ZnO thin films were grown on GaAs （001） substrates by metal-organic chemical vapor deposition （MOCVD） at low temperatures ranging from 100 to 400℃. DEZn and 1-12 O were used as the zinc precursor and oxygen precu...ZnO thin films were grown on GaAs （001） substrates by metal-organic chemical vapor deposition （MOCVD） at low temperatures ranging from 100 to 400℃. DEZn and 1-12 O were used as the zinc precursor and oxygen precursor, respectively. The effects of the growth temperatures on the growth characteristics and optical properties of ZnO films were investigated. The X-ray diffraction measurement （XRD） results indicated that all the thin films were grown with highly c- axis orientation. The surface morphologies and crystal properties of the films were critically dependent on the growth temperatures. Although there was no evidence of epitaxial growth, the scanning electron microscopy （SEM） image of ZnO film grown at 400℃ revealed the presence of ZnO microcrystallines with closed packed hexagon structure. The photoluminescence spectrum at room temperature showed only bright band-edge （3. 33eV） emissions with little or no deep-level e- mission related to defects.展开更多
The present report evaluates the effects of formaldehyde (FA) exposure on peripheral lymphocytes by using heth genetic and immunological parameters. Twenty-three non-smoking students in the study had inhalation exposu...The present report evaluates the effects of formaldehyde (FA) exposure on peripheral lymphocytes by using heth genetic and immunological parameters. Twenty-three non-smoking students in the study had inhalation exposure to 0.508 ±0. 299 mg/m3 of FA for a Period of 8 weeks (3h × 3 times each week) during anatomy classes. As for composition of lymphocyte subsets after FA exposare,significant increase was found in the percentage of CD19(B cells), while sighficant decrease was observed in CD3(total T cells), CD4(T helper-inducer cells), and CD8(T cytotoxic-suppressior cells) with a P<0 .01. Increase in the ratio of T-helper-inducer cells to T-cytotoxic-suppressor cells (T4 / T8) was also observed with statistical sighcance after exposure (P < 0.001). In the meanwhile,no significant difference (P > 0 .05) was reported between lymphocyte prolifendion rate and sisterchromatid exchange (SCE) at the exposure level and duration. It is suggested that the lymphocyte subsets may be most susceptible to the effects of FA, though a single immunological endpoint is rarely related with pathophysiological interpretation.展开更多
The frequency of micronuclei (MN) in cells of the nasal mucosa, oral mucosa and in lym-phocytes was evaluated for 25 students in anatomy classes exposed to formaldehyde (FA) overan 8-week period. Each student served a...The frequency of micronuclei (MN) in cells of the nasal mucosa, oral mucosa and in lym-phocytes was evaluated for 25 students in anatomy classes exposed to formaldehyde (FA) overan 8-week period. Each student served as his or her own control. The time-weighted averageconcentration (TWA) of fOrmaldehyde in anatomical laboratories and in students' dormitorieswas 0. 508 ± 0. 299 mg/m3 and 0. 012 ± 0. 0025mg/m3, respectively. A higher frequency ofmicronuclei was observed in nasal and oral exfoliative cells after formaldehyde exposure (3. 85± 1. 48 vs 1 .20± 0. 676 and 0. 857 ± 0. 558 vs 0. 568 ± 0. 317, paired-t test: P< 0. 001and P < 0. 01, respectively). No significant increase in the frequency of lymphocyte micronu-clei was found after formaldehyde exposure (P >0. 05 ). The present study shows that nasalmucosa cel1s exposed through respiration are the chief target of FA-induced genotoxic effects展开更多
Formaldehyde（HCHO）is carcinogenic and teratogenic,and is therefore a serious danger to human health.It also adversely affects air quality.Catalytic oxidation is an efficient technique for removing HCHO.The developme...Formaldehyde（HCHO）is carcinogenic and teratogenic,and is therefore a serious danger to human health.It also adversely affects air quality.Catalytic oxidation is an efficient technique for removing HCHO.The development of highly efficient and stable catalysts that can completely convert HCHO at low temperatures,even room temperature,is important.Supported Pt and Pd catalysts can completely convert HCHO at room temperature,but their industrial applications are limited because they are expensive.The catalytic activities in HCHO oxidation of transition-metal oxide catalysts such as manganese and cobalt oxides with unusual morphologies are better than those of traditional MnO2,Co3O4,or other metal oxides.This is attributed to their specific structures,high specific surface areas,and other factors such as active phase,reducibility,and amount of surface active oxygens.Such catalysts with various morphologies have great potential and can also be used as catalyst supports.The loading of relatively cheap Ag or Au on transition-metal oxides with special morphologies potentially improves the catalytic activity in HCHO removal at room temperature.The preparation and development of new nanocatalysts with various morphologies and structures is important for HCHO removal.In this paper,research progress on precious-metal and transition-metal oxide catalyst systems for HCHO oxidation is reviewed; topics such as oxidation properties,structure–activity relationships,and factors influencing the catalytic activity and reaction mechanism are discussed.Future prospects and directions for the development of such catalysts are also covered.展开更多
Methacrolein（MACR） is an abundant multifunctional carbonyl compound with high reactivity in the atmosphere. In this study, we investigated the hydroxyl radical initiated oxidation of MACR at various NO/MACR ratios（...Methacrolein（MACR） is an abundant multifunctional carbonyl compound with high reactivity in the atmosphere. In this study, we investigated the hydroxyl radical initiated oxidation of MACR at various NO/MACR ratios（0 to 4.04） and relative humidities（＆lt; 3% to80%） using a flow tube. Meanwhile, a box model based on the Master Chemical Mechanism was performed to test our current understanding of the mechanism. In contrast to the reasonable predictions for hydroxyacetone production, the modeled yields of formaldehyde（HCHO） were twice higher than the experimental results. The discrepancy was ascribed to the existence of unconsidered non-HCHO forming channels in the chemistry of CH3-UC（=CH2）OO, which account for approx. 50%. In addition, the production of hydroxyacetone and HCHO were affected by water vapor as well as the initial NO/MACR ratio. The yields of HCHO were higher under humid conditions than that under dry condition. The yields of hydroxyacetone were higher under humid conditions at low-NOx level, while lower at high-NOxlevel. The reasonable explanation for the lower hydroxyacetone yield under humid conditions at high-NOx level is that water vapor promotes the production of Umethacrolein nitrate in the reaction of HOCH2 C（CH3）（OO）CHO with NO due to the peroxy radical-water complex formation, which was evidenced by calculational results. And the minimum equilibrium constant of this water complex formation was estimated to be 1.89 × 10 （-18） cm3/molecule. These results provide new insights into the MACR oxidation mechanism and the effects of water vapor.展开更多
文摘ZnO thin films were grown on GaAs （001） substrates by metal-organic chemical vapor deposition （MOCVD） at low temperatures ranging from 100 to 400℃. DEZn and 1-12 O were used as the zinc precursor and oxygen precursor, respectively. The effects of the growth temperatures on the growth characteristics and optical properties of ZnO films were investigated. The X-ray diffraction measurement （XRD） results indicated that all the thin films were grown with highly c- axis orientation. The surface morphologies and crystal properties of the films were critically dependent on the growth temperatures. Although there was no evidence of epitaxial growth, the scanning electron microscopy （SEM） image of ZnO film grown at 400℃ revealed the presence of ZnO microcrystallines with closed packed hexagon structure. The photoluminescence spectrum at room temperature showed only bright band-edge （3. 33eV） emissions with little or no deep-level e- mission related to defects.
文摘The present report evaluates the effects of formaldehyde (FA) exposure on peripheral lymphocytes by using heth genetic and immunological parameters. Twenty-three non-smoking students in the study had inhalation exposure to 0.508 ±0. 299 mg/m3 of FA for a Period of 8 weeks (3h × 3 times each week) during anatomy classes. As for composition of lymphocyte subsets after FA exposare,significant increase was found in the percentage of CD19(B cells), while sighficant decrease was observed in CD3(total T cells), CD4(T helper-inducer cells), and CD8(T cytotoxic-suppressior cells) with a P<0 .01. Increase in the ratio of T-helper-inducer cells to T-cytotoxic-suppressor cells (T4 / T8) was also observed with statistical sighcance after exposure (P < 0.001). In the meanwhile,no significant difference (P > 0 .05) was reported between lymphocyte prolifendion rate and sisterchromatid exchange (SCE) at the exposure level and duration. It is suggested that the lymphocyte subsets may be most susceptible to the effects of FA, though a single immunological endpoint is rarely related with pathophysiological interpretation.
文摘The frequency of micronuclei (MN) in cells of the nasal mucosa, oral mucosa and in lym-phocytes was evaluated for 25 students in anatomy classes exposed to formaldehyde (FA) overan 8-week period. Each student served as his or her own control. The time-weighted averageconcentration (TWA) of fOrmaldehyde in anatomical laboratories and in students' dormitorieswas 0. 508 ± 0. 299 mg/m3 and 0. 012 ± 0. 0025mg/m3, respectively. A higher frequency ofmicronuclei was observed in nasal and oral exfoliative cells after formaldehyde exposure (3. 85± 1. 48 vs 1 .20± 0. 676 and 0. 857 ± 0. 558 vs 0. 568 ± 0. 317, paired-t test: P< 0. 001and P < 0. 01, respectively). No significant increase in the frequency of lymphocyte micronu-clei was found after formaldehyde exposure (P >0. 05 ). The present study shows that nasalmucosa cel1s exposed through respiration are the chief target of FA-induced genotoxic effects
基金supported by the National Natural Science Foundation of China(21325731,51478241,21221004)~~
文摘Formaldehyde（HCHO）is carcinogenic and teratogenic,and is therefore a serious danger to human health.It also adversely affects air quality.Catalytic oxidation is an efficient technique for removing HCHO.The development of highly efficient and stable catalysts that can completely convert HCHO at low temperatures,even room temperature,is important.Supported Pt and Pd catalysts can completely convert HCHO at room temperature,but their industrial applications are limited because they are expensive.The catalytic activities in HCHO oxidation of transition-metal oxide catalysts such as manganese and cobalt oxides with unusual morphologies are better than those of traditional MnO2,Co3O4,or other metal oxides.This is attributed to their specific structures,high specific surface areas,and other factors such as active phase,reducibility,and amount of surface active oxygens.Such catalysts with various morphologies have great potential and can also be used as catalyst supports.The loading of relatively cheap Ag or Au on transition-metal oxides with special morphologies potentially improves the catalytic activity in HCHO removal at room temperature.The preparation and development of new nanocatalysts with various morphologies and structures is important for HCHO removal.In this paper,research progress on precious-metal and transition-metal oxide catalyst systems for HCHO oxidation is reviewed; topics such as oxidation properties,structure–activity relationships,and factors influencing the catalytic activity and reaction mechanism are discussed.Future prospects and directions for the development of such catalysts are also covered.
基金supported by the National Natural Science Foundation of China (Nos. 21477002, 41421064)the National Key Research and Development Program of China (No. 2016YFC0202704)
文摘Methacrolein（MACR） is an abundant multifunctional carbonyl compound with high reactivity in the atmosphere. In this study, we investigated the hydroxyl radical initiated oxidation of MACR at various NO/MACR ratios（0 to 4.04） and relative humidities（＆lt; 3% to80%） using a flow tube. Meanwhile, a box model based on the Master Chemical Mechanism was performed to test our current understanding of the mechanism. In contrast to the reasonable predictions for hydroxyacetone production, the modeled yields of formaldehyde（HCHO） were twice higher than the experimental results. The discrepancy was ascribed to the existence of unconsidered non-HCHO forming channels in the chemistry of CH3-UC（=CH2）OO, which account for approx. 50%. In addition, the production of hydroxyacetone and HCHO were affected by water vapor as well as the initial NO/MACR ratio. The yields of HCHO were higher under humid conditions than that under dry condition. The yields of hydroxyacetone were higher under humid conditions at low-NOx level, while lower at high-NOxlevel. The reasonable explanation for the lower hydroxyacetone yield under humid conditions at high-NOx level is that water vapor promotes the production of Umethacrolein nitrate in the reaction of HOCH2 C（CH3）（OO）CHO with NO due to the peroxy radical-water complex formation, which was evidenced by calculational results. And the minimum equilibrium constant of this water complex formation was estimated to be 1.89 × 10 （-18） cm3/molecule. These results provide new insights into the MACR oxidation mechanism and the effects of water vapor.
