Mechanistic study of vacuum UV catalytic oxidation for toluene degradation over CeO_(2) nanorods

The present study specifically investigates vacuum ultraviolet (VUV) catalytic oxidation for toluene degradation over CeO_(2) nanorods.Synergetic effects of ultraviolet photocatalytic oxidation (UV-PCO) and ozone catalytic oxidation (OZCO) were manifested in the results of toluene removal and COx generation,while the combination of UV-PCO andOZCO (UV-OZCO) did not lead to improvement of mineralization.All the processes contribute to ozone decomposition,but no obvious synergetic effects of the different processes can be observed.Intermediate analysis results indicated that more toluene was oxidized into by-products,such as benzyl alcohol and benzaldehyde,by UV-OZCO rather than forming COx.Both hydroxyl radical (·OH) and superoxide radical (·O_(2)^(-)) were found in all the processes of the VUV-PCO-OZCO system(combination of VUV photolysis,UV-PCO,OZCO and UV-OZCO processes).In the UV-OZCO process,the formation of hydroxyl radical was promoted,while that of superoxide radical was impeded,resulting in lower mineralization level of toluene.The mechanistic study of toluene degradation over CeO_(2) nanorods in the VUV-PCO-OZCO system revealed that with the formation of·O_(2)^(-)and·OH,toluene is first oxidized to intermediates,followed by further ring–opening reaction and,finally,degradation into CO_(2) and H_(2)O.CeO_(2) nanorods function as both ozonation catalyst and photocatalyst,and the redox pair of Ce^(3+)and Ce^(4+)are interconvertible and can keep a balance.

Accelerated oxidation of VOCs via vacuum ultraviolet photolysis coupled with wet scrubbing process

Vacuum ultraviolet(VUV) photolysis is a facile method for volatile organic compounds(VOCs) elimination, but is greatly limited by the relatively low removal efficiency and the possible secondary pollution. To overcome above drawbacks, we developed an efficient method for VOCs elimination via VUV photolysis coupled with wet scrubbing process. In this coupled process, volatile toluene, a representative of VOCs, was oxidized by the gas-phase VUV photolysis, and then scrubbed into water for further oxidation by the liquid-phase VUV photolysis. More than 96% of toluene was efficiently removed by this coupled process, which was 2 times higher than that in the gas-phase VUV photolysis. This improvement was attributed to the synergistic effect between gas-phase and liquid-phase VUV photolysis. O3and HO·are the predomination reactive species for the toluene degradation in this coupled process, and the generation of O3in gas-phase VUV photolysis can efficiently enhance the HO·production in liquid-phase VUV photolysis. The result from in-situ proton transfer reaction ionization with mass analyzer(PTR-MS) further suggested that most intermediates were trapped by the wet scrubbing process and efficiently oxidized by the liquid-phase VUV photolysis, showing a high performance for controlling the secondary pollution. Furthermore, the result of stability test and the reuse of solution demonstrated that this coupled process has a highly stable and sustainable performance for toluene degradation. This study presents an environmentally benign and highly efficient VUV photolysis for gaseous VOCs removal in the wet scrubbing process.

Steady-state model for predicting size-resolved gas-particle partitioning of semi-volatile organic compounds (SVOCs) in indoor environments

Semi-volatile organic compounds(SVOCs)are ubiquitous and important pollutants in indoor environments.The strong partition between gas phase and suspended particles has significant effects on the transport,human exposure via inhalation,and control strategies of indoor SVOCs.Several models have been developed to simulate the gas–particle partitioning of indoor SVOCs,including a steady-state model by expanding the steady-state model suitable for the outdoor environment to indoor environments.However,the effects of two important indoor environment-specific parameters,i.e.,the particle size distribution(PSD)and the air-change rate(ACH),were not considered in the existing steady-state model,leading to the inaccurate predictions among buildings.To solve this problem,this study developed a novel steady-state model to more comprehensively simulate the gas-particle partitioning of indoor SVOCs by incorporating the effects of PSD and ACH.Better agreement between the predictions of the novel model and the results collected via both field tests and laboratory tests(retrieved from two different studies)supported the effectiveness of the improvements in the novel model.Sensitivity analysis further supported the necessity of involving PSD and ACH.Further implications of the novel model were also discussed.This study should be helpful for deepening the understanding and accurate simulation of the gas-particle partitioning,as well as the transport and human exposure via inhalation,of indoor SVOCs.

Photocatalysis and ambient catalysis for environmental remediation

Environmental pollution is a major challenge faced by human beings, and is becoming more serious due to increasing urbanization and industrialization. Catalysis is the key technology for environmental remediation. As a “green” technology, photocatalysis and ambient catalysis could offer numerous opportunities to realize environmental remediation under mild reaction conditions with low energy input. Over the past two decades, great advances have been made on the design and synthesis of the photocatalysts and ambient catalysts, precise control of catalyst active sites, and the mechanistic understanding on the catalytic process for environmental remediation.

Toluene decomposition performance and NOx by-product formation during a DBD-catalyst process

Characteristics of toluene decomposition and formation of nitrogen oxide（NOx） by-products were investigated in a dielectric barrier discharge（DBD） reactor with/without catalyst at room temperature and atmospheric pressure. Four kinds of metal oxides, i.e., manganese oxide（Mn Ox）, iron oxide（Fe Ox）, cobalt oxide（Co Ox） and copper oxide（Cu O）, supported on Al2O3/nickel foam, were used as catalysts. It was found that introducing catalysts could improve toluene removal efficiency, promote decomposition of by-product ozone and enhance CO2 selectivity. In addition, NOx was suppressed with the decrease of specific energy density（SED） and the increase of humidity, gas flow rate and toluene concentration, or catalyst introduction. Among the four kinds of catalysts, the Cu O catalyst showed the best performance in NOx suppression. The Mn Ox catalyst exhibited the lowest concentration of O3 and highest CO2 selectivity but the highest concentration of NOx. A possible pathway for NOx production in DBD was discussed. The contributions of oxygen active species and hydroxyl radicals are dominant in NOx suppression.

A novel Z-scheme CeO_(2)/g-C_(3)N_(4)heterojunction photocatalyst for degradation of Bisphenol A and hydrogen evolution and insight of the photocatalysis mechanism

CeO_(2)/g-C_(3)N_(4)heterojunction photocatalyst had been successfully fabricated through a one-step in-situ pyrolysis formation of 3D hollow CeO_(2)mesoporous nanospheres and 2D g-C_(3)N_(4)nanosheets together with simultaneous removal of carbon sphere templates after heat treatment.The sample shows high catalytic performances for photocatalytic hydrogen generation and photocatalytic oxidation of Bisphenol A(BPA)under visible light irradiation,and the catalytic degradation route of BPA was suggested by the degradation products determined by GC-MS.The enhancing catalytic activity was attributed to the effective interfacial charge migration and separation.Finally,it was proposed that the CeO_(2)/g-C_(3)N_(4)heterojunction photocatalyst could follow a more appropriate Z-scheme charge transfer mechanism,which was confirmed by the analysis of experiment and theoretical calculation results.

Regulation of mixed Ag valence state by non-thermal plasma for complete oxidation of formaldehyde

Formaldehyde is an important air pollutant and its removal is essential to protect human health and meet environmental regulations.Ag-based catalyst has a considerable potential for HCHO oxidation in low temperature range.The valence state of Ag is one of the key roles in formaldehyde catalytic oxidation.However,its effect on activity is still ambiguous.Non-thermal plasma and conventional calcination were employed to regulate Ag valence state in this study.Three Ag-Co/CeO_(2)catalysts with totally different distribution of Ag species were obtained.A special mixed Ag valence state,~50%Ag^(δ+)with a few Ag^(0)and Ag^(+),was achieved by plasma activation.It had the merits of both good activity and stability.A close relationship between Ag valence state and the activity for HCHO oxidation was established.The activity of different Ag species follows the order:Ag^(δ+)+Ag^(0)+Ag^(+)>Ag^(δ+)>Ag^(0)>Ag^(+).

Activity enhancement of acetate precursor prepared on MnO_(x)-CeO_(2) catalyst for low-temperature NH_(3)-SCR: Effect of gaseous acetone addition

MnO_(x)-CeO_(2) catalysts are developed by hydrolysis driving redox method using acetate precursor(3 Mn1 Ce-Ac) and nitrate precursor(3 Mn1 Ce-N) for the selective catalytic reduction(SCR) of NO_(x) by NH_(3).A counterpart sample(Cop-3 Mn1 Ce) was prepared by the NH_(3)·H_(2) O co-precipitation method for comparison purpose.Combining the results of physicochemical properties characterization and performance test,we find that the 3 Mn1 Ce-Ac catalyst with some nanorod structures is highly active for the deNOx process.The SCR activity of the 3 Mn1 Ce-Ac catalyst is more admirable than the 3 Mn1 Ce-N and the Cop-3 Mn1 Ce catalysts due to plentiful Lewis acid sites,excellent low-temperature reducibility,and superior surface area resulted from O_(2) generation during the pre paration procedure.The 3 Mn1 Ce-Ac still exhibits the greatest performance for the deNO_(x )process when gaseous acetone is in the SCR feed gas.The NOx conversion and N2 selectivity over the 3 Mn1 Ce-Ac are both improved by gaseous acetone above150℃ due to the inhibition of SCR undesired side reactions(NSCR & C-O reactions) and "slow-SCR" process.

Construction of a novel Ag/Ag_(3)PO_(4)/MIL-68(In)-NH_(2)plasmonic heterojunction photocatalyst for high-efficiency photocatalysis

To boost the visible light catalytic performance of typical metal-organic frameworks(MOFs)materials(MIL-68(In)-NH_(2)),a novel stable Z-scheme Ag/Ag_(3)PO_(4)/MIL-68(In)-NH_(2)plasmonic photocatalyst was constructed by electrostatic attraction,co-precipitation reaction,and in-situ photoreduction reaction methods for the first time.The photocatalytic activities of the photocatalysts are systematically explored by the photocatalytic degradation of bisphenol A(BPA)and reduction of Cr(VI)under visible light.Ag/Ag_(3)PO_(4)/MIL-68(In)-NH_(2)displays the best photocatalytic performance among the as-prepared photocatalysts.The rate constant of BPA degradation on Ag/Ag_(3)PO_(4)/MIL-68(In)-NH_(2)is 0.09655 min^(-1),which is better than many reported photocatalytic materials.It also achieved a maximum rate constant of 0.02074min^(-1)for Cr(VI)reduction.The boosted photocatalytic performance is due to the improved absorption caused by localized surface plasmon resonance(LSPR),effective interface charge transfer and separation,and more reactive sites provided by the large specific surface area.Besides,the photocatalytic degradation pathway of BPA is concluded according to GC-MS analysis.Finally,a more reasonable Z-scheme mechanism is speculated and verified through a series of characterizations and simulations,such as timeresolved photoluminescence spectroscopy(TRPL),electron spin resonance(ESR),and finite difference time domain(FDTD)method.