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The ecological toxicity imparted by non-biodegradable organic dyes has been considered as a major risk to handle in front of mankind. In this view, the low-cost zinc oxide nanoparticles (ZnO-NPs) were facially synthesized by coating the surface with surfactant (CTAB) and ionic liquid (BMTF) molecules for the effective removal of Eriochrome Black T (EBT) from aqueous media. Various advanced characterization techniques have given insight into the morphological features, crystalline structure and physio-chemical properties of as-synthesized ZnO-NPs. The systematic analysis of the adsorption isotherms and kinetics models specifies that the adsorption of EBT follow Freundlich model and pseudo-second-order kinetics. The intraparticle diffusion model displayed a linear relationship (R2 = 0.98, 0.97 and 0.94 for BMTF@ZnO, CTAB@ZnO and bare ZnO-NPs), which shows that pore diffusion rate is affected by surface modification and effects the overall EBT adsorption process. Furthermore, after the removal of 87% and 84% of EBT dye by BMTF@ZnO-NPs and CTAB@ZnO-NPs, the fabricated nanoadsorbents of ZnO were successfully regenerated and reused after the treatments up to four times. The adsorption aptitude of ZnO-NPs towards EBT dye was systematically explored in real wastewater samples and interference study of inorganic metallic salts was also performed. The toxicity estimations of the treated dye solutions were made using floral and fungal activities, to ascertain their non-toxic nature before releasing into the environment. These outcomes have supported the immense potential of ZnO-NPs towards the removal of EBT in a cost effective manner.

Heterostructured α-Bismuth zinc oxide (α-Bi2O3–ZnO) photocatalyst was fabricated by a facile and cost-effective, ultrasound assisted chemical precipitation method followed by hydrothermal growth technique. As synthesized α-Bi2O3–ZnO photocatalyst showed enhanced photocatalytic performance for the MB dye degradation in contrast to pure ZnO and α-Bi2O3. Light emitting diodes (UV-LED) were used in the experimental setup, which has several advantages over conventional lamps like wavelength selectivity, high efficacy, less power consumption, long lifespan, no disposal problem, no warming-up time, compactness, easy and economic installation. XRD study confirmed the presence of both the lattice phases i.e. monoclinic and hexagonal wurtzite phase corresponding to α-Bi2O3 and ZnO in the α-Bi2O3–ZnO composite photocatalyst. FESEM images showed that α-Bi2O3–ZnO photocatalyst is composed of dumbbell like structures of ZnO with breadth ranging 4–5 μm and length ranging from 10 to 11 μm respectively. It was observed that α-Bi2O3 nanoparticles were attached on the ZnO surface and were in contact with each other. Low recombination rate of photo-induced electron-hole pairs, due to the migration of electrons and holes between the photocatalyst could be responsible for the 100% photocatalytic efficiency of α-Bi2O3–ZnO composite. In addition, photocatalyst was also observed to show the excellent antimicrobial activity with 1.5 cm zone of inhibition for 1 mg L−1 dose, against the human pathogenic bacteria (S. aureus).

Heavy metals like chromium (Cr(VI)) and cadmium (Cd(II)) which are supposed to be indigenous components of rocks, are no longer bound to their place of origin thus manifesting significant toxic impacts on living beings. In the present study, the metal tolerance capacity of highly resistant microorganisms was harnessed individually and in the form of consortium, to remediate conundrum of pollution. These fungal strains were isolated from contaminated sites and screened under various processed conditions. Results of secondary screening had evinced more than 70% of removal percentage for Cr(VI) with the fungi Aspergillus flavus (FS4) and Aspergillus fumigatus (FS6), in the liquid medium. Similarly, one Cd (II) tolerant fungal isolate FS9, identified as Aspergillus fumigatus, showed removal up to 74%. The developed microbial consortium had also enhanced the removal of heavy metals in different industrial effluents. The metal acceptance quality that this fungal consortium possess, may specify its ability as an effective biosorbent for the environment contaminated with heavy metals.

Green chemistry-assisted biocompatible copper (Cu), silver (Ag), and iron oxide (Fe2O3) nanoparticles (NPs) synthesis along with surface modification using Koelreuteria apiculata is demonstrated in this research, for the first time. Appropriate analytical techniques were utilized to confirm the preparation, spherical morphology, and crystalline structure of each of the NPs. The antioxidant nature of synthesized NPs was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging. Besides, the antimicrobial activity was also performed using bacterial strains of Staphylococcus aureus, Escherichia coli, and Salmonella typhi. Aspergillus sp. was designed as marker specie for the antifungal studies. The outcomes of NPs exposure, analyzed with reference to Chlorella sp. of the algal family exhibit the numerical values around 833% for AgNPs, 497% of CuNPs, and 456% for Fe2O3NPs. Phytotoxicity assay performed on the seeds of Vigna radiata and Cicer arietinum further validate the accordant nature of NPs towards vivacity. Allium cepa was also used as a test model to ascertain the genotoxic effects of the NPs wherein the mitotic index (MI) was calculated for AgNPs, CuNPs, and Fe2O3NPs as 42.1, 51.7, and 54.2% respectively. The outcomes of this research proved the suitability and affordability of our NPs developed using green synthesis for new industrial applications of in-situ reduction of carcinogenic compounds from water and soil.