C3N4 modified with single layer ZIF67 nanoparticles for efficient photocatalytic degradation of organic pollutants under visible light

Uniformly distributed single layer of ZIF67-derived C3N4(ZIF67-C3N4)was synthesized and applied to the photocatalytic degradation of methylene blue(MB)under visible light.Results indicated that the obtained ZIF67-C3N4 has a maximum specific surface area of 541.392 m^2/g,which is much larger than that of raw C3N4 of 97.291 m^2/g.The investigation of C3N4 amount involved in ZIF67-C3N4 on the photoactivity revealed that 2.57 g ZIF67 with 0.3 g C3N4,which named ZIF67-C3N4(0.3)exhibited superior photocatalytic activities.More than 90%of MB at 10 mg/L was degraded within 70 min with the addition of 0.01 g ZIF67-C3N4(0.3),while this time required for raw C3N4 was over 140 min.The effects of pH of solution,initial concentration of MB and dosage of C3N4 in ZIF67-C3N4 composites on the photocatalytic efficiency for MB degradation were also evaluated.Quenching experiments indicated that the photo-induced holes(h^+)and superoxide radicals(O2-·)were mainly responsible for MB degradation.It is anticipated that the insertion of ZIF67 nanoparticles not only increases the adsorption capacity of C3N4 but also promotes the generation and migration of the photo-induced active species.

Interannual evolution of the chemical composition,sources and processes of PM_(2.5)in Chengdu,China:Insights from observations in four winters

The air quality in China has improved significantly in the last decade and,correspondingly,the characteristics of PM_(2.5)have also changed.We studied the interannual variation of PM_(2.5)in Chengdu,one of the most heavily polluted megacities in southwest China,during the most polluted season(winter).Our results show that the mass concentrations of PM_(2.5)decreased significantly year-by-year,from 195.8±91.0μg/m~3in winter 2016 to 96.1±39.3μg/m^(3)in winter 2020.The mass concentrations of organic matter(OM),SO_()4^(2-),NH_(4)^(+)and NO_(3)^(-)decreased by 49.6%,57.1%,49.7% and 28.7%,respectively.The differential reduction in the concentrations of chemical components increased the contributions from secondary organic carbon and NO_(3)^(-)and there was a larger contribution from mobile sources.The contribution of OM and NO_(3)^(-)not only increased with increasing levels of pollution,but also increased year-by-year at the same level of pollution.Four sources of PM_(2.5)were identified:combustion sources,vehicular emissions,dust and secondary aerosols.Secondary aerosols made the highest contribution and increased year-by-year,from 40.6%in winter 2016 to 46.3% in winter 2020.By contrast,the contribution from combustion sources decreased from 14.4% to 8.7%.Our results show the effectiveness of earlier pollution reduction policies and emphasizes that priority should be given to key pollutants(e.g.,OM and NO_(3)^(-))and sources(secondary aerosols and vehicular emissions)in future policies for the reduction of pollution in Chengdu during the winter months.

Real-time,single-particle chemical composition,volatility and mixing state measurements of urban aerosol particles in southwest China

To investigate the volatility of atmospheric particulates and the evolution of other particulate properties(chemical composition,particle size distribution and mixing state)with temperature,a thermodenuder coupled with a single particle aerosol mass spectrometer was used to conduct continuous observations of atmospheric fine particles in Chengdu,southwest China.Because of their complex sources and secondary reaction processes,the average mass spectra of single particles contained a variety of chemical components(including organic,inorganic and metal species).When the temperature rose from room temperature to280℃,the relative areas of volatile and semi-volatile components decreased,while the relative areas of less or non-volatile components increased.Most(>80%)nitrate and sulfate existed in the form of NH_(4)NO_(3)and(NH_(4))_(2)SO_(4),and their volatilization temperatures were50–100℃and 150–280℃,respectively.The contribution of biomass burning(BB)and vehicle emission(VE)particles increased significantly at 280℃,which emphasized the important role of regional biomass burning and local motor vehicle emissions to the core of particles.With the increase in temperature,the particle size of the particles coated with volatile or semi-volatile components was reduced,and their mixing with secondary inorganic components was significantly weakened.The formation of K-nitrate(KNO_(3))and K-sulfate(KSO_(4))particles was dominated by liquid-phase processes and photochemical reactions,respectively.Reducing KNO_(3)and BB particles is the key to improving visibility.These new results are helpful towards better understanding the initial sources,pollution formation mechanisms and climatic effects of fine particulate matter in this megacity in southwest China.

Characterization of Fe-containing particles in Chengdu,southwest China,using single-particle aerosol mass spectrometry

Single-particle aerosol mass spectrometry was used to study the characteristics of Fecontaining particles during winter in Chengdu,southwest China.The mass concentrations of PM_(2.5)and PM_(10)during the study period were 64±38 and 89±49μg/m~3,respectively,and NO_(2)and particulate matter were high compared with most other regions of China.The Fecontaining particles were divided into seven categories with different mass spectra,sources and aging characteristics.The highest contribution was from Fe mixed with carbonaceous components(Fe-C,23.1%)particles.Fe was more mixed with sulfate than nitrate and therefore the contribution of Fe mixed with sulfate(Fe-S,20.7%)particles was higher than that of Fe mixed with nitrate(Fe-N,12.5%)particles.The contributions from Fe-containing particles related to primary combustion were high in the small particle size range,whereas aged Fecontaining particles and dust-related particles were mostly found in the coarse particle size range.The air masses mainly originated from the west and east of Chengdu,and the corresponding PM_(2.5)concentrations were 79±36 and 55±36μg/m~3,respectively.The west and east air masses showed stronger contributions of Fe-containing particles related to biomass burning(Fe-B)and fossil fuel combustion(Fe-C and Fe-S)particles,respectively.The southwest area contributed the most Fe-containing particles.Future assessments of the effects of Fe-containing particles during heavy pollution period should pay more attention to Fe-C and Fe-S particles.Emission-reduction of Fe-containing particles should consider both local emissions and short-distance transmission from the surrounding areas.

Characteristics of PM_(2.5) pollution in Beijing after the improvement of air quality

Following the implementation of the strictest clean air policies to date in Beijing,the physicochemical characteristics and sources of PM_(2.5) have changed over the past few years.To improve pollution reduction policies and subsequent air quality further,it is necessary to explore the changes in PM_(2.5) over time.In this study,over one year(2017-2018)field study based on filter sampling(TH-150C;Wuhan Tianhong,China)was conducted in Fengtai District,Beijing,revealed that the annual average PM_(2.5) concentration(64.8±43.1μg/m^3)was significantly lower than in previous years and the highest PM_(2.5) concentration occurred in spring(84.4±59.9μg/m^3).Secondary nitrate was the largest source and accounted for 25.7%of the measured PM_(2.5).Vehicular emission,the second largest source(17.6%),deserves more attention when considering the increase in the number of motor vehicles and its contribution to gaseous pollutants.In addition,the contribution from coal combustion to PM_(2.5) decreased significantly.During weekends,the contribution from EC and NO3−increased whereas the contributions from SO4^2−,OM,and trace elements decreased,compared with weekdays.During the period of residential heating,PM_(2.5) mass decreased by 23.1%,compared with non-heating period,while the contributions from coal combustion and vehicular emission,and related species increased.With the aggravation of pollution,the contribution of vehicular emission and secondary sulfate increased and then decreased,while the contribution of NO3−and secondary nitrate continued to increase,and accounted for 34.0%and 57.5%of the PM_(2.5) during the heavily polluted days,respectively.

Characteristics,evolution,and regional differences of biomass burning particles in the Sichuan Basin,China

The Sichuan Basin has experienced serious air pollution from fine particulate matter(PM2.5) in the past few years with biomass burning has been identified as a major source of PM2.5 in this region.We used single particle aerosol mass spectrometer to investigate the characteristics of biomass burning particles in three interacting cities representing different types of urban environment in the Sichuan Basin.A total of 739,794,279,610,and380,636 biomass burning particles were detected at Ya’an,Guang’an,and Chengdu,which represented 42%,69%,and 61%,respectively,of the total number of particles.We analyzed the chemical composition,transportation,and evolution of biomass burning particles.The contribution of K-elemental carbon and K-secondary inorganic particles was highest in Ya’an(36%) and Guang’an(47%),respectively,reflecting the important role of fresh biomass burning particles and long-distance transport in these two cities.Air masses originating from different directions corresponded to different levels of PM2.5 and the contributions of polluted clusters increased significantly on polluted days.Fresh and secondary inorganic biomass burning particles increased pollution at Ya’an and Guang’an,respectively,but dominated different stages of pollution in Chengdu.K-nitrate particles were formed by photochemical reactions,whereas K-sulfate particles were formed by both photochemical and liquid-phase reactions.Investigation of the degree of particle aging showed that there were more fresh particles at Ya’an and more aged particles at Guang’an.These results are useful in helping our understanding of the characteristics of biomass burning particles and evaluating their role in PM2.5 pollution in the Sichuan Basin.

Environmental investigation of bio-modification of steel slag through microbially induced carbonate precipitation

Steel slag(SS)is one of byproduct of steel manufacture industry.The environmental concerns of SS may limit their re-use in different applications.The goal of this study was to investigate the leaching behavior of metals from SS before and after treated by microbially induced carbonate precipitation(MICP).Toxicity characteristic leaching procedure,synthetic precipitation leaching procedure and water leaching tests were performed to evaluate the leaching behavior of major elements(Fe,Mg and Ca)and trace elements(Ba,Cu and Mn)in three scenarios.The concentrations of leaching metals increased with the content of SS.After it reached the peak concentration,the leaching concentration decreased with the content of SS.The leachability of all elements concerned in this study was below 0.5%.The carbonate generated from the MICP process contributed to the low leachability of metals.After bio-modified by MICP process,the leaching concentrations of Ba from TCLP,SPLP and WLT tests were below 2.0 mg/L,which was the limit in drinking water regulated by U.S.EPA.The concentrations of Cu leached out from MICP-treated SS-sand samples were below 1.3 mg/L which is the limit regulated by national secondary drinking water.Compared with the regulations of U.S.EPA and Mississippi Department of Environment Quality(MDEQ),MICP-treated samples were classified as non-hazardous materials with respects to the leaching of metals.Meanwhile,maximum contaminant limits regulated by U.S.EPA states that MICP-treated SS are eco-friendly materials that can be reused as construction materials.

Enhancing the adsorption function of biochar by mechanochemical graphitization for organic pollutant removal

Biochar(BC)has been extensively studied as adsorbent for the treatment of water pollution.Despite the distinct advantages,the high calcination temperature and low adsorption capacity of pristine BC limit its practical applications.Most of the former studies focused on the structure and/or surface modification to improve the adsorption capacity of BC.However,the harsh experiment conditions involved in the biochar modification limited the application in industrial level.Herein,we introduced mechanical treatment into BC preparation to reduce the calcination temperature and improve the adsorption capacity simultaneously.The results indicated that the calcination temperature was reduced and the adsorption capacity of the treated BC was improved after mechanochemical treatment.Characterization of the samples disclosed that BCs were graphitized with the particle size reduced to nanoscale after treatment.Adsorption tests indicated that the mechanochemically treated BCs showed much better removal performance of organic contaminants than that of pristine BCs.For instance,among four pristine BCs(BC600,BC700,BC800,and BC900),only BC900 has strong adsorption capacity for MB,while BC600 has low adsorption capacity(1.2 mg/g).By comparison,the adsorption capacity of MB increased greatly to 173.96 mg/g by BC600-500/1(treated at 500 r/min for 1 hour).To optimize the mechanochemical treatment,the effects of rotation speed and agitation duration were also investigated.

Chemical fixation of toxic metals in stainless steel pickling residue by Na2S·xH2O,FeSO4·6H2O and phosphoric acid for beneficial uses

The leaching concentrations of different metals in stainless steel pickling residue(SSPR)were determined and the toxic metals were treated using Na2 S·xH2 O,FeSO4·6 H2 O,and phosphoric acid.A modified European Community Bureau of Reference(BCR)sequential extraction was used to identify the speciation of the concerned metals.Results showed that SSPR contains a large amount of Ca(58.41%),Fe(29.44%),Cr(3.83%),Ni(2.94%),Mn(2.82%)and some of Al,Cu,Mg,Zn.Among them,Cr and Ni were the most toxic metals in SSPR,thus the raw SSPR falls into hazardous waste category due to the leaching amount of Cr.In addition,the leached Cr was identified as Cr6+(MgCr04)in the waste.BCR test revealed that risk assessment code(RAC)of Cr and Ni were 33.29%and 61.7%,indicating they posed"high"and"very high"risk to the environment,respectively.After fixing by Na2 S·xH2 O and FeSO4·6 H2 O,the leaching concentrations of Cr and Ni were less than 1.5 and 0.5 mg/L,respectively.After fixing by Na2 S·xH2 O and FeSO4·6 H2 O the tre ated SSPR can be safely reused as roadbed materials,concrete and cement aggregates.This study provides a useful implication in treatment and beneficial reuse of heavy metal-containing hazardous wastes.

Characterization of submicron particles during autumn in Beijing,China

In this study, we performed a highly time-resolved chemical characterization of nonrefractory submicron particles（NR-PM_1） in Beijing by using an Aerodyne high-resolution time-of-flight aerosol mass spectrometer（HR-ToF-AMS）. The results showed the average NR-PM_1 mass concentration to be 56.4 ± 58.0 μg/m^3, with a peak at 307.4 μg/m^3. Due to the high frequency of biomass burning in autumn, submicron particles significantly increased in organic content, which accounted for 51% of NR-PM_1 on average. Secondary inorganic aerosols（sulfate ＋ nitrate ＋ ammonium） accounted for 46% of NR-PM_1, of which sulfate,nitrate, and ammonium contributed 15%, 20%, and 11%, respectively. To determine the intrinsic relationships between the organic and inorganic species, we used the positive matrix factorization（PMF） model to merge the high-resolution mass spectra of the organic species and NO＋and NO_2~＋ions. The PMF analysis separated the mixed organic and nitrate（NO＋and NO_2~＋） spectra into four organic factors, including hydrocarbon-like organic aerosol（HOA）, oxygenated organic aerosol（OOA）, cooking organic aerosol（COA）, and biomass burning organic aerosol（BBOA）, as well as one nitrate inorganic aerosol（NIA） factor. COA（33%） and OOA（30%） contributed the most to the total organic aerosol（OA） mass, followed by BBOA（20%） and HOA（17%）. We successfully quantified the mass concentrations of the organic and inorganic nitrates by the NO＋and NO2＋ions signal in the organic and NIA factors. The organic nitrate mass varied from 0.01-6.8 μg/m^3, with an average of 1.0 ±1.1 μg/m^3, and organic nitrate components accounted for 10% of the total nitrate mass in this observation.

Characterization and source identification of submicron aerosol dur ing ser ious haze pollution periods in Beijing

Submicron aerosol is of extensive concern not only due to its significant impact on air quality but also because it is detrimental to human health.In this study,we investigated the characteristics,sources and chemical processes of submicron aerosol based on realtime online measurements of submicron aerosols(NR-PM 1)during December 2015 at an urban site in Beijing.The average mass concentration of NR-PM 1 was 92.5±84.9μg/m^(3),the hourly maximum was 459.1μg/m^(3) during the entire observation.The organic aerosol(OA)(55%)was the largest contributor to NR-PM 1.The average mass concentration of PAHs was 0.217±0.247μg/m^(3),exhibiting the highest concentration at night and the lowest levels in the daytime.The average mass concentration of organic nitrate was 2.52±2.36μg/m^(3) and that of inorganic nitrate was 7.62±8.22μg/m^(3),accounting for 36%and 64%,respectively,of the total nitrate mass.Positive matrix factorization(PMF)differentiated the OA into five chemical components including LV-OOA,SV-OOA,COA,HOA and CCOA,accounting for 22%,16%,13%,25%and 24%respectively,of the total OA.The average NR-PM 1 mass concentration on the heavy polluted days(HPD)was 182.8±70.2μg/m^(3),which was approximately 9 times that on clean days(CD).The enhanced secondary formation of SNA was evident on HPD,especially the rapid increase of sulfate(23%)and nitrate(19%).