Because ozone (O3) is a significant air pollutant, advanced O3 elimination technologies, particularly those under high-humidity conditions, have become an essential research focus. In this study, a nickel-iron layered double hydroxide (NiFe-LDH) was modified via intercalation with octanoate to develop an effective hydrophobic catalyst (NiFe-OAa-LDH) for O3 decomposition. The NiFe-OAa-LDH catalyst sustained its O3 decomposition rate of >98% for 48 h under conditions of 90% relative humidity, 840 L/(g·h) space velocity, and 100 ppm inlet O3 concentration. Moreover, it maintained a decomposition rate of 90% even when tested at a higher airflow rate of 2500 L/(g·h). Based on the changes induced by the Ni-OII to Ni-OIII bonds in NiFe-OAa-LDH during O3 treatment, catalytic O3 decomposition was proposed to occur in two stages. The first stage involved the reaction between the hydroxyl groups and O3, leading to the breakage of the O-H bonds, formation of NiOOH, and structural changes in the catalyst. This transformation resulted in the formation of abundant and stable hydrogen vacancies. According to density functional theory calculations, O3 can be effectively decomposed at the hydrogen vacancies with a low energy barrier during the second stage. This study provides new insights into O3 decomposition.
The emission of highly-toxic gaseous As2O3 (As2O3 (g)) from nonferrous metal smelting poses environmental concerns. In this study, we prepared an adsorbent (SMIL-X) by loading an ionic liquid (IL) ([HOEtMI]NTf2) into MCM-41 through an impregnation-evaporation process and then applied it to adsorb As2O3 (g). SMIL-20% exhibited an As2O3 (g) adsorption capacity of 35.48 mg/g at 400 °C, which was 490% times higher than that of neat MCM-41. Characterization of SMIL-X indicated that the IL was mainly supported on MCM-41 through O-H O bonds formed between the hydroxyl groups (-OH) and the silanol groups (Si-OH) and the O-H F bonds formed between the C-F groups and the Si-OH groups. The hydrogen bonds significantly contributed to the adsorption of As2O3 (g), with -NH and -OH groups forming hydrogen bonds with As-O species (i.e., N-H O and O-H O). This showed superior performance to traditional adsorbents that rely on van der Waals forces and chemisorption. Moreover, after exposure to high concentrations of SO2, the adsorption capacities remained at 76% of their initial values, demonstrating some sulfur resistance. This study presents an excellent adsorbent for the purification of As2O3 (g) and shows promising application potential for treating flue gas emitted by nonferrous metal smelting processes.
The transformation of toxic arsine (AsH3) gas into valuable elemental arsenic (As0) from industrial exhaust gases is important for achieving sustainable development goals. Although advanced arsenic removal catalysts can improve the removal efficiency of AsH3, toxic arsenic oxides generated during this process have not received adequate attention. In light of this, a novel approach for obtaining stable As0 products was proposed by performing controlled moderate oxidation. We designed a tailored Ni-based catalyst through an acid etching approach to alter interactions between Ni and NaY. As a result, the 1Ni/NaY-H catalyst yielded an unprecedented proportion of As0 as the major product (65%), which is superior to those of other reported catalysts that only produced arsenic oxides. Density functional theory calculations clarified that Ni species changed the electronic structure of oxygen atoms, and the formed [NiIII-OH (µ-O)] active centers facilitated the adsorption of AsH2*, AsH*, and As* reaction intermediates for As-H bond cleavage, thereby decreasing the direct reactivity of oxygen with the arsenic intermediates. This work presents pioneering insights into inhibiting excessive oxidation during AsH3 removal, demonstrating potential environmental applications for recovery of As0 from toxic AsH3.
Arsenic , Zeolites , Nickel/chemistry , Electrons , Oxygen , Gases
Economic and environmentally friendly strategies are needed to promote the bifunctional catalytic removal of carbonyl sulfide (COS) by hydrolysis and hydrogen sulfide (H2S) by oxidation. N doping is considered to be an effective strategy, but the essential and intrinsic role of N dopants in catalysts is still not well understood. Herein, the conjugation of urea and biochar during Cu/biochar annealing produced pyridine N, which increased the combined COS/H2S capacity of the catalyst from 260.7 to 374.8 mg·g-1 and enhanced the turnover frequency of H2S from 2.50 × 10-4 to 5.35 × 10-4 s-1. The nucleophilic nature of pyridine N enhances the moderate basic sites of the catalyst, enabling the attack of protons and strong H2O dissociation. Moreover, pyridine N also forms cavity sites that anchor CuO, improving Cu dispersion and generating more reactive oxygen species. By providing original insight into the pyridine N-induced bifunctional catalytic removal of COS/H2S in a slightly oxygenated and humid atmosphere, this study offers valuable guidance for further CâS and C-S bond-breaking in the degradation of sulfur-containing pollutants.
Hydrogen Sulfide , Sulfur Oxides , Hydrogen Sulfide/metabolism , Charcoal , Pyridines
The competitive adsorption behavior, the synergistic catalytic reaction, and deactivation mechanisms under double components of sulfur-containing volatile organic compounds (VOCs) are a bridge to solve their actual pollution problems. However, they are still unknown. Herein, simultaneous catalytic decomposition of methyl mercaptan (CH3SH) and ethyl mercaptan (C2H5SH) is investigated over lanthanum (La)-modified ZSM-5, and kinetic and thermodynamic results confirm a great difference in the adsorption property and catalytic transformation behavior. Meanwhile, the new synergistic reaction and deactivation mechanisms are revealed at the molecular level by combining with in situ diffuse reflectance infrared spectroscopy (in situ DRIFTS) and density functional theory (DFT) calculations. The CH3CH2* and SH* groups are presented in decomposing C2H5SH, while the new species of CH2*, active H* and S*, instead of CH3* and SH*, are proved as the key elementary groups in decomposing CH3SH. The competitive recombining of SH* in C2H5SH with highly active H* in dimethyl sulfide (CH3SCH3), an intermediate in decomposing CH3SH, would aggravate the deposition of carbon and sulfur. La/ZSM-5 exhibits potential environmental application due to the excellent stability of 200 h and water resistance. This work gives an understanding of the adsorption, catalysis, reaction, and deactivation mechanisms for decomposing double components of sulfur-containing VOCs.
Traditional adsorbents undershot the expectations for arsine (AsH3) removal under low-temperature operation conditions in the industry. In this study, the copper (Cu) precursor was used to modify activated carbon and yield novel adsorbents by low-temperature roasting for high-efficiency removal of AsH3. The best conditions were determined as impregnation with 2 mol/L Cu(NO3)2 adsorbent and roasting at 180 °C. At a reaction temperature of 40 °C and an oxygen content of 1%, the AsH3 removal efficiency reached over 90% and lasted for 40 h and the best capacity of 369.6 mg/g was obtained with the Cu/Ac adsorbent. The characterization results showed the decomposition of Cu(NO3)2 during the low-temperature roasting process to form surface functional groups. The formation of the important intermediate Cu2(NO3)(OH)3 in the decomposition of Cu(NO3)2 into CuO plays a role in the good regeneration performance of the Cu/Ac adsorbent using water washing and the gas regeneration method. The results of in situ diffuse reflectance infrared Fourier transform spectroscopy combined with X-ray photoelectron spectroscopy demonstrated that the interaction of trace oxygen with Lewis (L) acid sites increased chemisorbed oxygen by 17.34%, significantly promoting the spontaneity of AsH3 oxidation reaction. These results provide a friendly economic method with industrial processes practical for AsH3 removal.
Ceria (CeO2)-based materials are potential catalysts for the removal of the Hg0 and AsH3 present in reducing atmospheres. However, theoretical studies investigating the Hg0 and AsH3 removal capacity of ceria remain limited. In this study, the adsorption behavior and mechanistic pathways for the catalytic oxidation of Hg0 and AsH3 on the CeO2(111) surface, including the calculation of optimized adsorption configurations and energies, were investigated using density functional theory calculations. The results suggest that Hg0 and AsH3 are favorably adsorbed on the CeO2(111) surface, whereas CO is not, which is crucial for selective removal when CO is a desirable gas component. Furthermore, AsH3 is adsorbed more favorably than Hg0. In addition, the calculations revealed that the Hg atom is initially adsorbed on the surface and then oxidized by lattice oxygen to form HgO. Concerning AsH3 decomposition, the stepwise dehydrogenation of AsH3 followed by bonding with lattice O atoms to form the As-O bond seems the most plausible. Finally, the adsorbed As-O bond is further forms elemental As and As2O3. Therefore, CeO2 can adsorb and remove Hg0 and AsH3, making it a promising catalyst for the simultaneous catalytic oxidation of Hg0 and AsH3 in strongly reducing off-gas.
A cubic SrTiO3 (STO) composite material co-doped with Ce and Cr ions was synthesized by solvothermal method. The fully characterized samples were employed as photocatalysts for the oxidation of Hg0. The co-doped samples afforded excellent catalytic removal efficiency of 98.99% using UV irradiation and 89.9% using visible light irradiation for Hg0 compared with the single-doped samples. It was found that co-doped samples had a lower electron-hole recombination rate, largest Brunauer-Emmett-Teller specific surface area, and reduced band gap. The electron spin resonance results revealed that ·O2- and ·OH were the main active species in the catalytic process. Moreover, the co-doped samples exhibited the best electron transfer rate and the highest photocurrent response intensity. The electron transfer between the elements in the co-doped sample enables it to achieve stable and efficient catalytic performance. In addition, even after five consecutive catalytic runs, the co-doped sample maintained high catalytic activity. This work highlights the potential of the perovskite-type STO materials in the photocatalytic oxidation of gaseous mercury.
Mercury , Catalysis , Gases , Light , Oxidation-Reduction
The abatement of SO2 and the utilization of copper tailings are identified as two attention-attracting environmental issues in the copper smelter. In this study, to improve the flue gas desulfurization performance and the utilization of copper tailings, SO2 removal from smelting flue gas by using copper tailings combined with MnSO4·H2O was investigated. The effects of operation variables, including inlet SO2 concentration, absorption temperature, slurry concentration, and MnSO4·H2O amount, on the flue gas desulfurization performance were studied based on the response surface method. It was found that the effect of operation variables on SO2 removal follows the descending order: the inlet SO2 concentration, MnSO4·H2O concentration, absorbent temperature, and solid-liquid ratio. The interaction between the inlet SO2 concentration and MnSO4·H2O concentration is an important factor for breakthrough sulfur capacity. Elevated temperature and high initial SO2 concentration inhibited the efficient removal of SO2. Moreover, a proposed equation exhibits good consistency in the prediction for the breakthrough sulfur dioxide capacity. Therefore, the results can provide a reliable reference and basis for industrial application for flue gas desulfurization with copper tailings.
Copper , Sulfur Dioxide , Sulfur , Temperature
La2O3/Bi2O3 photocatalysts were prepared by impregnation of Bi2O3 with an aqueous solution of lanthanum precursor followed by calcination at different temperatures. The composite materials were used for the first time for the photocatalytic removal of Hg0 from a simulated flue gas under UV light irradiation. The results showed that the sample containing 6 wt.% La2O3 and calcined at 500°C has the highest dispersion of the active sites, which was promoted by the strong interaction with the support (i.e., the formation of Bi-O-La species). Since they are fully accessible on the surface, the material also exhibits excellent optical properties while the heterojunction formed in La2O3/Bi2O3 promotes the separation and migration of photoelectron-hole pairs and thus Hg0 oxidation efficiency is enhanced. The effects of the various factors (e.g., the reaction temperature and composition of the simulated flue gas (i.e., O2, NO, H2O, and SO2)) on the efficiency of the Hg0 photocatalytic oxidation were investigated. The results demonstrated that O2 and SO2 enhanced the efficiency of the reaction while the reaction temperature, NO, and H2O had an inhibitory effect.
Air Pollutants , Mercury , Lanthanum , Oxides
Copper tailing is a widespread and intractable solid waste in copper production. Traditional leaching and recovery technology for copper tailing focuses on copper but neglects the leaching of iron. With the increase in applications and demands of iron-containing materials for environment, understanding the leaching behaviors of iron can promote the utilization of copper tailings. In this study, the kinetics and mechanism of the leaching of iron from copper tailings using sulfuric acid were studied. Under optimal conditions (40 °C, sulfuric acid concentration of 0.53 mol L-1, stirring speed of 400 rpm, solid/liquid ratio of 1 : 10 and leaching time of 120 min), 66.45% of Fe, along with 65.32% of Zn and 59.95% of Cu, were leached from the tailings. The leaching of iron was confirmed to be controlled by solid-film diffusion. The reaction orders for sulfuric acid concentration, solid/liquid ratio, and stirring speed were found to be 0.85, -0.70, and 0.40, respectively. Results from XRF, XRD, and SEM indicated that oxides (including CaO, CuO, and ZnO) were leached first, after which Fe2SiO4 was preferentially reacted compared to Fe3O4. The accumulation of CaSO4 and SiO2 inhibited the further leaching of iron.
This study focuses on the removal of C4H4S using DC corona discharge plasma. The influences of various factors such as C4H4S concentration (ppm), temperature (°C), O2 concentration (%), and dust concentration (mg/m3) on the conversion of C4H4S were studied. Furthermore, gaseous compositions were determined using Fourier transform infrared (FTIR) spectroscopy. Solid products, which were collected from earth and discharge electrodes, were analyzed using X-ray diffraction (XRD). The results showed that, under the condition of DC corona discharge plasma, C4H4S converted to CO, CO2, S, SO2, and SO42-, and that the conversion rate increased with the increase in specific input energy (SIE). The increase of O2 concentration led to further energy consumption that generated O3, which in turn decreased the conversion rate of C4H4S. The increase in temperature exhibited a positive influence on the conversion of C4H4S when the SIE was less than 268 J/L. However, above this value of SIE, the temperature affected the conversion of C4H4S negatively with the increase in SIE. When dust was introduced, the conversion of C4H4S was significantly improved and the yield of SO2 reduced due to the reaction which took place among C4H4S, SO2 and dust in the electric field. The results showed that the DC corona discharge plasma exhibited considerable potential to remove C4H4S, while dust contributed positively towards the disposal of C4H4S. Graphical abstract In this work, DC corona plasma was used to remove thiophene (C4H4S) from a dust-containing gas stream. The results showed that electron collision, oxidizability of radicals, and existence of O3 were the main causes of C4H4S decomposition. The electron collision effects, contents of radicals, O3, and the conversion rate of C4H4S were enhanced with the increase in SIE (specific input energy). The main products consisted of CO, CO2, SO2, and solid products. The solid products and dust moved to the earth electrode in the electric field.
Air Pollutants/isolation & purification , Plasma Gases/chemistry , Thiophenes/isolation & purification , Air Pollutants/chemistry , Carbon Dioxide/chemistry , Carbon Monoxide/chemistry , Dust , Oxygen/chemistry , Spectroscopy, Fourier Transform Infrared , Sulfates/chemistry , Sulfur Dioxide/chemistry , Temperature , Thiophenes/chemistry , X-Ray Diffraction
