Unveiling the activity difference cause and ring-opening reaction routes of typical radicals induced degradation of toluene.

This study employs five UV-AOPs (PMS, PDS, H2O2, NaClO and NaClO2) to produce radicals (•OH, SO4•-, ClO•, O2•- and 1O2) and further comparatively studies their activity sequence and activity difference cause in toluene degradation. The toluene mineralization efficiency as a descending order is 73 % (UV-PMS) > 71 % (UV-PDS) > 70 % (acidified-UV-NaClO) > 55 % (UV-H2O2) > 36 % (UV-NaClO) > 35 % (UV-NaClO2); that of conversion efficiency is 99 % (acidified-UV-NaClO) > 95 % (UV-PMS) > 90 % (UV-PDS) > 74 % (UV-H2O2) > 44 % (UV-NaClO) > 41 % (UV-NaClO2). Acidic pretreatment significantly boosts the reactivity of UV-NaClO. ESR combined with radical quenching tests reveals the radicals' generation and evolution, and their contribution rates to toluene conversion, i.e. ClO• > SO4•- > O2•- > 1O2 > â€¢OH. Theoretical calculations further unveil the ring-opening reaction routes and the nature of the activity difference of different radicals. The minimum energy required for ring-opening reaction is 116.77, 150.63, 168.29 and 191.92 kJ/mol with respect to ClO•, SO4•-, 1O2 and •OH, and finding that the ClO•-HO• pair is the best for toluene mineralization. The difficulty for eliminating typical VOCs by using UV-AOPs method is determined as toluene > chlorobenzene > benzene > ethyl acetate.

Electrochemical Reduction of Flue Gas Denitrification Wastewater to Ammonia Using a Dual-Defective Cu2O@Cu Heterojunction Electrode.

Wet flue gas denitrification offers a new route to convert industrial nitrogen oxides (NOx) into highly concentrated nitrate wastewater, from which the nitrogen resource can be recovered to ammonia (NH3) via electrochemical nitrate reduction reactions (NITRRs). Low-cost, scalable, and efficient cathodic materials need to be developed to enhance the NH3 production rate. Here, in situ electrodeposition was adopted to fabricate a foamy Cu-based heterojunction electrode containing both Cu-defects and oxygen vacancy loaded Cu2O (OVs-Cu2O), which achieved an NH3 yield rate of 3.59 mmol h-1 cm-2, NH3 Faradaic efficiency of 99.5%, and NH3 selectivity of 100%. Characterizations and theoretical calculations unveiled that the Cu-defects and OVs-Cu2O heterojunction boosted the H* yield, suppressed the hydrogen evolution reaction (HER), and served as dual reaction sites to coherently match the tandem reactions kinetics of NO3-to-NO2 and NO2-to-NH3. An integrated system was further built to combine wet flue gas denitrification and desulfurization, simultaneously converting NO and SO2 to produce the (NH4)2SO4 fertilizer. This study offers new insights into the application of low-cost Cu-based cathode for electrochemically driven wet denitrification wastewater valorization.

Multimedia Mercury Recovery from Coal-Fired Power Plants Utilizing N-Containing Conjugated Polymer Functionalized Fly Ash.

To recover multimedia mercury from coal-fired power plants, a novel N-containing conjugated polymer (polyaniline and polypyrrole) functionalized fly ash was prepared, which could continuously adsorb 99.2% of gaseous Hg0 at a high space velocity of 368,500 h-1 and nearly 100% of aqueous Hg2+ in the solution pH range of 2-12. The adsorption capacities of Hg0 and Hg2+ reach 1.62 and 101.36 mg/g, respectively. Such a kind of adsorbent has good environmental applicability, i.e. good resistance to coexisting O2/NO/SO2 and coexisting Na+/K+/Ca2+/Mg2+/SO42-. This adsorbent has very low specific resistances (6 × 106-5 × 109 Ω·cm) and thus can be easily collected by an electrostatic precipitator under low-voltage (0.1-0.8 kV). The Hg-saturated adsorbent can desorb almost 100% Hg under relatively low temperature (<250 °C). Characterization and theoretical calculations reveal that conjugated-N is the critical site for adsorbing both Hg0 and Hg2+ as well as activating chlorine. Gaseous Hg0 is oxidized and adsorbed in the form of HgXClX(ad), while aqueous Hg2+ is adsorbed to form a complex with conjugated-N, and parts of Hg2+ are reduced to Hg+ by conjugated-N. This adsorbent can be easily large-scale manufactured; thus, this novel solid waste functionalization method is promising to be applied in coal-fired power plants and other Hg-involving industrial scenes.

Microwave-Induced Deep Catalytic Oxidation of NO Using Molecular-Sieve-Supported Oxygen-Vacancy-Enriched Fe-Mn Bimetal Oxides.

A novel microwave (MW) catalytic oxidation denitrification method was developed, which can deeply oxidize NO into nitrate/nitrite with little NO2 yield. A molecular-sieve-supported oxygen-vacancy-enriched Fe2O3-MnO2 catalyst (Ov-Fe-Mn@MOS) was fabricated. Physicochemical properties of the catalyst were revealed by various characterization methods. MW irradiation was superior to the conventional heating method in NO oxidation (90.5 vs 70.6%), and MW empowered the catalyst with excellent low-temperature activity (100-200 °C) and good resistance to H2O and SO2. Ion chromatography analysis demonstrated that the amount of nitrate/nitrite accounted for over 90.0% of the N products, but the main product gradually varied from nitrate to nitrite as the reaction proceeded because of the switching of the main reaction path of NO removal. Mechanism analyses clarified that NO oxidation was a non-radical catalytic reaction: (i) the chemisorbed NO on ≡Mn(IV) reacted with O2* to produce nitrate and (ii) the excited NO* due to MW irradiation reacted with the active O* generated from Ov···O2 to form nitrite. Density functional theory calculations combined with electron paramagnetic resonance tests revealed the promotional effects of Fe2O3 in (i) boosting the Ov's quantity; (ii) facilitating O2 adsorption; (iii) increasing the nitrite formation; and (iv) alleviating the suppression of SO2.

A critical review on the technique and mechanism of microwave-based denitrification in flue gas.

Microwave radiation has received extensive attention due to its significant thermal and non-thermal effects, and the development of MW-based denitrification in flue gas has become one of the most promising methods to avoid the defects of ammonia escape, high temperature and cost in traditional SCR. This review introduces the thermal and non-thermal effects of microwaves and divides MW-based denitrification methods into MW reduction and oxidation denitrification, systematically summarizes these denitrification methods, including MW discharge reduction, MW-induced catalytic reduction using active carbon, molecular sieves, metal oxides (transition metals, perovskites, etc.), MW-induced oxidation denitrification with and without additional oxidant, and discusses their removal pathway and mechanism. Finally, several research prospects and directions regarding the development of microwave-based denitrification methods are provided.

Reaction Behavior and Influencing Mechanisms of Different Fly Ashes on the NO Removal by Using the Ultraviolet Irradiating Chlorite Method.

Our previous work had demonstrated that UV/NaClO2 was the best advanced oxidation method in terms of nitric oxide (NO) removal, but we have not studied the impact of the fly ash on NO removal under such conditions. For this, this paper selected six kinds of fly ashes and studied their effects on NO removal. The micromorphology, elemental composition, and the elemental oxidation states of these six fly ashes were characterized by scanning electron microscopy-energy-dispersive X-ray spectra, X-ray photoelectron spectroscopy, and inductively coupled plasma methods. The main inorganic components in the six fly ashes are metal oxides (Fe2O3/Fe3O4, SiO2, Al2O3, ZnO, MgO, and TiO2), carbonates (Na2CO3 and CaCO3), and chlorides (NaCl, KCl, and MgCl2). The experimental results suggested that high solubility was the premise condition for the fly ashes exhibiting an inhibitory effect on NO removal. Among all of the metal compounds, Fe2O3/Fe3O4 exhibited the highest inhibitory contribution rate to the NO removal (22.9-45.7%). The anions of Cl- and CO3 2- acted as scavengers for the free radicals which greatly impaired the oxidation of NO. Based on the simulation experimental results and the UV-vis analysis, the order of inhibitory contribution rates of various metal compounds to the NO removal was determined as Fe2O3/Fe3O4 > TiO2 ≈ Na2CO3 > Al2O3 ≈ ZnO ≈ MnO2 > CaCO3 > NaCl > KCl ≈ SiO2 ≈ MgCl2.

Simultaneous Nitrite Resourcing and Mercury Ion Removal Using MXene-Anchored Goethite Heterogeneous Fenton Composite.

The integrated system of gas-phase advanced oxidation process combined with sulfite-based wet absorption process is a desirable method for simultaneous removal of SO2, NO, and Hg0, but due to the enrichment of nitrite and Hg2+, resourcing harmless wastewater is still a challenge. To tackle this problem, this study fabricated a bifunctional ß-FeOOH@MXene heterogeneous Fenton material, of which the crystalline phase, morphology, structure, and composition were revealed by using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy-energy dispersive x-ray spectroscopy, and transmission electron microscopy. It exhibits excellent performance on nitrite oxidation (99.5%) and Hg2+ removal (99.7%) and can maintain stable outstanding ability after 13 cycles, with superior Hg2+ adsorption capacity (395 mg/g) and ultralow Fe leaching loss (<0.018 wt %). The synergism between MXene and ß-FeOOH appears as follows: (i) MXene, as an inductive agent, directionally converted Fe2O3 into ß-FeOOH in the hydrothermal method and greatly reduced its monomer size; (ii) the introduced ≡Ti(III)/≡Ti(II) accelerated the regeneration of ≡Fe(II) via rapid electron transfer, thereby improving the heterogeneous Fenton reaction; and (iii) MXene strongly immobilized ß-FeOOH to greatly inhibit Fe-leaching. HO•, •O2--, and 1O2 were the main radicals identified by electron spin resonance. Radical quenching tests showed their contributions to NO2- oxidation in the descending order HO• > 1O2 > •O2-. Quantum chemical calculations revealed that •OH-induced oxidation of NO2- or HNO2 was the primary reaction path. Density functional theory calculations combined with X-ray photoelectron spectroscopy and Raman characterizations displayed the Hg2+ removal mechanism, with Hg2Cl2, HgCl2, and HgO as the main byproducts. This novel material provides a new strategy for resourcing harmless wastewater containing nitrite and Hg2+.

Removal and Recovery of Gaseous Elemental Mercury Using a Cl-Doped Protonated Polypyrrole@MWCNTs Composite Membrane.

Due to the restrictions on mercury mining, recovering the mercury from mercury-containing waste is attracting increasing attention. This study successfully achieved the removal and recovery of gaseous elemental mercury (Hg0) by using membrane technology. A novel composite membrane of Cl-doped protonated polypyrrole-coated multiwall carbon nanotubes (Cl-PPy@MWCNTs) was fabricated in which MWCNTs acted as the framework to support the active component Cl-PPy. The morphology, structure, and composition of the prepared membranes were determined by field emission scanning electron microcopy, energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, etc. The composite membrane exhibited an excellent performance in Hg0 removal (97.3%) at a high space velocity of 200,000 h-1. The dynamical adsorption capacity of Hg0 was 3.87 mg/g when the Hg0 breakthrough reached 10%. The adsorbed Hg0 could be recovered/enriched via a leaching process using acidic NaCl solution; meanwhile, the membrane was regenerated. The recovered mercury was identified in the form of Hg2+, with a recovery efficiency of over 99%. Density functional theory calculations and mechanism analysis clarified that the electrons of Hg0 transported to the delocalized electron orbits of protonated PPy and then combined with Cl- to form Hg2Cl2/HgCl2. Finally, we first demonstrated that the analogous protonated conductive polymers (e.g., polyaniline) also possessed good Hg0 removal ability, implying that such species may offer more outstanding answers and attract attention in future.

Arsenic emission and distribution characteristics in the ultra-low emission coal-fired power plant.

The characteristics of arsenic emission and distribution of a typical Chinese coal-fired power plant renovated with ultra-low emission technique have been studied. The results showed that arsenic concentration in coal was 5.72 mg/kg, and the arsenic emissions in fly ash, bottom ash, gypsum, flue gas, and wastewater were 489.12 g/h, 5.15 g/h, 1.14 g/h, 0.46 g/h, and 0.03 g/h, respectively, corresponding to the proportion of arsenic in fly ash, bottom ash, gypsum, flue gas, and wastewater of 98.63%, 1.04%, 0.23%, 0.09%, and 0.01%, respectively. About 87.61% of the gaseous arsenic was absorbed by catalysts used for selective catalytic reduction (SCR). Low-low temperature electrostatic precipitator (LLT-ESP) plays a key role in decreasing particulate arsenic. Wet flue gas desulfurization (WFGD) has positive effects on absorbing both gaseous and particulate arsenic. The removal efficiencies across the air pollution control devices follow the order of LLT-ESP > WFGD > SCR. The LLT-ESP can achieve a significant arsenic removal efficiency of 99.94%, resulting in quite low arsenic emission to the atmosphere. According to the calculated arsenic emission factor, the total emission amount of arsenic to the atmosphere from all Chinese coal-fired stations with ultra-low emission control technique in 2020 is estimated to be about 9.67-11.59 tons/year.

Low-Medium Temperature-Selective Catalytic Reduction of NO with NH3 over a Mn/Co-MOF-74 Catalyst.

To realize the selective catalytic reduction of NO at low-medium temperatures and avoid secondary pollution, a highly active catalyst Mn/Co-MOF-74 was synthesized. X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, Brunauer-Emmett-Teller method, and scanning electron microscopy were employed to analyze the physicochemical properties of catalysts with different Mn/Co molar ratios and conjecture about the difference in the catalytic activity. Meanwhile, the effects of the molar ratio of Mn/Co, catalyst dosage, catalyst synthesis conditions, GHSV, and temperature on the NO conversion efficiencies were investigated and found that an optimal NO conversion efficiency of 93.5% was obtained at 200-225 °C. In the end, the stability of Mn/Co-MOF-74 was investigated and found that the catalyst has better sulfur and water resistance, and the NO conversion mechanism was speculated on the basis of characterizations and literature data.

Simultaneous removal of SO2, NO and Hg0 using an enhanced gas phase UV-AOP method.

The core for simultaneous removal of SO2, NO and Hg0 is the oxidation of NO and Hg0. Radical induced oxidation of NO and Hg0 is considered to be the most efficient method. We develop a novel gas phase advanced oxidation process (AOP) of UV-Heat/H2O2-NaClO2 to simultaneously remove SO2, NO and Hg0 due to a great synergism between H2O2 and NaClO2 under thermal and ultraviolet (UV) co-catalysis. The results indicated that the SO2 removal was always good, while the removal of NO and Hg0 was affected by NaClO2 and UV. Higher catalytic temperature and longer flue gas residence time favored the removal of NO and Hg0. The presence of SO2 and NO facilitated Hg0 removal. Kinetics analyses were conducted to provide the reaction rate of removal of NO and Hg0 under different conditions. X-ray photoelectron spectroscopy (XPS) revealed the product composition as Cl-, Hg2+, NO3- and SO42-. Electron spin resonance (ESR) tests confirmed the generation of HO. Cost analyses demonstrated the better cost performance of the proposed method compared to SCR-ACI combined method. HO and ClO2 were proved to be the main oxidant. The reaction mechanism for removal of NO and Hg0 by using UV-Heat/H2O2-NaClO2 were proposed finally.

Study on the Transport Mechanism of a Freestanding Graphene Oxide Membrane for Forward Osmosis.

Graphene oxide membranes (GOMs) are promising separation technologies. In forward osmosis (FO), we found that the water flux from the feed solution to the draw solution can prevent ions from diffusing to the feed solution in a highly tortuous and porous GOM. In reverse osmosis (RO), we found that the salt rejection is low compared to that in commercially available RO membranes. While this prohibits the use of GOMs for RO and FO water desalination, we believe that such membranes could be used for other water treatment applications and energy production. To examine the transport mechanism, we characterized the physical and chemical properties of GOMs and derived mass transfer models to analyze water and salt transport inside freestanding GOMs. The experimental reverse salt flux was between the largest and smallest theoretical values, which corresponds to the lowest and highest tortuosity, respectively, in FO. Furthermore, the concentration profile for the reverse salt flux shortened as the NaCl draw concentration increased because the water flux increased and the electrical double layer (EDL) decreased with increasing NaCl in the draw solution. We provide insights into the transport mechanisms in GOMs and provide guidance for future exploration of GOMs in efficient water treatment and energy production processes.

Multi-air-pollutant removal by using an integrated system: Key parameters assessment and reaction mechanism.

How to cost-efficiently and cooperatively remove SO2, NO and Hg0 in flue gas is a hot topic in the field of air pollution control. This work developed an integrated system that consists of a dual-absorption system and a vapor oxidation system, in which Na2CO3 and H2O2/Na2S2O8 were used as the absorbent and oxidant. The results indicated that the efficiencies of SO2 removal and NO conversion reached 99.5% and 93% respectively. Rising the vaporization temperature and decreasing the pH of H2O2/Na2S2O8 could facilitate the NO conversion. The spent Na2CO3 after desulfurization was demonstrated to be a good absorbent for NO2 removal. The best conditions of pH and temperatures for the dual-absorber were determined as 10/8 and 60/60 °C, respectively. The presence of 1000 mg/m3 SO2 and 300 mg/m3 NO favored the Hg0 removal. TMT-15, an organic sulfur compound, was demonstrated to be useful in retaining Hg2+, with an efficiency of 92%. According to the analyses of electron spin resonance (ESR), ion chromatography (IC), atom fluorescence spectrometry (AFS) and X-ray photoelectron spectroscopy (XPS), SO4- and HO were proved to be the key radicals, and the existing forms of N- and Hg- species in the product were identified as NaNO2/NaNO3 and HgCl2.

Photocatalytic removal of NO and Hg0 using microwave induced ultraviolet irradiating H2O/O2 mixture.

We developed a novel method, microwave (MW) induced ultraviolet (UV) irradiating H2O/O2, to cooperatively remove NO and Hg0, with the efficiencies of 89.3% and 99.5%. It also can remove 97% SO2. O2 at a content of 2-8% was sufficient to conduct a good removal of NO and Hg0. Ozone (O3) and hydroxyl radical (HO•) were proved to be the major oxidants for the removal of Hg0 and NO, respectively. High temperature facilitated NO removal but impaired Hg0 removal. SO2 greatly promoted the removal of NO and Hg0 due to the formation of SO4•-. The presence of Cl- and Br-suppressed NO removal but promoted Hg0 removal, because Cl- and Br-quenched HO• to produce Cl- and Br-radicals. The produced NO2 could be totally absorbed by the Na2SO3 solution that followed the main reactor. The O3 yield and the formation of HO• under different conditions were determined using iodine quantity method and electron spin resonance (ESR). The distributions of anion concentration and mercury proportion were obtained using ion chromatography (IC) and cold atom fluorescence spectrometry (AFS), and the main products were identified to be SO42-, NO3- and HgO. The mechanisms of removal of SO2, NO and Hg0 were speculated.

Radical-induced oxidation removal of multi-air-pollutant: A critical review.

Sulfur dioxide (SO2), nitric oxide (NO) and elemental mercury (Hg0) are three common air pollutants in flue gas. SO2 and NO are the main precursors for chemical smog and Hg0 is a bio-toxicant for human. Cooperative removal of multi-air-pollutant in flue gas using radical-induced oxidation reaction is considered as one of the most promising methods due to the high removal efficiency, low cost and less secondary environmental impact. The common radicals used in air pollution control can be classified into four types: (1) hydroxyl radical (OH), (2) sulfate radical (SO4-), (3) chlorine-containing radicals (Cl, ClO2, ClO, HOCl-, etc.) and (4) ozone. This review summarizes the generation methods and mechanism of the four kinds of radicals, as well as their applications in the removal of multi-air-pollutant in flue gas. The reactivity, selectivity and reaction mechanism of the four kinds of radicals in multi-air-pollutant removal were comprehensively described. Finally, some future research suggestions on the development of new technique for cooperative removal of multi-air-pollutant in flue gas were provided.

A novel catalytic oxidation process for removing elemental mercury by using diperiodatoargentate(III) in the catalysis of trace ruthenium(III).

A series of experiments were conducted at a bench scale reactor to investigate the effects of key influencing factors on the Hg0 removal from flue gas using the prepared diperiodatoargentate (III) (DPA) as an oxidant, trace ruthenium(III) as a catalyst, respectively. The experimental results showed that the average Hg0 removal efficiency reached to 87.5% under the optimal conditions in which the DPA concentration was 1.03 mmol/L, catalyst concentration was 2.0 µmol/L, reaction temperature was 40 °C and solution pH was 8.5. Meanwhile, it was found from the experiments that the high concentrations of SO2 and NO could inhibit the Hg0 removal due to the competition between Hg0 and SO2/NO, while the lower NO concentration exhibited a slight promotion for Hg0 removal. The evolutions of DPA(III) and Ru(III) before and after the reaction were characterized by an ultraviolet visible spectrophotometer (UV-vis), from which, the promotional mechanism of Ru(III) on Hg0 removal was analyzed. The spent solution was analyzed by a cold vapor atomic fluorescence spectrometer (CVAFS), which verified that Hg0 was oxidized into Hg2+ by the catalytic system of DPA(III)-Ru(III), and DPA was converted into Ag+.

Simultaneous Removal of SO2 and NO Using a Novel Method of Ultraviolet Irradiating Chlorite-Ammonia Complex.

A novel advanced oxidation process (AOP) using ultraviolet/sodium chlorite (UV/NaClO2) is developed for simultaneous removal of SO2 and NO. NH4OH, as an additive, was used to inhibit the generation of ClO2 and NO2. The removal efficiencies of SO2 and NO reached 98.7 and 99.1%. NO removal was enhanced by greater UV light intensity and shorter wavelengths but was insensitive to changes in pH and temperature. SO2 at 500-1000 mg/m3 improved NO removal, especially in the absence of UV. The coexistence of SO2 and O2 facilitated the removal of NO by ClO2-. HCO3-, Cl-, and Br- enhanced NO removal, but their roles were negligible when UV was added. The generation of ClO2 and ClO•/HO• was verified by an UV-vis spectrometer, electron spin resonance (ESR), and radical-quenching tests. The mechanisms responsible for the removal of SO2 and NO were attributed to the synergism between acid-base neutralization and radical-induced oxidation. The ClO2- evolution and product composition were demonstrated by UV-vis and X-ray photoelectron spectroscopy (XPS). Kinetics analyses showed that the Hatta numbers were 329-798 and 747-1000 without and with UV. Thus, the gas-film resistance mainly controlled the mass-transfer process.

Elemental Mercury Removal by a Method of Ultraviolet-Heat Synergistically Catalysis of H2O2-Halide Complex.

A novel method of ultraviolet-heat synergistically catalyzing H2O2-X (X: NaCl, NaBr, HCl, and HBr) for removal of elemental mercury (Hg0) was developed. In terms of Hg0 removal efficiency and economy, HCl and HBr were the suitable additives. Hg0 removal efficiencies reached 93.6% for H2O2-HCl and 91.4% for H2O2-HBr, the concentrations of H2O2, HCl and HBr were 1 M, 4.2 mM and 0.5 mM. The doses of gaseous Cl and Br-oxidants were 6.27 and 0.75 ppm. The costs by using H2O2-HCl and H2O2-HBr were 1,180 USD/lb-Hg0 and 1,170 USD/lb-Hg0. The best temperature for heat catalysis was 413 K. Hg0 removal was enhanced by 500 mg/m3 SO2 and 300 mg/m3 NO due to the formation of sulfuric and NO2. Mercury distribution analyses indicated that 500 mg/m3 SO2, 300 mg/m3 NO, and 6% O2 favored KCl retaining Hg2+. When the H2O2 concentration was adjusted to 3 M, the simultaneous removal efficiencies of NO and Hg0 reached 83.7% and 99.2% for H2O2-HCl, and 82.8% and 98.8% for H2O2-HBr. Electron spin resonance demonstrated that ClOH•-/BrOH•- and Cl2•-/Br2•- played leading roles in Hg0 oxidation, besides Cl2/Br2. The mercury forms in spent KCl were HgCl2, HgBr2, and HgNO3, according to X-ray photoelectron spectroscopy.

Research on sulfur oxides and nitric oxides released from coal-fired flue gas and vehicle exhaust: a bibliometric analysis.

A bibliometric method was used to evaluate the global scientific publications about sulfur oxides and nitric oxides released by coal-fired flue gas and vehicle exhaust from 1995 to 2018 and to provide insights into the characteristics of the articles and tendencies that may exist in the publications. Performance of publications, research tendency, and hotspots were analyzed. The article number had an explosive growth in 2004 and, then, began to grow steadily. China had an absolutely advantage in publication quantities; however, America had a leading position considering publication cited times. The simultaneous removal of mercury, particulate matter, and CO2 was a research hotpot in sulfur oxide and nitric oxide control process; oxidation, absorption, and catalytic reduction were the central control methods that had the most strength in relation with sulfur dioxide and nitric oxide. Considering the study of traditional flue gas pollutant control method (limestone-gypsum method, selective catalytic reduction, etc.) was perfection, it was speculated that adsorption by ionic liquid, electricity charging, advanced oxidation progress, and multi-pollutant removal, simultaneously, would be the new research orientation in flue gas pollutant control. One of the hot points of controlling the vehicle exhaust was the application of the "green energy" biodiesel; lots of keywords concerning human health suggested that quite a lot studies were focused on the health hazard brought by sulfur oxides and nitric oxide.

Elemental mercury removal by a novel advanced oxidation process of ultraviolet/chlorite-ammonia: Mechanism and kinetics.

A novel advanced oxidation process (AOP) of ultraviolet/chlorite-ammonia (UV/NaClO2-NH4OH) was developed to remove Hg0 from flue gas. The distribution of mercury concentration in three solutions of NaClO2-NH4OH, KCl, and H2SO4-KMnO4 was determined by cold atom fluorescence spectrometry (AFS). The role of NH4OH was to help NaClO2 preserving and/or stabilizing Hg2+ meanwhile inhibiting the photo-production of ClO2. In the absence of UV, decreasing pH promoted the release of Hg2+ from NaClO2-NH4OH; introducing NO, SO2, O2, Br-, Cl-, and HCO3- suppressed Hg0 oxidation. In the presence of UV, rising temperature accelerated the release of Hg2+ from NaClO2-NH4OH; while SO2, Br- and HCO3- facilitated Hg0 oxidation. In the absence and presence of UV, Hg0 oxidation was controlled by ClO2- and by ClO/Cl2O2/HO/ClO2, respectively. The formations of ClO/HO/ClO2 were confirmed by electron spin resonance (ESR). X-ray photoelectron spectroscopy (XPS) revealed that the products of Hg0 and ClO2- were HgCl2, and ClO2, Cl-, ClO3-, Cl2, and ClO4-, respectively. Analysis of kinetics showed that the Hatta numbers were 23-133 and 69-305 without and with UV, respectively, thus, the gas-film mass transfer was the rate-determining step. This paper gives a new insight in radical behavior in Hg0 oxidation.