soil A was 1 705. 0 µg.g-1 ± 424. 3 µg.g-1 (n =4), higher than Soil B (233. 0 µg.g-1 ± 80. 0, n = 4) and Soil C (225. 7 µg.g-1 ± 90. 2 µg.g-1, n = 4), indicating the soil was heavily polluted by PCBs. Trichlorobiphenyl and Tetrachlorobiphenyl dominated the homologues of PCBs. The mass fraction of chlorine in Soil A, Soil B and Soil C was 43. 7% 1. 0%, 45.5% ± 0. 5% and 44.9% ± 0.3%, respectively, which was similar as Aroclor1242 and l#PCB insulating oil. There was an obvious linear correlation between indicator PCBs and total PCBs (R2 = 0. 998), so indicator PCBs can be used to estimate the level of total PCBs. PCB77, PCB105, PCB118 were predominant in doxin-like PCBs, accounting for 89. 5% ± 4. 0% in total. The TEQ levels of the soil samples (in WHO-TEQ) were 3. 56-63. 55 ng.g-1, which demonstrated a high environmental risk in the area. PCB28/31, PCB33/20, PCB66/80, PCB70, PCB32 and PCB18 were the main PCBs isomers. Compared with other results, the local soil was heavily contaminated by PCBs and the surroundings were under a relatively high risk of environmental contamination.

[Inhibition of chlorobenzene formation via various routes during waste incineration by ammonium sulfate and urea].

Chlorobenzene (CBz) is the precursor of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/Fs) generated in the processes of waste incineration, and it is regarded as a good indicator of PCDD/Fs for realizing PCDD/Fs online monitoring, moreover, pentachlorobenzene (PeCBz) and Hexachlorobenzene (HxCBz) belong to Persistent Organic Pollutants (POPs). However, the emission control of CBz in waste incineration does not attract enough attention, so this study focused on the inhibition of the 3 CBz formation routes in waste combustion by ammonium sulfate and urea, including CB formation from fly ash, CB formation from 1,2-dichlorobenzene (1,2-DiCBz) and the combustion of model medical waste. The results showed that both ammonium sulfate and urea reduced CBz yield during these three thermal processes. For instance, the inhibition rates of tetrachlorobenzene (TeCBz), PeCBz and HxCBz were 66.8%, 57.4% and 50.4%, respectively, when 1% urea was co-combusted with medical waste. By comparing the effect of ammonium sulfate and urea on CBz formation by three routes, urea was considered as a comparatively stable inhibitor for CBz.

Some technical issues in managing PCBs.

Polychlorinated biphenyls (PCBs) were important industrial chemicals featuring high thermal and chemical stability and low flammability. They were widely used as dielectric and thermal fluid in closed electro-technical applications (transformers, capacitors…) and also in numerous dispersive uses, ranking from auto-copying paper to sealant or coatings. During the 1960s, severe environmental consequences started becoming apparent. The stability of PCBs contributed to their persistence in the environment, their lipophilic character to bio-magnification. Fish-eating species seemed threatened in their existence. In Japan and in Taiwan, thousands of people consumed PCB-contaminated oil. The production of PCBs stopped completely during the 1980s. Usage could continue in closed applications only. In this paper, particular attention is given to two issues: the cleaning of PCB electric transformers and the potential impact of PCB-containing building materials. Other contributions will cover the management and treatment of PCB-contaminated soil, sludge or fly ash. The complete survey is being prepared by request of the Knowledge Center for Engineers and Professionals.

Thermal desorption of PCBs from contaminated soil using nano zerovalent iron.

In this study, thermal desorption was combined with the addition of nano zerovalent iron (nZVI) to remediate polychlorinated biphenyl (PCB)-contaminated soil collected from a storage point for PCB-contaminated capacitors and transformers. The thermal desorption test conditions were varied from 300 to 600 °C, both with blank soil and with 100 mg of nZVI added. Next, the effect of the amount of nZVI added (0, 20, 40, 100, 200 mg) was investigated by thermal treatment at 400 °C. The test results show that thermal desorption eliminates most of the PCB load and that the presence of nZVI clearly enhances thermal desorption. After thermal treatment at 400 °C, a removal efficiency of 94.2 % was reached, with the use of 200 mg of nZVI. At 600 °C, the PCB removal efficiency after 1 h attained 98.35 % with 100 mg of nZVI and 97.40 % without nZVI. The presence of nZVI effectively decreased both the sum and the WHO-TEQ value of the 12 dl-PCBs.

Effect of temperature and particle size on the thermal desorption of PCBs from contaminated soil.

Thermal desorption is widely used for remediation of soil contaminated with volatiles, such as solvents and distillates. In this study, a soil contaminated with semivolatile polychlorinated biphenyls (PCBs) was sampled at an interim storage point for waste PCB transformers and heated to temperatures from 300 to 600 °C in a flow of nitrogen to investigate the effect of temperature and particle size on thermal desorption. Two size fractions were tested: coarse soil of 420-841 µm and fine soil with particles <250 µm. A PCB removal efficiency of 98.0 % was attained after 1 h of thermal treatment at 600 °C. The residual amount of PCBs in this soil decreased with rising thermal treatment temperature while the amount transferred to the gas phase increased up to 550 °C; at 600 °C, destruction of PCBs became more obvious. At low temperature, the thermally treated soil still had a similar PCB homologue distribution as raw soil, indicating thermal desorption as a main mechanism in removal. Dechlorination and decomposition increasingly occurred at high temperature, since shifts in average chlorination level were observed, from 3.34 in the raw soil to 2.75 in soil treated at 600 °C. Fine soil particles showed higher removal efficiency and destruction efficiency than coarse particles, suggesting that desorption from coarse particles is influenced by mass transfer.