Semiconducting nanocrystals have recently got significant interest due to their unique optical and physiochemical properties1. Nanoparticles developed from Transition metal Sulfide exhibit significant electronic, thermal, photoelectric and phase properties. NiS is an important member of inorganic Transition metal that exhibits a metal insulator transition as a function of temperature or via doping 2. NiS is a p type semiconductor based QDs that exhibits anti-ferromagnetic and paramagnetic characteristics in low and high phase temperatures respectively3–5. The optical property of NiS have been studied in the infrared, and it has been ascertained that they have narrow band gap energy up to 2.7ev at low temperatures below 260K6. NiS and Ni3S2 co-exist in pure nickel sulphide preparation and thin films of NiS materials have been used in solar cells as catalysts and coatings. [8]. Nickel sulphide has been increasingly used as toughening agent in lithium-ion batteries, catalyst semiconducting heterojunction material7–9. The metal-to-nonmetal phase transition in NiS has been investigated for a long time, Ni–S system with binary multi-phases, such as, NiS, NiS2,Ni3S2, Ni3 + xS2, Ni4S3 + x, Ni6S5, Ni7S6, Ni9S8 and Ni3S4 are known, but the transition processes are still unknown 10,11 12. NiS2 generally exists in two phase system which makes synthesis of single phase of pure NiS nanostructure difficult. So, Single phase synthesis of NiS has remained a challenge for researchers13. Cubic phase structure among the two phases of NiS2 has better electronic, magnetic and optical properties. NiS can exist in two polymorphic forms that is hexagonal phase at high temperature(α-NiS) and Rhombohedral phase at low temperature (β NiS) 14.
NiS has been synthesized with different phases and morphologies by various methods such as Hydrothermal10 Solvothermal15 Coprecipitation 16and Molecular procedure17.
The discharge of organic dyes through industrial wastewater, primarily from the processing of products such as textiles pharmaceutical, dye intermediate, fabrics, plastic and rubber industries has become a serious problem. The exposure of dye effluents even at low level of 1mg L− 1 into the natural water has seriously affect the quality of aqueous environment. The dye effluents such as Methyl orange (MO), rhodamine B (RhB), and methylene blue (MB) are common azo dyes that are poisonous, mutagenic, and non-biodegradable in aquatic ecosystem. The disposal of excessive amounts of dyes into water generates hazardous compounds during the redox reaction, hydrolysis or other chemical processes in the wastewater phase. Photocatalysis has been shown to have significant potential for the removal of dyes from wastewater as an eco-friendly and sustainable treatment process. Different photocatalysts with varied efficiency can be considered as an alternative approach to reduce pollution. Currently various nanomaterials have been synthesized with different size range which play their role as photocatalyst material. Researchers have studied and focused on the preparation of various pristine and doped nanomaterials to improve the photocatalytic activities and enhance the photo-activity range of photocatalysts in recent years18.Inorganic Semiconductors metals are commonly employed as photocatalysts due to their acceptable band gaps. The NiS has been extensively studied as photocatalyst material due to its efficient ionic conductivity created by oxygen vacancies. However, NiS has broad band gap energy which limits its activity in the presence of visible light, which is the most significant drawback in its photocatalysis. To solve the problem of band gap energy the nanomaterial was doped with Zinc metal to observe increase in photodegradation. The optical properties of NiS2 nanoparticles were investigated in this study, and it was discovered that this compound is an electron rich semiconductor 19. The photocatalytic activity of NiS and Zn Doped NiS was investigated against Methylene blue dye.
1.1 Materials and methods
The chemicals used were NiCl2.6H2O, CH4N2S, ZnCl2 and ethylene glycol. All the chemicals were obtained from Sigma Aldrich and are 100% pure therefore no further purification was required. Methylene blue dye was used as pollutant. Distilled water, Ethanol was used as a solvent to wash the sample obtained.