Matric suction is an important state variable required for the assessment of unsaturated soil properties.Tensiometers are commonly used for direct matric suction measurement but have a limited measuring range up to 90...Matric suction is an important state variable required for the assessment of unsaturated soil properties.Tensiometers are commonly used for direct matric suction measurement but have a limited measuring range up to 90 kPa due to the cavitation problem.Osmotic tensiometer(OT)can improve the measuring range of tensiometers by increasing the osmotic pressure of water to avoid the cavitation.However,the long-term water pressure decay that appeared in OTs caused a gradual decrease in their measuring range.In this study,crosslinked poly(acrylamide-co-acrylic acid)potassium salt(PAM-co-PAAK)was used for the preparation of OTs(five in total)to explore the mechanism of water pressure decay of OTs.The maximum water pressure in the OT versus the volume fraction of polymer filled in the OT was described based on the Flory-Huggins polymer theories and validated using WP4C dewpoint hygrometer.The long-term pressure decay of OT-1,OT-2,and OT-3 was observed for 130 d and constant pressures were found for OT-1 and OT-2,indicating that the pressure decay of OT was mainly caused by the stress relaxation of the polymer hydrogels,and standard linear solid(SLS)rheological model was appropriate to fit the decay data.For OT-1,OT-2 and OT-3,the theoretical osmotic pressure that was calculated based on the mass of retrieved polymer from OTs after 130-d pressure observation was higher than the actual osmotic pressure as observed,indicating that polymer leakage cannot explain the pressure decay of the OT.The ultravioletevisible(UVevisible)spectrophotometry examined the change in polymer concentrations in the water containers of OT-4 and OT-5 and demonstrated that there was no increase in polymer leakage during the period of pressure decay of OT-4 and OT-5.As a result,the pressure decay of OT was not caused by polymer leakage.The results of this research suggested that the viscoelastic properties of polymers should be taken into consideration in further OT development.展开更多
Recent extensive and important studies have provided detailed information and compelling evidence on how the presence of waves influences the vertical diffusivity/dispersivity in the coastal environment, which can aff...Recent extensive and important studies have provided detailed information and compelling evidence on how the presence of waves influences the vertical diffusivity/dispersivity in the coastal environment, which can affect various water quality considerations such as the distribution of suspended sediments in the water column as well as the potential of eutrophication. Comparatively, how the presence of waves influences the horizontal diffusivity/dispersivity has received only scant attention in the literature. Our previous works investigated the role played by the Taylor mechanism due to the wave-induced drift profile which leads to the longitudinal dispersion of contaminants in the horizontal direction, under regular sinusoidal waves and random waves with single-peak spectra. Natural waves in the coastal environment, however, often possess dual-peak spectra, comprising both higher frequency wind waves and lower frequency swells. In this study, the Taylor dispersion of contaminants under random waves with dual-peak spectra is examined through analytical derivation and numerical calculations. The effects of various dual-peak spectral parameters on the horizontal dispersion, including the proportion of lower frequency energy, peak frequency ratio and spectral shape parameter, are investigated. The results show that the relative energy distribution between the dual peaks has the most significant effect. Compared with single-peak spectra with equivalent energy, the Taylor dispersion with dual-peak spectra is stronger when the lower frequency is close to the peak frequency of the single-peak spectrum, and weaker with the higher frequency instead. Thus, it can be concluded that with a dual-peak wave spectrum, wind-dominated seas with higher frequency lead to stronger dispersion in the horizontal direction than swell-dominated seas with lower frequency.展开更多
Two-dimensional(2D) materials have exhibited great potential for replacing costly Pt for oxygen reduction reaction(ORR) because of their distinctive structural features and high pre-site activity.However,their perform...Two-dimensional(2D) materials have exhibited great potential for replacing costly Pt for oxygen reduction reaction(ORR) because of their distinctive structural features and high pre-site activity.However,their performance is generally hindered by the limited density of active sites(e.g.,at the layer edges).Although they feature a high exposure of surface sites,these sites are typically inert for ORR.Herein,through density functional theory calculations,we propose a promising ORR catalyst candidate,a 2D TaTe_(2) nanosheet,which has an intrinsic high basal-plane activity.Both of the thermodynamic and kinetic processes are explored,which demonstrates that the basal-plane Te sites of the TaTe_(2) nanosheet have great potential for facilitating ORR.Specifically,we construct a microkinetic model of ORR proceeding on TaTe_(2),which unveils its dynamic intermediate coverage under different electrode potentials and identifies the dominating associative pathway.The theoretical half-wave potential of TaTe_(2) is predicted to be 0.87 V,which exceeds those of the well-established Pt(111) and Fe–N–C single-atom catalysts computed at the same level.This study not only presents the first 2D,non-Pt ORR catalyst candidate with an intrinsic basal-plane activity but also offers a rational methodology for unveiling the mechanism/activity of ORR and other electrochemical reactions.展开更多
This study presents a numerical model for the thermal-elastohydrodynamic lubrication of heterogeneous materials in impact motion,in which a rigid ball bounces on a starved non-Newtonian oil-covered plane surface of an...This study presents a numerical model for the thermal-elastohydrodynamic lubrication of heterogeneous materials in impact motion,in which a rigid ball bounces on a starved non-Newtonian oil-covered plane surface of an elastic semi-infinite heterogeneous solid with inhomogeneous inclusions.The impact–rebound process and the microscopic response of the subsurface inhomogeneous inclusions are investigated.The inclusions are homogenized according to Eshelby’s equivalent inclusion method.The Elrod algorithm is adopted to determine the lubrication starvation based on the solutions of pressure and film thickness,while the lubricant velocity and shear rate of the non-Newtonian lubricant are derived by using the separation flow method.The dynamic response of the cases subjected to constant impact mass,momentum,and energy is discussed to reveal the influence of the initial drop height on the impact–rebound process.The results imply that the inclusion disturbs the subsurface stress field and affects the dynamic response of the contact system when the surface pressure is high.The impact energy is the decisive factor for the stress peak,maximum hydrodynamic force,and restitution coefficient,while the dynamic response during the early approaching process is controlled by the drop height.展开更多
A simple sol-gel approach is proposed herein to fabricate CaFe_(2)O_(4)for the degradation of various organic pollutants(rhodamine B(RhB),tetracycline hydrochloride,humic acid,and methylene orange)under LED light irra...A simple sol-gel approach is proposed herein to fabricate CaFe_(2)O_(4)for the degradation of various organic pollutants(rhodamine B(RhB),tetracycline hydrochloride,humic acid,and methylene orange)under LED light irradiation mediated by peroxymonosulfate(PMS).The results indicate that the calcination temperature can significantly influence the performance of CaFe_(2)O_(4)for PMS activation,and the CaFe_(2)O_(4)sample obtained at 800℃(CaFe_(2)O_(4)-800)exhibits the best efficiency in degrading RhB,which is much higher than that of Fe_2o_(3)-800.This can be attributed to the efficient separation of photogenerated electrons(e^(-))and holes(h^(+))by PMS,which is validated by transient photocurrent response and photoluminescence measurements.Results from density functio nal theo ry calculations indicate that the valence band of CaFe_(2)O_(4)-800 exhibits a high concentration of carriers and weak localization of electrons,which are favorable for PMS activation.Radical scavenging results confirm that h^(+)and O_(2)^(·-)are the dominant reactive species.Moreover,CaFe_(2)O_(4)-800 not only demonstrated a stable performance during eight cycling runs with negligible iron leaching but also exhibited excellent degradation efficiency under natural water and sunlight.Finally,the mechanism and pathway of RhB degradation by the CaFe_(2)O_(4)-800/PMS/LED system are also proposed.This work presents the enormous prospect of CaFe_(2)O_(4)as an environmentally benign photocatalyst for PMS activation.展开更多
A mesoporous cobalt aluminate(CoAl_(2)O_(4))spinel is synthesized through a combustion method and adopted for the activation of peroxymonosulfate(PMS)to degrade organic pollutants.Multiple characterization procedures ...A mesoporous cobalt aluminate(CoAl_(2)O_(4))spinel is synthesized through a combustion method and adopted for the activation of peroxymonosulfate(PMS)to degrade organic pollutants.Multiple characterization procedures are conducted to investigate the morphology and physicochemical properties of the CoAl_(2)O_(4)spinel.Due to its mesoporous structure,large surface area,and high electrical conductivity,the obtained CoAl_(2)O_(4)exhibits remarkable catalytic activity for Rhodamine B(RhB)degradation.Its RhB degradation rate is 89.0 and 10.5 times greater than those of Co_(3)O_(4) and CoAl_(2)O_(4)spinel prepared by a precipitation method,respectively.Moreover,the mesoporous CoAl_(2)O_(4)spinel demonstrates a broad operating pH range and excellent recyclability.The influence of several parameters(catalyst amount,PMS concentration,initial p H,and coexisting inorganic anions)on the oxidation of RhB is evaluated.Through quenching tests and electron paramagnetic resonance experiments,sulfate radicals are identified as the predominant reactive species in RhB degradation.This paper provides new insights for the development of efficient,stable,and reusable cobalt-based heterogeneous catalysts and promotes the application of persulfate activation technology for the treatment of refractory organic wastewater.展开更多
Industrial water treatment and industrial marine outfalls both function together to reduce the pollutant concentrations in the effluent and mitigate the potential impact on the environment. The former uses environ- me...Industrial water treatment and industrial marine outfalls both function together to reduce the pollutant concentrations in the effluent and mitigate the potential impact on the environment. The former uses environ- mental treatment technology with energy and material cost considerations, while the latter utilizes the natural assimilation potential of the coastal water environment achievable at the outfall location. Because of their synergistic nature, marine outfalls are now commonly used for the disposal of partially treated domestic and industrial effluents in many coastal cities around the world, with many successful examples of low and acceptable risks to the environment. The objective of this paper is to review their balance from both environmental and economic considerations. We also discuss the end-of-the-pipe and mixing zone approaches for industrial effluents, and give some recommendations particularly for developing coun- tries. Finally, we emphasize that a compulsory and vigorous monitoring program is essential regardless of how the balance is achieved.展开更多
The appropriate energy level position of photocatalysts dominates the photocatalytic redox reaction and utilization efficiency of solar energy for wastewater treatment.Herein,we report a near-infrared(NIR)light driven...The appropriate energy level position of photocatalysts dominates the photocatalytic redox reaction and utilization efficiency of solar energy for wastewater treatment.Herein,we report a near-infrared(NIR)light driven Bi^(5+)-rich Bi407 photocatalyst,achieving a greatly enhanced photocatalytic activity for pollutant removal compared with Bi3+-replenished Bi2O3.Density functional theory calculations show the formation of an intermediate band in the Bi_(4)O_(7)structure because of the hybridization of O 2p and Bi 4s orbits.The formation of the intermediate band not only narrows the band gap but also improves the optical absorption property and separation efficiency of the photoinduced carriers.The existence of the oxygen vacancies(OVs)in the Bi_(4)O_(7)nanosheets ensures high carriers’concentration,which is verified by the Hall effect test.The synergetic effects of the OVs and Bi^(5+)greatly accelerate the separation efficiency of the photogenerated carriers.Consequently,the Bi_(4)O_(7)nanosheets exhibit enhanced NIR light driven photocatalytic activity for the degradation of rhodamine B and ciprofloxacin compared with the bulk Bi2O3.This study paves the way to the design of highly efficient NIR light-responsive Bi-based photocatalysts for environmental purification.展开更多
文摘Matric suction is an important state variable required for the assessment of unsaturated soil properties.Tensiometers are commonly used for direct matric suction measurement but have a limited measuring range up to 90 kPa due to the cavitation problem.Osmotic tensiometer(OT)can improve the measuring range of tensiometers by increasing the osmotic pressure of water to avoid the cavitation.However,the long-term water pressure decay that appeared in OTs caused a gradual decrease in their measuring range.In this study,crosslinked poly(acrylamide-co-acrylic acid)potassium salt(PAM-co-PAAK)was used for the preparation of OTs(five in total)to explore the mechanism of water pressure decay of OTs.The maximum water pressure in the OT versus the volume fraction of polymer filled in the OT was described based on the Flory-Huggins polymer theories and validated using WP4C dewpoint hygrometer.The long-term pressure decay of OT-1,OT-2,and OT-3 was observed for 130 d and constant pressures were found for OT-1 and OT-2,indicating that the pressure decay of OT was mainly caused by the stress relaxation of the polymer hydrogels,and standard linear solid(SLS)rheological model was appropriate to fit the decay data.For OT-1,OT-2 and OT-3,the theoretical osmotic pressure that was calculated based on the mass of retrieved polymer from OTs after 130-d pressure observation was higher than the actual osmotic pressure as observed,indicating that polymer leakage cannot explain the pressure decay of the OT.The ultravioletevisible(UVevisible)spectrophotometry examined the change in polymer concentrations in the water containers of OT-4 and OT-5 and demonstrated that there was no increase in polymer leakage during the period of pressure decay of OT-4 and OT-5.As a result,the pressure decay of OT was not caused by polymer leakage.The results of this research suggested that the viscoelastic properties of polymers should be taken into consideration in further OT development.
基金financially supported by the State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering Research Foundation(Grant No.2015491311)the Fundamental Research Funds for the Central Universities(Grant No.DUT19LAB13)partially supported by the Ministry of Education,Singapore(Ac RF Tier 2 Grant No.MOE2013-T2-1-054)
文摘Recent extensive and important studies have provided detailed information and compelling evidence on how the presence of waves influences the vertical diffusivity/dispersivity in the coastal environment, which can affect various water quality considerations such as the distribution of suspended sediments in the water column as well as the potential of eutrophication. Comparatively, how the presence of waves influences the horizontal diffusivity/dispersivity has received only scant attention in the literature. Our previous works investigated the role played by the Taylor mechanism due to the wave-induced drift profile which leads to the longitudinal dispersion of contaminants in the horizontal direction, under regular sinusoidal waves and random waves with single-peak spectra. Natural waves in the coastal environment, however, often possess dual-peak spectra, comprising both higher frequency wind waves and lower frequency swells. In this study, the Taylor dispersion of contaminants under random waves with dual-peak spectra is examined through analytical derivation and numerical calculations. The effects of various dual-peak spectral parameters on the horizontal dispersion, including the proportion of lower frequency energy, peak frequency ratio and spectral shape parameter, are investigated. The results show that the relative energy distribution between the dual peaks has the most significant effect. Compared with single-peak spectra with equivalent energy, the Taylor dispersion with dual-peak spectra is stronger when the lower frequency is close to the peak frequency of the single-peak spectrum, and weaker with the higher frequency instead. Thus, it can be concluded that with a dual-peak wave spectrum, wind-dominated seas with higher frequency lead to stronger dispersion in the horizontal direction than swell-dominated seas with lower frequency.
基金financial support from the Nanyang Environment and Water Research Institute (Core Fund), Nanyang Technological University, Singapore。
文摘Two-dimensional(2D) materials have exhibited great potential for replacing costly Pt for oxygen reduction reaction(ORR) because of their distinctive structural features and high pre-site activity.However,their performance is generally hindered by the limited density of active sites(e.g.,at the layer edges).Although they feature a high exposure of surface sites,these sites are typically inert for ORR.Herein,through density functional theory calculations,we propose a promising ORR catalyst candidate,a 2D TaTe_(2) nanosheet,which has an intrinsic high basal-plane activity.Both of the thermodynamic and kinetic processes are explored,which demonstrates that the basal-plane Te sites of the TaTe_(2) nanosheet have great potential for facilitating ORR.Specifically,we construct a microkinetic model of ORR proceeding on TaTe_(2),which unveils its dynamic intermediate coverage under different electrode potentials and identifies the dominating associative pathway.The theoretical half-wave potential of TaTe_(2) is predicted to be 0.87 V,which exceeds those of the well-established Pt(111) and Fe–N–C single-atom catalysts computed at the same level.This study not only presents the first 2D,non-Pt ORR catalyst candidate with an intrinsic basal-plane activity but also offers a rational methodology for unveiling the mechanism/activity of ORR and other electrochemical reactions.
基金the National Research Foundation(NRF),Singapore,SMRT,Singapore and Nanyang Technological University,Singapore.Q.B.also acknowledges the support from National Natural Science Foundation of China,China(Grant No.51905051).
文摘This study presents a numerical model for the thermal-elastohydrodynamic lubrication of heterogeneous materials in impact motion,in which a rigid ball bounces on a starved non-Newtonian oil-covered plane surface of an elastic semi-infinite heterogeneous solid with inhomogeneous inclusions.The impact–rebound process and the microscopic response of the subsurface inhomogeneous inclusions are investigated.The inclusions are homogenized according to Eshelby’s equivalent inclusion method.The Elrod algorithm is adopted to determine the lubrication starvation based on the solutions of pressure and film thickness,while the lubricant velocity and shear rate of the non-Newtonian lubricant are derived by using the separation flow method.The dynamic response of the cases subjected to constant impact mass,momentum,and energy is discussed to reveal the influence of the initial drop height on the impact–rebound process.The results imply that the inclusion disturbs the subsurface stress field and affects the dynamic response of the contact system when the surface pressure is high.The impact energy is the decisive factor for the stress peak,maximum hydrodynamic force,and restitution coefficient,while the dynamic response during the early approaching process is controlled by the drop height.
基金financially supported by the National Natural Science Foundation of China(No.51604194)the Natural Science Foundation of Hubei Province of China(No.2016CFB169)+2 种基金the China Scholarship Council(No.201808420137)the Outstanding Talent Research Fund of Zhengzhou University(No.32340034)the Nanyang Environment and Water Research Institute(Core Fund),Nanyang Technological University,Singapore。
文摘A simple sol-gel approach is proposed herein to fabricate CaFe_(2)O_(4)for the degradation of various organic pollutants(rhodamine B(RhB),tetracycline hydrochloride,humic acid,and methylene orange)under LED light irradiation mediated by peroxymonosulfate(PMS).The results indicate that the calcination temperature can significantly influence the performance of CaFe_(2)O_(4)for PMS activation,and the CaFe_(2)O_(4)sample obtained at 800℃(CaFe_(2)O_(4)-800)exhibits the best efficiency in degrading RhB,which is much higher than that of Fe_2o_(3)-800.This can be attributed to the efficient separation of photogenerated electrons(e^(-))and holes(h^(+))by PMS,which is validated by transient photocurrent response and photoluminescence measurements.Results from density functio nal theo ry calculations indicate that the valence band of CaFe_(2)O_(4)-800 exhibits a high concentration of carriers and weak localization of electrons,which are favorable for PMS activation.Radical scavenging results confirm that h^(+)and O_(2)^(·-)are the dominant reactive species.Moreover,CaFe_(2)O_(4)-800 not only demonstrated a stable performance during eight cycling runs with negligible iron leaching but also exhibited excellent degradation efficiency under natural water and sunlight.Finally,the mechanism and pathway of RhB degradation by the CaFe_(2)O_(4)-800/PMS/LED system are also proposed.This work presents the enormous prospect of CaFe_(2)O_(4)as an environmentally benign photocatalyst for PMS activation.
基金financial support from the National Natural Science Foundation of China(No.51604194)China Scholarship Council(No.201808420137)Nanyang Environment and Water Research Institute(Core Fund),Nanyang Technological University,Singapore。
文摘A mesoporous cobalt aluminate(CoAl_(2)O_(4))spinel is synthesized through a combustion method and adopted for the activation of peroxymonosulfate(PMS)to degrade organic pollutants.Multiple characterization procedures are conducted to investigate the morphology and physicochemical properties of the CoAl_(2)O_(4)spinel.Due to its mesoporous structure,large surface area,and high electrical conductivity,the obtained CoAl_(2)O_(4)exhibits remarkable catalytic activity for Rhodamine B(RhB)degradation.Its RhB degradation rate is 89.0 and 10.5 times greater than those of Co_(3)O_(4) and CoAl_(2)O_(4)spinel prepared by a precipitation method,respectively.Moreover,the mesoporous CoAl_(2)O_(4)spinel demonstrates a broad operating pH range and excellent recyclability.The influence of several parameters(catalyst amount,PMS concentration,initial p H,and coexisting inorganic anions)on the oxidation of RhB is evaluated.Through quenching tests and electron paramagnetic resonance experiments,sulfate radicals are identified as the predominant reactive species in RhB degradation.This paper provides new insights for the development of efficient,stable,and reusable cobalt-based heterogeneous catalysts and promotes the application of persulfate activation technology for the treatment of refractory organic wastewater.
文摘Industrial water treatment and industrial marine outfalls both function together to reduce the pollutant concentrations in the effluent and mitigate the potential impact on the environment. The former uses environ- mental treatment technology with energy and material cost considerations, while the latter utilizes the natural assimilation potential of the coastal water environment achievable at the outfall location. Because of their synergistic nature, marine outfalls are now commonly used for the disposal of partially treated domestic and industrial effluents in many coastal cities around the world, with many successful examples of low and acceptable risks to the environment. The objective of this paper is to review their balance from both environmental and economic considerations. We also discuss the end-of-the-pipe and mixing zone approaches for industrial effluents, and give some recommendations particularly for developing coun- tries. Finally, we emphasize that a compulsory and vigorous monitoring program is essential regardless of how the balance is achieved.
基金supported by the National Natural Science Foundation of China(No.21806194)the Outstanding Talent Research Fund of Zhengzhou University(No.32340099)the Nanyang Environment and Water Research Institute(Core Fund),Nanyang Technological University,Singapore。
文摘The appropriate energy level position of photocatalysts dominates the photocatalytic redox reaction and utilization efficiency of solar energy for wastewater treatment.Herein,we report a near-infrared(NIR)light driven Bi^(5+)-rich Bi407 photocatalyst,achieving a greatly enhanced photocatalytic activity for pollutant removal compared with Bi3+-replenished Bi2O3.Density functional theory calculations show the formation of an intermediate band in the Bi_(4)O_(7)structure because of the hybridization of O 2p and Bi 4s orbits.The formation of the intermediate band not only narrows the band gap but also improves the optical absorption property and separation efficiency of the photoinduced carriers.The existence of the oxygen vacancies(OVs)in the Bi_(4)O_(7)nanosheets ensures high carriers’concentration,which is verified by the Hall effect test.The synergetic effects of the OVs and Bi^(5+)greatly accelerate the separation efficiency of the photogenerated carriers.Consequently,the Bi_(4)O_(7)nanosheets exhibit enhanced NIR light driven photocatalytic activity for the degradation of rhodamine B and ciprofloxacin compared with the bulk Bi2O3.This study paves the way to the design of highly efficient NIR light-responsive Bi-based photocatalysts for environmental purification.
