Study On Colorimetric Measurement Of Fe(Ⅲ), Cu(Ⅱ), Hg(Ⅱ) Using Functional Paper-based Sensors

Heavy metals are widely used in manufacture,agriculture and pharmaceuticals industry,which have brought serious environmental pollution and health problems.Therefore,development of simple,accurate and highly sensitive detection methods for heavy metals analysis is the key aspect of the control and treatment of heavy metals pollution.Presently,detection of heavy metals can be realized by traditional large-scale instruments.Despite the excellent accuracy and sensitivity,some unavoidable disadvantages such as complex pretreatment,high cost,requirement of professional operation limit their application in real-time field.In view of the above problems,colorimetric methods stand out cost-effective and easy to operate.So it has been widely used in heavy metal rapid detection and provided a potential and effective method for metal ion detection.In this work,optical nanomaterials or organic dyes with specific response to heavy metal was coated at the surface of TiO2-modified cellulose paper.We presented a more stable paper-based sensor for rapid detecting Iron（Ⅲ）,Copper（Ⅱ）,Mercury（Ⅱ）and provided more practicable solutions for detection of heavy metals.The work and results can be summarized as follows:The construction of a paper-based colorimetric sensor was presented by alternative modification of commercial cellulose paper with TiO2 membrane as intermediate layer,hydrophobic/hydrophilic coating to obtain uniform diffusion,and decoration of-NH2 and-SH groups for immobilization of gold nanoparticles（AuNPs）.Under the optimal conditions,the iron-responsive sensor showed a linear concentration-dependent colorimetric response（ΔG）in the presence of Fe³⁺ concentrations ranging from 1.0 to 37 μM（R2> 0.98）.The low detection limit was calculated to be 0.85 μM（S/N=3）with good selectivity.Besides,the sensor also showed high resistance to AuNPs leaking in aqueous solutions,and demonstrated consistent measurement of Fe³⁺ in serum samples.Those results suggested that as-prepared sensor strip is potential useful for Fe³⁺ ion determination in clinical and environmental samples.A facile and reliable colorimetric sensor in both solution and paper-based membrane was presented for the detection of copper ions.Commercial organometallic reagent zincon was incorporated in hollow Zn SiO3 nanospheres to form a hybrid ionophore,subsequently the blue color of which turned to orange after addition of tartaric acid（TA）due to competition and displacement of Zn²⁺.However,the blue color recovered again with the appearance of Cu²⁺ owing to the indicator displacement reaction.The detection solutions were further used to coat at cellulose membrane modified with TiO2 and silylating reagent to fabricate paper-based sensors for naked-eye detection of Cu²⁺.Under optimum conditions,a detection limit 43.2 nM was obtained with linear ranging from 50 nM to 30 μM in aqueous solution,while the detection limit of 83.6 nM with wide linear ranging from 250 nM to 100 μM for paper-based sensor assay.Testing the present paper sensor on real drilling wastewater shows a maximum 5% relative error,demonstrating the feasibility of as-present assays for real applications.A solid-state sensor based on rhodamine 6G derivative-modified papers for detection of Hg²⁺ ions was demonstrated with good sensitivity and selectivity.A Spirolactams structure in Rhodamine 6G derivative（Rh6GD）was obtained by the ester-amine reaction between rhodamine 6G and N-[3-（trimethoxysilyl）propyl]ethylenediamine（TPED）,masking its fluorescence and color.Magneli phase structure of Ti6O11 was coated at the surface of commercial cellulose filter papers to serve as intermediate linker to modify Rh6 GD.Rh6GD was covalently immobilized on TCP by hydrolysis reaction of silylation reagent.This solid-state sensor exhibited highly selective recognition ability for mercury ions with the distinct color change from colorless to amaranth.The concentration-dependent colorimetric response（G value）to mercury ions is fast（<5 min）.And a low detection limit of 157.6 nM（S/N=3）was acquired with a wide linear relationship ranging from 0.5μM to 60 μM.Measurement of a group of possible interfering ions and spiked real water samples demonstrated a good selectivity of the proposed paper-based sensor.