**Abstract**

In this study, tragacanth gum/chitosan/ZnO nanoprism-based electrochemical sensors were prepared for sensing reactive dyes in water. To use an electrochemical sensor, a ~250 nm-sized ZnO nanoprism was synthesized via ultrasonic-assisted green synthesis method, using tragacanth gum and chitosan polymer blend as a matrix. The electrochemical properties of tragacanth gum/chitosan/ZnO nanoprisms were compared against reactive red 35, reactive yellow 15, and reactive black 194. The electrochemical measurement results indicated that prepared tragacanth gum/chitosan/ZnO nanoprism-based electrochemical sensor detected 25 ppm reactive red 35 in 1 min at room temperature. This study reveals new high-potential novel tragacanth gum/chitosan/ZnO nanoprism-based sensing material for the detection of reactive red dye-consisted wastewater with high sensitivity and short response time.

**Keywords:** ZnO, chitosan, nanoprism, electrochemical sensor, environmental monitoring, reactive dye, wastewater

### **1. Introduction**

The physicochemical properties of nanomaterials make them suitable candidates for sensor applications due to their high surface area and surfactant functional groups. Nanomaterials with different morphologies help to adapt their applicationspecific detection properties. Therefore, researchers focus on effective detection platforms (reaction time, sensitivity, and selectivity) for the detection of aqueous reactive dyes based on different detection principles with sensors prepared with different morphological structures of nanomaterials (nanoparticles, nanowires, nanoprisms, etc.). Also, the materials in nanoscale exhibit higher dissolution and higher solubility than in microscale. Many types of nanomaterials such as metal oxide semiconductors, carbon-based nanomaterials, graphene/graphene-based nanomaterials, and metal-organic frameworks have been investigated for sensing reactive dyes in water [1–15].

Electrochemical sensing method involves the measurement of the redox transformation of reactive dye molecules upon contact with the sensing nanomaterial

surface. The method mainly consists of (a) conductometric/resistive, (b) amperometric/voltammetric, and (c) impedimetric electrochemical sensing. Voltammetric sensors work based on the current difference between reference and working electrodes. This approach utilizes the measurement of current as a function of variation in the applied potential difference in terms of the oxidation or reduction of an electroresponses of an electrochemical sensor. The peak current measured during voltammetry-mediated oxidation of analyte (e.g., reactive dye) is reflected as a function of its concentration. The sensitivity of the voltammetric electrochemical sensor is defined as (Ig − I0)/I0, where Ig and I0 are the currents while sensing film analyte (e.g., reactive dye) is interacting and not, respectively. The voltammetrictype electrochemical sensing allows the quantification of the redox state of analyte in terms of current variations [16–18].

Transducers of the electrochemical sensors have attractive attention for preparing highly sensitive sensors. Nonuniform ohmic drop on an electrochemical transducer significantly affects the cyclic voltammogram data. The shape of the cyclic voltammograms predicts various electrochemical transducer geometries and experimental conditions [19–35].

Zinc oxide (ZnO) nanomaterials have distinct properties such as high sensitivity, high surface area, nontoxic, good compatibility, specific shape, nanosize, and correspondingly high isoelectric point. The unique and adjustable properties of ZnO nanomaterials as n-type semiconductor materials show excellent chemical and thermal stability in a wide range of applications such as solar cells, optical devices, sensors, etc. As far as the morphological perspectives of ZnO are concerned, the synthesis and production procedures also play an important role. The different parameters such as surfactant, temperature, concentration, and time are very significant for the growth of nanomaterials with different morphologies in various synthesis processes. Numerous different methods have been reported worldwide for the synthesis of ZnO nanopowder, composites, and films with good surface structure. Noteworthy techniques for the synthesis of various ZnO nanomaterials are generally deposition, wet chemical technique, sol-gel treatment, hydrothermal process, solvothermal process, and microwave techniques [36, 37].

This is the first report of the preparation and structural characterization of novel tragacanth gum/chitosan/ZnO nanoprism and investigation of the voltammetric electrochemical sensing characteristics of tragacanth gum/chitosan/ZnO nanoprisms against reactive dyes in water towards environmental monitoring. We suggest that this tragacanth gum/chitosan/ZnO nanoprism material has a great potential for future applications in high-performance, low-cost, portable, smallscale voltammetric electrochemical sensors towards forthcoming electronics.
