Kinetics study on photochemical oxidation of polyacrylamide by ozone combined with hydrogen peroxide and ultraviolet radiation

An investigation on the process of ozone combined with hydrogen peroxide and ultraviolet radiation has been carried out in order to establish the kinetics for photochemical oxidation of polyacrylamide （PAM） in aqueous solution. Effects of operating parameters, including initial PAM concentration, dosages of ozone and hydrogen peroxide, UV radiation and pH value on the photochemical oxidation of PAM, have been studied. There was an increase in photochemical oxidation rate of PAM with increasing of dosages of 03, H2O2 and ultraviolet radiation. Upon increasing of the initial PAM concentration, the photochemical oxidation rate of PAM decreased. Slight effect of pH value on the photochemical oxidation rate of PAM was observed in the experiments. The kinetics equation for the photochemical oxidation of PAM by the system has been established.

Kinetics of Oxidation of Lactose with Photochemically Generated Radicals

Lactose milk sugar is found only in the milk of mammals. In order to understand the mechanism of oxidation of lactose, a systematic kinetic study of oxidation of lactose with photochemicaUy generated radicals was carried out. The reaction has a first order dependence on chloramine-T as well as on substrate. The reaction is catalysed by H＋ ions as well. On the basis of kinetic results and product analysis a probable mechanism were suggested.

Photoassisted fenton oxidation of refractory organics in UASB-pretreated leachate

Nearly 91% of organic pollutants in Hong Kong leachate could be effectively removed by the UASB(upflow anaerobic sludge blanket) process followed by the fenton coagulation. The COD (chemical oxygen demand) of leachate was lowered from an average of 5620 mg/L to 1910 mg/L after the UASB treatment at 37℃, and was further lowered to 513 mg/L after fenton coagulation. The remaining refractory residues could be further removed by photochemical oxidation with the addition of H 2O 2. The BOD/COD ratio was greatly increased from 0.062 to 0.142, indicating the biodegradability of organic residues was improved. The photochemical oxidation for the fenton\|coagulation supernatant was most effective at pH 3\_4, with the addition of 800 mg/L of H 2O 2, and UV radiation time of 30 minutes. The final effluent contained only 148 mg/L of COD, 21 mg/L of BOD(biochemical oxygen demand) and 56 mg/L of TOC (total organic carbon).

UV-catalytic treatment of spent caustic from ethene plant with hydrogen peroxide and ozone oxidation

The performance of UV/H 2O 2, UV/O 3 and UV/H 2O 2/O 3 oxidation systems for treating spent caustic from an ethylene plant was investigated. In UV/H 2O 2 system, with the increase of H 2O 2 dosage, removal efficiencies of COD and the ratio of biochemical oxygen demand(BOD) to chemical oxygen demand(COD) of the effluent were increased and a better performance was obtained than the H 2O 2 system alone. In UV/H 2O 2 system, removal efficiency of COD reach 68% under the optimum condition, and BOD/COD ratio was significantly increased from 0 22 to 0 52. In UV/O 3 system, with the increase of O 3 dosage, removal efficiency of COD and BOD/COD ratio were increased, and a better performance was obtained than the O 3 system alone. Under the optimum condition, removal efficiency of COD was 54%, and BOD/COD ratio was significantly increased from 0 22 to 0 48. In UV/H 2O 2/O 3 system, COD removal efficiency was found to be 22.0% higher than UV/O 3 system.

Treatment of spent caustic by three kinds of photocatalyticoxidation processes

The investigation of the performance of UV/H2O2, UV/O3 and UV/H2O2/O3 oxidation systems treating spent caustic from an ethylene plant shows that in UV/H2O2 system, with the increase of H2O2dosage, removal efficiencies of COD and the ratio of biochemical oxygen demand （BOD） to chemical oxygen demand （COD） of the effluent were increased and a better performance was obtained than the H2O2system alone. In UV/H2O2 system, removal efficiency of COD reached 68% under the optimum condition, and BOD/COD ratio was significantly increased from 0.22 to 0.52. In UV/O3 system, with the increase of O3dosage, removal efficiency of COD and BOD/COD ratio were increased, and a better performance was obtained than the O3system alone. Under the optimum condition, removal efficiency of COD was 54%, and BOD/COD ratio was significantly increased from 0.22 to 0.48. In UV/H2O2/O3 system, COD removal efficiency was found to be 22.0% higher than UV/O3 system.

Selective removal of sulfamethoxazole by a novel double Z-scheme photocatalyst:Preferential recognition and degradation mechanism

Sulfamethoxazole(SMX)is a significant environmental concern due to its adverse effects and ecological risks.SMX elimination in aquatic environments via photocatalysis presents a viable solution,given its high oxidation potential.However,such a solution remains controversial,primarily due to a lack of selectivity.Here we introduce a molecularly imprinted TiO2@Fe_(2)O_(3)@g-C_(3)N_(4)(MFTC)photocatalyst designed for the selective degradation of SMX.To assess MFTC's selectivity,we applied it to degrade synthetic wastewater containing SMX alongside interfering species sulfadiazine(SDZ),ibuprofen(IBU),and bisphenol A(BPA).The results demonstrated a selective degradation efficiency rate of 96.8%,nearly twice that of competing pollutants.The molecularly imprinted sites within the catalyst played a crucial role by selectively capturing SMX and enhancing its adsorption,thereby improving catalytic efficiency.The degradation process involvedOH and·O_(2)^(-)free radicals,with a newly proposed double Z-scheme mechanism and potential pathway for SMX degradation by the MFTC photocatalytic system.This study enriches the application of photocatalysis using molecularly imprinted nanocomposite materials for treating complex pollutant mixtures in water.

Roles of SO_2 oxidation in new particle formation events

The oxidation of SO2 is commonly regarded as a major driver for new particle formation（NPF） in the atmosphere. In this study, we explored the connection between measured mixing ratio of SO2 and observed long-term（duration 〉 3 hr） and short-term（duration〈 1.5 hr） NPF events at a semi-urban site in Toronto. Apparent NPF rates（J30） showed a moderate correlation with the concentration of sulfuric acid（[H2SO4]） calculated from the measured mixing ratio of SO2 in long-term NPF events and some short-term NPF events（Category I）（R^2= 0.66）. The exponent in the fitting line of J30~ [H2SO4]nin these events was1.6. It was also found that SO2 mixing ratios varied a lot during long-term NPF events,leading to a significant variation of new particle counts. In the SO2-unexplained short-term NPF events（Category II）, analysis showed that new particles were formed aloft and then mixed down to the ground level. Further calculation results showed that sulfuric acid oxidized from SO2 probably made a negligible contribution to the growth of 〉 10 nm new particles.

Photooxidation of arsenic(Ⅲ) to arsenic(Ⅴ) on the surface of kaolinite clay

As one of the most toxic heavy metals, the oxidation of inorganic arsenic has drawn great attention among environmental scientists. However, little has been reported on the solar photochemical behavior of arsenic species on top-soil. In the present work, the influencing factors（p H, relative humidity（RH）, humic acid（HA）, trisodium citrate, and additional iron ions） and the contributions of reactive oxygen species（ROS, mainly HO^- and HO2^-/O2^-） to photooxidation of As（Ⅲ） to As（Ⅴ） on kaolinite surfaces under UV irradiation（λ = 365 nm）were investigated. Results showed that lower p H facilitated photooxidation, and the photooxidation efficiency increased with the increase of RH and trisodium citrate.Promotion or inhibition of As（Ⅲ） photooxidation by HA was observed at low or high dosages, respectively. Additional iron ions greatly promoted the photooxidation, but excessive amounts of Fe^2＋competed with As（Ⅲ） for oxidation by ROS. Experiments on scavengers indicated that the HOUradical was the predominant oxidant in this system.Experiments on actual soil surfaces proved the occurrence of As（Ⅲ） photooxidation in real topsoil. This work demonstrates that the photooxidation process of As（Ⅲ） on the soil surface should be taken into account when studying the fate of arsenic in natural soil newly polluted with acidic wastewater containing As（Ⅲ）.

Assessing the role of mineral particles in the atmospheric photooxidation of typical carbonyl compound

Mineral particles are ubiquitous in the atmosphere and exhibit an important effect on the photooxidation of volatile organic compounds(VOCs).However,the role of mineral particles in the photochemical oxidation mechanism of VOCs remains unclear.Hence,the photooxi-dation reactions of acrolein(ARL)with OH radical(OH)in the presence and absence of SiO_(2) were investigated by theoretical approach.The gas-phase reaction without SiO_(2) has two distinct pathways(H-abstraction and OH-addition pathways),and carbonyl-H-abstraction is the dominant pathway.In the presence of SiO_(2),the reaction mechanism is changed,i.e.,the dominant pathway from carbonyl-H-abstraction to OH-addition to carbonyl C-atom.The energy barrier of OH-addition to carbonyl C-atom deceases 21.33 kcal/mol when SiO_(2) is added.Carbonyl H-atom of ARL is occupied by SiO_(2) via hydrogen bond,and carbonyl C-atom is ac-tivated by SiO_(2).Hence,the main product changes from H-abstraction product to OH-adduct in the presence of SiO_(2).The OH-adduct exhibits a thermodynamic feasibility to yield HO_(2) radical and carboxylic acid via the subsequent reactions with O_(2),with implications for O 3 formation and surface acidity of mineral particles.

Photochemical properties of hypocrellin A,B and their oxides

Hypocrellin A and B in methanol were autosensitized and photooxygenated to 1,4,6, 7 and 2,5,8,9 respectively.1 in methanol was photooxygenated to 6 and 7 under the sensitization by HB.1 in methanol was photooxygenated to 7 under the sensitization by Rose bengal.1 in benzene ir- radiated with medium-pressure-mercury lamp was photolyzed to 3 in the presence of iodine.

Seasonal variation and size distribution of biogenic secondary organic aerosols at urban and continental background sites of China

Size-resolved biogenic secondary organic aerosols （BSOA） derived from isoprene and monoterpene photooxidation in Qinghai Lake, Tibetan Plateau （a continental background site） and five cities of China were measured using gas chromatography/mass spectrometry （GC/MS）. Concentrations of the determined BSOA are higher in the cities than in the background and are also higher in summer than in winter. Moreover, strong positive correlations （R^2 = 0.44-0.90） between BSOA and sulfate were found at the six sites, suggesting that anthropogenic pollution （i.e., sulfate） could enhance SOA formation, because sulfate provides a surface favorable for acid-catalyzed formation of BSOA. Size distribution measurements showed that most of the determined SOA tracers are enriched in the fine mode （〈3.3 μm） except for cis-pinic and cis-pinonic acids, both presented a comparable mass in the fine and coarse （〉3.3 μm） modes, respectively. Mass ratio of oxidation products derived from isoprene to those from monoterpene in the five urban regions during summer are much less than those in Qinghai Lake region. In addition, in the five urban regions relative abundances of monoterpene oxidation products to SOA are much higher than those of isoprene. Such phenomena suggest that BSOA derived from monoterpenes are more abundant than those from isoprene in Chinese urban areas.

Spatiotemporal characterization and regional contributions of O3 and NO2:An investigation of two years of monitoring data in Henan,China

To investigate the characteristics of ground level ozone(O3)for Henan Province,the ambient air quality monitoring data of 2015 and 2016 were analyzed.The result showed that the 8 h-max-O3 concentrations displayed a distinct seasonality,where the maximum and minimum values,averaging 140.41,54.19μg/m3,occurred in summer and winter,respectively.There is a significant correlation between meteorological factors and O3 concentration.The Voronoi neighborhood averaging analysis indic ated that O3,temperature,and ultraviolet radiation in Henan province were decreased from northwest to southeast,while relative humidity and precipitation displayed the opposite trend.Besides meteorological factors,the chemical processes play an essential role in ozone formation.Reactions of NO,NO2 and O3 form a closed system,and the partitioning point of the OX-component(O3+NO2)was at 40 and 80μg/m3 for nitrogen oxide(NOx)in winter and summer,respectively,with NO2 dominating at higher NOx pollution and O3 being the m ajor component at lower levels.The relationship between oxidant(OX=O3+NO2)and NOx concentrations were evaluated to understand the regional and local contribution of OX.It showed that high regional contribution occurred in the spring,whereas the highest local contribution lead to the summer peak of O3 observed in Zhengzhou.This present study reveals important environment impacts from the photochemical process and the meteorological conditions in the region with better understanding on the O3 characterization.