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This paper deals with the intensive review of reactive azo dye, Reactive Black 5. Various physicochemical methods namely photo catalysis, electrochemical, adsorption, hydrolysis and biological methods like microbial degradation, biosorption and bioaccumulation have been analyzed thoroughly along with the merits and demerits of each method. Among these various methods, biological treatment methods are found to be the best for decolorization of Reactive Black 5. With respect to dye biosorption, microbial biomass (bacteria, fungi, microalgae, etc), and outperformed macroscopic materials (seaweeds, crab shell, etc.) are used for decolorization process. The use of living organisms may not be an option for the continuous treatment of highly toxic organic/inorganic contaminants. Once the toxicant concentration becomes too high or the process operated for a long time, the amount of toxicant accumulated will reach saturation. Beyond this point, an organism's metabolism may be interrupted, resulting in death of the organism. This scenario is not existed in the case of dead biomass, which is flexible to environmental conditions and toxicant concentrations. Thus, owing to its favorable characteristics, biosorption has received much attention in recent years.

Here, we have demonstrated the synthesis and characterization of hexacyanoferrate-complex-derived NiFe2O4/CoFe2O4 heterostructures (Ni/Co-HSs) blended with 10% multiwalled carbon nanotubes (MWCNTs) (C-Ni/Co-HS) as a composite for the first time to explore its performance in the electrocatalytic oxygen evolution reaction (OER). First, the structural and morphological analyses of the as-synthesized composite have been carried out using X-ray diffraction (XRD) patterns, Fourier-transform infrared (FT-IR) spectral studies, field emission-scanning electron microscopy (FE-SEM) with energy dispersive X-ray (EDAX), high-resolution transmission electron microscope (HR-TEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) analyses. Second, C-Ni/Co-HS loaded at a 316 stainless steel (SSL) mesh electrode was studied as an efficient and stable electrocatalyst, which firmly initiated the OER at a low potential of 1.47 V (vs reversible hydrogen electrode (RHE)) compared to the benchmark catalyst such as RuO2 or other counterparts, ferrite-loaded electrodes such as iron oxide (Fe2O3), nickel ferrite (NiFe2O4), cobalt ferrite (CoFe2O4), etc. Accordingly, a very low overpotential of 240 mV was observed for OER at a current density of 10 mA cm–2 under alkaline 1.0 M KOH conditions where the Tafel slope was calculated as 42 mV dec–1 at the C-Ni/Co-HS-loaded 316 SSL mesh electrode when compared to the counterpart, NiFe2O4/CoFe2O4 heterostructure (Ni/Co-HS)-loaded electrode, i.e., in the absence of 10% MWCNTs under identical electrochemical conditions. Besides, an excellent faradic efficiency was measured for C-Ni/Co-HS, propounding that the carbon support has minimized the corrosion and the additional oxidation of the active electrocatalyst during the course of the electrocatalytic OER test. The stability of the active C-Ni/Co-HS composites was studied under continued oxygen evolution for several hours at an applied potential of 1.67 V (vs RHE) to interpret the heterostructure phenomenal long-term stability and higher electrocatalytic activity toward OER. Thus, the developed inorganic-complex-derived heterostructure-based electrocatalyst provides an alternative to noble metal systems to afford a simple, highly efficient, and stable process for OER.

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Trifunctional thiospinel-like M–NixSn2xS4x nanocomposite was synthesized with ease.

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