One-step in situ growth of high-density POMOFs films on carbon cloth for the electrochemical detection of bromate

Two electroactive polyoxometalates (POMs)-based metal-organic frameworks (MOFs) films (POMOFs) in situ grown on carbon cloth (NENU-3/CC and NENU-5/CC) were synthesized by a facile one-step solvothermal method containing Cu(NO3)2, 1,3,5-benzentricarboxylate (H3BTC) and POMs (PMo12 and PW12), in which the POMs were wrapped into MOFs to increase stability. The analysis of electrochemical behavior of the NENU-3/CC and NENU-5/CC films reveals that they can serve as conductive electrode materials. Subsequently, two kinds of film electrodes exhibit enhanced electrocatalytic activity toward bromate reduction in acidic solution. Thus, they can act as electrochemical sensors to detect bromate. Amperometric detection results of NENU-3/CC to bromate show a high sensitivity of 45.11 μA cm −2 mM−1 and a low detection limit of 0.55 μM. Furthermore, NENU-5/CC can exhibit a detection limit of 1.18 μM, and a high sensitivity of 18.83 μA cm−2 mM−1. Experimental results show that two POMOFs films have high electrochemical stability as working electrode materials and good selectivity for detecting bromate as sensor materials. Up to now, electrochemical methods to detect bromated have attracted considerable attention due to their simplicity, rapidity, high sensitivity, excellent selectivity and environmentally friendliness with low-cost equipment compared with other techniques. Polyoxometalates (POMs) have been widely used for the electrocatalytic reduction of bromate because of their high redox properties. However, when POMs are used as conductive electrodes materials, they dissolve easily in the electrolyte, and the instability of POMs can increase performance degradation. For solving the above-mentioned problem, POMs are encapsulated into MOFs to generate POM-based MOFs (POMOFs), it combine the merits of POMs and MOFs and increase the stability of skeleton. However, POMOFs materials can increase the reversible electrochemical capacity, the leaching and dispersity of POMOFs in the electrocatalytic measurement can make them unstable, and it hinders the conductivity in electrochemical behaviors. Thus, Proper POMOFs films have been developed to overcome the aforementioned difficulties by packing POMOFs on the conductive substrates uniformly to increase the stability and performance in electrochemical catalysis. In this paper, two electroactive polyoxometalates (POMs)-based metal-organic frameworks (MOFs) films (NENU-3 and NENU-5) were chosen as target materials in the synthesis of POMOFs film. And they were located on the surface of the carbon cloth through a facile in situ one-step solvothermal method as conductive electrode materials. According to report, NENU-3 and NENU-5 were coated on the substrate using hot-pressing and electrochemical method, we firstly prepared NENU-3/CC and NENU-5/CC films by in situ one-step solvothermal method, and the as-synthesized POMOFs materials using this method are more uniform, facile, and stable than other methods. The results of amperometric detection of NENU-3/CC to bromate show a wide linear range of 5–560 μM with a high sensitivity of 45.11 μA cm−2 mM−1 and a low detection limit of 0.55 μM. Furthermore, NENU-5/CC can exhibit a good linearity range of 15–380 μM, a detection limit of 1.18 μM, and a high sensitivity of 18.83 μA cm−2 mM−1. As a result, the amperometric determination demonstrates that two as-synthesized POMOFs/CC films as working electrode materials exhibit good sensitivity, selectivity, and stability to detect bromate as sensor materials.