Semiconductor codoped nanomaterials have received significant interest due to their electronic, optoelectronic, magnetic, catalytical, electro-chemical, mechanical behaviors and their potential applications in different research areas. Semiconductor nanomaterials might be a promising due to their high-specific surface-area, low-resistances, high-catalytic activity, attractive electrochemical and optical properties [1, 2]. Nanomaterials are also scientifically important codoped nanostructure materials owing to their extraordinary mechanical, optical, electrical, electronic, thermal, and magnetic characteristics. Lately, it has attained significant attention in manganese doped-semiconductor materials in order to develop their physic-chemical behaviors and extend their efficient applications [3–5]. It has not only investigated the basic of magnetism, but also has huge potential in scientific features such as magnetic materials, bio & chemi-sensors, photo-catalysts, and absorbent nanomaterials [6–9]. Recently, very few articles are published based on transition-metal doped semiconductor nanomaterials synthesis and investigated the magnetic behaviors and potential applications only [10–13]. Here, it is prepared codoped Mn2O3-ZnO NPs by easy, facile, economical, non-toxic, repeatable, and reliable low-temperature wet-chemical technique. The nanostructure and morphology of the codoped Mn2O3-ZnO NPs were examined and potentially applied for the enhancement of higher-sensitive 4-nitrophenol chemo-sensor at room condition. Generally, chemo-sensing exploration have been developed with the transition-metal oxides nanostructures for the recognition and quantification of various toxic-chemicals such as phenyl-hydrazine, methanol, formaldehyde, ethanol, chloroform, dichloromethane etc., which are not ecologically safe and friendly [14–18]. The sensing mechanism with doped semiconductor metal oxides thin-film used primarily the properties of meso-porous thin-film generated by the physi-sorption and chemisorptions methods. The hazardous chemical detection is depended on the current responses of the fabricated thin-film, which cause by the presence of chemical components in the reaction-format in aqueous phase [19–21]. The key efforts are based on recongnition the least amount of 4-nitrophenol necessary for the fabricated Mn2O3-ZnO NPs chemo-sensors for electrochemical investigation.
Phenolic compounds have attained significant interest in last decade owing to their eco-toxic effects on human health, ecological, and environmental fields. These toxic compounds (i.e., 4-nitrophenol) are prepared using a number of polluting techniques, such as industry-related ways of plastic, pesticides, paint, drugs, composites, antioxidant, petroleum, and paper production . The 4-nitrophenol is recognized for its hazardous nature, carcinogenetic, toxicity, and persistence in the environment, which is become a common pollutant in nature and waste water . Because of its high solubility and stability in water, it has been also found in freshwater, sea environments and has been detected in industrial wastewaters and is difficult to degrade by conventional method. It is concerned in most of the degradation pathways of organo-phosphorous pesticides, which are decomposed in soil and water to form 4-nitrophenol as an intermediate or final-product in the reaction systems [24, 25]. Therefore, 4-nitrophenol is integrated in the Environmental Protection Agency List of Priority Pollutants (EPALPP) . Therefore, it is straight away desirable to fabricate a chemo-sensor for the detection of organic pollutants to accumulate the environment and human health. There is focused a significant attention for the development of simple, reliable, and ultra-sensitive in various detection methodology based on codoped nanomaterials. Generally, the detection of toxic 4-nitrophenol is consummated using chromatographic techniques, such as gas-chromatography [27, 28], high-performance liquid chromatography [29, 30], liquid chromatography connected with mass-spectroscopy , and capillary-electrophoresis . Electrochemical technique, which can offer fast, reliable, and direct real-time monitoring is one of the most utilized methods in the determination of nitro-phenolic stuffs. Electro-analytical techniques have been performed for 4-nitrophenol detection and quantification with a modified glassy carbon electrode [33, 34] hanging mercury drop electrode  and boron-doped diamond electrode . The analytical signal is derived from the four-electron reduction of the nitro-group  or by the direct two-electron oxidation of phenol to the corresponding o-benzoquinone [38–40]. Electrochemical chemo-sensors have attained huge interest in the recognition and quantification of environmental unsafe chemicals due to their reliable and fast response and determination [41–44]. Chemo-sensor technology plays a significant task in ecological protection that usually caused by environmental contamination and unintended seepage of harmful chemicals, which is a huge-menace for eco-systems. Thus for the attention of ecological and health monitoring, it is important to fabricate easy, simple, reproducible, reliable, and inexpensive chemo-sensors to detect toxic chemicals in aqueous systems. The sensitivity and low-detective of electrochemical chemo-sensor energetically dependent on the size, structure and properties of fabricated electrode doped nanomaterials. Hence doped nanostructure materials have received much attention and have widely been used as a redox mediator in chemo-sensors [45–48].
Codoped nanomaterial is largely established for the recognition of toxic chemicals in electro-chemical control method owing to their numerous benefits over conventional chemical methods in term of large-surface area for examining in medical, health-care and environmental fields [49–56]. In general electro-analytical technique, it was executed the slower responses, surface-fouling, noises, flexible-responses, and smaller dynamic-range and lower-sensitivity with bared codoped nanomaterials surfaces for chemical recognition. Therefore, the modification of the chemo-sensor surface with doped metal oxides nanostructure materials is urgently required to achieve higher sensitive, repeatability, and stable responses. Therefore, an easy and reliable I-V electrochemical approach is immediately needed for relatively simple, appropriate, and economical instrumentation which displays higher-sensitivity and lower-detection limits compared to general techniques. Here, a consistent, large-scale, and highly responsive I-V method is applied for detection of 4-nitrophenol chemical by codoped Mn2O3-ZnO NPs. The present approach represents a consistent, sensitive, low-sample volume, ease to handle, and specific electrochemical methods over the existing UV, CV, LC-MS, LSV, FL, and HPLC methods [57–60]. The simple coating technique for preparation of nanomaterials thin-film with conducting coating agents is developed for the fabrication of doped Mn2O3-ZnO NPs films. Here, low-dimensional doped Mn2O3-ZnO NPs films with conducting coating agents are synthesized and detected 4-nitrophenol in phosphate buffer solution (PBS) phase by reliable I-V method. To best of our knowledge, this is the first report for detection of 4-nitrophenol chemical with doped Mn2O3-ZnO NPs using easy and reliable I-V technique in short response time.