Spatial distribution and potential ecological and health risks associated with heavy metals in the Ijero-Ekiti mining site,Nigeria

Artisanal gold mining,a labor-intensive and antiquated technique,is a growing industry and the source of income for rural communities all over the world.However,artisanal gold mining has potential negative and long-term effects on economy,environment,and society.This study collected soil samples from 16 sample points including a control point to examine the pollution degrees and spatial distribution of heavy metals,as well as ecological and health risks associated with heavy metal pollution in the Ijero-Ekiti mining site,Nigeria.Geographical Information System(GIS)and remote sensing technologies were used to identify regions with high concentrations of heavy metals and assess the environmental impact of gold mining activities.The results show that the mean heavy metal concentrations of 16 soil pointa are 8.94(±5.97)mg/kg for As,0.18(±0.54)mg/kg for Cd,0.11(±1.06)mg/kg for Co,14.32(±3.43)mg/kg for Cr,6.89(±0.64)mg/kg for Cu,48.92(±11.77)mg/kg for Fe,135.81(±30.75)mg/kg for Mn,5.92(±0.96)mg/kg for Ni,5.72(±1.66)mg/kg for Pb,and 13.94(±1.38)mg/kg for Zn.The study reveals that heavy metal concentration in soils follows the order of Mn>Fe>Cr>Zn>As>Cu>Ni>Pb>Co>Cd.An analysis of soil samples indicates that 3 principal components(PCs)account for 70.008%of the total variance and there are strong positive correlations between various pairs of heavy metals.The total potential ecological risk index(309.599)in the study area is high.Non-carcinogenic risk suggests that there may be long-term health impacts on people who work in the mining areas due to chronic exposure to the environment.Based on the study,the hazard index of carcinogenic health risks associated with heavy metals through ingestion is 520.00×10^(–4).Dermal contact from As and Cr also increases the risk of cancer,with the highest hazard index value of 18.40×10^(–4).The lowest exposure pathway,with the hazard index value of 0.68×10^(–4),indicates that the inhalation of heavy metals has a comparatively low risk of cancer.This study recommends the formulation of policies to monitor the Ijero-Ekiti mining site and other regions in Nigeria where indiscriminate artisanal gold mining activities exist.

Transition metal-nitrogen sites for electrochemical carbon dioxide reduction reaction

Electrochemical CO2 reduction reaction(CO2RR)powered by renewable electricity has emerged as the most promising technique for CO2 conversion,making it possible to realize a carbon‐neutral cycle.Highly efficient,robust,and cost‐effective catalysts are highly demanded for the near‐future practical applications of CO2RR.Previous studies on atomically dispersed metal‐nitrogen(M‐Nx)sites constituted of earth abundant elements with maximum atom‐utilization efficiency have demonstrated their performance towards CO2RR.This review summarizes recent advances on a variety of M‐Nx sites‐containing transition metal‐centered macrocyclic complexes,metal organic frameworks,and M‐Nx‐doped carbon materials for efficient CO2RR,including both experimental and theoretical studies.The roles of metal centers,coordinated ligands,and conductive supports on the intrinsic activity and selectivity,together with the importance of reaction conditions for improved performance are discussed.The mechanisms of CO2RR over these M‐Nx‐containing materials are presented to provide useful guidance for the rational design of efficient catalysts towards CO2RR.

Tuning Atomically Dispersed Fe Sites in Metal–Organic Frameworks Boosts Peroxidase‑Like Activity for Sensitive Biosensing

Although nanozymes have been widely developed,accurate design of highly active sites at the atomic level to mimic the electronic and geometrical structure of enzymes and the exploration of underlying mechanisms still face significant challenges.Herein,two functional groups with opposite electron modulation abilities(nitro and amino)were introduced into the metal–organic frameworks(MIL-101(Fe))to tune the atomically dispersed metal sites and thus regulate the enzymelike activity.Notably,the functionalization of nitro can enhance the peroxidase(POD)-like activity of MIL-101(Fe),while the amino is poles apart.Theoretical calculations demonstrate that the introduction of nitro can not only regulate the geometry of adsorbed intermediates but also improve the electronic structure of metal active sites.Benefiting from both geometric and electronic effects,the nitro-functionalized MIL-101(Fe)with a low reaction energy barrier for the HO*formation exhibits a superior POD-like activity.As a concept of the application,a nitro-functionalized MIL-101(Fe)-based biosensor was elaborately applied for the sensitive detection of acetylcholinesterase activity in the range of 0.2–50 mU mL−1 with a limit of detection of 0.14 mU mL−1.Moreover,the detection of organophosphorus pesticides was also achieved.This work not only opens up new prospects for the rational design of highly active nanozymes at the atomic scale but also enhances the performance of nanozyme-based biosensors.

High-throughput computational screening of Cu-MOFs with open metal sites for efficient C_2H_2/C_2H_4 separation

Cost effective separation of acetylene(C_2H_2)and ethylene(C_2H_4)is of key importance to obtain essential chemical raw materials for polymer industry.Due to the low compression limit of C_2H_2,there is an urgent demand to develop suitable materials for efficiently separating the two gases under ambient conditions.In this paper,we provided a high-throughput screening strategy to study porous metal-organic frameworks(MOFs)containing open metal sites(OMS)for C_2H_2/C_2H_4 separation,followed by a rational design of novel MOFs in-silico.A set of accurate force fields was established from ab initio calculations to describe the critical role of OMS towards guest molecules.From a large-scale computational screening of 916 experimental Cu-paddlewheel-based MOFs,three materials were identified with excellent separation performance.The structure-performance relationships revealed that the optimal materials should have the largest cavity diameter around 5-10?and pore volume in-between 0.3-1.0 cm^3 g^(-1).Based on the systematic screening study result,three novel MOFs were further designed with the incorporation of fluorine functional group.The results showed that Cu-OMS and the-F group on the aromatic rings close to Cu sites could generate a synergistic effect on the preferential adsorption of C_2H_2 over C_2H_4,leading to a remarkable improvement of C_2H_2 separation performance of the materials.The findings could provide insight for future experimental design and synthesis of high-performance nanostructured materials for C_2H_2/C_2H_4 separation.

The effects of amino groups and open metal sites of MOFs on polymer-based electrolytes for all-solid-state lithium metal batteries

Metal-organic frameworks(MOFs) are becoming more and more popular as the fillers in polymer electrolytes in recent years. In this study, a series of MOFs(NH_(2)-MIL-101(Fe), MIL-101(Fe), activated NH_(2)-MIL-101(Fe) and activated MIL-101(Fe)) were synthesized and added to PEO-based solid composite electrolytes(SCEs). Furthermore, the role of the —NH_(2) groups and open metal sites(OMSs) were both examined. Different ratios of MOFs vs polymers were also studied by the electrochemical characterizations. At last, we successfully designed a novel solid composite electrolyte containing activated NH_(2)-MIL-101(Fe),PEO, Li TFSI and PVDF for the high-performance all-solid-state lithium-metal batteries. This work might provide new insight to understand the interactions between polymers and functional groups or OMSs of MOFs better.

Doping-induced metal–N active sites and bandgap engineering in graphitic carbon nitride for enhancing photocatalytic H_(2 )evolution performance

Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subjected to atomic-level structural engineering by doping with transition metals(M=Fe,Co,or Ni),which simultaneously induced the formation of metal-N active sites in the g-C_(3)N_(4)framework and modulated the bandgap of g-C_(3)N_(4).Experiments and density functional theory calculations further verified that the as-formed metal-N bonds in M-doped g-C_(3)N_(4)acted as an"electron transfer bridge",where the migration of photo-generated electrons along the bridge enhanced the efficiency of separation of the photogenerated charges,and the optimized bandgap of g-C_(3)N_(4)afforded stronger reduction ability and wider light absorption.As a result,doping with either Fe,Co,or Ni had a positive effect on the HER activity,where Co-doped g-C_(3)N_(4)exhibited the highest performance.The findings illustrate that this atomic-level structural engineering could efficiently improve the HER activity and inspire the design of powerful photocatalysts.

Atomically dispersed metal sites in COF-based nanomaterials for electrochemical energy conversion

Atomically dispersed metal sites(ADMSs)play key roles in electrochemical energy conversion.The covalent organic frameworks(COFs)enable the precise control of the chemical compositions and structures at the molecular level,making them ideal substrates for supporting ADMSs.In this review,we systematically summarize the recent progress on the design and synthesis of ADMSs in COFs,including embedding molecular catalysts into COFs,immobilizing ADMSs on heteroatom-containing COFs,and preparing COF-derived carbon materials through pyrolysis.The electrocatalytic performance of the resulting catalysts is presented for various electrochemical reactions,involving oxygen reduction reaction(ORR),carbon dioxide reduction reaction(CO_(2)RR),oxygen evolution reaction(OER),hydrogen evolution reaction(HER),and nitrogen reduction reaction(NRR).The modulation strategies of AMDSs in COFs for enhanced activity,selectivity,and stability are highlighted,together with a perspective of the current challenges and the future opportunities in this field.

A Universal Principle to Accurately Synthesize Atomically Dispersed Metal–N_4 Sites for CO_2 Electroreduction

Atomically dispersed metal-nitrogen sites-anchored carbon materials have been developed as effective catalysts for CO2 electroreduction(CO2 ER),but they still suffer from the imprecisely control of type and coordination number of N atoms bonded with central metal.Herein,we develop a family of single metal atom bonded by N atoms anchored on carbons(SAs-M-N-C,M=Fe,Co,Ni,Cu)for CO2 ER,which composed of accurate pyrrole-type M-N4 structures with isolated metal atom coordinated by four pyrrolic N atoms.Benefitting from atomically coordinated environment and specific selectivity of M-N4 centers,SAs-Ni-N-C exhibits superior CO2 ER performance with onset potential of-0.3 V,CO Faradaic efficiency(F.E.) of 98.5%at-0.7 V,along with low Tafel slope of 115 mV dec-1 and superior stability of 50 h,exceeding all the previously reported M-N-C electrocatalysts for CO2-to-CO conversion.Experimental results manifest that the different intrinsic activities of M-N4 structures in SAs-M-N-C result in the corresponding sequence of Ni> Fe> Cu> Co for CO2 ER performance.An integrated Zn-CO2 battery with Zn foil and SAs-Ni-N-C is constructed to simultaneously achieve CO2-to-CO conversion and electric energy output,which delivers a peak power density of 1.4 mW cm-2 and maximum CO F.E.of 93.3%.

Structural transformation of metal–organic framework with constructed tetravalent nickel sites for efficient water oxidation

A mixture of Ni and Fe oxides is among the most commonly active catalysts for the oxygen evolution reaction(OER)during the water oxidation process.In particular,Ni oxide incorporated with even a small amount of Fe leads to substantively enhanced OER activity.However,the critical role of Fe species during the electrocatalytic process is still under evaluation.Herein,we report nickel(oxy)hydroxide incorporated with Fe through the surface reconstruction of a bimetallic metal-organic framework(NiFe-MOF)during the water oxidation process.The spectroscopic investigations with theoretical calculations reveal the critical role of Fe in promoting the formation of highly oxidized Ni^(4+),which directly correlates with an enhanced OER activity.Both the geometric and electronic structu res of the as-reconstructed Ni_(1-x)Fe_(x)OOH electrocatalysts can be delicately tuned by the Ni-Fe ratio of the bimetallic NiFe-MOF,further affecting the catalytic activity.As a result,the Ni_(1-x)Fe_(x)OOH derived from Ni_(0.9)Fe_(0.1)-MOF delivers low overpotentials of 260 mV at 10 mA cm^(-2)and 400 mV at 300 mA cm^(-2).

Synergistic interaction of metal–acid sites for phenol hydrodeoxygenation over bifunctional Ag/TiO_2 nanocatalyst

The use of silver metal for hydrodeoxygenation(HDO) applications is scarce and different studies have indicated of its varying HDO activity. Several computational studies have reported of silver having almost zero turnover frequency for HDO owing to its high C\\O bond breaking energy barrier and low carbon and oxygen binding energies.Herein this work, titania supported silver catalysts were synthesized and firstly used to examine its phenol HDO activity via experimental reaction runs. BET, XRD, FESEM, TEM, EDX, ICP–OES, Pyridine-FTIR, NH_3-TPD and H_2-TPD analyses were done to investigate its physicochemical properties. Phenomena of hydrogen spillover and metal–acid site synergy were examined in this study. With the aid of TiO_2 reducible support, hydrogen spillover and metal–acid site interactions were observed to a certain extent but were not as superior as other Pt, Pd, Ni-based catalysts used in other HDO studies. The experimental findings showed that Ag/TiO_2 catalyst has mediocre phenol conversion but high benzene selectivity which confirms the explanation from other computational studies.

Role of local coordination in bimetallic sites for oxygen reduction: A theoretical analysis

Understanding of the oxygen reduction reaction(ORR)mechanism for single atom catalysts is pivotal for the rational design of non-precious metal cathode materials and the commercialization of fuel cells.Herein,a series of non-precious metal electrocatalysts based on nitrogen-doped bimetallic(Fe and Co)carbide were modeled by density functional theory calculations to predict the corresponding reaction pathways.The study elucidated prior oxygen adsorption on the Fe atom in the dual site and the modifier role of Co atoms to tune the electronic structures of Fe.The reaction activity was highly correlated with the bimetallic center and the coordination environment of the adjacent nitrogen.Interestingly,the preadsorption of*OH resulted in the apparent change of metal atoms'electronic states with the d-band center shifting toward the Fermi level,thereby boosting reaction activity.The result should help promote the fundamental understanding of active sites in ORR catalysts and provide an effective approach to the design of highly efficient ORR catalysts on an atomic scale.

Homogenous metallic deposition regulated by abundant lithiophilic sites in nickel/cobalt oxides nanoneedle arrays for lithium metal batteries

Although lithium(Li)metal delivers the highest theoretical capacity as a battery anode,its high reactivity can generate Li dendrites and"dead"Li during cycling,resulting in poor reversibility and low Li utilization.Inducing uniform Li plating/stripping is the core of solving these problems.Herein,we design a highly lithiophilic carbon film with an outer sheath of the nanoneedle arrays to induce homogeneous Li plating/stripping.The excellent conductivity and 3D framework of the carbon film not only offer fast charge transport across the entire electrode but also mitigate the volume change of Li metal during cycling.The abundant lithiophilic sites ensure stable Li plating/stripping,thereby inhibiting the Li dendritic growth and"dead"Li formation.The resulting composite anode allows for stable Li stripping/plating under 0.5 mA cm^(-2) with a capacity of 0.5 mA h cm^(-2) for 4000 h and 3 mA cm^(-2) with a capacity of3 mA h cm^(-2) for 1000 h.The Ex-SEM analysis reveals that lithiophilic property is different at the bottom,top,or channel in the structu re,which can regulate a bottom-up uniform Li deposition behavior.Full cells paired with LFP show a stable capacity of 155 mA h g^(-1) under a current density of 0.5C.The pouch cell can keep powering light-emitting diode even under 180°bending,suggesting its good flexibility and great practical applications.

DFT Study of Metal Atoms Adsorbed at Low-coordinated Sites of MgO (001) Surface

The adsorption of metal atoms, Ni, Pd, Pt, Cu, Ag and Au, at low-coordinated edge and corner oxygen sites of MgO (001) surface has been studied theoretically by using density functional method with cluster models embedded in a large array of point charges. For comparison, the interaction of metal atoms with perfect regular oxygen site of MgO (001) surface was also calculated. As regards these metal atoms adsorbed at perfect oxygen sites of MgO (001) surface, Cu, Ag and Au are very weakly bonded to the surface of MgO; Ni, Pd and Pt, on the other hand, exhibit strong interactions with perfect oxygen sites of MgO (001) surface; the large adsorption energy shows that there exist strong bonds formed between these metal atoms with surface oxygen sites. For the metal atoms adsorbed at edge and corner sites, the adsorption energy is much increased, consistent with our previous study of CO and Cl2 adsorption on MgO (001) surface. This illustrates that the low-coordinated sites, especially corner site, are more advantageous positions for those metal atoms adsorbed on MgO (001) surface. The Mulliken population analysis indicates that the electron transferred from MgO to the metal atoms were increased with the decrease of the coordination numbers, which may be one of the reasons for changing catalytic efficiency and selectivity of the metal particles supported by MgO.

Comparison of Soil Samples from Selected Anthropogenic Sites within Enugu Metropolis for Physicochemical Parameters and Heavy Metal Levels Determination

This study compared the physicochemical parameters and heavy metal levels in soil samples from selected anthropogenic sites within Enugu metropolis, Enugu State, Nigeria using standard analytical methods. Soil samples at depths (0 - 20 cm) and (20 - 40 cm) were collected from waste dump sites, metal scrap dumps, fuel filling stations and auto-mechanic workshops and analyzed for physicochemical characteristics and heavy metal levels. Atomic absorption spectrophotometer was used for heavy metal determination while conventional analytical methods were employed for physicochemical parameters evaluation of the soil samples. At soil depths 0 - 20 cm and 20 - 40 cm the respective mean range of pH, electrical conductivity, organic matter and organic carbon contents in the soil samples were, 6.33 - 6.74, 101.46 - 123.21 μS/cm, 6.41% - 8.35% and 13.73% - 16.14% for auto-mechanic workshops;6.92 - 7.43, 56.46 - 60.02 μS/cm, 1.53% - 2.20% and 11.93% - 12.60% for fuel filling stations;7.14 - 7.84, 70.81 - 77.71 μS/cm, 3.81% - 4.12% and 8.57% - 9.24% for metal scrap dumps;6.54 - 6.81, 94.40 - 100.71 μS/cm, 8.83% - 10.75% and 18.26% - 20.81% for waste dump sites. The pH of the top soil samples from auto-mechanical workshop was below the WHO recommended limits for agricultural purposes. The physic-chemical characteristics of the soil samples decreased with soil depths indicating therefore that anthropogenic activities greatly influence the soil characteristics at the top soils than the sub-soils. The electrical conductivity values of top and sub-soil samples from the studied auto-mechanical workshops were above the recommended limits. At soil depths 0 - 20 cm and 20 - 40 cm, the respective mean range of Zn, Pb and Cd in the soil samples were 17.29 - 19.16 μg/g, 0.704 - 0.96 μg/g and 0.26 - 0.33 μg/g for auto-mechanic workshops;4.13 - 4.88 μg/g, 0.21 - 0.32 μg/g and 0.03 - 0.11 μg/g for fuel filling stations;30.02 - 36.11 μg/g, 0.43 - 0.48 μg/g and 0.15 - 0.19 μg/g for metal scrap dumps;9.30 - 10.84 μg/g, 0.53 - 0.60 μg/g and 0.38 - 0.45 μg/g for waste dump sites. The mean levels of Pb in soil samples from mechanic workshops and waste dump sites were above the recommended permissible limits for agricultural purposes. The study therefore indicated that these sites (auto-mechanic workshops and waste dump sites) could be major sources of Pb pollution to nearby farmlands, streams and the general environment. Plants grown on or around these sites may not produce high yields and could be severely contaminated with heavy metals which portend health danger to food consumers within the environment.

Heavy Metal Levels and Potential Ecological Risks Assessed at an Agroecosystem Site in Tropical Region

The concentrations and distribution of thirteen metals and metalloids were investigated in soils, sediments, and two biological matrices (the fish Clarias gariepisnis and the earthworm Pontoscolex corethrurus) from the CECOMAF agroecosystem, in Kinshasa, Democratic Republic of the Congo, in order to assess the impact of anthropogenic activities. The results revealed high concentrations of heavy metals, such as Cu, Zn, As, Cd, Pb, and Hg all above values recommended by sediment quality guidelines and their probable effect levels on biota. According to the calculated Enrichment Factor, soil and sediments ranked from moderately to heavily polluted by Cu, Zn, Cd, Pb and Hg. The Contamination Degree and other ecological risk indices indicated very high contamination and very high ecological risks posed by Cd and Hg, respectively. The Geoaccumulation Index indicated that current metal concentrations in the agroecosystem originated from anthropogenic activities, while the Spearman correlation matrix values indicated that Hg could originate from different sources and pathways than the other metals. It was concluded that metals from unchecked anthropogenic activities have negatively impacted agricultural activities and fish production at the CECOMAF agroecosystem. Action to reduce the contamination level and the ecological risks by remediating and preventing metal pollution in the CECOMAF agroecosystem site is recommended.

Heavy Metals in Dust Deposition in the Vicinity of Coal Ash Disposal Site Divkovici Ⅱ

DD （Dust deposition） was monitored over a 6-month period （April to September, 2011） at four sites located in villages near CADDⅡ（coal ash disposal site Divkovici Ⅱ）, one inside recultivated CADDⅠ （coal ash disposal site Divkovici Ⅰ） and at one in the middle of forest barrier as control site. The main aim of this paper is to perform monitoring of air dust pollution in the area by measuring of dust deposition, different metals associated with it, and probable adverse effects on human health. Concentrations of metals were measured by using Perkin-Elmer model Inductively Coupled Plasma and statistically evaluated with SPSS 17.0 statistical program. There was a correlation between some metals （Mn, Mo and Pb） and DD distribution. The daily limit values for concentration of DD proposed by national ＂Regulations on air quality＂ （200 mg/m^2d average annual value and 350 mg/m^2d high value） exceed at three measuring sites. The average maximum content of DD was 684.8 mg/m^2d downwind of CADDII, and the average minimum was 46.8 mg/m^2d at measuring site F. Concentrations of pollutants hazardous to the environment as Ni, Cr, Cu, Mo, Mn and Pb vary from one site to another.

Building Fe atom–cluster composite sites using a site occupation strategy to boost electrochemical oxygen reduction

The high-temperature pyrolysis process for preparing M–N–C single-atom catalyst usually results in high heterogeneity in product structure concurrently contains multiscale metal phases from single atoms(SAs),atomic clusters to nanoparticles.Therefore,understanding the interactions among these components,especially the synergistic effects between single atomic sites and cluster sites,is crucial for improving the oxygen reduction reaction(ORR)activity of M–N–C catalysts.Accordingly,herein,we constructed a model catalyst composed of both atomically dispersed FeN4 SA sites and adjacent Fe clusters through a site occupation strategy.We found that the Fe clusters can optimize the adsorption strength of oxygen reduction intermediates on FeN4 SA sites by introducing electron-withdrawing–OH ligands and decreasing the d-band center of the Fe center.The as-developed catalyst exhibits encouraging ORR activity with halfwave potentials(E1/2)of 0.831 and 0.905 V in acidic and alkaline media,respectively.Moreover,the catalyst also represents excellent durability exceeding that of Fe–N–C SA catalyst.The practical application of Fe(Cd)–CNx catalyst is further validated by its superior activity and stability in a metalair battery device.Our work exhibits the great potential of synergistic effects between multiphase metal species for improvements of singleatom site catalysts.

Understanding the roles of Brønsted/Lewis acid sites on manganese oxide-zeolite hybrid catalysts for low-temperature NH_(3)-SCR

Although metal oxide-zeolite hybrid materials have long been known to achieve enhanced catalytic activity and selectivity in NO_(x)removal reactions through the inter-particle diffusion of intermediate species,their subsequent reaction mechanism on acid sites is still unclear and requires investigation.In this study,the distribution of Brønsted/Lewis acid sites in the hybrid materials was precisely adjusted by introducing potassium ions,which not only selectively bind to Brønsted acid sites but also potentially affect the formation and diffusion of activated NO species.Systematic in situ diffuse reflectance infrared Fourier transform spectroscopy analyses coupled with selective catalytic reduction of NO_(x)with NH_(3)(NH_(3)-SCR)reaction demonstrate that the Lewis acid sites over MnO_(x)are more active for NO reduction but have lower selectivity to N_(2)than Brønsted acids sites.Brønsted acid sites primarily produce N_(2),whereas Lewis acid sites primarily produce N_(2)O,contributing to unfavorable N_(2)selectivity.The Brønsted acid sites present in Y zeolite,which are stronger than those on MnO_(x),accelerate the NH_(3)-SCR reaction in which the nitrite/nitrate species diffused from the MnO_(x)particles rapidly convert into the N_(2).Therefore,it is important to design the catalyst so that the activated NO species formed in MnO_(x)diffuse to and are selectively decomposed on the Brønsted acid sites of H-Y zeolite rather than that of MnO_(x)particle.For the physically mixed H-MnO_(x)+H-Y sample,the abundant Brønsted/Lewis acid sites in H-MnO_(x)give rise to significant consumption of activated NO species before their inter-particle diffusion,thereby hindering the enhancement of the synergistic effects.Furthermore,we found that the intercalated K+in K-MnO_(x)has an unexpected favorable role in the NO reduction rate,probably owing to faster diffusion of the activated NO species on K-MnO_(x)than H-MnO_(x).This study will help to design promising metal oxide-zeolite hybrid catalysts by identifying the role of the acid sites in two different constituents.

Non-Destructive Detection and Evaluation of Heavy Metal Pollution in Tailings Reservoir

Heavy metal pollution is a negative effect generated in the process of utilizing non-ferrous mineral. Studies about heavy metal migration detection are very important. A new method for rapid detection of heavy metal migration based on ground penetrating radar (GPR) was provided. Comparative tests were studied from field to lab with GPR and X-ray fluorescence analysis (XRF). A tailings reservoir in the Xiangjiang River basin at Hunan Province was taken as experimental site. The downward transfer rule of heavy metal migration was confirmed through tests on systematically arranged survey lines and sampling points in tailings site. Results showed: 1) Through GPR image recognition, tailings reservoir had 3 layers. Reclaimed soil layer (the first layer) and tailings layer (the second layer) had a clear interface. However, tailings layer (the second layer) and subsoil layer (the third layer) had an obscure interface on radar images. It was concluded that heavy metal component had migrated downwards. 2) Chemical component analysis verified image recognition conclusions. Concentrations of As, Cd and Pb were significantly out of limit, while concentration of Cr was under limit according to analysis results on samples from different depths. 3) Pollution degree was evaluated. Downward migration was the main form of heavy metal migration in tailings site, upward migration occurred through adsorption at the same time.

激光诱导荧光技术与地下水重金属原位检测应用进展

对地下水重金属污染进行现场检测,是快速识别重金属种类和评价污染程度的重要手段。激光诱导荧光技术(LIF)利用特定荧光探针,在目标重金属存在下,通过激光诱导荧光探针产生/猝灭荧光,从而完成对重金属的识别和检测,具有快速甄别地下水重金属污染特性和无损获取其价态的优势。本文在简述LIF检测重金属原理和LIF原位检测地下水重金属装备基础上,重点从荧光探针合成及其在重金属传感检测方法的构建上总结了基于不同荧光探针的LIF现场检测重金属的研究进展。目前可用于重金属检测的荧光探针包括以小分子探针、有机大分子和聚集诱导发光为主的有机荧光探针和以金纳米簇、量子点和金属有机框架材料为代表的纳米荧光探针。这些探针的合成及其对应的传感检测方法的构建表明LIF技术在地下水重金属检测中具有巨大优势。而针对地下水重金属检测的LIF设备研发方面的成果虽不如荧光传感检测方法丰富,但已研制出部分重金属的传感器和检测装备,表现出良好的应用前景。未来研究将会聚焦在地下水重金属主控因子识别和抗干扰技术研发、荧光探针合成与LIF检测方法构建、重金属传感部件和检测装备集成研制,以及检测技术标准化,为后续场地地下水典型重金属LIF检测技术的研究提供参考。