Simultaneous removal of NO and SO2 using vacuum ultraviolet light (VUV)/heat/peroxymonosulfate (PMS)

Titanium oxide based photocatalytic materials development and their role of in the air pollutants degradation: Overview and forecast

Due to the anthropogenic pollution, especially the environmental crisis caused by air pollutants, the development of air pollutant degradation photocatalyst has become one of the major directions to the crisis relief. Among them, titania (titanium dioxide, TiO₂) family materials were extensively studied in the past two decades due to their strong activity in the photocatalytic reactions. However, TiO₂ had a drawback of large bandgap which limited its applications, several modification techniques were hence developed to enhance its catalytic activity and light sensitivity. In recent years, other metal oxide based materials have been developed as replacements for TiO₂ photocatalysts. In this review, background information and developments from pure TiO₂ to chemically modified TiO₂-based materials as photocatalysts were discussed in detail, which covered their basic properties and their role in the air pollutant removal. It also proposes to solve the shortcomings of TiO₂ by developing other metal oxide-based materials and predict the future development of TiO₂ materials in future environmental applications.

Highly efficient catalysis of chalcopyrite with surface bonded ferrous species for activation of peroxymonosulfate toward degradation of bisphenol A: A mechanism study

Chalcopyrite nanoparticles (CuFeS₂ NPs) with abundant surface bonded ferrous were successfully prepared, characterized and used as a catalyst for peroxymonosulfate (PMS) activation and BPA degradation. The effect of reaction parameters such as initial pH, catalyst load, PMS concentration, initial BPA concentration and reaction temperature on BPA degradation in CuFeS₂-PMS system was systematically investigated. As a bimetallic sulfide, CuFeS₂ exhibits ultra-high activity for PMS activation compared with Cu₂S, FeS₂, CuFeO₂ and Co₃O₄. It was found that by co-use of 0.1 g L^-1 CuFeS₂ and 0.3 mmol L^-1 PMS, 20 mg L^-1 of BPA was almost completely degraded (99.7%) and reached a mineralization rate of 75% within 20 min. The highly catalytic activity of CuFeS₂ is closely related to two aspects: one is that S^2- in the catalysts promotes the cycling of Fe³⁺/Fe²⁺ and Cu²⁺/Cu⁺ cycles on the surface, and the other is the synergistic effect of Fe³⁺/Fe²⁺ and Cu²⁺/Cu⁺ cycles in the PMS activation. These interesting findings shed some new insight on the development of metal sulfides for the oxidative treatment of organic contaminants.

Removal of multi-pollutant from flue gas utilizing ammonium persulfate solution catalyzed by Fe/ZSM-5

A nano-sized iron loaded ZSM-5 zeolite (Fe/ZSM-5) catalyst was firstly used to activate (NH₄)₂S₂O₈ solution for the simultaneous removal of multi-pollutant from flue gas. The simultaneous removal efficiencies 100% of SO₂, 72.6% of NO and 93.4% of Hg° were achieved under the condition that the catalyst dose was 0.8 g/L, concentration, pH and temperature of (NH₄)₂S₂O₈ solution were 0.03 mol/L, 5 and 65 °C, respectively. The stability of catalyst was checked by a continuous test, proving that the catalytic activity was maintained for 4 h and the leached iron reached low levels. Based on the catalyst characterizations, product analysis and literatures, the removal mechanism was speculated preliminarily, during which, OH and SO₄^- played key roles for oxidizing NO and Hg° into NO₃^- and Hg²⁺.

Combustion behavior, emission characteristics of SO2, SO3 and NO, and in situ control of SO2 and NO during the co-combustion of anthracite and dried sawdust sludge

The combustion behaviors of anthracite and dried sawmill sludge (DSS) were studied using thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTG). DSS was found to be a promoter for anthracite combustion, the addition of DSS in anthracite decreased the burnout temperature and time. But DSS caused the rapid releases of SO₂ and NO in the initial combustion stage. In overall, the increasing of DSS significantly decreased the emission factor of SO₂ from 13.42 ± 1.80 to 0.31 ± 0.08 g/kg; while the emission factor of NO was not obviously changed and stable at 0.7-0.8 g/kg in all cases. The oxygen-rich atmosphere was helpful for the rapid and sufficient combustion of blend; the oxygen-lean atmosphere delayed the combustion process and slowed down the releases of SO₂ and NO. The increasing combustion temperature improved the anthracite combustion, and the emission factors of SO₂ and NO were all increased with the temperature increasing. 900 °C was found to be the best combustion temperature for NO generation. SO₃ was detected in the combustion of anthracite under 21% and 30% of O₂. Two promising ways for control of SO₂ and NO were provided: 1) urea-fuel mixture combustion combined with the post-combustion wet absorption by Na₂CO₃; 2) post-combustion wet absorption by NaClO/Na₂CO₃. The removal efficiencies of SO₂ and NO could reach 100% and over 95% respectively. The removal products were determined as sulfate, sulfite and nitrate by IC, with no toxic byproducts being produced.

Simultaneous Removal of NOx and SO2 through a Simple Process Using a Composite Absorbent

In this work, the feasibility of the simultaneous removal of NOx and SO2 through a simple process using a composite absorbent (NaClO2/Na2S2O8) was evaluated. Factors affecting the removal of NOx and SO2, such as NaClO2 and Na2S2O8 concentrations, solution temperature, the initial pH of solution, gas flow rate, and SO2, NO, and O2 concentrations were studied, with a special attention to NOx removal. Results indicate that a synergistic effect on NOx removal has been obtained through combination of NaClO2 and Na2S2O8. NaClO2 in the solution played a more important role than did Na2S2O8 for the removal of NOx. The above factors had an important impact on the removal of NOx, especially the solution temperature, the initial pH of the solution, and the oxidant concentrations. The optimum experimental conditions were established, and a highest efficiency of NOx removal of more than 80% was obtained. Meanwhile, tandem double column absorption experiments were conducted, and a NOx removal efficiency of more than 90% was reached, using NaOH solution as an absorbant in the second reactor. A preliminary reaction mechanism for NOx and SO2 removal was deduced, based on experimental results. The composite absorbent has the potential to be used in the wet desulfurization and denitration process, to realize the synergistic removal of multi-pollutants.