The release of poorly treated industrial effluents enriched with several recalcitrant chemicals, into freshwater resources is a serious threat to the entire ecosystem (Chong et al., 2010; Zeydouni et al., 2018; Villegas et al., 2019). The major class of pollutants is phenols which are used in petrochemicals, pharmaceuticals, resin manufacturing, and plastics while dyes are utilized in textile, paint, paper, fabric industries (Caetano et al., 2009; Liu et al., 2019; Tian et al., 2020). However, many phenols have been used as precursors or intermediate in the industrial manufacturing of organic dyes and pesticides. Degradation of phenols and their derivatives are quite difficult due to higher half-life (t1/2 :15 to 72 days) and solubility (35 mg/mL) in water (San et al., 2001; Aimeur et al., 2020). Greater stability and toxicity of phenols and organic colorants (major leading pollutants) have resulted in hazardous exposure for all living beings even in very less quantity (Sas et al., 2020). They potentially act as endocrine disruptors because of easy absorption via the skin (Arques et al., 2007). The presence of amino phenols in water causes allergic reactions and respiratory diseases in humans (Tian et al., 2019). Distinguishing odor was produced by even minor exposure (5 mg L− 1). of chlorinated phenols which required removal on exceeding above the permissible limit set from 0.1-1 mg L− 1 in drinking water (Rachna et al., 2020). US-EPA has categorized phenols in the list of top main concern pollutants beyond concentration level of 0.01 µg L− 1 (Bagal et al., 2013; Li et al., 2018). Dyes are occupying chief portions of industrial effluent worldwide with the quantity of nearly 280,000 tons per annum (fabrics: 54%; paint: 8%; paper: 10% and dyeing: 21%) (Ghaly et al., 2014; Hanafi and Sapawe, 2020). Eriochrome Black T (EBT) (Sodium 1-[1-hydroxynaothylazo]-6-nitro-2-napthol-4-sulfonate) dye, anionic with an azo functional group, extensively used for silk textile (Barka et al., 2011). and in various Institutional laboratories to identify the hardness of water (0.05-0.08g as an indicator) (Kansal et al., 2013). The physo-chemical properties of EBT and 3-AP are highlighted in Table 1. Due to the high toxicity of omni-persistent organic pollutants, there is an urgency to develop low energy, easy to handle and cost-effective based state-of-the-art techniques for their detection and complete removal from water (Pitarch et al., 2010). Traditional methods (adsorption, filtration, coagulation, membrane separation) have lost their ground due to merely mass transfer of pollutants and other practical restrictions (Mukherjee et al., 2018). To overcome the hurdle associated with old methods, nanomaterials based photocatalysis (Semiconductor assisted degradation) is being widely promoted cum accepted for combating pollution credited to the most promising and adorable characteristics of the economy and mild reaction conditions with less energy consumption (Rani et al., 2017; Rani et al, 2018a). Transition metal oxides have peculiar properties high thermal stability, inherent oxidation state and economics (Mathew et al., 2011). ZnO and TiO2 (popular nanoparticles) have shown encouraging performance in photocatalysis and industries but their extensive use is causing bioenrichment in the ecosystem. Moreover, a large bandgap (> 3eV) requiring high UV energy for excitation and recombination of charges are putting pressure on researchers to develop new/alternative or modified nanomaterials with improved properties. Doping the surface of metal oxides or coupling with metals, non-metals or transition metals compounds shift bandgap energy level towards the visible region and also prevent charge recombination due to introductory-additional energy level of dopant (Rachna et al., 2018; Heinz et al., 2000; Watanabe et al., 2000). In light of those observations, nanoparticles of SnO2 (Honarmand et al., 2019), CeO2 (Mishra et al., 2018), Bi2WO6 (Lai et al., 2019), Zn0.3Al0.4O4.5 (Fegadae et al., 2020), Co-Co3O4 (Adekunle et al., 2019), SrFe2O4 (Zafar et al., 2018) for the elimination of EBT; and CuO (Nayak et al., 2020), CeO2 (Ahmad et al., 2020), Ni-ZnO (Sharma et al., 2016), CuFe2O4@r-GO (Othman et al., 2019) and peroxymonosulfate activated CuO-Co3O4@MnO2 (Khan et al., 2017) for phenols were employed. Superparamagnetic magnesium ferrite and MgFe2O4@γ–Al2O3 were used for the removal of renowned organic dyes (Atrak et al., 2018). However, some of the above-mentioned absorbents were reported with UV-light exposure.
Synergistic effects of various bi-or trimetallic nanoparticles of 3d-series synthesized via greener route containing gel, gum or plants have been reported (Farood et al., 2017; Farood et al., 2017a; Sorbiun et al., 2018). Spinel (AB2O4) nanoparticles are frequently utilized due to fascinating physicochemical and structural characteristics as well as environmental safety (Zhao et al., 2017). Cu replace M2+ cations in MFe2O4 which magnified catalytic property even at low temperature (Wang et al., 2019). Cu2+ ion shows John-Teller distortion and charges redistribution which generates a transfer of electron (Nedkov et al., 2006; Liu et al., 2016). As revealed from the published document, there is no data about green synthesis and subsequent comprehensive photo-application of CuFe2O4, CuMn2O4 and MnZn2O4 nanoparticles for degradation of selected toxic phenols and dye under sunlight. Adoption of the green process is appreciable because of its quickness, usage of plants, fabrications of highly pure (free from contaminants), and quantity enriched product while avoiding intermediate base groups and costly equipment and precursor. Plant parts have been hired for bio-reduction assisted production of several nanomaterials because of reducing cum capping and stabilization properties. Due to environmental concern, sunlight was preferred instead of UV-irradiation as polluted water face natural condition.
These facts embolden us for investigations on the synthesis of sunlight active nanoparticles of CuFe2O4, CuMn2O4 and MnZn2O4 by using leaves of Azadirachta indica and subsequent applications for potential degradation of toxic 3-AP and EBT in water. Phytochemicals (alkaloids and terpenoids) present in A.indica lesser down interfacial tension to regulate nucleation/ agglomeration of nanomaterials during the fabrication process (Rani et al., 2018b;Rani et al., 2020). Besides, toxicity and bioaccumulation, the selection of pollutants was based on the quantity of these pollutants used in the industries. Diverse parameters of contaminant concentration, nanocatalyst amount, pH, radiation environment and contact time were investigated to bring off the highest degradation. Langmuir isotherm and degradation pathways were studied to investigate the adsorbing behavior and types of metabolites formed. Reusability studies were also investigated for confirmation of the sustainability of nanomaterials. Scavenger analysis was explored to find out the role of free radicals under sunlight.