Surface protection method for the magnetic core using covalent organic framework shells and its application in As(III) depth removal from acid wastewater

Fe₃O₄-based materials are widely used for magnetic separation from wastewater. However, they often suffer from Fe-leaching behavior under acidic conditions, decreasing their activity and limiting sustainable practical applications. In this study, covalent organic frameworks (COFs) were used as the shell to protect the Fe₃O₄ core, and the Fe₃O₄@COF core-shell composites were synthesized for As(III) removal from acid wastewater. The imine-linked COFs can in situ grow on the surface of the Fe₃O₄ core layer by layer with [COFs/Fe₃O₄]_mol ratio of up to 2:1. The Fe-leaching behavior was weakened over a wide pH range of 1-13. Moreover, such composites keep their magnetic characteristic, making them favorable for nanomaterial separation. As(III) batch adsorption experiments results indicated that, when COFs are used as the shell for the Fe₃O₄ core, a balance between As(III) removal efficiencies and the thickness of the COF shell exists. Higher As(III) removal efficiencies are obtained when the [COFs/Fe₃O₄]_mol ratios were < 1.5:1, but thicker COF shells were not beneficial for As(III) removal. Such composites also exhibited better As(III) removal performances in the pH range of 1–7. Over a wide pH range, the zeta potential of Fe₃O₄@COF core-shell composites becomes more positive, which benefits the capture of negative arsenic ions. In addition, thinner surface COFs were favorable for mass transfer and facilitating the reaction of Fe and As elements. Our study highlights the promise of using COFs in nanomaterial surface protection and achieving As(III) depth removal under acidic conditions.     

Intensified wintertime secondary inorganic aerosol formation during heavy haze pollution episodes (HPEs) in Beijing, China

Air pollution in China is complex, and the formation mechanism of chemical components in particulate matter is still unclear. This study selected three consecutive heavy haze pollution episodes (HPEs) during winter in Beijing for continuous field observation, including an episode with heavy air pollution under red alert. Clean days during the observation period were selected for comparison. The HPE characteristics of Beijing in winter were: under the influence of adverse meteorological conditions such as high relative humidity, temperature inversion and low wind speed; and strengthening of secondary transformation reactions, which further intensified the accumulation of secondary aerosols and other pollutants, promoting the explosive growth of PM_2.5. PM_2.5/CO values, as indicators of the contribution of secondary transformation in PM_2.5, were approximately 2 times higher in the HPEs than the average PM_2.5/CO during the clean period. The secondary inorganic aerosols (sulfate nitrate and ammonium salt) were significantly enhanced during the HPEs, and the conversion coefficients were remarkably improved. In addition, it is interesting to observe that the production of sulfate tended to exceed that of nitrate in the late stage of all three HPEs. The existence of aqueous phase reactions led to the explosive growth sulfur oxidation ratio (SOR) and rapid generation of sulfate under high relative humidity (RH>70%).     

沙尘天气对兰州市PM10中主要水溶性离子的影响

利用在线监测仪器MARGA在兰州大学盘旋路校区对兰州市大气PM10中水溶性离子进行监测,监测期间(2011-04-01~2011-06-30)有15 d出现沙尘天气.兰州市PM10中主要水溶性离子物种为Ca2+、SO2-4和NO-3.扬沙天气期间NO-3和NH+4的浓度比非沙尘期间低,说明沙尘天气对当地人为源所排放污染物具有清除作用.沙尘天气期间,作为土壤污染源标识物的Mg2+、Na+和Ca2+离子都有明显增加,Na+和Mg2+相关系数为0.520,Na+和Ca2+相关系数为0.659,Mg2+和Ca2+相关系数为0.671,而非沙尘天气期间三者的相关系数并不高,Na+和Mg2+相关系数为0.065,Na+和Ca2+相关系数为0.131,Mg2+和Ca2+相关系数为0.163,说明沙尘天气期间三者之间具有相同的污染源,主要来自于土壤风沙尘,而非沙尘天气期间三者来源不同.Cl-的浓度在扬沙天气明显高于浮尘和非沙尘天气期间,说明外来的土壤风沙尘是Cl-的主要来源.     

培养转速与镁离子对生物合成次生铁矿物的影响研究

探析培养转速与镁离子浓度对氧化亚铁硫杆菌生物合成次生铁矿物的影响对酸性矿山废水(AMD)治理具有一定的工程指导意义.本研究通过摇瓶实验,研究了Mg2+浓度分别为48与4.8 mg·L-1,其它元素组成与富含Fe与SO2-4的9K液体培养基一致的体系在180 r·min-1与100 r·min-1转速条件下氧化亚铁硫杆菌催化合成次生铁矿物过程.考察了不同次生铁矿物合成体系pH、Fe2+氧化率、总Fe沉淀率及次生铁矿物矿相等相关指标.研究结果表明,在180 r·min-1的培养条件下,Mg2+浓度分别为4.8与48 mg·L-1两体系培养48 h后,pH从原始的2.50分别降低至2.07与2.12,Fe2+均可在48 h内实现完全氧化.Fe2+完全氧化时,Mg2+浓度为4.8 mg·L-1体系总Fe沉淀率为37.4%,合成的次生铁矿物均匀分散于溶液中,而Mg2+浓度为48 mg·L-1体系中,总铁沉淀率仅为31.7%,且70%的矿物牢固粘附于摇瓶底部.培养转速为100 r·min-1时,Mg2+浓度分别为4.8与48 mg·L-1两体系经过72 h培养后,pH均从原始的2.50降低至2.21与2.17.Fe2+需要72 h才能被完全氧化,两体系总Fe沉淀率分别仅为21.3%与23.0%,产生的次生铁矿物几乎全部牢固粘附于摇瓶底部.本研究所有体系产生的次生铁矿物均为黄铁矾与施氏矿物的混合物.研究结果可为生物合成次生铁矿物工艺的优化及其在酸性矿山废水治理领域的有效应用提供必要的参数支撑.     

COVID-19管控前后不同污染阶段PM2.5中二次无机离子变化特征

为探讨新冠肺炎疫情(COVID-19)管控前后不同污染阶段PM_2.5中二次无机离子变化特征,使用高分辨率(1 h)在线仪器对2019年12月15日至2020年2月15日郑州冬季气象、污染气体浓度和PM_2.5中水溶性离子水平进行在线监测,分析此次COVID-19管控前后霾过程的成因、大气污染物的日变化特征和在霾不同阶段下大气污染物的分布特征.结果表明,郑州主要受到高压脊控制,天气形势稳定,有利于大气污染物累积,二次无机气溶胶(SNA,包括SO₄^2-、NO^-₃和NH⁺₄)是水溶性离子的主要组分,占比高达90%以上,COVID-19期间居家隔离措施对霾不同阶段下大气污染物的分布特征产生不同的影响,COVID-19期间PM_2.5在干净、发生和消散阶段的浓度比COVID-19前有所提高,但是发展阶段明显降低,居家隔离明显使PM_2.5高值降低了;NO₂、SO<...     

南京北郊冬季霾天PM2.5水溶性离子的污染特征与消光作用研究

为了探讨霾天下大气细颗粒物(PM2.5)中水溶性离子的污染特征及其对大气消光的影响,在2013年1月25日至2月3日于南京北郊进行了PM2.5连续在线监测.利用颗粒物-液体转换采集系统(PILS)连续采集水溶性样品,与离子色谱联用分析了其中SO2-4、NO-3、NH+4、Cl-、Na+、K+、Mg2+和Ca2+的含量;同时采用扫描电迁移率粒径谱仪(SMPS)和空气动力学粒径谱仪(APS)测量细粒子的粒径谱分布;采用三波长光声黑碳光度计(PASS-3)实时在线测量细粒子的散射和吸收消光系数;并实时监测痕量气体浓度.结果表明,观测期间霾与非霾天PM2.5中水溶性离子的总质量浓度分别为70.3μg·m-3和22.9μg·m-3;二次吸湿性组分SO2-4、NO-3和NH+4为主要的污染离子.霾天有利于SO2和NOx向SO2-4和NO-3的转化,尤其是NOx的氧化.运用多元线性回归统计方法,建立了PM2.5干消光系数与气溶胶化学成分之间的经验公式,发现NH4NO3对南京冬季消光的贡献最大,其次为(NH4)2SO4、有机碳(OC)和元素碳(EC).两次重污染事件中,污染前体物的一次排放和二次转化的增加分别是造成离子浓度升高的主要原因.     

柠檬酸-沼气双发酵耦联工艺中钠离子的影响

提出了柠檬酸-沼气双发酵耦联工艺,用于处理柠檬酸发酵过程中产生的废水,柠檬酸废水经厌氧消化处理后作为配料水回用于下一批次的柠檬酸发酵,从而实现废水零排放。厌氧水中超过1 000mg/L的Na~+在回用过程中会严重抑制柠檬酸发酵,柠檬酸产量为118.5 g/L,较空白下降了15.6%。单因素试验表明,Na~+对柠檬酸发酵的抑制质量浓度为200 mg/L。通过对发酵过程中糖化酶、异麦芽糖酶及柠檬酸合成酶、异柠檬酸脱氢酶等胞内关键酶活力变化的分析,初步探讨了其影响机理。结果表明,高达1 000 mg/L的Na~+会导致黑曲霉胞内异柠檬酸脱氢酶活力升高,柠檬酸代谢活力增强。同时,培养基中糖化酶和异麦芽糖酶活力受到抑制,发酵结束时部分糊精和异麦芽糖不能被完全降解,残总糖质量浓度升高至30 g/L,黑曲霉可利用的糖浓度减小,柠檬酸合成速率和柠檬酸产量降低。加入过量糖化酶可以有效减弱高质量浓度Na~+的抑制作用,但柠檬酸产量仍然低于去离子水发酵。     

Ni,Co掺杂对Mn-Ce/TiO_2催化剂脱硝活性的影响

以Ti O_2为载体,采用浸渍法制备Ni或Co掺杂的Mn-Ce/Ti O_2催化剂,用于烟气的选择性催化还原法低温脱硝。考察Ni或Co的掺加对Mn-Ce/Ti O_2催化剂活性的影响,并对各催化剂进行了BET,XRD,H_2-TPR,XPS表征。实验结果表明:在NO,NH_3,O_2的体积分数分别为6×10~(-4),6×10~(-4),6×10~(-2),空速为16 000 h~(-1)的条件下,Mn-Ce/Ti O_2、Mn-Ce-Ni_(0.4)/Ti O_2和Mn-Ce-Co_(0.2)/Ti O_2催化剂的NO去除率在120℃时分别为38%,68%,74%,在150℃时分别为64%,92%,近100%,这表明掺加Ni或Co后Mn-Ce/Ti O_2催化剂的脱硝活性明显提高;在进气中加入体积分数为1×10~(-4)的SO_2后,Mn-Ce/Ti O_2催化剂的NO去除率在300 min内从98.2%下降至57.2%,而Mn-CeCo_(0.2)/Ti O_2和Mn-Ce-Ni_(0.4)/Ti O_2催化剂的NO去除率分别为73.9%和69.8%,这表明Ni或Co的掺加有助于提高催化剂的抗硫性能。表征结果表明:Ni或Co的掺加基本不影响Mn和Ce在载体Ti O_2上的分散;Ce元素以Ce~(3+)和Ce~(4+)价态存在,且主要为Ce~(4+);催化剂的比表面积变化不大;Mn O_x与Ce O_x的结晶度降低,催化剂的氧化还原能力增强。     

Characteristics of the water-soluble components of aerosol particles in Hefei, China

Size-classified daily aerosol mass concentrations and concentrations of water-soluble inorganic ions were measured in Hefei,China,in four representative months between September 2012 and August 2013.An annual average mass concentration of 169.09μg/m~3 for total suspended particulate(TSP)was measured using an Andersen Mark-II cascade impactor.The seasonal average mass concentration was highest in winter(234.73μg/m~3)and lowest in summer(91.71μg/m~3).Water-soluble ions accounted for 59.49%,32.90%,48.62%and 37.08%of the aerosol mass concentration in winter,spring,summer,and fall,respectively,which indicated that ionic species were the primary constituents of the atmospheric aerosols.The four most abundant ions were NO_3~-,SO_4~(2-),Ca~(2+) and NH_4~+.With the exception of Ca~(2+),the mass concentrations of water-soluble ions were in an intermediate range compared with the levels for other Chinese cities.Sulfate,nitrate,and ammonium were the dominant fine-particle species,which were bimodally distributed in spring,summer and fall;however,the size distribution became unimodal in winter,with a peak at 1.1–2.1μm.The Ca~(2+) peak occurred at approximately 4.7–5.8μm in all seasons.The cation to anion ratio was close to 1.4,which suggested that the aerosol particles were alkalescent in Hefei.The average NO_3~-/SO_4~(2-)mass ratio was 1.10 in Hefei,which indicated that mobile source emissions were predominant.Significant positive correlation coefficients between the concentrations of NH_4~+ and SO_4~(2-),NH_4~+ and NO_3~-,SO_4~(2-)and NO_3~-,and Mg~(2+) and Ca~(2+) were also indicated,suggesting that aerosol particles may be present as(NH_4)_2SO_4,NH_4HSO_4,and NH_4NO_3.     

Enhanced dechlorination of 2,4-dichlorophenol by recoverable Ni/Fe–Fe3O4 nanocomposites

Ni/Fe-Fe_3O_4 nanocomposites were synthesized for dechlorination of 2,4-dichlorophenol(2,4-DCP). The effects of the Ni content in Ni/Fe-Fe_3O_4 nanocomposites, solution pH, and common dissolved ions on the dechlorination efficiency were investigated, in addition to the reusability of the nanocomposites. The results showed that increasing content of Ni in Ni/Fe–Fe_3O_4 nanocomposites, from 1 to 5 wt.%, greatly increased the dechlorination efficiency; the Ni/Fe–Fe_3O_4 nanocomposites had much higher dechlorination efficiency than bare Ni/Fe nanoparticles. Ni content of 5 wt.% and initial p H below 6.0 was found to be the optimal conditions for the catalytic dechlorination of 2,4-DCP. Both 2,4-DCP and the intermediate product 2-chlorophenol(2-CP) were completely removed, and the concentration of the final product phenol was close to the theoretical phenol production from complete dechlorination of 20 mg/L of 2,4-DCP, after 3 hr reaction at initial p H value of 6.0,3 g/L Ni/Fe-Fe_3O_4 , 5 wt.% Ni content in the composite, and temperature of 22℃. 2,4-DCP dechlorination was enhanced by Cl-and inhibited by NO3-and SO_4~(2-). The nanocomposites were easily separated from the solution by an applied magnetic field. When the catalyst was reused, the removal efficiency of 2,4-DCP was almost 100% for the first seven uses, and gradually decreased to 75% in cycles 8–10. Therefore, the Ni/Fe–Fe_3O_4 nanocomposites can be considered as a potentially effective tool for remediation of pollution by 2,4-DCP.