Porphyrin-based metal–organic framework thin films for electrochemical nitrite detection

a r t i c l e i n f o Keywords: Electroactive metal–organic frameworks Electrocatalysis Electrochemical sensor Solvothermal growth Zirconium node Uniform zirconium-based porphyrin metal–organic framework (MOF-525) thin films are grown on conducting glass substrates by using a solvothermal approach. The obtained MOF-525 thin film is electrochemically addressable in aqueous solution and shows electrocatalytic activity for nitrite oxidation. The mechanism for the electrocatalytic oxidation of nitrite at the MOF-525 thin film is investigated by cyclic voltammetry. The redox mechanism of the MOF-525 thin film in the KCl aqueous solution is studied by amperometry. The MOF-525 thin film is deployed as an amperometric nitrite sensor. The linear range, sensitivity, and limit of detection are 20–800 μM, 95 μA/mM-cm 2 , and 2.1 μM, respectively. Nitrite has been widely used as a preserving agent and appearance builder in the food industry. However, excess uptake of nitrite is harmful to human health [1,2]. Furthermore, it is well known that the appearance of nitrite in human urine is often correlated with urinary tract infections [3]. Thus, accurate detection of nitrite becomes an important issue in both the food and health industries. Several analytical techniques have been developed for detecting nitrite [4–7]. Compared to other approaches, electrochemical detection shows the advantages of simple experimental procedures, short response time, and feasibility for building portable sensors [8]. Therefore , various materials have been utilized as electrocatalytic materials for detecting nitrite electrochemically [9–14]. In addition to these materials , porphyrins and metalloporphyrins have been reported as electrocatalysts for the oxidation of nitrite [15–17]. To further improve the sensitivity of the electrochemical sensor, more electrocatalytic sites are required on the modified electrode. Metal–organic frameworks (MOFs) are a series of porous materials which are constructed with metal-based nodes and organic linkers [18,19]. Due to their regular porosity and tunable pore compositions, MOFs have been examined for various applications [20–27]. The highest Brunauer–Emmett–Teller (BET) surface area of MOFs reported in the literature exceeds 7000 m 2 /g, which is much higher than the values of other porous materials [28]. Due to such high surface area, a few studies have utilized MOFs for electrochemical sensors [29–32]. Among various MOFs, porphyrin MOFs, which are constructed from porphyrinic or metalloporphyrinic linkers, have been widely reported [33–35]. The thin films of porphyrin MOFs grown on substrates have also been reported [36–39], however, only a few studies report their electrochemistry and electrochemical applications [38]. Given …