Synthesis of Nickel Phosphate Using Self Templated Method

Nickel phosphate has diverse applications, such as in glucose sensors, catalysts, and supercapacitors. Different synthesis methods affect its structure and properties, characterized by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) analysis. Metal phosphates have high ion conductivity, chemical stability, and unique 1D nanostructures. Self-templating techniques, like templating against colloidal particles, create hollow 1D metal phosphate structures, determined by the template size. Materials including triethyl phosphate and ethanol, were used in a self templated method to synthesize different forms of nickel phosphate with varying triethyl phosphate volumes, resulting in products labelled as nickel phosphate-500, nickel phosphate-800, and nickel phosphate-1000. The observation under SEM showed that microflower structures are formed while the XRD analysis revealed that the nickel phosphate material had an amorphous structure with randomly arranged particles, evident from the single broad peak in the XRD patterns. The current response showed that nickel phosphate-500 exhibited the highest reading with the value of 0.2 mA compared to the other two nickel phosphates.


Introduction
The use of nickel phosphate is varied.Some of these materials are employed in the production of glucose non-enzymatic sensors, high performance oxygen evolution reaction catalysts [1], water oxidation electrocatalysts, novel materials for high performance supercapacitors for energy storage, and so forth.Some of these materials can also be used as a catalyst to increase the efficiency and stability of glycerol oxidation in neutral electrolytes.There are numerous ways to make nickel phosphate, however differing synthetic processes and chemicals can cause differences in the material's crystal structure, morphology, and electrochemical characteristics.XRD and SEM are used to characterize the structure of nickel phosphates.Through the use of cyclic voltammetry (CV), the electrochemical performance of the materials is investigated.
High ion conductivity and charge storage capacity are provided by the open framework structures of metal phosphates, which include extensive channels and cavities and their rich redox activity.Additionally, metal phosphates have strong P-O covalent connections, which give them a high level of chemical stability [2].One-dimensional (1D) nanostructures among varied morphologies show distinctive physicochemical characteristics, great chemical stability [3]., rapid charge transfer, and remarkable mechanical flexibility [4].Self-templating techniques for creating hollow nanostructures are among the most popular ways to make 1D metal phosphate nanomaterials; among these techniques, templating against colloidal particles is perhaps the most successful one [5].Usually, a thin layer of the appropriate material is applied to the template to create a core-shell composite; once the template core is removed (by calcination or selective etching), hollow structures are created, whose inner diameter is primarily dictated by the size of the template.

Materials
Materials such as triethyl phosphate and ethanol are prepared while nickel triethanolamine is obtained from the reaction between nickel nitrate and triethanolamine.The materials were employed as sources of metal.Ethanol was also the other material that has been used for the synthesis of nickel triethyl phosphate where it is used in mixing with the nickel triethanolamine.

Materials Preparation
In 20 mL of ethanol solution, 30 mg of nickel triethanolamine and triethyl phosphate were dissolved.The variation for nickel triethyl phosphate was on its volume of triethyl phosphate where it consisted of 500, 800 and 1000 ߤ݈.Prepare about four to five glass bottles of that mixture and stir them for two hours.The mixture was then put into an autoclave lined with Teflon, sealed, and heated for 16 hours at 180°C before being cooled to room temperature.The end products were dried at 60°C for 12 hours after being rinsed and filtered with 100% ethanol.The obtained NiHPi powder was put into an alumina boat and calcined for two hours at a heating rate of 1 °C min-1 to further transform it into amorphous nickel phosphate.The calcination includes the three variations of triethyl phosphate's volume and the obtained products were labeled as nickel phosphate-500, nickel phosphate-800 and nickel phosphate-1000.

Materials Characterization
SEM, XRD and Cyclic Voltammetry (CV) are only a few of the characterisation tests that have been carried out on these nanoparticles.By using an electrochemical workstation (CHI-660E, CH Instruments, USA) with a three-electrode setup, electrochemical measurements of the catalysts as-prepared were carried out.Screen-printed carbon electrodes (SPCE) were used because they had three embedded electrodes-a working electrode, a reference electrode, and a counter electrode-and a ferricyanide solution as the electrolyte.

Result and Discussion
Figure 1 shows SEM pictures of the ideal nickel phosphate-500 sample.It is evident that the microflower structures of nickel phosphate-500, 800, and 1000 were created by the self-stacking of nanoplates with random orientation.The material of nickel phosphate exhibits an equal size distribution of microflower particles and the assembly of nanoplates.The nickel phosphate-500 product, in contrast, displays a structure with numerous obvious holes between the structures (Figure 1a-b).In all nickel phosphate variations, there is some self-stacking of the structures.It can be seen that when nickel phosphate is prepared via solvothermal techniques, the microflower shape of the SEM pictures for all variations in triethyl phosphate volume is nearly identical.Next, the crystallinity of material was analyzed using XRD and involved the material of nickel phosphate.Overall, it can be said from the XRD graph that this material having an amorphous structure where its particles are randomly arranged and do not have an ordered arrangement that results to irregular shape.Based on figure 2, every XRD patterns had a single large bump between two angles, which was due to its amorphous nature [6].Based on the figure 3, the cyclic voltammetry test was conducted for the three types of nickel phosphates (nickel phosphate-500, nickel phosphate-800 & nickel phosphate-1000).Nickel phosphate-500 showed the best current response among the other two nickel phosphates with the value of 0.2 mA which indicates that it has a good current conductivity.Other than that, the generated curve of nickel phosphate-500 gives the ideal shape of usual curve where it has the smooth minimum and maximum peaks.In addition, the current response for nickel phosphate-800 and nickel phosphate-1000 are lower than nickel phosphate-500 with the reading of 0.01 mA and 0.08 mA.

Conclusion
By using the self-templating method, our final material which is nickel phosphate can be achieved where for the first result, it discussed more on the morphology of the materials as the tested material is nickel phosphate.Under the magnification of 10000, it can be seen that bundles of nanorods were formed where there is no pore detected on the surface's structure of material.SEM result for the nickel phosphate showed the structure of this material look alike micro flower shaped.In term of electrochemical measurement, the CV method was done on SPCE in order to see the current response for every modification step.The highest current response is achieved after the immobilization of antibody.For comparison among the variation of nickel phosphates, nickel phosphate-500 having the highest magnitude of current response followed by nickel phosphate-1000 and nickel phosphate-800.These characterization tests have concluded that nickel phosphate with triethyl phosphate volume of 500 ߤ݈ giving the good reading of current response.