Ricerc@Sapienza

Nanotechnology offers a possible solutions to various environmental issues by means of better performing materials, characterized by peculiar physico-chemical properties due to their nano-size. A huge amount of different manufactured nanoparticles (NPs) have been developed in the last two decades, and a remarkable quantity of them have been used to face environmental problems.
The present research deals with a comprehensive study of heavy metals removal from wastewater by adsorption onto selected nanoparticles, aiming at achieving a better understanding of process mechanisms and kinetics.
The following main achievements are expected, as a result of experimental set up and process optimization:
- preparation and characterization of the reducing agents
- set up of the optimal conditions for nZVI and ION synthesis in batch mode and by spinning disk reactor (SDR)
- assessment of the best method for nanoparticles synthesis and delivery;
- complete characterization of nanoparticles before and after the treatment;
- assessment of adsorption mechanisms and kinetics;
- nanoparticles and heavy metal complete recovery from the reaction solution;
- process modeling, and model validation;
- identification of the critical points of the technology implementation from the safety and health point of view.
The obtained results are expected to contribute to a significant knowledge improvement with regards to the production and environmental applications of iron-based NPs, which represent the most widely employed NPs, both in industrial and environmental fields. The comparison among traditional NPs and green-coated NPs, focusing on their HM removal efficiency and residual toxicity, represents a topic which still requires several and in-depth researches, because of its fundamental importance towards environment protection and, as a consequence, human well-being.
Innovations of the proposed research mainly regards the following steps:
I. Green synthesis of NPs
The traditional synthesis of NP, such as nano zero-valent iron (nZVI) and iron-oxide nanoparticles (ION), involves hazardous and toxic reagents, such as NaBH4, NH4OH and N2H4.
Furthermore, bare NPs could lead to additional environmental issues during their employment in a treatment process; due to their nano-size in fact, they could enter through the cellular membrane in microrganism cells, causing various toxic effects.
The innovative aspect of this research deals with the production of ION and nZVI through `¿green¿¿ synthesis, exploiting the reducing effectiveness of selected agro-industrial wastes (such as banana, mango and other fruit peels), and employing natural extracts and biopolymer (such as CMC, Arabic gum, chitosan) as coating agents, to reduce NPs environmental impact and toxicity
II. Continuous production (process intensification)
The NPs production will be carried out using Spinning Disk Rector technology (SDR), a well-known equipment in process intesification field developed by the research team. SDR ensures the production optimization, with respect to the batch production, in terms of minor mean NPs size, narrow unimodal size distribution, larger surface area and, as a consequence, better performances during the wastewater treatment. In addition, the SDR technology assures a minor energy consumption and the well-known advantages of continuous production (more uniform production, easier process control system) besides the possibility to produce significative NPs amounts in less time; for instance, the nZVI production in batchwise requires more than one hour whereas the SDR employment guarantees the production of better nZVI in less than 1 minute.
III. Process modeling
The development of a physical-based model able to take into account the several phenomena and operative variables which characterized complex processes such as HM removal by means of NPs still represents a challenge for all researchers active in the field.
Experimental data and observations will be analyzed and used to validate a physical-based model able to forecast the selected contaminant efficiency removal in function of T, pH, mixed NPs presence, HM and NPs initial concentration, other contaminants presence and considering the final residual phytotoxicity of the treated wastewater.
IV. Ecological effects of the NPs
ION and nZVI have been already used for wastewater treatment and their remarkable efficiency in heavy metals (HM) and inorganic ions removal have been demonstrated. The present research aims to investigate also the residual toxicity of the treated streams, due to the remained NPs and HM traces after the separation step.
To evaluate the possible use of reclaimed water to irrigate plants in agriculture, macroscopic and microscopic observations, net photosynthesis, stomatal conductance, leaf temperature, transpiration rate, chlorophyll content, secondary metabolite production will be determined.