donshafi911@IAmTheFaceOfTruth🔻

 

Highly sensitive ascorbic acid sensors from EDTA chelation derived nickel hexacyanoferrate/ graphene nanocomposites

Significance of ascorbic acid (AA) determination has been increasing due to its importance in both human life and industrial applications. This work demonstrates the development of a highly sensitive non-enzymatic AA sensor by using Graphene/Nickel hexacyanoferrate nanocomposite (Gr/NiHCF). In this work, EDTA chelation strategy was used for the formation of homogeneously distributed NiHCF nanoparticles on graphene sheets. EDTA residue-supported pyramidal and spherical nanoparticles of NiHCF deposited on graphene sheets were used for the development of a highly sensitive AA sensor. The formation of EDTA residue supported NiHCF nanoparticleson graphene surface was confirmed by different characterization techniques (XRD, SEM, TEM, FTIR, XPS). Cyclic voltammetry(CV) of Gr/NiHCF nanocomposites confirmed the electrochemical sensing of AA by oxidation mechanism. The Sensitivity of the fabricated Gr/NiHCF based AA sensor as determined by amperometric characterization was found to be 7.029 µA µM⁻¹ cm⁻². The sensor fabricated in the present study shows much better sensitivity over other AA sensors reported in the literature. The LOD of the fabricated sensors was found as 0.25 µM. Repeatability, reproducibility, and interference studies of fabricated sensors reveal the high accuracy and selectivity of a fabricated sensor for AA measurement. Stability study of fabricated sensors showed excellent stability up to 30 days, indicating the potential usage of Gr/NiHCF for AA sensing. The real-time use of fabricated sensors in accurate determination of AA in samples like Vitamin C supplements and different fruit juices indicated their potential usage for AA measurement in real samples.

Ascorbic acid (AA) or Vitamin C is one of the safest and most effective nutrients in human diet. It is a water-soluble vitamin present in many biological systems, fruits, and vegetables. Vitamin C is essential for the development and repair of all body tissues. It is associated with many body functions, including the formation of collagen, retention of iron, the vulnerable immune system, recuperation of wounds, and the support of ligaments, bones, and teeth. Nutrient Vitamin C is one of the numerous cancer-preventing agents that can fight against harm brought by poisonous chemicals and pollutants like tobacco smoke [1,2]. The standard concentration of AA in the human body is in the range of 0.6 and 2 mg/dL [3]. The deficiency of AA can cause several diseases like rheumatoid joint inflammation, scurvy, parkinson's, alzheimer's, cardiovascular malady, and malignant growth. Excess intake of AA can cause problems like urinary stones, looseness of the bowels, and gastric bothering [4,5,6]. But AA is a highly unstable vitamin in food essentials, particularly in fruits and vegetables; its deterioration leads to a decrease in food nutritional values. Thus, the quantitative evaluation of AA is important for different industries, for example, cosmetics, pharmaceutical companies, and food enterprises [7,8]. Thinking about the noteworthiness of AA in both human lives and industrial applications, the precise determination of AA is one of the highly researched current themes. Various methods (electrophoresis [9,10], fluorescence [11,12], chemiluminescence[13], fluid chromatography [14,15], and electrochemical[16]) have been utilized for the measurement of AA. But the electrochemical techniques are suitable and convenient for AA measurement due to their high sensitivity, easy handling, cost-effectiveness, and miniaturization.

Electrochemical sensing of AA is based on the electrochemical activity of materials that form the electrodes. The AA sensing can be improved by enhancing the electrocatalytic activity of electrode materials towards the electrochemical oxidation of AA [17]. So, developing an effective electrode material is important for boosting the electrochemical AA sensor performance. Different materials like metal nanoparticles [18,19], metal oxides [20], [21], [22], [23], carbon materials (graphene, carbon nanotubes, and quantum dots) [24,25], polymers [26,27], different composites, and coordination compounds of hexacyanoferrates have been used for preparing electrodes for electrochemical sensing [28,29]. Among these, the composites of hexacyanoferrates have been found to be highly effective for electrochemical sensing applications[30].

Transition metal hexacyanoferrates (TMHCF) are one of the best materials for electrochemical sensing due to their excellent electroctrocatalytic behavior[31]. The zeolitic structure of these compounds allows easy access to electroactive sites making them highly compatible for electrochemical sensing applications. The excellent selectivity of TMHCF based materials has helped to develop different electrochemical sensors, like H₂O₂, uric acid, l-cysteine, hydrazine, glucose, and cholesterol [32,33,34]. TMHCF based sensing materials usually exhibit low conductivity and stability, especially in neutral and alkaline mediums, due to which the TMHCF based electrochemical sensors face problems like low sensitivity, poor limit of detection (LOD), and shelf-life [35,36]. The improvement of these TMHCF based electrochemical sensors is the focus of the current work.

One of the most common and effective approach to address some of the limitations as mentioned above is that of utilizing composites. Different nanocomposites of TMHCF have been synthesized by using noble metals, conducting polymers, carbon nanomaterials, and their combinations for improving the electrochemical sensing properties of TMHCF[30]. Among the composites, noble metal-based TMHCF based nanocomposites are not preferred due to their high cost[37]. Even though conducting polymer-based TMHCF composites exhibit superior electrochemical properties, the complex synthesis procedure and high cost of conducting polymers limits their usage[27]. Some conducting polymer-based TMHCF nanocomposites need electrochemical activation before their use as well. The performance of the conducting polymers-based TMHCF based nanocomposites also depends on environmental conditions like pH and temperature [38], [39], [40]. That is why mostly TMHCF nanocomposites with various forms of carbon as the second phase have been preferred, owing to the abundant availability of various forms of carbon and their cost-effectiveness. Different carbon materials like carbon nanotubes (CNTs), carbon quantum dots, carbon nano onions, reduced graphene oxide, and graphene have been tried for the TMHCF nanocomposites preparation [41], [42], [43], [44]. Among these, graphene-based TMHCF are preferred due to their excellent electrocatalytic activity, wide potential window, good conductivity, high specific surface area. Different TMHCF (Fe, Cu, Co, Mn, Zn, Ti, Ni) have been used in electrochemical applications, but their instability arising out of hydroxide formation in aqueous environments is a significant problem [35,36]. A comprehensive electrochemical study of TMHCFs reveals that Nickel hexacyanoferrate (NiHCF) compounds are highly stable in an aqueous environment [45,46]. So, in the present study, the NiHCF compound was chosen as a material of interest, and its composite with graphene was considered to attempt the development of a highly sensitive electrochemical sensor.

Different strategies for the synthesis of graphene-based TMHCF nanocomposites, like electrodeposition[47], layer-by-layer assembly [44,48], chemical synthesis[49] in the presence of conducting polymers and their combinations have been reported. Even though these methods improve the electrocatalytic activity of graphene-based TMHCF nanocomposites, the limitations like complex synthesis procedures, usage of conducting polymers, and scalability restrict their usage[30]. So, there is a need for a cost-effective and scalable method for the production of graphene-based TMHCF nanocomposites. This study demonstrates a novel, potentially scalable procedure for the production of graphene-based highly sensitive NiHCF nanocomposite for electrochemical sensing of AA.