Removal of heavy metal ions and dissolved organic compounds present in wastewater is a challenge for many countries owing to high cost of existing technologies and continued increase in water consumption. In this study, three natural materials, avocado, hamimelon and dragon fruit peels, were selected and used as simple and renewable adsorbents for water purification. The presence of surface functional groups such as −CO2H, −OH and morphologies of the peels were characterized using spectroscopic and electron microscopic techniques, respectively. All peals were effective toward removing dyes and toxic metal ions from water. The extraction capacity of peels increased with extraction time and a plateau was reached at equilibrium. Dragon fruit peels showed highest extraction efficiency toward alcian blue (71.85 mg/g) and methylene blue (62.58 mg/g). Hamimelon peels and avaocado peels showed moderate extraction capacity for Pb2+ (7.89 mg/g, 9.82 mg/g) and Ni2+ (9.45 mg/g, 4.93 mg/g) cations. The Langmuir isotherm model was useful to explain the adsorption process, dominated by electrostatic interaction between adsorbent and adsorbates, indicating a monolayer adsorption at the binding sites on the surface of the peels. However, the adsorption model for methylene blue and neutral red is still a matter of conjecture. The adsorbents can be regenerated at acidic pH and could reuse for a few cycles.

The presence of anions such as chromate, arsenate, and arsenite in drinking water is a major health concern in many parts of the world due to their high toxicity. Removal of such anions from water using low cost biomass is an efficient and affordable treatment process. Owing to the easy availability and biodegradability, we chose to use apple peel as a substrate for our investigations. Zirconium cations were immobilized onto the apple peel surface and used for the extraction of anions. Zirconium loaded apple peels were used to extract anions such as phosphate, arsenate, arsenite, and chromate ions from aqueous solutions. The presence of Zr cations on the apple peel surface was characterized using XPS. The modified adsorbent was characterized using SEM, EDS, and FT-IR. Zr treated apple peels showed efficient adsorption toward AsO2(-) (15.64 mg/g), AsO4(3-) (15.68 mg/g), Cr2O7(2-) (25.28 mg/g), and PO4(3-) (20.35 mg/g) anions. The adsorption and desorption studies revealed the adsorption mechanism involves electrostatic interactions. Anion removal efficiency was estimated by batch adsorption studies. Adsorption kinetic parameters for all anions at different concentrations were described using pseudo-first-order and pseudo-second-order rate equations. Langumir and Freundlich isotherms were used to validate our adsorption data. Arsenate and chromate anions were strongly adsorbed at the pH range from 2 to 6, while arsenite was extracted efficiently between pH 9 and 10. Overall, the Zr immobilized apple peel is an efficient adsorbent for common anionic pollutants.

Heavy metal ions and dissolved organic compounds in waste water are known to adversely affect human health, aquatic life and the overall ecosystem. Many hazardous pollutants need to be removed from drinking water; however, such technologies are not accessible for economically disadvantaged people around the world. Naturally abundant tomato peels or other biomembranes are used as an efficient biomaterial to remove toxic metal ions and organic pollutants from aqueous solution. The functional groups and morphologies of the tomato peels were characterized using FT-IR and FESEM, respectively. Factors such as pH, nature and amount of adsorbent used for extraction were studied to establish the optimum conditions. The maximum adsorption capacity was observed at different pH values for different pollutants. The equilibrium adsorption data were interpreted by using Freundlich and Langmuir isotherms and the adsorption mechanism was investigated by kinetic studies. Results showed that tomato peels have good potential as an efficient adsorbent to remove various pollutants from water.

Contamination of nanomaterials in the environment will pose significant health risks in the future. A viable purification method is necessary to address this problem. Here we report the synthesis and application of a series of metal oxides prepared using a biological template for the removal of nanoparticles from the aqueous environment. A simple synthesis of metal oxides such as ZnO, NiO, CuO, Co3O4 and CeO2 employing eggshell membrane (ESM) as a biotemplate is reported. The morphology of the metal oxide powders was characterized using electron microscopes and the lattice structure was established using X-ray diffraction methods. Extraction of nanoparticles from water was carried out to compare the efficiency of metal oxides. NiO showed good extraction efficiency in removing gold and silver nanoparticles from spiked water samples within an hour. Easy access and enhanced stability of metal oxides makes them interesting candidates for applications in industrial effluent treatments and water purifications.

Recent developments in nanotechnology led to the incorporation of many nanomaterials into consumer products. Disposal of such products will lead to potential contamination of the environment. Nanomaterials are emerging contaminants in water and show significant toxicity to living systems. Considering the diversity in structure and properties, removal of nanopollutants from water warrants novel methods and materials. The objective of this study was to prepare PVA/gluten hybrid nanofibers, which are nontoxic and biodegradable adsorbents for the extraction of nanopollutants from water. Surface morphology, elemental composition, and functional groups on the fiber surface were established using microscopic and spectroscopic techniques. Influence of analytical factors such as experimental pH, time, and concentration of the pollutants toward establishing the efficiency of extraction were quantified using UV–vis spectroscopy. Nanofiber mats with 5 wt % gluten exhibited high extraction efficiency of 99% toward citrate-capped silver (Ag) and gold (Au) nanoparticles with a maximum adsorptive capacity of 31.84 mg/g for Ag NPs and 36.54 mg/g for AuNPs. The kinetic and equilibrium adsorption data were interpreted using Freundlich and Langmuir isotherm models, and a potential adsorption mechanism was suggested. The adsorption kinetics showed a pseudo-second-order model for the extraction of nanoparticles. The prepared PVA/gluten hybrid nanofibers can be utilized as an efficient low-cost adsorbents for removal and recovery of metal nanoparticles from the aqueous environment.