H-bonding interactions enable a 3D pillared cobalt(Ⅱ) coordination polymer for touchless finger moisture detection

Coordination polymers(CPs) are emerging as the next generation of macromolecule materials in many industrial and technological applications,e.g.gas/humidity sensing.The design of CP-based sensors with high performance and low cost is of significance,but this work is still in the infancy stage.In this contribution,a new one dimensional(1D) CP has been successfully synthesized by a simple solvent evaporation method at room temperature,namely [Co(DPP)(H_(2)O)_(2)]n·(TCA)2(H_(2)O)_(4)(named as Co-1,HTCA=3-thiophenezoic acid,DPP=1,3-di(4-pyridyl)propane).The Co-1 structure contains abundant H-bonding interactions,weaving it from 1D chain structure into three dimensional(3D) pillared-layer structure.As an impedimetric humidity sensing material,this CP exhibits short response time,small hysteresis,excellent repeatability,and good stability in the working range of 11%-97% relative humidity(RH).Furthermore,it also shows excellent performance in monitoring the moisture content of human finger skin.By analyzing the complex impedance spectra,the humidity sensing mechanism of Co-1 sensor was expounded at different RH ranges.

Ultrathin CeO_(2) nanosheets as bifunctional sensing materials for humidity and formaldehyde detection

Issues like morphology control and further multifunctional applications are of significant importance for rare earth nano-oxides,e.g.,cerium dioxide(CeO_(2))nanostructures,however,relevant results in this respect are rather limited up to now.In the present work,ultrathin CeO_(2) nanosheets were synthesized through a facile lowtemperature hydrothermal method.The structure,morphology and specific surface area of these CeO_(2) nanosheets were characterized by X-ray diffraction(XRD),field emission scanning electron microscope(FESEM)and N2 adsorption-desorption.Significantly,CeO_(2) nanosheets have the potential as bifunctional sensing materials to detect both humidity and formaldehyde vapor.The CeO_(2) nanosheet humidity sensor exhibited excellent sensing characteristics in the relative humidity range of 11%-97% with the response value as high as 3.1×10^(4).Meanwhile,the CeO_(2) nanosheet gas sensor showed superior sensitivity and repeatability with fast response/recovery speed toward formaldehyde vapor at 300℃.Finally,the humidity and formaldehyde sensing mechanism were discussed as well.

Rich defects and nanograins boosted formaldehyde sensing performance of mesoporous polycrystalline ZnO nanosheets

Comprehensive consideration of structural and electronic sensitization is of significant importance for rational design and assembly of high-performance gas sensors based on metal oxides.In this work,hierarchically mesoporous ZnO nanosheets are synthesized via a hydrothermal method followed by calcination.Material characterization reveals polycrystalline feature of these ZnO nanosheets rich in mesopores and defects.Gas sensing performance of as-synthesized ZnO nanosheets was sys-tematically investigated,taking formaldehyde as probe molecules.Compared with commercial ZnO nanoparticles,ZnO nanosheets exhibited enhanced formaldehyde sensing properties,including lower operation temperature,higher sensitivity,faster response,and smaller detection limit.Notably,the response(S=227.4)of ZnO nanosheets to 200×10^(-6) formaldehyde is about 17 times larger than that of ZnO nanoparticles(S=13.5).Excluding effects of grain size and surface area,enhanced sensing properties,especially response value,are credited in large part to synergistic actions of surface defects,grain boundaries,as well as unique structural advantage of ZnO nanosheets.Furthermore,this work offers a guideline for boosting performance of metal oxide-based gas sensors via surface defect control and grain boundary construction.

A highly efficient humidity sensor based on lead(Ⅱ) coordination polymer via in-situ decarboxylation and hydrolysis synthesis

Function-oriented design of coordination polymers is emerging as an attracting topic to explore their practical applications, e.g., gas/humidity sensing. However,the successful synthesis of new coordination polymers showing splendid sensing property is an urgent need in fields of materials and sensors, yet still at the initial stage.In this contribution, a new one-dimensional(1D) coordination polymer with formula of [Pb(TAA)(BA)(H_(2)O)]_(n)(namedasPbL,HTAA = 3-thiopheneaceticacid,HBA = benzoic acid) has been successfully synthesized by a hydrothermal method, which involves in-situ synthesis of both decarboxylation and hydrolysis. As an impedimetric humidity sensing material, this coordination polymer exhibits excellent humidity sensing performance including high response, fast response, small hysteresis, and good repeatability. In the total relative humidity range(11%–97%) at room temperature, it is worth noting that the sensitivity of the humidity sensor is as high as 1.18×10^(4),the response time is only 2 s, and the max humidity hysteresis is as small as 1.8%. At last, we discussed the sensing mechanism using the alternating current(AC) impedance technique at various relative humidity.

DFT calculation on p-xylene sensing mechanism of (C_(4)H_(9)NH_(3))_(2)PbI_(4) single crystal based on physisorption

P-xylene(p-C_(8)H_(10))is extremely harmful and dangerous to human health due to high toxicity and strong carcinogenicity.Exploring sensitive material to effectively detect p-xylene is of importance.In this paper,perovskite single crystal(C_(4)H_(9)NH_(3))_(2)PbI_(4) has been successfully synthesized via solution method.The obtained product was analyzed by single crystal X-ray diffraction.With the space group Pbca,orthorhombic(C_(4)H_(9)NH_(3))_(2)PbI_(4) layered perovskite structure consists of an extended two-dimensional network of corner-sharing PbI_(6) octahedron.Single layer perovskite sheets of distorted PbI_(6) octahedron alternated with protonated n-butylammonium cation bilayers,which offers many advantages and provides the possibility of forming a gas sensor device based on the change of resistances.Density functional theory(DFT)simulations regarding the adsorption energy revealed that this organicinorganic hybrid perovskite compound has excellent selectivity toward p-xylene compared with other gases including C_(2)H_(5)OH,C_(6)H_(6),CH_(2)Cl_(2),HCHO,CH_(3)COCH_(3) and C_(7)H_(8).The calculation of electron density,density of states and electron density difference showed the sensing mechanism of p-C_(8)H_(10) is mainly derived from physical adsorption-desorption in view of electron transfer.